BASH (1)
GNU Bourne-Again SHell
SYNOPSIS
COPYRIGHT
n Bash is Copyright (C) 1989, 1991 by the Free Software Foundation, Inc.
t Bash is Copyright \(co 1989, 1991 by the Free Software Foundation, Inc.
DESCRIPTION
Bash
is an sh-compatible command language interpreter that
executes commands read from the standard input or from a file.
Bash
also incorporates useful features from the Korn and C
shells (ksh and csh).
Bash
is ultimately intended to be a conformant implementation of the IEEE
Posix Shell and Tools specification (IEEE Working Group 1003\.2).
OPTIONS
In addition to the single-character shell options documented in the
description of the set builtin command, bash
interprets the following flags when it is invoked:
-c \| string\^
If the
-c
flag is present, then commands are read from
string .
If there are arguments after the
string ,
they are assigned to the positional parameters, starting with
$0 .
-i
If the
-i
flag is present, the shell is
interactive .
-s
If the
-s
flag is present, or if no arguments remain after option
processing, then commands are read from the standard input.
This option allows the positional parameters to be set
when invoking an interactive shell.
-
A single
-
signals the end of options and disables further option processing.
Any arguments after the
-
are treated as filenames and arguments. An argument of
--
is equivalent to an argument of -.
Bash
also interprets a number of multi-character options. These options must
appear on the command line before the single-character options to be
recognized.
-norc
Do not read and execute the personal initialization file
~/.bashrc
if the shell is interactive.
This option is on by default if the shell is invoked as
sh .
-noprofile
Do not read either the system-wide startup file
/etc/profile
or any of the personal initialization files
~/.bash_profile ,
~/.bash_login ,
or
~/.profile .
By default,
bash
normally reads these files when it is invoked as a login shell (see
INVOCATION
below).
-rcfile file
Execute commands from
file
instead of the standard personal initialization file
~/.bashrc ,
if the shell is interactive (see
INVOCATION
below).
-version
Show the version number of this instance of
bash
when starting.
-quiet
Do not be verbose when starting up (do not show the shell version or any
other information). This is the default.
-login
Make
bash
act as if it had been invoked as a login shell.
-nobraceexpansion
Do not perform curly brace expansion (see
Brace Expansion
below).
-nolineediting
Do not use the GNU
readline
library to read command lines if interactive.
-posix
Change the behavior of bash where the default operation differs
from the Posix 1003.2 standard to match the standard
ARGUMENTS
If arguments remain after option processing, and neither the
-c
nor the
-s
option has been supplied, the first argument is assumed to
be the name of a file containing shell commands. If
bash
is invoked in this fashion,
$0
is set to the name of the file, and the positional parameters
are set to the remaining arguments.
Bash
reads and executes commands from this file, then exits.
Bash's
exit status is the exit status of the last command executed
in the script.
DEFINITIONS
RESERVED WORDS
Reserved words are words that have a special meaning to the shell.
The following words are recognized as reserved when unquoted and either
the first word of a simple command (see
SHELL GRAMMAR
below) or the third word of a
case
or
for
command:
t .RS
n ! case do done elif else esac fi for function if in select then until while { }
t ! case do done elif else esac fi for function if in select then until while { }
t .RE
SHELL GRAMMAR
A simple command is a sequence of optional variable assignments
followed by blank-separated words and redirections, and
terminated by a control operator. The first word
specifies the command to be executed. The remaining words are
passed as arguments to the invoked command.
The return value of a simple command is its exit status, or
128+n\^ if the command is terminated by signal
n .
A pipeline is a sequence of one or more commands separated by
the character
| .
The format for a pipeline is:
The standard output of
command
is connected to the standard input of
command2 .
This connection is performed before any redirections specified by the
command (see
REDIRECTION
below).
If the reserved word
!
precedes a pipeline, the exit status of that
pipeline is the logical NOT of the exit status of the last command.
Otherwise, the status of the pipeline is the exit status of the last
command. The shell waits for all commands in the pipeline to
terminate before returning a value.
Each command in a pipeline is executed as a separate process (i.e., in a
subshell).
A list is a sequence of one or more pipelines separated by one
of the operators
; ,
& ,
&& ,
or
\(bv\|\(bv ,
and terminated by one of
; ,
& ,
or
<newline> .
Of these list operators,
&&
and
\(bv\|\(bv
have equal precedence, followed by
;
and
&,
which have equal precedence.
If a command is terminated by the control operator
& ,
the shell executes the command in the background
in a subshell. The shell does not wait for the command to
finish, and the return status is 0. Commands separated by a
;
are executed sequentially; the shell waits for each
command to terminate in turn. The return status is the
exit status of the last command executed.
The control operators
&&
and
\(bv\|\(bv
denote AND lists and OR lists, respectively.
An AND list has the form
command2
is executed if, and only if,
command
returns an exit status of zero.
An OR list has the form
command2
is executed if and only if
command
returns a non-zero exit status. The return status of
AND and OR lists is the exit status of the last command
executed in the list.
A compound command is one of the following:
(list)
list is executed in a subshell. Variable assignments and builtin
commands that affect the shell's environment do not remain in effect
after the command completes. The return status is the exit status of
list.
{ list; }
list is simply executed in the current shell environment. This is
known as a group command. The return status is the exit status of
list.
for name [ in word; ] do list ; done
The list of words following in is expanded, generating a list
of items. The variable name is set to each element of this list
in turn, and list is executed each time. If the in
word is omitted, the for command executes list
once for each positional parameter that is set (see
PARAMETERS
below).
select name [ in word; ] do list ; done
The list of words following in is expanded, generating a list
of items. The set of expanded words is printed on the standard
error, each preceded by a number. If the in
word is omitted, the positional parameters are printed (see
PARAMETERS
below). The
PS3
prompt is then displayed and a line read from the standard input.
If the line consists of the number corresponding to one of
the displayed words, then the value of
name
is set to that word. If the line is empty, the words and prompt
are displayed again. If EOF is read, the command completes. Any
other value read causes
name
to be set to null. The line read is saved in the variable
REPLY .
The
list
is executed after each selection until a
break
or
return
command is executed.
