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Bash Reference ManualThis text is a brief description of the features that are present in the Bash shell (version 3.2, 28 September 2006).
This is Edition 3.2, last updated 28 September 2006,
of The GNU Bash Reference Manual,
for Bash contains features that appear in other popular shells, and some features that only appear in Bash. Some of the shells that Bash has borrowed concepts from are the Bourne Shell (`sh'), the Korn Shell (`ksh'), and the C-shell (`csh' and its successor, `tcsh'). The following menu breaks the features up into categories based upon which one of these other shells inspired the feature. This manual is meant as a brief introduction to features found in Bash. The Bash manual page should be used as the definitive reference on shell behavior.
1. Introduction
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 of
the current Unix shell
Bash is largely compatible with
While the GNU operating system provides other shells, including
a version of
1.2 What is a shell?At its base, a shell is simply a macro processor that executes commands. The term macro processor means functionality where text and symbols are expanded to create larger expressions. A Unix shell is both a command interpreter and a programming language. As a command interpreter, the shell provides the user interface to the rich set of GNU utilities. The programming language features allow these utilitites to be combined. Files containing commands can be created, and become commands themselves. These new commands have the same status as system commands in directories such as `/bin', allowing users or groups to establish custom environments to automate their common tasks. Shells may be used interactively or non-interactively. In interactive mode, they accept input typed from the keyboard. When executing non-interactively, shells execute commands read from a file. A shell allows execution of GNU commands, both synchronously and asynchronously. The shell waits for synchronous commands to complete before accepting more input; asynchronous commands continue to execute in parallel with the shell while it reads and executes additional commands. The redirection constructs permit fine-grained control of the input and output of those commands. Moreover, the shell allows control over the contents of commands' environments.
Shells also provide a small set of built-in
commands (builtins) implementing functionality impossible
or inconvenient to obtain via separate utilities.
For example, While executing commands is essential, most of the power (and complexity) of shells is due to their embedded programming languages. Like any high-level language, the shell provides variables, flow control constructs, quoting, and functions. Shells offer features geared specifically for interactive use rather than to augment the programming language. These interactive features include job control, command line editing, command history and aliases. Each of these features is described in this manual.
2. DefinitionsThese definitions are used throughout the remainder of this manual.
3. Basic Shell FeaturesBash is an acronym for `Bourne-Again SHell'. The Bourne shell is the traditional Unix shell originally written by Stephen Bourne. All of the Bourne shell builtin commands are available in Bash, The rules for evaluation and quoting are taken from the POSIX specification for the `standard' Unix shell. This chapter briefly summarizes the shell's `building blocks': commands, control structures, shell functions, shell parameters, shell expansions, redirections, which are a way to direct input and output from and to named files, and how the shell executes commands.
3.1 Shell Syntax
When the shell reads input, it proceeds through a sequence of operations. If the input indicates the beginning of a comment, the shell ignores the comment symbol (`#'), and the rest of that line. Otherwise, roughly speaking, the shell reads its input and divides the input into words and operators, employing the quoting rules to select which meanings to assign various words and characters. The shell then parses these tokens into commands and other constructs, removes the special meaning of certain words or characters, expands others, redirects input and output as needed, executes the specified command, waits for the command's exit status, and makes that exit status available for further inspection or processing.
3.1.1 Shell OperationThe following is a brief description of the shell's operation when it reads and executes a command. Basically, the shell does the following:
3.1.2 Quoting
Quoting is used to remove the special meaning of certain characters or words to the shell. Quoting can be used to disable special treatment for special characters, to prevent reserved words from being recognized as such, and to prevent parameter expansion. Each of the shell metacharacters (see section 2. Definitions) has special meaning to the shell and must be quoted if it is to represent itself. When the command history expansion facilities are being used (see section 9.3 History Expansion), the history expansion character, usually `!', must be quoted to prevent history expansion. See section 9.1 Bash History Facilities, for more details concerning history expansion. There are three quoting mechanisms: the escape character, single quotes, and double quotes.
3.1.2.1 Escape CharacterA non-quoted backslash `\' is the Bash escape character. It preserves the literal value of the next character that follows, with the exception ofnewline. If a \newline pair
appears, and the backslash itself is not quoted, the \newline
is treated as a line continuation (that is, it is removed from
the input stream and effectively ignored).
3.1.2.2 Single QuotesEnclosing characters in single quotes (`'') preserves the literal value of each character within the quotes. A single quote may not occur between single quotes, even when preceded by a backslash.
3.1.2.3 Double Quotes
Enclosing characters in double quotes (`"') preserves the literal value
of all characters within the quotes, with the exception of
`$', ``', `\',
and, when history expansion is enabled, `!'.
The characters `$' and ``'
retain their special meaning within double quotes (see section 3.5 Shell Expansions).
The backslash retains its special meaning only when followed by one of
the following characters:
`$', ``', `"', `\', or The special parameters `*' and `@' have special meaning when in double quotes (see section 3.5.3 Shell Parameter Expansion).
3.1.2.4 ANSI-C Quoting
Words of the form
The expanded result is single-quoted, as if the dollar sign had not been present.
3.1.2.5 Locale-Specific Translation
A double-quoted string preceded by a dollar sign (`$') will cause
the string to be translated according to the current locale.
If the current locale is
Some systems use the message catalog selected by the
3.1.3 Comments
In a non-interactive shell, or an interactive shell in which the
3.2 Shell Commands
A simple shell command such as More complex shell commands are composed of simple commands arranged together in a variety of ways: in a pipeline in which the output of one command becomes the input of a second, in a loop or conditional construct, or in some other grouping.
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
The return status (see section 3.7.5 Exit Status) of a simple command is
its exit status as provided
by the POSIX 1003.1
3.2.2 Pipelines
A
The output of each command in the pipeline is connected via a pipe to the input of the next command. That is, each command reads the previous command's output.
The reserved word If the pipeline is not executed asynchronously (see section 3.2.3 Lists of Commands), the shell 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 exit
status of a pipeline is the exit status of the last command in the
pipeline, unless the
3.2.3 Lists of Commands
A 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
If a command is terminated by the control operator `&',
the shell executes the command asynchronously in a subshell.
This is known as executing the command in the background.
The shell does not wait for the command to finish, and the return
status is 0 (true).
When job control is not active (see section 7. Job Control),
the standard input for asynchronous commands, in the absence of any
explicit redirections, is redirected from Commands separated by a `;' are executed sequentially; the shell waits for each command to terminate in turn. The return status is the exit status of the last command executed. The control operators `&&' and `||' denote AND lists and OR lists, respectively. An AND list has the form
command2 is executed if, and only if, command1 returns an exit status of zero. An OR list has the form
command2 is executed if, and only if, command1 returns a non-zero exit status. The return status of AND and OR lists is the exit status of the last command executed in the list.
3.2.4 Compound Commands
Compound commands are the shell programming constructs. Each construct begins with a reserved word or control operator and is terminated by a corresponding reserved word or operator. Any redirections (see section 3.6 Redirections) associated with a compound command apply to all commands within that compound command unless explicitly overridden. Bash provides looping constructs, conditional commands, and mechanisms to group commands and execute them as a unit.
3.2.4.1 Looping ConstructsBash supports the following looping constructs. Note that wherever a `;' appears in the description of a command's syntax, it may be replaced with one or more newlines.
The
3.2.4.2 Conditional Constructs
3.2.4.3 Grouping CommandsBash provides two ways to group a list of commands to be executed as a unit. When commands are grouped, redirections may be applied to the entire command list. For example, the output of all the commands in the list may be redirected to a single stream.
In addition to the creation of a subshell, there is a subtle difference
between these two constructs due to historical reasons. The braces
are The exit status of both of these constructs is the exit status of list.
3.3 Shell FunctionsShell functions are a way to group commands for later execution using a single name for the group. They are executed just like a "regular" command. When the name of a shell function is used as a simple command name, the list of commands associated with that function name is executed. Shell functions are executed in the current shell context; no new process is created to interpret them. Functions are declared using this syntax:
This defines a shell function named name. The reserved
word
A function definition may be deleted using the `-f' option to the
The exit status of a function definition is zero unless a syntax error occurs or a readonly function with the same name already exists. When executed, the exit status of a function is the exit status of the last command executed in the body.
Note that for historical reasons, in the most common usage the curly braces
that surround the body of the function must be separated from the body by
When a function is executed, the arguments to the
function become the positional parameters
during its execution (see section 3.4.1 Positional Parameters).
The special parameter `#' that expands to the number of
positional parameters is updated to reflect the change.
Special parameter
If the builtin command
Variables local to the function may be declared with the
Function names and definitions may be listed with the
`-f' option to the Functions may be recursive. No limit is placed on the number of recursive calls.
3.4 Shell Parameters
A parameter is an entity that stores values.
It can be a
A parameter is set if it has been assigned a value. The null string is
a valid value. Once a variable is set, it may be unset only by using
the A variable may be assigned to by a statement of the form
integer
attribute set, then value
is evaluated as an arithmetic expression even if the $((...))
expansion is not used (see section 3.5.5 Arithmetic Expansion).
Word splitting is not performed, with the exception
of "$@" as explained below.
Filename expansion is not performed.
Assignment statements may also appear as arguments to the
alias,
declare, typeset, export, readonly,
and local builtin commands.
In the context where an assignment statement is assigning a value to a shell variable or array index (see section 6.7 Arrays), the `+=' operator can be used to append to or add to the variable's previous value. When `+=' is applied to a variable for which the integer attribute has been set, value is evaluated as an arithmetic expression and added to the variable's current value, which is also evaluated. When `+=' is applied to an array variable using compound assignment (see section 6.7 Arrays), the variable's value is not unset (as it is when using `='), and new values are appended to the array beginning at one greater than the array's maximum index. When applied to a string-valued variable, value is expanded and appended to the variable's value.
