This text is a brief description of the features that are present in the Bash shell (version 4.1, 23 December 2009).
This is Edition 4.1, last updated 23 December 2009, of The GNU Bash Reference Manual, for Bash, Version 4.1.
Bash contains features that appear in other popular shells, and some features that only appear in Bash. Some of the shells that Bash has borrowed concepts from are the Bourne Shell (sh), the Korn Shell (ksh), and the C-shell (csh and its successor, tcsh). The following menu breaks the features up into categories based upon which one of these other shells inspired the feature.
This manual is meant as a brief introduction to features found in Bash. The Bash manual page should be used as the definitive reference on shell behavior.
Bash is the shell, or command language interpreter, for the gnu operating system. The name is an acronym for the ‘Bourne-Again SHell’, a pun on Stephen Bourne, the author of the direct ancestor of the current Unix shell sh, which appeared in the Seventh Edition Bell Labs Research version of Unix.
Bash is largely compatible with sh and incorporates useful features from the Korn shell ksh and the C shell csh. It is intended to be a conformant implementation of the ieeeposix Shell and Tools portion of the ieeeposix specification (ieee Standard 1003.1). It offers functional improvements over sh for both interactive and programming use.
While the gnu operating system provides other shells, including a version of csh, Bash is 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 ms-dos, os/2, and Windows platforms.
At its base, a shell is simply a macro processor that executes commands. The term macro processor means functionality where text and symbols are expanded to create larger expressions.
A Unix shell is both a command interpreter and a programming language. As a command interpreter, the shell provides the user interface to the rich set of gnu utilities. The programming language features allow these utilities to be combined. Files containing commands can be created, and become commands themselves. These new commands have the same status as system commands in directories such as /bin, allowing users or groups to establish custom environments to automate their common tasks.
Shells may be used interactively or non-interactively. In interactive mode, they accept input typed from the keyboard. When executing non-interactively, shells execute commands read from a file.
A shell allows execution of gnu commands, both synchronously and asynchronously. The shell waits for synchronous commands to complete before accepting more input; asynchronous commands continue to execute in parallel with the shell while it reads and executes additional commands. The redirection constructs permit fine-grained control of the input and output of those commands. Moreover, the shell allows control over the contents of commands' environments.
Shells also provide a small set of built-in commands (builtins) implementing functionality impossible or inconvenient to obtain via separate utilities. For example, cd, break, continue, and exec) cannot be implemented outside of the shell because they directly manipulate the shell itself. The history, getopts, kill, or pwd builtins, among others, could be implemented in separate utilities, but they are more convenient to use as builtin commands. 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 offer features geared specifically for interactive use rather than to augment the programming language. These interactive features include job control, command line editing, command history and aliases. Each of these features is described in this manual.
These definitions are used throughout the remainder of this manual.
POSIXblankbuiltincontrol operatortoken that performs a control function. It is a newline or one of the following: ‘||’, ‘&&’, ‘&’, ‘;’, ‘;;’, ‘|’, ‘|&’, ‘(’, or ‘)’. exit statusfieldfilenamejobjob controlmetacharacterblank or one of the following characters: ‘|’, ‘&’, ‘;’, ‘(’, ‘)’, ‘<’, or ‘>’. nameword consisting solely of letters, numbers, and underscores, and beginning with a letter or underscore. Names are used as shell variable and function names. Also referred to as an identifier. operatorcontrol operator or a redirection operator. See Redirections, for a list of redirection operators. Operators contain at least one unquoted metacharacter. process groupprocess group IDprocess group during its lifetime. reserved wordword that has a special meaning to the shell. Most reserved words introduce shell flow control constructs, such as for and while. return statusexit status. signalspecial builtintokenword or an operator. wordmetacharacters. 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, The rules for evaluation and quoting are taken from the posix 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.
When the shell reads input, it proceeds through a sequence of operations. If the input indicates the beginning of a comment, the shell ignores the comment symbol (‘#’), and the rest of that line.
Otherwise, roughly speaking, the shell reads its input and divides the input into words and operators, employing the quoting rules to select which meanings to assign various words and characters.
The shell then parses these tokens into commands and other constructs, removes the special meaning of certain words or characters, expands others, redirects input and output as needed, executes the specified command, waits for the command's exit status, and makes that exit status available for further inspection or processing.
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 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 Definitions) has special meaning to the shell and must be quoted if it is to represent itself. When the command history expansion facilities are being used (see History Interaction), the history expansion character, usually ‘!’, must be quoted to prevent history expansion. See Bash History Facilities, for more details concerning history expansion.
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 itself is not quoted, the \newline is treated as a line continuation (that is, it is removed from the input stream and 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 ‘$’, ‘`’, ‘\’, and, when history expansion is enabled, ‘!’. The characters ‘$’ and ‘`’ retain their special meaning within double quotes (see Shell Expansions). The backslash retains its special meaning only when followed by one of the following characters: ‘$’, ‘`’, ‘"’, ‘\’, or newline. Within double quotes, backslashes that are followed by one of these characters are removed. Backslashes preceding characters without a special meaning are left unmodified. A double quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed unless an ‘!’ appearing in double quotes is escaped using a backslash. The backslash preceding the ‘!’ is not removed.
The special parameters ‘*’ and ‘@’ have special meaning when in double quotes (see Shell Parameter Expansion).
Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows:
\a\b\e\E\f\n\r\t\v\\\'\"\nnn\xHH\cxThe expanded result is single-quoted, as if the dollar sign had not been present.
A double-quoted string preceded by a dollar sign (‘$’) 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.
Some systems use the message catalog selected by the LC_MESSAGES shell variable. Others create the name of the message catalog from the value of the TEXTDOMAIN shell variable, possibly adding a suffix of ‘.mo’. If you use the TEXTDOMAIN variable, you may need to set the TEXTDOMAINDIR variable to the location of the message catalog files. Still others use both variables in this fashion: TEXTDOMAINDIR/LC_MESSAGES/LC_MESSAGES/TEXTDOMAIN.mo.
In a non-interactive shell, or an interactive shell in which the interactive_comments option to the shopt builtin is enabled (see The Shopt Builtin), 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. See Interactive Shells, for a description of what makes a shell interactive.
A simple shell command such as echo a b c consists of the command itself followed by arguments, separated by spaces.
More complex shell commands are composed of simple commands arranged together in a variety of ways: in a pipeline in which the output of one command becomes the input of a second, in a loop or conditional construct, or in some other grouping.
A simple command is the kind of command encountered most often. It's just a sequence of words separated by blanks, terminated by one of the shell's control operators (see Definitions). The first word generally specifies a command to be executed, with the rest of the words being that command's arguments.
The return status (see Exit Status) of a simple command is its exit status as provided by the posix 1003.1 waitpid function, or 128+n if the command was terminated by signal n.
A pipeline is a sequence of simple commands separated by one of the control operators ‘|’ or ‘|&’.
[time[-p]] [!] command1 [ [|or|&] command2 ...]
The output of each command in the pipeline is connected via a pipe to the input of the next command. That is, each command reads the previous command's output. This connection is performed before any redirections specified by the command.
If ‘|&’ is used, the standard error of command1 is connected to command2's standard input through the pipe; it is shorthand for 2>&1 |. This implicit redirection of the standard error is performed after any redirections specified by the command.
The reserved word time causes timing statistics to be printed for the pipeline once it finishes. The statistics currently consist of elapsed (wall-clock) time and user and system time consumed by the command's execution. 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 Bash Variables, for a description of the available formats. 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.
If the pipeline is not executed asynchronously (see Lists), the shell waits for all commands in the pipeline to complete.
Each command in a pipeline is executed in its own subshell (see Command Execution Environment). The exit status of a pipeline is the exit status of the last command in the pipeline, unless the pipefail option is enabled (see The Set Builtin). If pipefail is enabled, the pipeline's return status is the value of the last (rightmost) command to exit with a non-zero status, or zero if all commands exit successfully. If the reserved word ‘!’ precedes the pipeline, the exit status is the logical negation of the exit status as described above. The shell waits for all commands in the pipeline to terminate before returning a value.
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.
A sequence of one or more newlines may appear in a list to delimit commands, equivalent to a semicolon.
If a command is terminated by the control operator ‘&’, the shell executes the command asynchronously in a subshell. This is known as executing the command in the background. The shell does not wait for the command to finish, and the return status is 0 (true). When job control is not active (see Job Control), the standard input for asynchronous commands, in the absence of any explicit redirections, is redirected from /dev/null.
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.
and and or lists are sequences of one or more pipelines separated by the control operators ‘&&’ and ‘||’, respectively. and and or lists are executed with left associativity.
An and list has the form
command1 && command2
command2 is executed if, and only if, command1 returns an exit status of zero.
An or list has the form
command1 || command2
command2 is executed if, and only if, command1 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.
Compound commands are the shell programming constructs. Each construct begins with a reserved word or control operator and is terminated by a corresponding reserved word or operator. Any redirections (see Redirections) associated with a compound command apply to all commands within that compound command unless explicitly overridden.
Bash provides looping constructs, conditional commands, and mechanisms to group commands and execute them as a unit.
Bash supports the following looping constructs.
Note that wherever a ‘;’ appears in the description of a command's syntax, it may be replaced with one or more newlines.
untiluntil command is: until test-commands; do consequent-commands; done
Execute consequent-commands as long as test-commands has an exit status which is not zero. The return status is the exit status of the last command executed in consequent-commands, or zero if none was executed.
whilewhile command is: while test-commands; do consequent-commands; done
Execute consequent-commands as long as test-commands has an exit status of zero. The return status is the exit status of the last command executed in consequent-commands, or zero if none was executed.
forfor command is: for name [ [in [words ...] ] ; ] do commands; done
Expand words, and execute commands once for each member in the resultant list, with name bound to the current member. If ‘in words’ is not present, the for command executes the commands once for each positional parameter that is set, as if ‘in "$@"’ had been specified (see Special Parameters). The return status is the exit status of the last command that executes. If there are no items in the expansion of words, no commands are executed, and the return status is zero.
An alternate form of the for command is also supported:
for (( expr1 ; expr2 ; expr3 )) ; do commands ; done
First, the arithmetic expression expr1 is evaluated according to the rules described below (see Shell Arithmetic). The arithmetic expression expr2 is then evaluated repeatedly until it evaluates to zero. Each time expr2 evaluates to a non-zero value, commands are executed and the arithmetic expression expr3 is evaluated. If any expression is omitted, it behaves as if it evaluates to 1. The return value is the exit status of the last command in list that is executed, or false if any of the expressions is invalid.
The break and continue builtins (see Bourne Shell Builtins) may be used to control loop execution.
ifif command is: if test-commands; then consequent-commands; [elif more-test-commands; then more-consequents;] [else alternate-consequents;] fi
The test-commands list is executed, and if its return status is zero, the consequent-commands list is executed. If test-commands returns a non-zero status, 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 alternate-consequents is executed. The return status is the exit status of the last command executed, or zero if no condition tested true.
casecase command is: casewordin [ [(]pattern[|pattern]...)command-list;;]... esac
case will selectively execute the command-list corresponding to the first pattern that matches word. If the shell option nocasematch (see the description of shopt in The Shopt Builtin) is enabled, the match is performed without regard to the case of alphabetic characters. The ‘|’ is used to separate multiple patterns, and the ‘)’ operator terminates a pattern list. A list of patterns and an associated command-list is known as a clause.
Each clause must be terminated with ‘;;’, ‘;&’, or ‘;;&’. The word undergoes tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal before matching is attempted. Each pattern undergoes tilde expansion, parameter expansion, command substitution, and arithmetic expansion.
There may be an arbitrary number of case clauses, each terminated by a ‘;;’, ‘;&’, or ‘;;&’. The first pattern that matches determines the command-list that is executed.
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 $ANIMAL in horse | dog | cat) echo -n "four";; man | kangaroo ) echo -n "two";; *) echo -n "an unknown number of";; esac echo " legs."
If the ‘;;’ operator is used, no subsequent matches are attempted after the first pattern match. Using ‘;&’ in place of ‘;;’ causes execution to continue with the command-list associated with the next clause, if any. Using ‘;;&’ in place of ‘;;’ causes the shell to test the patterns in the next clause, if any, and execute any associated command-list on a successful match.
The return status is zero if no pattern is matched. Otherwise, the return status is the exit status of the command-list executed.
selectselect construct allows the easy generation of menus. It has almost the same syntax as the for command: select name [in words ...]; do commands; done
The list of words following in is expanded, generating a list of items. The set of expanded words is printed on the standard error output stream, each preceded by a number. If the ‘in words’ is omitted, the positional parameters are printed, as if ‘in "$@"’ had been specified. 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 command is executed, at which point the select command completes.
Here is an example that allows the user to pick a filename from the current directory, and displays the name and index of the file selected.
select fname in *; do echo you picked $fname \($REPLY\) break; done
((...))(( expression ))
The arithmetic expression is evaluated according to the rules described below (see Shell Arithmetic). 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"
See Bash Builtins, for a full description of the let builtin.
[[...]][[ expression ]]
Return a status of 0 or 1 depending on the evaluation of the conditional expression expression. Expressions are composed of the primaries described below in Bash Conditional Expressions. Word splitting and filename expansion are not performed on the words between the ‘[[’ and ‘]]’; tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, process substitution, and quote removal are performed. Conditional operators such as ‘-f’ must be unquoted to be recognized as primaries.
When used with ‘[[’, The ‘<’ and ‘>’ operators sort lexicographically using the current locale.
When the ‘==’ and ‘!=’ operators are used, the string to the right of the operator is considered a pattern and matched according to the rules described below in Pattern Matching. If the shell option nocasematch (see the description of shopt in The Shopt Builtin) is enabled, the match is performed without regard to the case of alphabetic characters. The return value is 0 if the string matches (‘==’) or does not match (‘!=’)the pattern, and 1 otherwise. Any part of the pattern may be quoted to force it to be matched as a string.
An additional binary operator, ‘=~’, is available, with the same precedence as ‘==’ and ‘!=’. When it is used, the string to the right of the operator is considered an extended regular expression and matched accordingly (as in regex3)). The return value is 0 if the string matches the pattern, and 1 otherwise. If the regular expression is syntactically incorrect, the conditional expression's return value is 2. If the shell option nocasematch (see the description of shopt in The Shopt Builtin) is enabled, the match is performed without regard to the case of alphabetic characters. Any part of the pattern may be quoted to force it to be matched as a string. Substrings matched by parenthesized subexpressions within the regular expression are saved in the array variable BASH_REMATCH. The element of BASH_REMATCH with index 0 is the portion of the string matching the entire regular expression. The element of BASH_REMATCH with index n is the portion of the string matching the nth parenthesized subexpression.
Expressions may be combined using the following operators, listed in decreasing order of precedence:
( expression )! expression && expression2 || expression2&& and || operators do not evaluate expression2 if the value of expression1 is sufficient to determine the return value of the entire conditional expression. 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 environment to be created (see Command Execution Environment), and each of the commands in list 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 (or newline) 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 blanks or other shell metacharacters. The parentheses are operators, and are recognized as separate tokens by the shell even if they are not separated from the list by whitespace.
The exit status of both of these constructs is the exit status of list.
A coprocess is a shell command preceded by the coproc reserved word. A coprocess is executed asynchronously in a subshell, as if the command had been terminated with the ‘&’ control operator, with a two-way pipe established between the executing shell and the coprocess.
The format for a coprocess is:
coproc [NAME] command [redirections] This creates a coprocess named NAME. If NAME is not supplied, the default name is COPROC. NAME must not be supplied if command is a simple command (see Simple Commands); otherwise, it is interpreted as the first word of the simple command.
When the coproc is executed, the shell creates an array variable (see Arrays) named NAME in the context of the executing shell. The standard output of command is connected via a pipe to a file descriptor in the executing shell, and that file descriptor is assigned to NAME[0]. The standard input of command is connected via a pipe to a file descriptor in the executing shell, and that file descriptor is assigned to NAME[1]. This pipe is established before any redirections specified by the command (see Redirections). The file descriptors can be utilized as arguments to shell commands and redirections using standard word expansions.
The process id of the shell spawned to execute the coprocess is available as the value of the variable NAME_PID. The wait builtin command may be used to wait for the coprocess to terminate.
The return status of a coprocess is the exit status of command.
