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[gawk-diffs] [SCM] gawk branch, master, updated. 07fb393999d623541bf2e54


From: Arnold Robbins
Subject: [gawk-diffs] [SCM] gawk branch, master, updated. 07fb393999d623541bf2e54aeeb0d9c0311baace
Date: Fri, 17 Aug 2012 10:07:51 +0000

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The branch, master has been updated
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- Log -----------------------------------------------------------------
http://git.sv.gnu.org/cgit/gawk.git/commit/?id=07fb393999d623541bf2e54aeeb0d9c0311baace

commit 07fb393999d623541bf2e54aeeb0d9c0311baace
Merge: e6b05af a58fa49
Author: Arnold D. Robbins <address@hidden>
Date:   Fri Aug 17 13:07:27 2012 +0300

    Merge branch 'gawk-4.0-stable'

diff --cc ChangeLog
index 1cc23e7,7c0d638..c031111
--- a/ChangeLog
+++ b/ChangeLog
@@@ -1,715 -1,11 +1,724 @@@
  2012-08-12         Arnold D. Robbins     <address@hidden>
  
++<<<<<<< HEAD
 +      * gawkapi.h: Make the versions enum constants instead of defines.
 +
 +2012-08-11         Andrew J. Schorr     <address@hidden>
 +
 +      * awkgram.y (add_srcfile): It is now a fatal error to load the
 +      same file with -f and -i (or @include).
 +      * TODO.xgawk: Update to reflect this change.
 +
 +2012-08-10         Arnold D. Robbins     <address@hidden>
 +
 +      * FUTURES, TODO.xgawk: Updates.
 +
 +2012-08-08         Arnold D. Robbins     <address@hidden>
 +
 +      * configure.ac: Add -DNDEBUG to remove asserts if not developing.
 +
 +      * gawkapi.h: Document how to build up arrays.
 +      * gawkapi.c (api_sym_update): For an array, pass the new cookie
 +      back out to the extension.
 +
 +      * awk.h (IOBUF): Move struct stat into IOBUF_PUBLIC.
 +      (os_isreadable): Change to take an IOBUF_PUBLIC.
 +      * gawkapi.h (IOBUF_PUBLIC): Received struct stat.
 +      (INVALID_HANDLE): Moves to here.
 +      * io.c (iop_alloc): Stat the fd and fill in stat buf.
 +      (iop_finish): Use passed in stat info.
 +
 +2012-08-05         Arnold D. Robbins     <address@hidden>
 +
 +      * README.git: More stuff added.
 +
 +2012-08-01         Arnold D. Robbins     <address@hidden>
 +
 +      * io.c (iop_finish): New function.
 +      (iop_alloc): Add errno_val parameter. Move code into iop_finish.
 +      Add large explanatory leading comment.
 +      (after_beginfile): Rework logic. Check for input parser first, then
 +      check for invalid iop.
 +      (nextfile): Organize code better. Call iop_alloc then iop_finish.
 +      (redirect): Call iop_alloc, find_input_parser, iop_finish.
 +      (two_way_open): Call iop_alloc, find_input_parser, iop_finish.
 +      (gawk_popen): Call iop_alloc, find_input_parser, iop_finish.
 +      (find_input_parser): Set iop->valid if input parser takes control.
 +      (get_a_record): Rework setting RT to use macros.
 +
 +2012-07-29         Andrew J. Schorr     <address@hidden>
 +
 +      * awk.h (set_RT_to_null, set_RT): Removed.
 +      * gawkapi.h (api_set_RT): Removed.
 +      (get_record): Signature changed in input parser struct.
 +      * gawkapi.c (api_set_RT): Removed.
 +      * io.c (set_RT_to_null, set_RT): Removed.
 +      (get_a_record): Adjustments for new API for input parser.
 +
 +2012-07-29         Arnold D. Robbins     <address@hidden>
 +
 +      * awk.h (os_isreadable): Adjust declaration.
 +      (struct iobuf): Add new member `valid'.
 +      * io.c (iop_alloc): Remove do_input_parsers parameter, it's
 +      always true. Adjust logic to set things to invalid if could not
 +      find an input parser.
 +      (after_beginfile): Use valid member to check if iobuf is valid.
 +      Don't clear iop->errcode.
 +      (nextfile): Adjust logic to clear errcode if valid is true and
 +      also to update ERRNO.
 +      (redirect): Check iop->valid and cleanup as necessary, including
 +      setting ERRNO.
 +      (two_way_open): Ditto.
 +      (gawk_popen): Ditto.
 +      (devopen): Remove check for directory.
 +
 +2012-07-27         Andrew J. Schorr     <address@hidden>
 +
 +      * io.c (find_input_parser): Issue a warning if take_control_of fails.
 +
 +2012-07-27         Arnold D. Robbins     <address@hidden>
 +
 +      * awk.h (set_RT): Change to take a NODE * parameter.
 +      * io.c (set_RT): Change to take a NODE * parameter.
 +      * gawkapi.h: Change open hook to input parser in comment.
 +      * gawkapi.c (api_set_RT): Adjust call to set_RT.
 +
 +2012-07-26         Arnold D. Robbins     <address@hidden>
 +
 +      * awk.h (set_RT_to_null, set_RT): Declare functions.
 +      (os_isreadable): Declare function.
 +      * io.c (set_RT_to_null, set_RT): New functions.
 +      (iop_close): Init ret to zero.
 +      * gawkapi.c (api_register_input_parser): Check for null pointer.
 +      (api_set_RT): New function.
 +      * gawkapi.h (api_set_RT): New function.
 +
 +2012-07-26         Andrew J. Schorr     <address@hidden>
 +
 +      * gawkapi.h (IOBUF_PUBLIC): Document the get_record and close_func
 +      API.
 +      (awk_input_parser_t) Change can_take_file argument to const, and
 +      document the API.
 +      * io.c (get_a_record): Document that the caller initializes *errcode
 +      to 0, and remote the test for non-NULL errcode.
 +
 +2012-07-26         Andrew J. Schorr     <address@hidden>
 +
 +      * gawkapi.c (api_sym_update_scalar): Fix some minor bugs.  Was
 +      not updating AWK_NUMBER when valref != 1.  And strings were not
 +      freeing MPFR values.
 +
 +2012-07-25         Arnold D. Robbins     <address@hidden>
 +
 +      Start refactoring of IOBUF handling and turn "open hooks"
 +      into "input parsers".
 +
 +      * awk.h (IOP_NOFREE_OBJ): Flag removed.
 +      (register_input_parser): Renamed from register_open_hook.
 +      * ext.c (load_ext): Make sure lib_name is not NULL.
 +      * gawk_api.c (api_register_input_parser): Renamed from
 +      api_register_open_hook.
 +      * gawk_api.h (api_register_input_parser): Renamed from
 +      api_register_open_hook.  Rework structure to have "do you want it"
 +      and "take control of it" functions.
 +      * io.c (iop_alloc): Remove third argument which is IOBUF pointer.
 +      Always malloc it. Remove use of IOP_NOFREE_OBJ everywhere.
 +      (find_input_parser): Renamed from find_open_hook.
 +      (nextfile): Don't use static IOBUF.
 +      (iop_close): Call close_func first. Then close fd or remap it
 +      if it's still not INVALID_HANDLE.
 +      (register_input_parser): Renamed from register_open_hook.
 +      Use a FIFO list and check if more than one parser will accept the
 +      file. If so, fatal error.
 +
 +2012-07-25         Andrew J. Schorr     <address@hidden>
 +
 +      * configure.ac: Instead of using acl_shlibext for the shared library
 +      extension, define our own variable GAWKLIBEXT with a hack to work
 +      correctly on Mac OS X.
 +      * Makefile.am (SHLIBEXT): Use the value of GAWKLIBEXT instead of
 +      acl_shlibext.
 +
 +2012-07-24         Arnold D. Robbins     <address@hidden>
 +
 +      * configure.ac: Add crude but small hack to make plug-ins work
 +      on Mac OS X.
 +
 +2012-07-20         Arnold D. Robbins     <address@hidden>
 +
 +      * gawkapi.h: Rework table to not take up so much space.
 +      * gawkapi.c (api_sym_update_scalar): Rework optimization code
 +      to clean up the function.
 +
 +2012-07-17         Andrew J. Schorr     <address@hidden>
 +
 +      * gawkapi.h: Add comments explaining new api_create_value and
 +      api_release_value functions.
 +      * gawkapi.c (sym_update_real): Allow updates with AWK_SCALAR and
 +      AWK_VALUE_COOKIE types.  After creating a regular variable,
 +      remove the call to unref(node->var_value), since this is not
 +      done elsewhere in the code (see, for example, main.c:init_vars).
 +      If the update is for an existing variable, allow any val_type
 +      except AWK_ARRAY (was previously disallowing AWK_SCALAR and
 +      AWK_VALUE_COOKIE for no apparent reason).
 +      (api_sym_update_scalar): The switch should return false for an
 +      invalid val_type value, so change the AWK_ARRAY case to default.
 +      (valid_subscript_type): Any scalar value is good, so accept any valid
 +      type except AWK_ARRAY.
 +      (api_create_value): Accept only AWK_NUMBER and AWK_STRING values.
 +      Anything else should fail.
 +
 +2012-07-17         Arnold D. Robbins     <address@hidden>
 +
 +      Speedup:
 +
 +      * awk.h (r_free_wstr): Renamed from free_wstr.
 +      (free_wstr): Macro to test the WSTRCUR flag first.
 +      * node.c (r_free_wstr): Renamed from free_wstr.
 +
 +      Support value cookies:
 +
 +      * gawkapi.h (awk_val_type_t): Add AWK_VALUE_COOKIE.
 +      (awk_value_cookie_t): New type.
 +      (awk_value_t): Support AWK_VALUE_COOKIE.
 +      (api_create_value, api_release_value): New function pointers.
 +      * gawkapi.c (awk_value_to_node, api_sym_update_scalar,
 +      valid_subscript_type): Handle AWK_VALUE_COOKIE.
 +      (api_create_value, api_release_value): New functions.
 +
 +2012-07-16         Arnold D. Robbins     <address@hidden>
 +
 +      * gawkapi.c (awk_value_to_node): Support AWK_SCALAR.
 +      (api_sym_update_scalar): Performance improvements.
 +
 +2012-07-12         Arnold D. Robbins     <address@hidden>
 +
 +      Allow creation of constants. Thanks to John Haque for the
 +      implementation concept.
 +
 +      * gawk_api.h (api_sym_constant): Create a constant.
 +      * gawk_api.h (api_sym_update_real): Renamed from api_sym_update.
 +      Add is_const paramater and do the right thing if true.
 +      (api_sym_update, api_sym_constant): Call api_sym_update_real
 +      in the correct way.
 +      (set_constant): New function.
 +
 +2012-07-11         Andrew J. Schorr     <address@hidden>
 +
 +      * gawkapi.h: Fix typo in comment.
 +      (awk_value_t): Type for scalar_cookie should be awk_scalar_t,
 +      not awk_array_t.
 +      (gawk_api): Add new api_sym_lookup_scalar function.
 +      (sym_lookup_scalar): New wrapper macro for api_sym_lookup_scalar hook.
 +      * gawkapi.c (api_sym_lookup_scalar): New function for faster scalar
 +      lookup.
 +      (api_impl): Add entry for api_sym_lookup_scalar.
 +
 +2012-07-11         Andrew J. Schorr     <address@hidden>
 +
 +      * gawkapi.c (awk_value_to_node): Change to a switch statement
 +      so AWK_SCALAR or other invalid type is handled properly.
 +      (valid_subscript_type): Test whether a value type is acceptable
 +      for use as an array subscript (any scalar value will do).
 +      (api_get_array_element, api_set_array_element, api_del_array_element):
 +      Use new valid_subscript_type instead of restricting to string values.
 +
 +2012-07-11         Arnold D. Robbins     <address@hidden>
 +
 +      Lots of API work.
 +
 +      * gawkapi.h: Function pointer members renamed api_XXXX and
 +      macros adjusted. More documentation.
 +      (awk_valtype_t): New AWK_SCALAR enum for scalar cookies.
 +      (awk_scalar_t): New type.
 +      (awk_value_t): New member scalar_cookie.
 +      (api_sym_update_scalar): New API function.
 +      (erealloc): New macro.
 +      (make_const_string): New macro, renamed from dup_string.
 +      (make_malloced_string): New macro, renamed from make_string.
 +      (make_null_string): New inline function.
 +      (dl_load_func): Add call to init routine through pointer if
 +      not NULL.
 +
 +      * gawkapi.c (awk_value_to_node): Assume that string values came
 +      from malloc.
 +      (node_to_awk_value): Handle AWK_SCALAR.
 +      (api_sym_update): Ditto.
 +      (api_sym_update_scalar): New routine.
 +      (api_get_array_element): Return false if the element doesn't exist.
 +      Always unref the subscript.
 +      (remove_element): New helper routine.
 +      (api_del_array_element): Use it.
 +      (api_release_flattened_array): Ditto.
 +      (api_impl): Add the new routine.
 +
 +2012-07-11         Andrew J. Schorr     <address@hidden>
 +
 +      * gawkapi.c (api_sym_update): Allow val_type to be AWK_UNDEFINED
 +      for setting a variable to "", i.e. dupnode(Nnull_string).
 +
 +2012-07-10         Andrew J. Schorr     <address@hidden>
 +
 +      * awkgram.y (add_srcfile): Lint warning message for a previously loaded
 +      shared library should say "already loaded shared library" instead
 +      of "already included source file".
 +
 +2012-07-08         Arnold D. Robbins     <address@hidden>
 +
 +      * gawkapi.h (set_array_element): Use index + value instead
 +      of element structure. Matches get_array_element.
 +      (set_array_element_by_elem): New macro to use an element.
 +      * gawkapi.c (api_set_array_element): Make the necessary adjustments.
 +
 +2012-07-04         Arnold D. Robbins     <address@hidden>
 +
 +      * awkgram.y (tokentab): Remove limit on number of arguments
 +      for "and", "or", and "xor".
 +      * builtin.c (do_and, do_or, do_xor): Modify code to perform the
 +      respective operation on any number of arguments. There must be
 +      at least two.
 +
 +2012-06-29         Arnold D. Robbins     <address@hidden>
 +
 +      * gawkapi.h: Improve the documentation of the return values
 +      per Andrew Schorr.
 +
 +2012-06-25         Arnold D. Robbins     <address@hidden>
 +
 +      * TODO.xgawk: Updated.
 +      * awk.h (track_ext_func): Declared.
 +      * awkgram.y (enum defref): Add option for extension function.
 +      (struct fdesc): Add member for extension function.
 +      (func_use): Handle extension function, mark as extension and defined.
 +      (track_ext_func): New function.
 +      (check_funcs): Update logic for extension functions.
 +      * ext.c (make_builtin): Call track_ext_func.
 +
 +2012-06-24         Andrew J. Schorr     <address@hidden>
 +
 +      * TODO.xgawk: Most of IOBUF has been hidden.
 +      * gawkapi.h (IOBUF): Remove declaration (now back in awk.h).
 +      (IOBUF_PUBLIC): Declare new structure defining subset of IOBUF fields
 +      that should be exposed to extensions.
 +      (gawk_api): Update register_open_hook argument from IOBUF to
 +      IOBUF_PUBLIC.
 +      * awk.h (IOBUF): Restore declaration with 5 fields moved to new
 +      IOBUF_PUBLIC structure.
 +      (register_open_hook): Update open_func argument from IOBUF to
 +      IOBUF_PUBLIC.
 +      * gawkapi.c (api_register_open_hook): Ditto.
 +      * io.c (after_beginfile, nextfile, iop_close, gawk_pclose): Some fields
 +      such as fd and name are now inside the IOBUF public structure.
 +      (struct open_hook): Update open_func argument from IOBUF to
 +      (register_open_hook): Ditto.
 +      (find_open_hook): opaque now inside IOBUF_PUBLIC.
 +      (iop_alloc): fd and name now in IOBUF_PUBLIC.
 +      (get_a_record): If the get_record hook returns EOF, set the IOP_AT_EOF
 +      flag.  Access fd inside IOBUF_PUBLIC.
 +      (get_read_timeout): File name now inside IOBUF_PUBLIC.
 +      * interpret.h (r_interpret): File name now inside IOBUF_PUBLIC.
 +      * ext.c (load_ext): No need to call return at the end of a void
 +      function.
 +
 +2012-06-24         Arnold D. Robbins     <address@hidden>
 +
 +      * ext.c (load_ext): Don't retun a value from a void function.
 +      * gawkapi.c (api_set_array_element): Set up vname and parent_array.
 +
 +2012-06-21         Arnold D. Robbins     <address@hidden>
 +
 +      More API and cleanup:
 +
 +      * awk.h (stopme): Make signature match other built-ins.
 +      * awkgram.y (stopme): Make signature match other built-ins.
 +      (regexp): Minor edit.
 +      * gawkapi.c (api_set_argument): Remove unused variable.
 +      Set parent_array field of array value.
 +      * TODO.xgawk: Update some.
 +
 +      Remove extension() builtin.
 +
 +      * awk.h (do_ext): Removed.
 +      (load_ext): Signature changed.
 +      * awkgram.y (tokentab): Remove do_ext.
 +      Change calls to do_ext.
 +      * ext.c (load_ext): Make init function a constant.
 +      * main.c (main): Change calls to do_ext.
 +
 +2012-06-20         Arnold D. Robbins     <address@hidden>
 +
 +      Restore lost debugging function:
 +
 +      * awkgram.y (stopme): Restore long lost debugging function.
 +      * awk.h (stopme): Add declaration.
 +
 +      API work:
 +
 +      * ext.c (get_argument): Make extern.
 +      * awk.h (get_argument): Declare it.
 +      * gawkapi.c (api_set_argument): Call it. Finish off the logic.
 +      (api_get_argument): Refine logic to use get_argument.
 +      * gawkapi.h (set_argument): New API.
 +
 +2012-06-19         Arnold D. Robbins     <address@hidden>
 +
 +      Remove code duplication in gawkapi.c from msg.c:
 +
 +      * awk.h (err): Add `isfatal' first parameter.
 +      * awkgram.y (err): Adjust all calls.
 +      * msg.c (err): Adjust all calls. Move fatal code to here ...
 +      (r_fatal): From here.
 +      * gawkapi.c: Remove code duplication and adjust calls to `err'.
 +
 +      Handle deleting elements of flattened array:
 +
 +      * awk.h (get_argument): Remove declaration.
 +      * ext.c (get_argument): Make static.
 +      * gawkapi.h (awk_flat_array_t): Make opaque fields const. Add
 +      more descriptive comments.
 +      * gawkapi.c (release_flattened_array): Delete elements flagged
 +      for deletion. Free the flattened array also.
 +
 +      Add additional debugging when developing:
 +
 +      * configure.ac: Add additional debugging flags.
 +      * configure: Regenerated.
 +
 +2012-06-18         Arnold D. Robbins     <address@hidden>
 +
 +      * gawkapi.h (get_array_element): Restore `wanted' paramater.
 +      (awk_element_t): Use awk_value_t for index. Add awk_flat_array_t.
 +      (flatten_array): Change signature to use awk_flat_array_t;
 +      (release_flattened_array): Change signature to use awk_flat_array_t;
 +      * gawkapi.c (api_sym_update): Handle case where variable exists already.
 +      (api_get_array_element): Restore `wanted' paramater and pass it
 +      on to node_to_awk_value.
 +      (api_set_array_element): Revisse to match changed element type.
 +      (api_flatten_array): Revise signature, implement.
 +      (api_release_flattened_array): Revise signature, implement.
 +
 +2012-06-17         Arnold D. Robbins     <address@hidden>
 +
 +      API Work:
 +
 +      * gawkapi.h (get_array_element): Remove `wanted' parameter.
 +      (r_make_string): Comment the need for `api' and `ext_id' parameters.
 +      * gawkapi.c (api_sym_update): Move checks to front.
 +      Initial code for handling arrays. Still needs work.
 +      (api_get_array_element): Implemented.
 +      (api_set_array_element): Additional checking code.
 +      (api_del_array_element): Implemented.
 +      (api_create_array): Implemented.
 +      (init_ext_api): Force do_xxx values to be 1 or 0.
 +      (update_ext_api): Ditto.
 +
 +2012-06-12         Arnold D. Robbins     <address@hidden>
 +
 +      API Work:
 +
 +      * gawkapi.h (awk_value_t): Restore union.
 +      (get_curfunc_param): Renamed to get_argument. Return type changed
 +      to awk_bool_t. Semantics better thought out and documented.
 +      (awk_atexit, get_array_element): Return type now void.
 +      (sym_lookup): Return type now void. Argument order rationalized.
 +      * gawkapi.c (node_to_awk_value): Return type is now awk_bool_t.
 +      Semantics now match table in gawkawpi.h.
 +      (api_awk_atexit): Return type now void.
 +      (api_sym_lookup): Return type is now awk_bool_t. Change parameter
 +      order.
 +      (api_get_array_element): Return type is now awk_bool_t.
 +
 +      Further API implementations and fixes for extension/testext.c:
 +
 +      * awk.h (final_exit): Add declaration.
 +      * ext.c (load_ext): Change `func' to install_func.
 +      * gawkapi.c: Add casts to void for id param in all functions.
 +      (api_sym_update): Finish implementation.
 +      (api_get_array_element): Start implementation.
 +      (api_set_array_element): Add error checking.
 +      (api_get_element_count): Add error checking, return the right value.
 +      * main.c (main): Call final_exit instead of exit.
 +      (arg_assign): Ditto.
 +      * msg.c (final_exit): New routine to run the exit handlers and exit.
 +      (gawk_exit): Call it.
 +      * profile.c (dump_and_exit): Ditto.
 +
 +2012-06-10         Andrew J. Schorr     <address@hidden>
 +
 +      * TODO.xgawk: Addition of time extension moved to "done" section.
 +
 +2012-06-10         Andrew J. Schorr     <address@hidden>
 +
 +      * gawkapi.c (api_update_ERRNO_string): Treat boolean true as a request
 +      for TRANSLATE, and false as DONT_TRANSLATE.
 +
 +2012-06-06         Arnold D. Robbins     <address@hidden>
 +
 +      * cint_array.c (tree_print, leaf_print): Add additional casts
 +      for printf warnings.
 +
 +      * awk.h (update_ext_api): Add declaration.
 +      * gawkapi.c (update_ext_api): New function.
 +      * eval.c (set_LINT): Call update_ext_api() at the end.
 +      * gawkapi.h: Document that do_XXX could change on the fly.
 +
 +      * awk.h (run_ext_exit_handlers): Add declaration.
 +      * msg.c (gawk_exit): Call it.
 +
 +2012-06-05         Arnold D. Robbins     <address@hidden>
 +
 +      * ext.c (load_ext): Remove use of RTLD_GLOBAL. Not needed in new
 +      scheme. Clean up error messages.
 +
 +2012-06-04         Arnold D. Robbins     <address@hidden>
 +
 +      * configure.ac: Remove use of -export-dynamic for GCC.
 +      * configure: Regenerated.
 +
 +2012-05-30         Arnold D. Robbins     <address@hidden>
 +
 +      * main.c (is_off_limits_var): Minor coding style edit.
 +      * gawkapi.c (awk_value_to_node): More cleanup.
 +      (node_to_awk_value): Use `wanted' for decision making.
 +      (api_sym_update): Start implementation. Needs more work.
 +      General: More cleanup, comments.
 +      * gawkapi.h (api_sym_update): Add additional comments.
 +
 +2012-05-29         Arnold D. Robbins     <address@hidden>
 +
 +      * gawkapi.c (node_to_awk_value): Add third parameter indicating type
 +      of value desired. Based on that, do force_string or force_number
 +      to get the "other" type.
 +      (awk_value_to_node): Clean up the code a bit.
 +      (get_curfunc_param): Move forcing of values into node_to_awk_value.
 +      (api_sym_lookup): Add third parameter indicating type of value wanted.
 +      (api_get_array_element): Ditto.
 +      * gawk_api.h: Additional comments and clarifications. Revise APIs
 +      to take third 'wanted' argument as above.
 +      (awk_value_t): No longer a union so that both values may be accessed.
 +      All macros: Parenthesized the bodies.
 +      * bootstrap.sh: Rationalize a bit.
 +
 +2012-05-26         Andrew J. Schorr     <address@hidden>
 +
 +      * Makefile.am (include_HEADERS): Add so gawkapi.h will be installed.
 +      (base_sources): Add gawkapi.h so that it is in dist tarball.
 +      * TODO.xgawk: Update.
 +      * main.c (is_off_limits_var): Stop returning true for everything
 +      except PROCINFO.
 +
 +2012-05-25         Arnold D. Robbins     <address@hidden>
 +
 +      * main.c (is_off_limits_var): New function to check if a variable
 +      is one that an extension function may not change.
 +      * awk.h (is_off_limits_var): Declare it.
 +      * gawkapi.c (api_sym_lookup): Use it.
 +
 +      * bootstrap.sh: Touch various files in the extension directory also.
 +
 +2012-05-24         Andrew J. Schorr     <address@hidden>
 +
 +      * gawkapi.h (awk_param_type_t): Remove (use awk_valtype_t instead).
 +      (awk_ext_func_t): Pass a result argument, and return an awk_value_t *.
 +      (gawk_api.get_curfunc_param): Add a result argument.
 +      (gawk_api.set_return_value): Remove obsolete function.
 +      (gawk_api.sym_lookup, gawk_api.get_array_element): Add a result
 +      argument.
 +      (gawk_api.api_make_string, gawk_api.api_make_number): Remove hooks,
 +      since access to gawk internal state is not required to do this.
 +      (set_return_value): Remove obsolete macro.
 +      (get_curfunc_param, sym_lookup, get_array_element): Add result argument.
 +      (r_make_string, make_number): New static inline functions.
 +      (make_string, dup_string): Revise macro definitions.
 +      (dl_load_func): Remove global_api_p and global_ext_id args,
 +      and fix SEGV by setting api prior to checking its version members.
 +      (GAWK): Expand ifdef to include more stuff.
 +      * gawkapi.c (node_to_awk_value): Add result argument.
 +      (api_get_curfunc_param): Add result argument, and use awk_valtype_t.
 +      (api_set_return_value): Remove obsolete function.
 +      (awk_value_to_node): New global function to convert back into internal
 +      format.
 +      (api_add_ext_func): Simply call make_builtin.
 +      (node_to_awk_value): Add result argument, and handle Node_val case.
 +      (api_sym_lookup, api_get_array_element): Add result argument.
 +      (api_set_array_element): Implement.
 +      (api_make_string, api_make_number): Remove functions that belong on
 +      client side.
 +      (api_impl): Remove 3 obsolete entries.
 +      * TODO.xgawk: Update to reflect progress.
 +      * Makefile.am (base_sources): Add gawkapi.c.
 +      * awk.h: Include gawkapi.h earlier.
 +      (api_impl, init_ext_api, awk_value_to_node): Add declarations
 +      so we can hook in new API.
 +      (INSTRUCTION): Add new union type efptr for external functions.
 +      (extfunc): New define for d.efptr.
 +      (load_ext): Remove 3rd obj argument that was never used for anything.
 +      (make_builtin): Change signature for new API.
 +      * awkgram.y (load_library): Change 2nd argument to load_ext
 +      from dlload to dl_load, and remove pointless 3rd argument.
 +      * main.c (main): Call init_ext_api() before loading shared libraries.
 +      Change 2nd argument to load_ext from dlload to dl_load, and remove
 +      pointless 3rd argument.
 +      * ext.c (do_ext): Remove pointless 3rd argument to load_ext.
 +      (load_ext): Remove 3rd argument.  Port to new API (change initialization
 +      function signature).  If initialization function fails, issue a warning
 +      and return -1, else return 0.
 +      (make_builtin): Port to new API.
 +      * interpret.h (r_interpret): For Op_ext_builtin, call external functions
 +      with an awk_value_t result buffer, and convert the returned value
 +      to a NODE *.  For Node_ext_func, code now in extfunc instead of builtin.
 +
 +2012-05-21         Andrew J. Schorr     <address@hidden>
 +
 +      * configure.ac: Remove libtool, and call configure in the
 +      extension subdirectory.  Change pkgextensiondir to remove the
 +      version number, since the new API has builtin version checks.
 +      * TODO.xgawk: Update.
 +      * ltmain.sh: Removed, since libtool no longer used here.
 +
 +2012-05-19         Andrew J. Schorr     <address@hidden>
 +
 +      * TODO.xgawk: Update to reflect progress and new issues.
 +      * main.c (main): Add -i (--include) option.
 +      (usage): Ditto.
 +      * awkgram.y (add_srcfile): Eliminate duplicates only for SRC_INC
 +      and SRC_EXTLIB sources (i.e. -f duplicates should not be removed).
 +      * io.c (find_source): Set DEFAULT_FILETYPE to ".awk" if not defined
 +      elsewhere.
 +
 +2012-05-15         Arnold D. Robbins     <address@hidden>
 +
 +      * awk.h: Include "gawkapi.h" to get IOBUF.
 +      * gawkapi.h: Considerable updates.
 +      * gawkapi.c: New file. Start at implementing the APIs.
 +
 +2012-05-13         Andrew J. Schorr     <address@hidden>
 +
 +      * TODO.xgawk: Update to reflect recent discussions and deletion of
 +      extension/xreadlink.[ch].
 +
 +2012-05-11         Arnold D. Robbins     <address@hidden>
 +
 +      Sweeping change: Use `bool', `true', and `false' everywhere.
 +
 +2012-04-09         Andrew J. Schorr     <address@hidden>
 +
 +      * eval.c (unset_ERRNO): Fix memory management bug -- need to use
 +      dupnode with Nnull_string.
 +
 +2012-04-08         Andrew J. Schorr     <address@hidden>
 +
 +      * Makefile.am (valgrind): Define VALGRIND instead of redefining AWK.
 +      This allows test/Makefile.am to set up the command environment as
 +      desired.
 +      (valgrind-noleak): Ditto, plus set --leak-check=no instead of the
 +      default summary setting.
 +
 +2012-04-07         Andrew J. Schorr     <address@hidden>
 +
 +      * TODO.xgawk: Update to reflect progress.
 +
 +2012-04-01         Andrew J. Schorr     <address@hidden>
 +
 +      * TODO.xgawk: Move valgrind-noleak item into "done" section.
 +      * Makefile.am (valgrind-noleak): Add new valgrind rule that omits
 +      the "--leak-check=full" option to help spot more serious problems.
 +
 +2012-04-01         Andrew J. Schorr     <address@hidden>
 +
 +      * TODO.xgawk: Move ERRNO item into "done" section.
 +      * awk.h (update_ERRNO, update_ERRNO_saved): Remove declarations.
 +      (update_ERRNO_int, enum errno_translate, update_ERRNO_string,
 +      unset_ERRNO): Add new declarations.
 +      * eval.c (update_ERRNO_saved): Renamed to update_ERRNO_int.
 +      (update_ERRNO_string, unset_ERRNO): New functions.
 +      * ext.c (do_ext): Use new update_ERRNO_string function.
 +      * io.c (ERRNO_node): Remove redundant extern declaration (in awk.h).
 +      (after_beginfile, nextfile): Replace update_ERRNO() with
 +      update_ERRNO_int(errno).
 +      (inrec): Replace update_ERRNO_saved with update_ERRNO_int.
 +      (do_close): Use new function update_ERRNO_string.
 +      (close_redir, do_getline_redir, do_getline): Replace update_ERRNO_saved
 +      with update_ERRNO_int.
 +
 +2012-03-27         Andrew J. Schorr     <address@hidden>
 +
 +      * TODO.xgawk: Update to reflect debate about how to support Cygwin
 +      and other platforms that cannot link shared libraries with unresolved
 +      references.
 +      * awkgram.y (add_srcfile): Minor bug fix: reverse sense of test
 +      added by Arnold in last patch.
 +      * configure.ac: AC_DISABLE_STATIC must come before AC_PROG_LIBTOOL.
 +
 +2012-03-26         Arnold D. Robbins     <address@hidden>
 +
 +      Some cleanups.
 +
 +      * awkgram.y (add_srcfile): Use whole messages, better for
 +      translations.
 +      * io.c (init_awkpath): Small style tweak.
 +      * main.c (path_environ): Straighten out initial comment, fix
 +      compiler warning by making `val' const char *.
 +
 +2012-03-25         Andrew J. Schorr     <address@hidden>
 +
 +      * configure.ac (AC_DISABLE_STATIC): Add this to avoid building useless
 +      static extension libraries.
 +
 +2012-03-25         Andrew J. Schorr     <address@hidden>
 +
 +      * TODO.xgawk: New file listing completed and pending xgawk enhancements.
 +
 +2012-03-24         Andrew J. Schorr     <address@hidden>
 +
 +      * io.c (path_info): Fix white space.
 +      (pi_awkpath, pi_awklibpath): Avoid structure initializers.
 +      (do_find_source): Eliminate pointless parentheses.
 +      (find_source): Leave a space after "&".
 +      * main.c (load_environ): Fix typo in comment.
 +
 +2012-03-21         Andrew J. Schorr     <address@hidden>
 +
 +      * awkgram.y (LEX_LOAD): New token to support @load.
 +      (grammar): Add rules to support @load.
 +      (tokentab): Add "load".
 +      (add_srcfile): Improve error message to distinguish between source files
 +      and shared libraries.
 +      (load_library): New function to load libraries specified with @load.
 +      (yylex): Add support for LEX_LOAD (treated the same way as LEX_INCLUDE).
 +
 +2012-03-20         Andrew J. Schorr     <address@hidden>
 +
 +      * Makefile.am (EXTRA_DIST): Remove extension.
 +      (SUBDIRS): Add extension so libraries will be built.
 +      (DEFS): Define DEFLIBPATH and SHLIBEXT so we can find shared libraries.
 +      * awk.h (deflibpath): New extern declaration.
 +      * configure.ac: Add support for building shared libraries by adding
 +      AC_PROG_LIBTOOL and AC_SUBST for acl_shlibext and pkgextensiondir.
 +      (AC_CONFIG_FILES): Add extension/Makefile.
 +      * io.c (pi_awkpath, pi_awklibpath): New static structures to contain
 +      path information.
 +      (awkpath, max_pathlen): Remove static variables now inside pi_awkpath.
 +      (init_awkpath): Operate on path_info structure to support both
 +      AWKPATH and AWKLIBPATH.  No need for max_path to be static, since
 +      this should be called only once for each environment variable.
 +      (do_find_source): Add a path_info arg to specify which path to search.
 +      Check the try_cwd parameter to decide whether to search the current
 +      directory (not desirable for AWKLIBPATH).
 +      (find_source): Choose appropriate path_info structure based on value
 +      of the is_extlib argument.  Set EXTLIB_SUFFIX using SHLIBEXT define
 +      instead of hardcoding ".so".
 +      * main.c (path_environ): New function to add AWKPATH or AWKLIBPATH
 +      to the ENVIRON array.
 +      (load_environ): Call path_environ for AWKPATH and AWKLIBPATH.
++=======
+       * dfa.c: Sync w/GNU grep.
+ 
+ 2012-06-19         Arnold D. Robbins     <address@hidden>
+ 
+       * main.c (main): Do setlocale to "C" if --characters-as-bytes.
+       Thanks to "SP" <address@hidden> for the bug report.
++>>>>>>> gawk-4.0-stable
  
  2012-05-09         Arnold D. Robbins     <address@hidden>
  
diff --cc doc/ChangeLog
index 38b8ad9,f279986..7754974
--- a/doc/ChangeLog
+++ b/doc/ChangeLog
@@@ -1,68 -1,29 +1,94 @@@
 +2012-08-14         Arnold D. Robbins     <address@hidden>
 +
 +      * gawk.texi: Fixed a math bug in the chapter on multiple
 +      precision floating point. Thanks to John Haque.
 +
 +2012-08-12         Arnold D. Robbins     <address@hidden>
 +
 +      * gawk.texi: Merged discussion of numbers from Appendix C into
 +      the chapter on arbitrary precision arithmetic. Did some surgery
 +      on that chapter to organize it a little better.
 +
 +2012-08-10         Arnold D. Robbins     <address@hidden>
 +
 +      * awkcard.in, gawk.1, gawk.texi: Updated. Mostly for new API stuff
 +      but also some other things.
 +      * gawk.texi (Derived Files): New node.
 +
 +2012-08-01         Arnold D. Robbins     <address@hidden>
 +
 +      * Makefile.am (install-data-hook): Install a dgawk.1 link to the
 +      man page also. Remove it on uninstall.
 +
 +2012-07-29         Andrew J. Schorr     <address@hidden>
 +
 +      * gawk.texi: Document that RT is set by getline.
 +
 +2012-07-04         Arnold D. Robbins     <address@hidden>
 +
 +      * gawk.texi, gawk.1, awkcard.in: Document that and(), or(), and
 +      xor() can all take any number of arguments, with a minimum of two.
 +
 +2012-06-10         Andrew J. Schorr     <address@hidden>
 +
 +      * gawk.texi: Rename gettimeofday function to getlocaltime, since
 +      the new time extension will provide gettimeofday.
 +
 +2012-05-24         Andrew J. Schorr     <address@hidden>
 +
 +      * gawk.texi, gawk.1: Replace references to dlload with dl_load.
 +      But much more work needs to be done on the docs.
 +      
 +2012-05-19         Andrew J. Schorr     <address@hidden>
 +
 +      * gawk.texi, gawk.1: Document new -i option, and describe new default
 +      .awk suffix behavior.
 +
 +2012-04-01         Andrew J. Schorr     <address@hidden>
 +
 +      * gawk.texi: Replace documentation of removed functions update_ERRNO and
 +      update_ERRNO_saved with descriptions new functions update_ERRNO_int,
 +      update_ERRNO_string and unset_ERRNO.  And fix a couple of examples
 +      to use update_ERRNO_int instead of update_ERRNO.
 +
 +2012-03-26         Arnold D. Robbins     <address@hidden>
 +
 +      * gawk.texi: Minor style edits.
 +
 +2012-03-21         Andrew J. Schorr     <address@hidden>
 +
 +      * gawk.texi, gawk.1: Document new @load keyword.
 +
 +2012-03-20         Andrew J. Schorr     <address@hidden>
 +
 +      * gawk.texi, gawk.1: Add AWKLIBPATH.
 +
+ 2012-08-12         Arnold D. Robbins     <address@hidden>
+ 
+       * gawk.texi (Ranges and Locales): Clarified ranges and
+       locales. Again.
+ 
+ 2012-08-05         Arnold D. Robbins     <address@hidden>
+ 
+       * gawk.texi (PC Binary Installation): Document Eli Zaretskii's
+       site.
+       (Records): Update case of RS = "a". It only prints 1 if in
+       POSIX mode. Thanks to Jeroen Schot who first reported it.
+ 
+ 2012-07-20         Arnold D. Robbins     <address@hidden>
+ 
+       * gawk.texi (Ranges and Locales): Clarified ranges and
+       locales.
+ 
+ 2012-07-13         Arnold D. Robbins     <address@hidden>
+ 
+       * gawk.texi (Getline Notes): Discuss side effects in
+       argument expression.
+ 
+ 2012-06-29         Arnold D. Robbins     <address@hidden>
+ 
+       * gawk.texi, awkcard.in: Latest mawk understands /dev/stdin.
+ 
  2012-04-27         Arnold D. Robbins     <address@hidden>
  
        * gawk.texi: Add that -b affects output.
diff --cc doc/gawk.info
index 54a8ccf,275188e..4cc3f9f
--- a/doc/gawk.info
+++ b/doc/gawk.info
@@@ -33,456 -33,27863 +33,28819 @@@ texts being (a) (see below), and with t
       software freedom."
  
  
- Indirect:
- gawk.info-1: 1351
- gawk.info-2: 297599
- gawk.info-3: 596405
- gawk.info-4: 896127
- gawk.info-5: 1043758
+ File: gawk.info,  Node: Top,  Next: Foreword,  Up: (dir)
+ 
+ General Introduction
+ ********************
+ 
+ This file documents `awk', a program that you can use to select
+ particular records in a file and perform operations upon them.
+ 
+    Copyright (C) 1989, 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000,
+ 2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010, 2011, 2012 Free
+ Software Foundation, Inc.
+ 
+ 
+    This is Edition 4 of `GAWK: Effective AWK Programming: A User's
+ Guide for GNU Awk', for the 4.0.1 (or later) version of the GNU
+ implementation of AWK.
+ 
+    Permission is granted to copy, distribute and/or modify this document
+ under the terms of the GNU Free Documentation License, Version 1.3 or
+ any later version published by the Free Software Foundation; with the
+ Invariant Sections being "GNU General Public License", the Front-Cover
+ texts being (a) (see below), and with the Back-Cover Texts being (b)
+ (see below).  A copy of the license is included in the section entitled
+ "GNU Free Documentation License".
+ 
+   a. "A GNU Manual"
+ 
+   b. "You have the freedom to copy and modify this GNU manual.  Buying
+      copies from the FSF supports it in developing GNU and promoting
+      software freedom."
+ 
+ * Menu:
+ 
+ * Foreword::                       Some nice words about this
+                                    Info file.
+ * Preface::                        What this Info file is about; brief
+                                    history and acknowledgments.
+ * Getting Started::                A basic introduction to using
+                                    `awk'. How to run an `awk'
+                                    program. Command-line syntax.
+ * Invoking Gawk::                  How to run `gawk'.
+ * Regexp::                         All about matching things using regular
+                                    expressions.
+ * Reading Files::                  How to read files and manipulate fields.
+ * Printing::                       How to print using `awk'. Describes
+                                    the `print' and `printf'
+                                    statements. Also describes redirection of
+                                    output.
+ * Expressions::                    Expressions are the basic building blocks
+                                    of statements.
+ * Patterns and Actions::           Overviews of patterns and actions.
+ * Arrays::                         The description and use of arrays. Also
+                                    includes array-oriented control statements.
+ * Functions::                      Built-in and user-defined functions.
+ * Internationalization::           Getting `gawk' to speak your
+                                    language.
++* Arbitrary Precision Arithmetic:: Arbitrary precision arithmetic with
++                                   `gawk'.
+ * Advanced Features::              Stuff for advanced users, specific to
+                                    `gawk'.
+ * Library Functions::              A Library of `awk' Functions.
+ * Sample Programs::                Many `awk' programs with complete
+                                    explanations.
 -* Debugger::                       The `dgawk' debugger.
++* Debugger::                       The `gawk' debugger.
++* Dynamic Extensions::             Adding new built-in functions to
++                                   `gawk'.
+ * Language History::               The evolution of the `awk'
+                                    language.
+ * Installation::                   Installing `gawk' under various
+                                    operating systems.
 -* Notes::                          Notes about `gawk' extensions and
 -                                   possible future work.
++* Notes::                          Notes about adding things to `gawk'
++                                   and possible future work.
+ * Basic Concepts::                 A very quick introduction to programming
+                                    concepts.
+ * Glossary::                       An explanation of some unfamiliar terms.
+ * Copying::                        Your right to copy and distribute
+                                    `gawk'.
+ * GNU Free Documentation License:: The license for this Info file.
+ * Index::                          Concept and Variable Index.
+ 
+ * History::                        The history of `gawk' and
+                                    `awk'.
+ * Names::                          What name to use to find `awk'.
+ * This Manual::                    Using this Info file. Includes
+                                    sample input files that you can use.
+ * Conventions::                    Typographical Conventions.
+ * Manual History::                 Brief history of the GNU project and this
+                                    Info file.
+ * How To Contribute::              Helping to save the world.
+ * Acknowledgments::                Acknowledgments.
+ * Running gawk::                   How to run `gawk' programs;
+                                    includes command-line syntax.
+ * One-shot::                       Running a short throwaway `awk'
+                                    program.
+ * Read Terminal::                  Using no input files (input from terminal
+                                    instead).
+ * Long::                           Putting permanent `awk' programs in
+                                    files.
+ * Executable Scripts::             Making self-contained `awk'
+                                    programs.
+ * Comments::                       Adding documentation to `gawk'
+                                    programs.
+ * Quoting::                        More discussion of shell quoting issues.
+ * DOS Quoting::                    Quoting in Windows Batch Files.
+ * Sample Data Files::              Sample data files for use in the
+                                    `awk' programs illustrated in this
+                                    Info file.
+ * Very Simple::                    A very simple example.
+ * Two Rules::                      A less simple one-line example using two
+                                    rules.
+ * More Complex::                   A more complex example.
+ * Statements/Lines::               Subdividing or combining statements into
+                                    lines.
+ * Other Features::                 Other Features of `awk'.
+ * When::                           When to use `gawk' and when to use
+                                    other things.
+ * Command Line::                   How to run `awk'.
+ * Options::                        Command-line options and their meanings.
+ * Other Arguments::                Input file names and variable assignments.
+ * Naming Standard Input::          How to specify standard input with other
+                                    files.
+ * Environment Variables::          The environment variables `gawk'
+                                    uses.
+ * AWKPATH Variable::               Searching directories for `awk'
+                                    programs.
++* AWKLIBPATH Variable::            Searching directories for `awk'
++                                   shared libraries.
+ * Other Environment Variables::    The environment variables.
+ * Exit Status::                    `gawk''s exit status.
+ * Include Files::                  Including other files into your program.
++* Loading Shared Libraries::       Loading shared libraries into your program.
+ * Obsolete::                       Obsolete Options and/or features.
+ * Undocumented::                   Undocumented Options and Features.
+ * Regexp Usage::                   How to Use Regular Expressions.
+ * Escape Sequences::               How to write nonprinting characters.
+ * Regexp Operators::               Regular Expression Operators.
+ * Bracket Expressions::            What can go between `[...]'.
+ * GNU Regexp Operators::           Operators specific to GNU software.
+ * Case-sensitivity::               How to do case-insensitive matching.
+ * Leftmost Longest::               How much text matches.
+ * Computed Regexps::               Using Dynamic Regexps.
+ * Records::                        Controlling how data is split into records.
+ * Fields::                         An introduction to fields.
+ * Nonconstant Fields::             Nonconstant Field Numbers.
+ * Changing Fields::                Changing the Contents of a Field.
+ * Field Separators::               The field separator and how to change it.
+ * Default Field Splitting::        How fields are normally separated.
+ * Regexp Field Splitting::         Using regexps as the field separator.
+ * Single Character Fields::        Making each character a separate field.
+ * Command Line Field Separator::   Setting `FS' from the command-line.
+ * Field Splitting Summary::        Some final points and a summary table.
+ * Constant Size::                  Reading constant width data.
+ * Splitting By Content::           Defining Fields By Content
+ * Multiple Line::                  Reading multi-line records.
+ * Getline::                        Reading files under explicit program
+                                    control using the `getline' function.
+ * Plain Getline::                  Using `getline' with no arguments.
+ * Getline/Variable::               Using `getline' into a variable.
+ * Getline/File::                   Using `getline' from a file.
+ * Getline/Variable/File::          Using `getline' into a variable from a
+                                    file.
+ * Getline/Pipe::                   Using `getline' from a pipe.
+ * Getline/Variable/Pipe::          Using `getline' into a variable from a
+                                    pipe.
+ * Getline/Coprocess::              Using `getline' from a coprocess.
+ * Getline/Variable/Coprocess::     Using `getline' into a variable from a
+                                    coprocess.
+ * Getline Notes::                  Important things to know about
+                                    `getline'.
+ * Getline Summary::                Summary of `getline' Variants.
++* Read Timeout::                   Reading input with a timeout.
+ * Command line directories::       What happens if you put a directory on the
+                                    command line.
+ * Print::                          The `print' statement.
+ * Print Examples::                 Simple examples of `print' statements.
+ * Output Separators::              The output separators and how to change
+                                    them.
+ * OFMT::                           Controlling Numeric Output With
+                                    `print'.
+ * Printf::                         The `printf' statement.
+ * Basic Printf::                   Syntax of the `printf' statement.
+ * Control Letters::                Format-control letters.
+ * Format Modifiers::               Format-specification modifiers.
+ * Printf Examples::                Several examples.
+ * Redirection::                    How to redirect output to multiple files
+                                    and pipes.
+ * Special Files::                  File name interpretation in `gawk'.
+                                    `gawk' allows access to inherited
+                                    file descriptors.
+ * Special FD::                     Special files for I/O.
+ * Special Network::                Special files for network communications.
+ * Special Caveats::                Things to watch out for.
+ * Close Files And Pipes::          Closing Input and Output Files and Pipes.
+ * Values::                         Constants, Variables, and Regular
+                                    Expressions.
+ * Constants::                      String, numeric and regexp constants.
+ * Scalar Constants::               Numeric and string constants.
+ * Nondecimal-numbers::             What are octal and hex numbers.
+ * Regexp Constants::               Regular Expression constants.
+ * Using Constant Regexps::         When and how to use a regexp constant.
+ * Variables::                      Variables give names to values for later
+                                    use.
+ * Using Variables::                Using variables in your programs.
+ * Assignment Options::             Setting variables on the command-line and a
+                                    summary of command-line syntax. This is an
+                                    advanced method of input.
+ * Conversion::                     The conversion of strings to numbers and
+                                    vice versa.
+ * All Operators::                  `gawk''s operators.
+ * Arithmetic Ops::                 Arithmetic operations (`+', `-',
+                                    etc.)
+ * Concatenation::                  Concatenating strings.
+ * Assignment Ops::                 Changing the value of a variable or a
+                                    field.
+ * Increment Ops::                  Incrementing the numeric value of a
+                                    variable.
+ * Truth Values and Conditions::    Testing for true and false.
+ * Truth Values::                   What is ``true'' and what is ``false''.
+ * Typing and Comparison::          How variables acquire types and how this
+                                    affects comparison of numbers and strings
+                                    with `<', etc.
+ * Variable Typing::                String type versus numeric type.
+ * Comparison Operators::           The comparison operators.
+ * POSIX String Comparison::        String comparison with POSIX rules.
+ * Boolean Ops::                    Combining comparison expressions using
+                                    boolean operators `||' (``or''),
+                                    `&&' (``and'') and `!' (``not'').
+ * Conditional Exp::                Conditional expressions select between two
+                                    subexpressions under control of a third
+                                    subexpression.
+ * Function Calls::                 A function call is an expression.
+ * Precedence::                     How various operators nest.
+ * Locales::                        How the locale affects things.
+ * Pattern Overview::               What goes into a pattern.
+ * Regexp Patterns::                Using regexps as patterns.
+ * Expression Patterns::            Any expression can be used as a pattern.
+ * Ranges::                         Pairs of patterns specify record ranges.
+ * BEGIN/END::                      Specifying initialization and cleanup
+                                    rules.
+ * Using BEGIN/END::                How and why to use BEGIN/END rules.
+ * I/O And BEGIN/END::              I/O issues in BEGIN/END rules.
+ * BEGINFILE/ENDFILE::              Two special patterns for advanced control.
+ * Empty::                          The empty pattern, which matches every
+                                    record.
+ * Using Shell Variables::          How to use shell variables with
+                                    `awk'.
+ * Action Overview::                What goes into an action.
+ * Statements::                     Describes the various control statements in
+                                    detail.
+ * If Statement::                   Conditionally execute some `awk'
+                                    statements.
+ * While Statement::                Loop until some condition is satisfied.
+ * Do Statement::                   Do specified action while looping until
+                                    some condition is satisfied.
+ * For Statement::                  Another looping statement, that provides
+                                    initialization and increment clauses.
+ * Switch Statement::               Switch/case evaluation for conditional
+                                    execution of statements based on a value.
+ * Break Statement::                Immediately exit the innermost enclosing
+                                    loop.
+ * Continue Statement::             Skip to the end of the innermost enclosing
+                                    loop.
+ * Next Statement::                 Stop processing the current input record.
+ * Nextfile Statement::             Stop processing the current file.
+ * Exit Statement::                 Stop execution of `awk'.
+ * Built-in Variables::             Summarizes the built-in variables.
+ * User-modified::                  Built-in variables that you change to
+                                    control `awk'.
+ * Auto-set::                       Built-in variables where `awk'
+                                    gives you information.
+ * ARGC and ARGV::                  Ways to use `ARGC' and `ARGV'.
+ * Array Basics::                   The basics of arrays.
+ * Array Intro::                    Introduction to Arrays
+ * Reference to Elements::          How to examine one element of an array.
+ * Assigning Elements::             How to change an element of an array.
+ * Array Example::                  Basic Example of an Array
+ * Scanning an Array::              A variation of the `for' statement. It
+                                    loops through the indices of an array's
+                                    existing elements.
+ * Controlling Scanning::           Controlling the order in which arrays are
+                                    scanned.
+ * Delete::                         The `delete' statement removes an
+                                    element from an array.
+ * Numeric Array Subscripts::       How to use numbers as subscripts in
+                                    `awk'.
+ * Uninitialized Subscripts::       Using Uninitialized variables as
+                                    subscripts.
+ * Multi-dimensional::              Emulating multidimensional arrays in
+                                    `awk'.
+ * Multi-scanning::                 Scanning multidimensional arrays.
+ * Arrays of Arrays::               True multidimensional arrays.
+ * Built-in::                       Summarizes the built-in functions.
+ * Calling Built-in::               How to call built-in functions.
+ * Numeric Functions::              Functions that work with numbers, including
+                                    `int()', `sin()' and
+                                    `rand()'.
+ * String Functions::               Functions for string manipulation, such as
+                                    `split()', `match()' and
+                                    `sprintf()'.
+ * Gory Details::                   More than you want to know about `\'
+                                    and `&' with `sub()',
+                                    `gsub()', and `gensub()'.
+ * I/O Functions::                  Functions for files and shell commands.
+ * Time Functions::                 Functions for dealing with timestamps.
+ * Bitwise Functions::              Functions for bitwise operations.
+ * Type Functions::                 Functions for type information.
+ * I18N Functions::                 Functions for string translation.
+ * User-defined::                   Describes User-defined functions in detail.
+ * Definition Syntax::              How to write definitions and what they
+                                    mean.
+ * Function Example::               An example function definition and what it
+                                    does.
+ * Function Caveats::               Things to watch out for.
+ * Calling A Function::             Don't use spaces.
+ * Variable Scope::                 Controlling variable scope.
+ * Pass By Value/Reference::        Passing parameters.
+ * Return Statement::               Specifying the value a function returns.
+ * Dynamic Typing::                 How variable types can change at runtime.
+ * Indirect Calls::                 Choosing the function to call at runtime.
+ * I18N and L10N::                  Internationalization and Localization.
+ * Explaining gettext::             How GNU `gettext' works.
+ * Programmer i18n::                Features for the programmer.
+ * Translator i18n::                Features for the translator.
+ * String Extraction::              Extracting marked strings.
+ * Printf Ordering::                Rearranging `printf' arguments.
+ * I18N Portability::               `awk'-level portability issues.
+ * I18N Example::                   A simple i18n example.
+ * Gawk I18N::                      `gawk' is also internationalized.
++* General Arithmetic::             An introduction to computer arithmetic.
++* Floating Point Issues::          Stuff to know about floating-point numbers.
++* String Conversion Precision::    The String Value Can Lie.
++* Unexpected Results::             Floating Point Numbers Are Not Abstract
++                                   Numbers.
++* POSIX Floating Point Problems::  Standards Versus Existing Practice.
++* Integer Programming::            Effective integer programming.
++* Floating-point Programming::     Effective Floating-point Programming.
++* Floating-point Representation::  Binary floating-point representation.
++* Floating-point Context::         Floating-point context.
++* Rounding Mode::                  Floating-point rounding mode.
++* Gawk and MPFR::                  How `gawk' provides
++                                   aribitrary-precision arithmetic.
++* Arbitrary Precision Floats::     Arbitrary Precision Floating-point
++                                   Arithmetic with `gawk'.
++* Setting Precision::              Setting the working precision.
++* Setting Rounding Mode::          Setting the rounding mode.
++* Floating-point Constants::       Representing floating-point constants.
++* Changing Precision::             Changing the precision of a number.
++* Exact Arithmetic::               Exact arithmetic with floating-point
++                                   numbers.
++* Arbitrary Precision Integers::   Arbitrary Precision Integer Arithmetic with
++                                   `gawk'.
+ * Nondecimal Data::                Allowing nondecimal input data.
+ * Array Sorting::                  Facilities for controlling array traversal
+                                    and sorting arrays.
+ * Controlling Array Traversal::    How to use PROCINFO["sorted_in"].
+ * Array Sorting Functions::        How to use `asort()' and
+                                    `asorti()'.
+ * Two-way I/O::                    Two-way communications with another
+                                    process.
+ * TCP/IP Networking::              Using `gawk' for network
+                                    programming.
+ * Profiling::                      Profiling your `awk' programs.
+ * Library Names::                  How to best name private global variables
+                                    in library functions.
+ * General Functions::              Functions that are of general use.
+ * Strtonum Function::              A replacement for the built-in
+                                    `strtonum()' function.
+ * Assert Function::                A function for assertions in `awk'
+                                    programs.
+ * Round Function::                 A function for rounding if `sprintf()'
+                                    does not do it correctly.
+ * Cliff Random Function::          The Cliff Random Number Generator.
+ * Ordinal Functions::              Functions for using characters as numbers
+                                    and vice versa.
+ * Join Function::                  A function to join an array into a string.
 -* Gettimeofday Function::          A function to get formatted times.
++* Getlocaltime Function::          A function to get formatted times.
+ * Data File Management::           Functions for managing command-line data
+                                    files.
+ * Filetrans Function::             A function for handling data file
+                                    transitions.
+ * Rewind Function::                A function for rereading the current file.
+ * File Checking::                  Checking that data files are readable.
+ * Empty Files::                    Checking for zero-length files.
+ * Ignoring Assigns::               Treating assignments as file names.
+ * Getopt Function::                A function for processing command-line
+                                    arguments.
+ * Passwd Functions::               Functions for getting user information.
+ * Group Functions::                Functions for getting group information.
+ * Walking Arrays::                 A function to walk arrays of arrays.
+ * Running Examples::               How to run these examples.
+ * Clones::                         Clones of common utilities.
+ * Cut Program::                    The `cut' utility.
+ * Egrep Program::                  The `egrep' utility.
+ * Id Program::                     The `id' utility.
+ * Split Program::                  The `split' utility.
+ * Tee Program::                    The `tee' utility.
+ * Uniq Program::                   The `uniq' utility.
+ * Wc Program::                     The `wc' utility.
+ * Miscellaneous Programs::         Some interesting `awk' programs.
+ * Dupword Program::                Finding duplicated words in a document.
+ * Alarm Program::                  An alarm clock.
+ * Translate Program::              A program similar to the `tr'
+                                    utility.
+ * Labels Program::                 Printing mailing labels.
+ * Word Sorting::                   A program to produce a word usage count.
+ * History Sorting::                Eliminating duplicate entries from a
+                                    history file.
+ * Extract Program::                Pulling out programs from Texinfo source
+                                    files.
+ * Simple Sed::                     A Simple Stream Editor.
+ * Igawk Program::                  A wrapper for `awk' that includes
+                                    files.
+ * Anagram Program::                Finding anagrams from a dictionary.
+ * Signature Program::              People do amazing things with too much time
+                                    on their hands.
 -* Debugging::                      Introduction to `dgawk'.
 -* Debugging Concepts::             Debugging In General.
++* Debugging::                      Introduction to `gawk' debugger.
++* Debugging Concepts::             Debugging in General.
+ * Debugging Terms::                Additional Debugging Concepts.
+ * Awk Debugging::                  Awk Debugging.
 -* Sample dgawk session::           Sample `dgawk' session.
 -* dgawk invocation::               `dgawk' Invocation.
 -* Finding The Bug::                Finding The Bug.
 -* List of Debugger Commands::      Main `dgawk' Commands.
 -* Breakpoint Control::             Control of breakpoints.
 -* Dgawk Execution Control::        Control of execution.
 -* Viewing And Changing Data::      Viewing and changing data.
 -* Dgawk Stack::                    Dealing with the stack.
 -* Dgawk Info::                     Obtaining information about the program and
 -                                   the debugger state.
 -* Miscellaneous Dgawk Commands::   Miscellaneous Commands.
 -* Readline Support::               Readline Support.
 -* Dgawk Limitations::              Limitations and future plans.
++* Sample Debugging Session::       Sample debugging session.
++* Debugger Invocation::            How to Start the Debugger.
++* Finding The Bug::                Finding the Bug.
++* List of Debugger Commands::      Main debugger commands.
++* Breakpoint Control::             Control of Breakpoints.
++* Debugger Execution Control::     Control of Execution.
++* Viewing And Changing Data::      Viewing and Changing Data.
++* Execution Stack::                Dealing with the Stack.
++* Debugger Info::                  Obtaining Information about the Program and
++                                   the Debugger State.
++* Miscellaneous Debugger Commands:: Miscellaneous Commands.
++* Readline Support::               Readline support.
++* Limitations::                    Limitations and future plans.
++* Plugin License::                 A note about licensing.
++* Sample Library::                 A example of new functions.
++* Internal File Description::      What the new functions will do.
++* Internal File Ops::              The code for internal file operations.
++* Using Internal File Ops::        How to use an external extension.
+ * V7/SVR3.1::                      The major changes between V7 and System V
+                                    Release 3.1.
+ * SVR4::                           Minor changes between System V Releases 3.1
+                                    and 4.
+ * POSIX::                          New features from the POSIX standard.
+ * BTL::                            New features from Brian Kernighan's version
+                                    of `awk'.
+ * POSIX/GNU::                      The extensions in `gawk' not in
+                                    POSIX `awk'.
+ * Common Extensions::              Common Extensions Summary.
+ * Ranges and Locales::             How locales used to affect regexp ranges.
+ * Contributors::                   The major contributors to `gawk'.
+ * Gawk Distribution::              What is in the `gawk' distribution.
+ * Getting::                        How to get the distribution.
+ * Extracting::                     How to extract the distribution.
+ * Distribution contents::          What is in the distribution.
+ * Unix Installation::              Installing `gawk' under various
+                                    versions of Unix.
+ * Quick Installation::             Compiling `gawk' under Unix.
+ * Additional Configuration Options:: Other compile-time options.
+ * Configuration Philosophy::       How it's all supposed to work.
+ * Non-Unix Installation::          Installation on Other Operating Systems.
+ * PC Installation::                Installing and Compiling `gawk' on
+                                    MS-DOS and OS/2.
+ * PC Binary Installation::         Installing a prepared distribution.
+ * PC Compiling::                   Compiling `gawk' for MS-DOS,
+                                    Windows32, and OS/2.
+ * PC Testing::                     Testing `gawk' on PC systems.
+ * PC Using::                       Running `gawk' on MS-DOS, Windows32
+                                    and OS/2.
+ * Cygwin::                         Building and running `gawk' for
+                                    Cygwin.
+ * MSYS::                           Using `gawk' In The MSYS
+                                    Environment.
+ * VMS Installation::               Installing `gawk' on VMS.
+ * VMS Compilation::                How to compile `gawk' under VMS.
+ * VMS Installation Details::       How to install `gawk' under VMS.
+ * VMS Running::                    How to run `gawk' under VMS.
+ * VMS Old Gawk::                   An old version comes with some VMS systems.
+ * Bugs::                           Reporting Problems and Bugs.
+ * Other Versions::                 Other freely available `awk'
+                                    implementations.
+ * Compatibility Mode::             How to disable certain `gawk'
+                                    extensions.
+ * Additions::                      Making Additions To `gawk'.
+ * Accessing The Source::           Accessing the Git repository.
+ * Adding Code::                    Adding code to the main body of
+                                    `gawk'.
+ * New Ports::                      Porting `gawk' to a new operating
+                                    system.
 -* Dynamic Extensions::             Adding new built-in functions to
 -                                   `gawk'.
 -* Internals::                      A brief look at some `gawk'
 -                                   internals.
 -* Plugin License::                 A note about licensing.
 -* Sample Library::                 A example of new functions.
 -* Internal File Description::      What the new functions will do.
 -* Internal File Ops::              The code for internal file operations.
 -* Using Internal File Ops::        How to use an external extension.
++* Derived Files::                  Why derived files are kept in the
++                                   `git' repository.
+ * Future Extensions::              New features that may be implemented one
+                                    day.
+ * Basic High Level::               The high level view.
+ * Basic Data Typing::              A very quick intro to data types.
 -* Floating Point Issues::          Stuff to know about floating-point numbers.
 -* String Conversion Precision::    The String Value Can Lie.
 -* Unexpected Results::             Floating Point Numbers Are Not Abstract
 -                                   Numbers.
 -* POSIX Floating Point Problems::  Standards Versus Existing Practice.
+ 
+                   To Miriam, for making me complete.
+ 
+                   To Chana, for the joy you bring us.
+ 
+                 To Rivka, for the exponential increase.
+ 
+                   To Nachum, for the added dimension.
+ 
+                    To Malka, for the new beginning.
+ 
+ File: gawk.info,  Node: Foreword,  Next: Preface,  Prev: Top,  Up: Top
+ 
+ Foreword
+ ********
+ 
+ Arnold Robbins and I are good friends. We were introduced in 1990 by
+ circumstances--and our favorite programming language, AWK.  The
+ circumstances started a couple of years earlier. I was working at a new
+ job and noticed an unplugged Unix computer sitting in the corner.  No
+ one knew how to use it, and neither did I.  However, a couple of days
+ later it was running, and I was `root' and the one-and-only user.  That
+ day, I began the transition from statistician to Unix programmer.
+ 
+    On one of many trips to the library or bookstore in search of books
+ on Unix, I found the gray AWK book, a.k.a. Aho, Kernighan and
+ Weinberger, `The AWK Programming Language', Addison-Wesley, 1988.
+ AWK's simple programming paradigm--find a pattern in the input and then
+ perform an action--often reduced complex or tedious data manipulations
+ to few lines of code.  I was excited to try my hand at programming in
+ AWK.
+ 
+    Alas,  the `awk' on my computer was a limited version of the
+ language described in the AWK book.  I discovered that my computer had
+ "old `awk'" and the AWK book described "new `awk'."  I learned that
+ this was typical; the old version refused to step aside or relinquish
+ its name.  If a system had a new `awk', it was invariably called
+ `nawk', and few systems had it.  The best way to get a new `awk' was to
+ `ftp' the source code for `gawk' from `prep.ai.mit.edu'.  `gawk' was a
+ version of new `awk' written by David Trueman and Arnold, and available
+ under the GNU General Public License.
+ 
+    (Incidentally, it's no longer difficult to find a new `awk'. `gawk'
+ ships with GNU/Linux, and you can download binaries or source code for
+ almost any system; my wife uses `gawk' on her VMS box.)
+ 
+    My Unix system started out unplugged from the wall; it certainly was
+ not plugged into a network.  So, oblivious to the existence of `gawk'
+ and the Unix community in general, and desiring a new `awk', I wrote my
+ own, called `mawk'.  Before I was finished I knew about `gawk', but it
+ was too late to stop, so I eventually posted to a `comp.sources'
+ newsgroup.
+ 
+    A few days after my posting, I got a friendly email from Arnold
+ introducing himself.   He suggested we share design and algorithms and
+ attached a draft of the POSIX standard so that I could update `mawk' to
+ support language extensions added after publication of the AWK book.
+ 
+    Frankly, if our roles had been reversed, I would not have been so
+ open and we probably would have never met.  I'm glad we did meet.  He
+ is an AWK expert's AWK expert and a genuinely nice person.  Arnold
+ contributes significant amounts of his expertise and time to the Free
+ Software Foundation.
+ 
+    This book is the `gawk' reference manual, but at its core it is a
+ book about AWK programming that will appeal to a wide audience.  It is
+ a definitive reference to the AWK language as defined by the 1987 Bell
+ Laboratories release and codified in the 1992 POSIX Utilities standard.
+ 
+    On the other hand, the novice AWK programmer can study a wealth of
+ practical programs that emphasize the power of AWK's basic idioms: data
+ driven control-flow, pattern matching with regular expressions, and
+ associative arrays.  Those looking for something new can try out
+ `gawk''s interface to network protocols via special `/inet' files.
+ 
+    The programs in this book make clear that an AWK program is
+ typically much smaller and faster to develop than a counterpart written
+ in C.  Consequently, there is often a payoff to prototype an algorithm
+ or design in AWK to get it running quickly and expose problems early.
+ Often, the interpreted performance is adequate and the AWK prototype
+ becomes the product.
+ 
+    The new `pgawk' (profiling `gawk'), produces program execution
+ counts.  I recently experimented with an algorithm that for n lines of
+ input, exhibited ~ C n^2 performance, while theory predicted ~ C n log n
+ behavior. A few minutes poring over the `awkprof.out' profile
+ pinpointed the problem to a single line of code.  `pgawk' is a welcome
+ addition to my programmer's toolbox.
+ 
+    Arnold has distilled over a decade of experience writing and using
+ AWK programs, and developing `gawk', into this book.  If you use AWK or
+ want to learn how, then read this book.
+ 
+      Michael Brennan
+      Author of `mawk'
+      March, 2001
+ 
+ 
+ File: gawk.info,  Node: Preface,  Next: Getting Started,  Prev: Foreword,  
Up: Top
+ 
+ Preface
+ *******
+ 
+ Several kinds of tasks occur repeatedly when working with text files.
+ You might want to extract certain lines and discard the rest.  Or you
+ may need to make changes wherever certain patterns appear, but leave
+ the rest of the file alone.  Writing single-use programs for these
+ tasks in languages such as C, C++, or Java is time-consuming and
+ inconvenient.  Such jobs are often easier with `awk'.  The `awk'
+ utility interprets a special-purpose programming language that makes it
+ easy to handle simple data-reformatting jobs.
+ 
+    The GNU implementation of `awk' is called `gawk'; if you invoke it
+ with the proper options or environment variables (*note Options::), it
+ is fully compatible with the POSIX(1) specification of the `awk'
+ language and with the Unix version of `awk' maintained by Brian
+ Kernighan.  This means that all properly written `awk' programs should
+ work with `gawk'.  Thus, we usually don't distinguish between `gawk'
+ and other `awk' implementations.
+ 
+    Using `awk' allows you to:
+ 
+    * Manage small, personal databases
+ 
+    * Generate reports
+ 
+    * Validate data
+ 
+    * Produce indexes and perform other document preparation tasks
+ 
+    * Experiment with algorithms that you can adapt later to other
+      computer languages
+ 
+    In addition, `gawk' provides facilities that make it easy to:
+ 
+    * Extract bits and pieces of data for processing
+ 
+    * Sort data
+ 
+    * Perform simple network communications
+ 
+    This Info file teaches you about the `awk' language and how you can
+ use it effectively.  You should already be familiar with basic system
+ commands, such as `cat' and `ls',(2) as well as basic shell facilities,
+ such as input/output (I/O) redirection and pipes.
+ 
+    Implementations of the `awk' language are available for many
+ different computing environments.  This Info file, while describing the
+ `awk' language in general, also describes the particular implementation
+ of `awk' called `gawk' (which stands for "GNU awk").  `gawk' runs on a
+ broad range of Unix systems, ranging from Intel(R)-architecture
+ PC-based computers up through large-scale systems, such as Crays.
+ `gawk' has also been ported to Mac OS X, Microsoft Windows (all
+ versions) and OS/2 PCs, and VMS.  (Some other, obsolete systems to
+ which `gawk' was once ported are no longer supported and the code for
+ those systems has been removed.)
+ 
+ * Menu:
+ 
+ * History::                     The history of `gawk' and
+                                 `awk'.
+ * Names::                       What name to use to find `awk'.
+ * This Manual::                 Using this Info file. Includes sample
+                                 input files that you can use.
+ * Conventions::                 Typographical Conventions.
+ * Manual History::              Brief history of the GNU project and this
+                                 Info file.
+ * How To Contribute::           Helping to save the world.
+ * Acknowledgments::             Acknowledgments.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The 2008 POSIX standard can be found online at
+ `http://www.opengroup.org/onlinepubs/9699919799/'.
+ 
+    (2) These commands are available on POSIX-compliant systems, as well
+ as on traditional Unix-based systems. If you are using some other
+ operating system, you still need to be familiar with the ideas of I/O
+ redirection and pipes.
+ 
+ 
+ File: gawk.info,  Node: History,  Next: Names,  Up: Preface
+ 
+ History of `awk' and `gawk'
+ ===========================
+ 
+                    Recipe For A Programming Language
+ 
+           1 part  `egrep'   1 part  `snobol'
+           2 parts `ed'      3 parts C
+ 
+      Blend all parts well using `lex' and `yacc'.  Document minimally
+      and release.
+ 
+      After eight years, add another part `egrep' and two more parts C.
+      Document very well and release.
+ 
+    The name `awk' comes from the initials of its designers: Alfred V.
+ Aho, Peter J. Weinberger and Brian W. Kernighan.  The original version
+ of `awk' was written in 1977 at AT&T Bell Laboratories.  In 1985, a new
+ version made the programming language more powerful, introducing
+ user-defined functions, multiple input streams, and computed regular
+ expressions.  This new version became widely available with Unix System
+ V Release 3.1 (1987).  The version in System V Release 4 (1989) added
+ some new features and cleaned up the behavior in some of the "dark
+ corners" of the language.  The specification for `awk' in the POSIX
+ Command Language and Utilities standard further clarified the language.
+ Both the `gawk' designers and the original Bell Laboratories `awk'
+ designers provided feedback for the POSIX specification.
+ 
+    Paul Rubin wrote the GNU implementation, `gawk', in 1986.  Jay
+ Fenlason completed it, with advice from Richard Stallman.  John Woods
+ contributed parts of the code as well.  In 1988 and 1989, David
+ Trueman, with help from me, thoroughly reworked `gawk' for compatibility
+ with the newer `awk'.  Circa 1994, I became the primary maintainer.
+ Current development focuses on bug fixes, performance improvements,
+ standards compliance, and occasionally, new features.
+ 
+    In May of 1997, Ju"rgen Kahrs felt the need for network access from
+ `awk', and with a little help from me, set about adding features to do
+ this for `gawk'.  At that time, he also wrote the bulk of `TCP/IP
+ Internetworking with `gawk'' (a separate document, available as part of
+ the `gawk' distribution).  His code finally became part of the main
+ `gawk' distribution with `gawk' version 3.1.
+ 
+    John Haque rewrote the `gawk' internals, in the process providing an
+ `awk'-level debugger. This version became available as `gawk' version
+ 4.0, in 2011.
+ 
+    *Note Contributors::, for a complete list of those who made
+ important contributions to `gawk'.
+ 
+ 
+ File: gawk.info,  Node: Names,  Next: This Manual,  Prev: History,  Up: 
Preface
+ 
+ A Rose by Any Other Name
+ ========================
+ 
+ The `awk' language has evolved over the years. Full details are
+ provided in *note Language History::.  The language described in this
+ Info file is often referred to as "new `awk'" (`nawk').
+ 
+    Because of this, there are systems with multiple versions of `awk'.
+ Some systems have an `awk' utility that implements the original version
+ of the `awk' language and a `nawk' utility for the new version.  Others
+ have an `oawk' version for the "old `awk'" language and plain `awk' for
+ the new one.  Still others only have one version, which is usually the
+ new one.(1)
+ 
+    All in all, this makes it difficult for you to know which version of
+ `awk' you should run when writing your programs.  The best advice we
+ can give here is to check your local documentation. Look for `awk',
+ `oawk', and `nawk', as well as for `gawk'.  It is likely that you
+ already have some version of new `awk' on your system, which is what
+ you should use when running your programs.  (Of course, if you're
+ reading this Info file, chances are good that you have `gawk'!)
+ 
+    Throughout this Info file, whenever we refer to a language feature
+ that should be available in any complete implementation of POSIX `awk',
+ we simply use the term `awk'.  When referring to a feature that is
+ specific to the GNU implementation, we use the term `gawk'.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Often, these systems use `gawk' for their `awk' implementation!
+ 
+ 
+ File: gawk.info,  Node: This Manual,  Next: Conventions,  Prev: Names,  Up: 
Preface
+ 
+ Using This Book
+ ===============
+ 
+ The term `awk' refers to a particular program as well as to the
+ language you use to tell this program what to do.  When we need to be
+ careful, we call the language "the `awk' language," and the program
+ "the `awk' utility."  This Info file explains both how to write
+ programs in the `awk' language and how to run the `awk' utility.  The
+ term "`awk' program" refers to a program written by you in the `awk'
+ programming language.
+ 
+    Primarily, this Info file explains the features of `awk' as defined
+ in the POSIX standard.  It does so in the context of the `gawk'
+ implementation.  While doing so, it also attempts to describe important
+ differences between `gawk' and other `awk' implementations.(1) Finally,
+ any `gawk' features that are not in the POSIX standard for `awk' are
+ noted.
+ 
+    There are subsections labeled as *Advanced Notes* scattered
+ throughout the Info file.  They add a more complete explanation of
+ points that are relevant, but not likely to be of interest on first
+ reading.  All appear in the index, under the heading "advanced
+ features."
+ 
+    Most of the time, the examples use complete `awk' programs.  Some of
+ the more advanced sections show only the part of the `awk' program that
+ illustrates the concept currently being described.
+ 
+    While this Info file is aimed principally at people who have not been
+ exposed to `awk', there is a lot of information here that even the `awk'
+ expert should find useful.  In particular, the description of POSIX
+ `awk' and the example programs in *note Library Functions::, and in
+ *note Sample Programs::, should be of interest.
+ 
+    *note Getting Started::, provides the essentials you need to know to
+ begin using `awk'.
+ 
+    *note Invoking Gawk::, describes how to run `gawk', the meaning of
+ its command-line options, and how it finds `awk' program source files.
+ 
+    *note Regexp::, introduces regular expressions in general, and in
+ particular the flavors supported by POSIX `awk' and `gawk'.
+ 
+    *note Reading Files::, describes how `awk' reads your data.  It
+ introduces the concepts of records and fields, as well as the `getline'
+ command.  I/O redirection is first described here.  Network I/O is also
+ briefly introduced here.
+ 
+    *note Printing::, describes how `awk' programs can produce output
+ with `print' and `printf'.
+ 
+    *note Expressions::, describes expressions, which are the basic
+ building blocks for getting most things done in a program.
+ 
+    *note Patterns and Actions::, describes how to write patterns for
+ matching records, actions for doing something when a record is matched,
+ and the built-in variables `awk' and `gawk' use.
+ 
+    *note Arrays::, covers `awk''s one-and-only data structure:
+ associative arrays.  Deleting array elements and whole arrays is also
+ described, as well as sorting arrays in `gawk'.  It also describes how
+ `gawk' provides arrays of arrays.
+ 
+    *note Functions::, describes the built-in functions `awk' and `gawk'
+ provide, as well as how to define your own functions.
+ 
+    *note Internationalization::, describes special features in `gawk'
+ for translating program messages into different languages at runtime.
+ 
+    *note Advanced Features::, describes a number of `gawk'-specific
+ advanced features.  Of particular note are the abilities to have
+ two-way communications with another process, perform TCP/IP networking,
+ and profile your `awk' programs.
+ 
+    *note Library Functions::, and *note Sample Programs::, provide many
+ sample `awk' programs.  Reading them allows you to see `awk' solving
+ real problems.
+ 
 -   *note Debugger::, describes the `awk' debugger, `dgawk'.
++   *note Debugger::, describes the `awk' debugger.
+ 
+    *note Language History::, describes how the `awk' language has
+ evolved since its first release to present.  It also describes how
+ `gawk' has acquired features over time.
+ 
+    *note Installation::, describes how to get `gawk', how to compile it
+ on POSIX-compatible systems, and how to compile and use it on different
+ non-POSIX systems.  It also describes how to report bugs in `gawk' and
+ where to get other freely available `awk' implementations.
+ 
+    *note Notes::, describes how to disable `gawk''s extensions, as well
 -as how to contribute new code to `gawk', how to write extension
 -libraries, and some possible future directions for `gawk' development.
++as how to contribute new code to `gawk', and some possible future
++directions for `gawk' development.
+ 
+    *note Basic Concepts::, provides some very cursory background
+ material for those who are completely unfamiliar with computer
+ programming.  Also centralized there is a discussion of some of the
+ issues surrounding floating-point numbers.
+ 
+    The *note Glossary::, defines most, if not all, the significant
+ terms used throughout the book.  If you find terms that you aren't
+ familiar with, try looking them up here.
+ 
+    *note Copying::, and *note GNU Free Documentation License::, present
+ the licenses that cover the `gawk' source code and this Info file,
+ respectively.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) All such differences appear in the index under the entry
+ "differences in `awk' and `gawk'."
+ 
+ 
+ File: gawk.info,  Node: Conventions,  Next: Manual History,  Prev: This 
Manual,  Up: Preface
+ 
+ Typographical Conventions
+ =========================
+ 
+ This Info file is written in Texinfo (http://texinfo.org), the GNU
+ documentation formatting language.  A single Texinfo source file is
+ used to produce both the printed and online versions of the
+ documentation.  This minor node briefly documents the typographical
+ conventions used in Texinfo.
+ 
+    Examples you would type at the command-line are preceded by the
+ common shell primary and secondary prompts, `$' and `>'.  Input that
+ you type is shown `like this'.  Output from the command is preceded by
+ the glyph "-|".  This typically represents the command's standard
+ output.  Error messages, and other output on the command's standard
+ error, are preceded by the glyph "error-->".  For example:
+ 
+      $ echo hi on stdout
+      -| hi on stdout
+      $ echo hello on stderr 1>&2
+      error--> hello on stderr
+ 
+    Characters that you type at the keyboard look `like this'.  In
+ particular, there are special characters called "control characters."
+ These are characters that you type by holding down both the `CONTROL'
+ key and another key, at the same time.  For example, a `Ctrl-d' is typed
+ by first pressing and holding the `CONTROL' key, next pressing the `d'
+ key and finally releasing both keys.
+ 
+ Dark Corners
+ ............
+ 
+      Dark corners are basically fractal -- no matter how much you
+      illuminate, there's always a smaller but darker one.
+      Brian Kernighan
+ 
+    Until the POSIX standard (and `GAWK: Effective AWK Programming'),
+ many features of `awk' were either poorly documented or not documented
+ at all.  Descriptions of such features (often called "dark corners")
+ are noted in this Info file with "(d.c.)".  They also appear in the
+ index under the heading "dark corner."
+ 
+    As noted by the opening quote, though, any coverage of dark corners
+ is, by definition, incomplete.
+ 
+    Extensions to the standard `awk' language that are supported by more
+ than one `awk' implementation are marked "(c.e.)," and listed in the
+ index under "common extensions" and "extensions, common."
+ 
+ 
+ File: gawk.info,  Node: Manual History,  Next: How To Contribute,  Prev: 
Conventions,  Up: Preface
+ 
+ The GNU Project and This Book
+ =============================
+ 
+ The Free Software Foundation (FSF) is a nonprofit organization dedicated
+ to the production and distribution of freely distributable software.
+ It was founded by Richard M. Stallman, the author of the original Emacs
+ editor.  GNU Emacs is the most widely used version of Emacs today.
+ 
+    The GNU(1) Project is an ongoing effort on the part of the Free
+ Software Foundation to create a complete, freely distributable,
+ POSIX-compliant computing environment.  The FSF uses the "GNU General
+ Public License" (GPL) to ensure that their software's source code is
+ always available to the end user. A copy of the GPL is included for
+ your reference (*note Copying::).  The GPL applies to the C language
+ source code for `gawk'.  To find out more about the FSF and the GNU
+ Project online, see the GNU Project's home page (http://www.gnu.org).
+ This Info file may also be read from their web site
+ (http://www.gnu.org/software/gawk/manual/).
+ 
+    A shell, an editor (Emacs), highly portable optimizing C, C++, and
+ Objective-C compilers, a symbolic debugger and dozens of large and
+ small utilities (such as `gawk'), have all been completed and are
+ freely available.  The GNU operating system kernel (the HURD), has been
+ released but remains in an early stage of development.
+ 
+    Until the GNU operating system is more fully developed, you should
+ consider using GNU/Linux, a freely distributable, Unix-like operating
+ system for Intel(R), Power Architecture, Sun SPARC, IBM S/390, and other
+ systems.(2) Many GNU/Linux distributions are available for download
+ from the Internet.
+ 
+    (There are numerous other freely available, Unix-like operating
+ systems based on the Berkeley Software Distribution, and some of them
+ use recent versions of `gawk' for their versions of `awk'.  NetBSD
+ (http://www.netbsd.org), FreeBSD (http://www.freebsd.org), and OpenBSD
+ (http://www.openbsd.org) are three of the most popular ones, but there
+ are others.)
+ 
+    The Info file itself has gone through a number of previous editions.
+ Paul Rubin wrote the very first draft of `The GAWK Manual'; it was
+ around 40 pages in size.  Diane Close and Richard Stallman improved it,
+ yielding a version that was around 90 pages long and barely described
+ the original, "old" version of `awk'.
+ 
+    I started working with that version in the fall of 1988.  As work on
+ it progressed, the FSF published several preliminary versions (numbered
+ 0.X).  In 1996, Edition 1.0 was released with `gawk' 3.0.0.  The FSF
+ published the first two editions under the title `The GNU Awk User's
+ Guide'.
+ 
+    This edition maintains the basic structure of the previous editions.
+ For Edition 4.0, the content has been thoroughly reviewed and updated.
+ All references to versions prior to 4.0 have been removed.  Of
+ significant note for this edition is *note Debugger::.
+ 
+    `GAWK: Effective AWK Programming' will undoubtedly continue to
+ evolve.  An electronic version comes with the `gawk' distribution from
+ the FSF.  If you find an error in this Info file, please report it!
+ *Note Bugs::, for information on submitting problem reports
+ electronically.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) GNU stands for "GNU's not Unix."
+ 
+    (2) The terminology "GNU/Linux" is explained in the *note Glossary::.
+ 
+ 
+ File: gawk.info,  Node: How To Contribute,  Next: Acknowledgments,  Prev: 
Manual History,  Up: Preface
+ 
+ How to Contribute
+ =================
+ 
+ As the maintainer of GNU `awk', I once thought that I would be able to
+ manage a collection of publicly available `awk' programs and I even
+ solicited contributions.  Making things available on the Internet helps
+ keep the `gawk' distribution down to manageable size.
+ 
+    The initial collection of material, such as it is, is still available
+ at `ftp://ftp.freefriends.org/arnold/Awkstuff'.  In the hopes of doing
+ something more broad, I acquired the `awk.info' domain.
+ 
+    However, I found that I could not dedicate enough time to managing
+ contributed code: the archive did not grow and the domain went unused
+ for several years.
+ 
+    Fortunately, late in 2008, a volunteer took on the task of setting up
+ an `awk'-related web site--`http://awk.info'--and did a very nice job.
+ 
+    If you have written an interesting `awk' program, or have written a
+ `gawk' extension that you would like to share with the rest of the
+ world, please see `http://awk.info/?contribute' for how to contribute
+ it to the web site.
+ 
+ 
+ File: gawk.info,  Node: Acknowledgments,  Prev: How To Contribute,  Up: 
Preface
+ 
+ Acknowledgments
+ ===============
+ 
+ The initial draft of `The GAWK Manual' had the following
+ acknowledgments:
+ 
+      Many people need to be thanked for their assistance in producing
+      this manual.  Jay Fenlason contributed many ideas and sample
+      programs.  Richard Mlynarik and Robert Chassell gave helpful
+      comments on drafts of this manual.  The paper `A Supplemental
+      Document for `awk'' by John W.  Pierce of the Chemistry Department
+      at UC San Diego, pinpointed several issues relevant both to `awk'
+      implementation and to this manual, that would otherwise have
+      escaped us.
+ 
+    I would like to acknowledge Richard M. Stallman, for his vision of a
+ better world and for his courage in founding the FSF and starting the
+ GNU Project.
+ 
+    Earlier editions of this Info file had the following
+ acknowledgements:
+ 
+      The following people (in alphabetical order) provided helpful
+      comments on various versions of this book, Rick Adams, Dr. Nelson
+      H.F. Beebe, Karl Berry, Dr. Michael Brennan, Rich Burridge, Claire
+      Cloutier, Diane Close, Scott Deifik, Christopher ("Topher") Eliot,
+      Jeffrey Friedl, Dr. Darrel Hankerson, Michal Jaegermann, Dr.
+      Richard J. LeBlanc, Michael Lijewski, Pat Rankin, Miriam Robbins,
+      Mary Sheehan, and Chuck Toporek.
+ 
+      Robert J. Chassell provided much valuable advice on the use of
+      Texinfo.  He also deserves special thanks for convincing me _not_
+      to title this Info file `How To Gawk Politely'.  Karl Berry helped
+      significantly with the TeX part of Texinfo.
+ 
+      I would like to thank Marshall and Elaine Hartholz of Seattle and
+      Dr. Bert and Rita Schreiber of Detroit for large amounts of quiet
+      vacation time in their homes, which allowed me to make significant
+      progress on this Info file and on `gawk' itself.
+ 
+      Phil Hughes of SSC contributed in a very important way by loaning
+      me his laptop GNU/Linux system, not once, but twice, which allowed
+      me to do a lot of work while away from home.
+ 
+      David Trueman deserves special credit; he has done a yeoman job of
+      evolving `gawk' so that it performs well and without bugs.
+      Although he is no longer involved with `gawk', working with him on
+      this project was a significant pleasure.
+ 
+      The intrepid members of the GNITS mailing list, and most notably
+      Ulrich Drepper, provided invaluable help and feedback for the
+      design of the internationalization features.
+ 
+      Chuck Toporek, Mary Sheehan, and Claire Coutier of O'Reilly &
+      Associates contributed significant editorial help for this Info
+      file for the 3.1 release of `gawk'.
+ 
+    Dr. Nelson Beebe, Andreas Buening, Antonio Colombo, Stephen Davies,
+ Scott Deifik, John H. DuBois III, Darrel Hankerson, Michal Jaegermann,
+ Ju"rgen Kahrs, Dave Pitts, Stepan Kasal, Pat Rankin, Andrew Schorr,
+ Corinna Vinschen, Anders Wallin, and Eli Zaretskii (in alphabetical
+ order) make up the current `gawk' "crack portability team."  Without
+ their hard work and help, `gawk' would not be nearly the fine program
+ it is today.  It has been and continues to be a pleasure working with
+ this team of fine people.
+ 
+    John Haque contributed the modifications to convert `gawk' into a
 -byte-code interpreter, including the debugger. Stephen Davies
 -contributed to the effort to bring the byte-code changes into the
 -mainstream code base.  Efraim Yawitz contributed the initial text of
 -*note Debugger::.
++byte-code interpreter, including the debugger, and the additional
++modifications for support of arbitrary precision arithmetic.  Stephen
++Davies contributed to the effort to bring the byte-code changes into
++the mainstream code base.  Efraim Yawitz contributed the initial text
++of *note Debugger::.  John Haque contributed the initial text of *note
++Arbitrary Precision Arithmetic::.
+ 
+    I would like to thank Brian Kernighan for invaluable assistance
+ during the testing and debugging of `gawk', and for ongoing help and
+ advice in clarifying numerous points about the language.   We could not
+ have done nearly as good a job on either `gawk' or its documentation
+ without his help.
+ 
+    I must thank my wonderful wife, Miriam, for her patience through the
+ many versions of this project, for her proofreading, and for sharing me
+ with the computer.  I would like to thank my parents for their love,
+ and for the grace with which they raised and educated me.  Finally, I
+ also must acknowledge my gratitude to G-d, for the many opportunities
+ He has sent my way, as well as for the gifts He has given me with which
+ to take advantage of those opportunities.
+ 
+ 
+ Arnold Robbins
+ Nof Ayalon
+ ISRAEL
+ March, 2011
+ 
+ 
+ File: gawk.info,  Node: Getting Started,  Next: Invoking Gawk,  Prev: 
Preface,  Up: Top
+ 
+ 1 Getting Started with `awk'
+ ****************************
+ 
+ The basic function of `awk' is to search files for lines (or other
+ units of text) that contain certain patterns.  When a line matches one
+ of the patterns, `awk' performs specified actions on that line.  `awk'
+ keeps processing input lines in this way until it reaches the end of
+ the input files.
+ 
+    Programs in `awk' are different from programs in most other
+ languages, because `awk' programs are "data-driven"; that is, you
+ describe the data you want to work with and then what to do when you
+ find it.  Most other languages are "procedural"; you have to describe,
+ in great detail, every step the program is to take.  When working with
+ procedural languages, it is usually much harder to clearly describe the
+ data your program will process.  For this reason, `awk' programs are
+ often refreshingly easy to read and write.
+ 
+    When you run `awk', you specify an `awk' "program" that tells `awk'
+ what to do.  The program consists of a series of "rules".  (It may also
+ contain "function definitions", an advanced feature that we will ignore
+ for now.  *Note User-defined::.)  Each rule specifies one pattern to
+ search for and one action to perform upon finding the pattern.
+ 
+    Syntactically, a rule consists of a pattern followed by an action.
+ The action is enclosed in curly braces to separate it from the pattern.
+ Newlines usually separate rules.  Therefore, an `awk' program looks
+ like this:
+ 
+      PATTERN { ACTION }
+      PATTERN { ACTION }
+      ...
+ 
+ * Menu:
+ 
+ * Running gawk::                How to run `gawk' programs; includes
+                                 command-line syntax.
+ * Sample Data Files::           Sample data files for use in the `awk'
+                                 programs illustrated in this Info file.
+ * Very Simple::                 A very simple example.
+ * Two Rules::                   A less simple one-line example using two
+                                 rules.
+ * More Complex::                A more complex example.
+ * Statements/Lines::            Subdividing or combining statements into
+                                 lines.
+ * Other Features::              Other Features of `awk'.
+ * When::                        When to use `gawk' and when to use
+                                 other things.
+ 
+ 
+ File: gawk.info,  Node: Running gawk,  Next: Sample Data Files,  Up: Getting 
Started
+ 
+ 1.1 How to Run `awk' Programs
+ =============================
+ 
+ There are several ways to run an `awk' program.  If the program is
+ short, it is easiest to include it in the command that runs `awk', like
+ this:
+ 
+      awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ...
+ 
+    When the program is long, it is usually more convenient to put it in
+ a file and run it with a command like this:
+ 
+      awk -f PROGRAM-FILE INPUT-FILE1 INPUT-FILE2 ...
+ 
+    This minor node discusses both mechanisms, along with several
+ variations of each.
+ 
+ * Menu:
+ 
+ * One-shot::                    Running a short throwaway `awk'
+                                 program.
+ * Read Terminal::               Using no input files (input from terminal
+                                 instead).
+ * Long::                        Putting permanent `awk' programs in
+                                 files.
+ * Executable Scripts::          Making self-contained `awk' programs.
+ * Comments::                    Adding documentation to `gawk'
+                                 programs.
+ * Quoting::                     More discussion of shell quoting issues.
+ 
+ 
+ File: gawk.info,  Node: One-shot,  Next: Read Terminal,  Up: Running gawk
+ 
+ 1.1.1 One-Shot Throwaway `awk' Programs
+ ---------------------------------------
+ 
+ Once you are familiar with `awk', you will often type in simple
+ programs the moment you want to use them.  Then you can write the
+ program as the first argument of the `awk' command, like this:
+ 
+      awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ...
+ 
+ where PROGRAM consists of a series of PATTERNS and ACTIONS, as
+ described earlier.
+ 
+    This command format instructs the "shell", or command interpreter,
+ to start `awk' and use the PROGRAM to process records in the input
+ file(s).  There are single quotes around PROGRAM so the shell won't
+ interpret any `awk' characters as special shell characters.  The quotes
+ also cause the shell to treat all of PROGRAM as a single argument for
+ `awk', and allow PROGRAM to be more than one line long.
+ 
+    This format is also useful for running short or medium-sized `awk'
+ programs from shell scripts, because it avoids the need for a separate
+ file for the `awk' program.  A self-contained shell script is more
+ reliable because there are no other files to misplace.
+ 
+    *note Very Simple::, presents several short, self-contained programs.
+ 
+ 
+ File: gawk.info,  Node: Read Terminal,  Next: Long,  Prev: One-shot,  Up: 
Running gawk
+ 
+ 1.1.2 Running `awk' Without Input Files
+ ---------------------------------------
+ 
+ You can also run `awk' without any input files.  If you type the
+ following command line:
+ 
+      awk 'PROGRAM'
+ 
+ `awk' applies the PROGRAM to the "standard input", which usually means
+ whatever you type on the terminal.  This continues until you indicate
+ end-of-file by typing `Ctrl-d'.  (On other operating systems, the
+ end-of-file character may be different.  For example, on OS/2, it is
+ `Ctrl-z'.)
+ 
+    As an example, the following program prints a friendly piece of
+ advice (from Douglas Adams's `The Hitchhiker's Guide to the Galaxy'),
+ to keep you from worrying about the complexities of computer
+ programming(1) (`BEGIN' is a feature we haven't discussed yet):
+ 
+      $ awk "BEGIN { print \"Don't Panic!\" }"
+      -| Don't Panic!
+ 
+    This program does not read any input.  The `\' before each of the
+ inner double quotes is necessary because of the shell's quoting
+ rules--in particular because it mixes both single quotes and double
+ quotes.(2)
+ 
+    This next simple `awk' program emulates the `cat' utility; it copies
+ whatever you type on the keyboard to its standard output (why this
+ works is explained shortly).
+ 
+      $ awk '{ print }'
+      Now is the time for all good men
+      -| Now is the time for all good men
+      to come to the aid of their country.
+      -| to come to the aid of their country.
+      Four score and seven years ago, ...
+      -| Four score and seven years ago, ...
+      What, me worry?
+      -| What, me worry?
+      Ctrl-d
+ 
+    ---------- Footnotes ----------
+ 
+    (1) If you use Bash as your shell, you should execute the command
+ `set +H' before running this program interactively, to disable the C
+ shell-style command history, which treats `!' as a special character.
+ We recommend putting this command into your personal startup file.
+ 
+    (2) Although we generally recommend the use of single quotes around
+ the program text, double quotes are needed here in order to put the
+ single quote into the message.
+ 
+ 
+ File: gawk.info,  Node: Long,  Next: Executable Scripts,  Prev: Read 
Terminal,  Up: Running gawk
+ 
+ 1.1.3 Running Long Programs
+ ---------------------------
+ 
+ Sometimes your `awk' programs can be very long.  In this case, it is
+ more convenient to put the program into a separate file.  In order to
+ tell `awk' to use that file for its program, you type:
+ 
+      awk -f SOURCE-FILE INPUT-FILE1 INPUT-FILE2 ...
+ 
+    The `-f' instructs the `awk' utility to get the `awk' program from
+ the file SOURCE-FILE.  Any file name can be used for SOURCE-FILE.  For
+ example, you could put the program:
+ 
+      BEGIN { print "Don't Panic!" }
+ 
+ into the file `advice'.  Then this command:
+ 
+      awk -f advice
+ 
+ does the same thing as this one:
+ 
+      awk "BEGIN { print \"Don't Panic!\" }"
+ 
+ This was explained earlier (*note Read Terminal::).  Note that you
+ don't usually need single quotes around the file name that you specify
+ with `-f', because most file names don't contain any of the shell's
+ special characters.  Notice that in `advice', the `awk' program did not
+ have single quotes around it.  The quotes are only needed for programs
+ that are provided on the `awk' command line.
+ 
+    If you want to clearly identify your `awk' program files as such,
+ you can add the extension `.awk' to the file name.  This doesn't affect
+ the execution of the `awk' program but it does make "housekeeping"
+ easier.
+ 
+ 
+ File: gawk.info,  Node: Executable Scripts,  Next: Comments,  Prev: Long,  
Up: Running gawk
+ 
+ 1.1.4 Executable `awk' Programs
+ -------------------------------
+ 
+ Once you have learned `awk', you may want to write self-contained `awk'
+ scripts, using the `#!' script mechanism.  You can do this on many
+ systems.(1) For example, you could update the file `advice' to look
+ like this:
+ 
+      #! /bin/awk -f
+ 
+      BEGIN { print "Don't Panic!" }
+ 
+ After making this file executable (with the `chmod' utility), simply
+ type `advice' at the shell and the system arranges to run `awk'(2) as
+ if you had typed `awk -f advice':
+ 
+      $ chmod +x advice
+      $ advice
+      -| Don't Panic!
+ 
+ (We assume you have the current directory in your shell's search path
+ variable [typically `$PATH'].  If not, you may need to type `./advice'
+ at the shell.)
+ 
+    Self-contained `awk' scripts are useful when you want to write a
+ program that users can invoke without their having to know that the
+ program is written in `awk'.
+ 
+ Advanced Notes: Portability Issues with `#!'
+ --------------------------------------------
+ 
+ Some systems limit the length of the interpreter name to 32 characters.
+ Often, this can be dealt with by using a symbolic link.
+ 
+    You should not put more than one argument on the `#!' line after the
+ path to `awk'. It does not work. The operating system treats the rest
+ of the line as a single argument and passes it to `awk'.  Doing this
+ leads to confusing behavior--most likely a usage diagnostic of some
+ sort from `awk'.
+ 
+    Finally, the value of `ARGV[0]' (*note Built-in Variables::) varies
+ depending upon your operating system.  Some systems put `awk' there,
+ some put the full pathname of `awk' (such as `/bin/awk'), and some put
+ the name of your script (`advice').  (d.c.)  Don't rely on the value of
+ `ARGV[0]' to provide your script name.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The `#!' mechanism works on GNU/Linux systems, BSD-based systems
+ and commercial Unix systems.
+ 
+    (2) The line beginning with `#!' lists the full file name of an
+ interpreter to run and an optional initial command-line argument to
+ pass to that interpreter.  The operating system then runs the
+ interpreter with the given argument and the full argument list of the
+ executed program.  The first argument in the list is the full file name
+ of the `awk' program.  The rest of the argument list contains either
+ options to `awk', or data files, or both. Note that on many systems
+ `awk' may be found in `/usr/bin' instead of in `/bin'. Caveat Emptor.
+ 
+ 
+ File: gawk.info,  Node: Comments,  Next: Quoting,  Prev: Executable Scripts,  
Up: Running gawk
+ 
+ 1.1.5 Comments in `awk' Programs
+ --------------------------------
+ 
+ A "comment" is some text that is included in a program for the sake of
+ human readers; it is not really an executable part of the program.
+ Comments can explain what the program does and how it works.  Nearly all
+ programming languages have provisions for comments, as programs are
+ typically hard to understand without them.
+ 
+    In the `awk' language, a comment starts with the sharp sign
+ character (`#') and continues to the end of the line.  The `#' does not
+ have to be the first character on the line. The `awk' language ignores
+ the rest of a line following a sharp sign.  For example, we could have
+ put the following into `advice':
+ 
+      # This program prints a nice friendly message.  It helps
+      # keep novice users from being afraid of the computer.
+      BEGIN    { print "Don't Panic!" }
+ 
+    You can put comment lines into keyboard-composed throwaway `awk'
+ programs, but this usually isn't very useful; the purpose of a comment
+ is to help you or another person understand the program when reading it
+ at a later time.
+ 
+      CAUTION: As mentioned in *note One-shot::, you can enclose small
+      to medium programs in single quotes, in order to keep your shell
+      scripts self-contained.  When doing so, _don't_ put an apostrophe
+      (i.e., a single quote) into a comment (or anywhere else in your
+      program). The shell interprets the quote as the closing quote for
+      the entire program. As a result, usually the shell prints a
+      message about mismatched quotes, and if `awk' actually runs, it
+      will probably print strange messages about syntax errors.  For
+      example, look at the following:
+ 
+           $ awk '{ print "hello" } # let's be cute'
+           >
+ 
+      The shell sees that the first two quotes match, and that a new
+      quoted object begins at the end of the command line.  It therefore
+      prompts with the secondary prompt, waiting for more input.  With
+      Unix `awk', closing the quoted string produces this result:
+ 
+           $ awk '{ print "hello" } # let's be cute'
+           > '
+           error--> awk: can't open file be
+           error-->  source line number 1
+ 
+      Putting a backslash before the single quote in `let's' wouldn't
+      help, since backslashes are not special inside single quotes.  The
+      next node describes the shell's quoting rules.
+ 
+ 
+ File: gawk.info,  Node: Quoting,  Prev: Comments,  Up: Running gawk
+ 
+ 1.1.6 Shell-Quoting Issues
+ --------------------------
+ 
+ * Menu:
+ 
+ * DOS Quoting::                 Quoting in Windows Batch Files.
+ 
+    For short to medium length `awk' programs, it is most convenient to
+ enter the program on the `awk' command line.  This is best done by
+ enclosing the entire program in single quotes.  This is true whether
+ you are entering the program interactively at the shell prompt, or
+ writing it as part of a larger shell script:
+ 
+      awk 'PROGRAM TEXT' INPUT-FILE1 INPUT-FILE2 ...
+ 
+    Once you are working with the shell, it is helpful to have a basic
+ knowledge of shell quoting rules.  The following rules apply only to
+ POSIX-compliant, Bourne-style shells (such as Bash, the GNU Bourne-Again
+ Shell).  If you use the C shell, you're on your own.
+ 
+    * Quoted items can be concatenated with nonquoted items as well as
+      with other quoted items.  The shell turns everything into one
+      argument for the command.
+ 
+    * Preceding any single character with a backslash (`\') quotes that
+      character.  The shell removes the backslash and passes the quoted
+      character on to the command.
+ 
+    * Single quotes protect everything between the opening and closing
+      quotes.  The shell does no interpretation of the quoted text,
+      passing it on verbatim to the command.  It is _impossible_ to
+      embed a single quote inside single-quoted text.  Refer back to
+      *note Comments::, for an example of what happens if you try.
+ 
+    * Double quotes protect most things between the opening and closing
+      quotes.  The shell does at least variable and command substitution
+      on the quoted text.  Different shells may do additional kinds of
+      processing on double-quoted text.
+ 
+      Since certain characters within double-quoted text are processed
+      by the shell, they must be "escaped" within the text.  Of note are
+      the characters `$', ``', `\', and `"', all of which must be
+      preceded by a backslash within double-quoted text if they are to
+      be passed on literally to the program.  (The leading backslash is
+      stripped first.)  Thus, the example seen in *note Read Terminal::,
+      is applicable:
+ 
+           $ awk "BEGIN { print \"Don't Panic!\" }"
+           -| Don't Panic!
+ 
+      Note that the single quote is not special within double quotes.
+ 
+    * Null strings are removed when they occur as part of a non-null
+      command-line argument, while explicit non-null objects are kept.
+      For example, to specify that the field separator `FS' should be
+      set to the null string, use:
+ 
+           awk -F "" 'PROGRAM' FILES # correct
+ 
+      Don't use this:
+ 
+           awk -F"" 'PROGRAM' FILES  # wrong!
+ 
+      In the second case, `awk' will attempt to use the text of the
+      program as the value of `FS', and the first file name as the text
+      of the program!  This results in syntax errors at best, and
+      confusing behavior at worst.
+ 
+    Mixing single and double quotes is difficult.  You have to resort to
+ shell quoting tricks, like this:
+ 
+      $ awk 'BEGIN { print "Here is a single quote <'"'"'>" }'
+      -| Here is a single quote <'>
+ 
+ This program consists of three concatenated quoted strings.  The first
+ and the third are single-quoted, the second is double-quoted.
+ 
+    This can be "simplified" to:
+ 
+      $ awk 'BEGIN { print "Here is a single quote <'\''>" }'
+      -| Here is a single quote <'>
+ 
+ Judge for yourself which of these two is the more readable.
+ 
+    Another option is to use double quotes, escaping the embedded,
+ `awk'-level double quotes:
+ 
+      $ awk "BEGIN { print \"Here is a single quote <'>\" }"
+      -| Here is a single quote <'>
+ 
+ This option is also painful, because double quotes, backslashes, and
+ dollar signs are very common in more advanced `awk' programs.
+ 
+    A third option is to use the octal escape sequence equivalents
+ (*note Escape Sequences::) for the single- and double-quote characters,
+ like so:
+ 
+      $ awk 'BEGIN { print "Here is a single quote <\47>" }'
+      -| Here is a single quote <'>
+      $ awk 'BEGIN { print "Here is a double quote <\42>" }'
+      -| Here is a double quote <">
+ 
+ This works nicely, except that you should comment clearly what the
+ escapes mean.
+ 
+    A fourth option is to use command-line variable assignment, like
+ this:
+ 
+      $ awk -v sq="'" 'BEGIN { print "Here is a single quote <" sq ">" }'
+      -| Here is a single quote <'>
+ 
+    If you really need both single and double quotes in your `awk'
+ program, it is probably best to move it into a separate file, where the
+ shell won't be part of the picture, and you can say what you mean.
+ 
+ 
+ File: gawk.info,  Node: DOS Quoting,  Up: Quoting
+ 
+ 1.1.6.1 Quoting in MS-Windows Batch Files
+ .........................................
+ 
+ Although this Info file generally only worries about POSIX systems and
+ the POSIX shell, the following issue arises often enough for many users
+ that it is worth addressing.
+ 
+    The "shells" on Microsoft Windows systems use the double-quote
+ character for quoting, and make it difficult or impossible to include an
+ escaped double-quote character in a command-line script.  The following
+ example, courtesy of Jeroen Brink, shows how to print all lines in a
+ file surrounded by double quotes:
+ 
+      gawk "{ print \"\042\" $0 \"\042\" }" FILE
+ 
+ 
+ File: gawk.info,  Node: Sample Data Files,  Next: Very Simple,  Prev: Running 
gawk,  Up: Getting Started
+ 
+ 1.2 Data Files for the Examples
+ ===============================
+ 
+ Many of the examples in this Info file take their input from two sample
+ data files.  The first, `BBS-list', represents a list of computer
+ bulletin board systems together with information about those systems.
+ The second data file, called `inventory-shipped', contains information
+ about monthly shipments.  In both files, each line is considered to be
+ one "record".
+ 
+    In the data file `BBS-list', each record contains the name of a
+ computer bulletin board, its phone number, the board's baud rate(s),
+ and a code for the number of hours it is operational.  An `A' in the
+ last column means the board operates 24 hours a day.  A `B' in the last
+ column means the board only operates on evening and weekend hours.  A
+ `C' means the board operates only on weekends:
+ 
+      aardvark     555-5553     1200/300          B
+      alpo-net     555-3412     2400/1200/300     A
+      barfly       555-7685     1200/300          A
+      bites        555-1675     2400/1200/300     A
+      camelot      555-0542     300               C
+      core         555-2912     1200/300          C
+      fooey        555-1234     2400/1200/300     B
+      foot         555-6699     1200/300          B
+      macfoo       555-6480     1200/300          A
+      sdace        555-3430     2400/1200/300     A
+      sabafoo      555-2127     1200/300          C
+ 
+    The data file `inventory-shipped' represents information about
+ shipments during the year.  Each record contains the month, the number
+ of green crates shipped, the number of red boxes shipped, the number of
+ orange bags shipped, and the number of blue packages shipped,
+ respectively.  There are 16 entries, covering the 12 months of last year
+ and the first four months of the current year.
+ 
+      Jan  13  25  15 115
+      Feb  15  32  24 226
+      Mar  15  24  34 228
+      Apr  31  52  63 420
+      May  16  34  29 208
+      Jun  31  42  75 492
+      Jul  24  34  67 436
+      Aug  15  34  47 316
+      Sep  13  55  37 277
+      Oct  29  54  68 525
+      Nov  20  87  82 577
+      Dec  17  35  61 401
+ 
+      Jan  21  36  64 620
+      Feb  26  58  80 652
+      Mar  24  75  70 495
+      Apr  21  70  74 514
+ 
+    If you are reading this in GNU Emacs using Info, you can copy the
+ regions of text showing these sample files into your own test files.
+ This way you can try out the examples shown in the remainder of this
+ document.  You do this by using the command `M-x write-region' to copy
+ text from the Info file into a file for use with `awk' (*Note
+ Miscellaneous File Operations: (emacs)Misc File Ops, for more
+ information).  Using this information, create your own `BBS-list' and
+ `inventory-shipped' files and practice what you learn in this Info file.
+ 
+    If you are using the stand-alone version of Info, see *note Extract
+ Program::, for an `awk' program that extracts these data files from
+ `gawk.texi', the Texinfo source file for this Info file.
+ 
+ 
+ File: gawk.info,  Node: Very Simple,  Next: Two Rules,  Prev: Sample Data 
Files,  Up: Getting Started
+ 
+ 1.3 Some Simple Examples
+ ========================
+ 
+ The following command runs a simple `awk' program that searches the
+ input file `BBS-list' for the character string `foo' (a grouping of
+ characters is usually called a "string"; the term "string" is based on
+ similar usage in English, such as "a string of pearls," or "a string of
+ cars in a train"):
+ 
+      awk '/foo/ { print $0 }' BBS-list
+ 
+ When lines containing `foo' are found, they are printed because
+ `print $0' means print the current line.  (Just `print' by itself means
+ the same thing, so we could have written that instead.)
+ 
+    You will notice that slashes (`/') surround the string `foo' in the
+ `awk' program.  The slashes indicate that `foo' is the pattern to
+ search for.  This type of pattern is called a "regular expression",
+ which is covered in more detail later (*note Regexp::).  The pattern is
+ allowed to match parts of words.  There are single quotes around the
+ `awk' program so that the shell won't interpret any of it as special
+ shell characters.
+ 
+    Here is what this program prints:
+ 
+      $ awk '/foo/ { print $0 }' BBS-list
+      -| fooey        555-1234     2400/1200/300     B
+      -| foot         555-6699     1200/300          B
+      -| macfoo       555-6480     1200/300          A
+      -| sabafoo      555-2127     1200/300          C
+ 
+    In an `awk' rule, either the pattern or the action can be omitted,
+ but not both.  If the pattern is omitted, then the action is performed
+ for _every_ input line.  If the action is omitted, the default action
+ is to print all lines that match the pattern.
+ 
+    Thus, we could leave out the action (the `print' statement and the
+ curly braces) in the previous example and the result would be the same:
+ `awk' prints all lines matching the pattern `foo'.  By comparison,
+ omitting the `print' statement but retaining the curly braces makes an
+ empty action that does nothing (i.e., no lines are printed).
+ 
+    Many practical `awk' programs are just a line or two.  Following is a
+ collection of useful, short programs to get you started.  Some of these
+ programs contain constructs that haven't been covered yet. (The
+ description of the program will give you a good idea of what is going
+ on, but please read the rest of the Info file to become an `awk'
+ expert!)  Most of the examples use a data file named `data'.  This is
+ just a placeholder; if you use these programs yourself, substitute your
+ own file names for `data'.  For future reference, note that there is
+ often more than one way to do things in `awk'.  At some point, you may
+ want to look back at these examples and see if you can come up with
+ different ways to do the same things shown here:
+ 
+    * Print the length of the longest input line:
+ 
+           awk '{ if (length($0) > max) max = length($0) }
+                END { print max }' data
+ 
+    * Print every line that is longer than 80 characters:
+ 
+           awk 'length($0) > 80' data
+ 
+      The sole rule has a relational expression as its pattern and it
+      has no action--so the default action, printing the record, is used.
+ 
+    * Print the length of the longest line in `data':
+ 
+           expand data | awk '{ if (x < length()) x = length() }
+                         END { print "maximum line length is " x }'
+ 
+      The input is processed by the `expand' utility to change TABs into
+      spaces, so the widths compared are actually the right-margin
+      columns.
+ 
+    * Print every line that has at least one field:
+ 
+           awk 'NF > 0' data
+ 
+      This is an easy way to delete blank lines from a file (or rather,
+      to create a new file similar to the old file but from which the
+      blank lines have been removed).
+ 
+    * Print seven random numbers from 0 to 100, inclusive:
+ 
+           awk 'BEGIN { for (i = 1; i <= 7; i++)
+                            print int(101 * rand()) }'
+ 
+    * Print the total number of bytes used by FILES:
+ 
+           ls -l FILES | awk '{ x += $5 }
+                             END { print "total bytes: " x }'
+ 
+    * Print the total number of kilobytes used by FILES:
+ 
+           ls -l FILES | awk '{ x += $5 }
+              END { print "total K-bytes:", x / 1024 }'
+ 
+    * Print a sorted list of the login names of all users:
+ 
+           awk -F: '{ print $1 }' /etc/passwd | sort
+ 
+    * Count the lines in a file:
+ 
+           awk 'END { print NR }' data
+ 
+    * Print the even-numbered lines in the data file:
+ 
+           awk 'NR % 2 == 0' data
+ 
+      If you use the expression `NR % 2 == 1' instead, the program would
+      print the odd-numbered lines.
