Re: Improved tail patch

[Paul Eggert]

Should we instead fix 'tail' to use select?  Surely that would be
efficient (and easier) than all this stuff with O_NONBLOCK.
(O_NONBLOCK gives me the willies.  :-)

Also, how about this small patch to fix your immediate problem?  It
doesn't fix the general case, but it does fix a POSIX-conformance bug
and it fixes your test example.  (It's weird that "tail -f" and "tail
-f -" have different behavior when standard input is a pipe, but
that's what POSIX explicitly requires....)

2004-07-21  Paul Eggert  <address@hidden>

        * src/tail.c (main): Ignore -f if no file operand is specified
        and standard input is a pipe.
        * doc/coreutils.texi (tail invocation): Do not ignore -f for
        all pipes, just for when standard input is a pipe and no
        file operand is specified.
        * tests/tail/Test.pm: Reinstate f-1 test, since we now pass.

Index: doc/coreutils.texi
===================================================================
RCS file: /home/eggert/coreutils/cu/doc/coreutils.texi,v
retrieving revision 1.195
diff -p -u -r1.195 coreutils.texi
--- doc/coreutils.texi  6 Jul 2004 16:15:45 -0000       1.195
+++ doc/coreutils.texi  21 Jul 2004 18:46:55 -0000
@@ -2426,8 +2426,8 @@ by 1048576.
 @vindex name @r{follow option}
 @vindex descriptor @r{follow option}
 Loop forever trying to read more characters at the end of the file,
-presumably because the file is growing.  This option is ignored when
-reading from a pipe.
+presumably because the file is growing.  This option is ignored if
+no @var{file} operand is specified and standard input is a pipe.
 If more than one file is given, @command{tail} prints a header whenever it
 gets output from a different file, to indicate which file that output is
 from.
Index: src/tail.c
===================================================================
RCS file: /home/eggert/coreutils/cu/src/tail.c,v
retrieving revision 1.223
diff -p -u -r1.223 tail.c
--- src/tail.c  15 Jun 2004 18:00:58 -0000      1.223
+++ src/tail.c  21 Jul 2004 18:43:32 -0000
@@ -1687,6 +1687,15 @@ main (int argc, char **argv)
       static char *dummy_stdin = "-";
       n_files = 1;
       file = &dummy_stdin;
+
+      /* POSIX says that -f is ignored if no file operand is specified
+        and standard input is a pipe.  */
+      if (forever)
+       {
+         struct stat stats;
+         if (fstat (STDIN_FILENO, &stats) == 0 && S_ISFIFO (stats.st_mode))
+           forever = false;
+       }
     }
 
   {
Index: tests/tail/Test.pm
===================================================================
RCS file: /home/eggert/coreutils/cu/tests/tail/Test.pm,v
retrieving revision 1.11
diff -p -u -r1.11 Test.pm
--- tests/tail/Test.pm  18 Feb 2002 12:35:00 -0000      1.11
+++ tests/tail/Test.pm  21 Jul 2004 18:38:07 -0000
@@ -68,7 +68,7 @@ my @tv = (
 ['n-5b', '-n  0', "y\n" x 5, '', 0],
 
 # With textutils-1.22, this failed.
-#['f-1', '-f -n 1', "a\nb\n", "b\n", 0],
+['f-1', '-f -n 1', "a\nb\n", "b\n", 0],
 );
 
 sub test_vector