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. When the name of a shell function is used as a simple command name, the list of commands associated with that function name is executed. 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 () compound-command [ redirections ] This defines a shell function named name. The reserved word function is optional. If the function reserved word is supplied, the parentheses are optional. The body of the function is the compound command compound-command (see Compound Commands). That command is usually a list enclosed between { and }, but may be any compound command listed above. compound-command is executed whenever name is specified as the name of a command. Any redirections (see Redirections) associated with the shell function are performed when the function is executed.
A function definition may be deleted using the -f option to the unset builtin (see Bourne Shell Builtins).
The exit status of a function definition is zero unless a syntax error occurs or a readonly function with the same name already exists. When executed, the exit status of a function is the exit status of the last command executed in the body.
Note that for historical reasons, in the most common usage the curly braces that surround the body of the function must be separated from the body by blanks or newlines. This is because the braces are reserved words and are only recognized as such when they are separated from the command list by whitespace or another shell metacharacter. Also, when using the braces, the list must be terminated by a semicolon, a ‘&’, or a newline.
When a function is executed, the arguments to the function become the positional parameters during its execution (see Positional Parameters). The special parameter ‘#’ that expands to the number of positional parameters is updated to reflect the change. Special parameter 0 is unchanged. The first element of the FUNCNAME variable is set to the name of the function while the function is executing.
All other aspects of the shell execution environment are identical between a function and its caller with these exceptions: the DEBUG and RETURN traps are not inherited unless the function has been given the trace attribute using the declare builtin or the -o functrace option has been enabled with the set builtin, (in which case all functions inherit the DEBUG and RETURN traps), and the ERR trap is not inherited unless the -o errtrace shell option has been enabled. See Bourne Shell Builtins, for the description of the trap builtin.
If the builtin command return is executed in a function, the function completes and execution resumes with the next command after the function call. Any command associated with the RETURN trap is executed before execution resumes. When a function completes, the values of the positional parameters and the special parameter ‘#’ are restored to the values they had prior to the function's execution. If a numeric argument is given to return, that is the function's return status; otherwise the function's return status is the exit status of the last command executed before the return.
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.
Function names and definitions may be listed with the -f option to the declare or typeset builtin commands (see Bash Builtins). The -F option to declare or typeset will list the function names only (and optionally the source file and line number, if the extdebug shell option is enabled). Functions may be exported so that subshells automatically have them defined with the -f option to the export builtin (see Bourne Shell Builtins). Note that shell functions and variables with the same name may result in multiple identically-named entries in the environment passed to the shell's children. Care should be taken in cases where this may cause a problem.
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. A variable is a parameter denoted by a name. A variable has a value and zero or more attributes. Attributes are assigned using the declare builtin command (see the description of the declare builtin in Bash Builtins).
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 integer attribute set, then value is evaluated as an arithmetic expression even if the $((...)) expansion is not used (see Arithmetic Expansion). Word splitting is not performed, with the exception of "$@" as explained below. Filename expansion is not performed. Assignment statements may also appear as arguments to the alias, declare, typeset, export, readonly, and local builtin commands.
In the context where an assignment statement is assigning a value to a shell variable or array index (see Arrays), the ‘+=’ operator can be used to append to or add to the variable's previous value. When ‘+=’ is applied to a variable for which the integer attribute has been set, value is evaluated as an arithmetic expression and added to the variable's current value, which is also evaluated. When ‘+=’ is applied to an array variable using compound assignment (see Arrays), the variable's value is not unset (as it is when using ‘=’), and new values are appended to the array beginning at one greater than the array's maximum index (for indexed arrays), or added as additional key-value pairs in an associative array. When applied to a string-valued variable, value is expanded and appended to the variable's value.
A 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 parameter N may be referenced as ${N}, or as $N when N consists of a single digit. Positional parameters may not be assigned to with assignment statements. The set and shift builtins are used to set and unset them (see Shell Builtin Commands). The positional parameters are temporarily replaced when a shell function is executed (see Shell Functions).
When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces.
The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed.
*"$*" is equivalent to "$1c$2c...", where c is the first character of the value of the IFS variable. If IFS is unset, the parameters are separated by spaces. If IFS is null, the parameters are joined without intervening separators. @"$@" is equivalent to "$1" "$2" .... If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the beginning part of the original word, and the expansion of the last parameter is joined with the last part of the original word. When there are no positional parameters, "$@" and $@ expand to nothing (i.e., they are removed). #?-set builtin command, or those set by the shell itself (such as the -i option). $() subshell, it expands to the process id of the invoking shell, not the subshell. !0$0 is set to the name of that file. If Bash is started with the -c option (see Invoking Bash), then $0 is set to the first argument after the string to be executed, if one is present. Otherwise, it is set to the filename used to invoke Bash, as given by argument zero. _ Expansion is performed on the command line after it has been split into tokens. There are seven kinds of expansion performed:
The order of expansions is: brace expansion, tilde expansion, parameter, variable, and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and filename expansion.
On systems that can support it, there is an additional expansion available: process substitution. This is performed at the same time as parameter, variable, and arithmetic expansion and command substitution.
Only brace expansion, word splitting, and filename expansion can change the number of words of the expansion; other expansions expand a single word to a single word. The only exceptions to this are the expansions of "$@" (see Special Parameters) and "${name[@]}" (see Arrays).
After all expansions, quote removal (see Quote Removal) is performed.
Brace expansion is a mechanism by which arbitrary strings may be generated. This mechanism is similar to filename expansion (see Filename Expansion), but the file names generated need not exist. Patterns to be brace expanded take the form of an optional preamble, followed by either a series of comma-separated strings or a seqeunce expression between a pair of braces, followed by an optional postscript. The preamble is prefixed to each string contained within the braces, and the postscript is then appended to each resulting string, expanding left to right.
Brace expansions may be nested. The results of each expanded string are not sorted; left to right order is preserved. For example,
bash$ echo a{d,c,b}e ade ace abe A sequence expression takes the form {x..y[..incr]}, where x and y are either integers or single characters, and incr, an optional increment, is an integer. When integers are supplied, the expression expands to each number between x and y, inclusive. Supplied integers may be prefixed with ‘0’ to force each term to have the same width. When either x or y begins with a zero, the shell attempts to force all generated terms to contain the same number of digits, zero-padding where necessary. When characters are supplied, the expression expands to each character lexicographically between x and y, inclusive. Note that both x and y must be of the same type. When the increment is supplied, it is used as the difference between each term. The default increment is 1 or -1 as appropriate.
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. To avoid conflicts with parameter expansion, the string ‘${’ is not considered eligible for brace expansion.
A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma or a valid sequence expression. Any incorrectly formed brace expansion is left unchanged.
A { or ‘,’ may be quoted with a backslash to prevent its being considered part of a brace expression. To avoid conflicts with parameter expansion, the string ‘${’ is not considered eligible for brace expansion.
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}} If a word begins with an unquoted tilde character (‘~’), all of the characters up to the first unquoted slash (or all characters, if there is no unquoted slash) are considered a tilde-prefix. If none of the characters in the tilde-prefix are quoted, the characters in the tilde-prefix following the tilde are treated as a possible login name. If this login name is the null string, the tilde is replaced with the value of the HOME shell variable. If HOME is unset, the home directory of the user executing the shell is substituted instead. Otherwise, the tilde-prefix is replaced with the home directory associated with the specified login name.
If the tilde-prefix is ‘~+’, the value of the shell variable PWD replaces the tilde-prefix. If the tilde-prefix is ‘~-’, the value of the shell variable OLDPWD, if it is set, is substituted.
If the characters following the tilde in the tilde-prefix consist of a number N, optionally prefixed by a ‘+’ or a ‘-’, the tilde-prefix is replaced with the corresponding element from the directory stack, as it would be displayed by the dirs builtin invoked with the characters following tilde in the tilde-prefix as an argument (see The Directory Stack). If the tilde-prefix, sans the tilde, consists of a number without a leading ‘+’ or ‘-’, ‘+’ is assumed.
If the login name is invalid, or the tilde expansion fails, the word is left unchanged.
Each variable assignment is checked for unquoted tilde-prefixes immediately following a ‘:’ or the first ‘=’. In these cases, tilde expansion is also performed. Consequently, one may use file names with tildes in assignments to PATH, MAILPATH, and CDPATH, and the shell assigns the expanded value.
The following table shows how Bash treats unquoted tilde-prefixes:
~$HOME~/foo~fred/foofoo of the home directory of the user fred~+/foo~-/foo~N~+N~-NThe ‘$’ 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.
When braces are used, the matching ending brace is the first ‘}’ not escaped by a backslash or within a quoted string, and not within an embedded arithmetic expansion, command substitution, or parameter expansion.
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 is used in the rest of the substitution, rather than the value of parameter itself. This is known as indirect expansion. The exceptions to this are the expansions of ${!prefix*} and ${!name[@]} described below. The exclamation point must immediately follow the left brace in order to introduce indirection.
In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion.
When not performing substring expansion, using the form described below, Bash tests for a parameter that is unset or null. Omitting the colon results in a test only for a parameter that is unset. Put another way, if the colon is included, the operator tests for both parameter's existence and that its value is not null; if the colon is omitted, the operator tests only for existence.
${parameter:−word}${parameter:=word}${parameter:?word}${parameter:+word}${parameter:offset}${parameter:offset:length}length must evaluate to a number greater than or equal to zero. If offset evaluates to a number less than zero, the value is used as an offset from the end of the value of parameter. If parameter is ‘@’, the result is length positional parameters beginning at offset. If parameter is an indexed array name subscripted by ‘@’ or ‘*’, the result is the length members of the array beginning with ${parameter[offset]}. A negative offset is taken relative to one greater than the maximum index of the specified array. Substring expansion applied to an associative array produces undefined results.
Note that a negative offset must be separated from the colon by at least one space to avoid being confused with the ‘:-’ expansion. Substring indexing is zero-based unless the positional parameters are used, in which case the indexing starts at 1 by default. If offset is 0, and the positional parameters are used, $@ is prefixed to the list.
${!prefix*}${!prefix@}${!name[@]}${!name[*]}${#parameter}${parameter#word}${parameter##word}${parameter%word}${parameter%%word}${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. ${parameter^pattern}${parameter^^pattern}${parameter,pattern}${parameter,,pattern}Command substitution allows the output of a command to replace the command itself. Command substitution occurs when a command is enclosed as follows:
$(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. Embedded newlines are not deleted, but they may be removed during word splitting. The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).
When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by ‘$’, ‘`’, or ‘\’. The first backquote not preceded by a backslash terminates the command substitution. 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 backquoted 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.
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 parentheses is not treated specially. All tokens in the expression undergo parameter expansion, command substitution, and quote removal. Arithmetic expansions may be nested.
The evaluation is performed according to the rules listed below (see Shell Arithmetic). If the expression is invalid, Bash prints a message indicating failure to the standard error and no substitution occurs.
Process substitution is supported on systems that support named pipes (fifos) or the /dev/fd method of naming open files. It takes the form of
<(list)
or
>(list)
The process list is run with its input or output connected to a fifo or some file in /dev/fd. The name of this file is passed as an argument to the current command as the result of the expansion. If the >(list) form is used, writing to the file will provide input for list. If the <(list) form is used, the file passed as an argument should be read to obtain the output of list. Note that no space may appear between the < or > and the left parenthesis, otherwise the construct would be interpreted as a redirection.
When available, 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 sequences of <space>, <tab>, and <newline> at the beginning and end of the results of the previous expansions are ignored, and any sequence of IFS characters not at the beginning or end 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.
nullglob is disabled, the word is left unchanged. If the nullglob option is set, and no matches are found, the word is removed. If the failglob shell option is set, and no matches are found, an error message is printed and the command is not executed. If the shell option nocaseglob is enabled, the match is performed without regard to the case of alphabetic characters. When a pattern is used for filename expansion, the character ‘.’ at the start of a filename or immediately following a slash must be matched explicitly, unless the shell option dotglob is set. When matching a file name, the slash character must always be matched explicitly. In other cases, the ‘.’ character is not treated specially.
See the description of shopt in The Shopt Builtin, for a description of the nocaseglob, nullglob, failglob, 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 when GLOBIGNORE is set and not null. However, setting GLOBIGNORE to a non-null value 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.
Any character that appears in a pattern, other than the special pattern characters described below, matches itself. The nul character may not occur in a pattern. A backslash escapes the following character; the escaping backslash is discarded when matching. The special pattern characters must be quoted if they are to be matched literally.
The special pattern characters have the following meanings:
*globstar shell option is enabled, and ‘*’ is used in a filename expansion context, two adjacent ‘*’s used as a single pattern will match all files and zero or more directories and subdirectories. If followed by a ‘/’, two adjacent ‘*’s will match only directories and subdirectories. ?[...]For example, in the default C locale, ‘[a-dx-z]’ is equivalent to ‘[abcdxyz]’. Many locales sort characters in dictionary order, and in these locales ‘[a-dx-z]’ is typically not equivalent to ‘[abcdxyz]’; it might be equivalent to ‘[aBbCcDdxXyYz]’, for example. To obtain the traditional interpretation of ranges in bracket expressions, you can force the use of the C locale by setting the LC_COLLATE or LC_ALL environment variable to the value ‘C’.
Within ‘[’ and ‘]’, character classes can be specified using the syntax [:class:], where class is one of the following classes defined in the posix standard:
alnum alpha ascii blank cntrl digit graph lower print punct space upper word xdigit
A character class matches any character belonging to that class. The word character class matches letters, digits, and the character ‘_’.
Within ‘[’ and ‘]’, an equivalence class can be specified using the syntax [=c=], which matches all characters with the same collation weight (as defined by the current locale) as the character c.
Within ‘[’ and ‘]’, the syntax [.symbol.] matches the collating symbol symbol.
If the extglob shell option is enabled using the shopt builtin, several extended pattern matching operators are recognized. In the following description, a pattern-list is a list of one or more patterns separated by a ‘|’. Composite patterns may be formed using one or more of the following sub-patterns:
?(pattern-list)*(pattern-list)+(pattern-list)@(pattern-list)!(pattern-list)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.
Each redirection that may be preceded by a file descriptor number may instead be preceded by a word of the form {varname}. In this case, for each redirection operator except >&- and <&-, the shell will allocate a file descriptor greater than 10 and assign it to {varname}. If >&- or <&- is preceded by {varname}, the value of varname defines the file descriptor to close.
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 following the redirection operator in the following descriptions, unless otherwise noted, is subjected to brace expansion, tilde expansion, parameter expansion, command substitution, arithmetic expansion, quote removal, filename expansion, and word splitting. 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 (file descriptor 1) and standard error (file descriptor 2) to the file dirlist, while the command
ls 2>&1 > dirlist
directs only the standard output to file dirlist, because the standard error was made a copy of the standard output before the standard output was redirected to dirlist.
Bash handles several filenames specially when they are used in redirections, as described in the following table:
/dev/fd/fd/dev/stdin/dev/stdout/dev/stderr/dev/tcp/host/port/dev/udp/host/portA failure to open or create a file causes the redirection to fail.
Redirections using file descriptors greater than 9 should be used with care, as they may conflict with file descriptors the shell uses internally.
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 noclobber option to the set builtin has been enabled, the redirection will fail if the file whose name results from the expansion of word exists and is a regular file. If the redirection operator is ‘>|’, or the redirection operator is ‘>’ and the noclobber option is not enabled, 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
This construct 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.
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 construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be appended to the file whose name is the expansion of word.
The format for appending standard output and standard error is:
&>>word
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:
<<[−]wordhere-documentdelimiter
No parameter expansion, command substitution, arithmetic expansion, or filename 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. If word is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion. In the latter case, the character sequence \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.
A variant of here documents, the format is:
<<< word
The word is expanded and supplied to the command on its standard input.
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 the digits in word do not specify a file descriptor open for input, a redirection error occurs. 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. If the digits in word do not specify a file descriptor open for output, a redirection error occurs. 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]<&digit-
moves the file descriptor digit to file descriptor n, or the standard input (file descriptor 0) if n is not specified. digit is closed after being duplicated to n.
Similarly, the redirection operator
[n]>&digit-
moves the file descriptor digit to file descriptor n, or the standard output (file descriptor 1) if n is not specified.
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.