The exit status of
select
is the exit status of the last command executed in
list ,
or zero if no commands were executed.
case word in [ pattern [ | pattern ] \
. ) \fIlist\fP ;; ] ... \fBesac\fP
A case command first expands word, and tries to match
it against each pattern in turn, using the same matching rules
as for pathname expansion (see
Pathname Expansion
below). When a match is found, the
corresponding list is executed. After the first match, no
subsequent matches are attempted. The exit status is zero if no
patterns are matches. Otherwise, it is the exit status of the
last command executed in list.
if list then list \
[ elif list then list ] ... \
[ else list ] fi
The
if
list
is executed. If its exit status is zero, the
then list is executed. Otherwise, each elif
list is executed in turn, and if its exit status is zero,
the corresponding then list is executed and the
command completes. Otherwise, the else list is
executed, if present. The exit status is the exit status of the
last command executed, or zero if no condition tested true.
while list do list done
until list do list done
The while command continuously executes the do
list as long as the last command in list returns
an exit status of zero. The until command is identical
to the while command, except that the test is negated;
the
do
list
is executed as long as the last command in
list
returns a non-zero exit status.
The exit status of the while and until commands
is the exit status
of the last do list command executed, or zero if
none was executed.
[ function ] name () { list; }
This defines a function named name. The body of the
function is the
list
of commands between { and }. This list
is executed whenever name is specified as the
name of a simple command. The exit status of a function is
the exit status of the last command executed in the body. (See
FUNCTIONS
below.)
COMMENTS
In a non-interactive shell, or an interactive shell in which the
-o interactive-comments
option to the set builtin is enabled, a word beginning with
#
causes that word and all remaining characters on that line to
be ignored. An interactive shell without the
-o interactive-comments
option enabled does not allow comments.
QUOTING
Quoting is used to remove the special meaning of certain
characters or words to the shell. Quoting can be used to
disable special treatment for special characters, to prevent
reserved words from being recognized as such, and to prevent
parameter expansion.
Each of the metacharacters listed above under
DEFINITIONS
has special meaning to the shell and must be quoted if they are to
represent themselves. There are three quoting mechanisms: the
escape character
single quotes, and double quotes.
A non-quoted backslash (\e) is the
escape character .
It preserves the literal value of the next character that follows,
with the exception of <newline>. If a \e<newline> pair
appears, and the backslash is not quoted, the \e<newline>
is treated as a line continuation (that is, it is effectively ignored).
Enclosing characters in single quotes preserves the literal value
of each character within the quotes. A single quote may not occur
between single quotes, even when preceded by a backslash.
Enclosing characters in double quotes preserves the literal value
of all characters within the quotes, with the exception of
$ ,
` ,
and
\e .
The characters
$
and
`
retain their special meaning within double quotes. The backslash
retains its special meaning only when followed by one of the following
characters:
$ ,
` ,
\^"\^,
\e ,
or
<newline> .
A double quote may be quoted within double quotes by preceding it with
a backslash.
The special parameters
*
and
@
have special meaning when in double
quotes (see
PARAMETERS
below).
PARAMETERS
A
parameter
is an entity that stores values, somewhat like a
variable in a conventional programming language. It can be a
name ,
a number, or one of the special characters listed below under
Special Parameters .
For the shell's purposes, a
variable
is a parameter denoted by a
name .
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
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. If
the variable has its
-i
attribute set (see
declare
below in
SHELL BUILTIN COMMANDS )
then
value
is subject to arithmetic expansion even if the $[...] syntax does
not appear. Word splitting is not performed, with the exception
of "$@" as explained below under
Special Parameters .
Pathname expansion is not performed.
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).
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 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 null or unset, the parameters are separated by spaces.
@
Expands to the positional parameters, starting from one. When the
expansion occurs within double quotes, each parameter expands as a
separate word. That is, ``
$@ ''
is equivalent to
``$1'' ``$2'' ...
When there are no positional parameters, ``$@'' and
$@
expand to nothing (i.e., they are removed).
#
Expands to the number of positional parameters in decimal.
?
Expands to the 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
flag).
$
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 most recently executed background
(asynchronous) command.
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 pathname used to invoke
bash ,
as given by argument zero.
_
Expands to the last argument to the previous command, after expansion.
Also set to the full pathname of each command executed and placed in
the environment exported to that command.
The following variables are set by the shell:
PPID
The process ID of the shell's parent.
PWD
The current working directory as set by the
cd
command.
OLDPWD
The previous working directory as set by the
cd
command.
REPLY
Set to the line of input read by the
read
builtin command when no arguments are supplied.
UID
Expands to the user ID of the current user, initialized at shell startup.
EUID
Expands to the effective user ID of the current user, initialized at
shell startup.
BASH
Expands to the full pathname used to invoke this instance of
bash .
BASH_VERSION
Expands to the version number of this instance of
bash .
SHLVL
Incremented by one each time an instance of
bash
is started.
RANDOM
Each time this parameter is referenced, a random integer is
generated. The sequence of random numbers may be initialized by assigning
a value to
RANDOM .
If
RANDOM
is unset, it loses its special properties, even if it is
subsequently reset.
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.
If
SECONDS
is unset, it loses its special properties, even if it is
subsequently reset.
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. When in a function, the value is not
the number of the source line that the command appears
on (that information has been lost by the time the function is
executed), but is an approximation of the number of
simple commands
executed in the current function.
If
LINENO
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. If
HISTCMD
is unset, it loses its special properties, even if it is
subsequently reset.
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).
HOSTTYPE
Automatically set to a string that uniquely
describes the type of machine on which
bash
is executing. The default is system-dependent.
OSTYPE
Automatically set to a string that
describes the operating system on which
bash
is executing. The default is system-dependent.
The following variables are used by the shell. In some cases,
bash
assigns a default value to a variable; these cases are noted
below.
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>''.
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). The default path is system-dependent,
and is set by the administrator who installs
bash .
A common value is ``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin:.''.
HOME
The home directory of the current user; the default argument for the
cd builtin command.
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''.
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
ENV
is subjected to parameter expansion, command substitution, and arithmetic
expansion before being interpreted as a pathname.
PATH
is not used to search for the resultant pathname.
MAIL
If this parameter is set to a filename and the
MAILPATH
variable is not set,
bash
informs the user of the arrival of mail in the specified file.
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 prompting.
If this variable is unset, the shell disables mail checking.
MAILPATH
A colon-separated list of pathnames to be checked for mail.
The message to be printed may be specified by separating the pathname from
the message with a `?'. $_ stands for the name of the current mailfile.
Example:
MAILPATH='/usr/spool/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'
Bash
supplies a default value for this variable, but the location of the user
mail files that it uses is system dependent (e.g., /usr/spool/mail/$USER).
