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Bash-5.1-alpha available for download

From: Chet Ramey
Subject: Bash-5.1-alpha available for download
Date: Wed, 17 Jun 2020 10:47:42 -0400

The first alpha release of bash-5.1 is now available with the URL

and from the bash-5.1-testing branch in the bash git repository       

This tar file includes the formatted documentation (you should be able to
generate updated versions yourself).

This release fixes several outstanding bugs in bash-5.0 and introduces
several new features.  The most significant change is a return to the
bash-4.4 behavior of not performing pathname expansion on a word that
contains backslashes but does not contain any unquoted globbing special
characters.  This comes after a long POSIX discussion that resulted in a
change to the standard.  There are several changes regarding trap handling
while reading from the terminal (e.g, for `read' and `select'.) There are a
number of bug fixes, including several bugs that caused the shell to crash. 
Details are appended. 

The most notable new features are in the random number engine. There is a
new variable, SRANDOM, which gets its random data from the system's entropy
engine and so is not linear and cannot be reseeded to get an identical
random sequence. The PROMPT_COMMANDS array variable can be used to run
multiple commands before printing the primary prompt. Associative arrays may
be assigned using a series of key-value pairs within a compound assignment.
`wait' has a new `-p' option which stores PID information about the process
reaped by `wait -n'. Process substitution is now available in posix mode.
There are new parameter transformation operators. There is no new `compat50'
option; use the BASH_COMPAT variable to select the compatibility level.
All the new features are described below.

There are a few incompatible changes between bash-5.0 and bash-5.1. The
change to pathname expansion means that words containing backslashes, but no
special globbing characters, will not undergo pathname expansion. While
the bash-5.0 behavior was POSIX-conformant, the change was not well-received.
Changes to the random number engines mean that seeding RANDOM will produce
a different numeric sequence. Set the compatibility level to 50 to revert
to the bash-5.0 behavior.

`bashbug' may be used to report bugs with this version.  It will send
mail to if the shell's `release status' is alpha or

As always, thanks for your help.


+========== CHANGES ==========+
This document details the changes between this version, bash-5.1-alpha, and
the previous version, bash-5.0-release.

1. Changes to Bash

a. Fixed a bug that caused a posix-mode shell to not exit if the return builtin
   was executed outside a function or dot script.

b. Fixed a bug where `declare +f' could potentially turn off the function

c. Restored bash-4.4 pathname expansion behavior when a word to be expanded had
   only backslashes, not any of the other globbing characters. This came after
   an extensive POSIX group discussion (interp #1234).

d. There are more changes to avoid performing word expansions multiple times on
   arithmetic expressions.

e. Fixed a bug with alias expansion when the alias ends with a TAB.

f. Fixed a bug that caused programmable completion to return an error if the
   shell function name supplied as an argument to `complete -F' was invalid.

g. There are several fixes to buffer overflows found as the result of fuzzing
   with random input.

h. Fixed a bug that caused the edit-and-execute-command editing command to
   start with the previous history line if invoked on an empty line.

i. Fixed a bug that potentially caused `bind --help' to change readline's
   output stream.

j. Turning off posix mode now restores the vi-insertion mode binding for TAB
   that was in effect when posix mode was enabled.

k. Restore the previous state of job control being enabled if `exec' fails in
   an interactive shell.

l. Fixed a bug that caused the terminal's process group to be set incorrectly
   if job control was turned off before starting an interactive shell.

m. Fixed a bug that caused a crash when HISTSIZE=0.

n. Fixed a word expansion bug that caused null strings on the rhs of expansions
   to be discarded incorrectly.

o. History list management does a better job of handling the situation where
   the number of history entries from the current shell session is greater than
   the number of entries in the history list.

p. Fixed a bug that caused the `fc' builtin to attempt to dereference a newly-
   freed history entry.

q. Fixed a bug that made the `Q' variable transformation not work well with
   `set -u'.

r. There are several word expansion fixes for expanding $* and $@ in contexts
   where word splitting is not going to be performed, since each positional
   parameter must expand to a separate word.

s. Fixed a bug that could cause ^D to exit bash immediately even if there were
   stopped jobs.

t. Fixed a bug with double-quoting and backslash-quoting strings containing
   multibyte characters for reuse.

u. Fixed a bug that caused the line number to be reported incorrectly if the
   shell executed a (command) subshell.

v. Fixed a bug that caused the shell to fail to reap process substitutions
   when they went out of scope, which had unpredictable results.

w. Fixed a bug that caused null strings in arguments to [[ conditional command
   operators to compare incorrectly.

