source: Daodan/MSYS2/usr/share/doc/bash/NEWS@ 1167

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.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-5.0 since
the release of bash-4.4.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a. The `wait' builtin can now wait for the last process substitution created.

b. There is an EPOCHSECONDS variable, which expands to the time in seconds
   since the Unix epoch.

c. There is an EPOCHREALTIME variable, which expands to the time in seconds
   since the Unix epoch with microsecond granularity.

d. New loadable builtins: rm, stat, fdflags.

e. BASH_ARGV0: a new variable that expands to $0 and sets $0 on assignment.

f. When supplied a numeric argument, the shell-expand-line bindable readline
   command does not perform quote removal and suppresses command and process
   substitution.

g. `history -d' understands negative arguments: negative arguments offset from
   the end of the history list.

h. The `name' argument to the `coproc' reserved word now undergoes word
   expansion, so unique coprocs can be created in loops.

i. A nameref name resolution loop in a function now resolves to a variable by
   that name in the global scope.

j. The `wait' builtin now has a `-f' option, which signifies to wait until the
   specified job or process terminates, instead of waiting until it changes
   state.

k. There is a define in config-top.h that allows the shell to use a static
   value for $PATH, overriding whatever is in the environment at startup, for
   use by the restricted shell.

l. Process substitution does not inherit the `v' option, like command
   substitution.

m. If a non-interactive shell with job control enabled detects that a foreground
   job died due to SIGINT, it acts as if it received the SIGINT.

n. The SIGCHLD trap is run once for each exiting child process even if job
   control is not enabled when the shell is in Posix mode.

o. A new shopt option: localvar_inherit; if set, a local variable inherits the
   value of a variable with the same name at the nearest preceding scope.

p. `bind -r' now checks whether a key sequence is bound before binding it to
   NULL, to avoid creating keymaps for a multi-key sequence.

q. A numeric argument to the line editing `operate-and-get-next' command
   specifies which history entry to use.

r. The positional parameters are now assigned before running the shell startup
   files, so startup files can use $@.

s. There is a compile-time option that forces the shell to disable the check
   for an inherited OLDPWD being a directory.

t. The `history' builtin can now delete ranges of history entries using
   `-d start-end'.

u. The `vi-edit-and-execute-command' bindable readline command now puts readline
   back in vi insertion mode after executing commands from the edited file.

v. The command completion code now matches aliases and shell function names
   case-insensitively if the readline completion-ignore-case variable is set.

w. There is a new `assoc_expand_once' shell option that attempts to expand
   associative array subscripts only once.

x. The shell only sets up BASH_ARGV and BASH_ARGC at startup if extended
   debugging mode is active. The old behavior of unconditionally setting them
   is available as part of the shell compatibility options.

y. The `umask' builtin now allows modes and masks greater than octal 777.

z. The `times' builtin now honors the current locale when printing a decimal
   point.

aa. There is a new (disabled by default, undocumented) shell option to enable
    and disable sending history to syslog at runtime.

bb. Bash no longer allows variable assignments preceding a special builtin that
    changes variable attributes to propagate back to the calling environment
    unless the compatibility level is 44 or lower.

cc. You can set the default value for $HISTSIZE at build time in config-top.h.

dd. The `complete' builtin now accepts a -I option that applies the completion
    to the initial word on the line.

ee.  The internal bash malloc now uses mmap (if available) to satisfy requests
    greater than 128K bytes, so free can use mfree to return the pages to the
    kernel.

ff. The shell doesn't automatically set BASH_ARGC and BASH_ARGV at startup
    unless it's in debugging mode, as the documentation has always said, but
    will dynamically create them if a script references them at the top level
    without having enabled debugging mode.

gg. The localvar_inherit option will not attempt to inherit a value from a
    variable of an incompatible type (indexed vs. associative arrays, for
    example).

hh. The `globasciiranges' option is now enabled by default; it can be set to
    off by default at configuration time.

ii. Associative and indexed arrays now allow subscripts consisting solely of
    whitespace.

jj. `checkwinsize' is now enabled by default.

kk. The `localvar_unset' shopt option is now visible and documented.

ll. The `progcomp_alias' shopt option is now visible and documented.

mm. The signal name processing code now understands `SIGRTMIN+n' all the way
    up to SIGRTMAX.

nn. There is a new `seq' loadable builtin.

oo. Trap execution now honors the (internal) max invocations of `eval', since
    traps are supposed to be executed as if using `eval'.

pp. The $_ variable doesn't change when the shell executes a command that forks.

qq. The `kill' builtin now supports -sSIGNAME and -nSIGNUM, even though
    conforming applications aren't supposed to use them.

rr. POSIX mode now enables the `shift_verbose' option.

2.  New Features in Readline

a. Non-incremental vi-mode search (`N', `n') can search for a shell pattern, as
   Posix specifies (uses fnmatch(3) if available).

b. There are new `next-screen-line' and `previous-screen-line' bindable
   commands, which move the cursor to the same column in the next, or previous,
   physical line, respectively.

c. There are default key bindings for control-arrow-key key combinations.

d. A negative argument (-N) to `quoted-insert' means to insert the next N
   characters using quoted-insert.

e. New public function: rl_check_signals(), which allows applications to
   respond to signals that readline catches while waiting for input using
   a custom read function.

f. There is new support for conditionally testing the readline version in an
   inputrc file, with a full set of arithmetic comparison operators available.

g. There is a simple variable comparison facility available for use within an
   inputrc file. Allowable operators are equality and inequality; string
   variables may be compared to a value; boolean variables must be compared to
   either `on' or `off'; variable names are separated from the operator by
   whitespace.

h. The history expansion library now understands command and process
   substitution and extended globbing and allows them to appear anywhere in a
   word.

i. The history library has a new variable that allows applications to set the
   initial quoting state, so quoting state can be inherited from a previous
   line.

j. Readline now allows application-defined keymap names; there is a new public
   function, rl_set_keymap_name(), to do that.

k. The "Insert" keypad key, if available, now puts readline into overwrite
   mode.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-4.4 since
the release of bash-4.3.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  There is now a settable configuration #define that will cause the shell
    to exit if the shell is running setuid without the -p option and setuid
    to the real uid fails.

b.  Command and process substitutions now turn off the `-v' option when
    executing, as other shells seem to do.

c.  The default value for the `checkhash' shell option may now be set at
    compile time with a #define.

d.  The `mapfile' builtin now has a -d option to use an arbitrary character
    as the record delimiter, and a -t option  to strip the delimiter as
    supplied with -d.

e.  The maximum number of nested recursive calls to `eval' is now settable in
    config-top.h; the default is no limit.

f.  The `-p' option to declare and similar builtins will display attributes for
    named variables even when those variables have not been assigned values
    (which are technically unset).

g.  The maximum number of nested recursive calls to `source' is now settable
    in config-top.h; the default is no limit.

h.  All builtin commands recognize the `--help' option and print a usage
    summary.

i.  Bash does not allow function names containing `/' and `=' to be exported.

j.  The `ulimit' builtin has new -k (kqueues) and -P (pseudoterminals) options.

k.  The shell now allows `time ; othercommand' to time null commands.

l.  There is a new `--enable-function-import' configuration option to allow
    importing shell functions from the environment; import is enabled by
    default.

m.  `printf -v var ""' will now set `var' to the empty string, as if `var=""'
    had been executed.

n.  GLOBIGNORE, the pattern substitution word expansion, and programmable
    completion match filtering now honor the value of the `nocasematch' option.

o.  There is a new ${parameter@spec} family of operators to transform the
    value of `parameter'.

p.  Bash no longer attempts to perform compound assignment if a variable on the
    rhs of an assignment statement argument to `declare' has the form of a
    compound assignment (e.g., w='(word)' ; declare foo=$w); compound
    assignments are accepted if the variable was already declared as an array,
    but with a warning.

q.  The declare builtin no longer displays array variables using the compound
    assignment syntax with quotes; that will generate warnings when re-used as
    input, and isn't necessary.

r.  Executing the rhs of && and || will no longer cause the shell to fork if
    it's not necessary.

s.  The `local' builtin takes a new argument: `-', which will cause it to save
    and the single-letter shell options and restore their previous values at
    function return.

t.  `complete' and `compgen' have a new `-o nosort' option, which forces
    readline to not sort the completion matches.

u.  Bash now allows waiting for the most recent process substitution, since it
    appears as $!.

v.  The `unset' builtin now unsets a scalar variable if it is subscripted with
    a `0', analogous to the ${var[0]} expansion.

w.  `set -i' is no longer valid, as in other shells.

x.  BASH_SUBSHELL is now updated for process substitution and group commands
    in pipelines, and is available with the same value when running any exit
    trap.

y.  Bash now checks $INSIDE_EMACS as well as $EMACS when deciding whether or
    not bash is being run in a GNU Emacs shell window.

z.  Bash now treats SIGINT received when running a non-builtin command in a
    loop the way it has traditionally treated running a builtin command:
    running any trap handler and breaking out of the loop.

aa. New variable: EXECIGNORE; a colon-separate list of patterns that will
    cause matching filenames to be ignored when searching for commands.

bb. Aliases whose value ends in a shell metacharacter now expand in a way to
    allow them to be `pasted' to the next token, which can potentially change
    the meaning of a command (e.g., turning `&' into `&&').

cc. `make install' now installs the example loadable builtins and a set of
    bash headers to use when developing new loadable builtins.

dd. `enable -f' now attempts to call functions named BUILTIN_builtin_load when
    loading BUILTIN, and BUILTIN_builtin_unload when deleting it.  This allows
    loadable builtins to run initialization and cleanup code.