When a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to right.
If no command name results, the variable assignments affect the current shell environment. Otherwise, the variables are added to the environment of the executed command and do not affect the current shell environment. If any of the assignments attempts to assign a value to a readonly variable, an error occurs, and the command exits with a non-zero status.
If no command name results, redirections are performed, but do not affect the current shell environment. A redirection error causes the command to exit with a non-zero status.
If there is a command name left after expansion, execution proceeds as described below. Otherwise, the command exits. If one of the expansions contained a command substitution, the exit status of the command is the exit status of the last command substitution performed. If there were no command substitutions, the command exits with a status of zero.
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.
hash in Bourne Shell Builtins). 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 searches for a defined shell function named command_not_found_handle. If that function exists, it is invoked with the original command and the original command's arguments as its arguments, and the function's exit status becomes the exit status of the shell. If that function is not defined, the shell prints an error message and returns an exit status of 127. The shell has an execution environment, which consists of the following:
exec builtin cd, pushd, or popd, or inherited by the shell at invocation umask or inherited from the shell's parent trapset or inherited from the shell's parent in the environment setshopt (see The Shopt Builtin) alias (see Aliases) $$, and the value of $PPIDWhen a simple command other than a builtin or shell function is to be executed, it is invoked in a separate execution environment that consists of the following. Unless otherwise noted, the values are inherited from the shell.
A command invoked in this separate environment cannot affect the shell's execution environment.
Command substitution, commands grouped with parentheses, and asynchronous commands are invoked in a subshell environment that is a duplicate of the shell environment, except that traps caught by the shell are reset to the values that the shell inherited from its parent at invocation. Builtin commands that are invoked as part of a pipeline are also executed in a subshell environment. Changes made to the subshell environment cannot affect the shell's execution environment.
Subshells spawned to execute command substitutions inherit the value of the -e option from the parent shell. When not in posix mode, Bash clears the -e option in such subshells.
If a command is followed by a ‘&’ and job control is not active, the default standard input for the command is the empty file /dev/null. Otherwise, the invoked command inherits the file descriptors of the calling shell as modified by redirections.
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 provides several ways to manipulate the environment. 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 and ‘export -n’ commands, 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 Shell Parameters. These assignment statements affect only the environment seen by that command.
If the -k option is set (see 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.
The exit status of an executed command is the value returned by the waitpid system call or equivalent function. Exit statuses fall between 0 and 255, though, as explained below, the shell may use values above 125 specially. Exit statuses from shell builtins and compound commands are also limited to this range. Under certain circumstances, the shell will use special values to indicate specific failure modes.
For the shell's purposes, 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.
If a command fails because of an error during expansion or redirection, the exit status is greater than zero.
The exit status is used by the Bash conditional commands (see Conditional Constructs) and some of the list constructs (see Lists).
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. All builtins return an exit status of 2 to indicate incorrect usage.
When Bash is interactive, in the absence of any traps, 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 Job Control), Bash ignores SIGTTIN, SIGTTOU, and SIGTSTP.
Non-builtin commands started by Bash have signal handlers set to the values inherited by the shell from its parent. When job control is not in effect, asynchronous commands ignore SIGINT and SIGQUIT in addition to these inherited handlers. 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, an interactive shell resends the SIGHUP to all jobs, running or stopped. Stopped jobs are sent SIGCONT to ensure that they receive the SIGHUP. To prevent the shell from sending the SIGHUP signal to a particular job, it should be removed from the jobs table with the disown builtin (see Job Control Builtins) or marked to not receive SIGHUP using disown -h.
If the huponexit shell option has been set with shopt (see The Shopt Builtin), Bash sends a SIGHUP to all jobs when an interactive login shell exits.
If Bash is waiting for a command to complete and receives a signal for which a trap has been set, the trap will not be executed until the command completes. When Bash is waiting for an asynchronous command via the wait builtin, the reception of a signal for which a trap has been set will cause the wait builtin to return immediately with an exit status greater than 128, immediately after which the trap is executed.
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 Invoking Bash), Bash reads and executes commands from the file, then exits. This mode of operation creates a non-interactive shell. The shell first searches for the file in the current directory, and looks in the directories in $PATH if not found there.
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, with the exception that the locations of commands remembered by the parent (see the description of hash in Bourne Shell Builtins) are retained by the child.
Most versions of Unix make this a part of the operating system'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. Thus, you can specify Bash, awk, Perl, or some other interpreter and write the rest of the script file in that language.
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.
Bash scripts often begin with #! /bin/bash (assuming that Bash has been installed in /bin), since this ensures that Bash will be used to interpret the script, even if it is executed under another shell.
Builtin commands are contained within the shell itself. When the name of a builtin command is used as the first word of a simple command (see Simple Commands), the shell executes the command directly, without invoking another program. Builtin commands are necessary to implement functionality impossible or inconvenient to obtain with separate utilities.
This section briefly describes the builtins which Bash inherits from the Bourne Shell, as well as the builtin commands which are unique to or have been extended in Bash.
Several builtin commands are described in other chapters: builtin commands which provide the Bash interface to the job control facilities (see Job Control Builtins), the directory stack (see Directory Stack Builtins), the command history (see Bash History Builtins), and the programmable completion facilities (see Programmable Completion Builtins).
Many of the builtins have been extended by posix or Bash.
Unless otherwise noted, each builtin command documented as accepting options preceded by ‘-’ accepts ‘--’ to signify the end of the options. The :, true, false, and test builtins do not accept options and do not treat ‘--’ specially. The exit, logout, break, continue, let, and shift builtins accept and process arguments beginning with ‘-’ without requiring ‘--’. Other builtins that accept arguments but are not specified as accepting options interpret arguments beginning with ‘-’ as invalid options and require ‘--’ to prevent this interpretation.
The following shell builtin commands are inherited from the Bourne Shell. These commands are implemented as specified by the posix standard.
: (a colon): [arguments]
Do nothing beyond expanding arguments and performing redirections. The return status is zero.
. (a period). filename [arguments]
Read and execute commands from the filename argument in the current shell context. If filename does not contain a slash, the PATH variable is used to find filename. When Bash is not in posix mode, the current directory is searched if filename is not found in $PATH. If any arguments are supplied, they become the positional parameters when filename is executed. Otherwise the positional parameters are unchanged. The return status is the exit status of the last command executed, or zero if no commands are executed. If filename is not found, or cannot be read, the return status is non-zero. This builtin is equivalent to source.
breakbreak [n]
Exit from a for, while, until, or select loop. If n is supplied, the nth enclosing loop is exited. n must be greater than or equal to 1. The return status is zero unless n is not greater than or equal to 1.
cdcd [-L|-P] [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; symbolic links are followed by default or with the -L option. If directory is ‘-’, it is equivalent to $OLDPWD.
If a non-empty directory name from CDPATH is used, or if ‘-’ is the first argument, and the directory change is successful, the absolute pathname of the new working directory is written to the standard output.
The return status is zero if the directory is successfully changed, non-zero otherwise.
continuecontinue [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. n must be greater than or equal to 1. The return status is zero unless n is not greater than or equal to 1.
evaleval [arguments]
The arguments are concatenated together into a single command, which is then read and executed, and its exit status returned as the exit status of eval. If there are no arguments or only empty arguments, the return status is zero.
execexec [-cl] [-a name] [command [arguments]]
If command is supplied, it replaces the shell without creating a new process. If the -l option is supplied, the shell places a dash at the beginning of the zeroth argument 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. If there are no redirection errors, the return status is zero; otherwise the return status is non-zero.
exitexit [n]
Exit the shell, returning a status of n to the shell's parent. If n is omitted, the exit status is that of the last command executed. Any trap on EXIT is executed before the shell terminates.
exportexport [-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; otherwise the names refer to shell variables. 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. The -p option displays output in a form that may be reused as input. If a variable name is followed by =value, the value of the variable is set to value.
The return status is zero unless an invalid option is supplied, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a shell function.
getoptsgetopts optstringname [args]
getopts is used by shell scripts to parse positional parameters. optstring contains the option characters to be recognized; if a character is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. The colon (‘:’) and question mark (‘?’) may not be used as option characters. 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.
When the end of options is encountered, getopts exits with a return value greater than zero. OPTIND is set to the index of the first non-option argument, and name is set to ‘?’.
getopts normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead.
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 invalid options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error messages will be displayed, even if the first character of optstring is not a colon.
If an invalid 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.
hashhash [-r] [-p filename] [-dt] [name]
Remember the full pathnames of commands specified as name 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. The -d option causes the shell to forget the remembered location of each name. If the -t option is supplied, the full pathname to which each name corresponds is printed. If multiple name arguments are supplied with -t the name is printed before the hashed full pathname. The -l option causes output to be displayed in a format that may be reused as input. If no arguments are given, or if only -l is supplied, information about remembered commands is printed. The return status is zero unless a name is not found or an invalid option is supplied.
pwdpwd [-LP]
Print the absolute pathname of the current working directory. If the -P option is supplied, the pathname printed will not contain symbolic links. If the -L option is supplied, the pathname printed may contain symbolic links. The return status is zero unless an error is encountered while determining the name of the current directory or an invalid option is supplied.
readonlyreadonly [-aApf] [name[=value]] ...
Mark each name as readonly. 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 indexed array variable; the -A option means each name refers to an associative array variable. If no name arguments are given, or if the -p option is supplied, a list of all readonly names is printed. The -p option causes output to be displayed in a format that may be reused as input. If a variable name is followed by =value, the value of the variable is set to value. The return status is zero unless an invalid option is supplied, one of the name arguments is not a valid shell variable or function name, or the -f option is supplied with a name that is not a shell function.
returnreturn [n]
Cause a shell function to exit with the return value n. If n is not supplied, the return value is the exit status of the last command executed in the function. This may also be used to terminate execution of a script being executed with the . (or source) builtin, returning either n or the exit status of the last command executed within the script as the exit status of the script. Any command associated with the RETURN trap is executed before execution resumes after the function or script. The return status is non-zero if return is used outside a function and not during the execution of a script by . or source.
shiftshift [n]
Shift the positional parameters to the left by n. The positional parameters from n+1 ...$# are renamed to $1...$#-n. Parameters represented by the numbers $# to $#-n+1 are unset. n must be a non-negative number less than or equal to $#. If n is zero or greater than $#, the positional parameters are not changed. If n is not supplied, it is assumed to be 1. The return status is zero unless n is greater than $# or less than zero, non-zero otherwise.
test[test does not accept any options, nor does it accept and ignore an argument of -- as signifying the end of options. When the [ form is used, the last argument to the command must be a ].
Expressions may be combined using the following operators, listed in decreasing order of precedence. The evaluation depends on the number of arguments; see below.
! expr( expr ) -a expr2 -o expr2The test and [ builtins evaluate conditional expressions using a set of rules based on the number of arguments.
timestimes
Print out the user and system times used by the shell and its children. The return status is zero.
traptrap [-lp] [arg] [sigspec ...]
The commands in arg are to be read and executed when the shell receives signal sigspec. If arg is absent (and there is a single sigspec) or equal to ‘-’, each specified signal's disposition is reset to the value it had when the shell was started. If arg is the null string, then the signal specified by each sigspec is ignored by the shell and commands it invokes. If arg is not present and -p has been supplied, 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 in a form that may be reused as shell input. The -l option causes the shell to print a list of signal names and their corresponding numbers. Each sigspec is either a signal name or a signal number. Signal names are case insensitive and the SIG prefix is optional.
If a sigspec is 0 or EXIT, arg is executed when the shell exits. If a sigspec is DEBUG, the command arg is executed before every simple command, for command, case command, select command, every arithmetic for command, and before the first command executes in a shell function. Refer to the description of the extdebug option to the shopt builtin (see The Shopt Builtin) for details of its effect on the DEBUG trap. If a sigspec is RETURN, the command arg is executed each time a shell function or a script executed with the . or source builtins finishes executing.
If a sigspec is ERR, the command arg is executed whenever a simple command has a non-zero exit status, subject to the following conditions. The ERR trap is not executed if the failed command is part of the command list immediately following an until or while keyword, part of the test following the if or elif reserved words, part of a command executed in a && or || list, or if the command's return status is being inverted using !. These are the same conditions obeyed by the errexit option.
Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals that are not being ignored are reset to their original values in a subshell or subshell environment when one is created.
The return status is zero unless a sigspec does not specify a valid signal.
umaskumask [-p] [-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. If the -p option is supplied, and mode is omitted, the output is in a form that may be reused as input. The return status is zero if the mode is successfully changed or if no mode argument is supplied, and non-zero otherwise.
Note that when the mode is interpreted as an octal number, each number of the umask is subtracted from 7. Thus, a umask of 022 results in permissions of 755.
unsetunset [-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. Readonly variables and functions may not be unset. The return status is zero unless a name is readonly.
This section describes builtin commands which are unique to or have been extended in Bash. Some of these commands are specified in the posix standard.
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. Aliases are described in Aliases.
bindbind [-m keymap] [-lpsvPSV] bind [-m keymap] [-q function] [-u function] [-r keyseq] bind [-m keymap] -f filename bind [-m keymap] -x keyseq:shell-command bind [-m keymap] keyseq:function-name bind readline-command
Display current Readline (see Command Line Editing) key and function bindings, bind a key sequence to a Readline function or macro, or set a Readline variable. Each non-option argument is a command as it would appear in a Readline initialization file (see Readline Init File), but each binding or command 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 keymapemacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. -l-p-P-v-V-s-S-f filename-q function-u function-r keyseq-x keyseq:shell-commandREADLINE_LINE variable to the contents of the Readline line buffer and the READLINE_POINT variable to the current location of the insertion point. If the executed command changes the value of READLINE_LINE or READLINE_POINT, those new values will be reflected in the editing state. The return status is zero unless an invalid option is supplied or an error occurs.
builtinbuiltin [shell-builtin [args]]
Run a shell builtin, passing it args, and return its exit status. This is useful when defining a shell function with the same name as a shell builtin, retaining the functionality of the builtin within the function. The return status is non-zero if shell-builtin is not a shell builtin command.
callercaller [expr]
Returns the context of any active subroutine call (a shell function or a script executed with the . or source builtins).
Without expr, caller displays the line number and source filename of the current subroutine call. If a non-negative integer is supplied as expr, caller displays the line number, subroutine name, and source file corresponding to that position in the current execution call stack. This extra information may be used, for example, to print a stack trace. The current frame is frame 0.
The return value is 0 unless the shell is not executing a subroutine call or expr does not correspond to a valid position in the call stack.
commandcommand [-pVv] command [arguments ...]
Runs command with arguments ignoring any shell function named command. Only shell builtin commands or commands found by searching the PATH are executed. If there is a shell function named ls, running ‘command ls’ within the function will execute the external command ls instead of calling the function recursively. The -p option means to use a default value for PATH that is guaranteed to find all of the standard utilities. The return status in this case is 127 if command cannot be found or an error occurred, and the exit status of command otherwise.
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 displayed; the -V option produces a more verbose description. In this case, the return status is zero if command is found, and non-zero if not.
declaredeclare [-aAfFilrtux] [-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 with name arguments, additional options are ignored.
When -p is supplied without name arguments, declare will display the attributes and values of all variables having the attributes specified by the additional options. If no other options are supplied with -p, declare will display the attributes and values of all shell variables. The -f option will restrict the display to shell functions.
The -F option inhibits the display of function definitions; only the function name and attributes are printed. If the extdebug shell option is enabled using shopt (see The Shopt Builtin), the source file name and line number where the function is defined are displayed as well. -F implies -f. The following options can be used to restrict output to variables with the specified attributes or to give variables attributes:
-a-A-f-i-l-r-ttrace attribute. Traced functions inherit the DEBUG and RETURN traps from the calling shell. The trace attribute has no special meaning for variables. -u-xUsing ‘+’ instead of ‘-’ turns off the attribute instead, with the exceptions that ‘+a’ may not be used to destroy an array variable and ‘+r’ will not remove the readonly attribute. When used in a function, declare makes each name local, as with the local command. If a variable name is followed by =value, the value of the variable is set to value.
The return status is zero unless an invalid option is encountered, an attempt is made to define a function using ‘-f foo=bar’, an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see Arrays), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to display a non-existent function with -f.
echoecho [-neE] [arg ...]