3.4.1 Positional Parameters
A positional parameter is a parameter denoted by one or more
digits, other than the single digit When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces.
3.4.2 Special ParametersThe shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed.
3.5 Shell Expansions
Expansion is performed on the command line after it has been split into
The order of expansions is: brace expansion, tilde expansion, parameter, variable, and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and filename expansion. On systems that can support it, there is an additional expansion available: process substitution. This is performed at the same time as parameter, variable, and arithmetic expansion and command substitution.
Only brace expansion, word splitting, and filename expansion
can change the number of words of the expansion; other expansions
expand a single word to a single word.
The only exceptions to this are the expansions of
After all expansions,
3.5.1 Brace ExpansionBrace expansion is a mechanism by which arbitrary strings may be generated. This mechanism is similar to filename 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 either a series of comma-separated strings or a sequnce expression between a pair of braces, followed by an optional postscript. The preamble is prefixed to each string contained within the braces, and the postscript is then appended to each resulting string, expanding left to right. Brace expansions may be nested. The results of each expanded string are not sorted; left to right order is preserved. For example,
A sequence expression takes the form Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in the result. It is strictly textual. Bash does not apply any syntactic interpretation to the context of the expansion or the text between the braces. To avoid conflicts with parameter expansion, the string `${' is not considered eligible for brace expansion. A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma or a valid sequence expression. Any incorrectly formed brace expansion is left unchanged. A { or `,' may be quoted with a backslash to prevent its being considered part of a brace expression. To avoid conflicts with parameter expansion, the string `${' is not considered eligible for brace expansion. This construct is typically used as shorthand when the common prefix of the strings to be generated is longer than in the above example:
3.5.2 Tilde Expansion
If a word begins with an unquoted tilde character (`~'), all of the
characters up to the first unquoted slash (or all characters,
if there is no unquoted slash) are considered a tilde-prefix.
If none of the characters in the tilde-prefix are quoted, the
characters in the tilde-prefix following the tilde are treated as a
possible login name.
If this login name is the null string, the tilde is replaced with the
value of the
If the tilde-prefix is `~+', the value of
the shell variable
If the characters following the tilde in the tilde-prefix consist of a
number N, optionally prefixed by a `+' or a `-',
the tilde-prefix is replaced with the
corresponding element from the directory stack, as it would be displayed
by the If the login name is invalid, or the tilde expansion fails, the word is left unchanged.
Each variable assignment is checked for unquoted tilde-prefixes immediately
following a `:' or the first `='.
In these cases, tilde expansion is also performed.
Consequently, one may use file names with tildes in assignments to
The following table shows how Bash treats unquoted tilde-prefixes:
3.5.3 Shell Parameter ExpansionThe `$' character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded may be enclosed in braces, which are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name. When braces are used, the matching ending brace is the first `}' not escaped by a backslash or within a quoted string, and not within an embedded arithmetic expansion, command substitution, or parameter expansion. The basic form of parameter expansion is ${parameter}. The value of parameter is substituted. The braces are required when parameter is a positional parameter with more than one digit, or when parameter is followed by a character that is not to be interpreted as part of its name.
If the first character of parameter is an exclamation point,
a level of variable indirection is introduced.
Bash uses the value of the variable formed from the rest of
parameter as the name of the variable; this variable is then
expanded and that value is used in the rest of the substitution, rather
than the value of parameter itself.
This is known as In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion. When not performing substring expansion, Bash tests for a parameter that is unset or null; omitting the colon results in a test only for a parameter that is unset. Put another way, if the colon is included, the operator tests for both existence and that the value is not null; if the colon is omitted, the operator tests only for existence.
3.5.4 Command SubstitutionCommand substitution allows the output of a command to replace the command itself. Command substitution occurs when a command is enclosed as follows:
Bash performs the expansion by executing command and
replacing the command substitution with the standard output of the
command, with any trailing newlines deleted.
Embedded newlines are not deleted, but they may be removed during
word splitting.
The command substitution
When the old-style backquote form of substitution is used,
backslash retains its literal meaning except when followed by
`$', ``', or `\'.
The first backquote not preceded by a backslash terminates the
command substitution.
When using the Command substitutions may be nested. To nest when using the backquoted form, escape the inner backquotes with backslashes. If the substitution appears within double quotes, word splitting and filename expansion are not performed on the results.
3.5.5 Arithmetic ExpansionArithmetic expansion allows the evaluation of an arithmetic expression and the substitution of the result. The format for arithmetic expansion is:
The expression is treated as if it were within double quotes, but a double quote inside the parentheses is not treated specially. All tokens in the expression undergo parameter expansion, command substitution, and quote removal. Arithmetic expansions may be nested. The evaluation is performed according to the rules listed below (see section 6.5 Shell Arithmetic). If the expression is invalid, Bash prints a message indicating failure to the standard error and no substitution occurs.
3.5.6 Process SubstitutionProcess substitution is supported on systems that support named pipes (FIFOs) or the `/dev/fd' method of naming open files. It takes the form of
>(list) form is used, writing to
the file will provide input for list. If the
<(list) form is used, the file passed as an
argument should be read to obtain the output of list.
Note that no space may appear between the < or >
and the left parenthesis, otherwise the construct would be interpreted
as a redirection.
When available, process substitution is performed simultaneously with parameter and variable expansion, command substitution, and arithmetic expansion.
3.5.7 Word SplittingThe shell scans the results of parameter expansion, command substitution, and arithmetic expansion that did not occur within double quotes for word splitting.
The shell treats each character of
Explicit null arguments ( Note that if no expansion occurs, no splitting is performed.
3.5.8 Filename Expansion
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 is
regarded as a pattern,
and replaced with an alphabetically sorted list of
file names matching the pattern. If no matching file names are found,
and the shell option
When a pattern is used for filename generation, the character `.'
at the start of a filename or immediately following a slash
must be matched explicitly, unless the shell option
See the description of
The
3.5.8.1 Pattern MatchingAny character that appears in a pattern, other than the special pattern characters described below, matches itself. The NUL character may not occur in a pattern. A backslash escapes the following character; the escaping backslash is discarded when matching. The special pattern characters must be quoted if they are to be matched literally. The special pattern characters have the following meanings:
If the
3.5.9 Quote RemovalAfter the preceding expansions, all unquoted occurrences of the characters `\', `'', and `"' that did not result from one of the above expansions are removed.
3.6 RedirectionsBefore a command is executed, its input and output may be redirected using a special notation interpreted by the shell. Redirection may also be used to open and close files for the current shell execution environment. The following redirection operators may precede or appear anywhere within a simple command or may follow a command. Redirections are processed in the order they appear, from left to right. In the following descriptions, if the file descriptor number is omitted, and the first character of the redirection operator is `<', the redirection refers to the standard input (file descriptor 0). If the first character of the redirection operator is `>', the redirection refers to the standard output (file descriptor 1). The word following the redirection operator in the following descriptions, unless otherwise noted, is subjected to brace expansion, tilde expansion, parameter expansion, command substitution, arithmetic expansion, quote removal, filename expansion, and word splitting. If it expands to more than one word, Bash reports an error. Note that the order of redirections is significant. For example, the command
Bash handles several filenames specially when they are used in redirections, as described in the following table:
A failure to open or create a file causes the redirection to fail. Redirections using file descriptors greater than 9 should be used with care, as they may conflict with file descriptors the shell uses internally.
3.6.1 Redirecting InputRedirection of input causes the file whose name results from the expansion of word to be opened for reading on file descriptorn,
or the standard input (file descriptor 0) if n
is not specified.
The general format for redirecting input is:
3.6.2 Redirecting OutputRedirection of output causes the file whose name results from the expansion of word to be opened for writing on file descriptor n, or the standard output (file descriptor 1) if n is not specified. If the file does not exist it is created; if it does exist it is truncated to zero size.The general format for redirecting output is:
If the redirection operator is `>', and the
3.6.3 Appending Redirected OutputRedirection of output in this fashion causes the file whose name results from the expansion of word to be opened for appending on file descriptor n, or the standard output (file descriptor 1) if n is not specified. If the file does not exist it is created.The general format for appending output is:
3.6.4 Redirecting Standard Output and Standard ErrorBash allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be redirected to the file whose name is the expansion of word with this construct.There are two formats for redirecting standard output and standard error:
3.6.5 Here DocumentsThis type of redirection instructs the shell to read input from the current source until a line containing only word (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input for a command.The format of here-documents is:
No parameter expansion, command substitution, arithmetic expansion,
or filename expansion is performed on
word. If any characters in word are quoted, the
delimiter is the result of quote removal on word,
and the lines in the here-document are not expanded.
If word is unquoted,
all lines of the here-document are subjected to parameter expansion,
command substitution, and arithmetic expansion. In the latter
case, the character sequence If the redirection operator is `<<-', then all leading tab characters are stripped from input lines and the line containing delimiter. This allows here-documents within shell scripts to be indented in a natural fashion.
3.6.6 Here StringsA variant of here documents, the format is:
The word is expanded and supplied to the command on its standard input.