+ 
+ 
+ File: gawk.info,  Node: Two Rules,  Next: More Complex,  Prev: Very Simple,  
Up: Getting Started
+ 
+ 1.4 An Example with Two Rules
+ =============================
+ 
+ The `awk' utility reads the input files one line at a time.  For each
+ line, `awk' tries the patterns of each of the rules.  If several
+ patterns match, then several actions are run in the order in which they
+ appear in the `awk' program.  If no patterns match, then no actions are
+ run.
+ 
+    After processing all the rules that match the line (and perhaps
+ there are none), `awk' reads the next line.  (However, *note Next
+ Statement::, and also *note Nextfile Statement::).  This continues
+ until the program reaches the end of the file.  For example, the
+ following `awk' program contains two rules:
+ 
+      /12/  { print $0 }
+      /21/  { print $0 }
+ 
+ The first rule has the string `12' as the pattern and `print $0' as the
+ action.  The second rule has the string `21' as the pattern and also
+ has `print $0' as the action.  Each rule's action is enclosed in its
+ own pair of braces.
+ 
+    This program prints every line that contains the string `12' _or_
+ the string `21'.  If a line contains both strings, it is printed twice,
+ once by each rule.
+ 
+    This is what happens if we run this program on our two sample data
+ files, `BBS-list' and `inventory-shipped':
+ 
+      $ awk '/12/ { print $0 }
+      >      /21/ { print $0 }' BBS-list inventory-shipped
+      -| aardvark     555-5553     1200/300          B
+      -| alpo-net     555-3412     2400/1200/300     A
+      -| barfly       555-7685     1200/300          A
+      -| bites        555-1675     2400/1200/300     A
+      -| core         555-2912     1200/300          C
+      -| fooey        555-1234     2400/1200/300     B
+      -| foot         555-6699     1200/300          B
+      -| macfoo       555-6480     1200/300          A
+      -| sdace        555-3430     2400/1200/300     A
+      -| sabafoo      555-2127     1200/300          C
+      -| sabafoo      555-2127     1200/300          C
+      -| Jan  21  36  64 620
+      -| Apr  21  70  74 514
+ 
+ Note how the line beginning with `sabafoo' in `BBS-list' was printed
+ twice, once for each rule.
+ 
+ 
+ File: gawk.info,  Node: More Complex,  Next: Statements/Lines,  Prev: Two 
Rules,  Up: Getting Started
+ 
+ 1.5 A More Complex Example
+ ==========================
+ 
+ Now that we've mastered some simple tasks, let's look at what typical
+ `awk' programs do.  This example shows how `awk' can be used to
+ summarize, select, and rearrange the output of another utility.  It uses
+ features that haven't been covered yet, so don't worry if you don't
+ understand all the details:
+ 
+      LC_ALL=C ls -l | awk '$6 == "Nov" { sum += $5 }
+                            END { print sum }'
+ 
+    This command prints the total number of bytes in all the files in the
+ current directory that were last modified in November (of any year).
+ The `ls -l' part of this example is a system command that gives you a
+ listing of the files in a directory, including each file's size and the
+ date the file was last modified. Its output looks like this:
+ 
+      -rw-r--r--  1 arnold   user   1933 Nov  7 13:05 Makefile
+      -rw-r--r--  1 arnold   user  10809 Nov  7 13:03 awk.h
+      -rw-r--r--  1 arnold   user    983 Apr 13 12:14 awk.tab.h
+      -rw-r--r--  1 arnold   user  31869 Jun 15 12:20 awkgram.y
+      -rw-r--r--  1 arnold   user  22414 Nov  7 13:03 awk1.c
+      -rw-r--r--  1 arnold   user  37455 Nov  7 13:03 awk2.c
+      -rw-r--r--  1 arnold   user  27511 Dec  9 13:07 awk3.c
+      -rw-r--r--  1 arnold   user   7989 Nov  7 13:03 awk4.c
+ 
+ The first field contains read-write permissions, the second field
+ contains the number of links to the file, and the third field
+ identifies the owner of the file. The fourth field identifies the group
+ of the file.  The fifth field contains the size of the file in bytes.
+ The sixth, seventh, and eighth fields contain the month, day, and time,
+ respectively, that the file was last modified.  Finally, the ninth field
+ contains the file name.(1)
+ 
+    The `$6 == "Nov"' in our `awk' program is an expression that tests
+ whether the sixth field of the output from `ls -l' matches the string
+ `Nov'.  Each time a line has the string `Nov' for its sixth field, the
+ action `sum += $5' is performed.  This adds the fifth field (the file's
+ size) to the variable `sum'.  As a result, when `awk' has finished
+ reading all the input lines, `sum' is the total of the sizes of the
+ files whose lines matched the pattern.  (This works because `awk'
+ variables are automatically initialized to zero.)
+ 
+    After the last line of output from `ls' has been processed, the
+ `END' rule executes and prints the value of `sum'.  In this example,
+ the value of `sum' is 80600.
+ 
+    These more advanced `awk' techniques are covered in later sections
+ (*note Action Overview::).  Before you can move on to more advanced
+ `awk' programming, you have to know how `awk' interprets your input and
+ displays your output.  By manipulating fields and using `print'
+ statements, you can produce some very useful and impressive-looking
+ reports.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The `LC_ALL=C' is needed to produce this traditional-style
+ output from `ls'.
+ 
+ 
+ File: gawk.info,  Node: Statements/Lines,  Next: Other Features,  Prev: More 
Complex,  Up: Getting Started
+ 
+ 1.6 `awk' Statements Versus Lines
+ =================================
+ 
+ Most often, each line in an `awk' program is a separate statement or
+ separate rule, like this:
+ 
+      awk '/12/  { print $0 }
+           /21/  { print $0 }' BBS-list inventory-shipped
+ 
+    However, `gawk' ignores newlines after any of the following symbols
+ and keywords:
+ 
+      ,    {    ?    :    ||    &&    do    else
+ 
+ A newline at any other point is considered the end of the statement.(1)
+ 
+    If you would like to split a single statement into two lines at a
+ point where a newline would terminate it, you can "continue" it by
+ ending the first line with a backslash character (`\').  The backslash
+ must be the final character on the line in order to be recognized as a
+ continuation character.  A backslash is allowed anywhere in the
+ statement, even in the middle of a string or regular expression.  For
+ example:
+ 
+      awk '/This regular expression is too long, so continue it\
+       on the next line/ { print $1 }'
+ 
+ We have generally not used backslash continuation in our sample
+ programs.  `gawk' places no limit on the length of a line, so backslash
+ continuation is never strictly necessary; it just makes programs more
+ readable.  For this same reason, as well as for clarity, we have kept
+ most statements short in the sample programs presented throughout the
+ Info file.  Backslash continuation is most useful when your `awk'
+ program is in a separate source file instead of entered from the
+ command line.  You should also note that many `awk' implementations are
+ more particular about where you may use backslash continuation. For
+ example, they may not allow you to split a string constant using
+ backslash continuation.  Thus, for maximum portability of your `awk'
+ programs, it is best not to split your lines in the middle of a regular
+ expression or a string.
+ 
+      CAUTION: _Backslash continuation does not work as described with
+      the C shell._  It works for `awk' programs in files and for
+      one-shot programs, _provided_ you are using a POSIX-compliant
+      shell, such as the Unix Bourne shell or Bash.  But the C shell
+      behaves differently!  There, you must use two backslashes in a
+      row, followed by a newline.  Note also that when using the C
+      shell, _every_ newline in your `awk' program must be escaped with
+      a backslash. To illustrate:
+ 
+           % awk 'BEGIN { \
+           ?   print \\
+           ?       "hello, world" \
+           ? }'
+           -| hello, world
+ 
+      Here, the `%' and `?' are the C shell's primary and secondary
+      prompts, analogous to the standard shell's `$' and `>'.
+ 
+      Compare the previous example to how it is done with a
+      POSIX-compliant shell:
+ 
+           $ awk 'BEGIN {
+           >   print \
+           >       "hello, world"
+           > }'
+           -| hello, world
+ 
+    `awk' is a line-oriented language.  Each rule's action has to begin
+ on the same line as the pattern.  To have the pattern and action on
+ separate lines, you _must_ use backslash continuation; there is no
+ other option.
+ 
+    Another thing to keep in mind is that backslash continuation and
+ comments do not mix. As soon as `awk' sees the `#' that starts a
+ comment, it ignores _everything_ on the rest of the line. For example:
+ 
+      $ gawk 'BEGIN { print "dont panic" # a friendly \
+      >                                    BEGIN rule
+      > }'
+      error--> gawk: cmd. line:2:                BEGIN rule
+      error--> gawk: cmd. line:2:                ^ parse error
+ 
+ In this case, it looks like the backslash would continue the comment
+ onto the next line. However, the backslash-newline combination is never
+ even noticed because it is "hidden" inside the comment. Thus, the
+ `BEGIN' is noted as a syntax error.
+ 
+    When `awk' statements within one rule are short, you might want to
+ put more than one of them on a line.  This is accomplished by
+ separating the statements with a semicolon (`;').  This also applies to
+ the rules themselves.  Thus, the program shown at the start of this
+ minor node could also be written this way:
+ 
+      /12/ { print $0 } ; /21/ { print $0 }
+ 
+      NOTE: The requirement that states that rules on the same line must
+      be separated with a semicolon was not in the original `awk'
+      language; it was added for consistency with the treatment of
+      statements within an action.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The `?' and `:' referred to here is the three-operand
+ conditional expression described in *note Conditional Exp::.  Splitting
+ lines after `?' and `:' is a minor `gawk' extension; if `--posix' is
+ specified (*note Options::), then this extension is disabled.
+ 
+ 
+ File: gawk.info,  Node: Other Features,  Next: When,  Prev: Statements/Lines, 
 Up: Getting Started
+ 
+ 1.7 Other Features of `awk'
+ ===========================
+ 
+ The `awk' language provides a number of predefined, or "built-in",
+ variables that your programs can use to get information from `awk'.
+ There are other variables your program can set as well to control how
+ `awk' processes your data.
+ 
+    In addition, `awk' provides a number of built-in functions for doing
+ common computational and string-related operations.  `gawk' provides
+ built-in functions for working with timestamps, performing bit
+ manipulation, for runtime string translation (internationalization),
+ determining the type of a variable, and array sorting.
+ 
+    As we develop our presentation of the `awk' language, we introduce
+ most of the variables and many of the functions. They are described
+ systematically in *note Built-in Variables::, and *note Built-in::.
+ 
+ 
+ File: gawk.info,  Node: When,  Prev: Other Features,  Up: Getting Started
+ 
+ 1.8 When to Use `awk'
+ =====================
+ 
+ Now that you've seen some of what `awk' can do, you might wonder how
+ `awk' could be useful for you.  By using utility programs, advanced
+ patterns, field separators, arithmetic statements, and other selection
+ criteria, you can produce much more complex output.  The `awk' language
+ is very useful for producing reports from large amounts of raw data,
+ such as summarizing information from the output of other utility
+ programs like `ls'.  (*Note More Complex::.)
+ 
+    Programs written with `awk' are usually much smaller than they would
+ be in other languages.  This makes `awk' programs easy to compose and
+ use.  Often, `awk' programs can be quickly composed at your keyboard,
+ used once, and thrown away.  Because `awk' programs are interpreted, you
+ can avoid the (usually lengthy) compilation part of the typical
+ edit-compile-test-debug cycle of software development.
+ 
+    Complex programs have been written in `awk', including a complete
+ retargetable assembler for eight-bit microprocessors (*note Glossary::,
+ for more information), and a microcode assembler for a special-purpose
+ Prolog computer.  While the original `awk''s capabilities were strained
+ by tasks of such complexity, modern versions are more capable.  Even
+ Brian Kernighan's version of `awk' has fewer predefined limits, and
+ those that it has are much larger than they used to be.
+ 
+    If you find yourself writing `awk' scripts of more than, say, a few
+ hundred lines, you might consider using a different programming
+ language.  Emacs Lisp is a good choice if you need sophisticated string
+ or pattern matching capabilities.  The shell is also good at string and
+ pattern matching; in addition, it allows powerful use of the system
+ utilities.  More conventional languages, such as C, C++, and Java, offer
+ better facilities for system programming and for managing the complexity
+ of large programs.  Programs in these languages may require more lines
+ of source code than the equivalent `awk' programs, but they are easier
+ to maintain and usually run more efficiently.
+ 
+ 
+ File: gawk.info,  Node: Invoking Gawk,  Next: Regexp,  Prev: Getting Started, 
 Up: Top
+ 
+ 2 Running `awk' and `gawk'
+ **************************
+ 
+ This major node covers how to run awk, both POSIX-standard and
+ `gawk'-specific command-line options, and what `awk' and `gawk' do with
+ non-option arguments.  It then proceeds to cover how `gawk' searches
+ for source files, reading standard input along with other files,
+ `gawk''s environment variables, `gawk''s exit status, using include
+ files, and obsolete and undocumented options and/or features.
+ 
+    Many of the options and features described here are discussed in
+ more detail later in the Info file; feel free to skip over things in
+ this major node that don't interest you right now.
+ 
+ * Menu:
+ 
+ * Command Line::                How to run `awk'.
+ * Options::                     Command-line options and their meanings.
+ * Other Arguments::             Input file names and variable assignments.
+ * Naming Standard Input::       How to specify standard input with other
+                                 files.
+ * Environment Variables::       The environment variables `gawk' uses.
+ * Exit Status::                 `gawk''s exit status.
+ * Include Files::               Including other files into your program.
++* Loading Shared Libraries::    Loading shared libraries into your program.
+ * Obsolete::                    Obsolete Options and/or features.
+ * Undocumented::                Undocumented Options and Features.
+ 
+ 
+ File: gawk.info,  Node: Command Line,  Next: Options,  Up: Invoking Gawk
+ 
+ 2.1 Invoking `awk'
+ ==================
+ 
+ There are two ways to run `awk'--with an explicit program or with one
+ or more program files.  Here are templates for both of them; items
+ enclosed in [...] in these templates are optional:
+ 
+      awk [OPTIONS] -f progfile [`--'] FILE ...
+      awk [OPTIONS] [`--'] 'PROGRAM' FILE ...
+ 
+    Besides traditional one-letter POSIX-style options, `gawk' also
+ supports GNU long options.
+ 
+    It is possible to invoke `awk' with an empty program:
+ 
+      awk '' datafile1 datafile2
+ 
+ Doing so makes little sense, though; `awk' exits silently when given an
+ empty program.  (d.c.)  If `--lint' has been specified on the command
+ line, `gawk' issues a warning that the program is empty.
+ 
+ 
+ File: gawk.info,  Node: Options,  Next: Other Arguments,  Prev: Command Line, 
 Up: Invoking Gawk
+ 
+ 2.2 Command-Line Options
+ ========================
+ 
+ Options begin with a dash and consist of a single character.  GNU-style
+ long options consist of two dashes and a keyword.  The keyword can be
+ abbreviated, as long as the abbreviation allows the option to be
+ uniquely identified.  If the option takes an argument, then the keyword
+ is either immediately followed by an equals sign (`=') and the
+ argument's value, or the keyword and the argument's value are separated
+ by whitespace.  If a particular option with a value is given more than
+ once, it is the last value that counts.
+ 
+    Each long option for `gawk' has a corresponding POSIX-style short
+ option.  The long and short options are interchangeable in all contexts.
+ The following list describes options mandated by the POSIX standard:
+ 
+ `-F FS'
+ `--field-separator FS'
+      Set the `FS' variable to FS (*note Field Separators::).
+ 
+ `-f SOURCE-FILE'
+ `--file SOURCE-FILE'
+      Read `awk' program source from SOURCE-FILE instead of in the first
+      non-option argument.  This option may be given multiple times; the
+      `awk' program consists of the concatenation the contents of each
+      specified SOURCE-FILE.
+ 
++`-i SOURCE-FILE'
++`--include SOURCE-FILE'
++     Read `awk' source library from SOURCE-FILE.  This option is
++     completely equivalent to using the address@hidden' directive inside
++     your program.  This option is very similar to the `-f' option, but
++     there are two important differences.  First, when `-i' is used,
++     the program source will not be loaded if it has been previously
++     loaded, whereas the `-f' will always load the file.  Second,
++     because this option is intended to be used with code libraries, the
++     `awk' command does not recognize such files as constituting main
++     program input.  Thus, after processing an `-i' argument, we still
++     expect to find the main source code via the `-f' option or on the
++     command-line.
++
+ `-v VAR=VAL'
+ `--assign VAR=VAL'
+      Set the variable VAR to the value VAL _before_ execution of the
+      program begins.  Such variable values are available inside the
+      `BEGIN' rule (*note Other Arguments::).
+ 
+      The `-v' option can only set one variable, but it can be used more
+      than once, setting another variable each time, like this: `awk
+      -v foo=1 -v bar=2 ...'.
+ 
+           CAUTION: Using `-v' to set the values of the built-in
+           variables may lead to surprising results.  `awk' will reset
+           the values of those variables as it needs to, possibly
+           ignoring any predefined value you may have given.
+ 
+ `-W GAWK-OPT'
+      Provide an implementation-specific option.  This is the POSIX
+      convention for providing implementation-specific options.  These
+      options also have corresponding GNU-style long options.  Note that
+      the long options may be abbreviated, as long as the abbreviations
+      remain unique.  The full list of `gawk'-specific options is
+      provided next.
+ 
+ `--'
+      Signal the end of the command-line options.  The following
+      arguments are not treated as options even if they begin with `-'.
+      This interpretation of `--' follows the POSIX argument parsing
+      conventions.
+ 
+      This is useful if you have file names that start with `-', or in
+      shell scripts, if you have file names that will be specified by
+      the user that could start with `-'.  It is also useful for passing
+      options on to the `awk' program; see *note Getopt Function::.
+ 
+    The following list describes `gawk'-specific options:
+ 
+ `-b'
+ `--characters-as-bytes'
+      Cause `gawk' to treat all input data as single-byte characters.
+      In addition, all output written with `print' or `printf' are
+      treated as single-byte characters.
+ 
+      Normally, `gawk' follows the POSIX standard and attempts to process
+      its input data according to the current locale. This can often
+      involve converting multibyte characters into wide characters
+      (internally), and can lead to problems or confusion if the input
+      data does not contain valid multibyte characters. This option is
+      an easy way to tell `gawk': "hands off my data!".
+ 
+ `-c'
+ `--traditional'
+      Specify "compatibility mode", in which the GNU extensions to the
+      `awk' language are disabled, so that `gawk' behaves just like
+      Brian Kernighan's version `awk'.  *Note POSIX/GNU::, which
+      summarizes the extensions.  Also see *note Compatibility Mode::.
+ 
+ `-C'
+ `--copyright'
+      Print the short version of the General Public License and then
+      exit.
+ 
+ `-d[FILE]'
+ `--dump-variables[=FILE]'
+      Print a sorted list of global variables, their types, and final
+      values to FILE.  If no FILE is provided, print this list to the
+      file named `awkvars.out' in the current directory.  No space is
+      allowed between the `-d' and FILE, if FILE is supplied.
+ 
+      Having a list of all global variables is a good way to look for
+      typographical errors in your programs.  You would also use this
+      option if you have a large program with a lot of functions, and
+      you want to be sure that your functions don't inadvertently use
+      global variables that you meant to be local.  (This is a
+      particularly easy mistake to make with simple variable names like
+      `i', `j', etc.)
+ 
++`-D[FILE]'
++`--debug=[FILE]'
++     Enable debugging of `awk' programs (*note Debugging::).  By
++     default, the debugger reads commands interactively from the
++     terminal.  The optional FILE argument allows you to specify a file
++     with a list of commands for the debugger to execute
++     non-interactively.  No space is allowed between the `-D' and FILE,
++     if FILE is supplied.
++
+ `-e PROGRAM-TEXT'
+ `--source PROGRAM-TEXT'
+      Provide program source code in the PROGRAM-TEXT.  This option
+      allows you to mix source code in files with source code that you
+      enter on the command line.  This is particularly useful when you
+      have library functions that you want to use from your command-line
+      programs (*note AWKPATH Variable::).
+ 
+ `-E FILE'
+ `--exec FILE'
+      Similar to `-f', read `awk' program text from FILE.  There are two
+      differences from `-f':
+ 
+         * This option terminates option processing; anything else on
+           the command line is passed on directly to the `awk' program.
+ 
+         * Command-line variable assignments of the form `VAR=VALUE' are
+           disallowed.
+ 
+      This option is particularly necessary for World Wide Web CGI
+      applications that pass arguments through the URL; using this
+      option prevents a malicious (or other) user from passing in
+      options, assignments, or `awk' source code (via `--source') to the
+      CGI application.  This option should be used with `#!' scripts
+      (*note Executable Scripts::), like so:
+ 
+           #! /usr/local/bin/gawk -E
+ 
+           AWK PROGRAM HERE ...
+ 
+ `-g'
+ `--gen-pot'
+      Analyze the source program and generate a GNU `gettext' Portable
+      Object Template file on standard output for all string constants
+      that have been marked for translation.  *Note
+      Internationalization::, for information about this option.
+ 
+ `-h'
+ `--help'
+      Print a "usage" message summarizing the short and long style
+      options that `gawk' accepts and then exit.
+ 
++`-l LIB'
++`--load LIB'
++     Load a shared library LIB. This searches for the library using the
++     `AWKLIBPATH' environment variable.  The correct library suffix for
++     your platform will be supplied by default, so it need not be
++     specified in the library name.  The library initialization routine
++     should be named `dl_load()'.  An alternative is to use the 
address@hidden'
++     keyword inside the program to load a shared library.
++
+ `-L [value]'
+ `--lint[=value]'
+      Warn about constructs that are dubious or nonportable to other
+      `awk' implementations.  Some warnings are issued when `gawk' first
+      reads your program.  Others are issued at runtime, as your program
+      executes.  With an optional argument of `fatal', lint warnings
+      become fatal errors.  This may be drastic, but its use will
+      certainly encourage the development of cleaner `awk' programs.
+      With an optional argument of `invalid', only warnings about things
+      that are actually invalid are issued. (This is not fully
+      implemented yet.)
+ 
+      Some warnings are only printed once, even if the dubious
+      constructs they warn about occur multiple times in your `awk'
+      program.  Thus, when eliminating problems pointed out by `--lint',
+      you should take care to search for all occurrences of each
+      inappropriate construct. As `awk' programs are usually short,
+      doing so is not burdensome.
+ 
++`-M'
++`--bignum'
++     Force arbitrary precision arithmetic on numbers. This option has
++     no effect if `gawk' is not compiled to use the GNU MPFR and MP
++     libraries (*note Arbitrary Precision Arithmetic::).
++
+ `-n'
+ `--non-decimal-data'
+      Enable automatic interpretation of octal and hexadecimal values in
+      input data (*note Nondecimal Data::).
+ 
+           CAUTION: This option can severely break old programs.  Use
+           with care.
+ 
+ `-N'
+ `--use-lc-numeric'
+      Force the use of the locale's decimal point character when parsing
+      numeric input data (*note Locales::).
+ 
++`-o[FILE]'
++`--pretty-print[=FILE]'
++     Enable pretty-printing of `awk' programs.  By default, output
++     program is created in a file named `awkprof.out'.  The optional
++     FILE argument allows you to specify a different file name for the
++     output.  No space is allowed between the `-o' and FILE, if FILE is
++     supplied.
++
+ `-O'
+ `--optimize'
+      Enable some optimizations on the internal representation of the
+      program.  At the moment this includes just simple constant
+      folding. The `gawk' maintainer hopes to add more optimizations
+      over time.
+ 
+ `-p[FILE]'
+ `--profile[=FILE]'
+      Enable profiling of `awk' programs (*note Profiling::).  By
+      default, profiles are created in a file named `awkprof.out'.  The
+      optional FILE argument allows you to specify a different file name
+      for the profile file.  No space is allowed between the `-p' and
+      FILE, if FILE is supplied.
+ 
 -     When run with `gawk', the profile is just a "pretty printed"
 -     version of the program.  When run with `pgawk', the profile
 -     contains execution counts for each statement in the program in the
 -     left margin, and function call counts for each function.
++     The profile contains execution counts for each statement in the
++     program in the left margin, and function call counts for each
++     function.
+ 
+ `-P'
+ `--posix'
+      Operate in strict POSIX mode.  This disables all `gawk' extensions
+      (just like `--traditional') and disables all extensions not
+      allowed by POSIX.  *Note Common Extensions::, for a summary of the
+      extensions in `gawk' that are disabled by this option.  Also, the
+      following additional restrictions apply:
+ 
+         * Newlines do not act as whitespace to separate fields when
+           `FS' is equal to a single space (*note Fields::).
+ 
+         * Newlines are not allowed after `?' or `:' (*note Conditional
+           Exp::).
+ 
+         * Specifying `-Ft' on the command-line does not set the value
+           of `FS' to be a single TAB character (*note Field
+           Separators::).
+ 
+         * The locale's decimal point character is used for parsing input
+           data (*note Locales::).
+ 
+      If you supply both `--traditional' and `--posix' on the command
+      line, `--posix' takes precedence. `gawk' also issues a warning if
+      both options are supplied.
+ 
+ `-r'
+ `--re-interval'
+      Allow interval expressions (*note Regexp Operators::) in regexps.
+      This is now `gawk''s default behavior.  Nevertheless, this option
+      remains both for backward compatibility, and for use in
+      combination with the `--traditional' option.
+ 
 -`-R FILE'
 -`--command=FILE'
 -     `dgawk' only.  Read `dgawk' debugger options and commands from
 -     FILE.  *Note Dgawk Info::, for more information.
 -
+ `-S'
+ `--sandbox'
+      Disable the `system()' function, input redirections with `getline',
+      output redirections with `print' and `printf', and dynamic
+      extensions.  This is particularly useful when you want to run
+      `awk' scripts from questionable sources and need to make sure the
+      scripts can't access your system (other than the specified input
+      data file).
+ 
+ `-t'
+ `--lint-old'
+      Warn about constructs that are not available in the original
+      version of `awk' from Version 7 Unix (*note V7/SVR3.1::).
+ 
+ `-V'
+ `--version'
+      Print version information for this particular copy of `gawk'.
+      This allows you to determine if your copy of `gawk' is up to date
+      with respect to whatever the Free Software Foundation is currently
+      distributing.  It is also useful for bug reports (*note Bugs::).
+ 
+    As long as program text has been supplied, any other options are
+ flagged as invalid with a warning message but are otherwise ignored.
+ 
+    In compatibility mode, as a special case, if the value of FS supplied
+ to the `-F' option is `t', then `FS' is set to the TAB character
+ (`"\t"').  This is true only for `--traditional' and not for `--posix'
+ (*note Field Separators::).
+ 
+    The `-f' option may be used more than once on the command line.  If
+ it is, `awk' reads its program source from all of the named files, as
+ if they had been concatenated together into one big file.  This is
+ useful for creating libraries of `awk' functions.  These functions can
+ be written once and then retrieved from a standard place, instead of
+ having to be included into each individual program.  (As mentioned in
+ *note Definition Syntax::, function names must be unique.)
+ 
+    With standard `awk', library functions can still be used, even if
+ the program is entered at the terminal, by specifying `-f /dev/tty'.
+ After typing your program, type `Ctrl-d' (the end-of-file character) to
+ terminate it.  (You may also use `-f -' to read program source from the
+ standard input but then you will not be able to also use the standard
+ input as a source of data.)
+ 
+    Because it is clumsy using the standard `awk' mechanisms to mix
+ source file and command-line `awk' programs, `gawk' provides the
+ `--source' option.  This does not require you to pre-empt the standard
+ input for your source code; it allows you to easily mix command-line
+ and library source code (*note AWKPATH Variable::).  The `--source'
+ option may also be used multiple times on the command line.
+ 
+    If no `-f' or `--source' option is specified, then `gawk' uses the
+ first non-option command-line argument as the text of the program
+ source code.
+ 
+    If the environment variable `POSIXLY_CORRECT' exists, then `gawk'
+ behaves in strict POSIX mode, exactly as if you had supplied the
+ `--posix' command-line option.  Many GNU programs look for this
+ environment variable to suppress extensions that conflict with POSIX,
+ but `gawk' behaves differently: it suppresses all extensions, even
+ those that do not conflict with POSIX, and behaves in strict POSIX
+ mode. If `--lint' is supplied on the command line and `gawk' turns on
+ POSIX mode because of `POSIXLY_CORRECT', then it issues a warning
+ message indicating that POSIX mode is in effect.  You would typically
+ set this variable in your shell's startup file.  For a
+ Bourne-compatible shell (such as Bash), you would add these lines to
+ the `.profile' file in your home directory:
+ 
+      POSIXLY_CORRECT=true
+      export POSIXLY_CORRECT
+ 
+    For a C shell-compatible shell,(1) you would add this line to the
+ `.login' file in your home directory:
+ 
+      setenv POSIXLY_CORRECT true
+ 
+    Having `POSIXLY_CORRECT' set is not recommended for daily use, but
+ it is good for testing the portability of your programs to other
+ environments.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Not recommended.
+ 
+ 
+ File: gawk.info,  Node: Other Arguments,  Next: Naming Standard Input,  Prev: 
Options,  Up: Invoking Gawk
+ 
+ 2.3 Other Command-Line Arguments
+ ================================
+ 
+ Any additional arguments on the command line are normally treated as
+ input files to be processed in the order specified.   However, an
+ argument that has the form `VAR=VALUE', assigns the value VALUE to the
+ variable VAR--it does not specify a file at all.  (See *note Assignment
+ Options::.)
+ 
+    All these arguments are made available to your `awk' program in the
+ `ARGV' array (*note Built-in Variables::).  Command-line options and
+ the program text (if present) are omitted from `ARGV'.  All other
+ arguments, including variable assignments, are included.   As each
+ element of `ARGV' is processed, `gawk' sets the variable `ARGIND' to
+ the index in `ARGV' of the current element.
+ 
+    The distinction between file name arguments and variable-assignment
+ arguments is made when `awk' is about to open the next input file.  At
+ that point in execution, it checks the file name to see whether it is
+ really a variable assignment; if so, `awk' sets the variable instead of
+ reading a file.
+ 
+    Therefore, the variables actually receive the given values after all
+ previously specified files have been read.  In particular, the values of
+ variables assigned in this fashion are _not_ available inside a `BEGIN'
+ rule (*note BEGIN/END::), because such rules are run before `awk'
+ begins scanning the argument list.
+ 
+    The variable values given on the command line are processed for
+ escape sequences (*note Escape Sequences::).  (d.c.)
+ 
+    In some earlier implementations of `awk', when a variable assignment
+ occurred before any file names, the assignment would happen _before_
+ the `BEGIN' rule was executed.  `awk''s behavior was thus inconsistent;
+ some command-line assignments were available inside the `BEGIN' rule,
+ while others were not.  Unfortunately, some applications came to depend
+ upon this "feature."  When `awk' was changed to be more consistent, the
+ `-v' option was added to accommodate applications that depended upon
+ the old behavior.
+ 
+    The variable assignment feature is most useful for assigning to
+ variables such as `RS', `OFS', and `ORS', which control input and
+ output formats before scanning the data files.  It is also useful for
+ controlling state if multiple passes are needed over a data file.  For
+ example:
+ 
+      awk 'pass == 1  { PASS 1 STUFF }
+           pass == 2  { PASS 2 STUFF }' pass=1 mydata pass=2 mydata
+ 
+    Given the variable assignment feature, the `-F' option for setting
+ the value of `FS' is not strictly necessary.  It remains for historical
+ compatibility.
+ 
+ 
+ File: gawk.info,  Node: Naming Standard Input,  Next: Environment Variables,  
Prev: Other Arguments,  Up: Invoking Gawk
+ 
+ 2.4 Naming Standard Input
+ =========================
+ 
+ Often, you may wish to read standard input together with other files.
+ For example, you may wish to read one file, read standard input coming
+ from a pipe, and then read another file.
+ 
+    The way to name the standard input, with all versions of `awk', is
+ to use a single, standalone minus sign or dash, `-'.  For example:
+ 
+      SOME_COMMAND | awk -f myprog.awk file1 - file2
+ 
+ Here, `awk' first reads `file1', then it reads the output of
+ SOME_COMMAND, and finally it reads `file2'.
+ 
+    You may also use `"-"' to name standard input when reading files
+ with `getline' (*note Getline/File::).
+ 
+    In addition, `gawk' allows you to specify the special file name
+ `/dev/stdin', both on the command line and with `getline'.  Some other
+ versions of `awk' also support this, but it is not standard.  (Some
+ operating systems provide a `/dev/stdin' file in the file system,
+ however, `gawk' always processes this file name itself.)
+ 
+ 
+ File: gawk.info,  Node: Environment Variables,  Next: Exit Status,  Prev: 
Naming Standard Input,  Up: Invoking Gawk
+ 
+ 2.5 The Environment Variables `gawk' Uses
+ =========================================
+ 
+ A number of environment variables influence how `gawk' behaves.
+ 
+ * Menu:
+ 
+ * AWKPATH Variable::            Searching directories for `awk'
+                                 programs.
++* AWKLIBPATH Variable::         Searching directories for `awk' shared
++                                libraries.
+ * Other Environment Variables:: The environment variables.
+ 
+ 
 -File: gawk.info,  Node: AWKPATH Variable,  Next: Other Environment Variables, 
 Up: Environment Variables
++File: gawk.info,  Node: AWKPATH Variable,  Next: AWKLIBPATH Variable,  Up: 
Environment Variables
+ 
+ 2.5.1 The `AWKPATH' Environment Variable
+ ----------------------------------------
+ 
+ The previous minor node described how `awk' program files can be named
+ on the command-line with the `-f' option.  In most `awk'
+ implementations, you must supply a precise path name for each program
+ file, unless the file is in the current directory.  But in `gawk', if
 -the file name supplied to the `-f' option does not contain a `/', then
 -`gawk' searches a list of directories (called the "search path"), one
 -by one, looking for a file with the specified name.
++the file name supplied to the `-f' or `-i' options does not contain a
++`/', then `gawk' searches a list of directories (called the "search
++path"), one by one, looking for a file with the specified name.
+ 
+ The search path is a string consisting of directory names separated by
+ colons.  `gawk' gets its search path from the `AWKPATH' environment
+ variable.  If that variable does not exist, `gawk' uses a default path,
+ `.:/usr/local/share/awk'.(1)
+ 
+    The search path feature is particularly useful for building libraries
+ of useful `awk' functions.  The library files can be placed in a
+ standard directory in the default path and then specified on the
+ command line with a short file name.  Otherwise, the full file name
+ would have to be typed for each file.
+ 
 -   By using both the `--source' and `-f' options, your command-line
 -`awk' programs can use facilities in `awk' library files (*note Library
 -Functions::).  Path searching is not done if `gawk' is in compatibility
 -mode.  This is true for both `--traditional' and `--posix'.  *Note
 -Options::.
++   By using the `-i' option, or the `--source' and `-f' options, your
++command-line `awk' programs can use facilities in `awk' library files
++(*note Library Functions::).  Path searching is not done if `gawk' is
++in compatibility mode.  This is true for both `--traditional' and
++`--posix'.  *Note Options::.
++
++   If the source code is not found after the initial search, the path
++is searched again after adding the default `.awk' suffix to the
++filename.
+ 
+      NOTE: To include the current directory in the path, either place
+      `.' explicitly in the path or write a null entry in the path.  (A
+      null entry is indicated by starting or ending the path with a
+      colon or by placing two colons next to each other (`::').)  This
+      path search mechanism is similar to the shell's.
+ 
+      However, `gawk' always looks in the current directory _before_
+      searching `AWKPATH', so there is no real reason to include the
+      current directory in the search path.
+ 
+    If `AWKPATH' is not defined in the environment, `gawk' places its
+ default search path into `ENVIRON["AWKPATH"]'. This makes it easy to
+ determine the actual search path that `gawk' will use from within an
+ `awk' program.
+ 
+    While you can change `ENVIRON["AWKPATH"]' within your `awk' program,
+ this has no effect on the running program's behavior.  This makes
+ sense: the `AWKPATH' environment variable is used to find the program
+ source files.  Once your program is running, all the files have been
+ found, and `gawk' no longer needs to use `AWKPATH'.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Your version of `gawk' may use a different directory; it will
+ depend upon how `gawk' was built and installed. The actual directory is
+ the value of `$(datadir)' generated when `gawk' was configured.  You
+ probably don't need to worry about this, though.
+ 
+ 
 -File: gawk.info,  Node: Other Environment Variables,  Prev: AWKPATH Variable, 
 Up: Environment Variables
++File: gawk.info,  Node: AWKLIBPATH Variable,  Next: Other Environment 
Variables,  Prev: AWKPATH Variable,  Up: Environment Variables
++
++2.5.2 The `AWKLIBPATH' Environment Variable
++-------------------------------------------
++
++The `AWKLIBPATH' environment variable is similar to the `AWKPATH'
++variable, but it is used to search for shared libraries specified with
++the `-l' option rather than for source files.  If the library is not
++found, the path is searched again after adding the appropriate shared
++library suffix for the platform.  For example, on GNU/Linux systems,
++the suffix `.so' is used.
++
++
++File: gawk.info,  Node: Other Environment Variables,  Prev: AWKLIBPATH 
Variable,  Up: Environment Variables
+ 
 -2.5.2 Other Environment Variables
++2.5.3 Other Environment Variables
+ ---------------------------------
+ 
+ A number of other environment variables affect `gawk''s behavior, but
+ they are more specialized. Those in the following list are meant to be
+ used by regular users.
+ 
+ `POSIXLY_CORRECT'
+      Causes `gawk' to switch POSIX compatibility mode, disabling all
+      traditional and GNU extensions.  *Note Options::.
+ 
+ `GAWK_SOCK_RETRIES'
+      Controls the number of time `gawk' will attempt to retry a two-way
+      TCP/IP (socket) connection before giving up.  *Note TCP/IP
+      Networking::.
+ 
+ `GAWK_MSEC_SLEEP'
+      Specifies the interval between connection retries, in
+      milliseconds. On systems that do not support the `usleep()' system
+      call, the value is rounded up to an integral number of seconds.
+ 
++`GAWK_READ_TIMEOUT'
++     Specifies the time, in milliseconds, for `gawk' to wait for input
++     before returning with an error.  *Note Read Timeout::.
++
+    The environment variables in the following list are meant for use by
+ the `gawk' developers for testing and tuning.  They are subject to
+ change. The variables are:
+ 
+ `AVG_CHAIN_MAX'
+      The average number of items `gawk' will maintain on a hash chain
+      for managing arrays.
+ 
+ `AWK_HASH'
+      If this variable exists with a value of `gst', `gawk' will switch
+      to using the hash function from GNU Smalltalk for managing arrays.
+      This function may be marginally faster than the standard function.
+ 
+ `AWKREADFUNC'
+      If this variable exists, `gawk' switches to reading source files
+      one line at a time, instead of reading in blocks. This exists for
+      debugging problems on filesystems on non-POSIX operating systems
+      where I/O is performed in records, not in blocks.
+ 
+ `GAWK_NO_DFA'
+      If this variable exists, `gawk' does not use the DFA regexp matcher
+      for "does it match" kinds of tests. This can cause `gawk' to be
+      slower. Its purpose is to help isolate differences between the two
+      regexp matchers that `gawk' uses internally. (There aren't
+      supposed to be differences, but occasionally theory and practice
+      don't coordinate with each other.)
+ 
+ `GAWK_STACKSIZE'
+      This specifies the amount by which `gawk' should grow its internal
+      evaluation stack, when needed.
+ 
+ `TIDYMEM'
+      If this variable exists, `gawk' uses the `mtrace()' library calls
+      from GNU LIBC to help track down possible memory leaks.
+ 
+ 
+ File: gawk.info,  Node: Exit Status,  Next: Include Files,  Prev: Environment 
Variables,  Up: Invoking Gawk
+ 
+ 2.6 `gawk''s Exit Status
+ ========================
+ 
+ If the `exit' statement is used with a value (*note Exit Statement::),
+ then `gawk' exits with the numeric value given to it.
+ 
+    Otherwise, if there were no problems during execution, `gawk' exits
+ with the value of the C constant `EXIT_SUCCESS'.  This is usually zero.
+ 
+    If an error occurs, `gawk' exits with the value of the C constant
+ `EXIT_FAILURE'.  This is usually one.
+ 
+    If `gawk' exits because of a fatal error, the exit status is 2.  On
+ non-POSIX systems, this value may be mapped to `EXIT_FAILURE'.
+ 
+ 
 -File: gawk.info,  Node: Include Files,  Next: Obsolete,  Prev: Exit Status,  
Up: Invoking Gawk
++File: gawk.info,  Node: Include Files,  Next: Loading Shared Libraries,  
Prev: Exit Status,  Up: Invoking Gawk
+ 
+ 2.7 Including Other Files Into Your Program
+ ===========================================
+ 
+ This minor node describes a feature that is specific to `gawk'.
+ 
+    The address@hidden' keyword can be used to read external `awk' source
+ files.  This gives you the ability to split large `awk' source files
+ into smaller, more manageable pieces, and also lets you reuse common
+ `awk' code from various `awk' scripts.  In other words, you can group
+ together `awk' functions, used to carry out specific tasks, into
+ external files. These files can be used just like function libraries,
+ using the address@hidden' keyword in conjunction with the `AWKPATH'
 -environment variable.
++environment variable.  Note that source files may also be included
++using the `-i' option.
+ 
+    Let's see an example.  We'll start with two (trivial) `awk' scripts,
+ namely `test1' and `test2'. Here is the `test1' script:
+ 
+      BEGIN {
+          print "This is script test1."
+      }
+ 
+ and here is `test2':
+ 
+      @include "test1"
+      BEGIN {
+          print "This is script test2."
+      }
+ 
+    Running `gawk' with `test2' produces the following result:
+ 
+      $ gawk -f test2
+      -| This is file test1.
+      -| This is file test2.
+ 
+    `gawk' runs the `test2' script which includes `test1' using the
+ address@hidden' keyword.  So, to include external `awk' source files you just
+ use address@hidden' followed by the name of the file to be included,
+ enclosed in double quotes.
+ 
+      NOTE: Keep in mind that this is a language construct and the file
+      name cannot be a string variable, but rather just a literal string
+      in double quotes.
+ 
+    The files to be included may be nested; e.g., given a third script,
+ namely `test3':
+ 
+      @include "test2"
+      BEGIN {
+          print "This is script test3."
+      }
+ 
+ Running `gawk' with the `test3' script produces the following results:
+ 
+      $ gawk -f test3
+      -| This is file test1.
+      -| This is file test2.
+      -| This is file test3.
+ 
+    The file name can, of course, be a pathname. For example:
+ 
+      @include "../io_funcs"
+ 
+ or:
+ 
+      @include "/usr/awklib/network"
+ 
+ are valid. The `AWKPATH' environment variable can be of great value
+ when using address@hidden'. The same rules for the use of the `AWKPATH'
+ variable in command-line file searches (*note AWKPATH Variable::) apply
+ to address@hidden' also.
+ 
+    This is very helpful in constructing `gawk' function libraries.  If
+ you have a large script with useful, general purpose `awk' functions,
+ you can break it down into library files and put those files in a
+ special directory.  You can then include those "libraries," using
+ either the full pathnames of the files, or by setting the `AWKPATH'
+ environment variable accordingly and then using address@hidden' with just
+ the file part of the full pathname. Of course you can have more than
+ one directory to keep library files; the more complex the working
+ environment is, the more directories you may need to organize the files
+ to be included.
+ 
+    Given the ability to specify multiple `-f' options, the address@hidden'
+ mechanism is not strictly necessary.  However, the address@hidden' keyword
+ can help you in constructing self-contained `gawk' programs, thus
+ reducing the need for writing complex and tedious command lines.  In
+ particular, address@hidden' is very useful for writing CGI scripts to be run
+ from web pages.
+ 
+    As mentioned in *note AWKPATH Variable::, the current directory is
+ always searched first for source files, before searching in `AWKPATH',
+ and this also applies to files named with address@hidden'.
+ 
+ 
 -File: gawk.info,  Node: Obsolete,  Next: Undocumented,  Prev: Include Files,  
Up: Invoking Gawk
++File: gawk.info,  Node: Loading Shared Libraries,  Next: Obsolete,  Prev: 
Include Files,  Up: Invoking Gawk
++
++2.8 Loading Shared Libraries Into Your Program
++==============================================
++
++This minor node describes a feature that is specific to `gawk'.
++
++   The address@hidden' keyword can be used to read external `awk' shared
++libraries.  This allows you to link in compiled code that may offer
++superior performance and/or give you access to extended capabilities
++not supported by the `awk' language.  The `AWKLIBPATH' variable is used
++to search for the shared library.  Using address@hidden' is completely
++equivalent to using the `-l' command-line option.
++
++   If the shared library is not initially found in `AWKLIBPATH', another
++search is conducted after appending the platform's default shared
++library suffix to the filename.  For example, on GNU/Linux systems, the
++suffix `.so' is used.
++
++     $ gawk '@load "ordchr"; BEGIN {print chr(65)}'
++     -| A
++
++This is equivalent to the following example:
++
++     $ gawk -lordchr 'BEGIN {print chr(65)}'
++     -| A
++
++For command-line usage, the `-l' option is more convenient, but 
address@hidden'
++is useful for embedding inside an `awk' source file that requires
++access to a shared library.
++
++
++File: gawk.info,  Node: Obsolete,  Next: Undocumented,  Prev: Loading Shared 
Libraries,  Up: Invoking Gawk
+ 
 -2.8 Obsolete Options and/or Features
++2.9 Obsolete Options and/or Features
+ ====================================
+ 
+ This minor node describes features and/or command-line options from
+ previous releases of `gawk' that are either not available in the
+ current version or that are still supported but deprecated (meaning that
+ they will _not_ be in the next release).
+ 
+    The process-related special files `/dev/pid', `/dev/ppid',
+ `/dev/pgrpid', and `/dev/user' were deprecated in `gawk' 3.1, but still
+ worked.  As of version 4.0, they are no longer interpreted specially by
+ `gawk'.  (Use `PROCINFO' instead; see *note Auto-set::.)
+ 
+ 
+ File: gawk.info,  Node: Undocumented,  Prev: Obsolete,  Up: Invoking Gawk
+ 
 -2.9 Undocumented Options and Features
 -=====================================
++2.10 Undocumented Options and Features
++======================================
+ 
+      Use the Source, Luke!
+      Obi-Wan
+ 
+    This minor node intentionally left blank.
+ 
+ 
+ File: gawk.info,  Node: Regexp,  Next: Reading Files,  Prev: Invoking Gawk,  
Up: Top
+ 
+ 3 Regular Expressions
+ *********************
+ 
+ A "regular expression", or "regexp", is a way of describing a set of
+ strings.  Because regular expressions are such a fundamental part of
+ `awk' programming, their format and use deserve a separate major node.
+ 
+    A regular expression enclosed in slashes (`/') is an `awk' pattern
+ that matches every input record whose text belongs to that set.  The
+ simplest regular expression is a sequence of letters, numbers, or both.
+ Such a regexp matches any string that contains that sequence.  Thus,
+ the regexp `foo' matches any string containing `foo'.  Therefore, the
+ pattern `/foo/' matches any input record containing the three
+ characters `foo' _anywhere_ in the record.  Other kinds of regexps let
+ you specify more complicated classes of strings.
+ 
+ * Menu:
+ 
+ * Regexp Usage::                How to Use Regular Expressions.
+ * Escape Sequences::            How to write nonprinting characters.
+ * Regexp Operators::            Regular Expression Operators.
+ * Bracket Expressions::         What can go between `[...]'.
+ * GNU Regexp Operators::        Operators specific to GNU software.
+ * Case-sensitivity::            How to do case-insensitive matching.
+ * Leftmost Longest::            How much text matches.
+ * Computed Regexps::            Using Dynamic Regexps.
+ 
+ 
+ File: gawk.info,  Node: Regexp Usage,  Next: Escape Sequences,  Up: Regexp
+ 
+ 3.1 How to Use Regular Expressions
+ ==================================
+ 
+ A regular expression can be used as a pattern by enclosing it in
+ slashes.  Then the regular expression is tested against the entire text
+ of each record.  (Normally, it only needs to match some part of the
+ text in order to succeed.)  For example, the following prints the
+ second field of each record that contains the string `foo' anywhere in
+ it:
+ 
+      $ awk '/foo/ { print $2 }' BBS-list
+      -| 555-1234
+      -| 555-6699
+      -| 555-6480
+      -| 555-2127
+ 
+    Regular expressions can also be used in matching expressions.  These
+ expressions allow you to specify the string to match against; it need
+ not be the entire current input record.  The two operators `~' and `!~'
+ perform regular expression comparisons.  Expressions using these
+ operators can be used as patterns, or in `if', `while', `for', and `do'
+ statements.  (*Note Statements::.)  For example:
+ 
+      EXP ~ /REGEXP/
+ 
+ is true if the expression EXP (taken as a string) matches REGEXP.  The
+ following example matches, or selects, all input records with the
+ uppercase letter `J' somewhere in the first field:
+ 
+      $ awk '$1 ~ /J/' inventory-shipped
+      -| Jan  13  25  15 115
+      -| Jun  31  42  75 492
+      -| Jul  24  34  67 436
+      -| Jan  21  36  64 620
+ 
+    So does this:
+ 
+      awk '{ if ($1 ~ /J/) print }' inventory-shipped
+ 
+    This next example is true if the expression EXP (taken as a
+ character string) does _not_ match REGEXP:
+ 
+      EXP !~ /REGEXP/
+ 
+    The following example matches, or selects, all input records whose
+ first field _does not_ contain the uppercase letter `J':
+ 
+      $ awk '$1 !~ /J/' inventory-shipped
+      -| Feb  15  32  24 226
+      -| Mar  15  24  34 228
+      -| Apr  31  52  63 420
+      -| May  16  34  29 208
+      ...
+ 
+    When a regexp is enclosed in slashes, such as `/foo/', we call it a
+ "regexp constant", much like `5.27' is a numeric constant and `"foo"'
+ is a string constant.
+ 
+ 
+ File: gawk.info,  Node: Escape Sequences,  Next: Regexp Operators,  Prev: 
Regexp Usage,  Up: Regexp
+ 
+ 3.2 Escape Sequences
+ ====================
+ 
+ Some characters cannot be included literally in string constants
+ (`"foo"') or regexp constants (`/foo/').  Instead, they should be
+ represented with "escape sequences", which are character sequences
+ beginning with a backslash (`\').  One use of an escape sequence is to
+ include a double-quote character in a string constant.  Because a plain
+ double quote ends the string, you must use `\"' to represent an actual
+ double-quote character as a part of the string.  For example:
+ 
+      $ awk 'BEGIN { print "He said \"hi!\" to her." }'
+      -| He said "hi!" to her.
+ 
+    The  backslash character itself is another character that cannot be
+ included normally; you must write `\\' to put one backslash in the
+ string or regexp.  Thus, the string whose contents are the two
+ characters `"' and `\' must be written `"\"\\"'.
+ 
+    Other escape sequences represent unprintable characters such as TAB
+ or newline.  While there is nothing to stop you from entering most
+ unprintable characters directly in a string constant or regexp constant,
+ they may look ugly.
+ 
+    The following table lists all the escape sequences used in `awk' and
+ what they represent. Unless noted otherwise, all these escape sequences
+ apply to both string constants and regexp constants:
+ 
+ `\\'
+      A literal backslash, `\'.
+ 
+ `\a'
+      The "alert" character, `Ctrl-g', ASCII code 7 (BEL).  (This
+      usually makes some sort of audible noise.)
+ 
+ `\b'
+      Backspace, `Ctrl-h', ASCII code 8 (BS).
+ 
+ `\f'
+      Formfeed, `Ctrl-l', ASCII code 12 (FF).
+ 
+ `\n'
+      Newline, `Ctrl-j', ASCII code 10 (LF).
+ 
+ `\r'
+      Carriage return, `Ctrl-m', ASCII code 13 (CR).
+ 
+ `\t'
+      Horizontal TAB, `Ctrl-i', ASCII code 9 (HT).
+ 
+ `\v'
+      Vertical tab, `Ctrl-k', ASCII code 11 (VT).
+ 
+ `\NNN'
+      The octal value NNN, where NNN stands for 1 to 3 digits between
+      `0' and `7'.  For example, the code for the ASCII ESC (escape)
+      character is `\033'.
+ 
+ `\xHH...'
+      The hexadecimal value HH, where HH stands for a sequence of
+      hexadecimal digits (`0'-`9', and either `A'-`F' or `a'-`f').  Like
+      the same construct in ISO C, the escape sequence continues until
+      the first nonhexadecimal digit is seen. (c.e.)  However, using
+      more than two hexadecimal digits produces undefined results. (The
+      `\x' escape sequence is not allowed in POSIX `awk'.)
+ 
+ `\/'
+      A literal slash (necessary for regexp constants only).  This
+      sequence is used when you want to write a regexp constant that
+      contains a slash. Because the regexp is delimited by slashes, you
+      need to escape the slash that is part of the pattern, in order to
+      tell `awk' to keep processing the rest of the regexp.
+ 
+ `\"'
+      A literal double quote (necessary for string constants only).
+      This sequence is used when you want to write a string constant
+      that contains a double quote. Because the string is delimited by
+      double quotes, you need to escape the quote that is part of the
+      string, in order to tell `awk' to keep processing the rest of the
+      string.
+ 
+    In `gawk', a number of additional two-character sequences that begin
+ with a backslash have special meaning in regexps.  *Note GNU Regexp
+ Operators::.
+ 
+    In a regexp, a backslash before any character that is not in the
+ previous list and not listed in *note GNU Regexp Operators::, means
+ that the next character should be taken literally, even if it would
+ normally be a regexp operator.  For example, `/a\+b/' matches the three
+ characters `a+b'.
+ 
+    For complete portability, do not use a backslash before any
+ character not shown in the previous list.
+ 
+    To summarize:
+ 
+    * The escape sequences in the table above are always processed first,
+      for both string constants and regexp constants. This happens very
+      early, as soon as `awk' reads your program.
+ 
+    * `gawk' processes both regexp constants and dynamic regexps (*note
+      Computed Regexps::), for the special operators listed in *note GNU
+      Regexp Operators::.
+ 
+    * A backslash before any other character means to treat that
+      character literally.
+ 
+ Advanced Notes: Backslash Before Regular Characters
+ ---------------------------------------------------
+ 
+ If you place a backslash in a string constant before something that is
+ not one of the characters previously listed, POSIX `awk' purposely
+ leaves what happens as undefined.  There are two choices:
+ 
+ Strip the backslash out
+      This is what Brian Kernighan's `awk' and `gawk' both do.  For
+      example, `"a\qc"' is the same as `"aqc"'.  (Because this is such
+      an easy bug both to introduce and to miss, `gawk' warns you about
+      it.)  Consider `FS = "[ \t]+\|[ \t]+"' to use vertical bars
+      surrounded by whitespace as the field separator. There should be
+      two backslashes in the string: `FS = "[ \t]+\\|[ \t]+"'.)
+ 
+ Leave the backslash alone
+      Some other `awk' implementations do this.  In such
+      implementations, typing `"a\qc"' is the same as typing `"a\\qc"'.
+ 
+ Advanced Notes: Escape Sequences for Metacharacters
+ ---------------------------------------------------
+ 
+ Suppose you use an octal or hexadecimal escape to represent a regexp
+ metacharacter.  (See *note Regexp Operators::.)  Does `awk' treat the
+ character as a literal character or as a regexp operator?
+ 
+    Historically, such characters were taken literally.  (d.c.)
+ However, the POSIX standard indicates that they should be treated as
+ real metacharacters, which is what `gawk' does.  In compatibility mode
+ (*note Options::), `gawk' treats the characters represented by octal
+ and hexadecimal escape sequences literally when used in regexp
+ constants. Thus, `/a\52b/' is equivalent to `/a\*b/'.
+ 
+ 
+ File: gawk.info,  Node: Regexp Operators,  Next: Bracket Expressions,  Prev: 
Escape Sequences,  Up: Regexp
+ 
+ 3.3 Regular Expression Operators
+ ================================
+ 
+ You can combine regular expressions with special characters, called
+ "regular expression operators" or "metacharacters", to increase the
+ power and versatility of regular expressions.
+ 
+    The escape sequences described in *note Escape Sequences::, are
+ valid inside a regexp.  They are introduced by a `\' and are recognized
+ and converted into corresponding real characters as the very first step
+ in processing regexps.
+ 
+    Here is a list of metacharacters.  All characters that are not escape
+ sequences and that are not listed in the table stand for themselves:
+ 
+ `\'
+      This is used to suppress the special meaning of a character when
+      matching.  For example, `\$' matches the character `$'.
+ 
+ `^'
+      This matches the beginning of a string.  For example, address@hidden'
+      matches address@hidden' at the beginning of a string and can be used to
+      identify chapter beginnings in Texinfo source files.  The `^' is
+      known as an "anchor", because it anchors the pattern to match only
+      at the beginning of the string.
+ 
+      It is important to realize that `^' does not match the beginning of
+      a line embedded in a string.  The condition is not true in the
+      following example:
+ 
+           if ("line1\nLINE 2" ~ /^L/) ...
+ 
+ `$'
+      This is similar to `^', but it matches only at the end of a string.
+      For example, `p$' matches a record that ends with a `p'.  The `$'
+      is an anchor and does not match the end of a line embedded in a
+      string.  The condition in the following example is not true:
+ 
+           if ("line1\nLINE 2" ~ /1$/) ...
+ 
+ `. (period)'
+      This matches any single character, _including_ the newline
+      character.  For example, `.P' matches any single character
+      followed by a `P' in a string.  Using concatenation, we can make a
+      regular expression such as `U.A', which matches any
+      three-character sequence that begins with `U' and ends with `A'.
+ 
+      In strict POSIX mode (*note Options::), `.' does not match the NUL
+      character, which is a character with all bits equal to zero.
+      Otherwise, NUL is just another character. Other versions of `awk'
+      may not be able to match the NUL character.
+ 
+ `[...]'
+      This is called a "bracket expression".(1) It matches any _one_ of
+      the characters that are enclosed in the square brackets.  For
+      example, `[MVX]' matches any one of the characters `M', `V', or
+      `X' in a string.  A full discussion of what can be inside the
+      square brackets of a bracket expression is given in *note Bracket
+      Expressions::.
+ 
+ `[^ ...]'
+      This is a "complemented bracket expression".  The first character
+      after the `[' _must_ be a `^'.  It matches any characters _except_
+      those in the square brackets.  For example, `[^awk]' matches any
+      character that is not an `a', `w', or `k'.
+ 
+ `|'
+      This is the "alternation operator" and it is used to specify
+      alternatives.  The `|' has the lowest precedence of all the regular
+      expression operators.  For example, `^P|[[:digit:]]' matches any
+      string that matches either `^P' or `[[:digit:]]'.  This means it
+      matches any string that starts with `P' or contains a digit.
+ 
+      The alternation applies to the largest possible regexps on either
+      side.
+ 
+ `(...)'
+      Parentheses are used for grouping in regular expressions, as in
+      arithmetic.  They can be used to concatenate regular expressions
+      containing the alternation operator, `|'.  For example,
+      `@(samp|code)\{[^}]+\}' matches both address@hidden' and address@hidden'.
+      (These are Texinfo formatting control sequences. The `+' is
+      explained further on in this list.)
+ 
+ `*'
+      This symbol means that the preceding regular expression should be
+      repeated as many times as necessary to find a match.  For example,
+      `ph*' applies the `*' symbol to the preceding `h' and looks for
+      matches of one `p' followed by any number of `h's.  This also
+      matches just `p' if no `h's are present.
+ 
+      The `*' repeats the _smallest_ possible preceding expression.
+      (Use parentheses if you want to repeat a larger expression.)  It
+      finds as many repetitions as possible.  For example, `awk
+      '/\(c[ad][ad]*r x\)/ { print }' sample' prints every record in
+      `sample' containing a string of the form `(car x)', `(cdr x)',
+      `(cadr x)', and so on.  Notice the escaping of the parentheses by
+      preceding them with backslashes.
+ 
+ `+'
+      This symbol is similar to `*', except that the preceding
+      expression must be matched at least once.  This means that `wh+y'
+      would match `why' and `whhy', but not `wy', whereas `wh*y' would
+      match all three of these strings.  The following is a simpler way
+      of writing the last `*' example:
+ 
+           awk '/\(c[ad]+r x\)/ { print }' sample
+ 
+ `?'
+      This symbol is similar to `*', except that the preceding
+      expression can be matched either once or not at all.  For example,
+      `fe?d' matches `fed' and `fd', but nothing else.
+ 
+ `{N}'
+ `{N,}'
+ `{N,M}'
+      One or two numbers inside braces denote an "interval expression".
+      If there is one number in the braces, the preceding regexp is
+      repeated N times.  If there are two numbers separated by a comma,
+      the preceding regexp is repeated N to M times.  If there is one
+      number followed by a comma, then the preceding regexp is repeated
+      at least N times:
+ 
+     `wh{3}y'
+           Matches `whhhy', but not `why' or `whhhhy'.
+ 
+     `wh{3,5}y'
+           Matches `whhhy', `whhhhy', or `whhhhhy', only.
+ 
+     `wh{2,}y'
+           Matches `whhy' or `whhhy', and so on.
+ 
+      Interval expressions were not traditionally available in `awk'.
+      They were added as part of the POSIX standard to make `awk' and
+      `egrep' consistent with each other.
+ 
+      Initially, because old programs may use `{' and `}' in regexp
+      constants, `gawk' did _not_ match interval expressions in regexps.
+ 
+      However, beginning with version 4.0, `gawk' does match interval
+      expressions by default.  This is because compatibility with POSIX
+      has become more important to most `gawk' users than compatibility
+      with old programs.
+ 
+      For programs that use `{' and `}' in regexp constants, it is good
+      practice to always escape them with a backslash.  Then the regexp
+      constants are valid and work the way you want them to, using any
+      version of `awk'.(2)
+ 
+      Finally, when `{' and `}' appear in regexp constants in a way that
+      cannot be interpreted as an interval expression (such as
+      `/q{a}/'), then they stand for themselves.
+ 
+    In regular expressions, the `*', `+', and `?' operators, as well as
+ the braces `{' and `}', have the highest precedence, followed by
+ concatenation, and finally by `|'.  As in arithmetic, parentheses can
+ change how operators are grouped.
+ 
+    In POSIX `awk' and `gawk', the `*', `+', and `?' operators stand for
+ themselves when there is nothing in the regexp that precedes them.  For
+ example, `/+/' matches a literal plus sign.  However, many other
+ versions of `awk' treat such a usage as a syntax error.
+ 
+    If `gawk' is in compatibility mode (*note Options::), interval
+ expressions are not available in regular expressions.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) In other literature, you may see a bracket expression referred
+ to as either a "character set", a "character class", or a "character
+ list".
+ 
+    (2) Use two backslashes if you're using a string constant with a
+ regexp operator or function.
+ 
+ 
+ File: gawk.info,  Node: Bracket Expressions,  Next: GNU Regexp Operators,  
Prev: Regexp Operators,  Up: Regexp
+ 
+ 3.4 Using Bracket Expressions
+ =============================
+ 
+ As mentioned earlier, a bracket expression matches any character amongst
+ those listed between the opening and closing square brackets.
+ 
+    Within a bracket expression, a "range expression" consists of two
+ characters separated by a hyphen.  It matches any single character that
+ sorts between the two characters, based upon the system's native
+ character set.  For example, `[0-9]' is equivalent to `[0123456789]'.
+ (See *note Ranges and Locales::, for an explanation of how the POSIX
+ standard and `gawk' have changed over time.  This is mainly of
+ historical interest.)
+ 
+    To include one of the characters `\', `]', `-', or `^' in a bracket
+ expression, put a `\' in front of it.  For example:
+ 
+      [d\]]
+ 
+ matches either `d' or `]'.
+ 
+    This treatment of `\' in bracket expressions is compatible with
+ other `awk' implementations and is also mandated by POSIX.  The regular
+ expressions in `awk' are a superset of the POSIX specification for
+ Extended Regular Expressions (EREs).  POSIX EREs are based on the
+ regular expressions accepted by the traditional `egrep' utility.
+ 
+    "Character classes" are a feature introduced in the POSIX standard.
+ A character class is a special notation for describing lists of
+ characters that have a specific attribute, but the actual characters
+ can vary from country to country and/or from character set to character
+ set.  For example, the notion of what is an alphabetic character
+ differs between the United States and France.
+ 
+    A character class is only valid in a regexp _inside_ the brackets of
+ a bracket expression.  Character classes consist of `[:', a keyword
+ denoting the class, and `:]'.  *note table-char-classes:: lists the
+ character classes defined by the POSIX standard.
+ 
+ Class       Meaning
+ -------------------------------------------------------------------------- 
+ `[:alnum:]' Alphanumeric characters.
+ `[:alpha:]' Alphabetic characters.
+ `[:blank:]' Space and TAB characters.
+ `[:cntrl:]' Control characters.
+ `[:digit:]' Numeric characters.
+ `[:graph:]' Characters that are both printable and visible.  (A space is
+             printable but not visible, whereas an `a' is both.)
+ `[:lower:]' Lowercase alphabetic characters.
+ `[:print:]' Printable characters (characters that are not control
+             characters).
+ `[:punct:]' Punctuation characters (characters that are not letters,
+             digits, control characters, or space characters).
+ `[:space:]' Space characters (such as space, TAB, and formfeed, to name
+             a few).
+ `[:upper:]' Uppercase alphabetic characters.
+ `[:xdigit:]'Characters that are hexadecimal digits.
+ 
+ Table 3.1: POSIX Character Classes
+ 
+    For example, before the POSIX standard, you had to write
+ `/[A-Za-z0-9]/' to match alphanumeric characters.  If your character
+ set had other alphabetic characters in it, this would not match them.
+ With the POSIX character classes, you can write `/[[:alnum:]]/' to
+ match the alphabetic and numeric characters in your character set.
+ 
+    Two additional special sequences can appear in bracket expressions.
+ These apply to non-ASCII character sets, which can have single symbols
+ (called "collating elements") that are represented with more than one
+ character. They can also have several characters that are equivalent for
+ "collating", or sorting, purposes.  (For example, in French, a plain "e"
+ and a grave-accented "e`" are equivalent.)  These sequences are:
+ 
+ Collating symbols
+      Multicharacter collating elements enclosed between `[.' and `.]'.
+      For example, if `ch' is a collating element, then `[[.ch.]]' is a
+      regexp that matches this collating element, whereas `[ch]' is a
+      regexp that matches either `c' or `h'.
+ 
+ Equivalence classes
+      Locale-specific names for a list of characters that are equal. The
+      name is enclosed between `[=' and `=]'.  For example, the name `e'
+      might be used to represent all of "e," "e`," and "e'." In this
+      case, `[[=e=]]' is a regexp that matches any of `e', `e'', or `e`'.
+ 
+    These features are very valuable in non-English-speaking locales.
+ 
+      CAUTION: The library functions that `gawk' uses for regular
+      expression matching currently recognize only POSIX character
+      classes; they do not recognize collating symbols or equivalence
+      classes.
+ 
+ 
+ File: gawk.info,  Node: GNU Regexp Operators,  Next: Case-sensitivity,  Prev: 
Bracket Expressions,  Up: Regexp
+ 
+ 3.5 `gawk'-Specific Regexp Operators
+ ====================================
+ 
+ GNU software that deals with regular expressions provides a number of
+ additional regexp operators.  These operators are described in this
+ minor node and are specific to `gawk'; they are not available in other
+ `awk' implementations.  Most of the additional operators deal with word
+ matching.  For our purposes, a "word" is a sequence of one or more
+ letters, digits, or underscores (`_'):
+ 
+ `\s'
+      Matches any whitespace character.  Think of it as shorthand for
+      `[[:space:]]'.
+ 
+ `\S'
+      Matches any character that is not whitespace.  Think of it as
+      shorthand for `[^[:space:]]'.
+ 
+ `\w'
+      Matches any word-constituent character--that is, it matches any
+      letter, digit, or underscore. Think of it as shorthand for
+      `[[:alnum:]_]'.
+ 
+ `\W'
+      Matches any character that is not word-constituent.  Think of it
+      as shorthand for `[^[:alnum:]_]'.
+ 
+ `\<'
+      Matches the empty string at the beginning of a word.  For example,
+      `/\<away/' matches `away' but not `stowaway'.
+ 
+ `\>'
+      Matches the empty string at the end of a word.  For example,
+      `/stow\>/' matches `stow' but not `stowaway'.
+ 
+ `\y'
+      Matches the empty string at either the beginning or the end of a
+      word (i.e., the word boundar*y*).  For example, `\yballs?\y'
+      matches either `ball' or `balls', as a separate word.
+ 
+ `\B'
+      Matches the empty string that occurs between two word-constituent
+      characters. For example, `/\Brat\B/' matches `crate' but it does
+      not match `dirty rat'.  `\B' is essentially the opposite of `\y'.
+ 
+    There are two other operators that work on buffers.  In Emacs, a
+ "buffer" is, naturally, an Emacs buffer.  For other programs, `gawk''s
+ regexp library routines consider the entire string to match as the
+ buffer.  The operators are:
+ 
+ `\`'
+      Matches the empty string at the beginning of a buffer (string).
+ 
+ `\''
+      Matches the empty string at the end of a buffer (string).
+ 
+    Because `^' and `$' always work in terms of the beginning and end of
+ strings, these operators don't add any new capabilities for `awk'.
+ They are provided for compatibility with other GNU software.
+ 
+    In other GNU software, the word-boundary operator is `\b'. However,
+ that conflicts with the `awk' language's definition of `\b' as
+ backspace, so `gawk' uses a different letter.  An alternative method
+ would have been to require two backslashes in the GNU operators, but
+ this was deemed too confusing. The current method of using `\y' for the
+ GNU `\b' appears to be the lesser of two evils.
+ 
+    The various command-line options (*note Options::) control how
+ `gawk' interprets characters in regexps:
+ 
+ No options
+      In the default case, `gawk' provides all the facilities of POSIX
+      regexps and the GNU regexp operators described in *note Regexp
+      Operators::.
+ 
+ `--posix'
+      Only POSIX regexps are supported; the GNU operators are not special
+      (e.g., `\w' matches a literal `w').  Interval expressions are
+      allowed.
+ 
+ `--traditional'
+      Traditional Unix `awk' regexps are matched. The GNU operators are
+      not special, and interval expressions are not available.  The
+      POSIX character classes (`[[:alnum:]]', etc.) are supported, as
+      Brian Kernighan's `awk' does support them.  Characters described
+      by octal and hexadecimal escape sequences are treated literally,
+      even if they represent regexp metacharacters.
+ 
+ `--re-interval'
+      Allow interval expressions in regexps, if `--traditional' has been
+      provided.  Otherwise, interval expressions are available by
+      default.
+ 
+ 
+ File: gawk.info,  Node: Case-sensitivity,  Next: Leftmost Longest,  Prev: GNU 
Regexp Operators,  Up: Regexp
+ 
+ 3.6 Case Sensitivity in Matching
+ ================================
+ 
+ Case is normally significant in regular expressions, both when matching
+ ordinary characters (i.e., not metacharacters) and inside bracket
+ expressions.  Thus, a `w' in a regular expression matches only a
+ lowercase `w' and not an uppercase `W'.
+ 
+    The simplest way to do a case-independent match is to use a bracket
+ expression--for example, `[Ww]'.  However, this can be cumbersome if
+ you need to use it often, and it can make the regular expressions harder
+ to read.  There are two alternatives that you might prefer.
+ 
+    One way to perform a case-insensitive match at a particular point in
+ the program is to convert the data to a single case, using the
+ `tolower()' or `toupper()' built-in string functions (which we haven't
+ discussed yet; *note String Functions::).  For example:
+ 
+      tolower($1) ~ /foo/  { ... }
+ 
+ converts the first field to lowercase before matching against it.  This
+ works in any POSIX-compliant `awk'.
+ 
+    Another method, specific to `gawk', is to set the variable
+ `IGNORECASE' to a nonzero value (*note Built-in Variables::).  When
+ `IGNORECASE' is not zero, _all_ regexp and string operations ignore
+ case.  Changing the value of `IGNORECASE' dynamically controls the
+ case-sensitivity of the program as it runs.  Case is significant by
+ default because `IGNORECASE' (like most variables) is initialized to
+ zero:
+ 
+      x = "aB"
+      if (x ~ /ab/) ...   # this test will fail
+ 
+      IGNORECASE = 1
+      if (x ~ /ab/) ...   # now it will succeed
+ 
+    In general, you cannot use `IGNORECASE' to make certain rules
+ case-insensitive and other rules case-sensitive, because there is no
+ straightforward way to set `IGNORECASE' just for the pattern of a
+ particular rule.(1) To do this, use either bracket expressions or
+ `tolower()'.  However, one thing you can do with `IGNORECASE' only is
+ dynamically turn case-sensitivity on or off for all the rules at once.
+ 
+    `IGNORECASE' can be set on the command line or in a `BEGIN' rule
+ (*note Other Arguments::; also *note Using BEGIN/END::).  Setting
+ `IGNORECASE' from the command line is a way to make a program
+ case-insensitive without having to edit it.
+ 
+    Both regexp and string comparison operations are affected by
+ `IGNORECASE'.
+ 
+    In multibyte locales, the equivalences between upper- and lowercase
+ characters are tested based on the wide-character values of the
+ locale's character set.  Otherwise, the characters are tested based on
+ the ISO-8859-1 (ISO Latin-1) character set. This character set is a
+ superset of the traditional 128 ASCII characters, which also provides a
+ number of characters suitable for use with European languages.(2)
+ 
+    The value of `IGNORECASE' has no effect if `gawk' is in
+ compatibility mode (*note Options::).  Case is always significant in
+ compatibility mode.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Experienced C and C++ programmers will note that it is possible,
+ using something like `IGNORECASE = 1 && /foObAr/ { ... }' and
+ `IGNORECASE = 0 || /foobar/ { ... }'.  However, this is somewhat
+ obscure and we don't recommend it.
+ 
+    (2) If you don't understand this, don't worry about it; it just
+ means that `gawk' does the right thing.
+ 
+ 
+ File: gawk.info,  Node: Leftmost Longest,  Next: Computed Regexps,  Prev: 
Case-sensitivity,  Up: Regexp
+ 
+ 3.7 How Much Text Matches?
+ ==========================
+ 
+ Consider the following:
+ 
+      echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }'
+ 
+    This example uses the `sub()' function (which we haven't discussed
+ yet; *note String Functions::) to make a change to the input record.
+ Here, the regexp `/a+/' indicates "one or more `a' characters," and the
+ replacement text is `<A>'.
+ 
+    The input contains four `a' characters.  `awk' (and POSIX) regular
+ expressions always match the leftmost, _longest_ sequence of input
+ characters that can match.  Thus, all four `a' characters are replaced
+ with `<A>' in this example:
+ 
+      $ echo aaaabcd | awk '{ sub(/a+/, "<A>"); print }'
+      -| <A>bcd
+ 
+    For simple match/no-match tests, this is not so important. But when
+ doing text matching and substitutions with the `match()', `sub()',
+ `gsub()', and `gensub()' functions, it is very important.  *Note String
+ Functions::, for more information on these functions.  Understanding
+ this principle is also important for regexp-based record and field
+ splitting (*note Records::, and also *note Field Separators::).
+ 
+ 
+ File: gawk.info,  Node: Computed Regexps,  Prev: Leftmost Longest,  Up: Regexp
+ 
+ 3.8 Using Dynamic Regexps
+ =========================
+ 
+ The righthand side of a `~' or `!~' operator need not be a regexp
+ constant (i.e., a string of characters between slashes).  It may be any
+ expression.  The expression is evaluated and converted to a string if
+ necessary; the contents of the string are then used as the regexp.  A
+ regexp computed in this way is called a "dynamic regexp":
+ 
+      BEGIN { digits_regexp = "[[:digit:]]+" }
+      $0 ~ digits_regexp    { print }
+ 
+ This sets `digits_regexp' to a regexp that describes one or more digits,
+ and tests whether the input record matches this regexp.
+ 
+      NOTE: When using the `~' and `!~' operators, there is a difference
+      between a regexp constant enclosed in slashes and a string
+      constant enclosed in double quotes.  If you are going to use a
+      string constant, you have to understand that the string is, in
+      essence, scanned _twice_: the first time when `awk' reads your
+      program, and the second time when it goes to match the string on
+      the lefthand side of the operator with the pattern on the right.
+      This is true of any string-valued expression (such as
+      `digits_regexp', shown previously), not just string constants.
+ 
+    What difference does it make if the string is scanned twice? The
+ answer has to do with escape sequences, and particularly with
+ backslashes.  To get a backslash into a regular expression inside a
+ string, you have to type two backslashes.
+ 
+    For example, `/\*/' is a regexp constant for a literal `*'.  Only
+ one backslash is needed.  To do the same thing with a string, you have
+ to type `"\\*"'.  The first backslash escapes the second one so that
+ the string actually contains the two characters `\' and `*'.
+ 
+    Given that you can use both regexp and string constants to describe
+ regular expressions, which should you use?  The answer is "regexp
+ constants," for several reasons:
+ 
+    * String constants are more complicated to write and more difficult
+      to read. Using regexp constants makes your programs less
+      error-prone.  Not understanding the difference between the two
+      kinds of constants is a common source of errors.
+ 
+    * It is more efficient to use regexp constants. `awk' can note that
+      you have supplied a regexp and store it internally in a form that
+      makes pattern matching more efficient.  When using a string
+      constant, `awk' must first convert the string into this internal
+      form and then perform the pattern matching.
+ 
+    * Using regexp constants is better form; it shows clearly that you
+      intend a regexp match.
+ 
+ Advanced Notes: Using `\n' in Bracket Expressions of Dynamic Regexps
+ --------------------------------------------------------------------
+ 
+ Some commercial versions of `awk' do not allow the newline character to
+ be used inside a bracket expression for a dynamic regexp:
+ 
+      $ awk '$0 ~ "[ \t\n]"'
+      error--> awk: newline in character class [
+      error--> ]...
+      error-->  source line number 1
+      error-->  context is
+      error-->          >>>  <<<
+ 
+    But a newline in a regexp constant works with no problem:
+ 
+      $ awk '$0 ~ /[ \t\n]/'
+      here is a sample line
+      -| here is a sample line
+      Ctrl-d
+ 
+    `gawk' does not have this problem, and it isn't likely to occur
+ often in practice, but it's worth noting for future reference.
+ 
+ 
+ File: gawk.info,  Node: Reading Files,  Next: Printing,  Prev: Regexp,  Up: 
Top
+ 
+ 4 Reading Input Files
+ *********************
+ 
+ In the typical `awk' program, `awk' reads all input either from the
+ standard input (by default, this is the keyboard, but often it is a
+ pipe from another command) or from files whose names you specify on the
+ `awk' command line.  If you specify input files, `awk' reads them in
+ order, processing all the data from one before going on to the next.
+ The name of the current input file can be found in the built-in variable
+ `FILENAME' (*note Built-in Variables::).
+ 
+    The input is read in units called "records", and is processed by the
+ rules of your program one record at a time.  By default, each record is
+ one line.  Each record is automatically split into chunks called
+ "fields".  This makes it more convenient for programs to work on the
+ parts of a record.
+ 
+    On rare occasions, you may need to use the `getline' command.  The
+ `getline' command is valuable, both because it can do explicit input
+ from any number of files, and because the files used with it do not
+ have to be named on the `awk' command line (*note Getline::).
+ 
+ * Menu:
+ 
+ * Records::                     Controlling how data is split into records.
+ * Fields::                      An introduction to fields.
+ * Nonconstant Fields::          Nonconstant Field Numbers.
+ * Changing Fields::             Changing the Contents of a Field.
+ * Field Separators::            The field separator and how to change it.
+ * Constant Size::               Reading constant width data.
+ * Splitting By Content::        Defining Fields By Content
+ * Multiple Line::               Reading multi-line records.
+ * Getline::                     Reading files under explicit program control
+                                 using the `getline' function.
++* Read Timeout::                Reading input with a timeout.
+ * Command line directories::    What happens if you put a directory on the
+                                 command line.
+ 
+ 
+ File: gawk.info,  Node: Records,  Next: Fields,  Up: Reading Files
+ 
+ 4.1 How Input Is Split into Records
+ ===================================
+ 
+ The `awk' utility divides the input for your `awk' program into records
+ and fields.  `awk' keeps track of the number of records that have been
+ read so far from the current input file.  This value is stored in a
+ built-in variable called `FNR'.  It is reset to zero when a new file is
+ started.  Another built-in variable, `NR', records the total number of
+ input records read so far from all data files.  It starts at zero, but
+ is never automatically reset to zero.
+ 
+    Records are separated by a character called the "record separator".
+ By default, the record separator is the newline character.  This is why
+ records are, by default, single lines.  A different character can be
+ used for the record separator by assigning the character to the
+ built-in variable `RS'.
+ 
+    Like any other variable, the value of `RS' can be changed in the
+ `awk' program with the assignment operator, `=' (*note Assignment
+ Ops::).  The new record-separator character should be enclosed in
+ quotation marks, which indicate a string constant.  Often the right
+ time to do this is at the beginning of execution, before any input is
+ processed, so that the very first record is read with the proper
+ separator.  To do this, use the special `BEGIN' pattern (*note
+ BEGIN/END::).  For example:
+ 
+      awk 'BEGIN { RS = "/" }
+           { print $0 }' BBS-list
+ 
+ changes the value of `RS' to `"/"', before reading any input.  This is
+ a string whose first character is a slash; as a result, records are
+ separated by slashes.  Then the input file is read, and the second rule
+ in the `awk' program (the action with no pattern) prints each record.
+ Because each `print' statement adds a newline at the end of its output,
+ this `awk' program copies the input with each slash changed to a
+ newline.  Here are the results of running the program on `BBS-list':
+ 
+      $ awk 'BEGIN { RS = "/" }
+      >      { print $0 }' BBS-list
+      -| aardvark     555-5553     1200
+      -| 300          B
+      -| alpo-net     555-3412     2400
+      -| 1200
+      -| 300     A
+      -| barfly       555-7685     1200
+      -| 300          A
+      -| bites        555-1675     2400
+      -| 1200
+      -| 300     A
+      -| camelot      555-0542     300               C
+      -| core         555-2912     1200
+      -| 300          C
+      -| fooey        555-1234     2400
+      -| 1200
+      -| 300     B
+      -| foot         555-6699     1200
+      -| 300          B
+      -| macfoo       555-6480     1200
+      -| 300          A
+      -| sdace        555-3430     2400
+      -| 1200
+      -| 300     A
+      -| sabafoo      555-2127     1200
+      -| 300          C
+      -|
+ 
+ Note that the entry for the `camelot' BBS is not split.  In the
+ original data file (*note Sample Data Files::), the line looks like
+ this:
+ 
+      camelot      555-0542     300               C
+ 
+ It has one baud rate only, so there are no slashes in the record,
+ unlike the others which have two or more baud rates.  In fact, this
+ record is treated as part of the record for the `core' BBS; the newline
+ separating them in the output is the original newline in the data file,
+ not the one added by `awk' when it printed the record!
+ 
+    Another way to change the record separator is on the command line,
+ using the variable-assignment feature (*note Other Arguments::):
+ 
+      awk '{ print $0 }' RS="/" BBS-list
+ 
+ This sets `RS' to `/' before processing `BBS-list'.
+ 
+    Using an unusual character such as `/' for the record separator
+ produces correct behavior in the vast majority of cases.
+ 
+    There is one unusual case, that occurs when `gawk' is being fully
+ POSIX-compliant (*note Options::).  Then, the following (extreme)
+ pipeline prints a surprising `1':
+ 
+      $ echo | gawk --posix 'BEGIN { RS = "a" } ; { print NF }'
+      -| 1
+ 
+    There is one field, consisting of a newline.  The value of the
+ built-in variable `NF' is the number of fields in the current record.
+ (In the normal case, `gawk' treats the newline as whitespace, printing
+ `0' as the result. Most other versions of `awk' also act this way.)
+ 
+    Reaching the end of an input file terminates the current input
+ record, even if the last character in the file is not the character in
+ `RS'.  (d.c.)
+ 
+    The empty string `""' (a string without any characters) has a
+ special meaning as the value of `RS'. It means that records are
+ separated by one or more blank lines and nothing else.  *Note Multiple
+ Line::, for more details.
+ 
+    If you change the value of `RS' in the middle of an `awk' run, the
+ new value is used to delimit subsequent records, but the record
+ currently being processed, as well as records already processed, are not
+ affected.
+ 
+    After the end of the record has been determined, `gawk' sets the
+ variable `RT' to the text in the input that matched `RS'.
+ 
+    When using `gawk', the value of `RS' is not limited to a
+ one-character string.  It can be any regular expression (*note
+ Regexp::). (c.e.)  In general, each record ends at the next string that
+ matches the regular expression; the next record starts at the end of
+ the matching string.  This general rule is actually at work in the
+ usual case, where `RS' contains just a newline: a record ends at the
+ beginning of the next matching string (the next newline in the input),
+ and the following record starts just after the end of this string (at
+ the first character of the following line).  The newline, because it
+ matches `RS', is not part of either record.
+ 
+    When `RS' is a single character, `RT' contains the same single
+ character. However, when `RS' is a regular expression, `RT' contains
+ the actual input text that matched the regular expression.
+ 
+    If the input file ended without any text that matches `RS', `gawk'
+ sets `RT' to the null string.
+ 
+    The following example illustrates both of these features.  It sets
+ `RS' equal to a regular expression that matches either a newline or a
+ series of one or more uppercase letters with optional leading and/or
+ trailing whitespace:
+ 
+      $ echo record 1 AAAA record 2 BBBB record 3 |
+      > gawk 'BEGIN { RS = "\n|( *[[:upper:]]+ *)" }
+      >             { print "Record =", $0, "and RT =", RT }'
+      -| Record = record 1 and RT =  AAAA
+      -| Record = record 2 and RT =  BBBB
+      -| Record = record 3 and RT =
+      -|
+ 
+ The final line of output has an extra blank line. This is because the
+ value of `RT' is a newline, and the `print' statement supplies its own
+ terminating newline.  *Note Simple Sed::, for a more useful example of
+ `RS' as a regexp and `RT'.
+ 
+    If you set `RS' to a regular expression that allows optional
+ trailing text, such as `RS = "abc(XYZ)?"' it is possible, due to
+ implementation constraints, that `gawk' may match the leading part of
+ the regular expression, but not the trailing part, particularly if the
+ input text that could match the trailing part is fairly long.  `gawk'
+ attempts to avoid this problem, but currently, there's no guarantee
+ that this will never happen.
+ 
+      NOTE: Remember that in `awk', the `^' and `$' anchor
+      metacharacters match the beginning and end of a _string_, and not
+      the beginning and end of a _line_.  As a result, something like
+      `RS = "^[[:upper:]]"' can only match at the beginning of a file.
+      This is because `gawk' views the input file as one long string
+      that happens to contain newline characters in it.  It is thus best
+      to avoid anchor characters in the value of `RS'.
+ 
+    The use of `RS' as a regular expression and the `RT' variable are
+ `gawk' extensions; they are not available in compatibility mode (*note
+ Options::).  In compatibility mode, only the first character of the
+ value of `RS' is used to determine the end of the record.
+ 
+ Advanced Notes: `RS = "\0"' Is Not Portable
+ -------------------------------------------
+ 
+ There are times when you might want to treat an entire data file as a
+ single record.  The only way to make this happen is to give `RS' a
+ value that you know doesn't occur in the input file.  This is hard to
+ do in a general way, such that a program always works for arbitrary
+ input files.
+ 
+    You might think that for text files, the NUL character, which
+ consists of a character with all bits equal to zero, is a good value to
+ use for `RS' in this case:
+ 
+      BEGIN { RS = "\0" }  # whole file becomes one record?
+ 
+    `gawk' in fact accepts this, and uses the NUL character for the
+ record separator.  However, this usage is _not_ portable to other `awk'
+ implementations.
+ 
+    All other `awk' implementations(1) store strings internally as
+ C-style strings.  C strings use the NUL character as the string
+ terminator.  In effect, this means that `RS = "\0"' is the same as `RS
+ = ""'.  (d.c.)
+ 
+    The best way to treat a whole file as a single record is to simply
+ read the file in, one record at a time, concatenating each record onto
+ the end of the previous ones.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) At least that we know about.
+ 
+ 
+ File: gawk.info,  Node: Fields,  Next: Nonconstant Fields,  Prev: Records,  
Up: Reading Files
+ 
+ 4.2 Examining Fields
+ ====================
+ 
+ When `awk' reads an input record, the record is automatically "parsed"
+ or separated by the `awk' utility into chunks called "fields".  By
+ default, fields are separated by "whitespace", like words in a line.
+ Whitespace in `awk' means any string of one or more spaces, TABs, or
+ newlines;(1) other characters, such as formfeed, vertical tab, etc.,
+ that are considered whitespace by other languages, are _not_ considered
+ whitespace by `awk'.
+ 
+    The purpose of fields is to make it more convenient for you to refer
+ to these pieces of the record.  You don't have to use them--you can
+ operate on the whole record if you want--but fields are what make
+ simple `awk' programs so powerful.
+ 
+    A dollar-sign (`$') is used to refer to a field in an `awk' program,
+ followed by the number of the field you want.  Thus, `$1' refers to the
+ first field, `$2' to the second, and so on.  (Unlike the Unix shells,
+ the field numbers are not limited to single digits.  `$127' is the one
+ hundred twenty-seventh field in the record.)  For example, suppose the
+ following is a line of input:
+ 
+      This seems like a pretty nice example.
+ 
+ Here the first field, or `$1', is `This', the second field, or `$2', is
+ `seems', and so on.  Note that the last field, `$7', is `example.'.
+ Because there is no space between the `e' and the `.', the period is
+ considered part of the seventh field.
+ 
+    `NF' is a built-in variable whose value is the number of fields in
+ the current record.  `awk' automatically updates the value of `NF' each
+ time it reads a record.  No matter how many fields there are, the last
+ field in a record can be represented by `$NF'.  So, `$NF' is the same
+ as `$7', which is `example.'.  If you try to reference a field beyond
+ the last one (such as `$8' when the record has only seven fields), you
+ get the empty string.  (If used in a numeric operation, you get zero.)
+ 
+    The use of `$0', which looks like a reference to the "zero-th"
+ field, is a special case: it represents the whole input record when you
+ are not interested in specific fields.  Here are some more examples:
+ 
+      $ awk '$1 ~ /foo/ { print $0 }' BBS-list
+      -| fooey        555-1234     2400/1200/300     B
+      -| foot         555-6699     1200/300          B
+      -| macfoo       555-6480     1200/300          A
+      -| sabafoo      555-2127     1200/300          C
+ 
+ This example prints each record in the file `BBS-list' whose first
+ field contains the string `foo'.  The operator `~' is called a
+ "matching operator" (*note Regexp Usage::); it tests whether a string
+ (here, the field `$1') matches a given regular expression.
+ 
+    By contrast, the following example looks for `foo' in _the entire
+ record_ and prints the first field and the last field for each matching
+ input record:
+ 
+      $ awk '/foo/ { print $1, $NF }' BBS-list
+      -| fooey B
+      -| foot B
+      -| macfoo A
+      -| sabafoo C
+ 
+    ---------- Footnotes ----------
+ 
+    (1) In POSIX `awk', newlines are not considered whitespace for
+ separating fields.
+ 
+ 
+ File: gawk.info,  Node: Nonconstant Fields,  Next: Changing Fields,  Prev: 
Fields,  Up: Reading Files
+ 
+ 4.3 Nonconstant Field Numbers
+ =============================
+ 
+ The number of a field does not need to be a constant.  Any expression in
+ the `awk' language can be used after a `$' to refer to a field.  The
+ value of the expression specifies the field number.  If the value is a
+ string, rather than a number, it is converted to a number.  Consider
+ this example:
+ 
+      awk '{ print $NR }'
+ 
+ Recall that `NR' is the number of records read so far: one in the first
+ record, two in the second, etc.  So this example prints the first field
+ of the first record, the second field of the second record, and so on.
+ For the twentieth record, field number 20 is printed; most likely, the
+ record has fewer than 20 fields, so this prints a blank line.  Here is
+ another example of using expressions as field numbers:
+ 
+      awk '{ print $(2*2) }' BBS-list
+ 
+    `awk' evaluates the expression `(2*2)' and uses its value as the
+ number of the field to print.  The `*' sign represents multiplication,
+ so the expression `2*2' evaluates to four.  The parentheses are used so
+ that the multiplication is done before the `$' operation; they are
+ necessary whenever there is a binary operator in the field-number
+ expression.  This example, then, prints the hours of operation (the
+ fourth field) for every line of the file `BBS-list'.  (All of the `awk'
+ operators are listed, in order of decreasing precedence, in *note
+ Precedence::.)
+ 
+    If the field number you compute is zero, you get the entire record.
+ Thus, `$(2-2)' has the same value as `$0'.  Negative field numbers are
+ not allowed; trying to reference one usually terminates the program.
+ (The POSIX standard does not define what happens when you reference a
+ negative field number.  `gawk' notices this and terminates your
+ program.  Other `awk' implementations may behave differently.)
+ 
+    As mentioned in *note Fields::, `awk' stores the current record's
+ number of fields in the built-in variable `NF' (also *note Built-in
+ Variables::).  The expression `$NF' is not a special feature--it is the
+ direct consequence of evaluating `NF' and using its value as a field
+ number.
+ 
+ 
+ File: gawk.info,  Node: Changing Fields,  Next: Field Separators,  Prev: 
Nonconstant Fields,  Up: Reading Files
+ 
+ 4.4 Changing the Contents of a Field
+ ====================================
+ 
+ The contents of a field, as seen by `awk', can be changed within an
+ `awk' program; this changes what `awk' perceives as the current input
+ record.  (The actual input is untouched; `awk' _never_ modifies the
+ input file.)  Consider the following example and its output:
+ 
+      $ awk '{ nboxes = $3 ; $3 = $3 - 10
+      >        print nboxes, $3 }' inventory-shipped
+      -| 25 15
+      -| 32 22
+      -| 24 14
+      ...
+ 
+ The program first saves the original value of field three in the
+ variable `nboxes'.  The `-' sign represents subtraction, so this
+ program reassigns field three, `$3', as the original value of field
+ three minus ten: `$3 - 10'.  (*Note Arithmetic Ops::.)  Then it prints
+ the original and new values for field three.  (Someone in the warehouse
+ made a consistent mistake while inventorying the red boxes.)
+ 
+    For this to work, the text in field `$3' must make sense as a
+ number; the string of characters must be converted to a number for the
+ computer to do arithmetic on it.  The number resulting from the
+ subtraction is converted back to a string of characters that then
+ becomes field three.  *Note Conversion::.
+ 
+    When the value of a field is changed (as perceived by `awk'), the
+ text of the input record is recalculated to contain the new field where
+ the old one was.  In other words, `$0' changes to reflect the altered
+ field.  Thus, this program prints a copy of the input file, with 10
+ subtracted from the second field of each line:
+ 
+      $ awk '{ $2 = $2 - 10; print $0 }' inventory-shipped
+      -| Jan 3 25 15 115
+      -| Feb 5 32 24 226
+      -| Mar 5 24 34 228
+      ...
+ 
+    It is also possible to also assign contents to fields that are out
+ of range.  For example:
+ 
+      $ awk '{ $6 = ($5 + $4 + $3 + $2)
+      >        print $6 }' inventory-shipped
+      -| 168
+      -| 297
+      -| 301
+      ...
+ 
+ We've just created `$6', whose value is the sum of fields `$2', `$3',
+ `$4', and `$5'.  The `+' sign represents addition.  For the file
+ `inventory-shipped', `$6' represents the total number of parcels
+ shipped for a particular month.
+ 
+    Creating a new field changes `awk''s internal copy of the current
+ input record, which is the value of `$0'.  Thus, if you do `print $0'
+ after adding a field, the record printed includes the new field, with
+ the appropriate number of field separators between it and the previously
+ existing fields.
+ 
+    This recomputation affects and is affected by `NF' (the number of
+ fields; *note Fields::).  For example, the value of `NF' is set to the
+ number of the highest field you create.  The exact format of `$0' is
+ also affected by a feature that has not been discussed yet: the "output
+ field separator", `OFS', used to separate the fields (*note Output
+ Separators::).
+ 
+    Note, however, that merely _referencing_ an out-of-range field does
+ _not_ change the value of either `$0' or `NF'.  Referencing an
+ out-of-range field only produces an empty string.  For example:
+ 
+      if ($(NF+1) != "")
+          print "can't happen"
+      else
+          print "everything is normal"
+ 
+ should print `everything is normal', because `NF+1' is certain to be
+ out of range.  (*Note If Statement::, for more information about
+ `awk''s `if-else' statements.  *Note Typing and Comparison::, for more
+ information about the `!=' operator.)
+ 
+    It is important to note that making an assignment to an existing
+ field changes the value of `$0' but does not change the value of `NF',
+ even when you assign the empty string to a field.  For example:
+ 
+      $ echo a b c d | awk '{ OFS = ":"; $2 = ""
+      >                       print $0; print NF }'
+      -| a::c:d
+      -| 4
+ 
+ The field is still there; it just has an empty value, denoted by the
+ two colons between `a' and `c'.  This example shows what happens if you
+ create a new field:
+ 
+      $ echo a b c d | awk '{ OFS = ":"; $2 = ""; $6 = "new"
+      >                       print $0; print NF }'
+      -| a::c:d::new
+      -| 6
+ 
+ The intervening field, `$5', is created with an empty value (indicated
+ by the second pair of adjacent colons), and `NF' is updated with the
+ value six.
+ 
+    Decrementing `NF' throws away the values of the fields after the new
+ value of `NF' and recomputes `$0'.  (d.c.)  Here is an example:
+ 
+      $ echo a b c d e f | awk '{ print "NF =", NF;
+      >                            NF = 3; print $0 }'
+      -| NF = 6
+      -| a b c
+ 
+      CAUTION: Some versions of `awk' don't rebuild `$0' when `NF' is
+      decremented. Caveat emptor.
+ 
+    Finally, there are times when it is convenient to force `awk' to
+ rebuild the entire record, using the current value of the fields and
+ `OFS'.  To do this, use the seemingly innocuous assignment:
+ 
+      $1 = $1   # force record to be reconstituted
+      print $0  # or whatever else with $0
+ 
+ This forces `awk' to rebuild the record.  It does help to add a
+ comment, as we've shown here.
+ 
+    There is a flip side to the relationship between `$0' and the
+ fields.  Any assignment to `$0' causes the record to be reparsed into
+ fields using the _current_ value of `FS'.  This also applies to any
+ built-in function that updates `$0', such as `sub()' and `gsub()'
+ (*note String Functions::).
+ 
+ Advanced Notes: Understanding `$0'
+ ----------------------------------
+ 
+ It is important to remember that `$0' is the _full_ record, exactly as
+ it was read from the input.  This includes any leading or trailing
+ whitespace, and the exact whitespace (or other characters) that
+ separate the fields.
+ 
+    It is a not-uncommon error to try to change the field separators in
+ a record simply by setting `FS' and `OFS', and then expecting a plain
+ `print' or `print $0' to print the modified record.
+ 
+    But this does not work, since nothing was done to change the record
+ itself.  Instead, you must force the record to be rebuilt, typically
+ with a statement such as `$1 = $1', as described earlier.
+ 
+ 
+ File: gawk.info,  Node: Field Separators,  Next: Constant Size,  Prev: 
Changing Fields,  Up: Reading Files
+ 
+ 4.5 Specifying How Fields Are Separated
+ =======================================
+ 
+ * Menu:
+ 
+ * Default Field Splitting::      How fields are normally separated.
+ * Regexp Field Splitting::       Using regexps as the field separator.
+ * Single Character Fields::      Making each character a separate field.
+ * Command Line Field Separator:: Setting `FS' from the command-line.
+ * Field Splitting Summary::      Some final points and a summary table.
+ 
+    The "field separator", which is either a single character or a
+ regular expression, controls the way `awk' splits an input record into
+ fields.  `awk' scans the input record for character sequences that
+ match the separator; the fields themselves are the text between the
+ matches.
+ 
+    In the examples that follow, we use the bullet symbol (*) to
+ represent spaces in the output.  If the field separator is `oo', then
+ the following line:
+ 
+      moo goo gai pan
+ 
+ is split into three fields: `m', `*g', and `*gai*pan'.  Note the
+ leading spaces in the values of the second and third fields.
+ 
+    The field separator is represented by the built-in variable `FS'.
+ Shell programmers take note:  `awk' does _not_ use the name `IFS' that
+ is used by the POSIX-compliant shells (such as the Unix Bourne shell,
+ `sh', or Bash).
+ 
+    The value of `FS' can be changed in the `awk' program with the
+ assignment operator, `=' (*note Assignment Ops::).  Often the right
+ time to do this is at the beginning of execution before any input has
+ been processed, so that the very first record is read with the proper
+ separator.  To do this, use the special `BEGIN' pattern (*note
+ BEGIN/END::).  For example, here we set the value of `FS' to the string
+ `","':
+ 
+      awk 'BEGIN { FS = "," } ; { print $2 }'
+ 
+ Given the input line:
+ 
+      John Q. Smith, 29 Oak St., Walamazoo, MI 42139
+ 
+ this `awk' program extracts and prints the string `*29*Oak*St.'.
+ 
+    Sometimes the input data contains separator characters that don't
+ separate fields the way you thought they would.  For instance, the
+ person's name in the example we just used might have a title or suffix
+ attached, such as:
+ 
+      John Q. Smith, LXIX, 29 Oak St., Walamazoo, MI 42139
+ 
+ The same program would extract `*LXIX', instead of `*29*Oak*St.'.  If
+ you were expecting the program to print the address, you would be
+ surprised.  The moral is to choose your data layout and separator
+ characters carefully to prevent such problems.  (If the data is not in
+ a form that is easy to process, perhaps you can massage it first with a
+ separate `awk' program.)
+ 
+ 
+ File: gawk.info,  Node: Default Field Splitting,  Next: Regexp Field 
Splitting,  Up: Field Separators
+ 
+ 4.5.1 Whitespace Normally Separates Fields
+ ------------------------------------------
+ 
+ Fields are normally separated by whitespace sequences (spaces, TABs,
+ and newlines), not by single spaces.  Two spaces in a row do not
+ delimit an empty field.  The default value of the field separator `FS'
+ is a string containing a single space, `" "'.  If `awk' interpreted
+ this value in the usual way, each space character would separate
+ fields, so two spaces in a row would make an empty field between them.
+ The reason this does not happen is that a single space as the value of
+ `FS' is a special case--it is taken to specify the default manner of
+ delimiting fields.
+ 
+    If `FS' is any other single character, such as `","', then each
+ occurrence of that character separates two fields.  Two consecutive
+ occurrences delimit an empty field.  If the character occurs at the
+ beginning or the end of the line, that too delimits an empty field.  The
+ space character is the only single character that does not follow these
+ rules.
+ 
+ 
+ File: gawk.info,  Node: Regexp Field Splitting,  Next: Single Character 
Fields,  Prev: Default Field Splitting,  Up: Field Separators
+ 
+ 4.5.2 Using Regular Expressions to Separate Fields
+ --------------------------------------------------
+ 
+ The previous node discussed the use of single characters or simple
+ strings as the value of `FS'.  More generally, the value of `FS' may be
+ a string containing any regular expression.  In this case, each match
+ in the record for the regular expression separates fields.  For
+ example, the assignment:
+ 
+      FS = ", \t"
+ 
+ makes every area of an input line that consists of a comma followed by a
+ space and a TAB into a field separator.  (`\t' is an "escape sequence"
+ that stands for a TAB; *note Escape Sequences::, for the complete list
+ of similar escape sequences.)
+ 
+    For a less trivial example of a regular expression, try using single
+ spaces to separate fields the way single commas are used.  `FS' can be
+ set to `"[ ]"' (left bracket, space, right bracket).  This regular
+ expression matches a single space and nothing else (*note Regexp::).
+ 
+    There is an important difference between the two cases of `FS = " "'
+ (a single space) and `FS = "[ \t\n]+"' (a regular expression matching
+ one or more spaces, TABs, or newlines).  For both values of `FS',
+ fields are separated by "runs" (multiple adjacent occurrences) of
+ spaces, TABs, and/or newlines.  However, when the value of `FS' is
+ `" "', `awk' first strips leading and trailing whitespace from the
+ record and then decides where the fields are.  For example, the
+ following pipeline prints `b':
+ 
+      $ echo ' a b c d ' | awk '{ print $2 }'
+      -| b
+ 
+ However, this pipeline prints `a' (note the extra spaces around each
+ letter):
+ 
+      $ echo ' a  b  c  d ' | awk 'BEGIN { FS = "[ \t\n]+" }
+      >                                  { print $2 }'
+      -| a
+ 
+ In this case, the first field is "null" or empty.
+ 
+    The stripping of leading and trailing whitespace also comes into
+ play whenever `$0' is recomputed.  For instance, study this pipeline:
+ 
+      $ echo '   a b c d' | awk '{ print; $2 = $2; print }'
+      -|    a b c d
+      -| a b c d
+ 
+ The first `print' statement prints the record as it was read, with
+ leading whitespace intact.  The assignment to `$2' rebuilds `$0' by
+ concatenating `$1' through `$NF' together, separated by the value of
+ `OFS'.  Because the leading whitespace was ignored when finding `$1',
+ it is not part of the new `$0'.  Finally, the last `print' statement
+ prints the new `$0'.
+ 
+    There is an additional subtlety to be aware of when using regular
+ expressions for field splitting.  It is not well-specified in the POSIX
+ standard, or anywhere else, what `^' means when splitting fields.  Does
+ the `^'  match only at the beginning of the entire record? Or is each
+ field separator a new string?  It turns out that different `awk'
+ versions answer this question differently, and you should not rely on
+ any specific behavior in your programs.  (d.c.)
+ 
+    As a point of information, Brian Kernighan's `awk' allows `^' to
+ match only at the beginning of the record. `gawk' also works this way.
+ For example:
+ 
+      $ echo 'xxAA  xxBxx  C' |
+      > gawk -F '(^x+)|( +)' '{ for (i = 1; i <= NF; i++)
+      >                                   printf "-->%s<--\n", $i }'
+      -| --><--
+      -| -->AA<--
+      -| -->xxBxx<--
+      -| -->C<--
+ 
+ 
+ File: gawk.info,  Node: Single Character Fields,  Next: Command Line Field 
Separator,  Prev: Regexp Field Splitting,  Up: Field Separators
+ 
+ 4.5.3 Making Each Character a Separate Field
+ --------------------------------------------
+ 
+ There are times when you may want to examine each character of a record
+ separately.  This can be done in `gawk' by simply assigning the null
+ string (`""') to `FS'. (c.e.)  In this case, each individual character
+ in the record becomes a separate field.  For example:
+ 
+      $ echo a b | gawk 'BEGIN { FS = "" }
+      >                  {
+      >                      for (i = 1; i <= NF; i = i + 1)
+      >                          print "Field", i, "is", $i
+      >                  }'
+      -| Field 1 is a
+      -| Field 2 is
+      -| Field 3 is b
+ 
+    Traditionally, the behavior of `FS' equal to `""' was not defined.
+ In this case, most versions of Unix `awk' simply treat the entire record
+ as only having one field.  (d.c.)  In compatibility mode (*note
+ Options::), if `FS' is the null string, then `gawk' also behaves this
+ way.
+ 
+ 
+ File: gawk.info,  Node: Command Line Field Separator,  Next: Field Splitting 
Summary,  Prev: Single Character Fields,  Up: Field Separators
+ 
+ 4.5.4 Setting `FS' from the Command Line
+ ----------------------------------------
+ 
+ `FS' can be set on the command line.  Use the `-F' option to do so.
+ For example:
+ 
+      awk -F, 'PROGRAM' INPUT-FILES
+ 
+ sets `FS' to the `,' character.  Notice that the option uses an
+ uppercase `F' instead of a lowercase `f'. The latter option (`-f')
+ specifies a file containing an `awk' program.  Case is significant in
+ command-line options: the `-F' and `-f' options have nothing to do with
+ each other.  You can use both options at the same time to set the `FS'
+ variable _and_ get an `awk' program from a file.
+ 
+    The value used for the argument to `-F' is processed in exactly the
+ same way as assignments to the built-in variable `FS'.  Any special
+ characters in the field separator must be escaped appropriately.  For
+ example, to use a `\' as the field separator on the command line, you
+ would have to type:
+ 
+      # same as FS = "\\"
+      awk -F\\\\ '...' files ...
+ 
+ Because `\' is used for quoting in the shell, `awk' sees `-F\\'.  Then
+ `awk' processes the `\\' for escape characters (*note Escape
+ Sequences::), finally yielding a single `\' to use for the field
+ separator.
+ 
+    As a special case, in compatibility mode (*note Options::), if the
+ argument to `-F' is `t', then `FS' is set to the TAB character.  If you
+ type `-F\t' at the shell, without any quotes, the `\' gets deleted, so
+ `awk' figures that you really want your fields to be separated with
+ TABs and not `t's.  Use `-v FS="t"' or `-F"[t]"' on the command line if
+ you really do want to separate your fields with `t's.
+ 
+    As an example, let's use an `awk' program file called `baud.awk'
+ that contains the pattern `/300/' and the action `print $1':
+ 
+      /300/   { print $1 }
+ 
+    Let's also set `FS' to be the `-' character and run the program on
+ the file `BBS-list'.  The following command prints a list of the names
+ of the bulletin boards that operate at 300 baud and the first three
+ digits of their phone numbers:
+ 
+      $ awk -F- -f baud.awk BBS-list
+      -| aardvark     555
+      -| alpo
+      -| barfly       555
+      -| bites        555
+      -| camelot      555
+      -| core         555
+      -| fooey        555
+      -| foot         555
+      -| macfoo       555
+      -| sdace        555
+      -| sabafoo      555
+ 
+ Note the second line of output.  The second line in the original file
+ looked like this:
+ 
+      alpo-net     555-3412     2400/1200/300     A
+ 
+    The `-' as part of the system's name was used as the field
+ separator, instead of the `-' in the phone number that was originally
+ intended.  This demonstrates why you have to be careful in choosing
+ your field and record separators.
+ 
+    Perhaps the most common use of a single character as the field
+ separator occurs when processing the Unix system password file.  On
+ many Unix systems, each user has a separate entry in the system password
+ file, one line per user.  The information in these lines is separated
+ by colons.  The first field is the user's login name and the second is
+ the user's (encrypted or shadow) password.  A password file entry might
+ look like this:
+ 
+      arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/bash
+ 
+    The following program searches the system password file and prints
+ the entries for users who have no password:
+ 
+      awk -F: '$2 == ""' /etc/passwd
+ 
+ 
+ File: gawk.info,  Node: Field Splitting Summary,  Prev: Command Line Field 
Separator,  Up: Field Separators
+ 
+ 4.5.5 Field-Splitting Summary
+ -----------------------------
+ 
+ It is important to remember that when you assign a string constant as
+ the value of `FS', it undergoes normal `awk' string processing.  For
+ example, with Unix `awk' and `gawk', the assignment `FS = "\.."'
+ assigns the character string `".."' to `FS' (the backslash is
+ stripped).  This creates a regexp meaning "fields are separated by
+ occurrences of any two characters."  If instead you want fields to be
+ separated by a literal period followed by any single character, use `FS
+ = "\\.."'.
+ 
+    The following table summarizes how fields are split, based on the
+ value of `FS' (`==' means "is equal to"):
+ 
+ `FS == " "'
+      Fields are separated by runs of whitespace.  Leading and trailing
+      whitespace are ignored.  This is the default.
+ 
+ `FS == ANY OTHER SINGLE CHARACTER'
+      Fields are separated by each occurrence of the character.  Multiple
+      successive occurrences delimit empty fields, as do leading and
+      trailing occurrences.  The character can even be a regexp
+      metacharacter; it does not need to be escaped.
+ 
+ `FS == REGEXP'
+      Fields are separated by occurrences of characters that match
+      REGEXP.  Leading and trailing matches of REGEXP delimit empty
+      fields.
+ 
+ `FS == ""'
+      Each individual character in the record becomes a separate field.
+      (This is a `gawk' extension; it is not specified by the POSIX
+      standard.)
+ 
+ Advanced Notes: Changing `FS' Does Not Affect the Fields
+ --------------------------------------------------------
+ 
+ According to the POSIX standard, `awk' is supposed to behave as if each
+ record is split into fields at the time it is read.  In particular,
+ this means that if you change the value of `FS' after a record is read,
+ the value of the fields (i.e., how they were split) should reflect the
+ old value of `FS', not the new one.
+ 
+    However, many older implementations of `awk' do not work this way.
+ Instead, they defer splitting the fields until a field is actually
+ referenced.  The fields are split using the _current_ value of `FS'!
+ (d.c.)  This behavior can be difficult to diagnose. The following
+ example illustrates the difference between the two methods.  (The
+ `sed'(1) command prints just the first line of `/etc/passwd'.)
+ 
+      sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }'
+ 
+ which usually prints:
+ 
+      root
+ 
+ on an incorrect implementation of `awk', while `gawk' prints something
+ like:
+ 
+      root:nSijPlPhZZwgE:0:0:Root:/:
+ 
+ Advanced Notes: `FS' and `IGNORECASE'
+ -------------------------------------
+ 
+ The `IGNORECASE' variable (*note User-modified::) affects field
+ splitting _only_ when the value of `FS' is a regexp.  It has no effect
+ when `FS' is a single character, even if that character is a letter.
+ Thus, in the following code:
+ 
+      FS = "c"
+      IGNORECASE = 1
+      $0 = "aCa"
+      print $1
+ 
+ The output is `aCa'.  If you really want to split fields on an
+ alphabetic character while ignoring case, use a regexp that will do it
+ for you.  E.g., `FS = "[c]"'.  In this case, `IGNORECASE' will take
+ effect.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The `sed' utility is a "stream editor."  Its behavior is also
+ defined by the POSIX standard.
+ 
+ 
+ File: gawk.info,  Node: Constant Size,  Next: Splitting By Content,  Prev: 
Field Separators,  Up: Reading Files
+ 
+ 4.6 Reading Fixed-Width Data
+ ============================
+ 
+ (This minor node discusses an advanced feature of `awk'.  If you are a
+ novice `awk' user, you might want to skip it on the first reading.)
+ 
+ `gawk' provides a facility for dealing with fixed-width fields with no
+ distinctive field separator.  For example, data of this nature arises
+ in the input for old Fortran programs where numbers are run together,
+ or in the output of programs that did not anticipate the use of their
+ output as input for other programs.
+ 
+    An example of the latter is a table where all the columns are lined
+ up by the use of a variable number of spaces and _empty fields are just
+ spaces_.  Clearly, `awk''s normal field splitting based on `FS' does
+ not work well in this case.  Although a portable `awk' program can use
+ a series of `substr()' calls on `$0' (*note String Functions::), this
+ is awkward and inefficient for a large number of fields.
