That is, 5.1 with the four post-release patches available so far.
This is a terse description of the new features added to bash-5.1 since
the release of bash-5.0. As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.
1. New Features in Bash
a. `bind -x' now supports different bindings for different editing modes and
keymaps.
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
larger.
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
available.
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.
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
startup.
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
variables.
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,
respectively.
ee. PROMPT_COMMAND: can now be an array variable, each element of which can
contain a command to be executed like a string PROMPT_COMMAND variable.
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
systems.
pp. If the hash builtin is listing hashed filenames portably, don't print
anything if the table is empty.
qq. GLOBIGNORE now ignores `.' and `..' as a terminal pathname component.
rr. Bash attempts to optimize away forks in the last command in a function body
under appropriate circumstances.
ss. The globbing code now uses fnmatch(3) to check collation elements (if
available) even in cases without multibyte characters.
tt. The `fg' and `bg' builtins now return an error in a command substitution
when asked to restart a job inherited from the parent shell.
uu. The shell now attempts to unlink all FIFOs on exit, whether a consuming
process has finished with them or not.
vv. There is a new contributed loadable builtin: asort.
2. 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
appropriate.
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. This is tied to bracketed
paste and can be disabled by turning off bracketed paste.
g. Readline sets the mark in several additional commands.
h. Bracketed paste mode is enabled by default.
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.
k. The signal cleanup code now blocks SIGINT while processing after a SIGINT.
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