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Bash Reference Manual

This text is a brief description of the features that are present inthe Bash shell.

This is Edition 2.5b, last updated 15 July 2002,of The GNU Bash Reference Manual,for Bash, Version 2.05b.

Bash contains features that appear in other popular shells, and somefeatures that only appear in Bash. Some of the shells that Bash hasborrowed 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 intocategories based upon which one of these other shells inspired thefeature.

This manual is meant as a brief introduction to features found inBash. The Bash manual page should be used as the definitivereference on shell behavior.

1. Introduction    An introduction to the shell.
2. Definitions    Some definitions used in the rest of this manual.
3. Basic Shell Features    The shell "building blocks".
4. Shell Builtin Commands    Commands that are a part of the shell.
5. Shell Variables    Variables used or set by Bash.
6. Bash Features    Features found only in Bash.
7. Job Control    A chapter describing what job control is and how Bash allows you to use it.
9. Using History Interactively    Chapter dealing with history expansion rules.
8. Command Line Editing    Chapter describing the command line editing features.
10. Installing Bash    How to build and install Bash on your system.
A. Reporting Bugs    How to report bugs in Bash.
B. Major Differences From The Bourne Shell    A terse list of the differences between Bash and historical versions of /bin/sh.
Index of Shell Builtin Commands    Index of Bash builtin commands.
Index of Shell Reserved Words    Index of Bash reserved words.
Parameter and Variable Index    Quick reference helps you find the variable you want.
Function Index    Index of bindable Readline functions.
Concept Index    General index for concepts described in this manual.

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1. Introduction

1.1 What is Bash? A short description of Bash.
1.2 What is a shell? A brief introduction to shells.

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1.1 What is Bash?

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 ofthe current Unix shell /bin/sh,which appeared in the Seventh Edition Bell Labs Research versionof Unix.

Bash is largely compatible with sh and incorporates usefulfeatures from the Korn shell ksh and the C shell csh.It is intended to be a conformant implementation of the IEEEPOSIX Shell and Tools specification (IEEE Working Group 1003.2).It offers functional improvements over sh for both interactive andprogramming use.

While the GNU operating system provides other shells, includinga version of csh, Bash is the default shell.Like other GNU software, Bash is quite portable. It currently runson nearly every version of Unix and a few other operating systems -independently-supported ports exist for MS-DOS, OS/2,Windows 95/98, and Windows NT.

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1.2 What is a shell?

At its base, a shell is simply a macro processor that executescommands. A Unix shell is both a command interpreter, whichprovides the user interface to the rich set of GNU utilities,and a programming language, allowing these utilitites to becombined. Files containing commands can be created, and becomecommands themselves. These new commands have the same status assystem commands in directories such as `/bin', allowing usersor groups to establish custom environments.

A shell allows execution of GNU commands, both synchronously andasynchronously.The shell waits for synchronous commands to complete before acceptingmore input; asynchronous commands continue to execute in parallelwith the shell while it reads and executes additional commands.The redirection constructs permitfine-grained control of the input and output of those commands.Moreover, the shell allows control over the contents of commands'environments.Shells may be used interactively or non-interactively: they acceptinput typed from the keyboard or from a file.

Shells also provide a small set of built-incommands (builtins) implementing functionality impossibleor inconvenient to obtain via separate utilities.For example, cd, break, continue, andexec) cannot be implemented outside of the shell becausethey directly manipulate the shell itself.The history, getopts, kill, or pwdbuiltins, 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 insubsequent sections.

While executing commands is essential, most of the power (andcomplexity) of shells is due to their embedded programminglanguages. Like any high-level language, the shell providesvariables, flow control constructs, quoting, and functions.

Shells offer features geared specifically forinteractive use rather than to augment the programming language.These interactive features include job control, command lineediting, history and aliases. Each of these features isdescribed in this manual.

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2. Definitions

These definitions are used throughout the remainder of this manual.

POSIX: A family of open system standards based on Unix. Bashis concerned with POSIX 1003.2, the Shell and Tools Standard.
blank: A space or tab character.
builtin: A command that is implemented internally by the shell itself, ratherthan by an executable program somewhere in the file system.
control operator: A word that performs a control function. It is a newlineor one of the following:`||', `&&', `&', `;', `;;',`|', `(', or `)'.
exit status: The value returned by a command to its caller. The value is restrictedto eight bits, so the maximum value is 255.
field: A unit of text that is the result of one of the shell expansions. Afterexpansion, when executing a command, the resulting fields are used asthe command name and arguments.
filename: A string of characters used to identify a file.
job: A set of processes comprising a pipeline, and any processes descendedfrom it, that are all in the same process group.
job control: A mechanism by which users can selectively stop (suspend) and restart(resume) execution of processes.
metacharacter: A character that, when unquoted, separates words. A metacharacter isa blank or one of the following characters:`|', `&', `;', `(', `)', `<', or`>'.
name: A word consisting solely of letters, numbers, and underscores,and beginning with a letter or underscore. Names are used asshell variable and function names.Also referred to as an identifier.
operator: A control operator or a redirection operator.See section 3.6 Redirections, for a list of redirection operators.
process group: A collection of related processes each having the same processgroup ID.
process group ID: A unique identifer that represents a process groupduring its lifetime.
reserved word: A word that has a special meaning to the shell. Most reservedwords introduce shell flow control constructs, such as for andwhile.
return status: A synonym for exit status.
signal: A mechanism by which a process may be notified by the kernelof an event occurring in the system.
special builtin: A shell builtin command that has been classified as special by thePOSIX 1003.2 standard.
token: A sequence of characters considered a single unit by the shell. It iseither a word or an operator.
word: A token that is not an operator.

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3. Basic Shell Features

Bash is an acronym for `Bourne-Again SHell'.The Bourne shell isthe traditional Unix shell originally written by Stephen Bourne.All of the Bourne shell builtin commands are available in Bash,and the rules for evaluation and quoting are taken from the POSIX1003.2 specification for the `standard' Unix shell.

This chapter briefly summarizes the shell's `building blocks':commands, control structures, shell functions, shell parameters,shell expansions,redirections, which are a way to direct input and output fromand to named files, and how the shell executes commands.

3.1 Shell Syntax What your input means to the shell. 3.2 Shell Commands The types of commands you can use. 3.3 Shell Functions Grouping commands by name. 3.4 Shell Parameters Special shell variables. 3.5 Shell Expansions How Bash expands variables and the various expansions available. 3.6 Redirections A way to control where input and output go. 3.7 Executing Commands What happens when you run a command. 3.8 Shell Scripts Executing files of shell commands.

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3.1 Shell Syntax

3.1.1 Shell Operation    The basic operation of the shell.
3.1.2 Quoting    How to remove the special meaning from characters.
3.1.3 Comments    How to specify comments.

When the shell reads input, it proceeds through asequence of operations. If the input indicates the beginning of acomment, the shell ignores the comment symbol (`#'), and the restof that line.Otherwise, roughly speaking, the shell reads its input anddivides the input into words and operators, employing the quoting rulesto 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, expandsothers, redirects input and output as needed, executes the specifiedcommand, waits for the command's exit status, and makes that exit statusavailable for further inspection or processing.

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3.1.1 Shell Operation

The following is a brief description of the shell's operation when itreads and executes a command. Basically, the shell does thefollowing:

Reads its input from a file (see section 3.8 Shell Scripts), from a string supplied as an argument to the `-c' invocation option (see section 6.1 Invoking Bash), or from the user's terminal.
Breaks the input into words and operators, obeying the quoting rules described in 3.1.2 Quoting. These tokens are separated by metacharacters. Alias expansion is performed by this step (see section 6.6 Aliases).
Parses the tokens into simple and compound commands (see section 3.2 Shell Commands).
Performs the various shell expansions (see section 3.5 Shell Expansions), breaking the expanded tokens into lists of filenames (see section 3.5.8 Filename Expansion) and commands and arguments.
Performs any necessary redirections (see section 3.6 Redirections) and removes the redirection operators and their operands from the argument list.
Executes the command (see section 3.7 Executing Commands).
Optionally waits for the command to complete and collects its exit status (see section 3.7.5 Exit Status).

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3.1.2 Quoting

3.1.2.1 Escape Character How to remove the special meaning from a single character. 3.1.2.2 Single Quotes How to inhibit all interpretation of a sequence of characters. 3.1.2.3 Double Quotes How to suppress most of the interpretation of a sequence of characters. 3.1.2.4 ANSI-C Quoting How to expand ANSI-C sequences in quoted strings.
3.1.2.5 Locale-Specific Translation How to translate strings into different languages.

Quoting is used to remove the special meaning of certaincharacters or words to the shell. Quoting can be used todisable special treatment for special characters, to preventreserved words from being recognized as such, and to preventparameter expansion.

Each of the shell metacharacters (see section 2. Definitions)has special meaning to the shell and must be quoted if it is torepresent itself.When the command history expansion facilities are being used, thehistory expansion character, usually `!', must be quotedto prevent history expansion. See section 9.1 Bash History Facilities, formore details concerning history expansion.There are three quoting mechanisms: theescape character, single quotes, and double quotes.

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3.1.2.1 Escape Character

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 pairappears, and the backslash itself is not quoted, the \newlineis treated as a line continuation (that is, it is removed fromthe input stream and effectively ignored).

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3.1.2.2 Single Quotes

Enclosing characters in single quotes (`'') preserves the literal valueof each character within the quotes. A single quote may not occurbetween single quotes, even when preceded by a backslash.

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3.1.2.3 Double Quotes

Enclosing characters in double quotes (`"') preserves the literal valueof all characters within the quotes, with the exception of`$', ``', and `\'.The characters `$' and ``'retain their special meaning within double quotes (see section 3.5 Shell Expansions).The backslash retains its special meaning only when followed by one ofthe following characters:`$', ``', `"', `\', or newline.Within double quotes, backslashes that are followed by one of thesecharacters are removed. Backslashes preceding characters without aspecial meaning are left unmodified.A double quote may be quoted within double quotes by preceding it witha backslash.

The special parameters `*' and `@' have special meaningwhen in double quotes (see section 3.5.3 Shell Parameter Expansion).

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3.1.2.4 ANSI-C Quoting

Words of the form $'string' are treated specially. Theword expands to string, with backslash-escaped characters replacedas specified by the ANSI C standard. Backslash escape sequences, ifpresent, are decoded as follows:

\a: alert (bell)
\b: backspace
\e: an escape character (not ANSI C)
\f: form feed
\n: newline
\r: carriage return
\t: horizontal tab
\v: vertical tab
\\: backslash
\': single quote
\nnn: the eight-bit character whose value is the octal value nnn(one to three digits)
\xHH: the eight-bit character whose value is the hexadecimal value HH(one or two hex digits)
\cx: a control-x character

The expanded result is single-quoted, as if the dollar sign had notbeen present.

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3.1.2.5 Locale-Specific Translation

A double-quoted string preceded by a dollar sign (`$') will causethe string to be translated according to the current locale.If the current locale is C or POSIX, the dollar signis ignored.If the string is translated and replaced, the replacement isdouble-quoted.

Some systems use the message catalog selected by the LC_MESSAGESshell variable. Others create the name of the message catalog from thevalue of the TEXTDOMAIN shell variable, possibly adding asuffix of `.mo'. If you use the TEXTDOMAIN variable, youmay need to set the TEXTDOMAINDIR variable to the location ofthe message catalog files. Still others use both variables in thisfashion:TEXTDOMAINDIR/LC_MESSAGES/LC_MESSAGES/TEXTDOMAIN.mo.

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3.1.3 Comments

In a non-interactive shell, or an interactive shell in which theinteractive_comments option to the shoptbuiltin is enabled (see section 4.2 Bash Builtin Commands),a word beginning with `#'causes that word and all remaining characters on that line tobe ignored. An interactive shell without the interactive_commentsoption enabled does not allow comments. The interactive_commentsoption is on by default in interactive shells.See section 6.3 Interactive Shells, for a description of what makesa shell interactive.

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3.2 Shell Commands

A simple shell command such as echo a b c consists of the commanditself followed by arguments, separated by spaces.

More complex shell commands are composed of simple commands arranged togetherin a variety of ways: in a pipeline in which the output of one commandbecomes the input of a second, in a loop or conditional construct, or insome other grouping.

3.2.1 Simple Commands The most common type of command. 3.2.2 Pipelines Connecting the input and output of several commands. 3.2.3 Lists of Commands How to execute commands sequentially. 3.2.4 Looping Constructs Shell commands for iterative action. 3.2.5 Conditional Constructs Shell commands for conditional execution. 3.2.6 Grouping Commands Ways to group commands.

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3.2.1 Simple Commands

A simple command is the kind of command encountered most often.It's just a sequence of words separated by blanks, terminatedby one of the shell's control operators (see section 2. Definitions). Thefirst word generally specifies a command to be executed, with therest of the words being that command's arguments.

The return status (see section 3.7.5 Exit Status) of a simple command isits exit status as providedby the POSIX 1003.1 waitpid function, or 128+n ifthe command was terminated by signal n.

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3.2.2 Pipelines

A pipeline is a sequence of simple commands separated by`|'.

The format for a pipeline is

[time [-p]] [!] command1 [| command2 ...]

The output of each command in the pipeline is connected via a pipeto the input of the next command.That is, each command reads the previous command's output.

The reserved word time causes timing statisticsto be printed for the pipeline once it finishes.The statistics currently consist of elapsed (wall-clock) time anduser and system time consumed by the command's execution.The `-p' option changes the output format to that specifiedby POSIX.The TIMEFORMAT variable may be set to a format string thatspecifies how the timing information should be displayed.See section 5.2 Bash Variables, for a description of the available formats.The use of time as a reserved word permits the timing ofshell builtins, shell functions, and pipelines. An externaltime command cannot time these easily.

If the pipeline is not executed asynchronously (see section 3.2.3 Lists of Commands), theshell waits for all commands in the pipeline to complete.

Each command in a pipeline is executed in its own subshell(see section 3.7.3 Command Execution Environment). The exitstatus of a pipeline is the exit status of the last command in thepipeline. If the reserved word `!' precedes the pipeline, theexit status is the logical negation of the exit status of the last command.

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3.2.3 Lists of Commands

A list is a sequence of one or more pipelines separated by oneof the operators `;', `&', `&&', or `||',and optionally terminated by one of `;', `&', or anewline.

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 listto 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 returnstatus is 0 (true).When job control is not active (see section 7. Job Control),the standard input for asynchronous commands, in the absence of anyexplicit redirections, is redirected from /dev/null.

Commands separated by a `;' are executed sequentially; the shellwaits for each command to terminate in turn. The return status is theexit status of the last command executed.

The control operators `&&' and `||'denote AND lists and OR lists, respectively.An AND list has the form

command1 && command2

command2 is executed if, and only if, command1returns an exit status of zero.

An OR list has the form

command1 || command2

command2 is executed if, and only if, command1returns a non-zero exit status.

The return status ofAND and OR lists is the exit status of the last commandexecuted in the list.

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3.2.4 Looping Constructs

Bash supports the following looping constructs.

Note that wherever a `;' appears in the description of acommand's syntax, it may be replaced with one or more newlines.

until

The syntax of the until command is:

until test-commands; do consequent-commands; done

Execute consequent-commands as long astest-commands has an exit status which is not zero.The return status is the exit status of the last command executedin consequent-commands, or zero if none was executed.

while

The syntax of the while command is:

while test-commands; do consequent-commands; done

Execute consequent-commands as long astest-commands has an exit status of zero.The return status is the exit status of the last command executedin consequent-commands, or zero if none was executed.

for

The syntax of the for command is:

for name [in words ...]; do commands; done

Expand words, and execute commands once for each memberin the resultant list, with name bound to the current member.If `in words' is not present, the for commandexecutes the commands once for each positional parameter that isset, as if `in "$@"' had been specified(see section 3.4.2 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 areexecuted, 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 accordingto the rules described below (see section 6.5 Shell Arithmetic).The arithmetic expression expr2 is then evaluated repeatedlyuntil it evaluates to zero.Each time expr2 evaluates to a non-zero value, commands areexecuted 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 listthat is executed, or false if any of the expressions is invalid.

The break and continue builtins (see section 4.1 Bourne Shell Builtins)may be used to control loop execution.

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3.2.5 Conditional Constructs

if

The syntax of the if 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 listis executed in turn, and if its exit status is zero,the corresponding more-consequents is executed and thecommand completes.If `else alternate-consequents' is present, andthe final command in the final if or elif clausehas a non-zero exit status, then alternate-consequents is executed.The return status is the exit status of the last command executed, orzero if no condition tested true.

case

The syntax of the case command is:

case word in [ [(] pattern [| pattern]...) command-list ;;]... esac

case will selectively execute the command-list corresponding tothe first pattern that matches word.The `|' is used to separate multiple patterns, and the `)'operator terminates a pattern list.A list of patterns and an associated command-list is knownas a clause. Each clause must be terminated with `;;'.The word undergoes tilde expansion, parameter expansion, commandsubstitution, arithmetic expansion, and quote removal before matching isattempted. Each pattern undergoes tilde expansion, parameterexpansion, command substitution, and arithmetic expansion.

There may be an arbitrary number of case clauses, each terminatedby a `;;'. The first pattern that matches determines thecommand-list that is executed.

Here is an example using case in a script that could be used todescribe 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."

The return status is zero if no pattern is matched. Otherwise, thereturn status is the exit status of the command-list executed.

select

The select 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 listof items. The set of expanded words is printed on the standarderror output stream, each preceded by a number. If the`in words' is omitted, the positional parameters are printed,as if `in "$@"' had been specifed.The PS3 prompt is then displayed and a line is read from thestandard input.If the line consists of a number corresponding to one of the displayedwords, 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 abreak command is executed, at whichpoint the select command completes.

Here is an example that allows the user to pick a filename from thecurrent directory, and displays the name and index of the fileselected.

select fname in *;            do            echo you picked $fname \($REPLY\)            break;            done

((...))

(( expression ))

The arithmetic expression is evaluated according to the rulesdescribed below (see section 6.5 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 section 4.2 Bash Builtin Commands, for a full description of the let builtin.

[[...]]

[[ expression ]]

Return a status of 0 or 1 depending on the evaluation ofthe conditional expression expression.Expressions are composed of the primaries described below in6.4 Bash Conditional Expressions.Word splitting and filename expansion are not performed on the wordsbetween the `[[' and `]]'; tilde expansion, parameter andvariable expansion, arithmetic expansion, command substitution, processsubstitution, and quote removal are performed.

When the `==' and `!=' operators are used, the string to theright of the operator is considered a pattern and matched accordingto the rules described below in 3.5.8.1 Pattern Matching.The return value is 0 if the string matches or does not matchthe pattern, respectively, and 1 otherwise.Any part of the pattern may be quoted to force it to be matched as astring.

Expressions may be combined using the following operators, listedin decreasing order of precedence:

( expression ): Returns the value of expression.This may be used to override the normal precedence of operators.
! expression: True if expression is false.
expression1 && expression2: True if both expression1 and expression2 are true.
expression1 || expression2: True if either expression1 or expression2 is true.

The && and || operators do not evaluate expression2 if thevalue of expression1 is sufficient to determine the returnvalue of the entire conditional expression.

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3.2.6 Grouping Commands

Bash provides two ways to group a list of commands to be executedas a unit. When commands are grouped, redirections may be appliedto the entire command list. For example, the output of all thecommands in the list may be redirected to a single stream.

()

( list )

Placing a list of commands between parentheses causes a subshellto be created, and each of the commands in list to be executedin 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 tobe 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 differencebetween these two constructs due to historical reasons. The bracesare reserved words, so they must be separated from the listby blanks. The parentheses are operators, and arerecognized as separate tokens by the shell even if they are not separatedfrom the list by whitespace.

The exit status of both of these constructs is the exit status oflist.

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3.3 Shell Functions

Shell functions are a way to group commands for later executionusing a single name for the group. They are executed just likea "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 currentshell context; no new process is created to interpret them.

Functions are declared using this syntax:

[ function ] name () { command-list; }

This defines a shell function named name. The reservedword function is optional.If the function reservedword is supplied, the parentheses are optional.The body of the function is the command-list between { and }.This list is executed whenever name is specified as thename of a command. The exit status of a function isthe exit status of the last command executed in the body.

Note that for historical reasons, the curly braces that surroundthe body of the function must be separated from the body byblanks or newlines.This is because the braces are reserved words and are only recognizedas such when they are separated by whitespace.Also, the command-list must be terminated with a semicolonor a newline.

When a function is executed, the arguments to thefunction become the positional parametersduring its execution (see section 3.4.1 Positional Parameters).The special parameter `#' that expands to the number ofpositional parameters is updated to reflect the change.Positional parameter 0 is unchanged.The FUNCNAME variable is set to the name of the functionwhile the function is executing.

If the builtin command returnis executed in a function, the function completes andexecution resumes with the next command after the functioncall. When a function completes, the values of thepositional parameters and the special parameter `#'are restored to the values they had prior to the function'sexecution. If a numeric argument is given to return,that is the function's return status; otherwise the function'sreturn status is the exit status of the last command executedbefore the return.

Variables local to the function may be declared with thelocal builtin. These variables are visible only tothe function and the commands it invokes.

Functions may be recursive. No limit is placed on the number ofrecursive calls.

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3.4 Shell Parameters

3.4.1 Positional Parameters The shell's command-line arguments. 3.4.2 Special Parameters Parameters with special meanings.

A parameter is an entity that stores values.It can be a name, a number, or one of the special characterslisted below.For the shell's purposes, a variable is a parameter denoted by aname.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 4.2 Bash Builtin Commands).

A parameter is set if it has been assigned a value. The null string isa valid value. Once a variable is set, it may be unset only by usingthe unset builtin command.

A variable may be assigned to by a statement of the form

name=[value]

If valueis not given, the variable is assigned the null string. Allvalues undergo tilde expansion, parameter and variable expansion,command substitution, arithmetic expansion, and quoteremoval (detailed below). If the variable has its integerattribute set, then valueis subject to arithmetic expansion even if the $((...))expansion is not used (see section 3.5.5 Arithmetic Expansion).Word splitting is not performed, with the exceptionof "$@" as explained below.Filename expansion is not performed.Assignment statements may also appear as arguments to thedeclare, typeset, export, readonly,and local builtin commands.

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3.4.1 Positional Parameters

A positional parameter is a parameter denoted by one or moredigits, other than the single digit 0. Positional parameters areassigned 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}, oras $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 andunset them (see section 4. Shell Builtin Commands).The positional parameters aretemporarily replaced when a shell function is executed(see section 3.3 Shell Functions).

When a positional parameter consisting of more than a singledigit is expanded, it must be enclosed in braces.

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3.4.2 Special Parameters

The shell treats several parameters specially. These parameters mayonly be referenced; assignment to them is not allowed.

*: Expands to the positional parameters, starting from one. When theexpansion occurs within double quotes, it expands to a single wordwith the value of each parameter separated by the first characterof the IFSspecial variable. That is, "$*" is equivalentto "$1c$2c...", where cis the first character of the value of the IFSvariable.If IFS is unset, the parameters are separated by spaces.If IFS is null, the parameters are joined without interveningseparators.
@: Expands to the positional parameters, starting from one. When theexpansion occurs within double quotes, each parameter expands to aseparate word. That is, "$@" is equivalent to"$1" "$2" ....When there are no positional parameters, "$@" and$@expand to nothing (i.e., they are removed).
#: Expands to the number of positional parameters in decimal.
: Expands to the exit status of the most recently executed foregroundpipeline.
-: (A hyphen.) Expands to the current option flags as specified uponinvocation, by the setbuiltin command, or those set by the shell itself(such as the `-i' option).
$: Expands to the process ID of the shell. In a () subshell, itexpands to the process ID of the invoking shell, not the subshell.
!: Expands to the process ID of the most recently executed background(asynchronous) command.
0: Expands to the name of the shell or shell script. This is set atshell initialization. If Bash is invoked with a file of commands(see section 3.8 Shell Scripts), $0 is set to the name of that file.If Bash is started with the `-c' option (see section 6.1 Invoking Bash),then $0 is set to the first argument after the string to beexecuted, if one is present. Otherwise, it is setto the filename used to invoke Bash, as given by argument zero.
_: (An underscore.)At shell startup, set to the absolute filename of the shell or shellscript being executed as passed in the argument list.Subsequently, expands to the last argument to the previous command,after expansion.Also set to the full pathname of each command executed and placed inthe environment exported to that command.When checking mail, this parameter holds the name of the mail file.

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3.5 Shell Expansions

Expansion is performed on the command line after it has been split intotokens. There are seven kinds of expansion performed:

brace expansion
tilde expansion
parameter and variable expansion
command substitution
arithmetic expansion
word splitting
filename expansion

3.5.1 Brace Expansion Expansion of expressions within braces. 3.5.2 Tilde Expansion Expansion of the ~ character. 3.5.3 Shell Parameter Expansion How Bash expands variables to their values. 3.5.4 Command Substitution Using the output of a command as an argument. 3.5.5 Arithmetic Expansion How to use arithmetic in shell expansions. 3.5.6 Process Substitution A way to write and read to and from a command. 3.5.7 Word Splitting How the results of expansion are split into separate arguments. 3.5.8 Filename Expansion A shorthand for specifying filenames matching patterns. 3.5.9 Quote Removal How and when quote characters are removed from words.

The order of expansions is: brace expansion, tilde expansion,parameter, variable, and arithmetic expansion andcommand substitution(done in a left-to-right fashion), word splitting, and filenameexpansion.

On systems that can support it, there is an additional expansionavailable: process substitution. This is performed at thesame time as parameter, variable, and arithmetic expansion andcommand substitution.

Only brace expansion, word splitting, and filename expansioncan change the number of words of the expansion; other expansionsexpand a single word to a single word.The only exceptions to this are the expansions of"$@" (see section 3.4.2 Special Parameters) and "${name[@]}"(see section 6.7 Arrays).

After all expansions, quote removal (see section 3.5.9 Quote Removal)is performed.

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3.5.1 Brace Expansion

Brace expansion is a mechanism by which arbitrary strings may be generated.This mechanism is similar tofilename expansion (see section 3.5.8 Filename Expansion),but the file names generated need not exist.Patterns to be brace expanded take the form of an optional preamble,followed by a series of comma-separated strings between a pair of braces,followed by an optional postscript.The preamble is prefixed to each string contained within the braces, andthe postscript is then appended to each resulting string, expanding leftto right.

Brace expansions may be nested.The results of each expanded string are not sorted; left to right orderis preserved.For example,

bash$ echo a{d,c,b}e            ade ace abe

Brace expansion is performed before any other expansions,and any characters special to other expansions are preservedin the result. It is strictly textual. Bashdoes not apply any syntactic interpretation to the context of theexpansion 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 openingand closing braces, and at least one unquoted comma.Any incorrectly formed brace expansion is left unchanged.

This construct is typically used as shorthand when the commonprefix of the strings to be generated is longer than in theabove example:

mkdir /usr/local/src/bash/{old,new,dist,bugs}

chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

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3.5.2 Tilde Expansion

If a word begins with an unquoted tilde character (`~'), all of thecharacters 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, thecharacters in the tilde-prefix following the tilde are treated as apossible login name.If this login name is the null string, the tilde is replaced with thevalue of the HOME shell variable.If HOME is unset, the home directory of the user executing theshell is substituted instead.Otherwise, the tilde-prefix is replaced with the home directoryassociated with the specified login name.

If the tilde-prefix is `~+', the value ofthe shell variable PWD replaces the tilde-prefix.If the tilde-prefix is `~-', the value of the shell variableOLDPWD, if it is set, is substituted.

If the characters following the tilde in the tilde-prefix consist of anumber N, optionally prefixed by a `+' or a `-',the tilde-prefix is replaced with thecorresponding element from the directory stack, as it would be displayedby the dirs builtin invoked with the characters following tildein the tilde-prefix as an argument (see section 6.8 The Directory Stack).If the tilde-prefix, sans the tilde, consists of a number without aleading `+' or `-', `+' is assumed.

If the login name is invalid, or the tilde expansion fails, the word isleft unchanged.

Each variable assignment is checked for unquoted tilde-prefixes immediatelyfollowing a `:' or `='.In these cases, tilde expansion is also performed.Consequently, one may use file names with tildes in assignments toPATH, MAILPATH, and CDPATH,and the shell assigns the expanded value.

