Bash changes

This article is an incomplete overview of changes to Bash over the time. Not all changes are listed, just the ones interesting for normal scripting. The overviews are categorized by topic and inside, ordered by version.

If you have more detailed information, and also information about historical Bash versions below V2, feel free to mail me or use the discussion below the page.

Status: 4.2

Shell options

Note that the shopt builtin command appeared first in Bash 2.0.

For this topic, see also

Feature or change description	Appeared in Bash version	See also/remarks
`posix` (for `set -o`)	1.14.0
`hostcomplete`	2.0-alpha3
`expand_aliases`	2.0
`huponexit`	2.02-alpha1
`nocaseglob`	2.02-alpha1
`extglob`	2.02-alpha1	together with extended globbing, KSH88
`restricted_shell`	2.03-alpha
`xpg_echo`	2.04-beta1
`progcomp`	2.04-alpha1
`no_empty_command_completion`	2.04
`login_shell`	2.05a-alpha1
`nolog` (for `set -o`)	2.05a
`gnu_errfmt`	3.0-alpha
`force_fignore`	3.0-alpha
`failglob`	3.0-alpha
`extquote`	3.0-alpha	unsure – verify!
`extdebug`	3.0-alpha
`pipefail` (for `set -o`)	3.0
`functrace` (for `set -o`)	3.0
`errtrace` (for `set -o`)	3.0
`nocasematch`	3.1-alpha1
`dirspell`	4.0-alpha
`globstar`	4.0-alpha
`checkjobs`	4.0-alpha
`autocd`	4.0-alpha
`set -e` effects more intuitive	4.0	not directly specified by POSIX, but in consense with POSIX WG
`compat40`	4.1-beta
`lastpipe`	4.2-alpha	only works with job control disabled
`compat41`	4.2-alpha

Builtin commands and keywords

General (all/many builtins)

Feature or change description	Appeared in Bash version	See also/remarks
generally return 2 on usage error	2.0
generally accept `--` (end of options)	2.0
(where applicable) implement a `-p` option to produce reusable output	2.0	`shopt` and `umask` builtins were fixed to support that in 2.02

printf

For this topic, see also

The printf command

Feature or change description	Appeared in Bash version	See also/remarks
new `printf` command	2.02-alpha1
respects `0..` and `0x..` prefixed numbers	2.04-beta1	consistency with arithmetics
POSIX® length specifiers `j`, `t` and `z`	2.05a-alpha1	ISO C99
POSIX® flag `'`	2.05a-alpha1
conversion `a` and `A`	2.05a-rc1	if provided by the underlying printf(3)
conversion `F`	2.05a-rc1
conversion `n`	2.05a-rc1
new option `-v`	3.1-alpha1
escape sequences `\"` and `\?`	3.0-beta1
modified option `-v` to assign to individual array elements	4.1-alpha
conversion `(…)T`	4.2-alpha	support stftime(3) date/time formats
`\uNNNN` and `\UNNNNNNNN` escape sequences	4.2-alpha	for: `printf`, `echo -e`, `$'...'`

Conditional expressions and test command

For this topic, see also

Feature or change description	Appeared in Bash version	See also/remarks
`test`: `-o`, `==`, `<` and `>`	2.0
`test`: `-N`	2.02
`[[...]]`: new	2.02-alpha1	KSH93
`[[...]]`: regex support (`=~`)	3.0-alpha
`[[...]]`: quotable right-hand-side of `=~` forces string matching	3.2-alpha	for consistency with pattern matching
`[[...]]`: `<` and `>` operators respect locale	4.1-alpha	for consistency, since 4.1-beta: ensure you have set compatiblity to >4.0 (default)
`test`/`[`/`[[`: `-v`	4.2-alpha

