gNU Bourne-Again SHell (GNU Bourne-Again SHell)
Параметры (Parameters)
A parameter is an entity that stores values. It can be a name, a
number, or one of the special characters listed below under
Special Parameters. A variable is a parameter denoted by a name.
A variable has a value and zero or more attributes. Attributes
are assigned using the declare builtin command (see declare below
in SHELL BUILTIN COMMANDS).
A parameter is set if it has been assigned a value. The null
string is a valid value. Once a variable is set, it may be unset
only by using the unset builtin command (see SHELL BUILTIN
COMMANDS below).
A variable may be assigned to by a statement of the form
name=[value]
If value is not given, the variable is assigned the null string.
All values undergo tilde expansion, parameter and variable
expansion, command substitution, arithmetic expansion, and quote
removal (see EXPANSION below). If the variable has its integer
attribute set, then value is evaluated as an arithmetic
expression even if the $((...)) expansion is not used (see
Arithmetic Expansion below). Word splitting is not performed,
with the exception of "$@" as explained below under Special
Parameters. Pathname expansion is not performed. Assignment
statements may also appear as arguments to the alias, declare,
typeset, export, readonly, and local builtin commands
(declaration commands). When in posix mode, these builtins may
appear in a command after one or more instances of the command
builtin and retain these assignment statement properties.
In the context where an assignment statement is assigning a value
to a shell variable or array index, the += operator can be used
to append to or add to the variable's previous value. This
includes arguments to builtin commands such as declare that
accept assignment statements (declaration commands). When += is
applied to a variable for which the integer attribute has been
set, value is evaluated as an arithmetic expression and added to
the variable's current value, which is also evaluated. When +=
is applied to an array variable using compound assignment (see
Arrays below), the variable's value is not unset (as it is when
using =), and new values are appended to the array beginning at
one greater than the array's maximum index (for indexed arrays)
or added as additional key-value pairs in an associative array.
When applied to a string-valued variable, value is expanded and
appended to the variable's value.
A variable can be assigned the nameref attribute using the -n
option to the declare or local builtin commands (see the
descriptions of declare and local below) to create a nameref, or
a reference to another variable. This allows variables to be
manipulated indirectly. Whenever the nameref variable is
referenced, assigned to, unset, or has its attributes modified
(other than using or changing the nameref attribute itself), the
operation is actually performed on the variable specified by the
nameref variable's value. A nameref is commonly used within
shell functions to refer to a variable whose name is passed as an
argument to the function. For instance, if a variable name is
passed to a shell function as its first argument, running
declare -n ref=$1
inside the function creates a nameref variable ref whose value is
the variable name passed as the first argument. References and
assignments to ref, and changes to its attributes, are treated as
references, assignments, and attribute modifications to the
variable whose name was passed as $1. If the control variable in
a for loop has the nameref attribute, the list of words can be a
list of shell variables, and a name reference will be established
for each word in the list, in turn, when the loop is executed.
Array variables cannot be given the nameref attribute. However,
nameref variables can reference array variables and subscripted
array variables. Namerefs can be unset using the -n option to
the unset builtin. Otherwise, if unset is executed with the name
of a nameref variable as an argument, the variable referenced by
the nameref variable will be unset.
Positional Parameters
A positional parameter is a parameter denoted by one or more
digits, other than the single digit 0. Positional parameters are
assigned from the shell's arguments when it is invoked, and may
be reassigned using the set builtin command. Positional
parameters may not be assigned to with assignment statements.
The positional parameters are temporarily replaced when a shell
function is executed (see FUNCTIONS below).
When a positional parameter consisting of more than a single
digit is expanded, it must be enclosed in braces (see EXPANSION
below).
Special Parameters
The shell treats several parameters specially. These parameters
may only be referenced; assignment to them is not allowed.
* Expands to the positional parameters, starting from one.
When the expansion is not within double quotes, each
positional parameter expands to a separate word. In
contexts where it is performed, those words are subject to
further word splitting and pathname expansion. When the
expansion occurs within double quotes, it expands to a
single word with the value of each parameter separated by
the first character of the IFS special variable. That is,
"$*" is equivalent to "$1c$2c...", where c is the first
character of the value of the IFS variable. If IFS is
unset, the parameters are separated by spaces. If IFS is
null, the parameters are joined without intervening
separators.
