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5.2 Bash Variables ¶

These variables are set or used by Bash, but other shells do not normally treat them specially.

A few variables used by Bash are described in different chapters: variables for controlling the job control facilities (see Job Control Variables).

_ ¶

($_, an underscore.) This has a number of meanings depending on context. At shell startup, $_ set to the pathname used to invoke the shell or shell script being executed as passed in the environment or argument list. Subsequently, it expands to the last argument to the previous simple command executed in the foreground, after expansion. It is also set to the full pathname used to invoke each command executed and placed in the environment exported to that command. When checking mail, $_ expands to the name of the mail file.

BASH ¶

The full pathname used to execute the current instance of Bash.

BASHOPTS ¶

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 (see The Shopt Builtin). The options appearing in BASHOPTS are those reported as ‘on’ by ‘shopt’. If this variable is in the environment when Bash starts up, the shell enables each option in the list before reading any startup files. If this variable is exported, child shells will enable each option in the list. This variable is readonly.

BASHPID ¶

Expands to the process ID of the current Bash process. This differs from $$ under certain circumstances, such as subshells that do not require Bash to be re-initialized. Assignments to BASHPID have no effect. If BASHPID is unset, it loses its special properties, even if it is subsequently reset.

BASH_ALIASES ¶

An associative array variable whose members correspond to the internal list of aliases as maintained by the alias builtin. (see Bourne Shell Builtins). Elements added to this array appear in the alias list; however, unsetting array elements currently does not cause aliases to be removed from the alias list. If BASH_ALIASES is unset, it loses its special properties, even if it is subsequently reset.

BASH_ARGC ¶

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) is at the top of the stack. When a subroutine is executed, the number of parameters passed is pushed onto BASH_ARGC. The shell sets BASH_ARGC only when in extended debugging mode (see The Shopt Builtin for a description of the extdebug option to the shopt builtin). Setting extdebug after the shell has started to execute a subroutine, or referencing this variable when extdebug is not set, may result in inconsistent values. Assignments to BASH_ARGC have no effect, and it may not be unset.

BASH_ARGV ¶

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 shell pushes the supplied parameters onto BASH_ARGV. The shell sets BASH_ARGV only when in extended debugging mode (see The Shopt Builtin for a description of the extdebug option to the shopt builtin). Setting extdebug after the shell has started to execute a script, or referencing this variable when extdebug is not set, may result in inconsistent values. Assignments to BASH_ARGV have no effect, and it may not be unset.

BASH_ARGV0 ¶

When referenced, this variable expands to the name of the shell or shell script (identical to $0; See Special Parameters, for the description of special parameter 0). Assigning a value to BASH_ARGV0 sets $0 to the same value. If BASH_ARGV0 is unset, it loses its special properties, even if it is subsequently reset.

BASH_CMDS ¶

An associative array variable whose members correspond to the internal hash table of commands as maintained by the hash builtin (see Bourne Shell Builtins). Adding elements to this array makes them appear in the hash table; however, unsetting array elements currently does not remove command names from the hash table. If BASH_CMDS is unset, it loses its special properties, even if it is subsequently reset.

BASH_COMMAND ¶

Expands to 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. If BASH_COMMAND is unset, it loses its special properties, even if it is subsequently reset.

BASH_COMPAT ¶

The value is used to set the shell’s compatibility level. See Shell Compatibility Mode, for a description of the various compatibility levels and their effects. 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. A subset of the valid values correspond to the compatibility levels described below (see Shell Compatibility Mode). For example, 4.2 and 42 are valid values that correspond to the compat42 shopt option and set the compatibility level to 42. The current version is also a valid value.

BASH_ENV ¶

If this variable is set when Bash is invoked to execute a shell script, its value is expanded and used as the name of a startup file to read before executing the script. Bash does not use PATH to search for the resultant filename. See Bash Startup Files.

BASH_EXECUTION_STRING ¶

The command argument to the -c invocation option.

BASH_LINENO ¶

An array variable whose members are the line numbers in source files where each corresponding member of FUNCNAME was invoked. ${BASH_LINENO[$i]} is the line number in the source file (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]} was called (or ${BASH_LINENO[$i-1]} if referenced within another shell function). Use LINENO to obtain the current line number. Assignments to BASH_LINENO have no effect, and it may not be unset.

BASH_LOADABLES_PATH ¶

A colon-separated list of directories in which the enable command looks for dynamically loadable builtins.

BASH_MONOSECONDS ¶

Each time this variable is referenced, it expands to the value returned by the system’s monotonic clock, if one is available. If there is no monotonic clock, this is equivalent to EPOCHSECONDS. If BASH_MONOSECONDS is unset, it loses its special properties, even if it is subsequently reset.

