bash
Version 2.0.
Copyright (C) 1991, 1993, 1996 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Free Software Foundation.
Bash is the shell, or command language interpreter,
that will appear in the GNU operating system.
The name is an acronym for the `Bourne-Again SHell',
a pun on Steve Bourne, the author of the direct ancestor of the current
Unix shell /bin/sh
,
which appeared in the Seventh Edition Bell Labs Research version
of Unix.
Bash is an sh
-compatible shell that incorporates useful
features from the Korn shell ksh
and the C shell csh
.
It is ultimately intended to be a
conformant implementation of the IEEE POSIX Shell and Tools
specification (IEEE Working Group 1003.2). It offers functional
improvements over sh
for both interactive and programming use.
While the GNU operating system will include a version
of csh
, Bash will be the default shell.
Like other GNU software, Bash is quite portable. It currently runs
on nearly every version of Unix and a few other operating systems -
independently-supported ports exist for OS/2 and Windows NT.
At its base, a shell is simply a macro processor that executes commands. A Unix shell is both a command interpreter, which provides the user interface to the rich set of Unix utilities, and a programming language, allowing these utilitites to be combined. The shell reads commands either from a terminal or a file. Files containing commands can be created, and become commands themselves. These new commands have the same status as system commands in directories like `/bin', allowing users or groups to establish custom environments.
A shell allows execution of Unix commands, both synchronously and
asynchronously. The redirection constructs permit
fine-grained control of the input and output of those commands,
and the shell allows control over the contents of their
environment. Unix shells also provide a small set of built-in
commands (builtins) implementing functionality impossible
(e.g., cd
, break
, continue
, and
exec
), or inconvenient (history
, getopts
,
kill
, or pwd
, for example) to obtain via separate
utilities. Shells may be used interactively or
non-interactively: they accept input typed from the keyboard or
from a file. All of the shell builtins are described in
subsequent sections.
While executing commands is essential, most of the power (and complexity) of shells is due to their embedded programming languages. Like any high-level language, the shell provides variables, flow control constructs, quoting, and functions.
Shells have begun offering features geared specifically for interactive use rather than to augment the programming language. These interactive features include job control, command line editing, history and aliases. Each of these features is described in this manual.
These definitions are used throughout the remainder of this manual.
POSIX
blank
builtin
control operator
word
that performs a control function. It is a newline
or one of the following:
`||', `&&', `&', `;', `;;',
`|', `(', or `)'.
exit status
field
filename
job
job control
metacharacter
blank
or one of the following characters:
`|', `&', `;', `(', `)', `<', or
`>'.
name
word
consisting solely of letters, numbers, and underscores,
and beginning with a letter or underscore. Name
s are used as
shell variable and function names.
Also referred to as an identifier
.
operator
control operator
or a redirection operator
.
See section Redirections, for a list of redirection operators.
process group
process group ID
process group
during its lifetime.
reserved word
word
that has a special meaning to the shell. Most reserved
words introduce shell flow control constructs, such as for
and
while
.
return status
exit status
.
signal
special builtin
token
word
or an operator
.
word
token
that is not an operator
.
Bash is an acronym for `Bourne-Again SHell'. The Bourne shell is the traditional Unix shell originally written by Stephen Bourne. All of the Bourne shell builtin commands are available in Bash, and the rules for evaluation and quoting are taken from the POSIX 1003.2 specification for the `standard' Unix shell.
This chapter briefly summarizes the shell's "building blocks": commands, control structures, shell functions, shell parameters, shell expansions, redirections, which are a way to direct input and output from and to named files, and how the shell executes commands.
The following is a brief description of the shell's operation when it reads and executes a command. Basically, the shell does the following:
metacharacters
. Alias expansion is performed by this step
(see section Aliases).
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 shell metacharacters
(see section 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 `\' is the Bash escape character.
It preserves the literal value of the next character that follows,
with the exception of newline
. If a \newline
pair
appears, and the backslash is not quoted, the \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
`$', ``', and `\'.
The characters `$' and ``'
retain their special meaning within double quotes. The backslash
retains its special meaning only when followed by one of the following
characters:
`$', ``', `"', `\', 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 section Shell Parameter Expansion).
Words of the form $'string'
are treated specially. The
word expands to string, with backslash-escaped characters replaced
as specifed by the ANSI C standard. Backslash escape sequences, if
present, are decoded as follows:
\a
\b
\e
\f
\n
\r
\t
\v
\\
\nnn
ASCII
code is nnn in octal
The result is single-quoted, as if the dollar sign had not been present.
A double-quoted string preceded by a dollar sign (`$') will cause
the string to be translated according to the current locale.
If the current locale is C
or POSIX
, the dollar sign
is ignored.
If the string is translated and replaced, the replacement is
double-quoted.
In a non-interactive shell, or an interactive shell in which the
interactive_comments
option to the shopt
builtin is enabled (see section Bash Builtin Commands),
a word beginning with `#'
causes that word and all remaining characters on that line to
be ignored. An interactive shell without the interactive_comments
option enabled does not allow comments. The interactive_comments
option is on by default in interactive shells.
A simple command is the kind of command you'll encounter most often.
It's just a sequence of words separated by blank
s, terminated
by one of the shell control operators (see section Definitions). The
first word generally specifies a command to be executed.
The return status (see section Exit Status) of a simple command is
its exit status as provided
by the POSIX.1 waitpid
function, or 128+n if the command
was terminated by signal n.
A pipeline
is a sequence of simple commands separated by
`|'.
[time
[-p
]] [!
] command1 [|
command2 ...]
The output of each command in the pipeline is connected to the input of the next command. That is, each command reads the previous command's output.
The reserved word time
causes timing statistics
to be printed for the pipeline once it finishes.
The `-p' option changes the output format to that specified
by POSIX.
The TIMEFORMAT
variable may be set to a format string that
specifies how the timing information should be displayed.
See section Bash Variables, for a description of the available formats.
Each command in a pipeline is executed in its own subshell. The exit status of a pipeline is the exit status of the last command in the pipeline. If the reserved word `!' precedes the pipeline, the exit status is the logical NOT of the exit status of the last command.
A list
is a sequence of one or more pipelines separated by one
of the operators `;', `&', `&&', or `||',
and optionally terminated by one of `;', `&', or a
newline
.
Of these list operators, `&&' and `||' 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 (true). 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 `||' denote AND lists and OR lists, respectively. An AND list has the form
command && command2
command2 is executed if, and only if, command returns an exit status of zero.
An OR list has the form
command || command2
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.
Note that wherever you see a `;' in the description of a command's syntax, it may be replaced indiscriminately with one or more newlines.
Bash supports the following looping constructs.
until
until
command is:
until test-commands; do consequent-commands; doneExecute consequent-commands as long as the final command in test-commands has an exit status which is not zero.
while
while
command is:
while test-commands; do consequent-commands; doneExecute consequent-commands as long as the final command in test-commands has an exit status of zero.
for
for
command is:
for name [in words ...]; do commands; doneExecute commands for each member in words, with name bound to the current member. If `in words' is not present, `in "$@"' is assumed.
The break
and continue
builtins (see section Bourne Shell Builtins)
may be used to control loop execution.
if
if
command is:
if test-commands; then consequent-commands; [elif more-test-commands; then more-consequents;] [else alternate-consequents;] fiExecute consequent-commands only if the final command in test-commands has an exit status of zero. Otherwise, each
elif
list is executed in turn,
and if its exit status is zero,
the corresponding more-consequents is executed and the
command completes.
If `else alternate-consequents' is present, and
the final command in the final if
or elif
clause
has a non-zero exit status, then execute alternate-consequents.
case
case
command is:
case word in [pattern [| pattern]...) commands ;;]... esac
Selectively execute commands based upon word matching
pattern. The `|' is used to separate multiple patterns.
Here is an example using case
in a script that could be used to
describe one interesting feature of an animal:
echo -n "Enter the name of an animal: " read ANIMAL echo -n "The $ANIMAL has " case $ANIMAL in horse | dog | cat) echo -n "four";; man | kangaroo ) echo -n "two";; *) echo -n "an unknown number of";; esac echo " legs."
((...))
(( expression ))The expression is evaluated according to the rules described below ((see section Arithmetic Evaluation). If the value of the expression is non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to
let "expression"
The select
construct, which allows users to choose from a list
of items presented as a menu, is also available.
See section Korn Shell Constructs, for a full description of select
.
Bash provides two ways to group a list of commands to be executed as a unit. When commands are grouped, redirections may be applied to the entire command list. For example, the output of all the commands in the list may be redirected to a single stream.
()
( list )Placing a list of commands between parentheses causes a subshell to be created, and each of the commands to be executed in that subshell. Since the list is executed in a subshell, variable assignments do not remain in effect after the subshell completes.
{}
{ list; }Placing a list of commands between curly braces causes the list to be executed in the current shell context. No subshell is created. The semicolon following list is required.
In addition to the creation of a subshell, there is a subtle difference
between these two constructs due to historical reasons. The braces
are reserved words
, so they must be separated from the list
by blank
s. The parentheses are operators
, and are
recognized as separate tokens by the shell even if they are not separated
from list
by whitespace.
The exit status of both of these constructs is the exit status of list.
Shell functions are a way to group commands for later execution using a single name for the group. They are executed just like a "regular" command. Shell functions are executed in the current shell context; no new process is created to interpret them.
Functions are declared using this syntax:
[ function
] name () { command-list; }
This defines a shell function named name. The reserved
word function
is optional. The body of the
function is the command-list between { and }. This list
is executed whenever name is specified as the
name of a command. The exit status of a function is
the exit status of the last command executed in the body.
When a function is executed, the arguments to the
function become the positional parameters
during its execution (see section Positional Parameters).
The special parameter
`#' that gives the number of positional parameters
is updated to reflect the change. Positional parameter 0
is unchanged.
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. If a numeric argument is given to return
,
that is the function return status.
Variables local to the function may be declared with the
local
builtin. These variables are visible only to
the function and the commands it invokes.
Functions may be recursive. No limit is placed on the number of recursive calls.
A parameter is an entity that stores values.
It can be a name
, a number, or one of the special characters
listed below.
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.
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 (detailed below). If the variable has its `-i' attribute
set (see the description of the declare
builtin in
section Bash Builtin Commands), then value
is subject to arithmetic expansion even if the $((...))
syntax does not appear (see section Arithmetic Expansion).
Word splitting is not performed, with the exception
of "$@"
as explained below.
Filename 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 section Shell Functions).
When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces.
The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed.
*
IFS
special variable. That is, "$*"
is equivalent
to "$1c$2c..."