MAIL_WARNING
If set, and a file that bash is checking for mail has been
accessed since the last time it was checked, the message ``The mail in
mailfile has been read'' is printed.
PS1
The value of this parameter is expanded (see
PROMPTING
below) and used as the primary prompt string. The default value is
``bash\e$ ''.
PS2
The value of this parameter is expanded
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
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. The default is ``+ ''.
HISTSIZE
The number of commands to remember in the command history (see
HISTORY
below). The default value is 500.
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 an interactive 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. The default
value is 500.
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.
PROMPT_COMMAND
If set, the value is executed as a command prior to issuing each primary
prompt.
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 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. This is only in effect for
interactive shells.
TMOUT
If set to a value greater than zero, 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.
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:~''.
INPUTRC
The filename for the readline startup file, overriding the default
of
~/.inputrc
(see
READLINE
below).
notify
If set,
bash
reports terminated background jobs immediately, rather than waiting
until before printing the next primary prompt (see also the
-b
option to the
set
builtin command).
history_control
HISTCONTROL
If set to a value of
ignorespace ,
lines which begin with a
space
character are not entered on the history list. If set to
a value of
ignoredups ,
lines matching the last history line are not entered.
A value of
ignoreboth
combines the two options.
If unset, or if set to any other value than those above,
all lines read
by the parser are saved on the history list.
command_oriented_history
If set,
bash
attempts to save all lines of a multiple-line
command in the same history entry. This allows
easy re-editing of multi-line commands.
glob_dot_filenames
If set,
bash
includes filenames beginning with a `.' in the results of pathname
expansion.
allow_null_glob_expansion
If set,
bash
allows pathname patterns which match no
files (see
Pathname Expansion
below)
to expand to a null string, rather than themselves.
histchars
The two or three characters which control history expansion
and tokenization (see
HISTORY EXPANSION
below). The first character is the
history expansion character
that is, 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 signifies 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.
nolinks
If set, the shell does not follow symbolic links when executing
commands that change the current working directory. It uses the
physical directory structure instead. By default,
bash
follows the logical chain of directories when performing commands
which change the current directory, such as
cd .
See also the description of the -P option to the set
builtin (
SHELL BUILTIN COMMANDS
below).
hostname_completion_file
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 file may be changed interactively; the next
time hostname completion is attempted
bash
adds the contents of the new file to the already existing database.
noclobber
If set,
bash
does not overwrite an existing file with the
> ,
>& ,
and
<>
redirection operators. This variable may be overridden when
creating output files by using the redirection operator
>|
instead of
>
(see also the -C option to the
set
builtin command).
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 id (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
%
job id.
no_exit_on_failed_exec
If this variable exists, a non-interactive shell will not exit if
it cannot execute the file specified in the
exec
builtin command. An interactive shell does not exit if
exec
fails.
cdable_vars
If this is set, an argument to the
cd
builtin command that
is not a directory is assumed to be the name of a variable whose
value is the directory to change to.
EXPANSION
Expansion is performed on the command line after it has been split into
words. There are seven kinds of expansion performed:
brace expansion
tilde expansion
parameter and variable expansion
command substitution
arithmetic expansion
word splitting
and
pathname expansion .
The order of expansions is: brace expansion, tilde expansion,
parameter, variable, command, and arithmetic substitution (done
in a left-to-right fashion), word splitting, and pathname
expansion.
On systems that can support it, there is an additional expansion
available: process substitution.
Only brace expansion, word splitting, and pathname expansion
can change the number of words of the expansion; other expansions
expand a single word to a single word.
The single exception to this is the expansion of
``$@'' as explained above (see
PARAMETERS ).
Brace expansion
is a mechanism by which arbitrary strings
may be generated. This mechanism is similar to
pathname expansion, but the filenames generated
need not exist. Patterns to be brace expanded take
the form of an optional
preamble ,
followed by a series of comma-separated strings
between a pair of braces, followed by an optional
postamble .
The preamble is prepended to each string contained
within the braces, and the postamble is then appended
to each resulting string, expanding left to right.
Brace expansions may be nested. The results of each expanded
string are not sorted; left to right order is preserved.
For example, a{d,c,b}e expands into `ade ace abe'.
Brace expansion is performed before any other expansions,
and any characters special to other expansions are preserved
in the result. It is strictly textual.
Bash
does not apply any syntactic interpretation to the context of the
expansion or the text between the braces.
A correctly-formed brace expansion must contain unquoted opening
and closing braces, and at least one unquoted comma.
Any incorrectly formed brace expansion is left unchanged.
This construct is typically used as shorthand when the common
prefix of the strings to be generated is longer than in the
above example:
mkdir /usr/local/src/bash/{old,new,dist,bugs}
or
chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
Brace expansion introduces a slight incompatibility with
traditional versions of
sh ,
the Bourne shell.
sh
does not treat opening or closing braces specially when they
appear as part of a word, and preserves them in the output.
Bash
removes braces from words as a consequence of brace
expansion. For example, a word entered to
sh
as file{1,2}
appears identically in the output. The same word is
output as
file1 file2
after expansion by
bash .
If strict compatibility with
sh
is desired, start
bash
with the
-nobraceexpansion
flag (see
OPTIONS
above)
or disable brace expansion with the
+o braceexpand
option to the
set
command (see
SHELL BUILTIN COMMANDS
below).
If a word begins with a tilde character (`~'), all of the characters
preceding the first slash (or all characters, if there is no slash)
are treated as a possible login name. If this login name
is the null string, the tilde is replaced with the value of the
parameter
HOME .
If
HOME
is unset, the home directory of
the user executing the shell is substituted instead.
If a `+' follows the tilde, the value of
PWD
replaces the tilde and `+'. If
a `-' follows, the value of
OLDPWD
is substituted.
If the value following the tilde is a valid login name,
the tilde and login name are replaced with the home directory
associated with that name. If the name is invalid, or the tilde
expansion fails, the word is unchanged.
Each variable assignment is checked for unquoted
instances of tildes following a
:
or
= .
In these cases, tilde substitution is also performed. Consequently, one
may use pathnames with tildes in assignments to
PATH ,
MAILPATH ,
and
CDPATH ,
and the shell assigns the expanded value.
The `$' character introduces parameter expansion,
command substitution, or arithmetic expansion. The parameter name
or symbol to be expanded may be enclosed in braces, which
are optional but serve to protect the variable to be expanded from
characters immediately following it which could be
interpreted as part of the name.
${parameter}
The value of parameter is substituted. The braces are required
when
parameter
is a positional parameter with more than one digit,
or when
parameter
is followed by a character which is not to be
interpreted as part of its name.