ee. There is a new BASH_LOADABLES_PATH variable containing a list of directories
    where the `enable -f' command looks for shared objects containing loadable
    builtins.

ff. The `complete_fullquote' option to `shopt' changes filename completion to
    quote all shell metacharacters in filenames and directory names.

gg. The `kill' builtin now has a `-L' option, equivalent to `-l', for
    compatibility with Linux standalone versions of kill.

hh. BASH_COMPAT and FUNCNEST can be inherited and set from the shell's initial
    environment.

ii. inherit_errexit: a new `shopt' option that, when set, causes command
    substitutions to inherit the -e option.  By default, those subshells disable
    -e.  It's enabled as part of turning on posix mode.

jj. New prompt string: PS0.  Expanded and displayed by interactive shells after
    reading a complete command but before executing it.

kk. Interactive shells now behave as if SIGTSTP/SIGTTIN/SIGTTOU are set to
    SIG_DFL when the shell is started, so they are set to SIG_DFL in child
    processes.

ll. Posix-mode shells now allow double quotes to quote the history expansion
    character.

mm. OLDPWD can be inherited from the environment if it names a directory.

nn. Shells running as root no longer inherit PS4 from the environment, closing
    a security hole involving PS4 expansion performing command substitution.

oo. If executing an implicit `cd' when the `autocd' option is set, bash will
    now invoke a function named `cd' if one exists before executing the `cd'
    builtin.

pp. Value conversions (arithmetic expansions, case modification, etc.) now
    happen when assigning elements of an array using compound assignment.

qq. There is a new option settable in config-top.h that makes multiple
    directory arguments to `cd' a fatal error.

rr. Bash now uses mktemp() when creating internal temporary files; it produces
    a warning at build time on many Linux systems.

2.  New Features in Readline

a.  The history truncation code now uses the same error recovery mechanism as
    the history writing code, and restores the old version of the history file
    on error.  The error recovery mechanism handles symlinked history files.

b.  There is a new bindable variable, `enable-bracketed-paste', which enables
    support for a terminal's bracketed paste mode.

c.  The editing mode indicators can now be strings and are user-settable
    (new `emacs-mode-string', `vi-cmd-mode-string' and `vi-ins-mode-string'
    variables).  Mode strings can contain invisible character sequences.
    Setting mode strings to null strings restores the defaults.

d.  Prompt expansion adds the mode string to the last line of a multi-line
    prompt (one with embedded newlines).

e.  There is a new bindable variable, `colored-completion-prefix', which, if
    set, causes the common prefix of a set of possible completions to be
    displayed in color.

f.  There is a new bindable command `vi-yank-pop', a vi-mode version of emacs-
    mode yank-pop.

g.  The redisplay code underwent several efficiency improvements for multibyte
    locales.

h.  The insert-char function attempts to batch-insert all pending typeahead
    that maps to self-insert, as long as it is coming from the terminal.

i.  rl_callback_sigcleanup: a new application function that can clean up and
    unset any state set by readline's callback mode.  Intended to be used
    after a signal.

j.  If an incremental search string has its last character removed with DEL, the
    resulting empty search string no longer matches the previous line.

k.  If readline reads a history file that begins with `#' (or the value of
    the history comment character) and has enabled history timestamps, the
    history entries are assumed to be delimited by timestamps.  This allows
    multi-line history entries.

l.  Readline now throws an error if it parses a key binding without a
    terminating `:' or whitespace.

m.  The default binding for ^W in vi mode now uses word boundaries specified
    by Posix (vi-unix-word-rubout is bindable command name).

n.  rl_clear_visible_line: new application-callable function; clears all
    screen lines occupied by the current visible readline line.

o.  rl_tty_set_echoing: application-callable function that controls whether
    or not readline thinks it is echoing terminal output.

p.  Handle >| and strings of digits preceding and following redirection
    specifications as single tokens when tokenizing the line for history
    expansion.

q.  Fixed a bug with displaying completions when the prefix display length
    is greater than the length of the completions to be displayed.

r.  The :p history modifier now applies to the entire line, so any expansion
    specifying :p causes the line to be printed instead of expanded.

s.  New application-callable function: rl_pending_signal(): returns the signal
    number of any signal readline has caught but not yet handled.

t.  New application-settable variable: rl_persistent_signal_handlers: if set
    to a non-zero value, readline will enable the readline-6.2 signal handler
    behavior in callback mode: handlers are installed when
    rl_callback_handler_install is called and removed removed when a complete
    line has been read.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-4.3 since
the release of bash-4.2.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  The `helptopic' completion action now maps to all the help topics, not just
    the shell builtins.

b.  The `help' builtin no longer does prefix substring matching first, so
    `help read' does not match `readonly', but will do it if exact string
    matching fails.

c.  The shell can be compiled to not display a message about processes that
    terminate due to SIGTERM.

d.  Non-interactive shells now react to the setting of checkwinsize and set
    LINES and COLUMNS after a foreground job exits.

e.  There is a new shell option, `globasciiranges', which, when set to on,
    forces globbing range comparisons to use character ordering as if they
    were run in the C locale.

f.  There is a new shell option, `direxpand', which makes filename completion
    expand variables in directory names in the way bash-4.1 did.

g.  In Posix mode, the `command' builtin does not change whether or not a
    builtin it shadows is treated as an assignment builtin.

h.  The `return' and `exit' builtins accept negative exit status arguments.

i.  The word completion code checks whether or not a filename containing a
    shell variable expands to a directory name and appends `/' to the word
    as appropriate.  The same code expands shell variables in command names
    when performing command completion.

j.  In Posix mode, it is now an error to attempt to define a shell function
    with the same name as a Posix special builtin.

k.  When compiled for strict Posix conformance, history expansion is disabled
    by default.

l.  The history expansion character (!) does not cause history expansion when
    followed by the closing quote in a double-quoted string.

m.  `complete' and its siblings compgen/compopt now takes a new `-o noquote'
    option to inhibit quoting of the completions.

n.  Setting HISTSIZE to a value less than zero causes the history list to be
    unlimited (setting it 0 zero disables the history list).

o.  Setting HISTFILESIZE to a value less than zero causes the history file size
    to be unlimited (setting it to 0 causes the history file to be truncated
    to zero size).

p.  The `read' builtin now skips NUL bytes in the input.

q.  There is a new `bind -X' option to print all key sequences bound to Unix
    commands.

r.  When in Posix mode, `read' is interruptible by a trapped signal.  After
    running the trap handler, read returns 128+signal and throws away any
    partially-read input.

s.  The command completion code skips whitespace and assignment statements
    before looking for the command name word to be completed.

t.  The build process has a new mechanism for constructing separate help files
    that better reflects the current set of compilation options.

u.  The -nt and -ot options to test now work with files with nanosecond
    timestamp resolution.

v.  The shell saves the command history in any shell for which history is
    enabled and HISTFILE is set, not just interactive shells.

w.  The shell has `nameref' variables and new -n(/+n) options to declare and
    unset to use them, and a `test -R' option to test for them.

x.  The shell now allows assigning, referencing, and unsetting elements of
    indexed arrays using negative subscripts (a[-1]=2, echo ${a[-1]}) which
    count back from the last element of the array.

y.  The {x}<word redirection feature now allows words like {array[ind]} and
    can use variables with special meanings to the shell (e.g., BASH_XTRACEFD).

z.  There is a new CHILD_MAX special shell variable; its value controls the
    number of exited child statues the shell remembers.

aa. There is a new configuration option (--enable-direxpand-default) that
    causes the `direxpand' shell option to be enabled by default.

bb. Bash does not do anything special to ensure that the file descriptor
    assigned to X in {x}<foo remains open after the block containing it
    completes.

cc. The `wait' builtin has a new `-n' option to wait for the next child to
    change status.

dd. The `printf' %(...)T format specifier now uses the current time if no
    argument is supplied.

ee. There is a new variable, BASH_COMPAT, that controls the current shell
    compatibility level.

ff. The `popd' builtin now treats additional arguments as errors.

gg. The brace expansion code now treats a failed sequence expansion as a
    simple string and will continue to expand brace terms in the remainder
    of the word.

hh. Shells started to run process substitutions now run any trap set on EXIT.

ii. The fc builtin now interprets -0 as the current command line.

jj. Completing directory names containing shell variables now adds a trailing
    slash if the expanded result is a directory.

kk. `cd' has a new `-@' option to browse a file's extended attributes on
    systems that support O_XATTR.

ll. The test/[/[[ `-v variable' binary operator now understands array
    references.

2.  New Features in Readline

a.  Readline is now more responsive to SIGHUP and other fatal signals when
    reading input from the terminal or performing word completion but no
    longer attempts to run any not-allowable functions from a signal handler
    context.

b.  There are new bindable commands to search the history for the string of
    characters between the beginning of the line and the point
    (history-substring-search-forward, history-substring-search-backward)

c.  Readline allows quoted strings as the values of variables when setting
    them with `set'.  As a side effect, trailing spaces and tabs are ignored
    when setting a string variable's value.

d.  The history library creates a backup of the history file when writing it
    and restores the backup on a write error.

e.  New application-settable variable: rl_filename_stat_hook: a function called
    with a filename before using it in a call to stat(2).  Bash uses it to
    expand shell variables so things like $HOME/Downloads have a slash
    appended.

f.  New bindable function `print-last-kbd-macro', prints the most-recently-
    defined keyboard macro in a reusable format.

g.  New user-settable variable `colored-stats', enables use of colored text
    to denote file types when displaying possible completions (colored analog
    of visible-stats).

h.  New user-settable variable `keyseq-timout', acts as an inter-character
    timeout when reading input or incremental search strings.

i.  New application-callable function: rl_clear_history. Clears the history list
    and frees all readline-associated private data.

j.  New user-settable variable, show-mode-in-prompt, adds a characters to the
    beginning of the prompt indicating the current editing mode.

k.  New application-settable variable: rl_input_available_hook; function to be
    called when readline detects there is data available on its input file
    descriptor.

l.  Readline calls an application-set event hook (rl_event_hook) after it gets
    a signal while reading input (read returns -1/EINTR but readline does not
    handle the signal immediately) to allow the application to handle or
    otherwise note it.

m.  If the user-settable variable `history-size' is set to a value less than
    0, the history list size is unlimited.

n.  New application-settable variable: rl_signal_event_hook; function that is
    called when readline is reading terminal input and read(2) is interrupted
    by a signal.  Currently not called for SIGHUP or SIGTERM.

o.  rl_change_environment: new application-settable variable that controls
    whether or not Readline modifies the environment (currently readline
    modifies only LINES and COLUMNS).