, where c
is the first character of the value of the IFS
variable. If IFS
is null or unset, the parameters are separated by spaces.
@
"$@"
is equivalent to
"$1" "$2" ...
.
When there are no positional parameters, "$@"
and
$@
expand to nothing (i.e., they are removed).
#
?
-
set
builtin command, or those set by the shell itself
(such as the `-i' option).
$
()
subshell, it
expands to the process ID of the current shell, not the
subshell.
!
0
$0
is set to the name of that file. If Bash
is started with the `-c' option, then $0
is set to the first argument after the string to be
executed, if one is present. Otherwise, it is set
to the filename used to invoke Bash, as given by argument zero.
_
Expansion is performed on the command line after it has been split into
token
s. There are seven kinds of expansion performed:
Brace expansion, tilde expansion, and arithmetic expansion are described in other sections. For brace expansion, see section Brace Expansion; for tilde expansion, see section Tilde Expansion; and for arithmetic expansion, see section Arithmetic Expansion.
The order of expansions is: brace expansion, tilde expansion, parameter, variable, and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and filename expansion.
On systems that can support it, there is an additional expansion available: process substitution. This is performed at the same time as parameter, variable, and arithemtic expansion and command substitution.
Only brace expansion, word splitting, and filename expansion
can change the number of words of the expansion; other expansions
expand a single word to a single word.
The only exceptions to this are the expansions of
"$@"
(see section Special Parameters) and "${[@]}"
(see section Arrays).
After all expansions, quote removal
(see section Quote Removal)
is performed.
The `$' 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.
The basic form of parameter expansion is ${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 that is not to be interpreted as part of its name.
If the first character of parameter is an exclamation point,
a level of variable indirection is introduced.
Bash uses the value of the variable formed from the rest of
parameter as the name of the variable; this variable is then
expanded and that value used in the rest of the substitution, rather
than the value of parameter itself.
This is known as indirect expansion
.
In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion. When not performing substring 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}
${parameter:=word}
${parameter:?word}
${parameter:+word}
${parameter:offset}
${parameter:offset:length}
${#parameter}
${parameter#word}
${parameter##word}
${parameter%word}
${parameter%%word}
${parameter/pattern/string}
${parameter//pattern/string}
/
following pattern may be omitted.
If parameter is `@' or `*',
the substitution operation is applied to each positional
parameter in turn, and the expansion is the resultant list.
If parameter
is an array variable subscripted with `@' or `*',
the substitution operation is applied to each member of the
array in turn, and the expansion is the resultant list.
Command substitution allows the output of a command to replace the command name. There are two forms:
$(command)
or
`command`
Bash performs the expansion by executing command and replacing the command substitution with the standard output of the command, with any trailing newlines deleted.
When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
`$', ``', or `\'.
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 filename expansion are not performed on the results.
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
IFS
is unset, or its value 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.
Explicit null arguments (""
or "
) are retained.
Unquoted implicit null arguments, resulting from the expansion of
parameters
that have no values, are removed.
If a parameter with no value is expanded within double quotes, a
null argument results and is retained.
Note that if no expansion occurs, no splitting is performed.
After word splitting,
unless the `-f'
option has been set (see section The Set Builtin),
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
file names matching the pattern. If no matching file names are found,
and the shell option nullglob
is disabled, the word is left
unchanged. If the option is set, and no matches are found, the word
is removed. When a pattern is used for filename generation,
the character `.'
at the start of a filename or immediately following a slash
must be matched explicitly, unless the shell option dotglob
is set. The slash character must always be matched explicitly.
In other cases, the `.' character is not treated specially.
See the description of shopt
in section Bash Builtin Commands,
for a description of the nullglob
and dotglob
options.
The GLOBIGNORE
shell variable may be used to restrict the set of filenames matching a
pattern. If GLOBIGNORE
is set, each matching filename that also matches one of the patterns in
GLOBIGNORE
is removed from the list of matches. The filenames
`.' and `..'
are always ignored, even when GLOBIGNORE
.
is set. However, setting GLOBIGNORE
has the effect of
enabling the dotglob
shell option, so all other filenames beginning with a
`.' will match.
To get the old behavior of ignoring filenames beginning with a
`.', make `.*' one of the patterns in GLOBIGNORE
.
The dotglob
option is disabled when GLOBIGNORE
is unset.
The special pattern characters have the following meanings:
*
?
[...]
After the preceding expansions, all unquoted occurrences of the characters `\', `'', and `"' that did not result from one of the above expansions are removed.
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 filename 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
ls > dirlist 2>&1
directs both standard output and standard error to the file dirlist, while the command
ls 2>&1 > dirlist
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:
[n]<word
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:
[n]>[|]word
If the redirection operator is `>', and the `-C' option to the
set
builtin has been enabled, the redirection will fail if the
filename whose name results from the expansion of word exists.
If the redirection operator is `>|',
then the value of the `-C' option to the set
builtin command is not tested, and the redirection is attempted even
if the file named by word exists.
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:
[n]>>word
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:
&>word
and
>&word
Of the two forms, the first is preferred. This is semantically equivalent to
>word 2>&1
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, filename
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 \newline
is ignored, and `\'
must be used to quote the characters
`\', `$', 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
[n]<&word
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
[n]>&word
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
[n]<>word
causes the file whose name is the expansion of word
to be opened for both reading and writing on file descriptor
n
, or on file descriptor 0 if n
is not specified. If the file does not exist, it is created.
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.
$PATH
for a directory containing an executable file
by that name. Bash uses a hash table to remember the full
filenames of executable files (see the description of
hash
in section Bourne Shell Builtins) to avoid multiple
PATH
searches.
A full search of the directories in $PATH
is performed only if the command is not found in the hash table.
If the search is unsuccessful, the shell prints an error
message and returns a nonzero exit status.
When a program is invoked it is given an array of strings
called the environment.
This is a list of name-value pairs, of the form name=value
.
Bash allows you to manipulate the environment in several
ways. On invocation, the shell scans its own environment and
creates a parameter for each name found, automatically marking
it for export
to child processes. Executed commands inherit the environment.
The export
and `declare -x'
commands allow parameters and functions to be added to and
deleted from the environment. If the value of a parameter
in the environment is modified, the new value becomes part
of the environment, replacing the old. The environment
inherited by any executed command consists of the shell's
initial environment, whose values may be modified in the shell,
less any pairs removed by the unset
command, plus any
additions via the export
and `declare -x' commands.
The environment for any simple command or function may be augmented temporarily by prefixing it with parameter assignments, as described in section Shell Parameters. These assignment statements affect only the environment seen by that command.
If the `-k' flag is set (see section The Set Builtin, then all parameter assignments are placed in the environment for a command, not just those that precede the command name.
When Bash invokes an external command, the variable `$_' is set to the full path name of the command and passed to that command in its environment.
For the purposes of the shell, a command which exits with a zero exit status has succeeded. A non-zero exit status indicates failure. This seemingly counter-intuitive scheme is used so there is one well-defined way to indicate success and a variety of ways to indicate various failure modes. When a command terminates on a fatal signal whose number is n, Bash uses the value 128+n 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.
The exit status is used by the Bash conditional commands (see section Conditional Constructs) and some of the list constructs (see section Lists of Commands).
All of the Bash builtins return an exit status of zero if they succeed and a non-zero status on failure, so they may be used by the conditional and list constructs.
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).
When Bash receives a SIGINT
, it breaks out of any executing loops.
In all cases, Bash ignores SIGQUIT
.
If job control is in effect (see section Job Control), 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 (commands terminated with `&')
ignore SIGINT
and SIGQUIT
.
Commands run as a result of command substitution ignore the
keyboard-generated job control signals
SIGTTIN
, SIGTTOU
, and SIGTSTP
.
The shell exits by default upon receipt of a SIGHUP
.
Before exiting, it resends the SIGHUP
to all jobs, running or stopped. To prevent the shell from
sending the SIGHUP
signal to a particular job, remove it
from the jobs table with the disown
builtin
(see section Job Control Builtins)
or use disown -h
to mark it to not receive SIGHUP
.
A shell script is a text file containing shell commands. When such
a file is used as the first non-option argument when invoking Bash,
and neither the `-c' nor `-s' option is supplied
(see section Invoking Bash),
Bash reads and executes commands from the file, then exits. This
mode of operation creates a non-interactive shell. When Bash runs
a shell script, it sets the special parameter 0
to the name
of the file, rather than the name of the shell, and the positional
parameters are set to the remaining arguments, if any are given.
If no additional arguments are supplied, the positional parameters
are unset.
A shell script may be made executable by using the chmod
command
to turn on the execute bit. When Bash finds such a file while
searching the $PATH
for a command, it spawns a subshell to
execute it. In other words, executing
filename arguments
is equivalent to executing
bash filename arguments
if filename
is an executable shell script.
This subshell reinitializes itself, so that the effect is as if a
new shell had been invoked to interpret the script.
Most versions of Unix make this a part of the kernel's command execution mechanism. If the first line of a script begins with the two characters `#!', the remainder of the line specifies an interpreter for the program. The arguments to the interpreter consist of a single optional argument following the interpreter name on the first line of the script file, followed by the name of the script file, followed by the rest of the arguments. Bash will perform this action on operating systems that do not handle it themselves. Note that some older versions of Unix limit the interpreter name and argument to a maximum of 32 characters.
This section briefly summarizes things which Bash inherits from the Bourne Shell: builtins, variables, and other features. It also lists the significant differences between Bash and the Bourne Shell.
The following shell builtin commands are inherited from the Bourne Shell. These commands are implemented as specified by the POSIX 1003.2 standard.
:
: [arguments]Do nothing beyond expanding arguments and performing redirections.
.
. filenameRead and execute commands from the filename argument in the current shell context.
break
break [n]Exit from a
for
, while
, until
, or select
loop.
If n is supplied, the nth enclosing loop is exited.
cd
cd [-LP] [directory]Change the current working directory to directory. If directory is not given, the value of the
HOME
shell variable is used. If the
shell variable CDPATH
exists, it is used as a search path. If
directory begins with a slash, CDPATH
is not used.
The `-P' option means
to not follow symbolic links; symlinks are followed by default or with the
`-L' option.
continue
continue [n]Resume the next iteration of an enclosing
for
, while
,
until
, or select
loop.
If n is supplied, the execution of the
nth enclosing loop is resumed.
eval
eval [arguments]The arguments are concatenated together into a single command, which is then read and executed.
exec
exec [-cl] [-a name] [command] [arguments]If command is supplied, it replaces the shell. If the `-l' option is supplied, the shell places a dash in the zeroth arg passed to command. This is what the
login
program does.
The `-c' option causes command
to be executed with an empty environment.