In each of the cases below, word is subject to tilde expansion,
parameter expansion, command substitution, and arithmetic expansion.
Bash tests for a parameter that is unset or null; omitting the
colon results in a test only for a parameter that is unset.
${parameter:-word}
Use Default Values. If
parameter
is unset or null, the expansion of
word
is substituted. Otherwise, the value of
parameter
is substituted.
${parameter:=word}
Assign Default Values.
If
parameter
is unset or null, the expansion of
word
is assigned to
parameter .
The value of
parameter
is then substituted. Positional parameters and special parameters may
not be assigned to in this way.
${parameter:?word}
Display Error if Null or Unset.
If
parameter
is null or unset, the expansion of word (or a message to that effect
if
word
is not present) is written to the standard error and the shell, if it
is not interactive, exits. Otherwise, the value of parameter is
substituted.
${parameter:+word}
Use Alternate Value.
If
parameter
is null or unset, nothing is substituted, otherwise the expansion of
word
is substituted.
${#parameter}
The length in characters of the value of parameter is substituted.
If parameter is
*
or
@ ,
the length substituted is the length of
*
expanded within double quotes.
${parameter#word}
${parameter##word}
The
word
is expanded to produce a pattern just as in pathname
expansion. If the pattern matches the beginning of
the value of
parameter ,
then the expansion is the value of
parameter
with the shortest matching pattern deleted (the ``#''
case) or the longest
matching pattern deleted (the ``##'' case).
${parameter%word}
${parameter%%word}
The word is expanded to produce a pattern just as in
pathname expansion. If the pattern matches a
trailing portion of the value of
parameter ,
then the expansion is the value of
parameter
with the shortest matching pattern deleted
(the ``%'' case) or the longest
matching pattern deleted (the ``%%'' case).
Command substitution allows the output of a command to replace
the command name. There are two forms:
or
Bash
performs the expansion by executing command and
replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
$ ,
` ,
or
\e .
When using the $(\^command\|) form, all characters between the
parentheses make up the command; none are treated specially.
Command substitutions may be nested. To nest when using the old form,
escape the inner backquotes with backslashes.
If the substitution appears within double quotes, word splitting and
pathname expansion are not performed on the results.
Arithmetic expansion allows the evaluation of an arithmetic expression
and the substitution of the result. There are two formats for
arithmetic expansion:
$[expression]
$((expression))
The
expression
is treated as if it were within double quotes, but a double quote
inside the braces or parentheses
is not treated specially. All tokens in the
expression undergo parameter expansion, command substitution,
and quote removal. Arithmetic substitutions may be nested.
The evaluation is performed according to the rules listed below under
ARITHMETIC EVALUATION .
If
expression
is invalid,
bash
prints a message indicating failure and no substitution occurs.
Process substitution is supported on systems that support named
pipes (FIFOs) or the /dev/fd method of naming open files.
It takes the form of
<(list\^)
or
>(list\^).
The process list is run with its input or output connected to a
FIFO or some file in /dev/fd. The name of this file is
passed as an argument to the current command as the result of the
expansion. If the >(list\^) form is used, writing to
the file will provide input for list. If the
<(list\^) form is used, the file passed as an
argument should be read to obtain the output of list.
On systems that support it, process substitution is performed
simultaneously with
parameter and variable expansion
command substitution
and
arithmetic expansion .
The shell scans the results of
parameter expansion,
command substitution,
and
arithmetic expansion
that did not occur within double quotes for
word splitting .
The shell treats each character of
IFS
as a delimiter, and splits the results of the other
expansions into words on these characters. If the
value of
IFS
is exactly
<space><tab><newline> ,
the default, then
any sequence of
IFS
characters serves to delimit words. If
IFS
has a value other than the default, then sequences of
the whitespace characters
space
and
tab
are ignored at the beginning and end of the
word, as long as the whitespace character is in the
value of
IFS
(an
IFS
whitespace character).
Any character in
IFS
that is not
IFS
whitespace, along with any adjacent
IFS
whitespace characters, delimits a field.
A sequence of
IFS
whitespace characters is also treated as a delimiter.
If the value of
IFS
is null, no word splitting occurs.
IFS
cannot be unset.
Explicit null arguments (\^\f3"\^" or \^\f3'\^'\^)
are retained. Implicit null arguments, resulting from the expansion
of
parameters
that have no values, are removed.
Note that if no expansion occurs, no splitting
is performed.
After word splitting,
unless the
-f
option has been set,
bash
scans each
word
for the characters
* ,
? ,
and
[ .
If one of these characters appears, then the word is
regarded as a
pattern ,
and replaced with an alphabetically sorted list of
pathnames matching the pattern.
If no matching pathnames are found,
and the shell variable
allow_null_glob_expansion
is unset, the word is left unchanged.
If the variable is set, and no matches are found,
the word is removed.
When a pattern is used for pathname generation,
the character
``.''
at the start of a name or immediately following a slash
must be matched explicitly, unless the shell variable
glob_dot_filenames
is set. The slash character must always be matched
explicitly. In other cases, the
``.''
character is not treated specially.
The special pattern characters have the following meanings:
*
Matches any string, including the null string.
?
Matches any single character.
[...]
Matches any one of the enclosed characters. A pair of characters
separated by a minus sign denotes a
range ;
any character lexically between those two characters, inclusive,
is matched. If the first character following the
[
is a
!
or a
^
then any character not enclosed is matched. A
-
or
]
may be matched by including it as the first or last character
in the set.
After the preceding expansions, all unquoted occurrences of the
characters
\e ,
` ,
and \^\f3"\^ are removed.
REDIRECTION
Before a command is executed, its input and output
may be
redirected
using a special notation interpreted by the shell.
Redirection may also be used to open and close files for the
current shell execution environment. The following redirection
operators may precede or appear anywhere within a
simple command
or may follow a
command .
Redirections are processed in the order they appear, from
left to right.
In the following descriptions, if the file descriptor number is
omitted, and the first character of the redirection operator is
< ,
the redirection refers to the standard input (file descriptor
0). If the first character of the redirection operator is
> ,
the redirection refers to the standard output (file descriptor
1).
The word that follows the redirection operator in the following
descriptions is subjected to brace expansion, tilde expansion,
parameter expansion, command substitution, arithmetic expansion,
quote removal, and pathname expansion. If it expands to more
than one word,
bash
reports an error.