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-4.2 since
the release of bash-4.1.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  `exec -a foo' now sets $0 to `foo' in an executable shell script without a
    leading #!.

b.  Subshells begun to execute command substitutions or run shell functions or
    builtins in subshells do not reset trap strings until a new trap is
    specified.  This allows $(trap) to display the caller's traps and the
    trap strings to persist until a new trap is set.

c.  `trap -p' will now show signals ignored at shell startup, though their
    disposition still cannot be modified.

d.  $'...', echo, and printf understand \uXXXX and \UXXXXXXXX escape sequences.

e.  declare/typeset has a new `-g' option, which creates variables in the
    global scope even when run in a shell function.

f.  test/[/[[ have a new -v variable unary operator, which returns success if
    `variable' has been set.

g.  Posix parsing changes to allow `! time command' and multiple consecutive
    instances of `!' (which toggle) and `time' (which have no cumulative
    effect).

h.  Posix change to allow `time' as a command by itself to print the elapsed
    user, system, and real times for the shell and its children.

j.  $((...)) is always parsed as an arithmetic expansion first, instead of as
    a potential nested command substitution, as Posix requires.

k.  A new FUNCNEST variable to allow the user to control the maximum shell
    function nesting (recursive execution) level.

l.  The mapfile builtin now supplies a third argument to the callback command:
    the line about to be assigned to the supplied array index.

m.  The printf builtin has a new %(fmt)T specifier, which allows time values
    to use strftime-like formatting.

n.  There is a new `compat41' shell option.

o.  The cd builtin has a new Posix-mandated `-e' option.

p.  Negative subscripts to indexed arrays, previously errors, now are treated
    as offsets from the maximum assigned index + 1.

q.  Negative length specifications in the ${var:offset:length} expansion,
    previously errors, are now treated as offsets from the end of the variable.

r.  Parsing change to allow `time -p --'.

s.  Posix-mode parsing change to not recognize `time' as a keyword if the
    following token begins with a `-'.  This means no more Posix-mode
    `time -p'.  Posix interpretation 267.

t.  There is a new `lastpipe' shell option that runs the last command of a
    pipeline in the current shell context.  The lastpipe option has no
    effect if job control is enabled.

u.  History expansion no longer expands the `$!' variable expansion.

v.  Posix mode shells no longer exit if a variable assignment error occurs
    with an assignment preceding a command that is not a special builtin.

w.  Non-interactive mode shells exit if -u is enabled and an attempt is made
    to use an unset variable with the % or # expansions, the `//', `^', or
    `,' expansions, or the parameter length expansion.

x.  Posix-mode shells use the argument passed to `.' as-is if a $PATH search
    fails, effectively searching the current directory.  Posix-2008 change.

2.  New Features in Readline

a.  The history library does not try to write the history filename in the
    current directory if $HOME is unset.  This closes a potential security
    problem if the application does not specify a history filename.

b.  New bindable variable `completion-display-width' to set the number of
    columns used when displaying completions.

c.  New bindable variable `completion-case-map' to cause case-insensitive
    completion to treat `-' and `_' as identical.

d.  There are new bindable vi-mode command names to avoid readline's case-
    insensitive matching not allowing them to be bound separately.

e.  New bindable variable `menu-complete-display-prefix' causes the menu
    completion code to display the common prefix of the possible completions
    before cycling through the list, instead of after.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-4.1 since
the release of bash-4.0.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  Here-documents within $(...) command substitutions may once more be
    delimited by the closing right paren, instead of requiring a newline.

b.  Bash's file status checks (executable, readable, etc.) now take file
    system ACLs into account on file systems that support them.

c.  Bash now passes environment variables with names that are not valid
    shell variable names through into the environment passed to child
    processes.

d.  The `execute-unix-command' readline function now attempts to clear and
    reuse the current line rather than move to a new one after the command
    executes.

e.  `printf -v' can now assign values to array indices.

f.  New `complete -E' and `compopt -E' options that work on the "empty"
    completion: completion attempted on an empty command line.

g.  New complete/compgen/compopt -D option to define a `default' completion:
    a completion to be invoked on command for which no completion has been
    defined.  If this function returns 124, programmable completion is
    attempted again, allowing a user to dynamically build a set of completions
    as completion is attempted by having the default completion function
    install individual completion functions each time it is invoked.

h.  When displaying associative arrays, subscripts are now quoted.

i.  Changes to dabbrev-expand to make it more `emacs-like': no space appended
    after matches, completions are not sorted, and most recent history entries
    are presented first.

j.  The [[ and (( commands are now subject to the setting of `set -e' and the
    ERR trap.

k.  The source/. builtin now removes NUL bytes from the file before attempting
    to parse commands.

l.  There is a new configuration option (in config-top.h) that forces bash to
    forward all history entries to syslog.

m.  A new variable $BASHOPTS to export shell options settable using `shopt' to
    child processes.

n.  There is a new confgure option that forces the extglob option to be
    enabled by default.

o.  New variable $BASH_XTRACEFD; when set to an integer bash will write xtrace
    output to that file descriptor.

p.  If the optional left-hand-side of a redirection is of the form {var}, the
    shell assigns the file descriptor used to $var or uses $var as the file
    descriptor to move or close, depending on the redirection operator.

q.  The < and > operators to the [[ conditional command now do string
    comparison according to the current locale if the compatibility level
    is greater than 40.

r.  Programmable completion now uses the completion for `b' instead of `a'
    when completion is attempted on a line like: a $(b c.

s.  Force extglob on temporarily when parsing the pattern argument to
    the == and != operators to the [[ command, for compatibility.

t.  Changed the behavior of interrupting the wait builtin when a SIGCHLD is
    received and a trap on SIGCHLD is set to be Posix-mode only.

u.  The read builtin has a new `-N nchars' option, which reads exactly NCHARS
    characters, ignoring delimiters like newline.

v.  The mapfile/readarray builtin no longer stores the commands it invokes via
    callbacks in the history list.

w.  There is a new `compat40' shopt option.

2.  New Features in Readline

a.  New bindable function: menu-complete-backward.

b.  In the vi insertion keymap, C-n is now bound to menu-complete by default,
    and C-p to menu-complete-backward.

c.  When in vi command mode, repeatedly hitting ESC now does nothing, even
    when ESC introduces a bound key sequence.  This is closer to how
    historical vi behaves.

d.  New bindable function: skip-csi-sequence.  Can be used as a default to
    consume key sequences generated by keys like Home and End without having
    to bind all keys.

e.  New application-settable function: rl_filename_rewrite_hook.  Can be used
    to rewite or modify filenames read from the file system before they are
    compared to the word to be completed.

f.  New bindable variable: skip-completed-text, active when completing in the
    middle of a word.  If enabled, it means that characters in the completion
    that match characters in the remainder of the word are "skipped" rather
    than inserted into the line.

g.  The pre-readline-6.0 version of menu completion is available as
    "old-menu-complete" for users who do not like the readline-6.0 version.

h.  New bindable variable: echo-control-characters.  If enabled, and the
    tty ECHOCTL bit is set, controls the echoing of characters corresponding
    to keyboard-generated signals.

i.  New bindable variable: enable-meta-key.  Controls whether or not readline
    sends the smm/rmm sequences if the terminal indicates it has a meta key
    that enables eight-bit characters.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-4.0 since
the release of bash-3.2.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  When using substring expansion on the positional parameters, a starting
    index of 0 now causes $0 to be prefixed to the list.

b.  The `help' builtin now prints its columns with entries sorted vertically
    rather than horizontally.

c.  There is a new variable, $BASHPID, which always returns the process id of
    the current shell.

d.  There is a new `autocd' option that, when enabled, causes bash to attempt
    to `cd' to a directory name that is supplied as the first word of a
    simple command.

e.  There is a new `checkjobs' option that causes the shell to check for and
    report any running or stopped jobs at exit.

f.  The programmable completion code exports a new COMP_TYPE variable, set to
    a character describing the type of completion being attempted.

g.  The programmable completion code exports a new COMP_KEY variable, set to
    the character that caused the completion to be invoked (e.g., TAB).

h.  If creation of a child process fails due to insufficient resources, bash
    will try again several times before reporting failure.

i.  The programmable completion code now uses the same set of characters as
    readline when breaking the command line into a list of words.

j.  The block multiplier for the ulimit -c and -f options is now 512 when in
    Posix mode, as Posix specifies.

k.  Changed the behavior of the read builtin to save any partial input received
    in the specified variable when the read builtin times out.  This also
    results in variables specified as arguments to read to be set to the empty
    string when there is no input available.  When the read builtin times out,
    it returns an exit status greater than 128.