If `-a' is supplied, the shell passes name
as the zeroth argument to command.
If no command is specified, redirections may be used to affect
the current shell environment.
exit
exit [n]Exit the shell, returning a status of n to the shell's parent.
export
export [-fn] [-p] [name[=value]]Mark each name to be passed to child processes in the environment. If the `-f' option is supplied, the names refer to shell functions. The `-n' option means to no longer mark each name for export. If no names are supplied, or if the `-p' option is given, a list of exported names is displayed.
getopts
getopts optstring name [args]
getopts
is used by shell scripts to parse positional parameters.
optstring contains the option letters to be recognized; if a letter
is followed by a colon, the option is expected to have an
argument, which should be separated from it by white space.
Each time it is invoked, getopts
places the next option in the shell variable name, initializing
name if it does not exist,
and the index of the next argument to be processed into the
variable OPTIND
. OPTIND
is initialized to 1 each time the shell or a shell script
is invoked. When an option requires an argument,
getopts
places that argument into the variable OPTARG
.
The shell does not reset OPTIND
automatically; it must be manually reset between multiple
calls to getopts
within the same shell invocation if a new set of parameters
is to be used.
getopts
can report errors in two ways. If the first character of
optstring is a colon, silent
error reporting is used. In normal operation diagnostic messages
are printed when illegal options or missing option arguments are
encountered.
If the variable OPTERR
is set to 0, no error message will be displayed, even if the first
character of optstring
is not a colon.
If an illegal option is seen,
getopts
places `?' into name and, if not silent,
prints an error message and unsets OPTARG
.
If getopts
is silent, the option character found is placed in
OPTARG
and no diagnostic message is printed.
If a required argument is not found, and getopts
is not silent, a question mark (`?') is placed in name,
OPTARG
is unset, and a diagnostic message is printed.
If getopts
is silent, then a colon (`:') is placed in
name and OPTARG
is set to the option character found.
getopts
normally parses the positional parameters, but if more arguments are
given in args, getopts
parses those instead.
hash
hash [-r] [-p filename] [name]Remember the full filenames of commands specified as arguments, so they need not be searched for on subsequent invocations. The commands are found by searching through the directories listed in
$PATH
. The `-p' option inhibits the path search, and
filename is used as the location of name.
The `-r' option causes the shell to forget
all remembered locations. If no arguments are given, information
about remembered commands is printed.
pwd
pwd [-LP]Print the current working directory. If the `-P' option is supplied, the path printed will not contain symbolic links. If the `-L' option is supplied, the path printed may contain symbolic links.
readonly
readonly [-apf] [name] ...Mark each name as unchangable. The values of these names may not be changed by subsequent assignment. If the `-f' option is supplied, each name refers to a shell function. The `-a' option means each name refers to an array variable. If no name arguments are given, or if the `-p' option is supplied, a list of all readonly names is printed.
return
return [n]Cause a shell function to exit with value n. This may also be used to terminate execution of a script being executed with the
.
builtin.
shift
shift [n]Shift positional parameters to the left by n. The positional parameters from n+1 ... are renamed to
$1
... .
Parameters represented by the numbers
$#
to n+1 are unset. n
must be a non-negative number less than or equal to $#
.
test
[
times
timesPrint out the user and system times used by the shell and its children.
trap
trap [-lp] [arg] [sigspec]The commands in arg are to be read and executed when the shell receives signal sigspec. If arg is absent or equal to `-', all specified signals are reset to the values they had when the shell was started. If arg is the null string, then sigspec is ignored by the shell and commands it invokes. If arg is `-p', the shell displays the trap commands associated with each sigspec. If no arguments are supplied, or only `-p' is given,
trap
prints the list of commands
associated with each signal number. sigspec is either a signal
name such as SIGINT
or a signal number. If sigspec is
0
or EXIT
, arg is executed when the shell exits.
If sigspec is DEBUG
, the command arg is executed
after every simple command.
The `-l' option causes the shell to print a list of signal names
and their corresponding numbers.
Signals ignored upon entry to the shell cannot be trapped or reset.
Trapped signals are reset to their original values in a child
process when it is created.
umask
umask [-S] [mode]Set the shell process's file creation mask to mode. If mode begins with a digit, it is interpreted as an octal number; if not, it is interpreted as a symbolic mode mask similar to that accepted by the
chmod
command. If mode is
omitted, the current value of the mask is printed. If the `-S'
option is supplied without a mode argument, the mask is printed
in a symbolic format.
unset
unset [-fv] [name]Each variable or function name is removed. If no options are supplied, or the `-v' option is given, each name refers to a shell variable. If the `-f' option is given, the names refer to shell functions, and the function definition is removed. Read-only variables and functions may not be unset.
Bash uses certain shell variables in the same way as the Bourne shell. In some cases, Bash assigns a default value to the variable.
IFS
PATH
HOME
cd
builtin
command.
CDPATH
cd
command.
MAILPATH
$_
stands for the name of the current mailfile.
MAIL
MAILPATH
variable
is not set, Bash informs the user of the arrival of mail in
the specified file.
PS1
PS2
OPTIND
getopts
builtin.
OPTARG
getopts
builtin.
Bash implements essentially the same grammar, parameter and variable expansion, redirection, and quoting as the Bourne Shell. Bash uses the POSIX 1003.2 standard as the specification of how these features are to be implemented. There are some differences between the traditional Bourne shell and the POSIX standard; this section quickly details the differences of significance. A number of these differences are explained in greater depth in subsequent sections.
Bash is POSIX-conformant, even where the POSIX specification
differs from traditional sh
behavior.
Bash has multi-character invocation options (see section Invoking Bash).
Bash has command-line editing (see section Command Line Editing) and
the bind
builtin.
Bash has command history (see section Bash History Facilities) and the
history
and fc
builtins to manipulate it.
Bash implements csh
-like history expansion (see section Interactive History Expansion).
Bash has one-dimensional array variables (see section Arrays), and the appropriate variable expansions and assignment syntax to use them. Some of the Bash builtins take options to act on arrays. Bash provides some built-in array variables.
Bash implements the !
keyword to negate the return value of
a pipeline (see section Pipelines).
Very useful when an if
statement needs to act only if a test fails.
Bash includes the select
compound command, which allows the
generation of simple menus (see section Korn Shell Constructs).
Bash includes brace expansion (see section Brace Expansion) and tilde expansion (see section Tilde Expansion).
Bash implements command aliases and the alias
and unalias
builtins (see section Aliases).
Bash provides shell arithmetic and arithmetic expansion (see section Shell Arithmetic).
The POSIX and ksh
-style $()
form of command substitution
is implemented (see section Command Substitution),
and preferred to the Bourne shell's "
(which
is also implemented for backwards compatibility).
Variables present in the shell's initial environment are automatically
exported to child processes. The Bourne shell does not normally do
this unless the variables are explicitly marked using the export
command.
Bash includes the POSIX and ksh
-style pattern removal
`%', `#', `%%' and `##' constructs to remove
leading or trailing substrings from variable values
(see section Shell Parameter Expansion).
The expansion ${#xx}
, which returns the length of $xx
,
is supported (see section Shell Parameter Expansion).
The $'...'
quoting syntax, which expands ANSI-C
backslash-escaped characters in the text between the single quotes,
is supported (see section ANSI-C Quoting).
Bash supports the $"..."
quoting syntax to do
locale-specific translation of the characters between the double
quotes. The `-D' and `--dump-strings' invocation options
list the translatable strings found in a script
(see section Locale-Specific Translation).
The expansion ${var:
length[:
offset]}
,
which expands to the substring of var
's value of length
length, optionally beginning at offset, is present
(see section Shell Parameter Expansion).
The expansion
${var/[/]
pattern[/
replacement]}
,
which matches pattern and replaces it with replacement in
the value of var
, is available (see section Shell Parameter Expansion).
Bash has indirect variable expansion using ${!word}
(see section Shell Parameter Expansion).
Bash can expand positional parameters beyond $9
using
${num}
.
Bash has process substitution (see section Process Substitution).
Bash automatically assigns variables that provide information about the
current user (UID
and EUID
), the current host
(HOSTTYPE
, OSTYPE
, MACHTYPE
, and HOSTNAME
),
and the instance of Bash that is running (BASH
,
BASH_VERSION
, and BASH_VERSINFO
. See section Bash Variables,
for details.
The IFS
variable is used to split only the results of expansion,
not all words (see section Word Splitting).
This closes a longstanding shell security hole.
It is possible to have a variable and a function with the same name;
sh
does not separate the two name spaces.
Bash functions are permitted to have local variables using the
local
builtin, and thus useful recursive functions may be written.
Variable assignments preceding commands affect only that command, even
builtins and functions. In sh
, all variable assignments
preceding commands are global unless the command is executed from the
file system.
Bash performs filename expansion on filenames specified as operands to output redirection operators.
Bash contains the `<>' redirection operator, allowing a file to be opened for both reading and writing, and the `&>' redirection operator, for directing standard output and standard error to the same file (see section Redirections).
The noclobber
option is available to avoid overwriting existing
files with output redirection (see section The Set Builtin).
The `>|' redirection operator may be used to override noclobber
.
Bash interprets special backslash-escaped characters in the prompt strings when interactive (see section Controlling the Prompt).
Bash allows you to write a function to override a builtin, and provides
access to that builtin's functionality within the function via the
builtin
and command
builtins (see section Bash Builtin Commands).
The command
builtin allows selective disabling of functions
when command lookup is performed (see section Bash Builtin Commands).
Individual builtins may be enabled or disabled using the enable
builtin (see section Bash Builtin Commands).
The Bash hash
builtin allows a name to be associated with
an arbitrary filename, even when that filename cannot be found by
searching the $PATH
, using `hash -p'.
Shell functions may be exported to children via the environment (see section Shell Functions).
Bash includes a help
builtin for quick reference to shell
facilities (see section Bash Builtin Commands).
The Bash read
builtin (see section Bash Builtin Commands)
will read a line ending in `\' with
the `-r' option, and will use the REPLY
variable as a
default if no arguments are supplied. The Bash read
builtin
also accepts a prompt string with the `-p' option and will use
Readline to obtain the line when given the `-e' option.
Bash includes the shopt
builtin, for finer control of shell
optional capabilities (see section Bash Builtin Commands).
Bash has much more optional behavior controllable with the set
builtin (see section The Set Builtin).
The disown
builtin can remove a job from the internal shell
job table (see section Job Control Builtins).
The return
builtin may be used to abort execution of scripts
executed with the .
or source
builtins
(see section Bourne Shell Builtins).
