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bash-hackers-wiki/docs/syntax/shellvars.md
Hanson Char e966036f05 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
2024-01-28 17:26:10 -08:00

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# Special parameters and shell variables
## Special Parameters
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
parameter character expansion description
----------- ------------------ -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
`*` asterisk The positional parameters starting from the first. When used inside doublequotes (see [quoting](../syntax/quoting.md)), like `"$*"`, it expands to all positional parameters *as one word*, delimited by the first character of the `IFS` variable (a space in this example): `"$1 $2 $3 $4"`.\
If `IFS` is unset, the delimiter used will be always a space, if `IFS` is NULL, the delimiter will be nothing, which effectively concatenates all the positional parameters without any delimiter.\
When used unquoted, it will just expand to the strings, one by one, not preserving the word boundaries (i.e. word splitting will split the text again, if it contains `IFS` characters.\
See also the [scripting article about handling positional parameters](../scripting/posparams.md).
`@` at-sign The positional parameters starting from the first. When used inside doublequotes (see [quoting](../syntax/quoting.md)), like `"$@"`, it expands all positional parameters *as separate words*: `"$1" "$2" "$3" "$4"`\
Without doublequotes, the behaviour is like the one of `*` without doublequotes.\
See also the [scripting article about handling positional parameters](../scripting/posparams.md).
`#` hash mark Number of positional parameters (decimal)\
See also the [scripting article about handling positional parameters](../scripting/posparams.md).
`?` question mark Status of the most recently executed foreground-pipeline (exit/return code)
`-` dash Current option flags set by the shell itself, on invocation, or using the [set builtin command](../commands/builtin/set.md). It\'s just a set of characters, like `himB` for `h`, `i`, `m` and `B`.
`$` dollar-sign The process ID (PID) of the shell. In an [explicit subshell](../syntax/ccmd/grouping_subshell.md) it expands to the PID of the current \"main shell\", not the subshell. This is different from `$BASHPID`!
`!` exclamation mark The process ID (PID) of the most recently executed background pipeline (like started with `command &`)
`0` zero The name of the shell or the shell script (filename). Set by the shell itself.\
If Bash is started with a filename to execute (script), it\'s set to this filename. If started with the `-c <CMDLINE>` option (commandline given as argument), then `$0` will be the first argument after the given `<CMDLINE>`. Otherwise, it is set to the string given on invocation for `argv[0]`.\
Unlike popular belief, `$0` is *not a positional parameter*.
`_` underscore A kind of catch-all parameter. Directly after shell invocation, it\'s set to the filename used to invoke Bash, or the absolute or relative path to the script, just like `$0` would show it. Subsequently, expands to the last argument to the previous command. Placed into the environment when executing commands, and set to the full pathname of these commands. When checking mail, this parameter holds the name of the mail file currently being checked.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
## Shell Variables
### BASH
Variable: `BASH` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
Expands to the full file name used to invoke the current instance of
Bash.
### BASHOPTS
Variable: `BASHOPTS` Since: 4.1-alpha
-------------- ----------------- ------------ -----------
Type: normal variable Read-only: yes
Set by Bash: yes Default: n/a
A colon-separated list of enabled shell options.
Each word in the list is a valid argument for the `-s` option to the
[shopt builtin command](../commands/builtin/shopt.md). The options appearing
in `BASHOPTS` are those reported as on by `shopt`. If this variable is
in the environment when Bash starts up, each shell option in the list
will be enabled before reading any startup files.
Example content:
cmdhist:expand_aliases:extquote:force_fignore:hostcomplete:interactive_comments:progcomp:promptvars:sourcepath
This variable is read-only.
### BASHPID
Variable: `BASHPID` Since: 4.0-alpha
-------------- ------------------ ------------ -----------
Type: integer variable Read-only: yes
Set by Bash: yes Default: n/a
Always expands to the process ID of the current Bash process. This
differs from the special parameter `$` under certain circumstances, such
as subshells that do not require Bash to be re-initialized.
### BASH_ALIASES
Variable: `BASH_ALIASES` Since: unknown
-------------- ------------------- ------------ ---------
Type: associative array Read-only: no
Set by Bash: yes Default: n/a
An associative array variable whose members correspond to the internal
list of aliases as maintained by the alias builtin. Elements added to
this array appear in the alias list; unsetting array elements cause
aliases to be removed from the alias list.
The associative key is the name of the alias as used with the [alias
builtin command](../commands/builtin/alias.md).
### BASH_ARGC
Variable: `BASH_ARGC` Since: 3.0
-------------- --------------------------------- ------------ -----
Type: integer indexed array Read-only: no
Set by Bash: only in extended debugging mode Default: n/a
An array variable whose values are the number of parameters in each
frame of the current Bash execution call stack.
The number of parameters to the current subroutine (shell function or
script executed with [`.` or `source` builtin
command](../commands/builtin/source.md)) is at the top of the stack. When a
subroutine is executed, the number of parameters passed is pushed onto
`BASH_ARGC`.