l.  The shell now has the notion of a `compatibility level', controlled by
    new variables settable by `shopt'.  Setting this variable currently
    restores the bash-3.1 behavior when processing quoted strings on the rhs
    of the `=~' operator to the `[[' command.

m.  The `ulimit' builtin now has new -b (socket buffer size) and -T (number
    of threads) options.

n.  The -p option to `declare' now displays all variable values and attributes
    (or function values and attributes if used with -f).

o.  There is a new `compopt' builtin that allows completion functions to modify
    completion options for existing completions or the completion currently
    being executed.

p.  The `read' builtin has a new -i option which inserts text into the reply
    buffer when using readline.

q.  A new `-E' option to the complete builtin allows control of the default
    behavior for completion on an empty line.

r.  There is now limited support for completing command name words containing
    globbing characters.

s.  Changed format of internal help documentation for all builtins to roughly
    follow man page format.

t.  The `help' builtin now has a new -d option, to display a short description,
    and a -m option, to print help information in a man page-like format.

u.  There is a new `mapfile' builtin to populate an array with lines from a
    given file.  The name `readarray' is a synonym.

v.  If a command is not found, the shell attempts to execute a shell function
    named `command_not_found_handle', supplying the command words as the
    function arguments.

w.  There is a new shell option: `globstar'.  When enabled, the globbing code
    treats `**' specially -- it matches all directories (and files within
    them, when appropriate) recursively.

x.  There is a new shell option: `dirspell'.  When enabled, the filename
    completion code performs spelling correction on directory names during
    completion.

y.  The `-t' option to the `read' builtin now supports fractional timeout
    values.

z.  Brace expansion now allows zero-padding of expanded numeric values and
    will add the proper number of zeroes to make sure all values contain the
    same number of digits.

aa. There is a new bash-specific bindable readline function: `dabbrev-expand'.
    It uses menu completion on a set of words taken from the history list.

bb. The command assigned to a key sequence with `bind -x' now sets two new
    variables in the environment of the executed command:  READLINE_LINE_BUFFER
    and READLINE_POINT.  The command can change the current readline line
    and cursor position by modifying READLINE_LINE_BUFFER and READLINE_POINT,
    respectively.

cc. There is a new &>> redirection operator, which appends the standard output
    and standard error to the named file.

dd. The parser now understands `|&' as a synonym for `2>&1 |', which redirects
    the standard error for a command through a pipe.

ee. The new `;&' case statement action list terminator causes execution to
    continue with the action associated with the next pattern in the
    statement rather than terminating the command.

ff. The new `;;&' case statement action list terminator causes the shell to
    test the next set of patterns after completing execution of the current
    action, rather than terminating the command.

gg. The shell understands a new variable: PROMPT_DIRTRIM.  When set to an
    integer value greater than zero, prompt expansion of \w and \W  will
    retain only that number of trailing pathname components and replace
    the intervening characters with `...'.

hh. There are new case-modifying word expansions: uppercase (^[^]) and
    lowercase (,[,]).  They can work on either the first character or
    array element, or globally.  They accept an optional shell pattern
    that determines which characters to modify.  There is an optionally-
    configured feature to include capitalization operators.

ii. The shell provides associative array variables, with the appropriate
    support to create, delete, assign values to, and expand them.

jj. The `declare' builtin now has new -l (convert value to lowercase upon
    assignment) and -u (convert value to uppercase upon assignment) options.
    There is an optionally-configurable -c option to capitalize a value at
    assignment.

kk. There is a new `coproc' reserved word that specifies a coprocess: an
    asynchronous command run with two pipes connected to the creating shell.
    Coprocs can be named.  The input and output file descriptors and the
    PID of the coprocess are available to the calling shell in variables
    with coproc-specific names.

ll. A value of 0 for the -t option to `read' now returns success if there is
    input available to be read from the specified file descriptor.

mm. CDPATH and GLOBIGNORE are ignored when the shell is running in privileged
    mode.

nn. New bindable readline functions shell-forward-word and shell-backward-word,
    which move forward and backward words delimited by shell metacharacters
    and honor shell quoting.

oo.  New bindable readline functions shell-backward-kill-word and shell-kill-word
    which kill words backward and forward, but use the same word boundaries
    as shell-forward-word and shell-backward-word.

2.  New Features in Readline

a.  A new variable, rl_sort_completion_matches; allows applications to inhibit
    match list sorting (but beware: some things don't work right if
    applications do this).

b.  A new variable, rl_completion_invoking_key; allows applications to discover
    the key that invoked rl_complete or rl_menu_complete.

c.  The functions rl_block_sigint and rl_release_sigint are now public and
    available to calling applications who want to protect critical sections
    (like redisplay).

d.  The functions rl_save_state and rl_restore_state are now public and
    available to calling applications; documented rest of readline's state
    flag values.

e.  A new user-settable variable, `history-size', allows setting the maximum
    number of entries in the history list.

f.  There is a new implementation of menu completion, with several improvements
    over the old; the most notable improvement is a better `completions
    browsing' mode.

g.  The menu completion code now uses the rl_menu_completion_entry_function
    variable, allowing applications to provide their own menu completion
    generators.

h.  There is support for replacing a prefix  of a pathname with a `...' when
    displaying possible completions.  This is controllable by setting the
    `completion-prefix-display-length' variable.  Matches with a common prefix
    longer than this value have the common prefix replaced with `...'.

i.  There is a new `revert-all-at-newline' variable.  If enabled, readline will
    undo all outstanding changes to all history lines when `accept-line' is
    executed.

j.  If the kernel supports it, readline displays special characters
    corresponding to a keyboard-generated signal when the signal is received.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-3.2 since
the release of bash-3.1.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  Changed the parameter pattern replacement functions to not anchor the
    pattern at the beginning of the string if doing global replacement - that
    combination doesn't make any sense.

b.  When running in `word expansion only' mode (--wordexp option), inhibit
    process substitution.

c.  Loadable builtins now work on MacOS X 10.[34].

d.  Shells running in posix mode no longer set $HOME, as POSIX requires.

e.  The code that checks for binary files being executed as shell scripts now
    checks only for NUL rather than any non-printing character.

f.  Quoting the string argument to the [[ command's  =~ operator now forces
    string matching, as with the other pattern-matching operators.

2.  New Features in Readline

a.  Calling applications can now set the keyboard timeout to 0, allowing
    poll-like behavior.

b.  The value of SYS_INPUTRC (configurable at compilation time) is now used as
    the default last-ditch startup file.

c.  The history file reading functions now allow windows-like \r\n line
    terminators.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-3.1 since
the release of bash-3.0.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  Bash now understands LC_TIME as a special variable so that time display
    tracks the current locale.

b.  BASH_ARGC, BASH_ARGV, BASH_SOURCE, and BASH_LINENO are no longer created
    as `invisible' variables and may not be unset.

c.  In POSIX mode, if `xpg_echo' option is enabled, the `echo' builtin doesn't
    try to interpret any options at all, as POSIX requires.

d.  The `bg' builtin now accepts multiple arguments, as POSIX seems to specify.

e.  Fixed vi-mode word completion and glob expansion to perform tilde
    expansion.

f.  The `**' mathematic exponentiation operator is now right-associative.

g.  The `ulimit' builtin has new options: -i (max number of pending signals),
    -q (max size of POSIX message queues), and -x (max number of file locks).

h.  A bare `%' once again expands to the current job when used as a job
    specifier.

i.  The `+=' assignment operator (append to the value of a string or array) is
    now supported for assignment statements and arguments to builtin commands
    that accept assignment statements.

j.  BASH_COMMAND now preserves its value when a DEBUG trap is executed.

k.  The `gnu_errfmt' option is enabled automatically if the shell is running
    in an emacs terminal window.

l.  New configuration option:  --single-help-strings.  Causes long help text
    to be written as a single string; intended to ease translation.

m.  The COMP_WORDBREAKS variable now causes the list of word break characters
    to be emptied when the variable is unset.

n.  An unquoted expansion of $* when $IFS is empty now causes the positional
    parameters to be concatenated if the expansion doesn't undergo word
    splitting.

o.  Bash now inherits $_ from the environment if it appears there at startup.

p.  New shell option: nocasematch.  If non-zero, shell pattern matching ignores
    case when used by `case' and `[[' commands.

q.  The `printf' builtin takes a new option: -v var.  That causes the output
    to be placed into var instead of on stdout.

r.  By default, the shell no longer reports processes dying from SIGPIPE.

s.  Bash now sets the extern variable `environ' to the export environment it
    creates, so C library functions that call getenv() (and can't use the
    shell-provided replacement) get current values of environment variables.

t.  A new configuration option, `--enable-strict-posix-default', which will
    build bash to be POSIX conforming by default.

u.  If compiled for strict POSIX conformance, LINES and COLUMNS may now
    override the true terminal size.