The test
builtin (see section Bourne Shell Builtins)
is slightly different, as it implements the
POSIX 1003.2 algorithm, which specifies the behavior based on the
number of arguments.
The trap
builtin (see section Bourne Shell Builtins)
allows a DEBUG
pseudo-signal specification,
similar to EXIT
. Commands specified with a DEBUG
trap are
executed after every simple command. The DEBUG
trap is not
inherited by shell functions.
The Bash export
, readonly
, and declare
builtins can
take a `-f' option to act on shell functions, a `-p' option to
display variables with various attributes set in a format that can be
used as shell input, a `-n' option to remove various variable
attributes, and `name=value' arguments to set variable attributes
and values simultaneously.
The Bash cd
and pwd
builtins each take `-L' and
`-P' builtins to switch between logical and physical modes.
The Bash type
builtin is more extensive and gives more information
about the names it finds.
Bash implements a csh
-like directory stack, and provides the
pushd
, popd
, and dirs
builtins to manipulate it.
Bash also makes the directory stack visible as the value of the
DIRSTACK
shell variable.
The Bash restricted mode is more useful (see section The Restricted Shell); the SVR4.2 shell restricted mode is too limited.
Bash has the time
reserved word and command timing (see section Pipelines).
The display of the timing statistics may be controlled with the
TIMEFORMAT
variable.
The SVR4.2 shell has two privilege-related builtins
(mldmode
and priv
) not present in Bash.
Bash does not have the stop
or newgrp
builtins.
Bash does not use the SHACCT
variable or perform shell accounting.
The SVR4.2 sh
uses a TIMEOUT
variable like Bash uses
TMOUT
.
More features unique to Bash may be found in section Bash Features.
Since Bash is a completely new implementation, it does not suffer from many of the limitations of the SVR4.2 shell. For instance:
if
or while
statement.
EOF
under certain circumstances.
This can be the cause of some hard-to-find errors.
SIGSEGV
. If the shell is started from a process with
SIGSEGV
blocked (e.g., by using the system()
C library
function call), the shell misbehaves badly.
SIGALRM
or
SIGCHLD
.
MAILCHECK
variable to be unset.
-x -v
);
the SVR4.2 shell allows only one option argument (-xv
). In
fact, some versions of the shell dump core if the second argument begins
with a `-'.
POSIX.2
standard.
jsh
(it turns on job control).
The C-Shell (csh
) was created by Bill Joy at The
University of California at Berkeley. It
is generally considered to have better features for interactive use than
the original Bourne shell. Some of the csh
features present in
Bash include job control, history expansion, `protected' redirection, and
several variables to control the interactive behaviour of the shell
(e.g., IGNOREEOF
).
See section Using History Interactively, for details on history expansion.
Brace expansion is a mechanism by which arbitrary strings may be generated. This mechanism is similar to filename expansion (see section Filename Expansion), but the file names 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,
bash$ echo a{d,c,b}e 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}}
Bash has tilde (~) expansion, similar, but not identical, to that of
csh
. The following table shows what unquoted words beginning
with a tilde expand to.
~
$HOME
.
~/foo
~fred/foo
foo
of the home directory of the user
fred
.
~+/foo
~-/foo
Bash will also tilde expand words following redirection operators and words following `=' in assignment statements.
Bash has several builtin commands whose definition is very similar
to csh
.
pushd
pushd [dir | +N | -N] [-n]Save the current directory on a list and then
cd
to
dir. With no
arguments, exchanges the top two directories.
+N
dirs
) to the top of the list by rotating
the stack.
-N
dirs
) to the top of the list by rotating
the stack.
-n
dir
cd
s to dir. You can see the saved directory list
with the dirs
command.
popd
popd [+N | -N] [-n]Pop the directory stack, and
cd
to the new top directory. When
no arguments are given, popd
removes the top directory from the stack and
performs a cd
to the new top directory. The
elements are numbered from 0 starting at the first directory listed with
dirs
; i.e., popd
is equivalent to popd +0
.
+N
dirs
), starting with zero.
-N
dirs
), starting with zero.
-n
dirs
dirs [+N | -N] [-clvp]Display the list of currently remembered directories. Directories find their way onto the list with the
pushd
command; you can get
back up through the list with the popd
command.
+N
dirs
when invoked without options), starting
with zero.
-N
dirs
when invoked without options), starting
with zero.
-c
-l
-p
dirs
to print the directory stack with one entry per
line.
-v
dirs
to print the directory stack with one entry per
line, prepending each entry with its index in the stack.
history
history [-c] [n] history [-anrw] [filename] history -ps argDisplay the history list with line numbers. Lines prefixed with with a `*' have been modified. An argument of n says to list only the last n lines. Options, if supplied, have the following meanings:
-w
-r
-a
-n
-c
-s
-p
HISTFILE
variable is used.
logout
source
.
(see section Bourne Shell Builtins).
IGNOREEOF
EOF
s Bash will read before exiting. By default, Bash will exit
upon reading a single EOF
. If IGNOREEOF
is not set to
a numeric value, Bash acts as if its value were 10.
This section describes features primarily inspired by the
Korn Shell (ksh
). In some cases, the POSIX 1003.2
standard has adopted these commands and variables from the
Korn Shell; Bash implements those features using the POSIX
standard as a guide.
Bash includes the Korn Shell select
construct. This construct
allows the easy generation of menus. It has almost the same syntax as
the for
command.
The syntax of the select
command is:
select name [in words ...]; do commands; 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 words'
is omitted, the positional parameters are printed. The
PS3
prompt is then displayed and a line is read from the standard
input. If the line consists of a 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 select
command completes. Any other value read causes name
to be set to null. The line read is saved in the variable
REPLY
.
The commands are executed after each selection until a
break
or return
command is executed, at which
point the select
command completes.
Bash also has adopted command timing from the Korn shell. If the
time
reserved word precedes a pipeline or simple command,
timing statistics for the pipeline are displayed when it completes.
The statistics currently consist of elapsed (wall-clock) time and
user and system time consumed by the command's execution.
The use of time
as a reserved word permits the timing of
shell builtins, shell functions, and pipelines. An external
time
command cannot time these easily.
This section describes Bash builtin commands taken from ksh
.
fc
Fix Command. In the first form, a range of commands from first to last is selected from the history list. Both first and last may be specified as a string (to locate the most recent command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). If last is not specified it is set to first. If first is not specified it is set to the previous command for editing and -16 for listing. If the `-l' flag is given, the commands are listed on standard output. The `-n' flag suppresses the command numbers when listing. The `-r' flag reverses the order of the listing. Otherwise, the editor given by ename is invoked on a file containing those commands. If ename is not given, the value of the following variable expansion is used:fc [-e ename] [-nlr] [first] [last]
fc -s [pat=rep] [command]
${FCEDIT:-${EDITOR:-vi}}
. This says to use the
value of the FCEDIT
variable if set, or the value of the
EDITOR
variable if that is set, or vi
if neither is set.
When editing is complete, the edited commands are echoed and executed.
In the second form, command is re-executed after each instance
of pat in the selected command is replaced by rep.
A useful alias to use with the fc
command is r='fc -s'
, so
that typing `r cc' runs the last command beginning with cc
and typing `r' re-executes the last command (see section Aliases).
let
let
builtin allows arithmetic to be performed on shell variables.
For details, refer to section Arithmetic Builtins.
typeset
typeset
command is supplied for compatibility with the Korn
shell; however, it has been deprecated in favor of the
declare
command (see section Bash Builtin Commands).
REPLY
read
builtin.
RANDOM
SECONDS
PS3
select
command. If this variable is not set, the
select
command prompts with `#? '
PS4
PWD
cd
builtin.
OLDPWD
cd
builtin.
TMOUT
LINENO
ENV
FCEDIT
fc
builtin command.
The shell maintains a list of aliases
that may be set and unset with the alias
and
unalias
builtin commands.
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 shell metacharacters, 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
space or tab character, 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
(see section Shell Functions).
Aliases are not expanded when the shell is not interactive,
unless the expand_aliases
shell option is set using
shopt
(see section Bash Builtin Commands).
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.
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.
alias
alias [-p
] [name[=value] ...]
Without arguments or with the `-p' option, alias
prints
the list of aliases on the standard output in a form that allows
them to be reused as input.
If arguments are supplied, an alias is defined for each name
whose value is given. If no value is given, the name
and value of the alias is printed.
unalias
unalias [-a] [name ... ]Remove each name from the list of aliases. If `-a' is supplied, all aliases are removed.
This section describes features unique to Bash.
bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o option] [argument ...] bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o option] -c string [argument ...] bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o option] [argument ...]
In addition to the single-character shell command-line options (see section The Set Builtin), there are several multi-character options that you can use. These options must appear on the command line before the single-character options in order for them to be recognized.
--dump-strings
--help
--login
csh
. If you wanted to replace your
current login shell with a Bash login shell, you would say
`exec bash --login'.
--noediting
--noprofile
--norc
sh
.
--posix
--rcfile filename
--restricted
--verbose
--version
There are several single-character options you can give which are
not available with the set
builtin.
-c string
$0
.
-i
-r
-s
-D
C
or POSIX
(see section Locale-Specific Translation).
This implies the `-n' option; no commands will be executed.
An interactive shell is one whose input and output are both
connected to terminals (as determined by isatty()
), or one
started with the `-i' option.
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 (see section Shell Scripts).
When Bash is invoked in this fashion, $0
is set to the name of the file, and the positional parameters
are set to the remaining arguments.
Bash reads and executes commands from this file, then exits.
Bash's exit status is the exit status of the last command executed
in the script. If no commands are executed, the exit status is 0.
This section describs how bash executes its startup files. If any of the files exist but cannot be read, bash reports an error. Tildes are expanded in file names as described above under Tilde Expansion (see section Tilde Expansion).
When Bash is invoked as a login shell, it first reads and executes commands from the file `/etc/profile', if that file exists. After reading that file, it looks for `~/.bash_profile', `~/.bash_login', and `~/.profile', in that order, and reads and executes commands from the first one that exists and is readable. The `--noprofile' option may be used when the shell is started to inhibit this behavior.
When a login shell exits, Bash reads and executes commands from the file `~/.bash_logout', if it exists.
When an interactive shell that is not a login shell is started, Bash reads and executes commands from `~/.bashrc', if that file exists. This may be inhibited by using the `--norc' option. The `--rcfile file' option will force Bash to read and execute commands from file instead of `~/.bashrc'.
So, typically, your `~/.bash_profile' contains the line
if [ -f `~/.bashrc' ]; then . `~/.bashrc'; fi
after (or before) any login-specific initializations.
