This document details the changes between this version, bash-5.3-beta, and
the previous version, bash-5.3-alpha.

1. Changes to Bash

a. Per POSIX, a null pathname argument to `cd' is now an error.

b. Fixes for command completion when the directory portion of the pathname
   contains characters that require quoting.

c. Fix to prevent redirections from undergoing word expansion twice.

d. Fix for rare parsing issue with for loops where a newline appears before
   `in'.

e. The bash build process now assumes a C90 compilation environment and a
   POSIX.1-1990 execution environment.

f. Fixed a bug where bash's internal redirection flags could collide with
   the system's open/fcntl flags.

g. Fixed a problem with `jobs' run from a trap or `bind -x' command printing
   the status of terminated foreground jobs.

h. Bash works around a macOS gettext bug with translating the `command not
   found' message by caching the translated string.

i. Bash does not try to set the tty state after a process finishes if it is
   running a trap, running a readline key binding (bind -x), or executing a
   programmable completion.

j. Restricted shells are not allowed to run `enable -f', even when it's
   shorthand from `enable f'.

k. Work around an android problem with file descriptors if the read builtin
   gets both -u and -e.

l. Fixed some small memory leaks in bash completion and command parsing and
   execution.

m. Fix for crash when timed commands jump back to the top level after SIGINT.

n. Minor fixes for command substitution parsing in the foreground.

o. Fix to reset read builtin buffer after SIGINT.

p. Fix for inconsistency between arrays and scalar variables when declaring
   local variables and using values from previous variable contexts.

q. Bash doesn't try to give the terminal back to the original process group
   after running a trap unless job control is enabled.

r. Fix to inhibit fork optimizations in functions that set a RETURN trap.

s. Fixes for parsing commands within process substitutions where they should
   behave differently than command substitutions, including prohibiting the
   special case for redirections that is only available for command
   substitutions.

t. Restrict the effect of force_fignore to the cases where FIGNORE should
   affect completions.

u. Fix for `read' builtin and invalid multibyte characters that contain the
   delimiter character, so the delimiter acts as intended.

v. Fix for `read -e' so it restores the correct completion function if it's
   interrupted.

w. Fix an off-by-one error when parsing an improperly-formed printf time
   specification.

x. Fix for return status for commands whose return status is being inverted
   when set -e is ignored.

y. Fix for checking `read' builtin timeouts after we check for having read
   the delimiter.

z. Fixes for integer overflows and size_t variables.

aa. Fixes for the Makefiles to simplify, remove some unused variables, and
    clean up what `git' sees after running the various clean targets.

bb. Fix for the `exec' builtin to avoid duplicate error messages.

cc. `printf' now warns if there are no valid characters at all in an integer
    argument.

2. Changes to Readline

a. Make sure the bracketed-paste input buffer is null-terminated when read
   returns an error.

b. Fixed a small memory leak in execute-named-command if the command doesn't
   exist or the function doesn't return.

c. Fix for attempting to change case of invalid multibyte characters.

d. Fix for possible completions that compare identically when using case-
   insensitive completion but have different byte lengths.

e. Fix to make non-incremental searches use undo lists and set the history
   position the same way as incremental searches.

f. Don't check for signals when handling a received signal.

g. Fix off-by-one error when tokenizing words like $((expr)) while performing
   history expansion.

h. Fixes for incremental searches and redisplay in the C locale.

i. Fixes for some use-after-free of the undo list errors when stacking multiple
   commands that use rl_maybe_replace_line to save changes to a history entry.

j. Fixes to ensure that completion-prefix-display-length and
   colored-completion-prefix are mutually exclusive.