### BASH_ARGV
Variable: `BASH_ARGV` Since: 3.0
-------------- --------------------------------- ------------ -----
Type: integer indexed array Read-only: no
Set by Bash: only in extended debugging mode Default: n/a
An array variable containing all of the parameters in the current Bash
execution call stack.
The final parameter of the last subroutine call is at the top of the
stack; the first parameter of the initial call is at the bottom. When a
subroutine is executed, the parameters supplied are pushed onto
`BASH_ARGV`.
### BASH_ARGV0
Variable: `BASH_ARGV0` Since: 5.0-alpha
-------------- -------------- ------------ --------------
Type: string Read-only: no
Set by Bash: yes Default: same as `$0`
Expands to the name of the shell or shell script - as the special
parameter `$0` does. Assignments to `BASH_ARGV0` causes the value to be
assigned to `$0`.
If this parameter is unset, it loses its special properties, even if
subsequently reset.
### BASH_CMDS
Variable: `BASH_CMDS` Since: unknown
-------------- ------------------- ------------ ---------
Type: associative array Read-only: no
Set by Bash: yes Default: n/a
An associative array variable whose members correspond to the internal
hash table of commands as maintained by the [hash builtin
command](../commands/builtin/hash.md). Elements added to this array appear in
the hash table; unsetting array elements cause commands to be removed
from the hash table.
The associative key is the name of the command as used with the[hash
builtin command](../commands/builtin/hash.md).
### BASH_COMMAND
Variable: `BASH_COMMAND` Since: 3.0
-------------- ----------------- ------------ -----
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
The command currently being executed or about to be executed, unless the
shell is executing a command as the result of a trap, in which case it
is the command executing at the time of the trap.
### BASH_COMPAT
Variable: `BASH_COMPAT` Since: 4.3-alpha
-------------- ----------------- ------------ -----------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
The value is used to set the shell\'s compatibility level. The value may
be a decimal number (e.g., `4.2`) or an integer (e.g., `42`)
corresponding to the desired compatibility level. If `BASH_COMPAT` is
unset or set to the empty string, the compatibility level is set to the
default for the current version. If `BASH_COMPAT` is set to a value that
is not one of the valid compatibility levels, the shell prints an error
message and sets the compatibility level to the default for the current
version. The valid compatibility levels correspond to the compatibility
options accepted by the shopt builtin. The current version is also a
valid value.
### BASH_EXECUTION_STRING
Variable: `BASH_EXECUTION_STRING` Since: 3.0
-------------- ------------------------- ------------ -----
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
The command argument to the `-c` invocation option.
### BASH_LINENO
Variable: `BASH_LINENO` Since: 3.0
-------------- ----------------------- ------------ -----
Type: integer indexed array Read-only: no
Set by Bash: yes Default: n/a
An array variable whose members are the line numbers in source files
corresponding to each member of `FUNCNAME`.
`${BASH_LINENO[$i]}` is the line number in the source file where
`${FUNCNAME[$ifP]}` was called. The corresponding source file name is
`${BASH_SOURCE[$i]}`. Use `LINENO` to obtain the current line number.
### BASH_REMATCH
Variable: `BASH_REMATCH` Since: 3.0
-------------- ----------------------- ------------ -----
Type: integer indexed array Read-only: no
Set by Bash: yes Default: n/a
An array variable whose members are assigned by the `=~` binary operator
to the `[[` conditional command.
The element with index 0 is the portion of the string matching the
entire regular expression. The element with index `n` is the portion of
the string matching the nth parenthesized subexpression.
Before Bash version 5.1-alpha this variable was readonly.
### BASH_SOURCE
Variable: `BASH_SOURCE` Since: 3.0
-------------- ----------------------- ------------ -----
Type: integer indexed array Read-only: no
Set by Bash: yes Default: n/a
An array variable whose members are the source filenames corresponding
to the elements in the `FUNCNAME` array variable.
### BASH_SUBSHELL
Variable: `BASH_SUBSHELL` Since: 3.0
-------------- ----------------- ------------ -----
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
Incremented by one each time a subshell or subshell environment is
spawned. The initial value is 0.
### BASH_VERSINFO
Variable: `BASH_VERSINFO` Since: 2.0
-------------- ----------------------- ------------ -----
Type: integer indexed array Read-only: yes
Set by Bash: yes Default: n/a
A readonly array variable whose members hold version information for
this instance of Bash. The values assigned to the array members are as
follows:
-------------------- ----------------------------------------
BASH_VERSINFO\[0\] The major version number (the release)
BASH_VERSINFO\[1\] The minor version number (the version)
BASH_VERSINFO\[2\] The patch level
BASH_VERSINFO\[3\] The build version
BASH_VERSINFO\[4\] The release status (e.g., beta1)
BASH_VERSINFO\[5\] The value of `MACHTYPE`
-------------------- ----------------------------------------
### BASH_VERSION
Variable: `BASH_VERSION` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
Expands to a string describing the version of this instance of Bash.