Other builtins and keywords

Builtin	Feature or change description	Appeared in Bash version	See also/remarks
`bashbug`	new	1.14.0
`select`	new	1.14.0
`disown`	new	2.0
`shopt`	new	2.0	The shopt builtin command
`declare`	new options `-a` and `-F`	2.0
`enable`	builtin has basic plugin support (dlopen)	2.0
`exec`	options `-l`, `-c` and `-a`	2.0
`read`	options `-p`, `-e` and `-a`	2.0	The read builtin command
`readonly`	option `-a`	2.0	Arrays
`time`	new keyword	2.0
`shopt`	`-p` (reusable output)	2.02
`umask`	`-p` (reusable output)	2.02
`complete`	new	2.04-devel	for and together with support for programmable completion
`compgen`	new	2.04-devel	for and together with support for programmable completion
`read`	options `-t`, `-n`, `-d`, `-s`	2.04-devel	The read builtin command
`for ((...;...;...))`	new	2.04-devel	KSH93
`set`	print shell functions in a format reusable as input	2.05-beta1
`for`	allow an empty word list	2.05a-alpha1
`read`	new option `-u`	2.05b-alpha1	The read builtin command
`caller`	new	3.0	The caller builtin command
`coproc`	new	4.0-alpha
`declare`	new options `-l` and `-u`	4.0-alpha	together with case-changing expansion forms
`case`	new action list terminators `;;& and` ;&	4.0-alpha	`KSH`, at least `;&`
`read`	changed `-t` (fractional seconds)	4.0-alpha
`mapfile`	new	4.0-alpha
`read`	new option `-i`	4.0-alpha
`compopt`	new	4.0-alpha
`read`	modified option `-t` to test for data	4.0-beta
`read`	new option `-N`	4.1-alpha
`mapfile`	changed behaviour regarding history spamming	4.1-alpha
`declare`	new option `-g`	4.2-alpha
`mapfile`	calls the callback with an additional argument: The line (data)	4.2-alpha
`cd`	new option `-e`	4.2-alpha
`echo`	`\uNNNN` and `\UNNNNNNNN` escape sequences	4.2-alpha	for: `printf`, `echo -e`, `$'...'`
`exec`	option `-a` to give a `argv[0]` string	4.2-alpha
`time`	allowed as a command by itself to display timing values of the shell and its children	4.2-alpha	POSIX change

Builtin variables

Feature or change description	Appeared in Bash version	See also
`HISTCMD`	1.14.0	interactive usage
`PS1`, `PS2`, `PATH`, and `IFS` are unsettable	2.0
`DIRSTACK` array variable	2.0
`PIPESTATUS` array variable	2.0
`BASH_VERSINFO` array variable	2.0
`HOSTNAME`	2.0
`SHELLOPTS`	2.0
`MACHTYPE`	2.0
`GLOBIGNORE`	2.0
`HISTIGNORE`	2.0
respect `LC_ALL`	2.0
respect `LC_MESSAGES`	2.0
respect `LC_CTYPE`	2.0
respect `LC_COLLATE`	2.0
respect `LANG`	2.0
`GROUPS` array variable	2.01
`GROUPS` unsettable/takes (discarded) assignments	2.04
`FUNCNAME`	2.04
respect `LC_NUMERIC`	2.04
`TMOUT`	2.05b
`BASH_REMATCH`	3.0	together with regex support in `[[...]]`
`BASH_ARGC`	3.0	debugger support
`BASH_ARGV`	3.0	debugger support
`BASH_SOURCE`	3.0	debugger support
`BASH_LINENO`	3.0	debugger support
`BASH_SUBSHELL`	3.0	debugger support
`BASH_EXECUTION_STRING`	3.0	debugger support
`BASH_COMMAND`	3.0	debugger support
`HISTTIMEFORMAT`	3.0
`COMP_WORDBREAKS`	3.0
respect `LC_TIME`	3.1
`BASHPID`	4.0-alpha
`PROMPT_DIRTRIM`	4.0
`BASH_XTRACEFD`	4.1-alpha
`BASHOPTS`	4.1-alpha
`FUNCNEST`	4.2-alpha

Quoting, expansions, substitutions and related

For this topic, see also

Parameter expansion.