Output the args, 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. The xpg_echo shell option may be used to dynamically determine whether or not echo expands these escape characters by default. echo does not interpret -- to mean the end of options.
echo interprets the following escape sequences:
\a\b\c\e\f\n\r\t\v\\\0nnn\xHHenableenable [-a] [-dnps] [-f filename] [name ...]
Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell builtin to be executed without specifying a full pathname, even though the shell normally searches for builtins before disk commands. 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 special builtins. If -s is used with -f, the new builtin becomes a special builtin (see Special Builtins).
The return status is zero unless a name is not a shell builtin or there is an error loading a new builtin from a shared object.
helphelp [-dms] [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.
Options, if supplied, have the following meanings:
-d-m-sThe return status is zero unless no command matches pattern.
letlet expression [expression]
The let builtin allows arithmetic to be performed on shell variables. Each expression is evaluated according to the rules given below in Shell Arithmetic. If the last expression evaluates to 0, let returns 1; otherwise 0 is returned.
locallocal [option] name[=value] ...
For each argument, a local variable named name is created, and assigned value. The option can be any of the options accepted by declare. local can only be used within a function; it makes the variable name have a visible scope restricted to that function and its children. The return status is zero unless local is used outside a function, an invalid name is supplied, or name is a readonly variable.
logoutlogout [n]
Exit a login shell, returning a status of n to the shell's parent.
mapfilemapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [ -C callback] [-c quantum] [array]
Read lines from the standard input into the indexed array variable array, or from file descriptor fd if the -u option is supplied. The variable MAPFILE is the default array. Options, if supplied, have the following meanings:
-n-O-s-t-u-C-cIf -C is specified without -c, the default quantum is 5000. When callback is evaluated, it is supplied the index of the next array element to be assigned as an additional argument. callback is evaluated after the line is read but before the array element is assigned.
If not supplied with an explicit origin, mapfile will clear array before assigning to it.
mapfile returns successfully unless an invalid option or option argument is supplied, array is invalid or unassignable, or array is not an indexed array.
printfprintf [-v var] format [arguments]
Write the formatted arguments to the standard output under the control of the format. The format is a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences, which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive argument. In addition to the standard printf(1) formats, ‘%b’ causes printf to expand backslash escape sequences in the corresponding argument, (except that ‘\c’ terminates output, backslashes in ‘\'’, ‘\"’, and ‘\?’ are not removed, and octal escapes beginning with ‘\0’ may contain up to four digits), and ‘%q’ causes printf to output the corresponding argument in a format that can be reused as shell input.
The -v option causes the output to be assigned to the variable var rather than being printed to the standard output.
The format is reused as necessary to consume all of the arguments. If the format requires more arguments than are supplied, the extra format specifications behave as if a zero value or null string, as appropriate, had been supplied. The return value is zero on success, non-zero on failure.
readread [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
One line is read from the standard input, or from the file descriptor fd supplied as an argument to the -u option, and the first word is assigned to the first name, the second word to the second name, and so on, with leftover words and their intervening separators assigned to the last name. If there are fewer words read from the input stream than names, the remaining names are assigned empty values. The characters in the value of the IFS variable are used to split the line into words. The backslash character ‘\’ may be used to remove any special meaning for the next character read and for line continuation. 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, read times out (in which case the return code is greater than 128), or an invalid file descriptor is supplied as the argument to -u.
Options, if supplied, have the following meanings:
-a aname-d delim-e-i text-n ncharsread returns after reading nchars characters rather than waiting for a complete line of input, but honor a delimiter if fewer than nchars characters are read before the delimiter. -N ncharsread returns after reading exactly nchars characters rather than waiting for a complete line of input, unless EOF is encountered or read times out. Delimiter characters encountered in the input are not treated specially and do not cause read to return until nchars characters are read. -p prompt-r-s-t timeoutread to time out and return failure if a complete line of input is not read within timeout seconds. timeout may be a decimal number with a fractional portion following the decimal point. This option is only effective if read is reading input from a terminal, pipe, or other special file; it has no effect when reading from regular files. If timeout is 0, read returns success if input is available on the specified file descriptor, failure otherwise. The exit status is greater than 128 if the timeout is exceeded. -u fdreadarrayreadarray [-n count] [-O origin] [-s count] [-t] [-u fd] [ -C callback] [-c quantum] [array]
Read lines from the standard input into the indexed array variable array, or from file descriptor fd if the -u option is supplied.
A synonym for mapfile.
sourcesource filename
A synonym for . (see Bourne Shell Builtins).
typetype [-afptP] [name ...]
For each name, indicate how it would be interpreted if used as a command name.
If the -t option is used, type prints 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 -p option is used, type either returns the name of the disk file that would be executed, or nothing if -t would not return ‘file’.
The -P option forces a path search for each name, even if -t would not return ‘file’.
If a command is hashed, -p and -P print the hashed value, not necessarily the file that appears first in $PATH.
If the -a option is used, type returns all of the places that contain an executable named file. This includes aliases and functions, if and only if the -p option is not also used.
If the -f option is used, type does not attempt to find shell functions, as with the command builtin.
The return status is zero if all of the names are found, non-zero if any are not found.
typesettypeset [-afFrxi] [-p] [name[=value] ...]
The typeset command is supplied for compatibility with the Korn shell; however, it has been deprecated in favor of the declare builtin command.
ulimitulimit [-abcdefilmnpqrstuvxHST] [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-b-c-d-e-f-i-l-m-n-p-q-r-s-t-u-v-x-TIf limit is given, it is the new value of the specified resource; the special limit values hard, soft, and unlimited stand for the current hard limit, the current soft limit, and no limit, respectively. A hard limit cannot be increased by a non-root user once it is set; a soft limit may be increased up to the value of the hard limit. Otherwise, the current value of the soft limit for the specified resource is printed, unless the -H option is supplied. When setting new limits, if neither -H nor -S is supplied, both the hard and soft limits are set. If no option is given, then -f is assumed. Values are in 1024-byte increments, except for -t, which is in seconds, -p, which is in units of 512-byte blocks, and -n and -u, which are unscaled values.
The return status is zero unless an invalid option or argument is supplied, or an error occurs while setting a new limit.
unaliasunalias [-a] [name ... ]
Remove each name from the list of aliases. If -a is supplied, all aliases are removed. Aliases are described in Aliases.
This builtin is so complicated that it deserves its own section. set allows you to change the values of shell options and set the positional parameters, or to display the names and values of shell variables.
setset [--abefhkmnptuvxBCEHPT] [-o option] [argument ...] set [+abefhkmnptuvxBCEHPT] [+o option] [argument ...]
If no options or arguments are supplied, set displays the names and values of all shell variables and functions, sorted according to the current locale, in a format that may be reused as input for setting or resetting the currently-set variables. Read-only variables cannot be reset. In posix mode, only shell variables are listed.
When options are supplied, they set or unset shell attributes. Options, if specified, have the following meanings:
-a-b-ewhile or until keyword, part of the test in an if statement, part of any command executed in a && or || list except the command following the final && or ||, any command in a pipeline but the last, or if the command's return status is being inverted with !. A trap on ERR, if set, is executed before the shell exits. This option applies to the shell environment and each subshell environment separately (see Command Execution Environment), and may cause subshells to exit before executing all the commands in the subshell.
-f-h-k-m-n-o option-nameallexport-a. braceexpand-B. emacsemacs-style line editing interface (see Command Line Editing). This also affects the editing interface used for read -e. errexit-e. errtrace-E. functrace-T. hashall-h. histexpand-H. historyignoreeofkeyword-k. monitor-m. noclobber-C. noexec-n. noglob-f. nolognotify-b. nounset-u. onecmd-t. physical-P. pipefailposixprivileged-p. verbose-v. vivi-style line editing interface. This also affects the editing interface used for read -e. xtrace-x. -p-p option is not supplied, these actions are taken and the effective user id is set to the real user id. If the -p option is supplied at startup, the effective user id is not reset. Turning this option off causes the effective user and group ids to be set to the real user and group ids. -t-u-v-xfor commands, case commands, select commands, and arithmetic for commands and their arguments or associated word lists after they are expanded and before they are executed. The value of the PS4 variable is expanded and the resultant value is printed before the command and its expanded arguments. -B-C-EERR is inherited by shell functions, command substitutions, and commands executed in a subshell environment. The ERR trap is normally not inherited in such cases. -H-Pcd 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 symbolic link to /usr/local/sys then:
$ cd /usr/sys; echo $PWD /usr/sys $ cd ..; pwd /usr
If set -P is on, then:
$ cd /usr/sys; echo $PWD /usr/local/sys $ cd ..; pwd /usr/local
-TDEBUG and RETURN are inherited by shell functions, command substitutions, and commands executed in a subshell environment. The DEBUG and RETURN traps are normally not inherited in such cases. ---Using ‘+’ rather than ‘-’ causes these options to be turned off. The options can also be used upon invocation of the shell. The current set of options may be found in $-.
The remaining N arguments are positional parameters and are assigned, in order, to $1, $2, ...$N. The special parameter # is set to N.
The return status is always zero unless an invalid option is supplied.
This builtin allows you to change additional shell optional behavior.
shoptshopt [-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. The -p option causes output to be displayed in a form that may be reused as input. Other options have the following meanings:
-s-u-q-oset builtin (see The Set Builtin). If either -s or -u is used with no optname arguments, the display is limited to those options which are set or unset, respectively.
Unless otherwise noted, the 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 valid shell option.
The list of shopt options is:
autocdcd command. This option is only used by interactive shells. cdable_varscd builtin command that is not a directory is assumed to be the name of a variable whose value is the directory to change to. cdspellcd 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 only used by interactive shells. checkhashcheckjobscheckwinsizecmdhistcompat31dirspelldotglobexecfailexec builtin command. An interactive shell does not exit if exec fails. expand_aliasesextdebugdeclare builtin (see Bash Builtins) displays the source file name and line number corresponding to each function name supplied as an argument. DEBUG trap returns a non-zero value, the next command is skipped and not executed. DEBUG trap returns a value of 2, and the shell is executing in a subroutine (a shell function or a shell script executed by the . or source builtins), a call to return is simulated. BASH_ARGC and BASH_ARGV are updated as described in their descriptions (see Bash Variables). ( command ) inherit the DEBUG and RETURN traps. ( command ) inherit the ERROR trap. extglobextquote$'string' and $"string" quoting is performed within ${parameter} expansions enclosed in double quotes. This option is enabled by default. failglobforce_fignoreglobstargnu_errfmthistappendhistreedithistverifyhostcompletehuponexitSIGHUP to all jobs when an interactive login shell exits (see Signals). interactive_commentslithistcmdhist option is enabled, multi-line commands are saved to the history with embedded newlines rather than using semicolon separators where possible. login_shellmailwarn"The mail in mailfile has been read" is displayed. no_empty_cmd_completionnocaseglobnocasematchcase or [[ conditional commands. nullglobprogcomppromptvarsrestricted_shellshift_verboseshift builtin prints an error message when the shift count exceeds the number of positional parameters. sourcepathsource builtin uses the value of PATH to find the directory containing the file supplied as an argument. This option is enabled by default. xpg_echoecho builtin expands backslash-escape sequences 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 valid shell option.
For historical reasons, the posix standard has classified several builtin commands as special. When Bash is executing in posix mode, the special builtins differ from other builtin commands in three respects:
When Bash is not executing in posix mode, these builtins behave no differently than the rest of the Bash builtin commands. The Bash posix mode is described in Bash POSIX Mode.
These are the posix special builtins:
break : . continue eval exec exit export readonly return set shift trap unset
This chapter describes the shell variables that Bash uses. Bash automatically assigns default values to a number of variables.
Bash uses certain shell variables in the same way as the Bourne shell. In some cases, Bash assigns a default value to the variable.
CDPATHcd builtin command. HOMEcd builtin command. The value of this variable is also used by tilde expansion (see Tilde Expansion). IFSMAILMAILPATH$_ expands to the name of the current mail file. OPTARGgetopts builtin. OPTINDgetopts builtin. PATHPATH indicates the current directory. A null directory name may appear as two adjacent colons, or as an initial or trailing colon. PS1PS2These variables are set or used by Bash, but other shells do not normally treat them specially.
A few variables used by Bash are described in different chapters: variables for controlling the job control facilities (see Job Control Variables).
BASHBASHOPTSshopt builtin command (see The Shopt Builtin). The options appearing in BASHOPTS are those reported as ‘on’ by ‘shopt’. If this variable is in the environment when Bash starts up, each shell option in the list will be enabled before reading any startup files. This variable is readonly. BASHPID$$ under certain circumstances, such as subshells that do not require Bash to be re-initialized. BASH_ALIASESalias builtin (see Bourne Shell Builtins). Elements added to this array appear in the alias list; unsetting array elements cause aliases to be removed from the alias list. BASH_ARGC. or source) is at the top of the stack. When a subroutine is executed, the number of parameters passed is pushed onto BASH_ARGC. The shell sets BASH_ARGC only when in extended debugging mode (see The Shopt Builtin for a description of the extdebug option to the shopt builtin). BASH_ARGVBASH_ARGV. The shell sets BASH_ARGV only when in extended debugging mode (see The Shopt Builtin for a description of the extdebug option to the shopt builtin). BASH_CMDShash builtin (see Bourne Shell Builtins). Elements added to this array appear in the hash table; unsetting array elements cause commands to be removed from the hash table. BASH_COMMANDBASH_ENVBASH_EXECUTION_STRINGBASH_LINENO${BASH_LINENO[$i]} is the line number in the source file where ${FUNCNAME[$i]} was called (or ${BASH_LINENO[$i-1]} if referenced within another shell function). The corresponding source file name is ${BASH_SOURCE[$i]}. Use LINENO to obtain the current line number. BASH_REMATCH[[ conditional command (see Conditional Constructs). The element with index 0 is the portion of the string matching the entire regular expression. The element with index n is the portion of the string matching the nth parenthesized subexpression. This variable is read-only. BASH_SOURCEFUNCNAME array variable. BASH_SUBSHELLBASH_VERSINFOBASH_VERSINFO[0]BASH_VERSINFO[1]BASH_VERSINFO[2]BASH_VERSINFO[3]BASH_VERSINFO[4]BASH_VERSINFO[5]BASH_VERSIONBASH_XTRACEFDBASH_XTRACEFD is unset or assigned a new value. Unsetting BASH_XTRACEFD or assigning it the empty string causes the trace output to be sent to the standard error. Note that setting BASH_XTRACEFD to 2 (the standard error file descriptor) and then unsetting it will result in the standard error being closed. COLUMNSselect builtin command to determine the terminal width when printing selection lists. Automatically set upon receipt of a SIGWINCH. COMP_CWORDCOMP_LINECOMP_POINT${#COMP_LINE}. This variable is available only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Completion). COMP_TYPECOMP_KEYCOMP_WORDBREAKSCOMP_WORDBREAKS is unset, it loses its special properties, even if it is subsequently reset. COMP_WORDSCOMP_WORDBREAKS as described above. This variable is available only in shell functions invoked by the programmable completion facilities (see Programmable Completion). COMPREPLYDIRSTACKdirs 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. EMACSEUIDFCEDITfc builtin command. FIGNOREFUNCNAME"main". This variable exists only when a shell function is executing. Assignments to FUNCNAME have no effect and return an error status. If FUNCNAME is unset, it loses its special properties, even if it is subsequently reset. GLOBIGNOREGROUPShistcharsHISTCMDHISTCONTROLHISTFILEHISTFILESIZEHISTIGNOREHISTIGNORE 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.
HISTSIZEHISTTIMEFORMAThistory builtin. If this variable is set, time stamps are written to the history file so they may be preserved across shell sessions. This uses the history comment character to distinguish timestamps from other history lines. HOSTFILEHOSTNAMEHOSTTYPEIGNOREEOFEOF character as the sole input. If set, the value denotes 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. INPUTRCLANGLC_. LC_ALLLC_ variable specifying a locale category. LC_COLLATELC_CTYPELC_MESSAGESLC_NUMERICLINENOLINESselect builtin command to determine the column length for printing selection lists. Automatically set upon receipt of a SIGWINCH. MACHTYPEMAILCHECKOLDPWDcd builtin. OPTERRgetopts builtin command. OSTYPEPIPESTATUSPOSIXLY_CORRECTbash starts, the shell enters posix mode (see Bash POSIX Mode) before reading the startup files, as if the --posix invocation option had been supplied. If it is set while the shell is running, bash enables posix mode, as if the command set -o posixhad been executed.