Note that the order of redirections is significant. For example,
the command
directs both standard output and standard error to the file
dirlist ,
while the command
directs only the standard output to file
dirlist ,
because the standard error was duplicated as standard output
before the standard output was redirected to
dirlist .
Redirection of input causes the file whose name results from
the expansion of
word
to be opened for reading on file descriptor
n ,
or the standard input (file descriptor 0) if
n
is not specified.
The general format for redirecting input is:
Redirection of output causes the file whose name results from
the expansion of
word
to be opened for writing on file descriptor
n ,
or the standard output (file descriptor 1) if
n
is not specified. If the file does not exist it is created;
if it does exist it is truncated to zero size.
The general format for redirecting output is:
If the redirection operator is
>| ,
then the value of the
-C
option to the
set
builtin command is not tested, and file creation is attempted.
(See also the description of
noclobber
under
Shell Variables
above.)
Redirection of output in this fashion
causes the file whose name results from
the expansion of
word
to be opened for appending on file descriptor
n ,
or the standard output (file descriptor 1) if
n
is not specified. If the file does not exist it is created.
The general format for appending output is:
Bash
allows both the
standard output (file descriptor 1) and
the standard error output (file descriptor 2)
to be redirected to the file whose name is the
expansion of
word
with this construct.
There are two formats for redirecting standard output and
standard error:
and
Of the two forms, the first is preferred.
This is semantically equivalent to
This type of redirection instructs the shell to read input from the
current source until a line containing only
word
(with no trailing blanks)
is seen. All of
the lines read up to that point are then used as the standard
input for a command.
The format of here-documents is as follows:
<<[-]word
here-document
delimiter
No parameter expansion, command substitution, pathname
expansion, or arithmetic expansion is performed on
word .
If any characters in
word
are quoted, the
delimiter
is the result of quote removal on
word ,
and the lines in the here-document are not expanded. Otherwise,
all lines of the here-document are subjected to parameter expansion,
command substitution, and arithmetic expansion. In the latter
case, the pair
\e<newline>
is ignored, and
\e
must be used to quote the characters
\e ,
$ ,
and
` .
If the redirection operator is
<<- ,
then all leading tab characters are stripped from input lines and the
line containing
delimiter .
This allows
here-documents within shell scripts to be indented in a
natural fashion.
The redirection operator
is used to duplicate input file descriptors.
If
word
expands to one or more digits, the file descriptor denoted by
n
is made to be a copy of that file descriptor. If
word
evaluates to
- ,
file descriptor
n
is closed. If
n
is not specified, the standard input (file descriptor 0) is used.
The operator
is used similarly to duplicate output file descriptors. If
n
is not specified, the standard output (file descriptor 1) is used.
As a special case, if n is omitted, and word does not
expand to one or more digits, the standard output and standard
error are redirected as described previously.
The redirection operator
causes the file whose name is the expansion of
word
to be opened for both reading and writing on file descriptor
n ,
or as the standard input and standard output if
n
is not specified. If the file does not exist, it is created.
FUNCTIONS
A shell function, defined as described above under
SHELL GRAMMAR
stores a series of commands for later execution.
Functions are executed in the context of the
current shell; no new process is created to interpret
them (contrast this with the execution of a shell script).
When a function is executed, the arguments to the
function become the positional parameters
during its execution. The special parameter
#
is updated to reflect the change. Positional parameter 0
is unchanged.
Variables local to the function may be declared with the
local
builtin command. Ordinarily, variables and their values
are shared between the function and its caller.
If the builtin command
return
is executed in a function, the function completes and
execution resumes with the next command after the function
call. When a function completes, the values of the
positional parameters and the special parameter
#
are restored to the values they had prior to function
execution.
Function names and definitions may be listed with the
-f
option to the
declare
or
typeset
builtin commands. Functions may be exported so that subshells
automatically have them defined with the
-f
option to the
export
builtin.
Functions may be recursive. No limit is imposed on the number
of recursive calls.
ALIASES
The shell maintains a list of
aliases
that may be set and unset with the
alias
and
unalias
builtin commands (see
SHELL BUILTIN COMMANDS
below).
The first word of each command, if unquoted,
is checked to see if it has an
alias. If so, that word is replaced by the text of the alias.
The alias name and the replacement text may contain any valid
shell input, including the
metacharacters
listed above, with the exception that the alias name may not
contain =. The first word of the replacement text is tested
for aliases, but a word that is identical to an alias being expanded
is not expanded a second time. This means that one may alias
ls
to
ls -F
for instance, and
bash
does not try to recursively expand the replacement text.
If the last character of the alias value is a
blank ,
then the next command
word following the alias is also checked for alias expansion.
Aliases are created and listed with the
alias
command, and removed with the
unalias
command.
There is no mechanism for using arguments in the replacement text,
as in
csh .
If arguments are needed, a shell function should be used.
Aliases are not expanded when the shell is not interactive.
The rules concerning the definition and use of aliases are
somewhat confusing.
Bash
always reads at least one complete line
of input before executing any
of the commands on that line. Aliases are expanded when a
command is read, not when it is executed. Therefore, an
alias definition appearing on the same line as another
command does not take effect until the next line of input is read.
This means that the commands following the alias definition
on that line are not affected by the new alias.
This behavior is also an issue when functions are executed.
Aliases are expanded when the function definition is read,
not when the function is executed, because a function definition
is itself a compound command. As a consequence, aliases
defined in a function are not available until after that
function is executed. To be safe, always put
alias definitions on a separate line, and do not use
alias
in compound commands.
Note that for almost every purpose, aliases are superseded by
shell functions.
JOB CONTROL
Job control
refers to the ability to selectively stop (suspend)
the execution of processes and continue (resume)
their execution at a later point. A user typically employs
this facility via an interactive interface supplied jointly
by the system's terminal driver and
bash .
The shell associates a
job
with each pipeline. It keeps a table of currently executing
jobs, which may be listed with the
jobs
command. When
bash
starts a job asynchronously (in the
background ),
it prints a line that looks like:
indicating that this job is job number 1 and that the process ID
of the last process in the pipeline associated with this job is 25647.
All of the processes in a single pipeline are members of the same job.
Bash
uses the
job
abstraction as the basis for job control.
To facilitate the implementation of the user interface to job
control, the system maintains the notion of a current terminal
process group ID. Members of this process group (processes whose
process group ID is equal to the current terminal process group ID)
receive keyboard-generated signals such as
SIGINT .
These processes are said to be in the
foreground .