3. New Features in Bash

a. MULTIPLE_COPROCS is now enabled by default.

b. The `bind' builtin interprets additional non-option arguments after -p or
   -P as bindable command names and restricts output to the bindings for
   those names.

c. Bash now uses the login shell for $BASH if the shell is named `su' or `-su'.

d. Bash now prints job notifications if an interactive shell is running a trap,
   even though the shell is not interactive at that moment.

e. Programmable completion allows a new compspec loaded after a completion
   function returns 124 to be used in more cases.

f. ./source has a new -p PATH option, which makes it use the PATH argument
   instead of $PATH to look for the file.

g. GLOBSORT has a new `numeric' sort specifier, which sorts all-digit strings
   as numbers.

h. Documentation has been significantly updated.

i. `wait -n' can now return terminated process substitutions, jobs about
   which the user has already been notified (like `wait' without options),
   
j. `wait -n' removes jobs from the jobs table or list of terminated children
    when in posix mode.

k. Changed the `wait' builtin behavior regarding process substitutions to
   match the documentation.

l. There is a new `bash_source_fullpath' shopt option, which makes bash put
   full pathnames into BASH_SOURCE, and a way to set a default value for it
   at configure time.

m. Posix mode now forces job notifications to occur when the new edition of
   POSIX specifies (since it now specifies them).

n. Interactive shells don't print job notifications while sourcing scripts.

o. The parser prints more information about the command it's trying to parse
   when it encounters EOF before completing the command.

p. Posix mode no longer requires function names to be valid shell identifiers.

q. If `exit' is run in a trap and not supplied an exit status argument, it
   uses the value of $? from before the trap only if it's run at the trap's
   `top level' and would cause the trap to end (that is, not in a subshell).
   This is from Posix interp 1602.

4. New Features in Readline

a. Documentation has been significantly updated.

b. New `force-meta-prefix' bindable variable, which forces the use of ESC as
   the meta prefix when using "\M-" in key bindings instead of overloading
   convert-meta.

c. The default value for `readline-colored-completion-prefix' no longer has a
   leading `.'; the original report was based on a misunderstanding.

d. There is a new bindable command, `export-completions', which writes the
   possible completions for a word to the standard output in a defined format.

------------------------------------------------------------------------------
This document details the changes between this version, bash-5.3-alpha, and
the previous version, bash-5.2-release.

1. Changes to Bash

a. Stop checking for new mail if an interactive shell is in the middle of
   programmable completion or readline command dispatching.

b. Changes to multibyte character translation to handle shift states better.

c. Fixed a bug with subshell command execution that caused it to set LINENO
   incorrectly.

d. Fixed a bug that caused some array subscript references in arithmetic
   expansions to seg fault.

e. Don't report on foreground jobs that we won't notify the user about if
   jobs is run from a trap handler or a `bind -x' command.

f. Fixed a bug where temporarily turning on `extglob' while parsing a command
   substitution in compatibility mode could leave it set.

g. Fixed a bug where nested word expansions confused the state parser and
   resulted in quotes being required where they should not have been.

h. Fixed a bug where nested function definitions resulted in `display -F'
   printing incorrect line numbers.

i. Fixed the message printed when the shell gets ENOENT from execve: specific
   message about a bad interpreter before the generic error message.

j. Fixed a spurious debug message when errexit is set and the shell is
   exiting from an eval command in a shell function.

k. Fixed a bug where a pending signal would cause pattern matching to fail in
   an exit trap.

l. Fixed a crash caused by  a null replacement string in pattern replacement.

m. Fixed a bug in interactive shells where a SIGINT received while parsing a
   command substitution would leave the expand_aliases option disabled.

n. Fixed a bug with command printing when printing multiple shell functions
   with here-documents inside a command substitution.

o. Fixed a bug with expanding aliases while parsing command substitutions
   inside another word expansion.

p. Fixed a bug with alias expansion in posix mode in an eval command inside a
   command substitution.

q. Fixed a bug that caused the parser not to reset correctly if it encountered
   a syntax error while trying to read a WORD token.

r. Fixed a bug that caused `<(' and `>(' to trigger process substitution inside
   an arithmetic expression.

s. Fixed a bug that caused the shell to unlink FIFOs used for process
   substitution before a compound command completes.

t. Fixed a bug that caused the read builtin to not recognize some negative
   fractional arguments.