PPIDPROMPT_COMMANDPROMPT_DIRTRIM\w and \W prompt string escapes (see Printing a Prompt). Characters removed are replaced with an ellipsis. PS3select command. If this variable is not set, the select command prompts with ‘#? ’ PS4PWDcd builtin. RANDOMREPLYread builtin. SECONDSSHELLSHELLOPTSset builtin command (see The Set Builtin). The options appearing in SHELLOPTS are those reported as ‘on’ by ‘set -o’. If this variable is in the environment when Bash starts up, each shell option in the list will be enabled before reading any startup files. This variable is readonly. SHLVLTIMEFORMATtime 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%PThe optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. At most three places after the decimal point may be specified; values of p greater than 3 are changed to 3. If p is not specified, the value 3 is used.
The optional l specifies a longer format, including minutes, of the form MMmSS.FFs. The value of p determines whether or not the fraction is included.
If this variable is not set, Bash acts as if it had the value
$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'If the value is null, no timing information is displayed. A trailing newline is added when the format string is displayed.
TMOUTTMOUT is treated as the default timeout for the read builtin (see Bash Builtins). The select command (see Conditional Constructs) terminates if input does not arrive after TMOUT seconds when input is coming from a terminal. In an interactive shell, the value is interpreted as the number of seconds to wait for input after issuing the primary prompt when the shell is interactive. Bash terminates after that number of seconds if input does not arrive.
TMPDIRUIDThis section describes features unique to Bash.
bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o option] [-O shopt_option] [argument ...] bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o option] [-O shopt_option] -c string [argument ...] bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o option] [-O shopt_option] [argument ...]
In addition to the single-character shell command-line options (see 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 to be recognized.
--debuggerextdebug option to the shopt builtin) and shell function tracing (see The Set Builtin for a description of the -o functrace option). --dump-po-stringsgettext PO (portable object) file format. Equivalent to -D except for the output format. --dump-strings--help--init-file filename--rcfile filename--login--noediting--noprofile--norcsh. --posix--restricted--verbose--versionThere are several single-character options that may be supplied at invocation which are not available with the set builtin.
-c string$0. -i-l-r-s-DC or POSIX (see Locale Translation). This implies the -n option; no commands will be executed. [-+]O [shopt_option]shopt builtin (see The Shopt Builtin). If shopt_option is present, -O sets the value of that option; +O unsets it. If shopt_option is not supplied, the names and values of the shell options accepted by shopt are printed on the standard output. If the invocation option is +O, the output is displayed in a format that may be reused as input. ---- signals the end of options and disables further option processing. Any arguments after the -- are treated as filenames and arguments. A login shell is one whose first character of argument zero is ‘-’, or one invoked with the --login option.
An interactive shell is one started without non-option arguments, unless -s is specified, without specifying the -c option, and whose input and output are both connected to terminals (as determined by isatty(3)), or one started with the -i option. See Interactive Shells, for more information.
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 Shell Scripts). When Bash is invoked in this fashion, $0 is set to the name of the file, and the positional parameters are set to the remaining arguments. Bash reads and executes commands from this file, then exits. Bash's exit status is the exit status of the last command executed in the script. If no commands are executed, the exit status is 0.
This section describes how Bash executes its startup files. If any of the files exist but cannot be read, Bash reports an error. Tildes are expanded in file names as described above under Tilde Expansion (see Tilde Expansion).
Interactive shells are described in Interactive Shells.
When Bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.
When a login shell exits, Bash reads and executes commands from the file ~/.bash_logout, if it exists.
When an interactive shell that is not a login shell is started, Bash reads and executes commands from ~/.bashrc, if that file exists. This may be inhibited by using the --norc option. The --rcfile file option will force Bash to read and execute commands from file instead of ~/.bashrc.
So, typically, your ~/.bash_profile contains the line
if [ -f ~/.bashrc ]; then . ~/.bashrc; fiafter (or before) any login-specific initializations.
When Bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves as if the following command were executed:
if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fibut the value of the PATH variable is not used to search for the file name.
As noted above, if a non-interactive shell is invoked with the --login option, Bash attempts to read and execute commands from the login shell startup files.
shIf 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 an interactive login shell, or as a non-interactive shell with the --login option, 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 other 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, interactive shells expand the ENV variable and commands are read and executed from the file whose name is the expanded value. No other startup files are read.
Bash attempts to determine when it is being run with its standard input connected to a a network connection, as if by the remote shell daemon, usually rshd, or the secure shell daemon sshd. If Bash determines it is being run in this fashion, 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.
If Bash is started with the effective user (group) id not equal to the real user (group) id, and the -p option is not supplied, no startup files are read, shell functions are not inherited from the environment, the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear in the environment, are ignored, and the effective user id is set to the real user id. If the -p option is supplied at invocation, the startup behavior is the same, but the effective user id is not reset.
An interactive shell is one started without non-option arguments, unless -s is specified, without specifying the -c option, and whose input and error output are both connected to terminals (as determined by isatty(3)), or one started with the -i option.
An interactive shell generally reads from and writes to a user's terminal.
The -s invocation option may be used to set the positional parameters when an interactive shell is started.
To determine within a startup script whether or not Bash is running interactively, test the value of the ‘-’ special parameter. It contains i when the shell is interactive. For example:
case "$-" in *i*) echo This shell is interactive ;; *) echo This shell is not interactive ;; esac
Alternatively, startup scripts may 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
When the shell is running interactively, it changes its behavior in several ways.
SIGTTIN, SIGTTOU, and SIGTSTP. ignoreeof option to set -o instead of exiting immediately when it receives an EOF on its standard input when reading a command (see The Set Builtin). SIGTERM (see Signals). SIGINT is caught and handled ((see Signals). SIGINT will interrupt some shell builtins. SIGHUP to all jobs on exit if the huponexit shell option has been enabled (see Signals). ${var:?word} expansions (see Shell Parameter Expansion). exec will not cause the shell to exit (see Bourne Shell Builtins). cd builtin is enabled by default (see the description of the cdspell option to the shopt builtin in The Shopt Builtin). Conditional expressions are used by the [[ compound command and the test and [ builtin commands.
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. If the file argument to one of the primaries is of the form /dev/fd/N, then file descriptor N is checked. If the file argument to one of the primaries is one of /dev/stdin, /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2, respectively, is checked.
When used with ‘[[’, The ‘<’ and ‘>’ operators sort lexicographically using the current locale.
Unless otherwise specified, primaries that operate on files follow symbolic links and operate on the target of the link, rather than the link itself.
-a file-b file-c file-d file-e file-f file-g file-h file-k file-p file-r file-s file-t fd-u file-w file-x file-O file-G file-L file-S file-N file -nt file2 -ot file2 -ef file2-o optnameset builtin (see The Set Builtin). -z string-n string == string2 = string2test command for posix conformance. != string2 < string2 > string2 OP arg2OP 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 shell allows arithmetic expressions to be evaluated, as one of the shell expansions or by the let and the -i option to the declare builtins.
Evaluation is done in fixed-width integers with no check for overflow, though division by 0 is trapped and flagged as an error. The operators and their precedence, associativity, and values are the same as in the C language. The following list of operators is grouped into levels of equal-precedence operators. The levels are listed in order of decreasing precedence.
++ id--++id --id- +! ~*** / %+ -<< >><= >= < >== !=&^|&&||expr ? expr : expr= *= /= %= += -= <<= >>= &= ^= |=expr1 , expr2Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. Within an expression, shell variables may also be referenced by name without using the parameter expansion syntax. A shell variable that is null or unset evaluates to 0 when referenced by name without using the parameter expansion syntax. The value of a variable is evaluated as an arithmetic expression when it is referenced, or when a variable which has been given the integer attribute using ‘declare -i’ is assigned a value. A null value evaluates to 0. 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 interchangeably 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.
Aliases allow a string to be substituted for a word when it is used as the first word of a simple 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 simple 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 characters ‘/’, ‘$’, ‘`’, ‘=’ and any of the shell metacharacters or quoting characters listed above may not appear in an alias name. The replacement text may contain any valid shell input, including shell metacharacters. 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 Shell Functions).
Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt (see The Shopt Builtin).
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 a 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.
For almost every purpose, shell functions are preferred over aliases.
Bash provides one-dimensional indexed and associative array variables. Any variable may be used as an indexed array; the declare builtin will explicitly declare an array. There is no maximum limit on the size of an array, nor any requirement that members be indexed or assigned contiguously. Indexed arrays are referenced using integers (including arithmetic expressions (see Shell Arithmetic) and are zero-based; associative arrays use arbitrary strings.
An indexed array is created automatically if any variable is assigned to using the syntax
name[subscript]=value
The subscript is treated as an arithmetic expression that must evaluate to a number 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.
Associative arrays are created using
declare -A name.
Attributes may be specified for an array variable using the declare and readonly builtins. Each attribute applies to all members of an array.
Arrays are assigned to using compound assignments of the form
name=(value1 ... valuen)
where each value is of the form [subscript]=string. Indexed array assignments do not require the bracket and subscript. When assigning to indexed arrays, 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.
When assigning to an associative array, the subscript is required.
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. If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the beginning part of the original word, and the expansion of the last parameter is joined with the last part of the original word. This is analogous to the expansion of the special parameters ‘@’ and ‘*’. ${#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 with a subscript of 0.
An array variable is considered set if a subscript has been assigned a value. The null string is a valid value.
The unset builtin is used to destroy arrays. unsetname[subscript] destroys the array element at index subscript. Care must be taken to avoid unwanted side effects caused by filename expansion. unsetname, 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 indexed array and a -A option to specify an associative 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 directory stack is a list of recently-visited directories. The pushd builtin adds directories to the stack as it changes the current directory, and the popd builtin removes specified directories from the stack and changes the current directory to the directory removed. The dirs builtin displays the contents of the directory stack.
The contents of the directory stack are also visible as the value of the DIRSTACK shell variable.
dirsdirs [+N | -N] [-clpv]
Display the list of currently remembered directories. Directories are added to the list with the pushd command; the popd command removes directories from the list.
+Ndirs when invoked without options), starting with zero. -Ndirs when invoked without options), starting with zero. -c-l-pdirs to print the directory stack with one entry per line. -vdirs to print the directory stack with one entry per line, prefixing each entry with its index in the stack. popdpopd [+N | -N] [-n]
Remove the top entry from 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.
+Ndirs), starting with zero. -Ndirs), starting with zero. -npushdpushd [-n] [+N | -N | dir ]
Save the current directory on the top of the directory stack and then cd to dir. With no arguments, pushd exchanges the top two directories.
-n+Ndirs, starting with zero) to the top of the list by rotating the stack. -Ndirs, starting with zero) to the top of the list by rotating the stack. cddir'. cds to dir. The value of the variable PROMPT_COMMAND is examined just before Bash prints each primary prompt. If PROMPT_COMMAND is set and has a non-null value, then the value is executed just as if it had been typed on the command line.
In addition, the following table describes the special characters which can appear in the prompt variables:
\a\d\D{format}strftime(3) and the result is inserted into the prompt string; an empty format results in a locale-specific time representation. The braces are required. \e\h\H\j\l\n\r\s$0 (the portion following the final slash). \t\T\@\A\u\v\V\w\W\!\#\$#, otherwise $. \nnn\\\[\]The command number and the history number are usually different: the history number of a command is its position in the history list, which may include commands restored from the history file (see Bash History Facilities), while the command number is the position in the sequence of commands executed during the current shell session.
After the string is decoded, it is expanded via parameter expansion, command substitution, arithmetic expansion, and quote removal, subject to the value of the promptvars shell option (see Bash Builtins).
If Bash is started with the name rbash, or the --restricted or -r 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 or not performed:
cd builtin. . builtin command. hash builtin command. exec builtin to replace the shell with another command. enable builtin. enable builtin command to enable disabled shell builtins. command builtin. These restrictions are enforced after any startup files are read.
When a command that is found to be a shell script is executed (see Shell Scripts), rbash turns off any restrictions in the shell spawned to execute the script.
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 standard by changing the behavior to match that specified by posix in areas where the Bash default differs.
When invoked as sh, Bash enters posix mode after reading the startup files.
The following list is what's changed when `posix mode' is in effect:
SIGTSTP. bg builtin uses the required format to describe each job placed in the background, which does not include an indication of whether the job is the current or previous job. promptvars option. kill builtin does not accept signal names with a ‘SIG’ prefix. .filename is not found. names. 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 invalid name causes a fatal syntax error in non-interactive shells. cd builtin will not implicitly append the current directory to it. This means that cd will fail if no valid directory name can be constructed from any of the entries in $CDPATH, even if the a directory with the same name as the name given as an argument to cd exists in the current directory. for statement or the selection variable in a select statement is a readonly variable. export and readonly builtin commands display their output in the format required by posix. trap builtin displays signal names without the leading SIG. trap builtin doesn't check the first argument for a possible signal specification and revert the signal handling to the original disposition if it is, unless that argument consists solely of digits and is a valid signal number. If users want to reset the handler for a given signal to the original disposition, they should use ‘-’ as the first argument. . and source builtins do not search the current directory for the filename argument if it is not found by searching PATH. alias builtin displays alias definitions, it does not display them with a leading ‘alias ’ unless the -p option is supplied. set builtin is invoked without options, it does not display shell function names and definitions. set builtin is invoked without options, it displays variable values without quotes, unless they contain shell metacharacters, even if the result contains nonprinting characters. cd builtin is invoked in logical mode, and the pathname constructed from $PWD and the directory name supplied as an argument does not refer to an existing directory, cd will fail instead of falling back to physical mode. pwd builtin is supplied the -P option, it resets $PWD to a pathname containing no symlinks. pwd builtin verifies that the value it prints is the same as the current directory, even if it is not asked to check the file system with the -P option. fc builtin does not include an indication of whether or not a history entry has been modified. fc is ed. type and command builtins will not report a non-executable file as having been found, though the shell will attempt to execute such a file if it is the only so-named file found in $PATH. vi editing mode will invoke the vi editor directly when the ‘v’ command is run, instead of checking $VISUAL and $EDITOR. xpg_echo option is enabled, Bash does not attempt to interpret any arguments to echo as options. Each argument is displayed, after escape characters are converted. ulimit builtin uses a block size of 512 bytes for the -c and -f options. SIGCHLD when a trap is set on SIGCHLD does not interrupt the wait builtin and cause it to return immediately. The trap command is run once for each child that exits. There is other posix behavior that Bash does not implement by default even when in posix mode. Specifically:
fc builtin checks $EDITOR as a program to edit history entries if FCEDIT is unset, rather than defaulting directly to ed. fc uses ed if EDITOR is unset. xpg_echo option to be enabled for the echo builtin to be fully conformant. Bash can be configured to be posix-conformant by default, by specifying the --enable-strict-posix-default to configure when building (see Optional Features).
This chapter discusses 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 operating system kernel'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, 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 operating 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, if the user so specifies with stty tostop, write to the terminal. Background processes which attempt to read from (write to when stty tostop is in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal by the kernel's terminal driver, which, unless caught, suspends the process.
If the operating system on which Bash is running supports job control, Bash contains facilities to use it. Typing the suspend character (typically ‘^Z’, Control-Z) while a process is running causes that process to be stopped and returns control 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. The user then manipulates 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 specification (jobspec).
Job number n may be referred to as ‘%n’. 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 or started in the background. A single ‘%’ (with no accompanying job specification) also refers to the current job. The previous job may be referenced using ‘%-’. If there is only a single job, ‘%+’ and ‘%-’ can both be used to refer to that job. 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 ‘-’.
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.
Simply naming a job can be used to bring it into the foreground: ‘%1’ is a synonym for ‘fg %1’, bringing job 1 from the background into the foreground. Similarly, ‘%1 &’ resumes job 1 in the background, equivalent to ‘bg %1’
The shell learns immediately whenever a job changes state. Normally, Bash waits until it is about to print a prompt before reporting changes in a job's status so as to not interrupt any other output. If the -b option to the set builtin is enabled, Bash reports such changes immediately (see The Set Builtin). Any trap on SIGCHLD is executed for each child process that exits.