The following table shows how Bash treats unquoted tilde-prefixes:

~: The value of $HOME
~/foo: `$HOME/foo'
~fred/foo: The subdirectory foo of the home directory of the userfred
~+/foo: `$PWD/foo'
~-/foo: `${OLDPWD-'~-'}/foo'
~N: The string that would be displayed by `dirs +N'
~+N: The string that would be displayed by `dirs +N'
~-N: The string that would be displayed by `dirs -N'

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3.5.3 Shell Parameter Expansion

The `$' character introduces parameter expansion,command substitution, or arithmetic expansion. The parameter nameor symbol to be expanded may be enclosed in braces, whichare optional but serve to protect the variable to be expanded fromcharacters immediately following it which could beinterpreted 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 anembedded arithmetic expansion, command substitution, or parameterexpansion.

The basic form of parameter expansion is ${parameter}.The value of parameter is substituted. The braces are requiredwhen parameteris a positional parameter with more than one digit,or when parameteris followed by a character that is not to beinterpreted 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 ofparameter as the name of the variable; this variable is thenexpanded and that value is used in the rest of the substitution, ratherthan the value of parameter itself.This is known as indirect expansion.The exception to this is the expansion of ${!prefix*}described below.

In each of the cases below, word is subject to tilde expansion,parameter expansion, command substitution, and arithmetic expansion.

When not performing substring expansion, Bash tests for a parameterthat is unset or null; omitting the colon results in a test only for aparameter that is unset. Put another way, if the colon is included,the operator tests for both existence and that the value is not null;if the colon is omitted, the operator tests only for existence.

${parameter:-word}

If parameter is unset or null, the expansion ofword is substituted. Otherwise, the value ofparameter is substituted.

${parameter:=word}

If parameteris unset or null, the expansion of wordis assigned to parameter.The value of parameteris then substituted. Positional parameters and special parameters maynot be assigned to in this way.

${parameter:?word}

If parameteris null or unset, the expansion of word (or a messageto that effect if wordis not present) is written to the standard error and the shell, if itis not interactive, exits. Otherwise, the value of parameter issubstituted.

${parameter:+word}

If parameteris null or unset, nothing is substituted, otherwise the expansion ofword is substituted.

${parameter:offset}

${parameter:offset:length}

Expands to up to length characters of parameterstarting at the character specified by offset.If length is omitted, expands to the substring ofparameter starting at the character specified by offset.length and offset are arithmetic expressions(see section 6.5 Shell Arithmetic).This is referred to as Substring Expansion.

length must evaluate to a number greater than or equal to zero.If offset evaluates to a number less than zero, the valueis used as an offset from the end of the value of parameter.If parameter is `@', the result is length positionalparameters beginning at offset.If parameter is an array name indexed by `@' or `*',the result is the lengthmembers of the array beginning with ${parameter[offset]}.Substring indexing is zero-based unless the positional parametersare used, in which case the indexing starts at 1.

${!prefix*}

Expands to the names of variables whose names begin with prefix,separated by the first character of the IFS special variable.

${#parameter}

The length in characters of the expanded value of parameter issubstituted.If parameter is `*' or `@', the value substitutedis the number of positional parameters.If parameter is an array name subscripted by `*' or `@',the value substituted is the number of elements in the array.

${parameter#word}

${parameter##word}

The wordis expanded to produce a pattern just as in filenameexpansion (see section 3.5.8 Filename Expansion). If the pattern matchesthe beginning of the expanded value of parameter,then the result of the expansion is the expanded value of parameterwith the shortest matching pattern (the `#' case) or thelongest matching pattern (the `##' case) deleted.If parameter is `@' or `*',the pattern removal operation is applied to each positionalparameter in turn, and the expansion is the resultant list.If parameter is an array variable subscripted with`@' or `*',the pattern removal operation is applied to each member of thearray in turn, and the expansion is the resultant list.

${parameter%word}

${parameter%%word}

The word is expanded to produce a pattern just as infilename expansion.If the pattern matches a trailing portion of the expanded value ofparameter, then the result of the expansion is the value ofparameter with the shortest matching pattern (the `%' case)or the longest matching pattern (the `%%' case) deleted.If parameter is `@' or `*',the pattern removal operation is applied to each positionalparameter in turn, and the expansion is the resultant list.If parameteris an array variable subscripted with `@' or `*',the pattern removal operation is applied to each member of thearray in turn, and the expansion is the resultant list.

${parameter/pattern/string}

${parameter//pattern/string}

The pattern is expanded to produce a pattern just as infilename expansion.Parameter is expanded and the longest match of patternagainst its value is replaced with string.In the first form, only the first match is replaced.The second form causes all matches of pattern to bereplaced with string.If pattern begins with `#', it must match at the beginningof the expanded value of parameter.If pattern begins with `%', it must match at the endof the expanded value of parameter.If string is null, matches of pattern are deletedand the / following pattern may be omitted.If parameter is `@' or `*',the substitution operation is applied to each positionalparameter in turn, and the expansion is the resultant list.If parameteris an array variable subscripted with `@' or `*',the substitution operation is applied to each member of thearray in turn, and the expansion is the resultant list.

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3.5.4 Command Substitution

Command substitution allows the output of a command to replacethe command itself.Command substitution occurs when a command is enclosed as follows:

$(command)

`command`

Bash performs the expansion by executing command andreplacing the command substitution with the standard output of thecommand, with any trailing newlines deleted.Embedded newlines are not deleted, but they may be removed duringword splitting.The command substitution $(cat file) can bereplaced 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 thecommand substitution.When using the $(command) form, all characters betweenthe parentheses make up the command; none are treated specially.

Command substitutions may be nested. To nest when using the backquotedform, escape the inner backquotes with backslashes.

If the substitution appears within double quotes, word splitting andfilename expansion are not performed on the results.

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3.5.5 Arithmetic Expansion

Arithmetic expansion allows the evaluation of an arithmetic expressionand the substitution of the result. The format for arithmetic expansion is:

$(( expression ))

The expression is treated as if it were within double quotes, buta double quote inside the parentheses is not treated specially.All tokens in the expression undergo parameter expansion, commandsubstitution, and quote removal.Arithmetic substitutions may be nested.

The evaluation is performed according to the rules listed below(see section 6.5 Shell Arithmetic).If the expression is invalid, Bash prints a message indicatingfailure to the standard error and no substitution occurs.

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3.5.6 Process Substitution

Process substitution is supported on systems that support namedpipes (FIFOs) or the `/dev/fd' method of naming open files.It takes the form of

<(list)

>(list)

The process list is run with its input or output connected to aFIFO or some file in `/dev/fd'. The name of this file ispassed as an argument to the current command as the result of theexpansion. If the >(list) form is used, writing tothe file will provide input for list. If the<(list) form is used, the file passed as anargument 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 interpretedas a redirection.

When available, process substitution is performed simultaneously withparameter and variable expansion, command substitution, and arithmeticexpansion.

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3.5.7 Word Splitting

The shell scans the results of parameter expansion, command substitution,and arithmetic expansion that did not occur within double quotes forword splitting.

The shell treats each character of $IFSas a delimiter, and splits the results of the otherexpansions into words on these characters. IfIFS is unset, or its value is exactly ,the default, then any sequence of IFScharacters serves to delimit words. If IFShas a value other than the default, then sequences ofthe whitespace characters space and tabare ignored at the beginning and end of theword, as long as the whitespace character is in thevalue of IFS (an IFS whitespace character).Any character in IFS that is not IFSwhitespace, along with any adjacent IFSwhitespace characters, delimits a field. A sequence of IFSwhitespace 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 ofparameters that have no values, are removed.If a parameter with no value is expanded within double quotes, anull argument results and is retained.

Note that if no expansion occurs, no splittingis performed.

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3.5.8 Filename Expansion

3.5.8.1 Pattern Matching How the shell matches patterns.

After word splitting, unless the `-f' option has been set(see section 4.3 The Set Builtin), Bash scans each word for the characters`*', `?', and `['.If one of these characters appears, then the word isregarded as a pattern,and replaced with an alphabetically sorted list offile names matching the pattern. If no matching file names are found,and the shell option nullglob is disabled, the word is leftunchanged.If the nullglob option is set, and no matches are found, the wordis removed.If the shell option nocaseglob is enabled, the match is performedwithout regard to the case of alphabetic characters.

When a pattern is used for filename generation, the character `.'at the start of a filename or immediately following a slashmust be matched explicitly, unless the shell option dotglob is set.When matching a file name, the slash character must always bematched explicitly.In other cases, the `.' character is not treated specially.

See the description of shopt in 4.2 Bash Builtin Commands,for a description of the nocaseglob, nullglob,and dotglob options.

The GLOBIGNOREshell variable may be used to restrict the set of filenames matching apattern. If GLOBIGNOREis set, each matching filename that also matches one of the patterns inGLOBIGNORE is removed from the list of matches. The filenames`.' and `..'are always ignored, even when GLOBIGNOREis set. However, setting GLOBIGNORE has the effect ofenabling the dotglobshell 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 GLOBIGNOREis unset.

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3.5.8.1 Pattern Matching

Any character that appears in a pattern, other than the special patterncharacters described below, matches itself. The NUL character may notoccur in a pattern. The special pattern characters must be quoted ifthey are to be matched literally.

The special pattern characters have the following meanings:

*

Matches any string, including the null string.

Matches any single character.

[...]

Matches any one of the enclosed characters. A pair of charactersseparated by a hyphen denotes a range expression;any character that sorts between those two characters, inclusive,using the current locale's collating sequence and character set,is matched. If the first character following the`[' is a `!' or a `^'then any character not enclosed is matched. A `-'may be matched by including it as the first or last characterin the set. A `]' may be matched by including it as the firstcharacter in the set.The sorting order of characters in range expressions is determined bythe current locale and the value of the LC_COLLATE shell variable,if set.

For example, in the default C locale, `[a-dx-z]' is equivalent to`[abcdxyz]'. Many locales sort characters in dictionary order, and inthese locales `[a-dx-z]' is typically not equivalent to `[abcdxyz]';it might be equivalent to `[aBbCcDdxXyYz]', for example. To obtainthe traditional interpretation of ranges in bracket expressions, you canforce the use of the C locale by setting the LC_COLLATE orLC_ALL environment variable to the value `C'.

Within `[' and `]', character classes can be specifiedusing the syntax[:class:], where class is one of thefollowing classes defined in the POSIX 1003.2 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 bespecified using the syntax [=c=], whichmatches all characters with the same collation weight (as definedby 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 shoptbuiltin, several extended pattern matching operators are recognized.In the following description, a pattern-list is a list of oneor more patterns separated by a `|'.Composite patterns may be formed using one or more of the followingsub-patterns:

(pattern-list): Matches zero or one occurrence of the given patterns.
*(pattern-list): Matches zero or more occurrences of the given patterns.
+(pattern-list): Matches one or more occurrences of the given patterns.
@(pattern-list): Matches exactly one of the given patterns.
!(pattern-list): Matches anything except one of the given patterns.

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3.5.9 Quote Removal

After the preceding expansions, all unquoted occurrences of thecharacters `\', `'', and `"' that did notresult from one of the above expansions are removed.

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3.6 Redirections

Before a command is executed, its input and outputmay be redirectedusing a special notation interpreted by the shell.Redirection may also be used to open and close files for thecurrent shell execution environment. The following redirectionoperators may precede or appear anywhere within asimple command or may follow a command.Redirections are processed in the order they appear, fromleft to right.

In the following descriptions, if the file descriptor number isomitted, and the first character of the redirection operator is`<', the redirection refers to the standard input (filedescriptor 0). If the first character of the redirection operatoris `>', the redirection refers to the standard output (filedescriptor 1).

The word following the redirection operator in the followingdescriptions, unless otherwise noted, is subjected to brace expansion,tilde expansion, parameter expansion, command substitution, arithmeticexpansion, 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 duplicated as standard outputbefore the standard output was redirected to dirlist.

Bash handles several filenames specially when they are used inredirections, as described in the following table:

/dev/fd/fd: If fd is a valid integer, file descriptor fd is duplicated.
/dev/stdin: File descriptor 0 is duplicated.
/dev/stdout: File descriptor 1 is duplicated.
/dev/stderr: File descriptor 2 is duplicated.
/dev/tcp/host/port: If host is a valid hostname or Internet address, and portis an integer port number or service name, Bash attempts to open a TCPconnection to the corresponding socket.
/dev/udp/host/port: If host is a valid hostname or Internet address, and portis an integer port number or service name, Bash attempts to open a UDPconnection to the corresponding socket.

A failure to open or create a file causes the redirection to fail.

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3.6.1 Redirecting Input

Redirection of input causes the file whose name results fromthe expansion of wordto be opened for reading on file descriptor n,or the standard input (file descriptor 0) if nis not specified.

The general format for redirecting input is:

[n]<word

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3.6.2 Redirecting Output

Redirection of output causes the file whose name results fromthe expansion of wordto be opened for writing on file descriptor n,or the standard output (file descriptor 1) if nis 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 noclobberoption to the set builtin has been enabled, the redirectionwill fail if the file whose name results from the expansion ofword exists and is a regular file.If the redirection operator is `>|', or the redirection operator is`>' and the noclobber option is not enabled, the redirectionis attempted even if the file named by word exists.

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3.6.3 Appending Redirected Output

Redirection of output in this fashioncauses the file whose name results fromthe expansion of wordto be opened for appending on file descriptor n,or the standard output (file descriptor 1) if nis not specified. If the file does not exist it is created.

The general format for appending output is:

[n]>>word

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3.6.4 Redirecting Standard Output and Standard Error

Bash allows both thestandard output (file descriptor 1) andthe standard error output (file descriptor 2)to be redirected to the file whose name is theexpansion of word with this construct.

There are two formats for redirecting standard output andstandard error:

&>word

and

>&word

Of the two forms, the first is preferred.This is semantically equivalent to

>word 2>&1

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3.6.5 Here Documents

This type of redirection instructs the shell to read input from thecurrent source until a line containing only word(with no trailing blanks) is seen. All ofthe lines read up to that point are then used as the standardinput for a command.

The format of here-documents is:

<<[-]word            here-document            delimiter

No parameter expansion, command substitution, arithmetic expansion,or filename expansion is performed onword. If any characters in word are quoted, thedelimiter 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 lattercase, 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 theline containing delimiter.This allows here-documents within shell scripts to be indented in anatural fashion.

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3.6.6 Here Strings

A variant of here documents, the format is:

<<< word

The word is expanded and supplied to the command on its standardinput.

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3.6.7 Duplicating File Descriptors

The redirection operator

[n]<&word

is used to duplicate input file descriptors.If wordexpands to one or more digits, the file descriptor denoted by nis made to be a copy of that file descriptor.If the digits in word do not specify a file descriptor open forinput, a redirection error occurs.If wordevaluates to `-', file descriptor n is closed. Ifn is not specified, the standard input (file descriptor 0) is used.

The operator

[n]>&word

is used similarly to duplicate output file descriptors. Ifn is not specified, the standard output (file descriptor 1) is used.If the digits in word do not specify a file descriptor open foroutput, a redirection error occurs.As a special case, if n is omitted, and word does notexpand to one or more digits, the standard output and standarderror are redirected as described previously.

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3.6.8 Moving File Descriptors

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.

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3.6.9 Opening File Descriptors for Reading and Writing

The redirection operator

[n]<>word

causes the file whose name is the expansion of wordto be opened for both reading and writing on file descriptorn, or on file descriptor 0 if nis not specified. If the file does not exist, it is created.

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3.7 Executing Commands

3.7.1 Simple Command Expansion    How Bash expands simple commands before executing them.
3.7.2 Command Search and Execution    How Bash finds commands and runs them.
3.7.3 Command Execution Environment    The environment in which Bash executes commands that are not shell builtins.
3.7.4 Environment    The environment given to a command.
3.7.5 Exit Status    The status returned by commands and how Bash interprets it.
3.7.6 Signals    What happens when Bash or a command it runs receives a signal.

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3.7.1 Simple Command Expansion

When a simple command is executed, the shell performs the followingexpansions, assignments, and redirections, from left to right.

The words that the parser has marked as variable assignments (those preceding the command name) and redirections are saved for later processing.
The words that are not variable assignments or redirections are expanded (see section 3.5 Shell Expansions). If any words remain after expansion, the first word is taken to be the name of the command and the remaining words are the arguments.
Redirections are performed as described above (see section 3.6 Redirections).
The text after the `=' in each variable assignment undergoes tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal before being assigned to the variable.

If no command name results, the variable assignments affect the currentshell environment. Otherwise, the variables are added to the environmentof 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 notaffect the current shell environment. A redirection error causes thecommand to exit with a non-zero status.

If there is a command name left after expansion, execution proceeds asdescribed below. Otherwise, the command exits. If one of the expansionscontained a command substitution, the exit status of the command isthe exit status of the last command substitution performed. If therewere no command substitutions, the command exits with a status of zero.

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3.7.2 Command Search and Execution

After a command has been split into words, if it results in asimple command and an optional list of arguments, the followingactions are taken.

If the command name contains no slashes, the shell attempts to locate it. If there exists a shell function by that name, that function is invoked as described in 3.3 Shell Functions.
If the name does not match a function, the shell searches for it in the list of shell builtins. If a match is found, that builtin is invoked.
If the name is neither a shell function nor a builtin, and contains no slashes, Bash searches each element of $PATH for a directory containing an executable file by that name. Bash uses a hash table to remember the full pathnames of executable files to avoid multiple PATH searches (see the description of hash in 4.1 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 prints an error message and returns an exit status of 127.
If the search is successful, or if the command name contains one or more slashes, the shell executes the named program in a separate execution environment. Argument 0 is set to the name given, and the remaining arguments to the command are set to the arguments supplied, if any.
If this execution fails because the file is not in executable format, and the file is not a directory, it is assumed to be a shell script and the shell executes it as described in 3.8 Shell Scripts.
If the command was not begun asynchronously, the shell waits for the command to complete and collects its exit status.

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3.7.3 Command Execution Environment

The shell has an execution environment, which consists of thefollowing:

open files inherited by the shell at invocation, as modified by redirections supplied to the exec builtin
the current working directory as set by cd, pushd, or popd, or inherited by the shell at invocation
the file creation mode mask as set by umask or inherited from the shell's parent
current traps set by trap
shell parameters that are set by variable assignment or with set or inherited from the shell's parent in the environment
shell functions defined during execution or inherited from the shell's parent in the environment
options enabled at invocation (either by default or with command-line arguments) or by set
options enabled by shopt
shell aliases defined with alias (see section 6.6 Aliases)
various process IDs, including those of background jobs (see section 3.2.3 Lists of Commands), the value of $$, and the value of $PPID

When a simple command other than a builtin or shell functionis to be executed, itis invoked in a separate execution environment that consists ofthe following. Unless otherwise noted, the values are inheritedfrom the shell.

the shell's open files, plus any modifications and additions specified by redirections to the command
the current working directory
the file creation mode mask
shell variables marked for export, along with variables exported for the command, passed in the environment (see section 3.7.4 Environment)
traps caught by the shell are reset to the values inherited from the shell's parent, and traps ignored by the shell are ignored

A command invoked in this separate environment cannot affect theshell's execution environment.

Command substitution and asynchronous commands are invoked in asubshell environment that is a duplicate of the shell environment,except that traps caught by the shell are reset to the valuesthat the shell inherited from its parent at invocation. Builtincommands that are invoked as part of a pipeline are also executedin a subshell environment. Changes made to the subshell environmentcannot affect the shell's execution environment.

If a command is followed by a `&' and job control is not active, thedefault standard input for the command is the empty file `/dev/null'.Otherwise, the invoked command inherits the file descriptors of the callingshell as modified by redirections.

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3.7.4 Environment

When a program is invoked it is given an array of stringscalled 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 andcreates a parameter for each name found, automatically markingit for exportto child processes. Executed commands inherit the environment.The export and `declare -x'commands allow parameters and functions to be added to anddeleted from the environment. If the value of a parameterin the environment is modified, the new value becomes partof the environment, replacing the old. The environmentinherited by any executed command consists of the shell'sinitial 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 commandor function may be augmented temporarily by prefixing it withparameter assignments, as described in 3.4 Shell Parameters.These assignment statements affect only the environment seenby that command.

If the `-k' option is set (see section 4.3 The Set Builtin), then allparameter 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 thatcommand in its environment.

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3.7.5 Exit Status

For the shell's purposes, a command which exits with azero exit status has succeeded.A non-zero exit status indicates failure.This seemingly counter-intuitive scheme is used so thereis one well-defined way to indicate success and a variety ofways 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 toexecute it returns a status of 127. If a command is foundbut 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 section 3.2.5 Conditional Constructs) and some of the listconstructs (see section 3.2.3 Lists of Commands).

All of the Bash builtins return an exit status of zero if they succeedand a non-zero status on failure, so they may be used by theconditional and list constructs.All builtins return an exit status of 2 to indicate incorrect usage.

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3.7.6 Signals

When Bash is interactive, in the absence of any traps, it ignoresSIGTERM (so that `kill 0' does not kill an interactive shell),and SIGINTis caught and handled (so that the wait builtin is interruptible).When Bash receives a SIGINT, it breaks out of any executing loops.In all cases, Bash ignores SIGQUIT.If job control is in effect (see section 7. Job Control), Bashignores SIGTTIN, SIGTTOU, and SIGTSTP.

Commands started by Bash have signal handlers set to thevalues inherited by the shell from its parent.When job control is not in effect, asynchronous commandsignore SIGINT and SIGQUIT as well.Commands run as a result ofcommand substitution ignore the keyboard-generated job control signalsSIGTTIN, SIGTTOU, and SIGTSTP.

The shell exits by default upon receipt of a SIGHUP.Before exiting, an interactive shell resends the SIGHUP toall jobs, running or stopped.Stopped jobs are sent SIGCONT to ensure that they receivethe SIGHUP.To prevent the shell from sending the SIGHUP signal to aparticular job, it should be removedfrom the jobs table with the disownbuiltin (see section 7.2 Job Control Builtins) or markedto not receive SIGHUP using disown -h.

If the huponexit shell option has been set with shopt(see section 4.2 Bash Builtin Commands), Bash sends a SIGHUP to all jobs whenan interactive login shell exits.

When Bash receives a signal for which a trap has been set while waitingfor a command to complete, the trap will not be executed until thecommand completes.When Bash is waiting for an asynchronouscommand via the wait builtin, the reception of a signal forwhich a trap has been set will cause the wait builtin to returnimmediately with an exit status greater than 128, immediately afterwhich the trap is executed.

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3.8 Shell Scripts

A shell script is a text file containing shell commands. When sucha file is used as the first non-option argument when invoking Bash,and neither the `-c' nor `-s' option is supplied(see section 6.1 Invoking Bash),Bash reads and executes commands from the file, then exits. Thismode of operation creates a non-interactive shell. The shell firstsearches for the file in the current directory, and looks in thedirectories in $PATH if not found there.

When Bash runsa shell script, it sets the special parameter 0 to the nameof the file, rather than the name of the shell, and the positionalparameters are set to the remaining arguments, if any are given.If no additional arguments are supplied, the positional parametersare unset.

A shell script may be made executable by using the chmod commandto turn on the execute bit. When Bash finds such a file whilesearching the $PATH for a command, it spawns a subshell toexecute 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 anew shell had been invoked to interpret the script, with theexception that the locations of commands remembered by the parent(see the description of hash in 4.1 Bourne Shell Builtins)are retained by the child.

Most versions of Unix make this a part of the operating system's commandexecution mechanism. If the first line of a script begins withthe two characters `#!', the remainder of the line specifiesan interpreter for the program.Thus, you can specify Bash, awk, Perl, or some otherinterpreter and write the rest of the script file in that language.

The arguments to the interpreterconsist of a single optional argument following the interpretername on the first line of the script file, followed by the name ofthe script file, followed by the rest of the arguments. Bashwill perform this action on operating systems that do not handle itthemselves. Note that some older versions of Unix limit the interpretername and argument to a maximum of 32 characters.

Bash scripts often begin with #! /bin/bash (assuming thatBash has been installed in `/bin'), since this ensures thatBash will be used to interpret the script, even if it is executedunder another shell.

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4. Shell Builtin Commands

4.1 Bourne Shell Builtins Builtin commands inherited from the Bourne Shell. 4.2 Bash Builtin Commands Table of builtins specific to Bash. 4.3 The Set Builtin This builtin is so overloaded it deserves its own section. 4.4 Special Builtins Builtin commands classified specially by POSIX.2.

Builtin commands are contained within the shell itself.When the name of a builtin command is used as the first word ofa simple command (see section 3.2.1 Simple Commands), the shell executesthe command directly, without invoking another program.Builtin commands are necessary to implement functionality impossibleor inconvenient to obtain with separate utilities.

This section briefly the builtins which Bash inherits fromthe Bourne Shell, as well as the builtin commands which are uniqueto or have been extended in Bash.

Several builtin commands are described in other chapters: builtincommands which provide the Bash interface to the job controlfacilities (see section 7.2 Job Control Builtins), the directory stack(see section 6.8.1 Directory Stack Builtins), the command history(see section 9.2 Bash History Builtins), and the programmable completionfacilities (see section 8.7 Programmable Completion Builtins).

Many of the builtins have been extended by POSIX or Bash.

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4.1 Bourne Shell Builtins

The following shell builtin commands are inherited from the Bourne Shell.These commands are implemented as specified by the POSIX 1003.2 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 thecurrent 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 searchedif filename is not found in $PATH.If any arguments are supplied, they become the positionalparameters when filename is executed. Otherwise the positionalparameters are unchanged.The return status is the exit status of the last command executed, orzero if no commands are executed. If filename is not found, orcannot be read, the return status is non-zero.This builtin is equivalent to source.

break

break [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.

cd

cd [-L|-P] [directory]

Change the current working directory to directory. If directoryis not given, the value of the HOME shell variable is used. If theshell variable CDPATH exists, it is used as a search path. Ifdirectory begins with a slash, CDPATH is not used.The `-P' option meansto not follow symbolic links; symbolic links are followed by defaultor with the `-L' option.If directory is `-', it is equivalent to $OLDPWD.The return status is zero if the directory is successfully changed,non-zero otherwise.

continue

continue [n]

Resume the next iteration of an enclosing for, while,until, or select loop.If n is supplied, the execution of the nth enclosing loopis 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.

eval

eval [arguments]

The arguments are concatenated together into a single command, which isthen read and executed, and its exit status returned as the exit statusof eval.If there are no arguments or only empty arguments, the return status iszero.

exec

exec [-cl] [-a name] [command [arguments]]

If commandis supplied, it replaces the shell without creating a new process.If the `-l' option is supplied, the shell places a dash at thebeginning of the zeroth arg passed to command.This is what the login program does.The `-c' option causes command to be executed with an emptyenvironment.If `-a' is supplied, the shell passes name as the zerothargument to command.If no command is specified, redirections may be used to affectthe current shell environment. If there are no redirection errors, thereturn status is zero; otherwise the return status is non-zero.

exit

exit [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.

export

export [-fn] [-p] [name[=value]]

Mark each name to be passed to child processesin the environment. If the `-f' option is supplied, the namesrefer 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, alist of exported names is displayed.The `-p' option displays output in a form that may be reused as input.The return status is zero unless an invalid option is supplied, one ofthe names is not a valid shell variable name, or `-f' is suppliedwith a name that is not a shell function.

getopts

getopts optstring name [args]

getopts is used by shell scripts to parse positional parameters.optstring contains the option characters to be recognized; if acharacter is followed by a colon, the option is expected to have anargument, which should be separated from it by white space.The colon (`:') and question mark (`?') may not beused as option characters.Each time it is invoked, getoptsplaces the next option in the shell variable name, initializingname if it does not exist,and the index of the next argument to be processed into thevariable OPTIND.OPTIND is initialized to 1 each time the shell or a shell scriptis 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 manuallyreset between multiple calls to getopts within the same shellinvocation if a new set of parameters is to be used.