3.6.7 Duplicating File DescriptorsThe redirection operator
The operator
3.6.8 Moving File DescriptorsThe redirection operator
Similarly, the redirection operator
3.6.9 Opening File Descriptors for Reading and WritingThe redirection operator
3.7 Executing Commands
3.7.1 Simple Command ExpansionWhen a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to right.
If no command name results, the variable assignments affect the current shell environment. Otherwise, the variables are added to the environment of the executed command and do not affect the current shell environment. If any of the assignments attempts to assign a value to a readonly variable, an error occurs, and the command exits with a non-zero status. If no command name results, redirections are performed, but do not affect the current shell environment. A redirection error causes the command to exit with a non-zero status. If there is a command name left after expansion, execution proceeds as described below. Otherwise, the command exits. If one of the expansions contained a command substitution, the exit status of the command is the exit status of the last command substitution performed. If there were no command substitutions, the command exits with a status of zero.
3.7.2 Command Search and ExecutionAfter a command has been split into words, if it results in a simple command and an optional list of arguments, the following actions are taken.
3.7.3 Command Execution EnvironmentThe shell has an execution environment, which consists of the following:
When a simple command other than a builtin or shell function is to be executed, it is invoked in a separate execution environment that consists of the following. Unless otherwise noted, the values are inherited from the shell.
A command invoked in this separate environment cannot affect the shell's execution environment. Command substitution, commands grouped with parentheses, and asynchronous commands are invoked in a subshell environment that is a duplicate of the shell environment, except that traps caught by the shell are reset to the values that the shell inherited from its parent at invocation. Builtin commands that are invoked as part of a pipeline are also executed in a subshell environment. Changes made to the subshell environment cannot affect the shell's execution environment. If a command is followed by a `&' and job control is not active, the default standard input for the command is the empty file `/dev/null'. Otherwise, the invoked command inherits the file descriptors of the calling shell as modified by redirections.
3.7.4 Environment
When a program is invoked it is given an array of strings
called the environment.
This is a list of name-value pairs, of the form
Bash provides several ways to manipulate the environment.
On invocation, the shell scans its own environment and
creates a parameter for each name found, automatically marking
it for export
to child processes. Executed commands inherit the environment.
The The environment for any simple command or function may be augmented temporarily by prefixing it with parameter assignments, as described in 3.4 Shell Parameters. These assignment statements affect only the environment seen by that command. If the `-k' option is set (see section 4.3 The Set Builtin), then all parameter assignments are placed in the environment for a command, not just those that precede the command name. When Bash invokes an external command, the variable `$_' is set to the full path name of the command and passed to that command in its environment.
3.7.5 Exit StatusFor the shell's purposes, a command which exits with a zero exit status has succeeded. A non-zero exit status indicates failure. This seemingly counter-intuitive scheme is used so there is one well-defined way to indicate success and a variety of ways to indicate various failure modes. When a command terminates on a fatal signal whose number is N, Bash uses the value 128+N as the exit status. If a command is not found, the child process created to execute it returns a status of 127. If a command is found but is not executable, the return status is 126. If a command fails because of an error during expansion or redirection, the exit status is greater than zero. The exit status is used by the Bash conditional commands (see section 3.2.4.2 Conditional Constructs) and some of the list constructs (see section 3.2.3 Lists of Commands). All of the Bash builtins return an exit status of zero if they succeed and a non-zero status on failure, so they may be used by the conditional and list constructs. All builtins return an exit status of 2 to indicate incorrect usage.
3.7.6 Signals
When Bash is interactive, in the absence of any traps, it ignores
Non-builtin commands started by Bash have signal handlers set to the
values inherited by the shell from its parent.
When job control is not in effect, asynchronous commands
ignore
The shell exits by default upon receipt of a
If the
If Bash is waiting for a command to complete and receives a signal
for which a trap has been set, the trap will not be executed until
the command completes.
When Bash is waiting for an asynchronous
command via the
3.8 Shell Scripts
A shell script is a text file containing shell commands. When such
a file is used as the first non-option argument when invoking Bash,
and neither the `-c' nor `-s' option is supplied
(see section 6.1 Invoking Bash),
Bash reads and executes commands from the file, then exits. This
mode of operation creates a non-interactive shell. The shell first
searches for the file in the current directory, and looks in the
directories in
When Bash runs
a shell script, it sets the special parameter
A shell script may be made executable by using the
if
Most versions of Unix make this a part of the operating system's command
execution mechanism. If the first line of a script begins with
the two characters `#!', the remainder of the line specifies
an interpreter for the program.
Thus, you can specify Bash, The arguments to the interpreter consist of a single optional argument following the interpreter name on the first line of the script file, followed by the name of the script file, followed by the rest of the arguments. Bash will perform this action on operating systems that do not handle it themselves. Note that some older versions of Unix limit the interpreter name and argument to a maximum of 32 characters.
Bash scripts often begin with
4. Shell Builtin Commands
Builtin commands are contained within the shell itself. When the name of a builtin command is used as the first word of a simple command (see section 3.2.1 Simple Commands), the shell executes the command directly, without invoking another program. Builtin commands are necessary to implement functionality impossible or inconvenient to obtain with separate utilities. This section briefly describes the builtins which Bash inherits from the Bourne Shell, as well as the builtin commands which are unique to or have been extended in Bash. Several builtin commands are described in other chapters: builtin commands which provide the Bash interface to the job control facilities (see 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 completion facilities (see section 8.7 Programmable Completion Builtins). Many of the builtins have been extended by POSIX or Bash.
Unless otherwise noted, each builtin command documented as accepting
options preceded by `-' accepts `--'
to signify the end of the options.
For example, the
4.1 Bourne Shell BuiltinsThe following shell builtin commands are inherited from the Bourne Shell. These commands are implemented as specified by the POSIX standard.
4.2 Bash Builtin CommandsThis section describes builtin commands which are unique to or have been extended in Bash. Some of these commands are specified in the POSIX standard.
4.3 The Set BuiltinThis builtin is so complicated that it deserves its own section.
4.4 Special BuiltinsFor historical reasons, the POSIX standard has classified several builtin commands as special. When Bash is executing in POSIX mode, the special builtins differ from other builtin commands in three respects:
When Bash is not executing in POSIX mode, these builtins behave no differently than the rest of the Bash builtin commands. The Bash POSIX mode is described in 6.11 Bash POSIX Mode. These are the POSIX special builtins:
5. Shell Variables
This chapter describes the shell variables that Bash uses. Bash automatically assigns default values to a number of variables.
5.1 Bourne Shell VariablesBash uses certain shell variables in the same way as the Bourne shell. In some cases, Bash assigns a default value to the variable.
5.2 Bash VariablesThese variables are set or used by Bash, but other shells do not normally treat them specially. A few variables used by Bash are described in different chapters: variables for controlling the job control facilities (see section 7.3 Job Control Variables).
6. Bash FeaturesThis section describes features unique to Bash.
6.1 Invoking Bash
In addition to the single-character shell command-line options (see section 4.3 The Set Builtin), there are several multi-character options that you can use. These options must appear on the command line before the single-character options to be recognized.
There are several single-character options that may be supplied at
invocation which are not available with the
A login shell is one whose first character of argument zero is `-', or one invoked with the `--login' option.
An interactive shell is one started without non-option arguments,
unless `-s' is specified,
without specifying the `-c' option, and whose input and output are both
connected to terminals (as determined by
If arguments remain after option processing, and neither the
`-c' nor the `-s'
option has been supplied, the first argument is assumed to
be the name of a file containing shell commands (see section 3.8 Shell Scripts).
When Bash is invoked in this fashion,
6.2 Bash Startup FilesThis section describs how Bash executes its startup files. If any of the files exist but cannot be read, Bash reports an error. Tildes are expanded in file names as described above under Tilde Expansion (see section 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 a non-interactive shell with the `--login' option, it first reads and executes commands from the file `/etc/profile', if that file exists. After reading that file, it looks for `~/.bash_profile', `~/.bash_login', and `~/.profile', in that order, and reads and executes commands from the first one that exists and is readable. The `--noprofile' option may be used when the shell is started to inhibit this behavior. When a login shell exits, Bash reads and executes commands from the file `~/.bash_logout', if it exists. Invoked as an interactive non-login shellWhen an interactive shell that is not a login shell is started, Bash reads and executes commands from `~/.bashrc', if that file exists. This may be inhibited by using the `--norc' option. The `--rcfile file' option will force Bash to read and execute commands from file instead of `~/.bashrc'. So, typically, your `~/.bash_profile' contains the line
Invoked non-interactively
When Bash is started non-interactively, to run a shell script,
for example, it looks for the variable
PATH variable is not used to search for the
file name.
As noted above, if a non-interactive shell is invoked with the `--login' option, Bash attempts to read and execute commands from the login shell startup files. Invoked with name
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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 shell
is one started without non-option arguments, unless `-s' is
specified, without specifiying the `-c' option, and
whose input and error output are both
connected to terminals (as determined by isatty(3)),
or one started with the `-i' option.
An interactive shell generally reads from and writes to a user's terminal.
The `-s' invocation option may be used to set the positional parameters when an interactive shell is started.
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6.3.2 Is this Shell Interactive?
To determine within a startup script whether or not Bash is
running interactively,
test the value of the `-' special parameter.
It contains i when the shell is interactive. For example:
case "$-" in *i*) echo This shell is interactive ;; *) echo This shell is not interactive ;; esac |
Alternatively, startup scripts may examine the variable
PS1; it is unset in non-interactive shells, and set in
interactive shells. Thus:
if [ -z "$PS1" ]; then
echo This shell is not interactive
else
echo This shell is interactive
fi
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6.3.3 Interactive Shell Behavior
When the shell is running interactively, it changes its behavior in several ways.
-
Startup files are read and executed as described in 6.2 Bash Startup Files.
