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This is a terse description of the new features added to bash-5.2 since
the release of bash-5.1. As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.
1. New Features in Bash
a. The bash malloc returns memory that is aligned on 16-byte boundaries.
b. There is a new internal timer framework used for read builtin timeouts.
c. Rewrote the command substitution parsing code to call the parser recursively
and rebuild the command string from the parsed command. This allows better
syntax checking and catches errors much earlier. Along with this, if
command substitution parsing completes with here-documents remaining to be
read, the shell prints a warning message and reads the here-document bodies
from the current input stream.
d. The `ulimit' builtin now treats an operand remaining after all of the options
and arguments are parsed as an argument to the last command specified by
an option. This is for POSIX compatibility.
e. Here-document parsing now handles $'...' and $"..." quoting when reading the
here-document body.
f. The `shell-expand-line' and `history-and-alias-expand-line' bindable readline
commands now understand $'...' and $"..." quoting.
g. There is a new `spell-correct-word' bindable readline command to perform
spelling correction on the current word.
h. The `unset' builtin now attempts to treat arguments as array subscripts
without parsing or expanding the subscript, even when `assoc_expand_once'
is not set.
i. There is a default value for $BASH_LOADABLES_PATH in config-top.h.
j. Associative array assignment and certain instances of referencing (e.g.,
`test -v' now allow `@' and `*' to be used as keys.
k. Bash attempts to expand indexed array subscripts only once when executing
shell constructs and word expansions.
l. The `unset' builtin allows a subscript of `@' or `*' to unset a key with
that value for associative arrays instead of unsetting the entire array
(which you can still do with `unset arrayname'). For indexed arrays, it
removes all elements of the array without unsetting it (like `A=()').
m. Additional builtins (printf/test/read/wait) do a better job of not
parsing array subscripts if array_expand_once is set.
n. New READLINE_ARGUMENT variable set to numeric argument for readline commands
defined using `bind -x'.
o. The new `varredir_close' shell option causes bash to automatically close
file descriptors opened with {var}<fn and other styles of varassign
redirection unless they're arguments to the `exec' builtin.
p. The `$0' special parameter is now set to the name of the script when running
any (non-interactive) startup files such as $BASH_ENV.
q. The `enable' builtin tries to load a loadable builtin using the default
search path if `enable name' (without any options) attempts to enable a
non-existent builtin.
r. The `printf' builtin has a new format specifier: %Q. This acts like %q but
applies any specified precision to the original unquoted argument, then
quotes and outputs the result.
s. The new `noexpand_translations' option controls whether or not the translated
output of $"..." is single-quoted.
t. There is a new parameter transformation operator: @k. This is like @K, but
expands the result to separate words after word splitting.
u. There is an alternate array implementation, selectable at `configure' time,
that optimizes access speed over memory use (use the new configure
--enable-alt-array-implementation option).
v. If an [N]<&WORD- or [N]>&WORD- redirection has WORD expand to the empty
string, treat the redirection as [N]<&- or [N]>&- and close file descriptor
N (default 0).
w. Invalid parameter transformation operators are now invalid word expansions,
and so cause fatal errors in non-interactive shells.
x. New shell option: patsub_replacement. When enabled, a `&' in the replacement
string of the pattern substitution expansion is replaced by the portion of
the string that matched the pattern. Backslash will escape the `&' and
insert a literal `&'.
y. `command -p' no longer looks in the hash table for the specified command.
z. The new `--enable-translatable-strings' option to `configure' allows $"..."
support to be compiled in or out.
aa. The new `globskipdots' shell option forces pathname expansion never to
return `.' or `..' unless explicitly matched. It is enabled by default.
bb. Array references using `@' and `*' that are the value of nameref variables
(declare -n ref='v[@]' ; echo $ref) no longer cause the shell to exit if
set -u is enabled and the array (v) is unset.
cc. There is a new bindable readline command name:
`vi-edit-and-execute-command'.
dd. In posix mode, the `printf' builtin checks for the `L' length modifier and
uses long double for floating point conversion specifiers if it's present,
double otherwise.
ee. The `globbing' completion code now takes the `globstar' option into account.
ff. `suspend -f' now forces the shell to suspend even if job control is not
currently enabled.
gg. Since there is no `declare -' equivalent of `local -', make sure to use
`local -' in the output of `local -p'.
2. New Features in Readline
a. There is now an HS_HISTORY_VERSION containing the version number of the
history library for applications to use.
b. History expansion better understands multiple history expansions that may
contain strings that would ordinarily inhibit history expansion (e.g.,
`abc!$!$').
c. There is a new framework for readline timeouts, including new public
functions to set timeouts and query how much time is remaining before a
timeout hits, and a hook function that can trigger when readline times
out. There is a new state value to indicate a timeout.
d. Automatically bind termcap key sequences for page-up and page-down to
history-search-backward and history-search-forward, respectively.
e. There is a new `fetch-history' bindable command that retrieves the history
entry corresponding to its numeric argument. Negative arguments count back
from the end of the history.
f. `vi-undo' is now a bindable command.
g. There is a new option: `enable-active-region'. This separates control of
the active region and bracketed-paste. It has the same default value as
bracketed-paste, and enabling bracketed paste enables the active region.
Users can now turn off the active region while leaving bracketed paste
enabled.
h. rl_completer_word_break_characters is now `const char *' like
rl_basic_word_break_characters.
i. Readline looks in $LS_COLORS for a custom filename extension
(*.readline-colored-completion-prefix) and uses that as the default color
for the common prefix displayed when `colored-completion-prefix' is set.
j. Two new bindable string variables: active-region-start-color and
active-region-end-color. The first sets the color used to display the
active region; the second turns it off. If set, these are used in place
of terminal standout mode.
k. New readline state (RL_STATE_EOF) and application-visible variable
(rl_eof_found) to allow applications to detect when readline reads EOF
before calling the deprep-terminal hook.
l. There is a new configuration option: --with-shared-termcap-library, which
forces linking the shared readline library with the shared termcap (or
curses/ncurses/termlib) library so applications don't have to do it.
m. Readline now checks for changes to locale settings (LC_ALL/LC_CTYPE/LANG)
each time it is called, and modifies the appropriate locale-specific display
and key binding variables when the locale changes.
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