When Bash is started non-interactively, to run a shell script,
for example, it looks for the variable BASH_ENV
in the environment,
expands its value if it appears there, and uses the expanded value as
the name of a file to read and execute. Bash behaves as if the
following command were executed:
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
but the value of the PATH
variable is not used to search for the
file name.
If Bash is invoked with the name sh
, it tries to mimic the
startup behavior of historical versions of sh
as closely as
possible, while conforming to the POSIX standard as well.
When invoked as a login shell, it first attempts to read and execute
commands from `/etc/profile' and `~/.profile', in that order.
The `--noprofile' option may be used to inhibit this behavior.
When invoked as an interactive shell with the name sh
,
bash
looks for the variable ENV
,
expands its value if it is defined, and uses the
expanded value as the name of a file to read and execute.
Since a shell invoked as sh
does not attempt to read and execute
commands from any other startup files, the `--rcfile' option has
no effect.
A non-interactive shell invoked with the name sh
does not attempt
to read any startup files.
When invoked as sh
, Bash enters POSIX mode after
the startup files are read.
When Bash is started in POSIX mode, as with the
`--posix' command line option, it follows the POSIX standard
for startup files.
In this mode, the ENV
variable is expanded and commands are read
and executed from the file whose name is the expanded value.
No other startup files are read.
This is done by both interactive and non-interactive shells.
Bash attempts to determine when it is being run by the remote shell
daemon, usually rshd
. If Bash determines it is being run by
rshd, it reads and executes commands from `~/.bashrc', if that
file exists and is readable.
It will not do this if invoked as sh
.
The `--norc' option may be used to inhibit this behavior, and the
`--rcfile' option may be used to force another file to be read, but
rshd does not generally invoke the shell with those options or allow
them to be specified.
As defined in section Invoking Bash, an interactive shell
is one whose input and output are both
connected to terminals (as determined by isatty(3)
),
or one started with the `-i' option.
You may wish to determine within a startup script whether Bash is
running interactively or not. To do this, examine the variable
$PS1
; it is unset in non-interactive shells, and set in
interactive shells. Thus:
if [ -z "$PS1" ]; then echo This shell is not interactive else echo This shell is interactive fi
This section describes builtin commands which are unique to or have been extended in Bash.
bind
bind [-m keymap] [-lpsvPSV] [-q name] [-r keyseq] bind [-m keymap] -f filename bind [-m keymap] keyseq:function-nameDisplay current Readline (see section Command Line Editing) key and function bindings, or bind a key sequence to a Readline function or macro. The binding syntax accepted is identical to that of `.inputrc' (@xref{Readline Init File}), but each binding must be passed as a separate argument: e.g., `"\C-x\C-r":re-read-init-file'. Options, if supplied, have the following meanings:
-m keymap
emacs
,
emacs-standard
,
emacs-meta
,
emacs-ctlx
,
vi
,
vi-command
, and
vi-insert
.
vi
is equivalent to vi-command
;
emacs
is equivalent to emacs-standard
.
-l
-p
-P
-v
-V
-s
-S
-f filename
-q
-r keyseq
builtin
builtin [shell-builtin [args]]Run a shell builtin. This is useful when you wish to rename a shell builtin to be a function, but need the functionality of the builtin within the function itself.
command
command [-pVv] command [args ...]Runs command with arg ignoring shell functions. If you have a shell function called
ls
, and you wish to call
the command ls
, you can say `command ls'. The
`-p' option means to use a default value for $PATH
that is guaranteed to find all of the standard utilities.
If either the `-V' or `-v' option is supplied, a
description of command is printed. The `-v' option
causes a single word indicating the command or file name used to
invoke command to be printed; the `-V' option produces
a more verbose description.
declare
declare [-afFrxi] [-p] [name[=value]]Declare variables and give them attributes. If no names are given, then display the values of variables instead. The `-p' option will display the attributes and values of each name. When `-p' is used, additional options are ignored. The `-F' option inhibits the display of function definitions; only the function name and attributes are printed. `-F' implies `-f'. The following options can be used to restrict output to variables with the specified attributes or to give variables attributes:
-a
-f
-i
-r
-x
declare
makes each name local, as with the
local
command.
echo
echo [-neE] [arg ...]Output the
arg
s, separated by spaces, terminated with a
newline. The return status is always 0. If `-n' is
specified, the trailing newline is suppressed. If the `-e'
option is given, interpretation of the following backslash-escaped
characters is enabled. The `-E' option disables the interpretation
of these escape characters, even on systems where they are interpreted
by default.
echo
interprets the following escape sequences:
\a
\b
\c
\e
\f
\n
\r
\t
\v
\\
\nnn
nnn
(octal)
enable
enable [-n] [-p] [-f filename] [-ads] [name ...]Enable and disable builtin shell commands. This allows you to use a disk command which has the same name as a shell builtin. If `-n' is used, the names become disabled. Otherwise names are enabled. For example, to use the
test
binary
found via $PATH
instead of the shell builtin version, type
`enable -n test'.
If the `-p' option is supplied, or no name arguments appear,
a list of shell builtins is printed. With no other arguments, the list
consists of all enabled shell builtins.
The `-a' option means to list
each builtin with an indication of whether or not it is enabled.
The `-f' option means to load the new builtin command name
from shared object filename, on systems that support dynamic loading.
The `-d' option will delete a builtin loaded with `-f'.
If there are no options, a list of the shell builtins is displayed.
The `-s' option restricts enable
to the POSIX.2 special
builtins. If `-s' is used with `-f', the new builtin becomes
a special builtin.
help
help [pattern]Display helpful information about builtin commands. If pattern is specified,
help
gives detailed help
on all commands matching pattern, otherwise a list of
the builtins is printed.
local
local name[=value]For each argument, create a local variable called name, and give it value.
local
can only be used within a function; it makes the variable
name have a visible scope restricted to that function and its
children.
logout
logout [n]Exit a login shell, returning a status of n to the shell's parent.
read
read [-a aname] [-p prompt] [-er] [name ...]One line is read from the standard input, and the first word is assigned to the first name, the second word to the second name, and so on, with leftover words assigned to the last name. Only the characters in the value of the
IFS
variable
are recognized as word delimiters. If no names
are supplied, the line read is assigned to the variable REPLY
.
The return code is zero, unless end-of-file is encountered. Options,
if supplied, have the following meanings:
-r
-p prompt
prompt
, without a
trailing newline, before attempting to read any input. The prompt
is displayed only if input is coming from a terminal.
-a aname
-e
shopt
shopt [-pqsu] [-o] [optname ...]Toggle the values of variables controlling optional shell behavior. With no options, or with the `-p' option, a list of all settable options is displayed, with an indication of whether or not each is set. Other options have the following meanings:
-s
-u
-q
-o
set
builtin (see section The Set Builtin).
shopt
options are disabled (off)
by default.
The return status when listing options is zero if all optnames
are enabled, non-zero otherwise. When setting or unsetting options,
the return status is zero unless an optname is not a legal shell
option.
The list of shopt
options is:
cdable_vars
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.
cdspell
cd
command will be corrected.
The errors checked for are transposed characters,
a missing character, and a character too many.
If a correction is found, the corrected path is printed,
and the command proceeds.
This option is enabled by default, but is only used by interactive shells.
checkhash
checkwinsize
LINES
and COLUMNS
.
cmdhist
dotglob
execfail
exec
builtin command. An interactive shell does not exit if exec
fails.
histappend
HISTFILE
variable when the shell exits, rather than overwriting the file.
histreedit
histverify
hostcomplete
interactive_comments
lithist
cmdhist
option is enabled, multi-line commands are saved to the history with
embedded newlines rather than using semicolon separators where possible.
mailwarn
"The mail in mailfile has been read"
is displayed.
nullglob
promptvars
shift_verbose
shift
builtin prints an error message when the shift count exceeds the
number of positional parameters.
sourcepath
source
builtin uses the value of PATH
to find the directory containing the file supplied as an argument.
This is enabled by default.
type
type [-all] [-type | -path] [name ...]For each name, indicate how it would be interpreted if used as a command name. If the `-type' flag is used,
type
returns a single word
which is one of `alias', `function', `builtin',
`file' or `keyword',
if name is an alias, shell function, shell builtin,
disk file, or shell reserved word, respectively.
If the name is not found, then nothing is printed, and
type
returns a failure status.
If the `-path' flag is used, type
either returns the name
of the disk file that would be executed, or nothing if `-type'
would not return `file'.
If the `-all' flag is used, returns all of the places that contain
an executable named file. This includes aliases and functions,
if and only if the `-path' flag is not also used.
type
accepts `-a', `-t', and `-p' as equivalent to
`-all', `-type', and `-path', respectively.
ulimit
ulimit [-acdflmnpstuvSH] [limit]
ulimit
provides control over the resources available to processes
started by the shell, on systems that allow such control. If an
option is given, it is interpreted as follows:
-S
-H
-a
-c
-d
-f
-l
-m
-n
-p
-s
-t
-u
-v
This builtin is so overloaded that it deserves its own section.
set
set [-abefhkmnptuvxdBCHP] [-o option] [argument ...]
-a
-b
-e
-f
-h
-k
-m
-n
-o option-name
allexport
-a
.
braceexpand
-B
.
emacs
emacs
-style line editing interface (see section Command Line Editing).
errexit
-e
.
hashall
-h
.
histexpand
-H
.
history
ignoreeof
keyword
-k
.
monitor
-m
.
noclobber
-C
.
noexec
-n
.
noglob
-f
.
notify
-b
.
nounset
-u
.
onecmd
-t
.
physical
-P
.
posix
privileged
-p
.
verbose
-v
.
vi
vi
-style line editing interface.
xtrace
-x
.
-p
$ENV
file is not processed, and shell functions
are not inherited from the environment. This is enabled automatically
on startup if the effective user (group) id is not equal to the real
user (group) id. Turning this option off causes the effective user
and group ids to be set to the real user and group ids.
-t
-u
-v
-x
-B
-C
-H
-P
cd
which change the current directory. The physical directory
is used instead. By default, Bash follows
the logical chain of directories when performing commands
which change the current directory.
For example, if `/usr/sys' is a link to `/usr/local/sys' then:
$ cd /usr/sys; echo $PWD /usr/sys $ cd ..; pwd /usrIf
set -P
is on, then:
$ cd /usr/sys; echo $PWD /usr/local/sys $ cd ..; pwd /usr/local
--
-
$-
.
The remaining N arguments are positional parameters and are
assigned, in order, to $1
, $2
, ... $N
. If
no arguments are given, all shell variables are printed.
Conditional expressions are used by the test
and [
builtins.