-
Job Control (see section 7. Job Control) is enabled by default. When job
control is in effect, Bash ignores the keyboard-generated job control
signals
SIGTTIN,SIGTTOU, andSIGTSTP. -
Bash expands and displays
PS1before reading the first line of a command, and expands and displaysPS2before reading the second and subsequent lines of a multi-line command. -
Bash executes the value of the
PROMPT_COMMANDvariable as a command before printing the primary prompt,$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
ignoreeofoption toset -oinstead of exiting immediately when it receives anEOFon 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
$HISTFILEwhen 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,
SIGINTis caught and handled ((see section 3.7.6 Signals).SIGINTwill interrupt some shell builtins. -
An interactive login shell sends a
SIGHUPto all jobs on exit if thehupoxexitshell 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, andMAILCHECKshell 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
${var:?word}expansions (see section 3.5.3 Shell Parameter Expansion). -
Redirection errors encountered by shell builtins will not cause the
shell to exit.
-
When running in POSIX mode, a special builtin returning an error
status will not cause the shell to exit (see section 6.11 Bash POSIX Mode).
-
A failed
execwill not cause the shell to exit (see section 4.1 Bourne Shell Builtins). -
Parser syntax errors will not cause the shell to exit.
-
Simple spelling correction for directory arguments to the
cdbuiltin is enabled by default (see the description of thecdspelloption to theshoptbuiltin in 4.2 Bash Builtin Commands). -
The shell will check the value of the
TMOUTvariable and exit if a command is not read within the specified number of seconds after printing$PS1(see section 5.2 Bash Variables).
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6.4 Bash Conditional Expressions
Conditional expressions are used by the [[ compound command
and the test and [ builtin commands.
Expressions may be unary or binary. Unary expressions are often used to examine the status of a file. There are string operators and numeric comparison operators as well. If the file argument to one of the primaries is of the form `/dev/fd/N', then file descriptor N is checked. If the file argument to one of the primaries is one of `/dev/stdin', `/dev/stdout', or `/dev/stderr', file descriptor 0, 1, or 2, respectively, is checked.
Unless otherwise specified, primaries that operate on files follow symbolic links and operate on the target of the link, rather than the link itself.
-a file- 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 and
inode numbers.
-o optname- True if shell option optname is enabled.
The list of options appears in the description of the `-o'
option to the
setbuiltin (see section 4.3 The Set Builtin). -z string- True if the length of string is zero.
-n stringstring- 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 lexicographically
in the current locale.
string1 > string2- True if string1 sorts after string2 lexicographically
in the current locale.
arg1 OP arg2OPis one of `-eq', `-ne', `-lt', `-le', `-gt', or `-ge'. These arithmetic binary operators return true if arg1 is equal to, not equal to, less than, less than or equal to, greater than, or greater than or equal to arg2, respectively. Arg1 and arg2 may be positive or negative integers.
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6.5 Shell Arithmetic
The shell allows arithmetic expressions to be evaluated, as one of
the shell expansions or by the let and the `-i' option
to the declare builtins.
Evaluation is done in fixed-width integers with no check for overflow, though division by 0 is trapped and flagged as an error. The operators and their precedence, associativity, and values are the same as in the C language. The following list of operators is grouped into levels of equal-precedence operators. The levels are listed in order of decreasing precedence.
id++ id--- 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 operator
= *= /= %= += -= <<= >>= &= ^= |=- assignment
expr1 , expr2- comma
Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. Within an expression, shell variables may also be referenced by name without using the parameter expansion syntax. A shell variable that is null or unset evaluates to 0 when referenced by name without using the parameter expansion syntax. The value of a variable is evaluated as an arithmetic expression when it is referenced, or when a variable which has been given the integer attribute using `declare -i' is assigned a value. A null value evaluates to 0. A shell variable need not have its integer attribute turned on to be used in an expression.
Constants with a leading 0 are interpreted as octal numbers.
A leading `0x' or `0X' denotes hexadecimal. Otherwise,
numbers take the form [base#]n, where base
is a decimal number between 2 and 64 representing the arithmetic
base, and n is a number in that base. If base# is
omitted, then base 10 is used.
The digits greater than 9 are represented by the lowercase letters,
the uppercase letters, `@', and `_', in that order.
If base is less than or equal to 36, lowercase and uppercase
letters may be used interchangeably to represent numbers between 10
and 35.
Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated first and may override the precedence rules above.
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6.6 Aliases
Aliases allow a string to be substituted for a word when it is used
as the first word of a simple command.
The shell maintains a list of aliases that may be set and unset with
the alias and unalias builtin commands.
The first word of each simple command, if unquoted, is checked to see
if it has an alias.
If so, that word is replaced by the text of the alias.
The characters `/', `$', ``', `=' and any of the
shell metacharacters or quoting characters listed above may not appear
in an alias name.
The replacement text may contain any valid
shell input, including shell metacharacters.
The first word of the replacement text is tested for
aliases, but a word that is identical to an alias being expanded
is not expanded a second time.
This means that one may alias ls to "ls -F",
for instance, and Bash does not try to recursively expand the
replacement text. If the last character of the alias value is a
space or tab character, then the next command word following the
alias is also checked for alias expansion.
Aliases are created and listed with the alias
command, and removed with the unalias command.
There is no mechanism for using arguments in the replacement text,
as in csh.
If arguments are needed, a shell function should be used
(see section 3.3 Shell Functions).
Aliases are not expanded when the shell is not interactive,
unless the expand_aliases shell option is set using
shopt (see section 4.2 Bash Builtin Commands).
The rules concerning the definition and use of aliases are
somewhat confusing. Bash
always reads at least one complete line
of input before executing any
of the commands on that line. Aliases are expanded when a
command is read, not when it is executed. Therefore, an
alias definition appearing on the same line as another
command does not take effect until the next line of input is read.
The commands following the alias definition
on that line are not affected by the new alias.
This behavior is also an issue when functions are executed.
Aliases are expanded when a function definition is read,
not when the function is executed, because a function definition
is itself a compound command. As a consequence, aliases
defined in a function are not available until after that
function is executed. To be safe, always put
alias definitions on a separate line, and do not use alias
in compound commands.
For almost every purpose, shell functions are preferred over aliases.
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6.7 Arrays
Bash provides one-dimensional array variables. Any variable may be used as
an array; the declare builtin will explicitly declare an array.
There is no maximum
limit on the size of an array, nor any requirement that members
be indexed or assigned contiguously. Arrays are zero-based.
An array is created automatically if any variable is assigned to using the syntax
name[subscript]=value |
The subscript is treated as an arithmetic expression that must evaluate to a number greater than or equal to zero. To explicitly declare an array, use
declare -a name |
declare -a name[subscript] |
declare and
readonly builtins. Each attribute applies to all members of
an array.
Arrays are assigned to using compound assignments of the form
name=(value1 ... valuen) |
[[subscript]=]string. If
the optional subscript is supplied, that index is assigned to;
otherwise the index of the element assigned is the last index assigned
to by the statement plus one. Indexing starts at zero.
This syntax is also accepted by the declare
builtin. Individual array elements may be assigned to using the
name[subscript]=value syntax introduced above.
Any element of an array may be referenced using
${name[subscript]}.
The braces are required to avoid
conflicts with the shell's filename expansion operators. If the
subscript is `@' or `*', the word expands to all members
of the array name. These subscripts differ only when the word
appears within double quotes.
If the word is double-quoted,
${name[*]} expands to a single word with
the value of each array member separated by the first character of the
IFS variable, and ${name[@]} expands each element of
name to a separate word. When there are no array members,
${name[@]} expands to nothing.
If the double-quoted expansion occurs within a word, the expansion of
the first parameter is joined with the beginning part of the original
word, and the expansion of the last parameter is joined with the last
part of the original word.
This is analogous to the
expansion of the special parameters `@' and `*'.
${#name[subscript]} expands to the length of
${name[subscript]}.
If subscript is `@' or
`*', the expansion is the number of elements in the array.
Referencing an array variable without a subscript is equivalent to
referencing element zero.
The unset builtin is used to destroy arrays.
unset name[subscript]
destroys the array element at index subscript.
Care must be taken to avoid unwanted side effects caused by filename
generation.
unset name, where name is an array, removes the
entire array. A subscript of `*' or `@' also removes the
entire array.
The declare, local, and readonly
builtins each accept a `-a'
option to specify an array. The read
builtin accepts a `-a'
option to assign a list of words read from the standard input
to an array, and can read values from the standard input into
individual array elements. The set and declare
builtins display array values in a way that allows them to be
reused as input.
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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. The
pushd builtin adds directories to the stack as it changes
the current directory, and the popd builtin removes specified
directories from the stack and changes the current directory to
the directory removed. The dirs builtin displays the contents
of the directory stack.
The contents of the directory stack are also visible
as the value of the DIRSTACK shell variable.
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6.8.1 Directory Stack Builtins
dirs-
Display the list of currently remembered directories. Directories are added to the list with thedirs [+N | -N] [-clpv]
pushdcommand; thepopdcommand removes directories from the list.+N- Displays the Nth directory (counting from the left of the
list printed by
dirswhen invoked without options), starting with zero. -N- Displays the Nth directory (counting from the right of the
list printed by
dirswhen invoked without options), starting with zero. -c- Clears the directory stack by deleting all of the elements.
-l- Produces a longer listing; the default listing format uses a tilde to denote the home directory.