When the end of options is encountered, getopts exits with areturn value greater than zero.OPTIND is set to the index of the first non-option argument,and name is set to `?'.

getoptsnormally parses the positional parameters, but if more arguments aregiven in args, getopts parses those instead.

getopts can report errors in two ways. If the first character ofoptstring is a colon, silenterror reporting is used. In normal operation diagnostic messagesare printed when invalid options or missing option arguments areencountered.If the variable OPTERRis set to 0, no error messages will be displayed, even if the firstcharacter 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 inOPTARG and no diagnostic message is printed.

If a required argument is not found, and getoptsis 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 inname and OPTARG is set to the option character found.

hash

hash [-'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 isused 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 locationof each name.If the `-t' option is supplied, the full pathname to which eachname corresponds is printed. If multiple name arguments aresupplied with `-t' the name is printed before the hashedfull pathname.The `-l' option causes output to be displayed in a formatthat 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 invalidoption is supplied.

pwd

pwd [-LP]

Print the absolute pathname of the current working directory.If the `-P' option is supplied, the pathname printed will notcontain symbolic links.If the `-L' option is supplied, the pathname printed may containsymbolic links.The return status is zero unless an error is encountered whiledetermining the name of the current directory or an invalid optionis supplied.

readonly

readonly [-apf] [name] ...

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 shellfunction.The `-a' option means each name refers to an array variable.If no name arguments are given, or if the `-p'option is supplied, a list of all readonly names is printed.The `-p' option causes output to be displayed in a format thatmay be reused as input.The return status is zero unless an invalid option is supplied, one ofthe 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.

return

return [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 thelast command executed in the function.This may also be used to terminate execution of a script being executedwith the . (or source) builtin, returning either n orthe exit status of the last command executed within the script as the exitstatus of the script.The return status is non-zero if return is used outside a functionand not during the execution of a script by . or source.

shift

shift [n]

Shift the positional parameters to the left by n.The positional parameters from n+1 ... $# arerenamed to $1 ... $#-n+1.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 parametersare not changed.If n is not supplied, it is assumed to be 1.The return status is zero unless n is greater than $# orless than zero, non-zero otherwise.

test

[

Evaluate a conditional expression expr.Each operator and operand must be a separate argument.Expressions are composed of the primaries described below in6.4 Bash Conditional Expressions.

When the [ form is used, the last argument to the command mustbe a ].

Expressions may be combined using the following operators, listed indecreasing order of precedence.

! expr: True if expr is false.
( expr ): Returns the value of expr.This may be used to override the normal precedence of operators.
expr1 -a expr2: True if both expr1 and expr2 are true.
expr1 -o expr2: True if either expr1 or expr2 is true.

The test and [ builtins evaluate conditionalexpressions using a set of rules based on the number of arguments.

0 arguments: The expression is false.
1 argument: The expression is true if and only if the argument is not null.
2 arguments: If the first argument is `!', the expression is true if andonly if the second argument is null.If the first argument is one of the unary conditional operators(see section 6.4 Bash Conditional Expressions), the expressionis true if the unary test is true.If the first argument is not a valid unary operator, the expression isfalse.
3 arguments: If the second argument is one of the binary conditionaloperators (see section 6.4 Bash Conditional Expressions), theresult of the expression is the result of the binary test using thefirst and third arguments as operands.If the first argument is `!', the value is the negation ofthe two-argument test using the second and third arguments.If the first argument is exactly `(' and the third argument isexactly `)', the result is the one-argument test of the secondargument.Otherwise, the expression is false.The `-a' and `-o' operators are considered binary operatorsin this case.
4 arguments: If the first argument is `!', the result is the negation ofthe three-argument expression composed of the remaining arguments.Otherwise, the expression is parsed and evaluated according toprecedence using the rules listed above.
5 or more arguments: The expression is parsed and evaluated according to precedenceusing the rules listed above.

times

times

Print out the user and system times used by the shell and its children.The return status is zero.

trap

trap [-lp] [arg] [sigspec ...]

The commands in arg are to be read and executed when theshell receives signal sigspec. If arg is absent orequal to `-', all specified signals are reset to the valuesthey had when the shell was started.If arg is the null string, then the signal specified byeach 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, oronly `-p' is given, trap prints the list of commandsassociated with each signal number in a form that may be reused asshell input.Each sigspec is either a signal name such as SIGINT (withor without the SIG prefix) or a signal number.If a sigspecis 0 or EXIT, arg is executed when the shell exits.If a sigspec is DEBUG, the command arg is executedafter every simple command.If a sigspec is ERR, the command argis executed whenever a simple command has a non-zero exit status.The ERR trap is not executed if the failed command is part of anuntil or while loop, part of an if statement,part of a && or || list, or if the command's returnstatus is being inverted using !.The `-l' option causes the shell to print a list of signal namesand their corresponding numbers.

Signals ignored upon entry to the shell cannot be trapped or reset.Trapped signals are reset to their original values in a childprocess when it is created.

The return status is zero unless a sigspec does not specify avalid signal.

umask

umask [-p] [-S] [mode]

Set the shell process's file creation mask to mode. Ifmode begins with a digit, it is interpreted as an octal number;if not, it is interpreted as a symbolic mode mask similarto that accepted by the chmod command. If mode isomitted, the current value of the mask is printed. If the `-S'option is supplied without a mode argument, the mask is printedin a symbolic format.If the `-p' option is supplied, and modeis 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 ifno mode argument is supplied, and non-zero otherwise.

Note that when the mode is interpreted as an octal number, each numberof the umask is subtracted from 7. Thus, a umask of 022results in permissions of 755.

unset

unset [-fv] [name]

Each variable or function name is removed.If no options are supplied, or the `-v' option is given, eachname refers to a shell variable.If the `-f' option is given, the names refer to shellfunctions, and the function definition is removed.Readonly variables and functions may not be unset.The return status is zero unless a name does not exist or isreadonly.

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4.2 Bash Builtin Commands

This section describes builtin commands which are unique toor have been extended in Bash.Some of these commands are specified in the POSIX 1003.2 standard.

alias

alias [-p] [name[=value] ...]

Without arguments or with the `-p' option, alias printsthe list of aliases on the standard output in a form that allowsthem to be reused as input.If arguments are supplied, an alias is defined for each namewhose value is given. If no value is given, the nameand value of the alias is printed.Aliases are described in 6.6 Aliases.

bind

bind [-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 section 8. 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 aa Readline initialization file (see section 8.3 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 keymap: Use keymap as the keymap to be affected bythe subsequent bindings. Acceptable keymapnames areemacs,emacs-standard,emacs-meta,emacs-ctlx,vi,vi-move,vi-command, andvi-insert.vi is equivalent to vi-command;emacs is equivalent to emacs-standard.
-l: List the names of all Readline functions.
-p: Display Readline function names and bindings in such a way that theycan be used as input or in a Readline initialization file.
-P: List current Readline function names and bindings.
-v: Display Readline variable names and values in such a way that theycan be used as input or in a Readline initialization file.
-V: List current Readline variable names and values.
-s: Display Readline key sequences bound to macros and the strings they outputin such a way that they can be used as input or in a Readlineinitialization file.
-S: Display Readline key sequences bound to macros and the strings they output.
-f filename: Read key bindings from filename.
-q function: Query about which keys invoke the named function.
-u function: Unbind all keys bound to the named function.
-r keyseq: Remove any current binding for keyseq.
-x keyseq:shell-command: Cause shell-command to be executed whenever keyseq isentered.

The return status is zero unless an invalid option is supplied or anerror occurs.

builtin

builtin [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 samename as a shell builtin, retaining the functionality of the builtin withinthe function.The return status is non-zero if shell-builtin is not a shellbuiltin command.

command

command [-pVv] command [arguments ...]

Runs command with arguments ignoring any shell functionnamed command.Only shell builtin commands or commands found by searching thePATH are executed.If there is a shell function named ls, running `command ls'within the function will execute the external command lsinstead of calling the function recursively.The `-p' option means to use a default value for PATHthat is guaranteed to find all of the standard utilities.The return status in this case is 127 if command cannot befound or an error occurred, and the exit status of commandotherwise.

If either the `-V' or `-v' option is supplied, adescription of command is printed. The `-v' optioncauses a single word indicating the command or file name used toinvoke command to be displayed; the `-V' option producesa more verbose description. In this case, the return status iszero if command is found, and non-zero if not.

declare

declare [-afFirtx] [-p] [name[=value]]

Declare variables and give them attributes. If no namesare given, then display the values of variables instead.

The `-p' option will display the attributes and values of eachname. When `-p' is used, additional options are ignored.The `-F' option inhibits the display of function definitions;only the function name and attributes are printed. `-F' implies`-f'. The following options can be used to restrict outputto variables with the specified attributes or to give variablesattributes:

-a: Each name is an array variable (see section 6.7 Arrays).
-f: Use function names only.
-i: The variable is to be treated asan integer; arithmetic evaluation (see section 6.5 Shell Arithmetic) isperformed when the variable is assigned a value.
-r: Make names readonly. These names cannot then be assigned valuesby subsequent assignment statements or unset.
-t: Give each name the trace attribute.Traced functions inherit the DEBUG trap from the calling shell.The trace attribute has no special meaning for variables.
-x: Mark each name for export to subsequent commands viathe environment.

Using `+' instead of `-' turns off the attribute instead.When used in a function, declare makes each name local,as with the local command.

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 withoutusing the compound assignment syntax (see section 6.7 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'.

echo

echo [-neE] [arg ...]

Output the args, separated by spaces, terminated with anewline.The return status is always 0.If `-n' is specified, the trailing newline is suppressed.If the `-e' option is given, interpretation of the followingbackslash-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 todynamically determine whether or not echo expands theseescape characters by default.echo interprets the following escape sequences:

\a: alert (bell)
\b: backspace
\c: suppress trailing newline
\e: escape
\f: form feed
\n: new line
\r: carriage return
\t: horizontal tab
\v: vertical tab
\\: backslash
\0nnn: the eight-bit character whose value is the octal value nnn(zero to three octal digits)
\nnn: the eight-bit character whose value is the octal value nnn(one to three octal digits)
\xHH: the eight-bit character whose value is the hexadecimal value HH(one or two hex digits)

enable

enable [-n] [-p] [-f filename] [-ads] [name ...]

Enable and disable builtin shell commands.Disabling a builtin allows a disk command which has the same nameas 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. Otherwisenames are enabled. For example, to use the test binaryfound 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 listconsists of all enabled shell builtins.The `-a' option means to listeach builtin with an indication of whether or not it is enabled.

The `-f' option means to load the new builtin command namefrom 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 specialbuiltins. If `-s' is used with `-f', the new builtin becomesa special builtin (see section 4.4 Special Builtins).

The return status is zero unless a name is not a shell builtinor there is an error loading a new builtin from a shared object.

help

help [-s] [pattern]

Display helpful information about builtin commands.If pattern is specified, help gives detailed helpon all commands matching pattern, otherwise a list ofthe builtins is printed.The `-s' option restricts the information displayed to a shortusage synopsis.The return status is zero unless no command matches pattern.

let

let expression [expression]

The let builtin allows arithmetic to be performed on shellvariables. Each expression is evaluated according to therules given below in 6.5 Shell Arithmetic. If thelast expression evaluates to 0, let returns 1;otherwise 0 is returned.

local

local [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 variablename have a visible scope restricted to that function and itschildren. The return status is zero unless local is used outsidea function, an invalid name is supplied, or name is areadonly variable.

logout

logout [n]

Exit a login shell, returning a status of n to the shell'sparent.

printf

printf format [arguments]

Write the formatted arguments to the standard output under thecontrol of the format.The format is a character string which contains three types of objects:plain characters, which are simply copied to standard output, characterescape sequences, which are converted and copied to the standard output, andformat specifications, each of which causes printing of the next successiveargument.In addition to the standard printf(1) formats, `%b' causesprintf to expand backslash escape sequences in the correspondingargument, and `%q' causes printf to output thecorresponding argument in a format that can be reused as shell input.

The format is reused as necessary to consume all of the arguments.If the format requires more arguments than are supplied, theextra format specifications behave as if a zero value or null string, asappropriate, had been supplied. The return value is zero on success,non-zero on failure.

read

read [-ers] [-a aname] [-d delim] [-n nchars] [-p prompt] [-t timeout] [-u fd] [name ...]

One line is read from the standard input, or from the file descriptorfd supplied as an argument to the `-u' option, and the first wordis assigned to the first name, the second word to the second name,and so on, with leftover words and their intervening separators assignedto 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 variableare used to split the line into words.The backslash character `\' may be used to remove any specialmeaning for the next character read and for line continuation.If no names are supplied, the line read is assigned to thevariable REPLY.The return code is zero, unless end-of-file is encountered, readtimes out, or an invalid file descriptor is supplied as the argument to`-u'.Options, if supplied, have the following meanings:

-a aname: The words are assigned to sequential indices of the array variableaname, starting at 0.All elements are removed from aname before the assignment.Other name arguments are ignored.
-d delim: The first character of delim is used to terminate the input line,rather than newline.
-e: Readline (see section 8. Command Line Editing) is used to obtain the line.
-n nchars: read returns after reading nchars characters rather thanwaiting for a complete line of input.
-p prompt: Display prompt, without a trailing newline, before attemptingto read any input.The prompt is displayed only if input is coming from a terminal.
-r: If this option is given, backslash does not act as an escape character.The backslash is considered to be part of the line.In particular, a backslash-newline pair may not be used as a linecontinuation.
-s: Silent mode. If input is coming from a terminal, characters arenot echoed.
-t timeout: Cause read to time out and return failure if a complete line ofinput is not read within timeout seconds.This option has no effect if read is not reading input from theterminal or a pipe.
-u fd: Read input from file descriptor fd.

shopt

shopt [-pqsu] [-o] [optname ...]

Toggle the values of variables controlling optional shell behavior.With no options, or with the `-p' option, a list of all settableoptions is displayed, with an indication of whether or not each is set.The `-p' option causes output to be displayed in a form thatmay be reused as input.Other options have the following meanings:

-s: Enable (set) each optname.
-u: Disable (unset) each optname.
-q: Suppresses normal output; the return statusindicates whether the optname is set or unset.If multiple optname arguments are given with `-q',the return status is zero if all optnames are enabled;non-zero otherwise.
-o: Restricts the values ofoptname to be those defined for the `-o' option to theset builtin (see section 4.3 The Set Builtin).

If either `-s' or `-u'is used with no optname arguments, the display is limited tothose 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 optnamesare enabled, non-zero otherwise. When setting or unsetting options,the return status is zero unless an optname is not a valid shelloption.

The list of shopt options is:

cdable_vars: If this is set, an argument to the cdbuiltin command thatis not a directory is assumed to be the name of a variable whosevalue is the directory to change to.
cdspell: If set, minor errors in the spelling of a directory component in acd 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.
checkhash: If this is set, Bash checks that a command found in the hashtable exists before trying to execute it. If a hashed command nolonger exists, a normal path search is performed.
checkwinsize: If set, Bash checks the window size after each commandand, if necessary, updates the values ofLINES and COLUMNS.
cmdhist: If set, Bashattempts to save all lines of a multiple-linecommand in the same history entry. This allowseasy re-editing of multi-line commands.
dotglob: If set, Bash includes filenames beginning with a `.' inthe results of filename expansion.
execfail: If this is set, a non-interactive shell will not exit ifit cannot execute the file specified as an argument to the execbuiltin command. An interactive shell does not exit if execfails.
expand_aliases: If set, aliases are expanded as described below under Aliases,6.6 Aliases.This option is enabled by default for interactive shells.
extglob: If set, the extended pattern matching features described above(see section 3.5.8.1 Pattern Matching) are enabled.
histappend: If set, the history list is appended to the file named by the valueof the HISTFILEvariable when the shell exits, rather than overwriting the file.
histreedit: If set, and Readlineis being used, a user is given the opportunity to re-edit afailed history substitution.
histverify: If set, and Readlineis being used, the results of history substitution are not immediatelypassed to the shell parser. Instead, the resulting line is loaded intothe Readline editing buffer, allowing further modification.
hostcomplete: If set, and Readline is being used, Bash will attempt to performhostname completion when a word containing a `@' is beingcompleted (see section 8.4.6 Letting Readline Type For You). This option is enabledby default.
huponexit: If set, Bash will send SIGHUP to all jobs when an interactivelogin shell exits (see section 3.7.6 Signals).
interactive_comments: Allow a word beginning with `#'to cause that word and all remaining characters on thatline to be ignored in an interactive shell.This option is enabled by default.
lithist: If enabled, and the cmdhistoption is enabled, multi-line commands are saved to the history withembedded newlines rather than using semicolon separators where possible.
login_shell: The shell sets this option if it is started as a login shell(see section 6.1 Invoking Bash).The value may not be changed.
mailwarn: If set, and a file that Bash is checking for mail has beenaccessed since the last time it was checked, the message"The mail in mailfile has been read" is displayed.
no_empty_cmd_completion: If set, and Readline is being used, Bash will not attempt to searchthe PATH for possible completions when completion is attemptedon an empty line.
nocaseglob: If set, Bash matches filenames in a case-insensitive fashion whenperforming filename expansion.
nullglob: If set, Bash allows filename patterns which match nofiles to expand to a null string, rather than themselves.
progcomp: If set, the programmable completion facilities(see section 8.6 Programmable Completion) are enabled.This option is enabled by default.
promptvars: If set, prompt strings undergo variable and parameter expansion afterbeing expanded (see section 6.9 Controlling the Prompt).This option is enabled by default.
restricted_shell: The shell sets this option if it is started in restricted mode(see section 6.10 The Restricted Shell).The value may not be changed.This is not reset when the startup files are executed, allowingthe startup files to discover whether or not a shell is restricted.
shift_verbose: If this is set, the shiftbuiltin prints an error message when the shift count exceeds thenumber of positional parameters.
sourcepath: If set, the source builtin uses the value of PATHto find the directory containing the file supplied as an argument.This option is enabled by default.
xpg_echo: If set, the echo builtin expands backslash-escape sequencesby default.

The return status when listing options is zero if all optnamesare enabled, non-zero otherwise.When setting or unsetting options, the return status is zero unless anoptname is not a valid shell option.

source

source filename

A synonym for . (see section 4.1 Bourne Shell Builtins).

type

type [-afptP] [name ...]

For each name, indicate how it would be interpreted if used as acommand name.

If the `-t' option is used, type prints a single wordwhich 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, andtype returns a failure status.

If the `-p' option is used, type either returns the nameof 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 placesthat contain an executable named file.This includes aliases and functions, if and only if the `-p' optionis not also used.

If the `-f' option is used, type does not attempt to findshell functions, as with the command builtin.

The return status is zero if any of the names are found, non-zeroif none are found.

typeset

typeset [-afFrxi] [-p] [name[=value]]

The typeset command is supplied for compatibility with the Kornshell; however, it has been deprecated in favor of the declarebuiltin command.

ulimit

ulimit [-acdflmnpstuvSH] [limit]

ulimit provides control over the resources available to processesstarted by the shell, on systems that allow such control. If anoption is given, it is interpreted as follows:

-S: Change and report the soft limit associated with a resource.
-H: Change and report the hard limit associated with a resource.
-a: All current limits are reported.
-c: The maximum size of core files created.
-d: The maximum size of a process's data segment.
-f: The maximum size of files created by the shell.
-l: The maximum size that may be locked into memory.
-m: The maximum resident set size.
-n: The maximum number of open file descriptors.
-p: The pipe buffer size.
-s: The maximum stack size.
-t: The maximum amount of cpu time in seconds.
-u: The maximum number of processes available to a single user.
-v: The maximum amount of virtual memory available to the process.

If limit is given, it is the new value of the specified resource;the special limit values hard, soft, andunlimited stand for the current hard limit, the current soft limit,and no limit, respectively.Otherwise, the current value of the soft limit for the specified resourceis 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-byteincrements, except for `-t', which is in seconds, `-p',which is in units of 512-byte blocks, and `-n' and `-u', whichare unscaled values.

The return status is zero unless an invalid option or argument is supplied,or an error occurs while setting a new limit.

unalias

unalias [-a] [name ... ]

Remove each name from the list of aliases. If `-a' issupplied, all aliases are removed.Aliases are described in 6.6 Aliases.

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4.3 The Set Builtin

This builtin is so complicated that it deserves its own section.

set

set [--abefhkmnptuvxBCHP] [-o option] [argument ...]

If no options or arguments are supplied, set displays the namesand values of all shell variables and functions, sorted according to thecurrent locale, in a format that may be reused as input.

When options are supplied, they set or unset shell attributes.Options, if specified, have the following meanings:

-a

Mark variables and function which are modified or created for exportto the environment of subsequent commands.

-b

Cause the status of terminated background jobs to be reportedimmediately, rather than before printing the next primary prompt.

-e

Exit immediately if a simple command (see section 3.2.1 Simple Commands) exitswith a non-zero status, unless the command that fails is part of anuntil or while loop, part of an if statement,part of a && or || list, or if the command's returnstatus is being inverted using !.A trap on ERR, if set, is executed before the shell exits.

-f

Disable file name generation (globbing).

-h

Locate and remember (hash) commands as they are looked up for execution.This option is enabled by default.

-k

All arguments in the form of assignment statements are placedin the environment for a command, not just those that precedethe command name.

-m

Job control is enabled (see section 7. Job Control).

-n

Read commands but do not execute them; this may be used to check ascript for syntax errors.This option is ignored by interactive shells.

-o option-name

Set the option corresponding to option-name:

allexport: Same as -a.
braceexpand: Same as -B.
emacs: Use an emacs-style line editing interface (see section 8. Command Line Editing).
errexit: Same as -e.
hashall: Same as -h.
histexpand: Same as -H.
history: Enable command history, as described in 9.1 Bash History Facilities.This option is on by default in interactive shells.
ignoreeof: An interactive shell will not exit upon reading EOF.
keyword: Same as -k.
monitor: Same as -m.
noclobber: Same as -C.
noexec: Same as -n.
noglob: Same as -f.
nolog: Currently ignored.
notify: Same as -b.
nounset: Same as -u.
onecmd: Same as -t.
physical: Same as -P.
posix: Change the behavior of Bash where the default operation differsfrom the POSIX 1003.2 standard to match the standard(see section 6.11 Bash POSIX Mode).This is intended to make Bash behave as a strict superset of thatstandard.
privileged: Same as -p.
verbose: Same as -v.
vi: Use a vi-style line editing interface.
xtrace: Same as -x.

-p

Turn on privileged mode.In this mode, the $BASH_ENV and $ENV files are notprocessed, shell functions are not inherited from the environment,and the SHELLOPTS variable, if it appears in the environment,is ignored.If the shell is started with the effective user (group) id not equal to thereal user (group) id, and the -p option is not supplied, these actionsare 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 isnot reset.Turning this option off causes the effective userand group ids to be set to the real user and group ids.

-t

Exit after reading and executing one command.

-u

Treat unset variables as an error when performing parameter expansion.An error message will be written to the standard error, and a non-interactiveshell will exit.

-v

Print shell input lines as they are read.

-x

Print a trace of simple commands and their arguments after they areexpanded and before they are executed.

-B

The shell will perform brace expansion (see section 3.5.1 Brace Expansion).This option is on by default.

-C

Prevent output redirection using `>', `>&', and `<>'from overwriting existing files.

-H

Enable `!' style history substitution (see section 9.3 History Expansion).This option is on by default for interactive shells.

-P

If set, do not follow symbolic links when performing commands such ascd which change the current directory. The physical directoryis used instead. By default, Bash followsthe logical chain of directories when performing commandswhich 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

--

If no arguments follow this option, then the positional parameters areunset. Otherwise, the positional parameters are set to thearguments, even if some of them begin with a `-'.

-

Signal the end of options, cause all remaining argumentsto be assigned to the positional parameters. The `-x'and `-v' options are turned off.If there are no arguments, the positional parameters remain unchanged.

Using `+' rather than `-' causes these options to beturned off. The options can also be used upon invocation of theshell. The current set of options may be found in $-.

The remaining N arguments are positional parameters and areassigned, 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.

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4.4 Special Builtins

For historical reasons, the POSIX 1003.2 standard has classifiedseveral builtin commands as special.When Bash is executing in POSIX mode, the special builtinsdiffer from other builtin commands in three respects:

Special builtins are found before shell functions during command lookup.
If a special builtin returns an error status, a non-interactive shell exits.
Assignment statements preceding the command stay in effect in the shell environment after the command completes.

When Bash is not executing in POSIX mode, these builtins behave nodifferently than the rest of the Bash builtin commands.The Bash POSIX mode is described in 6.11 Bash POSIX Mode.

These are the POSIX special builtins:

break : . continue eval exec exit export readonly return set            shift trap unset

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5. Shell Variables

5.1 Bourne Shell Variables Variables which Bash uses in the same way as the Bourne Shell. 5.2 Bash Variables List of variables that exist in Bash.

This chapter describes the shell variables that Bash uses.Bash automatically assigns default values to a number of variables.

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5.1 Bourne Shell 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.

CDPATH: A colon-separated list of directories used as a search path forthe cd builtin command.
HOME: The current user's home directory; the default for the cd builtincommand.The value of this variable is also used by tilde expansion(see section 3.5.2 Tilde Expansion).
IFS: A list of characters that separate fields; used when the shell splitswords as part of expansion.
MAIL: If this parameter is set to a filename and the MAILPATH variableis not set, Bash informs the user of the arrival of mail inthe specified file.
MAILPATH: A colon-separated list of filenames which the shell periodically checksfor new mail.Each list entry can specify the message that is printed when new mailarrives in the mail file by separating the file name from the message witha `?'.When used in the text of the message, $_ expands to the name ofthe current mail file.
OPTARG: The value of the last option argument processed by the getopts builtin.
OPTIND: The index of the last option argument processed by the getopts builtin.
PATH: A colon-separated list of directories in which the shell looks forcommands.
PS1: The primary prompt string. The default value is `\s-\v\$ '.See section 6.9 Controlling the Prompt, for the complete list of escapesequences that are expanded before PS1 is displayed.
PS2: The secondary prompt string. The default value is `> '.

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5.2 Bash Variables

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

A few variables used by Bash are described in different chapters:variables for controlling the job control facilities(see section 7.3 Job Control Variables).

BASH

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

BASH_ENV

If this variable is set when Bash is invoked to execute a shellscript, its value is expanded and used as the name of a startup fileto read before executing the script. See section 6.2 Bash Startup Files.

BASH_VERSION

The version number of the current instance of Bash.

BASH_VERSINFO

A readonly array variable (see section 6.7 Arrays)whose members hold version information for this instance of Bash.The values assigned to the array members are as follows:

BASH_VERSINFO[0]: The major version number (the release).
BASH_VERSINFO[1]: The minor version number (the version).
BASH_VERSINFO[2]: The patch level.
BASH_VERSINFO[3]: The build version.
BASH_VERSINFO[4]: The release status (e.g., beta1).
BASH_VERSINFO[5]: The value of MACHTYPE.

COLUMNS

Used by the select builtin command to determine the terminal widthwhen printing selection lists. Automatically set upon receipt of aSIGWINCH.

COMP_CWORD

An index into ${COMP_WORDS} of the word containing the currentcursor position.This variable is available only in shell functions invoked by theprogrammable completion facilities (see section 8.6 Programmable Completion).

COMP_LINE

The current command line.This variable is available only in shell functions and externalcommands invoked by theprogrammable completion facilities (see section 8.6 Programmable Completion).

COMP_POINT

The index of the current cursor position relative to the beginning ofthe current command.If the current cursor position is at the end of the current command,the value of this variable is equal to ${#COMP_LINE}.This variable is available only in shell functions and externalcommands invoked by theprogrammable completion facilities (see section 8.6 Programmable Completion).

COMP_WORDS

An array variable consisting of the individualwords in the current command line.This variable is available only in shell functions invoked by theprogrammable completion facilities (see section 8.6 Programmable Completion).

COMPREPLY

An array variable from which Bash reads the possible completionsgenerated by a shell function invoked by the programmable completionfacility (see section 8.6 Programmable Completion).

DIRSTACK

An array variable containing the current contents of the directory stack.Directories appear in the stack in the order they are displayed by thedirs builtin.Assigning to members of this array variable may be used to modifydirectories already in the stack, but the pushd and popdbuiltins 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 ifit is subsequently reset.

EUID

The numeric effective user id of the current user. This variableis readonly.

FCEDIT

The editor used as a default by the `-e' option to the fcbuiltin command.