@ Expands to the positional parameters, starting from one.
In contexts where word splitting is performed, this
expands each positional parameter to a separate word; if
not within double quotes, these words are subject to word
splitting. In contexts where word splitting is not
performed, this expands to a single word with each
positional parameter separated by a space. When the
expansion occurs within double quotes, each parameter
expands to a separate word. That is, "$@" is equivalent
to "$1" "$2" ... If the double-quoted expansion occurs
within a word, the expansion of the first parameter is
joined with the beginning part of the original word, and
the expansion of the last parameter is joined with the
last part of the original word. When there are no
positional parameters, "$@" and $@ expand to nothing
(i.e., they are removed).
# Expands to the number of positional parameters in decimal.
? Expands to the exit status of the most recently executed
foreground pipeline.
- Expands to the current option flags as specified upon
invocation, by the set builtin command, or those set by
the shell itself (such as the -i option).
$ Expands to the process ID of the shell. In a () subshell,
it expands to the process ID of the current shell, not the
subshell.
! Expands to the process ID of the job most recently placed
into the background, whether executed as an asynchronous
command or using the bg builtin (see JOB CONTROL below).
0 Expands to the name of the shell or shell script. This is
set at shell initialization. If bash is invoked with a
file of commands, $0 is set to the name of that file. If
bash is started with the -c option, then $0 is set to the
first argument after the string to be executed, if one is
present. Otherwise, it is set to the filename used to
invoke bash, as given by argument zero.
Shell Variables
The following variables are set by the shell:
_ 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, expands to
the last argument to the previous simple command executed
in the foreground, after expansion. Also set to the full
pathname used to invoke each command executed and placed
in the environment exported to that command. When
checking mail, this parameter holds the name of the mail
file currently being checked.
BASH Expands to the full filename used to invoke this 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 SHELL BUILTIN COMMANDS
below). 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.
This variable is read-only.
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. 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 description of the extdebug option
to the shopt builtin below). 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.
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 parameters supplied are
pushed onto BASH_ARGV. The shell sets BASH_ARGV only when
in extended debugging mode (see the description of the
extdebug option to the shopt builtin below). 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.
BASH_ARGV0
When referenced, this variable expands to the name of the
shell or shell script (identical to $0; see the
description of special parameter 0 above). Assignment to
BASH_ARGV0 causes the value assigned to also be assigned
to $0. 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. Elements added to this array appear in the
hash table; however, unsetting array elements currently
does not cause command names to be removed from the hash
table. If BASH_CMDS is unset, it loses its special
properties, even if it is subsequently reset.
BASH_COMMAND
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_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.
BASH_LOADABLES_PATH
A colon-separated list of directories in which the shell
looks for dynamically loadable builtins specified by the
enable command.
BASH_REMATCH
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.
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]}.
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_VERSINFO
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
Expands to a string describing the version of this
instance of bash.
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 below).
COMP_KEY
The key (or final key of a key sequence) used to invoke
the current completion function.
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 below).
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 below).
COMP_TYPE
Set to an integer value corresponding to the type of
completion attempted 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 below).
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 (see Arrays below) 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 below).
COPROC An array variable (see Arrays below) created to hold the
file descriptors for output from and input to an unnamed
coprocess (see Coprocesses above).
DIRSTACK
An array variable (see Arrays below) 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 DIRSTACK is unset, it
loses its special properties, even if it is subsequently
reset.
EPOCHREALTIME
Each time this parameter is referenced, it expands to the
number of seconds since the Unix Epoch (see time(3)) as a
floating point value with micro-second granularity.
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 time(3)).
Assignments to EPOCHSECONDS are ignored. If EPOCHSECONDS
is unset, it loses its special properties, even if it is
subsequently reset.
EUID Expands to the effective user ID of the current user,
initialized at shell startup. This variable is readonly.
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.
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.