-p- Causes
dirsto print the directory stack with one entry per line. -v- Causes
dirsto print the directory stack with one entry per line, 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 and performs acdto the new top directory. The elements are numbered from 0 starting at the first directory listed withdirs; i.e.,popdis equivalent topopd +0.+N- Removes the Nth directory (counting from the left of the
list printed by
dirs), starting with zero. -N- Removes the Nth directory (counting from the right of the
list printed by
dirs), starting with zero. -n- Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated.
pushdpushd [dir | +N | -N] [-n]
Save the current directory on the top of the directory stack and then
cdto dir. With no arguments,pushdexchanges the top two directories.+N- Brings the Nth directory (counting from the left of the
list printed by
dirs, starting with zero) to the top of the list by rotating the stack. -N- Brings the Nth directory (counting from the right of the
list printed by
dirs, starting with zero) to the top of the list by rotating the stack. -n- Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipulated.
dir- Makes the current working directory be the top of the stack, and then
executes the equivalent of `
cddir'.cds to dir.
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6.9 Controlling the Prompt
The value of the variable PROMPT_COMMAND is examined just before
Bash prints each primary prompt. If PROMPT_COMMAND is set and
has a non-null value, then the
value is executed just as if it had been typed on the command line.
In addition, the following table describes the special characters which can appear in the prompt variables:
\a- 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 inserted into the prompt string; an empty format results in a locale-specific time 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 portion following 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, with
$HOMEabbreviated with a tilde. \W- The basename of
$PWD, with$HOMEabbreviated with a tilde. \!- 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.
\[- Begin a sequence of non-printing characters. This could be used to embed a terminal control sequence into the prompt.
\]- 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 history list, which may include commands restored from the history file (see section 9.1 Bash History Facilities), while the command number is the position in the sequence of commands executed during the current shell session.
After the string is decoded, it is expanded via
parameter expansion, command substitution, arithmetic
expansion, and quote removal, subject to the value of the
promptvars shell option (see 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 to
set up an environment more controlled than the standard shell.
A restricted shell behaves identically to bash
with the exception that the following are disallowed or not performed:
-
Changing directories with the
cdbuiltin. -
Setting or unsetting the values of the
SHELL,PATH,ENV, orBASH_ENVvariables. - 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
hashbuiltin command. - Importing function definitions from the shell environment at startup.
-
Parsing the value of
SHELLOPTSfrom the shell environment at startup. - Redirecting output using the `>', `>|', `<>', `>&', `&>', and `>>' redirection operators.
-
Using the
execbuiltin to replace the shell with another command. -
Adding or deleting builtin commands with the
`-f' and `-d' options to the
enablebuiltin. -
Using the
enablebuiltin command to enable disabled shell builtins. -
Specifying the `-p' option to the
commandbuiltin. - 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 in
the 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 more closely to the POSIX standard by changing the behavior to match that specified by POSIX in areas where the Bash default differs.
When invoked as sh, Bash enters POSIX mode after reading the
startup files.
The following list is what's changed when `POSIX mode' is in effect:
-
When a command in the hash table no longer exists, Bash will re-search
$PATHto 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. -
The
bgbuiltin uses the required format to describe each job placed in the background, which does not include an indication of whether the job is the current or previous job. -
Reserved words appearing in a context where reserved words are recognized
do not undergo alias expansion.
-
The POSIX
PS1andPS2expansions of `!' to the history number and `!!' to `!' are enabled, and parameter expansion is performed on the values ofPS1andPS2regardless of the setting of thepromptvarsoption. -
The POSIX 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
$HISTFILE). -
The output of `kill -l' prints all the signal names on a single line,
separated by spaces, without the `SIG' prefix.
-
The
killbuiltin does not accept signal names with a `SIG' prefix. -
Non-interactive shells exit if filename in
.filename is not found. -
Non-interactive shells exit if a syntax error in an arithmetic expansion
results in an invalid expression.
-
Redirection operators do not perform filename expansion on the word
in the redirection unless the shell is interactive.
-
Redirection operators do not perform word splitting on the word in the
redirection.
-
Function names must be valid shell
names. That is, they may not contain characters other than letters, digits, and underscores, and may not start with a digit. Declaring a function with an invalid name causes a fatal syntax error in non-interactive shells. -
POSIX special builtins are found before shell functions
during command lookup.
-
If a POSIX special builtin returns an error status, a
non-interactive shell exits. The fatal errors are those listed in
the POSIX standard, and include things like passing incorrect options,
redirection errors, variable assignment errors for assignments preceding
the command name, and so on.
-
If
CDPATHis set, thecdbuiltin will not implicitly append the current directory to it. This means thatcdwill fail if no valid directory name can be constructed from any of the entries in$CDPATH, even if the a directory with the same name as the name given as an argument tocdexists 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
forstatement or the selection variable in aselectstatement is a readonly variable. -
Process substitution is not available.
-
Assignment statements preceding POSIX 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
exportandreadonlybuiltin commands display their output in the format required by POSIX. -
The
trapbuiltin displays signal names without the leadingSIG. -
The
trapbuiltin doesn't check the first argument for a possible signal specification and revert the signal handling to the original disposition if it is, unless that argument consists solely of digits and is a valid signal number. If users want to reset the handler for a given signal to the original disposition, they should use `-' as the first argument. -
The
.andsourcebuiltins do not search the current directory for the filename argument if it is not found by searchingPATH. -
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
aliasbuiltin displays alias definitions, it does not display them with a leading `alias ' unless the `-p' option is supplied. -
When the
setbuiltin is invoked without options, it does not display shell function names and definitions. -
When the
setbuiltin is invoked without options, it displays variable values without quotes, unless they contain shell metacharacters, even if the result contains nonprinting characters. -
When the
cdbuiltin is invoked in logical mode, and the pathname constructed from$PWDand the directory name supplied as an argument does not refer to an existing directory,cdwill fail instead of falling back to physical mode. -
When the
pwdbuiltin is supplied the `-P' option, it resets$PWDto a pathname containing no symlinks. -
The
pwdbuiltin verifies that the value it prints is the same as the current directory, even if it is not asked to check the file system with the `-P' option. -
When listing the history, the
fcbuiltin does not include an indication of whether or not a history entry has been modified. -
The default editor used by
fcised. -
The
typeandcommandbuiltins will not report a non-executable file as having been found, though the shell will attempt to execute such a file if it is the only so-named file found in$PATH. -
The
viediting mode will invoke thevieditor directly when the `v' command is run, instead of checking$FCEDITand$EDITOR. -
When the
xpg_echooption is enabled, Bash does not attempt to interpret any arguments toechoas options. Each argument is displayed, after escape characters are converted.
There is other POSIX behavior that Bash does not implement by default even when in POSIX mode. Specifically:
-
The
fcbuiltin checks$EDITORas a program to edit history entries ifFCEDITis unset, rather than defaulting directly toed.fcusesedifEDITORis unset. -
As noted above, Bash requires the
xpg_echooption to be enabled for theechobuiltin to be fully conformant.
Bash can be configured to be POSIX-conformant by default, by specifying
the `--enable-strict-posix-default' to configure when building
(see section 10.8 Optional Features).
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7. Job Control
This chapter discusses what job control is, how it works, and how Bash 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 control refers to the ability to selectively stop (suspend) the execution of processes and continue (resume) their execution at a later point. A user typically employs this facility via an interactive interface supplied jointly by the system's terminal driver and Bash.
The shell associates a job with each pipeline. It keeps a
table of currently executing jobs, which may be listed with the
jobs command. When Bash starts a job
asynchronously, it prints a line that looks
like:
[1] 25647 |
To facilitate the implementation of the user interface to job
control, the operating system maintains the notion of a current terminal
process group ID. Members of this process group (processes whose
process group ID is equal to the current terminal process group
ID) receive keyboard-generated signals such as SIGINT.
These processes are said to be in the foreground. Background
processes are those whose process group ID differs from the
terminal's; such processes are immune to keyboard-generated
signals. Only foreground processes are allowed to read from or
write to the terminal. Background processes which attempt to
read from (write to) the terminal are sent a SIGTTIN
(SIGTTOU) signal by the terminal driver, which, unless
caught, suspends the process.
If the operating system on which Bash is running supports
job control, Bash contains facilities to use it. Typing the
suspend character (typically `^Z', Control-Z) while a
process is running causes that process to be stopped and returns
control to Bash. Typing the delayed suspend character
(typically `^Y', Control-Y) causes the process to be stopped
when it attempts to read input from the terminal, and control to
be returned to Bash. The user then manipulates the state of
this job, using the bg command to continue it in the
background, the fg command to continue it in the
foreground, or the kill command to kill it. A `^Z'
takes effect immediately, and has the additional side effect of
causing pending output and typeahead to be discarded.
There are a number of ways to refer to a job in the shell. The character `%' introduces a job name.
Job number n may be referred to as `%n'.
The symbols `%%' and `%+' refer to the shell's notion of the
current job, which is the last job stopped while it was in the foreground
or started in the background.
A single `%' (with no accompanying job specification) also refers
to the current job.
The previous job may be referenced using `%-'. In output
pertaining to jobs (e.g., the output of the jobs command),
the current job is always flagged with a `+', and the
previous job with a `-'.
A job may also be referred to
using a prefix of the name used to start it, or using a substring
that appears in its command line. For example, `%ce' refers
to a stopped ce job. Using `%?ce', on the
other hand, refers to any job containing the string `ce' in
its command line. If the prefix or substring matches more than one job,
Bash reports an error.
Simply naming a job can be used to bring it into the foreground: `%1' is a synonym for `fg %1', bringing job 1 from the background into the foreground. Similarly, `%1 &' resumes job 1 in the background, equivalent to `bg %1'
The shell learns immediately whenever a job changes state.