FIGNORE

A colon-separated list of suffixes to ignore when performingfilename completion.A file name whose suffix matches one of the entries inFIGNOREis excluded from the list of matched file names. A samplevalue is `.o:~'

FUNCNAME

The name of any currently-executing shell function.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 ifit is subsequently reset.

GLOBIGNORE

A colon-separated list of patterns defining the set of filenames tobe ignored by filename expansion.If a filename matched by a filename expansion pattern also matches oneof the patterns in GLOBIGNORE, it is removed from the listof matches.

GROUPS

An array variable containing the list of groups of which the currentuser is a member.Assignments to GROUPS have no effect and return an error status.If GROUPS is unset, it loses its special properties, even if it issubsequently reset.

histchars

Up to three characters which control history expansion, quicksubstitution, and tokenization (see section 9.3 History Expansion).The first character is thehistory expansion character, that is, the character which signifies thestart of a history expansion, normally `!'. The second character is thecharacter which signifies `quick substitution' when seen as the firstcharacter on a line, normally `^'. The optional third character is thecharacter which indicates that the remainder of the line is a comment whenfound as the first character of a word, usually `#'. The historycomment character causes history substitution to be skipped for theremaining words on the line. It does not necessarily cause the shellparser to treat the rest of the line as a comment.

HISTCMD

The history number, or index in the history list, of the currentcommand. If HISTCMD is unset, it loses its special properties,even if it is subsequently reset.

HISTCONTROL

A value of `ignorespace' means to not enter lines whichbegin with a space or tab into the history list.A value of `ignoredups' means to not enter lines which match the lastentered line.A value of `ignoreboth' combines the two options.Unset, or set to any other value than those above, means to saveall lines on the history list.The second and subsequent lines of a multi-line compound command arenot tested, and are added to the history regardless of the value ofHISTCONTROL.

HISTFILE

The name of the file to which the command history is saved. Thedefault value is `~/.bash_history'.

HISTFILESIZE

The maximum number of lines contained in the history file. When thisvariable is assigned a value, the history file is truncated, ifnecessary, to contain no more than that number of lines.The history file is also truncated to this size afterwriting it when an interactive shell exits.The default value is 500.

HISTIGNORE

A colon-separated list of patterns used to decide which commandlines should be saved on the history list. Each pattern isanchored at the beginning of the line and must match the completeline (no implicit `*' is appended). Each pattern is testedagainst the line after the checks specified by HISTCONTROLare applied. In addition to the normal shell pattern matchingcharacters, `&' matches the previous history line. `&'may be escaped using a backslash; the backslash is removedbefore attempting a match.The second and subsequent lines of a multi-line compound command arenot tested, and are added to the history regardless of the value ofHISTIGNORE.

HISTIGNORE subsumes the function of HISTCONTROL. Apattern of `&' is identical to ignoredups, and apattern of `[ ]*' is identical to ignorespace.Combining these two patterns, separating them with a colon,provides the functionality of ignoreboth.

HISTSIZE

The maximum number of commands to remember on the history list.The default value is 500.

HOSTFILE

Contains the name of a file in the same format as `/etc/hosts' thatshould be read when the shell needs to complete a hostname.The list of possible hostname completions may be changed while the shellis running;the next time hostname completion is attempted after thevalue is changed, Bash adds the contents of the new file to theexisting list.If HOSTFILE is set, but has no value, Bash attempts to read`/etc/hosts' to obtain the list of possible hostname completions.When HOSTFILE is unset, the hostname list is cleared.

HOSTNAME

The name of the current host.

HOSTTYPE

A string describing the machine Bash is running on.

IGNOREEOF

Controls the action of the shell on receipt of an EOF characteras the sole input. If set, the value denotes the numberof consecutive EOF characters that can be read as thefirst character on an input linebefore the shell will exit. If the variable exists but does nothave a numeric value (or has no value) then the default is 10.If the variable does not exist, then EOF signifies the end ofinput to the shell. This is only in effect for interactive shells.

INPUTRC

The name of the Readline initialization file, overriding the defaultof `~/.inputrc'.

LANG

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

LC_ALL

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

LC_COLLATE

This variable determines the collation order used when sorting theresults of filename expansion, anddetermines the behavior of range expressions, equivalence classes,and collating sequences within filename expansion and pattern matching(see section 3.5.8 Filename Expansion).

LC_CTYPE

This variable determines the interpretation of characters and thebehavior of character classes within filename expansion and patternmatching (see section 3.5.8 Filename Expansion).

LC_MESSAGES

This variable determines the locale used to translate double-quotedstrings preceded by a `$' (see section 3.1.2.5 Locale-Specific Translation).

LC_NUMERIC

This variable determines the locale category used for number formatting.

LINENO

The line number in the script or shell function currently executing.

LINES

Used by the select builtin command to determine the column lengthfor printing selection lists. Automatically set upon receipt of aSIGWINCH.

MACHTYPE

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

MAILCHECK

How often (in seconds) that the shell should check for mail in thefiles specified in the MAILPATH or MAIL variables.The default is 60 seconds. When it is time to checkfor mail, the shell does so before displaying the primary prompt.If this variable is unset, or set to a value that is not a numbergreater than or equal to zero, the shell disables mail checking.

OLDPWD

The previous working directory as set by the cd builtin.

OPTERR

If set to the value 1, Bash displays error messagesgenerated by the getopts builtin command.

OSTYPE

A string describing the operating system Bash is running on.

PIPESTATUS

An array variable (see section 6.7 Arrays)containing a list of exit status values from the processesin the most-recently-executed foreground pipeline (which maycontain only a single command).

POSIXLY_CORRECT

If this variable is in the environment when bash starts, the shellenters POSIX mode (see section 6.11 Bash POSIX Mode) before reading thestartup files, as if the `--posix' invocation option had been supplied.If it is set while the shell is running, bash enables POSIX mode,as if the command

set -o posix

had been executed.

PPID

The process ID of the shell's parent process. This variableis readonly.

PROMPT_COMMAND

If set, the value is interpreted as a command to executebefore the printing of each primary prompt ($PS1).

PS3

The value of this variable is used as the prompt for theselect command. If this variable is not set, theselect command prompts with `#? '

PS4

The value is the prompt printed before the command line is echoedwhen the `-x' option is set (see section 4.3 The Set Builtin).The first character of PS4 is replicated multiple times, asnecessary, to indicate multiple levels of indirection.The default is `+ '.

PWD

The current working directory as set by the cd builtin.

RANDOM

Each time this parameter is referenced, a random integerbetween 0 and 32767 is generated. Assigning a value to thisvariable seeds the random number generator.

REPLY

The default variable for the read builtin.

SECONDS

This variable expands to the number of seconds since theshell was started. Assignment to this variable resetsthe count to the value assigned, and the expanded valuebecomes the value assigned plus the number of secondssince the assignment.

SHELLOPTS

A colon-separated list of enabled shell options. Each word inthe list is a valid argument for the `-o' option to theset builtin command (see section 4.3 The Set Builtin).The options appearing in SHELLOPTS are those reportedas `on' by `set -o'.If this variable is in the environment when Bashstarts up, each shell option in the list will be enabled beforereading any startup files. This variable is readonly.

SHLVL

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

TIMEFORMAT

The value of this parameter is used as a format string specifyinghow the timing information for pipelines prefixed with the timereserved word should be displayed.The `%' character introduces anescape sequence that is expanded to a time value or otherinformation.The escape sequences and their meanings are asfollows; the braces denote optional portions.

%%: A literal `%'.
%[p][l]R: The elapsed time in seconds.
%[p][l]U: The number of CPU seconds spent in user mode.
%[p][l]S: The number of CPU seconds spent in system mode.
%P: The CPU percentage, computed as (%U + %S) / %R.

The optional p is a digit specifying the precision, the number offractional 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; valuesof 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, ofthe form MMmSS.FFs.The value of p determines whether or not the fraction is included.

If this variable is not set, Bash acts as if it had the value

$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'

If the value is null, no timing information is displayed.A trailing newline is added when the format string is displayed.

TMOUT

If set to a value greater than zero, TMOUT is treated as thedefault timeout for the read builtin (see section 4.2 Bash Builtin Commands).The select command (see section 3.2.5 Conditional Constructs) terminatesif input does not arrive after TMOUT seconds when input is comingfrom a terminal.

In an interative shell, the value is interpreted asthe number of seconds to wait for input after issuing the primaryprompt when the shell is interactive.Bash terminates after that number of seconds if input doesnot arrive.

UID

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

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6. Bash Features

This section describes features unique to Bash.

6.1 Invoking Bash Command line options that you can give to Bash. 6.2 Bash Startup Files When and how Bash executes scripts. 6.3 Interactive Shells What an interactive shell is. 6.4 Bash Conditional Expressions Primitives used in composing expressions for the test builtin. 6.5 Shell Arithmetic Arithmetic on shell variables. 6.6 Aliases Substituting one command for another. 6.7 Arrays Array Variables. 6.8 The Directory Stack History of visited directories. 6.9 Controlling the Prompt Controlling the PS1 string. 6.10 The Restricted Shell A more controlled mode of shell execution. 6.11 Bash POSIX Mode Making Bash behave more closely to what the POSIX standard specifies.

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6.1 Invoking 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 section 4.3 The Set Builtin), there are several multi-characteroptions that you can use. These options must appear on the commandline before the single-character options to be recognized.

--dump-po-strings: A list of all double-quoted strings preceded by `$'is printed on the standard ouputin the GNU gettext PO (portable object) file format.Equivalent to `-D' except for the output format.
--dump-strings: Equivalent to `-D'.
--help: Display a usage message on standard output and exit sucessfully.
--init-file filename
--rcfile filename: Execute commands from filename (instead of `~/.bashrc')in an interactive shell.
--login: Equivalent to `-l'.
--noediting: Do not use the GNU Readline library (see section 8. Command Line Editing)to read command lines when the shell is interactive.
--noprofile: Don't load the system-wide startup file `/etc/profile'or any of the personal initialization files`~/.bash_profile', `~/.bash_login', or `~/.profile'when Bash is invoked as a login shell.
--norc: Don't read the `~/.bashrc' initialization file in aninteractive shell. This is on by default if the shell isinvoked as sh.
--posix: Change the behavior of Bash where the default operation differsfrom the POSIX 1003.2 standard to match the standard. Thisis intended to make Bash behave as a strict superset of thatstandard. See section 6.11 Bash POSIX Mode, for a description of the BashPOSIX mode.
--restricted: Make the shell a restricted shell (see section 6.10 The Restricted Shell).
--verbose: Equivalent to `-v'. Print shell input lines as they're read.
--version: Show version information for this instance ofBash on the standard output and exit successfully.

There are several single-character options that may be supplied atinvocation which are not available with the set builtin.

-c string: Read and execute commands from string after processing theoptions, then exit. Any remaining arguments are assigned to thepositional parameters, starting with $0.
-i: Force the shell to run interactively. Interactive shells aredescribed in 6.3 Interactive Shells.
-l: Make this shell act as if it had been directly invoked by login.When the shell is interactive, this is equivalent to starting alogin shell with `exec -l bash'.When the shell is not interactive, the login shell startup files willbe executed.`exec bash -l' or `exec bash --login'will replace the current shell with a Bash login shell.See section 6.2 Bash Startup Files, for a description of the special behaviorof a login shell.
-r: Make the shell a restricted shell (see section 6.10 The Restricted Shell).
-s: If this option is present, or if no arguments remain after optionprocessing, then commands are read from the standard input.This option allows the positional parameters to be setwhen invoking an interactive shell.
-D: A list of all double-quoted strings preceded by `$'is printed on the standard ouput.These are the strings thatare subject to language translation when the current localeis not C or POSIX (see section 3.1.2.5 Locale-Specific Translation).This implies the `-n' option; no commands will be executed.
[-+]O [shopt_option]: shopt_option is one of the shell options accepted by theshopt builtin (see section 4. Shell Builtin Commands).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 shelloptions accepted by shopt are printed on the standard output.If the invocation option is `+O', the output is displayed in a formatthat may be reused as input.
--: A -- signals the end of options and disables further optionprocessing.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 bothconnected to terminals (as determined by isatty(3)), or onestarted with the `-i' option. See section 6.3 Interactive Shells, for moreinformation.

If arguments remain after option processing, and neither the`-c' nor the `-s'option has been supplied, the first argument is assumed tobe the name of a file containing shell commands (see section 3.8 Shell Scripts).When Bash is invoked in this fashion, $0is set to the name of the file, and the positional parametersare 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 executedin the script. If no commands are executed, the exit status is 0.

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6.2 Bash Startup Files

This section describs how Bash executes its startup files.If any of the files exist but cannot be read, Bash reports an error.Tildes are expanded in file names as described above underTilde Expansion (see section 3.5.2 Tilde Expansion).

Interactive shells are described in 6.3 Interactive Shells.

Invoked as an interactive login shell, or with `--login'

When Bash is invoked as an interactive login shell, or as anon-interactive shell with the `--login' option, it first reads andexecutes 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 readsand executes commands from the first one that exists and is readable.The `--noprofile' option may be used when the shell is started toinhibit this behavior.

When a login shell exits, Bash reads and executes commands fromthe file `~/.bash_logout', if it exists.

Invoked as an interactive non-login shell

When an interactive shell that is not a login shell is started, Bashreads 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 andexecute commands from file instead of `~/.bashrc'.

So, typically, your `~/.bash_profile' contains the line

if [ -f ~/.bashrc ]; then . ~/.bashrc; fi

after (or before) any login-specific initializations.

Invoked non-interactively

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 asthe name of a file to read and execute. Bash behaves as if thefollowing command were executed:

if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi

but the value of the PATH variable is not used to search for thefile name.

As noted above, if a non-interactive shell is invoked with the`--login' option, Bash attempts to read and execute commands from thelogin shell startup files.

Invoked with name `sh`

If Bash is invoked with the name sh, it tries to mimic thestartup behavior of historical versions of sh as closely aspossible, while conforming to the POSIX standard as well.

When invoked as an interactive login shell, or as a non-interactiveshell with the `--login' option, it first attempts to readand execute commands from `/etc/profile' and `~/.profile', inthat order.The `--noprofile' option may be used to inhibit this behavior.When invoked as an interactive shell with the name sh, Bashlooks 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 executecommands from any other startup files, the `--rcfile' option hasno effect.A non-interactive shell invoked with the name sh does not attemptto read any other startup files.

When invoked as sh, Bash enters POSIX mode afterthe startup files are read.

Invoked in POSIX mode

When Bash is started in POSIX mode, as with the`--posix' command line option, it follows the POSIX standardfor startup files.In this mode, interactive shells expand the ENV variableand commands are read and executed from the file whose name is theexpanded value.No other startup files are read.

Invoked by remote shell daemon

Bash attempts to determine when it is being run by the remote shelldaemon, usually rshd. If Bash determines it is being run byrshd, it reads and executes commands from `~/.bashrc', if thatfile 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, butrshd does not generally invoke the shell with those options orallow them to be specified.

Invoked with unequal effective and real UID/GIDs

If Bash is started with the effective user (group) id not equal to thereal user (group) id, and the -p option is not supplied, no startupfiles are read, shell functions are not inherited from the environment,the SHELLOPTS variable, if it appears in the environment, is ignored,and the effective user id is set to the real user id.If the -p option is supplied at invocation, the startup behavior isthe same, but the effective user id is not reset.

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6.3 Interactive Shells

6.3.1 What is an Interactive Shell? What determines whether a shell is Interactive. 6.3.2 Is this Shell Interactive? How to tell if a shell is interactive. 6.3.3 Interactive Shell Behavior What changes in a interactive shell?

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6.3.1 What is an Interactive Shell?

An interactive shellis one started without non-option arguments, unless `-s' isspecified, without specifiying the `-c' option, andwhose input and output are bothconnected 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'sterminal.

The `-s' invocation option may be used to set the positional parameterswhen an interactive shell is started.

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6.3.2 Is this Shell Interactive?

To determine within a startup script whether or not Bash isrunning 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 variablePS1; it is unset in non-interactive shells, and set ininteractive shells. Thus:

if [ -z "$PS1" ]; then            echo This shell is not interactive            else            echo This shell is interactive            fi

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6.3.3 Interactive Shell Behavior

When the shell is running interactively, it changes its behavior inseveral ways.

Startup files are read and executed as described in 6.2 Bash Startup Files.
Job Control (see section 7. Job Control) is enabled by default. When job control is in effect, Bash ignores the keyboard-generated job control signals SIGTTIN, SIGTTOU, and SIGTSTP.
Bash expands and displays PS1 before reading the first line of a command, and expands and displays PS2 before reading the second and subsequent lines of a multi-line command.
Bash executes the value of the PROMPT_COMMAND variable as a command before printing the primary prompt, $PS1 (see section 5.2 Bash Variables).
Readline (see section 8. Command Line Editing) is used to read commands from the user's terminal.
Bash inspects the value of the ignoreeof option to set -o instead of exiting immediately when it receives an EOF on its standard input when reading a command (see section 4.3 The Set Builtin).
Command history (see section 9.1 Bash History Facilities) and history expansion (see section 9.3 History Expansion) are enabled by default. Bash will save the command history to the file named by $HISTFILE when an interactive shell exits.
Alias expansion (see section 6.6 Aliases) is performed by default.
In the absence of any traps, Bash ignores SIGTERM (see section 3.7.6 Signals).
In the absence of any traps, SIGINT is caught and handled ((see section 3.7.6 Signals). SIGINT will interrupt some shell builtins.
An interactive login shell sends a SIGHUP to all jobs on exit if the hupoxexit shell option has been enabled (see section 3.7.6 Signals).
The `-n' invocation option is ignored, and `set -n' has no effect (see section 4.3 The Set Builtin).
Bash will check for mail periodically, depending on the values of the MAIL, MAILPATH, and MAILCHECK shell variables (see section 5.2 Bash Variables).
Expansion errors due to references to unbound shell variables after `set -u' has been enabled will not cause the shell to exit (see section 4.3 The Set Builtin).
The shell will not exit on expansion errors caused by var being unset or null in ${var:?word} expansions (see section 3.5.3 Shell Parameter Expansion).
Redirection errors encountered by shell builtins will not cause the shell to exit.
When running in POSIX mode, a special builtin returning an error status will not cause the shell to exit (see section 6.11 Bash POSIX Mode).
A failed exec will not cause the shell to exit (see section 4.1 Bourne Shell Builtins).
Parser syntax errors will not cause the shell to exit.
Simple spelling correction for directory arguments to the cd builtin is enabled by default (see the description of the cdspell option to the shopt builtin in 4.2 Bash Builtin Commands).
The shell will check the value of the TMOUT variable and exit if a command is not read within the specified number of seconds after printing $PS1 (see section 5.2 Bash Variables).

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6.4 Bash Conditional Expressions

Conditional expressions are used by the [[ compound commandand 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', filedescriptor 0, 1, or 2, respectively, is checked.

-a file: True if file exists.
-b file: True if file exists and is a block special file.
-c file: True if file exists and is a character special file.
-d file: True if file exists and is a directory.
-e file: True if file exists.
-f file: True if file exists and is a regular file.
-g file: True if file exists and its set-group-id bit is set.
-h file: True if file exists and is a symbolic link.
-k file: True if file exists and its "sticky" bit is set.
-p file: True if file exists and is a named pipe (FIFO).
-r file: True if file exists and is readable.
-s file: True if file exists and has a size greater than zero.
-t fd: True if file descriptor fd is open and refers to a terminal.
-u file: True if file exists and its set-user-id bit is set.
-w file: True if file exists and is writable.
-x file: True if file exists and is executable.
-O file: True if file exists and is owned by the effective user id.
-G file: True if file exists and is owned by the effective group id.
-L file: True if file exists and is a symbolic link.
-S file: True if file exists and is a socket.
-N file: True if file exists and has been modified since it was last read.
file1 -nt file2: True if file1 is newer (according to modification date)than file2, or if file1 exists and file2 does not.
file1 -ot file2: True if file1 is older than file2,or if file2 exists and file1 does not.
file1 -ef file2: True if file1 and file2 refer to the same device andinode numbers.
-o optname: True if shell option optname is enabled.The list of options appears in the description of the `-o'option to the set builtin (see section 4.3 The Set Builtin).
-z string: True if the length of string is zero.
-n string
string: True if the length of string is non-zero.
string1 == string2: True if the strings are equal.`=' may be used in place of `==' for strict POSIX compliance.
string1 != string2: True if the strings are not equal.
string1 < string2: True if string1 sorts before string2 lexicographicallyin the current locale.
string1 > string2: True if string1 sorts after string2 lexicographicallyin the current locale.
arg1 OP arg2: OP is one of`-eq', `-ne', `-lt', `-le', `-gt', or `-ge'.These arithmetic binary operators return true if arg1is equal to, not equal to, less than, less than or equal to,greater than, or greater than or equal to arg2,respectively. Arg1 and arg2may be positive or negative integers.

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6.5 Shell Arithmetic

The shell allows arithmetic expressions to be evaluated, as one ofthe shell expansions or by the let builtin.

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 and associativity are the sameas in the C language.The following list of operators is grouped into levels ofequal-precedence operators.The levels are listed in order of decreasing precedence.

id++ id--: variable post-increment and post-decrement
++id --id: variable pre-increment and pre-decrement
- +: unary minus and plus
! ~: logical and bitwise negation
**: exponentiation
* / %: multiplication, division, remainder
+ -: addition, subtraction
<< >>: left and right bitwise shifts
<= >= < >: comparison
== !=: equality and inequality
&: bitwise AND
^: bitwise exclusive OR
|: bitwise OR
&&: logical AND
||: logical OR
expr ? expr : expr: conditional evaluation
= *= /= %= += -= <<= >>= &= ^= |=: assignment
expr1 , expr2: comma

Shell variables are allowed as operands; parameter expansion isperformed before the expression is evaluated.Within an expression, shell variables may also be referenced by namewithout using the parameter expansion syntax.The value of a variable is evaluated as an arithmetic expressionwhen it is referenced.A shell variable need not have its integer attribute turned onto 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 baseis a decimal number between 2 and 64 representing the arithmeticbase, and n is a number in that base. If base# isomitted, 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 uppercaseletters may be used interchangably to represent numbers between 10and 35.

Operators are evaluated in order of precedence. Sub-expressions inparentheses are evaluated first and may override the precedencerules above.

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6.6 Aliases

Aliases allow a string to be substituted for a word when it is usedas the first word of a simple command.The shell maintains a list of aliases that may be set and unset withthe alias and unalias builtin commands.

The first word of each simple command, if unquoted, is checked to seeif it has an alias.If so, that word is replaced by the text of the alias.The alias name and the replacement text may contain any validshell input, including shell metacharacters, with the exceptionthat the alias name may not contain `='.The first word of the replacement text is tested foraliases, but a word that is identical to an alias being expandedis not expanded a second time. This means that one may aliasls to "ls -F",for instance, and Bash does not try to recursively expand thereplacement text. If the last character of the alias value is aspace or tab character, then the next command word following thealias is also checked for alias expansion.

Aliases are created and listed with the aliascommand, and removed with the unalias command.

There is no mechanism for using arguments in the replacement text,as in csh.If arguments are needed, a shell function should be used(see section 3.3 Shell Functions).

Aliases are not expanded when the shell is not interactive,unless the expand_aliases shell option is set usingshopt (see section 4.2 Bash Builtin Commands).

The rules concerning the definition and use of aliases aresomewhat confusing. Bashalways reads at least one complete lineof input before executing anyof the commands on that line. Aliases are expanded when acommand is read, not when it is executed. Therefore, analias definition appearing on the same line as anothercommand does not take effect until the next line of input is read.The commands following the alias definitionon 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 definitionis itself a compound command. As a consequence, aliasesdefined in a function are not available until after thatfunction is executed. To be safe, always putalias definitions on a separate line, and do not use aliasin compound commands.

For almost every purpose, shell functions are preferred over aliases.

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6.7 Arrays

Bash provides one-dimensional array variables. Any variable may be used asan array; the declare builtin will explicitly declare an array.There is no maximumlimit on the size of an array, nor any requirement that membersbe indexed or assigned contiguously. Arrays are zero-based.

An array is created automatically if any variable is assigned to usingthe syntax

name[subscript]=value

The subscriptis treated as an arithmetic expression that must evaluate to a numbergreater than or equal to zero. To explicitly declare an array, use

declare -a name

The syntax

declare -a name[subscript]

is also accepted; the subscript is ignored. Attributes may bespecified for an array variable using the declare andreadonly builtins. Each attribute applies to all members ofan array.

Arrays are assigned to using compound assignments of the form

name=(value1 ... valuen)

where eachvalue is of the form [[subscript]=]string. Ifthe optional subscript is supplied, that index is assigned to;otherwise the index of the element assigned is the last index assignedto by the statement plus one. Indexing starts at zero.This syntax is also accepted by the declarebuiltin. Individual array elements may be assigned to using thename[subscript]=value syntax introduced above.

Any element of an array may be referenced using${name[subscript]}.The braces are required to avoidconflicts with the shell's filename expansion operators. If thesubscript is `@' or `*', the word expands to all membersof the array name. These subscripts differ only when the wordappears within double quotes. If the word is double-quoted,${name[*]} expands to a single word withthe value of each array member separated by the first character of theIFS variable, and ${name[@]} expands each element ofname to a separate word. When there are no array members,${name[@]} expands to nothing. This is analogous to theexpansion 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 toreferencing element zero.

The unset builtin is used to destroy arrays.unset name[subscript]destroys the array element at index subscript.unset name, where name is an array, removes theentire array. A subscript of `*' or `@' also removes theentire array.

The declare, local, and readonlybuiltins each accept a `-a'option to specify an array. The readbuiltin accepts a `-a'option to assign a list of words read from the standard inputto an array, and can read values from the standard input intoindividual array elements. The set and declarebuiltins display array values in a way that allows them to bereused as input.

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6.8 The Directory Stack

6.8.1 Directory Stack Builtins Bash builtin commands to manipulate the directory stack.

The directory stack is a list of recently-visited directories. Thepushd builtin adds directories to the stack as it changesthe current directory, and the popd builtin removes specifieddirectories from the stack and changes the current directory tothe directory removed. The dirs builtin displays the contentsof the directory stack.

The contents of the directory stack are also visibleas the value of the DIRSTACK shell variable.

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6.8.1 Directory Stack Builtins

dirs

dirs [+N | -N] [-clpv]

Display the list of currently remembered directories. Directoriesare added to the list with the pushd command; thepopd command removes directories from the list.

+N: Displays the Nth directory (counting from the left of thelist printed by dirs when invoked without options), startingwith zero.
-N: Displays the Nth directory (counting from the right of thelist printed by dirs when invoked without options), startingwith zero.
-c: Clears the directory stack by deleting all of the elements.
-l: Produces a longer listing; the default listing format uses atilde to denote the home directory.
-p: Causes dirs to print the directory stack with one entry perline.
-v: Causes dirs to print the directory stack with one entry perline, prefixing each entry with its index in the stack.

popd

popd [+N | -N] [-n]

Remove the top entry from the directory stack, and cdto the new top directory.When no arguments are given, popdremoves the top directory from the stack andperforms a cd to the new top directory. Theelements are numbered from 0 starting at the first directory listed withdirs; i.e., popd is equivalent to popd +0.

+N: Removes the Nth directory (counting from the left of thelist printed by dirs), starting with zero.
-N: Removes the Nth directory (counting from the right of thelist printed by dirs), starting with zero.
-n: Suppresses the normal change of directory when removing directoriesfrom the stack, so that only the stack is manipulated.

pushd

pushd [dir | +N | -N] [-n]

Save the current directory on the top of the directory stackand then cd to dir.With no arguments, pushd exchanges the top two directories.

+N: Brings the Nth directory (counting from the left of thelist printed by dirs, starting with zero) to the top ofthe list by rotating the stack.
-N: Brings the Nth directory (counting from the right of thelist printed by dirs, starting with zero) to the top ofthe list by rotating the stack.
-n: Suppresses the normal change of directory when adding directoriesto the stack, so that only the stack is manipulated.
dir: Makes the current working directory be the top of the stack, and thenexecutes the equivalent of `cd dir'.cds to dir.

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6.9 Controlling the Prompt

The value of the variable PROMPT_COMMAND is examined just beforeBash prints each primary prompt. If PROMPT_COMMAND is set andhas a non-null value, then thevalue is executed just as if it had been typed on the command line.