HISTCMD
The history number, or index in the history list, of the
current command. Assignments to HISTCMD are ignored. If
HISTCMD is unset, it loses its special properties, even if
it is subsequently reset.
HOSTNAME
Automatically set to the name of the current host.
HOSTTYPE
Automatically set to a string that uniquely describes the
type of machine on which bash is executing. The default
is system-dependent.
LINENO 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 LINENO
is unset, it loses its special properties, even if it is
subsequently reset.
MACHTYPE
Automatically set to a string that fully describes the
system type on which bash is executing, in the standard
GNU cpu-company-system format. The default is system-
dependent.
MAPFILE
An array variable (see Arrays below) 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 command.
OPTARG The value of the last option argument processed by the
getopts builtin command (see SHELL BUILTIN COMMANDS
below).
OPTIND The index of the next argument to be processed by the
getopts builtin command (see SHELL BUILTIN COMMANDS
below).
OSTYPE Automatically set to a string that describes the operating
system on which bash is executing. The default is system-
dependent.
PIPESTATUS
An array variable (see Arrays below) 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 The process ID of the shell's parent. This variable is
readonly.
PWD The current working directory as set by the cd command.
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.
If RANDOM is unset, it loses its special properties, even
if it is subsequently reset.
READLINE_LINE
The contents of the readline line buffer, for use with
"bind -x" (see SHELL BUILTIN COMMANDS below).
READLINE_MARK
The position of the mark (saved insertion point) in the
readline line buffer, for use with "bind -x" (see SHELL
BUILTIN COMMANDS below). 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 SHELL BUILTIN COMMANDS
below).
REPLY Set to the line of input read by the read builtin command
when no arguments are supplied.
SECONDS
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. The number of seconds at shell
invocation and the current time is always determined by
querying the system clock. If SECONDS is unset, it loses
its special properties, even if it is subsequently reset.
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 SHELL BUILTIN COMMANDS
below). 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.
This variable is read-only.
SHLVL Incremented by one each time an instance of bash is
started.
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.
UID Expands to the user ID of the current user, initialized at
shell startup. This variable is readonly.
The following variables are used by the shell. In some cases,
bash assigns a default value to a variable; these cases are noted
below.
BASH_COMPAT
The value is used to set the shell's compatibility level.
See SHELL COMPATIBILITY MODE below 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. The valid
values correspond to the compatibility levels described
below under BSHELLCOMPATIBILITYMODE. 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 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,
command substitution, and arithmetic expansion before
being interpreted as a filename. PATH is not used to
search for the resultant filename.
BASH_XTRACEFD
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 The search path for the cd command. This is a colon-
separated list of directories in which the shell looks for
destination directories specified by the cd command. A
sample value is ".:~:/usr".
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 compound command to determine the
terminal width when printing selection lists.
Automatically set if the checkwinsize option is enabled or
in an interactive shell upon receipt of a SIGWINCH.
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 below). Each array element contains one
possible completion.
EMACS 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 Expanded and executed similarly to BASH_ENV (see
INVOCATION above) when an interactive shell is invoked in
posix mode.
EXECIGNORE
A colon-separated list of shell patterns (see Pattern
Matching) defining the list 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 default editor for the fc builtin command.
FIGNORE
A colon-separated list of suffixes to ignore when
performing filename completion (see READLINE below). A
filename whose suffix matches one of the entries in
FIGNORE is excluded from the list of matched filenames. A
sample value is ".o:~".
FUNCNEST
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.
GLOBIGNORE
A colon-separated list of patterns defining the set of
file names to be ignored by pathname expansion. If a file
name matched by a pathname expansion pattern also matches
one of the patterns in GLOBIGNORE, it is removed from the
list of matches.
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 matching the previous history
entry to not 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,
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
The name of the file in which command history is saved
(see HISTORY below). The default value is
~/.bash_history. If unset, the command history is not
saved when a shell 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 that
number of lines by removing the oldest entries. The
history file is also truncated to this size after writing
it when a shell exits. 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. 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. The
pattern matching honors the setting of the extglob shell
option.
HISTSIZE
The number of commands to remember in the command history
(see HISTORY below). 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, 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 The home directory of the current user; the default
argument for the cd builtin command. The value of this
variable is also used when performing tilde expansion.
