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Bash-5.1-alpha available for download
Bash-5.1-alpha available for download
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 firstname.lastname@example.org 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
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
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
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
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
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
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
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'
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
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
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
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
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
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
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-
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 email@example.com http://tiswww.cwru.edu/~chet/
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