In addition, the following table describes the special characters whichcan appear in the prompt variables:

\a: A bell character.
\d: The date, in "Weekday Month Date" format (e.g., "Tue May 26").
\D{format}: The format is passed to strftime(3) and the result is insertedinto the prompt string; an empty format results in a locale-specifictime representation. The braces are required.
\e: An escape character.
\h: The hostname, up to the first `.'.
\H: The hostname.
\j: The number of jobs currently managed by the shell.
\l: The basename of the shell's terminal device name.
\n: A newline.
\r: A carriage return.
\s: The name of the shell, the basename of $0 (the portionfollowing the final slash).
\t: The time, in 24-hour HH:MM:SS format.
\T: The time, in 12-hour HH:MM:SS format.
\@: The time, in 12-hour am/pm format.
\A: The time, in 24-hour HH:MM format.
\u: The username of the current user.
\v: The version of Bash (e.g., 2.00)
\V: The release of Bash, version + patchlevel (e.g., 2.00.0)
\w: The current working directory.
\W: The basename of $PWD.
\!: The history number of this command.
\#: The command number of this command.
\$: If the effective uid is 0, #, otherwise $.
\nnn: The character whose ASCII code is the octal value nnn.
\\: A backslash.
\[: Begin a sequence of non-printing characters. This could be used toembed a terminal control sequence into the prompt.
\]: End a sequence of non-printing characters.

The command number and the history number are usually different:the history number of a command is its position in the historylist, which may include commands restored from the history file(see section 9.1 Bash History Facilities), while the command number isthe position in the sequence of commands executed during the currentshell session.

After the string is decoded, it is expanded viaparameter expansion, command substitution, arithmeticexpansion, and quote removal, subject to the value of thepromptvars shell option (see section 4.2 Bash Builtin Commands).

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6.10 The Restricted Shell

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 toset up an environment more controlled than the standard shell.A restricted shell behaves identically to bashwith the exception that the following are disallowed or not performed:

Changing directories with the cd builtin.
Setting or unsetting the values of the SHELL, PATH, ENV, or BASH_ENV variables.
Specifying command names containing slashes.
Specifying a filename containing a slash as an argument to the . builtin command.
Specifying a filename containing a slash as an argument to the `-p' option to the hash builtin command.
Importing function definitions from the shell environment at startup.
Parsing the value of SHELLOPTS from the shell environment at startup.
Redirecting output using the `>', `>|', `<>', `>&', `&>', and `>>' redirection operators.
Using the exec builtin to replace the shell with another command.
Adding or deleting builtin commands with the `-f' and `-d' options to the enable builtin.
Using the enable builtin command to enable disabled shell builtins.
Specifying the `-p' option to the command builtin.
Turning off restricted mode with `set +r' or `set +o restricted'.

These restrictions are enforced after any startup files are read.

When a command that is found to be a shell script is executed(see section 3.8 Shell Scripts), rbash turns off any restrictions inthe shell spawned to execute the script.

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6.11 Bash POSIX Mode

Starting Bash with the `--posix' command-line option or executing`set -o posix' while Bash is running will cause Bash to conform moreclosely to the POSIX 1003.2 standard by changing the behavior tomatch that specified by POSIX in areas where the Bash default differs.

When invoked as sh, Bash enters POSIX mode after reading thestartup files.

The following list is what's changed when `POSIX mode' is in effect:

When a command in the hash table no longer exists, Bash will re-search $PATH to find the new location. This is also available with `shopt -s checkhash'.
The message printed by the job control code and builtins when a job exits with a non-zero status is `Done(status)'.
The message printed by the job control code and builtins when a job is stopped is `Stopped(signame)', where signame is, for example, SIGTSTP.
Reserved words may not be aliased.
The POSIX 1003.2 PS1 and PS2 expansions of `!' to the history number and `!!' to `!' are enabled, and parameter expansion is performed on the values of PS1 and PS2 regardless of the setting of the promptvars option.
Interactive comments are enabled by default. (Bash has them on by default anyway.)
The POSIX 1003.2 startup files are executed ($ENV) rather than the normal Bash files.
Tilde expansion is only performed on assignments preceding a command name, rather than on all assignment statements on the line.
The default history file is `~/.sh_history' (this is the default value of $HISTFILE).
The output of `kill -l' prints all the signal names on a single line, separated by spaces.
Non-interactive shells exit if filename in . filename is not found.
Non-interactive shells exit if a syntax error in an arithmetic expansion results in an invalid expression.
Redirection operators do not perform filename expansion on the word in the redirection unless the shell is interactive.
Redirection operators do not perform word splitting on the word in the redirection.
Function names must be valid shell 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.
POSIX 1003.2 `special' builtins are found before shell functions during command lookup.
If a POSIX 1003.2 special builtin returns an error status, a non-interactive shell exits. The fatal errors are those listed in the POSIX.2 standard, and include things like passing incorrect options, redirection errors, variable assignment errors for assignments preceding the command name, and so on.
If the cd builtin finds a directory to change to using $CDPATH, the value it assigns to the PWD variable does not contain any symbolic links, as if `cd -P' had been executed.
If CDPATH is set, the 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.
A non-interactive shell exits with an error status if a variable assignment error occurs when no command name follows the assignment statements. A variable assignment error occurs, for example, when trying to assign a value to a readonly variable.
A non-interactive shell exits with an error status if the iteration variable in a for statement or the selection variable in a select statement is a readonly variable.
Process substitution is not available.
Assignment statements preceding POSIX 1003.2 special builtins persist in the shell environment after the builtin completes.
Assignment statements preceding shell function calls persist in the shell environment after the function returns, as if a POSIX special builtin command had been executed.
The export and readonly builtin commands display their output in the format required by POSIX 1003.2.
The trap builtin displays signal names without the leading SIG.
The . and source builtins do not search the current directory for the filename argument if it is not found by searching PATH.
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.
Alias expansion is always enabled, even in non-interactive shells.
When the set builtin is invoked without options, it does not display shell function names and definitions.
When the set builtin is invoked without options, it displays variable values without quotes, unless they contain shell metacharacters, even if the result contains nonprinting characters.
When the 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.

There is other POSIX 1003.2 behavior that Bash does not implement.Specifically:

Assignment statements affect the execution environment of all builtins, not just special ones.
When a subshell is created to execute a shell script with execute permission, but without a leading `#!', Bash sets $0 to the full pathname of the script as found by searching $PATH, rather than the command as typed by the user.
When using `.' to source a shell script found in $PATH, bash checks execute permission bits rather than read permission bits, just as if it were searching for a command.

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7. Job Control

This chapter discusses what job control is, how it works, and howBash allows you to access its facilities.

7.1 Job Control Basics How job control works. 7.2 Job Control Builtins Bash builtin commands used to interact with job control. 7.3 Job Control Variables Variables Bash uses to customize job control.

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7.1 Job Control Basics

Job controlrefers to the ability to selectively stop (suspend)the execution of processes and continue (resume)their execution at a later point. A user typically employsthis facility via an interactive interface supplied jointlyby the system's terminal driver and Bash.

The shell associates a job with each pipeline. It keeps atable of currently executing jobs, which may be listed with thejobs command. When Bash starts a jobasynchronously, it prints a line that lookslike:

[1] 25647

indicating that this job is job number 1 and that the process IDof the last process in the pipeline associated with this job is25647. All of the processes in a single pipeline are members ofthe same job. Bash uses the job abstraction as thebasis for job control.

To facilitate the implementation of the user interface to jobcontrol, the operating system maintains the notion of a current terminalprocess group ID. Members of this process group (processes whoseprocess group ID is equal to the current terminal process groupID) receive keyboard-generated signals such as SIGINT.These processes are said to be in the foreground. Backgroundprocesses are those whose process group ID differs from theterminal's; such processes are immune to keyboard-generatedsignals. Only foreground processes are allowed to read from orwrite to the terminal. Background processes which attempt toread from (write to) the terminal are sent a SIGTTIN(SIGTTOU) signal by the terminal driver, which, unlesscaught, suspends the process.

If the operating system on which Bash is running supportsjob control, Bash contains facilities to use it. Typing thesuspend character (typically `^Z', Control-Z) while aprocess is running causes that process to be stopped and returnscontrol to Bash. Typing the delayed suspend character(typically `^Y', Control-Y) causes the process to be stoppedwhen it attempts to read input from the terminal, and control tobe returned to Bash. The user then manipulates the state ofthis job, using the bg command to continue it in thebackground, the fg command to continue it in theforeground, or the kill command to kill it. A `^Z'takes effect immediately, and has the additional side effect ofcausing pending output and typeahead to be discarded.

There are a number of ways to refer to a job in the shell. Thecharacter `%' introduces a job name.

Job number n may be referred to as `%n'.The symbols `%%' and`%+' refer to the shell's notion of the current job, whichis the last job stopped while it was in the foreground or startedin the background. Theprevious job may be referenced using `%-'. In outputpertaining to jobs (e.g., the output of the jobs command),the current job is always flagged with a `+', and theprevious job with a `-'.

A job may also be referred tousing a prefix of the name used to start it, or using a substringthat appears in its command line. For example, `%ce' refersto a stopped ce job. Using `%?ce', on theother hand, refers to any job containing the string `ce' inits 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 thebackground into the foreground. Similarly, `%1 &' resumesjob 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 promptbefore reporting changes in a job's status so as to not interruptany other output.If the `-b' option to the set builtin is enabled,Bash reports such changes immediately (see section 4.3 The Set Builtin).Any trap on SIGCHLD is executed for each child processthat exits.

If an attempt to exit Bash is while jobs are stopped, theshell prints a message warning that there are stopped jobs.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 the stopped jobs are terminated.

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7.2 Job Control Builtins

bg

bg [jobspec]

Resume the suspended job jobspec in the background, as if ithad 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 notenabled, or, when run with job control enabled, if jobspec wasnot found or jobspec specifies a job that was started withoutjob control.

fg

fg [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 withjob control enabled, jobspec does not specify a valid job orjobspec specifies a job that was started without job control.

jobs

jobs [-lnprs] [jobspec]            jobs -x command [arguments]

The first form lists the active jobs. The options have thefollowing meanings:

-l: List process IDs in addition to the normal information.
-n: Display information only about jobs that have changed status sincethe user was last notified of their status.
-p: List only the process ID of the job's process group leader.
-r: Restrict output to running jobs.
-s: Restrict output to stopped jobs.

If jobspec is given,output is restricted to information about that job.If jobspec is not supplied, the status of all jobs islisted.

If the `-x' option is supplied, jobs replaces anyjobspec found in command or arguments with thecorresponding process group ID, and executes command,passing it arguments, returning its exit status.

kill

kill [-s sigspec] [-n signum] [-sigspec] jobspec or pid            kill -l [exit_status]

Send a signal specified by sigspec or signum to the processnamed by job specification jobspec or process ID pid.sigspec is either a signal name such as SIGINT (with or withoutthe 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 thesignals corresponding to the arguments are listed, and the return statusis zero.exit_status is a number specifying a signal number or the exitstatus 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.

wait

wait [jobspec or pid]

Wait until the child process specified by process ID pid or jobspecification jobspec exits and return the exit status of the lastcommand 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 arewaited for, and the return status is zero.If neither jobspec nor pid specifies an active child processof the shell, the return status is 127.

disown

disown [-ar] [-h] [jobspec ...]

Without options, each jobspec is removed from the table ofactive 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 shellreceives 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 ormark all jobs; the `-r' option without a jobspecargument restricts operation to running jobs.

suspend

suspend [-f]

Suspend the execution of this shell until it receives aSIGCONT signal. The `-f' option means to suspendeven if the shell is a login shell.

When job control is not active, the kill and waitbuiltins do not accept jobspec arguments. They must besupplied process IDs.

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7.3 Job Control Variables

auto_resume: This variable controls how the shell interacts with the user andjob control. If this variable exists then single word simplecommands without redirections are treated as candidates for resumptionof an existing job. There is no ambiguity allowed; if there ismore than one job beginning with the string typed, thenthe most recently accessed job will be selected.The name of a stopped job, in this context, is the command lineused to start it. If this variable is set to the value `exact',the string supplied must match the name of a stopped job exactly;if set to `substring',the string supplied needs to match a substring of the name of astopped job. The `substring' value provides functionalityanalogous to the `%?' job ID (see section 7.1 Job Control Basics).If set to any other value, the supplied string mustbe a prefix of a stopped job's name; this provides functionalityanalogous to the `%' job ID.

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8. Command Line Editing

This chapter describes the basic features of the GNUcommand line editing interface.Command line editing is provided by the Readline library, which isused by several different programs, including Bash.

8.1 Introduction to Line Editing Notation used in this text. 8.2 Readline Interaction The minimum set of commands for editing a line. 8.3 Readline Init File Customizing Readline from a user's view. 8.4 Bindable Readline Commands A description of most of the Readline commands available for binding 8.5 Readline vi Mode A short description of how to make Readline behave like the vi editor. 8.6 Programmable Completion How to specify the possible completions for a specific command. 8.7 Programmable Completion Builtins Builtin commands to specify how to complete arguments for a particular command.

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8.1 Introduction to Line Editing

The following paragraphs describe the notation used to representkeystrokes.

The text C-k is read as `Control-K' and describes the characterproduced when the k key is pressed while the Control keyis depressed.

The text M-k is read as `Meta-K' and describes the characterproduced when the Meta key (if you have one) is depressed, and the kkey is pressed.The Meta key is labeled ALT on many keyboards.On keyboards with two keys labeled ALT (usually to either side ofthe space bar), the ALT on the left side is generally set towork as a Meta key.The ALT key on the right may also be configured to work as aMeta key or may be configured as some other modifier, such as aCompose key for typing accented characters.

If you do not have a Meta or ALT key, or another key working asa Meta key, the identical keystroke can be generated by typing ESCfirst, 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 thecharacter produced by metafying C-k.

In addition, several keys have their own names. Specifically,DEL, ESC, LFD, SPC, RET, and TAB allstand for themselves when seen in this text, or in an init file(see section 8.3 Readline Init File).If your keyboard lacks a LFD key, typing C-j willproduce the desired character.The RET key may be labeled Return or Enter onsome keyboards.

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8.2 Readline Interaction

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. TheReadline library gives you a set of commands for manipulating the textas you type it in, allowing you to just fix your typo, and not forcingyou to retype the majority of the line. Using these editing commands,you move the cursor to the place that needs correction, and delete orinsert the text of the corrections. Then, when you are satisfied withthe line, you simply press RET. You do not have to be at theend of the line to press RET; the entire line is acceptedregardless of the location of the cursor within the line.

8.2.1 Readline Bare Essentials The least you need to know about Readline. 8.2.2 Readline Movement Commands Moving about the input line. 8.2.3 Readline Killing Commands How to delete text, and how to get it back! 8.2.4 Readline Arguments Giving numeric arguments to commands. 8.2.5 Searching for Commands in the History Searching through previous lines.

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8.2.1 Readline Bare Essentials

In order to enter characters into the line, simply type them. The typedcharacter appears where the cursor was, and then the cursor moves onespace to the right. If you mistype a character, you can use yourerase character to back up and delete the mistyped character.

Sometimes you may mistype a character, andnot notice the error until you have typed several other characters. Inthat case, you can type C-b to move the cursor to the left, and thencorrect your mistake. Afterwards, you can move the cursor to the rightwith C-f.

When you add text in the middle of a line, you will notice that charactersto the right of the cursor are `pushed over' to make room for the textthat you have inserted. Likewise, when you delete text behind the cursor,characters to the right of the cursor are `pulled back' to fill in theblank space created by the removal of the text. A list of the bareessentials for editing the text of an input line follows.

C-b: Move back one character.
C-f: Move forward one character.
DEL or Backspace: Delete the character to the left of the cursor.
C-d: Delete the character underneath the cursor.
Printing characters: Insert the character into the line at the cursor.
C-_ or C-x C-u: Undo the last editing command. You can undo all the way back to anempty line.

(Depending on your configuration, the Backspace key be set todelete the character to the left of the cursor and the DEL key setto delete the character underneath the cursor, like C-d, ratherthan the character to the left of the cursor.)

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8.2.2 Readline Movement Commands

The above table describes the most basic keystrokes that you needin order to do editing of the input line. For your convenience, manyother commands have been added in addition to C-b, C-f,C-d, and DEL. Here are some commands for moving more rapidlyabout the line.

C-a: Move to the start of the line.
C-e: Move to the end of the line.
M-f: Move forward a word, where a word is composed of letters and digits.
M-b: Move backward a word.
C-l: Clear the screen, reprinting the current line at the top.

Notice how C-f moves forward a character, while M-f movesforward a word. It is a loose convention that control keystrokesoperate on characters while meta keystrokes operate on words.

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8.2.3 Readline Killing Commands

Killing text means to delete the text from the line, but to saveit 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 canbe 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, sothat when you yank it back, you get it all. The killring is not line specific; the text that you killed on a previouslytyped line is available to be yanked back later, when you are typinganother line.

Here is the list of commands for killing text.

C-k: Kill the text from the current cursor position to the end of the line.
M-d: Kill from the cursor to the end of the current word, or, if betweenwords, to the end of the next word.Word boundaries are the same as those used by M-f.
M-DEL: Kill from the cursor the start of the current word, or, if betweenwords, to the start of the previous word.Word boundaries are the same as those used by M-b.
C-w: Kill from the cursor to the previous whitespace. This is different thanM-DEL because the word boundaries differ.

Here is how to yank the text back into the line. Yankingmeans to copy the most-recently-killed text from the kill buffer.

C-y: Yank the most recently killed text back into the buffer at the cursor.
M-y: Rotate the kill-ring, and yank the new top. You can only do this ifthe prior command is C-y or M-y.

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8.2.4 Readline Arguments

You can pass numeric arguments to Readline commands. Sometimes theargument acts as a repeat count, other times it is the sign of theargument that is significant. If you pass a negative argument to acommand which normally acts in a forward direction, that command willact in a backward direction. For example, to kill text back to thestart of the line, you might type `M-- C-k'.

The general way to pass numeric arguments to a command is to type metadigits before the command. If the first `digit' typed is a minussign (`-'), then the sign of the argument will be negative. Onceyou have typed one meta digit to get the argument started, you can typethe remainder of the digits, and then the command. For example, to givethe 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.

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8.2.5 Searching for Commands in the History

Readline provides commands for searching through the command history(see section 9.1 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 thesearch string.As each character of the search string is typed, Readline displaysthe next entry from the history matching the string typed so far.An incremental search requires only as many characters as needed tofind the desired history entry.To search backward in the history for a particular string, typeC-r. Typing C-s searches forward through the history.The characters present in the value of the isearch-terminators variableare used to terminate an incremental search.If that variable has not been assigned a value, the ESC andC-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 thesearch string becomes the current line.

To find other matching entries in the history list, type C-r orC-s as appropriate.This will search backward or forward in the history for the nextentry matching the search string typed so far.Any other key sequence bound to a Readline command will terminatethe search and execute that command.For instance, a RET will terminate the search and acceptthe line, thereby executing the command from the history list.A movement command will terminate the search, make the last line foundthe current line, and begin editing.

Readline remembers the last incremental search string. If twoC-rs are typed without any intervening characters defining a newsearch string, any remembered search string is used.

Non-incremental searches read the entire search string before startingto search for matching history lines. The search string may betyped by the user or be part of the contents of the current line.

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8.3 Readline Init File

Although the Readline library comes with a set of Emacs-likekeybindings installed by default, it is possible to use a different setof keybindings.Any user can customize programs that use Readline by puttingcommands in an inputrc file, conventionally in his home directory.The name of thisfile is taken from the value of the shell variable INPUTRC. Ifthat variable is unset, the default is `~/.inputrc'.

When a program which uses the Readline library starts up, theinit file is read, and the key bindings are set.

In addition, the C-x C-r command re-reads this init file, thusincorporating any changes that you might have made to it.

8.3.1 Readline Init File Syntax    Syntax for the commands in the inputrc file.
8.3.2 Conditional Init Constructs    Conditional key bindings in the inputrc file.
8.3.3 Sample Init File    An example inputrc file.

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8.3.1 Readline Init File Syntax

There are only a few basic constructs allowed in theReadline init file. Blank lines are ignored.Lines beginning with a `#' are comments.Lines beginning with a `$' indicate conditionalconstructs (see section 8.3.2 Conditional Init Constructs). Other linesdenote variable settings and key bindings.

Variable Settings

You can modify the run-time behavior of Readline byaltering the values of variables in Readlineusing the set command within the init file.The syntax is simple:

set variable value

Here, for example, is how tochange from the default Emacs-like key binding to usevi line editing commands:

set editing-mode vi

Variable names and values, where appropriate, are recognized without regardto case.

The bind -V command lists the current Readline variable namesand values. See section 4.2 Bash Builtin Commands.

A great deal of run-time behavior is changeable with the followingvariables.

bell-style

Controls what happens when Readline wants to ring the terminal bell.If set to `none', Readline never rings the bell. If set to`visible', Readline uses a visible bell if one is available.If set to `audible' (the default), Readline attempts to ringthe terminal's bell.

comment-begin

The string to insert at the beginning of the line when theinsert-comment command is executed. The default valueis "#".

completion-ignore-case

If set to `on', Readline performs filename matching and completionin a case-insensitive fashion.The default value is `off'.

completion-query-items

The number of possible completions that determines when the user isasked whether he wants to see the list of possibilities. If thenumber of possible completions is greater than this value,Readline will ask the user whether or not he wishes to viewthem; otherwise, they are simply listed.This variable must be set to an integer value greater than or equal to 0.The default limit is 100.

convert-meta

If set to `on', Readline will convert characters with theeighth bit set to an ASCII key sequence by stripping the eighthbit and prefixing an ESC character, converting them to ameta-prefixed key sequence. The default value is `on'.

disable-completion

If set to `On', Readline will inhibit word completion.Completion characters will be inserted into the line as if they hadbeen mapped to self-insert. The default is `off'.

editing-mode

The editing-mode variable controls which default set ofkey bindings is used. By default, Readline starts up in Emacs editingmode, where the keystrokes are most similar to Emacs. This variable can beset to either `emacs' or `vi'.

enable-keypad

When set to `on', Readline will try to enable the applicationkeypad when it is called. Some systems need this to enable thearrow keys. The default is `off'.

expand-tilde

If set to `on', tilde expansion is performed when Readlineattempts word completion. The default is `off'.

If set to `on', the history code attempts to place point at thesame location on each history line retrived with previous-historyor next-history.

horizontal-scroll-mode

This variable can be set to either `on' or `off'. Setting itto `on' means that the text of the lines being edited will scrollhorizontally on a single screen line when they are longer than the widthof the screen, instead of wrapping onto a new screen line. By default,this variable is set to `off'.

input-meta

If set to `on', Readline will enable eight-bit input (itwill not clear the eighth bit in the characters it reads),regardless of what the terminal claims it can support. Thedefault value is `off'. The name meta-flag is asynonym for this variable.

isearch-terminators

The string of characters that should terminate an incremental search withoutsubsequently executing the character as a command (see section 8.2.5 Searching for Commands in the History).If this variable has not been given a value, the characters ESC andC-J will terminate an incremental search.

keymap

Sets Readline's idea of the current keymap for key binding commands.Acceptable keymap names areemacs,emacs-standard,emacs-meta,emacs-ctlx,vi,vi-move,vi-command, andvi-insert.vi is equivalent to vi-command; emacs isequivalent to emacs-standard. The default value is emacs.The value of the editing-mode variable also affects thedefault keymap.

mark-directories

If set to `on', completed directory names have a slashappended. The default is `on'.

mark-modified-lines

This variable, when set to `on', causes Readline to display anasterisk (`*') at the start of history lines which have been modified.This variable is `off' by default.

mark-symlinked-directories

If set to `on', completed names which are symbolic linksto directories have a slash appended (subject to the value ofmark-directories).The default is `off'.

match-hidden-files

This variable, when set to `on', causes Readline to match files whosenames begin with a `.' (hidden files) when performing filenamecompletion, unless the leading `.' issupplied by the user in the filename to be completed.This variable is `on' by default.

output-meta

If set to `on', Readline will display characters with theeighth bit set directly rather than as a meta-prefixed escapesequence. The default is `off'.

page-completions

If set to `on', Readline uses an internal more-like pagerto display a screenful of possible completions at a time.This variable is `on' by default.

print-completions-horizontally

If set to `on', Readline will display completions with matchessorted horizontally in alphabetical order, rather than down the screen.The default is `off'.

show-all-if-ambiguous

This alters the default behavior of the completion functions. Ifset to `on',words which have more than one possible completion cause thematches to be listed immediately instead of ringing the bell.The default value is `off'.

visible-stats

If set to `on', a character denoting a file's typeis appended to the filename when listing possiblecompletions. The default is `off'.

Key Bindings

The syntax for controlling key bindings in the init file issimple. First you need to find the name of the command that youwant to change. The following sections contain tables of the commandname, the default keybinding, if any, and a short description of whatthe command does.

Once you know the name of the command, simply place on a linein the init file the name of the keyyou wish to bind the command to, a colon, and then the name of thecommand. The name of the keycan be expressed in different ways, depending on what you find mostcomfortable.

In addition to command names, readline allows keys to be boundto a string that is inserted when the key is pressed (a macro).

The bind -p command displays Readline function names andbindings in a format that can put directly into an initialization file.See section 4.2 Bash Builtin Commands.

keyname: function-name or macro

keyname is the name of a key spelled out in English. For example:

Control-u: universal-argument            Meta-Rubout: backward-kill-word            Control-o: "> output"

In the above example, C-u is bound to the functionuniversal-argument,M-DEL is bound to the function backward-kill-word, andC-o is bound to run the macroexpressed on the right hand side (that is, to insert the text`> output' into the line).

A number of symbolic character names are recognized whileprocessing this key binding syntax:DEL,ESC,ESCAPE,LFD,NEWLINE,RET,RETURN,RUBOUT,SPACE,SPC,andTAB.

"keyseq": function-name or macro

keyseq differs from keyname above in that stringsdenoting an entire key sequence can be specified, by placingthe key sequence in double quotes. Some GNU Emacs style keyescapes can be used, as in the following example, but thespecial character names are not recognized.

"\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 functionuniversal-argument (just as it was in the first example),`C-x C-r' is bound to the function re-read-init-file,and `ESC [ 1 1 ~' is bound to insertthe text `Function Key 1'.

The following GNU Emacs style escape sequences are available whenspecifying key sequences:

\C-: control prefix
\M-: meta prefix
\e: an escape character
\\: backslash
\": ", a double quotation mark
\': ', a single quote or apostrophe

In addition to the GNU Emacs style escape sequences, a secondset of backslash escapes is available:

\a: alert (bell)
\b: backspace
\d: delete
\f: form feed
\n: newline
\r: carriage return
\t: horizontal tab
\v: vertical tab
\nnn: the eight-bit character whose value is the octal value nnn(one to three digits)
\xHH: the eight-bit character whose value is the hexadecimal value HH(one or two hex digits)

When entering the text of a macro, single or double quotes mustbe 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\\": "\\"

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8.3.2 Conditional Init Constructs

Readline implements a facility similar in spirit to the conditionalcompilation features of the C preprocessor which allows keybindings and variable settings to be performed as the resultof tests. There are four parser directives used.

$if

The $if construct allows bindings to be made based on theediting mode, the terminal being used, or the application usingReadline. The text of the test extends to the end of the line;no characters are required to isolate it.

mode

The mode= form of the $if directive is used to testwhether Readline is in emacs or vi mode.This may be used in conjunctionwith the `set keymap' command, for instance, to set bindings inthe emacs-standard and emacs-ctlx keymaps only ifReadline is starting out in emacs mode.

term

The term= form may be used to include terminal-specifickey bindings, perhaps to bind the key sequences output by theterminal's function keys. The word on the right side of the`=' is tested against both the full name of the terminal andthe portion of the terminal name before the first `-'. Thisallows sun to match both sun and sun-cmd,for instance.

application

The application construct is used to includeapplication-specific settings. Each program using the Readlinelibrary sets the application name, and you can test fora particular value.This could be used to bind key sequences to functions useful fora specific program. For instance, the following command adds akey sequence that quotes the current or previous word in Bash:

$if Bash            # Quote the current or previous word            "\C-xq": "\eb\"\ef\""            $endif

$endif

This command, as seen in the previous example, terminates an$if command.