BASH_REMATCH ¶

An array variable whose members are assigned by the ‘=~’ binary operator to the [[ conditional command (see Conditional Constructs). 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.

BASH_SOURCE ¶

An array variable whose members are the source filenames where the corresponding shell function names in the FUNCNAME array variable are defined. The shell function ${FUNCNAME[$i]} is defined in the file ${BASH_SOURCE[$i]} and called from ${BASH_SOURCE[$i+1]} Assignments to BASH_SOURCE have no effect, and it may not be unset.

BASH_SUBSHELL ¶

Incremented by one within each subshell or subshell environment when the shell begins executing in that environment. The initial value is 0. If BASH_SUBSHELL is unset, it loses its special properties, even if it is subsequently reset.

BASH_TRAPSIG ¶

Set to the signal number corresponding to the trap action being executed during its execution. See the description of trap (see Bourne Shell Builtins) for information about signal numbers and trap execution.

BASH_VERSINFO ¶

A readonly array variable (see Arrays) 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., beta).

BASH_VERSINFO[5]

The value of MACHTYPE.

BASH_VERSION ¶

Expands to a string describing the version of this instance of Bash (e.g., 5.2.37(3)-release).

BASH_XTRACEFD ¶

If set to an integer corresponding to a valid file descriptor, Bash writes the trace output generated when ‘set -x’ is enabled to that file descriptor, instead of the standard error. This allows tracing output to be separated from diagnostic and error messages. 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.

CHILD_MAX ¶

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.

COLUMNS ¶

Used by the select command to determine the terminal width when printing selection lists. Automatically set if the checkwinsize option is enabled (see The Shopt Builtin), or in an interactive shell upon receipt of a SIGWINCH.

COMP_CWORD ¶

An index into ${COMP_WORDS} of the word containing the current cursor position. This variable is available only in shell functions invoked by the programmable completion facilities (see Programmable Completion).

COMP_KEY ¶

The key (or final key of a key sequence) used to invoke the current completion function. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Completion).

COMP_LINE ¶

The current command line. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Completion).

COMP_POINT ¶

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}. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Completion).

COMP_TYPE ¶

Set to an integer value corresponding to the type of attempted completion that caused a completion function to be called: TAB, for normal completion, ‘?’, for listing completions after successive tabs, ‘!’, for listing alternatives on partial word completion, ‘@’, to list completions if the word is not unmodified, or ‘%’, for menu completion. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Completion).

COMP_WORDBREAKS ¶

The set of characters that the Readline library treats as word separators when performing word completion. If COMP_WORDBREAKS is unset, it loses its special properties, even if it is subsequently reset.

COMP_WORDS ¶

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. This variable is available only in shell functions invoked by the programmable completion facilities (see Programmable Completion).

COMPREPLY ¶

An array variable from which Bash reads the possible completions generated by a shell function invoked by the programmable completion facility (see Programmable Completion). Each array element contains one possible completion.

COPROC ¶

An array variable created to hold the file descriptors for output from and input to an unnamed coprocess (see Coprocesses).

DIRSTACK ¶

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. Assigning to this variable does not change the current directory. If DIRSTACK is unset, it loses its special properties, even if it is subsequently reset.

EMACS ¶

If Bash finds this variable in the environment when the shell starts, and its value is ‘t’, Bash assumes that the shell is running in an Emacs shell buffer and disables line editing.

ENV ¶

Expanded and executed similarly to BASH_ENV (see Bash Startup Files) when an interactive shell is invoked in POSIX mode (see Bash and POSIX).

EPOCHREALTIME ¶

Each time this parameter is referenced, it expands to the number of seconds since the Unix Epoch as a floating-point value with micro-second granularity (see the documentation for the C library function time for the definition of Epoch). Assignments to EPOCHREALTIME are ignored. If EPOCHREALTIME is unset, it loses its special properties, even if it is subsequently reset.

EPOCHSECONDS ¶

Each time this parameter is referenced, it expands to the number of seconds since the Unix Epoch (see the documentation for the C library function time for the definition of Epoch). Assignments to EPOCHSECONDS are ignored. If EPOCHSECONDS is unset, it loses its special properties, even if it is subsequently reset.

EUID ¶

The numeric effective user id of the current user. This variable is readonly.

EXECIGNORE ¶

A colon-separated list of shell patterns (see Pattern Matching) defining the set of filenames to be ignored by command search using PATH. Files whose full pathnames match one of these patterns are not considered executable files for the purposes of completion and command execution via PATH lookup. This does not affect the behavior of the [, test, and [[ commands. Full pathnames in the command hash table are not subject to EXECIGNORE. Use this variable to ignore shared library files that have the executable bit set, but are not executable files. The pattern matching honors the setting of the extglob shell option.