2.  New Features in Readline

a.  The key sequence sent by the keypad `delete' key is now automatically
    bound to delete-char.

b.  A negative argument to menu-complete now cycles backward through the
    completion list.

c.  A new bindable readline variable:  bind-tty-special-chars.  If non-zero,
    readline will bind the terminal special characters to their readline
    equivalents when it's called (on by default).

d.  New bindable command: vi-rubout.  Saves deleted text for possible
    reinsertion, as with any vi-mode `text modification' command; `X' is bound
    to this in vi command mode.

e.  A new external application-controllable variable that allows the LINES
    and COLUMNS environment variables to set the window size regardless of
    what the kernel returns: rl_prefer_env_winsize

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-3.0 since
the release of bash-2.05b.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  ANSI string expansion now implements the \x{hexdigits} escape.

b.  There is a new loadable `strftime' builtin.

c.  New variable, COMP_WORDBREAKS, which controls the readline completer's
    idea of word break characters.

d.  The `type' builtin no longer reports on aliases unless alias expansion
    will actually be performed.    

e.  HISTCONTROL is now a colon-separated list of values, which permits
    more extensibility and backwards compatibility.

f.  HISTCONTROL may now include the `erasedups' option, which causes all lines
    matching a line being added to be removed from the history list.

g.  `configure' has a new `--enable-multibyte' argument that permits multibyte
    character support to be disabled even on systems that support it.

h.  New variables to support the bash debugger:  BASH_ARGC, BASH_ARGV,
    BASH_SOURCE, BASH_LINENO, BASH_SUBSHELL, BASH_EXECUTION_STRING,
    BASH_COMMAND

i.  FUNCNAME has been changed to support the debugger: it's now an array
    variable.

j.  for, case, select, arithmetic commands now keep line number information
    for the debugger.

k.  There is a new `RETURN' trap executed when a function or sourced script
    returns (not inherited child processes; inherited by command substitution
    if function tracing is enabled and the debugger is active).

l.  New invocation option:  --debugger.  Enables debugging and turns on new
    `extdebug' shell option.

m.  New `functrace' and `errtrace' options to `set -o' cause DEBUG and ERR
    traps, respectively, to be inherited by shell functions.  Equivalent to
    `set -T' and `set -E' respectively.  The `functrace' option also controls
    whether or not the DEBUG trap is inherited by sourced scripts.

n.  The DEBUG trap is run before binding the variable and running the action
    list in a `for' command, binding the selection variable and running the
    query in a `select' command, and before attempting a match in a `case'
    command.

o.  New `--enable-debugger' option to `configure' to compile in the debugger
    support code.

p.  `declare -F' now prints out extra line number and source file information
    if the `extdebug' option is set.

q.  If `extdebug' is enabled, a non-zero return value from a DEBUG trap causes
    the next command to be skipped, and a return value of 2 while in a
    function or sourced script forces a `return'.

r.  New `caller' builtin to provide a call stack for the bash debugger.

s.  The DEBUG trap is run just before the first command in a function body is
    executed, for the debugger.

t.  `for', `select', and `case' command heads are printed when `set -x' is
    enabled.

u.  There is a new {x..y} brace expansion, which is shorthand for {x.x+1,
    x+2,...,y}.  x and y can be integers or single characters; the sequence
    may ascend or descend; the increment is always 1.

v.  New ksh93-like ${!array[@]} expansion, expands to all the keys (indices)
    of array.

w.  New `force_fignore' shopt option; if enabled, suffixes specified by
    FIGNORE cause words to be ignored when performing word completion even
    if they're the only possibilities.

x.  New `gnu_errfmt' shopt option; if enabled, error messages follow the `gnu
    style' (filename:lineno:message) format.

y.  New `-o bashdefault' option to complete and compgen; if set, causes the
    whole set of bash completions to be performed if the compspec doesn't
    result in a match.

z.  New `-o plusdirs' option to complete and compgen; if set, causes directory
    name completion to be performed and the results added to the rest of the
    possible completions.

aa. `kill' is available as a builtin even when the shell is built without
    job control.

bb. New HISTTIMEFORMAT variable; value is a format string to pass to
    strftime(3).  If set and not null, the `history' builtin prints out
    timestamp information according to the specified format when displaying
    history entries.  If set, bash tells the history library to write out
    timestamp information when the history file is written.

cc. The [[ ... ]] command has a new binary `=~' operator that performs
    extended regular expression (egrep-like) matching.

dd. `configure' has a new `--enable-cond-regexp' option (enabled by default)
    to enable the =~ operator and regexp matching in [[ ... ]].

ee. Subexpressions matched by the =~ operator are placed in the new
    BASH_REMATCH array variable.

ff. New `failglob' option that causes an expansion error when pathname
    expansion fails to produce a match.

gg. New `set -o pipefail' option that causes a pipeline to return a failure
    status if any of the processes in the pipeline fail, not just the last
    one.

hh. printf builtin understands two new escape sequences:  \" and \?.

ii. `echo -e' understands two new escape sequences:  \" and \?.

jj. The GNU `gettext' package and libintl have been integrated; the shell's
    messages can be translated into different languages.

kk. The `\W' prompt expansion now abbreviates $HOME as `~', like `\w'.

ll. The error message printed when bash cannot open a shell script supplied
    as argument 1 now includes the name of the shell, to better identify
    the error as coming from bash.

mm. The parameter pattern removal and substitution expansions are now much
    faster and more efficient when using multibyte characters.

nn. The `jobs', `kill', and `wait' builtins now accept job control notation
    even if job control is not enabled.

oo. The historical behavior of `trap' that allows a missing `action' argument
    to cause each specified signal's handling to be reset to its default is
    now only supported when `trap' is given a single non-option argument.

2.  New Features in Readline

a.  History expansion has a new `a' modifier equivalent to the `g' modifier
    for compatibility with the BSD csh.

b.  History expansion has a new `G' modifier equivalent to the BSD csh `g'
    modifier, which performs a substitution once per word.

c.  All non-incremental search operations may now undo the operation of
    replacing the current line with the history line.

d.  The text inserted by an `a' command in vi mode can be reinserted with
    `.'.

e.  New bindable variable, `show-all-if-unmodified'.  If set, the readline
    completer will list possible completions immediately if there is more
    than one completion and partial completion cannot be performed.

f.  There is a new application-callable `free_history_entry()' function.

g.  History list entries now contain timestamp information; the history file
    functions know how to read and write timestamp information associated
    with each entry.

h.  Four new key binding functions have been added:

        rl_bind_key_if_unbound()
        rl_bind_key_if_unbound_in_map()
        rl_bind_keyseq_if_unbound()
        rl_bind_keyseq_if_unbound_in_map()

i.  New application variable, rl_completion_quote_character, set to any
    quote character readline finds before it calls the application completion
    function.

j.  New application variable, rl_completion_suppress_quote, settable by an
    application completion function.  If set to non-zero, readline does not
    attempt to append a closing quote to a completed word.

k.  New application variable, rl_completion_found_quote, set to a non-zero
    value if readline determines that the word to be completed is quoted.
    Set before readline calls any application completion function.

l.  New function hook, rl_completion_word_break_hook, called when readline
    needs to break a line into words when completion is attempted.  Allows
    the word break characters to vary based on position in the line.

m.  New bindable command: unix-filename-rubout.  Does the same thing as
    unix-word-rubout, but adds `/' to the set of word delimiters.

n.  When listing completions, directories have a `/' appended if the
    `mark-directories' option has been enabled.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-2.05b since
the release of bash-2.05a.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  If set, TMOUT is the default timeout for the `read' builtin.

b.  `type' has two new options:  `-f' suppresses shell function lookup, and
    `-P' forces a $PATH search.

c.  New code to handle multibyte characters.

d.  `select' was changed to be more ksh-compatible, in that the menu is
    reprinted each time through the loop only if REPLY is set to NULL.
    The previous behavior is available as a compile-time option.

e.  `complete -d' and `complete -o dirnames' now force a slash to be
    appended to names which are symlinks to directories.

f.  There is now a bindable edit-and-execute-command readline command,
    like the vi-mode `v' command, bound to C-xC-e in emacs mode.

g.  Added support for ksh93-like [:word:] character class in pattern matching.

h.  The  $'...' quoting construct now expands \cX to Control-X.

i.  A new \D{...} prompt expansion; passes the `...' to strftime and inserts
    the result into the expanded prompt.

j.  The shell now performs arithmetic in the largest integer size the
    machine supports (intmax_t), instead of long.

k.  If a numeric argument is supplied to one of the bash globbing completion
    functions, a `*' is appended to the word before expansion is attempted.

l.  The bash globbing completion functions now allow completions to be listed
    with double tabs or if `show-all-if-ambiguous' is set.

m.  New `-o nospace' option for `complete' and `compgen' builtins; suppresses
    readline's appending a space to the completed word.

n.  New `here-string' redirection operator:  <<< word.

o.  When displaying variables, function attributes and definitions are shown
    separately, allowing them to be re-used as input (attempting to re-use
    the old output would result in syntax errors).

p.  There is a new configuration option `--enable-mem-scramble', controls
    bash malloc behavior of writing garbage characters into memory at
    allocation and free time.

q.  The `complete' and `compgen' builtins now have a new `-s/-A service'
    option to complete on names from /etc/services.

r.  `read' has a new `-u fd' option to read from a specified file descriptor.

s.  Fix the completion code so that expansion errors in a directory name
    don't cause a longjmp back to the command loop.

t.  Fixed word completion inside command substitution to work a little more
    intuitively.

u.  The `printf' %q format specifier now uses $'...' quoting to print the
    argument if it contains non-printing characters.

v.  The `declare' and `typeset' builtins have a new `-t' option.  When applied
    to functions, it causes the DEBUG trap to be inherited by the named
    function.  Currently has no effect on variables.

w.  The DEBUG trap is now run *before* simple commands, ((...)) commands,
    [[...]] conditional commands, and for ((...)) loops.

x.  The expansion of $LINENO inside a shell function is only relative to the
    function start if the shell is interactive -- if the shell is running a
    script, $LINENO expands to the line number in the script.  This is as
    POSIX-2001 requires.

y.  The bash debugger in examples/bashdb has been modified to work with the
    new DEBUG trap semantics, the command set has been made more gdb-like,
    and the changes to $LINENO make debugging functions work better.  Code
    from Gary Vaughan.

z.  New [n]<&word- and [n]>&word- redirections from ksh93 -- move fds (dup
    and close).

aa. There is a new `-l' invocation option, equivalent to `--login'.

bb. The `hash' builtin has a new `-l' option to list contents in a reusable
    format, and a `-d' option to remove a name from the hash table.

cc. There is now support for placing the long help text into separate files 
    installed into ${datadir}/bash.  Not enabled by default; can be turned  
    on with `--enable-separate-helpfiles' option to configure.
    
dd. All builtins that take operands accept a `--' pseudo-option, except
    `echo'.

ee. The `echo' builtin now accepts \0xxx (zero to three octal digits following
    the `0') in addition to \xxx (one to three octal digits) for SUSv3/XPG6/
    POSIX.1-2001 compliance.