Since Bash 2.0 it includes the shell\'s \"release status\" (alpha\[N\],
beta\[N\], release).
### CHILD_MAX
Variable: `CHILD_MAX` Since: 4.3-alpha
-------------- ----------------- ------------ -----------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
Set the number of exited child status values for the shell to remember.
Bash will not allow this value to be decreased below a POSIX-mandated
minimum, and there is a maximum value (currently 8192) that this may not
exceed. The minimum value is system-dependent.
### COMP_CWORD
Variable: `COMP_CWORD` Since: unknown
-------------- --------------------------------------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: only for programmable completion facilities Default: n/a
An index into `COMP_WORDS` of the word containing the current cursor
position.
### COMP_KEY
Variable: `COMP_KEY` Since: unknown
-------------- --------------------------------------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: only for programmable completion facilities Default: n/a
The key (or final key of a key sequence) used to invoke the current
completion function.
### COMP_LINE
Variable: `COMP_LINE` Since: unknown
-------------- --------------------------------------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: only for programmable completion facilities Default: n/a
The current command line.
### COMP_POINT
Variable: `COMP_POINT` Since: unknown
-------------- --------------------------------------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: only for programmable completion facilities Default: n/a
The index of the current cursor position relative to the beginning of
the current command. If the current cursor position is at the end of the
current command, the value of this variable is equal to `${#COMP_LINE}`.
### COMP_TYPE
Variable: `COMP_TYPET` Since: unknown
-------------- --------------------------------------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: only for programmable completion facilities Default: n/a
Set to an integer value corresponding to the type of completion
attempted that caused a completion function to be called:
------- ---------------------------------------------------
`TAB` normal completion
`?` listing completions after successive tabs
`!` listing alternatives on partial word completion
`@` to list completions if the word is not unmodified
`%` for menu completion
------- ---------------------------------------------------
FIXME where are the integer values?
### COMP_WORDBREAKS
Variable: `COMP_WORDBREAKS` Since: unknown
-------------- ------------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
Reports the set of characters that the readline library treats as word
separators when performing word completion.
If this parameter is unset, it loses its special properties, even if it
is subsequently reset.
### COMP_WORDS
Variable: `COMP_WORDS` Since: unknown
-------------- --------------------------------------------- ------------ ---------
Type: integer indexed array Read-only: no
Set by Bash: only for programmable completion facilities Default: n/a
An array variable consisting of the individual words in the current
command line. The line is split into words as readline would split it,
using `COMP_WORDBREAKS` as described above.
### COPROC
Variable: `COPROC` Since: unknown
-------------- ----------------------- ------------ ---------
Type: integer indexed array Read-only: no
Set by Bash: yes Default: n/a
An array variable created to hold the file descriptors for output from
and input to an unnamed coprocess.
### DIRSTACK
Variable: `DIRSTACK` Since: unknown
-------------- ----------------------- ------------ ---------
Type: integer indexed array Read-only: no
Set by Bash: yes Default: n/a
An array variable containing the current contents of the directory
stack.
Directories appear in the stack in the order they are displayed by the
dirs builtin. Assigning to members of this array variable may be used to
modify directories already in the stack, but the pushd and popd builtins
must be used to add and remove directories.
Assignment to this variable will not change the current directory.
If this parameter is unset, it loses its special properties, even if it
is subsequently reset.
### EPOCHREALTIME
Variable: `EPOCHREALTIME` Since: 5.0-alpha
-------------- ------------------ ------------ -----------
Type: integer variable Read-only: no
Set by Bash: yes Default: n/a
Expands to the number of seconds since Unix expoch as a floating point
value with micro-second granularity.
Assignments to this parameter are ignored. If this parameter is unset,
it loses its special properties, even if it is subsequently reset.
### EPOCHSECONDS
Variable: `EPOCHSECONDS` Since: 5.0-alpha
-------------- ------------------ ------------ -----------
Type: integer variable Read-only: no
Set by Bash: yes Default: n/a
Expands to the number of seconds since Unix expoch.
Assignments to this parameter are ignored. If this parameter is unset,
it loses its special properties, even if it is subsequently reset.
### EUID
Variable: `EUID` Since: unknown
-------------- ------------------ ------------ ---------
Type: integer variable Read-only: yes
Set by Bash: yes Default: n/a
Expands to the effective user ID of the current user, initialized at
shell startup.
:!: Do not rely on this variable when security is a concern.
### FUNCNAME
Variable: `FUNCNAME` Since: 2.04
-------------- ----------------------------- ------------ ------
Type: integer indexed array Read-only: no
Set by Bash: only inside shell functions Default: n/a
An array variable containing the names of all shell functions currently
in the execution call stack.
The element with index 0 is the name of any currently-executing shell
function. The bottom-most element (the one with the highest index) is
\"main\".
