This article is an incomplete overview of changes to Bash over time. Not all changes are listed, just the ones most likely to be useful for normal scripting. The overviews are categorized by topic and ordered by version.
A useful starting point is the NEWS file in bash sources. If you have more detailed information, or historical information about Bash versions earlier than V2, feel free to mail me, or use the discussion below.
Status: 5.1 (alpha)
Note that the shopt builtin command first appeared 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 consensus with POSIX WG |
compat40 | 4.1-beta | |
lastpipe | 4.2-alpha | only works with job control disabled |
compat41 | 4.2-alpha | |
globasciiranges | 4.3-alpha | enable "character range globbing" to always act as if in C locale |
compat42 | 4.3-alpha | |
compat43 | 4.4-alpha | |
compat44 | 5.0-alpha | |
localvar_inherit | 5.0-alpha | local variables inherit preceeding scope values if they have the same name |
syslog_history | 5.0-alpha | send history lines to syslog (undocumented, default off) if syslog is supported |
assoc_expand_once | 5.0-alpha | expand associative array subscripts only one |
globasciiranges | 5.0-beta | New default: on (default may be configured at compile time) |
localvar_inherit | 5.0-beta | guard code against inheriting from an incompatible data type |
checkwinsize | 5.0-beta2 | New default: on |
shift_verbose | 5.0-beta2 | Default on when in POSIX mode |
| 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 |
For this topic, see also
| 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 arithmetic |
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 format; uses current time |
\uNNNN and \UNNNNNNNN escape sequences | 4.2-alpha | for: printf, echo -e, $'...' |
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 | check if a variable is set |
test/[/[[: -v | 4.2-alpha | support array syntax to check for elements |
test/[/[[: -N accepts nanoseconds | 5.1-alpha | |
test/[/[[: -v accepts positional parameters | 5.1-alpha |
| 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 | ksh93: only ;&. zsh and mksh: ;|. mksh: all 4, (;;& is undocumented Bash compatibility) |
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 |
help | help now searches exact topic-strings (i.e. help read won't find readonly anymore) | 4.3-alpha | |
return | accept negative values as return value (e.g. return -1 will show as (8 bit) 255 in the caller) | 4.3-alpha | |
exit | accept negative values as return value (e.g. return -1 will show as (8 bit) 255 in the caller) | 4.3-alpha | |
read | read skips NUL (ASCII Code 0) in input | 4.3-alpha | |
declare | new option -n/+n to support nameref variable type | 4.3-alpha | |
wait | new option -n to wait for the next background job to finish, returning its exit status. | 4.3-alpha | |
read | read checks first variable argument for validity before trying to read inout | 4.3-beta | |
help | attempts substring matching (as it did through bash-4.2) if exact string matching fails | 4.3-beta2 | |
fc | interprets option -0 (zero) as the current command line | 4.3-beta2 | |
cd | new option -@ to browse a file's extended attributes (on systems that support O_XATTR) | 4.3-rc1 | |
kill | new option -L (upper case ell) to list signals like the normal lowercase option -l (compatiblity with some standalone kill commands) | 4.4-beta | |
mapfile | new option -d | 4.4-alpha | |
wait | new option -f | 5.0-alpha | |
history | option -d allows negative numbers to index from the end of the history list | 5.0-alpha | |
umask | allows modes greater than octal 777 | 5.0-alpha | |
times | honors current locale settings when printing decimal points | 5.0-alpha | |
kill | New options -n SIGNUMBER and -s SIGNAME | 5.0-beta2 | The kill builtin command |
select | Support for an empty wordlist following in | 5.0-beta2 | |
read | Option -e (use ReadLine to obtain input) now works with arbitrary file descriptors (given by -u option) | 5.1-alpha | |
trap | -p option prints signals with SIG_DFL/SIG_IGN on shell start (POSIX mode) | 5.1-alpha | |
unset | automatically tries to unset a function if the given name is an invalid variable name | 5.1-aplha | |
wait | option -n now accepts a list of jobs | 5.1-alpha | |
wait | new option -p NAME to store PID/JobID (useful when waiting for a list of jobs) | 5.1-alpha | |
local | new option -p to print local variables in the current scope | 5.1-alpha | |
ulimit | new option -R to get/set RLIMIT_RTTIME resource | 5.1-alpha |
| 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 | Added to mksh R41. |
PROMPT_DIRTRIM | 4.0 | |
BASH_XTRACEFD | 4.1-alpha | |
BASHOPTS | 4.1-alpha | |
FUNCNEST | 4.2-alpha | |
HISTSIZE | 4.3-alpha | can be set to negative values for unlimited history length |
HISTFILESIZE | 4.3-alpha | can be set to negative values for unlimit history file size |
CHILD_MAX | 4.3-alpha | max. number of exit status of children the shell remembers |
BASH_COMPAT | 4.3-alpha | set shell compatiblity levels |
EPOCHSECONDS | 5.0-alpha | expands to the time in seconds since Unix epoch |
EPOCHREALTIME | 5.0-alpha | expands to the time in seconds since Unix epoch with microsecond granularity |
BASH_ARGV0 | 5.0-alpha | get/set $0 |
PATH | 5.0-alpha | Possibility to set a static path for use in a restricted shell (at compile time) |
HISTSIZE | 5.0-beta | Default can now be set at runtime |
SRANDOM | 5.1-alpha | New random generator for 32bit numbers (using various methods in the backend) |
ARGV0 | 5.1-alpha | Respected when set in initial shell environment, then initially used to set $0 |
BASH_REMATCH | 5.1-alpha | Not readonly anymore |
PROMPT_COMMANDS | 5.1-alpha | New array variable. List of commands to be executed like PROMPT_COMMAND |
SECONDS | 5.1-alpha | Assignment using arithmetic expressions (is nominally an integer variabnle) |
RANDOM | 5.1-alpha | Assignment using arithmetic expressions (is nominally an integer variabnle) |
LINENO | 5.1-alpha | Not an integer variabe |
For this topic, see also
| 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 no longer allowed, changes the way 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 | 4.1-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 | Substrings only for Bash and ksh93. Works also for argument expansions in zsh. ksh93 can use ${arr[n..-m]}. |
Word expansions like ${foo##bar} understand indirect variable references | 4.3-beta | |
| Transformations | 4.4 | |
| Process substitution now works in POSIX mode | 5.1-alpha | |
New transformations: U, u, L | 5.1-alpha | Case-transformation |
New transformation: K | 5.1-alpha | Display associative arrays as key/value pairs |
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 |
For this topic, see also
| 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 | ksh93 |
{varname[idx]} fd allocation accepts array subscripts and special-meaning variables | 4.3-alpha | ksh93 |
| Feature or change description | Appeared in Bash version | See also/remarks |
|---|---|---|
DEBUG trap | 2.0 | |
ERR trap | 2.05a | KSH93 |
| Support for multibyte characters: Unicode / UTF8 | 2.05b | |
RETURN trap | 3.0 | ksh93 EXIT trap evaluates in caller scope (for function name {). Bash RETURN in same scope. |
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 | |
| Assignment to negative array indices | 4.3-alpha | ksh93, zsh |
declare/typeset -n | 4.3-alpha | Support for nameref variable type, a variable referencing another one by name |
shells started to run process substitutions now run any trap set on EXIT | 4.3-beta | |
process substitution does not inherit the v flag | 5.0-alpha | |
ERR trap | 5.0-alpha | Reports more reliable line numbers |
| Variable assignment | 5.0-beta | Assignments preceeding a special builtin that chages variable attributes are not propagated back unless compatiblity mode is 44 or lower |