Normally, Bash waits until it is about to print a prompt
before reporting changes in a job's status so as to not interrupt
any other output.
If the `-b' option to the set builtin is enabled,
Bash reports such changes immediately (see section 4.3 The Set Builtin).
Any trap on SIGCHLD is executed for each child process
that exits.
If an attempt to exit Bash is made while jobs are stopped, the
shell 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-
Resume each suspended job jobspec in the background, as if it had been started with `&'. If jobspec is not supplied, the current job is used. The return status is zero unless it is run when job control is not enabled, or, when run with job control enabled, any jobspec was not found or specifies a job that was started without job control.bg [jobspec ...]
fg-
Resume the job jobspec in the foreground and make it the current job. If jobspec is not supplied, the current job is used. The return status is that of the command placed into the foreground, or non-zero if run when job control is disabled or, when run with job control enabled, jobspec does not specify a valid job or jobspec specifies a job that was started without job control.fg [jobspec]
jobs-
jobs [-lnprs] [jobspec] jobs -x command [arguments]
The first form lists the active jobs. The options have the following meanings:
-l- List process IDs in addition to the normal information.
-n- Display information only about jobs that have changed status since
the 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 is listed.
If the `-x' option is supplied,
jobsreplaces any jobspec found in command or arguments with the corresponding process group ID, and executes command, passing it arguments, returning its exit status. kill-
Send a signal specified by sigspec or signum to the process named by job specification jobspec or process ID pid. sigspec is either a case-insensitive signal name such askill [-s sigspec] [-n signum] [-sigspec] jobspec or pid kill -l [exit_status]
SIGINT(with or without theSIGprefix) or a signal number; signum is a signal number. If sigspec and signum are not present,SIGTERMis used. The `-l' option lists the signal names. If any arguments are supplied when `-l' is given, the names of the signals corresponding to the arguments are listed, and the return status is zero. exit_status is a number specifying a signal number or the exit status of a process terminated by a signal. The return status is zero if at least one signal was successfully sent, or non-zero if an error occurs or an invalid option is encountered. wait-
Wait until the child process specified by each process ID pid or job specification jobspec exits and return the exit status of the last command waited for. If a job spec is given, all processes in the job are waited for. If no arguments are given, all currently active child processes are waited for, and the return status is zero. If neither jobspec nor pid specifies an active child process of the shell, the return status is 127.wait [jobspec or pid ...]
disown-
Without options, each jobspec is removed from the table of active jobs. If the `-h' option is given, the job is not removed from the table, but is marked so thatdisown [-ar] [-h] [jobspec ...]
SIGHUPis not sent to the job if the shell receives aSIGHUP. If jobspec is not present, and neither the `-a' nor `-r' option is supplied, the current job is used. If no jobspec is supplied, the `-a' option means to remove or mark all jobs; the `-r' option without a jobspec argument restricts operation to running jobs. suspend-
Suspend the execution of this shell until it receives asuspend [-f]
SIGCONTsignal. The `-f' option means to suspend even if the shell is a login shell.
When job control is not active, the kill and wait
builtins do not accept jobspec arguments. They must be
supplied process IDs.
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7.3 Job Control Variables
auto_resume-
This variable controls how the shell interacts with the user and
job control. If this variable exists then single word simple
commands without redirections are treated as candidates for resumption
of an existing job. There is no ambiguity allowed; if there is
more than one job beginning with the string typed, then
the most recently accessed job will be selected.
The name of a stopped job, in this context, is the command line
used 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 a
stopped job. The `substring' value provides functionality
analogous to the `%?' job ID (see section 7.1 Job Control Basics).
If set to any other value, the supplied string must
be a prefix of a stopped job's name; this provides functionality
analogous to the `%' job ID.
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8. Command Line Editing
This chapter describes the basic features of the GNU command line editing interface. Command line editing is provided by the Readline library, which is used by several different programs, including Bash.
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 represent keystrokes.
The text C-k is read as `Control-K' and describes the character produced when the k key is pressed while the Control key is depressed.
The text M-k is read as `Meta-K' and describes the character produced when the Meta key (if you have one) is depressed, and the k key is pressed. The Meta key is labeled ALT on many keyboards. On keyboards with two keys labeled ALT (usually to either side of the space bar), the ALT on the left side is generally set to work as a Meta key. The ALT key on the right may also be configured to work as a Meta key or may be configured as some other modifier, such as a Compose key for typing accented characters.
If you do not have a Meta or ALT key, or another key working as a Meta key, the identical keystroke can be generated by typing ESC first, and then typing k. Either process is known as metafying the k key.
The text M-C-k is read as `Meta-Control-k' and describes the character produced by metafying C-k.
In addition, several keys have their own names. Specifically, DEL, ESC, LFD, SPC, RET, and TAB all stand for themselves when seen in this text, or in an init file (see section 8.3 Readline Init File). If your keyboard lacks a LFD key, typing C-j will produce the desired character. The RET key may be labeled Return or Enter on some keyboards.
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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. The Readline library gives you a set of commands for manipulating the text as you type it in, allowing you to just fix your typo, and not forcing you to retype the majority of the line. Using these editing commands, you move the cursor to the place that needs correction, and delete or insert the text of the corrections. Then, when you are satisfied with the line, you simply press RET. You do not have to be at the end of the line to press RET; the entire line is accepted regardless of the location of the cursor within the line.
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 typed character appears where the cursor was, and then the cursor moves one space to the right. If you mistype a character, you can use your erase character to back up and delete the mistyped character.
Sometimes you may mistype a character, and not notice the error until you have typed several other characters. In that case, you can type C-b to move the cursor to the left, and then correct your mistake. Afterwards, you can move the cursor to the right with C-f.
When you add text in the middle of a line, you will notice that characters to the right of the cursor are `pushed over' to make room for the text that you have inserted. Likewise, when you delete text behind the cursor, characters to the right of the cursor are `pulled back' to fill in the blank space created by the removal of the text. A list of the bare essentials for editing the text of an input line follows.
- 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 an empty line.
(Depending on your configuration, the Backspace key be set to delete the character to the left of the cursor and the DEL key set to delete the character underneath the cursor, like C-d, rather than the character to the left of the cursor.)
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8.2.2 Readline Movement Commands
The above table describes the most basic keystrokes that you need in order to do editing of the input line. For your convenience, many other commands have been added in addition to C-b, C-f, C-d, and DEL. Here are some commands for moving more rapidly about the line.
- 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 moves forward a word. It is a loose convention that control keystrokes operate 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 save it away for later use, usually by yanking (re-inserting) it back into the line. (`Cut' and `paste' are more recent jargon for `kill' and `yank'.)
If the description for a command says that it `kills' text, then you can be sure that you can get the text back in a different (or the same) place later.
When you use a kill command, the text is saved in a kill-ring. Any number of consecutive kills save all of the killed text together, so that when you yank it back, you get it all. The kill ring is not line specific; the text that you killed on a previously typed line is available to be yanked back later, when you are typing another line.
Here is the list of commands for killing text.
- 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 between
words, 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 between
words, 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 than
M-DEL because the word boundaries differ.
Here is how to yank the text back into the line. Yanking means 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 if the 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 the argument acts as a repeat count, other times it is the sign of the argument that is significant. If you pass a negative argument to a command which normally acts in a forward direction, that command will act in a backward direction. For example, to kill text back to the start of the line, you might type `M-- C-k'.
The general way to pass numeric arguments to a command is to type meta digits before the command. If the first `digit' typed is a minus sign (`-'), then the sign of the argument will be negative. Once you have typed one meta digit to get the argument started, you can type the remainder of the digits, and then the command. For example, to give the C-d command an argument of 10, you could type `M-1 0 C-d', which will delete the next ten characters on the input line.
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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 the
search string.
As each character of the search string is typed, Readline displays
the next entry from the history matching the string typed so far.
An incremental search requires only as many characters as needed to
find the desired history entry.
To search backward in the history for a particular string, type
C-r. Typing C-s searches forward through the history.
The characters present in the value of the isearch-terminators variable
are used to terminate an incremental search.
If that variable has not been assigned a value, the ESC and
C-J characters will terminate an incremental search.
C-g will abort an incremental search and restore the original line.
When the search is terminated, the history entry containing the
search string becomes the current line.
To find other matching entries in the history list, type C-r or C-s as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a Readline command will terminate the search and execute that command. For instance, a RET will terminate the search and accept the line, thereby executing the command from the history list. A movement command will terminate the search, make the last line found the current line, and begin editing.
Readline remembers the last incremental search string. If two C-rs are typed without any intervening characters defining a new search string, any remembered search string is used.
Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line.
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8.3 Readline Init File
Although the Readline library comes with a set of Emacs-like
keybindings installed by default, it is possible to use a different set
of keybindings.
Any user can customize programs that use Readline by putting
commands in an inputrc file, conventionally in his home directory.
The name of this
file is taken from the value of the shell variable INPUTRC. If
that variable is unset, the default is `~/.inputrc'. If that
file does not exist or cannot be read, the ultimate default is
`/etc/inputrc'.
When a program which uses the Readline library starts up, the init file is read, and the key bindings are set.
In addition, the C-x C-r command re-reads this init file, thus
incorporating any changes that you might have made to it.
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 the Readline init file. Blank lines are ignored. Lines beginning with a `#' are comments. Lines beginning with a `$' indicate conditional constructs (see section 8.3.2 Conditional Init Constructs). Other lines denote variable settings and key bindings.