+ 
+    The splitting of an input record into fixed-width fields is
+ specified by assigning a string containing space-separated numbers to
+ the built-in variable `FIELDWIDTHS'.  Each number specifies the width
+ of the field, _including_ columns between fields.  If you want to
+ ignore the columns between fields, you can specify the width as a
+ separate field that is subsequently ignored.  It is a fatal error to
+ supply a field width that is not a positive number.  The following data
+ is the output of the Unix `w' utility.  It is useful to illustrate the
+ use of `FIELDWIDTHS':
+ 
+       10:06pm  up 21 days, 14:04,  23 users
+      User     tty       login  idle   JCPU   PCPU  what
+      hzuo     ttyV0     8:58pm            9      5  vi p24.tex
+      hzang    ttyV3     6:37pm    50                -csh
+      eklye    ttyV5     9:53pm            7      1  em thes.tex
+      dportein ttyV6     8:17pm  1:47                -csh
+      gierd    ttyD3    10:00pm     1                elm
+      dave     ttyD4     9:47pm            4      4  w
+      brent    ttyp0    26Jun91  4:46  26:46   4:41  bash
+      dave     ttyq4    26Jun9115days     46     46  wnewmail
+ 
+    The following program takes the above input, converts the idle time
+ to number of seconds, and prints out the first two fields and the
+ calculated idle time:
+ 
+      NOTE: This program uses a number of `awk' features that haven't
+      been introduced yet.
+ 
+      BEGIN  { FIELDWIDTHS = "9 6 10 6 7 7 35" }
+      NR > 2 {
+          idle = $4
+          sub(/^  */, "", idle)   # strip leading spaces
+          if (idle == "")
+              idle = 0
+          if (idle ~ /:/) {
+              split(idle, t, ":")
+              idle = t[1] * 60 + t[2]
+          }
+          if (idle ~ /days/)
+              idle *= 24 * 60 * 60
+ 
+          print $1, $2, idle
+      }
+ 
+    Running the program on the data produces the following results:
+ 
+      hzuo      ttyV0  0
+      hzang     ttyV3  50
+      eklye     ttyV5  0
+      dportein  ttyV6  107
+      gierd     ttyD3  1
+      dave      ttyD4  0
+      brent     ttyp0  286
+      dave      ttyq4  1296000
+ 
+    Another (possibly more practical) example of fixed-width input data
+ is the input from a deck of balloting cards.  In some parts of the
+ United States, voters mark their choices by punching holes in computer
+ cards.  These cards are then processed to count the votes for any
+ particular candidate or on any particular issue.  Because a voter may
+ choose not to vote on some issue, any column on the card may be empty.
+ An `awk' program for processing such data could use the `FIELDWIDTHS'
+ feature to simplify reading the data.  (Of course, getting `gawk' to
+ run on a system with card readers is another story!)
+ 
+    Assigning a value to `FS' causes `gawk' to use `FS' for field
+ splitting again.  Use `FS = FS' to make this happen, without having to
+ know the current value of `FS'.  In order to tell which kind of field
+ splitting is in effect, use `PROCINFO["FS"]' (*note Auto-set::).  The
+ value is `"FS"' if regular field splitting is being used, or it is
+ `"FIELDWIDTHS"' if fixed-width field splitting is being used:
+ 
+      if (PROCINFO["FS"] == "FS")
+          REGULAR FIELD SPLITTING ...
+      else if  (PROCINFO["FS"] == "FIELDWIDTHS")
+          FIXED-WIDTH FIELD SPLITTING ...
+      else
+          CONTENT-BASED FIELD SPLITTING ... (see next minor node)
+ 
+    This information is useful when writing a function that needs to
+ temporarily change `FS' or `FIELDWIDTHS', read some records, and then
+ restore the original settings (*note Passwd Functions::, for an example
+ of such a function).
+ 
+ 
+ File: gawk.info,  Node: Splitting By Content,  Next: Multiple Line,  Prev: 
Constant Size,  Up: Reading Files
+ 
+ 4.7 Defining Fields By Content
+ ==============================
+ 
+ (This minor node discusses an advanced feature of `awk'.  If you are a
+ novice `awk' user, you might want to skip it on the first reading.)
+ 
+ Normally, when using `FS', `gawk' defines the fields as the parts of
+ the record that occur in between each field separator. In other words,
+ `FS' defines what a field _is not_, instead of what a field _is_.
+ However, there are times when you really want to define the fields by
+ what they are, and not by what they are not.
+ 
+    The most notorious such case is so-called "comma separated value"
+ (CSV) data. Many spreadsheet programs, for example, can export their
+ data into text files, where each record is terminated with a newline,
+ and fields are separated by commas. If only commas separated the data,
+ there wouldn't be an issue. The problem comes when one of the fields
+ contains an _embedded_ comma. While there is no formal standard
+ specification for CSV data(1), in such cases, most programs embed the
+ field in double quotes. So we might have data like this:
+ 
+      Robbins,Arnold,"1234 A Pretty Street, NE",MyTown,MyState,12345-6789,USA
+ 
+    The `FPAT' variable offers a solution for cases like this.  The
+ value of `FPAT' should be a string that provides a regular expression.
+ This regular expression describes the contents of each field.
+ 
+    In the case of CSV data as presented above, each field is either
+ "anything that is not a comma," or "a double quote, anything that is
+ not a double quote, and a closing double quote."  If written as a
+ regular expression constant (*note Regexp::), we would have
+ `/([^,]+)|("[^"]+")/'.  Writing this as a string requires us to escape
+ the double quotes, leading to:
+ 
+      FPAT = "([^,]+)|(\"[^\"]+\")"
+ 
+    Putting this to use, here is a simple program to parse the data:
+ 
+      BEGIN {
+          FPAT = "([^,]+)|(\"[^\"]+\")"
+      }
+ 
+      {
+          print "NF = ", NF
+          for (i = 1; i <= NF; i++) {
+              printf("$%d = <%s>\n", i, $i)
+          }
+      }
+ 
+    When run, we get the following:
+ 
+      $ gawk -f simple-csv.awk addresses.csv
+      NF =  7
+      $1 = <Robbins>
+      $2 = <Arnold>
+      $3 = <"1234 A Pretty Street, NE">
+      $4 = <MyTown>
+      $5 = <MyState>
+      $6 = <12345-6789>
+      $7 = <USA>
+ 
+    Note the embedded comma in the value of `$3'.
+ 
+    A straightforward improvement when processing CSV data of this sort
+ would be to remove the quotes when they occur, with something like this:
+ 
+      if (substr($i, 1, 1) == "\"") {
+          len = length($i)
+          $i = substr($i, 2, len - 2)    # Get text within the two quotes
+      }
+ 
+    As with `FS', the `IGNORECASE' variable (*note User-modified::)
+ affects field splitting with `FPAT'.
+ 
+    Similar to `FIELDWIDTHS', the value of `PROCINFO["FS"]' will be
+ `"FPAT"' if content-based field splitting is being used.
+ 
+      NOTE: Some programs export CSV data that contains embedded
+      newlines between the double quotes.  `gawk' provides no way to
+      deal with this.  Since there is no formal specification for CSV
+      data, there isn't much more to be done; the `FPAT' mechanism
+      provides an elegant solution for the majority of cases, and the
+      `gawk' maintainer is satisfied with that.
+ 
+    As written, the regexp used for `FPAT' requires that each field have
+ a least one character.  A straightforward modification (changing
+ changed the first `+' to `*') allows fields to be empty:
+ 
+      FPAT = "([^,]*)|(\"[^\"]+\")"
+ 
+    Finally, the `patsplit()' function makes the same functionality
+ available for splitting regular strings (*note String Functions::).
+ 
+    ---------- Footnotes ----------
+ 
+    (1) At least, we don't know of one.
+ 
+ 
+ File: gawk.info,  Node: Multiple Line,  Next: Getline,  Prev: Splitting By 
Content,  Up: Reading Files
+ 
+ 4.8 Multiple-Line Records
+ =========================
+ 
+ In some databases, a single line cannot conveniently hold all the
+ information in one entry.  In such cases, you can use multiline
+ records.  The first step in doing this is to choose your data format.
+ 
+    One technique is to use an unusual character or string to separate
+ records.  For example, you could use the formfeed character (written
+ `\f' in `awk', as in C) to separate them, making each record a page of
+ the file.  To do this, just set the variable `RS' to `"\f"' (a string
+ containing the formfeed character).  Any other character could equally
+ well be used, as long as it won't be part of the data in a record.
+ 
+    Another technique is to have blank lines separate records.  By a
+ special dispensation, an empty string as the value of `RS' indicates
+ that records are separated by one or more blank lines.  When `RS' is set
+ to the empty string, each record always ends at the first blank line
+ encountered.  The next record doesn't start until the first nonblank
+ line that follows.  No matter how many blank lines appear in a row, they
+ all act as one record separator.  (Blank lines must be completely
+ empty; lines that contain only whitespace do not count.)
+ 
+    You can achieve the same effect as `RS = ""' by assigning the string
+ `"\n\n+"' to `RS'. This regexp matches the newline at the end of the
+ record and one or more blank lines after the record.  In addition, a
+ regular expression always matches the longest possible sequence when
+ there is a choice (*note Leftmost Longest::).  So the next record
+ doesn't start until the first nonblank line that follows--no matter how
+ many blank lines appear in a row, they are considered one record
+ separator.
+ 
+    There is an important difference between `RS = ""' and `RS =
+ "\n\n+"'. In the first case, leading newlines in the input data file
+ are ignored, and if a file ends without extra blank lines after the
+ last record, the final newline is removed from the record.  In the
+ second case, this special processing is not done.  (d.c.)
+ 
+    Now that the input is separated into records, the second step is to
+ separate the fields in the record.  One way to do this is to divide each
+ of the lines into fields in the normal manner.  This happens by default
+ as the result of a special feature.  When `RS' is set to the empty
+ string, _and_ `FS' is set to a single character, the newline character
+ _always_ acts as a field separator.  This is in addition to whatever
+ field separations result from `FS'.(1)
+ 
+    The original motivation for this special exception was probably to
+ provide useful behavior in the default case (i.e., `FS' is equal to
+ `" "').  This feature can be a problem if you really don't want the
+ newline character to separate fields, because there is no way to
+ prevent it.  However, you can work around this by using the `split()'
+ function to break up the record manually (*note String Functions::).
+ If you have a single character field separator, you can work around the
+ special feature in a different way, by making `FS' into a regexp for
+ that single character.  For example, if the field separator is a
+ percent character, instead of `FS = "%"', use `FS = "[%]"'.
+ 
+    Another way to separate fields is to put each field on a separate
+ line: to do this, just set the variable `FS' to the string `"\n"'.
+ (This single character separator matches a single newline.)  A
+ practical example of a data file organized this way might be a mailing
+ list, where each entry is separated by blank lines.  Consider a mailing
+ list in a file named `addresses', which looks like this:
+ 
+      Jane Doe
+      123 Main Street
+      Anywhere, SE 12345-6789
+ 
+      John Smith
+      456 Tree-lined Avenue
+      Smallville, MW 98765-4321
+      ...
+ 
+ A simple program to process this file is as follows:
+ 
+      # addrs.awk --- simple mailing list program
+ 
+      # Records are separated by blank lines.
+      # Each line is one field.
+      BEGIN { RS = "" ; FS = "\n" }
+ 
+      {
+            print "Name is:", $1
+            print "Address is:", $2
+            print "City and State are:", $3
+            print ""
+      }
+ 
+    Running the program produces the following output:
+ 
+      $ awk -f addrs.awk addresses
+      -| Name is: Jane Doe
+      -| Address is: 123 Main Street
+      -| City and State are: Anywhere, SE 12345-6789
+      -|
+      -| Name is: John Smith
+      -| Address is: 456 Tree-lined Avenue
+      -| City and State are: Smallville, MW 98765-4321
+      -|
+      ...
+ 
+    *Note Labels Program::, for a more realistic program that deals with
+ address lists.  The following table summarizes how records are split,
+ based on the value of `RS'.  (`==' means "is equal to.")
+ 
+ `RS == "\n"'
+      Records are separated by the newline character (`\n').  In effect,
+      every line in the data file is a separate record, including blank
+      lines.  This is the default.
+ 
+ `RS == ANY SINGLE CHARACTER'
+      Records are separated by each occurrence of the character.
+      Multiple successive occurrences delimit empty records.
+ 
+ `RS == ""'
+      Records are separated by runs of blank lines.  When `FS' is a
+      single character, then the newline character always serves as a
+      field separator, in addition to whatever value `FS' may have.
+      Leading and trailing newlines in a file are ignored.
+ 
+ `RS == REGEXP'
+      Records are separated by occurrences of characters that match
+      REGEXP.  Leading and trailing matches of REGEXP delimit empty
+      records.  (This is a `gawk' extension; it is not specified by the
+      POSIX standard.)
+ 
+    In all cases, `gawk' sets `RT' to the input text that matched the
+ value specified by `RS'.  But if the input file ended without any text
+ that matches `RS', then `gawk' sets `RT' to the null string.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) When `FS' is the null string (`""') or a regexp, this special
+ feature of `RS' does not apply.  It does apply to the default field
+ separator of a single space: `FS = " "'.
+ 
+ 
 -File: gawk.info,  Node: Getline,  Next: Command line directories,  Prev: 
Multiple Line,  Up: Reading Files
++File: gawk.info,  Node: Getline,  Next: Read Timeout,  Prev: Multiple Line,  
Up: Reading Files
+ 
+ 4.9 Explicit Input with `getline'
+ =================================
+ 
+ So far we have been getting our input data from `awk''s main input
+ stream--either the standard input (usually your terminal, sometimes the
+ output from another program) or from the files specified on the command
+ line.  The `awk' language has a special built-in command called
+ `getline' that can be used to read input under your explicit control.
+ 
+    The `getline' command is used in several different ways and should
+ _not_ be used by beginners.  The examples that follow the explanation
+ of the `getline' command include material that has not been covered
+ yet.  Therefore, come back and study the `getline' command _after_ you
+ have reviewed the rest of this Info file and have a good knowledge of
+ how `awk' works.
+ 
+    The `getline' command returns one if it finds a record and zero if
+ it encounters the end of the file.  If there is some error in getting a
+ record, such as a file that cannot be opened, then `getline' returns
+ -1.  In this case, `gawk' sets the variable `ERRNO' to a string
+ describing the error that occurred.
+ 
+    In the following examples, COMMAND stands for a string value that
+ represents a shell command.
+ 
+      NOTE: When `--sandbox' is specified (*note Options::), reading
+      lines from files, pipes and coprocesses is disabled.
+ 
+ * Menu:
+ 
+ * Plain Getline::               Using `getline' with no arguments.
+ * Getline/Variable::            Using `getline' into a variable.
+ * Getline/File::                Using `getline' from a file.
+ * Getline/Variable/File::       Using `getline' into a variable from a
+                                 file.
+ * Getline/Pipe::                Using `getline' from a pipe.
+ * Getline/Variable/Pipe::       Using `getline' into a variable from a
+                                 pipe.
+ * Getline/Coprocess::           Using `getline' from a coprocess.
+ * Getline/Variable/Coprocess::  Using `getline' into a variable from a
+                                 coprocess.
+ * Getline Notes::               Important things to know about `getline'.
+ * Getline Summary::             Summary of `getline' Variants.
+ 
+ 
+ File: gawk.info,  Node: Plain Getline,  Next: Getline/Variable,  Up: Getline
+ 
+ 4.9.1 Using `getline' with No Arguments
+ ---------------------------------------
+ 
+ The `getline' command can be used without arguments to read input from
+ the current input file.  All it does in this case is read the next
+ input record and split it up into fields.  This is useful if you've
+ finished processing the current record, but want to do some special
+ processing on the next record _right now_.  For example:
+ 
+      {
+           if ((t = index($0, "/*")) != 0) {
+                # value of `tmp' will be "" if t is 1
+                tmp = substr($0, 1, t - 1)
+                u = index(substr($0, t + 2), "*/")
+                offset = t + 2
+                while (u == 0) {
+                     if (getline <= 0) {
+                          m = "unexpected EOF or error"
+                          m = (m ": " ERRNO)
+                          print m > "/dev/stderr"
+                          exit
+                     }
+                     u = index($0, "*/")
+                     offset = 0
+                }
+                # substr() expression will be "" if */
+                # occurred at end of line
+                $0 = tmp substr($0, offset + u + 2)
+           }
+           print $0
+      }
+ 
+    This `awk' program deletes C-style comments (`/* ...  */') from the
+ input.  By replacing the `print $0' with other statements, you could
+ perform more complicated processing on the decommented input, such as
+ searching for matches of a regular expression.  (This program has a
+ subtle problem--it does not work if one comment ends and another begins
+ on the same line.)
+ 
+    This form of the `getline' command sets `NF', `NR', `FNR', and the
+ value of `$0'.
+ 
+      NOTE: The new value of `$0' is used to test the patterns of any
+      subsequent rules.  The original value of `$0' that triggered the
+      rule that executed `getline' is lost.  By contrast, the `next'
+      statement reads a new record but immediately begins processing it
+      normally, starting with the first rule in the program.  *Note Next
+      Statement::.
+ 
+ 
+ File: gawk.info,  Node: Getline/Variable,  Next: Getline/File,  Prev: Plain 
Getline,  Up: Getline
+ 
+ 4.9.2 Using `getline' into a Variable
+ -------------------------------------
+ 
+ You can use `getline VAR' to read the next record from `awk''s input
+ into the variable VAR.  No other processing is done.  For example,
+ suppose the next line is a comment or a special string, and you want to
+ read it without triggering any rules.  This form of `getline' allows
+ you to read that line and store it in a variable so that the main
+ read-a-line-and-check-each-rule loop of `awk' never sees it.  The
+ following example swaps every two lines of input:
+ 
+      {
+           if ((getline tmp) > 0) {
+                print tmp
+                print $0
+           } else
+                print $0
+      }
+ 
+ It takes the following list:
+ 
+      wan
+      tew
+      free
+      phore
+ 
+ and produces these results:
+ 
+      tew
+      wan
+      phore
+      free
+ 
+    The `getline' command used in this way sets only the variables `NR'
+ and `FNR' (and of course, VAR).  The record is not split into fields,
+ so the values of the fields (including `$0') and the value of `NF' do
+ not change.
+ 
+ 
+ File: gawk.info,  Node: Getline/File,  Next: Getline/Variable/File,  Prev: 
Getline/Variable,  Up: Getline
+ 
+ 4.9.3 Using `getline' from a File
+ ---------------------------------
+ 
+ Use `getline < FILE' to read the next record from FILE.  Here FILE is a
+ string-valued expression that specifies the file name.  `< FILE' is
+ called a "redirection" because it directs input to come from a
+ different place.  For example, the following program reads its input
+ record from the file `secondary.input' when it encounters a first field
+ with a value equal to 10 in the current input file:
+ 
+      {
+          if ($1 == 10) {
+               getline < "secondary.input"
+               print
+          } else
+               print
+      }
+ 
+    Because the main input stream is not used, the values of `NR' and
+ `FNR' are not changed. However, the record it reads is split into
+ fields in the normal manner, so the values of `$0' and the other fields
+ are changed, resulting in a new value of `NF'.
+ 
+    According to POSIX, `getline < EXPRESSION' is ambiguous if
+ EXPRESSION contains unparenthesized operators other than `$'; for
+ example, `getline < dir "/" file' is ambiguous because the
+ concatenation operator is not parenthesized.  You should write it as
+ `getline < (dir "/" file)' if you want your program to be portable to
+ all `awk' implementations.
+ 
+ 
+ File: gawk.info,  Node: Getline/Variable/File,  Next: Getline/Pipe,  Prev: 
Getline/File,  Up: Getline
+ 
+ 4.9.4 Using `getline' into a Variable from a File
+ -------------------------------------------------
+ 
+ Use `getline VAR < FILE' to read input from the file FILE, and put it
+ in the variable VAR.  As above, FILE is a string-valued expression that
+ specifies the file from which to read.
+ 
+    In this version of `getline', none of the built-in variables are
+ changed and the record is not split into fields.  The only variable
+ changed is VAR.(1) For example, the following program copies all the
+ input files to the output, except for records that say
+ address@hidden FILENAME'.  Such a record is replaced by the contents of the
+ file FILENAME:
+ 
+      {
+           if (NF == 2 && $1 == "@include") {
+                while ((getline line < $2) > 0)
+                     print line
+                close($2)
+           } else
+                print
+      }
+ 
+    Note here how the name of the extra input file is not built into the
+ program; it is taken directly from the data, specifically from the
+ second field on the address@hidden' line.
+ 
+    The `close()' function is called to ensure that if two identical
+ address@hidden' lines appear in the input, the entire specified file is
+ included twice.  *Note Close Files And Pipes::.
+ 
+    One deficiency of this program is that it does not process nested
+ address@hidden' statements (i.e., address@hidden' statements in included 
files)
+ the way a true macro preprocessor would.  *Note Igawk Program::, for a
+ program that does handle nested address@hidden' statements.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) This is not quite true. `RT' could be changed if `RS' is a
+ regular expression.
+ 
+ 
+ File: gawk.info,  Node: Getline/Pipe,  Next: Getline/Variable/Pipe,  Prev: 
Getline/Variable/File,  Up: Getline
+ 
+ 4.9.5 Using `getline' from a Pipe
+ ---------------------------------
+ 
+ The output of a command can also be piped into `getline', using
+ `COMMAND | getline'.  In this case, the string COMMAND is run as a
+ shell command and its output is piped into `awk' to be used as input.
+ This form of `getline' reads one record at a time from the pipe.  For
+ example, the following program copies its input to its output, except
+ for lines that begin with address@hidden', which are replaced by the output
+ produced by running the rest of the line as a shell command:
+ 
+      {
+           if ($1 == "@execute") {
+                tmp = substr($0, 10)        # Remove "@execute"
+                while ((tmp | getline) > 0)
+                     print
+                close(tmp)
+           } else
+                print
+      }
+ 
+ The `close()' function is called to ensure that if two identical
+ address@hidden' lines appear in the input, the command is run for each one.
+ *Note Close Files And Pipes::.  Given the input:
+ 
+      foo
+      bar
+      baz
+      @execute who
+      bletch
+ 
+ the program might produce:
+ 
+      foo
+      bar
+      baz
+      arnold     ttyv0   Jul 13 14:22
+      miriam     ttyp0   Jul 13 14:23     (murphy:0)
+      bill       ttyp1   Jul 13 14:23     (murphy:0)
+      bletch
+ 
+ Notice that this program ran the command `who' and printed the previous
+ result.  (If you try this program yourself, you will of course get
+ different results, depending upon who is logged in on your system.)
+ 
+    This variation of `getline' splits the record into fields, sets the
+ value of `NF', and recomputes the value of `$0'.  The values of `NR'
+ and `FNR' are not changed.
+ 
+    According to POSIX, `EXPRESSION | getline' is ambiguous if
+ EXPRESSION contains unparenthesized operators other than `$'--for
+ example, `"echo " "date" | getline' is ambiguous because the
+ concatenation operator is not parenthesized.  You should write it as
+ `("echo " "date") | getline' if you want your program to be portable to
+ all `awk' implementations.
+ 
+      NOTE: Unfortunately, `gawk' has not been consistent in its
+      treatment of a construct like `"echo " "date" | getline'.  Most
+      versions, including the current version, treat it at as `("echo "
+      "date") | getline'.  (This how Brian Kernighan's `awk' behaves.)
+      Some versions changed and treated it as `"echo " ("date" |
+      getline)'.  (This is how `mawk' behaves.)  In short, _always_ use
+      explicit parentheses, and then you won't have to worry.
+ 
+ 
+ File: gawk.info,  Node: Getline/Variable/Pipe,  Next: Getline/Coprocess,  
Prev: Getline/Pipe,  Up: Getline
+ 
+ 4.9.6 Using `getline' into a Variable from a Pipe
+ -------------------------------------------------
+ 
+ When you use `COMMAND | getline VAR', the output of COMMAND is sent
+ through a pipe to `getline' and into the variable VAR.  For example, the
+ following program reads the current date and time into the variable
+ `current_time', using the `date' utility, and then prints it:
+ 
+      BEGIN {
+           "date" | getline current_time
+           close("date")
+           print "Report printed on " current_time
+      }
+ 
+    In this version of `getline', none of the built-in variables are
+ changed and the record is not split into fields.
+ 
+    According to POSIX, `EXPRESSION | getline VAR' is ambiguous if
+ EXPRESSION contains unparenthesized operators other than `$'; for
+ example, `"echo " "date" | getline VAR' is ambiguous because the
+ concatenation operator is not parenthesized. You should write it as
+ `("echo " "date") | getline VAR' if you want your program to be
+ portable to other `awk' implementations.
+ 
+ 
+ File: gawk.info,  Node: Getline/Coprocess,  Next: Getline/Variable/Coprocess, 
 Prev: Getline/Variable/Pipe,  Up: Getline
+ 
+ 4.9.7 Using `getline' from a Coprocess
+ --------------------------------------
+ 
+ Input into `getline' from a pipe is a one-way operation.  The command
+ that is started with `COMMAND | getline' only sends data _to_ your
+ `awk' program.
+ 
+    On occasion, you might want to send data to another program for
+ processing and then read the results back.  `gawk' allows you to start
+ a "coprocess", with which two-way communications are possible.  This is
+ done with the `|&' operator.  Typically, you write data to the
+ coprocess first and then read results back, as shown in the following:
+ 
+      print "SOME QUERY" |& "db_server"
+      "db_server" |& getline
+ 
+ which sends a query to `db_server' and then reads the results.
+ 
+    The values of `NR' and `FNR' are not changed, because the main input
+ stream is not used.  However, the record is split into fields in the
+ normal manner, thus changing the values of `$0', of the other fields,
+ and of `NF'.
+ 
+    Coprocesses are an advanced feature. They are discussed here only
+ because this is the minor node on `getline'.  *Note Two-way I/O::,
+ where coprocesses are discussed in more detail.
+ 
+ 
+ File: gawk.info,  Node: Getline/Variable/Coprocess,  Next: Getline Notes,  
Prev: Getline/Coprocess,  Up: Getline
+ 
+ 4.9.8 Using `getline' into a Variable from a Coprocess
+ ------------------------------------------------------
+ 
+ When you use `COMMAND |& getline VAR', the output from the coprocess
+ COMMAND is sent through a two-way pipe to `getline' and into the
+ variable VAR.
+ 
+    In this version of `getline', none of the built-in variables are
+ changed and the record is not split into fields.  The only variable
+ changed is VAR.
+ 
+    Coprocesses are an advanced feature. They are discussed here only
+ because this is the minor node on `getline'.  *Note Two-way I/O::,
+ where coprocesses are discussed in more detail.
+ 
+ 
+ File: gawk.info,  Node: Getline Notes,  Next: Getline Summary,  Prev: 
Getline/Variable/Coprocess,  Up: Getline
+ 
+ 4.9.9 Points to Remember About `getline'
+ ----------------------------------------
+ 
+ Here are some miscellaneous points about `getline' that you should bear
+ in mind:
+ 
+    * When `getline' changes the value of `$0' and `NF', `awk' does
+      _not_ automatically jump to the start of the program and start
+      testing the new record against every pattern.  However, the new
+      record is tested against any subsequent rules.
+ 
+    * Many `awk' implementations limit the number of pipelines that an
+      `awk' program may have open to just one.  In `gawk', there is no
+      such limit.  You can open as many pipelines (and coprocesses) as
+      the underlying operating system permits.
+ 
+    * An interesting side effect occurs if you use `getline' without a
+      redirection inside a `BEGIN' rule. Because an unredirected
+      `getline' reads from the command-line data files, the first
+      `getline' command causes `awk' to set the value of `FILENAME'.
+      Normally, `FILENAME' does not have a value inside `BEGIN' rules,
+      because you have not yet started to process the command-line data
+      files.  (d.c.)  (*Note BEGIN/END::, also *note Auto-set::.)
+ 
+    * Using `FILENAME' with `getline' (`getline < FILENAME') is likely
+      to be a source for confusion.  `awk' opens a separate input stream
+      from the current input file.  However, by not using a variable,
+      `$0' and `NR' are still updated.  If you're doing this, it's
+      probably by accident, and you should reconsider what it is you're
+      trying to accomplish.
+ 
+    * *note Getline Summary::, presents a table summarizing the
+      `getline' variants and which variables they can affect.  It is
+      worth noting that those variants which do not use redirection can
+      cause `FILENAME' to be updated if they cause `awk' to start
+      reading a new input file.
+ 
+    * If the variable being assigned is an expression with side effects,
+      different versions of `awk' behave differently upon encountering
+      end-of-file.  Some versions don't evaluate the expression; many
+      versions (including `gawk') do.  Here is an example, due to Duncan
+      Moore:
+ 
+           BEGIN {
+               system("echo 1 > f")
+               while ((getline a[++c] < "f") > 0) { }
+               print c
+           }
+ 
+      Here, the side effect is the `++c'.  Is `c' incremented if end of
+      file is encountered, before the element in `a' is assigned?
+ 
+      `gawk' treats `getline' like a function call, and evaluates the
+      expression `a[++c]' before attempting to read from `f'.  Other
+      versions of `awk' only evaluate the expression once they know that
+      there is a string value to be assigned.  Caveat Emptor.
+ 
+ 
+ File: gawk.info,  Node: Getline Summary,  Prev: Getline Notes,  Up: Getline
+ 
+ 4.9.10 Summary of `getline' Variants
+ ------------------------------------
+ 
+ *note table-getline-variants:: summarizes the eight variants of
+ `getline', listing which built-in variables are set by each one, and
 -whether the variant is standard or a `gawk' extension.
++whether the variant is standard or a `gawk' extension.  Note: for each
++variant, `gawk' sets the `RT' built-in variable.
+ 
+ Variant                  Effect                      Standard /
+                                                      Extension
+ ------------------------------------------------------------------------- 
+ `getline'                Sets `$0', `NF', `FNR',     Standard
+                          and `NR'                    
+ `getline' VAR            Sets VAR, `FNR', and `NR'   Standard
+ `getline <' FILE         Sets `$0' and `NF'          Standard
+ `getline VAR < FILE'     Sets VAR                    Standard
+ COMMAND `| getline'      Sets `$0' and `NF'          Standard
+ COMMAND `| getline' VAR  Sets VAR                    Standard
+ COMMAND `|& getline'     Sets `$0' and `NF'          Extension
+ COMMAND `|& getline'     Sets VAR                    Extension
+ VAR                                                  
+ 
+ Table 4.1: getline Variants and What They Set
+ 
+ 
 -File: gawk.info,  Node: Command line directories,  Prev: Getline,  Up: 
Reading Files
++File: gawk.info,  Node: Read Timeout,  Next: Command line directories,  Prev: 
Getline,  Up: Reading Files
++
++4.10 Reading Input With A Timeout
++=================================
++
++You may specify a timeout in milliseconds for reading input from a
++terminal, pipe or two-way communication including, TCP/IP sockets. This
++can be done on a per input, command or connection basis, by setting a
++special element in the `PROCINFO' array:
++
++     PROCINFO["input_name", "READ_TIMEOUT"] = TIMEOUT IN MILLISECONDS
++
++   When set, this will cause `gawk' to time out and return failure if
++no data is available to read within the specified timeout period.  For
++example, a TCP client can decide to give up on receiving any response
++from the server after a certain amount of time:
++
++     Service = "/inet/tcp/0/localhost/daytime"
++     PROCINFO[Service, "READ_TIMEOUT"] = 100
++     if ((Service |& getline) > 0)
++         print $0
++     else if (ERRNO != "")
++         print ERRNO
++
++   Here is how to read interactively from the terminal(1) without
++waiting for more than five seconds:
++
++     PROCINFO["/dev/stdin", "READ_TIMEOUT"] = 5000
++     while ((getline < "/dev/stdin") > 0)
++         print $0
++
++   `gawk' will terminate the read operation if input does not arrive
++after waiting for the timeout period, return failure and set the
++`ERRNO' variable to an appropriate string value.  A negative or zero
++value for the timeout is the same as specifying no timeout at all.
++
++   A timeout can also be set for reading from the terminal in the
++implicit loop that reads input records and matches them against
++patterns, like so:
++
++     $  gawk 'BEGIN { PROCINFO["-", "READ_TIMEOUT"] = 5000 }
++     > { print "You entered: " $0 }'
++     gawk
++     -| You entered: gawk
++
++   In this case, failure to respond within five seconds results in the
++following error message:
++
++     error--> gawk: cmd. line:2: (FILENAME=- FNR=1) fatal: error reading 
input file `-': Connection timed out
++
++   The timeout can be set or changed at any time, and will take effect
++on the next attempt to read from the input device. In the following
++example, we start with a timeout value of one second, and progressively
++reduce it by one-tenth of a second until we wait indefinitely for the
++input to arrive:
++
++     PROCINFO[Service, "READ_TIMEOUT"] = 1000
++     while ((Service |& getline) > 0) {
++         print $0
++         PROCINFO[S, "READ_TIMEOUT"] -= 100
++     }
++
++     NOTE: You should not assume that the read operation will block
++     exactly after the tenth record has been printed. It is possible
++     that `gawk' will read and buffer more than one record's worth of
++     data the first time. Because of this, changing the value of
++     timeout like in the above example is not very useful.
++
++   If the `PROCINFO' element is not present and the environment
++variable `GAWK_READ_TIMEOUT' exists, `gawk' uses its value to
++initialize the timeout value.  The exclusive use of the environment
++variable to specify timeout has the disadvantage of not being able to
++control it on a per command or connection basis.
++
++   `gawk' considers a timeout event to be an error even though the
++attempt to read from the underlying device may succeed in a later
++attempt. This is a limitation, and it also means that you cannot use
++this to multiplex input from two or more sources.
++
++   Assigning a timeout value prevents read operations from blocking
++indefinitely. But bear in mind that there are other ways `gawk' can
++stall waiting for an input device to be ready.  A network client can
++sometimes take a long time to establish a connection before it can
++start reading any data, or the attempt to open a FIFO special file for
++reading can block indefinitely until some other process opens it for
++writing.
++
++   ---------- Footnotes ----------
++
++   (1) This assumes that standard input is the keyboard
++
++
++File: gawk.info,  Node: Command line directories,  Prev: Read Timeout,  Up: 
Reading Files
+ 
 -4.10 Directories On The Command Line
++4.11 Directories On The Command Line
+ ====================================
+ 
+ According to the POSIX standard, files named on the `awk' command line
+ must be text files.  It is a fatal error if they are not.  Most
+ versions of `awk' treat a directory on the command line as a fatal
+ error.
+ 
+    By default, `gawk' produces a warning for a directory on the command
+ line, but otherwise ignores it.  If either of the `--posix' or
+ `--traditional' options is given, then `gawk' reverts to treating a
+ directory on the command line as a fatal error.
+ 
+ 
+ File: gawk.info,  Node: Printing,  Next: Expressions,  Prev: Reading Files,  
Up: Top
+ 
+ 5 Printing Output
+ *****************
+ 
+ One of the most common programming actions is to "print", or output,
+ some or all of the input.  Use the `print' statement for simple output,
+ and the `printf' statement for fancier formatting.  The `print'
+ statement is not limited when computing _which_ values to print.
+ However, with two exceptions, you cannot specify _how_ to print
+ them--how many columns, whether to use exponential notation or not, and
+ so on.  (For the exceptions, *note Output Separators::, and *note
+ OFMT::.)  For printing with specifications, you need the `printf'
+ statement (*note Printf::).
+ 
+    Besides basic and formatted printing, this major node also covers
+ I/O redirections to files and pipes, introduces the special file names
+ that `gawk' processes internally, and discusses the `close()' built-in
+ function.
+ 
+ * Menu:
+ 
+ * Print::                       The `print' statement.
+ * Print Examples::              Simple examples of `print' statements.
+ * Output Separators::           The output separators and how to change them.
+ * OFMT::                        Controlling Numeric Output With `print'.
+ * Printf::                      The `printf' statement.
+ * Redirection::                 How to redirect output to multiple files and
+                                 pipes.
+ * Special Files::               File name interpretation in `gawk'.
+                                 `gawk' allows access to inherited file
+                                 descriptors.
+ * Close Files And Pipes::       Closing Input and Output Files and Pipes.
+ 
+ 
+ File: gawk.info,  Node: Print,  Next: Print Examples,  Up: Printing
+ 
+ 5.1 The `print' Statement
+ =========================
+ 
+ The `print' statement is used for producing output with simple,
+ standardized formatting.  Specify only the strings or numbers to print,
+ in a list separated by commas.  They are output, separated by single
+ spaces, followed by a newline.  The statement looks like this:
+ 
+      print ITEM1, ITEM2, ...
+ 
+ The entire list of items may be optionally enclosed in parentheses.  The
+ parentheses are necessary if any of the item expressions uses the `>'
+ relational operator; otherwise it could be confused with an output
+ redirection (*note Redirection::).
+ 
+    The items to print can be constant strings or numbers, fields of the
+ current record (such as `$1'), variables, or any `awk' expression.
+ Numeric values are converted to strings and then printed.
+ 
+    The simple statement `print' with no items is equivalent to `print
+ $0': it prints the entire current record.  To print a blank line, use
+ `print ""', where `""' is the empty string.  To print a fixed piece of
+ text, use a string constant, such as `"Don't Panic"', as one item.  If
+ you forget to use the double-quote characters, your text is taken as an
+ `awk' expression, and you will probably get an error.  Keep in mind
+ that a space is printed between any two items.
+ 
+ 
+ File: gawk.info,  Node: Print Examples,  Next: Output Separators,  Prev: 
Print,  Up: Printing
+ 
+ 5.2 `print' Statement Examples
+ ==============================
+ 
+ Each `print' statement makes at least one line of output.  However, it
+ isn't limited to only one line.  If an item value is a string
+ containing a newline, the newline is output along with the rest of the
+ string.  A single `print' statement can make any number of lines this
+ way.
+ 
+    The following is an example of printing a string that contains
+ embedded newlines (the `\n' is an escape sequence, used to represent
+ the newline character; *note Escape Sequences::):
+ 
+      $ awk 'BEGIN { print "line one\nline two\nline three" }'
+      -| line one
+      -| line two
+      -| line three
+ 
+    The next example, which is run on the `inventory-shipped' file,
+ prints the first two fields of each input record, with a space between
+ them:
+ 
+      $ awk '{ print $1, $2 }' inventory-shipped
+      -| Jan 13
+      -| Feb 15
+      -| Mar 15
+      ...
+ 
+    A common mistake in using the `print' statement is to omit the comma
+ between two items.  This often has the effect of making the items run
+ together in the output, with no space.  The reason for this is that
+ juxtaposing two string expressions in `awk' means to concatenate them.
+ Here is the same program, without the comma:
+ 
+      $ awk '{ print $1 $2 }' inventory-shipped
+      -| Jan13
+      -| Feb15
+      -| Mar15
+      ...
+ 
+    To someone unfamiliar with the `inventory-shipped' file, neither
+ example's output makes much sense.  A heading line at the beginning
+ would make it clearer.  Let's add some headings to our table of months
+ (`$1') and green crates shipped (`$2').  We do this using the `BEGIN'
+ pattern (*note BEGIN/END::) so that the headings are only printed once:
+ 
+      awk 'BEGIN {  print "Month Crates"
+                    print "----- ------" }
+                 {  print $1, $2 }' inventory-shipped
+ 
+ When run, the program prints the following:
+ 
+      Month Crates
+      ----- ------
+      Jan 13
+      Feb 15
+      Mar 15
+      ...
+ 
+ The only problem, however, is that the headings and the table data
+ don't line up!  We can fix this by printing some spaces between the two
+ fields:
+ 
+      awk 'BEGIN { print "Month Crates"
+                   print "----- ------" }
+                 { print $1, "     ", $2 }' inventory-shipped
+ 
+    Lining up columns this way can get pretty complicated when there are
+ many columns to fix.  Counting spaces for two or three columns is
+ simple, but any more than this can take up a lot of time. This is why
+ the `printf' statement was created (*note Printf::); one of its
+ specialties is lining up columns of data.
+ 
+      NOTE: You can continue either a `print' or `printf' statement
+      simply by putting a newline after any comma (*note
+      Statements/Lines::).
+ 
+ 
+ File: gawk.info,  Node: Output Separators,  Next: OFMT,  Prev: Print 
Examples,  Up: Printing
+ 
+ 5.3 Output Separators
+ =====================
+ 
+ As mentioned previously, a `print' statement contains a list of items
+ separated by commas.  In the output, the items are normally separated
+ by single spaces.  However, this doesn't need to be the case; a single
+ space is simply the default.  Any string of characters may be used as
+ the "output field separator" by setting the built-in variable `OFS'.
+ The initial value of this variable is the string `" "'--that is, a
+ single space.
+ 
+    The output from an entire `print' statement is called an "output
+ record".  Each `print' statement outputs one output record, and then
+ outputs a string called the "output record separator" (or `ORS').  The
+ initial value of `ORS' is the string `"\n"'; i.e., a newline character.
+ Thus, each `print' statement normally makes a separate line.
+ 
+    In order to change how output fields and records are separated,
+ assign new values to the variables `OFS' and `ORS'.  The usual place to
+ do this is in the `BEGIN' rule (*note BEGIN/END::), so that it happens
+ before any input is processed.  It can also be done with assignments on
+ the command line, before the names of the input files, or using the
+ `-v' command-line option (*note Options::).  The following example
+ prints the first and second fields of each input record, separated by a
+ semicolon, with a blank line added after each newline:
+ 
+      $ awk 'BEGIN { OFS = ";"; ORS = "\n\n" }
+      >            { print $1, $2 }' BBS-list
+      -| aardvark;555-5553
+      -|
+      -| alpo-net;555-3412
+      -|
+      -| barfly;555-7685
+      ...
+ 
+    If the value of `ORS' does not contain a newline, the program's
+ output runs together on a single line.
+ 
+ 
+ File: gawk.info,  Node: OFMT,  Next: Printf,  Prev: Output Separators,  Up: 
Printing
+ 
+ 5.4 Controlling Numeric Output with `print'
+ ===========================================
+ 
+ When printing numeric values with the `print' statement, `awk'
+ internally converts the number to a string of characters and prints
+ that string.  `awk' uses the `sprintf()' function to do this conversion
+ (*note String Functions::).  For now, it suffices to say that the
+ `sprintf()' function accepts a "format specification" that tells it how
+ to format numbers (or strings), and that there are a number of
+ different ways in which numbers can be formatted.  The different format
+ specifications are discussed more fully in *note Control Letters::.
+ 
+    The built-in variable `OFMT' contains the default format
+ specification that `print' uses with `sprintf()' when it wants to
+ convert a number to a string for printing.  The default value of `OFMT'
+ is `"%.6g"'.  The way `print' prints numbers can be changed by
+ supplying different format specifications as the value of `OFMT', as
+ shown in the following example:
+ 
+      $ awk 'BEGIN {
+      >   OFMT = "%.0f"  # print numbers as integers (rounds)
+      >   print 17.23, 17.54 }'
+      -| 17 18
+ 
+ According to the POSIX standard, `awk''s behavior is undefined if
+ `OFMT' contains anything but a floating-point conversion specification.
+ (d.c.)
+ 
+ 
+ File: gawk.info,  Node: Printf,  Next: Redirection,  Prev: OFMT,  Up: Printing
+ 
+ 5.5 Using `printf' Statements for Fancier Printing
+ ==================================================
+ 
+ For more precise control over the output format than what is provided
+ by `print', use `printf'.  With `printf' you can specify the width to
+ use for each item, as well as various formatting choices for numbers
+ (such as what output base to use, whether to print an exponent, whether
+ to print a sign, and how many digits to print after the decimal point).
+ You do this by supplying a string, called the "format string", that
+ controls how and where to print the other arguments.
+ 
+ * Menu:
+ 
+ * Basic Printf::                Syntax of the `printf' statement.
+ * Control Letters::             Format-control letters.
+ * Format Modifiers::            Format-specification modifiers.
+ * Printf Examples::             Several examples.
+ 
+ 
+ File: gawk.info,  Node: Basic Printf,  Next: Control Letters,  Up: Printf
+ 
+ 5.5.1 Introduction to the `printf' Statement
+ --------------------------------------------
+ 
+ A simple `printf' statement looks like this:
+ 
+      printf FORMAT, ITEM1, ITEM2, ...
+ 
+ The entire list of arguments may optionally be enclosed in parentheses.
+ The parentheses are necessary if any of the item expressions use the `>'
+ relational operator; otherwise, it can be confused with an output
+ redirection (*note Redirection::).
+ 
+    The difference between `printf' and `print' is the FORMAT argument.
+ This is an expression whose value is taken as a string; it specifies
+ how to output each of the other arguments.  It is called the "format
+ string".
+ 
+    The format string is very similar to that in the ISO C library
+ function `printf()'.  Most of FORMAT is text to output verbatim.
+ Scattered among this text are "format specifiers"--one per item.  Each
+ format specifier says to output the next item in the argument list at
+ that place in the format.
+ 
+    The `printf' statement does not automatically append a newline to
+ its output.  It outputs only what the format string specifies.  So if a
+ newline is needed, you must include one in the format string.  The
+ output separator variables `OFS' and `ORS' have no effect on `printf'
+ statements. For example:
+ 
+      $ awk 'BEGIN {
+      >    ORS = "\nOUCH!\n"; OFS = "+"
+      >    msg = "Dont Panic!"
+      >    printf "%s\n", msg
+      > }'
+      -| Dont Panic!
+ 
+ Here, neither the `+' nor the `OUCH' appear in the output message.
+ 
+ 
+ File: gawk.info,  Node: Control Letters,  Next: Format Modifiers,  Prev: 
Basic Printf,  Up: Printf
+ 
+ 5.5.2 Format-Control Letters
+ ----------------------------
+ 
+ A format specifier starts with the character `%' and ends with a
+ "format-control letter"--it tells the `printf' statement how to output
+ one item.  The format-control letter specifies what _kind_ of value to
+ print.  The rest of the format specifier is made up of optional
+ "modifiers" that control _how_ to print the value, such as the field
+ width.  Here is a list of the format-control letters:
+ 
+ `%c'
+      Print a number as an ASCII character; thus, `printf "%c", 65'
+      outputs the letter `A'. The output for a string value is the first
+      character of the string.
+ 
+           NOTE: The POSIX standard says the first character of a string
+           is printed.  In locales with multibyte characters, `gawk'
+           attempts to convert the leading bytes of the string into a
+           valid wide character and then to print the multibyte encoding
+           of that character.  Similarly, when printing a numeric value,
+           `gawk' allows the value to be within the numeric range of
+           values that can be held in a wide character.
+ 
+           Other `awk' versions generally restrict themselves to printing
+           the first byte of a string or to numeric values within the
+           range of a single byte (0-255).
+ 
+ `%d, %i'
+      Print a decimal integer.  The two control letters are equivalent.
+      (The `%i' specification is for compatibility with ISO C.)
+ 
+ `%e, %E'
+      Print a number in scientific (exponential) notation; for example:
+ 
+           printf "%4.3e\n", 1950
+ 
+      prints `1.950e+03', with a total of four significant figures,
+      three of which follow the decimal point.  (The `4.3' represents
+      two modifiers, discussed in the next node.)  `%E' uses `E' instead
+      of `e' in the output.
+ 
+ `%f'
+      Print a number in floating-point notation.  For example:
+ 
+           printf "%4.3f", 1950
+ 
+      prints `1950.000', with a total of four significant figures, three
+      of which follow the decimal point.  (The `4.3' represents two
+      modifiers, discussed in the next node.)
+ 
+      On systems supporting IEEE 754 floating point format, values
+      representing negative infinity are formatted as `-inf' or
+      `-infinity', and positive infinity as `inf' and `infinity'.  The
+      special "not a number" value formats as `-nan' or `nan'.
+ 
+ `%F'
+      Like `%f' but the infinity and "not a number" values are spelled
+      using uppercase letters.
+ 
+      The `%F' format is a POSIX extension to ISO C; not all systems
+      support it.  On those that don't, `gawk' uses `%f' instead.
+ 
+ `%g, %G'
+      Print a number in either scientific notation or in floating-point
+      notation, whichever uses fewer characters; if the result is
+      printed in scientific notation, `%G' uses `E' instead of `e'.
+ 
+ `%o'
+      Print an unsigned octal integer (*note Nondecimal-numbers::).
+ 
+ `%s'
+      Print a string.
+ 
+ `%u'
+      Print an unsigned decimal integer.  (This format is of marginal
+      use, because all numbers in `awk' are floating-point; it is
+      provided primarily for compatibility with C.)
+ 
+ `%x, %X'
+      Print an unsigned hexadecimal integer; `%X' uses the letters `A'
+      through `F' instead of `a' through `f' (*note
+      Nondecimal-numbers::).
+ 
+ `%%'
+      Print a single `%'.  This does not consume an argument and it
+      ignores any modifiers.
+ 
+      NOTE: When using the integer format-control letters for values
+      that are outside the range of the widest C integer type, `gawk'
+      switches to the `%g' format specifier. If `--lint' is provided on
+      the command line (*note Options::), `gawk' warns about this.
+      Other versions of `awk' may print invalid values or do something
+      else entirely.  (d.c.)
+ 
+ 
+ File: gawk.info,  Node: Format Modifiers,  Next: Printf Examples,  Prev: 
Control Letters,  Up: Printf
+ 
+ 5.5.3 Modifiers for `printf' Formats
+ ------------------------------------
+ 
+ A format specification can also include "modifiers" that can control
+ how much of the item's value is printed, as well as how much space it
+ gets.  The modifiers come between the `%' and the format-control letter.
+ We will use the bullet symbol "*" in the following examples to represent
+ spaces in the output. Here are the possible modifiers, in the order in
+ which they may appear:
+ 
+ `N$'
+      An integer constant followed by a `$' is a "positional specifier".
+      Normally, format specifications are applied to arguments in the
+      order given in the format string.  With a positional specifier,
+      the format specification is applied to a specific argument,
+      instead of what would be the next argument in the list.
+      Positional specifiers begin counting with one. Thus:
+ 
+           printf "%s %s\n", "don't", "panic"
+           printf "%2$s %1$s\n", "panic", "don't"
+ 
+      prints the famous friendly message twice.
+ 
+      At first glance, this feature doesn't seem to be of much use.  It
+      is in fact a `gawk' extension, intended for use in translating
+      messages at runtime.  *Note Printf Ordering::, which describes how
+      and why to use positional specifiers.  For now, we will not use
+      them.
+ 
+ `-'
+      The minus sign, used before the width modifier (see later on in
+      this list), says to left-justify the argument within its specified
+      width.  Normally, the argument is printed right-justified in the
+      specified width.  Thus:
+ 
+           printf "%-4s", "foo"
+ 
+      prints `foo*'.
+ 
+ `SPACE'
+      For numeric conversions, prefix positive values with a space and
+      negative values with a minus sign.
+ 
+ `+'
+      The plus sign, used before the width modifier (see later on in
+      this list), says to always supply a sign for numeric conversions,
+      even if the data to format is positive. The `+' overrides the
+      space modifier.
+ 
+ `#'
+      Use an "alternate form" for certain control letters.  For `%o',
+      supply a leading zero.  For `%x' and `%X', supply a leading `0x'
+      or `0X' for a nonzero result.  For `%e', `%E', `%f', and `%F', the
+      result always contains a decimal point.  For `%g' and `%G',
+      trailing zeros are not removed from the result.
+ 
+ `0'
+      A leading `0' (zero) acts as a flag that indicates that output
+      should be padded with zeros instead of spaces.  This applies only
+      to the numeric output formats.  This flag only has an effect when
+      the field width is wider than the value to print.
+ 
+ `''
+      A single quote or apostrophe character is a POSIX extension to ISO
+      C.  It indicates that the integer part of a floating point value,
+      or the entire part of an integer decimal value, should have a
+      thousands-separator character in it.  This only works in locales
+      that support such characters.  For example:
+ 
+           $ cat thousands.awk          Show source program
+           -| BEGIN { printf "%'d\n", 1234567 }
+           $ LC_ALL=C gawk -f thousands.awk
+           -| 1234567                   Results in "C" locale
+           $ LC_ALL=en_US.UTF-8 gawk -f thousands.awk
+           -| 1,234,567                 Results in US English UTF locale
+ 
+      For more information about locales and internationalization issues,
+      see *note Locales::.
+ 
+           NOTE: The `'' flag is a nice feature, but its use complicates
+           things: it becomes difficult to use it in command-line
+           programs.  For information on appropriate quoting tricks, see
+           *note Quoting::.
+ 
+ `WIDTH'
+      This is a number specifying the desired minimum width of a field.
+      Inserting any number between the `%' sign and the format-control
+      character forces the field to expand to this width.  The default
+      way to do this is to pad with spaces on the left.  For example:
+ 
+           printf "%4s", "foo"
+ 
+      prints `*foo'.
+ 
+      The value of WIDTH is a minimum width, not a maximum.  If the item
+      value requires more than WIDTH characters, it can be as wide as
+      necessary.  Thus, the following:
+ 
+           printf "%4s", "foobar"
+ 
+      prints `foobar'.
+ 
+      Preceding the WIDTH with a minus sign causes the output to be
+      padded with spaces on the right, instead of on the left.
+ 
+ `.PREC'
+      A period followed by an integer constant specifies the precision
+      to use when printing.  The meaning of the precision varies by
+      control letter:
+ 
+     `%d', `%i', `%o', `%u', `%x', `%X'
+           Minimum number of digits to print.
+ 
+     `%e', `%E', `%f', `%F'
+           Number of digits to the right of the decimal point.
+ 
+     `%g', `%G'
+           Maximum number of significant digits.
+ 
+     `%s'
+           Maximum number of characters from the string that should
+           print.
+ 
+      Thus, the following:
+ 
+           printf "%.4s", "foobar"
+ 
+      prints `foob'.
+ 
+    The C library `printf''s dynamic WIDTH and PREC capability (for
+ example, `"%*.*s"') is supported.  Instead of supplying explicit WIDTH
+ and/or PREC values in the format string, they are passed in the
+ argument list.  For example:
+ 
+      w = 5
+      p = 3
+      s = "abcdefg"
+      printf "%*.*s\n", w, p, s
+ 
+ is exactly equivalent to:
+ 
+      s = "abcdefg"
+      printf "%5.3s\n", s
+ 
+ Both programs output `**abc'.  Earlier versions of `awk' did not
+ support this capability.  If you must use such a version, you may
+ simulate this feature by using concatenation to build up the format
+ string, like so:
+ 
+      w = 5
+      p = 3
+      s = "abcdefg"
+      printf "%" w "." p "s\n", s
+ 
+ This is not particularly easy to read but it does work.
+ 
+    C programmers may be used to supplying additional `l', `L', and `h'
+ modifiers in `printf' format strings. These are not valid in `awk'.
+ Most `awk' implementations silently ignore them.  If `--lint' is
+ provided on the command line (*note Options::), `gawk' warns about
+ their use. If `--posix' is supplied, their use is a fatal error.
+ 
+ 
+ File: gawk.info,  Node: Printf Examples,  Prev: Format Modifiers,  Up: Printf
+ 
+ 5.5.4 Examples Using `printf'
+ -----------------------------
+ 
+ The following simple example shows how to use `printf' to make an
+ aligned table:
+ 
+      awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list
+ 
+ This command prints the names of the bulletin boards (`$1') in the file
+ `BBS-list' as a string of 10 characters that are left-justified.  It
+ also prints the phone numbers (`$2') next on the line.  This produces
+ an aligned two-column table of names and phone numbers, as shown here:
+ 
+      $ awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list
+      -| aardvark   555-5553
+      -| alpo-net   555-3412
+      -| barfly     555-7685
+      -| bites      555-1675
+      -| camelot    555-0542
+      -| core       555-2912
+      -| fooey      555-1234
+      -| foot       555-6699
+      -| macfoo     555-6480
+      -| sdace      555-3430
+      -| sabafoo    555-2127
+ 
+    In this case, the phone numbers had to be printed as strings because
+ the numbers are separated by a dash.  Printing the phone numbers as
+ numbers would have produced just the first three digits: `555'.  This
+ would have been pretty confusing.
+ 
+    It wasn't necessary to specify a width for the phone numbers because
+ they are last on their lines.  They don't need to have spaces after
+ them.
+ 
+    The table could be made to look even nicer by adding headings to the
+ tops of the columns.  This is done using the `BEGIN' pattern (*note
+ BEGIN/END::) so that the headers are only printed once, at the
+ beginning of the `awk' program:
+ 
+      awk 'BEGIN { print "Name      Number"
+                   print "----      ------" }
+           { printf "%-10s %s\n", $1, $2 }' BBS-list
+ 
+    The above example mixes `print' and `printf' statements in the same
+ program.  Using just `printf' statements can produce the same results:
+ 
+      awk 'BEGIN { printf "%-10s %s\n", "Name", "Number"
+                   printf "%-10s %s\n", "----", "------" }
+           { printf "%-10s %s\n", $1, $2 }' BBS-list
+ 
+ Printing each column heading with the same format specification used
+ for the column elements ensures that the headings are aligned just like
+ the columns.
+ 
+    The fact that the same format specification is used three times can
+ be emphasized by storing it in a variable, like this:
+ 
+      awk 'BEGIN { format = "%-10s %s\n"
+                   printf format, "Name", "Number"
+                   printf format, "----", "------" }
+           { printf format, $1, $2 }' BBS-list
+ 
+    At this point, it would be a worthwhile exercise to use the `printf'
+ statement to line up the headings and table data for the
+ `inventory-shipped' example that was covered earlier in the minor node
+ on the `print' statement (*note Print::).
+ 
+ 
+ File: gawk.info,  Node: Redirection,  Next: Special Files,  Prev: Printf,  
Up: Printing
+ 
+ 5.6 Redirecting Output of `print' and `printf'
+ ==============================================
+ 
+ So far, the output from `print' and `printf' has gone to the standard
+ output, usually the screen.  Both `print' and `printf' can also send
+ their output to other places.  This is called "redirection".
+ 
+      NOTE: When `--sandbox' is specified (*note Options::), redirecting
+      output to files and pipes is disabled.
+ 
+    A redirection appears after the `print' or `printf' statement.
+ Redirections in `awk' are written just like redirections in shell
+ commands, except that they are written inside the `awk' program.
+ 
+    There are four forms of output redirection: output to a file, output
+ appended to a file, output through a pipe to another command, and output
+ to a coprocess.  They are all shown for the `print' statement, but they
+ work identically for `printf':
+ 
+ `print ITEMS > OUTPUT-FILE'
+      This redirection prints the items into the output file named
+      OUTPUT-FILE.  The file name OUTPUT-FILE can be any expression.
+      Its value is changed to a string and then used as a file name
+      (*note Expressions::).
+ 
+      When this type of redirection is used, the OUTPUT-FILE is erased
+      before the first output is written to it.  Subsequent writes to
+      the same OUTPUT-FILE do not erase OUTPUT-FILE, but append to it.
+      (This is different from how you use redirections in shell scripts.)
+      If OUTPUT-FILE does not exist, it is created.  For example, here
+      is how an `awk' program can write a list of BBS names to one file
+      named `name-list', and a list of phone numbers to another file
+      named `phone-list':
+ 
+           $ awk '{ print $2 > "phone-list"
+           >        print $1 > "name-list" }' BBS-list
+           $ cat phone-list
+           -| 555-5553
+           -| 555-3412
+           ...
+           $ cat name-list
+           -| aardvark
+           -| alpo-net
+           ...
+ 
+      Each output file contains one name or number per line.
+ 
+ `print ITEMS >> OUTPUT-FILE'
+      This redirection prints the items into the pre-existing output file
+      named OUTPUT-FILE.  The difference between this and the single-`>'
+      redirection is that the old contents (if any) of OUTPUT-FILE are
+      not erased.  Instead, the `awk' output is appended to the file.
+      If OUTPUT-FILE does not exist, then it is created.
+ 
+ `print ITEMS | COMMAND'
+      It is possible to send output to another program through a pipe
+      instead of into a file.   This redirection opens a pipe to
+      COMMAND, and writes the values of ITEMS through this pipe to
+      another process created to execute COMMAND.
+ 
+      The redirection argument COMMAND is actually an `awk' expression.
+      Its value is converted to a string whose contents give the shell
+      command to be run.  For example, the following produces two files,
+      one unsorted list of BBS names, and one list sorted in reverse
+      alphabetical order:
+ 
+           awk '{ print $1 > "names.unsorted"
+                  command = "sort -r > names.sorted"
+                  print $1 | command }' BBS-list
+ 
+      The unsorted list is written with an ordinary redirection, while
+      the sorted list is written by piping through the `sort' utility.
+ 
+      The next example uses redirection to mail a message to the mailing
+      list `bug-system'.  This might be useful when trouble is
+      encountered in an `awk' script run periodically for system
+      maintenance:
+ 
+           report = "mail bug-system"
+           print "Awk script failed:", $0 | report
+           m = ("at record number " FNR " of " FILENAME)
+           print m | report
+           close(report)
+ 
+      The message is built using string concatenation and saved in the
+      variable `m'.  It's then sent down the pipeline to the `mail'
+      program.  (The parentheses group the items to concatenate--see
+      *note Concatenation::.)
+ 
+      The `close()' function is called here because it's a good idea to
+      close the pipe as soon as all the intended output has been sent to
+      it.  *Note Close Files And Pipes::, for more information.
+ 
+      This example also illustrates the use of a variable to represent a
+      FILE or COMMAND--it is not necessary to always use a string
+      constant.  Using a variable is generally a good idea, because (if
+      you mean to refer to that same file or command) `awk' requires
+      that the string value be spelled identically every time.
+ 
+ `print ITEMS |& COMMAND'
+      This redirection prints the items to the input of COMMAND.  The
+      difference between this and the single-`|' redirection is that the
+      output from COMMAND can be read with `getline'.  Thus COMMAND is a
+      "coprocess", which works together with, but subsidiary to, the
+      `awk' program.
+ 
+      This feature is a `gawk' extension, and is not available in POSIX
+      `awk'.  *Note Getline/Coprocess::, for a brief discussion.  *Note
+      Two-way I/O::, for a more complete discussion.
+ 
+    Redirecting output using `>', `>>', `|', or `|&' asks the system to
+ open a file, pipe, or coprocess only if the particular FILE or COMMAND
+ you specify has not already been written to by your program or if it
+ has been closed since it was last written to.
+ 
+    It is a common error to use `>' redirection for the first `print' to
+ a file, and then to use `>>' for subsequent output:
+ 
+      # clear the file
+      print "Don't panic" > "guide.txt"
+      ...
+      # append
+      print "Avoid improbability generators" >> "guide.txt"
+ 
+ This is indeed how redirections must be used from the shell.  But in
+ `awk', it isn't necessary.  In this kind of case, a program should use
+ `>' for all the `print' statements, since the output file is only
+ opened once. (It happens that if you mix `>' and `>>' that output is
+ produced in the expected order. However, mixing the operators for the
+ same file is definitely poor style, and is confusing to readers of your
+ program.)
+ 
+    Many older `awk' implementations limit the number of pipelines that
+ an `awk' program may have open to just one!  In `gawk', there is no
+ such limit.  `gawk' allows a program to open as many pipelines as the
+ underlying operating system permits.
+ 
+ Advanced Notes: Piping into `sh'
+ --------------------------------
+ 
+ A particularly powerful way to use redirection is to build command lines
+ and pipe them into the shell, `sh'.  For example, suppose you have a
+ list of files brought over from a system where all the file names are
+ stored in uppercase, and you wish to rename them to have names in all
+ lowercase.  The following program is both simple and efficient:
+ 
+      { printf("mv %s %s\n", $0, tolower($0)) | "sh" }
+ 
+      END { close("sh") }
+ 
+    The `tolower()' function returns its argument string with all
+ uppercase characters converted to lowercase (*note String Functions::).
+ The program builds up a list of command lines, using the `mv' utility
+ to rename the files.  It then sends the list to the shell for execution.
+ 
+ 
+ File: gawk.info,  Node: Special Files,  Next: Close Files And Pipes,  Prev: 
Redirection,  Up: Printing
+ 
+ 5.7 Special File Names in `gawk'
+ ================================
+ 
+ `gawk' provides a number of special file names that it interprets
+ internally.  These file names provide access to standard file
+ descriptors and TCP/IP networking.
+ 
+ * Menu:
+ 
+ * Special FD::                  Special files for I/O.
+ * Special Network::             Special files for network communications.
+ * Special Caveats::             Things to watch out for.
+ 
+ 
+ File: gawk.info,  Node: Special FD,  Next: Special Network,  Up: Special Files
+ 
+ 5.7.1 Special Files for Standard Descriptors
+ --------------------------------------------
+ 
+ Running programs conventionally have three input and output streams
+ already available to them for reading and writing.  These are known as
+ the "standard input", "standard output", and "standard error output".
+ These streams are, by default, connected to your keyboard and screen,
+ but they are often redirected with the shell, via the `<', `<<', `>',
+ `>>', `>&', and `|' operators.  Standard error is typically used for
+ writing error messages; the reason there are two separate streams,
+ standard output and standard error, is so that they can be redirected
+ separately.
+ 
+    In other implementations of `awk', the only way to write an error
+ message to standard error in an `awk' program is as follows:
+ 
+      print "Serious error detected!" | "cat 1>&2"
+ 
+ This works by opening a pipeline to a shell command that can access the
+ standard error stream that it inherits from the `awk' process.  This is
+ far from elegant, and it is also inefficient, because it requires a
+ separate process.  So people writing `awk' programs often don't do
+ this.  Instead, they send the error messages to the screen, like this:
+ 
+      print "Serious error detected!" > "/dev/tty"
+ 
+ (`/dev/tty' is a special file supplied by the operating system that is
+ connected to your keyboard and screen. It represents the "terminal,"(1)
+ which on modern systems is a keyboard and screen, not a serial console.)
+ This usually has the same effect but not always: although the standard
+ error stream is usually the screen, it can be redirected; when that
+ happens, writing to the screen is not correct.  In fact, if `awk' is
+ run from a background job, it may not have a terminal at all.  Then
+ opening `/dev/tty' fails.
+ 
+    `gawk' provides special file names for accessing the three standard
+ streams. (c.e.). It also provides syntax for accessing any other
+ inherited open files.  If the file name matches one of these special
+ names when `gawk' redirects input or output, then it directly uses the
+ stream that the file name stands for.  These special file names work
+ for all operating systems that `gawk' has been ported to, not just
+ those that are POSIX-compliant:
+ 
+ `/dev/stdin'
+      The standard input (file descriptor 0).
+ 
+ `/dev/stdout'
+      The standard output (file descriptor 1).
+ 
+ `/dev/stderr'
+      The standard error output (file descriptor 2).
+ 
+ `/dev/fd/N'
+      The file associated with file descriptor N.  Such a file must be
+      opened by the program initiating the `awk' execution (typically
+      the shell).  Unless special pains are taken in the shell from which
+      `gawk' is invoked, only descriptors 0, 1, and 2 are available.
+ 
+    The file names `/dev/stdin', `/dev/stdout', and `/dev/stderr' are
+ aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', respectively.
+ However, they are more self-explanatory.  The proper way to write an
+ error message in a `gawk' program is to use `/dev/stderr', like this:
+ 
+      print "Serious error detected!" > "/dev/stderr"
+ 
+    Note the use of quotes around the file name.  Like any other
+ redirection, the value must be a string.  It is a common error to omit
+ the quotes, which leads to confusing results.
+ 
+    Finally, using the `close()' function on a file name of the form
+ `"/dev/fd/N"', for file descriptor numbers above two, will actually
+ close the given file descriptor.
+ 
+    The `/dev/stdin', `/dev/stdout', and `/dev/stderr' special files are
+ also recognized internally by several other versions of `awk'.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The "tty" in `/dev/tty' stands for "Teletype," a serial terminal.
+ 
+ 
+ File: gawk.info,  Node: Special Network,  Next: Special Caveats,  Prev: 
Special FD,  Up: Special Files
+ 
+ 5.7.2 Special Files for Network Communications
+ ----------------------------------------------
+ 
+ `gawk' programs can open a two-way TCP/IP connection, acting as either
+ a client or a server.  This is done using a special file name of the
+ form:
+ 
+      `/NET-TYPE/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'
+ 
+    The NET-TYPE is one of `inet', `inet4' or `inet6'.  The PROTOCOL is
+ one of `tcp' or `udp', and the other fields represent the other
+ essential pieces of information for making a networking connection.
+ These file names are used with the `|&' operator for communicating with
+ a coprocess (*note Two-way I/O::).  This is an advanced feature,
+ mentioned here only for completeness.  Full discussion is delayed until
+ *note TCP/IP Networking::.
+ 
+ 
+ File: gawk.info,  Node: Special Caveats,  Prev: Special Network,  Up: Special 
Files
+ 
+ 5.7.3 Special File Name Caveats
+ -------------------------------
+ 
+ Here is a list of things to bear in mind when using the special file
+ names that `gawk' provides:
+ 
+    * Recognition of these special file names is disabled if `gawk' is in
+      compatibility mode (*note Options::).
+ 
+    * `gawk' _always_ interprets these special file names.  For example,
+      using `/dev/fd/4' for output actually writes on file descriptor 4,
+      and not on a new file descriptor that is `dup()''ed from file
+      descriptor 4.  Most of the time this does not matter; however, it
+      is important to _not_ close any of the files related to file
+      descriptors 0, 1, and 2.  Doing so results in unpredictable
+      behavior.
+ 
+ 
+ File: gawk.info,  Node: Close Files And Pipes,  Prev: Special Files,  Up: 
Printing
+ 
+ 5.8 Closing Input and Output Redirections
+ =========================================
+ 
+ If the same file name or the same shell command is used with `getline'
+ more than once during the execution of an `awk' program (*note
+ Getline::), the file is opened (or the command is executed) the first
+ time only.  At that time, the first record of input is read from that
+ file or command.  The next time the same file or command is used with
+ `getline', another record is read from it, and so on.
+ 
+    Similarly, when a file or pipe is opened for output, `awk' remembers
+ the file name or command associated with it, and subsequent writes to
+ the same file or command are appended to the previous writes.  The file
+ or pipe stays open until `awk' exits.
+ 
+    This implies that special steps are necessary in order to read the
+ same file again from the beginning, or to rerun a shell command (rather
+ than reading more output from the same command).  The `close()' function
+ makes these things possible:
+ 
+      close(FILENAME)
+ 
+ or:
+ 
+      close(COMMAND)
+ 
+    The argument FILENAME or COMMAND can be any expression.  Its value
+ must _exactly_ match the string that was used to open the file or start
+ the command (spaces and other "irrelevant" characters included). For
+ example, if you open a pipe with this:
+ 
+      "sort -r names" | getline foo
+ 
+ then you must close it with this:
+ 
+      close("sort -r names")
+ 
+    Once this function call is executed, the next `getline' from that
+ file or command, or the next `print' or `printf' to that file or
+ command, reopens the file or reruns the command.  Because the
+ expression that you use to close a file or pipeline must exactly match
+ the expression used to open the file or run the command, it is good
+ practice to use a variable to store the file name or command.  The
+ previous example becomes the following:
+ 
+      sortcom = "sort -r names"
+      sortcom | getline foo
+      ...
+      close(sortcom)
+ 
+ This helps avoid hard-to-find typographical errors in your `awk'
+ programs.  Here are some of the reasons for closing an output file:
+ 
+    * To write a file and read it back later on in the same `awk'
+      program.  Close the file after writing it, then begin reading it
+      with `getline'.
+ 
+    * To write numerous files, successively, in the same `awk' program.
+      If the files aren't closed, eventually `awk' may exceed a system
+      limit on the number of open files in one process.  It is best to
+      close each one when the program has finished writing it.
+ 
+    * To make a command finish.  When output is redirected through a
+      pipe, the command reading the pipe normally continues to try to
+      read input as long as the pipe is open.  Often this means the
+      command cannot really do its work until the pipe is closed.  For
+      example, if output is redirected to the `mail' program, the
+      message is not actually sent until the pipe is closed.
+ 
+    * To run the same program a second time, with the same arguments.
+      This is not the same thing as giving more input to the first run!
+ 
+      For example, suppose a program pipes output to the `mail' program.
+      If it outputs several lines redirected to this pipe without closing
+      it, they make a single message of several lines.  By contrast, if
+      the program closes the pipe after each line of output, then each
+      line makes a separate message.
+ 
+    If you use more files than the system allows you to have open,
+ `gawk' attempts to multiplex the available open files among your data
+ files.  `gawk''s ability to do this depends upon the facilities of your
+ operating system, so it may not always work.  It is therefore both good
+ practice and good portability advice to always use `close()' on your
+ files when you are done with them.  In fact, if you are using a lot of
+ pipes, it is essential that you close commands when done. For example,
+ consider something like this:
+ 
+      {
+          ...
+          command = ("grep " $1 " /some/file | my_prog -q " $3)
+          while ((command | getline) > 0) {
+              PROCESS OUTPUT OF command
+          }
+          # need close(command) here
+      }
+ 
+    This example creates a new pipeline based on data in _each_ record.
+ Without the call to `close()' indicated in the comment, `awk' creates
+ child processes to run the commands, until it eventually runs out of
+ file descriptors for more pipelines.
+ 
+    Even though each command has finished (as indicated by the
+ end-of-file return status from `getline'), the child process is not
+ terminated;(1) more importantly, the file descriptor for the pipe is
+ not closed and released until `close()' is called or `awk' exits.
+ 
+    `close()' will silently do nothing if given an argument that does
+ not represent a file, pipe or coprocess that was opened with a
+ redirection.
+ 
+    Note also that `close(FILENAME)' has no "magic" effects on the
+ implicit loop that reads through the files named on the command line.
+ It is, more likely, a close of a file that was never opened, so `awk'
+ silently does nothing.
+ 
+    When using the `|&' operator to communicate with a coprocess, it is
+ occasionally useful to be able to close one end of the two-way pipe
+ without closing the other.  This is done by supplying a second argument
+ to `close()'.  As in any other call to `close()', the first argument is
+ the name of the command or special file used to start the coprocess.
+ The second argument should be a string, with either of the values
+ `"to"' or `"from"'.  Case does not matter.  As this is an advanced
+ feature, a more complete discussion is delayed until *note Two-way
+ I/O::, which discusses it in more detail and gives an example.
+ 
+ Advanced Notes: Using `close()''s Return Value
+ ----------------------------------------------
+ 
+ In many versions of Unix `awk', the `close()' function is actually a
+ statement.  It is a syntax error to try and use the return value from
+ `close()': (d.c.)
+ 
+      command = "..."
+      command | getline info
+      retval = close(command)  # syntax error in many Unix awks
+ 
+    `gawk' treats `close()' as a function.  The return value is -1 if
+ the argument names something that was never opened with a redirection,
+ or if there is a system problem closing the file or process.  In these
+ cases, `gawk' sets the built-in variable `ERRNO' to a string describing
+ the problem.
+ 
+    In `gawk', when closing a pipe or coprocess (input or output), the
+ return value is the exit status of the command.(2) Otherwise, it is the
+ return value from the system's `close()' or `fclose()' C functions when
+ closing input or output files, respectively.  This value is zero if the
+ close succeeds, or -1 if it fails.
+ 
+    The POSIX standard is very vague; it says that `close()' returns
+ zero on success and nonzero otherwise.  In general, different
+ implementations vary in what they report when closing pipes; thus the
+ return value cannot be used portably.  (d.c.)  In POSIX mode (*note
+ Options::), `gawk' just returns zero when closing a pipe.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The technical terminology is rather morbid.  The finished child
+ is called a "zombie," and cleaning up after it is referred to as
+ "reaping."
+ 
+    (2) This is a full 16-bit value as returned by the `wait()' system
+ call. See the system manual pages for information on how to decode this
+ value.
+ 
+ 
+ File: gawk.info,  Node: Expressions,  Next: Patterns and Actions,  Prev: 
Printing,  Up: Top
+ 
+ 6 Expressions
+ *************
+ 
+ Expressions are the basic building blocks of `awk' patterns and
+ actions.  An expression evaluates to a value that you can print, test,
+ or pass to a function.  Additionally, an expression can assign a new
+ value to a variable or a field by using an assignment operator.
+ 
+    An expression can serve as a pattern or action statement on its own.
+ Most other kinds of statements contain one or more expressions that
+ specify the data on which to operate.  As in other languages,
+ expressions in `awk' include variables, array references, constants,
+ and function calls, as well as combinations of these with various
+ operators.
+ 
+ * Menu:
+ 
+ * Values::                      Constants, Variables, and Regular Expressions.
+ * All Operators::               `gawk''s operators.
+ * Truth Values and Conditions:: Testing for true and false.
+ * Function Calls::              A function call is an expression.
+ * Precedence::                  How various operators nest.
+ * Locales::                     How the locale affects things.
+ 
+ 
+ File: gawk.info,  Node: Values,  Next: All Operators,  Up: Expressions
+ 
+ 6.1 Constants, Variables and Conversions
+ ========================================
+ 
+ Expressions are built up from values and the operations performed upon
+ them. This minor node describes the elementary objects which provide
+ the values used in expressions.
+ 
+ * Menu:
+ 
+ * Constants::                   String, numeric and regexp constants.
+ * Using Constant Regexps::      When and how to use a regexp constant.
+ * Variables::                   Variables give names to values for later use.
+ * Conversion::                  The conversion of strings to numbers and vice
+                                 versa.
+ 
+ 
+ File: gawk.info,  Node: Constants,  Next: Using Constant Regexps,  Up: Values
+ 
+ 6.1.1 Constant Expressions
+ --------------------------
+ 
+ The simplest type of expression is the "constant", which always has the
+ same value.  There are three types of constants: numeric, string, and
+ regular expression.
+ 
+    Each is used in the appropriate context when you need a data value
+ that isn't going to change.  Numeric constants can have different
+ forms, but are stored identically internally.
+ 
+ * Menu:
+ 
+ * Scalar Constants::            Numeric and string constants.
+ * Nondecimal-numbers::          What are octal and hex numbers.
+ * Regexp Constants::            Regular Expression constants.
+ 
+ 
+ File: gawk.info,  Node: Scalar Constants,  Next: Nondecimal-numbers,  Up: 
Constants
+ 
+ 6.1.1.1 Numeric and String Constants
+ ....................................
+ 
+ A "numeric constant" stands for a number.  This number can be an
+ integer, a decimal fraction, or a number in scientific (exponential)
+ notation.(1) Here are some examples of numeric constants that all have
+ the same value:
+ 
+      105
+      1.05e+2
+      1050e-1
+ 
+    A string constant consists of a sequence of characters enclosed in
+ double-quotation marks.  For example:
+ 
+      "parrot"
+ 
+ represents the string whose contents are `parrot'.  Strings in `gawk'
+ can be of any length, and they can contain any of the possible
+ eight-bit ASCII characters including ASCII NUL (character code zero).
+ Other `awk' implementations may have difficulty with some character
+ codes.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The internal representation of all numbers, including integers,
+ uses double precision floating-point numbers.  On most modern systems,
+ these are in IEEE 754 standard format.
+ 
+ 
+ File: gawk.info,  Node: Nondecimal-numbers,  Next: Regexp Constants,  Prev: 
Scalar Constants,  Up: Constants
+ 
+ 6.1.1.2 Octal and Hexadecimal Numbers
+ .....................................
+ 
+ In `awk', all numbers are in decimal; i.e., base 10.  Many other
+ programming languages allow you to specify numbers in other bases, often
+ octal (base 8) and hexadecimal (base 16).  In octal, the numbers go 0,
+ 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, etc.  Just as `11', in decimal, is 1
+ times 10 plus 1, so `11', in octal, is 1 times 8, plus 1. This equals 9
+ in decimal.  In hexadecimal, there are 16 digits. Since the everyday
+ decimal number system only has ten digits (`0'-`9'), the letters `a'
+ through `f' are used to represent the rest.  (Case in the letters is
+ usually irrelevant; hexadecimal `a' and `A' have the same value.)
+ Thus, `11', in hexadecimal, is 1 times 16 plus 1, which equals 17 in
+ decimal.
+ 
+    Just by looking at plain `11', you can't tell what base it's in.
+ So, in C, C++, and other languages derived from C, there is a special
+ notation to signify the base.  Octal numbers start with a leading `0',
+ and hexadecimal numbers start with a leading `0x' or `0X':
+ 
+ `11'
+      Decimal value 11.
+ 
+ `011'
+      Octal 11, decimal value 9.
+ 
+ `0x11'
+      Hexadecimal 11, decimal value 17.
+ 
+    This example shows the difference:
+ 
+      $ gawk 'BEGIN { printf "%d, %d, %d\n", 011, 11, 0x11 }'
+      -| 9, 11, 17
+ 
+    Being able to use octal and hexadecimal constants in your programs
+ is most useful when working with data that cannot be represented
+ conveniently as characters or as regular numbers, such as binary data
+ of various sorts.
+ 
+    `gawk' allows the use of octal and hexadecimal constants in your
+ program text.  However, such numbers in the input data are not treated
+ differently; doing so by default would break old programs.  (If you
+ really need to do this, use the `--non-decimal-data' command-line
+ option; *note Nondecimal Data::.)  If you have octal or hexadecimal
+ data, you can use the `strtonum()' function (*note String Functions::)
+ to convert the data into a number.  Most of the time, you will want to
+ use octal or hexadecimal constants when working with the built-in bit
+ manipulation functions; see *note Bitwise Functions::, for more
+ information.
+ 
+    Unlike some early C implementations, `8' and `9' are not valid in
+ octal constants; e.g., `gawk' treats `018' as decimal 18:
+ 
+      $ gawk 'BEGIN { print "021 is", 021 ; print 018 }'
+      -| 021 is 17
+      -| 18
+ 
+    Octal and hexadecimal source code constants are a `gawk' extension.
+ If `gawk' is in compatibility mode (*note Options::), they are not
+ available.
+ 
+ Advanced Notes: A Constant's Base Does Not Affect Its Value
+ -----------------------------------------------------------
+ 
+ Once a numeric constant has been converted internally into a number,
+ `gawk' no longer remembers what the original form of the constant was;
+ the internal value is always used.  This has particular consequences
+ for conversion of numbers to strings:
+ 
+      $ gawk 'BEGIN { printf "0x11 is <%s>\n", 0x11 }'
+      -| 0x11 is <17>
+ 
+ 
+ File: gawk.info,  Node: Regexp Constants,  Prev: Nondecimal-numbers,  Up: 
Constants
+ 
+ 6.1.1.3 Regular Expression Constants
+ ....................................
+ 
+ A regexp constant is a regular expression description enclosed in
+ slashes, such as `/^beginning and end$/'.  Most regexps used in `awk'
+ programs are constant, but the `~' and `!~' matching operators can also
+ match computed or dynamic regexps (which are just ordinary strings or
+ variables that contain a regexp).
+ 
+ 
+ File: gawk.info,  Node: Using Constant Regexps,  Next: Variables,  Prev: 
Constants,  Up: Values
+ 
+ 6.1.2 Using Regular Expression Constants
+ ----------------------------------------
+ 
+ When used on the righthand side of the `~' or `!~' operators, a regexp
+ constant merely stands for the regexp that is to be matched.  However,
+ regexp constants (such as `/foo/') may be used like simple expressions.
+ When a regexp constant appears by itself, it has the same meaning as if
+ it appeared in a pattern, i.e., `($0 ~ /foo/)' (d.c.)  *Note Expression
+ Patterns::.  This means that the following two code segments:
+ 
+      if ($0 ~ /barfly/ || $0 ~ /camelot/)
+          print "found"
+ 
+ and:
+ 
+      if (/barfly/ || /camelot/)
+          print "found"
+ 
+ are exactly equivalent.  One rather bizarre consequence of this rule is
+ that the following Boolean expression is valid, but does not do what
+ the user probably intended:
+ 
+      # Note that /foo/ is on the left of the ~
+      if (/foo/ ~ $1) print "found foo"
+ 
+ This code is "obviously" testing `$1' for a match against the regexp
+ `/foo/'.  But in fact, the expression `/foo/ ~ $1' really means `($0 ~
+ /foo/) ~ $1'.  In other words, first match the input record against the
+ regexp `/foo/'.  The result is either zero or one, depending upon the
+ success or failure of the match.  That result is then matched against
+ the first field in the record.  Because it is unlikely that you would
+ ever really want to make this kind of test, `gawk' issues a warning
+ when it sees this construct in a program.  Another consequence of this
+ rule is that the assignment statement:
+ 
+      matches = /foo/
+ 
+ assigns either zero or one to the variable `matches', depending upon
+ the contents of the current input record.
+ 
+    Constant regular expressions are also used as the first argument for
+ the `gensub()', `sub()', and `gsub()' functions, as the second argument
+ of the `match()' function, and as the third argument of the
+ `patsplit()' function (*note String Functions::).  Modern
+ implementations of `awk', including `gawk', allow the third argument of
+ `split()' to be a regexp constant, but some older implementations do
+ not.  (d.c.)  This can lead to confusion when attempting to use regexp
+ constants as arguments to user-defined functions (*note User-defined::).
+ For example:
+ 
+      function mysub(pat, repl, str, global)
+      {
+          if (global)
+              gsub(pat, repl, str)
+          else
+              sub(pat, repl, str)
+          return str
+      }
+ 
+      {
+          ...
+          text = "hi! hi yourself!"
+          mysub(/hi/, "howdy", text, 1)
+          ...
+      }
+ 
+    In this example, the programmer wants to pass a regexp constant to
+ the user-defined function `mysub', which in turn passes it on to either
+ `sub()' or `gsub()'.  However, what really happens is that the `pat'
+ parameter is either one or zero, depending upon whether or not `$0'
+ matches `/hi/'.  `gawk' issues a warning when it sees a regexp constant
+ used as a parameter to a user-defined function, since passing a truth
+ value in this way is probably not what was intended.
+ 
+ 
+ File: gawk.info,  Node: Variables,  Next: Conversion,  Prev: Using Constant 
Regexps,  Up: Values
+ 
+ 6.1.3 Variables
+ ---------------
+ 
+ Variables are ways of storing values at one point in your program for
+ use later in another part of your program.  They can be manipulated
+ entirely within the program text, and they can also be assigned values
+ on the `awk' command line.
+ 
+ * Menu:
+ 
+ * Using Variables::             Using variables in your programs.
+ * Assignment Options::          Setting variables on the command-line and a
+                                 summary of command-line syntax. This is an
+                                 advanced method of input.
+ 
+ 
+ File: gawk.info,  Node: Using Variables,  Next: Assignment Options,  Up: 
Variables
+ 
+ 6.1.3.1 Using Variables in a Program
+ ....................................
+ 
+ Variables let you give names to values and refer to them later.
+ Variables have already been used in many of the examples.  The name of
+ a variable must be a sequence of letters, digits, or underscores, and
+ it may not begin with a digit.  Case is significant in variable names;
+ `a' and `A' are distinct variables.
+ 
+    A variable name is a valid expression by itself; it represents the
+ variable's current value.  Variables are given new values with
+ "assignment operators", "increment operators", and "decrement
+ operators".  *Note Assignment Ops::.  In addition, the `sub()' and
+ `gsub()' functions can change a variable's value, and the `match()',
+ `patsplit()' and `split()' functions can change the contents of their
+ array parameters. *Note String Functions::.
+ 
+    A few variables have special built-in meanings, such as `FS' (the
+ field separator), and `NF' (the number of fields in the current input
+ record).  *Note Built-in Variables::, for a list of the built-in
+ variables.  These built-in variables can be used and assigned just like
+ all other variables, but their values are also used or changed
+ automatically by `awk'.  All built-in variables' names are entirely
+ uppercase.
+ 
+    Variables in `awk' can be assigned either numeric or string values.
+ The kind of value a variable holds can change over the life of a
+ program.  By default, variables are initialized to the empty string,
+ which is zero if converted to a number.  There is no need to explicitly
+ "initialize" a variable in `awk', which is what you would do in C and
+ in most other traditional languages.
+ 
+ 
+ File: gawk.info,  Node: Assignment Options,  Prev: Using Variables,  Up: 
Variables
+ 
+ 6.1.3.2 Assigning Variables on the Command Line
+ ...............................................
+ 
+ Any `awk' variable can be set by including a "variable assignment"
+ among the arguments on the command line when `awk' is invoked (*note
+ Other Arguments::).  Such an assignment has the following form:
+ 
+      VARIABLE=TEXT
+ 
+ With it, a variable is set either at the beginning of the `awk' run or
+ in between input files.  When the assignment is preceded with the `-v'
+ option, as in the following:
+ 
+      -v VARIABLE=TEXT
+ 
+ the variable is set at the very beginning, even before the `BEGIN'
+ rules execute.  The `-v' option and its assignment must precede all the
+ file name arguments, as well as the program text.  (*Note Options::,
+ for more information about the `-v' option.)  Otherwise, the variable
+ assignment is performed at a time determined by its position among the
+ input file arguments--after the processing of the preceding input file
+ argument.  For example:
+ 
+      awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list
+ 
+ prints the value of field number `n' for all input records.  Before the
+ first file is read, the command line sets the variable `n' equal to
+ four.  This causes the fourth field to be printed in lines from
+ `inventory-shipped'.  After the first file has finished, but before the
+ second file is started, `n' is set to two, so that the second field is
+ printed in lines from `BBS-list':
+ 
+      $ awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list
+      -| 15
+      -| 24
+      ...
+      -| 555-5553
+      -| 555-3412
+      ...
+ 
+    Command-line arguments are made available for explicit examination by
+ the `awk' program in the `ARGV' array (*note ARGC and ARGV::).  `awk'
+ processes the values of command-line assignments for escape sequences
+ (*note Escape Sequences::).  (d.c.)
+ 
+ 
+ File: gawk.info,  Node: Conversion,  Prev: Variables,  Up: Values
+ 
+ 6.1.4 Conversion of Strings and Numbers
+ ---------------------------------------
+ 
+ Strings are converted to numbers and numbers are converted to strings,
+ if the context of the `awk' program demands it.  For example, if the
+ value of either `foo' or `bar' in the expression `foo + bar' happens to
+ be a string, it is converted to a number before the addition is
+ performed.  If numeric values appear in string concatenation, they are
+ converted to strings.  Consider the following:
+ 
+      two = 2; three = 3
+      print (two three) + 4
+ 
+ This prints the (numeric) value 27.  The numeric values of the
+ variables `two' and `three' are converted to strings and concatenated
+ together.  The resulting string is converted back to the number 23, to
+ which 4 is then added.
+ 
+    If, for some reason, you need to force a number to be converted to a
+ string, concatenate that number with the empty string, `""'.  To force
+ a string to be converted to a number, add zero to that string.  A
+ string is converted to a number by interpreting any numeric prefix of
+ the string as numerals: `"2.5"' converts to 2.5, `"1e3"' converts to
+ 1000, and `"25fix"' has a numeric value of 25.  Strings that can't be
+ interpreted as valid numbers convert to zero.
+ 
+    The exact manner in which numbers are converted into strings is
+ controlled by the `awk' built-in variable `CONVFMT' (*note Built-in
+ Variables::).  Numbers are converted using the `sprintf()' function
+ with `CONVFMT' as the format specifier (*note String Functions::).
+ 
+    `CONVFMT''s default value is `"%.6g"', which prints a value with at
+ most six significant digits.  For some applications, you might want to
+ change it to specify more precision.  On most modern machines, 17
+ digits is usually enough to capture a floating-point number's value
+ exactly.(1)
+ 
+    Strange results can occur if you set `CONVFMT' to a string that
+ doesn't tell `sprintf()' how to format floating-point numbers in a
+ useful way.  For example, if you forget the `%' in the format, `awk'
+ converts all numbers to the same constant string.
+ 
+    As a special case, if a number is an integer, then the result of
+ converting it to a string is _always_ an integer, no matter what the
+ value of `CONVFMT' may be.  Given the following code fragment:
+ 
+      CONVFMT = "%2.2f"
+      a = 12
+      b = a ""
+ 
+ `b' has the value `"12"', not `"12.00"'.  (d.c.)
+ 
+    Prior to the POSIX standard, `awk' used the value of `OFMT' for
+ converting numbers to strings.  `OFMT' specifies the output format to
+ use when printing numbers with `print'.  `CONVFMT' was introduced in
+ order to separate the semantics of conversion from the semantics of
+ printing.  Both `CONVFMT' and `OFMT' have the same default value:
+ `"%.6g"'.  In the vast majority of cases, old `awk' programs do not
+ change their behavior.  However, these semantics for `OFMT' are
+ something to keep in mind if you must port your new-style program to
+ older implementations of `awk'.  We recommend that instead of changing
+ your programs, just port `gawk' itself.  *Note Print::, for more
+ information on the `print' statement.
+ 
+    And, once again, where you are can matter when it comes to converting
+ between numbers and strings.  In *note Locales::, we mentioned that the
+ local character set and language (the locale) can affect how `gawk'
+ matches characters.  The locale also affects numeric formats.  In
+ particular, for `awk' programs, it affects the decimal point character.
+ The `"C"' locale, and most English-language locales, use the period
+ character (`.') as the decimal point.  However, many (if not most)
+ European and non-English locales use the comma (`,') as the decimal
+ point character.
+ 
+    The POSIX standard says that `awk' always uses the period as the
+ decimal point when reading the `awk' program source code, and for
+ command-line variable assignments (*note Other Arguments::).  However,
+ when interpreting input data, for `print' and `printf' output, and for
+ number to string conversion, the local decimal point character is used.
+ Here are some examples indicating the difference in behavior, on a
+ GNU/Linux system:
+ 
+      $ gawk 'BEGIN { printf "%g\n", 3.1415927 }'
+      -| 3.14159
+      $ LC_ALL=en_DK gawk 'BEGIN { printf "%g\n", 3.1415927 }'
+      -| 3,14159
+      $ echo 4,321 | gawk '{ print $1 + 1 }'
+      -| 5
+      $ echo 4,321 | LC_ALL=en_DK gawk '{ print $1 + 1 }'
+      -| 5,321
+ 
+ The `en_DK' locale is for English in Denmark, where the comma acts as
+ the decimal point separator.  In the normal `"C"' locale, `gawk' treats
+ `4,321' as `4', while in the Danish locale, it's treated as the full
+ number, 4.321.
+ 
+    Some earlier versions of `gawk' fully complied with this aspect of
+ the standard.  However, many users in non-English locales complained
+ about this behavior, since their data used a period as the decimal
+ point, so the default behavior was restored to use a period as the
+ decimal point character.  You can use the `--use-lc-numeric' option
+ (*note Options::) to force `gawk' to use the locale's decimal point
+ character.  (`gawk' also uses the locale's decimal point character when
+ in POSIX mode, either via `--posix', or the `POSIXLY_CORRECT'
+ environment variable.)
+ 
+    *note table-locale-affects:: describes the cases in which the
+ locale's decimal point character is used and when a period is used.
+ Some of these features have not been described yet.
+ 
+ Feature     Default        `--posix' or `--use-lc-numeric'
+ ------------------------------------------------------------ 
+ `%'g'       Use locale     Use locale
+ `%g'        Use period     Use locale
+ Input       Use period     Use locale
+ `strtonum()'Use period     Use locale
+ 
+ Table 6.1: Locale Decimal Point versus A Period
+ 
+    Finally, modern day formal standards and IEEE standard floating point
+ representation can have an unusual but important effect on the way
+ `gawk' converts some special string values to numbers.  The details are
+ presented in *note POSIX Floating Point Problems::.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Pathological cases can require up to 752 digits (!), but we
+ doubt that you need to worry about this.
+ 
+ 
+ File: gawk.info,  Node: All Operators,  Next: Truth Values and Conditions,  
Prev: Values,  Up: Expressions
+ 
+ 6.2 Operators: Doing Something With Values
+ ==========================================
+ 
+ This minor node introduces the "operators" which make use of the values
+ provided by constants and variables.
+ 
+ * Menu:
+ 
+ * Arithmetic Ops::              Arithmetic operations (`+', `-',
+                                 etc.)
+ * Concatenation::               Concatenating strings.
+ * Assignment Ops::              Changing the value of a variable or a field.
+ * Increment Ops::               Incrementing the numeric value of a variable.
+ 
+ 
+ File: gawk.info,  Node: Arithmetic Ops,  Next: Concatenation,  Up: All 
Operators
+ 
+ 6.2.1 Arithmetic Operators
+ --------------------------
+ 
+ The `awk' language uses the common arithmetic operators when evaluating
+ expressions.  All of these arithmetic operators follow normal
+ precedence rules and work as you would expect them to.
+ 
+    The following example uses a file named `grades', which contains a
+ list of student names as well as three test scores per student (it's a
+ small class):
+ 
+      Pat   100 97 58
+      Sandy  84 72 93
+      Chris  72 92 89
+ 
+ This program takes the file `grades' and prints the average of the
+ scores:
+ 
+      $ awk '{ sum = $2 + $3 + $4 ; avg = sum / 3
+      >        print $1, avg }' grades
+      -| Pat 85
+      -| Sandy 83
+      -| Chris 84.3333
+ 
+    The following list provides the arithmetic operators in `awk', in
+ order from the highest precedence to the lowest:
+ 
+ `- X'
+      Negation.
+ 
+ `+ X'
+      Unary plus; the expression is converted to a number.
+ 
+ `X ^ Y'
+ `X ** Y'
+      Exponentiation; X raised to the Y power.  `2 ^ 3' has the value
+      eight; the character sequence `**' is equivalent to `^'. (c.e.)
+ 
+ `X * Y'
+      Multiplication.
+ 
+ `X / Y'
+      Division;  because all numbers in `awk' are floating-point
+      numbers, the result is _not_ rounded to an integer--`3 / 4' has
+      the value 0.75.  (It is a common mistake, especially for C
+      programmers, to forget that _all_ numbers in `awk' are
+      floating-point, and that division of integer-looking constants
+      produces a real number, not an integer.)
+ 
+ `X % Y'
+      Remainder; further discussion is provided in the text, just after
+      this list.
+ 
+ `X + Y'
+      Addition.
+ 
+ `X - Y'
+      Subtraction.
+ 
+    Unary plus and minus have the same precedence, the multiplication
+ operators all have the same precedence, and addition and subtraction
+ have the same precedence.
+ 
+    When computing the remainder of `X % Y', the quotient is rounded
+ toward zero to an integer and multiplied by Y. This result is
+ subtracted from X; this operation is sometimes known as "trunc-mod."
+ The following relation always holds:
+ 
+      b * int(a / b) + (a % b) == a
+ 
+    One possibly undesirable effect of this definition of remainder is
+ that `X % Y' is negative if X is negative.  Thus:
+ 
+      -17 % 8 = -1
+ 
+    In other `awk' implementations, the signedness of the remainder may
+ be machine-dependent.
+ 
+      NOTE: The POSIX standard only specifies the use of `^' for
+      exponentiation.  For maximum portability, do not use the `**'
+      operator.
+ 
+ 
+ File: gawk.info,  Node: Concatenation,  Next: Assignment Ops,  Prev: 
Arithmetic Ops,  Up: All Operators
+ 
+ 6.2.2 String Concatenation
+ --------------------------
+ 
+      It seemed like a good idea at the time.
+      Brian Kernighan
+ 
+    There is only one string operation: concatenation.  It does not have
+ a specific operator to represent it.  Instead, concatenation is
+ performed by writing expressions next to one another, with no operator.
+ For example:
+ 
+      $ awk '{ print "Field number one: " $1 }' BBS-list
+      -| Field number one: aardvark
+      -| Field number one: alpo-net
+      ...
+ 
+    Without the space in the string constant after the `:', the line
+ runs together.  For example:
+ 
+      $ awk '{ print "Field number one:" $1 }' BBS-list
+      -| Field number one:aardvark
+      -| Field number one:alpo-net
+      ...
+ 
+    Because string concatenation does not have an explicit operator, it
+ is often necessary to insure that it happens at the right time by using
+ parentheses to enclose the items to concatenate.  For example, you
+ might expect that the following code fragment concatenates `file' and
+ `name':
+ 
+      file = "file"
+      name = "name"
+      print "something meaningful" > file name
+ 
+ This produces a syntax error with some versions of Unix `awk'.(1) It is
+ necessary to use the following:
+ 
+      print "something meaningful" > (file name)
+ 
+    Parentheses should be used around concatenation in all but the most
+ common contexts, such as on the righthand side of `='.  Be careful
+ about the kinds of expressions used in string concatenation.  In
+ particular, the order of evaluation of expressions used for
+ concatenation is undefined in the `awk' language.  Consider this
+ example:
+ 
+      BEGIN {
+          a = "don't"
+          print (a " " (a = "panic"))
+      }
+ 
+ It is not defined whether the assignment to `a' happens before or after
+ the value of `a' is retrieved for producing the concatenated value.
+ The result could be either `don't panic', or `panic panic'.
+ 
+    The precedence of concatenation, when mixed with other operators, is
+ often counter-intuitive.  Consider this example:
+ 
+      $ awk 'BEGIN { print -12 " " -24 }'
+      -| -12-24
+ 
+    This "obviously" is concatenating -12, a space, and -24.  But where
+ did the space disappear to?  The answer lies in the combination of
+ operator precedences and `awk''s automatic conversion rules.  To get
+ the desired result, write the program this way:
+ 
+      $ awk 'BEGIN { print -12 " " (-24) }'
+      -| -12 -24
+ 
+    This forces `awk' to treat the `-' on the `-24' as unary.
+ Otherwise, it's parsed as follows:
+ 
+          -12 (`" "' - 24)
+      => -12 (0 - 24)
+      => -12 (-24)
+      => -12-24
+ 
+    As mentioned earlier, when doing concatenation, _parenthesize_.
+ Otherwise, you're never quite sure what you'll get.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) It happens that Brian Kernighan's `awk', `gawk' and `mawk' all
+ "get it right," but you should not rely on this.
+ 
+ 
+ File: gawk.info,  Node: Assignment Ops,  Next: Increment Ops,  Prev: 
Concatenation,  Up: All Operators
+ 
+ 6.2.3 Assignment Expressions
+ ----------------------------
+ 
+ An "assignment" is an expression that stores a (usually different)
+ value into a variable.  For example, let's assign the value one to the
+ variable `z':
+ 
+      z = 1
+ 
+    After this expression is executed, the variable `z' has the value
+ one.  Whatever old value `z' had before the assignment is forgotten.
+ 
+    Assignments can also store string values.  For example, the
+ following stores the value `"this food is good"' in the variable
+ `message':
+ 
+      thing = "food"
+      predicate = "good"
+      message = "this " thing " is " predicate
+ 
+ This also illustrates string concatenation.  The `=' sign is called an
+ "assignment operator".  It is the simplest assignment operator because
+ the value of the righthand operand is stored unchanged.  Most operators
+ (addition, concatenation, and so on) have no effect except to compute a
+ value.  If the value isn't used, there's no reason to use the operator.
+ An assignment operator is different; it does produce a value, but even
+ if you ignore it, the assignment still makes itself felt through the
+ alteration of the variable.  We call this a "side effect".
+ 
+    The lefthand operand of an assignment need not be a variable (*note
+ Variables::); it can also be a field (*note Changing Fields::) or an
+ array element (*note Arrays::).  These are all called "lvalues", which
+ means they can appear on the lefthand side of an assignment operator.
+ The righthand operand may be any expression; it produces the new value
+ that the assignment stores in the specified variable, field, or array
+ element. (Such values are called "rvalues".)
+ 
+    It is important to note that variables do _not_ have permanent types.
+ A variable's type is simply the type of whatever value it happens to
+ hold at the moment.  In the following program fragment, the variable
+ `foo' has a numeric value at first, and a string value later on:
+ 
+      foo = 1
+      print foo
+      foo = "bar"
+      print foo
+ 
+ When the second assignment gives `foo' a string value, the fact that it
+ previously had a numeric value is forgotten.
+ 
+    String values that do not begin with a digit have a numeric value of
+ zero. After executing the following code, the value of `foo' is five:
+ 
+      foo = "a string"
+      foo = foo + 5
+ 
+      NOTE: Using a variable as a number and then later as a string can
+      be confusing and is poor programming style.  The previous two
+      examples illustrate how `awk' works, _not_ how you should write
+      your programs!
+ 
+    An assignment is an expression, so it has a value--the same value
+ that is assigned.  Thus, `z = 1' is an expression with the value one.
+ One consequence of this is that you can write multiple assignments
+ together, such as:
+ 
+      x = y = z = 5
+ 
+ This example stores the value five in all three variables (`x', `y',
+ and `z').  It does so because the value of `z = 5', which is five, is
+ stored into `y' and then the value of `y = z = 5', which is five, is
+ stored into `x'.
+ 
+    Assignments may be used anywhere an expression is called for.  For
+ example, it is valid to write `x != (y = 1)' to set `y' to one, and
+ then test whether `x' equals one.  But this style tends to make
+ programs hard to read; such nesting of assignments should be avoided,
+ except perhaps in a one-shot program.
+ 
+    Aside from `=', there are several other assignment operators that do
+ arithmetic with the old value of the variable.  For example, the
+ operator `+=' computes a new value by adding the righthand value to the
+ old value of the variable.  Thus, the following assignment adds five to
+ the value of `foo':
+ 
+      foo += 5
+ 
+ This is equivalent to the following:
+ 
+      foo = foo + 5
+ 
+ Use whichever makes the meaning of your program clearer.
+ 
+    There are situations where using `+=' (or any assignment operator)
+ is _not_ the same as simply repeating the lefthand operand in the
+ righthand expression.  For example:
+ 
+      # Thanks to Pat Rankin for this example
+      BEGIN  {
+          foo[rand()] += 5
+          for (x in foo)
+             print x, foo[x]
+ 
+          bar[rand()] = bar[rand()] + 5
+          for (x in bar)
+             print x, bar[x]
+      }
+ 
+ The indices of `bar' are practically guaranteed to be different, because
+ `rand()' returns different values each time it is called.  (Arrays and
+ the `rand()' function haven't been covered yet.  *Note Arrays::, and
+ see *note Numeric Functions::, for more information).  This example
+ illustrates an important fact about assignment operators: the lefthand
+ expression is only evaluated _once_.  It is up to the implementation as
+ to which expression is evaluated first, the lefthand or the righthand.
+ Consider this example:
+ 
+      i = 1
+      a[i += 2] = i + 1
+ 
+ The value of `a[3]' could be either two or four.
+ 
+    *note table-assign-ops:: lists the arithmetic assignment operators.
+ In each case, the righthand operand is an expression whose value is
+ converted to a number.
+ 
+ Operator               Effect
+ -------------------------------------------------------------------------- 
+ LVALUE `+=' INCREMENT  Adds INCREMENT to the value of LVALUE.
+ LVALUE `-=' DECREMENT  Subtracts DECREMENT from the value of LVALUE.
+ LVALUE `*='            Multiplies the value of LVALUE by COEFFICIENT.
+ COEFFICIENT            
+ LVALUE `/=' DIVISOR    Divides the value of LVALUE by DIVISOR.
+ LVALUE `%=' MODULUS    Sets LVALUE to its remainder by MODULUS.
+ LVALUE `^=' POWER      
+ LVALUE `**=' POWER     Raises LVALUE to the power POWER. (c.e.)
+ 
+ Table 6.2: Arithmetic Assignment Operators
+ 
+      NOTE: Only the `^=' operator is specified by POSIX.  For maximum
+      portability, do not use the `**=' operator.
+ 
+ Advanced Notes: Syntactic Ambiguities Between `/=' and Regular Expressions
+ --------------------------------------------------------------------------
+ 
+ There is a syntactic ambiguity between the `/=' assignment operator and
+ regexp constants whose first character is an `='.  (d.c.)  This is most
+ notable in commercial `awk' versions.  For example:
+ 
+      $ awk /==/ /dev/null
+      error--> awk: syntax error at source line 1
+      error-->  context is
+      error-->         >>> /= <<<
+      error--> awk: bailing out at source line 1
+ 
+ A workaround is:
+ 
+      awk '/[=]=/' /dev/null
+ 
+    `gawk' does not have this problem, nor do the other freely available
+ versions described in *note Other Versions::.
+ 
+ 
+ File: gawk.info,  Node: Increment Ops,  Prev: Assignment Ops,  Up: All 
Operators
+ 
+ 6.2.4 Increment and Decrement Operators
+ ---------------------------------------
+ 
+ "Increment" and "decrement operators" increase or decrease the value of
+ a variable by one.  An assignment operator can do the same thing, so
+ the increment operators add no power to the `awk' language; however,
+ they are convenient abbreviations for very common operations.
+ 
+    The operator used for adding one is written `++'.  It can be used to
+ increment a variable either before or after taking its value.  To
+ pre-increment a variable `v', write `++v'.  This adds one to the value
+ of `v'--that new value is also the value of the expression. (The
+ assignment expression `v += 1' is completely equivalent.)  Writing the
+ `++' after the variable specifies post-increment.  This increments the
+ variable value just the same; the difference is that the value of the
+ increment expression itself is the variable's _old_ value.  Thus, if
+ `foo' has the value four, then the expression `foo++' has the value
+ four, but it changes the value of `foo' to five.  In other words, the
+ operator returns the old value of the variable, but with the side
+ effect of incrementing it.
+ 
+    The post-increment `foo++' is nearly the same as writing `(foo += 1)
+ - 1'.  It is not perfectly equivalent because all numbers in `awk' are
+ floating-point--in floating-point, `foo + 1 - 1' does not necessarily
+ equal `foo'.  But the difference is minute as long as you stick to
+ numbers that are fairly small (less than 10e12).
+ 
+    Fields and array elements are incremented just like variables.  (Use
+ `$(i++)' when you want to do a field reference and a variable increment
+ at the same time.  The parentheses are necessary because of the
+ precedence of the field reference operator `$'.)
+ 
+    The decrement operator `--' works just like `++', except that it
+ subtracts one instead of adding it.  As with `++', it can be used before
+ the lvalue to pre-decrement or after it to post-decrement.  Following
+ is a summary of increment and decrement expressions:
+ 
+ `++LVALUE'
+      Increment LVALUE, returning the new value as the value of the
+      expression.
+ 
+ `LVALUE++'
+      Increment LVALUE, returning the _old_ value of LVALUE as the value
+      of the expression.
+ 
+ `--LVALUE'
+      Decrement LVALUE, returning the new value as the value of the
+      expression.  (This expression is like `++LVALUE', but instead of
+      adding, it subtracts.)
+ 
+ `LVALUE--'
+      Decrement LVALUE, returning the _old_ value of LVALUE as the value
+      of the expression.  (This expression is like `LVALUE++', but
+      instead of adding, it subtracts.)
+ 
+ Advanced Notes: Operator Evaluation Order
+ -----------------------------------------
+ 
+      Doctor, doctor!  It hurts when I do this!
+      So don't do that!
+      Groucho Marx
+ 
+ What happens for something like the following?
+ 
+      b = 6
+      print b += b++
+ 
+ Or something even stranger?
+ 
+      b = 6
+      b += ++b + b++
+      print b
+ 
+    In other words, when do the various side effects prescribed by the
+ postfix operators (`b++') take effect?  When side effects happen is
+ "implementation defined".  In other words, it is up to the particular
+ version of `awk'.  The result for the first example may be 12 or 13,
+ and for the second, it may be 22 or 23.
+ 
+    In short, doing things like this is not recommended and definitely
+ not anything that you can rely upon for portability.  You should avoid
+ such things in your own programs.
+ 
+ 
+ File: gawk.info,  Node: Truth Values and Conditions,  Next: Function Calls,  
Prev: All Operators,  Up: Expressions
+ 
+ 6.3 Truth Values and Conditions
+ ===============================
+ 
+ In certain contexts, expression values also serve as "truth values;"
+ i.e., they determine what should happen next as the program runs. This
+ minor node describes how `awk' defines "true" and "false" and how
+ values are compared.
+ 
+ * Menu:
+ 
+ * Truth Values::                What is ``true'' and what is ``false''.
+ * Typing and Comparison::       How variables acquire types and how this
+                                 affects comparison of numbers and strings with
+                                 `<', etc.
+ * Boolean Ops::                 Combining comparison expressions using boolean
+                                 operators `||' (``or''), `&&'
+                                 (``and'') and `!' (``not'').
+ * Conditional Exp::             Conditional expressions select between two
+                                 subexpressions under control of a third
+                                 subexpression.
+ 
+ 
+ File: gawk.info,  Node: Truth Values,  Next: Typing and Comparison,  Up: 
Truth Values and Conditions
+ 
+ 6.3.1 True and False in `awk'
+ -----------------------------
+ 
+ Many programming languages have a special representation for the
+ concepts of "true" and "false."  Such languages usually use the special
+ constants `true' and `false', or perhaps their uppercase equivalents.
+ However, `awk' is different.  It borrows a very simple concept of true
+ and false from C.  In `awk', any nonzero numeric value _or_ any
+ nonempty string value is true.  Any other value (zero or the null
+ string, `""') is false.  The following program prints `A strange truth
+ value' three times:
+ 
+      BEGIN {
+         if (3.1415927)
+             print "A strange truth value"
+         if ("Four Score And Seven Years Ago")
+             print "A strange truth value"
+         if (j = 57)
+             print "A strange truth value"
+      }
+ 
+    There is a surprising consequence of the "nonzero or non-null" rule:
+ the string constant `"0"' is actually true, because it is non-null.
+ (d.c.)
+ 
+ 
+ File: gawk.info,  Node: Typing and Comparison,  Next: Boolean Ops,  Prev: 
Truth Values,  Up: Truth Values and Conditions
+ 
+ 6.3.2 Variable Typing and Comparison Expressions
+ ------------------------------------------------
+ 
+      The Guide is definitive. Reality is frequently inaccurate.
+      The Hitchhiker's Guide to the Galaxy
+ 
+    Unlike other programming languages, `awk' variables do not have a
+ fixed type. Instead, they can be either a number or a string, depending
+ upon the value that is assigned to them.  We look now at how variables
+ are typed, and how `awk' compares variables.
+ 
+ * Menu:
+ 
+ * Variable Typing::             String type versus numeric type.
+ * Comparison Operators::        The comparison operators.
+ * POSIX String Comparison::     String comparison with POSIX rules.
+ 
+ 
+ File: gawk.info,  Node: Variable Typing,  Next: Comparison Operators,  Up: 
Typing and Comparison
+ 
+ 6.3.2.1 String Type Versus Numeric Type
+ .......................................
+ 
+ The 1992 POSIX standard introduced the concept of a "numeric string",
+ which is simply a string that looks like a number--for example,
+ `" +2"'.  This concept is used for determining the type of a variable.
+ The type of the variable is important because the types of two variables
+ determine how they are compared.  The various versions of the POSIX
+ standard did not get the rules quite right for several editions.
+ Fortunately, as of at least the 2008 standard (and possibly earlier),
+ the standard has been fixed, and variable typing follows these rules:(1)
+ 
+    * A numeric constant or the result of a numeric operation has the
+      NUMERIC attribute.
+ 
+    * A string constant or the result of a string operation has the
+      STRING attribute.
+ 
+    * Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON'
+      elements, and the elements of an array created by `patsplit()',
+      `split()' and `match()' that are numeric strings have the STRNUM
+      attribute.  Otherwise, they have the STRING attribute.
+      Uninitialized variables also have the STRNUM attribute.
+ 
+    * Attributes propagate across assignments but are not changed by any
+      use.
+ 
+    The last rule is particularly important. In the following program,
+ `a' has numeric type, even though it is later used in a string
+ operation:
+ 
+      BEGIN {
+           a = 12.345
+           b = a " is a cute number"
+           print b
+      }
+ 
+    When two operands are compared, either string comparison or numeric
+ comparison may be used. This depends upon the attributes of the
+ operands, according to the following symmetric matrix:
+ 
+              +---------------------------------------------
+              |       STRING          NUMERIC         STRNUM
+      -------+---------------------------------------------
+              |
+      STRING  |       string          string          string
+              |
+      NUMERIC |       string          numeric         numeric
+              |
+      STRNUM  |       string          numeric         numeric
+      -------+---------------------------------------------
+ 
+    The basic idea is that user input that looks numeric--and _only_
+ user input--should be treated as numeric, even though it is actually
+ made of characters and is therefore also a string.  Thus, for example,
+ the string constant `" +3.14"', when it appears in program source code,
+ is a string--even though it looks numeric--and is _never_ treated as
+ number for comparison purposes.
+ 
+    In short, when one operand is a "pure" string, such as a string
+ constant, then a string comparison is performed.  Otherwise, a numeric
+ comparison is performed.