Background
processes are those whose process group ID differs from the terminal's;
such processes are immune to keyboard-generated signals.
Only foreground processes are allowed to read from or write to the
terminal. Background processes which attempt to read from (write to) the
terminal are sent a
SIGTTIN (SIGTTOU)
signal by the terminal driver,
which, unless caught, suspends the process.
If the operating system on which
bash
is running supports
job control,
bash
allows you to use it.
Typing the
suspend
character (typically
^Z ,
Control-Z) while a process is running
causes that process to be stopped and returns you to
bash .
Typing the
delayed suspend
character (typically
^Y ,
Control-Y) causes the process to be stopped when it
attempts to read input from the terminal, and control to
be returned to
bash .
You may then manipulate the state of this job, using the
bg
command to continue it in the background, the
fg
command to continue it in the foreground, or
the
kill
command to kill it. A ^Z takes effect immediately,
and has the additional side effect of causing pending output
and typeahead to be discarded.
There are a number of ways to refer to a job in the shell.
The character
%
introduces a job name. Job number
n
may be referred to as
%n .
A job may also be referred to using a prefix of the name used to
start it, or using a substring that appears in its command line.
For example,
%ce
refers to a stopped
ce
job. If a prefix matches more than one job,
bash
reports an error. Using
%?ce ,
on the other hand, refers to any job containing the string
ce
in its command line. If the substring matches more than one job,
bash
reports an error. The symbols
%%
and
%+
refer to the shell's notion of the
current job
which is the last job stopped while it was in
the foreground.
The
previous job
may be referenced using
%- .
In output pertaining to jobs (e.g., the output of the
jobs
command), the current job is always flagged with a
+ ,
and the previous job with a
- .
Simply naming a job can be used to bring it into the
foreground:
%1
is a synonym for
``fg %1'',
bringing job 1 from the background into the foreground.
Similarly,
``%1 &''
resumes job 1 in the background, equivalent to
``bg %1''.
The shell learns immediately whenever a job changes state.
Normally,
bash
waits until it is about to print a prompt before reporting
changes in a job's status so as to not interrupt
any other output. If the
-b
option to the
set
builtin command
is set,
bash
reports such changes immediately. (See also the description of
notify
variable under
Shell Variables
above.)
If you attempt to exit
bash
while jobs are stopped, the shell prints a message warning you. You
may then use the
jobs
command to inspect their status. If you do this, or try to exit
again immediately, you are not warned again, and the stopped
jobs are terminated.
SIGNALS
When bash is interactive, it ignores
SIGTERM
(so that kill 0 does not kill an interactive shell),
and
SIGINT
is caught and handled (so that the wait builtin is interruptible).
In all cases, bash ignores
SIGQUIT .
If job control is in effect,
bash
ignores
SIGTTIN ,
SIGTTOU ,
and
SIGTSTP .
Synchronous jobs started by bash have signals set to the
values inherited by the shell from its parent. When job control
is not in effect, background jobs (jobs started with
& )
ignore
SIGINT
and
SIGQUIT .
Commands run as a result of command substitution ignore the
keyboard-generated job control signals
SIGTTIN ,
SIGTTOU ,
and
SIGTSTP .
COMMAND EXECUTION
After a command has been split into words, if it results in a
simple command and an optional list of arguments, the following
actions are taken.
If the command name contains no slashes, the shell attempts to
locate it. If there exists a shell function by that name, that
function is invoked as described above in
FUNCTIONS .
If the name does not match a function, the shell searches for
it in the list of shell builtins. If a match is found, that
builtin is invoked.
If the name is neither a shell function nor a builtin,
and contains no slashes,
bash
searches each element of the
PATH
for a directory containing an executable file by that name.
If the search is unsuccessful, the shell prints an error
message and returns a nonzero exit status.
If the search is successful, or if the command name contains
one or more slashes, the shell executes the named program.
Argument 0 is set to the name given, and the remaining arguments
to the command are set to the arguments given, if any.
If this execution fails because the file is not in executable
format, and the file is not a directory, it is assumed to be
a shell script, a file
containing shell commands. A subshell is spawned to execute
it. This subshell reinitializes itself, so
that the effect is as if a new shell had been invoked
to handle the script, with the exception that the locations of
commands remembered by the parent (see
hash
below under
SHELL BUILTIN COMMANDS)
are retained by the child.
If the program is a file beginning with
#! ,
the remainder of the first line specifies an interpreter
for the program. The shell executes the
specified interpreter on operating systems that do not
handle this executable format themselves. The arguments to the
interpreter consist of a single optional argument following the
interpreter name on the first line of the program, followed
by the name of the program, followed by the command
arguments, if any.
ENVIRONMENT
When a program is invoked it is given an array of strings
called the
environment .
This is a list of
name-value pairs, of the form
name\fR=\fPvalue .
The shell allows you to manipulate the environment in several
ways. On invocation, the shell scans its own environment and
creates a parameter for each name found, automatically marking
it for
export
to child processes. Executed commands inherit the environment.
The
export
and
declare -x
commands allow parameters and functions to be added to and
deleted from the environment. If the value of a parameter
in the environment is modified, the new value becomes part
of the environment, replacing the old. The environment
inherited by any executed command consists of the shell's
initial environment, whose values may be modified in the shell,
less any pairs removed by the
unset
command, plus any additions via the
export
and
declare -x
commands.
The environment for any
simple command
or function may be augmented temporarily by prefixing it with
parameter assignments, as described above in
PARAMETERS .
These assignment statements affect only the environment seen
by that command.
If the
-k
flag is set (see the
set
builtin command below), then
all
parameter assignments are placed in the environment for a command,
not just those that precede the command name.
When
bash
invokes an external command, the variable
_
is set to the full path name of the command and passed to that
command in its environment.
EXIT STATUS
For the purposes of the shell, a command which exits with a
zero exit status has succeeded. An exit status of zero
indicates success. A non-zero exit status indicates failure.
When a command terminates on a fatal signal, bash uses
the value of 128+signal as the exit status.
If a command is not found, the child process created to
execute it returns a status of 127. If a command is found
but is not executable, the return status is 126.
Bash itself returns the exit status of the last command
executed, unless a syntax error occurs, in which case it exits
with a non-zero value. See also the exit builtin
command below.
PROMPTING
When executing interactively,
bash
displays the primary prompt
PS1
when it is ready to read a command, and the secondary prompt
PS2
when it needs more input to complete a command.