If an attempt to exit Bash is made while jobs are stopped, (or running, if the checkjobs option is enabled – see The Shopt Builtin), the shell prints a warning message, and if the checkjobs option is enabled, lists the jobs and their statuses. The jobs command may then be used to inspect their status. If a second attempt to exit is made without an intervening command, Bash does not print another warning, and any stopped jobs are terminated.
bgbg [jobspec ...]
Resume each suspended job jobspec in the background, as if it had been started with ‘&’. If jobspec is not supplied, the current job is used. The return status is zero unless it is run when job control is not enabled, or, when run with job control enabled, any jobspec was not found or specifies a job that was started without job control.
fgfg [jobspec]
Resume the job jobspec in the foreground and make it the current job. If jobspec is not supplied, the current job is used. The return status is that of the command placed into the foreground, or non-zero if run when job control is disabled or, when run with job control enabled, jobspec does not specify a valid job or jobspec specifies a job that was started without job control.
jobsjobs [-lnprs] [jobspec] jobs -x command [arguments]
The first form lists the active jobs. The options have the following meanings:
-l-n-p-r-sIf jobspec is given, output is restricted to information about that job. If jobspec is not supplied, the status of all jobs is listed.
If the -x option is supplied, 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.
killkill [-s sigspec] [-n signum] [-sigspec] jobspec or pid kill -l [exit_status]
Send a signal specified by sigspec or signum to the process named by job specification jobspec or process idpid. sigspec is either a case-insensitive signal name such as SIGINT (with or without the SIG prefix) 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. If any arguments are supplied when -l is given, the names of the signals corresponding to the arguments are listed, and the return status is zero. exit_status is a number specifying a signal number or the exit status of a process terminated by a signal. The return status is zero if at least one signal was successfully sent, or non-zero if an error occurs or an invalid option is encountered.
waitwait [jobspec or pid ...]
Wait until the child process specified by each process idpid or job specification jobspec exits and return the exit status of the last command waited for. 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, and the return status is zero. If neither jobspec nor pid specifies an active child process of the shell, the return status is 127.
disowndisown [-ar] [-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, and neither the -a nor -r option is supplied, the current job is used. If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs.
suspendsuspend [-f]
Suspend the execution of this shell until it receives a SIGCONT signal. A login shell cannot be suspended; the -f option can be used to override this and force the suspension.
When job control is not active, the kill and wait builtins do not accept jobspec arguments. They must be supplied process ids.
auto_resumeThis chapter describes the basic features of the gnu command line editing interface. Command line editing is provided by the Readline library, which is used by several different programs, including Bash. Command line editing is enabled by default when using an interactive shell, unless the --noediting option is supplied at shell invocation. Line editing is also used when using the -e option to the read builtin command (see Bash Builtins). By default, the line editing commands are similar to those of emacs. A vi-style line editing interface is also available. Line editing can be enabled at any time using the -o emacs or -o vi options to the set builtin command (see The Set Builtin), or disabled using the +o emacs or +o vi options to set.
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. The Meta key is labeled <ALT> on many keyboards. On keyboards with two keys labeled <ALT> (usually to either side of the space bar), the <ALT> on the left side is generally set to work as a Meta key. The <ALT> key on the right may also be configured to work as a Meta key or may be configured as some other modifier, such as a Compose key for typing accented characters.
If you do not have a Meta or <ALT> key, or another key working as 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 metafyingC-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 (see Readline Init File). If your keyboard lacks a <LFD> key, typing <C-j> will produce the desired character. The <RET> key may be labeled <Return> or <Enter> on some keyboards.
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 <RET>. You do not have to be at the end of the line to press <RET>; the entire line is accepted regardless of the location of the cursor within the line.
In order to enter characters into the line, simply type them. The typed character appears where the cursor was, and then the cursor moves one space to the right. If you mistype a character, you can use your erase character to back up and delete the mistyped character.
Sometimes you may mistype a character, and not notice the error until you have typed several other characters. In that case, you can type C-b to move the cursor to the left, and then correct your mistake. Afterwards, you can move the cursor to the right with C-f.
When you add text in the middle of a line, you will notice that characters to the right of the cursor are `pushed over' to make room for the text that you have inserted. Likewise, when you delete text behind the cursor, characters to the right of the cursor are `pulled back' to fill in the blank space created by the removal of the text. A list of the bare essentials for editing the text of an input line follows.
(Depending on your configuration, the <Backspace> key be set to delete the character to the left of the cursor and the <DEL> key set to delete the character underneath the cursor, like C-d, rather than the character to the left of the cursor.)
The above table describes the most basic keystrokes that you need in order to do editing of the input line. For your convenience, many other commands have been added in addition to C-b, C-f, C-d, and <DEL>. Here are some commands for moving more rapidly about the line.
Notice how C-f moves forward a character, while M-f moves forward a word. It is a loose convention that control keystrokes operate on characters while meta keystrokes operate on words.
Killing text means to delete the text from the line, but to save it away for later use, usually by yanking (re-inserting) it back into the line. (`Cut' and `paste' are more recent jargon for `kill' and `yank'.)
If the description for a command says that it `kills' text, then you can be sure that you can get the text back in a different (or the same) place later.
When you use a kill command, the text is saved in a kill-ring. Any number of consecutive kills save all of the killed text together, so that when you yank it back, you get it all. The kill ring is not line specific; the text that you killed on a previously typed line is available to be yanked back later, when you are typing another line. Here is the list of commands for killing text.
Here is how to yank the text back into the line. Yanking means to copy the most-recently-killed text from the kill buffer.
You can pass numeric arguments to Readline commands. Sometimes the argument acts as a repeat count, other times it is the sign of the argument that is significant. If you pass a negative argument to a command which normally acts in a forward direction, that command will act in a backward direction. For example, to kill text back to the start of the line, you might type ‘M-- C-k’.
The general way to pass numeric arguments to a command is to type meta digits before the command. If the first `digit' typed is a minus sign (‘-’), then the sign of the argument will be negative. Once you have typed one meta digit to get the argument started, you can type the remainder of the digits, and then the command. For example, to give the C-d command an argument of 10, you could type ‘M-1 0 C-d’, which will delete the next ten characters on the input line.
Readline provides commands for searching through the command history (see Bash History Facilities) for lines containing a specified string. There are two search modes: incremental and non-incremental.
Incremental searches begin before the user has finished typing the search string. As each character of the search string is typed, Readline displays the next entry from the history matching the string typed so far. An incremental search requires only as many characters as needed to find the desired history entry. To search backward in the history for a particular string, type C-r. Typing C-s searches forward through the history. The characters present in the value of the isearch-terminators variable are used to terminate an incremental search. If that variable has not been assigned a value, the <ESC> and C-J characters will terminate an incremental search. C-g will abort an incremental search and restore the original line. When the search is terminated, the history entry containing the search string becomes the current line.
To find other matching entries in the history list, type C-r or C-s as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a Readline command will terminate the search and execute that command. For instance, a <RET> will terminate the search and accept the line, thereby executing the command from the history list. A movement command will terminate the search, make the last line found the current line, and begin editing.
Readline remembers the last incremental search string. If two C-rs are typed without any intervening characters defining a new search string, any remembered search string is used.
Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line.
Although the Readline library comes with a set of Emacs-like keybindings installed by default, it is possible to use a different set of keybindings. Any user can customize programs that use Readline by putting commands in an inputrc file, conventionally in his home directory. The name of this file is taken from the value of the shell variable INPUTRC. If that variable is unset, the default is ~/.inputrc. If that file does not exist or cannot be read, the ultimate default is /etc/inputrc.
When a program which uses the Readline library starts up, the init file is read, and the key bindings are set.
In addition, the C-x C-r command re-reads this init file, thus incorporating any changes that you might have made to it.
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 Conditional Init Constructs). Other lines denote variable settings and key bindings.
set command within the init file. The syntax is simple: set variablevalue
Here, for example, is how to change from the default Emacs-like key binding to use vi line editing commands:
set editing-mode vi
Variable names and values, where appropriate, are recognized without regard to case. Unrecognized variable names are ignored.
Boolean variables (those that can be set to on or off) are set to on if the value is null or empty, on (case-insensitive), or 1. Any other value results in the variable being set to off.
The bind -V command lists the current Readline variable names and values. See Bash Builtins.
A great deal of run-time behavior is changeable with the following variables.
bell-stylebind-tty-special-charscomment-begininsert-comment command is executed. The default value is "#". completion-ignore-casecompletion-prefix-display-lengthcompletion-query-items100. convert-metadisable-completionself-insert. The default is ‘off’. editing-modeediting-mode variable controls which default set of key bindings is used. 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’. echo-control-charactersenable-keypadenable-meta-keyexpand-tildehistory-preserve-pointprevious-history or next-history. The default is ‘off’. history-sizehorizontal-scroll-modeinput-metameta-flag is a synonym for this variable. isearch-terminatorskeymapkeymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. The default value is emacs. The value of the editing-mode variable also affects the default keymap. mark-directoriesmark-modified-linesmark-symlinked-directoriesmark-directories). The default is ‘off’. match-hidden-filesoutput-metapage-completionsmore-like pager to display a screenful of possible completions at a time. This variable is ‘on’ by default. print-completions-horizontallyrevert-all-at-newlineaccept-line is executed. By default, history lines may be modified and retain individual undo lists across calls to readline. The default is ‘off’. show-all-if-ambiguousshow-all-if-unmodifiedskip-completed-textvisible-statsOnce you know the name of the command, simply place on a line in the init file the name of the key you wish to bind the command to, a colon, and then the name of the command. There can be no space between the key name and the colon – that will be interpreted as part of the key name. The name of the key can be expressed in different ways, depending on what you find most comfortable.
In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro).
The bind -p command displays Readline function names and bindings in a format that can put directly into an initialization file. See Bash Builtins.
Control-u: universal-argument Meta-Rubout: backward-kill-word Control-o: "> output"
In the above example, C-u is bound to the function universal-argument, M-DEL is bound to the function backward-kill-word, and C-o is bound to run the macro expressed on the right hand side (that is, to insert the text ‘> output’ into the line).
A number of symbolic character names are recognized while processing this key binding syntax: DEL, ESC, ESCAPE, LFD, NEWLINE, RET, RETURN, RUBOUT, SPACE, SPC, and TAB.
"\C-u": universal-argument "\C-x\C-r": re-read-init-file "\e[11~": "Function Key 1"
In the above example, C-u is again bound to the function universal-argument (just as it was in the first example), ‘C-xC-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 gnu Emacs style escape sequences are available when specifying key sequences:
In addition to the gnu Emacs style escape sequences, a second set of backslash escapes is available:
\a\b\d\f\n\r\t\v\nnn\xHHWhen entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including ‘"’ and ‘'’. For example, the following binding will make ‘C-x \’ insert a single ‘\’ into the line:
"\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 four 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. modemode= form of the $if directive is used to test whether Readline is in emacs or vi mode. This may be used in conjunction with the ‘set keymap’ command, for instance, to set bindings in the emacs-standard and emacs-ctlx keymaps only if Readline is starting out in emacs mode. termterm= form may be used to include terminal-specific key bindings, perhaps to bind the key sequences output by the terminal's function keys. The word on the right side of the ‘=’ is tested against both the full name of the terminal and the portion of the terminal name before the first ‘-’. This allows sun to match both sun and sun-cmd, for instance. application$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. $include$include /etc/inputrc
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. # # First, include any systemwide bindings and variable # assignments from /etc/Inputrc $include /etc/Inputrc # # 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 $endif This section describes Readline commands that may be bound to key sequences. You can list your key bindings by executing bind -P or, for a more terse format, suitable for an inputrc file, bind -p. (See Bash Builtins.) Command names without an accompanying key sequence are unbound by default.
In the following descriptions, point refers to the current cursor position, and mark refers to a cursor position saved by the set-mark command. The text between the point and mark is referred to as the region.
beginning-of-line (C-a)end-of-line (C-e)forward-char (C-f)backward-char (C-b)forward-word (M-f)backward-word (M-b)shell-forward-word ()shell-backward-word ()clear-screen (C-l)redraw-current-line ()accept-line (Newline or Return)previous-history (C-p)next-history (C-n)beginning-of-history (M-<)end-of-history (M->)reverse-search-history (C-r)forward-search-history (C-s)non-incremental-reverse-search-history (M-p)non-incremental-forward-search-history (M-n)history-search-forward ()history-search-backward ()yank-nth-arg (M-C-y)yank-last-arg (M-. or M-_)yank-nth-arg. Successive calls to yank-last-arg move back through the history list, inserting the last argument of each line in turn. The history expansion facilities are used to extract the last argument, as if the ‘!$’ history expansion had been specified. delete-char (C-d)delete-char, then return eof. backward-delete-char (Rubout)forward-backward-delete-char ()quoted-insert (C-q or C-v)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)overwrite-mode ()emacs mode; vi mode does overwrite differently. Each call to readline() starts in insert mode. In overwrite mode, characters bound to self-insert replace the text at point rather than pushing the text to the right. Characters bound to backward-delete-char replace the character before point with a space.
By default, this command is unbound.
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. shell-kill-word ()shell-forward-word. backward-kill-word ()shell-backward-word. unix-word-rubout (C-w)unix-filename-rubout ()delete-horizontal-space ()kill-region ()copy-region-as-kill ()copy-backward-word ()backward-word. By default, this command is unbound. copy-forward-word ()forward-word. By default, this command is unbound. yank (C-y)yank-pop (M-y)yank or yank-pop. digit-argument (M-0, M-1, ... M--)universal-argument ()universal-argument again ends the numeric argument, but is otherwise ignored. As a special case, if this command is immediately followed by a character that is neither a digit or minus sign, the argument count for the next command is multiplied by four. The argument count is initially one, so executing this function the first time makes the argument count four, a second time makes the argument count sixteen, and so on. By default, this is not bound to a key. complete (<TAB>)possible-completions (M-?)insert-completions (M-*)possible-completions. menu-complete ()complete, but replaces the word to be completed with a single match from the list of possible completions. Repeated execution of menu-complete steps through the list of possible completions, inserting each match in turn. At the end of the list of completions, the bell is rung (subject to the setting of bell-style) and the original text is restored. An argument of n moves n positions forward in the list of matches; a negative argument may be used to move backward through the list. This command is intended to be bound to <TAB>, but is unbound by default. menu-complete-backward ()menu-complete, but moves backward through the list of possible completions, as if menu-complete had been given a negative argument. delete-char-or-list ()delete-char). If at the end of the line, behaves identically to possible-completions. This command is unbound by default. complete-filename (M-/)possible-filename-completions (C-x /)complete-username (M-~)possible-username-completions (C-x ~)complete-variable (M-$)possible-variable-completions (C-x $)complete-hostname (M-@)possible-hostname-completions (C-x @)complete-command (M-!)possible-command-completions (C-x !)dynamic-complete-history (M-<TAB>)dabbrev-expand ()complete-into-braces (M-{)start-kbd-macro (C-x ()end-kbd-macro (C-x ))call-last-kbd-macro (C-x e)re-read-init-file (C-x C-r)abort (C-g)bell-style). do-uppercase-version (M-a, M-b, M-x, ...)prefix-meta (<ESC>)undo (C-_ or C-x C-u)revert-line (M-r)undo command enough times to get back to the beginning. tilde-expand (M-&)set-mark (C-@)exchange-point-and-mark (C-x C-x)character-search (C-])character-search-backward (M-C-])skip-csi-sequence ()insert-comment (M-#)comment-begin variable is inserted at the beginning of the current line. If a numeric argument is supplied, this command acts as a toggle: if the characters at the beginning of the line do not match the value of comment-begin, the value is inserted, otherwise the characters in comment-begin are deleted from the beginning of the line. In either case, the line is accepted as if a newline had been typed. The default value of comment-begin causes this command to make the current line a shell comment. If a numeric argument causes the comment character to be removed, the line will be executed by the shell. dump-functions ()dump-variables ()dump-macros ()glob-complete-word (M-g)glob-expand-word (C-x *)glob-list-expansions (C-x g)glob-expand-word is displayed, and the line is redrawn. If a numeric argument is supplied, a ‘*’ is appended before pathname expansion. display-shell-version (C-x C-v)shell-expand-line (M-C-e)history-expand-line (M-^)magic-space ()alias-expand-line ()history-and-alias-expand-line ()insert-last-argument (M-. or M-_)yank-last-arg. operate-and-get-next (C-o)edit-and-execute-command (C-xC-e)$VISUAL, $EDITOR, and emacs as the editor, in that order. 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 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.