+ 
+    This point bears additional emphasis: All user input is made of
+ characters, and so is first and foremost of STRING type; input strings
+ that look numeric are additionally given the STRNUM attribute.  Thus,
+ the six-character input string ` +3.14' receives the STRNUM attribute.
+ In contrast, the eight-character literal `" +3.14"' appearing in
+ program text is a string constant.  The following examples print `1'
+ when the comparison between the two different constants is true, `0'
+ otherwise:
+ 
+      $ echo ' +3.14' | gawk '{ print $0 == " +3.14" }'    True
+      -| 1
+      $ echo ' +3.14' | gawk '{ print $0 == "+3.14" }'     False
+      -| 0
+      $ echo ' +3.14' | gawk '{ print $0 == "3.14" }'      False
+      -| 0
+      $ echo ' +3.14' | gawk '{ print $0 == 3.14 }'        True
+      -| 1
+      $ echo ' +3.14' | gawk '{ print $1 == " +3.14" }'    False
+      -| 0
+      $ echo ' +3.14' | gawk '{ print $1 == "+3.14" }'     True
+      -| 1
+      $ echo ' +3.14' | gawk '{ print $1 == "3.14" }'      False
+      -| 0
+      $ echo ' +3.14' | gawk '{ print $1 == 3.14 }'        True
+      -| 1
+ 
+    ---------- Footnotes ----------
+ 
+    (1) `gawk' has followed these rules for many years, and it is
+ gratifying that the POSIX standard is also now correct.
+ 
+ 
+ File: gawk.info,  Node: Comparison Operators,  Next: POSIX String Comparison, 
 Prev: Variable Typing,  Up: Typing and Comparison
+ 
+ 6.3.2.2 Comparison Operators
+ ............................
+ 
+ "Comparison expressions" compare strings or numbers for relationships
+ such as equality.  They are written using "relational operators", which
+ are a superset of those in C.  *note table-relational-ops:: describes
+ them.
+ 
+ Expression         Result
+ -------------------------------------------------------------------------- 
+ X `<' Y            True if X is less than Y.
+ X `<=' Y           True if X is less than or equal to Y.
+ X `>' Y            True if X is greater than Y.
+ X `>=' Y           True if X is greater than or equal to Y.
+ X `==' Y           True if X is equal to Y.
+ X `!=' Y           True if X is not equal to Y.
+ X `~' Y            True if the string X matches the regexp denoted by Y.
+ X `!~' Y           True if the string X does not match the regexp
+                    denoted by Y.
+ SUBSCRIPT `in'     True if the array ARRAY has an element with the
+ ARRAY              subscript SUBSCRIPT.
+ 
+ Table 6.3: Relational Operators
+ 
+    Comparison expressions have the value one if true and zero if false.
+ When comparing operands of mixed types, numeric operands are converted
+ to strings using the value of `CONVFMT' (*note Conversion::).
+ 
+    Strings are compared by comparing the first character of each, then
+ the second character of each, and so on.  Thus, `"10"' is less than
+ `"9"'.  If there are two strings where one is a prefix of the other,
+ the shorter string is less than the longer one.  Thus, `"abc"' is less
+ than `"abcd"'.
+ 
+    It is very easy to accidentally mistype the `==' operator and leave
+ off one of the `=' characters.  The result is still valid `awk' code,
+ but the program does not do what is intended:
+ 
+      if (a = b)   # oops! should be a == b
+         ...
+      else
+         ...
+ 
+ Unless `b' happens to be zero or the null string, the `if' part of the
+ test always succeeds.  Because the operators are so similar, this kind
+ of error is very difficult to spot when scanning the source code.
+ 
+    The following table of expressions illustrates the kind of comparison
+ `gawk' performs, as well as what the result of the comparison is:
+ 
+ `1.5 <= 2.0'
+      numeric comparison (true)
+ 
+ `"abc" >= "xyz"'
+      string comparison (false)
+ 
+ `1.5 != " +2"'
+      string comparison (true)
+ 
+ `"1e2" < "3"'
+      string comparison (true)
+ 
+ `a = 2; b = "2"'
+ `a == b'
+      string comparison (true)
+ 
+ `a = 2; b = " +2"'
+ 
+ `a == b'
+      string comparison (false)
+ 
+    In this example:
+ 
+      $ echo 1e2 3 | awk '{ print ($1 < $2) ? "true" : "false" }'
+      -| false
+ 
+ the result is `false' because both `$1' and `$2' are user input.  They
+ are numeric strings--therefore both have the STRNUM attribute,
+ dictating a numeric comparison.  The purpose of the comparison rules
+ and the use of numeric strings is to attempt to produce the behavior
+ that is "least surprising," while still "doing the right thing."
+ 
+    String comparisons and regular expression comparisons are very
+ different.  For example:
+ 
+      x == "foo"
+ 
+ has the value one, or is true if the variable `x' is precisely `foo'.
+ By contrast:
+ 
+      x ~ /foo/
+ 
+ has the value one if `x' contains `foo', such as `"Oh, what a fool am
+ I!"'.
+ 
+    The righthand operand of the `~' and `!~' operators may be either a
+ regexp constant (`/.../') or an ordinary expression. In the latter
+ case, the value of the expression as a string is used as a dynamic
+ regexp (*note Regexp Usage::; also *note Computed Regexps::).
+ 
+    In modern implementations of `awk', a constant regular expression in
+ slashes by itself is also an expression.  The regexp `/REGEXP/' is an
+ abbreviation for the following comparison expression:
+ 
+      $0 ~ /REGEXP/
+ 
+    One special place where `/foo/' is _not_ an abbreviation for `$0 ~
+ /foo/' is when it is the righthand operand of `~' or `!~'.  *Note Using
+ Constant Regexps::, where this is discussed in more detail.
+ 
+ 
+ File: gawk.info,  Node: POSIX String Comparison,  Prev: Comparison Operators, 
 Up: Typing and Comparison
+ 
+ 6.3.2.3 String Comparison With POSIX Rules
+ ..........................................
+ 
+ The POSIX standard says that string comparison is performed based on
+ the locale's collating order.  This is usually very different from the
+ results obtained when doing straight character-by-character
+ comparison.(1)
+ 
+    Because this behavior differs considerably from existing practice,
+ `gawk' only implements it when in POSIX mode (*note Options::).  Here
+ is an example to illustrate the difference, in an `en_US.UTF-8' locale:
+ 
+      $ gawk 'BEGIN { printf("ABC < abc = %s\n",
+      >                     ("ABC" < "abc" ? "TRUE" : "FALSE")) }'
+      -| ABC < abc = TRUE
+      $ gawk --posix 'BEGIN { printf("ABC < abc = %s\n",
+      >                             ("ABC" < "abc" ? "TRUE" : "FALSE")) }'
+      -| ABC < abc = FALSE
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Technically, string comparison is supposed to behave the same
+ way as if the strings are compared with the C `strcoll()' function.
+ 
+ 
+ File: gawk.info,  Node: Boolean Ops,  Next: Conditional Exp,  Prev: Typing 
and Comparison,  Up: Truth Values and Conditions
+ 
+ 6.3.3 Boolean Expressions
+ -------------------------
+ 
+ A "Boolean expression" is a combination of comparison expressions or
+ matching expressions, using the Boolean operators "or" (`||'), "and"
+ (`&&'), and "not" (`!'), along with parentheses to control nesting.
+ The truth value of the Boolean expression is computed by combining the
+ truth values of the component expressions.  Boolean expressions are
+ also referred to as "logical expressions".  The terms are equivalent.
+ 
+    Boolean expressions can be used wherever comparison and matching
+ expressions can be used.  They can be used in `if', `while', `do', and
+ `for' statements (*note Statements::).  They have numeric values (one
+ if true, zero if false) that come into play if the result of the
+ Boolean expression is stored in a variable or used in arithmetic.
+ 
+    In addition, every Boolean expression is also a valid pattern, so
+ you can use one as a pattern to control the execution of rules.  The
+ Boolean operators are:
+ 
+ `BOOLEAN1 && BOOLEAN2'
+      True if both BOOLEAN1 and BOOLEAN2 are true.  For example, the
+      following statement prints the current input record if it contains
+      both `2400' and `foo':
+ 
+           if ($0 ~ /2400/ && $0 ~ /foo/) print
+ 
+      The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is true.
+      This can make a difference when BOOLEAN2 contains expressions that
+      have side effects. In the case of `$0 ~ /foo/ && ($2 == bar++)',
+      the variable `bar' is not incremented if there is no substring
+      `foo' in the record.
+ 
+ `BOOLEAN1 || BOOLEAN2'
+      True if at least one of BOOLEAN1 or BOOLEAN2 is true.  For
+      example, the following statement prints all records in the input
+      that contain _either_ `2400' or `foo' or both:
+ 
+           if ($0 ~ /2400/ || $0 ~ /foo/) print
+ 
+      The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is false.
+      This can make a difference when BOOLEAN2 contains expressions that
+      have side effects.
+ 
+ `! BOOLEAN'
+      True if BOOLEAN is false.  For example, the following program
+      prints `no home!' in the unusual event that the `HOME' environment
+      variable is not defined:
+ 
+           BEGIN { if (! ("HOME" in ENVIRON))
+                          print "no home!" }
+ 
+      (The `in' operator is described in *note Reference to Elements::.)
+ 
+    The `&&' and `||' operators are called "short-circuit" operators
+ because of the way they work.  Evaluation of the full expression is
+ "short-circuited" if the result can be determined part way through its
+ evaluation.
+ 
+    Statements that use `&&' or `||' can be continued simply by putting
+ a newline after them.  But you cannot put a newline in front of either
+ of these operators without using backslash continuation (*note
+ Statements/Lines::).
+ 
+    The actual value of an expression using the `!' operator is either
+ one or zero, depending upon the truth value of the expression it is
+ applied to.  The `!' operator is often useful for changing the sense of
+ a flag variable from false to true and back again. For example, the
+ following program is one way to print lines in between special
+ bracketing lines:
+ 
+      $1 == "START"   { interested = ! interested; next }
+      interested == 1 { print }
+      $1 == "END"     { interested = ! interested; next }
+ 
+ The variable `interested', as with all `awk' variables, starts out
+ initialized to zero, which is also false.  When a line is seen whose
+ first field is `START', the value of `interested' is toggled to true,
+ using `!'. The next rule prints lines as long as `interested' is true.
+ When a line is seen whose first field is `END', `interested' is toggled
+ back to false.(1)
+ 
+      NOTE: The `next' statement is discussed in *note Next Statement::.
+      `next' tells `awk' to skip the rest of the rules, get the next
+      record, and start processing the rules over again at the top.  The
+      reason it's there is to avoid printing the bracketing `START' and
+      `END' lines.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) This program has a bug; it prints lines starting with `END'. How
+ would you fix it?
+ 
+ 
+ File: gawk.info,  Node: Conditional Exp,  Prev: Boolean Ops,  Up: Truth 
Values and Conditions
+ 
+ 6.3.4 Conditional Expressions
+ -----------------------------
+ 
+ A "conditional expression" is a special kind of expression that has
+ three operands.  It allows you to use one expression's value to select
+ one of two other expressions.  The conditional expression is the same
+ as in the C language, as shown here:
+ 
+      SELECTOR ? IF-TRUE-EXP : IF-FALSE-EXP
+ 
+ There are three subexpressions.  The first, SELECTOR, is always
+ computed first.  If it is "true" (not zero or not null), then
+ IF-TRUE-EXP is computed next and its value becomes the value of the
+ whole expression.  Otherwise, IF-FALSE-EXP is computed next and its
+ value becomes the value of the whole expression.  For example, the
+ following expression produces the absolute value of `x':
+ 
+      x >= 0 ? x : -x
+ 
+    Each time the conditional expression is computed, only one of
+ IF-TRUE-EXP and IF-FALSE-EXP is used; the other is ignored.  This is
+ important when the expressions have side effects.  For example, this
+ conditional expression examines element `i' of either array `a' or
+ array `b', and increments `i':
+ 
+      x == y ? a[i++] : b[i++]
+ 
+ This is guaranteed to increment `i' exactly once, because each time
+ only one of the two increment expressions is executed and the other is
+ not.  *Note Arrays::, for more information about arrays.
+ 
+    As a minor `gawk' extension, a statement that uses `?:' can be
+ continued simply by putting a newline after either character.  However,
+ putting a newline in front of either character does not work without
+ using backslash continuation (*note Statements/Lines::).  If `--posix'
+ is specified (*note Options::), then this extension is disabled.
+ 
+ 
+ File: gawk.info,  Node: Function Calls,  Next: Precedence,  Prev: Truth 
Values and Conditions,  Up: Expressions
+ 
+ 6.4 Function Calls
+ ==================
+ 
+ A "function" is a name for a particular calculation.  This enables you
+ to ask for it by name at any point in the program.  For example, the
+ function `sqrt()' computes the square root of a number.
+ 
+    A fixed set of functions are "built-in", which means they are
+ available in every `awk' program.  The `sqrt()' function is one of
+ these.  *Note Built-in::, for a list of built-in functions and their
+ descriptions.  In addition, you can define functions for use in your
+ program.  *Note User-defined::, for instructions on how to do this.
+ 
+    The way to use a function is with a "function call" expression,
+ which consists of the function name followed immediately by a list of
+ "arguments" in parentheses.  The arguments are expressions that provide
+ the raw materials for the function's calculations.  When there is more
+ than one argument, they are separated by commas.  If there are no
+ arguments, just write `()' after the function name.  The following
+ examples show function calls with and without arguments:
+ 
+      sqrt(x^2 + y^2)        one argument
+      atan2(y, x)            two arguments
+      rand()                 no arguments
+ 
+      CAUTION: Do not put any space between the function name and the
+      open-parenthesis!  A user-defined function name looks just like
+      the name of a variable--a space would make the expression look
+      like concatenation of a variable with an expression inside
+      parentheses.  With built-in functions, space before the
+      parenthesis is harmless, but it is best not to get into the habit
+      of using space to avoid mistakes with user-defined functions.
+ 
+    Each function expects a particular number of arguments.  For
+ example, the `sqrt()' function must be called with a single argument,
+ the number of which to take the square root:
+ 
+      sqrt(ARGUMENT)
+ 
+    Some of the built-in functions have one or more optional arguments.
+ If those arguments are not supplied, the functions use a reasonable
+ default value.  *Note Built-in::, for full details.  If arguments are
+ omitted in calls to user-defined functions, then those arguments are
+ treated as local variables and initialized to the empty string (*note
+ User-defined::).
+ 
+    As an advanced feature, `gawk' provides indirect function calls,
+ which is a way to choose the function to call at runtime, instead of
+ when you write the source code to your program. We defer discussion of
+ this feature until later; see *note Indirect Calls::.
+ 
+    Like every other expression, the function call has a value, which is
+ computed by the function based on the arguments you give it.  In this
+ example, the value of `sqrt(ARGUMENT)' is the square root of ARGUMENT.
+ The following program reads numbers, one number per line, and prints the
+ square root of each one:
+ 
+      $ awk '{ print "The square root of", $1, "is", sqrt($1) }'
+      1
+      -| The square root of 1 is 1
+      3
+      -| The square root of 3 is 1.73205
+      5
+      -| The square root of 5 is 2.23607
+      Ctrl-d
+ 
+    A function can also have side effects, such as assigning values to
+ certain variables or doing I/O.  This program shows how the `match()'
+ function (*note String Functions::) changes the variables `RSTART' and
+ `RLENGTH':
+ 
+      {
+          if (match($1, $2))
+              print RSTART, RLENGTH
+          else
+              print "no match"
+      }
+ 
+ Here is a sample run:
+ 
+      $ awk -f matchit.awk
+      aaccdd  c+
+      -| 3 2
+      foo     bar
+      -| no match
+      abcdefg e
+      -| 5 1
+ 
+ 
+ File: gawk.info,  Node: Precedence,  Next: Locales,  Prev: Function Calls,  
Up: Expressions
+ 
+ 6.5 Operator Precedence (How Operators Nest)
+ ============================================
+ 
+ "Operator precedence" determines how operators are grouped when
+ different operators appear close by in one expression.  For example,
+ `*' has higher precedence than `+'; thus, `a + b * c' means to multiply
+ `b' and `c', and then add `a' to the product (i.e., `a + (b * c)').
+ 
+    The normal precedence of the operators can be overruled by using
+ parentheses.  Think of the precedence rules as saying where the
+ parentheses are assumed to be.  In fact, it is wise to always use
+ parentheses whenever there is an unusual combination of operators,
+ because other people who read the program may not remember what the
+ precedence is in this case.  Even experienced programmers occasionally
+ forget the exact rules, which leads to mistakes.  Explicit parentheses
+ help prevent any such mistakes.
+ 
+    When operators of equal precedence are used together, the leftmost
+ operator groups first, except for the assignment, conditional, and
+ exponentiation operators, which group in the opposite order.  Thus, `a
+ - b + c' groups as `(a - b) + c' and `a = b = c' groups as `a = (b =
+ c)'.
+ 
+    Normally the precedence of prefix unary operators does not matter,
+ because there is only one way to interpret them: innermost first.
+ Thus, `$++i' means `$(++i)' and `++$x' means `++($x)'.  However, when
+ another operator follows the operand, then the precedence of the unary
+ operators can matter.  `$x^2' means `($x)^2', but `-x^2' means
+ `-(x^2)', because `-' has lower precedence than `^', whereas `$' has
+ higher precedence.  Also, operators cannot be combined in a way that
+ violates the precedence rules; for example, `$$0++--' is not a valid
+ expression because the first `$' has higher precedence than the `++';
+ to avoid the problem the expression can be rewritten as `$($0++)--'.
+ 
+    This table presents `awk''s operators, in order of highest to lowest
+ precedence:
+ 
+ `(...)'
+      Grouping.
+ 
+ `$'
+      Field reference.
+ 
+ `++ --'
+      Increment, decrement.
+ 
+ `^ **'
+      Exponentiation.  These operators group right-to-left.
+ 
+ `+ - !'
+      Unary plus, minus, logical "not."
+ 
+ `* / %'
+      Multiplication, division, remainder.
+ 
+ `+ -'
+      Addition, subtraction.
+ 
+ `String Concatenation'
+      There is no special symbol for concatenation.  The operands are
+      simply written side by side (*note Concatenation::).
+ 
+ `< <= == != > >= >> | |&'
+      Relational and redirection.  The relational operators and the
+      redirections have the same precedence level.  Characters such as
+      `>' serve both as relationals and as redirections; the context
+      distinguishes between the two meanings.
+ 
+      Note that the I/O redirection operators in `print' and `printf'
+      statements belong to the statement level, not to expressions.  The
+      redirection does not produce an expression that could be the
+      operand of another operator.  As a result, it does not make sense
+      to use a redirection operator near another operator of lower
+      precedence without parentheses.  Such combinations (for example,
+      `print foo > a ? b : c'), result in syntax errors.  The correct
+      way to write this statement is `print foo > (a ? b : c)'.
+ 
+ `~ !~'
+      Matching, nonmatching.
+ 
+ `in'
+      Array membership.
+ 
+ `&&'
+      Logical "and".
+ 
+ `||'
+      Logical "or".
+ 
+ `?:'
+      Conditional.  This operator groups right-to-left.
+ 
+ `= += -= *= /= %= ^= **='
+      Assignment.  These operators group right-to-left.
+ 
+      NOTE: The `|&', `**', and `**=' operators are not specified by
+      POSIX.  For maximum portability, do not use them.
+ 
+ 
+ File: gawk.info,  Node: Locales,  Prev: Precedence,  Up: Expressions
+ 
+ 6.6 Where You Are Makes A Difference
+ ====================================
+ 
+ Modern systems support the notion of "locales": a way to tell the
+ system about the local character set and language.
+ 
+    Once upon a time, the locale setting used to affect regexp matching
+ (*note Ranges and Locales::), but this is no longer true.
+ 
+    Locales can affect record splitting.  For the normal case of `RS =
+ "\n"', the locale is largely irrelevant.  For other single-character
+ record separators, setting `LC_ALL=C' in the environment will give you
+ much better performance when reading records.  Otherwise, `gawk' has to
+ make several function calls, _per input character_, to find the record
+ terminator.
+ 
+    According to POSIX, string comparison is also affected by locales
+ (similar to regular expressions).  The details are presented in *note
+ POSIX String Comparison::.
+ 
+    Finally, the locale affects the value of the decimal point character
+ used when `gawk' parses input data.  This is discussed in detail in
+ *note Conversion::.
+ 
+ 
+ File: gawk.info,  Node: Patterns and Actions,  Next: Arrays,  Prev: 
Expressions,  Up: Top
+ 
+ 7 Patterns, Actions, and Variables
+ **********************************
+ 
+ As you have already seen, each `awk' statement consists of a pattern
+ with an associated action.  This major node describes how you build
+ patterns and actions, what kinds of things you can do within actions,
+ and `awk''s built-in variables.
+ 
+    The pattern-action rules and the statements available for use within
+ actions form the core of `awk' programming.  In a sense, everything
+ covered up to here has been the foundation that programs are built on
+ top of.  Now it's time to start building something useful.
+ 
+ * Menu:
+ 
+ * Pattern Overview::            What goes into a pattern.
+ * Using Shell Variables::       How to use shell variables with `awk'.
+ * Action Overview::             What goes into an action.
+ * Statements::                  Describes the various control statements in
+                                 detail.
+ * Built-in Variables::          Summarizes the built-in variables.
+ 
+ 
+ File: gawk.info,  Node: Pattern Overview,  Next: Using Shell Variables,  Up: 
Patterns and Actions
+ 
+ 7.1 Pattern Elements
+ ====================
+ 
+ * Menu:
+ 
+ * Regexp Patterns::             Using regexps as patterns.
+ * Expression Patterns::         Any expression can be used as a pattern.
+ * Ranges::                      Pairs of patterns specify record ranges.
+ * BEGIN/END::                   Specifying initialization and cleanup rules.
+ * BEGINFILE/ENDFILE::           Two special patterns for advanced control.
+ * Empty::                       The empty pattern, which matches every record.
+ 
+    Patterns in `awk' control the execution of rules--a rule is executed
+ when its pattern matches the current input record.  The following is a
+ summary of the types of `awk' patterns:
+ 
+ `/REGULAR EXPRESSION/'
+      A regular expression. It matches when the text of the input record
+      fits the regular expression.  (*Note Regexp::.)
+ 
+ `EXPRESSION'
+      A single expression.  It matches when its value is nonzero (if a
+      number) or non-null (if a string).  (*Note Expression Patterns::.)
+ 
+ `PAT1, PAT2'
+      A pair of patterns separated by a comma, specifying a range of
+      records.  The range includes both the initial record that matches
+      PAT1 and the final record that matches PAT2.  (*Note Ranges::.)
+ 
+ `BEGIN'
+ `END'
+      Special patterns for you to supply startup or cleanup actions for
+      your `awk' program.  (*Note BEGIN/END::.)
+ 
+ `BEGINFILE'
+ `ENDFILE'
+      Special patterns for you to supply startup or cleanup actions to be
+      done on a per file basis.  (*Note BEGINFILE/ENDFILE::.)
+ 
+ `EMPTY'
+      The empty pattern matches every input record.  (*Note Empty::.)
+ 
+ 
+ File: gawk.info,  Node: Regexp Patterns,  Next: Expression Patterns,  Up: 
Pattern Overview
+ 
+ 7.1.1 Regular Expressions as Patterns
+ -------------------------------------
+ 
+ Regular expressions are one of the first kinds of patterns presented in
+ this book.  This kind of pattern is simply a regexp constant in the
+ pattern part of a rule.  Its  meaning is `$0 ~ /PATTERN/'.  The pattern
+ matches when the input record matches the regexp.  For example:
+ 
+      /foo|bar|baz/  { buzzwords++ }
+      END            { print buzzwords, "buzzwords seen" }
+ 
+ 
+ File: gawk.info,  Node: Expression Patterns,  Next: Ranges,  Prev: Regexp 
Patterns,  Up: Pattern Overview
+ 
+ 7.1.2 Expressions as Patterns
+ -----------------------------
+ 
+ Any `awk' expression is valid as an `awk' pattern.  The pattern matches
+ if the expression's value is nonzero (if a number) or non-null (if a
+ string).  The expression is reevaluated each time the rule is tested
+ against a new input record.  If the expression uses fields such as
+ `$1', the value depends directly on the new input record's text;
+ otherwise, it depends on only what has happened so far in the execution
+ of the `awk' program.
+ 
+    Comparison expressions, using the comparison operators described in
+ *note Typing and Comparison::, are a very common kind of pattern.
+ Regexp matching and nonmatching are also very common expressions.  The
+ left operand of the `~' and `!~' operators is a string.  The right
+ operand is either a constant regular expression enclosed in slashes
+ (`/REGEXP/'), or any expression whose string value is used as a dynamic
+ regular expression (*note Computed Regexps::).  The following example
+ prints the second field of each input record whose first field is
+ precisely `foo':
+ 
+      $ awk '$1 == "foo" { print $2 }' BBS-list
+ 
+ (There is no output, because there is no BBS site with the exact name
+ `foo'.)  Contrast this with the following regular expression match,
+ which accepts any record with a first field that contains `foo':
+ 
+      $ awk '$1 ~ /foo/ { print $2 }' BBS-list
+      -| 555-1234
+      -| 555-6699
+      -| 555-6480
+      -| 555-2127
+ 
+    A regexp constant as a pattern is also a special case of an
+ expression pattern.  The expression `/foo/' has the value one if `foo'
+ appears in the current input record. Thus, as a pattern, `/foo/'
+ matches any record containing `foo'.
+ 
+    Boolean expressions are also commonly used as patterns.  Whether the
+ pattern matches an input record depends on whether its subexpressions
+ match.  For example, the following command prints all the records in
+ `BBS-list' that contain both `2400' and `foo':
+ 
+      $ awk '/2400/ && /foo/' BBS-list
+      -| fooey        555-1234     2400/1200/300     B
+ 
+    The following command prints all records in `BBS-list' that contain
+ _either_ `2400' or `foo' (or both, of course):
+ 
+      $ awk '/2400/ || /foo/' BBS-list
+      -| alpo-net     555-3412     2400/1200/300     A
+      -| bites        555-1675     2400/1200/300     A
+      -| fooey        555-1234     2400/1200/300     B
+      -| foot         555-6699     1200/300          B
+      -| macfoo       555-6480     1200/300          A
+      -| sdace        555-3430     2400/1200/300     A
+      -| sabafoo      555-2127     1200/300          C
+ 
+    The following command prints all records in `BBS-list' that do _not_
+ contain the string `foo':
+ 
+      $ awk '! /foo/' BBS-list
+      -| aardvark     555-5553     1200/300          B
+      -| alpo-net     555-3412     2400/1200/300     A
+      -| barfly       555-7685     1200/300          A
+      -| bites        555-1675     2400/1200/300     A
+      -| camelot      555-0542     300               C
+      -| core         555-2912     1200/300          C
+      -| sdace        555-3430     2400/1200/300     A
+ 
+    The subexpressions of a Boolean operator in a pattern can be
+ constant regular expressions, comparisons, or any other `awk'
+ expressions.  Range patterns are not expressions, so they cannot appear
+ inside Boolean patterns.  Likewise, the special patterns `BEGIN', `END',
+ `BEGINFILE' and `ENDFILE', which never match any input record, are not
+ expressions and cannot appear inside Boolean patterns.
+ 
+    The precedence of the different operators which can appear in
+ patterns is described in *note Precedence::.
+ 
+ 
+ File: gawk.info,  Node: Ranges,  Next: BEGIN/END,  Prev: Expression Patterns, 
 Up: Pattern Overview
+ 
+ 7.1.3 Specifying Record Ranges with Patterns
+ --------------------------------------------
+ 
+ A "range pattern" is made of two patterns separated by a comma, in the
+ form `BEGPAT, ENDPAT'.  It is used to match ranges of consecutive input
+ records.  The first pattern, BEGPAT, controls where the range begins,
+ while ENDPAT controls where the pattern ends.  For example, the
+ following:
+ 
+      awk '$1 == "on", $1 == "off"' myfile
+ 
+ prints every record in `myfile' between `on'/`off' pairs, inclusive.
+ 
+    A range pattern starts out by matching BEGPAT against every input
+ record.  When a record matches BEGPAT, the range pattern is "turned on"
+ and the range pattern matches this record as well.  As long as the
+ range pattern stays turned on, it automatically matches every input
+ record read.  The range pattern also matches ENDPAT against every input
+ record; when this succeeds, the range pattern is turned off again for
+ the following record.  Then the range pattern goes back to checking
+ BEGPAT against each record.
+ 
+    The record that turns on the range pattern and the one that turns it
+ off both match the range pattern.  If you don't want to operate on
+ these records, you can write `if' statements in the rule's action to
+ distinguish them from the records you are interested in.
+ 
+    It is possible for a pattern to be turned on and off by the same
+ record. If the record satisfies both conditions, then the action is
+ executed for just that record.  For example, suppose there is text
+ between two identical markers (e.g., the `%' symbol), each on its own
+ line, that should be ignored.  A first attempt would be to combine a
+ range pattern that describes the delimited text with the `next'
+ statement (not discussed yet, *note Next Statement::).  This causes
+ `awk' to skip any further processing of the current record and start
+ over again with the next input record. Such a program looks like this:
+ 
+      /^%$/,/^%$/    { next }
+                     { print }
+ 
+ This program fails because the range pattern is both turned on and
+ turned off by the first line, which just has a `%' on it.  To
+ accomplish this task, write the program in the following manner, using
+ a flag:
+ 
+      /^%$/     { skip = ! skip; next }
+      skip == 1 { next } # skip lines with `skip' set
+ 
+    In a range pattern, the comma (`,') has the lowest precedence of all
+ the operators (i.e., it is evaluated last).  Thus, the following
+ program attempts to combine a range pattern with another, simpler test:
+ 
+      echo Yes | awk '/1/,/2/ || /Yes/'
+ 
+    The intent of this program is `(/1/,/2/) || /Yes/'.  However, `awk'
+ interprets this as `/1/, (/2/ || /Yes/)'.  This cannot be changed or
+ worked around; range patterns do not combine with other patterns:
+ 
+      $ echo Yes | gawk '(/1/,/2/) || /Yes/'
+      error--> gawk: cmd. line:1: (/1/,/2/) || /Yes/
+      error--> gawk: cmd. line:1:           ^ syntax error
+ 
+ 
+ File: gawk.info,  Node: BEGIN/END,  Next: BEGINFILE/ENDFILE,  Prev: Ranges,  
Up: Pattern Overview
+ 
+ 7.1.4 The `BEGIN' and `END' Special Patterns
+ --------------------------------------------
+ 
+ All the patterns described so far are for matching input records.  The
+ `BEGIN' and `END' special patterns are different.  They supply startup
+ and cleanup actions for `awk' programs.  `BEGIN' and `END' rules must
+ have actions; there is no default action for these rules because there
+ is no current record when they run.  `BEGIN' and `END' rules are often
+ referred to as "`BEGIN' and `END' blocks" by long-time `awk'
+ programmers.
+ 
+ * Menu:
+ 
+ * Using BEGIN/END::             How and why to use BEGIN/END rules.
+ * I/O And BEGIN/END::           I/O issues in BEGIN/END rules.
+ 
+ 
+ File: gawk.info,  Node: Using BEGIN/END,  Next: I/O And BEGIN/END,  Up: 
BEGIN/END
+ 
+ 7.1.4.1 Startup and Cleanup Actions
+ ...................................
+ 
+ A `BEGIN' rule is executed once only, before the first input record is
+ read. Likewise, an `END' rule is executed once only, after all the
+ input is read.  For example:
+ 
+      $ awk '
+      > BEGIN { print "Analysis of \"foo\"" }
+      > /foo/ { ++n }
+      > END   { print "\"foo\" appears", n, "times." }' BBS-list
+      -| Analysis of "foo"
+      -| "foo" appears 4 times.
+ 
+    This program finds the number of records in the input file `BBS-list'
+ that contain the string `foo'.  The `BEGIN' rule prints a title for the
+ report.  There is no need to use the `BEGIN' rule to initialize the
+ counter `n' to zero, since `awk' does this automatically (*note
+ Variables::).  The second rule increments the variable `n' every time a
+ record containing the pattern `foo' is read.  The `END' rule prints the
+ value of `n' at the end of the run.
+ 
+    The special patterns `BEGIN' and `END' cannot be used in ranges or
+ with Boolean operators (indeed, they cannot be used with any operators).
+ An `awk' program may have multiple `BEGIN' and/or `END' rules.  They
+ are executed in the order in which they appear: all the `BEGIN' rules
+ at startup and all the `END' rules at termination.  `BEGIN' and `END'
+ rules may be intermixed with other rules.  This feature was added in
+ the 1987 version of `awk' and is included in the POSIX standard.  The
+ original (1978) version of `awk' required the `BEGIN' rule to be placed
+ at the beginning of the program, the `END' rule to be placed at the
+ end, and only allowed one of each.  This is no longer required, but it
+ is a good idea to follow this template in terms of program organization
+ and readability.
+ 
+    Multiple `BEGIN' and `END' rules are useful for writing library
+ functions, because each library file can have its own `BEGIN' and/or
+ `END' rule to do its own initialization and/or cleanup.  The order in
+ which library functions are named on the command line controls the
+ order in which their `BEGIN' and `END' rules are executed.  Therefore,
+ you have to be careful when writing such rules in library files so that
+ the order in which they are executed doesn't matter.  *Note Options::,
+ for more information on using library functions.  *Note Library
+ Functions::, for a number of useful library functions.
+ 
+    If an `awk' program has only `BEGIN' rules and no other rules, then
+ the program exits after the `BEGIN' rule is run.(1)  However, if an
+ `END' rule exists, then the input is read, even if there are no other
+ rules in the program.  This is necessary in case the `END' rule checks
+ the `FNR' and `NR' variables.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The original version of `awk' kept reading and ignoring input
+ until the end of the file was seen.
+ 
+ 
+ File: gawk.info,  Node: I/O And BEGIN/END,  Prev: Using BEGIN/END,  Up: 
BEGIN/END
+ 
+ 7.1.4.2 Input/Output from `BEGIN' and `END' Rules
+ .................................................
+ 
+ There are several (sometimes subtle) points to remember when doing I/O
+ from a `BEGIN' or `END' rule.  The first has to do with the value of
+ `$0' in a `BEGIN' rule.  Because `BEGIN' rules are executed before any
+ input is read, there simply is no input record, and therefore no
+ fields, when executing `BEGIN' rules.  References to `$0' and the fields
+ yield a null string or zero, depending upon the context.  One way to
+ give `$0' a real value is to execute a `getline' command without a
+ variable (*note Getline::).  Another way is simply to assign a value to
+ `$0'.
+ 
+    The second point is similar to the first but from the other
+ direction.  Traditionally, due largely to implementation issues, `$0'
+ and `NF' were _undefined_ inside an `END' rule.  The POSIX standard
+ specifies that `NF' is available in an `END' rule. It contains the
+ number of fields from the last input record.  Most probably due to an
+ oversight, the standard does not say that `$0' is also preserved,
+ although logically one would think that it should be.  In fact, `gawk'
+ does preserve the value of `$0' for use in `END' rules.  Be aware,
+ however, that Brian Kernighan's `awk', and possibly other
+ implementations, do not.
+ 
+    The third point follows from the first two.  The meaning of `print'
+ inside a `BEGIN' or `END' rule is the same as always: `print $0'.  If
+ `$0' is the null string, then this prints an empty record.  Many long
+ time `awk' programmers use an unadorned `print' in `BEGIN' and `END'
+ rules, to mean `print ""', relying on `$0' being null.  Although one
+ might generally get away with this in `BEGIN' rules, it is a very bad
+ idea in `END' rules, at least in `gawk'.  It is also poor style, since
+ if an empty line is needed in the output, the program should print one
+ explicitly.
+ 
+    Finally, the `next' and `nextfile' statements are not allowed in a
+ `BEGIN' rule, because the implicit
+ read-a-record-and-match-against-the-rules loop has not started yet.
+ Similarly, those statements are not valid in an `END' rule, since all
+ the input has been read.  (*Note Next Statement::, and see *note
+ Nextfile Statement::.)
+ 
+ 
+ File: gawk.info,  Node: BEGINFILE/ENDFILE,  Next: Empty,  Prev: BEGIN/END,  
Up: Pattern Overview
+ 
+ 7.1.5 The `BEGINFILE' and `ENDFILE' Special Patterns
+ ----------------------------------------------------
+ 
+ This minor node describes a `gawk'-specific feature.
+ 
+    Two special kinds of rule, `BEGINFILE' and `ENDFILE', give you
+ "hooks" into `gawk''s command-line file processing loop.  As with the
+ `BEGIN' and `END' rules (*note BEGIN/END::), all `BEGINFILE' rules in a
+ program are merged, in the order they are read by `gawk', and all
+ `ENDFILE' rules are merged as well.
+ 
+    The body of the `BEGINFILE' rules is executed just before `gawk'
+ reads the first record from a file.  `FILENAME' is set to the name of
+ the current file, and `FNR' is set to zero.
+ 
+    The `BEGINFILE' rule provides you the opportunity for two tasks that
+ would otherwise be difficult or impossible to perform:
+ 
+    * You can test if the file is readable.  Normally, it is a fatal
+      error if a file named on the command line cannot be opened for
+      reading.  However, you can bypass the fatal error and move on to
+      the next file on the command line.
+ 
+      You do this by checking if the `ERRNO' variable is not the empty
+      string; if so, then `gawk' was not able to open the file. In this
+      case, your program can execute the `nextfile' statement (*note
+      Nextfile Statement::).  This causes `gawk' to skip the file
+      entirely.  Otherwise, `gawk' exits with the usual fatal error.
+ 
+    * If you have written extensions that modify the record handling (by
 -     inserting an "open hook"), you can invoke them at this point,
++     inserting an "input parser"), you can invoke them at this point,
+      before `gawk' has started processing the file.  (This is a _very_
 -     advanced feature, currently used only by the XMLgawk project
 -     (http://xmlgawk.sourceforge.net).)
++     advanced feature, currently used only by the `gawkextlib' project
++     (http://gawkextlib.sourceforge.net).)
+ 
+    The `ENDFILE' rule is called when `gawk' has finished processing the
+ last record in an input file.  For the last input file, it will be
+ called before any `END' rules.  The `ENDFILE' rule is executed even for
+ empty input files.
+ 
+    Normally, when an error occurs when reading input in the normal input
+ processing loop, the error is fatal.  However, if an `ENDFILE' rule is
+ present, the error becomes non-fatal, and instead `ERRNO' is set.  This
+ makes it possible to catch and process I/O errors at the level of the
+ `awk' program.
+ 
+    The `next' statement (*note Next Statement::) is not allowed inside
+ either a `BEGINFILE' or and `ENDFILE' rule.  The `nextfile' statement
+ (*note Nextfile Statement::) is allowed only inside a `BEGINFILE' rule,
+ but not inside an `ENDFILE' rule.
+ 
+    The `getline' statement (*note Getline::) is restricted inside both
+ `BEGINFILE' and `ENDFILE'.  Only the `getline VARIABLE < FILE' form is
+ allowed.
+ 
+    `BEGINFILE' and `ENDFILE' are `gawk' extensions.  In most other
+ `awk' implementations, or if `gawk' is in compatibility mode (*note
+ Options::), they are not special.
+ 
+ 
+ File: gawk.info,  Node: Empty,  Prev: BEGINFILE/ENDFILE,  Up: Pattern Overview
+ 
+ 7.1.6 The Empty Pattern
+ -----------------------
+ 
+ An empty (i.e., nonexistent) pattern is considered to match _every_
+ input record.  For example, the program:
+ 
+      awk '{ print $1 }' BBS-list
+ 
+ prints the first field of every record.
+ 
+ 
+ File: gawk.info,  Node: Using Shell Variables,  Next: Action Overview,  Prev: 
Pattern Overview,  Up: Patterns and Actions
+ 
+ 7.2 Using Shell Variables in Programs
+ =====================================
+ 
+ `awk' programs are often used as components in larger programs written
+ in shell.  For example, it is very common to use a shell variable to
+ hold a pattern that the `awk' program searches for.  There are two ways
+ to get the value of the shell variable into the body of the `awk'
+ program.
+ 
+    The most common method is to use shell quoting to substitute the
+ variable's value into the program inside the script.  For example, in
+ the following program:
+ 
+      printf "Enter search pattern: "
+      read pattern
+      awk "/$pattern/ "'{ nmatches++ }
+           END { print nmatches, "found" }' /path/to/data
+ 
+ the `awk' program consists of two pieces of quoted text that are
+ concatenated together to form the program.  The first part is
+ double-quoted, which allows substitution of the `pattern' shell
+ variable inside the quotes.  The second part is single-quoted.
+ 
+    Variable substitution via quoting works, but can be potentially
+ messy.  It requires a good understanding of the shell's quoting rules
+ (*note Quoting::), and it's often difficult to correctly match up the
+ quotes when reading the program.
+ 
+    A better method is to use `awk''s variable assignment feature (*note
+ Assignment Options::) to assign the shell variable's value to an `awk'
+ variable's value.  Then use dynamic regexps to match the pattern (*note
+ Computed Regexps::).  The following shows how to redo the previous
+ example using this technique:
+ 
+      printf "Enter search pattern: "
+      read pattern
+      awk -v pat="$pattern" '$0 ~ pat { nmatches++ }
+             END { print nmatches, "found" }' /path/to/data
+ 
+ Now, the `awk' program is just one single-quoted string.  The
+ assignment `-v pat="$pattern"' still requires double quotes, in case
+ there is whitespace in the value of `$pattern'.  The `awk' variable
+ `pat' could be named `pattern' too, but that would be more confusing.
+ Using a variable also provides more flexibility, since the variable can
+ be used anywhere inside the program--for printing, as an array
+ subscript, or for any other use--without requiring the quoting tricks
+ at every point in the program.
+ 
+ 
+ File: gawk.info,  Node: Action Overview,  Next: Statements,  Prev: Using 
Shell Variables,  Up: Patterns and Actions
+ 
+ 7.3 Actions
+ ===========
+ 
+ An `awk' program or script consists of a series of rules and function
+ definitions interspersed.  (Functions are described later.  *Note
+ User-defined::.)  A rule contains a pattern and an action, either of
+ which (but not both) may be omitted.  The purpose of the "action" is to
+ tell `awk' what to do once a match for the pattern is found.  Thus, in
+ outline, an `awk' program generally looks like this:
+ 
+      [PATTERN]  { ACTION }
+       PATTERN  [{ ACTION }]
+      ...
+      function NAME(ARGS) { ... }
+      ...
+ 
+    An action consists of one or more `awk' "statements", enclosed in
+ curly braces (`{...}').  Each statement specifies one thing to do.  The
+ statements are separated by newlines or semicolons.  The curly braces
+ around an action must be used even if the action contains only one
+ statement, or if it contains no statements at all.  However, if you
+ omit the action entirely, omit the curly braces as well.  An omitted
+ action is equivalent to `{ print $0 }':
+ 
+      /foo/  { }     match `foo', do nothing -- empty action
+      /foo/          match `foo', print the record -- omitted action
+ 
+    The following types of statements are supported in `awk':
+ 
+ Expressions
+      Call functions or assign values to variables (*note
+      Expressions::).  Executing this kind of statement simply computes
+      the value of the expression.  This is useful when the expression
+      has side effects (*note Assignment Ops::).
+ 
+ Control statements
+      Specify the control flow of `awk' programs.  The `awk' language
+      gives you C-like constructs (`if', `for', `while', and `do') as
+      well as a few special ones (*note Statements::).
+ 
+ Compound statements
+      Consist of one or more statements enclosed in curly braces.  A
+      compound statement is used in order to put several statements
+      together in the body of an `if', `while', `do', or `for' statement.
+ 
+ Input statements
+      Use the `getline' command (*note Getline::).  Also supplied in
+      `awk' are the `next' statement (*note Next Statement::), and the
+      `nextfile' statement (*note Nextfile Statement::).
+ 
+ Output statements
+      Such as `print' and `printf'.  *Note Printing::.
+ 
+ Deletion statements
+      For deleting array elements.  *Note Delete::.
+ 
+ 
+ File: gawk.info,  Node: Statements,  Next: Built-in Variables,  Prev: Action 
Overview,  Up: Patterns and Actions
+ 
+ 7.4 Control Statements in Actions
+ =================================
+ 
+ "Control statements", such as `if', `while', and so on, control the
+ flow of execution in `awk' programs.  Most of `awk''s control
+ statements are patterned after similar statements in C.
+ 
+    All the control statements start with special keywords, such as `if'
+ and `while', to distinguish them from simple expressions.  Many control
+ statements contain other statements.  For example, the `if' statement
+ contains another statement that may or may not be executed.  The
+ contained statement is called the "body".  To include more than one
+ statement in the body, group them into a single "compound statement"
+ with curly braces, separating them with newlines or semicolons.
+ 
+ * Menu:
+ 
+ * If Statement::                Conditionally execute some `awk'
+                                 statements.
+ * While Statement::             Loop until some condition is satisfied.
+ * Do Statement::                Do specified action while looping until some
+                                 condition is satisfied.
+ * For Statement::               Another looping statement, that provides
+                                 initialization and increment clauses.
+ * Switch Statement::            Switch/case evaluation for conditional
+                                 execution of statements based on a value.
+ * Break Statement::             Immediately exit the innermost enclosing loop.
+ * Continue Statement::          Skip to the end of the innermost enclosing
+                                 loop.
+ * Next Statement::              Stop processing the current input record.
+ * Nextfile Statement::          Stop processing the current file.
+ * Exit Statement::              Stop execution of `awk'.
+ 
+ 
+ File: gawk.info,  Node: If Statement,  Next: While Statement,  Up: Statements
+ 
+ 7.4.1 The `if'-`else' Statement
+ -------------------------------
+ 
+ The `if'-`else' statement is `awk''s decision-making statement.  It
+ looks like this:
+ 
+      if (CONDITION) THEN-BODY [else ELSE-BODY]
+ 
+ The CONDITION is an expression that controls what the rest of the
+ statement does.  If the CONDITION is true, THEN-BODY is executed;
+ otherwise, ELSE-BODY is executed.  The `else' part of the statement is
+ optional.  The condition is considered false if its value is zero or
+ the null string; otherwise, the condition is true.  Refer to the
+ following:
+ 
+      if (x % 2 == 0)
+          print "x is even"
+      else
+          print "x is odd"
+ 
+    In this example, if the expression `x % 2 == 0' is true (that is, if
+ the value of `x' is evenly divisible by two), then the first `print'
+ statement is executed; otherwise, the second `print' statement is
+ executed.  If the `else' keyword appears on the same line as THEN-BODY
+ and THEN-BODY is not a compound statement (i.e., not surrounded by
+ curly braces), then a semicolon must separate THEN-BODY from the `else'.
+ To illustrate this, the previous example can be rewritten as:
+ 
+      if (x % 2 == 0) print "x is even"; else
+              print "x is odd"
+ 
+ If the `;' is left out, `awk' can't interpret the statement and it
+ produces a syntax error.  Don't actually write programs this way,
+ because a human reader might fail to see the `else' if it is not the
+ first thing on its line.
+ 
+ 
+ File: gawk.info,  Node: While Statement,  Next: Do Statement,  Prev: If 
Statement,  Up: Statements
+ 
+ 7.4.2 The `while' Statement
+ ---------------------------
+ 
+ In programming, a "loop" is a part of a program that can be executed
+ two or more times in succession.  The `while' statement is the simplest
+ looping statement in `awk'.  It repeatedly executes a statement as long
+ as a condition is true.  For example:
+ 
+      while (CONDITION)
+        BODY
+ 
+ BODY is a statement called the "body" of the loop, and CONDITION is an
+ expression that controls how long the loop keeps running.  The first
+ thing the `while' statement does is test the CONDITION.  If the
+ CONDITION is true, it executes the statement BODY.  (The CONDITION is
+ true when the value is not zero and not a null string.)  After BODY has
+ been executed, CONDITION is tested again, and if it is still true, BODY
+ is executed again.  This process repeats until the CONDITION is no
+ longer true.  If the CONDITION is initially false, the body of the loop
+ is never executed and `awk' continues with the statement following the
+ loop.  This example prints the first three fields of each record, one
+ per line:
+ 
+      awk '{
+             i = 1
+             while (i <= 3) {
+                 print $i
+                 i++
+             }
+      }' inventory-shipped
+ 
+ The body of this loop is a compound statement enclosed in braces,
+ containing two statements.  The loop works in the following manner:
+ first, the value of `i' is set to one.  Then, the `while' statement
+ tests whether `i' is less than or equal to three.  This is true when
+ `i' equals one, so the `i'-th field is printed.  Then the `i++'
+ increments the value of `i' and the loop repeats.  The loop terminates
+ when `i' reaches four.
+ 
+    A newline is not required between the condition and the body;
+ however using one makes the program clearer unless the body is a
+ compound statement or else is very simple.  The newline after the
+ open-brace that begins the compound statement is not required either,
+ but the program is harder to read without it.
+ 
+ 
+ File: gawk.info,  Node: Do Statement,  Next: For Statement,  Prev: While 
Statement,  Up: Statements
+ 
+ 7.4.3 The `do'-`while' Statement
+ --------------------------------
+ 
+ The `do' loop is a variation of the `while' looping statement.  The
+ `do' loop executes the BODY once and then repeats the BODY as long as
+ the CONDITION is true.  It looks like this:
+ 
+      do
+        BODY
+      while (CONDITION)
+ 
+    Even if the CONDITION is false at the start, the BODY is executed at
+ least once (and only once, unless executing BODY makes CONDITION true).
+ Contrast this with the corresponding `while' statement:
+ 
+      while (CONDITION)
+        BODY
+ 
+ This statement does not execute BODY even once if the CONDITION is
+ false to begin with.  The following is an example of a `do' statement:
+ 
+      {
+             i = 1
+             do {
+                print $0
+                i++
+             } while (i <= 10)
+      }
+ 
+ This program prints each input record 10 times.  However, it isn't a
+ very realistic example, since in this case an ordinary `while' would do
+ just as well.  This situation reflects actual experience; only
+ occasionally is there a real use for a `do' statement.
+ 
+ 
+ File: gawk.info,  Node: For Statement,  Next: Switch Statement,  Prev: Do 
Statement,  Up: Statements
+ 
+ 7.4.4 The `for' Statement
+ -------------------------
+ 
+ The `for' statement makes it more convenient to count iterations of a
+ loop.  The general form of the `for' statement looks like this:
+ 
+      for (INITIALIZATION; CONDITION; INCREMENT)
+        BODY
+ 
+ The INITIALIZATION, CONDITION, and INCREMENT parts are arbitrary `awk'
+ expressions, and BODY stands for any `awk' statement.
+ 
+    The `for' statement starts by executing INITIALIZATION.  Then, as
+ long as the CONDITION is true, it repeatedly executes BODY and then
+ INCREMENT.  Typically, INITIALIZATION sets a variable to either zero or
+ one, INCREMENT adds one to it, and CONDITION compares it against the
+ desired number of iterations.  For example:
+ 
+      awk '{
+             for (i = 1; i <= 3; i++)
+                print $i
+      }' inventory-shipped
+ 
+ This prints the first three fields of each input record, with one field
+ per line.
+ 
+    It isn't possible to set more than one variable in the
+ INITIALIZATION part without using a multiple assignment statement such
+ as `x = y = 0'. This makes sense only if all the initial values are
+ equal.  (But it is possible to initialize additional variables by
+ writing their assignments as separate statements preceding the `for'
+ loop.)
+ 
+    The same is true of the INCREMENT part. Incrementing additional
+ variables requires separate statements at the end of the loop.  The C
+ compound expression, using C's comma operator, is useful in this
+ context but it is not supported in `awk'.
+ 
+    Most often, INCREMENT is an increment expression, as in the previous
+ example.  But this is not required; it can be any expression
+ whatsoever.  For example, the following statement prints all the powers
+ of two between 1 and 100:
+ 
+      for (i = 1; i <= 100; i *= 2)
+        print i
+ 
+    If there is nothing to be done, any of the three expressions in the
+ parentheses following the `for' keyword may be omitted.  Thus,
+ `for (; x > 0;)' is equivalent to `while (x > 0)'.  If the CONDITION is
+ omitted, it is treated as true, effectively yielding an "infinite loop"
+ (i.e., a loop that never terminates).
+ 
+    In most cases, a `for' loop is an abbreviation for a `while' loop,
+ as shown here:
+ 
+      INITIALIZATION
+      while (CONDITION) {
+        BODY
+        INCREMENT
+      }
+ 
+ The only exception is when the `continue' statement (*note Continue
+ Statement::) is used inside the loop. Changing a `for' statement to a
+ `while' statement in this way can change the effect of the `continue'
+ statement inside the loop.
+ 
+    The `awk' language has a `for' statement in addition to a `while'
+ statement because a `for' loop is often both less work to type and more
+ natural to think of.  Counting the number of iterations is very common
+ in loops.  It can be easier to think of this counting as part of
+ looping rather than as something to do inside the loop.
+ 
+    There is an alternate version of the `for' loop, for iterating over
+ all the indices of an array:
+ 
+      for (i in array)
+          DO SOMETHING WITH array[i]
+ 
+ *Note Scanning an Array::, for more information on this version of the
+ `for' loop.
+ 
+ 
+ File: gawk.info,  Node: Switch Statement,  Next: Break Statement,  Prev: For 
Statement,  Up: Statements
+ 
+ 7.4.5 The `switch' Statement
+ ----------------------------
+ 
+ The `switch' statement allows the evaluation of an expression and the
+ execution of statements based on a `case' match. Case statements are
+ checked for a match in the order they are defined.  If no suitable
+ `case' is found, the `default' section is executed, if supplied.
+ 
+    Each `case' contains a single constant, be it numeric, string, or
+ regexp.  The `switch' expression is evaluated, and then each `case''s
+ constant is compared against the result in turn. The type of constant
+ determines the comparison: numeric or string do the usual comparisons.
+ A regexp constant does a regular expression match against the string
+ value of the original expression.  The general form of the `switch'
+ statement looks like this:
+ 
+      switch (EXPRESSION) {
+      case VALUE OR REGULAR EXPRESSION:
+          CASE-BODY
+      default:
+          DEFAULT-BODY
+      }
+ 
+    Control flow in the `switch' statement works as it does in C. Once a
+ match to a given case is made, the case statement bodies execute until
+ a `break', `continue', `next', `nextfile'  or `exit' is encountered, or
+ the end of the `switch' statement itself. For example:
+ 
+      switch (NR * 2 + 1) {
+      case 3:
+      case "11":
+          print NR - 1
+          break
+ 
+      case /2[[:digit:]]+/:
+          print NR
+ 
+      default:
+          print NR + 1
+ 
+      case -1:
+          print NR * -1
+      }
+ 
+    Note that if none of the statements specified above halt execution
+ of a matched `case' statement, execution falls through to the next
+ `case' until execution halts. In the above example, for any case value
+ starting with `2' followed by one or more digits, the `print' statement
+ is executed and then falls through into the `default' section,
+ executing its `print' statement. In turn, the -1 case will also be
+ executed since the `default' does not halt execution.
+ 
+    This `switch' statement is a `gawk' extension.  If `gawk' is in
+ compatibility mode (*note Options::), it is not available.
+ 
+ 
+ File: gawk.info,  Node: Break Statement,  Next: Continue Statement,  Prev: 
Switch Statement,  Up: Statements
+ 
+ 7.4.6 The `break' Statement
+ ---------------------------
+ 
+ The `break' statement jumps out of the innermost `for', `while', or
+ `do' loop that encloses it.  The following example finds the smallest
+ divisor of any integer, and also identifies prime numbers:
+ 
+      # find smallest divisor of num
+      {
+         num = $1
+         for (div = 2; div * div <= num; div++) {
+           if (num % div == 0)
+             break
+         }
+         if (num % div == 0)
+           printf "Smallest divisor of %d is %d\n", num, div
+         else
+           printf "%d is prime\n", num
+      }
+ 
+    When the remainder is zero in the first `if' statement, `awk'
+ immediately "breaks out" of the containing `for' loop.  This means that
+ `awk' proceeds immediately to the statement following the loop and
+ continues processing.  (This is very different from the `exit'
+ statement, which stops the entire `awk' program.  *Note Exit
+ Statement::.)
+ 
+    The following program illustrates how the CONDITION of a `for' or
+ `while' statement could be replaced with a `break' inside an `if':
+ 
+      # find smallest divisor of num
+      {
+        num = $1
+        for (div = 2; ; div++) {
+          if (num % div == 0) {
+            printf "Smallest divisor of %d is %d\n", num, div
+            break
+          }
+          if (div * div > num) {
+            printf "%d is prime\n", num
+            break
+          }
+        }
+      }
+ 
+    The `break' statement is also used to break out of the `switch'
+ statement.  This is discussed in *note Switch Statement::.
+ 
+    The `break' statement has no meaning when used outside the body of a
+ loop or `switch'.  However, although it was never documented,
+ historical implementations of `awk' treated the `break' statement
+ outside of a loop as if it were a `next' statement (*note Next
+ Statement::).  (d.c.)  Recent versions of Brian Kernighan's `awk' no
+ longer allow this usage, nor does `gawk'.
+ 
+ 
+ File: gawk.info,  Node: Continue Statement,  Next: Next Statement,  Prev: 
Break Statement,  Up: Statements
+ 
+ 7.4.7 The `continue' Statement
+ ------------------------------
+ 
+ Similar to `break', the `continue' statement is used only inside `for',
+ `while', and `do' loops.  It skips over the rest of the loop body,
+ causing the next cycle around the loop to begin immediately.  Contrast
+ this with `break', which jumps out of the loop altogether.
+ 
+    The `continue' statement in a `for' loop directs `awk' to skip the
+ rest of the body of the loop and resume execution with the
+ increment-expression of the `for' statement.  The following program
+ illustrates this fact:
+ 
+      BEGIN {
+           for (x = 0; x <= 20; x++) {
+               if (x == 5)
+                   continue
+               printf "%d ", x
+           }
+           print ""
+      }
+ 
+ This program prints all the numbers from 0 to 20--except for 5, for
+ which the `printf' is skipped.  Because the increment `x++' is not
+ skipped, `x' does not remain stuck at 5.  Contrast the `for' loop from
+ the previous example with the following `while' loop:
+ 
+      BEGIN {
+           x = 0
+           while (x <= 20) {
+               if (x == 5)
+                   continue
+               printf "%d ", x
+               x++
+           }
+           print ""
+      }
+ 
+ This program loops forever once `x' reaches 5.
+ 
+    The `continue' statement has no special meaning with respect to the
+ `switch' statement, nor does it have any meaning when used outside the
+ body of a loop.  Historical versions of `awk' treated a `continue'
+ statement outside a loop the same way they treated a `break' statement
+ outside a loop: as if it were a `next' statement (*note Next
+ Statement::).  (d.c.)  Recent versions of Brian Kernighan's `awk' no
+ longer work this way, nor does `gawk'.
+ 
+ 
+ File: gawk.info,  Node: Next Statement,  Next: Nextfile Statement,  Prev: 
Continue Statement,  Up: Statements
+ 
+ 7.4.8 The `next' Statement
+ --------------------------
+ 
+ The `next' statement forces `awk' to immediately stop processing the
+ current record and go on to the next record.  This means that no
+ further rules are executed for the current record, and the rest of the
+ current rule's action isn't executed.
+ 
+    Contrast this with the effect of the `getline' function (*note
+ Getline::).  That also causes `awk' to read the next record
+ immediately, but it does not alter the flow of control in any way
+ (i.e., the rest of the current action executes with a new input record).
+ 
+    At the highest level, `awk' program execution is a loop that reads
+ an input record and then tests each rule's pattern against it.  If you
+ think of this loop as a `for' statement whose body contains the rules,
+ then the `next' statement is analogous to a `continue' statement. It
+ skips to the end of the body of this implicit loop and executes the
+ increment (which reads another record).
+ 
+    For example, suppose an `awk' program works only on records with
+ four fields, and it shouldn't fail when given bad input.  To avoid
+ complicating the rest of the program, write a "weed out" rule near the
+ beginning, in the following manner:
+ 
+      NF != 4 {
+        err = sprintf("%s:%d: skipped: NF != 4\n", FILENAME, FNR)
+        print err > "/dev/stderr"
+        next
+      }
+ 
+ Because of the `next' statement, the program's subsequent rules won't
+ see the bad record.  The error message is redirected to the standard
+ error output stream, as error messages should be.  For more detail see
+ *note Special Files::.
+ 
+    If the `next' statement causes the end of the input to be reached,
+ then the code in any `END' rules is executed.  *Note BEGIN/END::.
+ 
+    The `next' statement is not allowed inside `BEGINFILE' and `ENDFILE'
+ rules. *Note BEGINFILE/ENDFILE::.
+ 
+    According to the POSIX standard, the behavior is undefined if the
+ `next' statement is used in a `BEGIN' or `END' rule.  `gawk' treats it
+ as a syntax error.  Although POSIX permits it, some other `awk'
+ implementations don't allow the `next' statement inside function bodies
+ (*note User-defined::).  Just as with any other `next' statement, a
+ `next' statement inside a function body reads the next record and
+ starts processing it with the first rule in the program.
+ 
+ 
+ File: gawk.info,  Node: Nextfile Statement,  Next: Exit Statement,  Prev: 
Next Statement,  Up: Statements
+ 
+ 7.4.9 Using `gawk''s `nextfile' Statement
+ -----------------------------------------
+ 
+ `gawk' provides the `nextfile' statement, which is similar to the
+ `next' statement. (c.e.)  However, instead of abandoning processing of
+ the current record, the `nextfile' statement instructs `gawk' to stop
+ processing the current data file.
+ 
+    The `nextfile' statement is a `gawk' extension.  In most other `awk'
+ implementations, or if `gawk' is in compatibility mode (*note
+ Options::), `nextfile' is not special.
+ 
+    Upon execution of the `nextfile' statement, any `ENDFILE' rules are
+ executed except in the case as mentioned below, `FILENAME' is updated
+ to the name of the next data file listed on the command line, `FNR' is
+ reset to one, `ARGIND' is incremented, any `BEGINFILE' rules are
+ executed, and processing starts over with the first rule in the program.
+ (`ARGIND' hasn't been introduced yet. *Note Built-in Variables::.)  If
+ the `nextfile' statement causes the end of the input to be reached,
+ then the code in any `END' rules is executed. An exception to this is
+ when the `nextfile' is invoked during execution of any statement in an
+ `END' rule; In this case, it causes the program to stop immediately.
+ *Note BEGIN/END::.
+ 
+    The `nextfile' statement is useful when there are many data files to
+ process but it isn't necessary to process every record in every file.
+ Normally, in order to move on to the next data file, a program has to
+ continue scanning the unwanted records.  The `nextfile' statement
+ accomplishes this much more efficiently.
+ 
+    In addition, `nextfile' is useful inside a `BEGINFILE' rule to skip
+ over a file that would otherwise cause `gawk' to exit with a fatal
+ error. In this case, `ENDFILE' rules are not executed. *Note
+ BEGINFILE/ENDFILE::.
+ 
+    While one might think that `close(FILENAME)' would accomplish the
+ same as `nextfile', this isn't true.  `close()' is reserved for closing
+ files, pipes, and coprocesses that are opened with redirections.  It is
+ not related to the main processing that `awk' does with the files
+ listed in `ARGV'.
+ 
+    The current version of the Brian Kernighan's `awk' (*note Other
+ Versions::) also supports `nextfile'.  However, it doesn't allow the
+ `nextfile' statement inside function bodies (*note User-defined::).
+ `gawk' does; a `nextfile' inside a function body reads the next record
+ and starts processing it with the first rule in the program, just as
+ any other `nextfile' statement.
+ 
+ 
+ File: gawk.info,  Node: Exit Statement,  Prev: Nextfile Statement,  Up: 
Statements
+ 
+ 7.4.10 The `exit' Statement
+ ---------------------------
+ 
+ The `exit' statement causes `awk' to immediately stop executing the
+ current rule and to stop processing input; any remaining input is
+ ignored.  The `exit' statement is written as follows:
+ 
+      exit [RETURN CODE]
+ 
+    When an `exit' statement is executed from a `BEGIN' rule, the
+ program stops processing everything immediately.  No input records are
+ read.  However, if an `END' rule is present, as part of executing the
+ `exit' statement, the `END' rule is executed (*note BEGIN/END::).  If
+ `exit' is used in the body of an `END' rule, it causes the program to
+ stop immediately.
+ 
+    An `exit' statement that is not part of a `BEGIN' or `END' rule
+ stops the execution of any further automatic rules for the current
+ record, skips reading any remaining input records, and executes the
+ `END' rule if there is one.  Any `ENDFILE' rules are also skipped; they
+ are not executed.
+ 
+    In such a case, if you don't want the `END' rule to do its job, set
+ a variable to nonzero before the `exit' statement and check that
+ variable in the `END' rule.  *Note Assert Function::, for an example
+ that does this.
+ 
+    If an argument is supplied to `exit', its value is used as the exit
+ status code for the `awk' process.  If no argument is supplied, `exit'
+ causes `awk' to return a "success" status.  In the case where an
+ argument is supplied to a first `exit' statement, and then `exit' is
+ called a second time from an `END' rule with no argument, `awk' uses
+ the previously supplied exit value.  (d.c.)  *Note Exit Status::, for
+ more information.
+ 
+    For example, suppose an error condition occurs that is difficult or
+ impossible to handle.  Conventionally, programs report this by exiting
+ with a nonzero status.  An `awk' program can do this using an `exit'
+ statement with a nonzero argument, as shown in the following example:
+ 
+      BEGIN {
+             if (("date" | getline date_now) <= 0) {
+               print "Can't get system date" > "/dev/stderr"
+               exit 1
+             }
+             print "current date is", date_now
+             close("date")
+      }
+ 
+      NOTE: For full portability, exit values should be between zero and
+      126, inclusive.  Negative values, and values of 127 or greater,
+      may not produce consistent results across different operating
+      systems.
+ 
+ 
+ File: gawk.info,  Node: Built-in Variables,  Prev: Statements,  Up: Patterns 
and Actions
+ 
+ 7.5 Built-in Variables
+ ======================
+ 
+ Most `awk' variables are available to use for your own purposes; they
+ never change unless your program assigns values to them, and they never
+ affect anything unless your program examines them.  However, a few
+ variables in `awk' have special built-in meanings.  `awk' examines some
+ of these automatically, so that they enable you to tell `awk' how to do
+ certain things.  Others are set automatically by `awk', so that they
+ carry information from the internal workings of `awk' to your program.
+ 
+    This minor node documents all the built-in variables of `gawk', most
+ of which are also documented in the chapters describing their areas of
+ activity.
+ 
+ * Menu:
+ 
+ * User-modified::               Built-in variables that you change to control
+                                 `awk'.
+ * Auto-set::                    Built-in variables where `awk' gives
+                                 you information.
+ * ARGC and ARGV::               Ways to use `ARGC' and `ARGV'.
+ 
+ 
+ File: gawk.info,  Node: User-modified,  Next: Auto-set,  Up: Built-in 
Variables
+ 
+ 7.5.1 Built-in Variables That Control `awk'
+ -------------------------------------------
+ 
+ The following is an alphabetical list of variables that you can change
+ to control how `awk' does certain things. The variables that are
+ specific to `gawk' are marked with a pound sign (`#').
+ 
+ `BINMODE #'
+      On non-POSIX systems, this variable specifies use of binary mode
+      for all I/O.  Numeric values of one, two, or three specify that
+      input files, output files, or all files, respectively, should use
+      binary I/O.  A numeric value less than zero is treated as zero,
+      and a numeric value greater than three is treated as three.
+      Alternatively, string values of `"r"' or `"w"' specify that input
+      files and output files, respectively, should use binary I/O.  A
+      string value of `"rw"' or `"wr"' indicates that all files should
+      use binary I/O.  Any other string value is treated the same as
+      `"rw"', but causes `gawk' to generate a warning message.
+      `BINMODE' is described in more detail in *note PC Using::.
+ 
+      This variable is a `gawk' extension.  In other `awk'
+      implementations (except `mawk', *note Other Versions::), or if
+      `gawk' is in compatibility mode (*note Options::), it is not
+      special.
+ 
+ `CONVFMT'
+      This string controls conversion of numbers to strings (*note
+      Conversion::).  It works by being passed, in effect, as the first
+      argument to the `sprintf()' function (*note String Functions::).
+      Its default value is `"%.6g"'.  `CONVFMT' was introduced by the
+      POSIX standard.
+ 
+ `FIELDWIDTHS #'
+      This is a space-separated list of columns that tells `gawk' how to
+      split input with fixed columnar boundaries.  Assigning a value to
+      `FIELDWIDTHS' overrides the use of `FS' and `FPAT' for field
+      splitting.  *Note Constant Size::, for more information.
+ 
+      If `gawk' is in compatibility mode (*note Options::), then
+      `FIELDWIDTHS' has no special meaning, and field-splitting
+      operations occur based exclusively on the value of `FS'.
+ 
+ `FPAT #'
+      This is a regular expression (as a string) that tells `gawk' to
+      create the fields based on text that matches the regular
+      expression.  Assigning a value to `FPAT' overrides the use of `FS'
+      and `FIELDWIDTHS' for field splitting.  *Note Splitting By
+      Content::, for more information.
+ 
+      If `gawk' is in compatibility mode (*note Options::), then `FPAT'
+      has no special meaning, and field-splitting operations occur based
+      exclusively on the value of `FS'.
+ 
+ `FS'
+      This is the input field separator (*note Field Separators::).  The
+      value is a single-character string or a multi-character regular
+      expression that matches the separations between fields in an input
+      record.  If the value is the null string (`""'), then each
+      character in the record becomes a separate field.  (This behavior
+      is a `gawk' extension. POSIX `awk' does not specify the behavior
+      when `FS' is the null string.  Nonetheless, some other versions of
+      `awk' also treat `""' specially.)
+ 
+      The default value is `" "', a string consisting of a single space.
+      As a special exception, this value means that any sequence of
+      spaces, TABs, and/or newlines is a single separator.(1)  It also
+      causes spaces, TABs, and newlines at the beginning and end of a
+      record to be ignored.
+ 
+      You can set the value of `FS' on the command line using the `-F'
+      option:
+ 
+           awk -F, 'PROGRAM' INPUT-FILES
+ 
+      If `gawk' is using `FIELDWIDTHS' or `FPAT' for field splitting,
+      assigning a value to `FS' causes `gawk' to return to the normal,
+      `FS'-based field splitting. An easy way to do this is to simply
+      say `FS = FS', perhaps with an explanatory comment.
+ 
+ `IGNORECASE #'
+      If `IGNORECASE' is nonzero or non-null, then all string comparisons
+      and all regular expression matching are case independent.  Thus,
+      regexp matching with `~' and `!~', as well as the `gensub()',
+      `gsub()', `index()', `match()', `patsplit()', `split()', and
+      `sub()' functions, record termination with `RS', and field
+      splitting with `FS' and `FPAT', all ignore case when doing their
+      particular regexp operations.  However, the value of `IGNORECASE'
+      does _not_ affect array subscripting and it does not affect field
+      splitting when using a single-character field separator.  *Note
+      Case-sensitivity::.
+ 
+      If `gawk' is in compatibility mode (*note Options::), then
+      `IGNORECASE' has no special meaning.  Thus, string and regexp
+      operations are always case-sensitive.
+ 
+ `LINT #'
+      When this variable is true (nonzero or non-null), `gawk' behaves
+      as if the `--lint' command-line option is in effect.  (*note
+      Options::).  With a value of `"fatal"', lint warnings become fatal
+      errors.  With a value of `"invalid"', only warnings about things
+      that are actually invalid are issued. (This is not fully
+      implemented yet.)  Any other true value prints nonfatal warnings.
+      Assigning a false value to `LINT' turns off the lint warnings.
+ 
+      This variable is a `gawk' extension.  It is not special in other
+      `awk' implementations.  Unlike the other special variables,
+      changing `LINT' does affect the production of lint warnings, even
+      if `gawk' is in compatibility mode.  Much as the `--lint' and
+      `--traditional' options independently control different aspects of
+      `gawk''s behavior, the control of lint warnings during program
+      execution is independent of the flavor of `awk' being executed.
+ 
+ `OFMT'
+      This string controls conversion of numbers to strings (*note
+      Conversion::) for printing with the `print' statement.  It works
+      by being passed as the first argument to the `sprintf()' function
+      (*note String Functions::).  Its default value is `"%.6g"'.
+      Earlier versions of `awk' also used `OFMT' to specify the format
+      for converting numbers to strings in general expressions; this is
+      now done by `CONVFMT'.
+ 
+ `OFS'
+      This is the output field separator (*note Output Separators::).
+      It is output between the fields printed by a `print' statement.
+      Its default value is `" "', a string consisting of a single space.
+ 
+ `ORS'
+      This is the output record separator.  It is output at the end of
+      every `print' statement.  Its default value is `"\n"', the newline
+      character.  (*Note Output Separators::.)
+ 
++`PREC #'
++     The working precision of arbitrary precision floating-point
++     numbers, 53 by default (*note Setting Precision::).
++
++`ROUNDMODE #'
++     The rounding mode to use for arbitrary precision arithmetic on
++     numbers, by default `"N"' (`roundTiesToEven' in the IEEE-754
++     standard) (*note Setting Rounding Mode::).
++
+ `RS'
+      This is `awk''s input record separator.  Its default value is a
+      string containing a single newline character, which means that an
+      input record consists of a single line of text.  It can also be
+      the null string, in which case records are separated by runs of
+      blank lines.  If it is a regexp, records are separated by matches
+      of the regexp in the input text.  (*Note Records::.)
+ 
+      The ability for `RS' to be a regular expression is a `gawk'
+      extension.  In most other `awk' implementations, or if `gawk' is
+      in compatibility mode (*note Options::), just the first character
+      of `RS''s value is used.
+ 
+ `SUBSEP'
+      This is the subscript separator.  It has the default value of
+      `"\034"' and is used to separate the parts of the indices of a
+      multidimensional array.  Thus, the expression `foo["A", "B"]'
+      really accesses `foo["A\034B"]' (*note Multi-dimensional::).
+ 
+ `TEXTDOMAIN #'
+      This variable is used for internationalization of programs at the
+      `awk' level.  It sets the default text domain for specially marked
+      string constants in the source text, as well as for the
+      `dcgettext()', `dcngettext()' and `bindtextdomain()' functions
+      (*note Internationalization::).  The default value of `TEXTDOMAIN'
+      is `"messages"'.
+ 
+      This variable is a `gawk' extension.  In other `awk'
+      implementations, or if `gawk' is in compatibility mode (*note
+      Options::), it is not special.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) In POSIX `awk', newline does not count as whitespace.
+ 
+ 
+ File: gawk.info,  Node: Auto-set,  Next: ARGC and ARGV,  Prev: User-modified, 
 Up: Built-in Variables
+ 
+ 7.5.2 Built-in Variables That Convey Information
+ ------------------------------------------------
+ 
+ The following is an alphabetical list of variables that `awk' sets
+ automatically on certain occasions in order to provide information to
+ your program.  The variables that are specific to `gawk' are marked
+ with a pound sign (`#').
+ 
+ `ARGC, ARGV'
+      The command-line arguments available to `awk' programs are stored
+      in an array called `ARGV'.  `ARGC' is the number of command-line
+      arguments present.  *Note Other Arguments::.  Unlike most `awk'
+      arrays, `ARGV' is indexed from 0 to `ARGC' - 1.  In the following
+      example:
+ 
+           $ awk 'BEGIN {
+           >         for (i = 0; i < ARGC; i++)
+           >             print ARGV[i]
+           >      }' inventory-shipped BBS-list
+           -| awk
+           -| inventory-shipped
+           -| BBS-list
+ 
+      `ARGV[0]' contains `awk', `ARGV[1]' contains `inventory-shipped',
+      and `ARGV[2]' contains `BBS-list'.  The value of `ARGC' is three,
+      one more than the index of the last element in `ARGV', because the
+      elements are numbered from zero.
+ 
+      The names `ARGC' and `ARGV', as well as the convention of indexing
+      the array from 0 to `ARGC' - 1, are derived from the C language's
+      method of accessing command-line arguments.
+ 
+      The value of `ARGV[0]' can vary from system to system.  Also, you
+      should note that the program text is _not_ included in `ARGV', nor
+      are any of `awk''s command-line options.  *Note ARGC and ARGV::,
+      for information about how `awk' uses these variables.  (d.c.)
+ 
+ `ARGIND #'
+      The index in `ARGV' of the current file being processed.  Every
+      time `gawk' opens a new data file for processing, it sets `ARGIND'
+      to the index in `ARGV' of the file name.  When `gawk' is
+      processing the input files, `FILENAME == ARGV[ARGIND]' is always
+      true.
+ 
+      This variable is useful in file processing; it allows you to tell
+      how far along you are in the list of data files as well as to
+      distinguish between successive instances of the same file name on
+      the command line.
+ 
+      While you can change the value of `ARGIND' within your `awk'
+      program, `gawk' automatically sets it to a new value when the next
+      file is opened.
+ 
+      This variable is a `gawk' extension.  In other `awk'
+      implementations, or if `gawk' is in compatibility mode (*note
+      Options::), it is not special.
+ 
+ `ENVIRON'
+      An associative array containing the values of the environment.
+      The array indices are the environment variable names; the elements
+      are the values of the particular environment variables.  For
+      example, `ENVIRON["HOME"]' might be `/home/arnold'.  Changing this
+      array does not affect the environment passed on to any programs
+      that `awk' may spawn via redirection or the `system()' function.
+ 
+      Some operating systems may not have environment variables.  On
+      such systems, the `ENVIRON' array is empty (except for
 -     `ENVIRON["AWKPATH"]', *note AWKPATH Variable::).
++     `ENVIRON["AWKPATH"]', *note AWKPATH Variable:: and
++     `ENVIRON["AWKLIBPATH"]', *note AWKLIBPATH Variable::).
+ 
+ `ERRNO #'
+      If a system error occurs during a redirection for `getline',
+      during a read for `getline', or during a `close()' operation, then
+      `ERRNO' contains a string describing the error.
+ 
+      In addition, `gawk' clears `ERRNO' before opening each
+      command-line input file. This enables checking if the file is
+      readable inside a `BEGINFILE' pattern (*note BEGINFILE/ENDFILE::).
+ 
+      Otherwise, `ERRNO' works similarly to the C variable `errno'.
+      Except for the case just mentioned, `gawk' _never_ clears it (sets
+      it to zero or `""').  Thus, you should only expect its value to be
+      meaningful when an I/O operation returns a failure value, such as
+      `getline' returning -1.  You are, of course, free to clear it
+      yourself before doing an I/O operation.
+ 
+      This variable is a `gawk' extension.  In other `awk'
+      implementations, or if `gawk' is in compatibility mode (*note
+      Options::), it is not special.
+ 
+ `FILENAME'
+      The name of the file that `awk' is currently reading.  When no
+      data files are listed on the command line, `awk' reads from the
+      standard input and `FILENAME' is set to `"-"'.  `FILENAME' is
+      changed each time a new file is read (*note Reading Files::).
+      Inside a `BEGIN' rule, the value of `FILENAME' is `""', since
+      there are no input files being processed yet.(1) (d.c.)  Note,
+      though, that using `getline' (*note Getline::) inside a `BEGIN'
+      rule can give `FILENAME' a value.
+ 
+ `FNR'
+      The current record number in the current file.  `FNR' is
+      incremented each time a new record is read (*note Records::).  It
+      is reinitialized to zero each time a new input file is started.
+ 
+ `NF'
+      The number of fields in the current input record.  `NF' is set
+      each time a new record is read, when a new field is created or
+      when `$0' changes (*note Fields::).
+ 
+      Unlike most of the variables described in this node, assigning a
+      value to `NF' has the potential to affect `awk''s internal
+      workings.  In particular, assignments to `NF' can be used to
+      create or remove fields from the current record. *Note Changing
+      Fields::.
+ 
+ `NR'
+      The number of input records `awk' has processed since the
+      beginning of the program's execution (*note Records::).  `NR' is
+      incremented each time a new record is read.
+ 
+ `PROCINFO #'
+      The elements of this array provide access to information about the
+      running `awk' program.  The following elements (listed
+      alphabetically) are guaranteed to be available:
+ 
+     `PROCINFO["egid"]'
+           The value of the `getegid()' system call.
+ 
+     `PROCINFO["euid"]'
+           The value of the `geteuid()' system call.
+ 
+     `PROCINFO["FS"]'
+           This is `"FS"' if field splitting with `FS' is in effect,
+           `"FIELDWIDTHS"' if field splitting with `FIELDWIDTHS' is in
+           effect, or `"FPAT"' if field matching with `FPAT' is in
+           effect.
+ 
+     `PROCINFO["gid"]'
+           The value of the `getgid()' system call.
+ 
+     `PROCINFO["pgrpid"]'
+           The process group ID of the current process.
+ 
+     `PROCINFO["pid"]'
+           The process ID of the current process.
+ 
+     `PROCINFO["ppid"]'
+           The parent process ID of the current process.
+ 
+     `PROCINFO["sorted_in"]'
+           If this element exists in `PROCINFO', its value controls the
+           order in which array indices will be processed by `for (index
+           in array) ...' loops.  Since this is an advanced feature, we
+           defer the full description until later; see *note Scanning an
+           Array::.
+ 
+     `PROCINFO["strftime"]'
+           The default time format string for `strftime()'.  Assigning a
+           new value to this element changes the default.  *Note Time
+           Functions::.
+ 
+     `PROCINFO["uid"]'
+           The value of the `getuid()' system call.
+ 
+     `PROCINFO["version"]'
+           The version of `gawk'.
+ 
++     The following additional elements in the array are available to
++     provide information about the MPFR and GMP libraries if your
++     version of `gawk' supports arbitrary precision numbers (*note
++     Arbitrary Precision Arithmetic::):
++
++    `PROCINFO["mpfr_version"]'
++          The version of the GNU MPFR library.
++
++    `PROCINFO["gmp_version"]'
++          The version of the GNU MP library.
++
++    `PROCINFO["prec_max"]'
++          The maximum precision supported by MPFR.
++
++    `PROCINFO["prec_min"]'
++          The minimum precision required by MPFR.
++
+      On some systems, there may be elements in the array, `"group1"'
+      through `"groupN"' for some N. N is the number of supplementary
+      groups that the process has.  Use the `in' operator to test for
+      these elements (*note Reference to Elements::).
+ 
+      The `PROCINFO' array is also used to cause coprocesses to
+      communicate over pseudo-ttys instead of through two-way pipes;
+      this is discussed further in *note Two-way I/O::.
+ 
+      This array is a `gawk' extension.  In other `awk' implementations,
+      or if `gawk' is in compatibility mode (*note Options::), it is not
+      special.
+ 
+ `RLENGTH'
+      The length of the substring matched by the `match()' function
+      (*note String Functions::).  `RLENGTH' is set by invoking the
+      `match()' function.  Its value is the length of the matched
+      string, or -1 if no match is found.
+ 
+ `RSTART'
+      The start-index in characters of the substring that is matched by
+      the `match()' function (*note String Functions::).  `RSTART' is
+      set by invoking the `match()' function.  Its value is the position
+      of the string where the matched substring starts, or zero if no
+      match was found.
+ 
+ `RT #'
+      This is set each time a record is read. It contains the input text
+      that matched the text denoted by `RS', the record separator.
+ 
+      This variable is a `gawk' extension.  In other `awk'
+      implementations, or if `gawk' is in compatibility mode (*note
+      Options::), it is not special.
+ 
+ Advanced Notes: Changing `NR' and `FNR'
+ ---------------------------------------
+ 
+ `awk' increments `NR' and `FNR' each time it reads a record, instead of
+ setting them to the absolute value of the number of records read.  This
+ means that a program can change these variables and their new values
+ are incremented for each record.  (d.c.)  The following example shows
+ this:
+ 
+      $ echo '1
+      > 2
+      > 3
+      > 4' | awk 'NR == 2 { NR = 17 }
+      > { print NR }'
+      -| 1
+      -| 17
+      -| 18
+      -| 19
+ 
+ Before `FNR' was added to the `awk' language (*note V7/SVR3.1::), many
+ `awk' programs used this feature to track the number of records in a
+ file by resetting `NR' to zero when `FILENAME' changed.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Some early implementations of Unix `awk' initialized `FILENAME'
+ to `"-"', even if there were data files to be processed. This behavior
+ was incorrect and should not be relied upon in your programs.
+ 
+ 
+ File: gawk.info,  Node: ARGC and ARGV,  Prev: Auto-set,  Up: Built-in 
Variables
+ 
+ 7.5.3 Using `ARGC' and `ARGV'
+ -----------------------------
+ 
+ *note Auto-set::, presented the following program describing the
+ information contained in `ARGC' and `ARGV':
+ 
+      $ awk 'BEGIN {
+      >        for (i = 0; i < ARGC; i++)
+      >            print ARGV[i]
+      >      }' inventory-shipped BBS-list
+      -| awk
+      -| inventory-shipped
+      -| BBS-list
+ 
+ In this example, `ARGV[0]' contains `awk', `ARGV[1]' contains
+ `inventory-shipped', and `ARGV[2]' contains `BBS-list'.  Notice that
+ the `awk' program is not entered in `ARGV'.  The other command-line
+ options, with their arguments, are also not entered.  This includes
+ variable assignments done with the `-v' option (*note Options::).
+ Normal variable assignments on the command line _are_ treated as
+ arguments and do show up in the `ARGV' array.  Given the following
+ program in a file named `showargs.awk':
+ 
+      BEGIN {
+          printf "A=%d, B=%d\n", A, B
+          for (i = 0; i < ARGC; i++)
+              printf "\tARGV[%d] = %s\n", i, ARGV[i]
+      }
+      END   { printf "A=%d, B=%d\n", A, B }
+ 
+ Running it produces the following:
+ 
+      $ awk -v A=1 -f showargs.awk B=2 /dev/null
+      -| A=1, B=0
+      -|        ARGV[0] = awk
+      -|        ARGV[1] = B=2
+      -|        ARGV[2] = /dev/null
+      -| A=1, B=2
+ 
+    A program can alter `ARGC' and the elements of `ARGV'.  Each time
+ `awk' reaches the end of an input file, it uses the next element of
+ `ARGV' as the name of the next input file.  By storing a different
+ string there, a program can change which files are read.  Use `"-"' to
+ represent the standard input.  Storing additional elements and
+ incrementing `ARGC' causes additional files to be read.
+ 
+    If the value of `ARGC' is decreased, that eliminates input files
+ from the end of the list.  By recording the old value of `ARGC'
+ elsewhere, a program can treat the eliminated arguments as something
+ other than file names.
+ 
+    To eliminate a file from the middle of the list, store the null
+ string (`""') into `ARGV' in place of the file's name.  As a special
+ feature, `awk' ignores file names that have been replaced with the null
+ string.  Another option is to use the `delete' statement to remove
+ elements from `ARGV' (*note Delete::).
+ 
+    All of these actions are typically done in the `BEGIN' rule, before
+ actual processing of the input begins.  *Note Split Program::, and see
+ *note Tee Program::, for examples of each way of removing elements from
+ `ARGV'.  The following fragment processes `ARGV' in order to examine,
+ and then remove, command-line options:
+ 
+      BEGIN {
+          for (i = 1; i < ARGC; i++) {
+              if (ARGV[i] == "-v")
+                  verbose = 1
+              else if (ARGV[i] == "-q")
+                  debug = 1
+              else if (ARGV[i] ~ /^-./) {
+                  e = sprintf("%s: unrecognized option -- %c",
+                          ARGV[0], substr(ARGV[i], 2, 1))
+                  print e > "/dev/stderr"
+              } else
+                  break
+              delete ARGV[i]
+          }
+      }
+ 
+    To actually get the options into the `awk' program, end the `awk'
+ options with `--' and then supply the `awk' program's options, in the
+ following manner:
+ 
+      awk -f myprog -- -v -q file1 file2 ...
+ 
+    This is not necessary in `gawk'. Unless `--posix' has been
+ specified, `gawk' silently puts any unrecognized options into `ARGV'
+ for the `awk' program to deal with.  As soon as it sees an unknown
+ option, `gawk' stops looking for other options that it might otherwise
+ recognize.  The previous example with `gawk' would be:
+ 
+      gawk -f myprog -q -v file1 file2 ...
+ 
+ Because `-q' is not a valid `gawk' option, it and the following `-v'
+ are passed on to the `awk' program.  (*Note Getopt Function::, for an
+ `awk' library function that parses command-line options.)
+ 
+ 
+ File: gawk.info,  Node: Arrays,  Next: Functions,  Prev: Patterns and 
Actions,  Up: Top
+ 
+ 8 Arrays in `awk'
+ *****************
+ 
+ An "array" is a table of values called "elements".  The elements of an
+ array are distinguished by their "indices".  Indices may be either
+ numbers or strings.
+ 
+    This major node describes how arrays work in `awk', how to use array
+ elements, how to scan through every element in an array, and how to
+ remove array elements.  It also describes how `awk' simulates
+ multidimensional arrays, as well as some of the less obvious points
+ about array usage.  The major node moves on to discuss `gawk''s facility
+ for sorting arrays, and ends with a brief description of `gawk''s
+ ability to support true multidimensional arrays.
+ 
+    `awk' maintains a single set of names that may be used for naming
+ variables, arrays, and functions (*note User-defined::).  Thus, you
+ cannot have a variable and an array with the same name in the same
+ `awk' program.
+ 
+ * Menu:
+ 
+ * Array Basics::                The basics of arrays.
+ * Delete::                      The `delete' statement removes an element
+                                 from an array.
+ * Numeric Array Subscripts::    How to use numbers as subscripts in
+                                 `awk'.
+ * Uninitialized Subscripts::    Using Uninitialized variables as subscripts.
+ * Multi-dimensional::           Emulating multidimensional arrays in
+                                 `awk'.
+ * Arrays of Arrays::            True multidimensional arrays.
+ 
+ 
+ File: gawk.info,  Node: Array Basics,  Next: Delete,  Up: Arrays
+ 
+ 8.1 The Basics of Arrays
+ ========================
+ 
+ This minor node presents the basics: working with elements in arrays
+ one at a time, and traversing all of the elements in an array.
+ 
+ * Menu:
+ 
+ * Array Intro::                 Introduction to Arrays
+ * Reference to Elements::       How to examine one element of an array.
+ * Assigning Elements::          How to change an element of an array.
+ * Array Example::               Basic Example of an Array
+ * Scanning an Array::           A variation of the `for' statement. It
+                                 loops through the indices of an array's
+                                 existing elements.
+ * Controlling Scanning::        Controlling the order in which arrays are
+                                 scanned.
+ 
+ 
+ File: gawk.info,  Node: Array Intro,  Next: Reference to Elements,  Up: Array 
Basics
+ 
+ 8.1.1 Introduction to Arrays
+ ----------------------------
+ 
+      Doing linear scans over an associative array is like trying to
+      club someone to death with a loaded Uzi.
+      Larry Wall
+ 
+    The `awk' language provides one-dimensional arrays for storing
+ groups of related strings or numbers.  Every `awk' array must have a
+ name.  Array names have the same syntax as variable names; any valid
+ variable name would also be a valid array name.  But one name cannot be
+ used in both ways (as an array and as a variable) in the same `awk'
+ program.
+ 
+    Arrays in `awk' superficially resemble arrays in other programming
+ languages, but there are fundamental differences.  In `awk', it isn't
+ necessary to specify the size of an array before starting to use it.
+ Additionally, any number or string in `awk', not just consecutive
+ integers, may be used as an array index.
+ 
+    In most other languages, arrays must be "declared" before use,
+ including a specification of how many elements or components they
+ contain.  In such languages, the declaration causes a contiguous block
+ of memory to be allocated for that many elements.  Usually, an index in
+ the array must be a positive integer.  For example, the index zero
+ specifies the first element in the array, which is actually stored at
+ the beginning of the block of memory.  Index one specifies the second
+ element, which is stored in memory right after the first element, and
+ so on.  It is impossible to add more elements to the array, because it
+ has room only for as many elements as given in the declaration.  (Some
+ languages allow arbitrary starting and ending indices--e.g., `15 ..
+ 27'--but the size of the array is still fixed when the array is
+ declared.)
+ 
+    A contiguous array of four elements might look like the following
+ example, conceptually, if the element values are 8, `"foo"', `""', and
+ 30:
+ 
+      +---------+---------+--------+---------+
+      |    8    |  "foo"  |   ""   |    30   |    Value
+      +---------+---------+--------+---------+
+           0         1         2         3        Index
+ 
+ Only the values are stored; the indices are implicit from the order of
+ the values. Here, 8 is the value at index zero, because 8 appears in the
+ position with zero elements before it.
+ 
+    Arrays in `awk' are different--they are "associative".  This means
+ that each array is a collection of pairs: an index and its corresponding
+ array element value:
+ 
+      Index 3     Value 30
+      Index 1     Value "foo"
+      Index 0     Value 8
+      Index 2     Value ""
+ 
+ The pairs are shown in jumbled order because their order is irrelevant.
+ 
+    One advantage of associative arrays is that new pairs can be added
+ at any time.  For example, suppose a tenth element is added to the array
+ whose value is `"number ten"'.  The result is:
+ 
+      Index 10    Value "number ten"
+      Index 3     Value 30
+      Index 1     Value "foo"
+      Index 0     Value 8
+      Index 2     Value ""
+ 
+ Now the array is "sparse", which just means some indices are missing.
+ It has elements 0-3 and 10, but doesn't have elements 4, 5, 6, 7, 8, or
+ 9.
+ 
+    Another consequence of associative arrays is that the indices don't
+ have to be positive integers.  Any number, or even a string, can be an
+ index.  For example, the following is an array that translates words
+ from English to French:
+ 
+      Index "dog" Value "chien"
+      Index "cat" Value "chat"
+      Index "one" Value "un"
+      Index 1     Value "un"
+ 
+ Here we decided to translate the number one in both spelled-out and
+ numeric form--thus illustrating that a single array can have both
+ numbers and strings as indices.  In fact, array subscripts are always
+ strings; this is discussed in more detail in *note Numeric Array
+ Subscripts::.  Here, the number `1' isn't double-quoted, since `awk'
+ automatically converts it to a string.
+ 
+    The value of `IGNORECASE' has no effect upon array subscripting.
+ The identical string value used to store an array element must be used
+ to retrieve it.  When `awk' creates an array (e.g., with the `split()'
+ built-in function), that array's indices are consecutive integers
+ starting at one.  (*Note String Functions::.)
+ 
+    `awk''s arrays are efficient--the time to access an element is
+ independent of the number of elements in the array.
+ 
+ 
+ File: gawk.info,  Node: Reference to Elements,  Next: Assigning Elements,  
Prev: Array Intro,  Up: Array Basics
+ 
+ 8.1.2 Referring to an Array Element
+ -----------------------------------
+ 
+ The principal way to use an array is to refer to one of its elements.
+ An array reference is an expression as follows:
+ 
+      ARRAY[INDEX-EXPRESSION]
+ 
+ Here, ARRAY is the name of an array.  The expression INDEX-EXPRESSION is
+ the index of the desired element of the array.
+ 
+    The value of the array reference is the current value of that array
+ element.  For example, `foo[4.3]' is an expression for the element of
+ array `foo' at index `4.3'.
+ 
+    A reference to an array element that has no recorded value yields a
+ value of `""', the null string.  This includes elements that have not
+ been assigned any value as well as elements that have been deleted
+ (*note Delete::).
+ 
+      NOTE: A reference to an element that does not exist
+      _automatically_ creates that array element, with the null string
+      as its value.  (In some cases, this is unfortunate, because it
+      might waste memory inside `awk'.)
+ 
+      Novice `awk' programmers often make the mistake of checking if an
+      element exists by checking if the value is empty:
+ 
+           # Check if "foo" exists in a:         Incorrect!
+           if (a["foo"] != "") ...
+ 
+      This is incorrect, since this will _create_ `a["foo"]' if it
+      didn't exist before!
+ 
+    To determine whether an element exists in an array at a certain
+ index, use the following expression:
+ 
+      IND in ARRAY
+ 
+ This expression tests whether the particular index IND exists, without
+ the side effect of creating that element if it is not present.  The
+ expression has the value one (true) if `ARRAY[IND]' exists and zero
+ (false) if it does not exist.  For example, this statement tests
+ whether the array `frequencies' contains the index `2':
+ 
+      if (2 in frequencies)
+          print "Subscript 2 is present."
+ 
+    Note that this is _not_ a test of whether the array `frequencies'
+ contains an element whose _value_ is two.  There is no way to do that
+ except to scan all the elements.  Also, this _does not_ create
+ `frequencies[2]', while the following (incorrect) alternative does:
+ 
+      if (frequencies[2] != "")
+          print "Subscript 2 is present."
+ 
+ 
+ File: gawk.info,  Node: Assigning Elements,  Next: Array Example,  Prev: 
Reference to Elements,  Up: Array Basics
+ 
+ 8.1.3 Assigning Array Elements
+ ------------------------------
+ 
+ Array elements can be assigned values just like `awk' variables:
+ 
+      ARRAY[INDEX-EXPRESSION] = VALUE
+ 
+ ARRAY is the name of an array.  The expression INDEX-EXPRESSION is the
+ index of the element of the array that is assigned a value.  The
+ expression VALUE is the value to assign to that element of the array.
+ 
+ 
+ File: gawk.info,  Node: Array Example,  Next: Scanning an Array,  Prev: 
Assigning Elements,  Up: Array Basics
+ 
+ 8.1.4 Basic Array Example
+ -------------------------
+ 
+ The following program takes a list of lines, each beginning with a line
+ number, and prints them out in order of line number.  The line numbers
+ are not in order when they are first read--instead they are scrambled.
+ This program sorts the lines by making an array using the line numbers
+ as subscripts.  The program then prints out the lines in sorted order
+ of their numbers.  It is a very simple program and gets confused upon
+ encountering repeated numbers, gaps, or lines that don't begin with a
+ number:
+ 
+      {
+        if ($1 > max)
+          max = $1
+        arr[$1] = $0
+      }
+ 
+      END {
+        for (x = 1; x <= max; x++)
+          print arr[x]
+      }
+ 
+    The first rule keeps track of the largest line number seen so far;
+ it also stores each line into the array `arr', at an index that is the
+ line's number.  The second rule runs after all the input has been read,
+ to print out all the lines.  When this program is run with the
+ following input:
+ 
+      5  I am the Five man
+      2  Who are you?  The new number two!
+      4  . . . And four on the floor
+      1  Who is number one?
+      3  I three you.
+ 
+ Its output is:
+ 
+      1  Who is number one?
+      2  Who are you?  The new number two!
+      3  I three you.
+      4  . . . And four on the floor
+      5  I am the Five man
+ 
+    If a line number is repeated, the last line with a given number
+ overrides the others.  Gaps in the line numbers can be handled with an
+ easy improvement to the program's `END' rule, as follows:
+ 
+      END {
+        for (x = 1; x <= max; x++)
+          if (x in arr)
+            print arr[x]
+      }
+ 
+ 
+ File: gawk.info,  Node: Scanning an Array,  Next: Controlling Scanning,  
Prev: Array Example,  Up: Array Basics
+ 
+ 8.1.5 Scanning All Elements of an Array
+ ---------------------------------------
+ 
+ In programs that use arrays, it is often necessary to use a loop that
+ executes once for each element of an array.  In other languages, where
+ arrays are contiguous and indices are limited to positive integers,
+ this is easy: all the valid indices can be found by counting from the
+ lowest index up to the highest.  This technique won't do the job in
+ `awk', because any number or string can be an array index.  So `awk'
+ has a special kind of `for' statement for scanning an array:
+ 
+      for (VAR in ARRAY)
+        BODY
+ 
+ This loop executes BODY once for each index in ARRAY that the program
+ has previously used, with the variable VAR set to that index.
+ 
+    The following program uses this form of the `for' statement.  The
+ first rule scans the input records and notes which words appear (at
+ least once) in the input, by storing a one into the array `used' with
+ the word as index.  The second rule scans the elements of `used' to
+ find all the distinct words that appear in the input.  It prints each
+ word that is more than 10 characters long and also prints the number of
+ such words.  *Note String Functions::, for more information on the
+ built-in function `length()'.
+ 
+      # Record a 1 for each word that is used at least once
+      {
+          for (i = 1; i <= NF; i++)
+              used[$i] = 1
+      }
+ 
+      # Find number of distinct words more than 10 characters long
+      END {
+          for (x in used) {
+              if (length(x) > 10) {
+                  ++num_long_words
+                  print x
+              }
+          }
+          print num_long_words, "words longer than 10 characters"
+      }
+ 
+ *Note Word Sorting::, for a more detailed example of this type.
+ 
+    The order in which elements of the array are accessed by this
+ statement is determined by the internal arrangement of the array
+ elements within `awk' and normally cannot be controlled or changed.
+ This can lead to problems if new elements are added to ARRAY by
+ statements in the loop body; it is not predictable whether the `for'
+ loop will reach them.  Similarly, changing VAR inside the loop may
+ produce strange results.  It is best to avoid such things.
+ 
+ 
+ File: gawk.info,  Node: Controlling Scanning,  Prev: Scanning an Array,  Up: 
Array Basics
+ 
+ 8.1.6 Using Predefined Array Scanning Orders
+ --------------------------------------------
+ 
+ By default, when a `for' loop traverses an array, the order is
+ undefined, meaning that the `awk' implementation determines the order
+ in which the array is traversed.  This order is usually based on the
+ internal implementation of arrays and will vary from one version of
+ `awk' to the next.
+ 
+    Often, though, you may wish to do something simple, such as
+ "traverse the array by comparing the indices in ascending order," or
+ "traverse the array by on comparing the values in descending order."
+ `gawk' provides two mechanisms which give you this control.
+ 
+    * Set `PROCINFO["sorted_in"]' to one of a set of predefined values.
+      We describe this now.
+ 
+    * Set `PROCINFO["sorted_in"]' to the name of a user-defined function
+      to be used for comparison of array elements. This advanced feature
+      is described later, in *note Array Sorting::.
+ 
+    The following special values for `PROCINFO["sorted_in"]' are
+ available:
+ 
+ `"@unsorted"'
+      Array elements are processed in arbitrary order, which is the
+      default `awk' behavior.
+ 
+ `"@ind_str_asc"'
+      Order by indices compared as strings; this is the most basic sort.
+      (Internally, array indices are always strings, so with `a[2*5] = 1'
+      the index is `"10"' rather than numeric 10.)
+ 
+ `"@ind_num_asc"'
+      Order by indices but force them to be treated as numbers in the
+      process.  Any index with a non-numeric value will end up
+      positioned as if it were zero.
+ 
+ `"@val_type_asc"'
+      Order by element values rather than indices.  Ordering is by the
+      type assigned to the element (*note Typing and Comparison::).  All
+      numeric values come before all string values, which in turn come
+      before all subarrays.  (Subarrays have not been described yet;
+      *note Arrays of Arrays::).
+ 
+ `"@val_str_asc"'
+      Order by element values rather than by indices.  Scalar values are
+      compared as strings.  Subarrays, if present, come out last.
+ 
+ `"@val_num_asc"'
+      Order by element values rather than by indices.  Scalar values are
+      compared as numbers.  Subarrays, if present, come out last.  When
+      numeric values are equal, the string values are used to provide an
+      ordering: this guarantees consistent results across different
+      versions of the C `qsort()' function,(1) which `gawk' uses
+      internally to perform the sorting.
+ 
+ `"@ind_str_desc"'
+      Reverse order from the most basic sort.
+ 
+ `"@ind_num_desc"'
+      Numeric indices ordered from high to low.
+ 
+ `"@val_type_desc"'
+      Element values, based on type, in descending order.
+ 
+ `"@val_str_desc"'
+      Element values, treated as strings, ordered from high to low.
+      Subarrays, if present, come out first.
+ 
+ `"@val_num_desc"'
+      Element values, treated as numbers, ordered from high to low.
+      Subarrays, if present, come out first.
+ 
+    The array traversal order is determined before the `for' loop starts
+ to run. Changing `PROCINFO["sorted_in"]' in the loop body will not
+ affect the loop.
+ 
+    For example:
+ 
+      $ gawk 'BEGIN {
+      >    a[4] = 4
+      >    a[3] = 3
+      >    for (i in a)
+      >        print i, a[i]
+      > }'
+      -| 4 4
+      -| 3 3
+      $ gawk 'BEGIN {
+      >    PROCINFO["sorted_in"] = "@ind_str_asc"
+      >    a[4] = 4
+      >    a[3] = 3
+      >    for (i in a)
+      >        print i, a[i]
+      > }'
+      -| 3 3
+      -| 4 4
+ 
+    When sorting an array by element values, if a value happens to be a
+ subarray then it is considered to be greater than any string or numeric
+ value, regardless of what the subarray itself contains, and all
+ subarrays are treated as being equal to each other.  Their order
+ relative to each other is determined by their index strings.
+ 
+    Here are some additional things to bear in mind about sorted array
+ traversal.
+ 
+    * The value of `PROCINFO["sorted_in"]' is global. That is, it affects
+      all array traversal `for' loops.  If you need to change it within
+      your own code, you should see if it's defined and save and restore
+      the value:
+ 
+           ...
+           if ("sorted_in" in PROCINFO) {
+               save_sorted = PROCINFO["sorted_in"]
+               PROCINFO["sorted_in"] = "@val_str_desc" # or whatever
+           }
+           ...
+           if (save_sorted)
+               PROCINFO["sorted_in"] = save_sorted
+ 
+    * As mentioned, the default array traversal order is represented by
+      `"@unsorted"'.  You can also get the default behavior by assigning
+      the null string to `PROCINFO["sorted_in"]' or by just deleting the
+      `"sorted_in"' element from the `PROCINFO' array with the `delete'
+      statement.  (The `delete' statement hasn't been described yet;
+      *note Delete::.)
+ 
+    In addition, `gawk' provides built-in functions for sorting arrays;
+ see *note Array Sorting Functions::.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) When two elements compare as equal, the C `qsort()' function
+ does not guarantee that they will maintain their original relative
+ order after sorting.  Using the string value to provide a unique
+ ordering when the numeric values are equal ensures that `gawk' behaves
+ consistently across different environments.
+ 
+ 
+ File: gawk.info,  Node: Delete,  Next: Numeric Array Subscripts,  Prev: Array 
Basics,  Up: Arrays
+ 
+ 8.2 The `delete' Statement
+ ==========================
+ 
+ To remove an individual element of an array, use the `delete' statement:
+ 
+      delete ARRAY[INDEX-EXPRESSION]
+ 
+    Once an array element has been deleted, any value the element once
+ had is no longer available. It is as if the element had never been
+ referred to or been given a value.  The following is an example of
+ deleting elements in an array:
+ 
+      for (i in frequencies)
+        delete frequencies[i]
+ 
+ This example removes all the elements from the array `frequencies'.
+ Once an element is deleted, a subsequent `for' statement to scan the
+ array does not report that element and the `in' operator to check for
+ the presence of that element returns zero (i.e., false):
+ 
+      delete foo[4]
+      if (4 in foo)
+          print "This will never be printed"
+ 
+    It is important to note that deleting an element is _not_ the same
+ as assigning it a null value (the empty string, `""').  For example:
+ 
+      foo[4] = ""
+      if (4 in foo)
+        print "This is printed, even though foo[4] is empty"
+ 
+    It is not an error to delete an element that does not exist.
+ However, if `--lint' is provided on the command line (*note Options::),
+ `gawk' issues a warning message when an element that is not in the
+ array is deleted.
+ 
+    All the elements of an array may be deleted with a single statement
+ (c.e.)  by leaving off the subscript in the `delete' statement, as
+ follows:
+ 
+      delete ARRAY
+ 
+    This ability is a `gawk' extension; it is not available in
+ compatibility mode (*note Options::).
+ 
+    Using this version of the `delete' statement is about three times
+ more efficient than the equivalent loop that deletes each element one
+ at a time.
+ 
+    The following statement provides a portable but nonobvious way to
+ clear out an array:(1)
+ 
+      split("", array)
+ 
+    The `split()' function (*note String Functions::) clears out the
+ target array first. This call asks it to split apart the null string.
+ Because there is no data to split out, the function simply clears the
+ array and then returns.
+ 
+      CAUTION: Deleting an array does not change its type; you cannot
+      delete an array and then use the array's name as a scalar (i.e., a
+      regular variable). For example, the following does not work:
+ 
+           a[1] = 3
+           delete a
+           a = 3
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Thanks to Michael Brennan for pointing this out.
+ 
+ 
+ File: gawk.info,  Node: Numeric Array Subscripts,  Next: Uninitialized 
Subscripts,  Prev: Delete,  Up: Arrays
+ 
+ 8.3 Using Numbers to Subscript Arrays
+ =====================================
+ 
+ An important aspect to remember about arrays is that _array subscripts
+ are always strings_.  When a numeric value is used as a subscript, it
+ is converted to a string value before being used for subscripting
+ (*note Conversion::).  This means that the value of the built-in
+ variable `CONVFMT' can affect how your program accesses elements of an
+ array.  For example:
+ 
+      xyz = 12.153
+      data[xyz] = 1
+      CONVFMT = "%2.2f"
+      if (xyz in data)
+          printf "%s is in data\n", xyz
+      else
+          printf "%s is not in data\n", xyz
+ 
+ This prints `12.15 is not in data'.  The first statement gives `xyz' a
+ numeric value.  Assigning to `data[xyz]' subscripts `data' with the
+ string value `"12.153"' (using the default conversion value of
+ `CONVFMT', `"%.6g"').  Thus, the array element `data["12.153"]' is
+ assigned the value one.  The program then changes the value of
+ `CONVFMT'.  The test `(xyz in data)' generates a new string value from
+ `xyz'--this time `"12.15"'--because the value of `CONVFMT' only allows
+ two significant digits.  This test fails, since `"12.15"' is different
+ from `"12.153"'.
+ 
+    According to the rules for conversions (*note Conversion::), integer
+ values are always converted to strings as integers, no matter what the
+ value of `CONVFMT' may happen to be.  So the usual case of the
+ following works:
+ 
+      for (i = 1; i <= maxsub; i++)
+          do something with array[i]
+ 
+    The "integer values always convert to strings as integers" rule has
+ an additional consequence for array indexing.  Octal and hexadecimal
+ constants (*note Nondecimal-numbers::) are converted internally into
+ numbers, and their original form is forgotten.  This means, for
+ example, that `array[17]', `array[021]', and `array[0x11]' all refer to
+ the same element!
+ 
+    As with many things in `awk', the majority of the time things work
+ as one would expect them to.  But it is useful to have a precise
+ knowledge of the actual rules since they can sometimes have a subtle
+ effect on your programs.
+ 
+ 
+ File: gawk.info,  Node: Uninitialized Subscripts,  Next: Multi-dimensional,  
Prev: Numeric Array Subscripts,  Up: Arrays
+ 
+ 8.4 Using Uninitialized Variables as Subscripts
+ ===============================================
+ 
+ Suppose it's necessary to write a program to print the input data in
+ reverse order.  A reasonable attempt to do so (with some test data)
+ might look like this:
+ 
+      $ echo 'line 1
+      > line 2
+      > line 3' | awk '{ l[lines] = $0; ++lines }
+      > END {
+      >     for (i = lines-1; i >= 0; --i)
+      >        print l[i]
+      > }'
+      -| line 3
+      -| line 2
+ 
+    Unfortunately, the very first line of input data did not come out in
+ the output!
+ 
+    Upon first glance, we would think that this program should have
+ worked.  The variable `lines' is uninitialized, and uninitialized
+ variables have the numeric value zero.  So, `awk' should have printed
+ the value of `l[0]'.
+ 
+    The issue here is that subscripts for `awk' arrays are _always_
+ strings. Uninitialized variables, when used as strings, have the value
+ `""', not zero.  Thus, `line 1' ends up stored in `l[""]'.  The
+ following version of the program works correctly:
+ 
+      { l[lines++] = $0 }
+      END {
+          for (i = lines - 1; i >= 0; --i)
+             print l[i]
+      }
+ 
+    Here, the `++' forces `lines' to be numeric, thus making the "old
+ value" numeric zero. This is then converted to `"0"' as the array
+ subscript.
+ 
+    Even though it is somewhat unusual, the null string (`""') is a
+ valid array subscript.  (d.c.)  `gawk' warns about the use of the null
+ string as a subscript if `--lint' is provided on the command line
+ (*note Options::).
+ 
+ 
+ File: gawk.info,  Node: Multi-dimensional,  Next: Arrays of Arrays,  Prev: 
Uninitialized Subscripts,  Up: Arrays
+ 
+ 8.5 Multidimensional Arrays
+ ===========================
+ 
+ * Menu:
+ 
+ * Multi-scanning::              Scanning multidimensional arrays.
+ 
+    A multidimensional array is an array in which an element is
+ identified by a sequence of indices instead of a single index.  For
+ example, a two-dimensional array requires two indices.  The usual way
+ (in most languages, including `awk') to refer to an element of a
+ two-dimensional array named `grid' is with `grid[X,Y]'.
+ 
+    Multidimensional arrays are supported in `awk' through concatenation
+ of indices into one string.  `awk' converts the indices into strings
+ (*note Conversion::) and concatenates them together, with a separator
+ between them.  This creates a single string that describes the values
+ of the separate indices.  The combined string is used as a single index
+ into an ordinary, one-dimensional array.  The separator used is the
+ value of the built-in variable `SUBSEP'.
+ 
+    For example, suppose we evaluate the expression `foo[5,12] = "value"'
+ when the value of `SUBSEP' is `"@"'.  The numbers 5 and 12 are
+ converted to strings and concatenated with an `@' between them,
+ yielding `"address@hidden"'; thus, the array element `foo["address@hidden"]' 
is set to
+ `"value"'.
+ 
+    Once the element's value is stored, `awk' has no record of whether
+ it was stored with a single index or a sequence of indices.  The two
+ expressions `foo[5,12]' and `foo[5 SUBSEP 12]' are always equivalent.
+ 
+    The default value of `SUBSEP' is the string `"\034"', which contains
+ a nonprinting character that is unlikely to appear in an `awk' program
+ or in most input data.  The usefulness of choosing an unlikely
+ character comes from the fact that index values that contain a string
+ matching `SUBSEP' can lead to combined strings that are ambiguous.
+ Suppose that `SUBSEP' is `"@"'; then `foo["address@hidden", "c"]' and
+ `foo["a", "address@hidden"]' are indistinguishable because both are actually
+ stored as `foo["address@hidden@c"]'.
+ 
+    To test whether a particular index sequence exists in a
+ multidimensional array, use the same operator (`in') that is used for
+ single dimensional arrays.  Write the whole sequence of indices in
+ parentheses, separated by commas, as the left operand:
+ 
+      (SUBSCRIPT1, SUBSCRIPT2, ...) in ARRAY
+ 
+    The following example treats its input as a two-dimensional array of
+ fields; it rotates this array 90 degrees clockwise and prints the
+ result.  It assumes that all lines have the same number of elements:
+ 
+      {
+           if (max_nf < NF)
+                max_nf = NF
+           max_nr = NR
+           for (x = 1; x <= NF; x++)
+                vector[x, NR] = $x
+      }
+ 
+      END {
+           for (x = 1; x <= max_nf; x++) {
+                for (y = max_nr; y >= 1; --y)
+                     printf("%s ", vector[x, y])
+                printf("\n")
+           }
+      }
+ 
+ When given the input:
+ 
+      1 2 3 4 5 6
+      2 3 4 5 6 1
+      3 4 5 6 1 2
+      4 5 6 1 2 3
+ 
+ the program produces the following output:
+ 
+      4 3 2 1
+      5 4 3 2
+      6 5 4 3
+      1 6 5 4
+      2 1 6 5
+      3 2 1 6
+ 
+ 
+ File: gawk.info,  Node: Multi-scanning,  Up: Multi-dimensional
+ 
+ 8.5.1 Scanning Multidimensional Arrays
+ --------------------------------------
+ 
+ There is no special `for' statement for scanning a "multidimensional"
+ array. There cannot be one, because, in truth, `awk' does not have
+ multidimensional arrays or elements--there is only a multidimensional
+ _way of accessing_ an array.