Expressions may be unary or binary. Unary expressions are often used to examine the status of a file. There are string operators and numeric comparison operators as well. Each operator and operand must be a separate argument. If file is of the form `/dev/fd/N', then file descriptor N is checked. Expressions are composed of the following primaries:
-b file
-c file
-d file
-e file
-f file
-g file
-k file
-L file
-p file
-r file
-s file
-S file
-t fd
-u file
-w file
-x file
-O file
-G file
file1 -nt file2
file1 -ot file2
file1 -ef file2
-o optname
set
builtin (see section The Set Builtin).
-z string
-n string
string
string1 = string2
string1 != string2
string1 < string2
string1 > string2
! expr
expr1 -a expr2
expr1 -o expr2
arg1 OP arg2
OP
is one of
`-eq', `-ne', `-lt', `-le', `-gt', or `-ge'.
These arithmetic binary operators return true if arg1
is equal to, not equal to, less than, less than or equal to,
greater than, or greater than or equal to arg2,
respectively. Arg1 and arg2
may be positive or negative integers.
The Bash test
and [
builtins evaluate conditional
expressions using a set of rules based on the number of arguments.
These are the rules:
These variables are set or used by Bash, but other shells do not normally treat them specially.
TIMEFORMAT
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.
%%
%[p][l]R
%[p][l]U
%[p][l]S
%P
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.
HISTCONTROL
HISTIGNORE
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.
HISTIGNORE
subsumes the function of HISTCONTROL
. A
pattern of `&' is identical to ignoredups
, and a
pattern of `[ ]*' is identical to ignorespace
.
Combining these two patterns, separating them with a colon,
provides the functionality of ignoreboth
.
HISTFILE
HISTSIZE
HISTFILESIZE
histchars
HISTCMD
HISTCMD
is unset, it loses its special properties,
even if it is subsequently reset.
HOSTFILE
MAILCHECK
MAILPATH
.
PROMPT_COMMAND
$PS1
).
UID
EUID
PPID
HOSTNAME
HOSTTYPE
OSTYPE
MACHTYPE
SHELLOPTS
set
builtin command (see section The Set Builtin).
The options appearing in SHELLOPTS
are those reported
as `on' by `set -o'.
If this variable is in the environment when Bash
starts up, each shell option in the list will be enabled before
reading any startup files. This variable is readonly.
FIGNORE
FIGNORE
is excluded from the list of matched file names. A sample
value is `.o:~'
GLOBIGNORE
GLOBIGNORE
, it is removed from the list
of matches.
DIRSTACK
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.
PIPESTATUS
INPUTRC
BASH
BASH_VERSION
BASH_VERSINFO
BASH_VERSINFO[0]
BASH_VERSINFO[1]
BASH_VERSINFO[2]
BASH_VERSINFO[3]
BASH_VERSINFO[4]
BASH_VERSINFO[5]
MACHTYPE
.
SHLVL
OPTERR
getopts
builtin command.
LANG
LC_
.
LC_ALL
LANG
and any other
LC_
variable specifying a locale category.
LC_MESSAGES
IGNOREEOF
EOF
character
as the sole input. If set, then the value of it is the number
of consecutive EOF
characters that can be read as the
first character on an input line
before the shell will exit. If the variable exists but does not
have a numeric value (or has no value) then the default is 10.
If the variable does not exist, then EOF
signifies the end of
input to the shell. This is only in effect for interactive shells.
Bash includes several mechanisms to evaluate arithmetic expressions and display the result or use it as part of a command.
The shell allows arithmetic expressions to be evaluated, as one of
the shell expansions or by the let
builtin.
Evaluation is done in long integers with no check for overflow, though division by 0 is trapped and flagged as an error. The following list of operators is grouped into levels of equal-precedence operators. The levels are listed in order of decreasing precedence.
- +
! ~
* / %
+ -
<< >>
<= >= < >
== !=
&
^
|
&&
||
expr ? expr : expr
= *= /= %= += -= <<= >>= &= ^= |=
Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. The value of a parameter is coerced to a long integer within an expression. A shell variable need not have its integer attribute turned on to be used in an expression.
Constants with a leading 0 are interpreted as octal numbers.
A leading `0x' or `0X' denotes hexadecimal. Otherwise,
numbers take the form [base#
]n, where base
is a decimal number between 2 and 64 representing the arithmetic
base, and n is a number in that base. If base is
omitted, then base 10 is used.
The digits greater than 9 are represented by the lowercase letters,
the uppercase letters, `_', and `@', in that order.
If base is less than or equal to 36, lowercase and uppercase
letters may be used interchangably to represent numbers between 10
and 35.
Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated first and may override the precedence rules above.
Arithmetic expansion allows the evaluation of an arithmetic expression and the substitution of the result. The format for arithmetic expansion is:
$(( 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 above. If the expression is invalid, Bash prints a message indicating failure and no substitution occurs.
let
let expression [expression]The
let
builtin allows arithmetic to be performed on shell
variables. Each expression is evaluated according to the
rules given previously (see section Arithmetic Evaluation). If the
last expression evaluates to 0, let
returns 1;
otherwise 0 is returned.
Bash provides one-dimensional array variables. Any variable may be used as
an 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. Arrays are zero-based.
An 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 greater than or equal to zero. To explicitly declare an array, use
declare -a name
The syntax
declare -a name[subscript]
is also accepted; the subscript is ignored. 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 is of the form [[subscript]=]
string. If
the optional subscript is 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.
This syntax is also accepted by the declare
builtin. Individual array elements may be assigned to using the
name[
subscript]=
value syntax introduced above.
Any element of an array may be referenced using
${name[
subscript]}
.
The braces are required to avoid
conflicts with the shell's filename expansion operators. If the
subscript is `@' or `*', the word expands to all members
of the array 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
variable, and ${name[@]}
expands each element of
name to a separate word. When there are no array members,
${name[@]}
expands to nothing. This is analogous to the
expansion of the special parameters `@' and `*'.
${#name[
subscript]}
expands to the length of
${name[
subscript]}
.
If subscript is `@' or
`*', the expansion is the number of elements in the array.
Referencing an array variable without a subscript is equivalent to
referencing element zero.
The unset
builtin is used to destroy arrays.
unset
name[subscript]
destroys the array element at index subscript.
unset
name, where name is an array, removes the
entire array. A subscript of `*' or `@' also removes the
entire array.
The declare
, local
, and readonly
builtins each accept a `-a'
option to specify an array. The read
builtin accepts a `-a'
option to assign a list of words read from the standard input
to an array, and can read values from the standard input into
individual array elements. The set
and declare
builtins display array values in a way that allows them to be
reused as input.
The value of the variable PROMPT_COMMAND
is examined just before
Bash prints each primary prompt. If it is set and non-null, then the
value is executed just as if you had typed it on the command line.
In addition, the following table describes the special characters which can appear in the prompt variables:
\a
\d
\e
\h
\H
\n
\s
$0
(the portion
following the final slash).
\t
\T
\@
\v
\V
\w
\W
$PWD
.
\u
\!
\#
\$
#
, otherwise $
.
\nnn
nnn
.
\\
\[
\]
If Bash is started with the name rbash
, or the
`--restricted'
option is supplied at invocation, the shell becomes restricted.
A restricted shell is used to
set up an environment more controlled than the standard shell.
A restricted shell behaves identically to bash
with the exception that the following are disallowed:
cd
builtin.
SHELL
or PATH
variables.
.
builtin command.
exec
builtin to replace the shell with another command.
enable
builtin.
command
builtin.
Starting Bash with the `--posix' command-line option or executing `set -o posix' while Bash is running will cause Bash to conform more closely to the POSIX.2 standard by changing the behavior to match that specified by POSIX.2 in areas where the Bash default differs.
The following list is what's changed when `POSIX mode' is in effect:
$PATH
to find the new location. This is also available with
`shopt -s checkhash'.
PS1
and PS2
expansions of `!' to
the history number and `!!' to `!' are enabled,
and parameter expansion is performed on
the value regardless of the setting of the promptvars
option.
$ENV
) rather than
the normal Bash files.
$HISTFILE
).
.
filename
is not found.
name
s. That is, they may not
contain characters other than letters, digits, and underscores, and
may not start with a digit. Declaring a function with an illegal name
causes a fatal syntax error in non-interactive shells.
cd
builtin finds a directory to change to
using $CDPATH
, the
value it assigns to the PWD
variable does not contain any
symbolic links, as if `cd -P' had been executed.
for
statement or the selection variable in a
select
statement is a read-only variable.
special
builtins
persist in the shell environment after the builtin completes.
There is other POSIX.2 behavior that Bash does not implement. Specifically:
This chapter disusses what job control is, how it works, and how Bash allows you to access its facilities.
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:
[1] 25647
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. Using `%?ce', on the
other hand, refers to any job containing the string `ce' in
its command line. If the prefix or 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
the `-b' option to the set
builtin is set,
Bash reports such changes immediately (see section The Set Builtin).
If you attempt to exit Bash while jobs are stopped, the
shell prints a message warning you that you have stopped jobs.
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.
bg
bg [jobspec]Place jobspec into the background, as if it had been started with `&'. If jobspec is not supplied, the current job is used.
fg
fg [jobspec]Bring jobspec into the foreground and make it the current job. If jobspec is not supplied, the current job is used.
jobs
jobs [-lpnrs] [jobspec] jobs -x command [jobspec]The first form lists the active jobs. The options have the following meanings:
-l
-n
-p
-r
-s
jobs
replaces any
jobspec found in command or arguments with the
corresponding process group ID, and executes command,
passing it arguments, returning its exit status.
kill
kill [-s sigspec] [-n signum] [-sigspec] jobspec kill -l [sigspec]Send a signal specified by sigspec or signum to the process named by jobspec. sigspec is either a signal name such as
SIGINT
or a signal number; signum is a signal number. If
sigspec and signum are not present, SIGTERM
is used.
The `-l' option lists the signal names, or the signal name
corresponding to sigspec.
wait
wait [jobspec|pid]Wait until the child process specified by process ID pid or job specification jobspec exits and report its exit status. If a job spec is given, all processes in the job are waited for. If no arguments are given, all currently active child processes are waited for.
disown
disown [-h] [jobspec ...]Without options, each jobspec is removed from the table of active jobs. If the `-h' option is given, the job is not removed from the table, but is marked so that
SIGHUP
is not sent to the job if the shell
receives a SIGHUP
.
If jobspec is not present, the current job is used.
suspend
suspend [-f]Suspend the execution of this shell until it receives a
SIGCONT
signal. The `-f' option means to suspend
even if the shell is a login shell.