This variable can be used with `BASH_LINENO` and `BASH_SOURCE`: Each
element of `FUNCNAME` has corresponding elements in `BASH_LINENO` and
`BASH_SOURCE` to describe the call stack. For instance,
`${FUNCNAME[$i]}` was called from the file `${BASH_SOURCE[$i+1]}` at
line number `${BASH_LINENO[$i]}`. The [caller builtin
command](../commands/builtin/caller.md) displays the current call stack using
this information.
This variable exists only when a shell function is executing.
Assignments to this parameter have no effect and return an error status.
If this parameter is unset, it loses its special properties, even if it
is subsequently reset.
### GROUPS
Variable: `GROUPS` Since: 2.01
-------------- ----------------------- ------------ ------
Type: integer indexed array Read-only: no
Set by Bash: yes Default: n/a
An array variable containing the list of groups of which the current
user is a member.
Assignments to this parameter have no effect and return an error status.
If this parameter is unset, it loses its special properties, even if it
is subsequently reset.
### HISTCMD
Variable: `HISTCMD` Since: 1.14.0
-------------- ------------------ ------------ --------
Type: integer variable Read-only: no
Set by Bash: yes Default: n/a
Expands to the history number (index in the history list) of the current
command.
If this parameter is unset, it loses its special properties, even if it
is subsequently reset.
### HOSTNAME
Variable: `HOSTNAME` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
Automatically set to the name of the current host.
### HOSTTYPE
Variable: `HOSTTYPE` Since: unknown
-------------- ----------------- ------------ ------------------
Type: normal variable Read-only: no
Set by Bash: yes Default: system-dependent
Automatically set to a string that uniquely describes the type of
machine on which Bash is executing.
Example content:
x86_64
### LINENO
Variable: `LINENO` Since: unknown
-------------- ------------------ ------------ ---------
Type: integer variable Read-only: no
Set by Bash: yes Default: n/a
Each time this parameter is referenced, the shell substitutes a decimal
number representing the current sequential line number (starting with 1)
within a script or function.
When not in a script or function, the value substituted is not
guaranteed to be meaningful.
If this parameter is unset, it loses its special properties, even if it
is subsequently reset.
### MACHTYPE
Variable: `MACHTYPE` Since: unknown
-------------- ----------------- ------------ ------------------
Type: normal variable Read-only: no
Set by Bash: yes Default: system-dependent
Automatically set to a string that fully describes the system type on
which Bash is executing, in the standard GNU \"cpu-company-system\"
format.
Example content:
x86_64-unknown-linux-gnu
### MAPFILE
Variable: `MAPFILE` Since: unknown
-------------- ----------------------- ------------ ---------
Type: integer indexed array Read-only: no
Set by Bash: yes Default: n/a
An array variable created to hold the text read by the [mapfile builtin
command](../commands/builtin/mapfile.md) when no variable name is supplied.
### OLDPWD
Variable: `OLDPWD` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
The previous working directory as set by the cd command.
### OPTARG
Variable: `OPTARG` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
The value of the last option argument processed by the [getopts builtin
command](../commands/builtin/getopts.md).
### OPTIND
Variable: `OPTIND` Since: unknown
-------------- ------------------ ------------ ---------
Type: integer variable Read-only: no
Set by Bash: yes Default: n/a
The index of the next argument to be processed by the [getopts builtin
command](../commands/builtin/getopts.md).
### OSTYPE
Variable: `OSTYPE` Since: unknown
-------------- ----------------- ------------ ------------------
Type: normal variable Read-only: no
Set by Bash: yes Default: system-dependent
Automatically set to a string that describes the operating system on
which Bash is executing.
Example content:
linux-gnu
### PIPESTATUS
Variable: `PIPESTATUS` Since: 2.0
-------------- ----------------------- ------------ -----
Type: integer indexed array Read-only: no
Set by Bash: yes Default: n/a
An array variable containing a list of exit status values from the
processes in the most-recently-executed foreground pipeline (which may
contain only a single command).
### PPID
Variable: `PPID` Since: unknown
-------------- ------------------ ------------ ---------
Type: integer variable Read-only: yes
Set by Bash: yes Default: n/a
The process ID of the shell\'s parent process.
### PWD
Variable: `PWD` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
The current working directory as set by the [cd builtin
command](../commands/builtin/cd.md).
### RANDOM
Variable: `RANDOM` Since: unknown
-------------- ------------------ ------------ ---------
Type: integer variable Read-only: no
Set by Bash: yes Default: n/a
Each time this parameter is referenced, a random integer between 0 and
32767 is generated. The sequence of random numbers may be initialized by
assigning a value to `RANDOM`.
If this parameter is unset, it loses its special properties, even if it
is subsequently reset.
### READLINE_LINE
Variable: `READLINE_LINE` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
The contents of the readline line buffer, for use with `bind -x`.