+ 
+    However, if your program has an array that is always accessed as
+ multidimensional, you can get the effect of scanning it by combining
+ the scanning `for' statement (*note Scanning an Array::) with the
+ built-in `split()' function (*note String Functions::).  It works in
+ the following manner:
+ 
+      for (combined in array) {
+          split(combined, separate, SUBSEP)
+          ...
+      }
+ 
+ This sets the variable `combined' to each concatenated combined index
+ in the array, and splits it into the individual indices by breaking it
+ apart where the value of `SUBSEP' appears.  The individual indices then
+ become the elements of the array `separate'.
+ 
+    Thus, if a value is previously stored in `array[1, "foo"]', then an
+ element with index `"1\034foo"' exists in `array'.  (Recall that the
+ default value of `SUBSEP' is the character with code 034.)  Sooner or
+ later, the `for' statement finds that index and does an iteration with
+ the variable `combined' set to `"1\034foo"'.  Then the `split()'
+ function is called as follows:
+ 
+      split("1\034foo", separate, "\034")
+ 
+ The result is to set `separate[1]' to `"1"' and `separate[2]' to
+ `"foo"'.  Presto! The original sequence of separate indices is
+ recovered.
+ 
+ 
+ File: gawk.info,  Node: Arrays of Arrays,  Prev: Multi-dimensional,  Up: 
Arrays
+ 
+ 8.6 Arrays of Arrays
+ ====================
+ 
+ `gawk' goes beyond standard `awk''s multidimensional array access and
+ provides true arrays of arrays. Elements of a subarray are referred to
+ by their own indices enclosed in square brackets, just like the
+ elements of the main array.  For example, the following creates a
+ two-element subarray at index `1' of the main array `a':
+ 
+      a[1][1] = 1
+      a[1][2] = 2
+ 
+    This simulates a true two-dimensional array. Each subarray element
+ can contain another subarray as a value, which in turn can hold other
+ arrays as well. In this way, you can create arrays of three or more
+ dimensions.  The indices can be any `awk' expression, including scalars
+ separated by commas (that is, a regular `awk' simulated
+ multidimensional subscript). So the following is valid in `gawk':
+ 
+      a[1][3][1, "name"] = "barney"
+ 
+    Each subarray and the main array can be of different length. In
+ fact, the elements of an array or its subarray do not all have to have
+ the same type. This means that the main array and any of its subarrays
+ can be non-rectangular, or jagged in structure. One can assign a scalar
+ value to the index `4' of the main array `a':
+ 
+      a[4] = "An element in a jagged array"
+ 
+    The terms "dimension", "row" and "column" are meaningless when
+ applied to such an array, but we will use "dimension" henceforth to
+ imply the maximum number of indices needed to refer to an existing
+ element. The type of any element that has already been assigned cannot
+ be changed by assigning a value of a different type. You have to first
+ delete the current element, which effectively makes `gawk' forget about
+ the element at that index:
+ 
+      delete a[4]
+      a[4][5][6][7] = "An element in a four-dimensional array"
+ 
+ This removes the scalar value from index `4' and then inserts a
+ subarray of subarray of subarray containing a scalar. You can also
+ delete an entire subarray or subarray of subarrays:
+ 
+      delete a[4][5]
+      a[4][5] = "An element in subarray a[4]"
+ 
+    But recall that you can not delete the main array `a' and then use it
+ as a scalar.
+ 
+    The built-in functions which take array arguments can also be used
+ with subarrays. For example, the following code fragment uses `length()'
+ (*note String Functions::) to determine the number of elements in the
+ main array `a' and its subarrays:
+ 
+      print length(a), length(a[1]), length(a[1][3])
+ 
+ This results in the following output for our main array `a':
+ 
+      2, 3, 1
+ 
+ The `SUBSCRIPT in ARRAY' expression (*note Reference to Elements::)
+ works similarly for both regular `awk'-style arrays and arrays of
+ arrays. For example, the tests `1 in a', `3 in a[1]', and `(1, "name")
+ in a[1][3]' all evaluate to one (true) for our array `a'.
+ 
+    The `for (item in array)' statement (*note Scanning an Array::) can
+ be nested to scan all the elements of an array of arrays if it is
+ rectangular in structure. In order to print the contents (scalar
+ values) of a two-dimensional array of arrays (i.e., in which each
+ first-level element is itself an array, not necessarily of the same
+ length) you could use the following code:
+ 
+      for (i in array)
+          for (j in array[i])
+              print array[i][j]
+ 
+    The `isarray()' function (*note Type Functions::) lets you test if
+ an array element is itself an array:
+ 
+      for (i in array) {
+          if (isarray(array[i]) {
+              for (j in array[i]) {
+                  print array[i][j]
+              }
+          }
+      }
+ 
+    If the structure of a jagged array of arrays is known in advance,
+ you can often devise workarounds using control statements. For example,
+ the following code prints the elements of our main array `a':
+ 
+      for (i in a) {
+          for (j in a[i]) {
+              if (j == 3) {
+                  for (k in a[i][j])
+                      print a[i][j][k]
+              } else
+                  print a[i][j]
+          }
+      }
+ 
+ *Note Walking Arrays::, for a user-defined function that will "walk" an
+ arbitrarily-dimensioned array of arrays.
+ 
+    Recall that a reference to an uninitialized array element yields a
+ value of `""', the null string. This has one important implication when
+ you intend to use a subarray as an argument to a function, as
+ illustrated by the following example:
+ 
+      $ gawk 'BEGIN { split("a b c d", b[1]); print b[1][1] }'
+      error--> gawk: cmd. line:1: fatal: split: second argument is not an array
+ 
+    The way to work around this is to first force `b[1]' to be an array
+ by creating an arbitrary index:
+ 
+      $ gawk 'BEGIN { b[1][1] = ""; split("a b c d", b[1]); print b[1][1] }'
+      -| a
+ 
+ 
+ File: gawk.info,  Node: Functions,  Next: Internationalization,  Prev: 
Arrays,  Up: Top
+ 
+ 9 Functions
+ ***********
+ 
+ This major node describes `awk''s built-in functions, which fall into
+ three categories: numeric, string, and I/O.  `gawk' provides additional
+ groups of functions to work with values that represent time, do bit
+ manipulation, sort arrays, and internationalize and localize programs.
+ 
+    Besides the built-in functions, `awk' has provisions for writing new
+ functions that the rest of a program can use.  The second half of this
+ major node describes these "user-defined" functions.
+ 
+ * Menu:
+ 
+ * Built-in::                    Summarizes the built-in functions.
+ * User-defined::                Describes User-defined functions in detail.
+ * Indirect Calls::              Choosing the function to call at runtime.
+ 
+ 
+ File: gawk.info,  Node: Built-in,  Next: User-defined,  Up: Functions
+ 
+ 9.1 Built-in Functions
+ ======================
+ 
+ "Built-in" functions are always available for your `awk' program to
+ call.  This minor node defines all the built-in functions in `awk';
+ some of these are mentioned in other sections but are summarized here
+ for your convenience.
+ 
+ * Menu:
+ 
+ * Calling Built-in::            How to call built-in functions.
+ * Numeric Functions::           Functions that work with numbers, including
+                                 `int()', `sin()' and `rand()'.
+ * String Functions::            Functions for string manipulation, such as
+                                 `split()', `match()' and
+                                 `sprintf()'.
+ * I/O Functions::               Functions for files and shell commands.
+ * Time Functions::              Functions for dealing with timestamps.
+ * Bitwise Functions::           Functions for bitwise operations.
+ * Type Functions::              Functions for type information.
+ * I18N Functions::              Functions for string translation.
+ 
+ 
+ File: gawk.info,  Node: Calling Built-in,  Next: Numeric Functions,  Up: 
Built-in
+ 
+ 9.1.1 Calling Built-in Functions
+ --------------------------------
+ 
+ To call one of `awk''s built-in functions, write the name of the
+ function followed by arguments in parentheses.  For example, `atan2(y +
+ z, 1)' is a call to the function `atan2()' and has two arguments.
+ 
+    Whitespace is ignored between the built-in function name and the
+ open parenthesis, but nonetheless it is good practice to avoid using
+ whitespace there.  User-defined functions do not permit whitespace in
+ this way, and it is easier to avoid mistakes by following a simple
+ convention that always works--no whitespace after a function name.
+ 
+    Each built-in function accepts a certain number of arguments.  In
+ some cases, arguments can be omitted. The defaults for omitted
+ arguments vary from function to function and are described under the
+ individual functions.  In some `awk' implementations, extra arguments
+ given to built-in functions are ignored.  However, in `gawk', it is a
+ fatal error to give extra arguments to a built-in function.
+ 
+    When a function is called, expressions that create the function's
+ actual parameters are evaluated completely before the call is performed.
+ For example, in the following code fragment:
+ 
+      i = 4
+      j = sqrt(i++)
+ 
+ the variable `i' is incremented to the value five before `sqrt()' is
+ called with a value of four for its actual parameter.  The order of
+ evaluation of the expressions used for the function's parameters is
+ undefined.  Thus, avoid writing programs that assume that parameters
+ are evaluated from left to right or from right to left.  For example:
+ 
+      i = 5
+      j = atan2(i++, i *= 2)
+ 
+    If the order of evaluation is left to right, then `i' first becomes
+ 6, and then 12, and `atan2()' is called with the two arguments 6 and
+ 12.  But if the order of evaluation is right to left, `i' first becomes
+ 10, then 11, and `atan2()' is called with the two arguments 11 and 10.
+ 
+ 
+ File: gawk.info,  Node: Numeric Functions,  Next: String Functions,  Prev: 
Calling Built-in,  Up: Built-in
+ 
+ 9.1.2 Numeric Functions
+ -----------------------
+ 
+ The following list describes all of the built-in functions that work
+ with numbers.  Optional parameters are enclosed in square
+ brackets ([ ]):
+ 
+ `atan2(Y, X)'
+      Return the arctangent of `Y / X' in radians.  You can use `pi =
+      atan2(0, -1)' to retrieve the value of pi.
+ 
+ `cos(X)'
+      Return the cosine of X, with X in radians.
+ 
+ `exp(X)'
+      Return the exponential of X (`e ^ X') or report an error if X is
+      out of range.  The range of values X can have depends on your
+      machine's floating-point representation.
+ 
+ `int(X)'
+      Return the nearest integer to X, located between X and zero and
+      truncated toward zero.
+ 
+      For example, `int(3)' is 3, `int(3.9)' is 3, `int(-3.9)' is -3,
+      and `int(-3)' is -3 as well.
+ 
+ `log(X)'
+      Return the natural logarithm of X, if X is positive; otherwise,
+      report an error.
+ 
+ `rand()'
+      Return a random number.  The values of `rand()' are uniformly
+      distributed between zero and one.  The value could be zero but is
+      never one.(1)
+ 
+      Often random integers are needed instead.  Following is a
+      user-defined function that can be used to obtain a random
+      non-negative integer less than N:
+ 
+           function randint(n) {
+                return int(n * rand())
+           }
+ 
+      The multiplication produces a random number greater than zero and
+      less than `n'.  Using `int()', this result is made into an integer
+      between zero and `n' - 1, inclusive.
+ 
+      The following example uses a similar function to produce random
+      integers between one and N.  This program prints a new random
+      number for each input record:
+ 
+           # Function to roll a simulated die.
+           function roll(n) { return 1 + int(rand() * n) }
+ 
+           # Roll 3 six-sided dice and
+           # print total number of points.
+           {
+                 printf("%d points\n",
+                        roll(6)+roll(6)+roll(6))
+           }
+ 
+           CAUTION: In most `awk' implementations, including `gawk',
+           `rand()' starts generating numbers from the same starting
+           number, or "seed", each time you run `awk'.(2)  Thus, a
+           program generates the same results each time you run it.  The
+           numbers are random within one `awk' run but predictable from
+           run to run.  This is convenient for debugging, but if you want
+           a program to do different things each time it is used, you
+           must change the seed to a value that is different in each
+           run.  To do this, use `srand()'.
+ 
+ `sin(X)'
+      Return the sine of X, with X in radians.
+ 
+ `sqrt(X)'
+      Return the positive square root of X.  `gawk' prints a warning
+      message if X is negative.  Thus, `sqrt(4)' is 2.
+ 
+ `srand([X])'
+      Set the starting point, or seed, for generating random numbers to
+      the value X.
+ 
+      Each seed value leads to a particular sequence of random
+      numbers.(3) Thus, if the seed is set to the same value a second
+      time, the same sequence of random numbers is produced again.
+ 
+           CAUTION: Different `awk' implementations use different
+           random-number generators internally.  Don't expect the same
+           `awk' program to produce the same series of random numbers
+           when executed by different versions of `awk'.
+ 
+      If the argument X is omitted, as in `srand()', then the current
+      date and time of day are used for a seed.  This is the way to get
+      random numbers that are truly unpredictable.
+ 
+      The return value of `srand()' is the previous seed.  This makes it
+      easy to keep track of the seeds in case you need to consistently
+      reproduce sequences of random numbers.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The C version of `rand()' on many Unix systems is known to
+ produce fairly poor sequences of random numbers.  However, nothing
+ requires that an `awk' implementation use the C `rand()' to implement
+ the `awk' version of `rand()'.  In fact, `gawk' uses the BSD `random()'
+ function, which is considerably better than `rand()', to produce random
+ numbers.
+ 
+    (2) `mawk' uses a different seed each time.
+ 
+    (3) Computer-generated random numbers really are not truly random.
+ They are technically known as "pseudorandom."  This means that while
+ the numbers in a sequence appear to be random, you can in fact generate
+ the same sequence of random numbers over and over again.
+ 
+ 
+ File: gawk.info,  Node: String Functions,  Next: I/O Functions,  Prev: 
Numeric Functions,  Up: Built-in
+ 
+ 9.1.3 String-Manipulation Functions
+ -----------------------------------
+ 
+ The functions in this minor node look at or change the text of one or
+ more strings.  `gawk' understands locales (*note Locales::), and does
+ all string processing in terms of _characters_, not _bytes_.  This
+ distinction is particularly important to understand for locales where
+ one character may be represented by multiple bytes.  Thus, for example,
+ `length()' returns the number of characters in a string, and not the
+ number of bytes used to represent those characters, Similarly,
+ `index()' works with character indices, and not byte indices.
+ 
+    In the following list, optional parameters are enclosed in square
+ brackets ([ ]).  Several functions perform string substitution; the
+ full discussion is provided in the description of the `sub()' function,
+ which comes towards the end since the list is presented in alphabetic
+ order.  Those functions that are specific to `gawk' are marked with a
+ pound sign (`#'):
+ 
+ * Menu:
+ 
+ * Gory Details::                More than you want to know about `\' and
+                                 `&' with `sub()', `gsub()', and
+                                 `gensub()'.
+ 
+ `asort(SOURCE [, DEST [, HOW  ] ]) #'
+      Return the number of elements in the array SOURCE.  `gawk' sorts
+      the contents of SOURCE and replaces the indices of the sorted
+      values of SOURCE with sequential integers starting with one.  If
+      the optional array DEST is specified, then SOURCE is duplicated
+      into DEST.  DEST is then sorted, leaving the indices of SOURCE
+      unchanged.  The optional third argument HOW is a string which
+      controls the rule for comparing values, and the sort direction.  A
+      single space is required between the comparison mode, `string' or
+      `number', and the direction specification, `ascending' or
+      `descending'.  You can omit direction and/or mode in which case it
+      will default to `ascending' and `string', respectively.  An empty
+      string "" is the same as the default `"ascending string"' for the
+      value of HOW.  If the `source' array contains subarrays as values,
+      they will come out last(first) in the `dest' array for
+      `ascending'(`descending') order specification.  The value of
+      `IGNORECASE' affects the sorting.  The third argument can also be
+      a user-defined function name in which case the value returned by
+      the function is used to order the array elements before
+      constructing the result array.  *Note Array Sorting Functions::,
+      for more information.
+ 
+      For example, if the contents of `a' are as follows:
+ 
+           a["last"] = "de"
+           a["first"] = "sac"
+           a["middle"] = "cul"
+ 
+      A call to `asort()':
+ 
+           asort(a)
+ 
+      results in the following contents of `a':
+ 
+           a[1] = "cul"
+           a[2] = "de"
+           a[3] = "sac"
+ 
+      In order to reverse the direction of the sorted results in the
+      above example, `asort()' can be called with three arguments as
+      follows:
+ 
+           asort(a, a, "descending")
+ 
+      The `asort()' function is described in more detail in *note Array
+      Sorting Functions::.  `asort()' is a `gawk' extension; it is not
+      available in compatibility mode (*note Options::).
+ 
+ `asorti(SOURCE [, DEST [, HOW  ] ]) #'
+      Return the number of elements in the array SOURCE.  It works
+      similarly to `asort()', however, the _indices_ are sorted, instead
+      of the values. (Here too, `IGNORECASE' affects the sorting.)
+ 
+      The `asorti()' function is described in more detail in *note Array
+      Sorting Functions::.  `asorti()' is a `gawk' extension; it is not
+      available in compatibility mode (*note Options::).
+ 
+ `gensub(REGEXP, REPLACEMENT, HOW [, TARGET]) #'
+      Search the target string TARGET for matches of the regular
+      expression REGEXP.  If HOW is a string beginning with `g' or `G'
+      (short for "global"), then replace all matches of REGEXP with
+      REPLACEMENT.  Otherwise, HOW is treated as a number indicating
+      which match of REGEXP to replace. If no TARGET is supplied, use
+      `$0'.  It returns the modified string as the result of the
+      function and the original target string is _not_ changed.
+ 
+      `gensub()' is a general substitution function.  It's purpose is to
+      provide more features than the standard `sub()' and `gsub()'
+      functions.
+ 
+      `gensub()' provides an additional feature that is not available in
+      `sub()' or `gsub()': the ability to specify components of a regexp
+      in the replacement text.  This is done by using parentheses in the
+      regexp to mark the components and then specifying `\N' in the
+      replacement text, where N is a digit from 1 to 9.  For example:
+ 
+           $ gawk '
+           > BEGIN {
+           >      a = "abc def"
+           >      b = gensub(/(.+) (.+)/, "\\2 \\1", "g", a)
+           >      print b
+           > }'
+           -| def abc
+ 
+      As with `sub()', you must type two backslashes in order to get one
+      into the string.  In the replacement text, the sequence `\0'
+      represents the entire matched text, as does the character `&'.
+ 
+      The following example shows how you can use the third argument to
+      control which match of the regexp should be changed:
+ 
+           $ echo a b c a b c |
+           > gawk '{ print gensub(/a/, "AA", 2) }'
+           -| a b c AA b c
+ 
+      In this case, `$0' is the default target string.  `gensub()'
+      returns the new string as its result, which is passed directly to
+      `print' for printing.
+ 
+      If the HOW argument is a string that does not begin with `g' or
+      `G', or if it is a number that is less than or equal to zero, only
+      one substitution is performed.  If HOW is zero, `gawk' issues a
+      warning message.
+ 
+      If REGEXP does not match TARGET, `gensub()''s return value is the
+      original unchanged value of TARGET.
+ 
+      `gensub()' is a `gawk' extension; it is not available in
+      compatibility mode (*note Options::).
+ 
+ `gsub(REGEXP, REPLACEMENT [, TARGET])'
+      Search TARGET for _all_ of the longest, leftmost, _nonoverlapping_
+      matching substrings it can find and replace them with REPLACEMENT.
+      The `g' in `gsub()' stands for "global," which means replace
+      everywhere.  For example:
+ 
+           { gsub(/Britain/, "United Kingdom"); print }
+ 
+      replaces all occurrences of the string `Britain' with `United
+      Kingdom' for all input records.
+ 
+      The `gsub()' function returns the number of substitutions made.  If
+      the variable to search and alter (TARGET) is omitted, then the
+      entire input record (`$0') is used.  As in `sub()', the characters
+      `&' and `\' are special, and the third argument must be assignable.
+ 
+ `index(IN, FIND)'
+      Search the string IN for the first occurrence of the string FIND,
+      and return the position in characters where that occurrence begins
+      in the string IN.  Consider the following example:
+ 
+           $ awk 'BEGIN { print index("peanut", "an") }'
+           -| 3
+ 
+      If FIND is not found, `index()' returns zero.  (Remember that
+      string indices in `awk' start at one.)
+ 
+ `length([STRING])'
+      Return the number of characters in STRING.  If STRING is a number,
+      the length of the digit string representing that number is
+      returned.  For example, `length("abcde")' is five.  By contrast,
+      `length(15 * 35)' works out to three. In this example, 15 * 35 =
+      525, and 525 is then converted to the string `"525"', which has
+      three characters.
+ 
+      If no argument is supplied, `length()' returns the length of `$0'.
+ 
+           NOTE: In older versions of `awk', the `length()' function
+           could be called without any parentheses.  Doing so is
+           considered poor practice, although the 2008 POSIX standard
+           explicitly allows it, to support historical practice.  For
+           programs to be maximally portable, always supply the
+           parentheses.
+ 
+      If `length()' is called with a variable that has not been used,
+      `gawk' forces the variable to be a scalar.  Other implementations
+      of `awk' leave the variable without a type.  (d.c.)  Consider:
+ 
+           $ gawk 'BEGIN { print length(x) ; x[1] = 1 }'
+           -| 0
+           error--> gawk: fatal: attempt to use scalar `x' as array
+ 
+           $ nawk 'BEGIN { print length(x) ; x[1] = 1 }'
+           -| 0
+ 
+      If `--lint' has been specified on the command line, `gawk' issues a
+      warning about this.
+ 
+      With `gawk' and several other `awk' implementations, when given an
+      array argument, the `length()' function returns the number of
+      elements in the array. (c.e.)  This is less useful than it might
+      seem at first, as the array is not guaranteed to be indexed from
+      one to the number of elements in it.  If `--lint' is provided on
+      the command line (*note Options::), `gawk' warns that passing an
+      array argument is not portable.  If `--posix' is supplied, using
+      an array argument is a fatal error (*note Arrays::).
+ 
+ `match(STRING, REGEXP [, ARRAY])'
+      Search STRING for the longest, leftmost substring matched by the
+      regular expression, REGEXP and return the character position, or
+      "index", at which that substring begins (one, if it starts at the
+      beginning of STRING).  If no match is found, return zero.
+ 
+      The REGEXP argument may be either a regexp constant (`/.../') or a
+      string constant (`"..."').  In the latter case, the string is
+      treated as a regexp to be matched.  *Note Computed Regexps::, for a
+      discussion of the difference between the two forms, and the
+      implications for writing your program correctly.
+ 
+      The order of the first two arguments is backwards from most other
+      string functions that work with regular expressions, such as
+      `sub()' and `gsub()'.  It might help to remember that for
+      `match()', the order is the same as for the `~' operator: `STRING
+      ~ REGEXP'.
+ 
+      The `match()' function sets the built-in variable `RSTART' to the
+      index.  It also sets the built-in variable `RLENGTH' to the length
+      in characters of the matched substring.  If no match is found,
+      `RSTART' is set to zero, and `RLENGTH' to -1.
+ 
+      For example:
+ 
+           {
+                  if ($1 == "FIND")
+                    regex = $2
+                  else {
+                    where = match($0, regex)
+                    if (where != 0)
+                      print "Match of", regex, "found at",
+                                where, "in", $0
+                  }
+           }
+ 
+      This program looks for lines that match the regular expression
+      stored in the variable `regex'.  This regular expression can be
+      changed.  If the first word on a line is `FIND', `regex' is
+      changed to be the second word on that line.  Therefore, if given:
+ 
+           FIND ru+n
+           My program runs
+           but not very quickly
+           FIND Melvin
+           JF+KM
+           This line is property of Reality Engineering Co.
+           Melvin was here.
+ 
+      `awk' prints:
+ 
+           Match of ru+n found at 12 in My program runs
+           Match of Melvin found at 1 in Melvin was here.
+ 
+      If ARRAY is present, it is cleared, and then the zeroth element of
+      ARRAY is set to the entire portion of STRING matched by REGEXP.
+      If REGEXP contains parentheses, the integer-indexed elements of
+      ARRAY are set to contain the portion of STRING matching the
+      corresponding parenthesized subexpression.  For example:
+ 
+           $ echo foooobazbarrrrr |
+           > gawk '{ match($0, /(fo+).+(bar*)/, arr)
+           >         print arr[1], arr[2] }'
+           -| foooo barrrrr
+ 
+      In addition, multidimensional subscripts are available providing
+      the start index and length of each matched subexpression:
+ 
+           $ echo foooobazbarrrrr |
+           > gawk '{ match($0, /(fo+).+(bar*)/, arr)
+           >           print arr[1], arr[2]
+           >           print arr[1, "start"], arr[1, "length"]
+           >           print arr[2, "start"], arr[2, "length"]
+           > }'
+           -| foooo barrrrr
+           -| 1 5
+           -| 9 7
+ 
+      There may not be subscripts for the start and index for every
+      parenthesized subexpression, since they may not all have matched
+      text; thus they should be tested for with the `in' operator (*note
+      Reference to Elements::).
+ 
+      The ARRAY argument to `match()' is a `gawk' extension.  In
+      compatibility mode (*note Options::), using a third argument is a
+      fatal error.
+ 
+ `patsplit(STRING, ARRAY [, FIELDPAT [, SEPS ] ]) #'
+      Divide STRING into pieces defined by FIELDPAT and store the pieces
+      in ARRAY and the separator strings in the SEPS array.  The first
+      piece is stored in `ARRAY[1]', the second piece in `ARRAY[2]', and
+      so forth.  The third argument, FIELDPAT, is a regexp describing
+      the fields in STRING (just as `FPAT' is a regexp describing the
+      fields in input records).  It may be either a regexp constant or a
+      string.  If FIELDPAT is omitted, the value of `FPAT' is used.
+      `patsplit()' returns the number of elements created.  `SEPS[I]' is
+      the separator string between `ARRAY[I]' and `ARRAY[I+1]'.  Any
+      leading separator will be in `SEPS[0]'.
+ 
+      The `patsplit()' function splits strings into pieces in a manner
+      similar to the way input lines are split into fields using `FPAT'
+      (*note Splitting By Content::.
+ 
+      Before splitting the string, `patsplit()' deletes any previously
+      existing elements in the arrays ARRAY and SEPS.
+ 
+      The `patsplit()' function is a `gawk' extension.  In compatibility
+      mode (*note Options::), it is not available.
+ 
+ `split(STRING, ARRAY [, FIELDSEP [, SEPS ] ])'
+      Divide STRING into pieces separated by FIELDSEP and store the
+      pieces in ARRAY and the separator strings in the SEPS array.  The
+      first piece is stored in `ARRAY[1]', the second piece in
+      `ARRAY[2]', and so forth.  The string value of the third argument,
+      FIELDSEP, is a regexp describing where to split STRING (much as
+      `FS' can be a regexp describing where to split input records;
+      *note Regexp Field Splitting::).  If FIELDSEP is omitted, the
+      value of `FS' is used.  `split()' returns the number of elements
+      created.  SEPS is a `gawk' extension with `SEPS[I]' being the
+      separator string between `ARRAY[I]' and `ARRAY[I+1]'.  If FIELDSEP
+      is a single space then any leading whitespace goes into `SEPS[0]'
+      and any trailing whitespace goes into `SEPS[N]' where N is the
+      return value of `split()' (that is, the number of elements in
+      ARRAY).
+ 
+      The `split()' function splits strings into pieces in a manner
+      similar to the way input lines are split into fields.  For example:
+ 
+           split("cul-de-sac", a, "-", seps)
+ 
+      splits the string `cul-de-sac' into three fields using `-' as the
+      separator.  It sets the contents of the array `a' as follows:
+ 
+           a[1] = "cul"
+           a[2] = "de"
+           a[3] = "sac"
+ 
+      and sets the contents of the array `seps' as follows:
+ 
+           seps[1] = "-"
+           seps[2] = "-"
+ 
+      The value returned by this call to `split()' is three.
+ 
+      As with input field-splitting, when the value of FIELDSEP is
+      `" "', leading and trailing whitespace is ignored in values
+      assigned to the elements of ARRAY but not in SEPS, and the elements
+      are separated by runs of whitespace.  Also as with input
+      field-splitting, if FIELDSEP is the null string, each individual
+      character in the string is split into its own array element.
+      (c.e.)
+ 
+      Note, however, that `RS' has no effect on the way `split()' works.
+      Even though `RS = ""' causes newline to also be an input field
+      separator, this does not affect how `split()' splits strings.
+ 
+      Modern implementations of `awk', including `gawk', allow the third
+      argument to be a regexp constant (`/abc/') as well as a string.
+      (d.c.)  The POSIX standard allows this as well.  *Note Computed
+      Regexps::, for a discussion of the difference between using a
+      string constant or a regexp constant, and the implications for
+      writing your program correctly.
+ 
+      Before splitting the string, `split()' deletes any previously
+      existing elements in the arrays ARRAY and SEPS.
+ 
+      If STRING is null, the array has no elements. (So this is a
+      portable way to delete an entire array with one statement.  *Note
+      Delete::.)
+ 
+      If STRING does not match FIELDSEP at all (but is not null), ARRAY
+      has one element only. The value of that element is the original
+      STRING.
+ 
+ `sprintf(FORMAT, EXPRESSION1, ...)'
+      Return (without printing) the string that `printf' would have
+      printed out with the same arguments (*note Printf::).  For example:
+ 
+           pival = sprintf("pi = %.2f (approx.)", 22/7)
+ 
+      assigns the string `pi = 3.14 (approx.)' to the variable `pival'.
+ 
+ `strtonum(STR) #'
+      Examine STR and return its numeric value.  If STR begins with a
+      leading `0', `strtonum()' assumes that STR is an octal number.  If
+      STR begins with a leading `0x' or `0X', `strtonum()' assumes that
+      STR is a hexadecimal number.  For example:
+ 
+           $ echo 0x11 |
+           > gawk '{ printf "%d\n", strtonum($1) }'
+           -| 17
+ 
+      Using the `strtonum()' function is _not_ the same as adding zero
+      to a string value; the automatic coercion of strings to numbers
+      works only for decimal data, not for octal or hexadecimal.(1)
+ 
+      Note also that `strtonum()' uses the current locale's decimal point
+      for recognizing numbers (*note Locales::).
+ 
+      `strtonum()' is a `gawk' extension; it is not available in
+      compatibility mode (*note Options::).
+ 
+ `sub(REGEXP, REPLACEMENT [, TARGET])'
+      Search TARGET, which is treated as a string, for the leftmost,
+      longest substring matched by the regular expression REGEXP.
+      Modify the entire string by replacing the matched text with
+      REPLACEMENT.  The modified string becomes the new value of TARGET.
+      Return the number of substitutions made (zero or one).
+ 
+      The REGEXP argument may be either a regexp constant (`/.../') or a
+      string constant (`"..."').  In the latter case, the string is
+      treated as a regexp to be matched.  *Note Computed Regexps::, for a
+      discussion of the difference between the two forms, and the
+      implications for writing your program correctly.
+ 
+      This function is peculiar because TARGET is not simply used to
+      compute a value, and not just any expression will do--it must be a
+      variable, field, or array element so that `sub()' can store a
+      modified value there.  If this argument is omitted, then the
+      default is to use and alter `$0'.(2) For example:
+ 
+           str = "water, water, everywhere"
+           sub(/at/, "ith", str)
+ 
+      sets `str' to `wither, water, everywhere', by replacing the
+      leftmost longest occurrence of `at' with `ith'.
+ 
+      If the special character `&' appears in REPLACEMENT, it stands for
+      the precise substring that was matched by REGEXP.  (If the regexp
+      can match more than one string, then this precise substring may
+      vary.)  For example:
+ 
+           { sub(/candidate/, "& and his wife"); print }
+ 
+      changes the first occurrence of `candidate' to `candidate and his
+      wife' on each input line.  Here is another example:
+ 
+           $ awk 'BEGIN {
+           >         str = "daabaaa"
+           >         sub(/a+/, "C&C", str)
+           >         print str
+           > }'
+           -| dCaaCbaaa
+ 
+      This shows how `&' can represent a nonconstant string and also
+      illustrates the "leftmost, longest" rule in regexp matching (*note
+      Leftmost Longest::).
+ 
+      The effect of this special character (`&') can be turned off by
+      putting a backslash before it in the string.  As usual, to insert
+      one backslash in the string, you must write two backslashes.
+      Therefore, write `\\&' in a string constant to include a literal
+      `&' in the replacement.  For example, the following shows how to
+      replace the first `|' on each line with an `&':
+ 
+           { sub(/\|/, "\\&"); print }
+ 
+      As mentioned, the third argument to `sub()' must be a variable,
+      field or array element.  Some versions of `awk' allow the third
+      argument to be an expression that is not an lvalue.  In such a
+      case, `sub()' still searches for the pattern and returns zero or
+      one, but the result of the substitution (if any) is thrown away
+      because there is no place to put it.  Such versions of `awk'
+      accept expressions like the following:
+ 
+           sub(/USA/, "United States", "the USA and Canada")
+ 
+      For historical compatibility, `gawk' accepts such erroneous code.
+      However, using any other nonchangeable object as the third
+      parameter causes a fatal error and your program will not run.
+ 
+      Finally, if the REGEXP is not a regexp constant, it is converted
+      into a string, and then the value of that string is treated as the
+      regexp to match.
+ 
+ `substr(STRING, START [, LENGTH])'
+      Return a LENGTH-character-long substring of STRING, starting at
+      character number START.  The first character of a string is
+      character number one.(3) For example, `substr("washington", 5, 3)'
+      returns `"ing"'.
+ 
+      If LENGTH is not present, `substr()' returns the whole suffix of
+      STRING that begins at character number START.  For example,
+      `substr("washington", 5)' returns `"ington"'.  The whole suffix is
+      also returned if LENGTH is greater than the number of characters
+      remaining in the string, counting from character START.
+ 
+      If START is less than one, `substr()' treats it as if it was one.
+      (POSIX doesn't specify what to do in this case: Brian Kernighan's
+      `awk' acts this way, and therefore `gawk' does too.)  If START is
+      greater than the number of characters in the string, `substr()'
+      returns the null string.  Similarly, if LENGTH is present but less
+      than or equal to zero, the null string is returned.
+ 
+      The string returned by `substr()' _cannot_ be assigned.  Thus, it
+      is a mistake to attempt to change a portion of a string, as shown
+      in the following example:
+ 
+           string = "abcdef"
+           # try to get "abCDEf", won't work
+           substr(string, 3, 3) = "CDE"
+ 
+      It is also a mistake to use `substr()' as the third argument of
+      `sub()' or `gsub()':
+ 
+           gsub(/xyz/, "pdq", substr($0, 5, 20))  # WRONG
+ 
+      (Some commercial versions of `awk' treat `substr()' as assignable,
+      but doing so is not portable.)
+ 
+      If you need to replace bits and pieces of a string, combine
+      `substr()' with string concatenation, in the following manner:
+ 
+           string = "abcdef"
+           ...
+           string = substr(string, 1, 2) "CDE" substr(string, 6)
+ 
+ `tolower(STRING)'
+      Return a copy of STRING, with each uppercase character in the
+      string replaced with its corresponding lowercase character.
+      Nonalphabetic characters are left unchanged.  For example,
+      `tolower("MiXeD cAsE 123")' returns `"mixed case 123"'.
+ 
+ `toupper(STRING)'
+      Return a copy of STRING, with each lowercase character in the
+      string replaced with its corresponding uppercase character.
+      Nonalphabetic characters are left unchanged.  For example,
+      `toupper("MiXeD cAsE 123")' returns `"MIXED CASE 123"'.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Unless you use the `--non-decimal-data' option, which isn't
+ recommended.  *Note Nondecimal Data::, for more information.
+ 
+    (2) Note that this means that the record will first be regenerated
+ using the value of `OFS' if any fields have been changed, and that the
+ fields will be updated after the substitution, even if the operation is
+ a "no-op" such as `sub(/^/, "")'.
+ 
+    (3) This is different from C and C++, in which the first character
+ is number zero.
+ 
+ 
+ File: gawk.info,  Node: Gory Details,  Up: String Functions
+ 
+ 9.1.3.1 More About `\' and `&' with `sub()', `gsub()', and `gensub()'
+ .....................................................................
+ 
+ When using `sub()', `gsub()', or `gensub()', and trying to get literal
+ backslashes and ampersands into the replacement text, you need to
+ remember that there are several levels of "escape processing" going on.
+ 
+    First, there is the "lexical" level, which is when `awk' reads your
+ program and builds an internal copy of it that can be executed.  Then
+ there is the runtime level, which is when `awk' actually scans the
+ replacement string to determine what to generate.
+ 
+    At both levels, `awk' looks for a defined set of characters that can
+ come after a backslash.  At the lexical level, it looks for the escape
+ sequences listed in *note Escape Sequences::.  Thus, for every `\' that
+ `awk' processes at the runtime level, you must type two backslashes at
+ the lexical level.  When a character that is not valid for an escape
+ sequence follows the `\', Brian Kernighan's `awk' and `gawk' both
+ simply remove the initial `\' and put the next character into the
+ string. Thus, for example, `"a\qb"' is treated as `"aqb"'.
+ 
+    At the runtime level, the various functions handle sequences of `\'
+ and `&' differently.  The situation is (sadly) somewhat complex.
+ Historically, the `sub()' and `gsub()' functions treated the two
+ character sequence `\&' specially; this sequence was replaced in the
+ generated text with a single `&'.  Any other `\' within the REPLACEMENT
+ string that did not precede an `&' was passed through unchanged.  This
+ is illustrated in *note table-sub-escapes::.
+ 
+       You type         `sub()' sees          `sub()' generates
+       -------         ---------          --------------
+           `\&'              `&'            the matched text
+          `\\&'             `\&'            a literal `&'
+         `\\\&'             `\&'            a literal `&'
+        `\\\\&'            `\\&'            a literal `\&'
+       `\\\\\&'            `\\&'            a literal `\&'
+      `\\\\\\&'           `\\\&'            a literal `\\&'
+          `\\q'             `\q'            a literal `\q'
+ 
+ Table 9.1: Historical Escape Sequence Processing for `sub()' and
+ `gsub()'
+ 
+ This table shows both the lexical-level processing, where an odd number
+ of backslashes becomes an even number at the runtime level, as well as
+ the runtime processing done by `sub()'.  (For the sake of simplicity,
+ the rest of the following tables only show the case of even numbers of
+ backslashes entered at the lexical level.)
+ 
+    The problem with the historical approach is that there is no way to
+ get a literal `\' followed by the matched text.
+ 
+    The 1992 POSIX standard attempted to fix this problem. That standard
+ says that `sub()' and `gsub()' look for either a `\' or an `&' after
+ the `\'. If either one follows a `\', that character is output
+ literally.  The interpretation of `\' and `&' then becomes as shown in
+ *note table-sub-posix-92::.
+ 
+       You type         `sub()' sees          `sub()' generates
+       -------         ---------          --------------
+            `&'              `&'            the matched text
+          `\\&'             `\&'            a literal `&'
+        `\\\\&'            `\\&'            a literal `\', then the matched 
text
+      `\\\\\\&'           `\\\&'            a literal `\&'
+ 
+ Table 9.2: 1992 POSIX Rules for sub and gsub Escape Sequence Processing
+ 
+ This appears to solve the problem.  Unfortunately, the phrasing of the
+ standard is unusual. It says, in effect, that `\' turns off the special
+ meaning of any following character, but for anything other than `\' and
+ `&', such special meaning is undefined.  This wording leads to two
+ problems:
+ 
+    * Backslashes must now be doubled in the REPLACEMENT string, breaking
+      historical `awk' programs.
+ 
+    * To make sure that an `awk' program is portable, _every_ character
+      in the REPLACEMENT string must be preceded with a backslash.(1)
+ 
+    Because of the problems just listed, in 1996, the `gawk' maintainer
+ submitted proposed text for a revised standard that reverts to rules
+ that correspond more closely to the original existing practice. The
+ proposed rules have special cases that make it possible to produce a
+ `\' preceding the matched text. This is shown in *note
+ table-sub-proposed::.
+ 
+       You type         `sub()' sees         `sub()' generates
+       -------         ---------         --------------
+      `\\\\\\&'           `\\\&'            a literal `\&'
+        `\\\\&'            `\\&'            a literal `\', followed by the 
matched text
+          `\\&'             `\&'            a literal `&'
+          `\\q'             `\q'            a literal `\q'
+         `\\\\'             `\\'            `\\'
+ 
+ Table 9.3: Proposed rules for sub and backslash
+ 
+    In a nutshell, at the runtime level, there are now three special
+ sequences of characters (`\\\&', `\\&' and `\&') whereas historically
+ there was only one.  However, as in the historical case, any `\' that
+ is not part of one of these three sequences is not special and appears
+ in the output literally.
+ 
+    `gawk' 3.0 and 3.1 follow these proposed POSIX rules for `sub()' and
+ `gsub()'.  The POSIX standard took much longer to be revised than was
+ expected in 1996.  The 2001 standard does not follow the above rules.
+ Instead, the rules there are somewhat simpler.  The results are similar
+ except for one case.
+ 
+    The POSIX rules state that `\&' in the replacement string produces a
+ literal `&', `\\' produces a literal `\', and `\' followed by anything
+ else is not special; the `\' is placed straight into the output.  These
+ rules are presented in *note table-posix-sub::.
+ 
+       You type         `sub()' sees         `sub()' generates
+       -------         ---------         --------------
+      `\\\\\\&'           `\\\&'            a literal `\&'
+        `\\\\&'            `\\&'            a literal `\', followed by the 
matched text
+          `\\&'             `\&'            a literal `&'
+          `\\q'             `\q'            a literal `\q'
+         `\\\\'             `\\'            `\'
+ 
+ Table 9.4: POSIX rules for `sub()' and `gsub()'
+ 
+    The only case where the difference is noticeable is the last one:
+ `\\\\' is seen as `\\' and produces `\' instead of `\\'.
+ 
+    Starting with version 3.1.4, `gawk' followed the POSIX rules when
+ `--posix' is specified (*note Options::). Otherwise, it continued to
+ follow the 1996 proposed rules, since that had been its behavior for
+ many years.
+ 
+    When version 4.0.0, was released, the `gawk' maintainer made the
+ POSIX rules the default, breaking well over a decade's worth of
+ backwards compatibility.(2) Needless to say, this was a bad idea, and
+ as of version 4.0.1, `gawk' resumed its historical behavior, and only
+ follows the POSIX rules when `--posix' is given.
+ 
+    The rules for `gensub()' are considerably simpler. At the runtime
+ level, whenever `gawk' sees a `\', if the following character is a
+ digit, then the text that matched the corresponding parenthesized
+ subexpression is placed in the generated output.  Otherwise, no matter
+ what character follows the `\', it appears in the generated text and
+ the `\' does not, as shown in *note table-gensub-escapes::.
+ 
+        You type          `gensub()' sees         `gensub()' generates
+        -------          ------------         -----------------
+            `&'                    `&'            the matched text
+          `\\&'                   `\&'            a literal `&'
+         `\\\\'                   `\\'            a literal `\'
+        `\\\\&'                  `\\&'            a literal `\', then the 
matched text
+      `\\\\\\&'                 `\\\&'            a literal `\&'
+          `\\q'                   `\q'            a literal `q'
+ 
+ Table 9.5: Escape Sequence Processing for `gensub()'
+ 
+    Because of the complexity of the lexical and runtime level processing
+ and the special cases for `sub()' and `gsub()', we recommend the use of
+ `gawk' and `gensub()' when you have to do substitutions.
+ 
+ Advanced Notes: Matching the Null String
+ ----------------------------------------
+ 
+ In `awk', the `*' operator can match the null string.  This is
+ particularly important for the `sub()', `gsub()', and `gensub()'
+ functions.  For example:
+ 
+      $ echo abc | awk '{ gsub(/m*/, "X"); print }'
+      -| XaXbXcX
+ 
+ Although this makes a certain amount of sense, it can be surprising.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) This consequence was certainly unintended.
+ 
+    (2) This was rather naive of him, despite there being a note in this
+ section indicating that the next major version would move to the POSIX
+ rules.
+ 
+ 
+ File: gawk.info,  Node: I/O Functions,  Next: Time Functions,  Prev: String 
Functions,  Up: Built-in
+ 
+ 9.1.4 Input/Output Functions
+ ----------------------------
+ 
+ The following functions relate to input/output (I/O).  Optional
+ parameters are enclosed in square brackets ([ ]):
+ 
+ `close(FILENAME [, HOW])'
+      Close the file FILENAME for input or output. Alternatively, the
+      argument may be a shell command that was used for creating a
+      coprocess, or for redirecting to or from a pipe; then the
+      coprocess or pipe is closed.  *Note Close Files And Pipes::, for
+      more information.
+ 
+      When closing a coprocess, it is occasionally useful to first close
+      one end of the two-way pipe and then to close the other.  This is
+      done by providing a second argument to `close()'.  This second
+      argument should be one of the two string values `"to"' or `"from"',
+      indicating which end of the pipe to close.  Case in the string does
+      not matter.  *Note Two-way I/O::, which discusses this feature in
+      more detail and gives an example.
+ 
+ `fflush([FILENAME])'
+      Flush any buffered output associated with FILENAME, which is
+      either a file opened for writing or a shell command for
+      redirecting output to a pipe or coprocess. (c.e.).
+ 
+      Many utility programs "buffer" their output; i.e., they save
+      information to write to a disk file or the screen in memory until
+      there is enough for it to be worthwhile to send the data to the
+      output device.  This is often more efficient than writing every
+      little bit of information as soon as it is ready.  However,
+      sometimes it is necessary to force a program to "flush" its
+      buffers; that is, write the information to its destination, even
+      if a buffer is not full.  This is the purpose of the `fflush()'
+      function--`gawk' also buffers its output and the `fflush()'
+      function forces `gawk' to flush its buffers.
+ 
+      `fflush()' was added to Brian Kernighan's version of `awk' in
+      1994; it is not part of the POSIX standard and is not available if
+      `--posix' has been specified on the command line (*note Options::).
+ 
+      `gawk' extends the `fflush()' function in two ways.  The first is
+      to allow no argument at all. In this case, the buffer for the
+      standard output is flushed.  The second is to allow the null string
+      (`""') as the argument. In this case, the buffers for _all_ open
+      output files and pipes are flushed.  Brian Kernighan's `awk' also
+      supports these extensions.
+ 
+      `fflush()' returns zero if the buffer is successfully flushed;
+      otherwise, it returns -1.  In the case where all buffers are
+      flushed, the return value is zero only if all buffers were flushed
+      successfully.  Otherwise, it is -1, and `gawk' warns about the
+      problem FILENAME.
+ 
+      `gawk' also issues a warning message if you attempt to flush a
+      file or pipe that was opened for reading (such as with `getline'),
+      or if FILENAME is not an open file, pipe, or coprocess.  In such a
+      case, `fflush()' returns -1, as well.
+ 
+ `system(COMMAND)'
+      Execute the operating-system command COMMAND and then return to
+      the `awk' program.  Return COMMAND's exit status.
+ 
+      For example, if the following fragment of code is put in your `awk'
+      program:
+ 
+           END {
+                system("date | mail -s 'awk run done' root")
+           }
+ 
+      the system administrator is sent mail when the `awk' program
+      finishes processing input and begins its end-of-input processing.
+ 
+      Note that redirecting `print' or `printf' into a pipe is often
+      enough to accomplish your task.  If you need to run many commands,
+      it is more efficient to simply print them down a pipeline to the
+      shell:
+ 
+           while (MORE STUFF TO DO)
+               print COMMAND | "/bin/sh"
+           close("/bin/sh")
+ 
+      However, if your `awk' program is interactive, `system()' is
+      useful for running large self-contained programs, such as a shell
+      or an editor.  Some operating systems cannot implement the
+      `system()' function.  `system()' causes a fatal error if it is not
+      supported.
+ 
+           NOTE: When `--sandbox' is specified, the `system()' function
+           is disabled (*note Options::).
+ 
+ 
+ Advanced Notes: Interactive Versus Noninteractive Buffering
+ -----------------------------------------------------------
+ 
+ As a side point, buffering issues can be even more confusing, depending
+ upon whether your program is "interactive", i.e., communicating with a
+ user sitting at a keyboard.(1)
+ 
+    Interactive programs generally "line buffer" their output; i.e., they
+ write out every line.  Noninteractive programs wait until they have a
+ full buffer, which may be many lines of output.  Here is an example of
+ the difference:
+ 
+      $ awk '{ print $1 + $2 }'
+      1 1
+      -| 2
+      2 3
+      -| 5
+      Ctrl-d
+ 
+ Each line of output is printed immediately. Compare that behavior with
+ this example:
+ 
+      $ awk '{ print $1 + $2 }' | cat
+      1 1
+      2 3
+      Ctrl-d
+      -| 2
+      -| 5
+ 
+ Here, no output is printed until after the `Ctrl-d' is typed, because
+ it is all buffered and sent down the pipe to `cat' in one shot.
+ 
+ Advanced Notes: Controlling Output Buffering with `system()'
+ ------------------------------------------------------------
+ 
+ The `fflush()' function provides explicit control over output buffering
+ for individual files and pipes.  However, its use is not portable to
+ many other `awk' implementations.  An alternative method to flush output
+ buffers is to call `system()' with a null string as its argument:
+ 
+      system("")   # flush output
+ 
+ `gawk' treats this use of the `system()' function as a special case and
+ is smart enough not to run a shell (or other command interpreter) with
+ the empty command.  Therefore, with `gawk', this idiom is not only
+ useful, it is also efficient.  While this method should work with other
+ `awk' implementations, it does not necessarily avoid starting an
+ unnecessary shell.  (Other implementations may only flush the buffer
+ associated with the standard output and not necessarily all buffered
+ output.)
+ 
+    If you think about what a programmer expects, it makes sense that
+ `system()' should flush any pending output.  The following program:
+ 
+      BEGIN {
+           print "first print"
+           system("echo system echo")
+           print "second print"
+      }
+ 
+ must print:
+ 
+      first print
+      system echo
+      second print
+ 
+ and not:
+ 
+      system echo
+      first print
+      second print
+ 
+    If `awk' did not flush its buffers before calling `system()', you
+ would see the latter (undesirable) output.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) A program is interactive if the standard output is connected to
+ a terminal device. On modern systems, this means your keyboard and
+ screen.
+ 
+ 
+ File: gawk.info,  Node: Time Functions,  Next: Bitwise Functions,  Prev: I/O 
Functions,  Up: Built-in
+ 
+ 9.1.5 Time Functions
+ --------------------
+ 
+ `awk' programs are commonly used to process log files containing
+ timestamp information, indicating when a particular log record was
+ written.  Many programs log their timestamp in the form returned by the
+ `time()' system call, which is the number of seconds since a particular
+ epoch.  On POSIX-compliant systems, it is the number of seconds since
+ 1970-01-01 00:00:00 UTC, not counting leap seconds.(1) All known
+ POSIX-compliant systems support timestamps from 0 through 2^31 - 1,
+ which is sufficient to represent times through 2038-01-19 03:14:07 UTC.
+ Many systems support a wider range of timestamps, including negative
+ timestamps that represent times before the epoch.
+ 
+    In order to make it easier to process such log files and to produce
+ useful reports, `gawk' provides the following functions for working
+ with timestamps.  They are `gawk' extensions; they are not specified in
+ the POSIX standard, nor are they in any other known version of `awk'.(2)
+ Optional parameters are enclosed in square brackets ([ ]):
+ 
+ `mktime(DATESPEC)'
+      Turn DATESPEC into a timestamp in the same form as is returned by
+      `systime()'.  It is similar to the function of the same name in
+      ISO C.  The argument, DATESPEC, is a string of the form
+      `"YYYY MM DD HH MM SS [DST]"'.  The string consists of six or
+      seven numbers representing, respectively, the full year including
+      century, the month from 1 to 12, the day of the month from 1 to
+      31, the hour of the day from 0 to 23, the minute from 0 to 59, the
+      second from 0 to 60,(3) and an optional daylight-savings flag.
+ 
+      The values of these numbers need not be within the ranges
+      specified; for example, an hour of -1 means 1 hour before midnight.
+      The origin-zero Gregorian calendar is assumed, with year 0
+      preceding year 1 and year -1 preceding year 0.  The time is
+      assumed to be in the local timezone.  If the daylight-savings flag
+      is positive, the time is assumed to be daylight savings time; if
+      zero, the time is assumed to be standard time; and if negative
+      (the default), `mktime()' attempts to determine whether daylight
+      savings time is in effect for the specified time.
+ 
+      If DATESPEC does not contain enough elements or if the resulting
+      time is out of range, `mktime()' returns -1.
+ 
+ `strftime([FORMAT [, TIMESTAMP [, UTC-FLAG]]])'
+      Format the time specified by TIMESTAMP based on the contents of
+      the FORMAT string and return the result.  It is similar to the
+      function of the same name in ISO C.  If UTC-FLAG is present and is
+      either nonzero or non-null, the value is formatted as UTC
+      (Coordinated Universal Time, formerly GMT or Greenwich Mean Time).
+      Otherwise, the value is formatted for the local time zone.  The
+      TIMESTAMP is in the same format as the value returned by the
+      `systime()' function.  If no TIMESTAMP argument is supplied,
+      `gawk' uses the current time of day as the timestamp.  If no
+      FORMAT argument is supplied, `strftime()' uses the value of
+      `PROCINFO["strftime"]' as the format string (*note Built-in
+      Variables::).  The default string value is
+      `"%a %b %e %H:%M:%S %Z %Y"'.  This format string produces output
+      that is equivalent to that of the `date' utility.  You can assign
+      a new value to `PROCINFO["strftime"]' to change the default format.
+ 
+ `systime()'
+      Return the current time as the number of seconds since the system
+      epoch.  On POSIX systems, this is the number of seconds since
+      1970-01-01 00:00:00 UTC, not counting leap seconds.  It may be a
+      different number on other systems.
+ 
+    The `systime()' function allows you to compare a timestamp from a
+ log file with the current time of day.  In particular, it is easy to
+ determine how long ago a particular record was logged.  It also allows
+ you to produce log records using the "seconds since the epoch" format.
+ 
+    The `mktime()' function allows you to convert a textual
+ representation of a date and time into a timestamp.   This makes it
+ easy to do before/after comparisons of dates and times, particularly
+ when dealing with date and time data coming from an external source,
+ such as a log file.
+ 
+    The `strftime()' function allows you to easily turn a timestamp into
+ human-readable information.  It is similar in nature to the `sprintf()'
+ function (*note String Functions::), in that it copies nonformat
+ specification characters verbatim to the returned string, while
+ substituting date and time values for format specifications in the
+ FORMAT string.
+ 
+    `strftime()' is guaranteed by the 1999 ISO C standard(4) to support
+ the following date format specifications:
+ 
+ `%a'
+      The locale's abbreviated weekday name.
+ 
+ `%A'
+      The locale's full weekday name.
+ 
+ `%b'
+      The locale's abbreviated month name.
+ 
+ `%B'
+      The locale's full month name.
+ 
+ `%c'
+      The locale's "appropriate" date and time representation.  (This is
+      `%A %B %d %T %Y' in the `"C"' locale.)
+ 
+ `%C'
+      The century part of the current year.  This is the year divided by
+      100 and truncated to the next lower integer.
+ 
+ `%d'
+      The day of the month as a decimal number (01-31).
+ 
+ `%D'
+      Equivalent to specifying `%m/%d/%y'.
+ 
+ `%e'
+      The day of the month, padded with a space if it is only one digit.
+ 
+ `%F'
+      Equivalent to specifying `%Y-%m-%d'.  This is the ISO 8601 date
+      format.
+ 
+ `%g'
+      The year modulo 100 of the ISO 8601 week number, as a decimal
+      number (00-99).  For example, January 1, 1993 is in week 53 of
+      1992. Thus, the year of its ISO 8601 week number is 1992, even
+      though its year is 1993.  Similarly, December 31, 1973 is in week
+      1 of 1974. Thus, the year of its ISO week number is 1974, even
+      though its year is 1973.
+ 
+ `%G'
+      The full year of the ISO week number, as a decimal number.
+ 
+ `%h'
+      Equivalent to `%b'.
+ 
+ `%H'
+      The hour (24-hour clock) as a decimal number (00-23).
+ 
+ `%I'
+      The hour (12-hour clock) as a decimal number (01-12).
+ 
+ `%j'
+      The day of the year as a decimal number (001-366).
+ 
+ `%m'
+      The month as a decimal number (01-12).
+ 
+ `%M'
+      The minute as a decimal number (00-59).
+ 
+ `%n'
+      A newline character (ASCII LF).
+ 
+ `%p'
+      The locale's equivalent of the AM/PM designations associated with
+      a 12-hour clock.
+ 
+ `%r'
+      The locale's 12-hour clock time.  (This is `%I:%M:%S %p' in the
+      `"C"' locale.)
+ 
+ `%R'
+      Equivalent to specifying `%H:%M'.
+ 
+ `%S'
+      The second as a decimal number (00-60).
+ 
+ `%t'
+      A TAB character.
+ 
+ `%T'
+      Equivalent to specifying `%H:%M:%S'.
+ 
+ `%u'
+      The weekday as a decimal number (1-7).  Monday is day one.
+ 
+ `%U'
+      The week number of the year (the first Sunday as the first day of
+      week one) as a decimal number (00-53).
+ 
+ `%V'
+      The week number of the year (the first Monday as the first day of
+      week one) as a decimal number (01-53).  The method for determining
+      the week number is as specified by ISO 8601.  (To wit: if the week
+      containing January 1 has four or more days in the new year, then
+      it is week one; otherwise it is week 53 of the previous year and
+      the next week is week one.)
+ 
+ `%w'
+      The weekday as a decimal number (0-6).  Sunday is day zero.
+ 
+ `%W'
+      The week number of the year (the first Monday as the first day of
+      week one) as a decimal number (00-53).
+ 
+ `%x'
+      The locale's "appropriate" date representation.  (This is `%A %B
+      %d %Y' in the `"C"' locale.)
+ 
+ `%X'
+      The locale's "appropriate" time representation.  (This is `%T' in
+      the `"C"' locale.)
+ 
+ `%y'
+      The year modulo 100 as a decimal number (00-99).
+ 
+ `%Y'
+      The full year as a decimal number (e.g., 2011).
+ 
+ `%z'
+      The timezone offset in a +HHMM format (e.g., the format necessary
+      to produce RFC 822/RFC 1036 date headers).
+ 
+ `%Z'
+      The time zone name or abbreviation; no characters if no time zone
+      is determinable.
+ 
+ `%Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH'
+ `%OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy'
+      "Alternate representations" for the specifications that use only
+      the second letter (`%c', `%C', and so on).(5) (These facilitate
+      compliance with the POSIX `date' utility.)
+ 
+ `%%'
+      A literal `%'.
+ 
+    If a conversion specifier is not one of the above, the behavior is
+ undefined.(6)
+ 
+    Informally, a "locale" is the geographic place in which a program is
+ meant to run.  For example, a common way to abbreviate the date
+ September 4, 2012 in the United States is "9/4/12."  In many countries
+ in Europe, however, it is abbreviated "4.9.12."  Thus, the `%x'
+ specification in a `"US"' locale might produce `9/4/12', while in a
+ `"EUROPE"' locale, it might produce `4.9.12'.  The ISO C standard
+ defines a default `"C"' locale, which is an environment that is typical
+ of what many C programmers are used to.
+ 
+    For systems that are not yet fully standards-compliant, `gawk'
+ supplies a copy of `strftime()' from the GNU C Library.  It supports
+ all of the just-listed format specifications.  If that version is used
+ to compile `gawk' (*note Installation::), then the following additional
+ format specifications are available:
+ 
+ `%k'
+      The hour (24-hour clock) as a decimal number (0-23).  Single-digit
+      numbers are padded with a space.
+ 
+ `%l'
+      The hour (12-hour clock) as a decimal number (1-12).  Single-digit
+      numbers are padded with a space.
+ 
+ `%s'
+      The time as a decimal timestamp in seconds since the epoch.
+ 
+ 
+    Additionally, the alternate representations are recognized but their
+ normal representations are used.
+ 
+    The following example is an `awk' implementation of the POSIX `date'
+ utility.  Normally, the `date' utility prints the current date and time
+ of day in a well-known format.  However, if you provide an argument to
+ it that begins with a `+', `date' copies nonformat specifier characters
+ to the standard output and interprets the current time according to the
+ format specifiers in the string.  For example:
+ 
+      $ date '+Today is %A, %B %d, %Y.'
+      -| Today is Wednesday, March 30, 2011.
+ 
+    Here is the `gawk' version of the `date' utility.  It has a shell
+ "wrapper" to handle the `-u' option, which requires that `date' run as
+ if the time zone is set to UTC:
+ 
+      #! /bin/sh
+      #
+      # date --- approximate the POSIX 'date' command
+ 
+      case $1 in
+      -u)  TZ=UTC0     # use UTC
+           export TZ
+           shift ;;
+      esac
+ 
+      gawk 'BEGIN  {
+          format = "%a %b %e %H:%M:%S %Z %Y"
+          exitval = 0
+ 
+          if (ARGC > 2)
+              exitval = 1
+          else if (ARGC == 2) {
+              format = ARGV[1]
+              if (format ~ /^\+/)
+                  format = substr(format, 2)   # remove leading +
+          }
+          print strftime(format)
+          exit exitval
+      }' "$@"
+ 
+    ---------- Footnotes ----------
+ 
+    (1) *Note Glossary::, especially the entries "Epoch" and "UTC."
+ 
+    (2) The GNU `date' utility can also do many of the things described
+ here.  Its use may be preferable for simple time-related operations in
+ shell scripts.
+ 
+    (3) Occasionally there are minutes in a year with a leap second,
+ which is why the seconds can go up to 60.
+ 
+    (4) Unfortunately, not every system's `strftime()' necessarily
+ supports all of the conversions listed here.
+ 
+    (5) If you don't understand any of this, don't worry about it; these
+ facilities are meant to make it easier to "internationalize" programs.
+ Other internationalization features are described in *note
+ Internationalization::.
+ 
+    (6) This is because ISO C leaves the behavior of the C version of
+ `strftime()' undefined and `gawk' uses the system's version of
+ `strftime()' if it's there.  Typically, the conversion specifier either
+ does not appear in the returned string or appears literally.
+ 
+ 
+ File: gawk.info,  Node: Bitwise Functions,  Next: Type Functions,  Prev: Time 
Functions,  Up: Built-in
+ 
+ 9.1.6 Bit-Manipulation Functions
+ --------------------------------
+ 
+      I can explain it for you, but I can't understand it for you.
+      Anonymous
+ 
+    Many languages provide the ability to perform "bitwise" operations
+ on two integer numbers.  In other words, the operation is performed on
+ each successive pair of bits in the operands.  Three common operations
+ are bitwise AND, OR, and XOR.  The operations are described in *note
+ table-bitwise-ops::.
+ 
+                      Bit Operator
+                |  AND  |   OR  |  XOR
+                |--+--+--+--+--+--
+      Operands  | 0 | 1 | 0 | 1 | 0 | 1
+      ---------+--+--+--+--+--+--
+          0     | 0   0 | 0   1 | 0   1
+          1     | 0   1 | 1   1 | 1   0
+ 
+ Table 9.6: Bitwise Operations
+ 
+    As you can see, the result of an AND operation is 1 only when _both_
+ bits are 1.  The result of an OR operation is 1 if _either_ bit is 1.
+ The result of an XOR operation is 1 if either bit is 1, but not both.
+ The next operation is the "complement"; the complement of 1 is 0 and
+ the complement of 0 is 1. Thus, this operation "flips" all the bits of
+ a given value.
+ 
+    Finally, two other common operations are to shift the bits left or
+ right.  For example, if you have a bit string `10111001' and you shift
+ it right by three bits, you end up with `00010111'.(1) If you start over
+ again with `10111001' and shift it left by three bits, you end up with
+ `11001000'.  `gawk' provides built-in functions that implement the
+ bitwise operations just described. They are:
+ 
 -`and(V1, V2)'
 -     Return the bitwise AND of the values provided by V1 and V2.
++`and(V1, V2 [, ...])'
++     Return the bitwise AND of the arguments. There must be at least
++     two.
+ 
+ `compl(VAL)'
+      Return the bitwise complement of VAL.
+ 
+ `lshift(VAL, COUNT)'
+      Return the value of VAL, shifted left by COUNT bits.
+ 
 -`or(V1, V2)'
 -     Return the bitwise OR of the values provided by V1 and V2.
++`or(V1, V2 [, ...])'
++     Return the bitwise OR of the arguments. There must be at least two.
+ 
+ `rshift(VAL, COUNT)'
+      Return the value of VAL, shifted right by COUNT bits.
+ 
 -`xor(V1, V2)'
 -     Return the bitwise XOR of the values provided by V1 and V2.
++`xor(V1, V2 [, ...])'
++     Return the bitwise XOR of the arguments. There must be at least
++     two.
+ 
+    For all of these functions, first the double precision
+ floating-point value is converted to the widest C unsigned integer
+ type, then the bitwise operation is performed.  If the result cannot be
+ represented exactly as a C `double', leading nonzero bits are removed
+ one by one until it can be represented exactly.  The result is then
+ converted back into a C `double'.  (If you don't understand this
+ paragraph, don't worry about it.)
+ 
+    Here is a user-defined function (*note User-defined::) that
+ illustrates the use of these functions:
+ 
+      # bits2str --- turn a byte into readable 1's and 0's
+ 
+      function bits2str(bits,        data, mask)
+      {
+          if (bits == 0)
+              return "0"
+ 
+          mask = 1
+          for (; bits != 0; bits = rshift(bits, 1))
+              data = (and(bits, mask) ? "1" : "0") data
+ 
+          while ((length(data) % 8) != 0)
+              data = "0" data
+ 
+          return data
+      }
+ 
+      BEGIN {
+          printf "123 = %s\n", bits2str(123)
+          printf "0123 = %s\n", bits2str(0123)
+          printf "0x99 = %s\n", bits2str(0x99)
+          comp = compl(0x99)
+          printf "compl(0x99) = %#x = %s\n", comp, bits2str(comp)
+          shift = lshift(0x99, 2)
+          printf "lshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift)
+          shift = rshift(0x99, 2)
+          printf "rshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift)
+      }
+ 
+ This program produces the following output when run:
+ 
+      $ gawk -f testbits.awk
+      -| 123 = 01111011
+      -| 0123 = 01010011
+      -| 0x99 = 10011001
+      -| compl(0x99) = 0xffffff66 = 11111111111111111111111101100110
+      -| lshift(0x99, 2) = 0x264 = 0000001001100100
+      -| rshift(0x99, 2) = 0x26 = 00100110
+ 
+    The `bits2str()' function turns a binary number into a string.  The
+ number `1' represents a binary value where the rightmost bit is set to
+ 1.  Using this mask, the function repeatedly checks the rightmost bit.
+ ANDing the mask with the value indicates whether the rightmost bit is 1
+ or not. If so, a `"1"' is concatenated onto the front of the string.
+ Otherwise, a `"0"' is added.  The value is then shifted right by one
+ bit and the loop continues until there are no more 1 bits.
+ 
+    If the initial value is zero it returns a simple `"0"'.  Otherwise,
+ at the end, it pads the value with zeros to represent multiples of
+ 8-bit quantities. This is typical in modern computers.
+ 
+    The main code in the `BEGIN' rule shows the difference between the
+ decimal and octal values for the same numbers (*note
+ Nondecimal-numbers::), and then demonstrates the results of the
+ `compl()', `lshift()', and `rshift()' functions.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) This example shows that 0's come in on the left side. For
+ `gawk', this is always true, but in some languages, it's possible to
+ have the left side fill with 1's. Caveat emptor.
+ 
+ 
+ File: gawk.info,  Node: Type Functions,  Next: I18N Functions,  Prev: Bitwise 
Functions,  Up: Built-in
+ 
+ 9.1.7 Getting Type Information
+ ------------------------------
+ 
+ `gawk' provides a single function that lets you distinguish an array
+ from a scalar variable.  This is necessary for writing code that
+ traverses every element of a true multidimensional array (*note Arrays
+ of Arrays::).
+ 
+ `isarray(X)'
+      Return a true value if X is an array. Otherwise return false.
+ 
+ 
+ File: gawk.info,  Node: I18N Functions,  Prev: Type Functions,  Up: Built-in
+ 
+ 9.1.8 String-Translation Functions
+ ----------------------------------
+ 
+ `gawk' provides facilities for internationalizing `awk' programs.
+ These include the functions described in the following list.  The
+ descriptions here are purposely brief.  *Note Internationalization::,
+ for the full story.  Optional parameters are enclosed in square
+ brackets ([ ]):
+ 
+ `bindtextdomain(DIRECTORY [, DOMAIN])'
+      Set the directory in which `gawk' will look for message
+      translation files, in case they will not or cannot be placed in
+      the "standard" locations (e.g., during testing).  It returns the
+      directory in which DOMAIN is "bound."
+ 
+      The default DOMAIN is the value of `TEXTDOMAIN'.  If DIRECTORY is
+      the null string (`""'), then `bindtextdomain()' returns the
+      current binding for the given DOMAIN.
+ 
+ `dcgettext(STRING [, DOMAIN [, CATEGORY]])'
+      Return the translation of STRING in text domain DOMAIN for locale
+      category CATEGORY.  The default value for DOMAIN is the current
+      value of `TEXTDOMAIN'.  The default value for CATEGORY is
+      `"LC_MESSAGES"'.
+ 
+ `dcngettext(STRING1, STRING2, NUMBER [, DOMAIN [, CATEGORY]])'
+      Return the plural form used for NUMBER of the translation of
+      STRING1 and STRING2 in text domain DOMAIN for locale category
+      CATEGORY. STRING1 is the English singular variant of a message,
+      and STRING2 the English plural variant of the same message.  The
+      default value for DOMAIN is the current value of `TEXTDOMAIN'.
+      The default value for CATEGORY is `"LC_MESSAGES"'.
+ 
+ 
+ File: gawk.info,  Node: User-defined,  Next: Indirect Calls,  Prev: Built-in, 
 Up: Functions
+ 
+ 9.2 User-Defined Functions
+ ==========================
+ 
+ Complicated `awk' programs can often be simplified by defining your own
+ functions.  User-defined functions can be called just like built-in
+ ones (*note Function Calls::), but it is up to you to define them,
+ i.e., to tell `awk' what they should do.
+ 
+ * Menu:
+ 
+ * Definition Syntax::           How to write definitions and what they mean.
+ * Function Example::            An example function definition and what it
+                                 does.
+ * Function Caveats::            Things to watch out for.
+ * Return Statement::            Specifying the value a function returns.
+ * Dynamic Typing::              How variable types can change at runtime.
+ 
+ 
+ File: gawk.info,  Node: Definition Syntax,  Next: Function Example,  Up: 
User-defined
+ 
+ 9.2.1 Function Definition Syntax
+ --------------------------------
+ 
+ Definitions of functions can appear anywhere between the rules of an
+ `awk' program.  Thus, the general form of an `awk' program is extended
+ to include sequences of rules _and_ user-defined function definitions.
+ There is no need to put the definition of a function before all uses of
+ the function.  This is because `awk' reads the entire program before
+ starting to execute any of it.
+ 
+    The definition of a function named NAME looks like this:
+ 
+      function NAME([PARAMETER-LIST])
+      {
+           BODY-OF-FUNCTION
+      }
+ 
+ Here, NAME is the name of the function to define.  A valid function
+ name is like a valid variable name: a sequence of letters, digits, and
+ underscores that doesn't start with a digit.  Within a single `awk'
+ program, any particular name can only be used as a variable, array, or
+ function.
+ 
+    PARAMETER-LIST is an optional list of the function's arguments and
+ local variable names, separated by commas.  When the function is called,
+ the argument names are used to hold the argument values given in the
+ call.  The local variables are initialized to the empty string.  A
+ function cannot have two parameters with the same name, nor may it have
+ a parameter with the same name as the function itself.
+ 
+    In addition, according to the POSIX standard, function parameters
+ cannot have the same name as one of the special built-in variables
+ (*note Built-in Variables::.  Not all versions of `awk' enforce this
+ restriction.
+ 
+    The BODY-OF-FUNCTION consists of `awk' statements.  It is the most
+ important part of the definition, because it says what the function
+ should actually _do_.  The argument names exist to give the body a way
+ to talk about the arguments; local variables exist to give the body
+ places to keep temporary values.
+ 
+    Argument names are not distinguished syntactically from local
+ variable names. Instead, the number of arguments supplied when the
+ function is called determines how many argument variables there are.
+ Thus, if three argument values are given, the first three names in
+ PARAMETER-LIST are arguments and the rest are local variables.
+ 
+    It follows that if the number of arguments is not the same in all
+ calls to the function, some of the names in PARAMETER-LIST may be
+ arguments on some occasions and local variables on others.  Another way
+ to think of this is that omitted arguments default to the null string.
+ 
+    Usually when you write a function, you know how many names you
+ intend to use for arguments and how many you intend to use as local
+ variables.  It is conventional to place some extra space between the
+ arguments and the local variables, in order to document how your
+ function is supposed to be used.
+ 
+    During execution of the function body, the arguments and local
+ variable values hide, or "shadow", any variables of the same names used
+ in the rest of the program.  The shadowed variables are not accessible
+ in the function definition, because there is no way to name them while
+ their names have been taken away for the local variables.  All other
+ variables used in the `awk' program can be referenced or set normally
+ in the function's body.
+ 
+    The arguments and local variables last only as long as the function
+ body is executing.  Once the body finishes, you can once again access
+ the variables that were shadowed while the function was running.
+ 
+    The function body can contain expressions that call functions.  They
+ can even call this function, either directly or by way of another
+ function.  When this happens, we say the function is "recursive".  The
+ act of a function calling itself is called "recursion".
+ 
+    All the built-in functions return a value to their caller.
+ User-defined functions can do also, using the `return' statement, which
+ is described in detail in *note Return Statement::.  Many of the
+ subsequent examples in this minor node use the `return' statement.
+ 
+    In many `awk' implementations, including `gawk', the keyword
+ `function' may be abbreviated `func'. (c.e.)  However, POSIX only
+ specifies the use of the keyword `function'.  This actually has some
+ practical implications.  If `gawk' is in POSIX-compatibility mode
+ (*note Options::), then the following statement does _not_ define a
+ function:
+ 
+      func foo() { a = sqrt($1) ; print a }
+ 
+ Instead it defines a rule that, for each record, concatenates the value
+ of the variable `func' with the return value of the function `foo'.  If
+ the resulting string is non-null, the action is executed.  This is
+ probably not what is desired.  (`awk' accepts this input as
+ syntactically valid, because functions may be used before they are
+ defined in `awk' programs.(1))
+ 
+    To ensure that your `awk' programs are portable, always use the
+ keyword `function' when defining a function.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) This program won't actually run, since `foo()' is undefined.
+ 
+ 
+ File: gawk.info,  Node: Function Example,  Next: Function Caveats,  Prev: 
Definition Syntax,  Up: User-defined
+ 
+ 9.2.2 Function Definition Examples
+ ----------------------------------
+ 
+ Here is an example of a user-defined function, called `myprint()', that
+ takes a number and prints it in a specific format:
+ 
+      function myprint(num)
+      {
+           printf "%6.3g\n", num
+      }
+ 
+ To illustrate, here is an `awk' rule that uses our `myprint' function:
+ 
+      $3 > 0     { myprint($3) }
+ 
+ This program prints, in our special format, all the third fields that
+ contain a positive number in our input.  Therefore, when given the
+ following input:
+ 
+       1.2   3.4    5.6   7.8
+       9.10 11.12 -13.14 15.16
+      17.18 19.20  21.22 23.24
+ 
+ this program, using our function to format the results, prints:
+ 
+         5.6
+        21.2
+ 
+    This function deletes all the elements in an array:
+ 
+      function delarray(a,    i)
+      {
+          for (i in a)
+             delete a[i]
+      }
+ 
+    When working with arrays, it is often necessary to delete all the
+ elements in an array and start over with a new list of elements (*note
+ Delete::).  Instead of having to repeat this loop everywhere that you
+ need to clear out an array, your program can just call `delarray'.
+ (This guarantees portability.  The use of `delete ARRAY' to delete the
+ contents of an entire array is a nonstandard extension.)
+ 
+    The following is an example of a recursive function.  It takes a
+ string as an input parameter and returns the string in backwards order.
+ Recursive functions must always have a test that stops the recursion.
+ In this case, the recursion terminates when the starting position is
+ zero, i.e., when there are no more characters left in the string.
+ 
+      function rev(str, start)
+      {
+          if (start == 0)
+              return ""
+ 
+          return (substr(str, start, 1) rev(str, start - 1))
+      }
+ 
+    If this function is in a file named `rev.awk', it can be tested this
+ way:
+ 
+      $ echo "Don't Panic!" |
+      > gawk --source '{ print rev($0, length($0)) }' -f rev.awk
+      -| !cinaP t'noD
+ 
+    The C `ctime()' function takes a timestamp and returns it in a
+ string, formatted in a well-known fashion.  The following example uses
+ the built-in `strftime()' function (*note Time Functions::) to create
+ an `awk' version of `ctime()':
+ 
+      # ctime.awk
+      #
+      # awk version of C ctime(3) function
+ 
+      function ctime(ts,    format)
+      {
+          format = "%a %b %e %H:%M:%S %Z %Y"
+          if (ts == 0)
+              ts = systime()       # use current time as default
+          return strftime(format, ts)
+      }
+ 
+ 
+ File: gawk.info,  Node: Function Caveats,  Next: Return Statement,  Prev: 
Function Example,  Up: User-defined
+ 
+ 9.2.3 Calling User-Defined Functions
+ ------------------------------------
+ 
+ This section describes how to call a user-defined function.
+ 
+ * Menu:
+ 
+ * Calling A Function::          Don't use spaces.
+ * Variable Scope::              Controlling variable scope.
+ * Pass By Value/Reference::     Passing parameters.
+ 
+ 
+ File: gawk.info,  Node: Calling A Function,  Next: Variable Scope,  Up: 
Function Caveats
+ 
+ 9.2.3.1 Writing A Function Call
+ ...............................
+ 
+ "Calling a function" means causing the function to run and do its job.
+ A function call is an expression and its value is the value returned by
+ the function.
+ 
+    A function call consists of the function name followed by the
+ arguments in parentheses.  `awk' expressions are what you write in the
+ call for the arguments.  Each time the call is executed, these
+ expressions are evaluated, and the values become the actual arguments.
+ For example, here is a call to `foo()' with three arguments (the first
+ being a string concatenation):
+ 
+      foo(x y, "lose", 4 * z)
+ 
+      CAUTION: Whitespace characters (spaces and TABs) are not allowed
+      between the function name and the open-parenthesis of the argument
+      list.  If you write whitespace by mistake, `awk' might think that
+      you mean to concatenate a variable with an expression in
+      parentheses.  However, it notices that you used a function name
+      and not a variable name, and reports an error.
+ 
+ 
+ File: gawk.info,  Node: Variable Scope,  Next: Pass By Value/Reference,  
Prev: Calling A Function,  Up: Function Caveats
+ 
+ 9.2.3.2 Controlling Variable Scope
+ ..................................
+ 
+ There is no way to make a variable local to a `{ ... }' block in `awk',
+ but you can make a variable local to a function. It is good practice to
+ do so whenever a variable is needed only in that function.
+ 
+    To make a variable local to a function, simply declare the variable
+ as an argument after the actual function arguments (*note Definition
+ Syntax::).  Look at the following example where variable `i' is a
+ global variable used by both functions `foo()' and `bar()':
+ 
+      function bar()
+      {
+          for (i = 0; i < 3; i++)
+              print "bar's i=" i
+      }
+ 
+      function foo(j)
+      {
+          i = j + 1
+          print "foo's i=" i
+          bar()
+          print "foo's i=" i
+      }
+ 
+      BEGIN {
+            i = 10
+            print "top's i=" i
+            foo(0)
+            print "top's i=" i
+      }
+ 
+    Running this script produces the following, because the `i' in
+ functions `foo()' and `bar()' and at the top level refer to the same
+ variable instance:
+ 
+      top's i=10
+      foo's i=1
+      bar's i=0
+      bar's i=1
+      bar's i=2
+      foo's i=3
+      top's i=3
+ 
+    If you want `i' to be local to both `foo()' and `bar()' do as
+ follows (the extra-space before `i' is a coding convention to indicate
+ that `i' is a local variable, not an argument):
+ 
+      function bar(    i)
+      {
+          for (i = 0; i < 3; i++)
+              print "bar's i=" i
+      }
+ 
+      function foo(j,    i)
+      {
+          i = j + 1
+          print "foo's i=" i
+          bar()
+          print "foo's i=" i
+      }
+ 
+      BEGIN {
+            i = 10
+            print "top's i=" i
+            foo(0)
+            print "top's i=" i
+      }
+ 
+    Running the corrected script produces the following:
+ 
+      top's i=10
+      foo's i=1
+      bar's i=0
+      bar's i=1
+      bar's i=2
+      foo's i=1
+      top's i=10
+ 
+ 
+ File: gawk.info,  Node: Pass By Value/Reference,  Prev: Variable Scope,  Up: 
Function Caveats
+ 
+ 9.2.3.3 Passing Function Arguments By Value Or By Reference
+ ...........................................................
+ 
+ In `awk', when you declare a function, there is no way to declare
+ explicitly whether the arguments are passed "by value" or "by
+ reference".
+ 
+    Instead the passing convention is determined at runtime when the
+ function is called according to the following rule:
+ 
+    * If the argument is an array variable, then it is passed by
+      reference,
+ 
+    * Otherwise the argument is passed by value.
+ 
+    Passing an argument by value means that when a function is called, it
+ is given a _copy_ of the value of this argument.  The caller may use a
+ variable as the expression for the argument, but the called function
+ does not know this--it only knows what value the argument had.  For
+ example, if you write the following code:
+ 
+      foo = "bar"
+      z = myfunc(foo)
+ 
+ then you should not think of the argument to `myfunc()' as being "the
+ variable `foo'."  Instead, think of the argument as the string value
+ `"bar"'.  If the function `myfunc()' alters the values of its local
+ variables, this has no effect on any other variables.  Thus, if
+ `myfunc()' does this:
+ 
+      function myfunc(str)
+      {
+         print str
+         str = "zzz"
+         print str
+      }
+ 
+ to change its first argument variable `str', it does _not_ change the
+ value of `foo' in the caller.  The role of `foo' in calling `myfunc()'
+ ended when its value (`"bar"') was computed.  If `str' also exists
+ outside of `myfunc()', the function body cannot alter this outer value,
+ because it is shadowed during the execution of `myfunc()' and cannot be
+ seen or changed from there.
+ 
+    However, when arrays are the parameters to functions, they are _not_
+ copied.  Instead, the array itself is made available for direct
+ manipulation by the function.  This is usually termed "call by
+ reference".  Changes made to an array parameter inside the body of a
+ function _are_ visible outside that function.
+ 
+      NOTE: Changing an array parameter inside a function can be very
+      dangerous if you do not watch what you are doing.  For example:
+ 
+           function changeit(array, ind, nvalue)
+           {
+                array[ind] = nvalue
+           }
+ 
+           BEGIN {
+               a[1] = 1; a[2] = 2; a[3] = 3
+               changeit(a, 2, "two")
+               printf "a[1] = %s, a[2] = %s, a[3] = %s\n",
+                       a[1], a[2], a[3]
+           }
+ 
+      prints `a[1] = 1, a[2] = two, a[3] = 3', because `changeit' stores
+      `"two"' in the second element of `a'.
+ 
+    Some `awk' implementations allow you to call a function that has not
+ been defined. They only report a problem at runtime when the program
+ actually tries to call the function. For example:
+ 
+      BEGIN {
+          if (0)
+              foo()
+          else
+              bar()
+      }
+      function bar() { ... }
+      # note that `foo' is not defined
+ 
+ Because the `if' statement will never be true, it is not really a
+ problem that `foo()' has not been defined.  Usually, though, it is a
+ problem if a program calls an undefined function.
+ 
+    If `--lint' is specified (*note Options::), `gawk' reports calls to
+ undefined functions.
+ 
+    Some `awk' implementations generate a runtime error if you use the
+ `next' statement (*note Next Statement::) inside a user-defined
+ function.  `gawk' does not have this limitation.
+ 
+ 
+ File: gawk.info,  Node: Return Statement,  Next: Dynamic Typing,  Prev: 
Function Caveats,  Up: User-defined
+ 
+ 9.2.4 The `return' Statement
+ ----------------------------
+ 
+ As seen in several earlier examples, the body of a user-defined
+ function can contain a `return' statement.  This statement returns
+ control to the calling part of the `awk' program.  It can also be used
+ to return a value for use in the rest of the `awk' program.  It looks
+ like this:
+ 
+      return [EXPRESSION]
+ 
+    The EXPRESSION part is optional.  Due most likely to an oversight,
+ POSIX does not define what the return value is if you omit the
+ EXPRESSION.  Technically speaking, this make the returned value
+ undefined, and therefore, unpredictable.  In practice, though, all
+ versions of `awk' simply return the null string, which acts like zero
+ if used in a numeric context.
+ 
+    A `return' statement with no value expression is assumed at the end
+ of every function definition.  So if control reaches the end of the
+ function body, then technically, the function returns an unpredictable
+ value.  In practice, it returns the empty string.  `awk' does _not_
+ warn you if you use the return value of such a function.
+ 
+    Sometimes, you want to write a function for what it does, not for
+ what it returns.  Such a function corresponds to a `void' function in
+ C, C++ or Java, or to a `procedure' in Ada.  Thus, it may be
+ appropriate to not return any value; simply bear in mind that you
+ should not be using the return value of such a function.
+ 
+    The following is an example of a user-defined function that returns
+ a value for the largest number among the elements of an array:
+ 
+      function maxelt(vec,   i, ret)
+      {
+           for (i in vec) {
+                if (ret == "" || vec[i] > ret)
+                     ret = vec[i]
+           }
+           return ret
+      }
+ 
+ You call `maxelt()' with one argument, which is an array name.  The
+ local variables `i' and `ret' are not intended to be arguments; while
+ there is nothing to stop you from passing more than one argument to
+ `maxelt()', the results would be strange.  The extra space before `i'
+ in the function parameter list indicates that `i' and `ret' are local
+ variables.  You should follow this convention when defining functions.
+ 
+    The following program uses the `maxelt()' function.  It loads an
+ array, calls `maxelt()', and then reports the maximum number in that
+ array:
+ 
+      function maxelt(vec,   i, ret)
+      {
+           for (i in vec) {
+                if (ret == "" || vec[i] > ret)
+                     ret = vec[i]
+           }
+           return ret
+      }
+ 
+      # Load all fields of each record into nums.
+      {
+           for(i = 1; i <= NF; i++)
+                nums[NR, i] = $i
+      }
+ 
+      END {
+           print maxelt(nums)
+      }
+ 
+    Given the following input:
+ 
+       1 5 23 8 16
+      44 3 5 2 8 26
+      256 291 1396 2962 100
+      -6 467 998 1101
+      99385 11 0 225
+ 
+ the program reports (predictably) that 99,385 is the largest value in
+ the array.
+ 
+ 
+ File: gawk.info,  Node: Dynamic Typing,  Prev: Return Statement,  Up: 
User-defined
+ 
+ 9.2.5 Functions and Their Effects on Variable Typing
+ ----------------------------------------------------
+ 
+ `awk' is a very fluid language.  It is possible that `awk' can't tell
+ if an identifier represents a scalar variable or an array until runtime.
+ Here is an annotated sample program:
+ 
+      function foo(a)
+      {
+          a[1] = 1   # parameter is an array
+      }
+ 
+      BEGIN {
+          b = 1
+          foo(b)  # invalid: fatal type mismatch
+ 
+          foo(x)  # x uninitialized, becomes an array dynamically
+          x = 1   # now not allowed, runtime error
+      }
+ 
+    Usually, such things aren't a big issue, but it's worth being aware
+ of them.
+ 
+ 
+ File: gawk.info,  Node: Indirect Calls,  Prev: User-defined,  Up: Functions
+ 
+ 9.3 Indirect Function Calls
+ ===========================
+ 
+ This section describes a `gawk'-specific extension.
+ 
+    Often, you may wish to defer the choice of function to call until
+ runtime.  For example, you may have different kinds of records, each of
+ which should be processed differently.
+ 
+    Normally, you would have to use a series of `if'-`else' statements
+ to decide which function to call.  By using "indirect" function calls,
+ you can specify the name of the function to call as a string variable,
+ and then call the function.  Let's look at an example.
+ 
+    Suppose you have a file with your test scores for the classes you
+ are taking.  The first field is the class name. The following fields
+ are the functions to call to process the data, up to a "marker" field
+ `data:'.  Following the marker, to the end of the record, are the
+ various numeric test scores.
+ 
+    Here is the initial file; you wish to get the sum and the average of
+ your test scores:
+ 
+      Biology_101 sum average data: 87.0 92.4 78.5 94.9
+      Chemistry_305 sum average data: 75.2 98.3 94.7 88.2
+      English_401 sum average data: 100.0 95.6 87.1 93.4
+ 
+    To process the data, you might write initially:
+ 
+      {
+          class = $1
+          for (i = 2; $i != "data:"; i++) {
+              if ($i == "sum")
+                  sum()   # processes the whole record
+              else if ($i == "average")
+                  average()
+              ...           # and so on
+          }
+      }
+ 
+ This style of programming works, but can be awkward.  With "indirect"
+ function calls, you tell `gawk' to use the _value_ of a variable as the
+ name of the function to call.
+ 
+    The syntax is similar to that of a regular function call: an
+ identifier immediately followed by a left parenthesis, any arguments,
+ and then a closing right parenthesis, with the addition of a leading `@'
+ character:
+ 
+      the_func = "sum"
+      result = @the_func()   # calls the `sum' function
+ 
+    Here is a full program that processes the previously shown data,
+ using indirect function calls.
+ 
+      # indirectcall.awk --- Demonstrate indirect function calls
+ 
+      # average --- return the average of the values in fields $first - $last
+ 
+      function average(first, last,   sum, i)
+      {
+          sum = 0;
+          for (i = first; i <= last; i++)
+              sum += $i
+ 
+          return sum / (last - first + 1)
+      }
+ 
+      # sum --- return the sum of the values in fields $first - $last
+ 
+      function sum(first, last,   ret, i)
+      {
+          ret = 0;
+          for (i = first; i <= last; i++)
+              ret += $i
+ 
+          return ret
+      }
+ 
+    These two functions expect to work on fields; thus the parameters
+ `first' and `last' indicate where in the fields to start and end.
+ Otherwise they perform the expected computations and are not unusual.
+ 
+      # For each record, print the class name and the requested statistics
+ 
+      {
+          class_name = $1
+          gsub(/_/, " ", class_name)  # Replace _ with spaces
+ 
+          # find start
+          for (i = 1; i <= NF; i++) {
+              if ($i == "data:") {
+                  start = i + 1
+                  break
+              }
+          }
+ 
+          printf("%s:\n", class_name)
+          for (i = 2; $i != "data:"; i++) {
+              the_function = $i
+              printf("\t%s: <%s>\n", $i, @the_function(start, NF) "")
+          }
+          print ""
+      }
+ 
+    This is the main processing for each record. It prints the class
+ name (with underscores replaced with spaces). It then finds the start
+ of the actual data, saving it in `start'.  The last part of the code
+ loops through each function name (from `$2' up to the marker, `data:'),
+ calling the function named by the field. The indirect function call
+ itself occurs as a parameter in the call to `printf'.  (The `printf'
+ format string uses `%s' as the format specifier so that we can use
+ functions that return strings, as well as numbers. Note that the result
+ from the indirect call is concatenated with the empty string, in order
+ to force it to be a string value.)
+ 
+    Here is the result of running the program:
+ 
+      $ gawk -f indirectcall.awk class_data1
+      -| Biology 101:
+      -|     sum: <352.8>
+      -|     average: <88.2>
+      -|
+      -| Chemistry 305:
+      -|     sum: <356.4>
+      -|     average: <89.1>
+      -|
+      -| English 401:
+      -|     sum: <376.1>
+      -|     average: <94.025>
+ 
+    The ability to use indirect function calls is more powerful than you
+ may think at first.  The C and C++ languages provide "function
+ pointers," which are a mechanism for calling a function chosen at
+ runtime.  One of the most well-known uses of this ability is the C
+ `qsort()' function, which sorts an array using the famous "quick sort"
+ algorithm (see the Wikipedia article
+ (http://en.wikipedia.org/wiki/Quick_sort) for more information).  To
+ use this function, you supply a pointer to a comparison function.  This
+ mechanism allows you to sort arbitrary data in an arbitrary fashion.
+ 
+    We can do something similar using `gawk', like this:
+ 
+      # quicksort.awk --- Quicksort algorithm, with user-supplied
+      #                   comparison function
+      # quicksort --- C.A.R. Hoare's quick sort algorithm. See Wikipedia
+      #               or almost any algorithms or computer science text
+ 
+      function quicksort(data, left, right, less_than,    i, last)
+      {
+          if (left >= right)  # do nothing if array contains fewer
+              return          # than two elements
+ 
+          quicksort_swap(data, left, int((left + right) / 2))
+          last = left
+          for (i = left + 1; i <= right; i++)
+              if (@less_than(data[i], data[left]))
+                  quicksort_swap(data, ++last, i)
+          quicksort_swap(data, left, last)
+          quicksort(data, left, last - 1, less_than)
+          quicksort(data, last + 1, right, less_than)
+      }
+ 
+      # quicksort_swap --- helper function for quicksort, should really be 
inline
+ 
+      function quicksort_swap(data, i, j, temp)
+      {
+          temp = data[i]
+          data[i] = data[j]
+          data[j] = temp
+      }
+ 
+    The `quicksort()' function receives the `data' array, the starting
+ and ending indices to sort (`left' and `right'), and the name of a
+ function that performs a "less than" comparison.  It then implements
+ the quick sort algorithm.
+ 
+    To make use of the sorting function, we return to our previous
+ example. The first thing to do is write some comparison functions:
+ 
+      # num_lt --- do a numeric less than comparison
+ 
+      function num_lt(left, right)
+      {
+          return ((left + 0) < (right + 0))
+      }
+ 
+      # num_ge --- do a numeric greater than or equal to comparison
+ 
+      function num_ge(left, right)
+      {
+          return ((left + 0) >= (right + 0))
+      }
+ 
+    The `num_ge()' function is needed to perform a descending sort; when
+ used to perform a "less than" test, it actually does the opposite
+ (greater than or equal to), which yields data sorted in descending
+ order.
+ 
+    Next comes a sorting function.  It is parameterized with the
+ starting and ending field numbers and the comparison function. It
+ builds an array with the data and calls `quicksort' appropriately, and
+ then formats the results as a single string:
+ 
+      # do_sort --- sort the data according to `compare'
+      #             and return it as a string
+ 
+      function do_sort(first, last, compare,      data, i, retval)
+      {
+          delete data
+          for (i = 1; first <= last; first++) {
+              data[i] = $first
+              i++
+          }
+ 
+          quicksort(data, 1, i-1, compare)
+ 
+          retval = data[1]
+          for (i = 2; i in data; i++)
+              retval = retval " " data[i]
+ 
+          return retval
+      }
+ 
+    Finally, the two sorting functions call `do_sort()', passing in the
+ names of the two comparison functions:
+ 
+      # sort --- sort the data in ascending order and return it as a string
+ 
+      function sort(first, last)
+      {
+          return do_sort(first, last, "num_lt")
+      }
+ 
+      # rsort --- sort the data in descending order and return it as a string
+ 
+      function rsort(first, last)
+      {
+          return do_sort(first, last, "num_ge")
+      }
+ 
+    Here is an extended version of the data file:
+ 
+      Biology_101 sum average sort rsort data: 87.0 92.4 78.5 94.9
+      Chemistry_305 sum average sort rsort data: 75.2 98.3 94.7 88.2
+      English_401 sum average sort rsort data: 100.0 95.6 87.1 93.4
+ 
+    Finally, here are the results when the enhanced program is run:
+ 
+      $ gawk -f quicksort.awk -f indirectcall.awk class_data2
+      -| Biology 101:
+      -|     sum: <352.8>
+      -|     average: <88.2>
+      -|     sort: <78.5 87.0 92.4 94.9>
+      -|     rsort: <94.9 92.4 87.0 78.5>
+      -|
+      -| Chemistry 305:
+      -|     sum: <356.4>
+      -|     average: <89.1>
+      -|     sort: <75.2 88.2 94.7 98.3>
+      -|     rsort: <98.3 94.7 88.2 75.2>
+      -|
+      -| English 401:
+      -|     sum: <376.1>
+      -|     average: <94.025>
+      -|     sort: <87.1 93.4 95.6 100.0>
+      -|     rsort: <100.0 95.6 93.4 87.1>
+ 
+    Remember that you must supply a leading `@' in front of an indirect
+ function call.
+ 
+    Unfortunately, indirect function calls cannot be used with the
+ built-in functions.  However, you can generally write "wrapper"
+ functions which call the built-in ones, and those can be called
+ indirectly. (Other than, perhaps, the mathematical functions, there is
+ not a lot of reason to try to call the built-in functions indirectly.)
+ 
+    `gawk' does its best to make indirect function calls efficient.  For
+ example, in the following case:
+ 
+      for (i = 1; i <= n; i++)
+          @the_func()
+ 
+ `gawk' will look up the actual function to call only once.
+ 
+ 
 -File: gawk.info,  Node: Internationalization,  Next: Advanced Features,  
Prev: Functions,  Up: Top
++File: gawk.info,  Node: Internationalization,  Next: Arbitrary Precision 
Arithmetic,  Prev: Functions,  Up: Top
+ 
+ 10 Internationalization with `gawk'
+ ***********************************
+ 
+ Once upon a time, computer makers wrote software that worked only in
+ English.  Eventually, hardware and software vendors noticed that if
+ their systems worked in the native languages of non-English-speaking
+ countries, they were able to sell more systems.  As a result,
+ internationalization and localization of programs and software systems
+ became a common practice.
+ 
+    For many years, the ability to provide internationalization was
+ largely restricted to programs written in C and C++.  This major node
+ describes the underlying library `gawk' uses for internationalization,
+ as well as how `gawk' makes internationalization features available at
+ the `awk' program level.  Having internationalization available at the
+ `awk' level gives software developers additional flexibility--they are
+ no longer forced to write in C or C++ when internationalization is a
+ requirement.
+ 
+ * Menu:
+ 
+ * I18N and L10N::               Internationalization and Localization.
+ * Explaining gettext::          How GNU `gettext' works.
+ * Programmer i18n::             Features for the programmer.
+ * Translator i18n::             Features for the translator.
+ * I18N Example::                A simple i18n example.
+ * Gawk I18N::                   `gawk' is also internationalized.
+ 
+ 
+ File: gawk.info,  Node: I18N and L10N,  Next: Explaining gettext,  Up: 
Internationalization
+ 
+ 10.1 Internationalization and Localization
+ ==========================================
+ 
+ "Internationalization" means writing (or modifying) a program once, in
+ such a way that it can use multiple languages without requiring further
+ source-code changes.  "Localization" means providing the data necessary
+ for an internationalized program to work in a particular language.
+ Most typically, these terms refer to features such as the language used
+ for printing error messages, the language used to read responses, and
+ information related to how numerical and monetary values are printed
+ and read.
+ 
+ 
+ File: gawk.info,  Node: Explaining gettext,  Next: Programmer i18n,  Prev: 
I18N and L10N,  Up: Internationalization
+ 
+ 10.2 GNU `gettext'
+ ==================
+ 
+ The facilities in GNU `gettext' focus on messages; strings printed by a
+ program, either directly or via formatting with `printf' or
+ `sprintf()'.(1)
+ 
+    When using GNU `gettext', each application has its own "text
+ domain".  This is a unique name, such as `kpilot' or `gawk', that
+ identifies the application.  A complete application may have multiple
+ components--programs written in C or C++, as well as scripts written in
+ `sh' or `awk'.  All of the components use the same text domain.
+ 
+    To make the discussion concrete, assume we're writing an application
+ named `guide'.  Internationalization consists of the following steps,
+ in this order:
+ 
+   1. The programmer goes through the source for all of `guide''s
+      components and marks each string that is a candidate for
+      translation.  For example, `"`-F': option required"' is a good
+      candidate for translation.  A table with strings of option names
+      is not (e.g., `gawk''s `--profile' option should remain the same,
+      no matter what the local language).
+ 
+   2. The programmer indicates the application's text domain (`"guide"')
+      to the `gettext' library, by calling the `textdomain()' function.
+ 
+   3. Messages from the application are extracted from the source code
+      and collected into a portable object template file (`guide.pot'),
+      which lists the strings and their translations.  The translations
+      are initially empty.  The original (usually English) messages
+      serve as the key for lookup of the translations.
+ 
+   4. For each language with a translator, `guide.pot' is copied to a
+      portable object file (`.po') and translations are created and
+      shipped with the application.  For example, there might be a
+      `fr.po' for a French translation.
+ 
+   5. Each language's `.po' file is converted into a binary message
+      object (`.mo') file.  A message object file contains the original
+      messages and their translations in a binary format that allows
+      fast lookup of translations at runtime.
+ 
+   6. When `guide' is built and installed, the binary translation files
+      are installed in a standard place.
+ 
+   7. For testing and development, it is possible to tell `gettext' to
+      use `.mo' files in a different directory than the standard one by
+      using the `bindtextdomain()' function.
+ 
+   8. At runtime, `guide' looks up each string via a call to
+      `gettext()'.  The returned string is the translated string if
+      available, or the original string if not.
+ 
+   9. If necessary, it is possible to access messages from a different
+      text domain than the one belonging to the application, without
+      having to switch the application's default text domain back and
+      forth.
+ 
+    In C (or C++), the string marking and dynamic translation lookup are
+ accomplished by wrapping each string in a call to `gettext()':
+ 
+      printf("%s", gettext("Don't Panic!\n"));
+ 
+    The tools that extract messages from source code pull out all
+ strings enclosed in calls to `gettext()'.
+ 
+    The GNU `gettext' developers, recognizing that typing `gettext(...)'
+ over and over again is both painful and ugly to look at, use the macro
+ `_' (an underscore) to make things easier:
+ 
+      /* In the standard header file: */
+      #define _(str) gettext(str)
+ 
+      /* In the program text: */
+      printf("%s", _("Don't Panic!\n"));
+ 
+ This reduces the typing overhead to just three extra characters per
+ string and is considerably easier to read as well.
+ 
+    There are locale "categories" for different types of locale-related
+ information.  The defined locale categories that `gettext' knows about
+ are:
+ 
+ `LC_MESSAGES'
+      Text messages.  This is the default category for `gettext'
+      operations, but it is possible to supply a different one
+      explicitly, if necessary.  (It is almost never necessary to supply
+      a different category.)
+ 
+ `LC_COLLATE'
+      Text-collation information; i.e., how different characters and/or
+      groups of characters sort in a given language.
+ 
+ `LC_CTYPE'
+      Character-type information (alphabetic, digit, upper- or
+      lowercase, and so on).  This information is accessed via the POSIX
+      character classes in regular expressions, such as `/[[:alnum:]]/'
+      (*note Regexp Operators::).
+ 
+ `LC_MONETARY'
+      Monetary information, such as the currency symbol, and whether the
+      symbol goes before or after a number.
+ 
+ `LC_NUMERIC'
+      Numeric information, such as which characters to use for the
+      decimal point and the thousands separator.(2)
+ 
+ `LC_RESPONSE'
+      Response information, such as how "yes" and "no" appear in the
+      local language, and possibly other information as well.
+ 
+ `LC_TIME'
+      Time- and date-related information, such as 12- or 24-hour clock,
+      month printed before or after the day in a date, local month
+      abbreviations, and so on.
+ 
+ `LC_ALL'
+      All of the above.  (Not too useful in the context of `gettext'.)
+ 
+    ---------- Footnotes ----------
+ 
+    (1) For some operating systems, the `gawk' port doesn't support GNU
+ `gettext'.  Therefore, these features are not available if you are
+ using one of those operating systems. Sorry.
+ 
+    (2) Americans use a comma every three decimal places and a period
+ for the decimal point, while many Europeans do exactly the opposite:
+ 1,234.56 versus 1.234,56.
+ 
+ 
+ File: gawk.info,  Node: Programmer i18n,  Next: Translator i18n,  Prev: 
Explaining gettext,  Up: Internationalization
+ 
+ 10.3 Internationalizing `awk' Programs
+ ======================================
+ 
+ `gawk' provides the following variables and functions for
+ internationalization:
+ 
+ `TEXTDOMAIN'
+      This variable indicates the application's text domain.  For
+      compatibility with GNU `gettext', the default value is
+      `"messages"'.
+ 
+ `_"your message here"'
+      String constants marked with a leading underscore are candidates
+      for translation at runtime.  String constants without a leading
+      underscore are not translated.
+ 
+ `dcgettext(STRING [, DOMAIN [, CATEGORY]])'
+      Return the translation of STRING in text domain DOMAIN for locale
+      category CATEGORY.  The default value for DOMAIN is the current
+      value of `TEXTDOMAIN'.  The default value for CATEGORY is
+      `"LC_MESSAGES"'.
+ 
+      If you supply a value for CATEGORY, it must be a string equal to
+      one of the known locale categories described in *note Explaining
+      gettext::.  You must also supply a text domain.  Use `TEXTDOMAIN'
+      if you want to use the current domain.
+ 
+           CAUTION: The order of arguments to the `awk' version of the
+           `dcgettext()' function is purposely different from the order
+           for the C version.  The `awk' version's order was chosen to
+           be simple and to allow for reasonable `awk'-style default
+           arguments.
+ 
+ `dcngettext(STRING1, STRING2, NUMBER [, DOMAIN [, CATEGORY]])'
+      Return the plural form used for NUMBER of the translation of
+      STRING1 and STRING2 in text domain DOMAIN for locale category
+      CATEGORY. STRING1 is the English singular variant of a message,
+      and STRING2 the English plural variant of the same message.  The
+      default value for DOMAIN is the current value of `TEXTDOMAIN'.
+      The default value for CATEGORY is `"LC_MESSAGES"'.
+ 
+      The same remarks about argument order as for the `dcgettext()'
+      function apply.
+ 
+ `bindtextdomain(DIRECTORY [, DOMAIN])'
+      Change the directory in which `gettext' looks for `.mo' files, in
+      case they will not or cannot be placed in the standard locations
+      (e.g., during testing).  Return the directory in which DOMAIN is
+      "bound."
+ 
+      The default DOMAIN is the value of `TEXTDOMAIN'.  If DIRECTORY is
+      the null string (`""'), then `bindtextdomain()' returns the
+      current binding for the given DOMAIN.
+ 
+    To use these facilities in your `awk' program, follow the steps
+ outlined in *note Explaining gettext::, like so:
+ 
+   1. Set the variable `TEXTDOMAIN' to the text domain of your program.
+      This is best done in a `BEGIN' rule (*note BEGIN/END::), or it can
+      also be done via the `-v' command-line option (*note Options::):
+ 
+           BEGIN {
+               TEXTDOMAIN = "guide"
+               ...
+           }
+ 
+   2. Mark all translatable strings with a leading underscore (`_')
+      character.  It _must_ be adjacent to the opening quote of the
+      string.  For example:
+ 
+           print _"hello, world"
+           x = _"you goofed"
+           printf(_"Number of users is %d\n", nusers)
+ 
+   3. If you are creating strings dynamically, you can still translate
+      them, using the `dcgettext()' built-in function:
+ 
+           message = nusers " users logged in"
+           message = dcgettext(message, "adminprog")
+           print message
+ 
+      Here, the call to `dcgettext()' supplies a different text domain
+      (`"adminprog"') in which to find the message, but it uses the
+      default `"LC_MESSAGES"' category.
+ 
+   4. During development, you might want to put the `.mo' file in a
+      private directory for testing.  This is done with the
+      `bindtextdomain()' built-in function:
+ 
+           BEGIN {
+              TEXTDOMAIN = "guide"   # our text domain
+              if (Testing) {
+                  # where to find our files
+                  bindtextdomain("testdir")
+                  # joe is in charge of adminprog
+                  bindtextdomain("../joe/testdir", "adminprog")
+              }
+              ...
+           }
+ 
+ 
+    *Note I18N Example::, for an example program showing the steps to
+ create and use translations from `awk'.
+ 
+ 
+ File: gawk.info,  Node: Translator i18n,  Next: I18N Example,  Prev: 
Programmer i18n,  Up: Internationalization
+ 
+ 10.4 Translating `awk' Programs
+ ===============================
+ 
+ Once a program's translatable strings have been marked, they must be
+ extracted to create the initial `.po' file.  As part of translation, it
+ is often helpful to rearrange the order in which arguments to `printf'
+ are output.
+ 
+    `gawk''s `--gen-pot' command-line option extracts the messages and
+ is discussed next.  After that, `printf''s ability to rearrange the
+ order for `printf' arguments at runtime is covered.
+ 
+ * Menu:
+ 
+ * String Extraction::           Extracting marked strings.
+ * Printf Ordering::             Rearranging `printf' arguments.
+ * I18N Portability::            `awk'-level portability issues.
+ 
+ 
+ File: gawk.info,  Node: String Extraction,  Next: Printf Ordering,  Up: 
Translator i18n
+ 
+ 10.4.1 Extracting Marked Strings
+ --------------------------------
+ 
+ Once your `awk' program is working, and all the strings have been
+ marked and you've set (and perhaps bound) the text domain, it is time
+ to produce translations.  First, use the `--gen-pot' command-line
+ option to create the initial `.pot' file:
+ 
+      $ gawk --gen-pot -f guide.awk > guide.pot
+ 
+    When run with `--gen-pot', `gawk' does not execute your program.
+ Instead, it parses it as usual and prints all marked strings to
+ standard output in the format of a GNU `gettext' Portable Object file.
+ Also included in the output are any constant strings that appear as the
+ first argument to `dcgettext()' or as the first and second argument to
+ `dcngettext()'.(1) *Note I18N Example::, for the full list of steps to
+ go through to create and test translations for `guide'.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) The `xgettext' utility that comes with GNU `gettext' can handle
+ `.awk' files.
+ 
+ 
+ File: gawk.info,  Node: Printf Ordering,  Next: I18N Portability,  Prev: 
String Extraction,  Up: Translator i18n
+ 
+ 10.4.2 Rearranging `printf' Arguments
+ -------------------------------------
+ 
+ Format strings for `printf' and `sprintf()' (*note Printf::) present a
+ special problem for translation.  Consider the following:(1)
+ 
+      printf(_"String `%s' has %d characters\n",
+                string, length(string)))
+ 
+    A possible German translation for this might be:
+ 
+      "%d Zeichen lang ist die Zeichenkette `%s'\n"
+ 
+    The problem should be obvious: the order of the format
+ specifications is different from the original!  Even though `gettext()'
+ can return the translated string at runtime, it cannot change the
+ argument order in the call to `printf'.
+ 
+    To solve this problem, `printf' format specifiers may have an
+ additional optional element, which we call a "positional specifier".
+ For example:
+ 
+      "%2$d Zeichen lang ist die Zeichenkette `%1$s'\n"
+ 
+    Here, the positional specifier consists of an integer count, which
+ indicates which argument to use, and a `$'. Counts are one-based, and
+ the format string itself is _not_ included.  Thus, in the following
+ example, `string' is the first argument and `length(string)' is the
+ second:
+ 
+      $ gawk 'BEGIN {
+      >     string = "Dont Panic"
+      >     printf _"%2$d characters live in \"%1$s\"\n",
+      >                         string, length(string)
+      > }'
+      -| 10 characters live in "Dont Panic"
+ 
+    If present, positional specifiers come first in the format
+ specification, before the flags, the field width, and/or the precision.
+ 
+    Positional specifiers can be used with the dynamic field width and
+ precision capability:
+ 
+      $ gawk 'BEGIN {
+      >    printf("%*.*s\n", 10, 20, "hello")
+      >    printf("%3$*2$.*1$s\n", 20, 10, "hello")
+      > }'
+      -|      hello
+      -|      hello
+ 
+      NOTE: When using `*' with a positional specifier, the `*' comes
+      first, then the integer position, and then the `$'.  This is
+      somewhat counterintuitive.
+ 
+    `gawk' does not allow you to mix regular format specifiers and those
+ with positional specifiers in the same string:
+ 
+      $ gawk 'BEGIN { printf _"%d %3$s\n", 1, 2, "hi" }'
+      error--> gawk: cmd. line:1: fatal: must use `count$' on all formats or 
none
+ 
+      NOTE: There are some pathological cases that `gawk' may fail to
+      diagnose.  In such cases, the output may not be what you expect.
+      It's still a bad idea to try mixing them, even if `gawk' doesn't
+      detect it.
+ 
+    Although positional specifiers can be used directly in `awk'
+ programs, their primary purpose is to help in producing correct
+ translations of format strings into languages different from the one in
+ which the program is first written.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) This example is borrowed from the GNU `gettext' manual.
+ 
+ 
+ File: gawk.info,  Node: I18N Portability,  Prev: Printf Ordering,  Up: 
Translator i18n
+ 
+ 10.4.3 `awk' Portability Issues
+ -------------------------------
+ 
+ `gawk''s internationalization features were purposely chosen to have as
+ little impact as possible on the portability of `awk' programs that use
+ them to other versions of `awk'.  Consider this program:
+ 
+      BEGIN {
+          TEXTDOMAIN = "guide"
+          if (Test_Guide)   # set with -v
+              bindtextdomain("/test/guide/messages")
+          print _"don't panic!"
+      }
+ 
+ As written, it won't work on other versions of `awk'.  However, it is
+ actually almost portable, requiring very little change:
+ 
+    * Assignments to `TEXTDOMAIN' won't have any effect, since
+      `TEXTDOMAIN' is not special in other `awk' implementations.
+ 
+    * Non-GNU versions of `awk' treat marked strings as the
+      concatenation of a variable named `_' with the string following
+      it.(1) Typically, the variable `_' has the null string (`""') as
+      its value, leaving the original string constant as the result.
+ 
+    * By defining "dummy" functions to replace `dcgettext()',
+      `dcngettext()' and `bindtextdomain()', the `awk' program can be
+      made to run, but all the messages are output in the original
+      language.  For example:
+ 
+           function bindtextdomain(dir, domain)
+           {
+               return dir
+           }
+ 
+           function dcgettext(string, domain, category)
+           {
+               return string
+           }
+ 
+           function dcngettext(string1, string2, number, domain, category)
+           {
+               return (number == 1 ? string1 : string2)
+           }
+ 
+    * The use of positional specifications in `printf' or `sprintf()' is
+      _not_ portable.  To support `gettext()' at the C level, many
+      systems' C versions of `sprintf()' do support positional
+      specifiers.  But it works only if enough arguments are supplied in
+      the function call.  Many versions of `awk' pass `printf' formats
+      and arguments unchanged to the underlying C library version of
+      `sprintf()', but only one format and argument at a time.  What
+      happens if a positional specification is used is anybody's guess.
+      However, since the positional specifications are primarily for use
+      in _translated_ format strings, and since non-GNU `awk's never
+      retrieve the translated string, this should not be a problem in
+      practice.
+ 
+    ---------- Footnotes ----------
+ 
+    (1) This is good fodder for an "Obfuscated `awk'" contest.
+ 
+ 
+ File: gawk.info,  Node: I18N Example,  Next: Gawk I18N,  Prev: Translator 
i18n,  Up: Internationalization
+ 
+ 10.5 A Simple Internationalization Example
+ ==========================================
+ 
+ Now let's look at a step-by-step example of how to internationalize and
+ localize a simple `awk' program, using `guide.awk' as our original
+ source:
+ 
+      BEGIN {
+          TEXTDOMAIN = "guide"
+          bindtextdomain(".")  # for testing
+          print _"Don't Panic"
+          print _"The Answer Is", 42
+          print "Pardon me, Zaphod who?"