2.  New Features in Readline

a.  Support for key `subsequences':  allows, e.g., ESC and ESC-a to both
    be bound to readline functions.  Now the arrow keys may be used in vi
    insert mode.

b.  When listing completions, and the number of lines displayed is more than
    the screen length, readline uses an internal pager to display the results.
    This is controlled by the `page-completions' variable (default on).

c.  New code to handle editing and displaying multibyte characters.

d.  The behavior introduced in bash-2.05a of deciding whether or not to
    append a slash to a completed name that is a symlink to a directory has
    been made optional, controlled by the `mark-symlinked-directories'
    variable (default is the 2.05a behavior).

e.  The `insert-comment' command now acts as a toggle if given a numeric
    argument:  if the first characters on the line don't specify a
    comment, insert one; if they do, delete the comment text

f.  New application-settable completion variable:
    rl_completion_mark_symlink_dirs, allows an application's completion
    function to temporarily override the user's preference for appending
    slashes to names which are symlinks to directories.

g.  New function available to application completion functions:
    rl_completion_mode, to tell how the completion function was invoked
    and decide which argument to supply to rl_complete_internal (to list
    completions, etc.).

h.  Readline now has an overwrite mode, toggled by the `overwrite-mode'
    bindable command, which could be bound to `Insert'.

i.  New application-settable completion variable:
    rl_completion_suppress_append, inhibits appending of
    rl_completion_append_character to completed words.

j.  New key bindings when reading an incremental search string:  ^W yanks
    the currently-matched word out of the current line into the search
    string; ^Y yanks the rest of the current line into the search string,
    DEL or ^H deletes characters from the search string.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-2.05a since
the release of bash-2.05.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  Added support for DESTDIR installation root prefix, so you can do a
    `make install DESTDIR=bash-root' and do easier binary packaging.

b.  Added support for builtin printf "'" flag character as per latest POSIX
    drafts.

c.  Support for POSIX.2 printf(1) length specifiers `j', `t', and `z' (from
    ISO C99).

d.  New autoconf macro, RL_LIB_READLINE_VERSION, for use by other applications
    (bash doesn't use very much of what it returns).

e.  `set [-+]o nolog' is recognized as required by the latest POSIX drafts,
    but ignored.

f.  New read-only `shopt' option:  login_shell.  Set to non-zero value if the
    shell is a login shell.

g.  New `\A' prompt string escape sequence; expands to time in 24 HH:MM format.

h.  New `-A group/-g' option to complete and compgen; does group name
    completion.

i.  New `-t' option to `hash' to list hash values for each filename argument.

j.  New [-+]O invocation option to set and unset `shopt' options at startup.

k.  configure's `--with-installed-readline' option now takes an optional
    `=PATH' suffix to set the root of the tree where readline is installed
    to PATH.

l.  The ksh-like `ERR' trap has been added.  The `ERR' trap will be run
    whenever the shell would have exited if the -e option were enabled.
    It is not inherited by shell functions.

m.  `readonly', `export', and `declare' now print variables which have been
    given attributes but not set by assigning a value as just a command and
    a variable name (like `export foo') when listing, as the latest POSIX
    drafts require.

n.  `bashbug' now requires that the subject be changed from the default.

o.  configure has a new `--enable-largefile' option, like other GNU utilities.

p.  `for' loops now allow empty word lists after `in', like the latest POSIX
    drafts require.

q.  The builtin `ulimit' now takes two new non-numeric arguments:  `hard',
    meaning the current hard limit, and `soft', meaning the current soft  
    limit, in addition to `unlimited'
    
r.  `ulimit' now prints the option letter associated with a particular
    resource when printing more than one limit.

s.  `ulimit' prints `hard' or `soft' when a value is not `unlimited' but is
    one of RLIM_SAVED_MAX or RLIM_SAVED_CUR, respectively.

t.  The `printf' builtin now handles the %a and %A conversions if they're
    implemented by printf(3).

u.  The `printf' builtin now handles the %F conversion (just about like %f).

v.  The `printf' builtin now handles the %n conversion like printf(3).  The
    corresponding argument is the name of a shell variable to which the
    value is assigned.

2.  New Features in Readline

a.  Added extern declaration for rl_get_termcap to readline.h, making it a
    public function (it was always there, just not in readline.h).

b.  New #defines in readline.h:  RL_READLINE_VERSION, currently 0x0402,
    RL_VERSION_MAJOR, currently 4, and RL_VERSION_MINOR, currently 2.

c.  New readline variable:  rl_readline_version, mirrors RL_READLINE_VERSION.

d.  New bindable boolean readline variable:  match-hidden-files.  Controls
    completion of files beginning with a `.' (on Unix).  Enabled by default.

e.  The history expansion code now allows any character to terminate a
    `:first-' modifier, like csh.

f.  New bindable variable `history-preserve-point'.  If set, the history
    code attempts to place the user at the same location on each history
    line retrieved with previous-history or next-history.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-2.05 since
the release of bash-2.04.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  Added a new `--init-file' invocation argument as a synonym for `--rcfile',
    per the new GNU coding standards.

b.  The /dev/tcp and /dev/udp redirections now accept service names as well as
    port numbers.

c.  `complete' and `compgen' now take a `-o value' option, which controls some
    of the aspects of that compspec.  Valid values are:

        default - perform bash default completion if programmable
                  completion produces no matches
        dirnames - perform directory name completion if programmable
                   completion produces no matches
        filenames - tell readline that the compspec produces filenames,
                    so it can do things like append slashes to
                    directory names and suppress trailing spaces

d.  A new loadable builtin, realpath, which canonicalizes and expands symlinks
    in pathname arguments.
    
e.  When `set' is called without options, it prints function definitions in a
    way that allows them to be reused as input.  This affects `declare' and 
    `declare -p' as well.  This only happens when the shell is not in POSIX
    mode, since POSIX.2 forbids this behavior.

f.  Bash-2.05 once again honors the current locale setting when processing
    ranges within pattern matching bracket expressions (e.g., [A-Z]).

2.  New Features in Readline

a.  The blink timeout for paren matching is now settable by applications,
    via the rl_set_paren_blink_timeout() function.

b.  _rl_executing_macro has been renamed to rl_executing_macro, which means
    it's now part of the public interface.

c.  Readline has a new variable, rl_readline_state, which is a bitmap that
    encapsulates the current state of the library; intended for use by
    callbacks and hook functions.

d.  New application-callable function rl_set_prompt(const char *prompt):
    expands its prompt string argument and sets rl_prompt to the result.

e.  New application-callable function rl_set_screen_size(int rows, int cols):
    public method for applications to set readline's idea of the screen
    dimensions.

f.  New function, rl_get_screen_size (int *rows, int *columns), returns
    readline's idea of the screen dimensions.

g.  The timeout in rl_gather_tyi (readline keyboard input polling function)
    is now settable via a function (rl_set_keyboard_input_timeout()).

h.  Renamed the max_input_history variable to history_max_entries; the old
    variable is maintained for backwards compatibility.

i.  The list of characters that separate words for the history tokenizer is
    now settable with a variable:  history_word_delimiters.  The default
    value is as before.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-2.04 since
the release of bash-2.03.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  The history builtin has a `-d offset' option to delete the history entry
    at position `offset'.

b.  The prompt expansion code has two new escape sequences: \j, the number of
    active jobs; and \l, the basename of the shell's tty device name.

c.  The `bind' builtin has a new `-x' option to bind key sequences to shell   
    commands.

d.  There is a new shell option, no_empty_command_completion, which, when
    enabled, disables command completion when TAB is typed on an empty line.

e.  The `help' builtin has a `-s' option to just print a builtin's usage
    synopsis.

f.  There are several new arithmetic operators:  id++, id-- (variable
    post-increment/decrement), ++id, --id (variable pre-increment/decrement),
    expr1 , expr2 (comma operator).

g.  There is a new ksh-93 style arithmetic for command:
        for ((expr1 ; expr2; expr3 )); do list; done

h.  The `read' builtin has a number of new options:
        -t timeout      only wait timeout seconds for input
        -n nchars       only read nchars from input instead of a full line
        -d delim        read until delim rather than newline
        -s              don't echo input chars as they are read

i.  The redirection code now handles several filenames specially:
    /dev/fd/N, /dev/stdin, /dev/stdout, and /dev/stderr, whether or
    not they are present in the file system.

j.  The redirection code now recognizes pathnames of the form
    /dev/tcp/host/port and /dev/udp/host/port, and tries to open a socket
    of the appropriate type to the specified port on the specified host.

k.  The ksh-93 ${!prefix*} expansion, which expands to the names of all
    shell variables with prefix PREFIX, has been implemented.

l.  There is a new dynamic variable, FUNCNAME, which expands to the name of
    a currently-executing function.  Assignments to FUNCNAME have no effect.

m.  The GROUPS variable is no longer readonly; assignments to it are silently
    discarded.  This means it can be unset.

n.  A new programmable completion facility, with two new builtin commands:
    complete and compgen.

o.  configure has a new option, `--enable-progcomp', to compile in the
    programmable completion features (enabled by default).

p.  `shopt' has a new option, `progcomp', to enable and disable programmable
    completion at runtime.

q.  Unsetting HOSTFILE now clears the list of hostnames used for completion.

r.  configure has a new option, `--enable-bash-malloc', replacing the old
    `--with-gnu-malloc' (which is still present for backwards compatibility).

s.  There is a new manual page describing rbash, the restricted shell.

t.  `bashbug' has new `--help' and `--version' options.

u.  `shopt' has a new `xpg_echo' option, which controls the behavior of
    `echo' with respect to backslash-escaped characters at runtime.

v.  If NON_INTERACTIVE_LOGIN_SHELLS is defined, all login shells read the
    startup files, even if they are not interactive.

w.  The LC_NUMERIC variable is now treated specially, and used to set the
    LC_NUMERIC locale category for number formatting, e.g., when `printf'
    displays floating-point numbers.