When job control is not active, the kill
and wait
builtins do not accept jobspec arguments. They must be
supplied process IDs.
auto_resume
This chapter describes how to use the GNU History Library interactively, from a user's standpoint. It should be considered a user's guide. For information on using the GNU History Library in your own programs, see the GNU Readline Library Manual.
When the `-o history' option to the set
builtin
is enabled (see section The Set Builtin),
the shell provides access to the command history,
the list of commands previously typed. The text of the last
HISTSIZE
commands (default 500) is saved in a history list. The shell
stores each command in the history list prior to parameter and
variable expansion
but after history expansion is performed, subject to the
values of the shell variables
HISTIGNORE
and HISTCONTROL
.
When the shell starts up, the history is initialized from the
file named by the HISTFILE
variable (default `~/.bash_history').
HISTFILE
is truncated, if necessary, to contain no more than
the number of lines specified by the value of the HISTFILESIZE
variable. When an interactive shell exits, the last
HISTSIZE
lines are copied from the history list to HISTFILE
.
If the histappend
shell option is set (see section Bash Builtin Commands),
the lines are appended to the history file,
otherwise the history file is overwritten.
If HISTFILE
is unset, or if the history file is unwritable, the history is
not saved. After saving the history, the history file is truncated
to contain no more than $HISTFILESIZE
lines. If HISTFILESIZE
is not set, no truncation is performed.
The builtin command fc
(see section Korn Shell Builtins)
may be used to list or edit and re-execute a portion of
the history list. The history
builtin (see section C Shell Builtins)
can be used to display or modify the history list and
manipulate the history file.
When using the command-line editing, search commands
are available in each editing mode that provide access to the
history list.
The shell allows control over which commands are saved on the history
list. The HISTCONTROL
and HISTIGNORE
variables may be set to cause the shell to save only a subset of the
commands entered.
The cmdhist
shell option, if enabled, causes the shell to attempt to save each
line of a multi-line command in the same history entry, adding
semicolons where necessary to preserve syntactic correctness.
The lithist
shell option causes the shell to save the command with embedded newlines
instead of semicolons.
See section Bash Builtin Commands for a description of shopt
.
The History library provides a history expansion feature that is similar
to the history expansion provided by csh
. This section
describes the syntax used to manipulate the history information.
History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current input line, or fix errors in previous commands quickly.
History expansion takes place in two parts. The first is to determine which line from the previous history should be used during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the previous history is called the event, and the portions of that line that are acted upon are called words. Various modifiers are available to manipulate the selected words. The line is broken into words in the same fashion that Bash does, so that several English (or Unix) words surrounded by quotes are considered as one word. History expansions are introduced by the appearance of the history expansion character, which is `!' by default. Only `\' and `'' may be used to escape the history expansion character.
Several shell options settable with the shopt
builtin (see section Bash Builtin Commands) may be used to tailor
the behavior of history expansion. If the
histverify
shell option is enabled, and Readline
is being used, history substitutions are not immediately passed to
the shell parser.
Instead, the expanded line is reloaded into the Readline
editing buffer for further modification.
If Readline is being used, and the histreedit
shell option is enabled, a failed history expansion will be
reloaded into the Readline editing buffer for correction.
The `-p' option to the history
builtin command
may be used to see what a history expansion will do before using it.
The `-s' option to the history
builtin may be used to
add commands to the end of the history list without actually executing
them, so that they are available for subsequent recall.
The shell allows control of the various characters used by the
history expansion mechanism with the histchars
variable.
An event designator is a reference to a command line entry in the history list.
!
!n
!-n
!!
!string
!?string[?]
^string1^string2^
!!:s/string1/string2/
.
!#
Word designators are used to select desired words from the event. A `:' separates the event specification from the word designator. It can be omitted if the word designator begins with a `^', `$', `*', `-', or `%'. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.
0 (zero)
0
th word. For many applications, this is the command word.
n
^
$
%
x-y
*
0
th. This is a synonym for `1-$'.
It is not an error to use `*' if there is just one word in the event;
the empty string is returned in that case.
x*
x-
If a word designator is supplied without an event specification, the previous command is used as the event.
After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a `:'.
h
t
r
e
p
q
x
s/old/new/
&
g
gs/old/new/
,
or with `&'.
This chapter describes the basic features of the GNU command line editing interface.
The following paragraphs describe the notation used to represent keystrokes.
The text C-k is read as `Control-K' and describes the character produced when the k key is pressed while the Control key is depressed.
The text M-k is read as `Meta-K' and describes the character produced when the meta key (if you have one) is depressed, and the k key is pressed. If you do not have a meta key, the identical keystroke can be generated by typing ESC first, and then typing k. Either process is known as metafying the k key.
The text M-C-k is read as `Meta-Control-k' and describes the character produced by metafying C-k.
In addition, several keys have their own names. Specifically, DEL, ESC, LFD, SPC, RET, and TAB all stand for themselves when seen in this text, or in an init file (@xref{Readline Init File}).
Often during an interactive session you type in a long line of text, only to notice that the first word on the line is misspelled. The Readline library gives you a set of commands for manipulating the text as you type it in, allowing you to just fix your typo, and not forcing you to retype the majority of the line. Using these editing commands, you move the cursor to the place that needs correction, and delete or insert the text of the corrections. Then, when you are satisfied with the line, you simply press RETURN. You do not have to be at the end of the line to press RETURN; the entire line is accepted regardless of the location of the cursor within the line.
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 (see section Conditional Init Constructs). Other lines denote variable settings and key bindings.
set
command within the init file. Here is how you
would specify that you wish to use vi
line editing commands:
set editing-mode viRight now, there are only a few variables which can be set; so few, in fact, that we just list them here:
bell-style
comment-begin
insert-comment
command is executed. The default value
is "#"
.
completion-query-items
100
.
convert-meta
disable-completion
self-insert
. The default is `off'.
editing-mode
editing-mode
variable controls which editing mode you are
using. By default, Readline starts up in Emacs editing mode, where
the keystrokes are most similar to Emacs. This variable can be
set to either `emacs' or `vi'.
enable-keypad
expand-tilde
horizontal-scroll-mode
keymap
keymap
names are
emacs
,
emacs-standard
,
emacs-meta
,
emacs-ctlx
,
vi
,
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 the editing-mode
variable also affects the
default keymap.
mark-directories
mark-modified-lines
input-meta
meta-flag
is a
synonym for this variable.
output-meta
show-all-if-ambiguous
visible-stats
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
, 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).
"\C-u": universal-argument "\C-x\C-r": re-read-init-file "\e[11~": "Function Key 1"In the above example, `C-u' is bound to the function
universal-argument
(just as it was in the first example),
`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 following escape sequences are available when specifying key
sequences:
\C-
\M-
\e
\\
\"
\'
"\C-x\\": "\\"
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.
$if
$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.
mode
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.
term
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.
application
$if Bash # Quote the current or previous word "\C-xq": "\eb\"\ef\"" $endif
$endif
$if
command.
$else
$if
directive are executed if
the test fails.
Here is an example of an inputrc file. This illustrates key binding, variable assignment, and conditional syntax.
# This file controls the behaviour of line input editing for # programs that use the Gnu Readline library. Existing programs # include FTP, Bash, and Gdb. # # You can re-read the inputrc file with C-x C-r. # Lines beginning with '#' are comments. # # Set various bindings for emacs mode. set editing-mode emacs $if mode=emacs Meta-Control-h: backward-kill-word Text after the function name is ignored # # Arrow keys in keypad mode # #"\M-OD" backward-char #"\M-OC" forward-char #"\M-OA" previous-history #"\M-OB" next-history # # Arrow keys in ANSI mode # "\M-[D" backward-char "\M-[C" forward-char "\M-[A" previous-history "\M-[B" next-history # # Arrow keys in 8 bit keypad mode # #"\M-\C-OD" backward-char #"\M-\C-OC" forward-char #"\M-\C-OA" previous-history #"\M-\C-OB" next-history # # Arrow keys in 8 bit ANSI mode # #"\M-\C-[D" backward-char #"\M-\C-[C" forward-char #"\M-\C-[A" previous-history #"\M-\C-[B" next-history C-q: quoted-insert $endif # An old-style binding. This happens to be the default. TAB: complete # Macros that are convenient for shell interaction $if Bash # edit the path "\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f" # prepare to type a quoted word -- insert open and close double quotes # and move to just after the open quote "\C-x\"": "\"\"\C-b" # insert a backslash (testing backslash escapes in sequences and macros) "\C-x\\": "\\" # Quote the current or previous word "\C-xq": "\eb\"\ef\"" # Add a binding to refresh the line, which is unbound "\C-xr": redraw-current-line # Edit variable on current line. "\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y=" $endif # use a visible bell if one is available set bell-style visible # don't strip characters to 7 bits when reading set input-meta on # allow iso-latin1 characters to be inserted rather than converted to # prefix-meta sequences set convert-meta off # display characters with the eighth bit set directly rather than # as meta-prefixed characters set output-meta on # if there are more than 150 possible completions for a word, ask the # user if he wants to see all of them set completion-query-items 150 # For FTP $if Ftp "\C-xg": "get \M-?" "\C-xt": "put \M-?" "\M-.": yank-last-arg $endif
This section describes Readline commands that may be bound to key sequences.
beginning-of-line (C-a)
end-of-line (C-e)
forward-char (C-f)
backward-char (C-b)
forward-word (M-f)
backward-word (M-b)
clear-screen (C-l)
redraw-current-line ()
accept-line (Newline, Return)
HISTCONTROL
variable. If this line was a history
line, then restore the history line to its original state.
previous-history (C-p)
next-history (C-n)
beginning-of-history (M-<)
end-of-history (M->)
reverse-search-history (C-r)
forward-search-history (C-s)
non-incremental-reverse-search-history (M-p)
non-incremental-forward-search-history (M-n)
history-search-forward ()
history-search-backward ()
yank-nth-arg (M-C-y)
yank-last-arg (M-., M-_)
yank-nth-arg
.
delete-char (C-d)
EOF
.
backward-delete-char (Rubout)
quoted-insert (C-q, C-v)
tab-insert (M-TAB)
self-insert (a, b, A, 1, !, ...)
transpose-chars (C-t)
transpose-words (M-t)
upcase-word (M-u)
downcase-word (M-l)
capitalize-word (M-c)
kill-line (C-k)
backward-kill-line (C-x Rubout)
unix-line-discard (C-u)
kill-whole-line ()
kill-word (M-d)
forward-word
.
backward-kill-word (M-DEL)
backward-word
.
unix-word-rubout (C-w)
delete-horizontal-space ()
kill-region ()
copy-region-as-kill ()
copy-backward-word ()
copy-forward-word ()
yank (C-y)
yank-pop (M-y)
digit-argument (M-0, M-1, ... M--)
universal-argument ()
complete (TAB)
possible-completions (M-?)
insert-completions (M-*)
possible-completions
.
complete-filename (M-/)
possible-filename-completions (C-x /)
complete-username (M-~)
possible-username-completions (C-x ~)
complete-variable (M-$)
possible-variable-completions (C-x $)
complete-hostname (M-@)
possible-hostname-completions (C-x @)
complete-command (M-!)
possible-command-completions (C-x !)
dynamic-complete-history (M-TAB)
complete-into-braces (M-{)
start-kbd-macro (C-x ()
end-kbd-macro (C-x ))
call-last-kbd-macro (C-x e)
re-read-init-file (C-x C-r)
abort (C-g)
bell-style
).
do-uppercase-version (M-a, M-b, M-x, ...)
prefix-meta (ESC)
undo (C-_, C-x C-u)
revert-line (M-r)
undo
command enough times to get back to the beginning.
tilde-expand (M-~)
set-mark (C-@)
exchange-point-and-mark (C-x C-x)
character-search (C-])
character-search-backward (M-C-])
insert-comment (M-#)
comment-begin
variable is inserted at the beginning of the current line,
and the line is accepted as if a newline had been typed.