+      }
+ 
+ Run `gawk --gen-pot' to create the `.pot' file:
+ 
+      $ gawk --gen-pot -f guide.awk > guide.pot
+ 
+ This produces:
+ 
+      #: guide.awk:4
+      msgid "Don't Panic"
+      msgstr ""
+ 
+      #: guide.awk:5
+      msgid "The Answer Is"
+      msgstr ""
+ 
+    This original portable object template file is saved and reused for
+ each language into which the application is translated.  The `msgid' is
+ the original string and the `msgstr' is the translation.
+ 
+      NOTE: Strings not marked with a leading underscore do not appear
+      in the `guide.pot' file.
+ 
+    Next, the messages must be translated.  Here is a translation to a
+ hypothetical dialect of English, called "Mellow":(1)
+ 
+      $ cp guide.pot guide-mellow.po
+      ADD TRANSLATIONS TO guide-mellow.po ...
+ 
+ Following are the translations:
+ 
+      #: guide.awk:4
+      msgid "Don't Panic"
+      msgstr "Hey man, relax!"
+ 
+      #: guide.awk:5
+      msgid "The Answer Is"
+      msgstr "Like, the scoop is"
+ 
+    The next step is to make the directory to hold the binary message
+ object file and then to create the `guide.mo' file.  The directory
+ layout shown here is standard for GNU `gettext' on GNU/Linux systems.
+ Other versions of `gettext' may use a different layout:
+ 
+      $ mkdir en_US en_US/LC_MESSAGES
+ 
+    The `msgfmt' utility does the conversion from human-readable `.po'
+ file to machine-readable `.mo' file.  By default, `msgfmt' creates a
+ file named `messages'.  This file must be renamed and placed in the
+ proper directory so that `gawk' can find it:
+ 
+      $ msgfmt guide-mellow.po
+      $ mv messages en_US/LC_MESSAGES/guide.mo
+ 
+    Finally, we run the program to test it:
+ 
+      $ gawk -f guide.awk
+      -| Hey man, relax!
+      -| Like, the scoop is 42
+      -| Pardon me, Zaphod who?
+ 
+    If the three replacement functions for `dcgettext()', `dcngettext()'
+ and `bindtextdomain()' (*note I18N Portability::) are in a file named
+ `libintl.awk', then we can run `guide.awk' unchanged as follows:
+ 
+      $ gawk --posix -f guide.awk -f libintl.awk
+      -| Don't Panic
+      -| The Answer Is 42
+      -| Pardon me, Zaphod who?
+ 
+    ---------- Footnotes ----------
+ 
+    (1) Perhaps it would be better if it were called "Hippy." Ah, well.
+ 
+ 
+ File: gawk.info,  Node: Gawk I18N,  Prev: I18N Example,  Up: 
Internationalization
+ 
+ 10.6 `gawk' Can Speak Your Language
+ ===================================
+ 
+ `gawk' itself has been internationalized using the GNU `gettext'
+ package.  (GNU `gettext' is described in complete detail in *note (GNU
+ `gettext' utilities)Top:: gettext, GNU gettext tools.)  As of this
+ writing, the latest version of GNU `gettext' is version 0.18.1
+ (ftp://ftp.gnu.org/gnu/gettext/gettext-0.18.1.tar.gz).
+ 
+    If a translation of `gawk''s messages exists, then `gawk' produces
+ usage messages, warnings, and fatal errors in the local language.
+ 
+ 
 -File: gawk.info,  Node: Advanced Features,  Next: Library Functions,  Prev: 
Internationalization,  Up: Top
++File: gawk.info,  Node: Arbitrary Precision Arithmetic,  Next: Advanced 
Features,  Prev: Internationalization,  Up: Top
+ 
 -11 Advanced Features of `gawk'
 -******************************
++11 Arithmetic and Arbitrary Precision Arithmetic with `gawk'
++************************************************************
+ 
 -     Write documentation as if whoever reads it is a violent psychopath
 -     who knows where you live.
 -     Steve English, as quoted by Peter Langston
++     There's a credibility gap: We don't know how much of the
++     computer's answers to believe. Novice computer users solve this
++     problem by implicitly trusting in the computer as an infallible
++     authority; they tend to believe that all digits of a printed
++     answer are significant. Disillusioned computer users have just the
++     opposite approach; they are constantly afraid that their answers
++     are almost meaningless.
++     Donald Knuth(1)
+ 
 -   This major node discusses advanced features in `gawk'.  It's a bit
 -of a "grab bag" of items that are otherwise unrelated to each other.
 -First, a command-line option allows `gawk' to recognize nondecimal
 -numbers in input data, not just in `awk' programs.  Then, `gawk''s
 -special features for sorting arrays are presented.  Next, two-way I/O,
 -discussed briefly in earlier parts of this Info file, is described in
 -full detail, along with the basics of TCP/IP networking.  Finally,
 -`gawk' can "profile" an `awk' program, making it possible to tune it
 -for performance.
++   This major node discusses issues that you may encounter when
++performing arithmetic.  It begins by discussing some of the general
++atributes of computer arithmetic, along with how this can influence
++what you see when running `awk' programs.  This discussion applies to
++all versions of `awk'.
+ 
 -   *note Dynamic Extensions::, discusses the ability to dynamically add
 -new built-in functions to `gawk'.  As this feature is still immature
 -and likely to change, its description is relegated to an appendix.
++   Then the discussion moves on to "arbitrary precsion arithmetic", a
++feature which is specific to `gawk'.
+ 
+ * Menu:
+ 
 -* Nondecimal Data::             Allowing nondecimal input data.
 -* Array Sorting::               Facilities for controlling array traversal and
 -                                sorting arrays.
 -* Two-way I/O::                 Two-way communications with another process.
 -* TCP/IP Networking::           Using `gawk' for network programming.
 -* Profiling::                   Profiling your `awk' programs.
++* General Arithmetic::          An introduction to computer arithmetic.
++* Floating-point Programming::  Effective Floating-point Programming.
++* Gawk and MPFR::               How `gawk' provides
++                                aribitrary-precision arithmetic.
++* Arbitrary Precision Floats::  Arbitrary Precision Floating-point Arithmetic
++                                with `gawk'.
++* Arbitrary Precision Integers:: Arbitrary Precision Integer Arithmetic with
++                                `gawk'.
+ 
 -
 -File: gawk.info,  Node: Nondecimal Data,  Next: Array Sorting,  Up: Advanced 
Features
++   ---------- Footnotes ----------
+ 
 -11.1 Allowing Nondecimal Input Data
 -===================================
++   (1) Donald E. Knuth.  `The Art of Computer Programming'. Volume 2,
++`Seminumerical Algorithms', third edition, 1998, ISBN 0-201-89683-4, p.
++229.
+ 
 -If you run `gawk' with the `--non-decimal-data' option, you can have
 -nondecimal constants in your input data:
++
++File: gawk.info,  Node: General Arithmetic,  Next: Floating-point 
Programming,  Up: Arbitrary Precision Arithmetic
+ 
 -     $ echo 0123 123 0x123 |
 -     > gawk --non-decimal-data '{ printf "%d, %d, %d\n",
 -     >                                         $1, $2, $3 }'
 -     -| 83, 123, 291
++11.1 A General Description of Computer Arithmetic
++=================================================
+ 
 -   For this feature to work, write your program so that `gawk' treats
 -your data as numeric:
++Within computers, there are two kinds of numeric values: "integers" and
++"floating-point".  In school, integer values were referred to as
++"whole" numbers--that is, numbers without any fractional part, such as
++1, 42, or -17.  The advantage to integer numbers is that they represent
++values exactly.  The disadvantage is that their range is limited.  On
++most systems, this range is -2,147,483,648 to 2,147,483,647.  However,
++many systems now support a range from -9,223,372,036,854,775,808 to
++9,223,372,036,854,775,807.
+ 
 -     $ echo 0123 123 0x123 | gawk '{ print $1, $2, $3 }'
 -     -| 0123 123 0x123
++   Integer values come in two flavors: "signed" and "unsigned".  Signed
++values may be negative or positive, with the range of values just
++described.  Unsigned values are always positive.  On most systems, the
++range is from 0 to 4,294,967,295.  However, many systems now support a
++range from 0 to 18,446,744,073,709,551,615.
+ 
 -The `print' statement treats its expressions as strings.  Although the
 -fields can act as numbers when necessary, they are still strings, so
 -`print' does not try to treat them numerically.  You may need to add
 -zero to a field to force it to be treated as a number.  For example:
++   Floating-point numbers represent what are called "real" numbers;
++i.e., those that do have a fractional part, such as 3.1415927.  The
++advantage to floating-point numbers is that they can represent a much
++larger range of values.  The disadvantage is that there are numbers
++that they cannot represent exactly.  `awk' uses "double precision"
++floating-point numbers, which can hold more digits than "single
++precision" floating-point numbers.
+ 
 -     $ echo 0123 123 0x123 | gawk --non-decimal-data '
 -     > { print $1, $2, $3
 -     >   print $1 + 0, $2 + 0, $3 + 0 }'
 -     -| 0123 123 0x123
 -     -| 83 123 291
++   There a several important issues to be aware of, described next.
+ 
 -   Because it is common to have decimal data with leading zeros, and
 -because using this facility could lead to surprising results, the
 -default is to leave it disabled.  If you want it, you must explicitly
 -request it.
++* Menu:
+ 
 -     CAUTION: _Use of this option is not recommended._ It can break old
 -     programs very badly.  Instead, use the `strtonum()' function to
 -     convert your data (*note Nondecimal-numbers::).  This makes your
 -     programs easier to write and easier to read, and leads to less
 -     surprising results.
++* Floating Point Issues::       Stuff to know about floating-point numbers.
++* Integer Programming::         Effective integer programming.
+ 
+ 
 -File: gawk.info,  Node: Array Sorting,  Next: Two-way I/O,  Prev: Nondecimal 
Data,  Up: Advanced Features
++File: gawk.info,  Node: Floating Point Issues,  Next: Integer Programming,  
Up: General Arithmetic
+ 
 -11.2 Controlling Array Traversal and Array Sorting
 -==================================================
++11.1.1 Floating-Point Number Caveats
++------------------------------------
+ 
 -`gawk' lets you control the order in which a `for (i in array)' loop
 -traverses an array.
++As mentioned earlier, floating-point numbers represent what are called
++"real" numbers, i.e., those that have a fractional part.  `awk' uses
++double precision floating-point numbers to represent all numeric
++values.  This minor node describes some of the issues involved in using
++floating-point numbers.
+ 
 -   In addition, two built-in functions, `asort()' and `asorti()', let
 -you sort arrays based on the array values and indices, respectively.
 -These two functions also provide control over the sorting criteria used
 -to order the elements during sorting.
++   There is a very nice paper on floating-point arithmetic
++(http://www.validlab.com/goldberg/paper.pdf) by David Goldberg, "What
++Every Computer Scientist Should Know About Floating-point Arithmetic,"
++`ACM Computing Surveys' *23*, 1 (1991-03), 5-48.  This is worth reading
++if you are interested in the details, but it does require a background
++in computer science.
+ 
+ * Menu:
+ 
 -* Controlling Array Traversal:: How to use PROCINFO["sorted_in"].
 -* Array Sorting Functions::     How to use `asort()' and `asorti()'.
++* String Conversion Precision:: The String Value Can Lie.
++* Unexpected Results::          Floating Point Numbers Are Not Abstract
++                                Numbers.
++* POSIX Floating Point Problems:: Standards Versus Existing Practice.
+ 
+ 
 -File: gawk.info,  Node: Controlling Array Traversal,  Next: Array Sorting 
Functions,  Up: Array Sorting
 -
 -11.2.1 Controlling Array Traversal
 -----------------------------------
 -
 -By default, the order in which a `for (i in array)' loop scans an array
 -is not defined; it is generally based upon the internal implementation
 -of arrays inside `awk'.
++File: gawk.info,  Node: String Conversion Precision,  Next: Unexpected 
Results,  Up: Floating Point Issues
+ 
 -   Often, though, it is desirable to be able to loop over the elements
 -in a particular order that you, the programmer, choose.  `gawk' lets
 -you do this.
++11.1.1.1 The String Value Can Lie
++.................................
+ 
 -   *note Controlling Scanning::, describes how you can assign special,
 -pre-defined values to `PROCINFO["sorted_in"]' in order to control the
 -order in which `gawk' will traverse an array during a `for' loop.
++Internally, `awk' keeps both the numeric value (double precision
++floating-point) and the string value for a variable.  Separately, `awk'
++keeps track of what type the variable has (*note Typing and
++Comparison::), which plays a role in how variables are used in
++comparisons.
+ 
 -   In addition, the value of `PROCINFO["sorted_in"]' can be a function
 -name.  This lets you traverse an array based on any custom criterion.
 -The array elements are ordered according to the return value of this
 -function.  The comparison function should be defined with at least four
 -arguments:
++   It is important to note that the string value for a number may not
++reflect the full value (all the digits) that the numeric value actually
++contains.  The following program (`values.awk') illustrates this:
+ 
 -     function comp_func(i1, v1, i2, v2)
+      {
 -         COMPARE ELEMENTS 1 AND 2 IN SOME FASHION
 -         RETURN < 0; 0; OR > 0
++        sum = $1 + $2
++        # see it for what it is
++        printf("sum = %.12g\n", sum)
++        # use CONVFMT
++        a = "<" sum ">"
++        print "a =", a
++        # use OFMT
++        print "sum =", sum
+      }
+ 
 -   Here, I1 and I2 are the indices, and V1 and V2 are the corresponding
 -values of the two elements being compared.  Either V1 or V2, or both,
 -can be arrays if the array being traversed contains subarrays as values.
 -(*Note Arrays of Arrays::, for more information about subarrays.)  The
 -three possible return values are interpreted as follows:
++This program shows the full value of the sum of `$1' and `$2' using
++`printf', and then prints the string values obtained from both
++automatic conversion (via `CONVFMT') and from printing (via `OFMT').
+ 
 -`comp_func(i1, v1, i2, v2) < 0'
 -     Index I1 comes before index I2 during loop traversal.
++   Here is what happens when the program is run:
+ 
 -`comp_func(i1, v1, i2, v2) == 0'
 -     Indices I1 and I2 come together but the relative order with
 -     respect to each other is undefined.
++     $ echo 3.654321 1.2345678 | awk -f values.awk
++     -| sum = 4.8888888
++     -| a = <4.88889>
++     -| sum = 4.88889
+ 
 -`comp_func(i1, v1, i2, v2) > 0'
 -     Index I1 comes after index I2 during loop traversal.
++   This makes it clear that the full numeric value is different from
++what the default string representations show.
+ 
 -   Our first comparison function can be used to scan an array in
 -numerical order of the indices:
++   `CONVFMT''s default value is `"%.6g"', which yields a value with at
++least six significant digits.  For some applications, you might want to
++change it to specify more precision.  On most modern machines, most of
++the time, 17 digits is enough to capture a floating-point number's
++value exactly.(1)
+ 
 -     function cmp_num_idx(i1, v1, i2, v2)
 -     {
 -          # numerical index comparison, ascending order
 -          return (i1 - i2)
 -     }
++   ---------- Footnotes ----------
+ 
 -   Our second function traverses an array based on the string order of
 -the element values rather than by indices:
++   (1) Pathological cases can require up to 752 digits (!), but we
++doubt that you need to worry about this.
+ 
 -     function cmp_str_val(i1, v1, i2, v2)
 -     {
 -         # string value comparison, ascending order
 -         v1 = v1 ""
 -         v2 = v2 ""
 -         if (v1 < v2)
 -             return -1
 -         return (v1 != v2)
 -     }
++
++File: gawk.info,  Node: Unexpected Results,  Next: POSIX Floating Point 
Problems,  Prev: String Conversion Precision,  Up: Floating Point Issues
+ 
 -   The third comparison function makes all numbers, and numeric strings
 -without any leading or trailing spaces, come out first during loop
 -traversal:
++11.1.1.2 Floating Point Numbers Are Not Abstract Numbers
++........................................................
+ 
 -     function cmp_num_str_val(i1, v1, i2, v2,   n1, n2)
 -     {
 -          # numbers before string value comparison, ascending order
 -          n1 = v1 + 0
 -          n2 = v2 + 0
 -          if (n1 == v1)
 -              return (n2 == v2) ? (n1 - n2) : -1
 -          else if (n2 == v2)
 -              return 1
 -          return (v1 < v2) ? -1 : (v1 != v2)
 -     }
++Unlike numbers in the abstract sense (such as what you studied in high
++school or college arithmetic), numbers stored in computers are limited
++in certain ways.  They cannot represent an infinite number of digits,
++nor can they always represent things exactly.  In particular,
++floating-point numbers cannot always represent values exactly.  Here is
++an example:
+ 
 -   Here is a main program to demonstrate how `gawk' behaves using each
 -of the previous functions:
++     $ awk '{ printf("%010d\n", $1 * 100) }'
++     515.79
++     -| 0000051579
++     515.80
++     -| 0000051579
++     515.81
++     -| 0000051580
++     515.82
++     -| 0000051582
++     Ctrl-d
+ 
 -     BEGIN {
 -         data["one"] = 10
 -         data["two"] = 20
 -         data[10] = "one"
 -         data[100] = 100
 -         data[20] = "two"
++This shows that some values can be represented exactly, whereas others
++are only approximated.  This is not a "bug" in `awk', but simply an
++artifact of how computers represent numbers.
+ 
 -         f[1] = "cmp_num_idx"
 -         f[2] = "cmp_str_val"
 -         f[3] = "cmp_num_str_val"
 -         for (i = 1; i <= 3; i++) {
 -             printf("Sort function: %s\n", f[i])
 -             PROCINFO["sorted_in"] = f[i]
 -             for (j in data)
 -                 printf("\tdata[%s] = %s\n", j, data[j])
 -             print ""
 -         }
 -     }
++   Another peculiarity of floating-point numbers on modern systems is
++that they often have more than one representation for the number zero!
++In particular, it is possible to represent "minus zero" as well as
++regular, or "positive" zero.
+ 
 -   Here are the results when the program is run:
++   This example shows that negative and positive zero are distinct
++values when stored internally, but that they are in fact equal to each
++other, as well as to "regular" zero:
+ 
 -     $ gawk -f compdemo.awk
 -     -| Sort function: cmp_num_idx      Sort by numeric index
 -     -|     data[two] = 20
 -     -|     data[one] = 10              Both strings are numerically zero
 -     -|     data[10] = one
 -     -|     data[20] = two
 -     -|     data[100] = 100
 -     -|
 -     -| Sort function: cmp_str_val      Sort by element values as strings
 -     -|     data[one] = 10
 -     -|     data[100] = 100             String 100 is less than string 20
 -     -|     data[two] = 20
 -     -|     data[10] = one
 -     -|     data[20] = two
 -     -|
 -     -| Sort function: cmp_num_str_val  Sort all numeric values before all 
strings
 -     -|     data[one] = 10
 -     -|     data[two] = 20
 -     -|     data[100] = 100
 -     -|     data[10] = one
 -     -|     data[20] = two
++     $ gawk 'BEGIN { mz = -0 ; pz = 0
++     > printf "-0 = %g, +0 = %g, (-0 == +0) -> %d\n", mz, pz, mz == pz
++     > printf "mz == 0 -> %d, pz == 0 -> %d\n", mz == 0, pz == 0
++     > }'
++     -| -0 = -0, +0 = 0, (-0 == +0) -> 1
++     -| mz == 0 -> 1, pz == 0 -> 1
+ 
 -   Consider sorting the entries of a GNU/Linux system password file
 -according to login name.  The following program sorts records by a
 -specific field position and can be used for this purpose:
++   It helps to keep this in mind should you process numeric data that
++contains negative zero values; the fact that the zero is negative is
++noted and can affect comparisons.
+ 
 -     # sort.awk --- simple program to sort by field position
 -     # field position is specified by the global variable POS
++
++File: gawk.info,  Node: POSIX Floating Point Problems,  Prev: Unexpected 
Results,  Up: Floating Point Issues
+ 
 -     function cmp_field(i1, v1, i2, v2)
 -     {
 -         # comparison by value, as string, and ascending order
 -         return v1[POS] < v2[POS] ? -1 : (v1[POS] != v2[POS])
 -     }
++11.1.1.3 Standards Versus Existing Practice
++...........................................
+ 
 -     {
 -         for (i = 1; i <= NF; i++)
 -             a[NR][i] = $i
 -     }
++Historically, `awk' has converted any non-numeric looking string to the
++numeric value zero, when required.  Furthermore, the original
++definition of the language and the original POSIX standards specified
++that `awk' only understands decimal numbers (base 10), and not octal
++(base 8) or hexadecimal numbers (base 16).
+ 
 -     END {
 -         PROCINFO["sorted_in"] = "cmp_field"
 -         if (POS < 1 || POS > NF)
 -             POS = 1
 -         for (i in a) {
 -             for (j = 1; j <= NF; j++)
 -                 printf("%s%c", a[i][j], j < NF ? ":" : "")
 -             print ""
 -         }
 -     }
++   Changes in the language of the 2001 and 2004 POSIX standards can be
++interpreted to imply that `awk' should support additional features.
++These features are:
+ 
 -   The first field in each entry of the password file is the user's
 -login name, and the fields are separated by colons.  Each record
 -defines a subarray, with each field as an element in the subarray.
 -Running the program produces the following output:
++   * Interpretation of floating point data values specified in
++     hexadecimal notation (`0xDEADBEEF'). (Note: data values, _not_
++     source code constants.)
+ 
 -     $ gawk -vPOS=1 -F: -f sort.awk /etc/passwd
 -     -| adm:x:3:4:adm:/var/adm:/sbin/nologin
 -     -| apache:x:48:48:Apache:/var/www:/sbin/nologin
 -     -| avahi:x:70:70:Avahi daemon:/:/sbin/nologin
 -     ...
++   * Support for the special IEEE 754 floating point values "Not A
++     Number" (NaN), positive Infinity ("inf") and negative Infinity
++     ("-inf").  In particular, the format for these values is as
++     specified by the ISO 1999 C standard, which ignores case and can
++     allow machine-dependent additional characters after the `nan' and
++     allow either `inf' or `infinity'.
+ 
 -   The comparison should normally always return the same value when
 -given a specific pair of array elements as its arguments.  If
 -inconsistent results are returned then the order is undefined.  This
 -behavior can be exploited to introduce random order into otherwise
 -seemingly ordered data:
++   The first problem is that both of these are clear changes to
++historical practice:
+ 
 -     function cmp_randomize(i1, v1, i2, v2)
 -     {
 -         # random order
 -         return (2 - 4 * rand())
 -     }
++   * The `gawk' maintainer feels that supporting hexadecimal floating
++     point values, in particular, is ugly, and was never intended by the
++     original designers to be part of the language.
+ 
 -   As mentioned above, the order of the indices is arbitrary if two
 -elements compare equal.  This is usually not a problem, but letting the
 -tied elements come out in arbitrary order can be an issue, especially
 -when comparing item values.  The partial ordering of the equal elements
 -may change during the next loop traversal, if other elements are added
 -or removed from the array.  One way to resolve ties when comparing
 -elements with otherwise equal values is to include the indices in the
 -comparison rules.  Note that doing this may make the loop traversal
 -less efficient, so consider it only if necessary.  The following
 -comparison functions force a deterministic order, and are based on the
 -fact that the indices of two elements are never equal:
++   * Allowing completely alphabetic strings to have valid numeric
++     values is also a very severe departure from historical practice.
+ 
 -     function cmp_numeric(i1, v1, i2, v2)
 -     {
 -         # numerical value (and index) comparison, descending order
 -         return (v1 != v2) ? (v2 - v1) : (i2 - i1)
 -     }
++   The second problem is that the `gawk' maintainer feels that this
++interpretation of the standard, which requires a certain amount of
++"language lawyering" to arrive at in the first place, was not even
++intended by the standard developers.  In other words, "we see how you
++got where you are, but we don't think that that's where you want to be."
+ 
 -     function cmp_string(i1, v1, i2, v2)
 -     {
 -         # string value (and index) comparison, descending order
 -         v1 = v1 i1
 -         v2 = v2 i2
 -         return (v1 > v2) ? -1 : (v1 != v2)
 -     }
++   Recognizing the above issues, but attempting to provide compatibility
++with the earlier versions of the standard, the 2008 POSIX standard
++added explicit wording to allow, but not require, that `awk' support
++hexadecimal floating point values and special values for "Not A Number"
++and infinity.
+ 
 -   A custom comparison function can often simplify ordered loop
 -traversal, and the sky is really the limit when it comes to designing
 -such a function.
++   Although the `gawk' maintainer continues to feel that providing
++those features is inadvisable, nevertheless, on systems that support
++IEEE floating point, it seems reasonable to provide _some_ way to
++support NaN and Infinity values.  The solution implemented in `gawk' is
++as follows:
+ 
 -   When string comparisons are made during a sort, either for element
 -values where one or both aren't numbers, or for element indices handled
 -as strings, the value of `IGNORECASE' (*note Built-in Variables::)
 -controls whether the comparisons treat corresponding uppercase and
 -lowercase letters as equivalent or distinct.
++   * With the `--posix' command-line option, `gawk' becomes "hands
++     off." String values are passed directly to the system library's
++     `strtod()' function, and if it successfully returns a numeric
++     value, that is what's used.(1) By definition, the results are not
++     portable across different systems.  They are also a little
++     surprising:
+ 
 -   Another point to keep in mind is that in the case of subarrays the
 -element values can themselves be arrays; a production comparison
 -function should use the `isarray()' function (*note Type Functions::),
 -to check for this, and choose a defined sorting order for subarrays.
++          $ echo nanny | gawk --posix '{ print $1 + 0 }'
++          -| nan
++          $ echo 0xDeadBeef | gawk --posix '{ print $1 + 0 }'
++          -| 3735928559
+ 
 -   All sorting based on `PROCINFO["sorted_in"]' is disabled in POSIX
 -mode, since the `PROCINFO' array is not special in that case.
++   * Without `--posix', `gawk' interprets the four strings `+inf',
++     `-inf', `+nan', and `-nan' specially, producing the corresponding
++     special numeric values.  The leading sign acts a signal to `gawk'
++     (and the user) that the value is really numeric.  Hexadecimal
++     floating point is not supported (unless you also use
++     `--non-decimal-data', which is _not_ recommended). For example:
+ 
 -   As a side note, sorting the array indices before traversing the
 -array has been reported to add 15% to 20% overhead to the execution
 -time of `awk' programs. For this reason, sorted array traversal is not
 -the default.
++          $ echo nanny | gawk '{ print $1 + 0 }'
++          -| 0
++          $ echo +nan | gawk '{ print $1 + 0 }'
++          -| nan
++          $ echo 0xDeadBeef | gawk '{ print $1 + 0 }'
++          -| 0
++
++     `gawk' does ignore case in the four special values.  Thus `+nan'
++     and `+NaN' are the same.
++
++   ---------- Footnotes ----------
++
++   (1) You asked for it, you got it.
+ 
+ 
 -File: gawk.info,  Node: Array Sorting Functions,  Prev: Controlling Array 
Traversal,  Up: Array Sorting
++File: gawk.info,  Node: Integer Programming,  Prev: Floating Point Issues,  
Up: General Arithmetic
+ 
 -11.2.2 Sorting Array Values and Indices with `gawk'
 ----------------------------------------------------
++11.1.2 Mixing Integers And Floating-point
++-----------------------------------------
+ 
 -In most `awk' implementations, sorting an array requires writing a
 -`sort()' function.  While this can be educational for exploring
 -different sorting algorithms, usually that's not the point of the
 -program.  `gawk' provides the built-in `asort()' and `asorti()'
 -functions (*note String Functions::) for sorting arrays.  For example:
++As has been mentioned already, `gawk' ordinarily uses hardware double
++precision with 64-bit IEEE binary floating-point representation for
++numbers on most systems. A large integer like 9007199254740997 has a
++binary representation that, although finite, is more than 53 bits long;
++it must also be rounded to 53 bits.  The biggest integer that can be
++stored in a C `double' is usually the same as the largest possible
++value of a `double'. If your system `double' is an IEEE 64-bit
++`double', this largest possible value is an integer and can be
++represented precisely.  What more should one know about integers?
++
++   If you want to know what is the largest integer, such that it and
++all smaller integers can be stored in 64-bit doubles without losing
++precision, then the answer is 2^53.  The next representable number is
++the even number 2^53 + 2, meaning it is unlikely that you will be able
++to make `gawk' print 2^53 + 1 in integer format.  The range of integers
++exactly representable by a 64-bit double is [-2^53, 2^53].  If you ever
++see an integer outside this range in `gawk' using 64-bit doubles, you
++have reason to be very suspicious about the accuracy of the output.
++Here is a simple program with erroneous output:
++
++     $ gawk 'BEGIN { i = 2^53 - 1; for (j = 0; j < 4; j++) print i + j }'
++     -| 9007199254740991
++     -| 9007199254740992
++     -| 9007199254740992
++     -| 9007199254740994
++
++   The lesson is to not assume that any large integer printed by `gawk'
++represents an exact result from your computation, especially if it wraps
++around on your screen.
++
++
++File: gawk.info,  Node: Floating-point Programming,  Next: Gawk and MPFR,  
Prev: General Arithmetic,  Up: Arbitrary Precision Arithmetic
++
++11.2 Understanding Floating-point Programming
++=============================================
+ 
 -     POPULATE THE ARRAY data
 -     n = asort(data)
 -     for (i = 1; i <= n; i++)
 -         DO SOMETHING WITH data[i]
++Numerical programming is an extensive area; if you need to develop
++sophisticated numerical algorithms then `gawk' may not be the ideal
++tool, and this documentation may not be sufficient.  It might require
++digesting a book or two to really internalize how to compute with ideal
++accuracy and precision and the result often depends on the particular
++application.
++
++     NOTE: A floating-point calculation's "accuracy" is how close it
++     comes to the real value.  This is as opposed to the "precision",
++     which usually refers to the number of bits used to represent the
++     number (see the Wikipedia article
++     (http://en.wikipedia.org/wiki/Accuracy_and_precision) for more
++     information).
++
++   There are two options for doing floating-point calculations:
++hardware floating-point (as used by standard `awk' and the default for
++`gawk'), and "arbitrary-precision" floating-point, which is software
++based.  This major node aims to provide enough information to
++understand both, and then will focus on `gawk''s facilities for the
++latter.
++
++   Binary floating-point representations and arithmetic are inexact.
++Simple values like 0.1 cannot be precisely represented using binary
++floating-point numbers, and the limited precision of floating-point
++numbers means that slight changes in the order of operations or the
++precision of intermediate storage can change the result. To make
++matters worse, with arbitrary precision floating-point, you can set the
++precision before starting a computation, but then you cannot be sure of
++the number of significant decimal places in the final result.
++
++   Sometimes, before you start to write any code, you should think more
++about what you really want and what's really happening. Consider the
++two numbers in the following example:
++
++     x = 0.875             # 1/2 + 1/4 + 1/8
++     y = 0.425
++
++   Unlike the number in `y', the number stored in `x' is exactly
++representable in binary since it can be written as a finite sum of one
++or more fractions whose denominators are all powers of two.  When
++`gawk' reads a floating-point number from program source, it
++automatically rounds that number to whatever precision your machine
++supports. If you try to print the numeric content of a variable using
++an output format string of `"%.17g"', it may not produce the same
++number as you assigned to it:
++
++     $ gawk 'BEGIN { x = 0.875; y = 0.425
++     >               printf("%0.17g, %0.17g\n", x, y) }'
++     -| 0.875, 0.42499999999999999
++
++   Often the error is so small you do not even notice it, and if you do,
++you can always specify how much precision you would like in your output.
++Usually this is a format string like `"%.15g"', which when used in the
++previous example, produces an output identical to the input.
++
++   Because the underlying representation can be little bit off from the
++exact value, comparing floating-point values to see if they are equal
++is generally not a good idea.  Here is an example where it does not
++work like you expect:
++
++     $ gawk 'BEGIN { print (0.1 + 12.2 == 12.3) }'
++     -| 0
+ 
 -   After the call to `asort()', the array `data' is indexed from 1 to
 -some number N, the total number of elements in `data'.  (This count is
 -`asort()''s return value.)  `data[1]' <= `data[2]' <= `data[3]', and so
 -on.  The comparison is based on the type of the elements (*note Typing
 -and Comparison::).  All numeric values come before all string values,
 -which in turn come before all subarrays.
++   The loss of accuracy during a single computation with floating-point
++numbers usually isn't enough to worry about. However, if you compute a
++value which is the result of a sequence of floating point operations,
++the error can accumulate and greatly affect the computation itself.
++Here is an attempt to compute the value of the constant pi using one of
++its many series representations:
+ 
 -   An important side effect of calling `asort()' is that _the array's
 -original indices are irrevocably lost_.  As this isn't always
 -desirable, `asort()' accepts a second argument:
++     BEGIN {
++         x = 1.0 / sqrt(3.0)
++         n = 6
++         for (i = 1; i < 30; i++) {
++             n = n * 2.0
++             x = (sqrt(x * x + 1) - 1) / x
++             printf("%.15f\n", n * x)
++         }
++     }
+ 
 -     POPULATE THE ARRAY source
 -     n = asort(source, dest)
 -     for (i = 1; i <= n; i++)
 -         DO SOMETHING WITH dest[i]
++   When run, the early errors propagating through later computations
++cause the loop to terminate prematurely after an attempt to divide by
++zero.
+ 
 -   In this case, `gawk' copies the `source' array into the `dest' array
 -and then sorts `dest', destroying its indices.  However, the `source'
 -array is not affected.
++     $ gawk -f pi.awk
++     -| 3.215390309173475
++     -| 3.159659942097510
++     -| 3.146086215131467
++     -| 3.142714599645573
++     ...
++     -| 3.224515243534819
++     -| 2.791117213058638
++     -| 0.000000000000000
++     error--> gawk: pi.awk:6: fatal: division by zero attempted
+ 
 -   `asort()' accepts a third string argument to control comparison of
 -array elements.  As with `PROCINFO["sorted_in"]', this argument may be
 -one of the predefined names that `gawk' provides (*note Controlling
 -Scanning::), or the name of a user-defined function (*note Controlling
 -Array Traversal::).
++   Here is one more example where the inaccuracies in internal
++representations yield an unexpected result:
+ 
 -     NOTE: In all cases, the sorted element values consist of the
 -     original array's element values.  The ability to control
 -     comparison merely affects the way in which they are sorted.
++     $ gawk 'BEGIN {
++     >   for (d = 1.1; d <= 1.5; d += 0.1)
++     >       i++
++     >   print i
++     > }'
++     -| 4
+ 
 -   Often, what's needed is to sort on the values of the _indices_
 -instead of the values of the elements.  To do that, use the `asorti()'
 -function.  The interface is identical to that of `asort()', except that
 -the index values are used for sorting, and become the values of the
 -result array:
++   Can computation using aribitrary precision help with the previous
++examples?  If you are impatient to know, see *note Exact Arithmetic::.
+ 
 -     { source[$0] = some_func($0) }
++   Instead of aribitrary precision floating-point arithmetic, often all
++you need is an adjustment of your logic or a different order for the
++operations in your calculation.  The stability and the accuracy of the
++computation of the constant pi in the previous example can be enhanced
++by using the following simple algebraic transformation:
+ 
 -     END {
 -         n = asorti(source, dest)
 -         for (i = 1; i <= n; i++) {
 -             Work with sorted indices directly:
 -             DO SOMETHING WITH dest[i]
 -             ...
 -             Access original array via sorted indices:
 -             DO SOMETHING WITH source[dest[i]]
 -         }
 -     }
++     (sqrt(x * x + 1) - 1) / x = x / (sqrt(x * x + 1) + 1)
+ 
 -   Similar to `asort()', in all cases, the sorted element values
 -consist of the original array's indices.  The ability to control
 -comparison merely affects the way in which they are sorted.
++After making this, change the program does converge to pi in under 30
++iterations:
+ 
 -   Sorting the array by replacing the indices provides maximal
 -flexibility.  To traverse the elements in decreasing order, use a loop
 -that goes from N down to 1, either over the elements or over the
 -indices.(1)
++     $ gawk -f /tmp/pi2.awk
++     -| 3.215390309173473
++     -| 3.159659942097501
++     -| 3.146086215131436
++     -| 3.142714599645370
++     -| 3.141873049979825
++     ...
++     -| 3.141592653589797
++     -| 3.141592653589797
++
++   There is no need to be unduly suspicious about the results from
++floating-point arithmetic. The lesson to remember is that
++floating-point arithmetic is always more complex than the arithmetic
++using pencil and paper. In order to take advantage of the power of
++computer floating-point, you need to know its limitations and work
++within them. For most casual use of floating-point arithmetic, you will
++often get the expected result in the end if you simply round the
++display of your final results to the correct number of significant
++decimal digits. And, avoid presenting numerical data in a manner that
++implies better precision than is actually the case.
+ 
 -   Copying array indices and elements isn't expensive in terms of
 -memory.  Internally, `gawk' maintains "reference counts" to data.  For
 -example, when `asort()' copies the first array to the second one, there
 -is only one copy of the original array elements' data, even though both
 -arrays use the values.
++* Menu:
+ 
 -   Because `IGNORECASE' affects string comparisons, the value of
 -`IGNORECASE' also affects sorting for both `asort()' and `asorti()'.
 -Note also that the locale's sorting order does _not_ come into play;
 -comparisons are based on character values only.(2) Caveat Emptor.
++* Floating-point Representation:: Binary floating-point representation.
++* Floating-point Context::        Floating-point context.
++* Rounding Mode::                 Floating-point rounding mode.
+ 
 -   ---------- Footnotes ----------
++
++File: gawk.info,  Node: Floating-point Representation,  Next: Floating-point 
Context,  Up: Floating-point Programming
+ 
 -   (1) You may also use one of the predefined sorting names that sorts
 -in decreasing order.
++11.2.1 Binary Floating-point Representation
++-------------------------------------------
+ 
 -   (2) This is true because locale-based comparison occurs only when in
 -POSIX compatibility mode, and since `asort()' and `asorti()' are `gawk'
 -extensions, they are not available in that case.
++Although floating-point representations vary from machine to machine,
++the most commonly encountered representation is that defined by the
++IEEE 754 Standard. An IEEE-754 format value has three components:
++
++   * A sign bit telling whether the number is positive or negative.
++
++   * An "exponent" giving its order of magnitude, E.
++
++   * A "significand", S, specifying the actual digits of the number.
++
++   The value of the number is then S * 2^E.  The first bit of a
++non-zero binary significand is always one, so the significand in an
++IEEE-754 format only includes the fractional part, leaving the leading
++one implicit.
++
++   Three of the standard IEEE-754 types are 32-bit single precision,
++64-bit double precision and 128-bit quadruple precision.  The standard
++also specifies extended precision formats to allow greater precisions
++and larger exponent ranges.
++
++   The significand is stored in "normalized" format, which means that
++the first bit is always a one.
+ 
+ 
 -File: gawk.info,  Node: Two-way I/O,  Next: TCP/IP Networking,  Prev: Array 
Sorting,  Up: Advanced Features
++File: gawk.info,  Node: Floating-point Context,  Next: Rounding Mode,  Prev: 
Floating-point Representation,  Up: Floating-point Programming
+ 
 -11.3 Two-Way Communications with Another Process
 -================================================
++11.2.2 Floating-point Context
++-----------------------------
+ 
 -     From: address@hidden (Mike Brennan)
 -     Newsgroups: comp.lang.awk
 -     Subject: Re: Learn the SECRET to Attract Women Easily
 -     Date: 4 Aug 1997 17:34:46 GMT
 -     Message-ID: <address@hidden>
++A floating-point "context" defines the environment for arithmetic
++operations.  It governs precision, sets rules for rounding, and limits
++the range for exponents.  The context has the following primary
++components:
+ 
 -     On 3 Aug 1997 13:17:43 GMT, Want More Dates???
 -     <address@hidden> wrote:
 -     >Learn the SECRET to Attract Women Easily
 -     >
 -     >The SCENT(tm)  Pheromone Sex Attractant For Men to Attract Women
++"Precision"
++     Precision of the floating-point format in bits.
+ 
 -     The scent of awk programmers is a lot more attractive to women than
 -     the scent of perl programmers.
 -     --
 -     Mike Brennan
++"emax"
++     Maximum exponent allowed for this format.
+ 
 -   It is often useful to be able to send data to a separate program for
 -processing and then read the result.  This can always be done with
 -temporary files:
++"emin"
++     Minimum exponent allowed for this format.
+ 
 -     # Write the data for processing
 -     tempfile = ("mydata." PROCINFO["pid"])
 -     while (NOT DONE WITH DATA)
 -         print DATA | ("subprogram > " tempfile)
 -     close("subprogram > " tempfile)
++"Underflow behavior"
++     The format may or may not support gradual underflow.
+ 
 -     # Read the results, remove tempfile when done
 -     while ((getline newdata < tempfile) > 0)
 -         PROCESS newdata APPROPRIATELY
 -     close(tempfile)
 -     system("rm " tempfile)
++"Rounding"
++     The rounding mode of this context.
+ 
 -This works, but not elegantly.  Among other things, it requires that
 -the program be run in a directory that cannot be shared among users;
 -for example, `/tmp' will not do, as another user might happen to be
 -using a temporary file with the same name.
++   *note table-ieee-formats:: lists the precision and exponent field
++values for the basic IEEE-754 binary formats:
+ 
 -   However, with `gawk', it is possible to open a _two-way_ pipe to
 -another process.  The second process is termed a "coprocess", since it
 -runs in parallel with `gawk'.  The two-way connection is created using
 -the `|&' operator (borrowed from the Korn shell, `ksh'):(1)
++Name           Total bits     Precision      emin           emax
++--------------------------------------------------------------------------- 
++Single         32             24             -126           +127
++Double         64             53             -1022          +1023
++Quadruple      128            113            -16382         +16383
+ 
 -     do {
 -         print DATA |& "subprogram"
 -         "subprogram" |& getline results
 -     } while (DATA LEFT TO PROCESS)
 -     close("subprogram")
++Table 11.1: Basic IEEE Format Context Values
+ 
 -   The first time an I/O operation is executed using the `|&' operator,
 -`gawk' creates a two-way pipeline to a child process that runs the
 -other program.  Output created with `print' or `printf' is written to
 -the program's standard input, and output from the program's standard
 -output can be read by the `gawk' program using `getline'.  As is the
 -case with processes started by `|', the subprogram can be any program,
 -or pipeline of programs, that can be started by the shell.
++     NOTE: The precision numbers include the implied leading one that
++     gives them one extra bit of significand.
+ 
 -   There are some cautionary items to be aware of:
++   A floating-point context can also determine which signals are treated
++as exceptions, and can set rules for arithmetic with special values.
++Please consult the IEEE-754 standard or other resources for details.
+ 
 -   * As the code inside `gawk' currently stands, the coprocess's
 -     standard error goes to the same place that the parent `gawk''s
 -     standard error goes. It is not possible to read the child's
 -     standard error separately.
++   `gawk' ordinarily uses the hardware double precision representation
++for numbers.  On most systems, this is IEEE-754 floating-point format,
++corresponding to 64-bit binary with 53 bits of precision.
+ 
 -   * I/O buffering may be a problem.  `gawk' automatically flushes all
 -     output down the pipe to the coprocess.  However, if the coprocess
 -     does not flush its output, `gawk' may hang when doing a `getline'
 -     in order to read the coprocess's results.  This could lead to a
 -     situation known as "deadlock", where each process is waiting for
 -     the other one to do something.
++     NOTE: In case an underflow occurs, the standard allows, but does
++     not require, the result from an arithmetic operation to be a
++     number smaller than the smallest nonzero normalized number. Such
++     numbers do not have as many significant digits as normal numbers,
++     and are called "denormals" or "subnormals". The alternative,
++     simply returning a zero, is called "flush to zero". The basic
++     IEEE-754 binary formats support subnormal numbers.
+ 
 -   It is possible to close just one end of the two-way pipe to a
 -coprocess, by supplying a second argument to the `close()' function of
 -either `"to"' or `"from"' (*note Close Files And Pipes::).  These
 -strings tell `gawk' to close the end of the pipe that sends data to the
 -coprocess or the end that reads from it, respectively.
++
++File: gawk.info,  Node: Rounding Mode,  Prev: Floating-point Context,  Up: 
Floating-point Programming
+ 
 -   This is particularly necessary in order to use the system `sort'
 -utility as part of a coprocess; `sort' must read _all_ of its input
 -data before it can produce any output.  The `sort' program does not
 -receive an end-of-file indication until `gawk' closes the write end of
 -the pipe.
++11.2.3 Floating-point Rounding Mode
++-----------------------------------
+ 
 -   When you have finished writing data to the `sort' utility, you can
 -close the `"to"' end of the pipe, and then start reading sorted data
 -via `getline'.  For example:
++The "rounding mode" specifies the behavior for the results of numerical
++operations when discarding extra precision. Each rounding mode indicates
++how the least significant returned digit of a rounded result is to be
++calculated.  *note table-rounding-modes:: lists the IEEE-754 defined
++rounding modes:
++
++Rounding Mode                    IEEE Name
++-------------------------------------------------------------------------- 
++Round to nearest, ties to even   `roundTiesToEven'
++Round toward plus Infinity       `roundTowardPositive'
++Round toward negative Infinity   `roundTowardNegative'
++Round toward zero                `roundTowardZero'
++Round to nearest, ties away      `roundTiesToAway'
++from zero                        
++
++Table 11.2: IEEE 754 Rounding Modes
++
++   The default mode `roundTiesToEven' is the most preferred, but the
++least intuitive. This method does the obvious thing for most values, by
++rounding them up or down to the nearest digit.  For example, rounding
++1.132 to two digits yields 1.13, and rounding 1.157 yields 1.16.
++
++   However, when it comes to rounding a value that is exactly halfway
++between, things do not work the way you probably learned in school.  In
++this case, the number is rounded to the nearest even digit.  So
++rounding 0.125 to two digits rounds down to 0.12, but rounding 0.6875
++to three digits rounds up to 0.688.  You probably have already
++encountered this rounding mode when using the `printf' routine to
++format floating-point numbers.  For example:
+ 
+      BEGIN {
 -         command = "LC_ALL=C sort"
 -         n = split("abcdefghijklmnopqrstuvwxyz", a, "")
++         x = -4.5
++         for (i = 1; i < 10; i++) {
++             x += 1.0
++             printf("%4.1f => %2.0f\n", x, x)
++         }
++     }
+ 
 -         for (i = n; i > 0; i--)
 -             print a[i] |& command
 -         close(command, "to")
++produces the following output when run:(1)
++
++     -3.5 => -4
++     -2.5 => -2
++     -1.5 => -2
++     -0.5 => 0
++      0.5 => 0
++      1.5 => 2
++      2.5 => 2
++      3.5 => 4
++      4.5 => 4
++
++   The theory behind the rounding mode `roundTiesToEven' is that it
++more or less evenly distributes upward and downward rounds of exact
++halves, which might cause the round-off error to cancel itself out.
++This is the default rounding mode used in IEEE-754 computing functions
++and operators.
++
++   The other rounding modes are rarely used.  Round toward positive
++infinity (`roundTowardPositive') and round toward negative infinity
++(`roundTowardNegative') are often used to implement interval arithmetic,
++where you adjust the rounding mode to calculate upper and lower bounds
++for the range of output. The `roundTowardZero' mode can be used for
++converting floating-point numbers to integers.  The rounding mode
++`roundTiesToAway' rounds the result to the nearest number and selects
++the number with the larger magnitude if a tie occurs.
++
++   Some numerical analysts will tell you that your choice of rounding
++style has tremendous impact on the final outcome, and advise you to
++wait until final output for any rounding. Instead, you can often avoid
++round-off error problems by setting the precision initially to some
++value sufficiently larger than the final desired precision, so that the
++accumulation of round-off error does not influence the outcome.  If you
++suspect that results from your computation are sensitive to
++accumulation of round-off error, one way to be sure is to look for a
++significant difference in output when you change the rounding mode.
+ 
 -         while ((command |& getline line) > 0)
 -             print "got", line
 -         close(command)
 -     }
++   ---------- Footnotes ----------
+ 
 -   This program writes the letters of the alphabet in reverse order, one
 -per line, down the two-way pipe to `sort'.  It then closes the write
 -end of the pipe, so that `sort' receives an end-of-file indication.
 -This causes `sort' to sort the data and write the sorted data back to
 -the `gawk' program.  Once all of the data has been read, `gawk'
 -terminates the coprocess and exits.
++   (1) It is possible for the output to be completely different if the
++C library in your system does not use the IEEE-754 even-rounding rule
++to round halfway cases for `printf()'.
+ 
 -   As a side note, the assignment `LC_ALL=C' in the `sort' command
 -ensures traditional Unix (ASCII) sorting from `sort'.
++
++File: gawk.info,  Node: Gawk and MPFR,  Next: Arbitrary Precision Floats,  
Prev: Floating-point Programming,  Up: Arbitrary Precision Arithmetic
+ 
 -   You may also use pseudo-ttys (ptys) for two-way communication
 -instead of pipes, if your system supports them.  This is done on a
 -per-command basis, by setting a special element in the `PROCINFO' array
 -(*note Auto-set::), like so:
++11.3 `gawk' + MPFR = Powerful Arithmetic
++========================================
+ 
 -     command = "sort -nr"           # command, save in convenience variable
 -     PROCINFO[command, "pty"] = 1   # update PROCINFO
 -     print ... |& command       # start two-way pipe
++The rest of this major node decsribes how to use the arbitrary precision
++(also known as "multiple precision" or "infinite precision") numeric
++capabilites in `gawk' to produce maximally accurate results when you
++need it.
++
++   But first you should check if your version of `gawk' supports
++arbitrary precision arithmetic.  The easiest way to find out is to look
++at the output of the following command:
++
++     $ gawk --version
++     -| GNU Awk 4.1.0 (GNU MPFR 3.1.0, GNU MP 5.0.3)
++     -| Copyright (C) 1989, 1991-2012 Free Software Foundation.
+      ...
+ 
 -Using ptys avoids the buffer deadlock issues described earlier, at some
 -loss in performance.  If your system does not have ptys, or if all the
 -system's ptys are in use, `gawk' automatically falls back to using
 -regular pipes.
++   `gawk' uses the GNU MPFR (http://www.mpfr.org) and GNU MP
++(http://gmplib.org) (GMP) libraries for arbitrary precision arithmetic
++on numbers. So if you do not see the names of these libraries in the
++output, then your version of `gawk' does not support arbitrary
++precision arithmetic.
++
++   Additionally, there are a few elements available in the `PROCINFO'
++array to provide information about the MPFR and GMP libraries.  *Note
++Auto-set::, for more information.
++
++
++File: gawk.info,  Node: Arbitrary Precision Floats,  Next: Arbitrary 
Precision Integers,  Prev: Gawk and MPFR,  Up: Arbitrary Precision Arithmetic
++
++11.4 Arbitrary Precision Floating-point Arithmetic with `gawk'
++==============================================================
++
++`gawk' uses the GNU MPFR library for arbitrary precision floating-point
++arithmetic.  The MPFR library provides precise control over precisions
++and rounding modes, and gives correctly rounded reproducible
++platform-independent results.  With the command-line option `--bignum'
++or `-M', all floating-point arithmetic operators and numeric functions
++can yield results to any desired precision level supported by MPFR.
++Two built-in variables `PREC' (*note Setting Precision::) and
++`ROUNDMODE' (*note Setting Rounding Mode::) provide control over the
++working precision and the rounding mode.  The precision and the
++rounding mode are set globally for every operation to follow.
++
++   The default working precision for arbitrary precision floating-point
++values is 53, and the default value for `ROUNDMODE' is `"N"', which
++selects the IEEE-754 `roundTiesToEven' (*note Rounding Mode::) rounding
++mode.(1) `gawk' uses the default exponent range in MPFR (EMAX = 2^30 -
++1, EMIN = -EMAX) for all floating-point contexts.  There is no explicit
++mechanism to adjust the exponent range.  MPFR does not implement
++subnormal numbers by default, and this behavior cannot be changed in
++`gawk'.
++
++     NOTE: When emulating an IEEE-754 format (*note Setting
++     Precision::), `gawk' internally adjusts the exponent range to the
++     value defined for the format and also performs computations needed
++     for gradual underflow (subnormal numbers).
++
++     NOTE: MPFR numbers are variable-size entities, consuming only as
++     much space as needed to store the significant digits. Since the
++     performance using MPFR numbers pales in comparison to doing
++     arithmetic using the underlying machine types, you should consider
++     using only as much precision as needed by your program.
++
++* Menu:
++
++* Setting Precision::           Setting the working precision.
++* Setting Rounding Mode::       Setting the rounding mode.
++* Floating-point Constants::    Representing floating-point constants.
++* Changing Precision::          Changing the precision of a number.
++* Exact Arithmetic::            Exact arithmetic with floating-point numbers.
+ 
+    ---------- Footnotes ----------
+ 
 -   (1) This is very different from the same operator in the C shell.
++   (1) The default precision is 53, since according to the MPFR
++documentation, the library should be able to exactly reproduce all
++computations with double-precision machine floating-point numbers
++(`double' type in C), except the default exponent range is much wider
++and subnormal numbers are not implemented.
+ 
+ 
 -File: gawk.info,  Node: TCP/IP Networking,  Next: Profiling,  Prev: Two-way 
I/O,  Up: Advanced Features
++File: gawk.info,  Node: Setting Precision,  Next: Setting Rounding Mode,  Up: 
Arbitrary Precision Floats
+ 
 -11.4 Using `gawk' for Network Programming
 -=========================================
++11.4.1 Setting the Working Precision
++------------------------------------
+ 
 -     `EMISTERED':
 -     A host is a host from coast to coast,
 -     and no-one can talk to host that's close,
 -     unless the host that isn't close
 -     is busy hung or dead.
++`gawk' uses a global working precision; it does not keep track of the
++precision or accuracy of individual numbers. Performing an arithmetic
++operation or calling a built-in function rounds the result to the
++current working precision. The default working precision is 53 which
++can be modified using the built-in variable `PREC'. You can also set the
++value to one of the following pre-defined case-insensitive strings to
++emulate an IEEE-754 binary format:
++
++`PREC'       IEEE-754 Binary Format
++--------------------------------------------------- 
++`"half"'     16-bit half-precision.
++`"single"'   Basic 32-bit single precision.
++`"double"'   Basic 64-bit double precision.
++`"quad"'     Basic 128-bit quadruple precision.
++`"oct"'      256-bit octuple precision.
++
++   The following example illustrates the effects of changing precision
++on arithmetic operations:
++
++     $ gawk -M -vPREC=100 'BEGIN { x = 1.0e-400; print x + 0; \
++     >   PREC = "double"; print x + 0 }'
++     -| 1e-400
++     -| 0
+ 
 -   In addition to being able to open a two-way pipeline to a coprocess
 -on the same system (*note Two-way I/O::), it is possible to make a
 -two-way connection to another process on another system across an IP
 -network connection.
++   Binary and decimal precisions are related approximately according to
++the formula:
++
++   PREC = 3.322 * DPS
++
++Here, PREC denotes the binary precision (measured in bits) and DPS
++(short for decimal places) is the decimal digits. We can easily
++calculate how many decimal digits the 53-bit significand of an IEEE
++double is equivalent to: 53 / 3.332 which is equal to about 15.95.  But
++what does 15.95 digits actually mean? It depends whether you are
++concerned about how many digits you can rely on, or how many digits you
++need.
++
++   It is important to know how many bits it takes to uniquely identify
++a double-precision value (the C type `double').  If you want to convert
++from `double' to decimal and back to `double' (e.g., saving a `double'
++representing an intermediate result to a file, and later reading it
++back to restart the computation), then a few more decimal digits are
++required. 17 digits is generally enough for a `double'.
++
++   It can also be important to know what decimal numbers can be uniquely
++represented with a `double'. If you want to convert from decimal to
++`double' and back again, 15 digits is the most that you can get. Stated
++differently, you should not present the numbers from your
++floating-point computations with more than 15 significant digits in
++them.
+ 
 -   You can think of this as just a _very long_ two-way pipeline to a
 -coprocess.  The way `gawk' decides that you want to use TCP/IP
 -networking is by recognizing special file names that begin with one of
 -`/inet/', `/inet4/' or `/inet6'.
++   Conversely, it takes a precision of 332 bits to hold an approximation
++of the constant pi that is accurate to 100 decimal places.  You should
++always add some extra bits in order to avoid the confusing round-off
++issues that occur because numbers are stored internally in binary.
+ 
 -   The full syntax of the special file name is
 -`/NET-TYPE/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'.  The
 -components are:
++
++File: gawk.info,  Node: Setting Rounding Mode,  Next: Floating-point 
Constants,  Prev: Setting Precision,  Up: Arbitrary Precision Floats
+ 
 -NET-TYPE
 -     Specifies the kind of Internet connection to make.  Use `/inet4/'
 -     to force IPv4, and `/inet6/' to force IPv6.  Plain `/inet/' (which
 -     used to be the only option) uses the system default, most likely
 -     IPv4.
++11.4.2 Setting the Rounding Mode
++--------------------------------
+ 
 -PROTOCOL
 -     The protocol to use over IP.  This must be either `tcp', or `udp',
 -     for a TCP or UDP IP connection, respectively.  The use of TCP is
 -     recommended for most applications.
++The `ROUNDMODE' variable provides program level control over the
++rounding mode.  The correspondance between `ROUNDMODE' and the IEEE
++rounding modes is shown in *note table-gawk-rounding-modes::.
+ 
 -LOCAL-PORT
 -     The local TCP or UDP port number to use.  Use a port number of `0'
 -     when you want the system to pick a port. This is what you should do
 -     when writing a TCP or UDP client.  You may also use a well-known
 -     service name, such as `smtp' or `http', in which case `gawk'
 -     attempts to determine the predefined port number using the C
 -     `getaddrinfo()' function.
++Rounding Mode                    IEEE Name              `ROUNDMODE'
++--------------------------------------------------------------------------- 
++Round to nearest, ties to even   `roundTiesToEven'      `"N"' or `"n"'
++Round toward plus Infinity       `roundTowardPositive'  `"U"' or `"u"'
++Round toward negative Infinity   `roundTowardNegative'  `"D"' or `"d"'
++Round toward zero                `roundTowardZero'      `"Z"' or `"z"'
++Round to nearest, ties away      `roundTiesToAway'      `"A"' or `"a"'
++from zero                                               
+ 
 -REMOTE-HOST
 -     The IP address or fully-qualified domain name of the Internet host
 -     to which you want to connect.
++Table 11.3: `gawk' Rounding Modes
+ 
 -REMOTE-PORT
 -     The TCP or UDP port number to use on the given REMOTE-HOST.
 -     Again, use `0' if you don't care, or else a well-known service
 -     name.
++   `ROUNDMODE' has the default value `"N"', which selects the IEEE-754
++rounding mode `roundTiesToEven'.  Besides the values listed in *note
++Table 11.3: table-gawk-rounding-modes, `gawk' also accepts `"A"' to
++select the IEEE-754 mode `roundTiesToAway' if your version of the MPFR
++library supports it; otherwise setting `ROUNDMODE' to this value has no
++effect. *Note Rounding Mode::, for the meanings of the various rounding
++modes.
+ 
 -     NOTE: Failure in opening a two-way socket will result in a
 -     non-fatal error being returned to the calling code. The value of
 -     `ERRNO' indicates the error (*note Auto-set::).
++   Here is an example of how to change the default rounding behavior of
++`printf''s output:
+ 
 -   Consider the following very simple example:
++     $ gawk -M -vROUNDMODE="Z" 'BEGIN { printf("%.2f\n", 1.378) }'
++     -| 1.37
+ 
 -     BEGIN {
 -       Service = "/inet/tcp/0/localhost/daytime"
 -       Service |& getline
 -       print $0
 -       close(Service)
 -     }
++
++File: gawk.info,  Node: Floating-point Constants,  Next: Changing Precision,  
Prev: Setting Rounding Mode,  Up: Arbitrary Precision Floats
+ 
 -   This program reads the current date and time from the local system's
 -TCP `daytime' server.  It then prints the results and closes the
 -connection.
++11.4.3 Representing Floating-point Constants
++--------------------------------------------
+ 
 -   Because this topic is extensive, the use of `gawk' for TCP/IP
 -programming is documented separately.  See *note (General
 -Introduction)Top:: gawkinet, TCP/IP Internetworking with `gawk', for a
 -much more complete introduction and discussion, as well as extensive
 -examples.
++Be wary of floating-point constants! When reading a floating-point
++constant from program source code, `gawk' uses the default precision,
++unless overridden by an assignment to the special variable `PREC' on
++the command line, to store it internally as a MPFR number.  Changing
++the precision using `PREC' in the program text does not change the
++precision of a constant. If you need to represent a floating-point
++constant at a higher precision than the default and cannot use a
++command line assignment to `PREC', you should either specify the
++constant as a string, or as a rational number whenever possible. The
++following example illustrates the differences among various ways to
++print a floating-point constant:
++
++     $ gawk -M 'BEGIN { PREC = 113; printf("%0.25f\n", 0.1) }'
++     -| 0.1000000000000000055511151
++     $ gawk -M -vPREC = 113 'BEGIN { printf("%0.25f\n", 0.1) }'
++     -| 0.1000000000000000000000000
++     $ gawk -M 'BEGIN { PREC = 113; printf("%0.25f\n", "0.1") }'
++     -| 0.1000000000000000000000000
++     $ gawk -M 'BEGIN { PREC = 113; printf("%0.25f\n", 1/10) }'
++     -| 0.1000000000000000000000000
++
++   In the first case, the number is stored with the default precision
++of 53.
++
++
++File: gawk.info,  Node: Changing Precision,  Next: Exact Arithmetic,  Prev: 
Floating-point Constants,  Up: Arbitrary Precision Floats
++
++11.4.4 Changing the Precision of a Number
++-----------------------------------------
+ 
 -
 -File: gawk.info,  Node: Profiling,  Prev: TCP/IP Networking,  Up: Advanced 
Features
++     The point is that in any variable-precision package, a decision is
++     made on how to treat numbers given as data, or arising in
++     intermediate results, which are represented in floating-point
++     format to a precision lower than working precision.  Do we promote
++     them to full membership of the high-precision club, or do we treat
++     them and all their associates as second-class citizens?  Sometimes
++     the first course is proper, sometimes the second, and it takes
++     careful analysis to tell which.
++
++     Dirk Laurie(1)
++
++   `gawk' does not implicitly modify the precision of any previously
++computed results when the working precision is changed with an
++assignment to `PREC'.  The precision of a number is always the one that
++was used at the time of its creation, and there is no way for the user
++to explicitly change it afterwards. However, since the result of a
++floating-point arithmetic operation is always an arbitrary precision
++floating-point value--with a precision set by the value of `PREC'--one
++of the following workarounds effectively accomplishes the desired
++behavior:
++
++     x = x + 0.0
+ 
 -11.5 Profiling Your `awk' Programs
 -==================================
++or:
+ 
 -You may produce execution traces of your `awk' programs.  This is done
 -with a specially compiled version of `gawk', called `pgawk' ("profiling
 -`gawk'").
++     x += 0.0
+ 
 -   `pgawk' is identical in every way to `gawk', except that when it has
 -finished running, it creates a profile of your program in a file named
 -`awkprof.out'.  Because it is profiling, it also executes up to 45%
 -slower than `gawk' normally does.
++   ---------- Footnotes ----------
+ 
 -   As shown in the following example, the `--profile' option can be
 -used to change the name of the file where `pgawk' will write the
 -profile:
++   (1) Dirk Laurie.  `Variable-precision Arithmetic Considered Perilous
++-- A Detective Story'.  Electronic Transactions on Numerical Analysis.
++Volume 28, pp. 168-173, 2008.
+ 
 -     pgawk --profile=myprog.prof -f myprog.awk data1 data2
++
++File: gawk.info,  Node: Exact Arithmetic,  Prev: Changing Precision,  Up: 
Arbitrary Precision Floats
+ 
 -In the above example, `pgawk' places the profile in `myprog.prof'
 -instead of in `awkprof.out'.
++11.4.5 Exact Arithmetic with Floating-point Numbers
++---------------------------------------------------
+ 
 -   Here is a sample session showing a simple `awk' program, its input
 -data, and the results from running `pgawk'.  First, the `awk' program:
++     CAUTION: Never depend on the exactness of floating-point
++     arithmetic, even for apparently simple expressions!
+ 
 -     BEGIN { print "First BEGIN rule" }
++   Can arbitrary precision arithmetic give exact results? There are no
++easy answers. The standard rules of algebra often do not apply when
++using floating-point arithmetic.  Among other things, the distributive
++and associative laws do not hold completely, and order of operation may
++be important for your computation. Rounding error, cumulative precision
++loss and underflow are often troublesome.
+ 
 -     END { print "First END rule" }
++   When `gawk' tests the expressions `0.1 + 12.2' and `12.3' for
++equality using the machine double precision arithmetic, it decides that
++they are not equal!  (*Note Floating-point Programming::.)  You can get
++the result you want by increasing the precision; 56 in this case will
++get the job done:
+ 
 -     /foo/ {
 -         print "matched /foo/, gosh"
 -         for (i = 1; i <= 3; i++)
 -             sing()
 -     }
++     $ gawk -M -vPREC=56 'BEGIN { print (0.1 + 12.2 == 12.3) }'
++     -| 1
+ 
 -     {
 -         if (/foo/)
 -             print "if is true"
 -         else
 -             print "else is true"
 -     }
++   If adding more bits is good, perhaps adding even more bits of
++precision is better?  Here is what happens if we use an even larger
++value of `PREC':
+ 
 -     BEGIN { print "Second BEGIN rule" }
++     $ gawk -M -vPREC=201 'BEGIN { print (0.1 + 12.2 == 12.3) }'
++     -| 0
+ 
 -     END { print "Second END rule" }
++   This is not a bug in `gawk' or in the MPFR library.  It is easy to
++forget that the finite number of bits used to store the value is often
++just an approximation after proper rounding.  The test for equality
++succeeds if and only if _all_ bits in the two operands are exactly the
++same. Since this is not necessarily true after floating-point
++computations with a particular precision and effective rounding rule, a
++straight test for equality may not work.
++
++   So, don't assume that floating-point values can be compared for
++equality.  You should also exercise caution when using other forms of
++comparisons.  The standard way to compare between floating-point
++numbers is to determine how much error (or "tolerance") you will allow
++in a comparison and check to see if one value is within this error
++range of the other.
++
++   In applications where 15 or fewer decimal places suffice, hardware
++double precision arithmetic can be adequate, and is usually much faster.
++But you do need to keep in mind that every floating-point operation can
++suffer a new rounding error with catastrophic consequences as
++illustrated by our attempt to compute the value of the constant pi
++(*note Floating-point Programming::).  Extra precision can greatly
++enhance the stability and the accuracy of your computation in such
++cases.
++
++   Repeated addition is not necessarily equivalent to multiplication in
++floating-point arithmetic. In the example in *note Floating-point
++Programming:::
+ 
 -     function sing(    dummy)
 -     {
 -         print "I gotta be me!"
 -     }
++     $ gawk 'BEGIN {
++     >   for (d = 1.1; d <= 1.5; d += 0.1)
++     >       i++
++     >   print i
++     > }'
++     -| 4
+ 
 -   Following is the input data:
++you may or may not succeed in getting the correct result by choosing an
++arbitrarily large value for `PREC'. Reformulation of the problem at
++hand is often the correct approach in such situations.
+ 
 -     foo
 -     bar
 -     baz
 -     foo
 -     junk
++
++File: gawk.info,  Node: Arbitrary Precision Integers,  Prev: Arbitrary 
Precision Floats,  Up: Arbitrary Precision Arithmetic
+ 
 -   Here is the `awkprof.out' that results from running `pgawk' on this
 -program and data (this example also illustrates that `awk' programmers
 -sometimes have to work late):
++11.5 Arbitrary Precision Integer Arithmetic with `gawk'
++=======================================================
+ 
 -             # gawk profile, created Sun Aug 13 00:00:15 2000
++If the option `--bignum' or `-M' is specified, `gawk' performs all
++integer arithmetic using GMP arbitrary precision integers.  Any number
++that looks like an integer in a program source or data file is stored
++as an arbitrary precision integer.  The size of the integer is limited
++only by your computer's memory.  The current floating-point context has
++no effect on operations involving integers.  For example, the following
++computes 5^4^3^2, the result of which is beyond the limits of ordinary
++`gawk' numbers:
+ 
 -             # BEGIN block(s)
++     $ gawk -M 'BEGIN {
++     >   x = 5^4^3^2
++     >   print "# of digits =", length(x)
++     >   print substr(x, 1, 20), "...", substr(x, length(x) - 19, 20)
++     > }'
++     -| # of digits = 183231
++     -| 62060698786608744707 ... 92256259918212890625
++
++   If you were to compute the same value using arbitrary precision
++floating-point values instead, the precision needed for correct output
++(using the formula `prec = 3.322 * dps'), would be 3.322 x 183231, or
++608693.  (Thus, the floating-point representation requires over 30
++times as many decimal digits!)
++
++   The result from an arithmetic operation with an integer and a
++floating-point value is a floating-point value with a precision equal
++to the working precision.  The following program calculates the eighth
++term in Sylvester's sequence(1) using a recurrence:
++
++     $ gawk -M 'BEGIN {
++     >   s = 2.0
++     >   for (i = 1; i <= 7; i++)
++     >       s = s * (s - 1) + 1
++     >   print s
++     > }'
++     -| 113423713055421845118910464
++
++   The output differs from the acutal number,
++113423713055421844361000443, because the default precision of 53 is not
++enough to represent the floating-point results exactly. You can either
++increase the precision (100 is enough in this case), or replace the
++floating-point constant `2.0' with an integer, to perform all
++computations using integer arithmetic to get the correct output.
++
++   It will sometimes be necessary for `gawk' to implicitly convert an
++arbitrary precision integer into an arbitrary precision floating-point
++value.  This is primarily because the MPFR library does not always
++provide the relevant interface to process arbitrary precision integers
++or mixed-mode numbers as needed by an operation or function.  In such a
++case, the precision is set to the minimum value necessary for exact
++conversion, and the working precision is not used for this purpose.  If
++this is not what you need or want, you can employ a subterfuge like
++this:
+ 
 -             BEGIN {
 -          1          print "First BEGIN rule"
 -          1          print "Second BEGIN rule"
 -             }
++     gawk -M 'BEGIN { n = 13; print (n + 0.0) % 2.0 }'
+ 
 -             # Rule(s)
++   You can avoid this issue altogether by specifying the number as a
++floating-point value to begin with:
+ 
 -          5  /foo/   { # 2
 -          2          print "matched /foo/, gosh"
 -          6          for (i = 1; i <= 3; i++) {
 -          6                  sing()
 -                     }
 -             }
++     gawk -M 'BEGIN { n = 13.0; print n % 2.0 }'
+ 
 -          5  {
 -          5          if (/foo/) { # 2
 -          2                  print "if is true"
 -          3          } else {
 -          3                  print "else is true"
 -                     }
 -             }
++   Note that for the particular example above, there is likely best to
++just use the following:
+ 
 -             # END block(s)
++     gawk -M 'BEGIN { n = 13; print n % 2 }'
+ 
 -             END {
 -          1          print "First END rule"
 -          1          print "Second END rule"
 -             }
++   ---------- Footnotes ----------
+ 
 -             # Functions, listed alphabetically
++   (1) Weisstein, Eric W.  `Sylvester's Sequence'. From MathWorld--A
++Wolfram Web Resource.
++`http://mathworld.wolfram.com/SylvestersSequence.html'
+ 
 -          6  function sing(dummy)
 -             {
 -          6          print "I gotta be me!"
 -             }
++
++File: gawk.info,  Node: Advanced Features,  Next: Library Functions,  Prev: 
Arbitrary Precision Arithmetic,  Up: Top
+ 
 -   This example illustrates many of the basic features of profiling
 -output.  They are as follows:
++12 Advanced Features of `gawk'
++******************************
+ 
 -   * The program is printed in the order `BEGIN' rule, `BEGINFILE' rule,
 -     pattern/action rules, `ENDFILE' rule, `END' rule and functions,
 -     listed alphabetically.  Multiple `BEGIN' and `END' rules are
 -     merged together, as are multiple `BEGINFILE' and `ENDFILE' rules.
++     Write documentation as if whoever reads it is a violent psychopath
++     who knows where you live.
++     Steve English, as quoted by Peter Langston
+ 
 -   * Pattern-action rules have two counts.  The first count, to the
 -     left of the rule, shows how many times the rule's pattern was
 -     _tested_.  The second count, to the right of the rule's opening
 -     left brace in a comment, shows how many times the rule's action
 -     was _executed_.  The difference between the two indicates how many
 -     times the rule's pattern evaluated to false.
++   This major node discusses advanced features in `gawk'.  It's a bit
++of a "grab bag" of items that are otherwise unrelated to each other.
++First, a command-line option allows `gawk' to recognize nondecimal
++numbers in input data, not just in `awk' programs.  Then, `gawk''s
++special features for sorting arrays are presented.  Next, two-way I/O,
++discussed briefly in earlier parts of this Info file, is described in
++full detail, along with the basics of TCP/IP networking.  Finally,
++`gawk' can "profile" an `awk' program, making it possible to tune it
++for performance.
+ 
 -   * Similarly, the count for an `if'-`else' statement shows how many
 -     times the condition was tested.  To the right of the opening left
 -     brace for the `if''s body is a count showing how many times the
 -     condition was true.  The count for the `else' indicates how many
 -     times the test failed.
++   *note Dynamic Extensions::, discusses the ability to dynamically add
++new built-in functions to `gawk'.  As this feature is still immature
++and likely to change, its description is relegated to an appendix.
+ 
 -   * The count for a loop header (such as `for' or `while') shows how
 -     many times the loop test was executed.  (Because of this, you
 -     can't just look at the count on the first statement in a rule to
 -     determine how many times the rule was executed.  If the first
 -     statement is a loop, the count is misleading.)
++* Menu:
+ 
 -   * For user-defined functions, the count next to the `function'
 -     keyword indicates how many times the function was called.  The
 -     counts next to the statements in the body show how many times
 -     those statements were executed.
++* Nondecimal Data::             Allowing nondecimal input data.
++* Array Sorting::               Facilities for controlling array traversal and
++                                sorting arrays.
++* Two-way I/O::                 Two-way communications with another process.
++* TCP/IP Networking::           Using `gawk' for network programming.
++* Profiling::                   Profiling your `awk' programs.
+ 
 -   * The layout uses "K&R" style with TABs.  Braces are used
 -     everywhere, even when the body of an `if', `else', or loop is only
 -     a single statement.
++
++File: gawk.info,  Node: Nondecimal Data,  Next: Array Sorting,  Up: Advanced 
Features
+ 
 -   * Parentheses are used only where needed, as indicated by the
 -     structure of the program and the precedence rules.  For example,
 -     `(3 + 5) * 4' means add three plus five, then multiply the total
 -     by four.  However, `3 + 5 * 4' has no parentheses, and means `3 +
 -     (5 * 4)'.
++12.1 Allowing Nondecimal Input Data
++===================================
+ 
 -   * Parentheses are used around the arguments to `print' and `printf'
 -     only when the `print' or `printf' statement is followed by a
 -     redirection.  Similarly, if the target of a redirection isn't a
 -     scalar, it gets parenthesized.
++If you run `gawk' with the `--non-decimal-data' option, you can have
++nondecimal constants in your input data:
+ 
 -   * `pgawk' supplies leading comments in front of the `BEGIN' and
 -     `END' rules, the pattern/action rules, and the functions.
++     $ echo 0123 123 0x123 |
++     > gawk --non-decimal-data '{ printf "%d, %d, %d\n",
++     >                                         $1, $2, $3 }'
++     -| 83, 123, 291
+ 
++   For this feature to work, write your program so that `gawk' treats
++your data as numeric:
+ 
 -   The profiled version of your program may not look exactly like what
 -you typed when you wrote it.  This is because `pgawk' creates the
 -profiled version by "pretty printing" its internal representation of
 -the program.  The advantage to this is that `pgawk' can produce a
 -standard representation.  The disadvantage is that all source-code
 -comments are lost, as are the distinctions among multiple `BEGIN',
 -`END', `BEGINFILE', and `ENDFILE' rules.  Also, things such as:
++     $ echo 0123 123 0x123 | gawk '{ print $1, $2, $3 }'
++     -| 0123 123 0x123
+ 
 -     /foo/
++The `print' statement treats its expressions as strings.  Although the
++fields can act as numbers when necessary, they are still strings, so
++`print' does not try to treat them numerically.  You may need to add
++zero to a field to force it to be treated as a number.  For example:
+ 
 -come out as:
++     $ echo 0123 123 0x123 | gawk --non-decimal-data '
++     > { print $1, $2, $3
++     >   print $1 + 0, $2 + 0, $3 + 0 }'
++     -| 0123 123 0x123
++     -| 83 123 291
+ 
 -     /foo/   {
 -         print $0
 -     }
++   Because it is common to have decimal data with leading zeros, and
++because using this facility could lead to surprising results, the
++default is to leave it disabled.  If you want it, you must explicitly
++request it.
+ 
 -which is correct, but possibly surprising.
++     CAUTION: _Use of this option is not recommended._ It can break old
++     programs very badly.  Instead, use the `strtonum()' function to
++     convert your data (*note Nondecimal-numbers::).  This makes your
++     programs easier to write and easier to read, and leads to less
++     surprising results.
+ 
 -   Besides creating profiles when a program has completed, `pgawk' can
 -produce a profile while it is running.  This is useful if your `awk'
 -program goes into an infinite loop and you want to see what has been
 -executed.  To use this feature, run `pgawk' in the background:
++
++File: gawk.info,  Node: Array Sorting,  Next: Two-way I/O,  Prev: Nondecimal 
Data,  Up: Advanced Features
+ 
 -     $ pgawk -f myprog &
 -     [1] 13992
++12.2 Controlling Array Traversal and Array Sorting
++==================================================
+ 
 -The shell prints a job number and process ID number; in this case,
 -13992.  Use the `kill' command to send the `USR1' signal to `pgawk':
++`gawk' lets you control the order in which a `for (i in array)' loop
++traverses an array.
+ 
 -     $ kill -USR1 13992
++   In addition, two built-in functions, `asort()' and `asorti()', let
++you sort arrays based on the array values and indices, respectively.
++These two functions also provide control over the sorting criteria used
++to order the elements during sorting.
+ 
 -As usual, the profiled version of the program is written to
 -`awkprof.out', or to a different file if you use the `--profile' option.
++* Menu:
+ 
 -   Along with the regular profile, as shown earlier, the profile
 -includes a trace of any active functions:
++* Controlling Array Traversal:: How to use PROCINFO["sorted_in"].
++* Array Sorting Functions::     How to use `asort()' and `asorti()'.
+ 
 -     # Function Call Stack:
++
++File: gawk.info,  Node: Controlling Array Traversal,  Next: Array Sorting 
Functions,  Up: Array Sorting
+ 
 -     #   3. baz
 -     #   2. bar
 -     #   1. foo
 -     # -- main --
++12.2.1 Controlling Array Traversal
++----------------------------------
+ 
 -   You may send `pgawk' the `USR1' signal as many times as you like.
 -Each time, the profile and function call trace are appended to the
 -output profile file.
++By default, the order in which a `for (i in array)' loop scans an array
++is not defined; it is generally based upon the internal implementation
++of arrays inside `awk'.
+ 
 -   If you use the `HUP' signal instead of the `USR1' signal, `pgawk'
 -produces the profile and the function call trace and then exits.
++   Often, though, it is desirable to be able to loop over the elements
++in a particular order that you, the programmer, choose.  `gawk' lets
++you do this.
+ 
 -   When `pgawk' runs on MS-Windows systems, it uses the `INT' and
 -`QUIT' signals for producing the profile and, in the case of the `INT'
 -signal, `pgawk' exits.  This is because these systems don't support the
 -`kill' command, so the only signals you can deliver to a program are
 -those generated by the keyboard.  The `INT' signal is generated by the
 -`Ctrl-<C>' or `Ctrl-<BREAK>' key, while the `QUIT' signal is generated
 -by the `Ctrl-<\>' key.
++   *note Controlling Scanning::, describes how you can assign special,
++pre-defined values to `PROCINFO["sorted_in"]' in order to control the
++order in which `gawk' will traverse an array during a `for' loop.
+ 
 -   Finally, regular `gawk' also accepts the `--profile' option.  When
 -called this way, `gawk' "pretty prints" the program into `awkprof.out',
 -without any execution counts.
++   In addition, the value of `PROCINFO["sorted_in"]' can be a function
++name.  This lets you traverse an array based on any custom criterion.
++The array elements are ordered according to the return value of this
++function.  The comparison function should be defined with at least four
++arguments:
+ 
 -
 -File: gawk.info,  Node: Library Functions,  Next: Sample Programs,  Prev: 
Advanced Features,  Up: Top
++     function comp_func(i1, v1, i2, v2)
++     {
++         COMPARE ELEMENTS 1 AND 2 IN SOME FASHION
++         RETURN < 0; 0; OR > 0
++     }
+ 
 -12 A Library of `awk' Functions
 -*******************************
++   Here, I1 and I2 are the indices, and V1 and V2 are the corresponding
++values of the two elements being compared.  Either V1 or V2, or both,
++can be arrays if the array being traversed contains subarrays as values.
++(*Note Arrays of Arrays::, for more information about subarrays.)  The
++three possible return values are interpreted as follows:
+ 
 -*note User-defined::, describes how to write your own `awk' functions.
 -Writing functions is important, because it allows you to encapsulate
 -algorithms and program tasks in a single place.  It simplifies
 -programming, making program development more manageable, and making
 -programs more readable.
++`comp_func(i1, v1, i2, v2) < 0'
++     Index I1 comes before index I2 during loop traversal.
+ 
 -   One valuable way to learn a new programming language is to _read_
 -programs in that language.  To that end, this major node and *note
 -Sample Programs::, provide a good-sized body of code for you to read,
 -and hopefully, to learn from.
++`comp_func(i1, v1, i2, v2) == 0'
++     Indices I1 and I2 come together but the relative order with
++     respect to each other is undefined.
+ 
 -   This major node presents a library of useful `awk' functions.  Many
 -of the sample programs presented later in this Info file use these
 -functions.  The functions are presented here in a progression from
 -simple to complex.
++`comp_func(i1, v1, i2, v2) > 0'
++     Index I1 comes after index I2 during loop traversal.
+ 
 -   *note Extract Program::, presents a program that you can use to
 -extract the source code for these example library functions and
 -programs from the Texinfo source for this Info file.  (This has already
 -been done as part of the `gawk' distribution.)
++   Our first comparison function can be used to scan an array in
++numerical order of the indices:
+ 
 -   If you have written one or more useful, general-purpose `awk'
 -functions and would like to contribute them to the `awk' user
 -community, see *note How To Contribute::, for more information.
++     function cmp_num_idx(i1, v1, i2, v2)
++     {
++          # numerical index comparison, ascending order
++          return (i1 - i2)
++     }
+ 
 -   The programs in this major node and in *note Sample Programs::,
 -freely use features that are `gawk'-specific.  Rewriting these programs
 -for different implementations of `awk' is pretty straightforward.
++   Our second function traverses an array based on the string order of
++the element values rather than by indices:
+ 
 -   * Diagnostic error messages are sent to `/dev/stderr'.  Use `| "cat
 -     1>&2"' instead of `> "/dev/stderr"' if your system does not have a
 -     `/dev/stderr', or if you cannot use `gawk'.
++     function cmp_str_val(i1, v1, i2, v2)
++     {
++         # string value comparison, ascending order
++         v1 = v1 ""
++         v2 = v2 ""
++         if (v1 < v2)
++             return -1
++         return (v1 != v2)
++     }
+ 
 -   * A number of programs use `nextfile' (*note Nextfile Statement::)
 -     to skip any remaining input in the input file.
++   The third comparison function makes all numbers, and numeric strings
++without any leading or trailing spaces, come out first during loop
++traversal:
+ 
 -   * Finally, some of the programs choose to ignore upper- and lowercase
 -     distinctions in their input. They do so by assigning one to
 -     `IGNORECASE'.  You can achieve almost the same effect(1) by adding
 -     the following rule to the beginning of the program:
++     function cmp_num_str_val(i1, v1, i2, v2,   n1, n2)
++     {
++          # numbers before string value comparison, ascending order
++          n1 = v1 + 0
++          n2 = v2 + 0
++          if (n1 == v1)
++              return (n2 == v2) ? (n1 - n2) : -1
++          else if (n2 == v2)
++              return 1
++          return (v1 < v2) ? -1 : (v1 != v2)
++     }
+ 
 -          # ignore case
 -          { $0 = tolower($0) }
++   Here is a main program to demonstrate how `gawk' behaves using each
++of the previous functions:
+ 
 -     Also, verify that all regexp and string constants used in
 -     comparisons use only lowercase letters.
++     BEGIN {
++         data["one"] = 10
++         data["two"] = 20
++         data[10] = "one"
++         data[100] = 100
++         data[20] = "two"
+ 
 -* Menu:
++         f[1] = "cmp_num_idx"
++         f[2] = "cmp_str_val"
++         f[3] = "cmp_num_str_val"
++         for (i = 1; i <= 3; i++) {
++             printf("Sort function: %s\n", f[i])
++             PROCINFO["sorted_in"] = f[i]
++             for (j in data)
++                 printf("\tdata[%s] = %s\n", j, data[j])
++             print ""
++         }
++     }
+ 
 -* Library Names::               How to best name private global variables in
 -                                library functions.
 -* General Functions::           Functions that are of general use.
 -* Data File Management::        Functions for managing command-line data
 -                                files.
 -* Getopt Function::             A function for processing command-line
 -                                arguments.
 -* Passwd Functions::            Functions for getting user information.
 -* Group Functions::             Functions for getting group information.
 -* Walking Arrays::              A function to walk arrays of arrays.
++   Here are the results when the program is run:
+ 
 -   ---------- Footnotes ----------
++     $ gawk -f compdemo.awk
++     -| Sort function: cmp_num_idx      Sort by numeric index
++     -|     data[two] = 20
++     -|     data[one] = 10              Both strings are numerically zero
++     -|     data[10] = one
++     -|     data[20] = two
++     -|     data[100] = 100
++     -|
++     -| Sort function: cmp_str_val      Sort by element values as strings
++     -|     data[one] = 10
++     -|     data[100] = 100             String 100 is less than string 20
++     -|     data[two] = 20
++     -|     data[10] = one
++     -|     data[20] = two
++     -|
++     -| Sort function: cmp_num_str_val  Sort all numeric values before all 
strings
++     -|     data[one] = 10
++     -|     data[two] = 20
++     -|     data[100] = 100
++     -|     data[10] = one
++     -|     data[20] = two
+ 
 -   (1) The effects are not identical.  Output of the transformed record
 -will be in all lowercase, while `IGNORECASE' preserves the original
 -contents of the input record.
++   Consider sorting the entries of a GNU/Linux system password file
++according to login name.  The following program sorts records by a
++specific field position and can be used for this purpose:
+ 
 -
 -File: gawk.info,  Node: Library Names,  Next: General Functions,  Up: Library 
Functions
++     # sort.awk --- simple program to sort by field position
++     # field position is specified by the global variable POS
+ 
 -12.1 Naming Library Function Global Variables
 -=============================================
++     function cmp_field(i1, v1, i2, v2)
++     {
++         # comparison by value, as string, and ascending order
++         return v1[POS] < v2[POS] ? -1 : (v1[POS] != v2[POS])
++     }
+ 
 -Due to the way the `awk' language evolved, variables are either
 -"global" (usable by the entire program) or "local" (usable just by a
 -specific function).  There is no intermediate state analogous to
 -`static' variables in C.
++     {
++         for (i = 1; i <= NF; i++)
++             a[NR][i] = $i
++     }
+ 
 -   Library functions often need to have global variables that they can
 -use to preserve state information between calls to the function--for
 -example, `getopt()''s variable `_opti' (*note Getopt Function::).  Such
 -variables are called "private", since the only functions that need to
 -use them are the ones in the library.
++     END {
++         PROCINFO["sorted_in"] = "cmp_field"
++         if (POS < 1 || POS > NF)
++             POS = 1
++         for (i in a) {
++             for (j = 1; j <= NF; j++)
++                 printf("%s%c", a[i][j], j < NF ? ":" : "")
++             print ""
++         }
++     }
+ 
 -   When writing a library function, you should try to choose names for
 -your private variables that will not conflict with any variables used by
 -either another library function or a user's main program.  For example,
 -a name like `i' or `j' is not a good choice, because user programs
 -often use variable names like these for their own purposes.
++   The first field in each entry of the password file is the user's
++login name, and the fields are separated by colons.  Each record
++defines a subarray, with each field as an element in the subarray.
++Running the program produces the following output:
+ 
 -   The example programs shown in this major node all start the names of
 -their private variables with an underscore (`_').  Users generally
 -don't use leading underscores in their variable names, so this
 -convention immediately decreases the chances that the variable name
 -will be accidentally shared with the user's program.
++     $ gawk -vPOS=1 -F: -f sort.awk /etc/passwd
++     -| adm:x:3:4:adm:/var/adm:/sbin/nologin
++     -| apache:x:48:48:Apache:/var/www:/sbin/nologin
++     -| avahi:x:70:70:Avahi daemon:/:/sbin/nologin
++     ...
+ 
 -   In addition, several of the library functions use a prefix that helps
 -indicate what function or set of functions use the variables--for
 -example, `_pw_byname' in the user database routines (*note Passwd
 -Functions::).  This convention is recommended, since it even further
 -decreases the chance of inadvertent conflict among variable names.
 -Note that this convention is used equally well for variable names and
 -for private function names.(1)
++   The comparison should normally always return the same value when
++given a specific pair of array elements as its arguments.  If
++inconsistent results are returned then the order is undefined.  This
++behavior can be exploited to introduce random order into otherwise
++seemingly ordered data:
+ 
 -   As a final note on variable naming, if a function makes global
 -variables available for use by a main program, it is a good convention
 -to start that variable's name with a capital letter--for example,
 -`getopt()''s `Opterr' and `Optind' variables (*note Getopt Function::).
 -The leading capital letter indicates that it is global, while the fact
 -that the variable name is not all capital letters indicates that the
 -variable is not one of `awk''s built-in variables, such as `FS'.
++     function cmp_randomize(i1, v1, i2, v2)
++     {
++         # random order
++         return (2 - 4 * rand())
++     }
+ 
 -   It is also important that _all_ variables in library functions that
 -do not need to save state are, in fact, declared local.(2) If this is
 -not done, the variable could accidentally be used in the user's
 -program, leading to bugs that are very difficult to track down:
++   As mentioned above, the order of the indices is arbitrary if two
++elements compare equal.  This is usually not a problem, but letting the
++tied elements come out in arbitrary order can be an issue, especially
++when comparing item values.  The partial ordering of the equal elements
++may change during the next loop traversal, if other elements are added
++or removed from the array.  One way to resolve ties when comparing
++elements with otherwise equal values is to include the indices in the
++comparison rules.  Note that doing this may make the loop traversal
++less efficient, so consider it only if necessary.  The following
++comparison functions force a deterministic order, and are based on the
++fact that the indices of two elements are never equal:
+ 
 -     function lib_func(x, y,    l1, l2)
++     function cmp_numeric(i1, v1, i2, v2)
+      {
 -         ...
 -         USE VARIABLE some_var   # some_var should be local
 -         ...                     # but is not by oversight
++         # numerical value (and index) comparison, descending order
++         return (v1 != v2) ? (v2 - v1) : (i2 - i1)
+      }
+ 
 -   A different convention, common in the Tcl community, is to use a
 -single associative array to hold the values needed by the library
 -function(s), or "package."  This significantly decreases the number of
 -actual global names in use.  For example, the functions described in
 -*note Passwd Functions::, might have used array elements
 -`PW_data["inited"]', `PW_data["total"]', `PW_data["count"]', and
 -`PW_data["awklib"]', instead of `_pw_inited', `_pw_awklib', `_pw_total',
 -and `_pw_count'.
 -
 -   The conventions presented in this minor node are exactly that:
 -conventions. You are not required to write your programs this way--we
 -merely recommend that you do so.
++     function cmp_string(i1, v1, i2, v2)
++     {
++         # string value (and index) comparison, descending order
++         v1 = v1 i1
++         v2 = v2 i2
++         return (v1 > v2) ? -1 : (v1 != v2)
++     }
+ 
 -   ---------- Footnotes ----------
++   A custom comparison function can often simplify ordered loop
++traversal, and the sky is really the limit when it comes to designing
++such a function.
+ 
 -   (1) While all the library routines could have been rewritten to use
 -this convention, this was not done, in order to show how our own `awk'
 -programming style has evolved and to provide some basis for this
 -discussion.
++   When string comparisons are made during a sort, either for element
++values where one or both aren't numbers, or for element indices handled
++as strings, the value of `IGNORECASE' (*note Built-in Variables::)
++controls whether the comparisons treat corresponding uppercase and
++lowercase letters as equivalent or distinct.
+ 
 -   (2) `gawk''s `--dump-variables' command-line option is useful for
 -verifying this.
++   Another point to keep in mind is that in the case of subarrays the
++element values can themselves be arrays; a production comparison
++function should use the `isarray()' function (*note Type Functions::),
++to check for this, and choose a defined sorting order for subarrays.
++
++   All sorting based on `PROCINFO["sorted_in"]' is disabled in POSIX
++mode, since the `PROCINFO' array is not special in that case.
++
++   As a side note, sorting the array indices before traversing the
++array has been reported to add 15% to 20% overhead to the execution
++time of `awk' programs. For this reason, sorted array traversal is not
++the default.
+ 
+ 
 -File: gawk.info,  Node: General Functions,  Next: Data File Management,  
Prev: Library Names,  Up: Library Functions
++File: gawk.info,  Node: Array Sorting Functions,  Prev: Controlling Array 
Traversal,  Up: Array Sorting
+ 
 -12.2 General Programming
 -========================
++12.2.2 Sorting Array Values and Indices with `gawk'
++---------------------------------------------------
+ 
 -This minor node presents a number of functions that are of general
 -programming use.
++In most `awk' implementations, sorting an array requires writing a
++`sort()' function.  While this can be educational for exploring
++different sorting algorithms, usually that's not the point of the
++program.  `gawk' provides the built-in `asort()' and `asorti()'
++functions (*note String Functions::) for sorting arrays.  For example:
+ 
 -* Menu:
++     POPULATE THE ARRAY data
++     n = asort(data)
++     for (i = 1; i <= n; i++)
++         DO SOMETHING WITH data[i]
+ 
 -* Strtonum Function::           A replacement for the built-in
 -                                `strtonum()' function.
 -* Assert Function::             A function for assertions in `awk'
 -                                programs.
 -* Round Function::              A function for rounding if `sprintf()'
 -                                does not do it correctly.
 -* Cliff Random Function::       The Cliff Random Number Generator.
 -* Ordinal Functions::           Functions for using characters as numbers and
 -                                vice versa.
 -* Join Function::               A function to join an array into a string.
 -* Gettimeofday Function::       A function to get formatted times.
++   After the call to `asort()', the array `data' is indexed from 1 to
++some number N, the total number of elements in `data'.  (This count is
++`asort()''s return value.)  `data[1]' <= `data[2]' <= `data[3]', and so
++on.  The comparison is based on the type of the elements (*note Typing
++and Comparison::).  All numeric values come before all string values,
++which in turn come before all subarrays.
+ 
 -
 -File: gawk.info,  Node: Strtonum Function,  Next: Assert Function,  Up: 
General Functions
++   An important side effect of calling `asort()' is that _the array's
++original indices are irrevocably lost_.  As this isn't always
++desirable, `asort()' accepts a second argument:
+ 
 -12.2.1 Converting Strings To Numbers
 -------------------------------------
++     POPULATE THE ARRAY source
++     n = asort(source, dest)
++     for (i = 1; i <= n; i++)
++         DO SOMETHING WITH dest[i]
+ 
 -The `strtonum()' function (*note String Functions::) is a `gawk'
 -extension.  The following function provides an implementation for other
 -versions of `awk':
++   In this case, `gawk' copies the `source' array into the `dest' array
++and then sorts `dest', destroying its indices.  However, the `source'
++array is not affected.
+ 
 -     # mystrtonum --- convert string to number
++   `asort()' accepts a third string argument to control comparison of
++array elements.  As with `PROCINFO["sorted_in"]', this argument may be
++one of the predefined names that `gawk' provides (*note Controlling
++Scanning::), or the name of a user-defined function (*note Controlling
++Array Traversal::).
+ 
 -     function mystrtonum(str,        ret, chars, n, i, k, c)
 -     {
 -         if (str ~ /^0[0-7]*$/) {
 -             # octal
 -             n = length(str)
 -             ret = 0
 -             for (i = 1; i <= n; i++) {
 -                 c = substr(str, i, 1)
 -                 if ((k = index("01234567", c)) > 0)
 -                     k-- # adjust for 1-basing in awk
++     NOTE: In all cases, the sorted element values consist of the
++     original array's element values.  The ability to control
++     comparison merely affects the way in which they are sorted.
+ 
 -                 ret = ret * 8 + k
 -             }
 -         } else if (str ~ /^0[xX][[:xdigit:]]+/) {
 -             # hexadecimal
 -             str = substr(str, 3)    # lop off leading 0x
 -             n = length(str)
 -             ret = 0
 -             for (i = 1; i <= n; i++) {
 -                 c = substr(str, i, 1)
 -                 c = tolower(c)
 -                 if ((k = index("0123456789", c)) > 0)
 -                     k-- # adjust for 1-basing in awk
 -                 else if ((k = index("abcdef", c)) > 0)
 -                     k += 9
++   Often, what's needed is to sort on the values of the _indices_
++instead of the values of the elements.  To do that, use the `asorti()'
++function.  The interface is identical to that of `asort()', except that
++the index values are used for sorting, and become the values of the
++result array:
+ 
 -                 ret = ret * 16 + k
 -             }
 -         } else if (str ~ \
 -       
/^[-+]?([0-9]+([.][0-9]*([Ee][0-9]+)?)?|([.][0-9]+([Ee][-+]?[0-9]+)?))$/) {
 -             # decimal number, possibly floating point
 -             ret = str + 0
 -         } else
 -             ret = "NOT-A-NUMBER"
++     { source[$0] = some_func($0) }
+ 
 -         return ret
++     END {
++         n = asorti(source, dest)
++         for (i = 1; i <= n; i++) {
++             Work with sorted indices directly:
++             DO SOMETHING WITH dest[i]
++             ...
++             Access original array via sorted indices:
++             DO SOMETHING WITH source[dest[i]]
++         }
+      }
+ 
 -     # BEGIN {     # gawk test harness
 -     #     a[1] = "25"
 -     #     a[2] = ".31"
 -     #     a[3] = "0123"
 -     #     a[4] = "0xdeadBEEF"
 -     #     a[5] = "123.45"
 -     #     a[6] = "1.e3"
 -     #     a[7] = "1.32"
 -     #     a[7] = "1.32E2"
 -     #
 -     #     for (i = 1; i in a; i++)
 -     #         print a[i], strtonum(a[i]), mystrtonum(a[i])
 -     # }
++   Similar to `asort()', in all cases, the sorted element values
++consist of the original array's indices.  The ability to control
++comparison merely affects the way in which they are sorted.
+ 
 -   The function first looks for C-style octal numbers (base 8).  If the
 -input string matches a regular expression describing octal numbers,
 -then `mystrtonum()' loops through each character in the string.  It
 -sets `k' to the index in `"01234567"' of the current octal digit.
 -Since the return value is one-based, the `k--' adjusts `k' so it can be
 -used in computing the return value.
++   Sorting the array by replacing the indices provides maximal
++flexibility.  To traverse the elements in decreasing order, use a loop
++that goes from N down to 1, either over the elements or over the
++indices.(1)
+ 
 -   Similar logic applies to the code that checks for and converts a
 -hexadecimal value, which starts with `0x' or `0X'.  The use of
 -`tolower()' simplifies the computation for finding the correct numeric
 -value for each hexadecimal digit.
++   Copying array indices and elements isn't expensive in terms of
++memory.  Internally, `gawk' maintains "reference counts" to data.  For
++example, when `asort()' copies the first array to the second one, there
++is only one copy of the original array elements' data, even though both
++arrays use the values.
+ 
 -   Finally, if the string matches the (rather complicated) regexp for a
 -regular decimal integer or floating-point number, the computation `ret
 -= str + 0' lets `awk' convert the value to a number.
++   Because `IGNORECASE' affects string comparisons, the value of
++`IGNORECASE' also affects sorting for both `asort()' and `asorti()'.
++Note also that the locale's sorting order does _not_ come into play;
++comparisons are based on character values only.(2) Caveat Emptor.
+ 
 -   A commented-out test program is included, so that the function can
 -be tested with `gawk' and the results compared to the built-in
 -`strtonum()' function.
++   ---------- Footnotes ----------
+ 
 -
 -File: gawk.info,  Node: Assert Function,  Next: Round Function,  Prev: 
Strtonum Function,  Up: General Functions
++   (1) You may also use one of the predefined sorting names that sorts
++in decreasing order.
+ 
 -12.2.2 Assertions
 ------------------
++   (2) This is true because locale-based comparison occurs only when in
++POSIX compatibility mode, and since `asort()' and `asorti()' are `gawk'
++extensions, they are not available in that case.
+ 
 -When writing large programs, it is often useful to know that a
 -condition or set of conditions is true.  Before proceeding with a
 -particular computation, you make a statement about what you believe to
 -be the case.  Such a statement is known as an "assertion".  The C
 -language provides an `<assert.h>' header file and corresponding
 -`assert()' macro that the programmer can use to make assertions.  If an
 -assertion fails, the `assert()' macro arranges to print a diagnostic
 -message describing the condition that should have been true but was
 -not, and then it kills the program.  In C, using `assert()' looks this:
++
++File: gawk.info,  Node: Two-way I/O,  Next: TCP/IP Networking,  Prev: Array 
Sorting,  Up: Advanced Features
+ 
 -     #include <assert.h>
++12.3 Two-Way Communications with Another Process
++================================================
+ 
 -     int myfunc(int a, double b)
 -     {
 -          assert(a <= 5 && b >= 17.1);
 -          ...
 -     }
++     From: address@hidden (Mike Brennan)
++     Newsgroups: comp.lang.awk
++     Subject: Re: Learn the SECRET to Attract Women Easily
++     Date: 4 Aug 1997 17:34:46 GMT
++     Message-ID: <address@hidden>
+ 
 -   If the assertion fails, the program prints a message similar to this:
++     On 3 Aug 1997 13:17:43 GMT, Want More Dates???
++     <address@hidden> wrote:
++     >Learn the SECRET to Attract Women Easily
++     >
++     >The SCENT(tm)  Pheromone Sex Attractant For Men to Attract Women
+ 
 -     prog.c:5: assertion failed: a <= 5 && b >= 17.1
++     The scent of awk programmers is a lot more attractive to women than
++     the scent of perl programmers.
++     --
++     Mike Brennan
+ 
 -   The C language makes it possible to turn the condition into a string
 -for use in printing the diagnostic message.  This is not possible in
 -`awk', so this `assert()' function also requires a string version of
 -the condition that is being tested.  Following is the function:
++   It is often useful to be able to send data to a separate program for
++processing and then read the result.  This can always be done with
++temporary files:
+ 
 -     # assert --- assert that a condition is true. Otherwise exit.
++     # Write the data for processing
++     tempfile = ("mydata." PROCINFO["pid"])
++     while (NOT DONE WITH DATA)
++         print DATA | ("subprogram > " tempfile)
++     close("subprogram > " tempfile)
+ 
 -     function assert(condition, string)
 -     {
 -         if (! condition) {
 -             printf("%s:%d: assertion failed: %s\n",
 -                 FILENAME, FNR, string) > "/dev/stderr"
 -             _assert_exit = 1
 -             exit 1
 -         }
 -     }
++     # Read the results, remove tempfile when done
++     while ((getline newdata < tempfile) > 0)
++         PROCESS newdata APPROPRIATELY
++     close(tempfile)
++     system("rm " tempfile)
+ 
 -     END {
 -         if (_assert_exit)
 -             exit 1
 -     }
++This works, but not elegantly.  Among other things, it requires that
++the program be run in a directory that cannot be shared among users;
++for example, `/tmp' will not do, as another user might happen to be
++using a temporary file with the same name.
+ 
 -   The `assert()' function tests the `condition' parameter. If it is
 -false, it prints a message to standard error, using the `string'
 -parameter to describe the failed condition.  It then sets the variable
 -`_assert_exit' to one and executes the `exit' statement.  The `exit'
 -statement jumps to the `END' rule. If the `END' rules finds
 -`_assert_exit' to be true, it exits immediately.
++   However, with `gawk', it is possible to open a _two-way_ pipe to
++another process.  The second process is termed a "coprocess", since it
++runs in parallel with `gawk'.  The two-way connection is created using
++the `|&' operator (borrowed from the Korn shell, `ksh'):(1)
+ 
 -   The purpose of the test in the `END' rule is to keep any other `END'
 -rules from running.  When an assertion fails, the program should exit
 -immediately.  If no assertions fail, then `_assert_exit' is still false
 -when the `END' rule is run normally, and the rest of the program's
 -`END' rules execute.  For all of this to work correctly, `assert.awk'
 -must be the first source file read by `awk'.  The function can be used
 -in a program in the following way:
++     do {
++         print DATA |& "subprogram"
++         "subprogram" |& getline results
++     } while (DATA LEFT TO PROCESS)
++     close("subprogram")
+ 
 -     function myfunc(a, b)
 -     {
 -          assert(a <= 5 && b >= 17.1, "a <= 5 && b >= 17.1")
 -          ...
++   The first time an I/O operation is executed using the `|&' operator,
++`gawk' creates a two-way pipeline to a child process that runs the
++other program.  Output created with `print' or `printf' is written to
++the program's standard input, and output from the program's standard
++output can be read by the `gawk' program using `getline'.  As is the
++case with processes started by `|', the subprogram can be any program,
++or pipeline of programs, that can be started by the shell.
++
++   There are some cautionary items to be aware of:
++
++   * As the code inside `gawk' currently stands, the coprocess's
++     standard error goes to the same place that the parent `gawk''s
++     standard error goes. It is not possible to read the child's
++     standard error separately.
++
++   * I/O buffering may be a problem.  `gawk' automatically flushes all
++     output down the pipe to the coprocess.  However, if the coprocess
++     does not flush its output, `gawk' may hang when doing a `getline'
++     in order to read the coprocess's results.  This could lead to a
++     situation known as "deadlock", where each process is waiting for
++     the other one to do something.
++
++   It is possible to close just one end of the two-way pipe to a
++coprocess, by supplying a second argument to the `close()' function of
++either `"to"' or `"from"' (*note Close Files And Pipes::).  These
++strings tell `gawk' to close the end of the pipe that sends data to the
++coprocess or the end that reads from it, respectively.
++
++   This is particularly necessary in order to use the system `sort'
++utility as part of a coprocess; `sort' must read _all_ of its input
++data before it can produce any output.  The `sort' program does not
++receive an end-of-file indication until `gawk' closes the write end of
++the pipe.
++
++   When you have finished writing data to the `sort' utility, you can
++close the `"to"' end of the pipe, and then start reading sorted data
++via `getline'.  For example:
++
++     BEGIN {
++         command = "LC_ALL=C sort"
++         n = split("abcdefghijklmnopqrstuvwxyz", a, "")
++
++         for (i = n; i > 0; i--)
++             print a[i] |& command
++         close(command, "to")
++
++         while ((command |& getline line) > 0)
++             print "got", line
++         close(command)
+      }
+ 
 -If the assertion fails, you see a message similar to the following:
++   This program writes the letters of the alphabet in reverse order, one
++per line, down the two-way pipe to `sort'.  It then closes the write
++end of the pipe, so that `sort' receives an end-of-file indication.
++This causes `sort' to sort the data and write the sorted data back to
++the `gawk' program.  Once all of the data has been read, `gawk'
++terminates the coprocess and exits.
+ 
 -     mydata:1357: assertion failed: a <= 5 && b >= 17.1
++   As a side note, the assignment `LC_ALL=C' in the `sort' command
++ensures traditional Unix (ASCII) sorting from `sort'.
+ 
 -   There is a small problem with this version of `assert()'.  An `END'
 -rule is automatically added to the program calling `assert()'.
 -Normally, if a program consists of just a `BEGIN' rule, the input files
 -and/or standard input are not read. However, now that the program has
 -an `END' rule, `awk' attempts to read the input data files or standard
 -input (*note Using BEGIN/END::), most likely causing the program to
 -hang as it waits for input.
++   You may also use pseudo-ttys (ptys) for two-way communication
++instead of pipes, if your system supports them.  This is done on a
++per-command basis, by setting a special element in the `PROCINFO' array
++(*note Auto-set::), like so:
+ 
 -   There is a simple workaround to this: make sure that such a `BEGIN'
 -rule always ends with an `exit' statement.
++     command = "sort -nr"           # command, save in convenience variable
++     PROCINFO[command, "pty"] = 1   # update PROCINFO
++     print ... |& command       # start two-way pipe
++     ...
++
++Using ptys avoids the buffer deadlock issues described earlier, at some
++loss in performance.  If your system does not have ptys, or if all the
++system's ptys are in use, `gawk' automatically falls back to using
++regular pipes.
++
++   ---------- Footnotes ----------
++
++   (1) This is very different from the same operator in the C shell.
+ 
+ 
 -File: gawk.info,  Node: Round Function,  Next: Cliff Random Function,  Prev: 
Assert Function,  Up: General Functions
++File: gawk.info,  Node: TCP/IP Networking,  Next: Profiling,  Prev: Two-way 
I/O,  Up: Advanced Features
+ 
 -12.2.3 Rounding Numbers
 ------------------------
++12.4 Using `gawk' for Network Programming
++=========================================
+ 
 -The way `printf' and `sprintf()' (*note Printf::) perform rounding
 -often depends upon the system's C `sprintf()' subroutine.  On many
 -machines, `sprintf()' rounding is "unbiased," which means it doesn't
 -always round a trailing `.5' up, contrary to naive expectations.  In
 -unbiased rounding, `.5' rounds to even, rather than always up, so 1.5
 -rounds to 2 but 4.5 rounds to 4.  This means that if you are using a
 -format that does rounding (e.g., `"%.0f"'), you should check what your
 -system does.  The following function does traditional rounding; it
 -might be useful if your `awk''s `printf' does unbiased rounding:
++     `EMISTERED':
++     A host is a host from coast to coast,
++     and no-one can talk to host that's close,
++     unless the host that isn't close
++     is busy hung or dead.
+ 
 -     # round.awk --- do normal rounding
++   In addition to being able to open a two-way pipeline to a coprocess
++on the same system (*note Two-way I/O::), it is possible to make a
++two-way connection to another process on another system across an IP
++network connection.
+ 
 -     function round(x,   ival, aval, fraction)
 -     {
 -        ival = int(x)    # integer part, int() truncates
++   You can think of this as just a _very long_ two-way pipeline to a
++coprocess.  The way `gawk' decides that you want to use TCP/IP
++networking is by recognizing special file names that begin with one of
++`/inet/', `/inet4/' or `/inet6'.
+ 
 -        # see if fractional part
 -        if (ival == x)   # no fraction
 -           return ival   # ensure no decimals
++   The full syntax of the special file name is
++`/NET-TYPE/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'.  The
++components are:
+ 
 -        if (x < 0) {
 -           aval = -x     # absolute value
 -           ival = int(aval)
 -           fraction = aval - ival
 -           if (fraction >= .5)
 -              return int(x) - 1   # -2.5 --> -3
 -           else
 -              return int(x)       # -2.3 --> -2
 -        } else {
 -           fraction = x - ival
 -           if (fraction >= .5)
 -              return ival + 1
 -           else
 -              return ival
 -        }
 -     }
++NET-TYPE
++     Specifies the kind of Internet connection to make.  Use `/inet4/'
++     to force IPv4, and `/inet6/' to force IPv6.  Plain `/inet/' (which
++     used to be the only option) uses the system default, most likely
++     IPv4.
+ 
 -     # test harness
 -     { print $0, round($0) }
++PROTOCOL
++     The protocol to use over IP.  This must be either `tcp', or `udp',
++     for a TCP or UDP IP connection, respectively.  The use of TCP is
++     recommended for most applications.
+ 
 -
 -File: gawk.info,  Node: Cliff Random Function,  Next: Ordinal Functions,  
Prev: Round Function,  Up: General Functions
++LOCAL-PORT
++     The local TCP or UDP port number to use.  Use a port number of `0'
++     when you want the system to pick a port. This is what you should do
++     when writing a TCP or UDP client.  You may also use a well-known
++     service name, such as `smtp' or `http', in which case `gawk'
++     attempts to determine the predefined port number using the C
++     `getaddrinfo()' function.
+ 
 -12.2.4 The Cliff Random Number Generator
 -----------------------------------------
++REMOTE-HOST
++     The IP address or fully-qualified domain name of the Internet host
++     to which you want to connect.
+ 
 -The Cliff random number generator
 -(http://mathworld.wolfram.com/CliffRandomNumberGenerator.html) is a
 -very simple random number generator that "passes the noise sphere test
 -for randomness by showing no structure."  It is easily programmed, in
 -less than 10 lines of `awk' code:
++REMOTE-PORT
++     The TCP or UDP port number to use on the given REMOTE-HOST.
++     Again, use `0' if you don't care, or else a well-known service
++     name.
+ 
 -     # cliff_rand.awk --- generate Cliff random numbers
++     NOTE: Failure in opening a two-way socket will result in a
++     non-fatal error being returned to the calling code. The value of
++     `ERRNO' indicates the error (*note Auto-set::).
+ 
 -     BEGIN { _cliff_seed = 0.1 }
++   Consider the following very simple example:
+ 
 -     function cliff_rand()
 -     {
 -         _cliff_seed = (100 * log(_cliff_seed)) % 1
 -         if (_cliff_seed < 0)
 -             _cliff_seed = - _cliff_seed
 -         return _cliff_seed
++     BEGIN {
++       Service = "/inet/tcp/0/localhost/daytime"
++       Service |& getline
++       print $0
++       close(Service)
+      }
+ 
 -   This algorithm requires an initial "seed" of 0.1.  Each new value
 -uses the current seed as input for the calculation.  If the built-in
 -`rand()' function (*note Numeric Functions::) isn't random enough, you
 -might try using this function instead.
++   This program reads the current date and time from the local system's
++TCP `daytime' server.  It then prints the results and closes the
++connection.
++
++   Because this topic is extensive, the use of `gawk' for TCP/IP
++programming is documented separately.  See *note (General
++Introduction)Top:: gawkinet, TCP/IP Internetworking with `gawk', for a
++much more complete introduction and discussion, as well as extensive
++examples.
+ 
+ 
 -File: gawk.info,  Node: Ordinal Functions,  Next: Join Function,  Prev: Cliff 
Random Function,  Up: General Functions
++File: gawk.info,  Node: Profiling,  Prev: TCP/IP Networking,  Up: Advanced 
Features
+ 
 -12.2.5 Translating Between Characters and Numbers
 --------------------------------------------------
++12.5 Profiling Your `awk' Programs
++==================================
+ 
 -One commercial implementation of `awk' supplies a built-in function,
 -`ord()', which takes a character and returns the numeric value for that
 -character in the machine's character set.  If the string passed to
 -`ord()' has more than one character, only the first one is used.