Bash
allows these prompt strings to be customized by inserting a number of
backslash-escaped special characters that are decoded as follows:
\et
the current time in HH:MM:SS format
\ed
the date in "Weekday Month Date" format (e.g., "Tue May 26")
\en
\es
the name of the shell, the basename of
$0
(the portion following the final slash)
\ew
the current working directory
\eW
the basename of the current working directory
\eu
the username of the current user
\eh
\e#
the command number of this command
\e!
the history number of this command
\e$
if the effective UID is 0, a
# ,
otherwise a
$
\ennn
the character corresponding to the octal number nnn
\e\e
\e[
begin a sequence of non-printing characters, which could be used to
embed a terminal control sequence into the prompt
\e]
end a sequence of non-printing characters
The command number and the history number are usually different:
the history number of a command is its position in the history
list, which may include commands restored from the history file
(see
HISTORY
below), while the command number is the position in the sequence
of commands executed during the current shell session.
After the string is decoded, it is expanded via
parameter expansion,
command substitution, arithmetic expansion, and word splitting.
READLINE
This is the library that handles reading input when using an interactive
shell, unless the
-nolineediting
option is given. By default, the line editing commands
are similar to those of emacs.
A vi-style line editing interface is also available.
In this section, the emacs-style notation is used to denote
keystrokes. Control keys are denoted by C-key, e.g., C-n
means Control-N. Similarly,
meta
keys are denoted by M-key, so M-x means Meta-X. (On keyboards
without a
meta
key, M-x means ESC x, i.e., press the Escape key
then the
x
key. This makes ESC the meta prefix.
The combination M-C-x means ESC-Control-x,
or press the Escape key
then hold the Control key while pressing the
x
key.)
The default key-bindings may be changed with an
~/.inputrc
file. The value of the shell variable
INPUTRC ,
if set, is used instead of
~/.inputrc .
Other programs that use this library may add their own commands
and bindings.
For example, placing
or
C-Meta-u: universal-argument
into the
~/.inputrc
would make M-C-u execute the readline command
universal-argument .
The following symbolic character names are recognized:
RUBOUT ,
DEL ,
ESC ,
LFD ,
NEWLINE ,
RET ,
RETURN ,
SPC ,
SPACE ,
and
TAB .
In addition to command names, readline allows keys to be bound
to a string that is inserted when the key is pressed (a macro).
Readline is customized by putting commands in an initialization
file. The name of this file is taken from the value of the
INPUTRC
variable. If that variable is unset, the default is
~/.inputrc .
When a program which uses the readline library starts up, the
init file is read, and the key bindings and variables are set.
There are only a few basic constructs allowed in the
readline init file. Blank lines are ignored.
Lines beginning with a # are comments.
Lines beginning with a $ indicate conditional
constructs. Other lines
denote key bindings and variable settings.
The syntax for controlling key bindings in the
~/.inputrc
file is simple. All that is required is the name of the
command or the text of a macro and a key sequence to which
it should be bound. The name may be specified in one of two ways:
as a symbolic key name, possibly with Meta- or Control-
prefixes, or as a key sequence.
When using the form keyname:function-name or macro,
keyname
is the name of a key spelled out in English. For example:
Control-u: universal-argument
Meta-Rubout: backward-kill-word
Control-o: ">&output"
In the above example,
C-u
is bound to the function
universal-argument ,
M-DEL
is bound to the function
backward-kill-word ,
and
C-o
is bound to run the macro
expressed on the right hand side (that is, to insert the text
>&output
into the line).
In the second form, "keyseq":function-name or macro,
keyseq
differs from
keyname
above in that strings denoting
an entire key sequence may be specified by placing the sequence
within double quotes. Some GNU Emacs style key escapes can be
used, as in the following example.
"\eC-u": universal-argument
"\eC-x\eC-r": re-read-init-file
"\ee[11~": "Function Key 1"
In this example,
C-u
is again bound to the function
universal-argument .
C-x C-r
is bound to the function
re-read-init-file ,
and
ESC [ 1 1 ~
is bound to insert the text
Function Key 1 .
The full set of escape sequences is
\eC-
\eM-
\ee
\e\e
\e"
\e'
When entering the text of a macro, single or double quotes should
be used to indicate a macro definition. Unquoted text
is assumed to be a function name. Backslash
will quote any character in the macro text, including " and '.
Bash
allows the current readline key bindings to be displayed or modified
with the
bind
builtin command. The editing mode may be switched during interactive
use by using the
-o
option to the
set
builtin command (see
SHELL BUILTIN COMMANDS
below).
Readline has variables that can be used to further customize its
behavior. A variable may be set in the
inputrc
file with a statement of the form
Except where noted, readline variables can take the values
On
or
Off .
The variables and their default values are:
horizontal-scroll-mode (Off)
When set to On, makes readline use a single line for display,
scrolling the input horizontally on a single screen line when it
becomes longer than the screen width rather than wrapping to a new line.
editing-mode (emacs)
Controls whether readline begins with a set of key bindings similar
to emacs or vi.
editing-mode
can be set to either
emacs
or
vi .
mark-modified-lines (Off)
If set to On, history lines that have been modified are displayed
with a preceding asterisk (*).
bell-style (audible)
Controls what happens when readline wants to ring the terminal bell.
If set to none, readline never rings the bell. If set to
visible, readline uses a visible bell if one is available.
If set to audible, readline attempts to ring the terminal's bell.
comment-begin (``#'')
The string that is inserted in vi mode when the
vi-comment
command is executed.
meta-flag (Off)
If set to On, readline will enable eight-bit input (that is,
it will not strip the high bit from the characters it reads),
regardless of what the terminal claims it can support.
convert-meta (On)
If set to On, readline will convert characters with the
eighth bit set to an ASCII key sequence
by stripping the eighth bit and prepending an
escape character (in effect, using escape as the meta prefix).
output-meta (Off)
If set to On, readline will display characters with the
eighth bit set directly rather than as a meta-prefixed escape
sequence.
completion-query-items (100)
This determines when the user is queried about viewing
the number of possible completions
generated by the possible-completions command.
It may be set to any integer value greater than or equal to
zero. If the number of possible completions is greater than
or equal to the value of this variable, the user is asked whether
or not he wishes to view them; otherwise they are simply listed
on the terminal.
keymap (emacs)
Set the current readline keymap. The set of legal keymap names is
emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move,
vi-command, and
vi-insert .
vi is equivalent to vi-command; emacs is
equivalent to emacs-standard. The default value is
emacs ;
the value of
editing-mode
also affects the default keymap.
show-all-if-ambiguous (Off)
This alters the default behavior of the completion functions. If
set to
on ,
words which have more than one possible completion cause the
matches to be listed immediately instead of ringing the bell.
expand-tilde (Off)
If set to on, tilde expansion is performed when readline
attempts word completion.