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, the hostname list is
cleared.
IFS The Internal Field Separator that is used for word
splitting after expansion and to split lines into words
with the read builtin command. The default value is
``<space><tab><newline>''.
IGNOREEOF
Controls the action of an interactive shell on receipt of
an EOF character 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
The filename for the readline startup file, overriding the
default of ~/.inputrc (see READLINE below).
INSIDE_EMACS
If this variable appears in the environment when the shell
starts, bash assumes that it is running inside 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 pathname expansion, and determines
the behavior of range expressions, equivalence classes,
and collating sequences within pathname expansion and
pattern matching.
LC_CTYPE
This variable determines the interpretation of characters
and the behavior of character classes within pathname
expansion and pattern matching.
LC_MESSAGES
This variable determines the locale used to translate
double-quoted strings preceded by a $.
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.
LINES Used by the select compound command to determine the
column length for printing selection lists. Automatically
set if the checkwinsize option is enabled or in an
interactive shell upon receipt of a SIGWINCH.
MAIL 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 directory.
MAILCHECK
Specifies how often (in seconds) bash checks for mail.
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.
MAILPATH
A colon-separated list of filenames to be checked for
mail. The message to be printed when mail arrives in a
particular file may be specified by separating the
filename from the message with a `?'. When used in the
text of the message, $_ expands to the name of the current
mailfile. Example:
MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_
has mail!"'
Bash can be configured to supply a default value for this
variable (there is no value by default), but the location
of the user mail files that it uses is system dependent
(e.g., /var/mail/$USER).
OPTERR If set to the value 1, bash displays error messages
generated by the getopts builtin command (see SHELL
BUILTIN COMMANDS below). OPTERR is initialized to 1 each
time the shell is invoked or a shell script is executed.
PATH The search path for commands. It is a colon-separated
list of directories in which the shell looks for commands
(see COMMAND EXECUTION below). 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. The
default path is system-dependent, and is set by the
administrator who installs bash. A common value is
``/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
POSIXLY_CORRECT
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. When the shell enters posix mode, it sets
this variable if it was not already set.
PROMPT_COMMAND
If this variable is set, and is an array, the value of
each set element is executed as a command prior to issuing
each primary prompt. 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
PROMPTING below). Characters removed are replaced with an
ellipsis.
PS0 The value of this parameter is expanded (see PROMPTING
below) and displayed by interactive shells after reading a
command and before the command is executed.
PS1 The value of this parameter is expanded (see PROMPTING
below) and used as the primary prompt string. The default
value is ``\s-\v\$ ''.
PS2 The value of this parameter is expanded as with PS1 and
used as the secondary prompt string. The default is ``>
''.
PS3 The value of this parameter is used as the prompt for the
select command (see SHELL GRAMMAR above).
PS4 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 the
expanded value of PS4 is replicated multiple times, as
necessary, to indicate multiple levels of indirection.
The default is ``+ ''.
SHELL This 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.
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 braces
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. At most three places after the decimal point may
be specified; values of p greater than 3 are changed to 3.
If p is not specified, the value 3 is used.
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, no timing information is displayed. A
trailing newline is added when the format string is
displayed.
TMOUT If set to a value greater than zero, TMOUT is treated as
the default timeout for the read builtin. The 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 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.
auto_resume
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 (see JOB CONTROL
below). 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
The two or three characters which control history
expansion and tokenization (see HISTORY EXPANSION below).
The first character is the history expansion character,
the character which signals the start of a history
expansion, normally `!'. The second character is the
quick substitution character, which is used as shorthand
for re-running the previous command entered, substituting
one string for another in the command. The default is
`^'. 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 `#'. 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.
Arrays
Bash provides one-dimensional indexed and associative array
variables. Any variable may be used as an indexed array; the
declare builtin will explicitly declare an array. There is no
maximum limit on the size of an array, nor any requirement that
members be indexed or assigned contiguously. Indexed arrays are
referenced using integers (including arithmetic expressions) and
are zero-based; associative arrays are referenced using arbitrary
strings. Unless otherwise noted, indexed array indices must be
non-negative integers.