++You may produce execution traces of your `awk' programs.  This is done
++by passing the option `--profile' to `gawk'.  When `gawk' has finished
++running, it creates a profile of your program in a file named
++`awkprof.out'. Because it is profiling, it also executes up to 45%
++slower than `gawk' normally does.
+ 
 -   The inverse of this function is `chr()' (from the function of the
 -same name in Pascal), which takes a number and returns the
 -corresponding character.  Both functions are written very nicely in
 -`awk'; there is no real reason to build them into the `awk' interpreter:
++   As shown in the following example, the `--profile' option can be
++used to change the name of the file where `gawk' will write the profile:
+ 
 -     # ord.awk --- do ord and chr
++     gawk --profile=myprog.prof -f myprog.awk data1 data2
+ 
 -     # Global identifiers:
 -     #    _ord_:        numerical values indexed by characters
 -     #    _ord_init:    function to initialize _ord_
++In the above example, `gawk' places the profile in `myprog.prof'
++instead of in `awkprof.out'.
+ 
 -     BEGIN    { _ord_init() }
++   Here is a sample session showing a simple `awk' program, its input
++data, and the results from running `gawk' with the `--profile' option.
++First, the `awk' program:
+ 
 -     function _ord_init(    low, high, i, t)
 -     {
 -         low = sprintf("%c", 7) # BEL is ascii 7
 -         if (low == "\a") {    # regular ascii
 -             low = 0
 -             high = 127
 -         } else if (sprintf("%c", 128 + 7) == "\a") {
 -             # ascii, mark parity
 -             low = 128
 -             high = 255
 -         } else {        # ebcdic(!)
 -             low = 0
 -             high = 255
 -         }
 -
 -         for (i = low; i <= high; i++) {
 -             t = sprintf("%c", i)
 -             _ord_[t] = i
 -         }
 -     }
++     BEGIN { print "First BEGIN rule" }
+ 
 -   Some explanation of the numbers used by `chr' is worthwhile.  The
 -most prominent character set in use today is ASCII.(1) Although an
 -8-bit byte can hold 256 distinct values (from 0 to 255), ASCII only
 -defines characters that use the values from 0 to 127.(2) In the now
 -distant past, at least one minicomputer manufacturer used ASCII, but
 -with mark parity, meaning that the leftmost bit in the byte is always
 -1.  This means that on those systems, characters have numeric values
 -from 128 to 255.  Finally, large mainframe systems use the EBCDIC
 -character set, which uses all 256 values.  While there are other
 -character sets in use on some older systems, they are not really worth
 -worrying about:
++     END { print "First END rule" }
+ 
 -     function ord(str,    c)
 -     {
 -         # only first character is of interest
 -         c = substr(str, 1, 1)
 -         return _ord_[c]
++     /foo/ {
++         print "matched /foo/, gosh"
++         for (i = 1; i <= 3; i++)
++             sing()
+      }
+ 
 -     function chr(c)
+      {
 -         # force c to be numeric by adding 0
 -         return sprintf("%c", c + 0)
++         if (/foo/)
++             print "if is true"
++         else
++             print "else is true"
+      }
+ 
 -     #### test code ####
 -     # BEGIN    \
 -     # {
 -     #    for (;;) {
 -     #        printf("enter a character: ")
 -     #        if (getline var <= 0)
 -     #            break
 -     #        printf("ord(%s) = %d\n", var, ord(var))
 -     #    }
 -     # }
++     BEGIN { print "Second BEGIN rule" }
+ 
 -   An obvious improvement to these functions is to move the code for the
 -`_ord_init' function into the body of the `BEGIN' rule.  It was written
 -this way initially for ease of development.  There is a "test program"
 -in a `BEGIN' rule, to test the function.  It is commented out for
 -production use.
++     END { print "Second END rule" }
+ 
 -   ---------- Footnotes ----------
++     function sing(    dummy)
++     {
++         print "I gotta be me!"
++     }
+ 
 -   (1) This is changing; many systems use Unicode, a very large
 -character set that includes ASCII as a subset.  On systems with full
 -Unicode support, a character can occupy up to 32 bits, making simple
 -tests such as used here prohibitively expensive.
++   Following is the input data:
+ 
 -   (2) ASCII has been extended in many countries to use the values from
 -128 to 255 for country-specific characters.  If your  system uses these
 -extensions, you can simplify `_ord_init' to loop from 0 to 255.
++     foo
++     bar
++     baz
++     foo
++     junk
+ 
 -
 -File: gawk.info,  Node: Join Function,  Next: Gettimeofday Function,  Prev: 
Ordinal Functions,  Up: General Functions
++   Here is the `awkprof.out' that results from running the `gawk'
++profiler on this program and data (this example also illustrates that
++`awk' programmers sometimes have to work late):
+ 
 -12.2.6 Merging an Array into a String
 --------------------------------------
++             # gawk profile, created Sun Aug 13 00:00:15 2000
+ 
 -When doing string processing, it is often useful to be able to join all
 -the strings in an array into one long string.  The following function,
 -`join()', accomplishes this task.  It is used later in several of the
 -application programs (*note Sample Programs::).
++             # BEGIN block(s)
+ 
 -   Good function design is important; this function needs to be general
 -but it should also have a reasonable default behavior.  It is called
 -with an array as well as the beginning and ending indices of the
 -elements in the array to be merged.  This assumes that the array
 -indices are numeric--a reasonable assumption since the array was likely
 -created with `split()' (*note String Functions::):
++             BEGIN {
++          1          print "First BEGIN rule"
++          1          print "Second BEGIN rule"
++             }
+ 
 -     # join.awk --- join an array into a string
++             # Rule(s)
+ 
 -     function join(array, start, end, sep,    result, i)
 -     {
 -         if (sep == "")
 -            sep = " "
 -         else if (sep == SUBSEP) # magic value
 -            sep = ""
 -         result = array[start]
 -         for (i = start + 1; i <= end; i++)
 -             result = result sep array[i]
 -         return result
 -     }
++          5  /foo/   { # 2
++          2          print "matched /foo/, gosh"
++          6          for (i = 1; i <= 3; i++) {
++          6                  sing()
++                     }
++             }
+ 
 -   An optional additional argument is the separator to use when joining
 -the strings back together.  If the caller supplies a nonempty value,
 -`join()' uses it; if it is not supplied, it has a null value.  In this
 -case, `join()' uses a single space as a default separator for the
 -strings.  If the value is equal to `SUBSEP', then `join()' joins the
 -strings with no separator between them.  `SUBSEP' serves as a "magic"
 -value to indicate that there should be no separation between the
 -component strings.(1)
++          5  {
++          5          if (/foo/) { # 2
++          2                  print "if is true"
++          3          } else {
++          3                  print "else is true"
++                     }
++             }
+ 
 -   ---------- Footnotes ----------
++             # END block(s)
+ 
 -   (1) It would be nice if `awk' had an assignment operator for
 -concatenation.  The lack of an explicit operator for concatenation
 -makes string operations more difficult than they really need to be.
++             END {
++          1          print "First END rule"
++          1          print "Second END rule"
++             }
+ 
 -
 -File: gawk.info,  Node: Gettimeofday Function,  Prev: Join Function,  Up: 
General Functions
++             # Functions, listed alphabetically
+ 
 -12.2.7 Managing the Time of Day
 --------------------------------
++          6  function sing(dummy)
++             {
++          6          print "I gotta be me!"
++             }
+ 
 -The `systime()' and `strftime()' functions described in *note Time
 -Functions::, provide the minimum functionality necessary for dealing
 -with the time of day in human readable form.  While `strftime()' is
 -extensive, the control formats are not necessarily easy to remember or
 -intuitively obvious when reading a program.
++   This example illustrates many of the basic features of profiling
++output.  They are as follows:
+ 
 -   The following function, `gettimeofday()', populates a user-supplied
 -array with preformatted time information.  It returns a string with the
 -current time formatted in the same way as the `date' utility:
++   * The program is printed in the order `BEGIN' rule, `BEGINFILE' rule,
++     pattern/action rules, `ENDFILE' rule, `END' rule and functions,
++     listed alphabetically.  Multiple `BEGIN' and `END' rules are
++     merged together, as are multiple `BEGINFILE' and `ENDFILE' rules.
+ 
 -     # gettimeofday.awk --- get the time of day in a usable format
++   * Pattern-action rules have two counts.  The first count, to the
++     left of the rule, shows how many times the rule's pattern was
++     _tested_.  The second count, to the right of the rule's opening
++     left brace in a comment, shows how many times the rule's action
++     was _executed_.  The difference between the two indicates how many
++     times the rule's pattern evaluated to false.
+ 
 -     # Returns a string in the format of output of date(1)
 -     # Populates the array argument time with individual values:
 -     #    time["second"]       -- seconds (0 - 59)
 -     #    time["minute"]       -- minutes (0 - 59)
 -     #    time["hour"]         -- hours (0 - 23)
 -     #    time["althour"]      -- hours (0 - 12)
 -     #    time["monthday"]     -- day of month (1 - 31)
 -     #    time["month"]        -- month of year (1 - 12)
 -     #    time["monthname"]    -- name of the month
 -     #    time["shortmonth"]   -- short name of the month
 -     #    time["year"]         -- year modulo 100 (0 - 99)
 -     #    time["fullyear"]     -- full year
 -     #    time["weekday"]      -- day of week (Sunday = 0)
 -     #    time["altweekday"]   -- day of week (Monday = 0)
 -     #    time["dayname"]      -- name of weekday
 -     #    time["shortdayname"] -- short name of weekday
 -     #    time["yearday"]      -- day of year (0 - 365)
 -     #    time["timezone"]     -- abbreviation of timezone name
 -     #    time["ampm"]         -- AM or PM designation
 -     #    time["weeknum"]      -- week number, Sunday first day
 -     #    time["altweeknum"]   -- week number, Monday first day
++   * Similarly, the count for an `if'-`else' statement shows how many
++     times the condition was tested.  To the right of the opening left
++     brace for the `if''s body is a count showing how many times the
++     condition was true.  The count for the `else' indicates how many
++     times the test failed.
+ 
 -     function gettimeofday(time,    ret, now, i)
 -     {
 -         # get time once, avoids unnecessary system calls
 -         now = systime()
++   * The count for a loop header (such as `for' or `while') shows how
++     many times the loop test was executed.  (Because of this, you
++     can't just look at the count on the first statement in a rule to
++     determine how many times the rule was executed.  If the first
++     statement is a loop, the count is misleading.)
+ 
 -         # return date(1)-style output
 -         ret = strftime("%a %b %e %H:%M:%S %Z %Y", now)
++   * For user-defined functions, the count next to the `function'
++     keyword indicates how many times the function was called.  The
++     counts next to the statements in the body show how many times
++     those statements were executed.
+ 
 -         # clear out target array
 -         delete time
++   * The layout uses "K&R" style with TABs.  Braces are used
++     everywhere, even when the body of an `if', `else', or loop is only
++     a single statement.
+ 
 -         # fill in values, force numeric values to be
 -         # numeric by adding 0
 -         time["second"]       = strftime("%S", now) + 0
 -         time["minute"]       = strftime("%M", now) + 0
 -         time["hour"]         = strftime("%H", now) + 0
 -         time["althour"]      = strftime("%I", now) + 0
 -         time["monthday"]     = strftime("%d", now) + 0
 -         time["month"]        = strftime("%m", now) + 0
 -         time["monthname"]    = strftime("%B", now)
 -         time["shortmonth"]   = strftime("%b", now)
 -         time["year"]         = strftime("%y", now) + 0
 -         time["fullyear"]     = strftime("%Y", now) + 0
 -         time["weekday"]      = strftime("%w", now) + 0
 -         time["altweekday"]   = strftime("%u", now) + 0
 -         time["dayname"]      = strftime("%A", now)
 -         time["shortdayname"] = strftime("%a", now)
 -         time["yearday"]      = strftime("%j", now) + 0
 -         time["timezone"]     = strftime("%Z", now)
 -         time["ampm"]         = strftime("%p", now)
 -         time["weeknum"]      = strftime("%U", now) + 0
 -         time["altweeknum"]   = strftime("%W", now) + 0
++   * Parentheses are used only where needed, as indicated by the
++     structure of the program and the precedence rules.  For example,
++     `(3 + 5) * 4' means add three plus five, then multiply the total
++     by four.  However, `3 + 5 * 4' has no parentheses, and means `3 +
++     (5 * 4)'.
+ 
 -         return ret
 -     }
++   * Parentheses are used around the arguments to `print' and `printf'
++     only when the `print' or `printf' statement is followed by a
++     redirection.  Similarly, if the target of a redirection isn't a
++     scalar, it gets parenthesized.
+ 
 -   The string indices are easier to use and read than the various
 -formats required by `strftime()'.  The `alarm' program presented in
 -*note Alarm Program::, uses this function.  A more general design for
 -the `gettimeofday()' function would have allowed the user to supply an
 -optional timestamp value to use instead of the current time.
++   * `gawk' supplies leading comments in front of the `BEGIN' and `END'
++     rules, the pattern/action rules, and the functions.
+ 
 -
 -File: gawk.info,  Node: Data File Management,  Next: Getopt Function,  Prev: 
General Functions,  Up: Library Functions
+ 
 -12.3 Data File Management
 -=========================
++   The profiled version of your program may not look exactly like what
++you typed when you wrote it.  This is because `gawk' creates the
++profiled version by "pretty printing" its internal representation of
++the program.  The advantage to this is that `gawk' can produce a
++standard representation.  The disadvantage is that all source-code
++comments are lost, as are the distinctions among multiple `BEGIN',
++`END', `BEGINFILE', and `ENDFILE' rules.  Also, things such as:
+ 
 -This minor node presents functions that are useful for managing
 -command-line data files.
++     /foo/
+ 
 -* Menu:
++come out as:
+ 
 -* Filetrans Function::          A function for handling data file transitions.
 -* Rewind Function::             A function for rereading the current file.
 -* File Checking::               Checking that data files are readable.
 -* Empty Files::                 Checking for zero-length files.
 -* Ignoring Assigns::            Treating assignments as file names.
++     /foo/   {
++         print $0
++     }
+ 
 -
 -File: gawk.info,  Node: Filetrans Function,  Next: Rewind Function,  Up: Data 
File Management
++which is correct, but possibly surprising.
+ 
 -12.3.1 Noting Data File Boundaries
 -----------------------------------
++   Besides creating profiles when a program has completed, `gawk' can
++produce a profile while it is running.  This is useful if your `awk'
++program goes into an infinite loop and you want to see what has been
++executed.  To use this feature, run `gawk' with the `--profile' option
++in the background:
+ 
 -The `BEGIN' and `END' rules are each executed exactly once at the
 -beginning and end of your `awk' program, respectively (*note
 -BEGIN/END::).  We (the `gawk' authors) once had a user who mistakenly
 -thought that the `BEGIN' rule is executed at the beginning of each data
 -file and the `END' rule is executed at the end of each data file.
++     $ gawk --profile -f myprog &
++     [1] 13992
+ 
 -   When informed that this was not the case, the user requested that we
 -add new special patterns to `gawk', named `BEGIN_FILE' and `END_FILE',
 -that would have the desired behavior.  He even supplied us the code to
 -do so.
++The shell prints a job number and process ID number; in this case,
++13992.  Use the `kill' command to send the `USR1' signal to `gawk':
+ 
 -   Adding these special patterns to `gawk' wasn't necessary; the job
 -can be done cleanly in `awk' itself, as illustrated by the following
 -library program.  It arranges to call two user-supplied functions,
 -`beginfile()' and `endfile()', at the beginning and end of each data
 -file.  Besides solving the problem in only nine(!) lines of code, it
 -does so _portably_; this works with any implementation of `awk':
++     $ kill -USR1 13992
+ 
 -     # transfile.awk
 -     #
 -     # Give the user a hook for filename transitions
 -     #
 -     # The user must supply functions beginfile() and endfile()
 -     # that each take the name of the file being started or
 -     # finished, respectively.
++As usual, the profiled version of the program is written to
++`awkprof.out', or to a different file if one specified with the
++`--profile' option.
+ 
 -     FILENAME != _oldfilename \
 -     {
 -         if (_oldfilename != "")
 -             endfile(_oldfilename)
 -         _oldfilename = FILENAME
 -         beginfile(FILENAME)
 -     }
++   Along with the regular profile, as shown earlier, the profile
++includes a trace of any active functions:
+ 
 -     END   { endfile(FILENAME) }
++     # Function Call Stack:
+ 
 -   This file must be loaded before the user's "main" program, so that
 -the rule it supplies is executed first.
++     #   3. baz
++     #   2. bar
++     #   1. foo
++     # -- main --
+ 
 -   This rule relies on `awk''s `FILENAME' variable that automatically
 -changes for each new data file.  The current file name is saved in a
 -private variable, `_oldfilename'.  If `FILENAME' does not equal
 -`_oldfilename', then a new data file is being processed and it is
 -necessary to call `endfile()' for the old file.  Because `endfile()'
 -should only be called if a file has been processed, the program first
 -checks to make sure that `_oldfilename' is not the null string.  The
 -program then assigns the current file name to `_oldfilename' and calls
 -`beginfile()' for the file.  Because, like all `awk' variables,
 -`_oldfilename' is initialized to the null string, this rule executes
 -correctly even for the first data file.
++   You may send `gawk' the `USR1' signal as many times as you like.
++Each time, the profile and function call trace are appended to the
++output profile file.
+ 
 -   The program also supplies an `END' rule to do the final processing
 -for the last file.  Because this `END' rule comes before any `END' rules
 -supplied in the "main" program, `endfile()' is called first.  Once
 -again the value of multiple `BEGIN' and `END' rules should be clear.
++   If you use the `HUP' signal instead of the `USR1' signal, `gawk'
++produces the profile and the function call trace and then exits.
+ 
 -   If the same data file occurs twice in a row on the command line, then
 -`endfile()' and `beginfile()' are not executed at the end of the first
 -pass and at the beginning of the second pass.  The following version
 -solves the problem:
++   When `gawk' runs on MS-Windows systems, it uses the `INT' and `QUIT'
++signals for producing the profile and, in the case of the `INT' signal,
++`gawk' exits.  This is because these systems don't support the `kill'
++command, so the only signals you can deliver to a program are those
++generated by the keyboard.  The `INT' signal is generated by the
++`Ctrl-<C>' or `Ctrl-<BREAK>' key, while the `QUIT' signal is generated
++by the `Ctrl-<\>' key.
+ 
 -     # ftrans.awk --- handle data file transitions
 -     #
 -     # user supplies beginfile() and endfile() functions
++   Finally, `gawk' also accepts another option `--pretty-print'.  When
++called this way, `gawk' "pretty prints" the program into `awkprof.out',
++without any execution counts.
+ 
 -     FNR == 1 {
 -         if (_filename_ != "")
 -             endfile(_filename_)
 -         _filename_ = FILENAME
 -         beginfile(FILENAME)
 -     }
++
++File: gawk.info,  Node: Library Functions,  Next: Sample Programs,  Prev: 
Advanced Features,  Up: Top
+ 
 -     END  { endfile(_filename_) }
++13 A Library of `awk' Functions
++*******************************
+ 
 -   *note Wc Program::, shows how this library function can be used and
 -how it simplifies writing the main program.
++*note User-defined::, describes how to write your own `awk' functions.
++Writing functions is important, because it allows you to encapsulate
++algorithms and program tasks in a single place.  It simplifies
++programming, making program development more manageable, and making
++programs more readable.
+ 
 -Advanced Notes: So Why Does `gawk' have `BEGINFILE' and `ENDFILE'?
 -------------------------------------------------------------------
++   One valuable way to learn a new programming language is to _read_
++programs in that language.  To that end, this major node and *note
++Sample Programs::, provide a good-sized body of code for you to read,
++and hopefully, to learn from.
+ 
 -You are probably wondering, if `beginfile()' and `endfile()' functions
 -can do the job, why does `gawk' have `BEGINFILE' and `ENDFILE' patterns
 -(*note BEGINFILE/ENDFILE::)?
++   This major node presents a library of useful `awk' functions.  Many
++of the sample programs presented later in this Info file use these
++functions.  The functions are presented here in a progression from
++simple to complex.
+ 
 -   Good question.  Normally, if `awk' cannot open a file, this causes
 -an immediate fatal error.  In this case, there is no way for a
 -user-defined function to deal with the problem, since the mechanism for
 -calling it relies on the file being open and at the first record.  Thus,
 -the main reason for `BEGINFILE' is to give you a "hook" to catch files
 -that cannot be processed.  `ENDFILE' exists for symmetry, and because
 -it provides an easy way to do per-file cleanup processing.
++   *note Extract Program::, presents a program that you can use to
++extract the source code for these example library functions and
++programs from the Texinfo source for this Info file.  (This has already
++been done as part of the `gawk' distribution.)
+ 
 -
 -File: gawk.info,  Node: Rewind Function,  Next: File Checking,  Prev: 
Filetrans Function,  Up: Data File Management
++   If you have written one or more useful, general-purpose `awk'
++functions and would like to contribute them to the `awk' user
++community, see *note How To Contribute::, for more information.
+ 
 -12.3.2 Rereading the Current File
 ----------------------------------
++   The programs in this major node and in *note Sample Programs::,
++freely use features that are `gawk'-specific.  Rewriting these programs
++for different implementations of `awk' is pretty straightforward.
+ 
 -Another request for a new built-in function was for a `rewind()'
 -function that would make it possible to reread the current file.  The
 -requesting user didn't want to have to use `getline' (*note Getline::)
 -inside a loop.
++   * Diagnostic error messages are sent to `/dev/stderr'.  Use `| "cat
++     1>&2"' instead of `> "/dev/stderr"' if your system does not have a
++     `/dev/stderr', or if you cannot use `gawk'.
+ 
 -   However, as long as you are not in the `END' rule, it is quite easy
 -to arrange to immediately close the current input file and then start
 -over with it from the top.  For lack of a better name, we'll call it
 -`rewind()':
++   * A number of programs use `nextfile' (*note Nextfile Statement::)
++     to skip any remaining input in the input file.
+ 
 -     # rewind.awk --- rewind the current file and start over
++   * Finally, some of the programs choose to ignore upper- and lowercase
++     distinctions in their input. They do so by assigning one to
++     `IGNORECASE'.  You can achieve almost the same effect(1) by adding
++     the following rule to the beginning of the program:
+ 
 -     function rewind(    i)
 -     {
 -         # shift remaining arguments up
 -         for (i = ARGC; i > ARGIND; i--)
 -             ARGV[i] = ARGV[i-1]
++          # ignore case
++          { $0 = tolower($0) }
+ 
 -         # make sure gawk knows to keep going
 -         ARGC++
++     Also, verify that all regexp and string constants used in
++     comparisons use only lowercase letters.
+ 
 -         # make current file next to get done
 -         ARGV[ARGIND+1] = FILENAME
++* Menu:
+ 
 -         # do it
 -         nextfile
 -     }
++* Library Names::               How to best name private global variables in
++                                library functions.
++* General Functions::           Functions that are of general use.
++* Data File Management::        Functions for managing command-line data
++                                files.
++* Getopt Function::             A function for processing command-line
++                                arguments.
++* Passwd Functions::            Functions for getting user information.
++* Group Functions::             Functions for getting group information.
++* Walking Arrays::              A function to walk arrays of arrays.
+ 
 -   This code relies on the `ARGIND' variable (*note Auto-set::), which
 -is specific to `gawk'.  If you are not using `gawk', you can use ideas
 -presented in *note Filetrans Function::, to either update `ARGIND' on
 -your own or modify this code as appropriate.
++   ---------- Footnotes ----------
+ 
 -   The `rewind()' function also relies on the `nextfile' keyword (*note
 -Nextfile Statement::).
++   (1) The effects are not identical.  Output of the transformed record
++will be in all lowercase, while `IGNORECASE' preserves the original
++contents of the input record.
+ 
+ 
 -File: gawk.info,  Node: File Checking,  Next: Empty Files,  Prev: Rewind 
Function,  Up: Data File Management
++File: gawk.info,  Node: Library Names,  Next: General Functions,  Up: Library 
Functions
+ 
 -12.3.3 Checking for Readable Data Files
 ----------------------------------------
++13.1 Naming Library Function Global Variables
++=============================================
+ 
 -Normally, if you give `awk' a data file that isn't readable, it stops
 -with a fatal error.  There are times when you might want to just ignore
 -such files and keep going.  You can do this by prepending the following
 -program to your `awk' program:
++Due to the way the `awk' language evolved, variables are either
++"global" (usable by the entire program) or "local" (usable just by a
++specific function).  There is no intermediate state analogous to
++`static' variables in C.
+ 
 -     # readable.awk --- library file to skip over unreadable files
++   Library functions often need to have global variables that they can
++use to preserve state information between calls to the function--for
++example, `getopt()''s variable `_opti' (*note Getopt Function::).  Such
++variables are called "private", since the only functions that need to
++use them are the ones in the library.
+ 
 -     BEGIN {
 -         for (i = 1; i < ARGC; i++) {
 -             if (ARGV[i] ~ /^[[:alpha:]_][[:alnum:]_]*=.*/ \
 -                 || ARGV[i] == "-" || ARGV[i] == "/dev/stdin")
 -                 continue    # assignment or standard input
 -             else if ((getline junk < ARGV[i]) < 0) # unreadable
 -                 delete ARGV[i]
 -             else
 -                 close(ARGV[i])
 -         }
 -     }
++   When writing a library function, you should try to choose names for
++your private variables that will not conflict with any variables used by
++either another library function or a user's main program.  For example,
++a name like `i' or `j' is not a good choice, because user programs
++often use variable names like these for their own purposes.
+ 
 -   This works, because the `getline' won't be fatal.  Removing the
 -element from `ARGV' with `delete' skips the file (since it's no longer
 -in the list).  See also *note ARGC and ARGV::.
++   The example programs shown in this major node all start the names of
++their private variables with an underscore (`_').  Users generally
++don't use leading underscores in their variable names, so this
++convention immediately decreases the chances that the variable name
++will be accidentally shared with the user's program.
+ 
 -
 -File: gawk.info,  Node: Empty Files,  Next: Ignoring Assigns,  Prev: File 
Checking,  Up: Data File Management
++   In addition, several of the library functions use a prefix that helps
++indicate what function or set of functions use the variables--for
++example, `_pw_byname' in the user database routines (*note Passwd
++Functions::).  This convention is recommended, since it even further
++decreases the chance of inadvertent conflict among variable names.
++Note that this convention is used equally well for variable names and
++for private function names.(1)
+ 
 -12.3.4 Checking For Zero-length Files
 --------------------------------------
++   As a final note on variable naming, if a function makes global
++variables available for use by a main program, it is a good convention
++to start that variable's name with a capital letter--for example,
++`getopt()''s `Opterr' and `Optind' variables (*note Getopt Function::).
++The leading capital letter indicates that it is global, while the fact
++that the variable name is not all capital letters indicates that the
++variable is not one of `awk''s built-in variables, such as `FS'.
+ 
 -All known `awk' implementations silently skip over zero-length files.
 -This is a by-product of `awk''s implicit
 -read-a-record-and-match-against-the-rules loop: when `awk' tries to
 -read a record from an empty file, it immediately receives an end of
 -file indication, closes the file, and proceeds on to the next
 -command-line data file, _without_ executing any user-level `awk'
 -program code.
++   It is also important that _all_ variables in library functions that
++do not need to save state are, in fact, declared local.(2) If this is
++not done, the variable could accidentally be used in the user's
++program, leading to bugs that are very difficult to track down:
+ 
 -   Using `gawk''s `ARGIND' variable (*note Built-in Variables::), it is
 -possible to detect when an empty data file has been skipped.  Similar
 -to the library file presented in *note Filetrans Function::, the
 -following library file calls a function named `zerofile()' that the
 -user must provide.  The arguments passed are the file name and the
 -position in `ARGV' where it was found:
++     function lib_func(x, y,    l1, l2)
++     {
++         ...
++         USE VARIABLE some_var   # some_var should be local
++         ...                     # but is not by oversight
++     }
+ 
 -     # zerofile.awk --- library file to process empty input files
++   A different convention, common in the Tcl community, is to use a
++single associative array to hold the values needed by the library
++function(s), or "package."  This significantly decreases the number of
++actual global names in use.  For example, the functions described in
++*note Passwd Functions::, might have used array elements
++`PW_data["inited"]', `PW_data["total"]', `PW_data["count"]', and
++`PW_data["awklib"]', instead of `_pw_inited', `_pw_awklib', `_pw_total',
++and `_pw_count'.
+ 
 -     BEGIN { Argind = 0 }
++   The conventions presented in this minor node are exactly that:
++conventions. You are not required to write your programs this way--we
++merely recommend that you do so.
+ 
 -     ARGIND > Argind + 1 {
 -         for (Argind++; Argind < ARGIND; Argind++)
 -             zerofile(ARGV[Argind], Argind)
 -     }
++   ---------- Footnotes ----------
+ 
 -     ARGIND != Argind { Argind = ARGIND }
++   (1) While all the library routines could have been rewritten to use
++this convention, this was not done, in order to show how our own `awk'
++programming style has evolved and to provide some basis for this
++discussion.
+ 
 -     END {
 -         if (ARGIND > Argind)
 -             for (Argind++; Argind <= ARGIND; Argind++)
 -                 zerofile(ARGV[Argind], Argind)
 -     }
++   (2) `gawk''s `--dump-variables' command-line option is useful for
++verifying this.
+ 
 -   The user-level variable `Argind' allows the `awk' program to track
 -its progress through `ARGV'.  Whenever the program detects that
 -`ARGIND' is greater than `Argind + 1', it means that one or more empty
 -files were skipped.  The action then calls `zerofile()' for each such
 -file, incrementing `Argind' along the way.
++
++File: gawk.info,  Node: General Functions,  Next: Data File Management,  
Prev: Library Names,  Up: Library Functions
+ 
 -   The `Argind != ARGIND' rule simply keeps `Argind' up to date in the
 -normal case.
++13.2 General Programming
++========================
+ 
 -   Finally, the `END' rule catches the case of any empty files at the
 -end of the command-line arguments.  Note that the test in the condition
 -of the `for' loop uses the `<=' operator, not `<'.
++This minor node presents a number of functions that are of general
++programming use.
+ 
 -   As an exercise, you might consider whether this same problem can be
 -solved without relying on `gawk''s `ARGIND' variable.
++* Menu:
+ 
 -   As a second exercise, revise this code to handle the case where an
 -intervening value in `ARGV' is a variable assignment.
++* Strtonum Function::           A replacement for the built-in
++                                `strtonum()' function.
++* Assert Function::             A function for assertions in `awk'
++                                programs.
++* Round Function::              A function for rounding if `sprintf()'
++                                does not do it correctly.
++* Cliff Random Function::       The Cliff Random Number Generator.
++* Ordinal Functions::           Functions for using characters as numbers and
++                                vice versa.
++* Join Function::               A function to join an array into a string.
++* Getlocaltime Function::       A function to get formatted times.
+ 
+ 
 -File: gawk.info,  Node: Ignoring Assigns,  Prev: Empty Files,  Up: Data File 
Management
 -
 -12.3.5 Treating Assignments as File Names
 ------------------------------------------
++File: gawk.info,  Node: Strtonum Function,  Next: Assert Function,  Up: 
General Functions
+ 
 -Occasionally, you might not want `awk' to process command-line variable
 -assignments (*note Assignment Options::).  In particular, if you have a
 -file name that contain an `=' character, `awk' treats the file name as
 -an assignment, and does not process it.
++13.2.1 Converting Strings To Numbers
++------------------------------------
+ 
 -   Some users have suggested an additional command-line option for
 -`gawk' to disable command-line assignments.  However, some simple
 -programming with a library file does the trick:
++The `strtonum()' function (*note String Functions::) is a `gawk'
++extension.  The following function provides an implementation for other
++versions of `awk':
+ 
 -     # noassign.awk --- library file to avoid the need for a
 -     # special option that disables command-line assignments
++     # mystrtonum --- convert string to number
+ 
 -     function disable_assigns(argc, argv,    i)
++     function mystrtonum(str,        ret, chars, n, i, k, c)
+      {
 -         for (i = 1; i < argc; i++)
 -             if (argv[i] ~ /^[[:alpha:]_][[:alnum:]_]*=.*/)
 -                 argv[i] = ("./" argv[i])
 -     }
 -
 -     BEGIN {
 -         if (No_command_assign)
 -             disable_assigns(ARGC, ARGV)
 -     }
 -
 -   You then run your program this way:
++         if (str ~ /^0[0-7]*$/) {
++             # octal
++             n = length(str)
++             ret = 0
++             for (i = 1; i <= n; i++) {
++                 c = substr(str, i, 1)
++                 if ((k = index("01234567", c)) > 0)
++                     k-- # adjust for 1-basing in awk
+ 
 -     awk -v No_command_assign=1 -f noassign.awk -f yourprog.awk *
++                 ret = ret * 8 + k
++             }
++         } else if (str ~ /^0[xX][[:xdigit:]]+/) {
++             # hexadecimal
++             str = substr(str, 3)    # lop off leading 0x
++             n = length(str)
++             ret = 0
++             for (i = 1; i <= n; i++) {
++                 c = substr(str, i, 1)
++                 c = tolower(c)
++                 if ((k = index("0123456789", c)) > 0)
++                     k-- # adjust for 1-basing in awk
++                 else if ((k = index("abcdef", c)) > 0)
++                     k += 9
+ 
 -   The function works by looping through the arguments.  It prepends
 -`./' to any argument that matches the form of a variable assignment,
 -turning that argument into a file name.
++                 ret = ret * 16 + k
++             }
++         } else if (str ~ \
++       
/^[-+]?([0-9]+([.][0-9]*([Ee][0-9]+)?)?|([.][0-9]+([Ee][-+]?[0-9]+)?))$/) {
++             # decimal number, possibly floating point
++             ret = str + 0
++         } else
++             ret = "NOT-A-NUMBER"
+ 
 -   The use of `No_command_assign' allows you to disable command-line
 -assignments at invocation time, by giving the variable a true value.
 -When not set, it is initially zero (i.e., false), so the command-line
 -arguments are left alone.
++         return ret
++     }
+ 
 -
 -File: gawk.info,  Node: Getopt Function,  Next: Passwd Functions,  Prev: Data 
File Management,  Up: Library Functions
++     # BEGIN {     # gawk test harness
++     #     a[1] = "25"
++     #     a[2] = ".31"
++     #     a[3] = "0123"
++     #     a[4] = "0xdeadBEEF"
++     #     a[5] = "123.45"
++     #     a[6] = "1.e3"
++     #     a[7] = "1.32"
++     #     a[7] = "1.32E2"
++     #
++     #     for (i = 1; i in a; i++)
++     #         print a[i], strtonum(a[i]), mystrtonum(a[i])
++     # }
+ 
 -12.4 Processing Command-Line Options
 -====================================
++   The function first looks for C-style octal numbers (base 8).  If the
++input string matches a regular expression describing octal numbers,
++then `mystrtonum()' loops through each character in the string.  It
++sets `k' to the index in `"01234567"' of the current octal digit.
++Since the return value is one-based, the `k--' adjusts `k' so it can be
++used in computing the return value.
+ 
 -Most utilities on POSIX compatible systems take options on the command
 -line that can be used to change the way a program behaves.  `awk' is an
 -example of such a program (*note Options::).  Often, options take
 -"arguments"; i.e., data that the program needs to correctly obey the
 -command-line option.  For example, `awk''s `-F' option requires a
 -string to use as the field separator.  The first occurrence on the
 -command line of either `--' or a string that does not begin with `-'
 -ends the options.
++   Similar logic applies to the code that checks for and converts a
++hexadecimal value, which starts with `0x' or `0X'.  The use of
++`tolower()' simplifies the computation for finding the correct numeric
++value for each hexadecimal digit.
+ 
 -   Modern Unix systems provide a C function named `getopt()' for
 -processing command-line arguments.  The programmer provides a string
 -describing the one-letter options. If an option requires an argument,
 -it is followed in the string with a colon.  `getopt()' is also passed
 -the count and values of the command-line arguments and is called in a
 -loop.  `getopt()' processes the command-line arguments for option
 -letters.  Each time around the loop, it returns a single character
 -representing the next option letter that it finds, or `?' if it finds
 -an invalid option.  When it returns -1, there are no options left on
 -the command line.
++   Finally, if the string matches the (rather complicated) regexp for a
++regular decimal integer or floating-point number, the computation `ret
++= str + 0' lets `awk' convert the value to a number.
+ 
 -   When using `getopt()', options that do not take arguments can be
 -grouped together.  Furthermore, options that take arguments require
 -that the argument be present.  The argument can immediately follow the
 -option letter, or it can be a separate command-line argument.
++   A commented-out test program is included, so that the function can
++be tested with `gawk' and the results compared to the built-in
++`strtonum()' function.
+ 
 -   Given a hypothetical program that takes three command-line options,
 -`-a', `-b', and `-c', where `-b' requires an argument, all of the
 -following are valid ways of invoking the program:
++
++File: gawk.info,  Node: Assert Function,  Next: Round Function,  Prev: 
Strtonum Function,  Up: General Functions
+ 
 -     prog -a -b foo -c data1 data2 data3
 -     prog -ac -bfoo -- data1 data2 data3
 -     prog -acbfoo data1 data2 data3
++13.2.2 Assertions
++-----------------
+ 
 -   Notice that when the argument is grouped with its option, the rest of
 -the argument is considered to be the option's argument.  In this
 -example, `-acbfoo' indicates that all of the `-a', `-b', and `-c'
 -options were supplied, and that `foo' is the argument to the `-b'
 -option.
++When writing large programs, it is often useful to know that a
++condition or set of conditions is true.  Before proceeding with a
++particular computation, you make a statement about what you believe to
++be the case.  Such a statement is known as an "assertion".  The C
++language provides an `<assert.h>' header file and corresponding
++`assert()' macro that the programmer can use to make assertions.  If an
++assertion fails, the `assert()' macro arranges to print a diagnostic
++message describing the condition that should have been true but was
++not, and then it kills the program.  In C, using `assert()' looks this:
+ 
 -   `getopt()' provides four external variables that the programmer can
 -use:
++     #include <assert.h>
+ 
 -`optind'
 -     The index in the argument value array (`argv') where the first
 -     nonoption command-line argument can be found.
++     int myfunc(int a, double b)
++     {
++          assert(a <= 5 && b >= 17.1);
++          ...
++     }
+ 
 -`optarg'
 -     The string value of the argument to an option.
++   If the assertion fails, the program prints a message similar to this:
+ 
 -`opterr'
 -     Usually `getopt()' prints an error message when it finds an invalid
 -     option.  Setting `opterr' to zero disables this feature.  (An
 -     application might want to print its own error message.)
++     prog.c:5: assertion failed: a <= 5 && b >= 17.1
+ 
 -`optopt'
 -     The letter representing the command-line option.
++   The C language makes it possible to turn the condition into a string
++for use in printing the diagnostic message.  This is not possible in
++`awk', so this `assert()' function also requires a string version of
++the condition that is being tested.  Following is the function:
+ 
 -   The following C fragment shows how `getopt()' might process
 -command-line arguments for `awk':
++     # assert --- assert that a condition is true. Otherwise exit.
+ 
 -     int
 -     main(int argc, char *argv[])
++     function assert(condition, string)
+      {
 -         ...
 -         /* print our own message */
 -         opterr = 0;
 -         while ((c = getopt(argc, argv, "v:f:F:W:")) != -1) {
 -             switch (c) {
 -             case 'f':    /* file */
 -                 ...
 -                 break;
 -             case 'F':    /* field separator */
 -                 ...
 -                 break;
 -             case 'v':    /* variable assignment */
 -                 ...
 -                 break;
 -             case 'W':    /* extension */
 -                 ...
 -                 break;
 -             case '?':
 -             default:
 -                 usage();
 -                 break;
 -             }
++         if (! condition) {
++             printf("%s:%d: assertion failed: %s\n",
++                 FILENAME, FNR, string) > "/dev/stderr"
++             _assert_exit = 1
++             exit 1
+          }
 -         ...
+      }
+ 
 -   As a side point, `gawk' actually uses the GNU `getopt_long()'
 -function to process both normal and GNU-style long options (*note
 -Options::).
++     END {
++         if (_assert_exit)
++             exit 1
++     }
+ 
 -   The abstraction provided by `getopt()' is very useful and is quite
 -handy in `awk' programs as well.  Following is an `awk' version of
 -`getopt()'.  This function highlights one of the greatest weaknesses in
 -`awk', which is that it is very poor at manipulating single characters.
 -Repeated calls to `substr()' are necessary for accessing individual
 -characters (*note String Functions::).(1)
++   The `assert()' function tests the `condition' parameter. If it is
++false, it prints a message to standard error, using the `string'
++parameter to describe the failed condition.  It then sets the variable
++`_assert_exit' to one and executes the `exit' statement.  The `exit'
++statement jumps to the `END' rule. If the `END' rules finds
++`_assert_exit' to be true, it exits immediately.
+ 
 -   The discussion that follows walks through the code a bit at a time:
++   The purpose of the test in the `END' rule is to keep any other `END'
++rules from running.  When an assertion fails, the program should exit
++immediately.  If no assertions fail, then `_assert_exit' is still false
++when the `END' rule is run normally, and the rest of the program's
++`END' rules execute.  For all of this to work correctly, `assert.awk'
++must be the first source file read by `awk'.  The function can be used
++in a program in the following way:
+ 
 -     # getopt.awk --- Do C library getopt(3) function in awk
++     function myfunc(a, b)
++     {
++          assert(a <= 5 && b >= 17.1, "a <= 5 && b >= 17.1")
++          ...
++     }
+ 
 -     # External variables:
 -     #    Optind -- index in ARGV of first nonoption argument
 -     #    Optarg -- string value of argument to current option
 -     #    Opterr -- if nonzero, print our own diagnostic
 -     #    Optopt -- current option letter
++If the assertion fails, you see a message similar to the following:
+ 
 -     # Returns:
 -     #    -1     at end of options
 -     #    "?"    for unrecognized option
 -     #    <c>    a character representing the current option
++     mydata:1357: assertion failed: a <= 5 && b >= 17.1
+ 
 -     # Private Data:
 -     #    _opti  -- index in multi-flag option, e.g., -abc
++   There is a small problem with this version of `assert()'.  An `END'
++rule is automatically added to the program calling `assert()'.
++Normally, if a program consists of just a `BEGIN' rule, the input files
++and/or standard input are not read. However, now that the program has
++an `END' rule, `awk' attempts to read the input data files or standard
++input (*note Using BEGIN/END::), most likely causing the program to
++hang as it waits for input.
+ 
 -   The function starts out with comments presenting a list of the
 -global variables it uses, what the return values are, what they mean,
 -and any global variables that are "private" to this library function.
 -Such documentation is essential for any program, and particularly for
 -library functions.
++   There is a simple workaround to this: make sure that such a `BEGIN'
++rule always ends with an `exit' statement.
+ 
 -   The `getopt()' function first checks that it was indeed called with
 -a string of options (the `options' parameter).  If `options' has a zero
 -length, `getopt()' immediately returns -1:
++
++File: gawk.info,  Node: Round Function,  Next: Cliff Random Function,  Prev: 
Assert Function,  Up: General Functions
+ 
 -     function getopt(argc, argv, options,    thisopt, i)
 -     {
 -         if (length(options) == 0)    # no options given
 -             return -1
++13.2.3 Rounding Numbers
++-----------------------
+ 
 -         if (argv[Optind] == "--") {  # all done
 -             Optind++
 -             _opti = 0
 -             return -1
 -         } else if (argv[Optind] !~ /^-[^:[:space:]]/) {
 -             _opti = 0
 -             return -1
 -         }
++The way `printf' and `sprintf()' (*note Printf::) perform rounding
++often depends upon the system's C `sprintf()' subroutine.  On many
++machines, `sprintf()' rounding is "unbiased," which means it doesn't
++always round a trailing `.5' up, contrary to naive expectations.  In
++unbiased rounding, `.5' rounds to even, rather than always up, so 1.5
++rounds to 2 but 4.5 rounds to 4.  This means that if you are using a
++format that does rounding (e.g., `"%.0f"'), you should check what your
++system does.  The following function does traditional rounding; it
++might be useful if your `awk''s `printf' does unbiased rounding:
+ 
 -   The next thing to check for is the end of the options.  A `--' ends
 -the command-line options, as does any command-line argument that does
 -not begin with a `-'.  `Optind' is used to step through the array of
 -command-line arguments; it retains its value across calls to
 -`getopt()', because it is a global variable.
++     # round.awk --- do normal rounding
+ 
 -   The regular expression that is used, `/^-[^:[:space:]/', checks for
 -a `-' followed by anything that is not whitespace and not a colon.  If
 -the current command-line argument does not match this pattern, it is
 -not an option, and it ends option processing. Continuing on:
++     function round(x,   ival, aval, fraction)
++     {
++        ival = int(x)    # integer part, int() truncates
+ 
 -         if (_opti == 0)
 -             _opti = 2
 -         thisopt = substr(argv[Optind], _opti, 1)
 -         Optopt = thisopt
 -         i = index(options, thisopt)
 -         if (i == 0) {
 -             if (Opterr)
 -                 printf("%c -- invalid option\n",
 -                                       thisopt) > "/dev/stderr"
 -             if (_opti >= length(argv[Optind])) {
 -                 Optind++
 -                 _opti = 0
 -             } else
 -                 _opti++
 -             return "?"
 -         }
++        # see if fractional part
++        if (ival == x)   # no fraction
++           return ival   # ensure no decimals
+ 
 -   The `_opti' variable tracks the position in the current command-line
 -argument (`argv[Optind]').  If multiple options are grouped together
 -with one `-' (e.g., `-abx'), it is necessary to return them to the user
 -one at a time.
++        if (x < 0) {
++           aval = -x     # absolute value
++           ival = int(aval)
++           fraction = aval - ival
++           if (fraction >= .5)
++              return int(x) - 1   # -2.5 --> -3
++           else
++              return int(x)       # -2.3 --> -2
++        } else {
++           fraction = x - ival
++           if (fraction >= .5)
++              return ival + 1
++           else
++              return ival
++        }
++     }
+ 
 -   If `_opti' is equal to zero, it is set to two, which is the index in
 -the string of the next character to look at (we skip the `-', which is
 -at position one).  The variable `thisopt' holds the character, obtained
 -with `substr()'.  It is saved in `Optopt' for the main program to use.
++     # test harness
++     { print $0, round($0) }
+ 
 -   If `thisopt' is not in the `options' string, then it is an invalid
 -option.  If `Opterr' is nonzero, `getopt()' prints an error message on
 -the standard error that is similar to the message from the C version of
 -`getopt()'.
++
++File: gawk.info,  Node: Cliff Random Function,  Next: Ordinal Functions,  
Prev: Round Function,  Up: General Functions
+ 
 -   Because the option is invalid, it is necessary to skip it and move
 -on to the next option character.  If `_opti' is greater than or equal
 -to the length of the current command-line argument, it is necessary to
 -move on to the next argument, so `Optind' is incremented and `_opti' is
 -reset to zero. Otherwise, `Optind' is left alone and `_opti' is merely
 -incremented.
++13.2.4 The Cliff Random Number Generator
++----------------------------------------
+ 
 -   In any case, because the option is invalid, `getopt()' returns `"?"'.
 -The main program can examine `Optopt' if it needs to know what the
 -invalid option letter actually is. Continuing on:
++The Cliff random number generator
++(http://mathworld.wolfram.com/CliffRandomNumberGenerator.html) is a
++very simple random number generator that "passes the noise sphere test
++for randomness by showing no structure."  It is easily programmed, in
++less than 10 lines of `awk' code:
+ 
 -         if (substr(options, i + 1, 1) == ":") {
 -             # get option argument
 -             if (length(substr(argv[Optind], _opti + 1)) > 0)
 -                 Optarg = substr(argv[Optind], _opti + 1)
 -             else
 -                 Optarg = argv[++Optind]
 -             _opti = 0
 -         } else
 -             Optarg = ""
++     # cliff_rand.awk --- generate Cliff random numbers
+ 
 -   If the option requires an argument, the option letter is followed by
 -a colon in the `options' string.  If there are remaining characters in
 -the current command-line argument (`argv[Optind]'), then the rest of
 -that string is assigned to `Optarg'.  Otherwise, the next command-line
 -argument is used (`-xFOO' versus `-x FOO'). In either case, `_opti' is
 -reset to zero, because there are no more characters left to examine in
 -the current command-line argument. Continuing:
++     BEGIN { _cliff_seed = 0.1 }
+ 
 -         if (_opti == 0 || _opti >= length(argv[Optind])) {
 -             Optind++
 -             _opti = 0
 -         } else
 -             _opti++
 -         return thisopt
++     function cliff_rand()
++     {
++         _cliff_seed = (100 * log(_cliff_seed)) % 1
++         if (_cliff_seed < 0)
++             _cliff_seed = - _cliff_seed
++         return _cliff_seed
+      }
+ 
 -   Finally, if `_opti' is either zero or greater than the length of the
 -current command-line argument, it means this element in `argv' is
 -through being processed, so `Optind' is incremented to point to the
 -next element in `argv'.  If neither condition is true, then only
 -`_opti' is incremented, so that the next option letter can be processed
 -on the next call to `getopt()'.
++   This algorithm requires an initial "seed" of 0.1.  Each new value
++uses the current seed as input for the calculation.  If the built-in
++`rand()' function (*note Numeric Functions::) isn't random enough, you
++might try using this function instead.
+ 
 -   The `BEGIN' rule initializes both `Opterr' and `Optind' to one.
 -`Opterr' is set to one, since the default behavior is for `getopt()' to
 -print a diagnostic message upon seeing an invalid option.  `Optind' is
 -set to one, since there's no reason to look at the program name, which
 -is in `ARGV[0]':
++
++File: gawk.info,  Node: Ordinal Functions,  Next: Join Function,  Prev: Cliff 
Random Function,  Up: General Functions
+ 
 -     BEGIN {
 -         Opterr = 1    # default is to diagnose
 -         Optind = 1    # skip ARGV[0]
++13.2.5 Translating Between Characters and Numbers
++-------------------------------------------------
+ 
 -         # test program
 -         if (_getopt_test) {
 -             while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1)
 -                 printf("c = <%c>, optarg = <%s>\n",
 -                                            _go_c, Optarg)
 -             printf("non-option arguments:\n")
 -             for (; Optind < ARGC; Optind++)
 -                 printf("\tARGV[%d] = <%s>\n",
 -                                         Optind, ARGV[Optind])
 -         }
 -     }
++One commercial implementation of `awk' supplies a built-in function,
++`ord()', which takes a character and returns the numeric value for that
++character in the machine's character set.  If the string passed to
++`ord()' has more than one character, only the first one is used.
+ 
 -   The rest of the `BEGIN' rule is a simple test program.  Here is the
 -result of two sample runs of the test program:
++   The inverse of this function is `chr()' (from the function of the
++same name in Pascal), which takes a number and returns the
++corresponding character.  Both functions are written very nicely in
++`awk'; there is no real reason to build them into the `awk' interpreter:
+ 
 -     $ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x
 -     -| c = <a>, optarg = <>
 -     -| c = <c>, optarg = <>
 -     -| c = <b>, optarg = <ARG>
 -     -| non-option arguments:
 -     -|         ARGV[3] = <bax>
 -     -|         ARGV[4] = <-x>
++     # ord.awk --- do ord and chr
+ 
 -     $ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc
 -     -| c = <a>, optarg = <>
 -     error--> x -- invalid option
 -     -| c = <?>, optarg = <>
 -     -| non-option arguments:
 -     -|         ARGV[4] = <xyz>
 -     -|         ARGV[5] = <abc>
++     # Global identifiers:
++     #    _ord_:        numerical values indexed by characters
++     #    _ord_init:    function to initialize _ord_
+ 
 -   In both runs, the first `--' terminates the arguments to `awk', so
 -that it does not try to interpret the `-a', etc., as its own options.
++     BEGIN    { _ord_init() }
+ 
 -     NOTE: After `getopt()' is through, it is the responsibility of the
 -     user level code to clear out all the elements of `ARGV' from 1 to
 -     `Optind', so that `awk' does not try to process the command-line
 -     options as file names.
++     function _ord_init(    low, high, i, t)
++     {
++         low = sprintf("%c", 7) # BEL is ascii 7
++         if (low == "\a") {    # regular ascii
++             low = 0
++             high = 127
++         } else if (sprintf("%c", 128 + 7) == "\a") {
++             # ascii, mark parity
++             low = 128
++             high = 255
++         } else {        # ebcdic(!)
++             low = 0
++             high = 255
++         }
+ 
 -   Several of the sample programs presented in *note Sample Programs::,
 -use `getopt()' to process their arguments.
++         for (i = low; i <= high; i++) {
++             t = sprintf("%c", i)
++             _ord_[t] = i
++         }
++     }
+ 
 -   ---------- Footnotes ----------
++   Some explanation of the numbers used by `chr' is worthwhile.  The
++most prominent character set in use today is ASCII.(1) Although an
++8-bit byte can hold 256 distinct values (from 0 to 255), ASCII only
++defines characters that use the values from 0 to 127.(2) In the now
++distant past, at least one minicomputer manufacturer used ASCII, but
++with mark parity, meaning that the leftmost bit in the byte is always
++1.  This means that on those systems, characters have numeric values
++from 128 to 255.  Finally, large mainframe systems use the EBCDIC
++character set, which uses all 256 values.  While there are other
++character sets in use on some older systems, they are not really worth
++worrying about:
+ 
 -   (1) This function was written before `gawk' acquired the ability to
 -split strings into single characters using `""' as the separator.  We
 -have left it alone, since using `substr()' is more portable.
++     function ord(str,    c)
++     {
++         # only first character is of interest
++         c = substr(str, 1, 1)
++         return _ord_[c]
++     }
+ 
 -
 -File: gawk.info,  Node: Passwd Functions,  Next: Group Functions,  Prev: 
Getopt Function,  Up: Library Functions
++     function chr(c)
++     {
++         # force c to be numeric by adding 0
++         return sprintf("%c", c + 0)
++     }
+ 
 -12.5 Reading the User Database
 -==============================
++     #### test code ####
++     # BEGIN    \
++     # {
++     #    for (;;) {
++     #        printf("enter a character: ")
++     #        if (getline var <= 0)
++     #            break
++     #        printf("ord(%s) = %d\n", var, ord(var))
++     #    }
++     # }
+ 
 -The `PROCINFO' array (*note Built-in Variables::) provides access to
 -the current user's real and effective user and group ID numbers, and if
 -available, the user's supplementary group set.  However, because these
 -are numbers, they do not provide very useful information to the average
 -user.  There needs to be some way to find the user information
 -associated with the user and group ID numbers.  This minor node
 -presents a suite of functions for retrieving information from the user
 -database.  *Note Group Functions::, for a similar suite that retrieves
 -information from the group database.
++   An obvious improvement to these functions is to move the code for the
++`_ord_init' function into the body of the `BEGIN' rule.  It was written
++this way initially for ease of development.  There is a "test program"
++in a `BEGIN' rule, to test the function.  It is commented out for
++production use.
+ 
 -   The POSIX standard does not define the file where user information is
 -kept.  Instead, it provides the `<pwd.h>' header file and several C
 -language subroutines for obtaining user information.  The primary
 -function is `getpwent()', for "get password entry."  The "password"
 -comes from the original user database file, `/etc/passwd', which stores
 -user information, along with the encrypted passwords (hence the name).
++   ---------- Footnotes ----------
+ 
 -   While an `awk' program could simply read `/etc/passwd' directly,
 -this file may not contain complete information about the system's set
 -of users.(1) To be sure you are able to produce a readable and complete
 -version of the user database, it is necessary to write a small C
 -program that calls `getpwent()'.  `getpwent()' is defined as returning
 -a pointer to a `struct passwd'.  Each time it is called, it returns the
 -next entry in the database.  When there are no more entries, it returns
 -`NULL', the null pointer.  When this happens, the C program should call
 -`endpwent()' to close the database.  Following is `pwcat', a C program
 -that "cats" the password database:
++   (1) This is changing; many systems use Unicode, a very large
++character set that includes ASCII as a subset.  On systems with full
++Unicode support, a character can occupy up to 32 bits, making simple
++tests such as used here prohibitively expensive.
+ 
 -     /*
 -      * pwcat.c
 -      *
 -      * Generate a printable version of the password database
 -      */
 -     #include <stdio.h>
 -     #include <pwd.h>
++   (2) ASCII has been extended in many countries to use the values from
++128 to 255 for country-specific characters.  If your  system uses these
++extensions, you can simplify `_ord_init' to loop from 0 to 255.
+ 
 -     int
 -     main(int argc, char **argv)
 -     {
 -         struct passwd *p;
++
++File: gawk.info,  Node: Join Function,  Next: Getlocaltime Function,  Prev: 
Ordinal Functions,  Up: General Functions
+ 
 -         while ((p = getpwent()) != NULL)
 -             printf("%s:%s:%ld:%ld:%s:%s:%s\n",
 -                 p->pw_name, p->pw_passwd, (long) p->pw_uid,
 -                 (long) p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell);
++13.2.6 Merging an Array into a String
++-------------------------------------
+ 
 -         endpwent();
 -         return 0;
 -     }
++When doing string processing, it is often useful to be able to join all
++the strings in an array into one long string.  The following function,
++`join()', accomplishes this task.  It is used later in several of the
++application programs (*note Sample Programs::).
+ 
 -   If you don't understand C, don't worry about it.  The output from
 -`pwcat' is the user database, in the traditional `/etc/passwd' format
 -of colon-separated fields.  The fields are:
++   Good function design is important; this function needs to be general
++but it should also have a reasonable default behavior.  It is called
++with an array as well as the beginning and ending indices of the
++elements in the array to be merged.  This assumes that the array
++indices are numeric--a reasonable assumption since the array was likely
++created with `split()' (*note String Functions::):
+ 
 -Login name
 -     The user's login name.
++     # join.awk --- join an array into a string
+ 
 -Encrypted password
 -     The user's encrypted password.  This may not be available on some
 -     systems.
++     function join(array, start, end, sep,    result, i)
++     {
++         if (sep == "")
++            sep = " "
++         else if (sep == SUBSEP) # magic value
++            sep = ""
++         result = array[start]
++         for (i = start + 1; i <= end; i++)
++             result = result sep array[i]
++         return result
++     }
+ 
 -User-ID
 -     The user's numeric user ID number.  (On some systems it's a C
 -     `long', and not an `int'.  Thus we cast it to `long' for all
 -     cases.)
++   An optional additional argument is the separator to use when joining
++the strings back together.  If the caller supplies a nonempty value,
++`join()' uses it; if it is not supplied, it has a null value.  In this
++case, `join()' uses a single space as a default separator for the
++strings.  If the value is equal to `SUBSEP', then `join()' joins the
++strings with no separator between them.  `SUBSEP' serves as a "magic"
++value to indicate that there should be no separation between the
++component strings.(1)
+ 
 -Group-ID
 -     The user's numeric group ID number.  (Similar comments about
 -     `long' vs. `int' apply here.)
++   ---------- Footnotes ----------
+ 
 -Full name
 -     The user's full name, and perhaps other information associated
 -     with the user.
++   (1) It would be nice if `awk' had an assignment operator for
++concatenation.  The lack of an explicit operator for concatenation
++makes string operations more difficult than they really need to be.
+ 
 -Home directory
 -     The user's login (or "home") directory (familiar to shell
 -     programmers as `$HOME').
++
++File: gawk.info,  Node: Getlocaltime Function,  Prev: Join Function,  Up: 
General Functions
+ 
 -Login shell
 -     The program that is run when the user logs in.  This is usually a
 -     shell, such as Bash.
++13.2.7 Managing the Time of Day
++-------------------------------
+ 
 -   A few lines representative of `pwcat''s output are as follows:
++The `systime()' and `strftime()' functions described in *note Time
++Functions::, provide the minimum functionality necessary for dealing
++with the time of day in human readable form.  While `strftime()' is
++extensive, the control formats are not necessarily easy to remember or
++intuitively obvious when reading a program.
+ 
 -     $ pwcat
 -     -| root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh
 -     -| nobody:*:65534:65534::/:
 -     -| daemon:*:1:1::/:
 -     -| sys:*:2:2::/:/bin/csh
 -     -| bin:*:3:3::/bin:
 -     -| arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh
 -     -| miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh
 -     -| andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh
 -     ...
++   The following function, `getlocaltime()', populates a user-supplied
++array with preformatted time information.  It returns a string with the
++current time formatted in the same way as the `date' utility:
+ 
 -   With that introduction, following is a group of functions for
 -getting user information.  There are several functions here,
 -corresponding to the C functions of the same names:
++     # getlocaltime.awk --- get the time of day in a usable format
+ 
 -     # passwd.awk --- access password file information
++     # Returns a string in the format of output of date(1)
++     # Populates the array argument time with individual values:
++     #    time["second"]       -- seconds (0 - 59)
++     #    time["minute"]       -- minutes (0 - 59)
++     #    time["hour"]         -- hours (0 - 23)
++     #    time["althour"]      -- hours (0 - 12)
++     #    time["monthday"]     -- day of month (1 - 31)
++     #    time["month"]        -- month of year (1 - 12)
++     #    time["monthname"]    -- name of the month
++     #    time["shortmonth"]   -- short name of the month
++     #    time["year"]         -- year modulo 100 (0 - 99)
++     #    time["fullyear"]     -- full year
++     #    time["weekday"]      -- day of week (Sunday = 0)
++     #    time["altweekday"]   -- day of week (Monday = 0)
++     #    time["dayname"]      -- name of weekday
++     #    time["shortdayname"] -- short name of weekday
++     #    time["yearday"]      -- day of year (0 - 365)
++     #    time["timezone"]     -- abbreviation of timezone name
++     #    time["ampm"]         -- AM or PM designation
++     #    time["weeknum"]      -- week number, Sunday first day
++     #    time["altweeknum"]   -- week number, Monday first day
+ 
 -     BEGIN {
 -         # tailor this to suit your system
 -         _pw_awklib = "/usr/local/libexec/awk/"
 -     }
 -
 -     function _pw_init(    oldfs, oldrs, olddol0, pwcat, using_fw, using_fpat)
++     function getlocaltime(time,    ret, now, i)
+      {
 -         if (_pw_inited)
 -             return
++         # get time once, avoids unnecessary system calls
++         now = systime()
+ 
 -         oldfs = FS
 -         oldrs = RS
 -         olddol0 = $0
 -         using_fw = (PROCINFO["FS"] == "FIELDWIDTHS")
 -         using_fpat = (PROCINFO["FS"] == "FPAT")
 -         FS = ":"
 -         RS = "\n"
++         # return date(1)-style output
++         ret = strftime("%a %b %e %H:%M:%S %Z %Y", now)
+ 
 -         pwcat = _pw_awklib "pwcat"
 -         while ((pwcat | getline) > 0) {
 -             _pw_byname[$1] = $0
 -             _pw_byuid[$3] = $0
 -             _pw_bycount[++_pw_total] = $0
 -         }
 -         close(pwcat)
 -         _pw_count = 0
 -         _pw_inited = 1
 -         FS = oldfs
 -         if (using_fw)
 -             FIELDWIDTHS = FIELDWIDTHS
 -         else if (using_fpat)
 -             FPAT = FPAT
 -         RS = oldrs
 -         $0 = olddol0
++         # clear out target array
++         delete time
++
++         # fill in values, force numeric values to be
++         # numeric by adding 0
++         time["second"]       = strftime("%S", now) + 0
++         time["minute"]       = strftime("%M", now) + 0
++         time["hour"]         = strftime("%H", now) + 0
++         time["althour"]      = strftime("%I", now) + 0
++         time["monthday"]     = strftime("%d", now) + 0
++         time["month"]        = strftime("%m", now) + 0
++         time["monthname"]    = strftime("%B", now)
++         time["shortmonth"]   = strftime("%b", now)
++         time["year"]         = strftime("%y", now) + 0
++         time["fullyear"]     = strftime("%Y", now) + 0
++         time["weekday"]      = strftime("%w", now) + 0
++         time["altweekday"]   = strftime("%u", now) + 0
++         time["dayname"]      = strftime("%A", now)
++         time["shortdayname"] = strftime("%a", now)
++         time["yearday"]      = strftime("%j", now) + 0
++         time["timezone"]     = strftime("%Z", now)
++         time["ampm"]         = strftime("%p", now)
++         time["weeknum"]      = strftime("%U", now) + 0
++         time["altweeknum"]   = strftime("%W", now) + 0
++
++         return ret
+      }
+ 
 -   The `BEGIN' rule sets a private variable to the directory where
 -`pwcat' is stored.  Because it is used to help out an `awk' library
 -routine, we have chosen to put it in `/usr/local/libexec/awk'; however,
 -you might want it to be in a different directory on your system.
++   The string indices are easier to use and read than the various
++formats required by `strftime()'.  The `alarm' program presented in
++*note Alarm Program::, uses this function.  A more general design for
++the `getlocaltime()' function would have allowed the user to supply an
++optional timestamp value to use instead of the current time.
+ 
 -   The function `_pw_init()' keeps three copies of the user information
 -in three associative arrays.  The arrays are indexed by username
 -(`_pw_byname'), by user ID number (`_pw_byuid'), and by order of
 -occurrence (`_pw_bycount').  The variable `_pw_inited' is used for
 -efficiency, since `_pw_init()' needs to be called only once.
++
++File: gawk.info,  Node: Data File Management,  Next: Getopt Function,  Prev: 
General Functions,  Up: Library Functions
+ 
 -   Because this function uses `getline' to read information from
 -`pwcat', it first saves the values of `FS', `RS', and `$0'.  It notes
 -in the variable `using_fw' whether field splitting with `FIELDWIDTHS'
 -is in effect or not.  Doing so is necessary, since these functions
 -could be called from anywhere within a user's program, and the user may
 -have his or her own way of splitting records and fields.
++13.3 Data File Management
++=========================
+ 
 -   The `using_fw' variable checks `PROCINFO["FS"]', which is
 -`"FIELDWIDTHS"' if field splitting is being done with `FIELDWIDTHS'.
 -This makes it possible to restore the correct field-splitting mechanism
 -later.  The test can only be true for `gawk'.  It is false if using
 -`FS' or `FPAT', or on some other `awk' implementation.
++This minor node presents functions that are useful for managing
++command-line data files.
+ 
 -   The code that checks for using `FPAT', using `using_fpat' and
 -`PROCINFO["FS"]' is similar.
++* Menu:
+ 
 -   The main part of the function uses a loop to read database lines,
 -split the line into fields, and then store the line into each array as
 -necessary.  When the loop is done, `_pw_init()' cleans up by closing
 -the pipeline, setting `_pw_inited' to one, and restoring `FS' (and
 -`FIELDWIDTHS' or `FPAT' if necessary), `RS', and `$0'.  The use of
 -`_pw_count' is explained shortly.
++* Filetrans Function::          A function for handling data file transitions.
++* Rewind Function::             A function for rereading the current file.
++* File Checking::               Checking that data files are readable.
++* Empty Files::                 Checking for zero-length files.
++* Ignoring Assigns::            Treating assignments as file names.
+ 
 -   The `getpwnam()' function takes a username as a string argument. If
 -that user is in the database, it returns the appropriate line.
 -Otherwise, it relies on the array reference to a nonexistent element to
 -create the element with the null string as its value:
++
++File: gawk.info,  Node: Filetrans Function,  Next: Rewind Function,  Up: Data 
File Management
+ 
 -     function getpwnam(name)
 -     {
 -         _pw_init()
 -         return _pw_byname[name]
 -     }
++13.3.1 Noting Data File Boundaries
++----------------------------------
+ 
 -   Similarly, the `getpwuid' function takes a user ID number argument.
 -If that user number is in the database, it returns the appropriate
 -line. Otherwise, it returns the null string:
++The `BEGIN' and `END' rules are each executed exactly once at the
++beginning and end of your `awk' program, respectively (*note
++BEGIN/END::).  We (the `gawk' authors) once had a user who mistakenly
++thought that the `BEGIN' rule is executed at the beginning of each data
++file and the `END' rule is executed at the end of each data file.
+ 
 -     function getpwuid(uid)
 -     {
 -         _pw_init()
 -         return _pw_byuid[uid]
 -     }
++   When informed that this was not the case, the user requested that we
++add new special patterns to `gawk', named `BEGIN_FILE' and `END_FILE',
++that would have the desired behavior.  He even supplied us the code to
++do so.
+ 
 -   The `getpwent()' function simply steps through the database, one
 -entry at a time.  It uses `_pw_count' to track its current position in
 -the `_pw_bycount' array:
++   Adding these special patterns to `gawk' wasn't necessary; the job
++can be done cleanly in `awk' itself, as illustrated by the following
++library program.  It arranges to call two user-supplied functions,
++`beginfile()' and `endfile()', at the beginning and end of each data
++file.  Besides solving the problem in only nine(!) lines of code, it
++does so _portably_; this works with any implementation of `awk':
+ 
 -     function getpwent()
++     # transfile.awk
++     #
++     # Give the user a hook for filename transitions
++     #
++     # The user must supply functions beginfile() and endfile()
++     # that each take the name of the file being started or
++     # finished, respectively.
++
++     FILENAME != _oldfilename \
+      {
 -         _pw_init()
 -         if (_pw_count < _pw_total)
 -             return _pw_bycount[++_pw_count]
 -         return ""
++         if (_oldfilename != "")
++             endfile(_oldfilename)
++         _oldfilename = FILENAME
++         beginfile(FILENAME)
+      }
+ 
 -   The `endpwent()' function resets `_pw_count' to zero, so that
 -subsequent calls to `getpwent()' start over again:
++     END   { endfile(FILENAME) }
+ 
 -     function endpwent()
 -     {
 -         _pw_count = 0
 -     }
++   This file must be loaded before the user's "main" program, so that
++the rule it supplies is executed first.
+ 
 -   A conscious design decision in this suite is that each subroutine
 -calls `_pw_init()' to initialize the database arrays.  The overhead of
 -running a separate process to generate the user database, and the I/O
 -to scan it, are only incurred if the user's main program actually calls
 -one of these functions.  If this library file is loaded along with a
 -user's program, but none of the routines are ever called, then there is
 -no extra runtime overhead.  (The alternative is move the body of
 -`_pw_init()' into a `BEGIN' rule, which always runs `pwcat'.  This
 -simplifies the code but runs an extra process that may never be needed.)
++   This rule relies on `awk''s `FILENAME' variable that automatically
++changes for each new data file.  The current file name is saved in a
++private variable, `_oldfilename'.  If `FILENAME' does not equal
++`_oldfilename', then a new data file is being processed and it is
++necessary to call `endfile()' for the old file.  Because `endfile()'
++should only be called if a file has been processed, the program first
++checks to make sure that `_oldfilename' is not the null string.  The
++program then assigns the current file name to `_oldfilename' and calls
++`beginfile()' for the file.  Because, like all `awk' variables,
++`_oldfilename' is initialized to the null string, this rule executes
++correctly even for the first data file.
+ 
 -   In turn, calling `_pw_init()' is not too expensive, because the
 -`_pw_inited' variable keeps the program from reading the data more than
 -once.  If you are worried about squeezing every last cycle out of your
 -`awk' program, the check of `_pw_inited' could be moved out of
 -`_pw_init()' and duplicated in all the other functions.  In practice,
 -this is not necessary, since most `awk' programs are I/O-bound, and
 -such a change would clutter up the code.
++   The program also supplies an `END' rule to do the final processing
++for the last file.  Because this `END' rule comes before any `END' rules
++supplied in the "main" program, `endfile()' is called first.  Once
++again the value of multiple `BEGIN' and `END' rules should be clear.
+ 
 -   The `id' program in *note Id Program::, uses these functions.
++   If the same data file occurs twice in a row on the command line, then
++`endfile()' and `beginfile()' are not executed at the end of the first
++pass and at the beginning of the second pass.  The following version
++solves the problem:
+ 
 -   ---------- Footnotes ----------
++     # ftrans.awk --- handle data file transitions
++     #
++     # user supplies beginfile() and endfile() functions
+ 
 -   (1) It is often the case that password information is stored in a
 -network database.
++     FNR == 1 {
++         if (_filename_ != "")
++             endfile(_filename_)
++         _filename_ = FILENAME
++         beginfile(FILENAME)
++     }
+ 
 -
 -File: gawk.info,  Node: Group Functions,  Next: Walking Arrays,  Prev: Passwd 
Functions,  Up: Library Functions
++     END  { endfile(_filename_) }
+ 
 -12.6 Reading the Group Database
 -===============================
++   *note Wc Program::, shows how this library function can be used and
++how it simplifies writing the main program.
+ 
 -Much of the discussion presented in *note Passwd Functions::, applies
 -to the group database as well.  Although there has traditionally been a
 -well-known file (`/etc/group') in a well-known format, the POSIX
 -standard only provides a set of C library routines (`<grp.h>' and
 -`getgrent()') for accessing the information.  Even though this file may
 -exist, it may not have complete information.  Therefore, as with the
 -user database, it is necessary to have a small C program that generates
 -the group database as its output.  `grcat', a C program that "cats" the
 -group database, is as follows:
++Advanced Notes: So Why Does `gawk' have `BEGINFILE' and `ENDFILE'?
++------------------------------------------------------------------
+ 
 -     /*
 -      * grcat.c
 -      *
 -      * Generate a printable version of the group database
 -      */
 -     #include <stdio.h>
 -     #include <grp.h>
++You are probably wondering, if `beginfile()' and `endfile()' functions
++can do the job, why does `gawk' have `BEGINFILE' and `ENDFILE' patterns
++(*note BEGINFILE/ENDFILE::)?
+ 
 -     int
 -     main(int argc, char **argv)
 -     {
 -         struct group *g;
 -         int i;
++   Good question.  Normally, if `awk' cannot open a file, this causes
++an immediate fatal error.  In this case, there is no way for a
++user-defined function to deal with the problem, since the mechanism for
++calling it relies on the file being open and at the first record.  Thus,
++the main reason for `BEGINFILE' is to give you a "hook" to catch files
++that cannot be processed.  `ENDFILE' exists for symmetry, and because
++it provides an easy way to do per-file cleanup processing.
+ 
 -         while ((g = getgrent()) != NULL) {
 -             printf("%s:%s:%ld:", g->gr_name, g->gr_passwd,
 -                                          (long) g->gr_gid);
 -             for (i = 0; g->gr_mem[i] != NULL; i++) {
 -                 printf("%s", g->gr_mem[i]);
 -                 if (g->gr_mem[i+1] != NULL)
 -                     putchar(',');
 -             }
 -             putchar('\n');
 -         }
 -         endgrent();
 -         return 0;
 -     }
++
++File: gawk.info,  Node: Rewind Function,  Next: File Checking,  Prev: 
Filetrans Function,  Up: Data File Management
+ 
 -   Each line in the group database represents one group.  The fields are
 -separated with colons and represent the following information:
++13.3.2 Rereading the Current File
++---------------------------------
+ 
 -Group Name
 -     The group's name.
++Another request for a new built-in function was for a `rewind()'
++function that would make it possible to reread the current file.  The
++requesting user didn't want to have to use `getline' (*note Getline::)
++inside a loop.
+ 
 -Group Password
 -     The group's encrypted password. In practice, this field is never
 -     used; it is usually empty or set to `*'.
++   However, as long as you are not in the `END' rule, it is quite easy
++to arrange to immediately close the current input file and then start
++over with it from the top.  For lack of a better name, we'll call it
++`rewind()':
+ 
 -Group ID Number
 -     The group's numeric group ID number; this number must be unique
 -     within the file.  (On some systems it's a C `long', and not an
 -     `int'.  Thus we cast it to `long' for all cases.)
++     # rewind.awk --- rewind the current file and start over
+ 
 -Group Member List
 -     A comma-separated list of user names.  These users are members of
 -     the group.  Modern Unix systems allow users to be members of
 -     several groups simultaneously.  If your system does, then there
 -     are elements `"group1"' through `"groupN"' in `PROCINFO' for those
 -     group ID numbers.  (Note that `PROCINFO' is a `gawk' extension;
 -     *note Built-in Variables::.)
++     function rewind(    i)
++     {
++         # shift remaining arguments up
++         for (i = ARGC; i > ARGIND; i--)
++             ARGV[i] = ARGV[i-1]
+ 
 -   Here is what running `grcat' might produce:
++         # make sure gawk knows to keep going
++         ARGC++
+ 
 -     $ grcat
 -     -| wheel:*:0:arnold
 -     -| nogroup:*:65534:
 -     -| daemon:*:1:
 -     -| kmem:*:2:
 -     -| staff:*:10:arnold,miriam,andy
 -     -| other:*:20:
 -     ...
++         # make current file next to get done
++         ARGV[ARGIND+1] = FILENAME
+ 
 -   Here are the functions for obtaining information from the group
 -database.  There are several, modeled after the C library functions of
 -the same names:
++         # do it
++         nextfile
++     }
+ 
 -     # group.awk --- functions for dealing with the group file
++   This code relies on the `ARGIND' variable (*note Auto-set::), which
++is specific to `gawk'.  If you are not using `gawk', you can use ideas
++presented in *note Filetrans Function::, to either update `ARGIND' on
++your own or modify this code as appropriate.
+ 
 -     BEGIN    \
 -     {
 -         # Change to suit your system
 -         _gr_awklib = "/usr/local/libexec/awk/"
 -     }
++   The `rewind()' function also relies on the `nextfile' keyword (*note
++Nextfile Statement::).
+ 
 -     function _gr_init(    oldfs, oldrs, olddol0, grcat,
 -                                  using_fw, using_fpat, n, a, i)
 -     {
 -         if (_gr_inited)
 -             return
++
++File: gawk.info,  Node: File Checking,  Next: Empty Files,  Prev: Rewind 
Function,  Up: Data File Management
+ 
 -         oldfs = FS
 -         oldrs = RS
 -         olddol0 = $0
 -         using_fw = (PROCINFO["FS"] == "FIELDWIDTHS")
 -         using_fpat = (PROCINFO["FS"] == "FPAT")
 -         FS = ":"
 -         RS = "\n"
++13.3.3 Checking for Readable Data Files
++---------------------------------------
+ 
 -         grcat = _gr_awklib "grcat"
 -         while ((grcat | getline) > 0) {
 -             if ($1 in _gr_byname)
 -                 _gr_byname[$1] = _gr_byname[$1] "," $4
 -             else
 -                 _gr_byname[$1] = $0
 -             if ($3 in _gr_bygid)
 -                 _gr_bygid[$3] = _gr_bygid[$3] "," $4
 -             else
 -                 _gr_bygid[$3] = $0
++Normally, if you give `awk' a data file that isn't readable, it stops
++with a fatal error.  There are times when you might want to just ignore
++such files and keep going.  You can do this by prepending the following
++program to your `awk' program:
+ 
 -             n = split($4, a, "[ \t]*,[ \t]*")
 -             for (i = 1; i <= n; i++)
 -                 if (a[i] in _gr_groupsbyuser)
 -                     _gr_groupsbyuser[a[i]] = \
 -                         _gr_groupsbyuser[a[i]] " " $1
 -                 else
 -                     _gr_groupsbyuser[a[i]] = $1
++     # readable.awk --- library file to skip over unreadable files
+ 
 -             _gr_bycount[++_gr_count] = $0
++     BEGIN {
++         for (i = 1; i < ARGC; i++) {
++             if (ARGV[i] ~ /^[[:alpha:]_][[:alnum:]_]*=.*/ \
++                 || ARGV[i] == "-" || ARGV[i] == "/dev/stdin")
++                 continue    # assignment or standard input
++             else if ((getline junk < ARGV[i]) < 0) # unreadable
++                 delete ARGV[i]
++             else
++                 close(ARGV[i])
+          }
 -         close(grcat)
 -         _gr_count = 0
 -         _gr_inited++
 -         FS = oldfs
 -         if (using_fw)
 -             FIELDWIDTHS = FIELDWIDTHS
 -         else if (using_fpat)
 -             FPAT = FPAT
 -         RS = oldrs
 -         $0 = olddol0
+      }
+ 
 -   The `BEGIN' rule sets a private variable to the directory where
 -`grcat' is stored.  Because it is used to help out an `awk' library
 -routine, we have chosen to put it in `/usr/local/libexec/awk'.  You
 -might want it to be in a different directory on your system.
 -
 -   These routines follow the same general outline as the user database
 -routines (*note Passwd Functions::).  The `_gr_inited' variable is used
 -to ensure that the database is scanned no more than once.  The
 -`_gr_init()' function first saves `FS', `RS', and `$0', and then sets
 -`FS' and `RS' to the correct values for scanning the group information.
 -It also takes care to note whether `FIELDWIDTHS' or `FPAT' is being
 -used, and to restore the appropriate field splitting mechanism.
++   This works, because the `getline' won't be fatal.  Removing the
++element from `ARGV' with `delete' skips the file (since it's no longer
++in the list).  See also *note ARGC and ARGV::.
+ 
 -   The group information is stored is several associative arrays.  The
 -arrays are indexed by group name (`_gr_byname'), by group ID number
 -(`_gr_bygid'), and by position in the database (`_gr_bycount').  There
 -is an additional array indexed by user name (`_gr_groupsbyuser'), which
 -is a space-separated list of groups to which each user belongs.
++
++File: gawk.info,  Node: Empty Files,  Next: Ignoring Assigns,  Prev: File 
Checking,  Up: Data File Management
+ 
 -   Unlike the user database, it is possible to have multiple records in
 -the database for the same group.  This is common when a group has a
 -large number of members.  A pair of such entries might look like the
 -following:
++13.3.4 Checking For Zero-length Files
++-------------------------------------
+ 
 -     tvpeople:*:101:johnny,jay,arsenio
 -     tvpeople:*:101:david,conan,tom,joan
++All known `awk' implementations silently skip over zero-length files.
++This is a by-product of `awk''s implicit
++read-a-record-and-match-against-the-rules loop: when `awk' tries to
++read a record from an empty file, it immediately receives an end of
++file indication, closes the file, and proceeds on to the next
++command-line data file, _without_ executing any user-level `awk'
++program code.
+ 
 -   For this reason, `_gr_init()' looks to see if a group name or group
 -ID number is already seen.  If it is, then the user names are simply
 -concatenated onto the previous list of users.  (There is actually a
 -subtle problem with the code just presented.  Suppose that the first
 -time there were no names. This code adds the names with a leading
 -comma. It also doesn't check that there is a `$4'.)
++   Using `gawk''s `ARGIND' variable (*note Built-in Variables::), it is
++possible to detect when an empty data file has been skipped.  Similar
++to the library file presented in *note Filetrans Function::, the
++following library file calls a function named `zerofile()' that the
++user must provide.  The arguments passed are the file name and the
++position in `ARGV' where it was found:
+ 
 -   Finally, `_gr_init()' closes the pipeline to `grcat', restores `FS'
 -(and `FIELDWIDTHS' or `FPAT' if necessary), `RS', and `$0', initializes
 -`_gr_count' to zero (it is used later), and makes `_gr_inited' nonzero.
++     # zerofile.awk --- library file to process empty input files
+ 
 -   The `getgrnam()' function takes a group name as its argument, and if
 -that group exists, it is returned.  Otherwise, it relies on the array
 -reference to a nonexistent element to create the element with the null
 -string as its value:
++     BEGIN { Argind = 0 }
+ 
 -     function getgrnam(group)
 -     {
 -         _gr_init()
 -         return _gr_byname[group]
++     ARGIND > Argind + 1 {
++         for (Argind++; Argind < ARGIND; Argind++)
++             zerofile(ARGV[Argind], Argind)
+      }
+ 
 -   The `getgrgid()' function is similar; it takes a numeric group ID and
 -looks up the information associated with that group ID:
++     ARGIND != Argind { Argind = ARGIND }
+ 
 -     function getgrgid(gid)
 -     {
 -         _gr_init()
 -         return _gr_bygid[gid]
++     END {
++         if (ARGIND > Argind)
++             for (Argind++; Argind <= ARGIND; Argind++)
++                 zerofile(ARGV[Argind], Argind)
+      }
+ 
 -   The `getgruser()' function does not have a C counterpart. It takes a
 -user name and returns the list of groups that have the user as a member:
++   The user-level variable `Argind' allows the `awk' program to track
++its progress through `ARGV'.  Whenever the program detects that
++`ARGIND' is greater than `Argind + 1', it means that one or more empty
++files were skipped.  The action then calls `zerofile()' for each such
++file, incrementing `Argind' along the way.
+ 
 -     function getgruser(user)
 -     {
 -         _gr_init()
 -         return _gr_groupsbyuser[user]
 -     }
++   The `Argind != ARGIND' rule simply keeps `Argind' up to date in the
++normal case.
+ 
 -   The `getgrent()' function steps through the database one entry at a
 -time.  It uses `_gr_count' to track its position in the list:
++   Finally, the `END' rule catches the case of any empty files at the
++end of the command-line arguments.  Note that the test in the condition
++of the `for' loop uses the `<=' operator, not `<'.
+ 
 -     function getgrent()
 -     {
 -         _gr_init()
 -         if (++_gr_count in _gr_bycount)
 -             return _gr_bycount[_gr_count]
 -         return ""
 -     }
++   As an exercise, you might consider whether this same problem can be
++solved without relying on `gawk''s `ARGIND' variable.
+ 
 -   The `endgrent()' function resets `_gr_count' to zero so that
 -`getgrent()' can start over again:
++   As a second exercise, revise this code to handle the case where an
++intervening value in `ARGV' is a variable assignment.
+ 
 -     function endgrent()
 -     {
 -         _gr_count = 0
 -     }
++
++File: gawk.info,  Node: Ignoring Assigns,  Prev: Empty Files,  Up: Data File 
Management
+ 
 -   As with the user database routines, each function calls `_gr_init()'
 -to initialize the arrays.  Doing so only incurs the extra overhead of
 -running `grcat' if these functions are used (as opposed to moving the
 -body of `_gr_init()' into a `BEGIN' rule).
++13.3.5 Treating Assignments as File Names
++-----------------------------------------
+ 
 -   Most of the work is in scanning the database and building the various
 -associative arrays.  The functions that the user calls are themselves
 -very simple, relying on `awk''s associative arrays to do work.
 -
 -   The `id' program in *note Id Program::, uses these functions.
 -
 -
 -File: gawk.info,  Node: Walking Arrays,  Prev: Group Functions,  Up: Library 
Functions
++Occasionally, you might not want `awk' to process command-line variable
++assignments (*note Assignment Options::).  In particular, if you have a
++file name that contain an `=' character, `awk' treats the file name as
++an assignment, and does not process it.
+ 
 -12.7 Traversing Arrays of Arrays
 -================================
++   Some users have suggested an additional command-line option for
++`gawk' to disable command-line assignments.  However, some simple
++programming with a library file does the trick:
+ 
 -*note Arrays of Arrays::, described how `gawk' provides arrays of
 -arrays.  In particular, any element of an array may be either a scalar,
 -or another array. The `isarray()' function (*note Type Functions::)
 -lets you distinguish an array from a scalar.  The following function,
 -`walk_array()', recursively traverses an array, printing each element's
 -indices and value.  You call it with the array and a string
 -representing the name of the array:
++     # noassign.awk --- library file to avoid the need for a
++     # special option that disables command-line assignments
+ 
 -     function walk_array(arr, name,      i)
++     function disable_assigns(argc, argv,    i)
+      {
 -         for (i in arr) {
 -             if (isarray(arr[i]))
 -                 walk_array(arr[i], (name "[" i "]"))
 -             else
 -                 printf("%s[%s] = %s\n", name, i, arr[i])
 -         }
++         for (i = 1; i < argc; i++)
++             if (argv[i] ~ /^[[:alpha:]_][[:alnum:]_]*=.*/)
++                 argv[i] = ("./" argv[i])
+      }
+ 
 -It works by looping over each element of the array. If any given
 -element is itself an array, the function calls itself recursively,
 -passing the subarray and a new string representing the current index.
 -Otherwise, the function simply prints the element's name, index, and
 -value.  Here is a main program to demonstrate:
 -
+      BEGIN {
 -         a[1] = 1
 -         a[2][1] = 21
 -         a[2][2] = 22
 -         a[3] = 3
 -         a[4][1][1] = 411
 -         a[4][2] = 42
 -
 -         walk_array(a, "a")
++         if (No_command_assign)
++             disable_assigns(ARGC, ARGV)
+      }
+ 
 -   When run, the program produces the following output:
 -
 -     $ gawk -f walk_array.awk
 -     -| a[4][1][1] = 411
 -     -| a[4][2] = 42
 -     -| a[1] = 1
 -     -| a[2][1] = 21
 -     -| a[2][2] = 22
 -     -| a[3] = 3
 -
 -
 -File: gawk.info,  Node: Sample Programs,  Next: Debugger,  Prev: Library 
Functions,  Up: Top
 -
 -13 Practical `awk' Programs
 -***************************
 -
 -*note Library Functions::, presents the idea that reading programs in a
 -language contributes to learning that language.  This major node
 -continues that theme, presenting a potpourri of `awk' programs for your
 -reading enjoyment.
++   You then run your program this way:
+ 
 -   Many of these programs use library functions presented in *note
 -Library Functions::.
++     awk -v No_command_assign=1 -f noassign.awk -f yourprog.awk *
+ 
 -* Menu:
++   The function works by looping through the arguments.  It prepends
++`./' to any argument that matches the form of a variable assignment,
++turning that argument into a file name.
+ 
 -* Running Examples::            How to run these examples.
 -* Clones::                      Clones of common utilities.
 -* Miscellaneous Programs::      Some interesting `awk' programs.
++   The use of `No_command_assign' allows you to disable command-line
++assignments at invocation time, by giving the variable a true value.
++When not set, it is initially zero (i.e., false), so the command-line
++arguments are left alone.
+ 
+ 
 -File: gawk.info,  Node: Running Examples,  Next: Clones,  Up: Sample Programs
 -
 -13.1 Running the Example Programs
 -=================================
++File: gawk.info,  Node: Getopt Function,  Next: Passwd Functions,  Prev: Data 
File Management,  Up: Library Functions
+ 
 -To run a given program, you would typically do something like this:
++13.4 Processing Command-Line Options
++====================================
+ 
 -     awk -f PROGRAM -- OPTIONS FILES
++Most utilities on POSIX compatible systems take options on the command
++line that can be used to change the way a program behaves.  `awk' is an
++example of such a program (*note Options::).  Often, options take
++"arguments"; i.e., data that the program needs to correctly obey the
++command-line option.  For example, `awk''s `-F' option requires a
++string to use as the field separator.  The first occurrence on the
++command line of either `--' or a string that does not begin with `-'
++ends the options.
+ 
 -Here, PROGRAM is the name of the `awk' program (such as `cut.awk'),
 -OPTIONS are any command-line options for the program that start with a
 -`-', and FILES are the actual data files.
++   Modern Unix systems provide a C function named `getopt()' for
++processing command-line arguments.  The programmer provides a string
++describing the one-letter options. If an option requires an argument,
++it is followed in the string with a colon.  `getopt()' is also passed
++the count and values of the command-line arguments and is called in a
++loop.  `getopt()' processes the command-line arguments for option
++letters.  Each time around the loop, it returns a single character
++representing the next option letter that it finds, or `?' if it finds
++an invalid option.  When it returns -1, there are no options left on
++the command line.
+ 
 -   If your system supports the `#!' executable interpreter mechanism
 -(*note Executable Scripts::), you can instead run your program directly:
++   When using `getopt()', options that do not take arguments can be
++grouped together.  Furthermore, options that take arguments require
++that the argument be present.  The argument can immediately follow the
++option letter, or it can be a separate command-line argument.
+ 
 -     cut.awk -c1-8 myfiles > results
++   Given a hypothetical program that takes three command-line options,
++`-a', `-b', and `-c', where `-b' requires an argument, all of the
++following are valid ways of invoking the program:
+ 
 -   If your `awk' is not `gawk', you may instead need to use this:
++     prog -a -b foo -c data1 data2 data3
++     prog -ac -bfoo -- data1 data2 data3
++     prog -acbfoo data1 data2 data3
+ 
 -     cut.awk -- -c1-8 myfiles > results
++   Notice that when the argument is grouped with its option, the rest of
++the argument is considered to be the option's argument.  In this
++example, `-acbfoo' indicates that all of the `-a', `-b', and `-c'
++options were supplied, and that `foo' is the argument to the `-b'
++option.
+ 
 -
 -File: gawk.info,  Node: Clones,  Next: Miscellaneous Programs,  Prev: Running 
Examples,  Up: Sample Programs
++   `getopt()' provides four external variables that the programmer can
++use:
+ 
 -13.2 Reinventing Wheels for Fun and Profit
 -==========================================
++`optind'
++     The index in the argument value array (`argv') where the first
++     nonoption command-line argument can be found.
+ 
 -This minor node presents a number of POSIX utilities implemented in
 -`awk'.  Reinventing these programs in `awk' is often enjoyable, because
 -the algorithms can be very clearly expressed, and the code is usually
 -very concise and simple.  This is true because `awk' does so much for
 -you.
++`optarg'
++     The string value of the argument to an option.
+ 
 -   It should be noted that these programs are not necessarily intended
 -to replace the installed versions on your system.  Nor may all of these
 -programs be fully compliant with the most recent POSIX standard.  This
 -is not a problem; their purpose is to illustrate `awk' language
 -programming for "real world" tasks.
++`opterr'
++     Usually `getopt()' prints an error message when it finds an invalid
++     option.  Setting `opterr' to zero disables this feature.  (An
++     application might want to print its own error message.)
+ 
 -   The programs are presented in alphabetical order.
++`optopt'
++     The letter representing the command-line option.
+ 
 -* Menu:
++   The following C fragment shows how `getopt()' might process
++command-line arguments for `awk':
+ 
 -* Cut Program::                 The `cut' utility.
 -* Egrep Program::               The `egrep' utility.
 -* Id Program::                  The `id' utility.
 -* Split Program::               The `split' utility.
 -* Tee Program::                 The `tee' utility.
 -* Uniq Program::                The `uniq' utility.
 -* Wc Program::                  The `wc' utility.
++     int
++     main(int argc, char *argv[])
++     {
++         ...
++         /* print our own message */
++         opterr = 0;
++         while ((c = getopt(argc, argv, "v:f:F:W:")) != -1) {
++             switch (c) {
++             case 'f':    /* file */
++                 ...
++                 break;
++             case 'F':    /* field separator */
++                 ...
++                 break;
++             case 'v':    /* variable assignment */
++                 ...
++                 break;
++             case 'W':    /* extension */
++                 ...
++                 break;
++             case '?':
++             default:
++                 usage();
++                 break;
++             }
++         }
++         ...
++     }
+ 
 -
 -File: gawk.info,  Node: Cut Program,  Next: Egrep Program,  Up: Clones
++   As a side point, `gawk' actually uses the GNU `getopt_long()'
++function to process both normal and GNU-style long options (*note
++Options::).
+ 
 -13.2.1 Cutting out Fields and Columns
 --------------------------------------
++   The abstraction provided by `getopt()' is very useful and is quite
++handy in `awk' programs as well.  Following is an `awk' version of
++`getopt()'.  This function highlights one of the greatest weaknesses in
++`awk', which is that it is very poor at manipulating single characters.
++Repeated calls to `substr()' are necessary for accessing individual
++characters (*note String Functions::).(1)
+ 
 -The `cut' utility selects, or "cuts," characters or fields from its
 -standard input and sends them to its standard output.  Fields are
 -separated by TABs by default, but you may supply a command-line option
 -to change the field "delimiter" (i.e., the field-separator character).
 -`cut''s definition of fields is less general than `awk''s.
++   The discussion that follows walks through the code a bit at a time:
+ 
 -   A common use of `cut' might be to pull out just the login name of
 -logged-on users from the output of `who'.  For example, the following
 -pipeline generates a sorted, unique list of the logged-on users:
++     # getopt.awk --- Do C library getopt(3) function in awk
+ 
 -     who | cut -c1-8 | sort | uniq
++     # External variables:
++     #    Optind -- index in ARGV of first nonoption argument
++     #    Optarg -- string value of argument to current option
++     #    Opterr -- if nonzero, print our own diagnostic
++     #    Optopt -- current option letter
+ 
 -   The options for `cut' are:
++     # Returns:
++     #    -1     at end of options
++     #    "?"    for unrecognized option
++     #    <c>    a character representing the current option
+ 
 -`-c LIST'
 -     Use LIST as the list of characters to cut out.  Items within the
 -     list may be separated by commas, and ranges of characters can be
 -     separated with dashes.  The list `1-8,15,22-35' specifies
 -     characters 1 through 8, 15, and 22 through 35.
++     # Private Data:
++     #    _opti  -- index in multi-flag option, e.g., -abc
+ 
 -`-f LIST'
 -     Use LIST as the list of fields to cut out.
++   The function starts out with comments presenting a list of the
++global variables it uses, what the return values are, what they mean,
++and any global variables that are "private" to this library function.
++Such documentation is essential for any program, and particularly for
++library functions.
+ 
 -`-d DELIM'
 -     Use DELIM as the field-separator character instead of the TAB
 -     character.
++   The `getopt()' function first checks that it was indeed called with
++a string of options (the `options' parameter).  If `options' has a zero
++length, `getopt()' immediately returns -1:
+ 
 -`-s'
 -     Suppress printing of lines that do not contain the field delimiter.
++     function getopt(argc, argv, options,    thisopt, i)
++     {
++         if (length(options) == 0)    # no options given
++             return -1
+ 
 -   The `awk' implementation of `cut' uses the `getopt()' library
 -function (*note Getopt Function::) and the `join()' library function
 -(*note Join Function::).
++         if (argv[Optind] == "--") {  # all done
++             Optind++
++             _opti = 0
++             return -1
++         } else if (argv[Optind] !~ /^-[^:[:space:]]/) {
++             _opti = 0
++             return -1
++         }
+ 
 -   The program begins with a comment describing the options, the library
 -functions needed, and a `usage()' function that prints out a usage
 -message and exits.  `usage()' is called if invalid arguments are
 -supplied:
++   The next thing to check for is the end of the options.  A `--' ends
++the command-line options, as does any command-line argument that does
++not begin with a `-'.  `Optind' is used to step through the array of
++command-line arguments; it retains its value across calls to
++`getopt()', because it is a global variable.
+ 
 -     # cut.awk --- implement cut in awk
++   The regular expression that is used, `/^-[^:[:space:]/', checks for
++a `-' followed by anything that is not whitespace and not a colon.  If
++the current command-line argument does not match this pattern, it is
++not an option, and it ends option processing. Continuing on:
+ 
 -     # Options:
 -     #    -f list     Cut fields
 -     #    -d c        Field delimiter character
 -     #    -c list     Cut characters
 -     #
 -     #    -s          Suppress lines without the delimiter
 -     #
 -     # Requires getopt() and join() library functions
++         if (_opti == 0)
++             _opti = 2
++         thisopt = substr(argv[Optind], _opti, 1)
++         Optopt = thisopt
++         i = index(options, thisopt)
++         if (i == 0) {
++             if (Opterr)
++                 printf("%c -- invalid option\n",
++                                       thisopt) > "/dev/stderr"
++             if (_opti >= length(argv[Optind])) {
++                 Optind++
++                 _opti = 0
++             } else
++                 _opti++
++             return "?"
++         }
+ 
 -     function usage(    e1, e2)
 -     {
 -         e1 = "usage: cut [-f list] [-d c] [-s] [files...]"
 -         e2 = "usage: cut [-c list] [files...]"
 -         print e1 > "/dev/stderr"
 -         print e2 > "/dev/stderr"
 -         exit 1
 -     }
++   The `_opti' variable tracks the position in the current command-line
++argument (`argv[Optind]').  If multiple options are grouped together
++with one `-' (e.g., `-abx'), it is necessary to return them to the user
++one at a time.
+ 
 -The variables `e1' and `e2' are used so that the function fits nicely
 -on the screen.
++   If `_opti' is equal to zero, it is set to two, which is the index in
++the string of the next character to look at (we skip the `-', which is
++at position one).  The variable `thisopt' holds the character, obtained
++with `substr()'.  It is saved in `Optopt' for the main program to use.
+ 
 -   Next comes a `BEGIN' rule that parses the command-line options.  It
 -sets `FS' to a single TAB character, because that is `cut''s default
 -field separator. The rule then sets the output field separator to be the
 -same as the input field separator.  A loop using `getopt()' steps
 -through the command-line options.  Exactly one of the variables
 -`by_fields' or `by_chars' is set to true, to indicate that processing
 -should be done by fields or by characters, respectively.  When cutting
 -by characters, the output field separator is set to the null string:
++   If `thisopt' is not in the `options' string, then it is an invalid
++option.  If `Opterr' is nonzero, `getopt()' prints an error message on
++the standard error that is similar to the message from the C version of
++`getopt()'.
+ 
 -     BEGIN    \
 -     {
 -         FS = "\t"    # default
 -         OFS = FS
 -         while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) {
 -             if (c == "f") {
 -                 by_fields = 1
 -                 fieldlist = Optarg
 -             } else if (c == "c") {
 -                 by_chars = 1
 -                 fieldlist = Optarg
 -                 OFS = ""
 -             } else if (c == "d") {
 -                 if (length(Optarg) > 1) {
 -                     printf("Using first character of %s" \
 -                            " for delimiter\n", Optarg) > "/dev/stderr"
 -                     Optarg = substr(Optarg, 1, 1)
 -                 }
 -                 FS = Optarg
 -                 OFS = FS
 -                 if (FS == " ")    # defeat awk semantics
 -                     FS = "[ ]"
 -             } else if (c == "s")
 -                 suppress++
++   Because the option is invalid, it is necessary to skip it and move
++on to the next option character.  If `_opti' is greater than or equal
++to the length of the current command-line argument, it is necessary to
++move on to the next argument, so `Optind' is incremented and `_opti' is
++reset to zero. Otherwise, `Optind' is left alone and `_opti' is merely
++incremented.
++
++   In any case, because the option is invalid, `getopt()' returns `"?"'.
++The main program can examine `Optopt' if it needs to know what the
++invalid option letter actually is. Continuing on:
++
++         if (substr(options, i + 1, 1) == ":") {
++             # get option argument
++             if (length(substr(argv[Optind], _opti + 1)) > 0)
++                 Optarg = substr(argv[Optind], _opti + 1)
+              else
 -                 usage()
 -         }
++                 Optarg = argv[++Optind]
++             _opti = 0
++         } else
++             Optarg = ""
+ 
 -         # Clear out options
 -         for (i = 1; i < Optind; i++)
 -             ARGV[i] = ""
++   If the option requires an argument, the option letter is followed by
++a colon in the `options' string.  If there are remaining characters in
++the current command-line argument (`argv[Optind]'), then the rest of
++that string is assigned to `Optarg'.  Otherwise, the next command-line
++argument is used (`-xFOO' versus `-x FOO'). In either case, `_opti' is
++reset to zero, because there are no more characters left to examine in
++the current command-line argument. Continuing:
+ 
 -   The code must take special care when the field delimiter is a space.
 -Using a single space (`" "') for the value of `FS' is incorrect--`awk'
 -would separate fields with runs of spaces, TABs, and/or newlines, and
 -we want them to be separated with individual spaces.  Also remember
 -that after `getopt()' is through (as described in *note Getopt
 -Function::), we have to clear out all the elements of `ARGV' from 1 to
 -`Optind', so that `awk' does not try to process the command-line options
 -as file names.
++         if (_opti == 0 || _opti >= length(argv[Optind])) {
++             Optind++
++             _opti = 0
++         } else
++             _opti++
++         return thisopt
++     }
+ 
 -   After dealing with the command-line options, the program verifies
 -that the options make sense.  Only one or the other of `-c' and `-f'
 -should be used, and both require a field list.  Then the program calls
 -either `set_fieldlist()' or `set_charlist()' to pull apart the list of
 -fields or characters:
++   Finally, if `_opti' is either zero or greater than the length of the
++current command-line argument, it means this element in `argv' is
++through being processed, so `Optind' is incremented to point to the
++next element in `argv'.  If neither condition is true, then only
++`_opti' is incremented, so that the next option letter can be processed
++on the next call to `getopt()'.
+ 
 -         if (by_fields && by_chars)
 -             usage()
++   The `BEGIN' rule initializes both `Opterr' and `Optind' to one.
++`Opterr' is set to one, since the default behavior is for `getopt()' to
++print a diagnostic message upon seeing an invalid option.  `Optind' is
++set to one, since there's no reason to look at the program name, which
++is in `ARGV[0]':
+ 
 -         if (by_fields == 0 && by_chars == 0)
 -             by_fields = 1    # default
++     BEGIN {
++         Opterr = 1    # default is to diagnose
++         Optind = 1    # skip ARGV[0]
+ 
 -         if (fieldlist == "") {
 -             print "cut: needs list for -c or -f" > "/dev/stderr"
 -             exit 1
++         # test program
++         if (_getopt_test) {
++             while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1)
++                 printf("c = <%c>, optarg = <%s>\n",
++                                            _go_c, Optarg)
++             printf("non-option arguments:\n")
++             for (; Optind < ARGC; Optind++)
++                 printf("\tARGV[%d] = <%s>\n",
++                                         Optind, ARGV[Optind])
+          }
 -
 -         if (by_fields)
 -             set_fieldlist()
 -         else
 -             set_charlist()
+      }
+ 
 -   `set_fieldlist()' splits the field list apart at the commas into an
 -array.  Then, for each element of the array, it looks to see if the
 -element is actually a range, and if so, splits it apart.  The function
 -checks the range to make sure that the first number is smaller than the
 -second.  Each number in the list is added to the `flist' array, which
 -simply lists the fields that will be printed.  Normal field splitting
 -is used.  The program lets `awk' handle the job of doing the field
 -splitting:
++   The rest of the `BEGIN' rule is a simple test program.  Here is the
++result of two sample runs of the test program:
+ 
 -     function set_fieldlist(        n, m, i, j, k, f, g)
 -     {
 -         n = split(fieldlist, f, ",")
 -         j = 1    # index in flist
 -         for (i = 1; i <= n; i++) {
 -             if (index(f[i], "-") != 0) { # a range
 -                 m = split(f[i], g, "-")
 -                 if (m != 2 || g[1] >= g[2]) {
 -                     printf("bad field list: %s\n",
 -                                       f[i]) > "/dev/stderr"
 -                     exit 1
 -                 }
 -                 for (k = g[1]; k <= g[2]; k++)
 -                     flist[j++] = k
 -             } else
 -                 flist[j++] = f[i]
 -         }
 -         nfields = j - 1
 -     }
++     $ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x
++     -| c = <a>, optarg = <>
++     -| c = <c>, optarg = <>
++     -| c = <b>, optarg = <ARG>
++     -| non-option arguments:
++     -|         ARGV[3] = <bax>
++     -|         ARGV[4] = <-x>
+ 
 -   The `set_charlist()' function is more complicated than
 -`set_fieldlist()'.  The idea here is to use `gawk''s `FIELDWIDTHS'
 -variable (*note Constant Size::), which describes constant-width input.
 -When using a character list, that is exactly what we have.
++     $ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc
++     -| c = <a>, optarg = <>
++     error--> x -- invalid option
++     -| c = <?>, optarg = <>
++     -| non-option arguments:
++     -|         ARGV[4] = <xyz>
++     -|         ARGV[5] = <abc>
+ 
 -   Setting up `FIELDWIDTHS' is more complicated than simply listing the
 -fields that need to be printed.  We have to keep track of the fields to
 -print and also the intervening characters that have to be skipped.  For
 -example, suppose you wanted characters 1 through 8, 15, and 22 through
 -35.  You would use `-c 1-8,15,22-35'.  The necessary value for
 -`FIELDWIDTHS' is `"8 6 1 6 14"'.  This yields five fields, and the
 -fields to print are `$1', `$3', and `$5'.  The intermediate fields are
 -"filler", which is stuff in between the desired data.  `flist' lists
 -the fields to print, and `t' tracks the complete field list, including
 -filler fields:
++   In both runs, the first `--' terminates the arguments to `awk', so
++that it does not try to interpret the `-a', etc., as its own options.
+ 
 -     function set_charlist(    field, i, j, f, g, t,
 -                               filler, last, len)
 -     {
 -         field = 1   # count total fields
 -         n = split(fieldlist, f, ",")
 -         j = 1       # index in flist
 -         for (i = 1; i <= n; i++) {
 -             if (index(f[i], "-") != 0) { # range
++     NOTE: After `getopt()' is through, it is the responsibility of the
++     user level code to clear out all the elements of `ARGV' from 1 to
++     `Optind', so that `awk' does not try to process the command-line
++     options as file names.
++
++   Several of the sample programs presented in *note Sample Programs::,
++use `getopt()' to process their arguments.
++
++   ---------- Footnotes ----------
++
++   (1) This function was written before `gawk' acquired the ability to
++split strings into single characters using `""' as the separator.  We
++have left it alone, since using `substr()' is more portable.
++
++
++File: gawk.info,  Node: Passwd Functions,  Next: Group Functions,  Prev: 
Getopt Function,  Up: Library Functions
++
++13.5 Reading the User Database
++==============================
++
++The `PROCINFO' array (*note Built-in Variables::) provides access to
++the current user's real and effective user and group ID numbers, and if
++available, the user's supplementary group set.  However, because these
++are numbers, they do not provide very useful information to the average
++user.  There needs to be some way to find the user information
++associated with the user and group ID numbers.  This minor node
++presents a suite of functions for retrieving information from the user
++database.  *Note Group Functions::, for a similar suite that retrieves
++information from the group database.
++
++   The POSIX standard does not define the file where user information is
++kept.  Instead, it provides the `<pwd.h>' header file and several C
++language subroutines for obtaining user information.  The primary
++function is `getpwent()', for "get password entry."  The "password"
++comes from the original user database file, `/etc/passwd', which stores
++user information, along with the encrypted passwords (hence the name).
++
++   While an `awk' program could simply read `/etc/passwd' directly,
++this file may not contain complete information about the system's set
++of users.(1) To be sure you are able to produce a readable and complete
++version of the user database, it is necessary to write a small C
++program that calls `getpwent()'.  `getpwent()' is defined as returning
++a pointer to a `struct passwd'.  Each time it is called, it returns the
++next entry in the database.  When there are no more entries, it returns
++`NULL', the null pointer.  When this happens, the C program should call
++`endpwent()' to close the database.  Following is `pwcat', a C program
++that "cats" the password database:
++
++     /*
++      * pwcat.c
++      *
++      * Generate a printable version of the password database
++      */
++     #include <stdio.h>
++     #include <pwd.h>
++
++     int
++     main(int argc, char **argv)
++     {
++         struct passwd *p;
++
++         while ((p = getpwent()) != NULL)
++             printf("%s:%s:%ld:%ld:%s:%s:%s\n",
++                 p->pw_name, p->pw_passwd, (long) p->pw_uid,
++                 (long) p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell);
++
++         endpwent();
++         return 0;
++     }
++
++   If you don't understand C, don't worry about it.  The output from
++`pwcat' is the user database, in the traditional `/etc/passwd' format
++of colon-separated fields.  The fields are:
++
++Login name
++     The user's login name.
++
++Encrypted password
++     The user's encrypted password.  This may not be available on some
++     systems.
++
++User-ID
++     The user's numeric user ID number.  (On some systems it's a C
++     `long', and not an `int'.  Thus we cast it to `long' for all
++     cases.)
++
++Group-ID
++     The user's numeric group ID number.  (Similar comments about
++     `long' vs. `int' apply here.)
++
++Full name
++     The user's full name, and perhaps other information associated
++     with the user.
++
++Home directory
++     The user's login (or "home") directory (familiar to shell
++     programmers as `$HOME').
++
++Login shell
++     The program that is run when the user logs in.  This is usually a
++     shell, such as Bash.
++
++   A few lines representative of `pwcat''s output are as follows:
++
++     $ pwcat
++     -| root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh
++     -| nobody:*:65534:65534::/:
++     -| daemon:*:1:1::/:
++     -| sys:*:2:2::/:/bin/csh
++     -| bin:*:3:3::/bin:
++     -| arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh
++     -| miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh
++     -| andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh
++     ...
++
++   With that introduction, following is a group of functions for
++getting user information.  There are several functions here,
++corresponding to the C functions of the same names:
++
++     # passwd.awk --- access password file information
++
++     BEGIN {
++         # tailor this to suit your system
++         _pw_awklib = "/usr/local/libexec/awk/"
++     }
++
++     function _pw_init(    oldfs, oldrs, olddol0, pwcat, using_fw, using_fpat)
++     {
++         if (_pw_inited)
++             return
++
++         oldfs = FS
++         oldrs = RS
++         olddol0 = $0
++         using_fw = (PROCINFO["FS"] == "FIELDWIDTHS")
++         using_fpat = (PROCINFO["FS"] == "FPAT")
++         FS = ":"
++         RS = "\n"
++
++         pwcat = _pw_awklib "pwcat"
++         while ((pwcat | getline) > 0) {
++             _pw_byname[$1] = $0
++             _pw_byuid[$3] = $0
++             _pw_bycount[++_pw_total] = $0
++         }
++         close(pwcat)
++         _pw_count = 0
++         _pw_inited = 1
++         FS = oldfs
++         if (using_fw)
++             FIELDWIDTHS = FIELDWIDTHS
++         else if (using_fpat)
++             FPAT = FPAT
++         RS = oldrs
++         $0 = olddol0
++     }
++
++   The `BEGIN' rule sets a private variable to the directory where
++`pwcat' is stored.  Because it is used to help out an `awk' library
++routine, we have chosen to put it in `/usr/local/libexec/awk'; however,
++you might want it to be in a different directory on your system.
++
++   The function `_pw_init()' keeps three copies of the user information
++in three associative arrays.  The arrays are indexed by username
++(`_pw_byname'), by user ID number (`_pw_byuid'), and by order of
++occurrence (`_pw_bycount').  The variable `_pw_inited' is used for
++efficiency, since `_pw_init()' needs to be called only once.
++
++   Because this function uses `getline' to read information from
++`pwcat', it first saves the values of `FS', `RS', and `$0'.  It notes
++in the variable `using_fw' whether field splitting with `FIELDWIDTHS'
++is in effect or not.  Doing so is necessary, since these functions
++could be called from anywhere within a user's program, and the user may
++have his or her own way of splitting records and fields.
++
++   The `using_fw' variable checks `PROCINFO["FS"]', which is
++`"FIELDWIDTHS"' if field splitting is being done with `FIELDWIDTHS'.
++This makes it possible to restore the correct field-splitting mechanism
++later.  The test can only be true for `gawk'.  It is false if using
++`FS' or `FPAT', or on some other `awk' implementation.
++
++   The code that checks for using `FPAT', using `using_fpat' and
++`PROCINFO["FS"]' is similar.
++
++   The main part of the function uses a loop to read database lines,
++split the line into fields, and then store the line into each array as
++necessary.  When the loop is done, `_pw_init()' cleans up by closing
++the pipeline, setting `_pw_inited' to one, and restoring `FS' (and
++`FIELDWIDTHS' or `FPAT' if necessary), `RS', and `$0'.  The use of
++`_pw_count' is explained shortly.
++
++   The `getpwnam()' function takes a username as a string argument. If
++that user is in the database, it returns the appropriate line.
++Otherwise, it relies on the array reference to a nonexistent element to
++create the element with the null string as its value:
++
++     function getpwnam(name)
++     {
++         _pw_init()
++         return _pw_byname[name]
++     }
++
++   Similarly, the `getpwuid' function takes a user ID number argument.