u. Fixed a bug that caused subshells not to run the EXIT trap if a signal
   arrived after the command and before returning to the caller.

v. Fixed a bug where `wait' without arguments could wait for inherited
   process substitutions, which are not children of this shell.

w. Fixed a bug with expanding $* in a here-document body.

x. Fixed a bug where `declare -p' in a shell function would show the wrong
   command for `local -'.

y. Change for POSIX interpretation 1602 about the default return status for
   `return' in a trap command.

z. Fixed a bug that caused double evaluation of a dynamic variable like
   $RANDOM when using certain parameter expansions.

aa. Fixed a bug where `read -e -t' would cause an interactive shell to exit.

bb. Fixed a number of bugs with pathname expansion/pattern matching and
    slashes in bracket expressions.

cc. Fixed several bugs with optimizing out forks.

dd. Fixed a memory leak when referencing unset associative array elements.

ee. System-specific changes for: WIN32

ff. Perform more cleanup if the shell exceeds maximum function nesting level.

gg. Fixed a bug that caused `eval' to run the ERR trap in commands where it
    should not.

hh. Fixed nameref expansion where nameref values are valid length expansion
    expressions but invalid identifiers.

ii. Fixed an error that caused syntax errors when expanding nested word
    expansions inside a here-document.

jj. POSIX special builtins now exit the shell in posix mode on more failure
    cases.

kk. Brace expansion is interruptible at more spots, so long expansions can
    be interrupted more quickly.

ll. Fixed a crash caused by running `set -o emacs' in `bash -c command'.

mm. Fixed a bug that caused bash to reset the terminal process group before
    a command exited if it received a SIGINT in a non-interactive shell.

nn. Significant changes to the source code to make it C23-conformant, including
    C23 undefined behavior.

oo. Treat read(2) errors while reading input as immediately fatal errors
    instead of the traditional EOF; POSIX interp 1629

pp. Fix to allow asynchronous commands to use `trap' to reset signals that
    are ignored during the command; POSIX interp 751.

qq. Fix a posix-mode bug with alias expansion when checking for reserved
    words and the previous alias expansion ends with a space.

rr. Programmable completion now creates empty elements in COMP_WORDS if the
    cursor is on whitespace just preceding a word.

ss. Fixed a bug that prevented aliases ending with a space from alias
    expanding the next word if more than two aliases are expanded from a
    single word.

tt. Fixed a bug that caused the shell to give the terminal to the shell's
    process group when reaping a background job.

uu. Command printing is more consistent when to print `function' before a
    shell function name.

vv. Fixed a bug that caused unset not to remove a function named a[b] if
    there was no array variable a.

ww. Posix mode doesn't perform function lookup for function names containing
    a slash.

xx. <( and >( can now be used in function names.

yy. Fixed a bug that caused tilde expansion not to be performed on some
    array subscripts.

zz. Fixed key-value pair associative array assignment to be more consistent
    with compound array assignment, and indexed array assignment (a=(zero one))
    to be more consistent with explicitly assigning indices one by one.

aaa. In posix mode, extra arguments to `fc' are now an error.

bbb. The bash readline commands that perform history and alias expansion try
     to place point closer to where it was in the unexpanded line.

ccc. Fixed multiple invocations of `local -' in the same shell function to
     have the same effect as one.

ddd. Don't export $_ if allexport is set.

eee. Don't add extra newlines to the history if parsing a delimited construct.

fff. Dynamically-loaded builtins cannot have slashes in their names, since
     they'll never be called.

ggg. Fixed a bug that could cause reading EOF while parsing a quoted string
     to terminate the shell.

hhh. Fixed a bug that caused local variables with the same name as variables
     in `declare's temporary environment to be propagated back to the caller.

iii. Don't try to perform brace expansion on assignment statements in compound
     assignments.

jjj. Fixed a bug that could cause a crash while evaluating an arithmetic for
     command if one of the expressions expands to NULL.

kkk. In posix mode, cd tries to change to what the user typed if the
     canonicalized version of that pathname is longer than PATH_MAX.