### READLINE_POINT
Variable: `READLINE_POINT` Since: unknown
-------------- ------------------ ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
The position of the insertion point in the readline line buffer, for use
with `bind -x`.
### REPLY
Variable: `REPLY` Since: unknown
-------------- ------------------------------------------------------------ ------------ ---------
Type: normal variable Read-only: no
Set by Bash: only by the [read builtin command](../commands/builtin/read.md) Default: n/a
Set to the line of input read by the [read builtin
command](../commands/builtin/read.md) when no arguments are supplied that
name target variables.
### SECONDS
Variable: `SECONDS` Since: unknown
-------------- ------------------ ------------ ---------
Type: integer variable Read-only: no
Set by Bash: yes Default: n/a
Each time this parameter is referenced, the number of seconds since
shell invocation is returned. If a value is assigned to SECONDS, the
value returned upon subsequent references is the number of seconds since
the assignment plus the value assigned.
If this parameter is unset, it loses its special properties, even if it
is subsequently reset.
### SHELLOPTS
Variable: `SHELLOPTS` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: yes
Set by Bash: yes Default: n/a
A colon-separated list of enabled shell options. Each word in the list
is a valid argument for the `-o` option to the [set builtin
command](../commands/builtin/set.md). The options appearing in `SHELLOPTS`
are those reported as on by `set -o`.
If this variable is in the environment when Bash starts up, each shell
option in the list will be enabled before reading any startup files.
### SHLVL
Variable: `SHLVL` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
Incremented by one each time an instance of Bash is started.
### UID
Variable: `UID` Since: unknown
-------------- ------------------ ------------ ---------
Type: integer variable Read-only: yes
Set by Bash: yes Default: n/a
Expands to the user ID of the current user, initialized at shell
startup.
:!: Do not rely on this variable when security is a concern.
### BASH_ENV
Variable: `BASH_ENV` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If this parameter is set when Bash is executing a shell script, its
value is interpreted as a filename containing commands to initialize the
shell, as in `~/.bashrc`. The value of `BASH_ENV` is subjected to
- [parameter expansion](../syntax/pe.md)
- [command substitution](../syntax/expansion/cmdsubst.md)
- [arithmetic expansion](../syntax/expansion/arith.md)
before being interpreted as a file name.
`PATH` is not used to search for the resultant file name.
### BASH_XTRACEFD
Variable: `BASH_XTRACEFD` Since: 4.1-alpha
-------------- ----------------- ------------ -----------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If set to an integer corresponding to a valid file descriptor, Bash will
write the trace output generated when `set -x` is enabled to that file
descriptor.
The file descriptor is closed when `BASH_XTRACEFD` is unset or assigned
a new value.
Unsetting `BASH_XTRACEFD` or assigning it the empty string causes the
trace output to be sent to the standard error. Note that setting
`BASH_XTRACEFD` to 2 (the standard error file descriptor) and then
unsetting it will result in the standard error being closed.
### CDPATH
Variable: `CDPATH` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
The search path for the [cd builtin command](../commands/builtin/cd.md).
This is a colon-separated list of directories in which the shell looks
for destination directories specified by the `cd` command.
Example content:
.:~:/usr
### COLUMNS
Variable: `COLUMNS` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: on `SIGWINCH` Default: n/a
Used by the select compound command to determine the terminal width when
printing selection lists. Automatically set upon receipt of a
`SIGWINCH`.
### COMPREPLY
Variable: `COMPREPLY` Since: unknown
-------------- ----------------------- ------------ ---------
Type: integer indexed array Read-only: no
Set by Bash: no Default: n/a
An array variable from which Bash reads the possible completions
generated by a shell function invoked by the programmable completion
facility.
### EMACS
Variable: `EMACS` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If Bash finds this variable in the environment when the shell starts
with value \"t\", it assumes that the shell is running in an Emacs shell
buffer and disables line editing.
### ENV
Variable: `ENV` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
Similar to `BASH_ENV`: Used when the shell is invoked in POSIX(r) mode.
### FCEDIT
Variable: `FCEDIT` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
The default editor for the [fc builtin command](../commands/builtin/fc.md).
### FIGNORE
Variable: `FIGNORE` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
A colon-separated list of suffixes to ignore when performing filename
completion. A filename whose suffix matches one of the entries in
`FIGNORE` is excluded from the list of matched filenames.
Example content:
.o:~
### FUNCNEST
Variable: `FUNCNEST` Since: 4.2-alpha
-------------- ----------------- ------------ -----------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If set to a numeric value greater than 0, defines a maximum function
nesting level. Function invocations that exceed this nesting level will
cause the current command to abort.
Negative values, 0 or non-numeric assignments have the effect as if
`FUNCNEST` was unset or empty: No nest control
### GLOBIGNORE
Variable: `GLOBIGNORE` Since: 2.0
-------------- ----------------- ------------ -----
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
A colon-separated list of patterns defining the set of filenames to be
ignored by pathname expansion. If a filename matched by a pathname
expansion pattern also matches one of the patterns in `GLOBIGNORE`, it
is removed from the list of matches.