2.  New features in Readline

a.  Parentheses matching is now always compiled into readline, and enabled
    or disabled when the value of the `blink-matching-paren' variable is
    changed.

b.  MS-DOS systems now use ~/_inputrc as the last-ditch inputrc filename.

c.  MS-DOS systems now use ~/_history as the default history file.

d.  history-search-{forward,backward} now leave the point at the end of the
    line when the string to search for is empty, like
    {reverse,forward}-search-history.

e.  history-search-{forward,backward} now leave the last history line found
    in the readline buffer if the second or subsequent search fails.

f.  New function for use by applications:  rl_on_new_line_with_prompt, used
    when an application displays the prompt itself before calling readline().

g.  New variable for use by applications:  rl_already_prompted.  An application
    that displays the prompt itself before calling readline() must set this to
    a non-zero value.

h.  A new variable, rl_gnu_readline_p, always 1.  The intent is that an
    application can verify whether or not it is linked with the `real'
    readline library or some substitute.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-2.03 since
the release of bash-2.02.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  New `shopt' option, `restricted_shell', indicating whether or not the
    shell was started in restricted mode, for use in startup files.

b.  Filename generation is now performed on the words between ( and ) in
    array assignments (which it probably should have done all along).

c.  OLDPWD is now auto-exported, as POSIX.2 seems to require.

d.  ENV and BASH_ENV are read-only variables in a restricted shell.

e.  A change was made to the startup file code so that any shell begun with
    the `--login' option, even non-interactive shells, will source the login
    shell startup files.

2.  New Features in Readline

a.  Many changes to the signal handling:
        o Readline now catches SIGQUIT and cleans up the tty before returning;
        o A new variable, rl_catch_signals, is available to application writers 
          to indicate to readline whether or not it should install its own
          signal handlers for SIGINT, SIGTERM, SIGQUIT, SIGALRM, SIGTSTP,
          SIGTTIN, and SIGTTOU;
        o A new variable, rl_catch_sigwinch, is available to application
          writers to indicate to readline whether or not it should install its
          own signal handler for SIGWINCH, which will chain to the calling
          applications's SIGWINCH handler, if one is installed;
        o There is a new function, rl_free_line_state, for application signal
          handlers to call to free up the state associated with the current
          line after receiving a signal;
        o There is a new function, rl_cleanup_after_signal, to clean up the
          display and terminal state after receiving a signal;
        o There is a new function, rl_reset_after_signal, to reinitialize the
          terminal and display state after an application signal handler
          returns and readline continues

b.  There is a new function, rl_resize_terminal, to reset readline's idea of
    the screen size after a SIGWINCH.

c.  New public functions: rl_save_prompt and rl_restore_prompt.  These were
    previously private functions with a `_' prefix.

d.  New function hook: rl_pre_input_hook, called just before readline starts
    reading input, after initialization.

e.  New function hook: rl_display_matches_hook, called when readline would
    display the list of completion matches.  The new function
    rl_display_match_list is what readline uses internally, and is available
    for use by application functions called via this hook.

f.  New bindable function, delete-char-or-list, like tcsh.

g.  A new variable, rl_erase_empty_line, which, if set by an application using
    readline, will cause readline to erase, prompt and all, lines on which the
    only thing typed was a newline.

h.  New bindable variable: `isearch-terminators'.

i.  New bindable function: `forward-backward-delete-char' (unbound by default).

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-2.02 since
the release of bash-2.01.1.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1. New Features in Bash

a.  A new version of malloc, based on the older GNU malloc, that has many
    changes, is more page-based, is more conservative with memory usage,
    and does not `orphan' large blocks when they are freed.

b.  A new version of gmalloc, based on the old GLIBC malloc, with many
    changes and range checking included by default.

c.  A new implementation of fnmatch(3) that includes full POSIX.2 Basic
    Regular Expression matching, including character classes, collating
    symbols, equivalence classes, and support for case-insensitive pattern
    matching.

d.  ksh-88 egrep-style extended pattern matching ([@+*?!](patlist)) has been
    implemented, controlled by a new `shopt' option, `extglob'.  
    
e.  There is a new ksh-like `[[' compound command, which implements   
    extended `test' functionality.
    
f.  There is a new `printf' builtin, implemented according to the POSIX.2
    specification.
    
g.  There is a new feature for command substitution: $(< filename) now expands
    to the contents of `filename', with any trailing newlines removed
    (equivalent to $(cat filename)).

h.  There are new tilde prefixes which expand to directories from the
    directory stack.

i.  There is a new `**' arithmetic operator to do exponentiation.

j.  There are new configuration options to control how bash is linked:
    `--enable-profiling', to allow bash to be profiled with gprof, and
    `--enable-static-link', to allow bash to be linked statically.

k.  There is a new configuration option, `--enable-cond-command', which
    controls whether or not the `[[' command is included.  It is on by
    default. 

l.  There is a new configuration option, `--enable-extended-glob', which
    controls whether or not the ksh extended globbing feature is included.
    It is enabled by default.

m.  There is a new configuration #define in config.h.top that, when enabled,
    will cause all login shells to source /etc/profile and one of the user-
    specific login shell startup files, whether or not the shell is
    interactive.  
    
n.  There is a new invocation option, `--dump-po-strings', to dump
    a shell script's translatable strings ($"...") in GNU `po' format. 
    
o.  There is a new `shopt' option, `nocaseglob', to enable case-insensitive
    pattern matching when globbing filenames and using the `case' construct.

p.  There is a new `shopt' option, `huponexit', which, when enabled, causes
    the shell to send SIGHUP to all jobs when an interactive login shell
    exits.

q.  `bind' has a new `-u' option, which takes a readline function name as an
    argument and unbinds all key sequences bound to that function in a
    specified keymap.
    
r.  `disown' now has `-a' and `-r' options, to limit operation to all jobs
    and running jobs, respectively.

s.  The `shopt' `-p' option now causes output to be displayed in a reusable
    format.
    
t.  `test' has a new `-N' option, which returns true if the filename argument
    has been modified since it was last accessed.

u.  `umask' now has a `-p' option to print output in a reusable format.
    
v.  A new escape sequence, `\xNNN', has been added to the `echo -e' and $'...'
    translation code.  It expands to the character whose ascii code is NNN
    in hexadecimal.
    
w.  The prompt string expansion code has a new `\r' escape sequence.

x.  The shell may now be cross-compiled for the CYGWIN32 environment on
    a Unix machine.

2. New Features in Readline

a.  There is now an option for `iterative' yank-last-arg handline, so a user
    can keep entering `M-.', yanking the last argument of successive history
    lines.

b.  New variable, `print-completions-horizontally', which causes completion
    matches to be displayed across the screen (like `ls -x') rather than up
    and down the screen (like `ls').

c.  New variable, `completion-ignore-case', which causes filename completion
    and matching to be performed case-insensitively.

d.  There is a new bindable command, `magic-space', which causes history
    expansion to be performed on the current readline buffer and a space to
    be inserted into the result.

e.  There is a new bindable command, `menu-complete', which enables tcsh-like
    menu completion (successive executions of menu-complete insert a single
    completion match, cycling through the list of possible completions).

f.  There is a new bindable command, `paste-from-clipboard', for use on Win32
    systems, to insert the text from the Win32 clipboard into the editing
    buffer.

g.  The key sequence translation code now understands printf-style backslash
    escape sequences, including \NNN octal escapes.  These escape sequences
    may be used in key sequence definitions or macro values.

h.  An `$include' inputrc file parser directive has been added.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-2.01 since
the release of bash-2.0.  As always, the manual page (doc/bash.1) is the
place to look for complete descriptions.

1. New Features in Bash

a.  There is a new builtin array variable: GROUPS, the set of groups to which
    the user belongs.  This is used by the test suite.

2.  New Features in Readline

a.  If a key sequence bound to `universal-argument' is read while reading a
    numeric argument started with `universal-argument', it terminates the
    argument but is otherwise ignored.  This provides a way to insert multiple
    instances of a digit string, and is how GNU emacs does it.

-------------------------------------------------------------------------------
This is a terse description of the new features added to bash-2.0 since
the release of bash-1.14.7.  As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.