FCEDIT ¶

The editor used as a default by the fc builtin command.

FIGNORE ¶

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. A sample value is ‘.o:~’

FUNCNAME ¶

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 exists only when a shell function is executing. Assignments to FUNCNAME have no effect. If FUNCNAME is unset, it loses its special properties, even if it is subsequently reset.

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 displays the current call stack using this information.

FUNCNEST ¶

A numeric value greater than 0 defines a maximum function nesting level. Function invocations that exceed this nesting level cause the current command to abort.

GLOBIGNORE ¶

A colon-separated list of patterns defining the set of file names to be ignored by filename expansion. If a file name matched by a filename expansion pattern also matches one of the patterns in GLOBIGNORE, it is removed from the list of matches. The pattern matching honors the setting of the extglob shell option.

GLOBSORT ¶

Controls how the results of filename expansion are sorted. The value of this variable specifies the sort criteria and sort order for the results of filename expansion. If this variable is unset or set to the null string, filename expansion uses the historical behavior of sorting by name, in ascending lexicographic order as determined by the LC_COLLATE shell variable.

If set, a valid value begins with an optional ‘+’, which is ignored, or ‘-’, which reverses the sort order from ascending to descending, followed by a sort specifier. The valid sort specifiers are ‘name’, ‘numeric’, ‘size’, ‘mtime’, ‘atime’, ‘ctime’, and ‘blocks’, which sort the files on name, names in numeric rather than lexicographic order, file size, modification time, access time, inode change time, and number of blocks, respectively. If any of the non-name keys compare as equal (e.g., if two files are the same size), sorting uses the name as a secondary sort key.

For example, a value of -mtime sorts the results in descending order by modification time (newest first).

The ‘numeric’ specifier treats names consisting solely of digits as numbers and sorts them using their numeric value (so “2” sorts before “10”, for example). When using ‘numeric’, names containing non-digits sort after all the all-digit names and are sorted by name using the traditional behavior.

A sort specifier of ‘nosort’ disables sorting completely; Bash returns the results in the order they are read from the file system, ignoring any leading ‘-’.

If the sort specifier is missing, it defaults to name, so a value of ‘+’ is equivalent to the null string, and a value of ‘-’ sorts by name in descending order.

Any invalid value restores the historical sorting behavior.

GROUPS ¶

An array variable containing the list of groups of which the current user is a member. Assignments to GROUPS have no effect. If GROUPS is unset, it loses its special properties, even if it is subsequently reset.

histchars ¶

The two or three characters which control history expansion, quick substitution, and tokenization (see History Expansion). The first character is the history expansion character, the character which begins a history expansion, normally ‘!’. The second character is the quick substitution character, normally ‘^’. When it appears as the first character on the line, history substitution repeats the previous command, replacing one string with another. The optional third character is the history comment character, normally ‘#’, which indicates that the remainder of the line is a comment when it appears as the first character of a word. The history comment character disables history substitution 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.

HISTCMD ¶

The history number, or index in the history list, of the current command. Assignments to HISTCMD have no effect. If HISTCMD is unset, it loses its special properties, even if it is subsequently reset.

HISTCONTROL ¶

A colon-separated list of values controlling how commands are saved on the history list. If the list of values includes ‘ignorespace’, lines which begin with a space character are not saved in the history list. A value of ‘ignoredups’ causes lines which match the previous history entry not to be saved. A value of ‘ignoreboth’ is shorthand for ‘ignorespace’ and ‘ignoredups’. A value of ‘erasedups’ causes all previous lines matching the current line to be removed from the history list before that line is saved. Any value not in the above list is ignored. If HISTCONTROL is unset, or does not include a valid value, Bash saves all lines read by the shell parser on the history list, subject to the value of HISTIGNORE. If the first line of a multi-line compound command was saved, the second and subsequent lines are not tested, and are added to the history regardless of the value of HISTCONTROL. If the first line was not saved, the second and subsequent lines of the command are not saved either.

HISTFILE ¶

The name of the file to which the command history is saved. Bash assigns a default value of ~/.bash_history. If HISTFILE is unset or null, the shell does not save the command history when it exits.

HISTFILESIZE ¶

The maximum number of lines contained in the history file. When this variable is assigned a value, the history file is truncated, if necessary, to contain no more than the number of history entries that total no more than that number of lines by removing the oldest entries. If the history list contains multi-line entries, the history file may contain more lines than this maximum to avoid leaving partial history entries. The history file is also truncated to this size after writing it when a shell exits or by the history builtin. If the value is 0, the history file is truncated to zero size. Non-numeric values and numeric values less than zero inhibit truncation. The shell sets the default value to the value of HISTSIZE after reading any startup files.