### HISTCONTROL
Variable: `HISTCONTROL` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
A colon-separated list of values controlling how commands are saved on
the history list:
--------------- ------------------------------------------------------------------------------------------------------------
`ignorespace` lines which begin with a space character are not saved in the history list
`ignoredups` don\'t save lines matching the previous history entry
`ignoreboth` short for `ignorespace:ignoredups`
`erasedups` remove all previous lines matching the current line from the history list before the current line is saved
--------------- ------------------------------------------------------------------------------------------------------------
Any value not in the above list is ignored.
If `HISTCONTROL` is unset, or does not include a valid value, all lines
read by the shell parser are saved on the history list, subject to the
value of `HISTIGNORE`. The second and subsequent lines of a multi-line
compound command are not tested, and are added to the history regardless
of the value of `HISTCONTROL`.
### HISTFILE
Variable: `HISTFILE` Since: unknown
-------------- ----------------- ------------ ---------------------------
Type: normal variable Read-only: no
Set by Bash: if unset Default: \'\' \~/.bash_history\'\'
The name of the file in which command history is saved.
If unset, the command history is not saved when an interactive shell
exits.
### HISTFILESIZE
Variable: `HISTFILESIZE` Since: unknown
-------------- ----------------- ------------ ------------
Type: normal variable Read-only: no
Set by Bash: if unset Default: `HISTSIZE`
The maximum number of lines contained in the history file.
When this variable is assigned a value, the history file is truncated,
if necessary, by removing the oldest entries, to contain no more than
the given number of lines. If the given number of lines is 0 (zero), the
file is truncated to zero size. Non-numeric values and numeric values
less than zero inhibit truncation.
The history file is also truncated to this size after writing it when an
interactive shell exits.
### HISTIGNORE
Variable: `HISTIGNORE` Since: 2.0
-------------- ----------------- ------------ -----
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
A colon-separated list of patterns used to decide which command lines
should be saved on the history list. Each pattern is anchored at the
beginning of the line and must match the complete line (no implicit
\'\*\' is appended).
Each pattern is tested against the line after the checks specified by
`HISTCONTROL` are applied.
In addition to the normal shell pattern matching characters, \"&\"
matches the previous history line. \"&\" may be escaped using a
backslash; the backslash is removed before attempting a match.
The second and subsequent lines of a multi-line compound command are not
tested, and are added to the history regardless of the value of
`HISTIGNORE`.
### HISTSIZE
Variable: `HISTSIZE` Since: unknown
-------------- ----------------- ------------ -----------------------------------
Type: normal variable Read-only: no
Set by Bash: if unset Default: set at compile time (default 500)
The number of commands to remember in the command history.
If the number is set to 0 (zero), then the history list is disabled. If
the number is set to any negative number, then the history list is
unlimited.
### HISTTIMEFORMAT
Variable: `HISTTIMEFORMAT` Since: unknown
-------------- ------------------ ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If this variable is set and not null, its value is used as a format
string for `strftime(3)` to print the time stamp associated with each
history entry displayed by the history builtin.
If this variable is set, time stamps are written to the history file so
they may be preserved across shell sessions. This uses the history
comment character to distinguish timestamps from other history lines.
### HOME
Variable: `HOME` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
The home directory of the current user.
The default argument for the [cd builtin command](../commands/builtin/cd.md).
The value of this variable is also used when performing [tilde
expansion](../syntax/expansion/tilde.md).
### HOSTFILE
Variable: `HOSTFILE` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
Contains the name of a file in the same format as `/etc/hosts` that
should be read when the shell needs to complete a hostname.
The list of possible hostname completions may be changed while the shell
is running. the next time hostname completion is attempted after the
value is changed, Bash adds the contents of the new file to the existing
list.
If `HOSTFILE` is set, but has no value, or does not name a readable
file, Bash attempts to read `/etc/hosts` to obtain the list of possible
hostname completions.
When `HOSTFILE` is unset, the hostname list is cleared.
### IFS
Variable: `IFS` Since: unknown
-------------- ----------------- ------------ -------------------------
Type: normal variable Read-only: no
Set by Bash: no Default: `<space><tab><newline>`
The Internal Field Separator that is used for word splitting after
expansion and to split lines into words with the read builtin command.
### IGNOREEOF
Variable: `IGNOREEOF` Since: unknown
-------------- ----------------- ------------ -------------------
Type: normal variable Read-only: no
Set by Bash: no Default: 10 (when invalid)
Controls the action of an interactive shell on receipt of an `EOF`
character (e.g. by Ctrl-D) as the sole input.
If set, the value is the number of consecutive EOF characters which must
be typed as the first characters on an input line before Bash exits.
If the variable exists but does not have a numeric value, or has no
value, the default value is 10.