lll. Fixes for some errors revealed by address sanitizer.

mmm. If fork(2) fails, kill the current pipeline processes with SIGKILL after
     SIGTERM, in case they're ignoring SIGTERM.

nnn. Fix to adding command substitutions to history to avoid adding semicolons
     where they shouldn't be.

ooo. Programmable completion and compgen honor the setting of `dotglob'.

ppp. Use gettimeofday(2) to get time information instead of using time(3).

qqq. Save and restore readline variables affecting filename completions in
     case someone runs `compgen' in the foreground.

rrr. Treat the failure to open file in $(<file) as a non-fatal expansion
     error instead of a fatal redirection error.

sss. In posix mode, command substitution doesn't affect $? except when
     specified for commands consisting solely of assignment statements.

ttt. Fix {var}>&- so it doesn't silently close stdin if var is not a number.

uuu. Follow namerefs in ${name=word} so the shell can implement the POSIX
     semantics of returning "the final value of parameter."

vvv. Bash performs better nameref loop detection in several lookup cases.

www. SIGINT will now break out of loops if a process executed in the loop dies
     due to SIGINT, not just if the loop body is a list. This is no longer
     dependent on the compatibility level.

xxx. FIGNORE suffixes can now match the entire pathname, like tcsh, instead
     of requiring a non-empty prefix.

yyy. Fix bug that caused FUNCNAME not to be reset after a parse error with
     compound assignments to local variables.

zzz. Fix bug that caused `jobs' not to remove jobs from the list in a SIGCHLD
     trap.

aaaa. Fix bug that caused `ignoreeof' to be ignored if EOF is read at a
      secondary prompt or while parsing a command substitution.

bbbb. Fixes to removing jobs from the jobs table when the user isn't notified;
      has effects of fixing issues with `wait -n' not finding jobs.

cccc. Fixes to loadable builtin processing so that we never pass a null
      pathname or try to load a builtin that's not found if the -n option is
      supplied.

dddd. Work around system-specific problems (macOS) where isblank(3) returns
      true for characters >= 0x80 in a UTF-8 locale.

eeee. Fix for crash while parsing alias expansions that include compound
      assignments.

ffff. Fixe for non-interactive shells reading a script file that ends with
      backslash preceding EOF.

gggg. Fix to command printing when here-documents are attached to compound
      commands in lists.

hhhh. Fix bug with sourcing `files' created by process substitutions inside
      a `.' script.

iiii. Fixes to declare builtin to treat arguments to declare -f that look like
      assignment statements or array references as function names.

jjjj. Fixed a variable conversion problem when exporting a variable in the
      temporary environment back to the calling scope.

kkkk. BASH_REMATCH can now be a local variable.

llll. Subshell commands clear process substitutions so anything created by a
      redirection doesn't affect the subshell.

mmmm. Fixes for several small memory leaks.

nnnn. The shell simply ignores attempts to assign to `noassign' variables
      instead of treating them as an assignment error and possibly causing
      the shell to exit.

oooo. If the cd builtin uses $OLDPWD, allow it to use $CDPATH if the user has
      set it to something that's not a full pathname.

pppp. The test builtin only supports the optional argument to -t if parsing
      an expression with more than four arguments and not in posix mode.

qqqq. Changes to filename quoting and rewriting to deal with NFC and NFD
      Unicode forms (primarily for macOS).

rrrr. Send SIGCONT to a job we've just restarted with fg or bg, even if we
      think it's already running.

ssss. Fixes for setting the line number associated with a simple command.

tttt. Many changes for integer overflow and out-of-range arguments to printf.

uuuu. Fixes for the read builtin and unescaped backslashes preceding NULs or
      the end of the input.

vvvv. The -[anrw] options to the history builtin should have no effect if
      HISTFILE is unset or null.

wwww. If programmable completion uses something different than what the user
      typed as the command name (full pathname, alias, etc.), display what's
      actually used in `compopt' output.

xxxx. Fix bug with closing /dev/fd process substitutions in shell functions.