An indexed array is created automatically if any variable is
assigned to using the syntax name[subscript]=value. The
subscript is treated as an arithmetic expression that must
evaluate to a number. To explicitly declare an indexed array,
use declare -a name (see SHELL BUILTIN COMMANDS below). declare
-a name[subscript] is also accepted; the subscript is ignored.
Associative arrays are created using declare -A name.
Attributes may be specified for an array variable using the
declare and readonly builtins. Each attribute applies to all
members of an array.
Arrays are assigned to using compound assignments of the form
name=(value1 ... valuen), where each value may be of the form
[subscript]=string. Indexed array assignments do not require
anything but string. Each value in the list is expanded using
all the shell expansions described below under EXPANSION. When
assigning to indexed arrays, if the optional brackets and
subscript are supplied, that index is assigned to; otherwise the
index of the element assigned is the last index assigned to by
the statement plus one. Indexing starts at zero.
When assigning to an associative array, the words in a compound
assignment may be either assignment statements, for which the
subscript is required, or a list of words that is interpreted as
a sequence of alternating keys and values: name=( key1 value1
key2 value2 ...). These are treated identically to name=(
[key1]=value1 [key2]=value2 ...). The first word in the list
determines how the remaining words are interpreted; all
assignments in a list must be of the same type. When using
key/value pairs, the keys may not be missing or empty; a final
missing value is treated like the empty string.
This syntax is also accepted by the declare builtin. Individual
array elements may be assigned to using the name[subscript]=value
syntax introduced above. When assigning to an indexed array, if
name is subscripted by a negative number, that number is
interpreted as relative to one greater than the maximum index of
name, so negative indices count back from the end of the array,
and an index of -1 references the last element.
Any element of an array may be referenced using
${name[subscript]}. The braces are required to avoid conflicts
with pathname expansion. If subscript is @ or *, the word
expands to all members of name. These subscripts differ only
when the word appears within double quotes. If the word is
double-quoted, ${name[*]} expands to a single word with the value
of each array member separated by the first character of the IFS
special variable, and ${name[@]} expands each element of name to
a separate word. When there are no array members, ${name[@]}
expands to nothing. If the double-quoted expansion occurs within
a word, the expansion of the first parameter is joined with the
beginning part of the original word, and the expansion of the
last parameter is joined with the last part of the original word.
This is analogous to the expansion of the special parameters *
and @ (see Special Parameters above). ${#name[subscript]}
expands to the length of ${name[subscript]}. If subscript is *
or @, the expansion is the number of elements in the array. If
the subscript used to reference an element of an indexed array
evaluates to a number less than zero, it is interpreted as
relative to one greater than the maximum index of the array, so
negative indices count back from the end of the array, and an
index of -1 references the last element.
Referencing an array variable without a subscript is equivalent
to referencing the array with a subscript of 0. Any reference to
a variable using a valid subscript is legal, and bash will create
an array if necessary.
An array variable is considered set if a subscript has been
assigned a value. The null string is a valid value.
It is possible to obtain the keys (indices) of an array as well
as the values. ${!name[@]} and ${!name[*]} expand to the indices
assigned in array variable name. The treatment when in double
quotes is similar to the expansion of the special parameters @
and * within double quotes.
The unset builtin is used to destroy arrays. unset
name[subscript] destroys the array element at index subscript,
for both indexed and associative arrays. Negative subscripts to
indexed arrays are interpreted as described above. Unsetting the
last element of an array variable does not unset the variable.
unset name, where name is an array, or unset name[subscript],
where subscript is * or @, removes the entire array.
When using a variable name with a subscript as an argument to a
command, such as with unset, without using the word expansion
syntax described above, the argument is subject to pathname
expansion. If pathname expansion is not desired, the argument
should be quoted.
The declare, local, and readonly builtins each accept a -a option
to specify an indexed array and a -A option to specify an
associative array. If both options are supplied, -A takes
precedence. The read builtin accepts a -a option to assign a
list of words read from the standard input to an array. The set
and declare builtins display array values in a way that allows
them to be reused as assignments.