When word completion is attempted for an argument to a command for which a completion specification (a compspec) has been defined using the complete builtin (see Programmable Completion Builtins), the programmable completion facilities are invoked.
First, the command name is identified. If a compspec has been defined for that command, the compspec is used to generate the list of possible completions for the word. If the command word is the empty string (completion attempted at the beginning of an empty line), any compspec defined with the -E option to complete is used. If the command word is a full pathname, a compspec for the full pathname is searched for first. If no compspec is found for the full pathname, an attempt is made to find a compspec for the portion following the final slash. If those searches do not result in a compspec, any compspec defined with the -D option to complete is used as the default.
Once a compspec has been found, it is used to generate the list of matching words. If a compspec is not found, the default Bash completion described above (see Commands For Completion) is performed.
First, the actions specified by the compspec are used. Only matches which are prefixed by the word being completed are returned. When the -f or -d option is used for filename or directory name completion, the shell variable FIGNORE is used to filter the matches. See Bash Variables, for a description of FIGNORE.
Any completions specified by a filename expansion pattern to the -G option are generated next. The words generated by the pattern need not match the word being completed. The GLOBIGNORE shell variable is not used to filter the matches, but the FIGNORE shell variable is used.
Next, the string specified as the argument to the -W option is considered. The string is first split using the characters in the IFS special variable as delimiters. Shell quoting is honored. Each word is then expanded using brace expansion, tilde expansion, parameter and variable expansion, command substitution, and arithmetic expansion, as described above (see Shell Expansions). The results are split using the rules described above (see Word Splitting). The results of the expansion are prefix-matched against the word being completed, and the matching words become the possible completions.
After these matches have been generated, any shell function or command specified with the -F and -C options is invoked. When the command or function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE variables are assigned values as described above (see Bash Variables). If a shell function is being invoked, the COMP_WORDS and COMP_CWORD variables are also set. When the function or command is invoked, the first argument is the name of the command whose arguments are being completed, the second argument is the word being completed, and the third argument is the word preceding the word being completed on the current command line. No filtering of the generated completions against the word being completed is performed; the function or command has complete freedom in generating the matches.
Any function specified with -F is invoked first. The function may use any of the shell facilities, including the compgen and compopt builtins described below (see Programmable Completion Builtins), to generate the matches. It must put the possible completions in the COMPREPLY array variable.
Next, any command specified with the -C option is invoked in an environment equivalent to command substitution. It should print a list of completions, one per line, to the standard output. Backslash may be used to escape a newline, if necessary.
After all of the possible completions are generated, any filter specified with the -X option is applied to the list. The filter is a pattern as used for pathname expansion; a ‘&’ in the pattern is replaced with the text of the word being completed. A literal ‘&’ may be escaped with a backslash; the backslash is removed before attempting a match. Any completion that matches the pattern will be removed from the list. A leading ‘!’ negates the pattern; in this case any completion not matching the pattern will be removed.
Finally, any prefix and suffix specified with the -P and -S options are added to each member of the completion list, and the result is returned to the Readline completion code as the list of possible completions.
If the previously-applied actions do not generate any matches, and the -o dirnames option was supplied to complete when the compspec was defined, directory name completion is attempted.
If the -o plusdirs option was supplied to complete when the compspec was defined, directory name completion is attempted and any matches are added to the results of the other actions.
By default, if a compspec is found, whatever it generates is returned to the completion code as the full set of possible completions. The default Bash completions are not attempted, and the Readline default of filename completion is disabled. If the -o bashdefault option was supplied to complete when the compspec was defined, the default Bash completions are attempted if the compspec generates no matches. If the -o default option was supplied to complete when the compspec was defined, Readline's default completion will be performed if the compspec (and, if attempted, the default Bash completions) generate no matches.
When a compspec indicates that directory name completion is desired, the programmable completion functions force Readline to append a slash to completed names which are symbolic links to directories, subject to the value of the mark-directories Readline variable, regardless of the setting of the mark-symlinked-directories Readline variable.
There is some support for dynamically modifying completions. This is most useful when used in combination with a default completion specified with -D. It's possible for shell functions executed as completion handlers to indicate that completion should be retried by returning an exit status of 124. If a shell function returns 124, and changes the compspec associated with the command on which completion is being attempted (supplied as the first argument when the function is executed), programmable completion restarts from the beginning, with an attempt to find a compspec for that command. This allows a set of completions to be built dynamically as completion is attempted, rather than being loaded all at once.
For instance, assuming that there is a library of compspecs, each kept in a file corresponding to the name of the command, the following default completion function would load completions dynamically:
_completion_loader() { . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124 } complete -D -F _completion_loader Two builtin commands are available to manipulate the programmable completion facilities.
compgencompgen [option] [word]
Generate possible completion matches for word according to the options, which may be any option accepted by the complete builtin with the exception of -p and -r, and write the matches to the standard output. When using the -F or -C options, the various shell variables set by the programmable completion facilities, while available, will not have useful values.
The matches will be generated in the same way as if the programmable completion code had generated them directly from a completion specification with the same flags. If word is specified, only those completions matching word will be displayed.
The return value is true unless an invalid option is supplied, or no matches were generated.
completecomplete [-abcdefgjksuv] [-ocomp-option] [-DE] [-Aaction] [-Gglobpat] [-Wwordlist] [-Ffunction] [-Ccommand] [-Xfilterpat] [-Pprefix] [-Ssuffix]name[name...]complete -pr [-DE] [name...]
Specify how arguments to each name should be completed. If the -p option is supplied, or if no options are supplied, existing completion specifications are printed in a way that allows them to be reused as input. The -r option removes a completion specification for each name, or, if no names are supplied, all completion specifications. The -D option indicates that the remaining options and actions should apply to the “default” command completion; that is, completion attempted on a command for which no completion has previously been defined. The -E option indicates that the remaining options and actions should apply to “empty” command completion; that is, completion attempted on a blank line.
The process of applying these completion specifications when word completion is attempted is described above (see Programmable Completion). The -D option takes precedence over -E.
Other options, if specified, have the following meanings. The arguments to the -G, -W, and -X options (and, if necessary, the -P and -S options) should be quoted to protect them from expansion before the complete builtin is invoked.
-o comp-optionbashdefaultdefaultdirnamesfilenamesnospaceplusdirs-A actionaliasarrayvarbindingbuiltincommanddirectorydisabledenabledexportfilefunctiongrouphelptopichelp builtin (see Bash Builtins). hostnamejobkeywordrunningservicesetoptset builtin (see The Set Builtin). shoptshopt builtin (see Bash Builtins). signalstoppeduservariable-G globpat-W wordlist-C command-F function-X filterpat-P prefix-S suffixThe return value is true unless an invalid option is supplied, an option other than -p or -r is supplied without a name argument, an attempt is made to remove a completion specification for a name for which no specification exists, or an error occurs adding a completion specification.
compoptcompopt [-o option] [-DE] [+o option] [name] Modify completion options for each name according to the options, or for the currently-execution completion if no names are supplied. If no options are given, display the completion options for each name or the current completion. The possible values of option are those valid for the complete builtin described above. The -D option indicates that the remaining options should apply to the “default” command completion; that is, completion attempted on a command for which no completion has previously been defined. The -E option indicates that the remaining options should apply to “empty” command completion; that is, completion attempted on a blank line.
The -D option takes precedence over -E.
The return value is true unless an invalid option is supplied, an attempt is made to modify the options for a name for which no completion specification exists, or an output error occurs.
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 other programs, see the gnu Readline Library Manual.
When the -o history option to the set builtin is enabled (see The Set Builtin), the shell provides access to the command history, the list of commands previously typed. The value of the HISTSIZE shell variable is used as the number of commands to save in a history list. The text of the last $HISTSIZE commands (default 500) is saved. 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). The file named by the value of 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 the file named by $HISTFILE. If the histappend shell option is set (see Bash Builtins), 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.
If the HISTTIMEFORMAT is set, the time stamp information associated with each history entry is written to the history file, marked with the history comment character. When the history file is read, lines beginning with the history comment character followed immediately by a digit are interpreted as timestamps for the previous history line.
The builtin command fc may be used to list or edit and re-execute a portion of the history list. The history builtin may be used to display or modify the history list and manipulate the history file. When using command-line editing, search commands are available in each editing mode that provide access to the history list (see Commands For History).
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. The shopt builtin is used to set these options. See Bash Builtins, for a description of shopt.
Bash provides two builtin commands which manipulate the history list and history file.
fcfc [-eename] [-lnr] [first] [last]fc -s [pat=rep] [command]
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: ${FCEDIT:-${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 Aliases).
historyhistory [n] history -c history -d offset history [-anrw] [filename] history -ps arg
With no options, display the history list with line numbers. Lines prefixed with a ‘*’ have been modified. An argument of n lists only the last n lines. If the shell variable HISTTIMEFORMAT is set and not null, it is used as a format string for strftime to display the time stamp associated with each displayed history entry. No intervening blank is printed between the formatted time stamp and the history line.
Options, if supplied, have the following meanings:
-c-d offset-a-n-r-w-p-sWhen any of the -w, -r, -a, or -n options is used, if filename is given, then it is used as the history file. If not, then the value of the HISTFILE variable is used.
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 history list 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 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 words surrounded by quotes are considered 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 Bash Builtins) 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. This is most useful in conjunction with Readline.
The shell allows control of the various characters used by the history expansion mechanism with the histchars variable, as explained above (see Bash Variables). The shell uses the history comment character to mark history timestamps when writing the history file.
An event designator is a reference to a command line entry in the history list.
!extglob shell option is enabled using the shopt builtin). !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 may be omitted if the word designator begins with a ‘^’, ‘$’, ‘*’, ‘-’, or ‘%’. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.
For example,
!!!!:$!$. !fi:2fi. Here are the word designators:
0 (zero)0th word. For many applications, this is the command word. ^$%-y*0th. 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. *-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 ‘:’.
htrepqxs/old/new/&gags/old/new/, or with ‘&’. GThis chapter provides basic instructions for installing Bash on the various supported platforms. The distribution supports the gnu operating systems, nearly every version of Unix, and several non-Unix systems such as BeOS and Interix. Other independent ports exist for ms-dos, os/2, and Windows platforms.
These are installation instructions for Bash.
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 some time. While running, it prints 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. 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, doc, and support directories, each directory under lib, and several others). 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.
To find out more about the options and arguments that the configure script understands, type
bash-2.04$ ./configure --help
at the Bash prompt in your Bash source directory.
If you need to do unusual things to compile Bash, please try to figure out how configure could check whether or not to do them, and mail diffs or instructions to bash-maintainers@gnu.org 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 2.50 or newer.
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, or by specifying a value for the DESTDIR ‘make’ variable when running ‘make install’.
You can specify separate installation prefixes for architecture-specific files and architecture-independent files. If you give configure the option --exec-prefix=PATH, ‘make install’ 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 need to determine by the type of host Bash 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., ‘i386-unknown-freebsd4.2’).
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=fileconfigure. --helpconfigure, and exit. --quiet--silent-q--srcdir=dirconfigure can determine that directory automatically. --versionconfigure script, and exit. configure also accepts some other, not widely used, boilerplate options. ‘configure --help’ prints the complete list.
The Bash configure has a number of --enable-feature options, where feature indicates an optional part of Bash. There are also several --with-package options, where package is something like ‘bash-malloc’ or ‘purify’. 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-afs--with-bash-mallocmalloc in the directory lib/malloc. This is not the same malloc that appears in gnu libc, but an older version originally derived from the 4.2 bsdmalloc. This malloc is very fast, but wastes some space on each allocation. This option is enabled by default. The NOTES file contains a list of systems for which this should be turned off, and configure disables this option automatically for a number of systems. --with-curses--with-gnu-malloc--with-bash-malloc. --with-installed-readline[=PREFIX]yes or not supplied, configure uses the values of the make variables includedir and libdir, which are subdirectories of prefix by default, to find the installed version of Readline if it is not in the standard system include and library directories. If PREFIX is no, Bash links with the version in lib/readline. If PREFIX is set to any other value, configure treats it as a directory pathname and looks for the installed version of Readline in subdirectories of that directory (include files in PREFIX/include and the library in PREFIX/lib). --with-purify--enable-minimal-configThere are several --enable- options that alter how Bash is compiled and linked, rather than changing run-time features.
--enable-largefile--enable-profilinggprof each time it is executed. --enable-static-linkgcc is being used. This could be used to build a version to use as root's shell. 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 ‘xpg-echo-default’ are enabled by default, unless the operating system does not provide the necessary support.
--enable-aliasalias and unalias builtins (see Aliases). --enable-arith-for-commandfor command that behaves like the C language for statement (see Looping Constructs). --enable-array-variables--enable-bang-historycsh-like history substitution (see History Interaction). --enable-brace-expansioncsh-like brace expansion ( b{a,b}c ==> bac bbc ). See Brace Expansion, for a complete description. --enable-casemod-attributesdeclare builtin and assignment statements. Variables with the uppercase attribute, for example, will have their values converted to uppercase upon assignment. --enable-casemod-expansion--enable-command-timingtime as a reserved word and for displaying timing statistics for the pipeline following time (see Pipelines). This allows pipelines as well as shell builtins and functions to be timed. --enable-cond-command[[ conditional command. (see Conditional Constructs). --enable-cond-regexp[[ conditional command. (see Conditional Constructs). --enable-coprocessescoproc reserved word (see Pipelines). --enable-debugger--enable-directory-stackcsh-like directory stack and the pushd, popd, and dirs builtins (see The Directory Stack). --enable-disabled-builtinsxxx has been disabled using ‘enable -n xxx’. See Bash Builtins, for details of the builtin and enable builtin commands. --enable-dparen-arithmetic((...)) command (see Conditional Constructs). --enable-extended-glob--enable-extended-glob-default--enable-help-builtinhelp builtin, which displays help on shell builtins and variables (see Bash Builtins). --enable-historyfc and history builtin commands (see Bash History Facilities). --enable-job-control--enable-multibyte--enable-net-redirections/dev/tcp/host/port and /dev/udp/host/port when used in redirections (see Redirections). --enable-process-substitution--enable-progcomp--enable-prompt-string-decoding--enable-readline--enable-restrictedrbash, enters a restricted mode. See The Restricted Shell, for a description of restricted mode. --enable-selectselect builtin, which allows the generation of simple menus (see Conditional Constructs). --enable-separate-helpfileshelp builtin instead of storing the text internally. --enable-single-help-stringshelp builtin as a single string for each help topic. This aids in translating the text to different languages. You may need to disable this if your compiler cannot handle very long string literals. --enable-strict-posix-default--enable-usg-echo-default--enable-xpg-echo-default. --enable-xpg-echo-defaultecho builtin expand backslash-escaped characters by default, without requiring the -e option. This sets the default value of the xpg_echo shell option to on, which makes the Bash echo behave more like the version specified in the Single Unix Specification, version 3. See Bash Builtins, for a description of the escape sequences that echo recognizes. The file config-top.h 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. The latest version of Bash is always available for FTP from ftp://ftp.gnu.org/pub/gnu/bash/.
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 encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to bug-bash@gnu.org 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.ramey@case.edu.