$else

Commands in this branch of the $if directive are executed ifthe test fails.

$include

This directive takes a single filename as an argument and reads commandsand bindings from that file.For example, the following directive reads from `/etc/inputrc':

$include /etc/inputrc

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8.3.3 Sample Init File

Here is an example of an inputrc file. This illustrates keybinding, 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-wordText 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

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8.4 Bindable Readline Commands

8.4.1 Commands For Moving Moving about the line. 8.4.2 Commands For Manipulating The History Getting at previous lines. 8.4.3 Commands For Changing Text Commands for changing text. 8.4.4 Killing And Yanking Commands for killing and yanking. 8.4.5 Specifying Numeric Arguments Specifying numeric arguments, repeat counts. 8.4.6 Letting Readline Type For You Getting Readline to do the typing for you. 8.4.7 Keyboard Macros Saving and re-executing typed characters 8.4.8 Some Miscellaneous Commands Other miscellaneous commands.

This section describes Readline commands that may be bound to keysequences.You can list your key bindings by executingbind -P or, for a more terse format, suitable for aninputrc file, bind -p. (See section 4.2 Bash Builtin Commands.)Command names without an accompanying key sequence are unbound by default.

In the following descriptions, point refers to the current cursorposition, and mark refers to a cursor position saved by theset-mark command.The text between the point and mark is referred to as the region.

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8.4.1 Commands For Moving

beginning-of-line (C-a): Move to the start of the current line.
end-of-line (C-e): Move to the end of the line.
forward-char (C-f): Move forward a character.
backward-char (C-b): Move back a character.
forward-word (M-f): Move forward to the end of the next word. Words are composed ofletters and digits.
backward-word (M-b): Move back to the start of the current or previous word. Words arecomposed of letters and digits.
clear-screen (C-l): Clear the screen and redraw the current line,leaving the current line at the top of the screen.
redraw-current-line (): Refresh the current line. By default, this is unbound.

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8.4.2 Commands For Manipulating The History

accept-line (Newline or Return): Accept the line regardless of where the cursor is.If this line isnon-empty, add it to the history list according to the setting ofthe HISTCONTROL and HISTIGNORE variables.If this line is a modified history line, then restore the history lineto its original state.
previous-history (C-p): Move `back' through the history list, fetching the previous command.
next-history (C-n): Move `forward' through the history list, fetching the next command.
beginning-of-history (M-<): Move to the first line in the history.
end-of-history (M->): Move to the end of the input history, i.e., the line currentlybeing entered.
reverse-search-history (C-r): Search backward starting at the current line and moving `up' throughthe history as necessary. This is an incremental search.
forward-search-history (C-s): Search forward starting at the current line and moving `down' throughthe the history as necessary. This is an incremental search.
non-incremental-reverse-search-history (M-p): Search backward starting at the current line and moving `up'through the history as necessary using a non-incremental searchfor a string supplied by the user.
non-incremental-forward-search-history (M-n): Search forward starting at the current line and moving `down'through the the history as necessary using a non-incremental searchfor a string supplied by the user.
history-search-forward (): Search forward through the history for the string of charactersbetween the start of the current line and the point.This is a non-incremental search.By default, this command is unbound.
history-search-backward (): Search backward through the history for the string of charactersbetween the start of the current line and the point. Thisis a non-incremental search. By default, this command is unbound.
yank-nth-arg (M-C-y): Insert the first argument to the previous command (usuallythe second word on the previous line) at point.With an argument n,insert the nth word from the previous command (the wordsin the previous command begin with word 0). A negative argumentinserts the nth word from the end of the previous command.
yank-last-arg (M-. or M-_): Insert last argument to the previous command (the last word of theprevious history entry). With anargument, behave exactly like yank-nth-arg.Successive calls to yank-last-arg move back through the historylist, inserting the last argument of each line in turn.

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8.4.3 Commands For Changing Text

delete-char (C-d)

Delete the character at point. If point is at thebeginning of the line, there are no characters in the line, andthe last character typed was not bound to delete-char, thenreturn EOF.

backward-delete-char (Rubout)

Delete the character behind the cursor. A numeric argument meansto kill the characters instead of deleting them.

forward-backward-delete-char ()

Delete the character under the cursor, unless the cursor is at theend of the line, in which case the character behind the cursor isdeleted. By default, this is not bound to a key.

quoted-insert (C-q or C-v)

Add the next character typed to the line verbatim. This ishow to insert key sequences like C-q, for example.

self-insert (a, b, A, 1, !, ...)

Insert yourself.

transpose-chars (C-t)

Drag the character before the cursor forward overthe character at the cursor, moving thecursor forward as well. If the insertion pointis at the end of the line, then thistransposes the last two characters of the line.Negative arguments have no effect.

transpose-words (M-t)

Drag the word before point past the word after point,moving point past that word as well.If the insertion point is at the end of the line, this transposesthe last two words on the line.

upcase-word (M-u)

Uppercase the current (or following) word. With a negative argument,uppercase the previous word, but do not move the cursor.

downcase-word (M-l)

Lowercase the current (or following) word. With a negative argument,lowercase the previous word, but do not move the cursor.

capitalize-word (M-c)

Capitalize the current (or following) word. With a negative argument,capitalize the previous word, but do not move the cursor.

overwrite-mode ()

Toggle overwrite mode. With an explicit positive numeric argument,switches to overwrite mode. With an explicit non-positive numericargument, switches to insert mode. This command affects onlyemacs mode; vi mode does overwrite differently.Each call to readline() starts in insert mode.

In overwrite mode, characters bound to self-insert replacethe text at point rather than pushing the text to the right.Characters bound to backward-delete-char replace the characterbefore point with a space.

By default, this command is unbound.

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8.4.4 Killing And Yanking

kill-line (C-k): Kill the text from point to the end of the line.
backward-kill-line (C-x Rubout): Kill backward to the beginning of the line.
unix-line-discard (C-u): Kill backward from the cursor to the beginning of the current line.
kill-whole-line (): Kill all characters on the current line, no matter where point is.By default, this is unbound.
kill-word (M-d): Kill from point to the end of the current word, or if betweenwords, to the end of the next word.Word boundaries are the same as forward-word.
backward-kill-word (M-DEL): Kill the word behind point.Word boundaries are the same as backward-word.
unix-word-rubout (C-w): Kill the word behind point, using white space as a word boundary.The killed text is saved on the kill-ring.
delete-horizontal-space (): Delete all spaces and tabs around point. By default, this is unbound.
kill-region (): Kill the text in the current region.By default, this command is unbound.
copy-region-as-kill (): Copy the text in the region to the kill buffer, so it can be yankedright away. By default, this command is unbound.
copy-backward-word (): Copy the word before point to the kill buffer.The word boundaries are the same as backward-word.By default, this command is unbound.
copy-forward-word (): Copy the word following point to the kill buffer.The word boundaries are the same as forward-word.By default, this command is unbound.
yank (C-y): Yank the top of the kill ring into the buffer at point.
yank-pop (M-y): Rotate the kill-ring, and yank the new top. You can only do this ifthe prior command is yank or yank-pop.

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8.4.5 Specifying Numeric Arguments

digit-argument (M-0, M-1, ... M--): Add this digit to the argument already accumulating, or start a newargument. M-- starts a negative argument.
universal-argument (): This is another way to specify an argument.If this command is followed by one or more digits, optionally with aleading minus sign, those digits define the argument.If the command is followed by digits, executing universal-argumentagain ends the numeric argument, but is otherwise ignored.As a special case, if this command is immediately followed by acharacter that is neither a digit or minus sign, the argument countfor the next command is multiplied by four.The argument count is initially one, so executing this function thefirst time makes the argument count four, a second time makes theargument count sixteen, and so on.By default, this is not bound to a key.

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8.4.6 Letting Readline Type For You

complete (TAB): Attempt to perform completion on the text before point.The actual completion performed is application-specific.Bash attempts completion treating the text as a variable (if thetext begins with `$'), username (if the text begins with`~'), hostname (if the text begins with `@'), orcommand (including aliases and functions) in turn. If noneof these produces a match, filename completion is attempted.
possible-completions (M-?): List the possible completions of the text before point.
insert-completions (M-*): Insert all completions of the text before point that would havebeen generated by possible-completions.
menu-complete (): Similar to complete, but replaces the word to be completedwith a single match from the list of possible completions.Repeated execution of menu-complete steps through the listof possible completions, inserting each match in turn.At the end of the list of completions, the bell is rung(subject to the setting of bell-style)and the original text is restored.An argument of n moves n positions forward in the listof matches; a negative argument may be used to move backwardthrough the list.This command is intended to be bound to TAB, but is unboundby default.
delete-char-or-list (): Deletes the character under the cursor if not at the beginning orend of the line (like delete-char).If at the end of the line, behaves identically topossible-completions.This command is unbound by default.
complete-filename (M-/): Attempt filename completion on the text before point.
possible-filename-completions (C-x /): List the possible completions of the text before point,treating it as a filename.
complete-username (M-~): Attempt completion on the text before point, treatingit as a username.
possible-username-completions (C-x ~): List the possible completions of the text before point,treating it as a username.
complete-variable (M-$): Attempt completion on the text before point, treatingit as a shell variable.
possible-variable-completions (C-x $): List the possible completions of the text before point,treating it as a shell variable.
complete-hostname (M-@): Attempt completion on the text before point, treatingit as a hostname.
possible-hostname-completions (C-x @): List the possible completions of the text before point,treating it as a hostname.
complete-command (M-!): Attempt completion on the text before point, treatingit as a command name. Command completion attempts tomatch the text against aliases, reserved words, shellfunctions, shell builtins, and finally executable filenames,in that order.
possible-command-completions (C-x !): List the possible completions of the text before point,treating it as a command name.
dynamic-complete-history (M-TAB): Attempt completion on the text before point, comparingthe text against lines from the history list for possiblecompletion matches.
complete-into-braces (M-{): Perform filename completion and insert the list of possible completionsenclosed within braces so the list is available to the shell(see section 3.5.1 Brace Expansion).

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8.4.7 Keyboard Macros

start-kbd-macro (C-x (): Begin saving the characters typed into the current keyboard macro.
end-kbd-macro (C-x )): Stop saving the characters typed into the current keyboard macroand save the definition.
call-last-kbd-macro (C-x e): Re-execute the last keyboard macro defined, by making the charactersin the macro appear as if typed at the keyboard.

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8.4.8 Some Miscellaneous Commands

re-read-init-file (C-x C-r): Read in the contents of the inputrc file, and incorporateany bindings or variable assignments found there.
abort (C-g): Abort the current editing command andring the terminal's bell (subject to the setting ofbell-style).
do-uppercase-version (M-a, M-b, M-x, ...): If the metafied character x is lowercase, run the commandthat is bound to the corresponding uppercase character.
prefix-meta (ESC): Metafy the next character typed. This is for keyboardswithout a meta key. Typing `ESC f' is equivalent to typingM-f.
undo (C-_ or C-x C-u): Incremental undo, separately remembered for each line.
revert-line (M-r): Undo all changes made to this line. This is like executing the undocommand enough times to get back to the beginning.
tilde-expand (M-&): Perform tilde expansion on the current word.
set-mark (C-@): Set the mark to the point. If anumeric argument is supplied, the mark is set to that position.
exchange-point-and-mark (C-x C-x): Swap the point with the mark. The current cursor position is set tothe saved position, and the old cursor position is saved as the mark.
character-search (C-]): A character is read and point is moved to the next occurrence of thatcharacter. A negative count searches for previous occurrences.
character-search-backward (M-C-]): A character is read and point is moved to the previous occurrenceof that character. A negative count searches for subsequentoccurrences.
insert-comment (M-#): Without a numeric argument, the value of the comment-beginvariable is inserted at the beginning of the current line.If a numeric argument is supplied, this command acts as a toggle: ifthe characters at the beginning of the line do not match the valueof comment-begin, the value is inserted, otherwisethe characters in comment-begin are deleted from the beginning ofthe line.In either case, the line is accepted as if a newline had been typed.The default value of comment-begin causes this commandto make the current line a shell comment.If a numeric argument causes the comment character to be removed, the linewill be executed by the shell.
dump-functions (): Print all of the functions and their key bindings to theReadline output stream. If a numeric argument is supplied,the output is formatted in such a way that it can be made partof an inputrc file. This command is unbound by default.
dump-variables (): Print all of the settable variables and their values to theReadline output stream. If a numeric argument is supplied,the output is formatted in such a way that it can be made partof an inputrc file. This command is unbound by default.
dump-macros (): Print all of the Readline key sequences bound to macros and thestrings they output. If a numeric argument is supplied,the output is formatted in such a way that it can be made partof an inputrc file. This command is unbound by default.
glob-complete-word (M-g): The word before point is treated as a pattern for pathname expansion,with an asterisk implicitly appended. This pattern is used togenerate a list of matching file names for possible completions.
glob-expand-word (C-x *): The word before point is treated as a pattern for pathname expansion,and the list of matching file names is inserted, replacing the word.If a numeric argument is supplied, a `*' is appended beforepathname expansion.
glob-list-expansions (C-x g): The list of expansions that would have been generated byglob-expand-word is displayed, and the line is redrawn.If a numeric argument is supplied, a `*' is appended beforepathname expansion.
display-shell-version (C-x C-v): Display version information about the current instance of Bash.
shell-expand-line (M-C-e): Expand the line as the shell does.This performs alias and history expansion as well as all of the shellword expansions (see section 3.5 Shell Expansions).
history-expand-line (M-^): Perform history expansion on the current line.
magic-space (): Perform history expansion on the current line and insert a space(see section 9.3 History Expansion).
alias-expand-line (): Perform alias expansion on the current line (see section 6.6 Aliases).
history-and-alias-expand-line (): Perform history and alias expansion on the current line.
insert-last-argument (M-. or M-_): A synonym for yank-last-arg.
operate-and-get-next (C-o): Accept the current line for execution and fetch the next linerelative to the current line from the history for editing. Anyargument is ignored.
edit-and-execute-command (C-xC-e): Invoke an editor on the current command line, and execute the result as shellcommands.Bash attempts to invoke$FCEDIT, $EDITOR, and emacsas the editor, in that order.

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8.5 Readline vi Mode

While the Readline library does not have a full set of viediting functions, it does contain enough to allow simple editingof the line. The Readline vi mode behaves as specified inthe POSIX 1003.2 standard.

In order to switch interactively between emacs and viediting modes, use the `set -o emacs' and `set -o vi'commands (see section 4.3 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 ESCswitches you into `command' mode, where you can edit the text of theline with the standard vi movement keys, move to previoushistory lines with `k' and subsequent lines with `j', andso forth.

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8.6 Programmable Completion

When word completion is attempted for an argument to a command forwhich a completion specification (a compspec) has been definedusing the complete builtin (see section 8.7 Programmable Completion Builtins),the programmable completion facilities are invoked.

First, the command name is identified.If a compspec has been defined for that command, thecompspec is used to generate the list of possible completions for the word.If the command word is a full pathname, a compspec for the fullpathname is searched for first.If no compspec is found for the full pathname, an attempt is made tofind a compspec for the portion following the final slash.

Once a compspec has been found, it is used to generate the list ofmatching words.If a compspec is not found, the default Bash completiondescribed above (see section 8.4.6 Letting Readline Type For You) is performed.

First, the actions specified by the compspec are used.Only matches which are prefixed by the word being completed arereturned.When the `-f' or `-d' option is used for filename ordirectory name completion, the shell variable FIGNORE isused to filter the matches.See section 5.2 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' optionis considered.The string is first split using the characters in the IFSspecial variable as delimiters.Shell quoting is honored.Each word is then expanded usingbrace expansion, tilde expansion, parameter and variable expansion,command substitution, arithmetic expansion, and pathname expansion,as described above (see section 3.5 Shell Expansions).The results are split using the rules described above(see section 3.5.7 Word Splitting).The results of the expansion are prefix-matched against the word beingcompleted, and the matching words become the possible completions.

After these matches have been generated, any shell function or commandspecified with the `-F' and `-C' options is invoked.When the command or function is invoked, the COMP_LINE andCOMP_POINT variables are assigned values as described above(see section 5.2 Bash Variables).If a shell function is being invoked, the COMP_WORDS andCOMP_CWORD variables are also set.When the function or command is invoked, the first argument is thename of the command whose arguments are being completed, thesecond argument is the word being completed, and the third argumentis the word preceding the word being completed on the current command line.No filtering of the generated completions against the word being completedis performed; the function or command has complete freedom in generatingthe matches.

Any function specified with `-F' is invoked first.The function may use any of the shell facilities, including thecompgen builtin described below(see section 8.7 Programmable Completion Builtins), to generate the matches.It must put the possible completions in the COMPREPLY arrayvariable.

Next, any command specified with the `-C' option is invokedin an environment equivalent to command substitution.It should print a list of completions, one per line, tothe standard output.Backslash may be used to escape a newline, if necessary.

After all of the possible completions are generated, any filterspecified 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 backslashis 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 completionnot 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 isreturned to the Readline completion code as the list of possiblecompletions.

If the previously-applied actions do not generate any matches, and the`-o dirnames' option was supplied to complete when thecompspec was defined, directory name completion is attempted.

By default, if a compspec is found, whatever it generates is returned tothe completion code as the full set of possible completions.The default Bash completions are not attempted, and the Readline defaultof filename completion is disabled.If the `-o default' option was supplied to complete when thecompspec was defined, Readline's default completion will be performedif the compspec generates no matches.

When a compspec indicates that directory name completion is desired,the programmable completion functions force Readline to append a slashto completed names which are symbolic links to directories, subject tothe value of the mark-directories Readline variable, regardlessof the setting of the mark-symlinked-directories Readline variable.

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8.7 Programmable Completion Builtins

Two builtin commands are available to manipulate the programmable completionfacilities.

compgen

compgen [option] [word]

Generate possible completion matches for word according tothe options, which may be any option accepted by thecompletebuiltin with the exception of `-p' and `-r', and writethe matches to the standard output.When using the `-F' or `-C' options, the various shell variablesset by the programmable completion facilities, while available, will nothave useful values.

The matches will be generated in the same way as if the programmablecompletion code had generated them directly from a completion specificationwith the same flags.If word is specified, only those completions matching wordwill be displayed.

The return value is true unless an invalid option is supplied, or nomatches were generated.

complete

complete [-abcdefgjksuv] [-o comp-option] [-A action] [-G globpat] [-W wordlist]            [-P prefix] [-S suffix] [-X filterpat] [-F function]            [-C command] name [name ...]            complete -pr [name ...]

Specify how arguments to each name should be completed.If the `-p' option is supplied, or if no options are supplied, existingcompletion specifications are printed in a way that allows them to bereused as input.The `-r' option removes a completion specification foreach name, or, if no names are supplied, allcompletion specifications.

The process of applying these completion specifications when word completionis attempted is described above (see section 8.6 Programmable Completion).

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 thecomplete builtin is invoked.

-o comp-option

The comp-option controls several aspects of the compspec's behaviorbeyond the simple generation of completions.comp-option may be one of:

default: Use Readline's default filename completion if the compspec generatesno matches.
dirnames: Perform directory name completion if the compspec generates no matches.
filenames: Tell Readline that the compspec generates filenames, so it can perform anyfilename\-specific processing (like adding a slash to directory names orsuppressing trailing spaces). This option is intended to be used withshell functions specified with `-F'.
nospace: Tell Readline not to append a space (the default) to words completed atthe end of the line.

-A action

The action may be one of the following to generate a list of possiblecompletions:

alias: Alias names. May also be specified as `-a'.
arrayvar: Array variable names.
binding: Readline key binding names (see section 8.4 Bindable Readline Commands).
builtin: Names of shell builtin commands. May also be specified as `-b'.
command: Command names. May also be specified as `-c'.
directory: Directory names. May also be specified as `-d'.
disabled: Names of disabled shell builtins.
enabled: Names of enabled shell builtins.
export: Names of exported shell variables. May also be specified as `-e'.
file: File names. May also be specified as `-f'.
function: Names of shell functions.
group: Group names. May also be specified as `-g'.
helptopic: Help topics as accepted by the help builtin (see section 4.2 Bash Builtin Commands).
hostname: Hostnames, as taken from the file specified by theHOSTFILE shell variable (see section 5.2 Bash Variables).
job: Job names, if job control is active. May also be specified as `-j'.
keyword: Shell reserved words. May also be specified as `-k'.
running: Names of running jobs, if job control is active.
service: Service names. May also be specified as `-s'.
setopt: Valid arguments for the `-o' option to the set builtin(see section 4.3 The Set Builtin).
shopt: Shell option names as accepted by the shopt builtin(see section 4.2 Bash Builtin Commands).
signal: Signal names.
stopped: Names of stopped jobs, if job control is active.
user: User names. May also be specified as `-u'.
variable: Names of all shell variables. May also be specified as `-v'.

-G globpat

The filename expansion pattern globpat is expanded to generatethe possible completions.

-W wordlist

The wordlist is split using the characters in theIFS special variable as delimiters, and each resultant wordis expanded.The possible completions are the members of the resultant list whichmatch the word being completed.

-C command

command is executed in a subshell environment, and its output isused as the possible completions.

-F function

The shell function function is executed in the current shellenvironment.When it finishes, the possible completions are retrieved from the valueof the COMPREPLY array variable.

-X filterpat

filterpat is a pattern as used for filename expansion.It is applied to the list of possible completions generated by thepreceding options and arguments, and each completion matchingfilterpat is removed from the list.A leading `!' in filterpat negates the pattern; in thiscase, any completion not matching filterpat is removed.

-P prefix

prefix is added at the beginning of each possible completionafter all other options have been applied.

-S suffix

suffix is appended to each possible completionafter all other options have been applied.

The return value is true unless an invalid option is supplied, an optionother than `-p' or `-r' is supplied without a nameargument, an attempt is made to remove a completion specification fora name for which no specification exists, oran error occurs adding a completion specification.

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9. Using History Interactively

This chapter describes how to use the GNU History Libraryinteractively, 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.

9.1 Bash History Facilities How Bash lets you manipulate your command history. 9.2 Bash History Builtins The Bash builtin commands that manipulate the command history. 9.3 History Expansion What it feels like using History as a user.

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9.1 Bash History Facilities

When the `-o history' option to the set builtinis enabled (see section 4.3 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 thenumber of commands to save in a history list.The text of the last $HISTSIZEcommands (default 500) is saved.The shell stores each command in the history list prior toparameter and variable expansionbut after history expansion is performed, subject to thevalues of the shell variablesHISTIGNORE and HISTCONTROL.

When the shell starts up, the history is initialized from thefile named by the HISTFILE variable (default `~/.bash_history').The file named by the value of HISTFILE is truncated, ifnecessary, to contain no more than the number of lines specified bythe value of the HISTFILESIZE variable.When an interactive shell exits, the last$HISTSIZE lines are copied from the history list to the filenamed by $HISTFILE.If the histappend shell option is set (see section 4.2 Bash Builtin Commands),the lines are appended to the history file,otherwise the history file is overwritten.If HISTFILEis unset, or if the history file is unwritable, the history isnot saved. After saving the history, the history file is truncatedto contain no more than $HISTFILESIZElines. If HISTFILESIZE is not set, no truncation is performed.

The builtin command fc may be used to list or edit and re-executea portion of the history list.The history builtin may be used to display or modify the historylist and manipulate the history file.When using command-line editing, search commandsare available in each editing mode that provide access to thehistory list (see section 8.4.2 Commands For Manipulating The History).

The shell allows control over which commands are saved on the historylist. The HISTCONTROL and HISTIGNOREvariables may be set to cause the shell to save only a subset of thecommands entered.The cmdhistshell option, if enabled, causes the shell to attempt to save eachline of a multi-line command in the same history entry, addingsemicolons where necessary to preserve syntactic correctness.The lithistshell option causes the shell to save the command with embedded newlinesinstead of semicolons.The shopt builtin is used to set these options.See section 4.2 Bash Builtin Commands, for a description of shopt.

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9.2 Bash History Builtins

Bash provides two builtin commands which manipulate thehistory list and history file.

fc

fc [-e ename] [-nlr] [first] [last]            fc -s [pat=rep] [command]

Fix Command. In the first form, a range of commands from first tolast is selected from the history list. Both first andlast may be specified as a string (to locate the most recentcommand beginning with that string) or as a number (an index into thehistory list, where a negative number is used as an offset from thecurrent command number). If last is not specified it is set tofirst. If first is not specified it is set to the previouscommand for editing and -16 for listing. If the `-l' flag isgiven, the commands are listed on standard output. The `-n' flagsuppresses the command numbers when listing. The `-r' flagreverses the order of the listing. Otherwise, the editor given byename is invoked on a file containing those commands. Ifename is not given, the value of the following variable expansionis used: ${FCEDIT:-${EDITOR:-vi}}. This says to use thevalue of the FCEDIT variable if set, or the value of theEDITOR 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 instanceof pat in the selected command is replaced by rep.

A useful alias to use with the fc command is r='fc -s', sothat typing `r cc' runs the last command beginning with ccand typing `r' re-executes the last command (see section 6.6 Aliases).

history

history [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.Options, if supplied, have the following meanings:

-c: Clear the history list. This may be combinedwith the other options to replace the history list completely.
-d offset: Delete the history entry at position offset.offset should be specified as it appears when the history isdisplayed.
-a: Append the newhistory lines (history lines entered since the beginning of thecurrent Bash session) to the history file.
-n: Append the history lines not already read from the history fileto the current history list. These are lines appended to the historyfile since the beginning of the current Bash session.
-r: Read the current history file and append its contents tothe history list.
-w: Write out the current history to the history file.
-p: Perform history substitution on the args and display the resulton the standard output, without storing the results in the history list.
-s: The args are added to the end ofthe history list as a single entry.

When any of the `-w', `-r', `-a', or `-n' options isused, if filenameis given, then it is used as the history file. If not, thenthe value of the HISTFILE variable is used.

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9.3 History Expansion

The History library provides a history expansion feature that is similarto the history expansion provided by csh. This sectiondescribes the syntax used to manipulate the history information.

History expansions introduce words from the history list intothe input stream, making it easy to repeat commands, insert thearguments to a previous command into the current input line, orfix errors in previous commands quickly.

History expansion takes place in two parts. The first is to determinewhich line from the history list should be used during substitution.The second is to select portions of that line for inclusion into thecurrent one. The line selected from the history is called theevent, and the portions of that line that are acted upon arecalled words. Various modifiers are available to manipulatethe selected words. The line is broken into words in the same fashionthat Bash does, so that several wordssurrounded by quotes are considered one word.History expansions are introduced by the appearance of thehistory expansion character, which is `!' by default.Only `\' and `'' may be used to escape the history expansioncharacter.

Several shell options settable with the shoptbuiltin (see section 4.2 Bash Builtin Commands) may be used to tailorthe behavior of history expansion. If thehistverify shell option is enabled, and Readlineis being used, history substitutions are not immediately passed tothe shell parser.Instead, the expanded line is reloaded into the Readlineediting buffer for further modification.If Readline is being used, and the histreeditshell option is enabled, a failed history expansion will bereloaded into the Readline editing buffer for correction.The `-p' option to the history builtin commandmay be used to see what a history expansion will do before using it.The `-s' option to the history builtin may be used toadd commands to the end of the history list without actually executingthem, 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 thehistory expansion mechanism with the histchars variable.

9.3.1 Event Designators How to specify which history line to use. 9.3.2 Word Designators Specifying which words are of interest. 9.3.3 Modifiers Modifying the results of substitution.

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9.3.1 Event Designators

An event designator is a reference to a command line entry in thehistory list.

!: Start a history substitution, except when followed by a space, tab,the end of the line, `=' or `('.
!n: Refer to command line n.
!-n: Refer to the command n lines back.
!!: Refer to the previous command. This is a synonym for `!-1'.
!string: Refer to the most recent command starting with string.
!?string[?]: Refer to the most recent command containing string. The trailing`?' may be omitted if the string is followed immediately bya newline.
^string1^string2^: Quick Substitution. Repeat the last command, replacing string1with string2. Equivalent to!!:s/string1/string2/.
!#: The entire command line typed so far.