If it does not exist, `EOF` signifies the end of input to the shell.
### INPUTRC
Variable: `INPUTRC` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
The filename for the readline startup file, overriding the default of
`~/.inputrc`.
### LANG
Variable: `LANG` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
Used to determine the locale category for any category not specifically
selected with a variable starting with `LC_`.
### LC_ALL
Variable: `LC_ALL` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
This variable overrides the value of `LANG` and any other `LC_` variable
specifying a locale category.
### LC_COLLATE
Variable: `LC_COLLATE` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
This variable determines the collation order used when sorting the
results of pathname expansion, and determines the behavior of range
expressions, equivalence classes, and collating sequences within
pathname expansion and pattern matching.
### LC_CTYPE
Variable: `LC_CTYPE` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
This variable determines the interpretation of characters and the
behavior of character classes within pathname expansion and pattern
matching.
### LC_MESSAGES
Variable: `LC_MESSAGES` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
This variable determines the locale used to translate double- quoted
strings preceded by a `$`.
### LC_NUMERIC
Variable: `LC_NUMERIC` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
This variable determines the locale category used for number formatting.
### LINES
Variable: `LINES` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: on `SIGWINCH` Default: n/a
Used by the select compound command to determine the column length for
printing selection lists. Automatically set upon receipt of a
`SIGWINCH`.
### MAIL
Variable: `MAIL` Since: unknown
-------------- ----------------- ------------ ------------------
Type: normal variable Read-only: no
Set by Bash: no Default: system-dependent
If this parameter is set to a file or directory name and the `MAILPATH`
variable is not set, Bash informs the user of the arrival of mail in the
specified file or Maildir-format direc‐ tory.
### MAILCHECK
Variable: `MAILCHECK` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: 60
Specifies how often (in seconds) Bash checks for mail.
When it is time to check for mail, the shell does so before displaying
the primary prompt.
If this variable is unset, or set to a value that is not a number
greater than or equal to zero, the shell disables mail checking.
### MAILPATH
Variable: `MAILPATH` Since: unknown
-------------- ----------------- ------------ ------------------
Type: normal variable Read-only: no
Set by Bash: no Default: system-dependent
A colon-separated list of file names to be checked for mail.
The message to be printed when mail arrives in a particular file may be
specified by separating the file name from the message with a \'?\'
(question mark).
When used in the text of the message, `$_` expands to the name of the
current mailfile.
Example content:
/var/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"
### OPTERR
Variable: `OPTERR` Since: unknown
-------------- ----------------- ------------ --------------------
Type: normal variable Read-only: no
Set by Bash: yes Default: 1 (set on startup)
If set to the value 1, Bash displays error messages generated by the
[getopts builtin command](../commands/builtin/getopts.md).
`OPTERR` is initialized to 1 each time the shell is invoked or a shell
script is executed.
### PATH
Variable: `PATH` Since: unknown
-------------- ----------------- ------------ ----------------------------------------
Type: normal variable Read-only: no
Set by Bash: no Default: system-dependent (set on compile time)
The search path for commands. This is a colon-separated list of
directories in which the shell looks for commands.
A zero-length (null) directory name in the value of `PATH` indicates the
current directory.
A null directory name may appear as two adjacent colons, or as an
initial or trailing colon.
There can be a static path compiled in for use in a restricted shell.
### POSIXLY_CORRECT
Variable: `POSIXLY_CORRECT` Since: unknown
-------------- ------------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If this variable is in the environment when Bash starts, the shell
enters posix mode before reading the startup files, as if the `--posix`
invocation option had been supplied.
If it is set while the shell is running, Bash enables posix mode, as if
the command `set -o posix` had been executed.
### PROMPT_COMMAND
Variable: `PROMPT_COMMAND` Since: unknown
-------------- ------------------ ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If set, the value is executed as a command prior to issuing each primary
prompt.
### PROMPT_COMMANDS
Variable: `PROMPT_COMMANDS` Since: 5.1-alpha
-------------- ----------------------- ------------ -----------
Type: integer indexed array Read-only: no
Set by Bash: no Default: n/a
If set, each element is executed as a command prior to issuing each
primary prompt (like `PROMPT_COMMAND`, just as array).
### PROMPT_DIRTRIM
Variable: `PROMPT_DIRTRIM` Since: unknown
-------------- ------------------ ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If set to a number greater than zero, the value is used as the number of
trailing directory components to retain when expanding the `\w` and `\W`
prompt string escapes.
Characters removed are replaced with an ellipsis.
### PS0
Variable: `PS0` Since: 4.4.0
-------------- ----------------- ------------ --------------
Type: normal variable Read-only: no
Set by Bash: if unset Default: \"\'\'\'\'\"
Expanded and displayed by interactive shells after reading a complete
command but before executing it.