++If that user number is in the database, it returns the appropriate
++line. Otherwise, it returns the null string:
++
++     function getpwuid(uid)
++     {
++         _pw_init()
++         return _pw_byuid[uid]
++     }
++
++   The `getpwent()' function simply steps through the database, one
++entry at a time.  It uses `_pw_count' to track its current position in
++the `_pw_bycount' array:
++
++     function getpwent()
++     {
++         _pw_init()
++         if (_pw_count < _pw_total)
++             return _pw_bycount[++_pw_count]
++         return ""
++     }
++
++   The `endpwent()' function resets `_pw_count' to zero, so that
++subsequent calls to `getpwent()' start over again:
++
++     function endpwent()
++     {
++         _pw_count = 0
++     }
++
++   A conscious design decision in this suite is that each subroutine
++calls `_pw_init()' to initialize the database arrays.  The overhead of
++running a separate process to generate the user database, and the I/O
++to scan it, are only incurred if the user's main program actually calls
++one of these functions.  If this library file is loaded along with a
++user's program, but none of the routines are ever called, then there is
++no extra runtime overhead.  (The alternative is move the body of
++`_pw_init()' into a `BEGIN' rule, which always runs `pwcat'.  This
++simplifies the code but runs an extra process that may never be needed.)
++
++   In turn, calling `_pw_init()' is not too expensive, because the
++`_pw_inited' variable keeps the program from reading the data more than
++once.  If you are worried about squeezing every last cycle out of your
++`awk' program, the check of `_pw_inited' could be moved out of
++`_pw_init()' and duplicated in all the other functions.  In practice,
++this is not necessary, since most `awk' programs are I/O-bound, and
++such a change would clutter up the code.
++
++   The `id' program in *note Id Program::, uses these functions.
++
++   ---------- Footnotes ----------
++
++   (1) It is often the case that password information is stored in a
++network database.
++
++
++File: gawk.info,  Node: Group Functions,  Next: Walking Arrays,  Prev: Passwd 
Functions,  Up: Library Functions
++
++13.6 Reading the Group Database
++===============================
++
++Much of the discussion presented in *note Passwd Functions::, applies
++to the group database as well.  Although there has traditionally been a
++well-known file (`/etc/group') in a well-known format, the POSIX
++standard only provides a set of C library routines (`<grp.h>' and
++`getgrent()') for accessing the information.  Even though this file may
++exist, it may not have complete information.  Therefore, as with the
++user database, it is necessary to have a small C program that generates
++the group database as its output.  `grcat', a C program that "cats" the
++group database, is as follows:
++
++     /*
++      * grcat.c
++      *
++      * Generate a printable version of the group database
++      */
++     #include <stdio.h>
++     #include <grp.h>
++
++     int
++     main(int argc, char **argv)
++     {
++         struct group *g;
++         int i;
++
++         while ((g = getgrent()) != NULL) {
++             printf("%s:%s:%ld:", g->gr_name, g->gr_passwd,
++                                          (long) g->gr_gid);
++             for (i = 0; g->gr_mem[i] != NULL; i++) {
++                 printf("%s", g->gr_mem[i]);
++                 if (g->gr_mem[i+1] != NULL)
++                     putchar(',');
++             }
++             putchar('\n');
++         }
++         endgrent();
++         return 0;
++     }
++
++   Each line in the group database represents one group.  The fields are
++separated with colons and represent the following information:
++
++Group Name
++     The group's name.
++
++Group Password
++     The group's encrypted password. In practice, this field is never
++     used; it is usually empty or set to `*'.
++
++Group ID Number
++     The group's numeric group ID number; this number must be unique
++     within the file.  (On some systems it's a C `long', and not an
++     `int'.  Thus we cast it to `long' for all cases.)
++
++Group Member List
++     A comma-separated list of user names.  These users are members of
++     the group.  Modern Unix systems allow users to be members of
++     several groups simultaneously.  If your system does, then there
++     are elements `"group1"' through `"groupN"' in `PROCINFO' for those
++     group ID numbers.  (Note that `PROCINFO' is a `gawk' extension;
++     *note Built-in Variables::.)
++
++   Here is what running `grcat' might produce:
++
++     $ grcat
++     -| wheel:*:0:arnold
++     -| nogroup:*:65534:
++     -| daemon:*:1:
++     -| kmem:*:2:
++     -| staff:*:10:arnold,miriam,andy
++     -| other:*:20:
++     ...
++
++   Here are the functions for obtaining information from the group
++database.  There are several, modeled after the C library functions of
++the same names:
++
++     # group.awk --- functions for dealing with the group file
++
++     BEGIN    \
++     {
++         # Change to suit your system
++         _gr_awklib = "/usr/local/libexec/awk/"
++     }
++
++     function _gr_init(    oldfs, oldrs, olddol0, grcat,
++                                  using_fw, using_fpat, n, a, i)
++     {
++         if (_gr_inited)
++             return
++
++         oldfs = FS
++         oldrs = RS
++         olddol0 = $0
++         using_fw = (PROCINFO["FS"] == "FIELDWIDTHS")
++         using_fpat = (PROCINFO["FS"] == "FPAT")
++         FS = ":"
++         RS = "\n"
++
++         grcat = _gr_awklib "grcat"
++         while ((grcat | getline) > 0) {
++             if ($1 in _gr_byname)
++                 _gr_byname[$1] = _gr_byname[$1] "," $4
++             else
++                 _gr_byname[$1] = $0
++             if ($3 in _gr_bygid)
++                 _gr_bygid[$3] = _gr_bygid[$3] "," $4
++             else
++                 _gr_bygid[$3] = $0
++
++             n = split($4, a, "[ \t]*,[ \t]*")
++             for (i = 1; i <= n; i++)
++                 if (a[i] in _gr_groupsbyuser)
++                     _gr_groupsbyuser[a[i]] = \
++                         _gr_groupsbyuser[a[i]] " " $1
++                 else
++                     _gr_groupsbyuser[a[i]] = $1
++
++             _gr_bycount[++_gr_count] = $0
++         }
++         close(grcat)
++         _gr_count = 0
++         _gr_inited++
++         FS = oldfs
++         if (using_fw)
++             FIELDWIDTHS = FIELDWIDTHS
++         else if (using_fpat)
++             FPAT = FPAT
++         RS = oldrs
++         $0 = olddol0
++     }
++
++   The `BEGIN' rule sets a private variable to the directory where
++`grcat' is stored.  Because it is used to help out an `awk' library
++routine, we have chosen to put it in `/usr/local/libexec/awk'.  You
++might want it to be in a different directory on your system.
++
++   These routines follow the same general outline as the user database
++routines (*note Passwd Functions::).  The `_gr_inited' variable is used
++to ensure that the database is scanned no more than once.  The
++`_gr_init()' function first saves `FS', `RS', and `$0', and then sets
++`FS' and `RS' to the correct values for scanning the group information.
++It also takes care to note whether `FIELDWIDTHS' or `FPAT' is being
++used, and to restore the appropriate field splitting mechanism.
++
++   The group information is stored is several associative arrays.  The
++arrays are indexed by group name (`_gr_byname'), by group ID number
++(`_gr_bygid'), and by position in the database (`_gr_bycount').  There
++is an additional array indexed by user name (`_gr_groupsbyuser'), which
++is a space-separated list of groups to which each user belongs.
++
++   Unlike the user database, it is possible to have multiple records in
++the database for the same group.  This is common when a group has a
++large number of members.  A pair of such entries might look like the
++following:
++
++     tvpeople:*:101:johnny,jay,arsenio
++     tvpeople:*:101:david,conan,tom,joan
++
++   For this reason, `_gr_init()' looks to see if a group name or group
++ID number is already seen.  If it is, then the user names are simply
++concatenated onto the previous list of users.  (There is actually a
++subtle problem with the code just presented.  Suppose that the first
++time there were no names. This code adds the names with a leading
++comma. It also doesn't check that there is a `$4'.)
++
++   Finally, `_gr_init()' closes the pipeline to `grcat', restores `FS'
++(and `FIELDWIDTHS' or `FPAT' if necessary), `RS', and `$0', initializes
++`_gr_count' to zero (it is used later), and makes `_gr_inited' nonzero.
++
++   The `getgrnam()' function takes a group name as its argument, and if
++that group exists, it is returned.  Otherwise, it relies on the array
++reference to a nonexistent element to create the element with the null
++string as its value:
++
++     function getgrnam(group)
++     {
++         _gr_init()
++         return _gr_byname[group]
++     }
++
++   The `getgrgid()' function is similar; it takes a numeric group ID and
++looks up the information associated with that group ID:
++
++     function getgrgid(gid)
++     {
++         _gr_init()
++         return _gr_bygid[gid]
++     }
++
++   The `getgruser()' function does not have a C counterpart. It takes a
++user name and returns the list of groups that have the user as a member:
++
++     function getgruser(user)
++     {
++         _gr_init()
++         return _gr_groupsbyuser[user]
++     }
++
++   The `getgrent()' function steps through the database one entry at a
++time.  It uses `_gr_count' to track its position in the list:
++
++     function getgrent()
++     {
++         _gr_init()
++         if (++_gr_count in _gr_bycount)
++             return _gr_bycount[_gr_count]
++         return ""
++     }
++
++   The `endgrent()' function resets `_gr_count' to zero so that
++`getgrent()' can start over again:
++
++     function endgrent()
++     {
++         _gr_count = 0
++     }
++
++   As with the user database routines, each function calls `_gr_init()'
++to initialize the arrays.  Doing so only incurs the extra overhead of
++running `grcat' if these functions are used (as opposed to moving the
++body of `_gr_init()' into a `BEGIN' rule).
++
++   Most of the work is in scanning the database and building the various
++associative arrays.  The functions that the user calls are themselves
++very simple, relying on `awk''s associative arrays to do work.
++
++   The `id' program in *note Id Program::, uses these functions.
++
++
++File: gawk.info,  Node: Walking Arrays,  Prev: Group Functions,  Up: Library 
Functions
++
++13.7 Traversing Arrays of Arrays
++================================
++
++*note Arrays of Arrays::, described how `gawk' provides arrays of
++arrays.  In particular, any element of an array may be either a scalar,
++or another array. The `isarray()' function (*note Type Functions::)
++lets you distinguish an array from a scalar.  The following function,
++`walk_array()', recursively traverses an array, printing each element's
++indices and value.  You call it with the array and a string
++representing the name of the array:
++
++     function walk_array(arr, name,      i)
++     {
++         for (i in arr) {
++             if (isarray(arr[i]))
++                 walk_array(arr[i], (name "[" i "]"))
++             else
++                 printf("%s[%s] = %s\n", name, i, arr[i])
++         }
++     }
++
++It works by looping over each element of the array. If any given
++element is itself an array, the function calls itself recursively,
++passing the subarray and a new string representing the current index.
++Otherwise, the function simply prints the element's name, index, and
++value.  Here is a main program to demonstrate:
++
++     BEGIN {
++         a[1] = 1
++         a[2][1] = 21
++         a[2][2] = 22
++         a[3] = 3
++         a[4][1][1] = 411
++         a[4][2] = 42
++
++         walk_array(a, "a")
++     }
++
++   When run, the program produces the following output:
++
++     $ gawk -f walk_array.awk
++     -| a[4][1][1] = 411
++     -| a[4][2] = 42
++     -| a[1] = 1
++     -| a[2][1] = 21
++     -| a[2][2] = 22
++     -| a[3] = 3
++
++
++File: gawk.info,  Node: Sample Programs,  Next: Debugger,  Prev: Library 
Functions,  Up: Top
++
++14 Practical `awk' Programs
++***************************
++
++*note Library Functions::, presents the idea that reading programs in a
++language contributes to learning that language.  This major node
++continues that theme, presenting a potpourri of `awk' programs for your
++reading enjoyment.
++
++   Many of these programs use library functions presented in *note
++Library Functions::.
++
++* Menu:
++
++* Running Examples::            How to run these examples.
++* Clones::                      Clones of common utilities.
++* Miscellaneous Programs::      Some interesting `awk' programs.
++
++
++File: gawk.info,  Node: Running Examples,  Next: Clones,  Up: Sample Programs
++
++14.1 Running the Example Programs
++=================================
++
++To run a given program, you would typically do something like this:
++
++     awk -f PROGRAM -- OPTIONS FILES
++
++Here, PROGRAM is the name of the `awk' program (such as `cut.awk'),
++OPTIONS are any command-line options for the program that start with a
++`-', and FILES are the actual data files.
++
++   If your system supports the `#!' executable interpreter mechanism
++(*note Executable Scripts::), you can instead run your program directly:
++
++     cut.awk -c1-8 myfiles > results
++
++   If your `awk' is not `gawk', you may instead need to use this:
++
++     cut.awk -- -c1-8 myfiles > results
++
++
++File: gawk.info,  Node: Clones,  Next: Miscellaneous Programs,  Prev: Running 
Examples,  Up: Sample Programs
++
++14.2 Reinventing Wheels for Fun and Profit
++==========================================
++
++This minor node presents a number of POSIX utilities implemented in
++`awk'.  Reinventing these programs in `awk' is often enjoyable, because
++the algorithms can be very clearly expressed, and the code is usually
++very concise and simple.  This is true because `awk' does so much for
++you.
++
++   It should be noted that these programs are not necessarily intended
++to replace the installed versions on your system.  Nor may all of these
++programs be fully compliant with the most recent POSIX standard.  This
++is not a problem; their purpose is to illustrate `awk' language
++programming for "real world" tasks.
++
++   The programs are presented in alphabetical order.
++
++* Menu:
++
++* Cut Program::                 The `cut' utility.
++* Egrep Program::               The `egrep' utility.
++* Id Program::                  The `id' utility.
++* Split Program::               The `split' utility.
++* Tee Program::                 The `tee' utility.
++* Uniq Program::                The `uniq' utility.
++* Wc Program::                  The `wc' utility.
++
++
++File: gawk.info,  Node: Cut Program,  Next: Egrep Program,  Up: Clones
++
++14.2.1 Cutting out Fields and Columns
++-------------------------------------
++
++The `cut' utility selects, or "cuts," characters or fields from its
++standard input and sends them to its standard output.  Fields are
++separated by TABs by default, but you may supply a command-line option
++to change the field "delimiter" (i.e., the field-separator character).
++`cut''s definition of fields is less general than `awk''s.
++
++   A common use of `cut' might be to pull out just the login name of
++logged-on users from the output of `who'.  For example, the following
++pipeline generates a sorted, unique list of the logged-on users:
++
++     who | cut -c1-8 | sort | uniq
++
++   The options for `cut' are:
++
++`-c LIST'
++     Use LIST as the list of characters to cut out.  Items within the
++     list may be separated by commas, and ranges of characters can be
++     separated with dashes.  The list `1-8,15,22-35' specifies
++     characters 1 through 8, 15, and 22 through 35.
++
++`-f LIST'
++     Use LIST as the list of fields to cut out.
++
++`-d DELIM'
++     Use DELIM as the field-separator character instead of the TAB
++     character.
++
++`-s'
++     Suppress printing of lines that do not contain the field delimiter.
++
++   The `awk' implementation of `cut' uses the `getopt()' library
++function (*note Getopt Function::) and the `join()' library function
++(*note Join Function::).
++
++   The program begins with a comment describing the options, the library
++functions needed, and a `usage()' function that prints out a usage
++message and exits.  `usage()' is called if invalid arguments are
++supplied:
++
++     # cut.awk --- implement cut in awk
++
++     # Options:
++     #    -f list     Cut fields
++     #    -d c        Field delimiter character
++     #    -c list     Cut characters
++     #
++     #    -s          Suppress lines without the delimiter
++     #
++     # Requires getopt() and join() library functions
++
++     function usage(    e1, e2)
++     {
++         e1 = "usage: cut [-f list] [-d c] [-s] [files...]"
++         e2 = "usage: cut [-c list] [files...]"
++         print e1 > "/dev/stderr"
++         print e2 > "/dev/stderr"
++         exit 1
++     }
++
++The variables `e1' and `e2' are used so that the function fits nicely
++on the screen.
++
++   Next comes a `BEGIN' rule that parses the command-line options.  It
++sets `FS' to a single TAB character, because that is `cut''s default
++field separator. The rule then sets the output field separator to be the
++same as the input field separator.  A loop using `getopt()' steps
++through the command-line options.  Exactly one of the variables
++`by_fields' or `by_chars' is set to true, to indicate that processing
++should be done by fields or by characters, respectively.  When cutting
++by characters, the output field separator is set to the null string:
++
++     BEGIN    \
++     {
++         FS = "\t"    # default
++         OFS = FS
++         while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) {
++             if (c == "f") {
++                 by_fields = 1
++                 fieldlist = Optarg
++             } else if (c == "c") {
++                 by_chars = 1
++                 fieldlist = Optarg
++                 OFS = ""
++             } else if (c == "d") {
++                 if (length(Optarg) > 1) {
++                     printf("Using first character of %s" \
++                            " for delimiter\n", Optarg) > "/dev/stderr"
++                     Optarg = substr(Optarg, 1, 1)
++                 }
++                 FS = Optarg
++                 OFS = FS
++                 if (FS == " ")    # defeat awk semantics
++                     FS = "[ ]"
++             } else if (c == "s")
++                 suppress++
++             else
++                 usage()
++         }
++
++         # Clear out options
++         for (i = 1; i < Optind; i++)
++             ARGV[i] = ""
++
++   The code must take special care when the field delimiter is a space.
++Using a single space (`" "') for the value of `FS' is incorrect--`awk'
++would separate fields with runs of spaces, TABs, and/or newlines, and
++we want them to be separated with individual spaces.  Also remember
++that after `getopt()' is through (as described in *note Getopt
++Function::), we have to clear out all the elements of `ARGV' from 1 to
++`Optind', so that `awk' does not try to process the command-line options
++as file names.
++
++   After dealing with the command-line options, the program verifies
++that the options make sense.  Only one or the other of `-c' and `-f'
++should be used, and both require a field list.  Then the program calls
++either `set_fieldlist()' or `set_charlist()' to pull apart the list of
++fields or characters:
++
++         if (by_fields && by_chars)
++             usage()
++
++         if (by_fields == 0 && by_chars == 0)
++             by_fields = 1    # default
++
++         if (fieldlist == "") {
++             print "cut: needs list for -c or -f" > "/dev/stderr"
++             exit 1
++         }
++
++         if (by_fields)
++             set_fieldlist()
++         else
++             set_charlist()
++     }
++
++   `set_fieldlist()' splits the field list apart at the commas into an
++array.  Then, for each element of the array, it looks to see if the
++element is actually a range, and if so, splits it apart.  The function
++checks the range to make sure that the first number is smaller than the
++second.  Each number in the list is added to the `flist' array, which
++simply lists the fields that will be printed.  Normal field splitting
++is used.  The program lets `awk' handle the job of doing the field
++splitting:
++
++     function set_fieldlist(        n, m, i, j, k, f, g)
++     {
++         n = split(fieldlist, f, ",")
++         j = 1    # index in flist
++         for (i = 1; i <= n; i++) {
++             if (index(f[i], "-") != 0) { # a range
++                 m = split(f[i], g, "-")
++                 if (m != 2 || g[1] >= g[2]) {
++                     printf("bad field list: %s\n",
++                                       f[i]) > "/dev/stderr"
++                     exit 1
++                 }
++                 for (k = g[1]; k <= g[2]; k++)
++                     flist[j++] = k
++             } else
++                 flist[j++] = f[i]
++         }
++         nfields = j - 1
++     }
++
++   The `set_charlist()' function is more complicated than
++`set_fieldlist()'.  The idea here is to use `gawk''s `FIELDWIDTHS'
++variable (*note Constant Size::), which describes constant-width input.
++When using a character list, that is exactly what we have.
++
++   Setting up `FIELDWIDTHS' is more complicated than simply listing the
++fields that need to be printed.  We have to keep track of the fields to
++print and also the intervening characters that have to be skipped.  For
++example, suppose you wanted characters 1 through 8, 15, and 22 through
++35.  You would use `-c 1-8,15,22-35'.  The necessary value for
++`FIELDWIDTHS' is `"8 6 1 6 14"'.  This yields five fields, and the
++fields to print are `$1', `$3', and `$5'.  The intermediate fields are
++"filler", which is stuff in between the desired data.  `flist' lists
++the fields to print, and `t' tracks the complete field list, including
++filler fields:
++
++     function set_charlist(    field, i, j, f, g, t,
++                               filler, last, len)
++     {
++         field = 1   # count total fields
++         n = split(fieldlist, f, ",")
++         j = 1       # index in flist
++         for (i = 1; i <= n; i++) {
++             if (index(f[i], "-") != 0) { # range
+                  m = split(f[i], g, "-")
+                  if (m != 2 || g[1] >= g[2]) {
+                      printf("bad character list: %s\n",
+                                     f[i]) > "/dev/stderr"
+                      exit 1
+                  }
+                  len = g[2] - g[1] + 1
+                  if (g[1] > 1)  # compute length of filler
+                      filler = g[1] - last - 1
+                  else
+                      filler = 0
+                  if (filler)
+                      t[field++] = filler
+                  t[field++] = len  # length of field
+                  last = g[2]
+                  flist[j++] = field - 1
+              } else {
+                  if (f[i] > 1)
+                      filler = f[i] - last - 1
+                  else
+                      filler = 0
+                  if (filler)
+                      t[field++] = filler
+                  t[field++] = 1
+                  last = f[i]
+                  flist[j++] = field - 1
+              }
+          }
 -         FIELDWIDTHS = join(t, 1, field - 1)
 -         nfields = j - 1
++         FIELDWIDTHS = join(t, 1, field - 1)
++         nfields = j - 1
++     }
++
++   Next is the rule that actually processes the data.  If the `-s'
++option is given, then `suppress' is true.  The first `if' statement
++makes sure that the input record does have the field separator.  If
++`cut' is processing fields, `suppress' is true, and the field separator
++character is not in the record, then the record is skipped.
++
++   If the record is valid, then `gawk' has split the data into fields,
++either using the character in `FS' or using fixed-length fields and
++`FIELDWIDTHS'.  The loop goes through the list of fields that should be
++printed.  The corresponding field is printed if it contains data.  If
++the next field also has data, then the separator character is written
++out between the fields:
++
++     {
++         if (by_fields && suppress && index($0, FS) != 0)
++             next
++
++         for (i = 1; i <= nfields; i++) {
++             if ($flist[i] != "") {
++                 printf "%s", $flist[i]
++                 if (i < nfields && $flist[i+1] != "")
++                     printf "%s", OFS
++             }
++         }
++         print ""
++     }
++
++   This version of `cut' relies on `gawk''s `FIELDWIDTHS' variable to
++do the character-based cutting.  While it is possible in other `awk'
++implementations to use `substr()' (*note String Functions::), it is
++also extremely painful.  The `FIELDWIDTHS' variable supplies an elegant
++solution to the problem of picking the input line apart by characters.
++
++
++File: gawk.info,  Node: Egrep Program,  Next: Id Program,  Prev: Cut Program, 
 Up: Clones
++
++14.2.2 Searching for Regular Expressions in Files
++-------------------------------------------------
++
++The `egrep' utility searches files for patterns.  It uses regular
++expressions that are almost identical to those available in `awk'
++(*note Regexp::).  You invoke it as follows:
++
++     egrep [ OPTIONS ] 'PATTERN' FILES ...
++
++   The PATTERN is a regular expression.  In typical usage, the regular
++expression is quoted to prevent the shell from expanding any of the
++special characters as file name wildcards.  Normally, `egrep' prints
++the lines that matched.  If multiple file names are provided on the
++command line, each output line is preceded by the name of the file and
++a colon.
++
++   The options to `egrep' are as follows:
++
++`-c'
++     Print out a count of the lines that matched the pattern, instead
++     of the lines themselves.
++
++`-s'
++     Be silent.  No output is produced and the exit value indicates
++     whether the pattern was matched.
++
++`-v'
++     Invert the sense of the test. `egrep' prints the lines that do
++     _not_ match the pattern and exits successfully if the pattern is
++     not matched.
++
++`-i'
++     Ignore case distinctions in both the pattern and the input data.
++
++`-l'
++     Only print (list) the names of the files that matched, not the
++     lines that matched.
++
++`-e PATTERN'
++     Use PATTERN as the regexp to match.  The purpose of the `-e'
++     option is to allow patterns that start with a `-'.
++
++   This version uses the `getopt()' library function (*note Getopt
++Function::) and the file transition library program (*note Filetrans
++Function::).
++
++   The program begins with a descriptive comment and then a `BEGIN' rule
++that processes the command-line arguments with `getopt()'.  The `-i'
++(ignore case) option is particularly easy with `gawk'; we just use the
++`IGNORECASE' built-in variable (*note Built-in Variables::):
++
++     # egrep.awk --- simulate egrep in awk
++     #
++     # Options:
++     #    -c    count of lines
++     #    -s    silent - use exit value
++     #    -v    invert test, success if no match
++     #    -i    ignore case
++     #    -l    print filenames only
++     #    -e    argument is pattern
++     #
++     # Requires getopt and file transition library functions
++
++     BEGIN {
++         while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) {
++             if (c == "c")
++                 count_only++
++             else if (c == "s")
++                 no_print++
++             else if (c == "v")
++                 invert++
++             else if (c == "i")
++                 IGNORECASE = 1
++             else if (c == "l")
++                 filenames_only++
++             else if (c == "e")
++                 pattern = Optarg
++             else
++                 usage()
++         }
++
++   Next comes the code that handles the `egrep'-specific behavior. If no
++pattern is supplied with `-e', the first nonoption on the command line
++is used.  The `awk' command-line arguments up to `ARGV[Optind]' are
++cleared, so that `awk' won't try to process them as files.  If no files
++are specified, the standard input is used, and if multiple files are
++specified, we make sure to note this so that the file names can precede
++the matched lines in the output:
++
++         if (pattern == "")
++             pattern = ARGV[Optind++]
++
++         for (i = 1; i < Optind; i++)
++             ARGV[i] = ""
++         if (Optind >= ARGC) {
++             ARGV[1] = "-"
++             ARGC = 2
++         } else if (ARGC - Optind > 1)
++             do_filenames++
++
++     #    if (IGNORECASE)
++     #        pattern = tolower(pattern)
++     }
++
++   The last two lines are commented out, since they are not needed in
++`gawk'.  They should be uncommented if you have to use another version
++of `awk'.
++
++   The next set of lines should be uncommented if you are not using
++`gawk'.  This rule translates all the characters in the input line into
++lowercase if the `-i' option is specified.(1) The rule is commented out
++since it is not necessary with `gawk':
++
++     #{
++     #    if (IGNORECASE)
++     #        $0 = tolower($0)
++     #}
++
++   The `beginfile()' function is called by the rule in `ftrans.awk'
++when each new file is processed.  In this case, it is very simple; all
++it does is initialize a variable `fcount' to zero. `fcount' tracks how
++many lines in the current file matched the pattern.  Naming the
++parameter `junk' shows we know that `beginfile()' is called with a
++parameter, but that we're not interested in its value:
++
++     function beginfile(junk)
++     {
++         fcount = 0
++     }
++
++   The `endfile()' function is called after each file has been
++processed.  It affects the output only when the user wants a count of
++the number of lines that matched.  `no_print' is true only if the exit
++status is desired.  `count_only' is true if line counts are desired.
++`egrep' therefore only prints line counts if printing and counting are
++enabled.  The output format must be adjusted depending upon the number
++of files to process.  Finally, `fcount' is added to `total', so that we
++know the total number of lines that matched the pattern:
++
++     function endfile(file)
++     {
++         if (! no_print && count_only) {
++             if (do_filenames)
++                 print file ":" fcount
++             else
++                 print fcount
++         }
++
++         total += fcount
++     }
++
++   The following rule does most of the work of matching lines. The
++variable `matches' is true if the line matched the pattern. If the user
++wants lines that did not match, the sense of `matches' is inverted
++using the `!' operator. `fcount' is incremented with the value of
++`matches', which is either one or zero, depending upon a successful or
++unsuccessful match.  If the line does not match, the `next' statement
++just moves on to the next record.
++
++   A number of additional tests are made, but they are only done if we
++are not counting lines.  First, if the user only wants exit status
++(`no_print' is true), then it is enough to know that _one_ line in this
++file matched, and we can skip on to the next file with `nextfile'.
++Similarly, if we are only printing file names, we can print the file
++name, and then skip to the next file with `nextfile'.  Finally, each
++line is printed, with a leading file name and colon if necessary:
++
++     {
++         matches = ($0 ~ pattern)
++         if (invert)
++             matches = ! matches
++
++         fcount += matches    # 1 or 0
++
++         if (! matches)
++             next
++
++         if (! count_only) {
++             if (no_print)
++                 nextfile
++
++             if (filenames_only) {
++                 print FILENAME
++                 nextfile
++             }
++
++             if (do_filenames)
++                 print FILENAME ":" $0
++             else
++                 print
++         }
++     }
++
++   The `END' rule takes care of producing the correct exit status. If
++there are no matches, the exit status is one; otherwise it is zero:
++
++     END    \
++     {
++         if (total == 0)
++             exit 1
++         exit 0
++     }
++
++   The `usage()' function prints a usage message in case of invalid
++options, and then exits:
++
++     function usage(    e)
++     {
++         e = "Usage: egrep [-csvil] [-e pat] [files ...]"
++         e = e "\n\tegrep [-csvil] pat [files ...]"
++         print e > "/dev/stderr"
++         exit 1
++     }
++
++   The variable `e' is used so that the function fits nicely on the
++printed page.
++
++   Just a note on programming style: you may have noticed that the `END'
++rule uses backslash continuation, with the open brace on a line by
++itself.  This is so that it more closely resembles the way functions
++are written.  Many of the examples in this major node use this style.
++You can decide for yourself if you like writing your `BEGIN' and `END'
++rules this way or not.
++
++   ---------- Footnotes ----------
++
++   (1) It also introduces a subtle bug; if a match happens, we output
++the translated line, not the original.
++
++
++File: gawk.info,  Node: Id Program,  Next: Split Program,  Prev: Egrep 
Program,  Up: Clones
++
++14.2.3 Printing out User Information
++------------------------------------
++
++The `id' utility lists a user's real and effective user ID numbers,
++real and effective group ID numbers, and the user's group set, if any.
++`id' only prints the effective user ID and group ID if they are
++different from the real ones.  If possible, `id' also supplies the
++corresponding user and group names.  The output might look like this:
++
++     $ id
++     -| uid=500(arnold) gid=500(arnold) groups=6(disk),7(lp),19(floppy)
++
++   This information is part of what is provided by `gawk''s `PROCINFO'
++array (*note Built-in Variables::).  However, the `id' utility provides
++a more palatable output than just individual numbers.
++
++   Here is a simple version of `id' written in `awk'.  It uses the user
++database library functions (*note Passwd Functions::) and the group
++database library functions (*note Group Functions::):
++
++   The program is fairly straightforward.  All the work is done in the
++`BEGIN' rule.  The user and group ID numbers are obtained from
++`PROCINFO'.  The code is repetitive.  The entry in the user database
++for the real user ID number is split into parts at the `:'. The name is
++the first field.  Similar code is used for the effective user ID number
++and the group numbers:
++
++     # id.awk --- implement id in awk
++     #
++     # Requires user and group library functions
++     # output is:
++     # uid=12(foo) euid=34(bar) gid=3(baz) \
++     #             egid=5(blat) groups=9(nine),2(two),1(one)
++
++     BEGIN    \
++     {
++         uid = PROCINFO["uid"]
++         euid = PROCINFO["euid"]
++         gid = PROCINFO["gid"]
++         egid = PROCINFO["egid"]
++
++         printf("uid=%d", uid)
++         pw = getpwuid(uid)
++         if (pw != "") {
++             split(pw, a, ":")
++             printf("(%s)", a[1])
++         }
++
++         if (euid != uid) {
++             printf(" euid=%d", euid)
++             pw = getpwuid(euid)
++             if (pw != "") {
++                 split(pw, a, ":")
++                 printf("(%s)", a[1])
++             }
++         }
++
++         printf(" gid=%d", gid)
++         pw = getgrgid(gid)
++         if (pw != "") {
++             split(pw, a, ":")
++             printf("(%s)", a[1])
++         }
++
++         if (egid != gid) {
++             printf(" egid=%d", egid)
++             pw = getgrgid(egid)
++             if (pw != "") {
++                 split(pw, a, ":")
++                 printf("(%s)", a[1])
++             }
++         }
++
++         for (i = 1; ("group" i) in PROCINFO; i++) {
++             if (i == 1)
++                 printf(" groups=")
++             group = PROCINFO["group" i]
++             printf("%d", group)
++             pw = getgrgid(group)
++             if (pw != "") {
++                 split(pw, a, ":")
++                 printf("(%s)", a[1])
++             }
++             if (("group" (i+1)) in PROCINFO)
++                 printf(",")
++         }
++
++         print ""
++     }
++
++   The test in the `for' loop is worth noting.  Any supplementary
++groups in the `PROCINFO' array have the indices `"group1"' through
++`"groupN"' for some N, i.e., the total number of supplementary groups.
++However, we don't know in advance how many of these groups there are.
++
++   This loop works by starting at one, concatenating the value with
++`"group"', and then using `in' to see if that value is in the array.
++Eventually, `i' is incremented past the last group in the array and the
++loop exits.
++
++   The loop is also correct if there are _no_ supplementary groups;
++then the condition is false the first time it's tested, and the loop
++body never executes.
++
++
++File: gawk.info,  Node: Split Program,  Next: Tee Program,  Prev: Id Program, 
 Up: Clones
++
++14.2.4 Splitting a Large File into Pieces
++-----------------------------------------
++
++The `split' program splits large text files into smaller pieces.  Usage
++is as follows:(1)
++
++     split [-COUNT] file [ PREFIX ]
++
++   By default, the output files are named `xaa', `xab', and so on. Each
++file has 1000 lines in it, with the likely exception of the last file.
++To change the number of lines in each file, supply a number on the
++command line preceded with a minus; e.g., `-500' for files with 500
++lines in them instead of 1000.  To change the name of the output files
++to something like `myfileaa', `myfileab', and so on, supply an
++additional argument that specifies the file name prefix.
++
++   Here is a version of `split' in `awk'. It uses the `ord()' and
++`chr()' functions presented in *note Ordinal Functions::.
++
++   The program first sets its defaults, and then tests to make sure
++there are not too many arguments.  It then looks at each argument in
++turn.  The first argument could be a minus sign followed by a number.
++If it is, this happens to look like a negative number, so it is made
++positive, and that is the count of lines.  The data file name is
++skipped over and the final argument is used as the prefix for the
++output file names:
++
++     # split.awk --- do split in awk
++     #
++     # Requires ord() and chr() library functions
++     # usage: split [-num] [file] [outname]
++
++     BEGIN {
++         outfile = "x"    # default
++         count = 1000
++         if (ARGC > 4)
++             usage()
++
++         i = 1
++         if (ARGV[i] ~ /^-[[:digit:]]+$/) {
++             count = -ARGV[i]
++             ARGV[i] = ""
++             i++
++         }
++         # test argv in case reading from stdin instead of file
++         if (i in ARGV)
++             i++    # skip data file name
++         if (i in ARGV) {
++             outfile = ARGV[i]
++             ARGV[i] = ""
++         }
++
++         s1 = s2 = "a"
++         out = (outfile s1 s2)
+      }
+ 
 -   Next is the rule that actually processes the data.  If the `-s'
 -option is given, then `suppress' is true.  The first `if' statement
 -makes sure that the input record does have the field separator.  If
 -`cut' is processing fields, `suppress' is true, and the field separator
 -character is not in the record, then the record is skipped.
 -
 -   If the record is valid, then `gawk' has split the data into fields,
 -either using the character in `FS' or using fixed-length fields and
 -`FIELDWIDTHS'.  The loop goes through the list of fields that should be
 -printed.  The corresponding field is printed if it contains data.  If
 -the next field also has data, then the separator character is written
 -out between the fields:
++   The next rule does most of the work. `tcount' (temporary count)
++tracks how many lines have been printed to the output file so far. If
++it is greater than `count', it is time to close the current file and
++start a new one.  `s1' and `s2' track the current suffixes for the file
++name. If they are both `z', the file is just too big.  Otherwise, `s1'
++moves to the next letter in the alphabet and `s2' starts over again at
++`a':
+ 
+      {
 -         if (by_fields && suppress && index($0, FS) != 0)
 -             next
 -
 -         for (i = 1; i <= nfields; i++) {
 -             if ($flist[i] != "") {
 -                 printf "%s", $flist[i]
 -                 if (i < nfields && $flist[i+1] != "")
 -                     printf "%s", OFS
++         if (++tcount > count) {
++             close(out)
++             if (s2 == "z") {
++                 if (s1 == "z") {
++                     printf("split: %s is too large to split\n",
++                            FILENAME) > "/dev/stderr"
++                     exit 1
++                 }
++                 s1 = chr(ord(s1) + 1)
++                 s2 = "a"
+              }
++             else
++                 s2 = chr(ord(s2) + 1)
++             out = (outfile s1 s2)
++             tcount = 1
+          }
 -         print ""
++         print > out
+      }
+ 
 -   This version of `cut' relies on `gawk''s `FIELDWIDTHS' variable to
 -do the character-based cutting.  While it is possible in other `awk'
 -implementations to use `substr()' (*note String Functions::), it is
 -also extremely painful.  The `FIELDWIDTHS' variable supplies an elegant
 -solution to the problem of picking the input line apart by characters.
 -
 -
 -File: gawk.info,  Node: Egrep Program,  Next: Id Program,  Prev: Cut Program, 
 Up: Clones
 -
 -13.2.2 Searching for Regular Expressions in Files
 --------------------------------------------------
++The `usage()' function simply prints an error message and exits:
+ 
 -The `egrep' utility searches files for patterns.  It uses regular
 -expressions that are almost identical to those available in `awk'
 -(*note Regexp::).  You invoke it as follows:
++     function usage(   e)
++     {
++         e = "usage: split [-num] [file] [outname]"
++         print e > "/dev/stderr"
++         exit 1
++     }
+ 
 -     egrep [ OPTIONS ] 'PATTERN' FILES ...
++The variable `e' is used so that the function fits nicely on the screen.
+ 
 -   The PATTERN is a regular expression.  In typical usage, the regular
 -expression is quoted to prevent the shell from expanding any of the
 -special characters as file name wildcards.  Normally, `egrep' prints
 -the lines that matched.  If multiple file names are provided on the
 -command line, each output line is preceded by the name of the file and
 -a colon.
++   This program is a bit sloppy; it relies on `awk' to automatically
++close the last file instead of doing it in an `END' rule.  It also
++assumes that letters are contiguous in the character set, which isn't
++true for EBCDIC systems.
+ 
 -   The options to `egrep' are as follows:
++   ---------- Footnotes ----------
+ 
 -`-c'
 -     Print out a count of the lines that matched the pattern, instead
 -     of the lines themselves.
++   (1) This is the traditional usage. The POSIX usage is different, but
++not relevant for what the program aims to demonstrate.
+ 
 -`-s'
 -     Be silent.  No output is produced and the exit value indicates
 -     whether the pattern was matched.
++
++File: gawk.info,  Node: Tee Program,  Next: Uniq Program,  Prev: Split 
Program,  Up: Clones
+ 
 -`-v'
 -     Invert the sense of the test. `egrep' prints the lines that do
 -     _not_ match the pattern and exits successfully if the pattern is
 -     not matched.
++14.2.5 Duplicating Output into Multiple Files
++---------------------------------------------
+ 
 -`-i'
 -     Ignore case distinctions in both the pattern and the input data.
++The `tee' program is known as a "pipe fitting."  `tee' copies its
++standard input to its standard output and also duplicates it to the
++files named on the command line.  Its usage is as follows:
+ 
 -`-l'
 -     Only print (list) the names of the files that matched, not the
 -     lines that matched.
++     tee [-a] file ...
+ 
 -`-e PATTERN'
 -     Use PATTERN as the regexp to match.  The purpose of the `-e'
 -     option is to allow patterns that start with a `-'.
++   The `-a' option tells `tee' to append to the named files, instead of
++truncating them and starting over.
+ 
 -   This version uses the `getopt()' library function (*note Getopt
 -Function::) and the file transition library program (*note Filetrans
 -Function::).
++   The `BEGIN' rule first makes a copy of all the command-line arguments
++into an array named `copy'.  `ARGV[0]' is not copied, since it is not
++needed.  `tee' cannot use `ARGV' directly, since `awk' attempts to
++process each file name in `ARGV' as input data.
+ 
 -   The program begins with a descriptive comment and then a `BEGIN' rule
 -that processes the command-line arguments with `getopt()'.  The `-i'
 -(ignore case) option is particularly easy with `gawk'; we just use the
 -`IGNORECASE' built-in variable (*note Built-in Variables::):
++   If the first argument is `-a', then the flag variable `append' is
++set to true, and both `ARGV[1]' and `copy[1]' are deleted. If `ARGC' is
++less than two, then no file names were supplied and `tee' prints a
++usage message and exits.  Finally, `awk' is forced to read the standard
++input by setting `ARGV[1]' to `"-"' and `ARGC' to two:
+ 
 -     # egrep.awk --- simulate egrep in awk
++     # tee.awk --- tee in awk
+      #
 -     # Options:
 -     #    -c    count of lines
 -     #    -s    silent - use exit value
 -     #    -v    invert test, success if no match
 -     #    -i    ignore case
 -     #    -l    print filenames only
 -     #    -e    argument is pattern
++     # Copy standard input to all named output files.
++     # Append content if -a option is supplied.
+      #
 -     # Requires getopt and file transition library functions
++     BEGIN    \
++     {
++         for (i = 1; i < ARGC; i++)
++             copy[i] = ARGV[i]
+ 
 -     BEGIN {
 -         while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) {
 -             if (c == "c")
 -                 count_only++
 -             else if (c == "s")
 -                 no_print++
 -             else if (c == "v")
 -                 invert++
 -             else if (c == "i")
 -                 IGNORECASE = 1
 -             else if (c == "l")
 -                 filenames_only++
 -             else if (c == "e")
 -                 pattern = Optarg
 -             else
 -                 usage()
++         if (ARGV[1] == "-a") {
++             append = 1
++             delete ARGV[1]
++             delete copy[1]
++             ARGC--
+          }
++         if (ARGC < 2) {
++             print "usage: tee [-a] file ..." > "/dev/stderr"
++             exit 1
++         }
++         ARGV[1] = "-"
++         ARGC = 2
++     }
+ 
 -   Next comes the code that handles the `egrep'-specific behavior. If no
 -pattern is supplied with `-e', the first nonoption on the command line
 -is used.  The `awk' command-line arguments up to `ARGV[Optind]' are
 -cleared, so that `awk' won't try to process them as files.  If no files
 -are specified, the standard input is used, and if multiple files are
 -specified, we make sure to note this so that the file names can precede
 -the matched lines in the output:
 -
 -         if (pattern == "")
 -             pattern = ARGV[Optind++]
 -
 -         for (i = 1; i < Optind; i++)
 -             ARGV[i] = ""
 -         if (Optind >= ARGC) {
 -             ARGV[1] = "-"
 -             ARGC = 2
 -         } else if (ARGC - Optind > 1)
 -             do_filenames++
++   The following single rule does all the work.  Since there is no
++pattern, it is executed for each line of input.  The body of the rule
++simply prints the line into each file on the command line, and then to
++the standard output:
+ 
 -     #    if (IGNORECASE)
 -     #        pattern = tolower(pattern)
++     {
++         # moving the if outside the loop makes it run faster
++         if (append)
++             for (i in copy)
++                 print >> copy[i]
++         else
++             for (i in copy)
++                 print > copy[i]
++         print
+      }
+ 
 -   The last two lines are commented out, since they are not needed in
 -`gawk'.  They should be uncommented if you have to use another version
 -of `awk'.
++It is also possible to write the loop this way:
+ 
 -   The next set of lines should be uncommented if you are not using
 -`gawk'.  This rule translates all the characters in the input line into
 -lowercase if the `-i' option is specified.(1) The rule is commented out
 -since it is not necessary with `gawk':
++     for (i in copy)
++         if (append)
++             print >> copy[i]
++         else
++             print > copy[i]
+ 
 -     #{
 -     #    if (IGNORECASE)
 -     #        $0 = tolower($0)
 -     #}
++This is more concise but it is also less efficient.  The `if' is tested
++for each record and for each output file.  By duplicating the loop
++body, the `if' is only tested once for each input record.  If there are
++N input records and M output files, the first method only executes N
++`if' statements, while the second executes N`*'M `if' statements.
+ 
 -   The `beginfile()' function is called by the rule in `ftrans.awk'
 -when each new file is processed.  In this case, it is very simple; all
 -it does is initialize a variable `fcount' to zero. `fcount' tracks how
 -many lines in the current file matched the pattern.  Naming the
 -parameter `junk' shows we know that `beginfile()' is called with a
 -parameter, but that we're not interested in its value:
++   Finally, the `END' rule cleans up by closing all the output files:
+ 
 -     function beginfile(junk)
++     END    \
+      {
 -         fcount = 0
++         for (i in copy)
++             close(copy[i])
+      }
+ 
 -   The `endfile()' function is called after each file has been
 -processed.  It affects the output only when the user wants a count of
 -the number of lines that matched.  `no_print' is true only if the exit
 -status is desired.  `count_only' is true if line counts are desired.
 -`egrep' therefore only prints line counts if printing and counting are
 -enabled.  The output format must be adjusted depending upon the number
 -of files to process.  Finally, `fcount' is added to `total', so that we
 -know the total number of lines that matched the pattern:
++
++File: gawk.info,  Node: Uniq Program,  Next: Wc Program,  Prev: Tee Program,  
Up: Clones
+ 
 -     function endfile(file)
 -     {
 -         if (! no_print && count_only) {
 -             if (do_filenames)
 -                 print file ":" fcount
 -             else
 -                 print fcount
 -         }
++14.2.6 Printing Nonduplicated Lines of Text
++-------------------------------------------
++
++The `uniq' utility reads sorted lines of data on its standard input,
++and by default removes duplicate lines.  In other words, it only prints
++unique lines--hence the name.  `uniq' has a number of options. The
++usage is as follows:
+ 
 -         total += fcount
 -     }
++     uniq [-udc [-N]] [+N] [ INPUT FILE [ OUTPUT FILE ]]
+ 
 -   The following rule does most of the work of matching lines. The
 -variable `matches' is true if the line matched the pattern. If the user
 -wants lines that did not match, the sense of `matches' is inverted
 -using the `!' operator. `fcount' is incremented with the value of
 -`matches', which is either one or zero, depending upon a successful or
 -unsuccessful match.  If the line does not match, the `next' statement
 -just moves on to the next record.
++   The options for `uniq' are:
+ 
 -   A number of additional tests are made, but they are only done if we
 -are not counting lines.  First, if the user only wants exit status
 -(`no_print' is true), then it is enough to know that _one_ line in this
 -file matched, and we can skip on to the next file with `nextfile'.
 -Similarly, if we are only printing file names, we can print the file
 -name, and then skip to the next file with `nextfile'.  Finally, each
 -line is printed, with a leading file name and colon if necessary:
++`-d'
++     Print only repeated lines.
+ 
 -     {
 -         matches = ($0 ~ pattern)
 -         if (invert)
 -             matches = ! matches
++`-u'
++     Print only nonrepeated lines.
+ 
 -         fcount += matches    # 1 or 0
++`-c'
++     Count lines. This option overrides `-d' and `-u'.  Both repeated
++     and nonrepeated lines are counted.
+ 
 -         if (! matches)
 -             next
++`-N'
++     Skip N fields before comparing lines.  The definition of fields is
++     similar to `awk''s default: nonwhitespace characters separated by
++     runs of spaces and/or TABs.
+ 
 -         if (! count_only) {
 -             if (no_print)
 -                 nextfile
++`+N'
++     Skip N characters before comparing lines.  Any fields specified
++     with `-N' are skipped first.
+ 
 -             if (filenames_only) {
 -                 print FILENAME
 -                 nextfile
 -             }
++`INPUT FILE'
++     Data is read from the input file named on the command line,
++     instead of from the standard input.
+ 
 -             if (do_filenames)
 -                 print FILENAME ":" $0
 -             else
 -                 print
 -         }
 -     }
++`OUTPUT FILE'
++     The generated output is sent to the named output file, instead of
++     to the standard output.
+ 
 -   The `END' rule takes care of producing the correct exit status. If
 -there are no matches, the exit status is one; otherwise it is zero:
++   Normally `uniq' behaves as if both the `-d' and `-u' options are
++provided.
+ 
 -     END    \
 -     {
 -         if (total == 0)
 -             exit 1
 -         exit 0
 -     }
++   `uniq' uses the `getopt()' library function (*note Getopt Function::)
++and the `join()' library function (*note Join Function::).
+ 
 -   The `usage()' function prints a usage message in case of invalid
 -options, and then exits:
++   The program begins with a `usage()' function and then a brief
++outline of the options and their meanings in comments.  The `BEGIN'
++rule deals with the command-line arguments and options. It uses a trick
++to get `getopt()' to handle options of the form `-25', treating such an
++option as the option letter `2' with an argument of `5'. If indeed two
++or more digits are supplied (`Optarg' looks like a number), `Optarg' is
++concatenated with the option digit and then the result is added to zero
++to make it into a number.  If there is only one digit in the option,
++then `Optarg' is not needed. In this case, `Optind' must be decremented
++so that `getopt()' processes it next time.  This code is admittedly a
++bit tricky.
++
++   If no options are supplied, then the default is taken, to print both
++repeated and nonrepeated lines.  The output file, if provided, is
++assigned to `outputfile'.  Early on, `outputfile' is initialized to the
++standard output, `/dev/stdout':
++
++     # uniq.awk --- do uniq in awk
++     #
++     # Requires getopt() and join() library functions
+ 
+      function usage(    e)
+      {
 -         e = "Usage: egrep [-csvil] [-e pat] [files ...]"
 -         e = e "\n\tegrep [-csvil] pat [files ...]"
++         e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]"
+          print e > "/dev/stderr"
+          exit 1
+      }
+ 
 -   The variable `e' is used so that the function fits nicely on the
 -printed page.
++     # -c    count lines. overrides -d and -u
++     # -d    only repeated lines
++     # -u    only nonrepeated lines
++     # -n    skip n fields
++     # +n    skip n characters, skip fields first
+ 
 -   Just a note on programming style: you may have noticed that the `END'
 -rule uses backslash continuation, with the open brace on a line by
 -itself.  This is so that it more closely resembles the way functions
 -are written.  Many of the examples in this major node use this style.
 -You can decide for yourself if you like writing your `BEGIN' and `END'
 -rules this way or not.
++     BEGIN   \
++     {
++         count = 1
++         outputfile = "/dev/stdout"
++         opts = "udc0:1:2:3:4:5:6:7:8:9:"
++         while ((c = getopt(ARGC, ARGV, opts)) != -1) {
++             if (c == "u")
++                 non_repeated_only++
++             else if (c == "d")
++                 repeated_only++
++             else if (c == "c")
++                 do_count++
++             else if (index("0123456789", c) != 0) {
++                 # getopt requires args to options
++                 # this messes us up for things like -5
++                 if (Optarg ~ /^[[:digit:]]+$/)
++                     fcount = (c Optarg) + 0
++                 else {
++                     fcount = c + 0
++                     Optind--
++                 }
++             } else
++                 usage()
++         }
+ 
 -   ---------- Footnotes ----------
++         if (ARGV[Optind] ~ /^\+[[:digit:]]+$/) {
++             charcount = substr(ARGV[Optind], 2) + 0
++             Optind++
++         }
+ 
 -   (1) It also introduces a subtle bug; if a match happens, we output
 -the translated line, not the original.
++         for (i = 1; i < Optind; i++)
++             ARGV[i] = ""
+ 
 -
 -File: gawk.info,  Node: Id Program,  Next: Split Program,  Prev: Egrep 
Program,  Up: Clones
++         if (repeated_only == 0 && non_repeated_only == 0)
++             repeated_only = non_repeated_only = 1
+ 
 -13.2.3 Printing out User Information
 -------------------------------------
++         if (ARGC - Optind == 2) {
++             outputfile = ARGV[ARGC - 1]
++             ARGV[ARGC - 1] = ""
++         }
++     }
+ 
 -The `id' utility lists a user's real and effective user ID numbers,
 -real and effective group ID numbers, and the user's group set, if any.
 -`id' only prints the effective user ID and group ID if they are
 -different from the real ones.  If possible, `id' also supplies the
 -corresponding user and group names.  The output might look like this:
++   The following function, `are_equal()', compares the current line,
++`$0', to the previous line, `last'.  It handles skipping fields and
++characters.  If no field count and no character count are specified,
++`are_equal()' simply returns one or zero depending upon the result of a
++simple string comparison of `last' and `$0'.  Otherwise, things get more
++complicated.  If fields have to be skipped, each line is broken into an
++array using `split()' (*note String Functions::); the desired fields
++are then joined back into a line using `join()'.  The joined lines are
++stored in `clast' and `cline'.  If no fields are skipped, `clast' and
++`cline' are set to `last' and `$0', respectively.  Finally, if
++characters are skipped, `substr()' is used to strip off the leading
++`charcount' characters in `clast' and `cline'.  The two strings are
++then compared and `are_equal()' returns the result:
+ 
 -     $ id
 -     -| uid=500(arnold) gid=500(arnold) groups=6(disk),7(lp),19(floppy)
++     function are_equal(    n, m, clast, cline, alast, aline)
++     {
++         if (fcount == 0 && charcount == 0)
++             return (last == $0)
+ 
 -   This information is part of what is provided by `gawk''s `PROCINFO'
 -array (*note Built-in Variables::).  However, the `id' utility provides
 -a more palatable output than just individual numbers.
++         if (fcount > 0) {
++             n = split(last, alast)
++             m = split($0, aline)
++             clast = join(alast, fcount+1, n)
++             cline = join(aline, fcount+1, m)
++         } else {
++             clast = last
++             cline = $0
++         }
++         if (charcount) {
++             clast = substr(clast, charcount + 1)
++             cline = substr(cline, charcount + 1)
++         }
+ 
 -   Here is a simple version of `id' written in `awk'.  It uses the user
 -database library functions (*note Passwd Functions::) and the group
 -database library functions (*note Group Functions::):
++         return (clast == cline)
++     }
+ 
 -   The program is fairly straightforward.  All the work is done in the
 -`BEGIN' rule.  The user and group ID numbers are obtained from
 -`PROCINFO'.  The code is repetitive.  The entry in the user database
 -for the real user ID number is split into parts at the `:'. The name is
 -the first field.  Similar code is used for the effective user ID number
 -and the group numbers:
++   The following two rules are the body of the program.  The first one
++is executed only for the very first line of data.  It sets `last' equal
++to `$0', so that subsequent lines of text have something to be compared
++to.
+ 
 -     # id.awk --- implement id in awk
 -     #
 -     # Requires user and group library functions
 -     # output is:
 -     # uid=12(foo) euid=34(bar) gid=3(baz) \
 -     #             egid=5(blat) groups=9(nine),2(two),1(one)
++   The second rule does the work. The variable `equal' is one or zero,
++depending upon the results of `are_equal()''s comparison. If `uniq' is
++counting repeated lines, and the lines are equal, then it increments
++the `count' variable.  Otherwise, it prints the line and resets `count',
++since the two lines are not equal.
+ 
 -     BEGIN    \
 -     {
 -         uid = PROCINFO["uid"]
 -         euid = PROCINFO["euid"]
 -         gid = PROCINFO["gid"]
 -         egid = PROCINFO["egid"]
++   If `uniq' is not counting, and if the lines are equal, `count' is
++incremented.  Nothing is printed, since the point is to remove
++duplicates.  Otherwise, if `uniq' is counting repeated lines and more
++than one line is seen, or if `uniq' is counting nonrepeated lines and
++only one line is seen, then the line is printed, and `count' is reset.
+ 
 -         printf("uid=%d", uid)
 -         pw = getpwuid(uid)
 -         if (pw != "") {
 -             split(pw, a, ":")
 -             printf("(%s)", a[1])
 -         }
++   Finally, similar logic is used in the `END' rule to print the final
++line of input data:
+ 
 -         if (euid != uid) {
 -             printf(" euid=%d", euid)
 -             pw = getpwuid(euid)
 -             if (pw != "") {
 -                 split(pw, a, ":")
 -                 printf("(%s)", a[1])
 -             }
 -         }
++     NR == 1 {
++         last = $0
++         next
++     }
+ 
 -         printf(" gid=%d", gid)
 -         pw = getgrgid(gid)
 -         if (pw != "") {
 -             split(pw, a, ":")
 -             printf("(%s)", a[1])
 -         }
++     {
++         equal = are_equal()
+ 
 -         if (egid != gid) {
 -             printf(" egid=%d", egid)
 -             pw = getgrgid(egid)
 -             if (pw != "") {
 -                 split(pw, a, ":")
 -                 printf("(%s)", a[1])
++         if (do_count) {    # overrides -d and -u
++             if (equal)
++                 count++
++             else {
++                 printf("%4d %s\n", count, last) > outputfile
++                 last = $0
++                 count = 1    # reset
+              }
++             next
+          }
+ 
 -         for (i = 1; ("group" i) in PROCINFO; i++) {
 -             if (i == 1)
 -                 printf(" groups=")
 -             group = PROCINFO["group" i]
 -             printf("%d", group)
 -             pw = getgrgid(group)
 -             if (pw != "") {
 -                 split(pw, a, ":")
 -                 printf("(%s)", a[1])
 -             }
 -             if (("group" (i+1)) in PROCINFO)
 -                 printf(",")
++         if (equal)
++             count++
++         else {
++             if ((repeated_only && count > 1) ||
++                 (non_repeated_only && count == 1))
++                     print last > outputfile
++             last = $0
++             count = 1
+          }
++     }
+ 
 -         print ""
++     END {
++         if (do_count)
++             printf("%4d %s\n", count, last) > outputfile
++         else if ((repeated_only && count > 1) ||
++                 (non_repeated_only && count == 1))
++             print last > outputfile
++         close(outputfile)
+      }
+ 
 -   The test in the `for' loop is worth noting.  Any supplementary
 -groups in the `PROCINFO' array have the indices `"group1"' through
 -`"groupN"' for some N, i.e., the total number of supplementary groups.
 -However, we don't know in advance how many of these groups there are.
++
++File: gawk.info,  Node: Wc Program,  Prev: Uniq Program,  Up: Clones
+ 
 -   This loop works by starting at one, concatenating the value with
 -`"group"', and then using `in' to see if that value is in the array.
 -Eventually, `i' is incremented past the last group in the array and the
 -loop exits.
++14.2.7 Counting Things
++----------------------
+ 
 -   The loop is also correct if there are _no_ supplementary groups;
 -then the condition is false the first time it's tested, and the loop
 -body never executes.
++The `wc' (word count) utility counts lines, words, and characters in
++one or more input files. Its usage is as follows:
+ 
 -
 -File: gawk.info,  Node: Split Program,  Next: Tee Program,  Prev: Id Program, 
 Up: Clones
++     wc [-lwc] [ FILES ... ]
+ 
 -13.2.4 Splitting a Large File into Pieces
 ------------------------------------------
++   If no files are specified on the command line, `wc' reads its
++standard input. If there are multiple files, it also prints total
++counts for all the files.  The options and their meanings are shown in
++the following list:
+ 
 -The `split' program splits large text files into smaller pieces.  Usage
 -is as follows:(1)
++`-l'
++     Count only lines.
+ 
 -     split [-COUNT] file [ PREFIX ]
++`-w'
++     Count only words.  A "word" is a contiguous sequence of
++     nonwhitespace characters, separated by spaces and/or TABs.
++     Luckily, this is the normal way `awk' separates fields in its
++     input data.
+ 
 -   By default, the output files are named `xaa', `xab', and so on. Each
 -file has 1000 lines in it, with the likely exception of the last file.
 -To change the number of lines in each file, supply a number on the
 -command line preceded with a minus; e.g., `-500' for files with 500
 -lines in them instead of 1000.  To change the name of the output files
 -to something like `myfileaa', `myfileab', and so on, supply an
 -additional argument that specifies the file name prefix.
++`-c'
++     Count only characters.
+ 
 -   Here is a version of `split' in `awk'. It uses the `ord()' and
 -`chr()' functions presented in *note Ordinal Functions::.
++   Implementing `wc' in `awk' is particularly elegant, since `awk' does
++a lot of the work for us; it splits lines into words (i.e., fields) and
++counts them, it counts lines (i.e., records), and it can easily tell us
++how long a line is.
+ 
 -   The program first sets its defaults, and then tests to make sure
 -there are not too many arguments.  It then looks at each argument in
 -turn.  The first argument could be a minus sign followed by a number.
 -If it is, this happens to look like a negative number, so it is made
 -positive, and that is the count of lines.  The data file name is
 -skipped over and the final argument is used as the prefix for the
 -output file names:
++   This program uses the `getopt()' library function (*note Getopt
++Function::) and the file-transition functions (*note Filetrans
++Function::).
+ 
 -     # split.awk --- do split in awk
++   This version has one notable difference from traditional versions of
++`wc': it always prints the counts in the order lines, words, and
++characters.  Traditional versions note the order of the `-l', `-w', and
++`-c' options on the command line, and print the counts in that order.
++
++   The `BEGIN' rule does the argument processing.  The variable
++`print_total' is true if more than one file is named on the command
++line:
++
++     # wc.awk --- count lines, words, characters
++
++     # Options:
++     #    -l    only count lines
++     #    -w    only count words
++     #    -c    only count characters
+      #
 -     # Requires ord() and chr() library functions
 -     # usage: split [-num] [file] [outname]
++     # Default is to count lines, words, characters
++     #
++     # Requires getopt() and file transition library functions
+ 
+      BEGIN {
 -         outfile = "x"    # default
 -         count = 1000
 -         if (ARGC > 4)
 -             usage()
 -
 -         i = 1
 -         if (ARGV[i] ~ /^-[[:digit:]]+$/) {
 -             count = -ARGV[i]
 -             ARGV[i] = ""
 -             i++
++         # let getopt() print a message about
++         # invalid options. we ignore them
++         while ((c = getopt(ARGC, ARGV, "lwc")) != -1) {
++             if (c == "l")
++                 do_lines = 1
++             else if (c == "w")
++                 do_words = 1
++             else if (c == "c")
++                 do_chars = 1
+          }
 -         # test argv in case reading from stdin instead of file
 -         if (i in ARGV)
 -             i++    # skip data file name
 -         if (i in ARGV) {
 -             outfile = ARGV[i]
++         for (i = 1; i < Optind; i++)
+              ARGV[i] = ""
 -         }
+ 
 -         s1 = s2 = "a"
 -         out = (outfile s1 s2)
++         # if no options, do all
++         if (! do_lines && ! do_words && ! do_chars)
++             do_lines = do_words = do_chars = 1
++
++         print_total = (ARGC - i > 2)
+      }
+ 
 -   The next rule does most of the work. `tcount' (temporary count)
 -tracks how many lines have been printed to the output file so far. If
 -it is greater than `count', it is time to close the current file and
 -start a new one.  `s1' and `s2' track the current suffixes for the file
 -name. If they are both `z', the file is just too big.  Otherwise, `s1'
 -moves to the next letter in the alphabet and `s2' starts over again at
 -`a':
++   The `beginfile()' function is simple; it just resets the counts of
++lines, words, and characters to zero, and saves the current file name in
++`fname':
+ 
++     function beginfile(file)
+      {
 -         if (++tcount > count) {
 -             close(out)
 -             if (s2 == "z") {
 -                 if (s1 == "z") {
 -                     printf("split: %s is too large to split\n",
 -                            FILENAME) > "/dev/stderr"
 -                     exit 1
 -                 }
 -                 s1 = chr(ord(s1) + 1)
 -                 s2 = "a"
 -             }
 -             else
 -                 s2 = chr(ord(s2) + 1)
 -             out = (outfile s1 s2)
 -             tcount = 1
 -         }
 -         print > out
++         lines = words = chars = 0
++         fname = FILENAME
+      }
+ 
 -The `usage()' function simply prints an error message and exits:
++   The `endfile()' function adds the current file's numbers to the
++running totals of lines, words, and characters.(1)  It then prints out
++those numbers for the file that was just read. It relies on
++`beginfile()' to reset the numbers for the following data file:
+ 
 -     function usage(   e)
++     function endfile(file)
+      {
 -         e = "usage: split [-num] [file] [outname]"
 -         print e > "/dev/stderr"
 -         exit 1
++         tlines += lines
++         twords += words
++         tchars += chars
++         if (do_lines)
++             printf "\t%d", lines
++         if (do_words)
++             printf "\t%d", words
++         if (do_chars)
++             printf "\t%d", chars
++         printf "\t%s\n", fname
+      }
+ 
 -The variable `e' is used so that the function fits nicely on the screen.
 -
 -   This program is a bit sloppy; it relies on `awk' to automatically
 -close the last file instead of doing it in an `END' rule.  It also
 -assumes that letters are contiguous in the character set, which isn't
 -true for EBCDIC systems.
++   There is one rule that is executed for each line. It adds the length
++of the record, plus one, to `chars'.(2) Adding one plus the record
++length is needed because the newline character separating records (the
++value of `RS') is not part of the record itself, and thus not included
++in its length.  Next, `lines' is incremented for each line read, and
++`words' is incremented by the value of `NF', which is the number of
++"words" on this line:
+ 
 -   ---------- Footnotes ----------
++     # do per line
++     {
++         chars += length($0) + 1    # get newline
++         lines++
++         words += NF
++     }
+ 
 -   (1) This is the traditional usage. The POSIX usage is different, but
 -not relevant for what the program aims to demonstrate.
++   Finally, the `END' rule simply prints the totals for all the files:
+ 
 -
 -File: gawk.info,  Node: Tee Program,  Next: Uniq Program,  Prev: Split 
Program,  Up: Clones
++     END {
++         if (print_total) {
++             if (do_lines)
++                 printf "\t%d", tlines
++             if (do_words)
++                 printf "\t%d", twords
++             if (do_chars)
++                 printf "\t%d", tchars
++             print "\ttotal"
++         }
++     }
+ 
 -13.2.5 Duplicating Output into Multiple Files
 ----------------------------------------------
++   ---------- Footnotes ----------
+ 
 -The `tee' program is known as a "pipe fitting."  `tee' copies its
 -standard input to its standard output and also duplicates it to the
 -files named on the command line.  Its usage is as follows:
++   (1) `wc' can't just use the value of `FNR' in `endfile()'. If you
++examine the code in *note Filetrans Function::, you will see that `FNR'
++has already been reset by the time `endfile()' is called.
+ 
 -     tee [-a] file ...
++   (2) Since `gawk' understands multibyte locales, this code counts
++characters, not bytes.
+ 
 -   The `-a' option tells `tee' to append to the named files, instead of
 -truncating them and starting over.
++
++File: gawk.info,  Node: Miscellaneous Programs,  Prev: Clones,  Up: Sample 
Programs
+ 
 -   The `BEGIN' rule first makes a copy of all the command-line arguments
 -into an array named `copy'.  `ARGV[0]' is not copied, since it is not
 -needed.  `tee' cannot use `ARGV' directly, since `awk' attempts to
 -process each file name in `ARGV' as input data.
++14.3 A Grab Bag of `awk' Programs
++=================================
+ 
 -   If the first argument is `-a', then the flag variable `append' is
 -set to true, and both `ARGV[1]' and `copy[1]' are deleted. If `ARGC' is
 -less than two, then no file names were supplied and `tee' prints a
 -usage message and exits.  Finally, `awk' is forced to read the standard
 -input by setting `ARGV[1]' to `"-"' and `ARGC' to two:
++This minor node is a large "grab bag" of miscellaneous programs.  We
++hope you find them both interesting and enjoyable.
+ 
 -     # tee.awk --- tee in awk
 -     #
 -     # Copy standard input to all named output files.
 -     # Append content if -a option is supplied.
 -     #
 -     BEGIN    \
 -     {
 -         for (i = 1; i < ARGC; i++)
 -             copy[i] = ARGV[i]
++* Menu:
+ 
 -         if (ARGV[1] == "-a") {
 -             append = 1
 -             delete ARGV[1]
 -             delete copy[1]
 -             ARGC--
 -         }
 -         if (ARGC < 2) {
 -             print "usage: tee [-a] file ..." > "/dev/stderr"
 -             exit 1
 -         }
 -         ARGV[1] = "-"
 -         ARGC = 2
 -     }
++* Dupword Program::             Finding duplicated words in a document.
++* Alarm Program::               An alarm clock.
++* Translate Program::           A program similar to the `tr' utility.
++* Labels Program::              Printing mailing labels.
++* Word Sorting::                A program to produce a word usage count.
++* History Sorting::             Eliminating duplicate entries from a history
++                                file.
++* Extract Program::             Pulling out programs from Texinfo source
++                                files.
++* Simple Sed::                  A Simple Stream Editor.
++* Igawk Program::               A wrapper for `awk' that includes
++                                files.
++* Anagram Program::             Finding anagrams from a dictionary.
++* Signature Program::           People do amazing things with too much time on
++                                their hands.
+ 
 -   The following single rule does all the work.  Since there is no
 -pattern, it is executed for each line of input.  The body of the rule
 -simply prints the line into each file on the command line, and then to
 -the standard output:
++
++File: gawk.info,  Node: Dupword Program,  Next: Alarm Program,  Up: 
Miscellaneous Programs
+ 
 -     {
 -         # moving the if outside the loop makes it run faster
 -         if (append)
 -             for (i in copy)
 -                 print >> copy[i]
 -         else
 -             for (i in copy)
 -                 print > copy[i]
 -         print
 -     }
++14.3.1 Finding Duplicated Words in a Document
++---------------------------------------------
+ 
 -It is also possible to write the loop this way:
++A common error when writing large amounts of prose is to accidentally
++duplicate words.  Typically you will see this in text as something like
++"the the program does the following..."  When the text is online, often
++the duplicated words occur at the end of one line and the beginning of
++another, making them very difficult to spot.
+ 
 -     for (i in copy)
 -         if (append)
 -             print >> copy[i]
 -         else
 -             print > copy[i]
++   This program, `dupword.awk', scans through a file one line at a time
++and looks for adjacent occurrences of the same word.  It also saves the
++last word on a line (in the variable `prev') for comparison with the
++first word on the next line.
+ 
 -This is more concise but it is also less efficient.  The `if' is tested
 -for each record and for each output file.  By duplicating the loop
 -body, the `if' is only tested once for each input record.  If there are
 -N input records and M output files, the first method only executes N
 -`if' statements, while the second executes N`*'M `if' statements.
++   The first two statements make sure that the line is all lowercase,
++so that, for example, "The" and "the" compare equal to each other.  The
++next statement replaces nonalphanumeric and nonwhitespace characters
++with spaces, so that punctuation does not affect the comparison either.
++The characters are replaced with spaces so that formatting controls
++don't create nonsense words (e.g., the Texinfo address@hidden' becomes
++`codeNF' if punctuation is simply deleted).  The record is then resplit
++into fields, yielding just the actual words on the line, and ensuring
++that there are no empty fields.
+ 
 -   Finally, the `END' rule cleans up by closing all the output files:
++   If there are no fields left after removing all the punctuation, the
++current record is skipped.  Otherwise, the program loops through each
++word, comparing it to the previous one:
+ 
 -     END    \
++     # dupword.awk --- find duplicate words in text
+      {
 -         for (i in copy)
 -             close(copy[i])
++         $0 = tolower($0)
++         gsub(/[^[:alnum:][:blank:]]/, " ");
++         $0 = $0         # re-split
++         if (NF == 0)
++             next
++         if ($1 == prev)
++             printf("%s:%d: duplicate %s\n",
++                 FILENAME, FNR, $1)
++         for (i = 2; i <= NF; i++)
++             if ($i == $(i-1))
++                 printf("%s:%d: duplicate %s\n",
++                     FILENAME, FNR, $i)
++         prev = $NF
+      }
+ 
+ 
 -File: gawk.info,  Node: Uniq Program,  Next: Wc Program,  Prev: Tee Program,  
Up: Clones
++File: gawk.info,  Node: Alarm Program,  Next: Translate Program,  Prev: 
Dupword Program,  Up: Miscellaneous Programs
+ 
 -13.2.6 Printing Nonduplicated Lines of Text
 --------------------------------------------
++14.3.2 An Alarm Clock Program
++-----------------------------
+ 
 -The `uniq' utility reads sorted lines of data on its standard input,
 -and by default removes duplicate lines.  In other words, it only prints
 -unique lines--hence the name.  `uniq' has a number of options. The
 -usage is as follows:
++     Nothing cures insomnia like a ringing alarm clock.
++     Arnold Robbins
+ 
 -     uniq [-udc [-N]] [+N] [ INPUT FILE [ OUTPUT FILE ]]
++   The following program is a simple "alarm clock" program.  You give
++it a time of day and an optional message.  At the specified time, it
++prints the message on the standard output. In addition, you can give it
++the number of times to repeat the message as well as a delay between
++repetitions.
+ 
 -   The options for `uniq' are:
++   This program uses the `getlocaltime()' function from *note
++Getlocaltime Function::.
+ 
 -`-d'
 -     Print only repeated lines.
++   All the work is done in the `BEGIN' rule.  The first part is argument
++checking and setting of defaults: the delay, the count, and the message
++to print.  If the user supplied a message without the ASCII BEL
++character (known as the "alert" character, `"\a"'), then it is added to
++the message.  (On many systems, printing the ASCII BEL generates an
++audible alert. Thus when the alarm goes off, the system calls attention
++to itself in case the user is not looking at the computer.)  Just for a
++change, this program uses a `switch' statement (*note Switch
++Statement::), but the processing could be done with a series of
++`if'-`else' statements instead.  Here is the program:
+ 
 -`-u'
 -     Print only nonrepeated lines.
++     # alarm.awk --- set an alarm
++     #
++     # Requires getlocaltime() library function
++     # usage: alarm time [ "message" [ count [ delay ] ] ]
+ 
 -`-c'
 -     Count lines. This option overrides `-d' and `-u'.  Both repeated
 -     and nonrepeated lines are counted.
++     BEGIN    \
++     {
++         # Initial argument sanity checking
++         usage1 = "usage: alarm time ['message' [count [delay]]]"
++         usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1])
+ 
 -`-N'
 -     Skip N fields before comparing lines.  The definition of fields is
 -     similar to `awk''s default: nonwhitespace characters separated by
 -     runs of spaces and/or TABs.
++         if (ARGC < 2) {
++             print usage1 > "/dev/stderr"
++             print usage2 > "/dev/stderr"
++             exit 1
++         }
++         switch (ARGC) {
++         case 5:
++             delay = ARGV[4] + 0
++             # fall through
++         case 4:
++             count = ARGV[3] + 0
++             # fall through
++         case 3:
++             message = ARGV[2]
++             break
++         default:
++             if (ARGV[1] !~ /[[:digit:]]?[[:digit:]]:[[:digit:]]{2}/) {
++                 print usage1 > "/dev/stderr"
++                 print usage2 > "/dev/stderr"
++                 exit 1
++             }
++             break
++         }
+ 
 -`+N'
 -     Skip N characters before comparing lines.  Any fields specified
 -     with `-N' are skipped first.
++         # set defaults for once we reach the desired time
++         if (delay == 0)
++             delay = 180    # 3 minutes
++         if (count == 0)
++             count = 5
++         if (message == "")
++             message = sprintf("\aIt is now %s!\a", ARGV[1])
++         else if (index(message, "\a") == 0)
++             message = "\a" message "\a"
+ 
 -`INPUT FILE'
 -     Data is read from the input file named on the command line,
 -     instead of from the standard input.
++   The next minor node of code turns the alarm time into hours and
++minutes, converts it (if necessary) to a 24-hour clock, and then turns
++that time into a count of the seconds since midnight.  Next it turns
++the current time into a count of seconds since midnight.  The
++difference between the two is how long to wait before setting off the
++alarm:
+ 
 -`OUTPUT FILE'
 -     The generated output is sent to the named output file, instead of
 -     to the standard output.
++         # split up alarm time
++         split(ARGV[1], atime, ":")
++         hour = atime[1] + 0    # force numeric
++         minute = atime[2] + 0  # force numeric
+ 
 -   Normally `uniq' behaves as if both the `-d' and `-u' options are
 -provided.
++         # get current broken down time
++         getlocaltime(now)
+ 
 -   `uniq' uses the `getopt()' library function (*note Getopt Function::)
 -and the `join()' library function (*note Join Function::).
++         # if time given is 12-hour hours and it's after that
++         # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m.,
++         # then add 12 to real hour
++         if (hour < 12 && now["hour"] > hour)
++             hour += 12
+ 
 -   The program begins with a `usage()' function and then a brief
 -outline of the options and their meanings in comments.  The `BEGIN'
 -rule deals with the command-line arguments and options. It uses a trick
 -to get `getopt()' to handle options of the form `-25', treating such an
 -option as the option letter `2' with an argument of `5'. If indeed two
 -or more digits are supplied (`Optarg' looks like a number), `Optarg' is
 -concatenated with the option digit and then the result is added to zero
 -to make it into a number.  If there is only one digit in the option,
 -then `Optarg' is not needed. In this case, `Optind' must be decremented
 -so that `getopt()' processes it next time.  This code is admittedly a
 -bit tricky.
++         # set target time in seconds since midnight
++         target = (hour * 60 * 60) + (minute * 60)
++
++         # get current time in seconds since midnight
++         current = (now["hour"] * 60 * 60) + \
++                    (now["minute"] * 60) + now["second"]
++
++         # how long to sleep for
++         naptime = target - current
++         if (naptime <= 0) {
++             print "time is in the past!" > "/dev/stderr"
++             exit 1
++         }
++
++   Finally, the program uses the `system()' function (*note I/O
++Functions::) to call the `sleep' utility.  The `sleep' utility simply
++pauses for the given number of seconds.  If the exit status is not zero,
++the program assumes that `sleep' was interrupted and exits. If `sleep'
++exited with an OK status (zero), then the program prints the message in
++a loop, again using `sleep' to delay for however many seconds are
++necessary:
+ 
 -   If no options are supplied, then the default is taken, to print both
 -repeated and nonrepeated lines.  The output file, if provided, is
 -assigned to `outputfile'.  Early on, `outputfile' is initialized to the
 -standard output, `/dev/stdout':
++         # zzzzzz..... go away if interrupted
++         if (system(sprintf("sleep %d", naptime)) != 0)
++             exit 1
+ 
 -     # uniq.awk --- do uniq in awk
 -     #
 -     # Requires getopt() and join() library functions
++         # time to notify!
++         command = sprintf("sleep %d", delay)
++         for (i = 1; i <= count; i++) {
++             print message
++             # if sleep command interrupted, go away
++             if (system(command) != 0)
++                 break
++         }
+ 
 -     function usage(    e)
 -     {
 -         e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]"
 -         print e > "/dev/stderr"
 -         exit 1
++         exit 0
+      }
+ 
 -     # -c    count lines. overrides -d and -u
 -     # -d    only repeated lines
 -     # -u    only nonrepeated lines
 -     # -n    skip n fields
 -     # +n    skip n characters, skip fields first
++
++File: gawk.info,  Node: Translate Program,  Next: Labels Program,  Prev: 
Alarm Program,  Up: Miscellaneous Programs
+ 
 -     BEGIN   \
 -     {
 -         count = 1
 -         outputfile = "/dev/stdout"
 -         opts = "udc0:1:2:3:4:5:6:7:8:9:"
 -         while ((c = getopt(ARGC, ARGV, opts)) != -1) {
 -             if (c == "u")
 -                 non_repeated_only++
 -             else if (c == "d")
 -                 repeated_only++
 -             else if (c == "c")
 -                 do_count++
 -             else if (index("0123456789", c) != 0) {
 -                 # getopt requires args to options
 -                 # this messes us up for things like -5
 -                 if (Optarg ~ /^[[:digit:]]+$/)
 -                     fcount = (c Optarg) + 0
 -                 else {
 -                     fcount = c + 0
 -                     Optind--
 -                 }
 -             } else
 -                 usage()
 -         }
++14.3.3 Transliterating Characters
++---------------------------------
+ 
 -         if (ARGV[Optind] ~ /^\+[[:digit:]]+$/) {
 -             charcount = substr(ARGV[Optind], 2) + 0
 -             Optind++
 -         }
++The system `tr' utility transliterates characters.  For example, it is
++often used to map uppercase letters into lowercase for further
++processing:
+ 
 -         for (i = 1; i < Optind; i++)
 -             ARGV[i] = ""
++     GENERATE DATA | tr 'A-Z' 'a-z' | PROCESS DATA ...
+ 
 -         if (repeated_only == 0 && non_repeated_only == 0)
 -             repeated_only = non_repeated_only = 1
++   `tr' requires two lists of characters.(1)  When processing the
++input, the first character in the first list is replaced with the first
++character in the second list, the second character in the first list is
++replaced with the second character in the second list, and so on.  If
++there are more characters in the "from" list than in the "to" list, the
++last character of the "to" list is used for the remaining characters in
++the "from" list.
+ 
 -         if (ARGC - Optind == 2) {
 -             outputfile = ARGV[ARGC - 1]
 -             ARGV[ARGC - 1] = ""
 -         }
 -     }
++   Some time ago, a user proposed that a transliteration function should
++be added to `gawk'.  The following program was written to prove that
++character transliteration could be done with a user-level function.
++This program is not as complete as the system `tr' utility but it does
++most of the job.
+ 
 -   The following function, `are_equal()', compares the current line,
 -`$0', to the previous line, `last'.  It handles skipping fields and
 -characters.  If no field count and no character count are specified,
 -`are_equal()' simply returns one or zero depending upon the result of a
 -simple string comparison of `last' and `$0'.  Otherwise, things get more
 -complicated.  If fields have to be skipped, each line is broken into an
 -array using `split()' (*note String Functions::); the desired fields
 -are then joined back into a line using `join()'.  The joined lines are
 -stored in `clast' and `cline'.  If no fields are skipped, `clast' and
 -`cline' are set to `last' and `$0', respectively.  Finally, if
 -characters are skipped, `substr()' is used to strip off the leading
 -`charcount' characters in `clast' and `cline'.  The two strings are
 -then compared and `are_equal()' returns the result:
++   The `translate' program demonstrates one of the few weaknesses of
++standard `awk': dealing with individual characters is very painful,
++requiring repeated use of the `substr()', `index()', and `gsub()'
++built-in functions (*note String Functions::).(2) There are two
++functions.  The first, `stranslate()', takes three arguments:
+ 
 -     function are_equal(    n, m, clast, cline, alast, aline)
 -     {
 -         if (fcount == 0 && charcount == 0)
 -             return (last == $0)
++`from'
++     A list of characters from which to translate.
+ 
 -         if (fcount > 0) {
 -             n = split(last, alast)
 -             m = split($0, aline)
 -             clast = join(alast, fcount+1, n)
 -             cline = join(aline, fcount+1, m)
 -         } else {
 -             clast = last
 -             cline = $0
 -         }
 -         if (charcount) {
 -             clast = substr(clast, charcount + 1)
 -             cline = substr(cline, charcount + 1)
 -         }
++`to'
++     A list of characters to which to translate.
+ 
 -         return (clast == cline)
 -     }
++`target'
++     The string on which to do the translation.
+ 
 -   The following two rules are the body of the program.  The first one
 -is executed only for the very first line of data.  It sets `last' equal
 -to `$0', so that subsequent lines of text have something to be compared
 -to.
++   Associative arrays make the translation part fairly easy. `t_ar'
++holds the "to" characters, indexed by the "from" characters.  Then a
++simple loop goes through `from', one character at a time.  For each
++character in `from', if the character appears in `target', it is
++replaced with the corresponding `to' character.
+ 
 -   The second rule does the work. The variable `equal' is one or zero,
 -depending upon the results of `are_equal()''s comparison. If `uniq' is
 -counting repeated lines, and the lines are equal, then it increments
 -the `count' variable.  Otherwise, it prints the line and resets `count',
 -since the two lines are not equal.
++   The `translate()' function simply calls `stranslate()' using `$0' as
++the target.  The main program sets two global variables, `FROM' and
++`TO', from the command line, and then changes `ARGV' so that `awk'
++reads from the standard input.
+ 
 -   If `uniq' is not counting, and if the lines are equal, `count' is
 -incremented.  Nothing is printed, since the point is to remove
 -duplicates.  Otherwise, if `uniq' is counting repeated lines and more
 -than one line is seen, or if `uniq' is counting nonrepeated lines and
 -only one line is seen, then the line is printed, and `count' is reset.
++   Finally, the processing rule simply calls `translate()' for each
++record:
+ 
 -   Finally, similar logic is used in the `END' rule to print the final
 -line of input data:
++     # translate.awk --- do tr-like stuff
++     # Bugs: does not handle things like: tr A-Z a-z, it has
++     # to be spelled out. However, if `to' is shorter than `from',
++     # the last character in `to' is used for the rest of `from'.
+ 
 -     NR == 1 {
 -         last = $0
 -         next
++     function stranslate(from, to, target,     lf, lt, ltarget, t_ar, i, c,
++                                                                    result)
++     {
++         lf = length(from)
++         lt = length(to)
++         ltarget = length(target)
++         for (i = 1; i <= lt; i++)
++             t_ar[substr(from, i, 1)] = substr(to, i, 1)
++         if (lt < lf)
++             for (; i <= lf; i++)
++                 t_ar[substr(from, i, 1)] = substr(to, lt, 1)
++         for (i = 1; i <= ltarget; i++) {
++             c = substr(target, i, 1)
++             if (c in t_ar)
++                 c = t_ar[c]
++             result = result c
++         }
++         return result
+      }
+ 
++     function translate(from, to)
+      {
 -         equal = are_equal()
 -
 -         if (do_count) {    # overrides -d and -u
 -             if (equal)
 -                 count++
 -             else {
 -                 printf("%4d %s\n", count, last) > outputfile
 -                 last = $0
 -                 count = 1    # reset
 -             }
 -             next
 -         }
++         return $0 = stranslate(from, to, $0)
++     }
+ 
 -         if (equal)
 -             count++
 -         else {
 -             if ((repeated_only && count > 1) ||
 -                 (non_repeated_only && count == 1))
 -                     print last > outputfile
 -             last = $0
 -             count = 1
++     # main program
++     BEGIN {
++         if (ARGC < 3) {
++             print "usage: translate from to" > "/dev/stderr"
++             exit
+          }
++         FROM = ARGV[1]
++         TO = ARGV[2]
++         ARGC = 2
++         ARGV[1] = "-"
+      }
+ 
 -     END {
 -         if (do_count)
 -             printf("%4d %s\n", count, last) > outputfile
 -         else if ((repeated_only && count > 1) ||
 -                 (non_repeated_only && count == 1))
 -             print last > outputfile
 -         close(outputfile)
++     {
++         translate(FROM, TO)
++         print
+      }
+ 
 -
 -File: gawk.info,  Node: Wc Program,  Prev: Uniq Program,  Up: Clones
++   While it is possible to do character transliteration in a user-level
++function, it is not necessarily efficient, and we (the `gawk' authors)
++started to consider adding a built-in function.  However, shortly after
++writing this program, we learned that the System V Release 4 `awk' had
++added the `toupper()' and `tolower()' functions (*note String
++Functions::).  These functions handle the vast majority of the cases
++where character transliteration is necessary, and so we chose to simply
++add those functions to `gawk' as well and then leave well enough alone.
+ 
 -13.2.7 Counting Things
 -----------------------
++   An obvious improvement to this program would be to set up the `t_ar'
++array only once, in a `BEGIN' rule. However, this assumes that the
++"from" and "to" lists will never change throughout the lifetime of the
++program.
+ 
 -The `wc' (word count) utility counts lines, words, and characters in
 -one or more input files. Its usage is as follows:
++   ---------- Footnotes ----------
+ 
 -     wc [-lwc] [ FILES ... ]
++   (1) On some older systems, `tr' may require that the lists be
++written as range expressions enclosed in square brackets (`[a-z]') and
++quoted, to prevent the shell from attempting a file name expansion.
++This is not a feature.
+ 
 -   If no files are specified on the command line, `wc' reads its
 -standard input. If there are multiple files, it also prints total
 -counts for all the files.  The options and their meanings are shown in
 -the following list:
++   (2) This program was written before `gawk' acquired the ability to
++split each character in a string into separate array elements.
+ 
 -`-l'
 -     Count only lines.
++
++File: gawk.info,  Node: Labels Program,  Next: Word Sorting,  Prev: Translate 
Program,  Up: Miscellaneous Programs
+ 
 -`-w'
 -     Count only words.  A "word" is a contiguous sequence of
 -     nonwhitespace characters, separated by spaces and/or TABs.
 -     Luckily, this is the normal way `awk' separates fields in its
 -     input data.
++14.3.4 Printing Mailing Labels
++------------------------------
+ 
 -`-c'
 -     Count only characters.
++Here is a "real world"(1) program.  This script reads lists of names and
++addresses and generates mailing labels.  Each page of labels has 20
++labels on it, two across and 10 down.  The addresses are guaranteed to
++be no more than five lines of data.  Each address is separated from the
++next by a blank line.
+ 
 -   Implementing `wc' in `awk' is particularly elegant, since `awk' does
 -a lot of the work for us; it splits lines into words (i.e., fields) and
 -counts them, it counts lines (i.e., records), and it can easily tell us
 -how long a line is.
++   The basic idea is to read 20 labels worth of data.  Each line of
++each label is stored in the `line' array.  The single rule takes care
++of filling the `line' array and printing the page when 20 labels have
++been read.
+ 
 -   This program uses the `getopt()' library function (*note Getopt
 -Function::) and the file-transition functions (*note Filetrans
 -Function::).
++   The `BEGIN' rule simply sets `RS' to the empty string, so that `awk'
++splits records at blank lines (*note Records::).  It sets `MAXLINES' to
++100, since 100 is the maximum number of lines on the page (20 * 5 =
++100).
+ 
 -   This version has one notable difference from traditional versions of
 -`wc': it always prints the counts in the order lines, words, and
 -characters.  Traditional versions note the order of the `-l', `-w', and
 -`-c' options on the command line, and print the counts in that order.
++   Most of the work is done in the `printpage()' function.  The label
++lines are stored sequentially in the `line' array.  But they have to
++print horizontally; `line[1]' next to `line[6]', `line[2]' next to
++`line[7]', and so on.  Two loops are used to accomplish this.  The
++outer loop, controlled by `i', steps through every 10 lines of data;
++this is each row of labels.  The inner loop, controlled by `j', goes
++through the lines within the row.  As `j' goes from 0 to 4, `i+j' is
++the `j'-th line in the row, and `i+j+5' is the entry next to it.  The
++output ends up looking something like this:
+ 
 -   The `BEGIN' rule does the argument processing.  The variable
 -`print_total' is true if more than one file is named on the command
 -line:
++     line 1          line 6
++     line 2          line 7
++     line 3          line 8
++     line 4          line 9
++     line 5          line 10
++     ...
+ 
 -     # wc.awk --- count lines, words, characters
++The `printf' format string `%-41s' left-aligns the data and prints it
++within a fixed-width field.
+ 
 -     # Options:
 -     #    -l    only count lines
 -     #    -w    only count words
 -     #    -c    only count characters
 -     #
 -     # Default is to count lines, words, characters
 -     #
 -     # Requires getopt() and file transition library functions
++   As a final note, an extra blank line is printed at lines 21 and 61,
++to keep the output lined up on the labels.  This is dependent on the
++particular brand of labels in use when the program was written.  You
++will also note that there are two blank lines at the top and two blank
++lines at the bottom.
+ 
 -     BEGIN {
 -         # let getopt() print a message about
 -         # invalid options. we ignore them
 -         while ((c = getopt(ARGC, ARGV, "lwc")) != -1) {
 -             if (c == "l")
 -                 do_lines = 1
 -             else if (c == "w")
 -                 do_words = 1
 -             else if (c == "c")
 -                 do_chars = 1
 -         }
 -         for (i = 1; i < Optind; i++)
 -             ARGV[i] = ""
++   The `END' rule arranges to flush the final page of labels; there may
++not have been an even multiple of 20 labels in the data:
+ 
 -         # if no options, do all
 -         if (! do_lines && ! do_words && ! do_chars)
 -             do_lines = do_words = do_chars = 1
++     # labels.awk --- print mailing labels
+ 
 -         print_total = (ARGC - i > 2)
 -     }
++     # Each label is 5 lines of data that may have blank lines.
++     # The label sheets have 2 blank lines at the top and 2 at
++     # the bottom.
+ 
 -   The `beginfile()' function is simple; it just resets the counts of
 -lines, words, and characters to zero, and saves the current file name in
 -`fname':
++     BEGIN    { RS = "" ; MAXLINES = 100 }
+ 
 -     function beginfile(file)
++     function printpage(    i, j)
+      {
 -         lines = words = chars = 0
 -         fname = FILENAME
 -     }
++         if (Nlines <= 0)
++             return
+ 
 -   The `endfile()' function adds the current file's numbers to the
 -running totals of lines, words, and characters.(1)  It then prints out
 -those numbers for the file that was just read. It relies on
 -`beginfile()' to reset the numbers for the following data file:
++         printf "\n\n"        # header
+ 
 -     function endfile(file)
 -     {
 -         tlines += lines
 -         twords += words
 -         tchars += chars
 -         if (do_lines)
 -             printf "\t%d", lines
 -         if (do_words)
 -             printf "\t%d", words
 -         if (do_chars)
 -             printf "\t%d", chars
 -         printf "\t%s\n", fname
 -     }
++         for (i = 1; i <= Nlines; i += 10) {
++             if (i == 21 || i == 61)
++                 print ""
++             for (j = 0; j < 5; j++) {
++                 if (i + j > MAXLINES)
++                     break
++                 printf "   %-41s %s\n", line[i+j], line[i+j+5]
++             }
++             print ""
++         }
+ 
 -   There is one rule that is executed for each line. It adds the length
 -of the record, plus one, to `chars'.(2) Adding one plus the record
 -length is needed because the newline character separating records (the
 -value of `RS') is not part of the record itself, and thus not included
 -in its length.  Next, `lines' is incremented for each line read, and
 -`words' is incremented by the value of `NF', which is the number of
 -"words" on this line:
++         printf "\n\n"        # footer
+ 
 -     # do per line
 -     {
 -         chars += length($0) + 1    # get newline
 -         lines++
 -         words += NF
++         delete line
+      }
+ 
 -   Finally, the `END' rule simply prints the totals for all the files:
 -
 -     END {
 -         if (print_total) {
 -             if (do_lines)
 -                 printf "\t%d", tlines
 -             if (do_words)
 -                 printf "\t%d", twords
 -             if (do_chars)
 -                 printf "\t%d", tchars
 -             print "\ttotal"
++     # main rule
++     {
++         if (Count >= 20) {
++             printpage()
++             Count = 0
++             Nlines = 0
+          }
++         n = split($0, a, "\n")
++         for (i = 1; i <= n; i++)
++             line[++Nlines] = a[i]
++         for (; i <= 5; i++)
++             line[++Nlines] = ""
++         Count++
+      }
+ 
 -   ---------- Footnotes ----------
++     END    \
++     {
++         printpage()
++     }
+ 
 -   (1) `wc' can't just use the value of `FNR' in `endfile()'. If you
 -examine the code in *note Filetrans Function::, you will see that `FNR'
 -has already been reset by the time `endfile()' is called.
++   ---------- Footnotes ----------
+ 
 -   (2) Since `gawk' understands multibyte locales, this code counts
 -characters, not bytes.
++   (1) "Real world" is defined as "a program actually used to get
++something done."
+ 
+ 
 -File: gawk.info,  Node: Miscellaneous Programs,  Prev: Clones,  Up: Sample 
Programs
++File: gawk.info,  Node: Word Sorting,  Next: History Sorting,  Prev: Labels 
Program,  Up: Miscellaneous Programs
+ 
 -13.3 A Grab Bag of `awk' Programs
 -=================================
++14.3.5 Generating Word-Usage Counts
++-----------------------------------
+ 
 -This minor node is a large "grab bag" of miscellaneous programs.  We
 -hope you find them both interesting and enjoyable.
++When working with large amounts of text, it can be interesting to know
++how often different words appear.  For example, an author may overuse
++certain words, in which case she might wish to find synonyms to
++substitute for words that appear too often. This node develops a
++program for counting words and presenting the frequency information in
++a useful format.
+ 
 -* Menu:
++   At first glance, a program like this would seem to do the job:
+ 
 -* Dupword Program::             Finding duplicated words in a document.
 -* Alarm Program::               An alarm clock.
 -* Translate Program::           A program similar to the `tr' utility.
 -* Labels Program::              Printing mailing labels.
 -* Word Sorting::                A program to produce a word usage count.
 -* History Sorting::             Eliminating duplicate entries from a history
 -                                file.
 -* Extract Program::             Pulling out programs from Texinfo source
 -                                files.
 -* Simple Sed::                  A Simple Stream Editor.
 -* Igawk Program::               A wrapper for `awk' that includes
 -                                files.
 -* Anagram Program::             Finding anagrams from a dictionary.
 -* Signature Program::           People do amazing things with too much time on
 -                                their hands.
++     # Print list of word frequencies
+ 
 -
 -File: gawk.info,  Node: Dupword Program,  Next: Alarm Program,  Up: 
Miscellaneous Programs
++     {
++         for (i = 1; i <= NF; i++)
++             freq[$i]++
++     }
+ 
 -13.3.1 Finding Duplicated Words in a Document
 ----------------------------------------------
++     END {
++         for (word in freq)
++             printf "%s\t%d\n", word, freq[word]
++     }
+ 
 -A common error when writing large amounts of prose is to accidentally
 -duplicate words.  Typically you will see this in text as something like
 -"the the program does the following..."  When the text is online, often
 -the duplicated words occur at the end of one line and the beginning of
 -another, making them very difficult to spot.
++   The program relies on `awk''s default field splitting mechanism to
++break each line up into "words," and uses an associative array named
++`freq', indexed by each word, to count the number of times the word
++occurs. In the `END' rule, it prints the counts.
+ 
 -   This program, `dupword.awk', scans through a file one line at a time
 -and looks for adjacent occurrences of the same word.  It also saves the
 -last word on a line (in the variable `prev') for comparison with the
 -first word on the next line.
++   This program has several problems that prevent it from being useful
++on real text files:
+ 
 -   The first two statements make sure that the line is all lowercase,
 -so that, for example, "The" and "the" compare equal to each other.  The
 -next statement replaces nonalphanumeric and nonwhitespace characters
 -with spaces, so that punctuation does not affect the comparison either.
 -The characters are replaced with spaces so that formatting controls
 -don't create nonsense words (e.g., the Texinfo address@hidden' becomes
 -`codeNF' if punctuation is simply deleted).  The record is then resplit
 -into fields, yielding just the actual words on the line, and ensuring
 -that there are no empty fields.
++   * The `awk' language considers upper- and lowercase characters to be
++     distinct.  Therefore, "bartender" and "Bartender" are not treated
++     as the same word.  This is undesirable, since in normal text, words
++     are capitalized if they begin sentences, and a frequency analyzer
++     should not be sensitive to capitalization.
++
++   * Words are detected using the `awk' convention that fields are
++     separated just by whitespace.  Other characters in the input
++     (except newlines) don't have any special meaning to `awk'.  This
++     means that punctuation characters count as part of words.
++
++   * The output does not come out in any useful order.  You're more
++     likely to be interested in which words occur most frequently or in
++     having an alphabetized table of how frequently each word occurs.
+ 
 -   If there are no fields left after removing all the punctuation, the
 -current record is skipped.  Otherwise, the program loops through each
 -word, comparing it to the previous one:
++   The first problem can be solved by using `tolower()' to remove case
++distinctions.  The second problem can be solved by using `gsub()' to
++remove punctuation characters.  Finally, we solve the third problem by
++using the system `sort' utility to process the output of the `awk'
++script.  Here is the new version of the program:
++
++     # wordfreq.awk --- print list of word frequencies
+ 
 -     # dupword.awk --- find duplicate words in text
+      {
 -         $0 = tolower($0)
 -         gsub(/[^[:alnum:][:blank:]]/, " ");
 -         $0 = $0         # re-split
 -         if (NF == 0)
 -             next
 -         if ($1 == prev)
 -             printf("%s:%d: duplicate %s\n",
 -                 FILENAME, FNR, $1)
 -         for (i = 2; i <= NF; i++)
 -             if ($i == $(i-1))
 -                 printf("%s:%d: duplicate %s\n",
 -                     FILENAME, FNR, $i)
 -         prev = $NF
++         $0 = tolower($0)    # remove case distinctions
++         # remove punctuation
++         gsub(/[^[:alnum:]_[:blank:]]/, "", $0)
++         for (i = 1; i <= NF; i++)
++             freq[$i]++
+      }
+ 
 -
 -File: gawk.info,  Node: Alarm Program,  Next: Translate Program,  Prev: 
Dupword Program,  Up: Miscellaneous Programs
 -
 -13.3.2 An Alarm Clock Program
 ------------------------------
++     END {
++         for (word in freq)
++             printf "%s\t%d\n", word, freq[word]
++     }
+ 
 -     Nothing cures insomnia like a ringing alarm clock.
 -     Arnold Robbins
++   Assuming we have saved this program in a file named `wordfreq.awk',
++and that the data is in `file1', the following pipeline:
+ 
 -   The following program is a simple "alarm clock" program.  You give
 -it a time of day and an optional message.  At the specified time, it
 -prints the message on the standard output. In addition, you can give it
 -the number of times to repeat the message as well as a delay between
 -repetitions.
++     awk -f wordfreq.awk file1 | sort -k 2nr
+ 
 -   This program uses the `gettimeofday()' function from *note
 -Gettimeofday Function::.
++produces a table of the words appearing in `file1' in order of
++decreasing frequency.
+ 
 -   All the work is done in the `BEGIN' rule.  The first part is argument
 -checking and setting of defaults: the delay, the count, and the message
 -to print.  If the user supplied a message without the ASCII BEL
 -character (known as the "alert" character, `"\a"'), then it is added to
 -the message.  (On many systems, printing the ASCII BEL generates an
 -audible alert. Thus when the alarm goes off, the system calls attention
 -to itself in case the user is not looking at the computer.)  Just for a
 -change, this program uses a `switch' statement (*note Switch
 -Statement::), but the processing could be done with a series of
 -`if'-`else' statements instead.  Here is the program:
++   The `awk' program suitably massages the data and produces a word
++frequency table, which is not ordered.  The `awk' script's output is
++then sorted by the `sort' utility and printed on the screen.
+ 
 -     # alarm.awk --- set an alarm
 -     #
 -     # Requires gettimeofday() library function
 -     # usage: alarm time [ "message" [ count [ delay ] ] ]
++   The options given to `sort' specify a sort that uses the second
++field of each input line (skipping one field), that the sort keys
++should be treated as numeric quantities (otherwise `15' would come
++before `5'), and that the sorting should be done in descending
++(reverse) order.
+ 
 -     BEGIN    \
 -     {
 -         # Initial argument sanity checking
 -         usage1 = "usage: alarm time ['message' [count [delay]]]"
 -         usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1])
++   The `sort' could even be done from within the program, by changing
++the `END' action to:
+ 
 -         if (ARGC < 2) {
 -             print usage1 > "/dev/stderr"
 -             print usage2 > "/dev/stderr"
 -             exit 1
 -         }
 -         switch (ARGC) {
 -         case 5:
 -             delay = ARGV[4] + 0
 -             # fall through
 -         case 4:
 -             count = ARGV[3] + 0
 -             # fall through
 -         case 3:
 -             message = ARGV[2]
 -             break
 -         default:
 -             if (ARGV[1] !~ /[[:digit:]]?[[:digit:]]:[[:digit:]]{2}/) {
 -                 print usage1 > "/dev/stderr"
 -                 print usage2 > "/dev/stderr"
 -                 exit 1
 -             }
 -             break
 -         }
++     END {
++         sort = "sort -k 2nr"
++         for (word in freq)
++             printf "%s\t%d\n", word, freq[word] | sort
++         close(sort)
++     }
+ 
 -         # set defaults for once we reach the desired time
 -         if (delay == 0)
 -             delay = 180    # 3 minutes
 -         if (count == 0)
 -             count = 5
 -         if (message == "")
 -             message = sprintf("\aIt is now %s!\a", ARGV[1])
 -         else if (index(message, "\a") == 0)
 -             message = "\a" message "\a"
++   This way of sorting must be used on systems that do not have true
++pipes at the command-line (or batch-file) level.  See the general
++operating system documentation for more information on how to use the
++`sort' program.
+ 
 -   The next minor node of code turns the alarm time into hours and
 -minutes, converts it (if necessary) to a 24-hour clock, and then turns
 -that time into a count of the seconds since midnight.  Next it turns
 -the current time into a count of seconds since midnight.  The
 -difference between the two is how long to wait before setting off the
 -alarm:
++
++File: gawk.info,  Node: History Sorting,  Next: Extract Program,  Prev: Word 
Sorting,  Up: Miscellaneous Programs
+ 
 -         # split up alarm time
 -         split(ARGV[1], atime, ":")
 -         hour = atime[1] + 0    # force numeric
 -         minute = atime[2] + 0  # force numeric
++14.3.6 Removing Duplicates from Unsorted Text
++---------------------------------------------
+ 
 -         # get current broken down time
 -         gettimeofday(now)
++The `uniq' program (*note Uniq Program::), removes duplicate lines from
++_sorted_ data.
+ 
 -         # if time given is 12-hour hours and it's after that
 -         # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m.,
 -         # then add 12 to real hour
 -         if (hour < 12 && now["hour"] > hour)
 -             hour += 12
++   Suppose, however, you need to remove duplicate lines from a data
++file but that you want to preserve the order the lines are in.  A good
++example of this might be a shell history file.  The history file keeps
++a copy of all the commands you have entered, and it is not unusual to
++repeat a command several times in a row.  Occasionally you might want
++to compact the history by removing duplicate entries.  Yet it is
++desirable to maintain the order of the original commands.
+ 
 -         # set target time in seconds since midnight
 -         target = (hour * 60 * 60) + (minute * 60)
++   This simple program does the job.  It uses two arrays.  The `data'
++array is indexed by the text of each line.  For each line, `data[$0]'
++is incremented.  If a particular line has not been seen before, then
++`data[$0]' is zero.  In this case, the text of the line is stored in
++`lines[count]'.  Each element of `lines' is a unique command, and the
++indices of `lines' indicate the order in which those lines are
++encountered.  The `END' rule simply prints out the lines, in order:
+ 
 -         # get current time in seconds since midnight
 -         current = (now["hour"] * 60 * 60) + \
 -                    (now["minute"] * 60) + now["second"]
++     # histsort.awk --- compact a shell history file
++     # Thanks to Byron Rakitzis for the general idea
+ 
 -         # how long to sleep for
 -         naptime = target - current
 -         if (naptime <= 0) {
 -             print "time is in the past!" > "/dev/stderr"
 -             exit 1
 -         }
++     {
++         if (data[$0]++ == 0)
++             lines[++count] = $0
++     }
+ 
 -   Finally, the program uses the `system()' function (*note I/O
 -Functions::) to call the `sleep' utility.  The `sleep' utility simply
 -pauses for the given number of seconds.  If the exit status is not zero,
 -the program assumes that `sleep' was interrupted and exits. If `sleep'
 -exited with an OK status (zero), then the program prints the message in
 -a loop, again using `sleep' to delay for however many seconds are
 -necessary:
++     END {
++         for (i = 1; i <= count; i++)
++             print lines[i]
++     }
+ 
 -         # zzzzzz..... go away if interrupted
 -         if (system(sprintf("sleep %d", naptime)) != 0)
 -             exit 1
++   This program also provides a foundation for generating other useful
++information.  For example, using the following `print' statement in the
++`END' rule indicates how often a particular command is used:
+ 
 -         # time to notify!
 -         command = sprintf("sleep %d", delay)
 -         for (i = 1; i <= count; i++) {
 -             print message
 -             # if sleep command interrupted, go away
 -             if (system(command) != 0)
 -                 break
 -         }
++     print data[lines[i]], lines[i]
+ 
 -         exit 0
 -     }
++   This works because `data[$0]' is incremented each time a line is
++seen.
+ 
+ 
 -File: gawk.info,  Node: Translate Program,  Next: Labels Program,  Prev: 
Alarm Program,  Up: Miscellaneous Programs
++File: gawk.info,  Node: Extract Program,  Next: Simple Sed,  Prev: History 
Sorting,  Up: Miscellaneous Programs
+ 
 -13.3.3 Transliterating Characters
 ----------------------------------
++14.3.7 Extracting Programs from Texinfo Source Files
++----------------------------------------------------
+ 
 -The system `tr' utility transliterates characters.  For example, it is
 -often used to map uppercase letters into lowercase for further
 -processing:
++The nodes *note Library Functions::, and *note Sample Programs::, are
++the top level nodes for a large number of `awk' programs.  If you want
++to experiment with these programs, it is tedious to have to type them
++in by hand.  Here we present a program that can extract parts of a
++Texinfo input file into separate files.
+ 
 -     GENERATE DATA | tr 'A-Z' 'a-z' | PROCESS DATA ...
++This Info file is written in Texinfo (http://texinfo.org), the GNU
++project's document formatting language.  A single Texinfo source file
++can be used to produce both printed and online documentation.  The
++Texinfo language is described fully, starting with *note (Texinfo)Top::
++texinfo,Texinfo--The GNU Documentation Format.
+ 
 -   `tr' requires two lists of characters.(1)  When processing the
 -input, the first character in the first list is replaced with the first
 -character in the second list, the second character in the first list is
 -replaced with the second character in the second list, and so on.  If
 -there are more characters in the "from" list than in the "to" list, the
 -last character of the "to" list is used for the remaining characters in
 -the "from" list.
++   For our purposes, it is enough to know three things about Texinfo
++input files:
+ 
 -   Some time ago, a user proposed that a transliteration function should
 -be added to `gawk'.  The following program was written to prove that
 -character transliteration could be done with a user-level function.
 -This program is not as complete as the system `tr' utility but it does
 -most of the job.
++   * The "at" symbol (`@') is special in Texinfo, much as the backslash
++     (`\') is in C or `awk'.  Literal `@' symbols are represented in
++     Texinfo source files as `@@'.
++
++   * Comments start with either address@hidden' or address@hidden'.  The
++     file-extraction program works by using special comments that start
++     at the beginning of a line.
++
++   * Lines containing address@hidden' and address@hidden group' commands 
bracket
++     example text that should not be split across a page boundary.
++     (Unfortunately, TeX isn't always smart enough to do things exactly
++     right, so we have to give it some help.)
++
++   The following program, `extract.awk', reads through a Texinfo source
++file and does two things, based on the special comments.  Upon seeing
address@hidden system ...', it runs a command, by extracting the command text 
from
++the control line and passing it on to the `system()' function (*note
++I/O Functions::).  Upon seeing address@hidden file FILENAME', each subsequent 
line
++is sent to the file FILENAME, until address@hidden endfile' is encountered.  
The
++rules in `extract.awk' match either address@hidden' or address@hidden' by 
letting the
++`omment' part be optional.  Lines containing address@hidden' and 
address@hidden group'
++are simply removed.  `extract.awk' uses the `join()' library function
++(*note Join Function::).
+ 
 -   The `translate' program demonstrates one of the few weaknesses of
 -standard `awk': dealing with individual characters is very painful,
 -requiring repeated use of the `substr()', `index()', and `gsub()'
 -built-in functions (*note String Functions::).(2) There are two
 -functions.  The first, `stranslate()', takes three arguments:
++   The example programs in the online Texinfo source for `GAWK:
++Effective AWK Programming' (`gawk.texi') have all been bracketed inside
++`file' and `endfile' lines.  The `gawk' distribution uses a copy of
++`extract.awk' to extract the sample programs and install many of them
++in a standard directory where `gawk' can find them.  The Texinfo file
++looks something like this:
+ 
 -`from'
 -     A list of characters from which to translate.
++     ...
++     This program has a @code{BEGIN} rule,
++     that prints a nice message:
+ 
 -`to'
 -     A list of characters to which to translate.
++     @example
++     @c file examples/messages.awk
++     BEGIN @{ print "Don't panic!" @}
++     @c end file
++     @end example
+ 
 -`target'
 -     The string on which to do the translation.
++     It also prints some final advice:
+ 
 -   Associative arrays make the translation part fairly easy. `t_ar'
 -holds the "to" characters, indexed by the "from" characters.  Then a
 -simple loop goes through `from', one character at a time.  For each
 -character in `from', if the character appears in `target', it is
 -replaced with the corresponding `to' character.
++     @example
++     @c file examples/messages.awk
++     END @{ print "Always avoid bored archeologists!" @}
++     @c end file
++     @end example
++     ...
+ 
 -   The `translate()' function simply calls `stranslate()' using `$0' as
 -the target.  The main program sets two global variables, `FROM' and
 -`TO', from the command line, and then changes `ARGV' so that `awk'
 -reads from the standard input.
++   `extract.awk' begins by setting `IGNORECASE' to one, so that mixed
++upper- and lowercase letters in the directives won't matter.
+ 
 -   Finally, the processing rule simply calls `translate()' for each
 -record:
++   The first rule handles calling `system()', checking that a command is
++given (`NF' is at least three) and also checking that the command exits
++with a zero exit status, signifying OK:
+ 
 -     # translate.awk --- do tr-like stuff
 -     # Bugs: does not handle things like: tr A-Z a-z, it has
 -     # to be spelled out. However, if `to' is shorter than `from',
 -     # the last character in `to' is used for the rest of `from'.
++     # extract.awk --- extract files and run programs
++     #                 from texinfo files
+ 
 -     function stranslate(from, to, target,     lf, lt, ltarget, t_ar, i, c,
 -                                                                    result)
 -     {
 -         lf = length(from)
 -         lt = length(to)
 -         ltarget = length(target)
 -         for (i = 1; i <= lt; i++)
 -             t_ar[substr(from, i, 1)] = substr(to, i, 1)
 -         if (lt < lf)
 -             for (; i <= lf; i++)
 -                 t_ar[substr(from, i, 1)] = substr(to, lt, 1)
 -         for (i = 1; i <= ltarget; i++) {
 -             c = substr(target, i, 1)
 -             if (c in t_ar)
 -                 c = t_ar[c]
 -             result = result c
 -         }
 -         return result
 -     }
++     BEGIN    { IGNORECASE = 1 }
+ 
 -     function translate(from, to)
++     /address@hidden(omment)?[ \t]+system/    \
+      {
 -         return $0 = stranslate(from, to, $0)
 -     }
 -
 -     # main program
 -     BEGIN {
 -         if (ARGC < 3) {
 -             print "usage: translate from to" > "/dev/stderr"
 -             exit
++         if (NF < 3) {
++             e = (FILENAME ":" FNR)
++             e = (e  ": badly formed `system' line")
++             print e > "/dev/stderr"
++             next
++         }
++         $1 = ""
++         $2 = ""
++         stat = system($0)
++         if (stat != 0) {
++             e = (FILENAME ":" FNR)
++             e = (e ": warning: system returned " stat)
++             print e > "/dev/stderr"
+          }
 -         FROM = ARGV[1]
 -         TO = ARGV[2]
 -         ARGC = 2
 -         ARGV[1] = "-"
 -     }
 -
 -     {
 -         translate(FROM, TO)
 -         print
+      }
+ 
 -   While it is possible to do character transliteration in a user-level
 -function, it is not necessarily efficient, and we (the `gawk' authors)
 -started to consider adding a built-in function.  However, shortly after
 -writing this program, we learned that the System V Release 4 `awk' had
 -added the `toupper()' and `tolower()' functions (*note String
 -Functions::).  These functions handle the vast majority of the cases
 -where character transliteration is necessary, and so we chose to simply
 -add those functions to `gawk' as well and then leave well enough alone.
 -
 -   An obvious improvement to this program would be to set up the `t_ar'
 -array only once, in a `BEGIN' rule. However, this assumes that the
 -"from" and "to" lists will never change throughout the lifetime of the
 -program.
 -
 -   ---------- Footnotes ----------
++The variable `e' is used so that the rule fits nicely on the screen.
+ 
 -   (1) On some older systems, `tr' may require that the lists be
 -written as range expressions enclosed in square brackets (`[a-z]') and
 -quoted, to prevent the shell from attempting a file name expansion.
 -This is not a feature.
++   The second rule handles moving data into files.  It verifies that a
++file name is given in the directive.  If the file named is not the
++current file, then the current file is closed.  Keeping the c