x. Changed the behavior of `wait' without arguments to only wait for background
   processes the current shell instance started, not background children it may
   have inherited.

y. Fixed a bug that could cause command substitution to leave file descriptors
   open if the shell received many SIGINTs.

z. Bash now behaves better if the `**' filename expansion operator encounters a
   symbolic link to a directory, avoiding more cases where it might return
   duplicate pathnames.

aa. Programmable completion now canonicalizes directory names in the same way
    as bash word completion, so `..' is handled consistently.

bb. Fixed a bug when using RETURN as the delimiter to the read builtin; it
    caused readline to set the binding for RETURN incorrectly.

cc. Fixed a bug that caused `history -d' to delay printing an out-of-range
    error message.

dd. Fixed a bug with `bash -c command' where `command' ends with an expanded

ee. Fixed a bug that could result in `history -n' adding spurious line feeds to
    commands in the history list.

ff. The $RANDOM random number generator now XORs the top and bottom halves of
    the internal 32-bit value to introduce more randomness. Setting the shell
    compatibility level to 50 or lower undoes this.

gg. Fixed several problems caused by running the DEBUG trap on simple commands
    executed as part of a pipeline.

ii. Fixed a bug that didn't allow `bind -r' to remove the binding for \C-@.

jj. Several fixes to the bash-backward-shellword bindable readline command to
    behave better when at the last character on the line.

kk. If `set -x' is enabled, bash doesn't print a command twice if it's run by
    the `command' builtin.

ll. Fixed a bug with printing function definitions containing here documents.

mm. Fixed a bug that could cause the `bind' builtin to set $? to -1.

nn. Fixed a bug that didn't reset the timezone information correctly when the
    TZ variable was unset.

oo. Fixed several issues with assigning an associative array variable using a
    compound assignment that expands the value of the same variable.

pp. Fixed several places where the shell set $? without setting PIPESTATUS.

qq. Fixed a problem with glob bracket expressions containing invalid character
    classes, collating symbols, or equivalence classes -- they should not
    require a closing right bracket.

rr. Fixed a bug where running a builtin in a subshell did not run the EXIT trap.

ss. Fixed several problems with posix-mode variable assignments preceding
    shell function calls and posix special builtins, so that they create and
    modify variables at the current scope.

tt. Fix history initialization so `bash +o history' works as expected.

uu. Fixed a bug in the bindable edit-and-execute-command command that could
    interfere with the shell's parsing state.

vv. Fixed an issue with nested traps running command substitutions in command
    lines with command substitutions.

ww. Fixed a bug with globbing pathnames that contain invalid multibyte
    characters (sequences that don't correspond to a character in the current

xx. Fixed a bug that caused the shell not to exit if a function definition
    failed while errexit was enabled.

yy. Process substitution processes now get their input from /dev/null, since
    they are asynchronous, not interactive, and not jobs.

zz. Setting nocaseglob no longer turns on case-insensitive regexp matching.

aaa. Fixed a bug that resulted in extra blank lines being added to some history
     entries containing here-documents.

bbb. Fixed a bug that resulted in incorrect matching of some patterns in word
     expansion if they expanded to the empty string.

ccc. Fixed here-string expansion so it behaves the same as expansion of the
     rhs of an assignment statement.

ddd. Changed here-document parsing to no longer allow the end of the here
     document to delimit a command substitution.

eee. Several fixes to history expansion: multiple :p modifiers work, a ^ word
     designator works as part of a range, and a `-' is treated as part of a
     search string if it immediately follows a `!'.

fff. Fixed a bug in pattern substitution with null matches in a string
     containing multibyte characters.

ggg. Unbinding a key sequence bound with `bind -x' now removes the key sequence
     from the additional keymap `bind -x' uses.

hhh. Fixed a bug with command start detection for completion so that it doesn't
     mistake brace expansion for the start of a command.

iii. Fixed a bug that caused local variables with the same name as variables
     appearing in a function's temporary environment to not be marked as local.

jjj. Fixed a bug that could cause SIGCHLD to be blocked when executing return
     or exec in the rightmost pipeline element with lastpipe enabled.

kkk. Fixed a bug that could result in commands without the execute bit set
     being added to the command hash table.

lll. Fixed a bug that allowed non-digits to follow the `#' in a `base#number'
     integer constant.

mmm. Fixed a bug that made `time -- command' attempt to execute `--'.

nnn. Fixed a couple of bugs with variable transformation using arrays
     subscripted with `*' or `@'.

