wiki.bash-hackers.org/syntax/shellvars.md

====== Special parameters and shell variables ======

===== Special Parameters =====

^parameter^character^expansion description^
|''*''|asterisk|The positional parameters starting from the first. When used inside doublequotes (see [[syntax:quoting | quoting]]), 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 $4"''. \\ If ''IFS'' is unset, the delimiter used will be always a space, if ''IFS'' is NULL, the delimiter will be nothing, which effectively concatenates all the positional parameters without any delimiter. \\ When used unquoted, it will just expand to the strings, one by one, not preserving the word boundaries (i.e. word splitting will split the text again, if it contains ''IFS'' characters. \\ See also the [[scripting:posparams | scripting article about handling positional parameters]].|
|''@''|at-sign|The positional parameters starting from the first. When used inside doublequotes (see [[syntax:quoting | quoting]]), like ''"$@"'', it expands all positional parameters //as separate words//: ''"$1" "$2" "$3" "$4"'' \\ Without doublequotes, the behaviour is like the one of ''*'' without doublequotes. \\ See also the [[scripting:posparams | scripting article about handling positional parameters]].|
|''#''|hash mark|Number of positional parameters (decimal) \\ See also the [[scripting:posparams | scripting article about handling positional parameters]].|
|''?''|question mark|Status of the most recently executed foreground-pipeline (exit/return code)|
|''-''|dash|Current option flags set by the shell itself, on invocation, or using the [[commands:builtin:set | set builtin command]]. It's just a set of characters, like ''himB'' for ''h'', ''i'', ''m'' and ''B''.|
|''$''|dollar-sign|The process ID (PID) of the shell. In an [[syntax:ccmd:grouping_subshell | explicit subshell]] 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
[[commands:builtin:shopt|shopt builtin command]]. 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:
<code>
cmdhist:expand_aliases:extquote:force_fignore:hostcomplete:interactive_comments:progcomp:promptvars:sourcepath
</code>

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
[[commands:builtin:alias | alias builtin command]].

==== 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 [[commands:builtin:source|''.'' or ''source'' builtin command]])
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 [[commands:builtin:hash|hash builtin command]].
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[[commands:builtin:hash|hash builtin command]].

==== 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 ''<nowiki>[[</nowiki>'' 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 &quot;release status&quot; (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 &quot;main&quot;.

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 [[commands:builtin:caller|caller builtin command]]
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:
<code>
x86_64
</code>

==== 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 &quot;cpu-company-system&quot; format.

Example content:
<code>
x86_64-unknown-linux-gnu
</code>

==== 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
[[commands:builtin:mapfile|mapfile builtin command]] 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
[[commands:builtin:getopts|getopts builtin command]].

==== 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
[[commands:builtin:getopts|getopts builtin command]].

==== 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:
<code>
linux-gnu
</code>


==== 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
[[commands:builtin:cd|cd builtin command]].

==== 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 [[commands:builtin:read|read builtin command]]  ^Default: |n/a  |

Set to the line of input read by the
[[commands:builtin:read|read builtin command]] 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 [[commands:builtin:set|set builtin command]].
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
  * [[syntax:pe|parameter expansion]]
  * [[syntax:expansion:cmdsubst|command substitution]]
  * [[syntax:expansion:arith|arithmetic expansion]]
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 [[commands:builtin:cd|cd builtin command]].

This is a colon-separated list of directories in which the shell looks for
destination directories specified by the ''cd'' command.

Example content:
<code>.:~:/usr</code>

==== 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 &quot;t&quot;, 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 [[commands:builtin:fc|fc builtin command]].

==== 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:
<code>.o:~</code>

==== 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, &quot;&&quot; matches the
previous history line. &quot;&&quot; 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 [[commands:builtin:cd|cd builtin command]].

The value of this variable is also used when performing
[[syntax:expansion:tilde|tilde expansion]].

==== 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:
<code>/var/mail/bfox?&quot;You have mail&quot;:~/shell-mail?&quot;$_ has mail!&quot;</code>

==== 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 [[commands:builtin:getopts|getopts builtin command]].

''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: |&quot;''''&quot;  |

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: |&quot;''\s-\v\$ ''&quot;  |

The value of this parameter is expanded and used as the primary prompt string.

==== PS2 ====
^Variable:  |''PS2''  ^Since:  |unknown   |
^Type:  |normal variable  ^Read-only:  |no  |
^Set by Bash:  |if unset  ^Default: |&quot;''> ''&quot;  |

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: |&quot;''+ ''&quot;  |

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
<code>$'\nreal\t%3lR\nuser\t%3lU\nsys%3lS'</code>

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 [[commands:builtin:read|read builtin command]].

The [[commands:builtin:select|select command]] 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.