HISTIGNORE ¶

A colon-separated list of patterns used to decide which command lines should be saved on the history list. If a command line matches one of the patterns in the value of HISTIGNORE, it is not saved on the history list. Each pattern is anchored at the beginning of the line and must match the complete line (Bash does not implicitly append a ‘*’). 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. A backslash escapes the ‘&’; the backslash is removed before attempting a match. If the first line of a multi-line compound command was saved, the second and subsequent lines are not tested, and are added to the history regardless of the value of HISTIGNORE. If the first line was not saved, the second and subsequent lines of the command are not saved either. The pattern matching honors the setting of the extglob shell option.

HISTIGNORE subsumes some of the function of HISTCONTROL. A pattern of ‘&’ is identical to ignoredups, and a pattern of ‘[ ]*’ is identical to ignorespace. Combining these two patterns, separating them with a colon, provides the functionality of ignoreboth.

HISTSIZE ¶

The maximum number of commands to remember on the history list. If the value is 0, commands are not saved in the history list. Numeric values less than zero result in every command being saved on the history list (there is no limit). The shell sets the default value to 500 after reading any startup files.

HISTTIMEFORMAT ¶

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, the shell writes time stamps 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.

HOSTFILE ¶

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, Bash clears the hostname list.

HOSTNAME ¶

The name of the current host.

HOSTTYPE ¶

A string describing the machine Bash is running on.

IGNOREEOF ¶

Controls the action of the shell on receipt of an EOF character as the sole input. If set, the value is the number of consecutive EOF characters that can be read as the first character on an input line before Bash exits. If the variable is set but does not have a numeric value, or the value is null, then the default is 10. If the variable is unset, then EOF signifies the end of input to the shell. This is only in effect for interactive shells.

INPUTRC ¶

The name of the Readline initialization file, overriding the default of ~/.inputrc.

INSIDE_EMACS ¶

If Bash finds this variable in the environment when the shell starts, it assumes that the shell is running in an Emacs shell buffer and may disable line editing depending on the value of TERM.

LANG ¶

Used to determine the locale category for any category not specifically selected with a variable starting with LC_.

LC_ALL ¶

This variable overrides the value of LANG and any other LC_ variable specifying a locale category.

LC_COLLATE ¶

This variable determines the collation order used when sorting the results of filename expansion, and determines the behavior of range expressions, equivalence classes, and collating sequences within filename expansion and pattern matching (see Filename Expansion).

LC_CTYPE ¶

This variable determines the interpretation of characters and the behavior of character classes within filename expansion and pattern matching (see Filename Expansion).

LC_MESSAGES ¶

This variable determines the locale used to translate double-quoted strings preceded by a ‘$’ (see Locale-Specific Translation).

LC_NUMERIC ¶

This variable determines the locale category used for number formatting.

LC_TIME ¶

This variable determines the locale category used for data and time formatting.

LINENO ¶

The line number in the script or shell function currently executing. Line numbers start with 1. When not in a script or function, the value is not guaranteed to be meaningful. If LINENO is unset, it loses its special properties, even if it is subsequently reset.

LINES ¶

Used by the select command to determine the column length for printing selection lists. Automatically set if the checkwinsize option is enabled (see The Shopt Builtin), or in an interactive shell upon receipt of a SIGWINCH.

MACHTYPE ¶

A string that fully describes the system type on which Bash is executing, in the standard GNU cpu-company-system format.

MAILCHECK ¶

How often (in seconds) that the shell should check for mail in the files specified in the MAILPATH or MAIL variables. The default is 60 seconds. 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.

MAPFILE ¶

An array variable created to hold the text read by the mapfile builtin when no variable name is supplied.

OLDPWD ¶

The previous working directory as set by the cd builtin.

OPTERR ¶

If set to the value 1, Bash displays error messages generated by the getopts builtin command. OPTERR is initialized to 1 each time the shell is invoked.

OSTYPE ¶

A string describing the operating system Bash is running on.

PIPESTATUS ¶

An array variable (see Arrays) containing a list of exit status values from the commands in the most-recently-executed foreground pipeline, which may consist of only a simple command (see Shell Commands). Bash sets PIPESTATUS after executing multi-element pipelines, timed and negated pipelines, simple commands, subshells created with the ‘(’ operator, the [[ and (( compound commands, and after error conditions that result in the shell aborting command execution.