This makes the current line a shell comment.
dump-functions ()
dump-variables ()
dump-macros ()
glob-expand-word (C-x *)
glob-list-expansions (C-x g)
glob-expand-word
is inserted into the line, replacing the word before point.
display-shell-version (C-x C-v)
shell-expand-line (M-C-e)
history-expand-line (M-^)
insert-last-argument (M-., M-_)
yank-last-arg
.
operate-and-get-next (C-o)
emacs-editing-mode (C-e)
vi
editing mode, this causes a switch back to
emacs
editing mode, as if the command `set -o emacs' had
been executed.
While the Readline library does not have a full set of vi
editing functions, it does contain enough to allow simple editing
of the line. The Readline vi
mode behaves as specified in
the POSIX 1003.2 standard.
In order to switch interactively between emacs
and vi
editing modes, use the `set -o emacs' and `set -o vi'
commands (see section The Set Builtin).
The Readline default is emacs
mode.
When you enter a line in vi
mode, you are already placed in
`insertion' mode, as if you had typed an `i'. Pressing ESC
switches you into `command' mode, where you can edit the text of the
line with the standard vi
movement keys, move to previous
history lines with `k' and subsequent lines with `j', and
so forth.
This chapter provides basic instructions for installing Bash on the various supported platforms. The distribution supports nearly every version of Unix (and, someday, GNU). Other independent ports exist for OS/2, Windows 95, and Windows NT.
These are generic installation instructions for Bash.
The configure
shell script attempts to guess correct
values for various system-dependent variables used during
compilation. It uses those values to create a `Makefile' in
each directory of the package (the top directory, the
`builtins' and `doc' directories, and the
each directory under `lib'). It also creates a
`config.h' file containing system-dependent definitions.
Finally, it creates a shell script named config.status
that you
can run in the future to recreate the current configuration, a
file `config.cache' that saves the results of its tests to
speed up reconfiguring, and a file `config.log' containing
compiler output (useful mainly for debugging configure
).
If at some point
`config.cache' contains results you don't want to keep, you
may remove or edit it.
If you need to do unusual things to compile the package, please
try to figure out how configure
could check whether or not
to do them, and mail diffs or instructions to
bash-maintainers@prep.ai.mit.edu
so they can be
considered for the next release.
The file `configure.in' is used to create configure
by a program called Autoconf. You only need
`configure.in' if you want to change it or regenerate
configure
using a newer version of Autoconf. If
you do this, make sure you are using Autoconf version 2.9 or
newer.
The simplest way to compile Bash is:
cd
to the directory containing the source code and type
`./configure' to configure Bash for your system. If you're
using csh
on an old version of System V, you might need to
type `sh ./configure' instead to prevent csh
from trying
to execute configure
itself.
Running configure
takes awhile. While running, it prints some
messages telling which features it is checking for.
bashbug
bug
reporting script.
bash
and bashbug
.
This will also install the manual pages and Info file.
You can remove the program binaries and object files from the
source code directory by typing `make clean'. To also remove the
files that configure
created (so you can compile Bash for
a different kind of computer), type `make distclean'.
Some systems require unusual options for compilation or linking
that the configure
script does not know about. You can
give configure
initial values for variables by setting
them in the environment. Using a Bourne-compatible shell, you
can do that on the command line like this:
CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure
On systems that have the env
program, you can do it like this:
env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure
The configuration process uses GCC to build Bash if it is available.
You can compile Bash for more than one kind of computer at the
same time, by placing the object files for each architecture in their
own directory. To do this, you must use a version of make
that
supports the VPATH
variable, such as GNU make
.
cd
to the
directory where you want the object files and executables to go and run
the configure
script from the source directory. You may need to
supply the `--srcdir=PATH' argument to tell configure
where the
source files are. configure
automatically checks for the
source code in the directory that configure
is in and in `..'.
If you have to use a make
that does not supports the VPATH
variable, you can compile Bash for one architecture at a
time in the source code directory. After you have installed
Bash for one architecture, use `make distclean' before
reconfiguring for another architecture.
Alternatively, if your system supports symbolic links, you can use the `support/mkclone' script to create a build tree which has symbolic links back to each file in the source directory. Here's an example that creates a build directory in the current directory from a source directory `/usr/gnu/src/bash-2.0':
bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
The mkclone
script requires Bash, so you must have already built
Bash for at least one architecture before you can create build
directories for other architectures.
By default, `make install' will install into
`/usr/local/bin', `/usr/local/man', etc. You can
specify an installation prefix other than `/usr/local' by
giving configure
the option `--prefix=PATH'.
You can specify separate installation prefixes for
architecture-specific files and architecture-independent files.
If you give configure
the option
`--exec-prefix=PATH', the package will use `PATH' as the
prefix for installing programs and libraries. Documentation and
other data files will still use the regular prefix.
There may be some features configure
can not figure out
automatically, but needs to determine by the type of host the
package will run on. Usually configure
can figure that
out, but if it prints a message saying it can not guess the host
type, give it the `--host=TYPE' option. `TYPE' can
either be a short name for the system type, such as `sun4',
or a canonical name with three fields: `CPU-COMPANY-SYSTEM'
(e.g., `sparc-sun-sunos4.1.2').
See the file `support/config.sub' for the possible values of each field.
If you want to set default values for configure
scripts to
share, you can create a site shell script called
config.site
that gives default values for variables like
CC
, cache_file
, and prefix
. configure
looks for `PREFIX/share/config.site' if it exists, then
`PREFIX/etc/config.site' if it exists. Or, you can set the
CONFIG_SITE
environment variable to the location of the site
script. A warning: the Bash configure
looks for a site script,
but not all configure
scripts do.
configure
recognizes the following options to control how it
operates.
--cache-file=FILE
configure
.
--help
configure
, and exit.
--quiet
--silent
-q
--srcdir=DIR
configure
can determine that directory automatically.
--version
configure
script, and exit.
configure
also accepts some other, not widely used, boilerplate
options.
The Bash configure
has a number of `--enable-FEATURE'
options, where FEATURE indicates an optional part of the
package. There are also several `--with-PACKAGE' options,
where PACKAGE is something like `gnu-malloc' or
`purify' (for the Purify memory allocation checker). To
turn off the default use of a package, use
`--without-PACKAGE'. To configure Bash without a feature
that is enabled by default, use `--disable-FEATURE'.
Here is a complete list of the `--enable-' and
`--with-' options that the Bash configure
recognizes.
--with-gnu-malloc
malloc
in `lib/malloc/malloc.c'. This is not the same
malloc
that appears in GNU libc, but an older version
derived from the 4.2 BSD malloc
. This malloc
is
very fast, but wastes a lot of space. This option is enabled by
default. The `NOTES' file contains a list of systems for
which this should be turned off.
--with-glibc-malloc
malloc
in
`lib/malloc/gmalloc.c'. This is somewhat slower than the
default malloc
, but wastes considerably less space.
--with-afs
--with-purify
--enable-minimal-config
The `minimal-config' option can be used to disable all of the following options, but it is processed first, so individual options may be enabled using `enable-FEATURE'.
All of the following options except for `disabled-builtins' and `usg-echo-default' are enabled by default, unless the operating system does not provide the necessary support.
--enable-job-control
--enable-alias
alias
and unalias
builtins.
--enable-readline
--enable-history
fc
and history
builtin commands.
--enable-bang-history
csh
-like history substitution.
--enable-directory-stack
csh
-like directory stack and the
pushd
, popd
, and dirs
builtins.
--enable-restricted
rbash
, enters a restricted mode. See
section The Restricted Shell, for a description of restricted mode.
--enable-process-substitution
--enable-prompt-string-decoding
$PS1
, $PS2
, $PS3
, and $PS4
prompt
strings.
--enable-select
ksh
select
builtin, which allows the
generation of simple menus.
--enable-help-builtin
help
builtin, which displays help on shell builtins and
variables.
--enable-array-variables
--enable-dparen-arithmetic
ksh
((...))
command.
--enable-brace-expansion
csh
-like brace expansion
( b{a,b}c
==> bac bbc
).
--enable-disabled-builtins
xxx
has been disabled using `enable -n xxx'.
See section Bash Builtin Commands, for details of the builtin
and
enable
builtin commands.
--enable-command-timing
time
as a reserved word and for
displaying timing statistics for the pipeline following time
. This
allows pipelines as well as shell builtins and functions to be timed.
--enable-usg-echo-default
echo
builtin expand backslash-escaped characters by default,
without requiring the `-e' option. This makes the Bash echo
behave more like the System V version.
The file `config.h.top' contains C Preprocessor
`#define' statements for options which are not settable from
configure
.
Some of these are not meant to be changed; beware of the consequences if
you do.
Read the comments associated with each definition for more
information about its effect.
Please report all bugs you find in Bash. But first, you should make sure that it really is a bug, and that it appears in the latest version of Bash that you have.
Once you have determined that a bug actually exists, use the
bashbug
command to submit a bug report.
If you have a fix, you are welcome to mail that as well!
Suggestions and `philosophical' bug reports may be mailed
to bug-bash@prep.ai.MIT.Edu
or posted to the Usenet
newsgroup gnu.bash.bug
.
All bug reports should include:
bashbug
inserts the first three items automatically into
the template it provides for filing a bug report.
Please send all reports concerning this manual to
chet@ins.CWRU.Edu
.
This document was generated on 18 December 1996 using the texi2html translator version 1.51.