Feature or change description	Appeared in Bash version	Remarks
Support for integer-indexed arrays	2.0	relevant builtins also got array support
`${PARAMETER//PATTERN/REPLACEMENT}`	2.0
`${PARAMETER:OFFSET:LENGTH}`	2.0
`${!PARAMETER}` (indirection)	2.0
`$"..."` (localized strings)	2.0
`$'...'` (ANSI-C-like strings)	2.0
`\xNNN` in `$'...'` (and `echo -e`)	2.02-alpha1
`$(< FILENAME)` (file content)	2.02-alpha1
globbing (`fnmatch()`) capable of POSIX® character classes etc.	2.02-alpha1
extended globbing	2.02-alpha1	KSH88
globbing inside array mass-assignment: `ARRAY=(*.txt)`	2.03-alpha
`$'...\'...'` escaped single quote inside ANSI-C-like strings	2.04-devel	KSH93
`${!PREFIX*}` (parameter name expansion)	2.04	KSH93
`$'...'` expands `\cx` (Control-x)	2.05b
`[:class:]` syntax for pattern matching	2.05b	KSH93
`${!ARRAY[@]}` (array index expansion)	3.0-alpha	KSH93
`{x..y}` (range brace expansion)	3.0-alpha
`$'...'` expands `\xNNN` (Hexdigits)	3.0
`+=` operator for arrays and strings	3.1-alpha1
`${PARAMETER//PATTERN/REPLACEMENT}` behaviour changed	3.2-alpha	anchoring for global substitution is not allowed anymore, changes how old syntax may work
`${@:0:x}` includes `$0`	4.0-alpha
Support for associative arrays	4.0-alpha	relevant builtins also got associative array support
case modification operators for expansions	4.0-alpha
`{0x..0y}` (zeropadding brace expansion)	4.0-alpha
numerically indexed arrays can be accessed (on expansion time) from the end using negative indexes	4.2-alpha
`\uNNNN` and `\uNNNNNNNN` in `$'...'`	4.2-alpha	for: `printf`, `echo -e`, `$'...'`
`${PARAMETER:OFFSET:LENGTH}`: Negative `LENGTH` values are used as offset from the end of the string	4.2-alpha

Arithmetics

For this topic, see also

Feature or change description	Appeared in Bash version	Remarks
`((...))`	2.0-beta2	KSH93
ternary operator	2.0
base 64 integer constants	2.0	the max. base before is unknown. Anybody?
deprecated `$[…]` in favor of `$((...))`	2.0
exponentiaition operator (`**`)	2.02-alpha1
comma operator `EXPR,EXPR`	2.04-devel
pre- and postfix operators	2.04-devel

Redirection and related

For this topic, see also

Redirection

Feature or change description	Appeared in Bash version	Remarks
socket redirection (`/dev/tcp/`, `/dev/udp/`)	2.04-devel
OS/filesystem-independent support for `/dev/std(in\|out\|err)` and `/dev/fd/*`	2.04
socket redirection accepts service names	2.05
`[n]<&word-` and `[n]>&word-` FD-duplicate/closing	2.05b-alpha1	KSH93
Here strings: `<<< WORD`	2.05b-alpha1
`\|&` (synonym for `2>&1 \|`)	4.0-alpha
`&>>` (equiv. to `>>FILE 2>&1`)	4.0-alpha
`{varname}` style automatic file descriptor allocation	4.1-alpha

Misc

Feature or change description	Appeared in Bash version	See also/remarks
`DEBUG` trap	2.0
`ERR` trap	2.05a	KSH93
better handling of multibyte characters	2.05b
`RETURN` trap	3.0
`command_not_found_handle` handler function	4.0-alpha
official introduction of switchable "compatiblity levels"	4.0-alpha	`compat31` was introduced in a 3.2 version, mainly because of the incompatibilities that were introduced by the changed `=~` operator
`[[...]]` and `((...))` conditional commands are subject to the `ERR` trap and `set -e` feature	4.1-alpha
ACL support for file status checks	4.1-alpha