ooo. A failure to create a variable using `declare' in a function no longer
     causes the function to return immediately.

ppp. Fixed a bug that could cause the := word expansion to add a non-null
     value if attempting to assign a null string when double-quoted.

qqq. Fixed a bug that could cause backslashes quoting double quotes in here
     document bodies to not be removed when expanding the body.

rrr. Fixed a bug that caused commands following a subshell while the shell is
     reading input from stdin but not interactive, while job control is
     enabled, to be executed twice.

sss. Fixed a bug where receiving SIGTERM from a different process while
     readline was active could cause the shell to terminate.

ttt. In posix mode, running a trap after the read builtin now sees the exit
     status of the read builtin (e.g., 130 after a SIGINT) in $?.

uuu. Fixed a bug with nameref variables referencing array subscripts used in
     arithmetic expressions.

vvv. Fixed a bug that caused the pipeline process group id to be reset in the
     middle of a command list run by a shell started to run a command

www. Restricted shells can no longer read and write history files with pathnames
     containing slashes.

xxx. Fixed a couple of problems with 0 and -0 used as arguments to `fc' when
     not listing commands from the history.

yyy. When `test' is supplied four or more arguments, treat an argument that
     looks like an operator (e.g., -e), but is in a place where only a string
     is valid, as a string, as it would be when using the POSIX rules, instead
     of an operator with a missing argument.

zzz. There is no `compat50' shopt option. Changes to the shell compatibility
     level should use the BASH_COMPAT variable.

aaaa. Redirection failures with compound commands are now treated as errors
      that cause the shell to exit if `errexit' is enabled.

bbbb. Redirection failure error messages no longer expand the word in the
      redirection again.

cccc. History expansion is no longer performed while parsing a here-document
      inside a command substitution.

2. Changes to Readline

a. There are a number of fixes that were found as the result of fuzzing with
   random input.

b. Changed the revert-all-at-newline behavior to make sure to start at the end
   of the history list when doing it, instead of the line where the user hit

c. When parsing `set' commands from the inputrc file or an application, readline
   now allows trailing whitespace.

d. Fixed a bug that left a file descriptor open to the history file if the
   file size was 0.

e. Fixed a problem with binding key sequences containing meta characters.

f. Fixed a bug that caused the wrong line to be displayed if the user tried to
   move back beyond the beginning of the history list, or forward past the end
   of the history list.

g. If readline catches SIGTSTP, it now sets a hook that allows the calling
   application to handle it if it desires.

h. Fixed a redisplay problem with a prompt string containing embedded newlines.

i. Fixed a problem with completing filenames containing invalid multibyte
   sequences when case-insensitive comparisons are enabled.

j. Fixed a redisplay problem with prompt strings containing invisible multibyte

k. Fixed a problem with multibyte characters mapped to editing commands that
   modify the search string in incremental search.

l. Fixed a bug with maintaining the key sequence while resolving a bound
   command in the presence of ambiguous sequences (sequences with a common
   prefix), in most cases while attempting to unbind it.

m. Fixed several buffer overflows found as the result of fuzzing.

n. Reworked backslash handling when translating key sequences for key binding
   to be more uniform and consistent, which introduces a slight backwards

o. Fixed a bug with saving the history that resulted in errors not being
   propagated to the calling application when the history file is not writable.

p. Readline only calls chown(2) on a newly-written history file if it really
   needs to, instead of having it be a no-op.

q. Readline now behaves better when operate-and-get-next is used when the
   history list is `full': when there are already $HISTSIZE entries.

r. Fixed a bug that could cause vi redo (`.') of a replace command not to work
   correctly in the C or POSIX locale.

3. New Features in Bash

a. `bind -x' now supports different bindings for different editing modes and

b. Bash attempts to optimize the number of times it forks when executing
   commands in subshells and from `bash -c'.

c. Here documents and here strings now use pipes for the expanded document if
   it's smaller than the pipe buffer size, reverting to temporary files if it's

d. There are new loadable builtins: mktemp, accept, mkfifo, csv, cut/lcut

e. In posix mode, `trap -p' now displays signals whose disposition is SIG_DFL
   and those that were SIG_IGN when the shell starts.

f. The shell now expands the history number (e.g., in PS1) even if it is not
   currently saving commands to the history list.

g. `read -e' may now be used with arbitrary file descriptors (`read -u N').

h. The `select' builtin now runs traps if its internal call to the read builtin
   is interrupted by a signal.

i. SRANDOM: a new variable that expands to a 32-bit random number that is not
   produced by an LCRNG, and uses getrandom/getentropy, falling back to
   /dev/urandom or arc4random if available. There is a fallback generator if
   none of these are available.