yyyy. Fix bug with `declare -g' trying to convert a global associative array
      to an indexed array.

zzzz. Fix bash history expansion characters so we don't get empty history
      events.

aaaaa. Allow `time' and `!' reserved words to be followed by `&', which POSIX
       interp 267 says is required.

bbbbb. Upgrade intl library to the one from gettext-0.21.1.

ccccc. Fix line number in the event that a simple command jumps back to the
       top level on error.

ddddd. Make the order of setting BASH_COMMAND, running the DEBUG trap, and
       printing PS4 consistent across all command types.

eeeee. Rely on child processes to set the terminal process group instead of
       having the parent do it as well.

fffff. Fix `printf' to consume entire multibyte characters in the format string,
       in case the encoding contains `/' or `%'.

ggggg. Fix `hash' to return 1 if -d is supplied and the hash table is empty.

hhhhh. Fix `select' command to be like `for' in that an invalid selection
       variable is a fatal error in posix mode.

iiiii. Fix to parameter length expansion to avoid expanding dynamic variables
       (e.g., RANDOM) more than once.

jjjjj. Fix to `shift', `break', and `continue' to skip over a `--' when
       printing an invalid argument error message.

kkkkk. Fix bug that caused an invalid arithmetic expression in an arithmetic
       `for' command to leave the loop level set to the wrong value, preventing
       `break' and `continue' from working.

lllll. Fix problem with removing escapes in the `E' variable transformation.

mmmmm. Fix bug with word splitting if `read' assigns to IFS.

nnnnn. Fix posix-mode cases where failure of special builtins did not cause
       the shell to exit.

ooooo. Some fixes to cases where the shell quotes characters that are special
       internally.

ppppp. Fix error with read builtin trying to assign to a readonly variable.

qqqqq. Fix a slight race condition when bash receives a SIGINT while waiting
       for a foreground job.

rrrrr. Fix integer parsing to accept more whitespace characters after the
       digit string -- the same ones we accept before the digits.

sssss. Fix a crash when attempting to brace-expand a very large list of
       strings fails.

ttttt. Fix dynamic loading of builtins not to look in the current directory
       if looking in BASH_LOADABLES_PATH is not successful, like $PATH
       searching.

uuuuu. Fix `bind -x' commands to understand negative argument counts.

vvvvv. Disable fork optimization if the shell is running startup files because
       SSH_SOURCE_BASHRC was enabled; prevents infinite recursion.

wwwww. Fix `unset' builtin to implement POSIX interp 1009, which says that
       unsetting a variable in the temporary environment unsets the variable
       in the enclosing scope also, in posix mode.

xxxxx. Fix parser to read here-document body from the current alias, if that's
       where input is being read from.

yyyyy. Fix an off-by-one error that caused completion to fail for certain
       pathnames containing backslash-quoted single-quotes.

zzzzz. Fix command printing to print a coproc name only if the coproc command
       is not a simple command.

aaaaaa. Fix prompt string decoding to preserve the value of $_.

bbbbbb. In posix mode, supplying a non-identifier as a function name to `export'
        or `readonly' should cause the shell to exit, since these are special
        builtins.

cccccc. Fix a crash that happens due to accessing freed memory if the parser
        encounters a syntax error while parsing an alias or a compound
        assignment.

dddddd. Fix a bug that could cause errors while executing a DEBUG trap in a
        pipeline.

eeeeee. Fix a bug where exiting a subshell should not try to restore the
        terminal settings if that subshell didn't reinitialize them.

ffffff. Remove long-lived workaround for old AFS bug that causes problems with
        modern implementations.

gggggg. Fix a bug that caused an assignment error to BASHOPTS or SHELLOPTS to
        remove the variable's readonly attribute.

hhhhhh. Fix for a crash if a pathname argument to `cd' is NULL and the current
        directory has been removed.

iiiiii. Fix a bug with shell-expand-line readline command that caused it to
        interpret quoted single quotes incorrectly when inside $'...'.

