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# 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](https://github.com/bminor/bash/blob/master/NEWS) 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
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- [shell_options](../internals/shell_options.md)
- [set](../commands/builtin/set.md)
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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
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- [printf](../commands/builtin/printf.md)
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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
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- [conditional_expression](../syntax/ccmd/conditional_expression.md)
- [classictest](../commands/classictest.md)
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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
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`shopt` new 2.0 [shopt](../commands/builtin/shopt.md)
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`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
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`read` options `-p`, `-e` and `-a` 2.0 [read](../commands/builtin/read.md)
`readonly` option `-a` 2.0 [arrays](../syntax/arrays.md)
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`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
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`read` options `-t`, `-n`, `-d`, `-s` 2.04-devel [read](../commands/builtin/read.md)
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`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
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`read` new option `-u` 2.05b-alpha1 [read](../commands/builtin/read.md)
`caller` new 3.0 [caller](../commands/builtin/caller.md)
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`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
format(docs): remove escaped t's
2024-03-30 20:09:26 +01:00
`help` `help` now searches exact topic-strings (i.e. `help read` won't find `readonly` anymore) 4.3-alpha
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`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
format(docs): remove escaped 's character pairs
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`cd` new option `-@` to browse a file's extended attributes (on systems that support `O_XATTR`) 4.3-rc1
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`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
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`kill` New options `-n SIGNUMBER` and `-s SIGNAME` 5.0-beta2 [kill](../commands/builtin/kill.md)
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`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
Fix hyperlinks of markdown pages at depth 2 find docs/ -depth 2 -name '*.md' | xargs grep '(.*/' -l | \ xargs -I{} \ sed -i '' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)\(.md\)\{0\})%(../\1/\2.md)%g' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)#\([0-9a-zA-Z_-][0-9a-zA-Z_-]*\))%(../\1/\2.md#\3)%g' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)\(.md\)\{0\})%(../\1/\2/\3.md)%g' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)#\([0-9a-zA-Z_-][0-9a-zA-Z_-]*\))%(../\1/\2/\3.md#\4)%g' \ -e 's%](\([^:.>)#][^:.>)#]*\))%](../\1.md)%g' \ -e 's%](\([^:.>)#][^:.>)#]*\)#\([^:.>)#][^:.>)#]*\))%](../\1.md#\2)%g' \ {} Related to https://github.com/flokoe/bash-hackers-wiki/issues/10
2024-01-29 02:01:50 +01:00
- [pe](../syntax/pe.md).
Convert scripting pages to Markdown
2023-07-05 11:31:29 +02:00
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
Fix hyperlinks of markdown pages at depth 2 find docs/ -depth 2 -name '*.md' | xargs grep '(.*/' -l | \ xargs -I{} \ sed -i '' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)\(.md\)\{0\})%(../\1/\2.md)%g' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)#\([0-9a-zA-Z_-][0-9a-zA-Z_-]*\))%(../\1/\2.md#\3)%g' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)\(.md\)\{0\})%(../\1/\2/\3.md)%g' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)#\([0-9a-zA-Z_-][0-9a-zA-Z_-]*\))%(../\1/\2/\3.md#\4)%g' \ -e 's%](\([^:.>)#][^:.>)#]*\))%](../\1.md)%g' \ -e 's%](\([^:.>)#][^:.>)#]*\)#\([^:.>)#][^:.>)#]*\))%](../\1.md#\2)%g' \ {} Related to https://github.com/flokoe/bash-hackers-wiki/issues/10
2024-01-29 02:01:50 +01:00
- [arith_expr](../syntax/arith_expr.md)
- [arith](../syntax/expansion/arith.md)
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2023-07-05 11:31:29 +02:00
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
Fix hyperlinks of markdown pages at depth 2 find docs/ -depth 2 -name '*.md' | xargs grep '(.*/' -l | \ xargs -I{} \ sed -i '' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)\(.md\)\{0\})%(../\1/\2.md)%g' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)#\([0-9a-zA-Z_-][0-9a-zA-Z_-]*\))%(../\1/\2.md#\3)%g' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)\(.md\)\{0\})%(../\1/\2/\3.md)%g' \ -e 's%(/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)/\([^/#).][^/#).]*\)#\([0-9a-zA-Z_-][0-9a-zA-Z_-]*\))%(../\1/\2/\3.md#\4)%g' \ -e 's%](\([^:.>)#][^:.>)#]*\))%](../\1.md)%g' \ -e 's%](\([^:.>)#][^:.>)#]*\)#\([^:.>)#][^:.>)#]*\))%](../\1.md#\2)%g' \ {} Related to https://github.com/flokoe/bash-hackers-wiki/issues/10
2024-01-29 02:01:50 +01:00
- [redirection](../syntax/redirection.md)
Convert scripting pages to Markdown
2023-07-05 11:31:29 +02:00
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
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