- Variable Settings
- You can modify the run-time behavior of Readline by
altering the values of variables in Readline
using the
setcommand within the init file. The syntax is simple:set variable value
Here, for example, is how to change from the default Emacs-like key binding to use
viline editing commands:set editing-mode vi
Variable names and values, where appropriate, are recognized without regard to case. Unrecognized variable names are ignored.
Boolean variables (those that can be set to on or off) are set to on if the value is null or empty, on (case-insensitive), or 1. Any other value results in the variable being set to off.
The
bind -Vcommand lists the current Readline variable names and values. See section 4.2 Bash Builtin Commands.A great deal of run-time behavior is changeable with the following variables.
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 ring
the terminal's bell.
bind-tty-special-chars-
If set to `on', Readline attempts to bind the control characters
treated specially by the kernel's terminal driver to their Readline
equivalents.
comment-begin-
The string to insert at the beginning of the line when the
insert-commentcommand is executed. The default value is"#". completion-ignore-case- If set to `on', Readline performs filename matching and completion
in a case-insensitive fashion.
The default value is `off'.
completion-query-items-
The number of possible completions that determines when the user is
asked whether the list of possibilities should be displayed.
If the number of possible completions is greater than this value,
Readline will ask the user whether or not he wishes to view
them; otherwise, they are simply listed.
This variable must be set to an integer value greater than or equal to 0.
A negative value means Readline should never ask.
The default limit is
100. convert-meta-
If set to `on', Readline will convert characters with the
eighth bit set to an ASCII key sequence by stripping the eighth
bit and prefixing an ESC character, converting them to a
meta-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 had
been mapped to
self-insert. The default is `off'. editing-mode-
The
editing-modevariable controls which default set of key bindings is used. By default, Readline starts up in Emacs editing mode, where the keystrokes are most similar to Emacs. This variable can be set to either `emacs' or `vi'. enable-keypad-
When set to `on', Readline will try to enable the application
keypad when it is called. Some systems need this to enable the
arrow keys. The default is `off'.
expand-tilde-
If set to `on', tilde expansion is performed when Readline
attempts word completion. The default is `off'.
history-preserve-point-
If set to `on', the history code attempts to place point at the
same location on each history line retrieved with
previous-historyornext-history. The default is `off'. horizontal-scroll-mode-
This variable can be set to either `on' or `off'. Setting it
to `on' means that the text of the lines being edited will scroll
horizontally on a single screen line when they are longer than the width
of 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 (it
will not clear the eighth bit in the characters it reads),
regardless of what the terminal claims it can support. The
default value is `off'. The name
meta-flagis a synonym for this variable. isearch-terminators-
The string of characters that should terminate an incremental search without
subsequently 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 and
C-J will terminate an incremental search.
keymap-
Sets Readline's idea of the current keymap for key binding commands.
Acceptable
keymapnames areemacs,emacs-standard,emacs-meta,emacs-ctlx,vi,vi-move,vi-command, andvi-insert.viis equivalent tovi-command;emacsis equivalent toemacs-standard. The default value isemacs. The value of theediting-modevariable also affects the default keymap. mark-directories- If set to `on', completed directory names have a slash
appended. The default is `on'.
mark-modified-lines-
This variable, when set to `on', causes Readline to display an
asterisk (`*') 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 links
to directories have a slash appended (subject to the value of
mark-directories). The default is `off'. match-hidden-files-
This variable, when set to `on', causes Readline to match files whose
names begin with a `.' (hidden files) when performing filename
completion, unless the leading `.' is
supplied 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 the
eighth bit set directly rather than as a meta-prefixed escape
sequence. The default is `off'.
page-completions-
If set to `on', Readline uses an internal
more-like pager to 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 matches
sorted 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. If
set to `on',
words which have more than one possible completion cause the
matches to be listed immediately instead of ringing the bell.
The default value is `off'.
show-all-if-unmodified-
This alters the default behavior of the completion functions in
a fashion similar to show-all-if-ambiguous.
If set to `on',
words which have more than one possible completion without any
possible partial completion (the possible completions don't share
a common prefix) cause the matches 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 type
is appended to the filename when listing possible
completions. The default is `off'.
- Key Bindings
- The syntax for controlling key bindings in the init file is
simple. First you need to find the name of the command that you
want to change. The following sections contain tables of the command
name, the default keybinding, if any, and a short description of what
the command does.
Once you know the name of the command, simply place on a line in the init file the name of the key you wish to bind the command to, a colon, and then the name of the command. There can be no space between the key name and the colon -- that will be interpreted as part of the key name. The name of the key can be expressed in different ways, depending on what you find most comfortable.
In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro).
The
bind -pcommand displays Readline function names and bindings 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 function
universal-argument, M-DEL is bound to the functionbackward-kill-word, and C-o is bound to run the macro expressed on the right hand side (that is, to insert the text `> output' into the line).A number of symbolic character names are recognized while processing this key binding syntax: DEL, ESC, ESCAPE, LFD, NEWLINE, RET, RETURN, RUBOUT, SPACE, SPC, and TAB.
- "keyseq": function-name or macro
- keyseq differs from keyname above in that strings
denoting an entire key sequence can be specified, by placing
the key sequence in double quotes. Some GNU Emacs style key
escapes can be used, as in the following example, but the
special 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 function
universal-argument(just as it was in the first example), `C-x C-r' is bound to the functionre-read-init-file, and `ESC [ 1 1 ~' is bound to insert the text `Function Key 1'.
The following GNU Emacs style escape sequences are available when specifying key sequences:
\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 second set 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 must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including `"' and `''. For example, the following binding will make `C-x \' insert a single `\' into the line:
"\C-x\\": "\\"
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8.3.2 Conditional Init Constructs
Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be performed as the result of tests. There are four parser directives used.
$if- The
$ifconstruct allows bindings to be made based on the editing mode, the terminal being used, or the application using Readline. The text of the test extends to the end of the line; no characters are required to isolate it.mode- The
mode=form of the$ifdirective is used to test whether Readline is inemacsorvimode. This may be used in conjunction with the `set keymap' command, for instance, to set bindings in theemacs-standardandemacs-ctlxkeymaps only if Readline is starting out inemacsmode. term- The
term=form may be used to include terminal-specific key bindings, perhaps to bind the key sequences output by the terminal's function keys. The word on the right side of the `=' is tested against both the full name of the terminal and the portion of the terminal name before the first `-'. This allowssunto match bothsunandsun-cmd, for instance. application- The application construct is used to include
application-specific settings. Each program using the Readline
library sets the application name, and you can test for
a particular value.
This could be used to bind key sequences to functions useful for
a specific program. For instance, the following command adds a
key sequence that quotes the current or previous word in Bash:
$if Bash # Quote the current or previous word "\C-xq": "\eb\"\ef\"" $endif
$endif- This command, as seen in the previous example, terminates an
$ifcommand. $else- Commands in this branch of the
$ifdirective are executed if the test fails. $include- This directive takes a single filename as an argument and reads commands
and 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 key binding, variable assignment, and conditional syntax.
# This file controls the behaviour of line input editing for
# programs that use the GNU Readline library. Existing
# programs include FTP, Bash, and GDB.
#
# You can re-read the inputrc file with C-x C-r.
# Lines beginning with '#' are comments.
#
# First, include any systemwide bindings and variable
# assignments from /etc/Inputrc
$include /etc/Inputrc
#
# Set various bindings for emacs mode.
set editing-mode emacs
$if mode=emacs
Meta-Control-h: backward-kill-word Text after the function name is ignored
#
# Arrow keys in keypad mode
#
#"\M-OD": backward-char
#"\M-OC": forward-char
#"\M-OA": previous-history
#"\M-OB": next-history
#
# Arrow keys in ANSI mode
#
"\M-[D": backward-char
"\M-[C": forward-char
"\M-[A": previous-history
"\M-[B": next-history
#
# Arrow keys in 8 bit keypad mode
#
#"\M-\C-OD": backward-char
#"\M-\C-OC": forward-char
#"\M-\C-OA": previous-history
#"\M-\C-OB": next-history
#
# Arrow keys in 8 bit ANSI mode
#
#"\M-\C-[D": backward-char
#"\M-\C-[C": forward-char
#"\M-\C-[A": previous-history
#"\M-\C-[B": next-history
C-q: quoted-insert
$endif
# An old-style binding. This happens to be the default.
TAB: complete
# Macros that are convenient for shell interaction
$if Bash
# edit the path
"\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"
# prepare to type a quoted word --
# insert open and close double quotes
# and move to just after the open quote
"\C-x\"": "\"\"\C-b"
# insert a backslash (testing backslash escapes
# in sequences and macros)
"\C-x\\": "\\"
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
# Add a binding to refresh the line, which is unbound
"\C-xr": redraw-current-line
# Edit variable on current line.
"\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="
$endif
# use a visible bell if one is available
set bell-style visible
# don't strip characters to 7 bits when reading
set input-meta on
# allow iso-latin1 characters to be inserted rather
# than converted to prefix-meta sequences
set convert-meta off
# display characters with the eighth bit set directly
# rather than as meta-prefixed characters
set output-meta on
# if there are more than 150 possible completions for
# a word, ask the user if he wants to see all of them
set completion-query-items 150
# For FTP
$if Ftp
"\C-xg": "get \M-?"
"\C-xt": "put \M-?"
"\M-.": yank-last-arg
$endif
|
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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 key
sequences.
You can list your key bindings by executing
bind -P or, for a more terse format, suitable for an
inputrc file, bind -p. (See 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 cursor
position, and mark refers to a cursor position saved by the
set-mark command.
The text between the point and mark is referred to as the region.