jjjjjj. Fix to the declare builtin to catch more invalid option combinations.

kkkkkk. Fix to avoid unsafe execution of the EXIT trap if a terminating signal
        arrives while bash is waiting for a foreground process.

llllll. Fixed a bug that allowed attribute changes to readonly variables that
        changed the effects of attempted assignments.

mmmmmm. Fix bug that caused quoting errors if $* was expanded in a context
        where word splitting was not performed. 

oooooo. Fix bug that caused declare commands with `-' and `+' options and an
        assignment statement to be misinterpreted.

pppppp. Retry opening startup files if the open is interrupted by a signal
        and is not automatically restarted.

qqqqqq. Fix printing a case command where one of the case command lists begins
        with the word `esac'.

rrrrrr. Fix for history and command number expansion when expanding a prompt
        string that contains the @P variable transformation.

ssssss. Fix a bug that could cause the shell to hang if a script used multiple
        coprocesses without manually closing file descriptors associated with
        existing coprocesses.

2. Changes to Readline

a. Fixed a bug in clearing the visible line structure before redisplay.

b. Fix a bug where setlocale(3) returning NULL caused a crash.

c. Fixed signal checking in callback mode to handle signals that arrive before
   readline restores the application's signal handlers.

d. Fixed a bug with word completion where the directory name needs to be
   dequoted and tilde-expanded.

e. Fixed a bug that caused compilation to fail on systems with select but not
   pselect.

f. System-specific changes for: WIN32, z/OS, Cygwin, MSYS

g. Fixed a bug that caused word completion mismatches if the quoted text the
   user typed was longer than the unquoted match.

h. Fixes for freeing undo lists that might appear in history list entries
   after non-incremental searches.

i. Fixes for some errors revealed by address sanitizer.

j. In vi mode, if an `f' or `F' move command associated with a `c' or `C'
   command fails, don't enter insert mode.

k. Fixed bug with truncating a history file containing timestamps that caused
   the timestamp associated with the first history entry not to be written.

l. Fix vi-mode so that a motion command attached to d/D, y/Y, or t/T must
   consume or delete at least one character.

m. Fix a redisplay error when displaying meta characters as octal sequences
   and other C locale issues.

n. Fix error that caused characters composing an incomplete multibyte
   character not to be inserted into the line.

o. In callback mode, let the application echo the signal characters (e.g., ^C)
   when the application's signal handlers are installed.

p. Added some support for lines that consume more than the physical number of
   screen lines.

q. Make sure dump-variables returns the string values for active-region-start-color
   and active-region-end-color if they're set.

r. Fixes to how characters between 128 and 159 are printed when displaying
   macro values (use symbolic notation instead of directly printing the
   character).

s. Don't convert meta characters that contain NULL (\M-\C-@) to actual NULs,
   which prematurely terminates the macro value.

t. Fix typo in the readline color prefix extension that it uses for coloring
   filename prefixes when displaying possible completions.

u. Call the filename rewrite hook on the word being completed before comparing
   it against possible completions from the file system to get consistent
   strings.

v. Fix infinite recursion that can happen if someone binds a key that doesn't
   have a different upper and lower case representation to do-lowercase-version.

w. Check for non-ANSI (dumb) terminals a little more thoroughly.

x. Don't attempt to history-expand the `quick substitution' character at the
   beginning of a line if the application has set the quoting state to single
   quotes.

y. Fix small memory leak if non-incremental or incremental search is
   interrupted by a signal.

z. Loading very large history files should be much faster.

aa. Retry opening startup files if the open is interrupted by a signal
    and is not automatically restarted.