### PS1
Variable: `PS1` Since: unknown
-------------- ----------------- ------------ --------------------------
Type: normal variable Read-only: no
Set by Bash: if unset Default: \"\'\'\\s-\\v\\\$ \'\'\"
The value of this parameter is expanded and used as the primary prompt
string. See [Controlling the
Prompt](https://www.gnu.org/software/bash/manual/bash.html#Controlling-the-Prompt).
### PS2
Variable: `PS2` Since: unknown
-------------- ----------------- ------------ -----------------
Type: normal variable Read-only: no
Set by Bash: if unset Default: \"\'\'\> \'\'\"
The value of this parameter is expanded as with PS1 and used as the
secondary prompt string.
### PS3
Variable: `PS3` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
The value of this parameter is used as the prompt for the select
command.
### PS4
Variable: `PS4` Since: unknown
-------------- ----------------- ------------ ----------------
Type: normal variable Read-only: no
Set by Bash: if unset Default: \"\'\'+ \'\'\"
The value of this parameter is expanded as with `PS1` and the value is
printed before each command Bash displays during an execution trace. The
first character of `PS4` is replicated multiple times, as necessary, to
indicate multiple levels of indirection.
### SHELL
Variable: `SHELL` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
The full pathname to the shell is kept in this environment variable. If
it is not set when the shell starts, Bash assigns the full pathname of
the current user\'s login shell.
### SRANDOM
Variable: `SRANDOM` Since: 5.1-alpha
-------------- ----------------- ------------ -----------
Type: normal variable Read-only: no
Set by Bash: yes Default: n/a
A variable that delivers a 32bit random number. The random number
generation uses platform specific generators in the background and a
builtin fallback generator.
### TIMEFORMAT
Variable: `TIMEFORMAT` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
The value of this parameter is used as a format string specifying how
the timing information for pipelines prefixed with the time reserved
word should be displayed.
The % character introduces an escape sequence that is expanded to a time
value or other information. The escape sequences and their meanings are
as follows, the braces denote optional portions:
------------ ----------------------------------------------
`%%` a literal `%` (percent sign)
`%[p][l]R` elapsed time in seconds
`%[p][l]U` number of CPU seconds spent in user mode
`%[p][l]S` number of CPU seconds spent in system mode
`%P` CPU percentage, computed as `(%U + %S) / %R`
------------ ----------------------------------------------
The optional modifiers (p and l) are:
----- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
`p` A digit specifying the precision. A value of 0 causes no decimal point or fraction to be output. At most three digits after the decimal point are shown. If not specified, the value 3 is used.
`l` A longer format, including minutes, of the form MMmSS.FFs. The value of p determines whether or not the fraction is included.
----- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
If this variable is not set, Bash acts as if it had the value
$'\nreal\t%3lR\nuser\t%3lU\nsys%3lS'
If the value is null, no timing information is displayed.
A trailing newline is added when the format string is displayed.
### TMOUT
Variable: `TMOUT` Since: 2.05b
-------------- ----------------- ------------ -------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If set to a value greater than zero, `TMOUT` is treated as the default
timeout for the [read builtin command](../commands/builtin/read.md).
The [select command](../commands/builtin/select.md) terminates if input does
not arrive after `TMOUT` seconds when input is coming from a terminal.
In an interactive shell, the value is interpreted as the number of
seconds to wait for input after issuing the primary prompt. Bash
terminates after waiting for that number of seconds if input does not
arrive.
### TMPDIR
Variable: `TMPDIR` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
If set, Bash uses its value as the name of a directory in which Bash
creates temporary files for the shell\'s use.
### auto_resume
Variable: `auto_resume` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
This variable controls how the shell interacts with the user and job
control. If this variable is set, single word simple commands without
redirections are treated as candidates for resumption of an existing
stopped job. There is no ambiguity allowed; if there is more than one
job beginning with the string typed, the job most recently accessed is
selected. The name of a stopped job, in this context, is the command
line used to start it. If set to the value exact, the string supplied
must match the name of a stopped job exactly; if set to substring, the
string supplied needs to match a substring of the name of a stopped job.
The substring value provides functionality analogous to the %? job
identifier.
If set to any other value, the supplied string must be a prefix of a
stopped job\'s name; this provides functionality analogous to the
`%string` job identifier.
### histchars
Variable: `histchars` Since: unknown
-------------- ----------------- ------------ ---------
Type: normal variable Read-only: no
Set by Bash: no Default: n/a
The two or three characters which control history expansion and
tokenization.
The first character is the history expansion character, the character
which signals the start of a history expansion, normally \'!\'
(exlamation mark).
The second character is the quick substitution character, which is used
as shorthand for re-running the previous command entered, substi tuting
one string for another in the command. The default is \'\^\' (carret).
The optional third character is the character which indicates that the
remainder of the line is a comment when found as the first character of
a word, normally \'#\' (hash mark). The history comment character causes
history substitution to be skipped for the remaining words on the line.
It does not necessarily cause the shell parser to treat the rest of the
line as a comment.
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