POSIXLY_CORRECT ¶

If this variable is in the environment when Bash starts, the shell enters POSIX mode (see Bash and POSIX) 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. When the shell enters POSIX mode, it sets this variable if it was not already set.

PPID ¶

The process ID of the shell’s parent process. This variable is readonly.

PROMPT_COMMAND ¶

If this variable is set, and is an array, the value of each set element is interpreted as a command to execute before printing the primary prompt ($PS1). If this is set but not an array variable, its value is used as a command to execute instead.

PROMPT_DIRTRIM ¶

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 (see Controlling the Prompt). Characters removed are replaced with an ellipsis.

PS0 ¶

The value of this parameter is expanded like PS1 and displayed by interactive shells after reading a command and before the command is executed.

PS3 ¶

The value of this variable is used as the prompt for the select command. If this variable is not set, the select command prompts with ‘#? ’

PS4 ¶

The value of this parameter is expanded like PS1 and the expanded value is the prompt printed before the command line is echoed when the -x option is set (see The Set Builtin). The first character of the expanded value is replicated multiple times, as necessary, to indicate multiple levels of indirection. The default is ‘+ ’.

PWD ¶

The current working directory as set by the cd builtin.

RANDOM ¶

Each time this parameter is referenced, it expands to a random integer between 0 and 32767. Assigning a value to RANDOM initializes (seeds) the sequence of random numbers. Seeding the random number generator with the same constant value produces the same sequence of values. If RANDOM is unset, it loses its special properties, even if it is subsequently reset.

READLINE_ARGUMENT ¶

Any numeric argument given to a Readline command that was defined using ‘bind -x’ (see Bash Builtin Commands when it was invoked.

READLINE_LINE ¶

The contents of the Readline line buffer, for use with ‘bind -x’ (see Bash Builtin Commands).

READLINE_MARK ¶

The position of the mark (saved insertion point) in the Readline line buffer, for use with ‘bind -x’ (see Bash Builtin Commands). The characters between the insertion point and the mark are often called the region.

READLINE_POINT ¶

The position of the insertion point in the Readline line buffer, for use with ‘bind -x’ (see Bash Builtin Commands).

REPLY ¶

The default variable for the read builtin; set to the line read when read is not supplied a variable name argument.

SECONDS ¶

This variable expands to the number of seconds since the shell was started. Assignment to this variable resets the count to the value assigned, and the expanded value becomes the value assigned plus the number of seconds since the assignment. The number of seconds at shell invocation and the current time are always determined by querying the system clock at one-second resolution. If SECONDS is unset, it loses its special properties, even if it is subsequently reset.

SHELL ¶

This environment variable expands to the full pathname to the shell. If it is not set when the shell starts, Bash assigns to it the full pathname of the current user’s login shell.

SHELLOPTS ¶

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 (see The Set Builtin). The options appearing in SHELLOPTS are those reported as ‘on’ by ‘set -o’. If this variable is in the environment when Bash starts up, the shell enables each option in the list before reading any startup files. If this variable is exported, child shells will enable each option in the list. This variable is readonly.

SHLVL ¶

Incremented by one each time a new instance of Bash is started. This is intended to be a count of how deeply your Bash shells are nested.

SRANDOM ¶

This variable expands to a 32-bit pseudo-random number each time it is referenced. The random number generator is not linear on systems that support /dev/urandom or arc4random, so each returned number has no relationship to the numbers preceding it. The random number generator cannot be seeded, so assignments to this variable have no effect. If SRANDOM is unset, it loses its special properties, even if it is subsequently reset.

TIMEFORMAT ¶

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 brackets denote optional portions.

%%

A literal ‘%’.

%[p][l]R

The elapsed time in seconds.

%[p][l]U

The number of CPU seconds spent in user mode.

%[p][l]S

The number of CPU seconds spent in system mode.

%P

The CPU percentage, computed as (%U + %S) / %R.

The optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. time prints at most six digits after the decimal point; values of p greater than 6 are changed to 6. If p is not specified, time prints three digits after the decimal point.

The optional l specifies 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\t%3lS'

If the value is null, Bash does not display any timing information. A trailing newline is added when the format string is displayed.

TMOUT ¶

If set to a value greater than zero, the read builtin uses the value as its default timeout (see Bash Builtin Commands). The select command (see Conditional Constructs) 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 a line of input after issuing the primary prompt. Bash terminates after waiting for that number of seconds if a complete line of input does not arrive.

TMPDIR ¶

If set, Bash uses its value as the name of a directory in which Bash creates temporary files for the shell’s use.

UID ¶

The numeric real user id of the current user. This variable is readonly.