Readline implements a facility similar in spirit to the conditional
compilation features of the C preprocessor which allows key
bindings and variable settings to be performed as the result
of tests. There are three parser directives used.
The
$if
construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
readline. The text of the test extends to the end of the line;
no characters are required to isolate it.
The mode= form of the $if directive is used to test
whether readline is in emacs or vi mode.
This may be used in conjunction
with the set keymap command, for instance, to set bindings in
the emacs-standard and emacs-ctlx keymaps only if
readline is starting out in emacs mode.
The term= form may be used to include terminal-specific
key bindings, perhaps to bind the key sequences output by the
terminal's function keys. The word on the right side of the
=
is tested against the full name of the terminal and the portion
of the terminal name before the first -. This allows
sun
to match both
sun
and
sun-cmd ,
for instance.
The application construct is used to include
application-specific settings. Each program using the readline
library sets the application name, and an initialization
file can test for a particular value.
This could be used to bind key sequences to functions useful for
a specific program. For instance, the following command adds a
key sequence that quotes the current or previous word in Bash:
$if Bash
# Quote the current or previous word
"\eC-xq": "\eeb\e"\eef\e""
$endif
This command, as you saw in the previous example, terminates an
$if command.
Commands in this branch of the $if directive are executed if
the test fails.
Readline commands may be given numeric
arguments ,
which normally act as a repeat count. Sometimes, however, it is the
sign of the argument that is significant. Passing a negative argument
to a command that acts in the forward direction (e.g., kill-line)
causes that command to act in a backward direction. Commands whose
behavior with arguments deviates from this are noted.
When a command is described as killing text, the text
deleted is saved for possible future retrieval
(yanking). The killed text is saved in a
kill-ring. Consecutive kills cause the text to be
accumulated into one unit, which can be yanked all at once.
Commands which do not kill text separate the chunks of text
on the kill-ring.
The following is a list of the names of the commands and the default
key sequences to which they are bound.
beginning-of-line (C-a)
Move to the start of the current line.
end-of-line (C-e)
Move to the end of the line.
forward-char (C-f)
Move forward a character.
backward-char (C-b)
forward-word (M-f)
Move forward to the end of the next word. Words are composed of
alphanumeric characters (letters and digits).
backward-word (M-b)
Move back to the start of this, or the previous, word. Words are
composed of alphanumeric characters (letters and digits).
clear-screen (C-l)
Clear the screen leaving the current line at the top of the screen.
With an argument, refresh the current line without clearing the
screen.
redraw-current-line
Refresh the current line. By default, this is unbound.
accept-line (Newline, Return)
Accept the line regardless of where the cursor is. If this line is
non-empty, add it to the history list according to the state of the
HISTCONTROL
variable. If the line is a modified history
line, then restore the history line to its original state.
previous-history (C-p)
Fetch the previous command from the history list, moving back in
the list.
next-history (C-n)
Fetch the next command from the history list, moving forward in the
list.
beginning-of-history (M-<)
Move to the first line in the history.
end-of-history (M->)
Move to the end of the input history, i.e., the line currently being
entered.
reverse-search-history (C-r)
Search backward starting at the current line and moving `up' through
the history as necessary. This is an incremental search.
forward-search-history (C-s)
Search forward starting at the current line and moving `down' through
the history as necessary. This is an incremental search.
non-incremental-reverse-search-history (M-p)
Search backward through the history starting at the current line
using a non-incremental search for a string supplied by the user.
non-incremental-forward-search-history (M-n)
Search forward through the history using a non-incremental search for
a string supplied by the user.
history-search-forward
Search forward through the history for the string of characters
between the start of the current line and the current point. This
is a non-incremental search. By default, this command is unbound.
history-search-backward
Search backward through the history for the string of characters
between the start of the current line and the current point. This
is a non-incremental search. By default, this command is unbound.
yank-nth-arg (M-C-y)
Insert the first argument to the previous command (usually
the second word on the previous line) at point (the current
cursor position). With an argument
n ,
insert the nth word from the previous command (the words
in the previous command begin with word 0). A negative argument
inserts the nth word from the end of the previous command.
yank-last-arg (M-.\^, M-_\^)
Insert the last argument to the previous command (the last word on
the previous line). With an argument,
behave exactly like yank-nth-arg.
shell-expand-line (M-C-e)
Expand the line the way the shell does when it reads it. This
performs alias and history expansion as well as all of the shell
word expansions. See
HISTORY EXPANSION
below for a description of history expansion.
history-expand-line (M-^)
Perform history expansion on the current line. See
HISTORY EXPANSION
below for a description of history expansion.
insert-last-argument (M-.\^, M-_\^)
A synonym for yank-last-arg.
operate-and-get-next (C-o)
Accept the current line for execution and fetch the next line
relative to the current line from the history for editing. Any
argument is ignored.
delete-char (C-d)
Delete the character under the cursor. If point is at the
beginning of the line, there are no characters in the line, and
the last character typed was not
C-d ,
then return
EOF .
backward-delete-char (Rubout)
Delete the character behind the cursor. When given a numeric argument,
save the deleted text on the kill-ring.
quoted-insert (C-q, C-v)
Add the next character that you type to the line verbatim. This is
how to insert characters like C-q, for example.
tab-insert (C-v TAB)
self-insert (a,\ b,\ A,\ 1,\ !,\ ...)
Insert the character typed.
transpose-chars (C-t)
Drag the character before point forward over the character at point.
Point moves forward as well. If point is at the end of the line, then
transpose the two characters before point. Negative arguments don't work.
transpose-words (M-t)
Drag the word behind the cursor past the word in front of the cursor
moving the cursor over that word as well.
upcase-word (M-u)
Uppercase the current (or following) word. With a negative argument,
do the previous word, but do not move point.
downcase-word (M-l)
Lowercase the current (or following) word. With a negative argument,
do the previous word, but do not move point.
capitalize-word (M-c)
Capitalize the current (or following) word. With a negative argument,
do the previous word, but do not move point.
kill-line (C-k)
Kill the text from the current cursor position to the end of the line.
backward-kill-line (C-x C-Rubout)
Kill backward to the beginning of the line.
unix-line-discard (C-u)
Kill backward from point to the beginning of the line.
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