3. New Features in Bash

a. When checking whether a script file argument is a binary file, check the
   first two lines of a script if the first line begins with `#!'.

b. Bash does a better job of preserving user-supplied quotes around a word
   completion, instead of requoting it.

c. Bash reports the starting line number in an error message about an
   unterminated compound command like `if' without a `fi'.

d. Implement the POSIX requirement that running the `jobs' builtin removes
   jobs from the jobs list.

f. Call bash signal handlers while executing programmable completion commands,
   instead of readline's.

g. Print an error message if a regular expression used with [[ fails to compile.

h. The `umask' builtin now has additional features for full POSIX conformance.

i. `type -a -P' reports both hashed pathnames and the result of a $PATH search.

j. `trap' has a new -P option that prints the trap action associated with each
   signal argument.

k. The `command' builtin preceding a declaration builtin (e.g., `declare')
   preserves the special asisgnment statement parsing for the declaration
   builtin. This is a new POSIX requirement.

l. `printf' uses the `alternate form' for %q and %Q to force single quoting.

m. `printf' now interprets %ls (%S) and %lc (%C) as referring to wide strings
   and characters, respectively, when in a multibyte locale.

n. The shell can be compiled with a different default value for the
   patsub_replacement option.

o. Check for window size changes during trap commands, `bind -x' commands,
   and programmable completion.

p. Treat a NULL value for $PATH as equivalent to ".".

p. New loadable builtins: kv, strptime

q. GLOBSORT: new variable to specify how to sort the results of pathname
   expansion (name, size, blocks, mtime, atime, ctime, none) in ascending
   or descending order.

r. `compgen' has a new option: -V varname. If supplied, it stores the generated
   completions into VARNAME instead of printing them on stdout.

s. New form of command substitution: ${ command; } or ${|command;} to capture
   the output of COMMAND without forking a child process and using pipes.

t. array_expand_once: new shopt option, replaces assoc_expand_once

u. complete/compopt new option: fullquote; sets rl_full_quoting_desired so all
   possible completions are quoted as if they were filenames.

v. Command timing now allows precisions up to 6 digits instead of 3 in
   $TIMEFORMAT.

w. BASH_MONOSECONDS: new dynamic variable that returns the value of the
   system's monotonic clock, if one is available.

x. BASH_TRAPSIG: new variable, set to the numeric signal number of the trap
   being executed while it's running.

y. The checkwinsize option can be used in subshell commands started from
   interactive shells.

z. In posix mode, the test command < and > binary primaries compare strings
   using the current locale.

aa. bind -x allows new key binding syntax: separate the key sequence and the
    command string with whitespace, but require the command string to be
    double-quoted if this is used. This allows different quoting options for
    the command string.

bb. Print commands bound to key sequences using `bind -x' with the new key
    binding syntax it allows.

cc. `read' has a new `-E' option to use readline but with the default bash
    completion (including programmable completion).

dd. New bindable readline command name: `bash-vi-complete'.

ee. New test builtin behavior when parsing a parenthesized subexpression and
    test was given more than 4 arguments: scan forward for a closing paren and
    call posixtest() if there are 4 or fewer arguments between the parentheses.
    Added for compatibility with coreutils test, dependent on the shell
    compatibility level. Such expressions remain ambiguous.

4. New Features in Readline

a. Output a newline if there is no prompt and readline reads an empty line.

b. The history library falls back to stdio when writing the history list if
   mmap fails.

c. New bindable variable `search-ignore-case', causes readline to perform
   case-insensitive incremental and non-incremental history searches.

d. rl_full_quoting_desired: new application-settable variable, causes all
   completions to be quoted as if they were filenames.

e. rl_macro_display_hook: new application-settable function pointer, used if
   the application wants to print macro values itself instead of letting
   readline do it

f. rl_reparse_colors: new application-callable function, reparses $LS_COLORS
   (presumably after the user changes it)

g. rl_completion_rewrite_hook: new application-settable function pointer,
   called to modify the word being completed before comparing it against
   pathnames from the file system.

h. execute-named-command: a new bindable command that reads the name of a
   readline command from the standard input and executes it. Bound to M-x
   in emacs mode by default.

i. Incremental and non-incremental searches now allow ^V/^Q (or, in the former
   case, anything bound to quoted-insert) to quote characters in the search
   string.

j. There is a new rl_print_keybinding function that prints the key bindings
   for a single bindable function specified by name.