j. shell-transpose-words: a new bindable readline command that uses the same
   definition of word as shell-forward-word, etc.

k. The shell now adds default bindings for shell-forward-word,
   shell-backward-word, shell-transpose-words, and shell-kill-word.

l. Bash now allows ARGV0 appearing in the initial shell environment to set $0.

m. If `unset' is executed without option arguments, bash tries to unset a shell
   function if a name argument cannot be a shell variable name because it's not
   an identifier.

n. The `test -N' operator uses nanosecond timestamp granularity if it's

o. Bash posix mode now treats assignment statements preceding shell function
   definitions the same as in its default mode, since POSIX has changed and
   no longer requires those assignments to persist after the function returns
   (POSIX interp 654).

p. BASH_REMATCH is no longer readonly.

q. wait: has a new -p VARNAME option, which stores the PID returned by `wait -n'
   or `wait' without arguments.

r. Sorting the results of pathname expansion now uses byte-by-byte comparisons
   if two strings collate equally to impose a total order; the result of a
   POSIX interpretation (#963 and #1070).

s. Bash now allows SIGINT trap handlers to execute recursively.

t. Bash now saves and restores state around setting and unsetting posix mode,
   instead of having unsetting posix mode set a known state.

u. Process substitution is now available in posix mode.

v. READLINE_MARK: a new variable available while executing commands bound with
   `bind -x', contains the value of the mark.

w. Bash removes SIGCHLD from the set of blocked signals if it's blocked at shell

x. `test -v N' can now test whether or not positional parameter N is set.

y. `local' now honors the `-p' option to display all local variables at the
    current context.

z. The `@a' variable transformation now prints attributes for unset array

aa. The `@A' variable transformation now prints a declare command that sets a
    variable's attributes if the variable has attributes but is unset.

bb. `declare' and `local' now have a -I option that inherits attributes and
    value from a variable with the same name at a previous scope.

cc. When run from a -c command, `jobs' now reports the status of completed jobs.

dd. New `U', `u', and `L' parameter transformations to convert to uppercase,
    convert first character to uppercase, and convert to lowercase,

ee. PROMPT_COMMANDS: a new array variable, each element of which can contain a
    command to be executed like PROMPT_COMMAND.

ff. `ulimit' has a -R option to report and set the RLIMIT_RTTIME resource.

gg. Associative arrays may be assigned using a list of key-value pairs within
    a compound assignment. Compound assignments where the words are not of
    the form [key]=value are assumed to be key-value assignments. A missing or
    empty key is an error; a missing value is treated as NULL. Assignments may
    not mix the two forms.

hh. New `K' parameter transformation to display associative arrays as key-
    value pairs.

ii. Writing history to syslog now handles messages longer than the syslog max
    length by writing multiple messages with a sequence number.

jj. SECONDS and RANDOM may now be assigned using arithmetic expressions, since
    they are nominally integer variables. LINENO is not an integer variable.

kk. Bash temporarily suppresses the verbose option when running the DEBUG trap
    while running a command from the `fc' builtin.

ll. `wait -n' now accepts a list of job specifications as arguments and will
    wait for the first one in the list to change state.

mm. The associative array implementation can now dynamically increase the
    size of the hash table based on insertion patterns.

nn. HISTFILE is now readonly in a restricted shell.

oo. The bash malloc now returns memory that is 16-byte aligned on 64-bit

4. New Features in Readline

a. If a second consecutive completion attempt produces matches where the first
   did not, treat it as a new completion attempt and insert a match as

b. Bracketed paste mode works in more places: incremental search strings, vi
   overstrike mode, character search, and reading numeric arguments.

c. Readline automatically switches to horizontal scrolling if the terminal has
   only one line.

d. Unbinding all key sequences bound to a particular readline function now
   descends into keymaps for multi-key sequences.

e. rl-clear-display: new bindable command that clears the screen and, if
   possible, the scrollback buffer (bound to emacs mode M-C-l by default).

f. New active mark and face feature: when enabled, it will highlight the text
   inserted by a bracketed paste (the `active region') and the text found by
   incremental and non-incremental history searches.

g. Readline sets the mark in several additional commands.

h. Bracketed paste mode is enabled by default (for now).

i. Readline tries to take advantage of the more regular structure of UTF-8
   characters to identify the beginning and end of characters when moving
   through the line buffer.

j. The bindable operate-and-get-next command (and its default bindings) are
   now part of readline instead of a bash-specific addition.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU

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