Bash implements essentially the same grammar, parameter and variable expansion, redirection, and quoting as the Bourne Shell. Bash uses the posix standard as the specification of how these features are to be implemented. There are some differences between the traditional Bourne shell and Bash; this section quickly details the differences of significance. A number of these differences are explained in greater depth in previous sections. This section uses the version of sh included in SVR4.2 (the last version of the historical Bourne shell) as the baseline reference.
sh behavior (see Bash POSIX Mode). bind builtin. complete, compgen, and compopt, to manipulate it. history and fc builtins to manipulate it. The Bash history list maintains timestamp information and uses the value of the HISTTIMEFORMAT variable to display it. csh-like history expansion (see History Interaction). $'...' quoting syntax, which expands ANSI-C backslash-escaped characters in the text between the single quotes, is supported (see ANSI-C Quoting). $"..." quoting syntax to do locale-specific translation of the characters between the double quotes. The -D, --dump-strings, and --dump-po-strings invocation options list the translatable strings found in a script (see Locale Translation). ! keyword to negate the return value of a pipeline (see Pipelines). Very useful when an if statement needs to act only if a test fails. The Bash ‘-o pipefail’ option to set will cause a pipeline to return a failure status if any command fails. time reserved word and command timing (see Pipelines). The display of the timing statistics may be controlled with the TIMEFORMAT variable. for (( expr1 ; expr2 ; expr3 )) arithmetic for command, similar to the C language (see Looping Constructs). select compound command, which allows the generation of simple menus (see Conditional Constructs). [[ compound command, which makes conditional testing part of the shell grammar (see Conditional Constructs), including optional regular expression matching. case and [[ constructs. alias and unalias builtins (see Aliases). (( compound command (see Conditional Constructs), and arithmetic expansion (see Shell Arithmetic). export command. ${#xx}, which returns the length of ${xx}, is supported (see Shell Parameter Expansion). ${var:offset[:length]}, which expands to the substring of var's value of length length, beginning at offset, is present (see Shell Parameter Expansion). ${var/[/]pattern[/replacement]}, which matches pattern and replaces it with replacement in the value of var, is available (see Shell Parameter Expansion). ${!prefix}* expansion, which expands to the names of all shell variables whose names begin with prefix, is available (see Shell Parameter Expansion). ${!word} (see Shell Parameter Expansion). $9 using ${num}. $() form of command substitution is implemented (see Command Substitution), and preferred to the Bourne shell's `` (which is also implemented for backwards compatibility). extglob shell option is enabled (see Pattern Matching). sh does not separate the two name spaces. local builtin, and thus useful recursive functions may be written (see Bash Builtins). sh, all variable assignments preceding commands are global unless the command is executed from the file system. noclobber option is available to avoid overwriting existing files with output redirection (see The Set Builtin). The ‘>|’ redirection operator may be used to override noclobber. cd and pwd builtins (see Bourne Shell Builtins) each take -L and -P options to switch between logical and physical modes. builtin and command builtins (see Bash Builtins). command builtin allows selective disabling of functions when command lookup is performed (see Bash Builtins). enable builtin (see Bash Builtins). exec builtin takes additional options that allow users to control the contents of the environment passed to the executed command, and what the zeroth argument to the command is to be (see Bourne Shell Builtins). export -f (see Shell Functions). 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. 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’ (see Bourne Shell Builtins). help builtin for quick reference to shell facilities (see Bash Builtins). printf builtin is available to display formatted output (see Bash Builtins). read builtin (see Bash Builtins) will read a line ending in ‘\’ with the -r option, and will use the REPLY variable as a default if no non-option 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. The read builtin also has additional options to control input: the -s option will turn off echoing of input characters as they are read, the -t option will allow read to time out if input does not arrive within a specified number of seconds, the -n option will allow reading only a specified number of characters rather than a full line, and the -d option will read until a particular character rather than newline. return builtin may be used to abort execution of scripts executed with the . or source builtins (see Bourne Shell Builtins). shopt builtin, for finer control of shell optional capabilities (see The Shopt Builtin), and allows these options to be set and unset at shell invocation (see Invoking Bash). set builtin (see The Set Builtin). xtrace) option displays commands other than simple commands when performing an execution trace (see The Set Builtin). test builtin (see Bourne Shell Builtins) is slightly different, as it implements the posix algorithm, which specifies the behavior based on the number of arguments. caller builtin, which displays the context of any active subroutine call (a shell function or a script executed with the . or source builtins). This supports the bash debugger. trap builtin (see Bourne Shell Builtins) allows a DEBUG pseudo-signal specification, similar to EXIT. Commands specified with a DEBUG trap are executed before every simple command, for command, case command, select command, every arithmetic for command, and before the first command executes in a shell function. The DEBUG trap is not inherited by shell functions unless the function has been given the trace attribute or the functrace option has been enabled using the shopt builtin. The extdebug shell option has additional effects on the DEBUG trap. The trap builtin (see Bourne Shell Builtins) allows an ERR pseudo-signal specification, similar to EXIT and DEBUG. Commands specified with an ERR trap are executed after a simple command fails, with a few exceptions. The ERR trap is not inherited by shell functions unless the -o errtrace option to the set builtin is enabled.
The trap builtin (see Bourne Shell Builtins) allows a RETURN pseudo-signal specification, similar to EXIT and DEBUG. Commands specified with an RETURN trap are executed before execution resumes after a shell function or a shell script executed with . or source returns. The RETURN trap is not inherited by shell functions unless the function has been given the trace attribute or the functrace option has been enabled using the shopt builtin.
type builtin is more extensive and gives more information about the names it finds (see Bash Builtins). umask builtin permits a -p option to cause the output to be displayed in the form of a umask command that may be reused as input (see Bourne Shell Builtins). csh-like directory stack, and provides the pushd, popd, and dirs builtins to manipulate it (see The Directory Stack). Bash also makes the directory stack visible as the value of the DIRSTACK shell variable. disown builtin can remove a job from the internal shell job table (see Job Control Builtins) or suppress the sending of SIGHUP to a job when the shell exits as the result of a SIGHUP. mldmode and priv) not present in Bash. stop or newgrp builtins. sh uses a TIMEOUT variable like Bash uses TMOUT. More features unique to Bash may be found in 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), it misbehaves badly. SIGSEGV, SIGALRM, or SIGCHLD. -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 ‘-’. jsh (it turns on job control). Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. http://fsf.org/ Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
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.: Bourne Shell Builtins:: Bourne Shell Builtins[: Bourne Shell Builtinsalias: Bash Builtinsbg: Job Control Builtinsbind: Bash Builtinsbreak: Bourne Shell Builtinsbuiltin: Bash Builtinscaller: Bash Builtinscd: Bourne Shell Builtinscommand: Bash Builtinscompgen: Programmable Completion Builtinscomplete: Programmable Completion Builtinscompopt: Programmable Completion Builtinscontinue: Bourne Shell Builtinsdeclare: Bash Builtinsdirs: Directory Stack Builtinsdisown: Job Control Builtinsecho: Bash Builtinsenable: Bash Builtinseval: Bourne Shell Builtinsexec: Bourne Shell Builtinsexit: Bourne Shell Builtinsexport: Bourne Shell Builtinsfc: Bash History Builtinsfg: Job Control Builtinsgetopts: Bourne Shell Builtinshash: Bourne Shell Builtinshelp: Bash Builtinshistory: Bash History Builtinsjobs: Job Control Builtinskill: Job Control Builtinslet: Bash Builtinslocal: Bash Builtinslogout: Bash Builtinsmapfile: Bash Builtinspopd: Directory Stack Builtinsprintf: Bash Builtinspushd: Directory Stack Builtinspwd: Bourne Shell Builtinsread: Bash Builtinsreadarray: Bash Builtinsreadonly: Bourne Shell Builtinsreturn: Bourne Shell Builtinsset: The Set Builtinshift: Bourne Shell Builtinsshopt: The Shopt Builtinsource: Bash Builtinssuspend: Job Control Builtinstest: Bourne Shell Builtinstimes: Bourne Shell Builtinstrap: Bourne Shell Builtinstype: Bash Builtinstypeset: Bash Builtinsulimit: Bash Builtinsumask: Bourne Shell Builtinsunalias: Bash Builtinsunset: Bourne Shell Builtinswait: Job Control Builtins!: Pipelines[[: Conditional Constructs]]: Conditional Constructscase: Conditional Constructsdo: Looping Constructsdone: Looping Constructselif: Conditional Constructselse: Conditional Constructsesac: Conditional Constructsfi: Conditional Constructsfor: Looping Constructsfunction: Shell Functionsif: Conditional Constructsin: Conditional Constructsselect: Conditional Constructsthen: Conditional Constructstime: Pipelinesuntil: Looping Constructswhile: Looping Constructs{: Command Grouping}: Command Grouping!: Special Parameters#: Special Parameters$: Special Parameters*: Special Parameters-: Special Parameters0: Special Parameters?: Special Parameters@: Special Parameters_: Special Parametersauto_resume: Job Control VariablesBASH: Bash VariablesBASH_ALIASES: Bash VariablesBASH_ARGC: Bash VariablesBASH_ARGV: Bash VariablesBASH_CMDS: Bash VariablesBASH_COMMAND: Bash VariablesBASH_ENV: Bash VariablesBASH_EXECUTION_STRING: Bash VariablesBASH_LINENO: Bash VariablesBASH_REMATCH: Bash VariablesBASH_SOURCE: Bash VariablesBASH_SUBSHELL: Bash VariablesBASH_VERSINFO: Bash VariablesBASH_VERSION: Bash VariablesBASH_XTRACEFD: Bash VariablesBASHOPTS: Bash VariablesBASHPID: Bash Variablesbell-style: Readline Init File Syntaxbind-tty-special-chars: Readline Init File SyntaxCDPATH: Bourne Shell VariablesCOLUMNS: Bash Variablescomment-begin: Readline Init File SyntaxCOMP_CWORD: Bash VariablesCOMP_KEY: Bash VariablesCOMP_LINE: Bash VariablesCOMP_POINT: Bash VariablesCOMP_TYPE: Bash VariablesCOMP_WORDBREAKS: Bash VariablesCOMP_WORDS: Bash Variablescompletion-prefix-display-length: Readline Init File Syntaxcompletion-query-items: Readline Init File SyntaxCOMPREPLY: Bash Variablesconvert-meta: Readline Init File SyntaxDIRSTACK: Bash Variablesdisable-completion: Readline Init File Syntaxediting-mode: Readline Init File SyntaxEMACS: Bash Variablesenable-keypad: Readline Init File SyntaxEUID: Bash Variablesexpand-tilde: Readline Init File SyntaxFCEDIT: Bash VariablesFIGNORE: Bash VariablesFUNCNAME: Bash VariablesGLOBIGNORE: Bash VariablesGROUPS: Bash Variableshistchars: Bash VariablesHISTCMD: Bash VariablesHISTCONTROL: Bash VariablesHISTFILE: Bash VariablesHISTFILESIZE: Bash VariablesHISTIGNORE: Bash Variableshistory-preserve-point: Readline Init File Syntaxhistory-size: Readline Init File SyntaxHISTSIZE: Bash VariablesHISTTIMEFORMAT: Bash VariablesHOME: Bourne Shell Variableshorizontal-scroll-mode: Readline Init File SyntaxHOSTFILE: Bash VariablesHOSTNAME: Bash VariablesHOSTTYPE: Bash VariablesIFS: Bourne Shell VariablesIGNOREEOF: Bash Variablesinput-meta: Readline Init File SyntaxINPUTRC: Bash Variablesisearch-terminators: Readline Init File Syntaxkeymap: Readline Init File SyntaxLANG: Bash VariablesLC_ALL: Bash VariablesLC_COLLATE: Bash VariablesLC_CTYPE: Bash VariablesLC_MESSAGES: Bash VariablesLC_MESSAGES: Locale TranslationLC_NUMERIC: Bash VariablesLINENO: Bash VariablesLINES: Bash VariablesMACHTYPE: Bash VariablesMAIL: Bourne Shell VariablesMAILCHECK: Bash VariablesMAILPATH: Bourne Shell Variablesmark-modified-lines: Readline Init File Syntaxmark-symlinked-directories: Readline Init File Syntaxmatch-hidden-files: Readline Init File Syntaxmeta-flag: Readline Init File SyntaxOLDPWD: Bash VariablesOPTARG: Bourne Shell VariablesOPTERR: Bash VariablesOPTIND: Bourne Shell VariablesOSTYPE: Bash Variablesoutput-meta: Readline Init File Syntaxpage-completions: Readline Init File SyntaxPATH: Bourne Shell VariablesPIPESTATUS: Bash VariablesPOSIXLY_CORRECT: Bash VariablesPPID: Bash VariablesPROMPT_COMMAND: Bash VariablesPROMPT_DIRTRIM: Bash VariablesPS1: Bourne Shell VariablesPS2: Bourne Shell VariablesPS3: Bash VariablesPS4: Bash VariablesPWD: Bash VariablesRANDOM: Bash VariablesREPLY: Bash Variablesrevert-all-at-newline: Readline Init File SyntaxSECONDS: Bash VariablesSHELL: Bash VariablesSHELLOPTS: Bash VariablesSHLVL: Bash Variablesshow-all-if-ambiguous: Readline Init File Syntaxshow-all-if-unmodified: Readline Init File Syntaxskip-completed-text: Readline Init File SyntaxTEXTDOMAIN: Locale TranslationTEXTDOMAINDIR: Locale TranslationTIMEFORMAT: Bash VariablesTMOUT: Bash VariablesTMPDIR: Bash VariablesUID: Bash Variablesvisible-stats: Readline Init File Syntaxabort (C-g): Miscellaneous Commandsaccept-line (Newline or Return): Commands For Historybackward-char (C-b): Commands For Movingbackward-delete-char (Rubout): Commands For Textbackward-kill-line (C-x Rubout): Commands For Killingbackward-kill-word (M-<DEL>): Commands For Killingbackward-word (M-b): Commands For Movingbeginning-of-history (M-<): Commands For Historybeginning-of-line (C-a): Commands For Movingcall-last-kbd-macro (C-x e): Keyboard Macroscapitalize-word (M-c): Commands For Textcharacter-search (C-]): Miscellaneous Commandscharacter-search-backward (M-C-]): Miscellaneous Commandsclear-screen (C-l): Commands For Movingcomplete (<TAB>): Commands For Completioncopy-backward-word (): Commands For Killingcopy-forward-word (): Commands For Killingcopy-region-as-kill (): Commands For Killingdelete-char (C-d): Commands For Textdelete-char-or-list (): Commands For Completiondelete-horizontal-space (): Commands For Killingdigit-argument (M-0, M-1, ... M--): Numeric Argumentsdo-uppercase-version (M-a, M-b, M-x, ...): Miscellaneous Commandsdowncase-word (M-l): Commands For Textdump-functions (): Miscellaneous Commandsdump-macros (): Miscellaneous Commandsdump-variables (): Miscellaneous Commandsend-kbd-macro (C-x )): Keyboard Macrosend-of-history (M->): Commands For Historyend-of-line (C-e): Commands For Movingexchange-point-and-mark (C-x C-x): Miscellaneous Commandsforward-backward-delete-char (): Commands For Textforward-char (C-f): Commands For Movingforward-search-history (C-s): Commands For Historyforward-word (M-f): Commands For Movinghistory-search-backward (): Commands For Historyhistory-search-forward (): Commands For Historyinsert-comment (M-#): Miscellaneous Commandsinsert-completions (M-*): Commands For Completionkill-line (C-k): Commands For Killingkill-region (): Commands For Killingkill-whole-line (): Commands For Killingkill-word (M-d): Commands For Killingmenu-complete (): Commands For Completionmenu-complete-backward (): Commands For Completionnext-history (C-n): Commands For Historynon-incremental-forward-search-history (M-n): Commands For Historynon-incremental-reverse-search-history (M-p): Commands For Historyoverwrite-mode (): Commands For Textpossible-completions (M-?): Commands For Completionprefix-meta (<ESC>): Miscellaneous Commandsprevious-history (C-p): Commands For Historyquoted-insert (C-q or C-v): Commands For Textre-read-init-file (C-x C-r): Miscellaneous Commandsredraw-current-line (): Commands For Movingreverse-search-history (C-r): Commands For Historyrevert-line (M-r): Miscellaneous Commandsself-insert (a, b, A, 1, !, ...): Commands For Textset-mark (C-@): Miscellaneous Commandsskip-csi-sequence (): Miscellaneous Commandsstart-kbd-macro (C-x (): Keyboard Macrostranspose-chars (C-t): Commands For Texttranspose-words (M-t): Commands For Textundo (C-_ or C-x C-u): Miscellaneous Commandsuniversal-argument (): Numeric Argumentsunix-filename-rubout (): Commands For Killingunix-line-discard (C-u): Commands For Killingunix-word-rubout (C-w): Commands For Killingupcase-word (M-u): Commands For Textyank (C-y): Commands For Killingyank-last-arg (M-. or M-_): Commands For Historyyank-nth-arg (M-C-y): Commands For Historyyank-pop (M-y): Commands For Killing