1.  New Features in Bash

a.  There is a new invocation option, -D, that dumps translatable strings
    in a script.

b.  The `long' invocation options must now be prefixed with `--'.

c.  New long invocation options:  --dump-strings, --help, --verbose

d.  The `nolineediting' invocation option was renamed to `noediting'.

e.  The `nobraceexpansion' and `quiet' long invocation options were removed.

f.  The `--help' and `--version' long options now work as the GNU coding
    standards specify.

g.  If invoked as `sh', bash now enters posix mode after reading the
    startup files, and reads and executes commands from the file named
    by $ENV if interactive (as POSIX.2 specifies).  A login shell invoked
    as `sh' reads $ENV after /etc/profile and ~/.profile.

h.  There is a new reserved word, `time', for timing pipelines, builtin
    commands, and shell functions.  It uses the value of the TIMEFORMAT
    variable as a format string describing how to print the timing
    statistics.

i.  The $'...' quoting syntax expands ANSI-C escapes in ... and leaves the
    result single-quoted.

j.  The $"..." quoting syntax performs locale-specific translation of ...
    and leaves the result double-quoted.

k.  LINENO now works correctly in functions.

l.  New variables: DIRSTACK, PIPESTATUS, BASH_VERSINFO, HOSTNAME, SHELLOPTS,
    MACHTYPE.  The first three are array variables.

m.  The BASH_VERSION and BASH_VERSINFO variables now include the shell's
    `release status' (alpha[N], beta[N], release).

n.  Some variables have been removed:  MAIL_WARNING, notify, history_control,
    command_oriented_history, glob_dot_filenames, allow_null_glob_expansion,
    nolinks, hostname_completion_file, noclobber, no_exit_on_failed_exec, and
    cdable_vars.  Most of them are now implemented with the new `shopt'
    builtin; others were already implemented by `set'.

o.  Bash now uses some new variables:  LC_ALL, LC_MESSAGES, LC_CTYPE,
    LC_COLLATE, LANG, GLOBIGNORE, HISTIGNORE.

p.  The shell now supports integer-indexed arrays of unlimited length,
    with a new compound assignment syntax and changes to the appropriate
    builtin commands (declare/typeset, read, readonly, etc.).  The array
    index may be an arithmetic expression.

q.  ${!var}: indirect variable expansion, equivalent to eval \${$var}.

r.  ${parameter:offset[:length]}: variable substring extraction.

s.  ${parameter/pattern[/[/]string]}: variable pattern substitution.

t.  The $[...] arithmetic expansion syntax is no longer supported, in
    favor of $((...)).

u.  Aliases can now be expanded in shell scripts with a shell option
    (shopt expand_aliases).

v.  History and history expansion can now be used in scripts with
    set -o history and set -H.

w.  All builtins now return an exit status of 2 for incorrect usage.

x.  Interactive shells resend SIGHUP to all running or stopped children
    if (and only if) they exit due to a SIGHUP.

y.  New prompting expansions: \a, \e, \H, \T, \@, \v, \V.

z.  Variable expansion in prompt strings is now controllable via a shell
    option (shopt promptvars).

aa. Bash now defaults to using command-oriented history.

bb. The history file ($HISTFILE) is now truncated to $HISTFILESIZE after
    being written.

cc. The POSIX.2 conditional arithmetic evaluation syntax (expr ? expr : expr)
    has been implemented.

dd. Each builtin now accepts `--' to signify the end of the options, except
    as documented (echo, etc.).

ee. All builtins use -p to display values in a re-readable format where
    appropriate, except as documented (echo, type, etc.).

ff. The `alias' builtin has a new -p option.

gg. Changes to the `bind' builtin:
        o has new options: -psPSVr.
        o the `-d' option was renamed to `-p'
        o the `-v' option now dumps variables; the old `-v' is now `-P'

hh. The `bye' synonym for `exit' was removed.

ii. The -L and -P options to `cd' and `pwd' have been documented.

jj. The `cd' builtin now does spelling correction on the directory name
    by default.  This is settable with a shell option (shopt cdspell).

kk. The `declare' builtin has new options: -a, -F, -p.

ll. The `dirs' builtin has new options: -c, -p, -v.

mm. The new `disown' builtin removes jobs from the shell's jobs table
    or inhibits the resending of SIGHUP when the shell receives a
    SIGHUP.

nn. The `echo' builtin has a new escape character: \e.

oo. The `enable' builtin can now load new builtins dynamically from shared
    objects on systems with the dlopen/dlsym interface.  There are a number
    of examples in the examples/loadables directory.  There are also
    new options: -d, -f, -s, -p.

pp. The `-all' option to `enable' was removed in favor of `-a'.

qq. The `exec' builtin has new options: -l, -c, -a.

rr. The `hash' builtin has a new option: -p.

ss. The `history' builtin has new options: -c, -p, -s.

tt. The `jobs' builtin has new options: -r, -s.

uu. The `kill' builtin has new options: -n signum, -l signame.

vv. The `pushd' and `popd' builtins have a new option: -n.

ww. The `read' builtin has new options: -p prompt, -e, -a.

xx. The `readonly' builtin has a new -a option, and the -n option was removed.

yy. Changes to the `set' builtin:
        o new options: -B, -o keyword, -o onecmd, -o history
        o options removed: -l, -d, -o nohash
        o options changed: +o, -h, -o hashall
        o now displays variables in a format that can be re-read as input

zz. The new `shopt' builtin controls shell optional behavior previously
    done by setting and unsetting certain shell variables.

aaa. The `test' builtin has new operators: -o option, s1 == s2, s1 < s2,
     and s1 > s2, where s1 and s2 are strings.

bbb. There is a new trap, DEBUG, executed after every simple command.

ccc. The `trap' builtin has a new -p option.

ddd. The `ulimit' builtin has a new -l option on 4.4BSD-based systems.

eee. The PS1, PS2, PATH, and IFS variables may now be unset.

fff. The restricted shell mode has been expanded and is now documented.

ggg. Security improvements:
        o functions are not imported from the environment if running setuid
          or with -p
        o no startup files are sourced if running setuid or with -p

hhh. The documentation has been overhauled:  the texinfo manual was
     expanded, and HTML versions of the man page and texinfo manual
     are included.

iii. Changes to Posix mode:
        o Command lookup now finds special builtins before shell functions.
        o Failure of a special builtin causes a non-interactive shell to
          exit.  Failures are defined in the POSIX.2 specification.
        o If the `cd' builtin finds a directory to change to using $CDPATH,
          the value assigned to PWD when `cd' completes does not contain
          any symbolic links.
        o A non-interactive shell exits if a variable assignment error
          occurs when no command name follows the assignment statements.
        o A non-interactive shell exits if the iteration variable in a
          `for' statement or the selection variable in a `select' statement
          is read-only or another variable assignment error occurs.
        o The `<>' redirection operator now opens a file for both stdin and
          stdout by default, not just when in posix mode.
        o Assignment statements preceding special builtins now persist in
          the shell's environment when the builtin completes.

     Posix mode is now completely POSIX.2-compliant (modulo bugs).  When
     invoked as sh, bash should be completely POSIX.2-compliant.

jjj. The default value of PS1 is now "\s-\v\$ ".

kkk. The ksh-like ((...)) arithmetic command syntax has been implemented.
     This is exactly equivalent to `let "..."'.

lll. Integer constants have been extended to base 64.

mmm. The `ulimit' builtin now sets both hard and soft limits and reports the
     soft limit by default.

2.  New Features in Readline

a.  New variables:  enable-keypad, input-meta (new name for meta-flag),
    mark-directories, visible-stats (now documented), disable-completion,
    comment-begin.

b.  New bindable commands:  kill-region, copy-region-as-kill,
    copy-backward-word, copy-forward-word, set-mark, exchange-point-and-mark,
    character-search, character-search-backward, insert-comment,
    glob-expand-word, glob-list-expansions, dump-variables, dump-macros.

c.  New emacs keybindings:  delete-horizontal-space (M-\),
    insert-completions (M-*), possible-completions (M-=).

d.  The history-search-backward and history-search-forward commands were
    modified to be the same as previous-line and next-line if point is at
    the start of the line.

e.  More file types are available for the visible-stats mode.

3.  Changes of interest in the Bash implementation

a.  There is a new autoconf-based configuration mechanism.

b.  More things have been moved from Posix mode to standard shell behavior.

c.  The trace output (set -x) now inserts quotes where necessary so it can
    be reused as input.

d.  There is a compile-time option for a system-wide interactive shell
    startup file (disabled by default).

e.  The YACC grammar is smaller and tighter, and all 66 shift-reduce
    conflicts are gone.  Several parsing bugs have been fixed.

f.  Builtin option parsing has been regularized (using internal_getopt()),
    with the exception of `echo', `type', and `set'.

g.  Builtins now return standard usage messages constructed from the
    `short doc' used by the help builtin.

h.  Completion now quotes using backslashes by default, but honors
    user-supplied quotes.

i.  The GNU libc malloc is available as a configure-time option.

j.  There are more internationalization features; bash uses gettext if
    it is available.  The $"..." translation syntax uses the current
    locale and gettext.

k.  There is better reporting of job termination when the shell is not
    interactive.

l.  The shell is somewhat more efficient: it uses a little less memory and
    makes fewer system calls.

4.  Changes of interest in the Readline implementation

a.  There is now support for readline `callback' functions.

b.  There is now support for user-supplied input, redisplay, and terminal
    preparation functions.

c.  Most of the shell-specific code in readline has been generalized or
    removed.

d.  Most of the annoying redisplay bugs have been fixed, notably the problems
    with incremental search and excessive redrawing when special characters
    appear in the prompt string.

e.  There are new library functions and variables available to application
    writers, most having to do with completion and quoting.

f.  The NEWLINE character (^J) is now treated as a search terminator by the
    incremental search functions.
-------------------------------------------------------------------------------

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