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9.3.2 Word Designators

Word designators are used to select desired words from the event.A `:' separates the event specification from the word designator. Itmay be omitted if the word designator begins with a `^', `$',`*', `-', or `%'. Words are numbered from the beginningof the line, with the first word being denoted by 0 (zero). Words areinserted into the current line separated by single spaces.

For example,

!!: designates the preceding command. When you type this, the precedingcommand is repeated in toto.
!!:$: designates the last argument of the preceding command. This may beshortened to !$.
!fi:2: designates the second argument of the most recent command starting withthe letters fi.

Here are the word designators:

0 (zero): The 0th word. For many applications, this is the command word.
n: The nth word.
^: The first argument; that is, word 1.
$: The last argument.
%: The word matched by the most recent `?string' search.
x-y: A range of words; `-y' abbreviates `0-y'.
*: All of the words, except the 0th. This is a synonym for `1-$'.It is not an error to use `*' if there is just one word in the event;the empty string is returned in that case.
x*: Abbreviates `x-$'
x-: Abbreviates `x-$' like `x*', but omits the last word.

If a word designator is supplied without an event specification, theprevious command is used as the event.

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9.3.3 Modifiers

After the optional word designator, you can add a sequence of one or moreof the following modifiers, each preceded by a `:'.

h: Remove a trailing pathname component, leaving only the head.
t: Remove all leading pathname components, leaving the tail.
r: Remove a trailing suffix of the form `.suffix', leavingthe basename.
e: Remove all but the trailing suffix.
p: Print the new command but do not execute it.
q: Quote the substituted words, escaping further substitutions.
x: Quote the substituted words as with `q',but break into words at spaces, tabs, and newlines.
s/old/new/: Substitute new for the first occurrence of old in theevent line. Any delimiter may be used in place of `/'.The delimiter may be quoted in old and newwith a single backslash. If `&' appears in new,it is replaced by old. A single backslash will quotethe `&'. The final delimiter is optional if it is the lastcharacter on the input line.
&: Repeat the previous substitution.
g: Cause changes to be applied over the entire event line. Used inconjunction with `s', as in gs/old/new/,or with `&'.

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10. Installing Bash

This chapter provides basic instructions for installing Bash onthe various supported platforms. The distribution supports theGNU operating systems, nearly every version of Unix, and severalnon-Unix systems such as BeOS and Interix.Other independent ports exist forMS-DOS, OS/2, Windows 95/98, and Windows NT.

10.1 Basic Installation    Installation instructions.
10.2 Compilers and Options    How to set special options for various systems.
10.3 Compiling For Multiple Architectures    How to compile Bash for more than one kind of system from the same source tree.
10.4 Installation Names    How to set the various paths used by the installation.
10.5 Specifying the System Type    How to configure Bash for a particular system.
10.6 Sharing Defaults    How to share default configuration values among GNU programs.
10.7 Operation Controls    Options recognized by the configuration program.
10.8 Optional Features    How to enable and disable optional features when building Bash.

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10.1 Basic Installation

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.
Type `make' to compile Bash and build the bashbug bug reporting script.
Optionally, type `make tests' to run the Bash test suite.
Type `make install' to install bash and bashbug. This will also install the manual pages and Info file.

The configure shell script attempts to guess correctvalues for various system-dependent variables used duringcompilation. It uses those values to create a `Makefile' ineach 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 youcan run in the future to recreate the current configuration, afile `config.cache' that saves the results of its tests tospeed up reconfiguring, and a file `config.log' containingcompiler output (useful mainly for debugging configure).If at some point`config.cache' contains results you don't want to keep, youmay remove or edit it.

To find out more about the options and arguments that theconfigure 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, pleasetry to figure out how configure could check whether or notto do them, and mail diffs or instructions tobash-maintainers@gnu.org so they can beconsidered for the next release.

The file `configure.in' is used to create configureby a program called Autoconf. You only need`configure.in' if you want to change it or regenerateconfigure using a newer version of Autoconf. Ifyou do this, make sure you are using Autoconf version 2.50 ornewer.

You can remove the program binaries and object files from thesource code directory by typing `make clean'. To also remove thefiles that configure created (so you can compile Bash fora different kind of computer), type `make distclean'.

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10.2 Compilers and Options

Some systems require unusual options for compilation or linkingthat the configure script does not know about. You cangive configure initial values for variables by settingthem in the environment. Using a Bourne-compatible shell, youcan 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 itis available.

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10.3 Compiling For Multiple Architectures

You can compile Bash for more than one kind of computer at thesame time, by placing the object files for each architecture in theirown directory. To do this, you must use a version of make thatsupports the VPATH variable, such as GNU make.cd to thedirectory where you want the object files and executables to go and runthe configure script from the source directory. You may need tosupply the `--srcdir=PATH' argument to tell configure where thesource files are. configure automatically checks for thesource code in the directory that configure is in and in `..'.

If you have to use a make that does not supports the VPATHvariable, you can compile Bash for one architecture at atime in the source code directory. After you have installedBash for one architecture, use `make distclean' beforereconfiguring for another architecture.

Alternatively, if your system supports symbolic links, you can use the`support/mkclone' script to create a build tree which hassymbolic links back to each file in the source directory. Here's anexample that creates a build directory in the current directory from asource 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 builtBash for at least one architecture before you can create builddirectories for other architectures.

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10.4 Installation Names

By default, `make install' will install into`/usr/local/bin', `/usr/local/man', etc. You canspecify an installation prefix other than `/usr/local' bygiving 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 forarchitecture-specific files and architecture-independent files.If you give configure the option`--exec-prefix=PATH', `make install' will usePATH as the prefix for installing programs and libraries.Documentation and other data files will still use the regular prefix.

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10.5 Specifying the System Type

There may be some features configure can not figure outautomatically, but need to determine by the type of host Bashwill run on. Usually configure can figure thatout, but if it prints a message saying it can not guess the hosttype, give it the `--host=TYPE' option. `TYPE' caneither 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 possiblevalues of each field.

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10.6 Sharing Defaults

If you want to set default values for configure scripts toshare, you can create a site shell script calledconfig.site that gives default values for variables likeCC, cache_file, and prefix. configurelooks for `PREFIX/share/config.site' if it exists, then`PREFIX/etc/config.site' if it exists. Or, you can set theCONFIG_SITE environment variable to the location of the sitescript. A warning: the Bash configure looks for a site script,but not all configure scripts do.

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10.7 Operation Controls

configure recognizes the following options to control how itoperates.

--cache-file=file: Use and save the results of the tests infile instead of `./config.cache'. Set file to`/dev/null' to disable caching, for debuggingconfigure.
--help: Print a summary of the options to configure, and exit.
--quiet
--silent
-q: Do not print messages saying which checks are being made.
--srcdir=dir: Look for the Bash source code in directory dir. Usuallyconfigure can determine that directory automatically.
--version: Print the version of Autoconf used to generate the configurescript, and exit.

configure also accepts some other, not widely used, boilerplateoptions. `configure --help' prints the complete list.

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10.8 Optional Features

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 featurethat 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: Define if you are using the Andrew File System from Transarc.
--with-bash-malloc: Use the Bash version ofmalloc in `lib/malloc/malloc.c'. This is not the samemalloc that appears in GNU libc, but an older versionderived from the 4.2 BSD malloc. This malloc isvery fast, but wastes some space on each allocation.This option is enabled by default.The `NOTES' file contains a list of systems forwhich this should be turned off, and configure disables thisoption automatically for a number of systems.
--with-curses: Use the curses library instead of the termcap library. This shouldbe supplied if your system has an inadequate or incomplete termcapdatabase.
--with-gnu-malloc: A synonym for --with-bash-malloc.
--with-installed-readline[=PREFIX]: Define this to make Bash link with a locally-installed version of Readlinerather than the version in `lib/readline'. This works only withReadline 4.3 and later versions. If PREFIX is yes or notsupplied, configure uses the values of the make variablesincludedir and libdir, which are subdirectories of prefixby default, to find the installed version of Readline if it is not inthe 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 asa directory pathname and looks forthe installed version of Readline in subdirectories of that directory(include files in PREFIX/include and the library inPREFIX/lib).
--with-purify: Define this to use the Purify memory allocation checker from RationalSoftware.
--enable-minimal-config: This produces a shell with minimal features, close to the historicalBourne shell.

There are several `--enable-' options that alter how Bash iscompiled and linked, rather than changing run-time features.

--enable-largefile: Enable support for large files if the operating system requires special compiler optionsto build programs which can access large files. This is enabled bydefault, if the operating system provides large file support.
--enable-profiling: This builds a Bash binary that produces profiling information to beprocessed by gprof each time it is executed.
--enable-static-link: This causes Bash to be linked statically, if gcc 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 ofthe following options, but it is processed first, so individualoptions may be enabled using `enable-feature'.

All of the following options except for `disabled-builtins' and`xpg-echo-default' areenabled by default, unless the operating system does not provide thenecessary support.

--enable-alias: Allow alias expansion and include the alias and unaliasbuiltins (see section 6.6 Aliases).
--enable-arith-for-command: Include support for the alternate form of the for commandthat behaves like the C language for statement(see section 3.2.4 Looping Constructs).
--enable-array-variables: Include support for one-dimensional array shell variables(see section 6.7 Arrays).
--enable-bang-history: Include support for csh-like history substitution(see section 9.3 History Expansion).
--enable-brace-expansion: Include csh-like brace expansion( b{a,b}c ==> bac bbc ).See 3.5.1 Brace Expansion, for a complete description.
--enable-command-timing: Include support for recognizing time as a reserved word and fordisplaying timing statistics for the pipeline following time(see section 3.2.2 Pipelines).This allows pipelines as well as shell builtins and functions to be timed.
--enable-cond-command: Include support for the [[ conditional command(see section 3.2.5 Conditional Constructs).
--enable-directory-stack: Include support for a csh-like directory stack and thepushd, popd, and dirs builtins(see section 6.8 The Directory Stack).
--enable-disabled-builtins: Allow builtin commands to be invoked via `builtin xxx'even after xxx has been disabled using `enable -n xxx'.See 4.2 Bash Builtin Commands, for details of the builtin andenable builtin commands.
--enable-dparen-arithmetic: Include support for the ((...)) command(see section 3.2.5 Conditional Constructs).
--enable-extended-glob: Include support for the extended pattern matching features describedabove under 3.5.8.1 Pattern Matching.
--enable-help-builtin: Include the help builtin, which displays help on shell builtins andvariables (see section 4.2 Bash Builtin Commands).
--enable-history: Include command history and the fc and historybuiltin commands (see section 9.1 Bash History Facilities).
--enable-job-control: This enables the job control features (see section 7. Job Control),if the operating system supports them.
--enable-net-redirections: This enables the special handling of filenames of the form/dev/tcp/host/port and/dev/udp/host/portwhen used in redirections (see section 3.6 Redirections).
--enable-process-substitution: This enables process substitution (see section 3.5.6 Process Substitution) ifthe operating system provides the necessary support.
--enable-prompt-string-decoding: Turn on the interpretation of a number of backslash-escaped charactersin the $PS1, $PS2, $PS3, and $PS4 promptstrings. See 6.9 Controlling the Prompt, for a complete list of promptstring escape sequences.
--enable-progcomp: Enable the programmable completion facilities(see section 8.6 Programmable Completion).If Readline is not enabled, this option has no effect.
--enable-readline: Include support for command-line editing and history with the Bashversion of the Readline library (see section 8. Command Line Editing).
--enable-restricted: Include support for a restricted shell. If this is enabled, Bash,when called as rbash, enters a restricted mode. See6.10 The Restricted Shell, for a description of restricted mode.
--enable-select: Include the select builtin, which allows the generation of simplemenus (see section 3.2.5 Conditional Constructs).
--enable-usg-echo-default: A synonym for --enable-xpg-echo-default.
--enable-xpg-echo-default: Make the echo 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 inthe Single Unix Specification, version 2.See section 4.2 Bash Builtin Commands, for a description of the escape sequences thatecho recognizes.

The file `config-top.h' contains C Preprocessor`#define' statements for options which are not settable fromconfigure.Some of these are not meant to be changed; beware of the consequences ifyou do.Read the comments associated with each definition for moreinformation about its effect.

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A. Reporting Bugs

Please report all bugs you find in Bash.But first, you shouldmake sure that it really is a bug, and that it appears in the latestversion of Bash that you have.

Once you have determined that a bug actually exists, use thebashbug 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 mailedto bug-bash@gnu.org or posted to the Usenetnewsgroup gnu.bash.bug.

All bug reports should include:

The version number of Bash.
The hardware and operating system.
The compiler used to compile Bash.
A description of the bug behaviour.
A short script or `recipe' which exercises the bug and may be used to reproduce it.

bashbug inserts the first three items automatically intothe template it provides for filing a bug report.

Please send all reports concerning this manual tochet@po.CWRU.Edu.

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B. Major Differences From The Bourne Shell

Bash implements essentially the same grammar, parameter andvariable expansion, redirection, and quoting as the Bourne Shell.Bash uses the POSIX 1003.2 standard as the specification ofhow these features are to be implemented. There are somedifferences between the traditional Bourne shell and Bash; thissection quickly details the differences of significance. Anumber of these differences are explained in greater depth inprevious sections.This section uses the version of sh included in SVR4.2 asthe baseline reference.

Bash is POSIX-conformant, even where the POSIX specification differs from traditional sh behavior (see section 6.11 Bash POSIX Mode).
Bash has multi-character invocation options (see section 6.1 Invoking Bash).
Bash has command-line editing (see section 8. Command Line Editing) and the bind builtin.
Bash provides a programmable word completion mechanism (see section 8.6 Programmable Completion), and two builtin commands, complete and compgen, to manipulate it.
Bash has command history (see section 9.1 Bash History Facilities) and the history and fc builtins to manipulate it.
Bash implements csh-like history expansion (see section 9.3 History Expansion).
Bash has one-dimensional array variables (see section 6.7 Arrays), and the appropriate variable expansions and assignment syntax to use them. Several of the Bash builtins take options to act on arrays. Bash provides a number of built-in array variables.
The $'...' quoting syntax, which expands ANSI-C backslash-escaped characters in the text between the single quotes, is supported (see section 3.1.2.4 ANSI-C Quoting).
Bash supports the $"..." 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 section 3.1.2.5 Locale-Specific Translation).
Bash implements the ! keyword to negate the return value of a pipeline (see section 3.2.2 Pipelines). Very useful when an if statement needs to act only if a test fails.
Bash has the time reserved word and command timing (see section 3.2.2 Pipelines). The display of the timing statistics may be controlled with the TIMEFORMAT variable.
Bash implements the for (( expr1 ; expr2 ; expr3 )) arithmetic for command, similar to the C language (see section 3.2.4 Looping Constructs).
Bash includes the select compound command, which allows the generation of simple menus (see section 3.2.5 Conditional Constructs).
Bash includes the [[ compound command, which makes conditional testing part of the shell grammar (see section 3.2.5 Conditional Constructs).
Bash includes brace expansion (see section 3.5.1 Brace Expansion) and tilde expansion (see section 3.5.2 Tilde Expansion).
Bash implements command aliases and the alias and unalias builtins (see section 6.6 Aliases).
Bash provides shell arithmetic, the (( compound command (see section 3.2.5 Conditional Constructs), and arithmetic expansion (see section 6.5 Shell Arithmetic).
Variables present in the shell's initial environment are automatically exported to child processes. The Bourne shell does not normally do this unless the variables are explicitly marked using the export command.
Bash includes the POSIX pattern removal `%', `#', `%%' and `##' expansions to remove leading or trailing substrings from variable values (see section 3.5.3 Shell Parameter Expansion).
The expansion ${#xx}, which returns the length of ${xx}, is supported (see section 3.5.3 Shell Parameter Expansion).
The expansion ${var:offset[:length]}, which expands to the substring of var's value of length length, beginning at offset, is present (see section 3.5.3 Shell Parameter Expansion).
The expansion ${var/[/]pattern[/replacement]}, which matches pattern and replaces it with replacement in the value of var, is available (see section 3.5.3 Shell Parameter Expansion).
The expansion ${!prefix}* expansion, which expands to the names of all shell variables whose names begin with prefix, is available (see section 3.5.3 Shell Parameter Expansion).
Bash has indirect variable expansion using ${!word} (see section 3.5.3 Shell Parameter Expansion).
Bash can expand positional parameters beyond $9 using ${num}.
The POSIX $() form of command substitution is implemented (see section 3.5.4 Command Substitution), and preferred to the Bourne shell's " (which is also implemented for backwards compatibility).
Bash has process substitution (see section 3.5.6 Process Substitution).
Bash automatically assigns variables that provide information about the current user (UID, EUID, and GROUPS), the current host (HOSTTYPE, OSTYPE, MACHTYPE, and HOSTNAME), and the instance of Bash that is running (BASH, BASH_VERSION, and BASH_VERSINFO). See section 5.2 Bash Variables, for details.
The IFS variable is used to split only the results of expansion, not all words (see section 3.5.7 Word Splitting). This closes a longstanding shell security hole.
Bash implements the full set of POSIX 1003.2 filename expansion operators, including character classes, equivalence classes, and collating symbols (see section 3.5.8 Filename Expansion).
Bash implements extended pattern matching features when the extglob shell option is enabled (see section 3.5.8.1 Pattern Matching).
It is possible to have a variable and a function with the same name; sh does not separate the two name spaces.
Bash functions are permitted to have local variables using the local builtin, and thus useful recursive functions may be written (see section 4.2 Bash Builtin Commands).
Variable assignments preceding commands affect only that command, even builtins and functions (see section 3.7.4 Environment). In sh, all variable assignments preceding commands are global unless the command is executed from the file system.
Bash performs filename expansion on filenames specified as operands to input and output redirection operators (see section 3.6 Redirections).
Bash contains the `<>' redirection operator, allowing a file to be opened for both reading and writing, and the `&>' redirection operator, for directing standard output and standard error to the same file (see section 3.6 Redirections).
Bash treats a number of filenames specially when they are used in redirection operators (see section 3.6 Redirections).
Bash can open network connections to arbitrary machines and services with the redirection operators (see section 3.6 Redirections).
The noclobber option is available to avoid overwriting existing files with output redirection (see section 4.3 The Set Builtin). The `>|' redirection operator may be used to override noclobber.
The Bash cd and pwd builtins (see section 4.1 Bourne Shell Builtins) each take `-L' and `-P' options to switch between logical and physical modes.
Bash allows a function to override a builtin with the same name, and provides access to that builtin's functionality within the function via the builtin and command builtins (see section 4.2 Bash Builtin Commands).
The command builtin allows selective disabling of functions when command lookup is performed (see section 4.2 Bash Builtin Commands).
Individual builtins may be enabled or disabled using the enable builtin (see section 4.2 Bash Builtin Commands).
The Bash 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 section 4.1 Bourne Shell Builtins).
Shell functions may be exported to children via the environment using export -f (see section 3.3 Shell Functions).
The Bash export, readonly, and declare builtins can take a `-f' option to act on shell functions, a `-p' option to display variables with various attributes set in a format that can be used as shell input, a `-n' option to remove various variable attributes, and `name=value' arguments to set variable attributes and values simultaneously.
The Bash 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 section 4.1 Bourne Shell Builtins).
Bash includes a help builtin for quick reference to shell facilities (see section 4.2 Bash Builtin Commands).
The printf builtin is available to display formatted output (see section 4.2 Bash Builtin Commands).
The Bash read builtin (see section 4.2 Bash Builtin Commands) 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.
The return builtin may be used to abort execution of scripts executed with the . or source builtins (see section 4.1 Bourne Shell Builtins).
Bash includes the shopt builtin, for finer control of shell optional capabilities (see section 4.2 Bash Builtin Commands), and allows these options to be set and unset at shell invocation (see section 6.1 Invoking Bash).
Bash has much more optional behavior controllable with the set builtin (see section 4.3 The Set Builtin).
The test builtin (see section 4.1 Bourne Shell Builtins) is slightly different, as it implements the POSIX algorithm, which specifies the behavior based on the number of arguments.
The trap builtin (see section 4.1 Bourne Shell Builtins) allows a DEBUG pseudo-signal specification, similar to EXIT. Commands specified with a DEBUG trap are executed after every simple command. The DEBUG trap is not inherited by shell functions unless the function has been given the trace attribute.
The trap builtin (see section 4.1 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.
The Bash type builtin is more extensive and gives more information about the names it finds (see section 4.2 Bash Builtin Commands).
The Bash 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 section 4.1 Bourne Shell Builtins).
Bash implements a csh-like directory stack, and provides the pushd, popd, and dirs builtins to manipulate it (see section 6.8 The Directory Stack). Bash also makes the directory stack visible as the value of the DIRSTACK shell variable.
Bash interprets special backslash-escaped characters in the prompt strings when interactive (see section 6.9 Controlling the Prompt).
The Bash restricted mode is more useful (see section 6.10 The Restricted Shell); the SVR4.2 shell restricted mode is too limited.
The disown builtin can remove a job from the internal shell job table (see section 7.2 Job Control Builtins) or suppress the sending of SIGHUP to a job when the shell exits as the result of a SIGHUP.
The SVR4.2 shell has two privilege-related builtins (mldmode and priv) not present in Bash.
Bash does not have the stop or newgrp builtins.
Bash does not use the SHACCT variable or perform shell accounting.
The SVR4.2 sh uses a TIMEOUT variable like Bash uses TMOUT.

More features unique to Bash may be found in 6. Bash Features.

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B.1 Implementation Differences From The SVR4.2 Shell

Since Bash is a completely new implementation, it does not suffer frommany of the limitations of the SVR4.2 shell. For instance:

Bash does not fork a subshell when redirecting into or out of a shell control structure such as an if or while statement.
Bash does not allow unbalanced quotes. The SVR4.2 shell will silently insert a needed closing quote at EOF under certain circumstances. This can be the cause of some hard-to-find errors.
The SVR4.2 shell uses a baroque memory management scheme based on trapping 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.
In a questionable attempt at security, the SVR4.2 shell, when invoked without the `-p' option, will alter its real and effective UID and GID if they are less than some magic threshold value, commonly 100. This can lead to unexpected results.
The SVR4.2 shell does not allow users to trap SIGSEGV, SIGALRM, or SIGCHLD.
The SVR4.2 shell does not allow the IFS, MAILCHECK, PATH, PS1, or PS2 variables to be unset.
The SVR4.2 shell treats `^' as the undocumented equivalent of `|'.
Bash allows multiple option arguments when it is invoked (-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 `-'.
The SVR4.2 shell exits a script if any builtin fails; Bash exits a script only if one of the POSIX 1003.2 special builtins fails, and only for certain failures, as enumerated in the POSIX 1003.2 standard.
The SVR4.2 shell behaves differently when invoked as jsh (it turns on job control).

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Index of Shell Builtin Commands

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A B C D E F G H J K L P R S T U W

Index Entry Section

. . 4.1 Bourne Shell Builtins

: : 4.1 Bourne Shell Builtins

[ [ 4.1 Bourne Shell Builtins

A alias 4.2 Bash Builtin Commands

B bg 7.2 Job Control Builtins bind 4.2 Bash Builtin Commands break 4.1 Bourne Shell Builtins builtin 4.2 Bash Builtin Commands

C cd 4.1 Bourne Shell Builtins command 4.2 Bash Builtin Commands compgen 8.7 Programmable Completion Builtins complete 8.7 Programmable Completion Builtins continue 4.1 Bourne Shell Builtins

D declare 4.2 Bash Builtin Commands dirs 6.8.1 Directory Stack Builtins disown 7.2 Job Control Builtins

E echo 4.2 Bash Builtin Commands enable 4.2 Bash Builtin Commands eval 4.1 Bourne Shell Builtins exec 4.1 Bourne Shell Builtins exit 4.1 Bourne Shell Builtins export 4.1 Bourne Shell Builtins

F fc 9.2 Bash History Builtins fg 7.2 Job Control Builtins

G getopts 4.1 Bourne Shell Builtins

H hash 4.1 Bourne Shell Builtins help 4.2 Bash Builtin Commands history 9.2 Bash History Builtins

J jobs 7.2 Job Control Builtins

K kill 7.2 Job Control Builtins

L let 4.2 Bash Builtin Commands local 4.2 Bash Builtin Commands logout 4.2 Bash Builtin Commands

P popd 6.8.1 Directory Stack Builtins printf 4.2 Bash Builtin Commands pushd 6.8.1 Directory Stack Builtins pwd 4.1 Bourne Shell Builtins

R read 4.2 Bash Builtin Commands readonly 4.1 Bourne Shell Builtins return 4.1 Bourne Shell Builtins

S set 4.3 The Set Builtin shift 4.1 Bourne Shell Builtins shopt 4.2 Bash Builtin Commands source 4.2 Bash Builtin Commands suspend 7.2 Job Control Builtins

T test 4.1 Bourne Shell Builtins times 4.1 Bourne Shell Builtins trap 4.1 Bourne Shell Builtins type 4.2 Bash Builtin Commands typeset 4.2 Bash Builtin Commands

U ulimit 4.2 Bash Builtin Commands umask 4.1 Bourne Shell Builtins unalias 4.2 Bash Builtin Commands unset 4.1 Bourne Shell Builtins

W wait 7.2 Job Control Builtins

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A B C D E F G H J K L P R S T U W

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Index of Shell Reserved Words

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C D E F I S T U W

Index Entry Section

! ! 3.2.2 Pipelines

[ [[ 3.2.5 Conditional Constructs

] ]] 3.2.5 Conditional Constructs

{ { 3.2.6 Grouping Commands

} } 3.2.6 Grouping Commands

C case 3.2.5 Conditional Constructs

D do 3.2.4 Looping Constructs done 3.2.4 Looping Constructs

E elif 3.2.5 Conditional Constructs else 3.2.5 Conditional Constructs esac 3.2.5 Conditional Constructs

F fi 3.2.5 Conditional Constructs for 3.2.4 Looping Constructs function 3.3 Shell Functions

I if 3.2.5 Conditional Constructs in 3.2.5 Conditional Constructs

S select 3.2.5 Conditional Constructs

T then 3.2.5 Conditional Constructs time 3.2.2 Pipelines

U until 3.2.4 Looping Constructs

W while 3.2.4 Looping Constructs

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C D E F I S T U W

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Parameter and Variable Index

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Index Entry Section

! ! 3.4.2 Special Parameters ! 3.4.2 Special Parameters

# # 3.4.2 Special Parameters # 3.4.2 Special Parameters

$ $ 3.4.2 Special Parameters $ 3.4.2 Special Parameters

* * 3.4.2 Special Parameters * 3.4.2 Special Parameters

- - 3.4.2 Special Parameters - 3.4.2 Special Parameters

0 0 3.4.2 Special Parameters 0 3.4.2 Special Parameters

3.4.2 Special Parameters 3.4.2 Special Parameters

@ @ 3.4.2 Special Parameters @ 3.4.2 Special Parameters

_ _ 3.4.2 Special Parameters _ 3.4.2 Special Parameters

A auto_resume 7.3 Job Control Variables auto_resume 7.3 Job Control Variables

B BASH 5.2 Bash Variables BASH 5.2 Bash Variables BASH_ENV 5.2 Bash Variables BASH_ENV 5.2 Bash Variables BASH_VERSINFO 5.2 Bash Variables BASH_VERSINFO 5.2 Bash Variables BASH_VERSION 5.2 Bash Variables BASH_VERSION 5.2 Bash Variables bell-style 8.3.1 Readline Init File Syntax

C CDPATH 5.1 Bourne Shell Variables CDPATH 5.1 Bourne Shell Variables COLUMNS 5.2 Bash Variables COLUMNS 5.2 Bash Variables comment-begin 8.3.1 Readline Init File Syntax COMP_CWORD 5.2 Bash Variables COMP_CWORD 5.2 Bash Variables COMP_LINE 5.2 Bash Variables COMP_LINE 5.2 Bash Variables COMP_POINT 5.2 Bash Variables COMP_POINT 5.2 Bash Variables COMP_WORDS 5.2 Bash Variables COMP_WORDS 5.2 Bash Variables completion-query-items 8.3.1 Readline Init File Syntax COMPREPLY 5.2 Bash Variables COMPREPLY 5.2 Bash Variables convert-meta 8.3.1 Readline Init File Syntax

