36 KiB
Bash changes
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)
Shell options
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
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
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(r) length specifiers j, t and z 2.05a-alpha1 ISO C99
POSIX(r) 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, $'...'
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 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
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 shopt
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 read
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 read
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 read
caller new 3.0 caller
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 kill
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
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 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
Quoting, expansions, substitutions and related
For this topic, see also
- pe.
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(r) 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
Arithmetic
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
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
Misc
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