D DIRSTACK 5.2 Bash Variables DIRSTACK 5.2 Bash Variables disable-completion 8.3.1 Readline Init File Syntax

E editing-mode 8.3.1 Readline Init File Syntax enable-keypad 8.3.1 Readline Init File Syntax EUID 5.2 Bash Variables EUID 5.2 Bash Variables expand-tilde 8.3.1 Readline Init File Syntax

F FCEDIT 5.2 Bash Variables FCEDIT 5.2 Bash Variables FIGNORE 5.2 Bash Variables FIGNORE 5.2 Bash Variables FUNCNAME 5.2 Bash Variables FUNCNAME 5.2 Bash Variables

G GLOBIGNORE 5.2 Bash Variables GLOBIGNORE 5.2 Bash Variables GROUPS 5.2 Bash Variables GROUPS 5.2 Bash Variables

H histchars 5.2 Bash Variables histchars 5.2 Bash Variables HISTCMD 5.2 Bash Variables HISTCMD 5.2 Bash Variables HISTCONTROL 5.2 Bash Variables HISTCONTROL 5.2 Bash Variables HISTFILE 5.2 Bash Variables HISTFILE 5.2 Bash Variables HISTFILESIZE 5.2 Bash Variables HISTFILESIZE 5.2 Bash Variables HISTIGNORE 5.2 Bash Variables HISTIGNORE 5.2 Bash Variables history-preserve-point 8.3.1 Readline Init File Syntax HISTSIZE 5.2 Bash Variables HISTSIZE 5.2 Bash Variables HOME 5.1 Bourne Shell Variables HOME 5.1 Bourne Shell Variables horizontal-scroll-mode 8.3.1 Readline Init File Syntax HOSTFILE 5.2 Bash Variables HOSTFILE 5.2 Bash Variables HOSTNAME 5.2 Bash Variables HOSTNAME 5.2 Bash Variables HOSTTYPE 5.2 Bash Variables HOSTTYPE 5.2 Bash Variables

I IFS 5.1 Bourne Shell Variables IFS 5.1 Bourne Shell Variables IGNOREEOF 5.2 Bash Variables IGNOREEOF 5.2 Bash Variables input-meta 8.3.1 Readline Init File Syntax INPUTRC 5.2 Bash Variables INPUTRC 5.2 Bash Variables isearch-terminators 8.3.1 Readline Init File Syntax

K keymap 8.3.1 Readline Init File Syntax

L LANG 5.2 Bash Variables LANG 5.2 Bash Variables LC_ALL 5.2 Bash Variables LC_ALL 5.2 Bash Variables LC_COLLATE 5.2 Bash Variables LC_COLLATE 5.2 Bash Variables LC_CTYPE 5.2 Bash Variables LC_CTYPE 5.2 Bash Variables LC_MESSAGES 3.1.2.5 Locale-Specific Translation LC_MESSAGES 5.2 Bash Variables LC_MESSAGES 5.2 Bash Variables LC_NUMERIC 5.2 Bash Variables LC_NUMERIC 5.2 Bash Variables LINENO 5.2 Bash Variables LINENO 5.2 Bash Variables LINES 5.2 Bash Variables LINES 5.2 Bash Variables

M MACHTYPE 5.2 Bash Variables MACHTYPE 5.2 Bash Variables MAIL 5.1 Bourne Shell Variables MAIL 5.1 Bourne Shell Variables MAILCHECK 5.2 Bash Variables MAILCHECK 5.2 Bash Variables MAILPATH 5.1 Bourne Shell Variables MAILPATH 5.1 Bourne Shell Variables mark-modified-lines 8.3.1 Readline Init File Syntax mark-symlinked-directories 8.3.1 Readline Init File Syntax match-hidden-files 8.3.1 Readline Init File Syntax meta-flag 8.3.1 Readline Init File Syntax

O OLDPWD 5.2 Bash Variables OLDPWD 5.2 Bash Variables OPTARG 5.1 Bourne Shell Variables OPTARG 5.1 Bourne Shell Variables OPTERR 5.2 Bash Variables OPTERR 5.2 Bash Variables OPTIND 5.1 Bourne Shell Variables OPTIND 5.1 Bourne Shell Variables OSTYPE 5.2 Bash Variables OSTYPE 5.2 Bash Variables output-meta 8.3.1 Readline Init File Syntax

P page-completions 8.3.1 Readline Init File Syntax PATH 5.1 Bourne Shell Variables PATH 5.1 Bourne Shell Variables PIPESTATUS 5.2 Bash Variables PIPESTATUS 5.2 Bash Variables POSIXLY_CORRECT 5.2 Bash Variables POSIXLY_CORRECT 5.2 Bash Variables PPID 5.2 Bash Variables PPID 5.2 Bash Variables PROMPT_COMMAND 5.2 Bash Variables PROMPT_COMMAND 5.2 Bash Variables PS1 5.1 Bourne Shell Variables PS1 5.1 Bourne Shell Variables PS2 5.1 Bourne Shell Variables PS2 5.1 Bourne Shell Variables PS3 5.2 Bash Variables PS3 5.2 Bash Variables PS4 5.2 Bash Variables PS4 5.2 Bash Variables PWD 5.2 Bash Variables PWD 5.2 Bash Variables

R RANDOM 5.2 Bash Variables RANDOM 5.2 Bash Variables REPLY 5.2 Bash Variables REPLY 5.2 Bash Variables

S SECONDS 5.2 Bash Variables SECONDS 5.2 Bash Variables SHELLOPTS 5.2 Bash Variables SHELLOPTS 5.2 Bash Variables SHLVL 5.2 Bash Variables SHLVL 5.2 Bash Variables show-all-if-ambiguous 8.3.1 Readline Init File Syntax

T TEXTDOMAIN 3.1.2.5 Locale-Specific Translation TEXTDOMAINDIR 3.1.2.5 Locale-Specific Translation TIMEFORMAT 5.2 Bash Variables TIMEFORMAT 5.2 Bash Variables TMOUT 5.2 Bash Variables TMOUT 5.2 Bash Variables

U UID 5.2 Bash Variables UID 5.2 Bash Variables

V visible-stats 8.3.1 Readline Init File Syntax

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A B C D E F G H I K L M O P R S T U V

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Function Index

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Index Entry Section

A abort (C-g) 8.4.8 Some Miscellaneous Commands abort (C-g) 8.4.8 Some Miscellaneous Commands accept-line (Newline or Return) 8.4.2 Commands For Manipulating The History accept-line (Newline or Return) 8.4.2 Commands For Manipulating The History alias-expand-line () 8.4.8 Some Miscellaneous Commands alias-expand-line () 8.4.8 Some Miscellaneous Commands

B backward-char (C-b) 8.4.1 Commands For Moving backward-char (C-b) 8.4.1 Commands For Moving backward-delete-char (Rubout) 8.4.3 Commands For Changing Text backward-delete-char (Rubout) 8.4.3 Commands For Changing Text backward-kill-line (C-x Rubout) 8.4.4 Killing And Yanking backward-kill-line (C-x Rubout) 8.4.4 Killing And Yanking backward-kill-word (M-DEL) 8.4.4 Killing And Yanking backward-kill-word (M-DEL) 8.4.4 Killing And Yanking backward-word (M-b) 8.4.1 Commands For Moving backward-word (M-b) 8.4.1 Commands For Moving beginning-of-history (M-<) 8.4.2 Commands For Manipulating The History beginning-of-history (M-<) 8.4.2 Commands For Manipulating The History beginning-of-line (C-a) 8.4.1 Commands For Moving beginning-of-line (C-a) 8.4.1 Commands For Moving

C call-last-kbd-macro (C-x e) 8.4.7 Keyboard Macros call-last-kbd-macro (C-x e) 8.4.7 Keyboard Macros capitalize-word (M-c) 8.4.3 Commands For Changing Text capitalize-word (M-c) 8.4.3 Commands For Changing Text character-search (C-]) 8.4.8 Some Miscellaneous Commands character-search (C-]) 8.4.8 Some Miscellaneous Commands character-search-backward (M-C-]) 8.4.8 Some Miscellaneous Commands character-search-backward (M-C-]) 8.4.8 Some Miscellaneous Commands clear-screen (C-l) 8.4.1 Commands For Moving clear-screen (C-l) 8.4.1 Commands For Moving complete (TAB) 8.4.6 Letting Readline Type For You complete (TAB) 8.4.6 Letting Readline Type For You complete-command (M-!) 8.4.6 Letting Readline Type For You complete-command (M-!) 8.4.6 Letting Readline Type For You complete-filename (M-/) 8.4.6 Letting Readline Type For You complete-filename (M-/) 8.4.6 Letting Readline Type For You complete-hostname (M-@) 8.4.6 Letting Readline Type For You complete-hostname (M-@) 8.4.6 Letting Readline Type For You complete-into-braces (M-{) 8.4.6 Letting Readline Type For You complete-into-braces (M-{) 8.4.6 Letting Readline Type For You complete-username (M-~) 8.4.6 Letting Readline Type For You complete-username (M-~) 8.4.6 Letting Readline Type For You complete-variable (M-$) 8.4.6 Letting Readline Type For You complete-variable (M-$) 8.4.6 Letting Readline Type For You copy-backward-word () 8.4.4 Killing And Yanking copy-backward-word () 8.4.4 Killing And Yanking copy-forward-word () 8.4.4 Killing And Yanking copy-forward-word () 8.4.4 Killing And Yanking copy-region-as-kill () 8.4.4 Killing And Yanking copy-region-as-kill () 8.4.4 Killing And Yanking

D delete-char (C-d) 8.4.3 Commands For Changing Text delete-char (C-d) 8.4.3 Commands For Changing Text delete-char-or-list () 8.4.6 Letting Readline Type For You delete-char-or-list () 8.4.6 Letting Readline Type For You delete-horizontal-space () 8.4.4 Killing And Yanking delete-horizontal-space () 8.4.4 Killing And Yanking digit-argument (M-0, M-1, ... M--) 8.4.5 Specifying Numeric Arguments digit-argument (M-0, M-1, ... M--) 8.4.5 Specifying Numeric Arguments display-shell-version (C-x C-v) 8.4.8 Some Miscellaneous Commands display-shell-version (C-x C-v) 8.4.8 Some Miscellaneous Commands do-uppercase-version (M-a, M-b, M-x, ...) 8.4.8 Some Miscellaneous Commands do-uppercase-version (M-a, M-b, M-x, ...) 8.4.8 Some Miscellaneous Commands downcase-word (M-l) 8.4.3 Commands For Changing Text downcase-word (M-l) 8.4.3 Commands For Changing Text dump-functions () 8.4.8 Some Miscellaneous Commands dump-functions () 8.4.8 Some Miscellaneous Commands dump-macros () 8.4.8 Some Miscellaneous Commands dump-macros () 8.4.8 Some Miscellaneous Commands dump-variables () 8.4.8 Some Miscellaneous Commands dump-variables () 8.4.8 Some Miscellaneous Commands dynamic-complete-history (M-TAB) 8.4.6 Letting Readline Type For You dynamic-complete-history (M-TAB) 8.4.6 Letting Readline Type For You

E edit-and-execute-command (C-xC-e) 8.4.8 Some Miscellaneous Commands edit-and-execute-command (C-xC-e) 8.4.8 Some Miscellaneous Commands end-kbd-macro (C-x )) 8.4.7 Keyboard Macros end-kbd-macro (C-x )) 8.4.7 Keyboard Macros end-of-history (M->) 8.4.2 Commands For Manipulating The History end-of-history (M->) 8.4.2 Commands For Manipulating The History end-of-line (C-e) 8.4.1 Commands For Moving end-of-line (C-e) 8.4.1 Commands For Moving exchange-point-and-mark (C-x C-x) 8.4.8 Some Miscellaneous Commands exchange-point-and-mark (C-x C-x) 8.4.8 Some Miscellaneous Commands

F forward-backward-delete-char () 8.4.3 Commands For Changing Text forward-backward-delete-char () 8.4.3 Commands For Changing Text forward-char (C-f) 8.4.1 Commands For Moving forward-char (C-f) 8.4.1 Commands For Moving forward-search-history (C-s) 8.4.2 Commands For Manipulating The History forward-search-history (C-s) 8.4.2 Commands For Manipulating The History forward-word (M-f) 8.4.1 Commands For Moving forward-word (M-f) 8.4.1 Commands For Moving

G glob-complete-word (M-g) 8.4.8 Some Miscellaneous Commands glob-complete-word (M-g) 8.4.8 Some Miscellaneous Commands glob-expand-word (C-x *) 8.4.8 Some Miscellaneous Commands glob-expand-word (C-x *) 8.4.8 Some Miscellaneous Commands glob-list-expansions (C-x g) 8.4.8 Some Miscellaneous Commands glob-list-expansions (C-x g) 8.4.8 Some Miscellaneous Commands

H history-and-alias-expand-line () 8.4.8 Some Miscellaneous Commands history-and-alias-expand-line () 8.4.8 Some Miscellaneous Commands history-expand-line (M-^) 8.4.8 Some Miscellaneous Commands history-expand-line (M-^) 8.4.8 Some Miscellaneous Commands history-search-backward () 8.4.2 Commands For Manipulating The History history-search-backward () 8.4.2 Commands For Manipulating The History history-search-forward () 8.4.2 Commands For Manipulating The History history-search-forward () 8.4.2 Commands For Manipulating The History

I insert-comment (M-#) 8.4.8 Some Miscellaneous Commands insert-comment (M-#) 8.4.8 Some Miscellaneous Commands insert-completions (M-*) 8.4.6 Letting Readline Type For You insert-completions (M-*) 8.4.6 Letting Readline Type For You insert-last-argument (M-. or M-_) 8.4.8 Some Miscellaneous Commands insert-last-argument (M-. or M-_) 8.4.8 Some Miscellaneous Commands

K kill-line (C-k) 8.4.4 Killing And Yanking kill-line (C-k) 8.4.4 Killing And Yanking kill-region () 8.4.4 Killing And Yanking kill-region () 8.4.4 Killing And Yanking kill-whole-line () 8.4.4 Killing And Yanking kill-whole-line () 8.4.4 Killing And Yanking kill-word (M-d) 8.4.4 Killing And Yanking kill-word (M-d) 8.4.4 Killing And Yanking

M magic-space () 8.4.8 Some Miscellaneous Commands magic-space () 8.4.8 Some Miscellaneous Commands menu-complete () 8.4.6 Letting Readline Type For You menu-complete () 8.4.6 Letting Readline Type For You

N next-history (C-n) 8.4.2 Commands For Manipulating The History next-history (C-n) 8.4.2 Commands For Manipulating The History non-incremental-forward-search-history (M-n) 8.4.2 Commands For Manipulating The History non-incremental-forward-search-history (M-n) 8.4.2 Commands For Manipulating The History non-incremental-reverse-search-history (M-p) 8.4.2 Commands For Manipulating The History non-incremental-reverse-search-history (M-p) 8.4.2 Commands For Manipulating The History

O operate-and-get-next (C-o) 8.4.8 Some Miscellaneous Commands operate-and-get-next (C-o) 8.4.8 Some Miscellaneous Commands overwrite-mode () 8.4.3 Commands For Changing Text overwrite-mode () 8.4.3 Commands For Changing Text

P possible-command-completions (C-x !) 8.4.6 Letting Readline Type For You possible-command-completions (C-x !) 8.4.6 Letting Readline Type For You possible-completions (M-?) 8.4.6 Letting Readline Type For You possible-completions (M-?) 8.4.6 Letting Readline Type For You possible-filename-completions (C-x /) 8.4.6 Letting Readline Type For You possible-filename-completions (C-x /) 8.4.6 Letting Readline Type For You possible-hostname-completions (C-x @) 8.4.6 Letting Readline Type For You possible-hostname-completions (C-x @) 8.4.6 Letting Readline Type For You possible-username-completions (C-x ~) 8.4.6 Letting Readline Type For You possible-username-completions (C-x ~) 8.4.6 Letting Readline Type For You possible-variable-completions (C-x $) 8.4.6 Letting Readline Type For You possible-variable-completions (C-x $) 8.4.6 Letting Readline Type For You prefix-meta (ESC) 8.4.8 Some Miscellaneous Commands prefix-meta (ESC) 8.4.8 Some Miscellaneous Commands previous-history (C-p) 8.4.2 Commands For Manipulating The History previous-history (C-p) 8.4.2 Commands For Manipulating The History

Q quoted-insert (C-q or C-v) 8.4.3 Commands For Changing Text quoted-insert (C-q or C-v) 8.4.3 Commands For Changing Text

R re-read-init-file (C-x C-r) 8.4.8 Some Miscellaneous Commands re-read-init-file (C-x C-r) 8.4.8 Some Miscellaneous Commands redraw-current-line () 8.4.1 Commands For Moving redraw-current-line () 8.4.1 Commands For Moving reverse-search-history (C-r) 8.4.2 Commands For Manipulating The History reverse-search-history (C-r) 8.4.2 Commands For Manipulating The History revert-line (M-r) 8.4.8 Some Miscellaneous Commands revert-line (M-r) 8.4.8 Some Miscellaneous Commands

S self-insert (a, b, A, 1, !, ...) 8.4.3 Commands For Changing Text self-insert (a, b, A, 1, !, ...) 8.4.3 Commands For Changing Text set-mark (C-@) 8.4.8 Some Miscellaneous Commands set-mark (C-@) 8.4.8 Some Miscellaneous Commands shell-expand-line (M-C-e) 8.4.8 Some Miscellaneous Commands shell-expand-line (M-C-e) 8.4.8 Some Miscellaneous Commands start-kbd-macro (C-x () 8.4.7 Keyboard Macros start-kbd-macro (C-x () 8.4.7 Keyboard Macros

T tilde-expand (M-&) 8.4.8 Some Miscellaneous Commands tilde-expand (M-&) 8.4.8 Some Miscellaneous Commands transpose-chars (C-t) 8.4.3 Commands For Changing Text transpose-chars (C-t) 8.4.3 Commands For Changing Text transpose-words (M-t) 8.4.3 Commands For Changing Text transpose-words (M-t) 8.4.3 Commands For Changing Text

U undo (C-_ or C-x C-u) 8.4.8 Some Miscellaneous Commands undo (C-_ or C-x C-u) 8.4.8 Some Miscellaneous Commands universal-argument () 8.4.5 Specifying Numeric Arguments universal-argument () 8.4.5 Specifying Numeric Arguments unix-line-discard (C-u) 8.4.4 Killing And Yanking unix-line-discard (C-u) 8.4.4 Killing And Yanking unix-word-rubout (C-w) 8.4.4 Killing And Yanking unix-word-rubout (C-w) 8.4.4 Killing And Yanking upcase-word (M-u) 8.4.3 Commands For Changing Text upcase-word (M-u) 8.4.3 Commands For Changing Text

Y yank (C-y) 8.4.4 Killing And Yanking yank (C-y) 8.4.4 Killing And Yanking yank-last-arg (M-. or M-_) 8.4.2 Commands For Manipulating The History yank-last-arg (M-. or M-_) 8.4.2 Commands For Manipulating The History yank-nth-arg (M-C-y) 8.4.2 Commands For Manipulating The History yank-nth-arg (M-C-y) 8.4.2 Commands For Manipulating The History yank-pop (M-y) 8.4.4 Killing And Yanking yank-pop (M-y) 8.4.4 Killing And Yanking

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Concept Index

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Index Entry Section

A alias expansion 6.6 Aliases arithmetic evaluation 6.5 Shell Arithmetic arithmetic expansion 3.5.5 Arithmetic Expansion arithmetic, shell 6.5 Shell Arithmetic arrays 6.7 Arrays

B background 7.1 Job Control Basics Bash configuration 10.1 Basic Installation Bash installation 10.1 Basic Installation Bourne shell 3. Basic Shell Features brace expansion 3.5.1 Brace Expansion builtin 2. Definitions

C command editing 8.2.1 Readline Bare Essentials command execution 3.7.2 Command Search and Execution command expansion 3.7.1 Simple Command Expansion command history 9.1 Bash History Facilities command search 3.7.2 Command Search and Execution command substitution 3.5.4 Command Substitution command timing 3.2.2 Pipelines commands, conditional 3.2.5 Conditional Constructs commands, grouping 3.2.6 Grouping Commands commands, lists 3.2.3 Lists of Commands commands, looping 3.2.4 Looping Constructs commands, pipelines 3.2.2 Pipelines commands, shell 3.2 Shell Commands commands, simple 3.2.1 Simple Commands comments, shell 3.1.3 Comments completion builtins 8.7 Programmable Completion Builtins configuration 10.1 Basic Installation control operator 2. Definitions

D directory stack 6.8 The Directory Stack

E editing command lines 8.2.1 Readline Bare Essentials environment 3.7.4 Environment evaluation, arithmetic 6.5 Shell Arithmetic event designators 9.3.1 Event Designators execution environment 3.7.3 Command Execution Environment exit status 2. Definitions exit status 3.7.5 Exit Status expansion 3.5 Shell Expansions expansion, arithmetic 3.5.5 Arithmetic Expansion expansion, brace 3.5.1 Brace Expansion expansion, filename 3.5.8 Filename Expansion expansion, parameter 3.5.3 Shell Parameter Expansion expansion, pathname 3.5.8 Filename Expansion expansion, tilde 3.5.2 Tilde Expansion expressions, arithmetic 6.5 Shell Arithmetic expressions, conditional 6.4 Bash Conditional Expressions

F field 2. Definitions filename 2. Definitions filename expansion 3.5.8 Filename Expansion foreground 7.1 Job Control Basics functions, shell 3.3 Shell Functions

H history builtins 9.2 Bash History Builtins history events 9.3.1 Event Designators history expansion 9.3 History Expansion history list 9.1 Bash History Facilities History, how to use 8.7 Programmable Completion Builtins

I identifier 2. Definitions initialization file, readline 8.3 Readline Init File installation 10.1 Basic Installation interaction, readline 8.2 Readline Interaction interactive shell 6.1 Invoking Bash interactive shell 6.3 Interactive Shells internationalization 3.1.2.5 Locale-Specific Translation

J job 2. Definitions job control 2. Definitions job control 7.1 Job Control Basics

K kill ring 8.2.3 Readline Killing Commands killing text 8.2.3 Readline Killing Commands

L localization 3.1.2.5 Locale-Specific Translation login shell 6.1 Invoking Bash

M matching, pattern 3.5.8.1 Pattern Matching metacharacter 2. Definitions

N name 2. Definitions native languages 3.1.2.5 Locale-Specific Translation notation, readline 8.2.1 Readline Bare Essentials

O operator, shell 2. Definitions

P parameter expansion 3.5.3 Shell Parameter Expansion parameters 3.4 Shell Parameters parameters, positional 3.4.1 Positional Parameters parameters, special 3.4.2 Special Parameters pathname expansion 3.5.8 Filename Expansion pattern matching 3.5.8.1 Pattern Matching pipeline 3.2.2 Pipelines POSIX 2. Definitions POSIX Mode 6.11 Bash POSIX Mode process group 2. Definitions process group ID 2. Definitions process substitution 3.5.6 Process Substitution programmable completion 8.6 Programmable Completion prompting 6.9 Controlling the Prompt

Q quoting 3.1.2 Quoting quoting, ANSI 3.1.2.4 ANSI-C Quoting

R Readline, how to use 7.3 Job Control Variables redirection 3.6 Redirections reserved word 2. Definitions restricted shell 6.10 The Restricted Shell return status 2. Definitions

S shell arithmetic 6.5 Shell Arithmetic shell function 3.3 Shell Functions shell script 3.8 Shell Scripts shell variable 3.4 Shell Parameters shell, interactive 6.3 Interactive Shells signal 2. Definitions signal handling 3.7.6 Signals special builtin 2. Definitions special builtin 4.4 Special Builtins startup files 6.2 Bash Startup Files suspending jobs 7.1 Job Control Basics

T tilde expansion 3.5.2 Tilde Expansion token 2. Definitions translation, native languages 3.1.2.5 Locale-Specific Translation

V variable, shell 3.4 Shell Parameters variables, readline 8.3.1 Readline Init File Syntax

W word 2. Definitions word splitting 3.5.7 Word Splitting

Y yanking text 8.2.3 Readline Killing Commands

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Short Table of Contents

1. Introduction
2. Definitions
3. Basic Shell Features
4. Shell Builtin Commands
5. Shell Variables
6. Bash Features
7. Job Control
8. Command Line Editing
9. Using History Interactively
10. Installing Bash
A. Reporting Bugs
B. Major Differences From The Bourne Shell
Index of Shell Builtin Commands
Index of Shell Reserved Words
Parameter and Variable Index
Function Index
Concept Index

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About this document

This document was generated by John Paul Wallington on November, 6 2003using texi2html

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Bash Reference Manual: MySQL :: MySQL 5.0 Reference Manual :: 11.17.2 DECIMAL Data Type Changes C++ Reference [C++ Reference] Git Reference Finance.Reference const reference和nonconst reference g++ Manual Page OSI reference model undefined reference to 'pthread undefined reference to rpl Bash 实例，第一部分 bash脚本-创建函数 Bash编程实例一 sed命令专区 Bash 实例，第 2 部分 Bash 实例，第 3 部分 Manual reseal and hiding the "FBReseal" window Graphitron 5 user manual译文(编程资料) Reference from another team-building perspective Linux 技巧: Bash 参数和参数扩展 How to cross-compile BASH for Android Bash中关于日期时间操作的常用自定义函数 - Bash @ Linux - JavaEy... Graphitron 5 user manual译文(编程资料)1 BartPE: manual for a Windows XP based PE

香港 论坛 讨论区:Bash Reference Manual:

Bash Reference Manual

1. Introduction

1.1 What is Bash?

1.2 What is a shell?

2. Definitions

3. Basic Shell Features

3.1 Shell Syntax

3.1.1 Shell Operation

3.1.2 Quoting

3.1.2.1 Escape Character

3.1.2.2 Single Quotes

3.1.2.3 Double Quotes

3.1.2.4 ANSI-C Quoting

3.1.2.5 Locale-Specific Translation

3.1.3 Comments

3.2 Shell Commands

3.2.1 Simple Commands

3.2.2 Pipelines

3.2.3 Lists of Commands

3.2.4 Looping Constructs

3.2.5 Conditional Constructs

3.2.6 Grouping Commands

3.3 Shell Functions

3.4 Shell Parameters

3.4.1 Positional Parameters

3.4.2 Special Parameters

3.5 Shell Expansions

3.5.1 Brace Expansion

3.5.2 Tilde Expansion

3.5.3 Shell Parameter Expansion

3.5.4 Command Substitution

3.5.5 Arithmetic Expansion

3.5.6 Process Substitution

3.5.7 Word Splitting

3.5.8 Filename Expansion

3.5.8.1 Pattern Matching

3.5.9 Quote Removal

3.6 Redirections

3.6.1 Redirecting Input

3.6.2 Redirecting Output

3.6.3 Appending Redirected Output

3.6.4 Redirecting Standard Output and Standard Error

3.6.5 Here Documents

3.6.6 Here Strings

3.6.7 Duplicating File Descriptors

3.6.8 Moving File Descriptors

3.6.9 Opening File Descriptors for Reading and Writing

3.7 Executing Commands

3.7.1 Simple Command Expansion

3.7.2 Command Search and Execution

3.7.3 Command Execution Environment

3.7.4 Environment

3.7.5 Exit Status

3.7.6 Signals

3.8 Shell Scripts

4. Shell Builtin Commands

4.1 Bourne Shell Builtins

4.2 Bash Builtin Commands

4.3 The Set Builtin

4.4 Special Builtins

5. Shell Variables

5.1 Bourne Shell Variables

5.2 Bash Variables

6. Bash Features

6.1 Invoking Bash

6.2 Bash Startup Files

Invoked as an interactive login shell, or with `--login'

Invoked as an interactive non-login shell

Invoked non-interactively

Invoked with name sh

Invoked in POSIX mode

Invoked by remote shell daemon

Invoked with unequal effective and real UID/GIDs

6.3 Interactive Shells

6.3.1 What is an Interactive Shell?

6.3.2 Is this Shell Interactive?

6.3.3 Interactive Shell Behavior

6.4 Bash Conditional Expressions

6.5 Shell Arithmetic

香港论坛讨论区:Bash Reference Manual:

Invoked with name `sh`