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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 of letters and digits.
backward-word (M-b)- Move back to the start of the current or previous word. Words are composed 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 is
non-empty, add it to the history list according to the setting of
the
HISTCONTROLandHISTIGNOREvariables. If this line is a modified history line, then restore the history line to 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 currently being entered.
reverse-search-history (C-r)- Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental search.
forward-search-history (C-s)- Search forward starting at the current line and moving `down' through the 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 search for 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 search for a string supplied by the user.
history-search-forward ()- Search forward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search. By default, this command is unbound.
history-search-backward ()- Search backward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search. By default, this command is unbound.
yank-nth-arg (M-C-y)- Insert the first argument to the previous command (usually the second word on the previous line) at point. With an argument n, insert the nth word from the previous command (the words in the previous command begin with word 0). A negative argument inserts the nth word from the end of the previous command. Once the argument n is computed, the argument is extracted as if the `!n' history expansion had been specified.
yank-last-arg (M-. or M-_)-
Insert last argument to the previous command (the last word of the
previous history entry). With an
argument, behave exactly like
yank-nth-arg. Successive calls toyank-last-argmove back through the history list, inserting the last argument of each line in turn. The history expansion facilities are used to extract the last argument, as if the `!$' history expansion had been specified.
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8.4.3 Commands For Changing Text
delete-char (C-d)-
Delete the character at point. If point is at the
beginning of the line, there are no characters in the line, and
the last character typed was not bound to
delete-char, then return EOF. backward-delete-char (Rubout)- Delete the character behind the cursor. A numeric argument means to kill the characters instead of deleting them.
forward-backward-delete-char ()- Delete the character under the cursor, unless the cursor is at the end of the line, in which case the character behind the cursor is deleted. 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 is how 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 over the character at the cursor, moving the cursor forward as well. If the insertion point is at the end of the line, then this transposes 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 transposes the 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 numeric
argument, switches to insert mode. This command affects only
emacsmode;vimode does overwrite differently. Each call toreadline()starts in insert mode.In overwrite mode, characters bound to
self-insertreplace the text at point rather than pushing the text to the right. Characters bound tobackward-delete-charreplace the character before 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 between
words, 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.
unix-filename-rubout ()- Kill the word behind point, using white space and the slash character as the word boundaries. 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 yanked right 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 if
the prior command is
yankoryank-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 new argument. 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 a
leading 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 a character that is neither a digit or minus sign, the argument count for the next command is multiplied by four. The argument count is initially one, so executing this function the first time makes the argument count four, a second time makes the argument count sixteen, and so on. By default, this is not bound to a key.
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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 the text begins with `$'), username (if the text begins with `~'), hostname (if the text begins with `@'), or command (including aliases and functions) in turn. If none of these produces a match, filename completion is attempted.
possible-completions (M-?)- List the possible completions of the text before point.
insert-completions (M-*)-
Insert all completions of the text before point that would have
been generated by
possible-completions. menu-complete ()-
Similar to
complete, but replaces the word to be completed with a single match from the list of possible completions. Repeated execution ofmenu-completesteps through the list of possible completions, inserting each match in turn. At the end of the list of completions, the bell is rung (subject to the setting ofbell-style) and the original text is restored. An argument of n moves n positions forward in the list of matches; a negative argument may be used to move backward through the list. This command is intended to be bound to TAB, but is unbound by default. delete-char-or-list ()-
Deletes the character under the cursor if not at the beginning or
end of the line (like
delete-char). If at the end of the line, behaves identically topossible-completions. This command is unbound by default. complete-filename (M-/)- Attempt filename completion on the text before point.
possible-filename-completions (C-x /)- List the possible completions of the text before point, treating it as a filename.
complete-username (M-~)- Attempt completion on the text before point, treating it as a username.
possible-username-completions (C-x ~)- List the possible completions of the text before point, treating it as a username.
complete-variable (M-$)- Attempt completion on the text before point, treating it 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, treating it 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, treating it as a command name. Command completion attempts to match the text against aliases, reserved words, shell functions, 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, comparing the text against lines from the history list for possible completion matches.
complete-into-braces (M-{)-
Perform filename completion and insert the list of possible completions
enclosed 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 macro and save the definition.
call-last-kbd-macro (C-x e)-
Re-execute the last keyboard macro defined, by making the characters
in 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 incorporate any bindings or variable assignments found there.
abort (C-g)-
Abort the current editing command and
ring the terminal's bell (subject to the setting of
bell-style). do-uppercase-version (M-a, M-b, M-x, ...)- If the metafied character x is lowercase, run the command that is bound to the corresponding uppercase character.
prefix-meta (ESC)- Metafy the next character typed. This is for keyboards without a meta key. Typing `ESC f' is equivalent to typing M-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 a numeric 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 to the 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 that character. A negative count searches for previous occurrences.
character-search-backward (M-C-])- A character is read and point is moved to the previous occurrence of that character. A negative count searches for subsequent occurrences.
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: if the characters at the beginning of the line do not match the value ofcomment-begin, the value is inserted, otherwise the characters incomment-beginare deleted from the beginning of the line. In either case, the line is accepted as if a newline had been typed. The default value ofcomment-begincauses this command to make the current line a shell comment. If a numeric argument causes the comment character to be removed, the line will be executed by the shell. dump-functions ()- Print all of the functions and their key bindings to the Readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file. This command is unbound by default.
dump-variables ()- Print all of the settable variables and their values to the Readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file. This command is unbound by default.
dump-macros ()- Print all of the Readline key sequences bound to macros and the strings they output. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of 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 to generate 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 before pathname expansion.
glob-list-expansions (C-x g)-
The list of expansions that would have been generated by
glob-expand-wordis displayed, and the line is redrawn. If a numeric argument is supplied, a `*' is appended before pathname expansion. display-shell-version (C-x C-v)- 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 shell word 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 line relative to the current line from the history for editing. Any argument is ignored.
edit-and-execute-command (C-xC-e)-
Invoke an editor on the current command line, and execute the result as shell
commands.
Bash attempts to invoke
$VISUAL,$EDITOR, andemacsas 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 vi
editing functions, it does contain enough to allow simple editing
of the line. The Readline vi mode behaves as specified in
the POSIX 1003.2 standard.
In order to switch interactively between emacs and vi
editing modes, use the `set -o emacs' and `set -o vi'
commands (see section 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 ESC
switches you into `command' mode, where you can edit the text of the
line with the standard vi movement keys, move to previous
history lines with `k' and subsequent lines with `j', and
so forth.
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8.6 Programmable Completion
When word completion is attempted for an argument to a command for
which a completion specification (a compspec) has been defined
using the complete builtin (see 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, the compspec is used to generate the list of possible completions for the word. If the command word is a full pathname, a compspec for the full pathname is searched for first. If no compspec is found for the full pathname, an attempt is made to find a compspec for the portion following the final slash.
Once a compspec has been found, it is used to generate the list of matching words. If a compspec is not found, the default Bash completion described above (see 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 are
returned.
When the `-f' or `-d' option is used for filename or
directory name completion, the shell variable FIGNORE is
used to filter the matches.
See 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' option
is considered.
The string is first split using the characters in the IFS
special variable as delimiters.
Shell quoting is honored.
Each word is then expanded using
brace expansion, tilde expansion, parameter and variable expansion,
command substitution, and arithmetic expansion,
as described above (see 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 being
completed, and the matching words become the possible completions.
After these matches have been generated, any shell function or command
specified with the `-F' and `-C' options is invoked.
When the command or function is invoked, the COMP_LINE and
COMP_POINT variables are assigned values as described above
(see section 5.2 Bash Variables).
If a shell function is being invoked, the COMP_WORDS and
COMP_CWORD variables are also set.
When the function or command is invoked, the first argument is the
name of the command whose arguments are being completed, the
second argument is the word being completed, and the third argument
is the word preceding the word being completed on the current command line.
No filtering of the generated completions against the word being completed
is performed; the function or command has complete freedom in generating
the matches.
Any function specified with `-F' is invoked first.
The function may use any of the shell facilities, including the
compgen builtin described below
(see section 8.7 Programmable Completion Builtins), to generate the matches.
It must put the possible completions in the COMPREPLY array
variable.
Next, any command specified with the `-C' option is invoked in an environment equivalent to command substitution. It should print a list of completions, one per line, to the standard output. Backslash may be used to escape a newline, if necessary.
After all of the possible completions are generated, any filter specified with the `-X' option is applied to the list. The filter is a pattern as used for pathname expansion; a `&' in the pattern is replaced with the text of the word being completed. A literal `&' may be escaped with a backslash; the backslash is removed before attempting a match. Any completion that matches the pattern will be removed from the list. A leading `!' negates the pattern; in this case any completion not matching the pattern will be removed.
Finally, any prefix and suffix specified with the `-P' and `-S' options are added to each member of the completion list, and the result is returned to the Readline completion code as the list of possible completions.
If the previously-applied actions do not generate any matches, and the
`-o dirnames' option was supplied to complete when the
compspec was defined, directory name completion is attempted.
If the `-o plusdirs' option was supplied to complete when
the compspec was defined, directory name completion is attempted and any
matches are added to the results of the other actions.
By default, if a compspec is found, whatever it generates is returned to
the completion code as the full set of possible completions.
The default Bash completions are not attempted, and the Readline default
of filename completion is disabled.
If the `-o bashdefault' option was supplied to complete when
the compspec was defined, the default Bash completions are attempted
if the compspec generates no matches.
If the `-o default' option was supplied to complete when the
compspec was defined, Readline's default completion will be performed
if the compspec (and, if attempted, the default Bash completions)
generate no matches.
When a compspec indicates that directory name completion is desired, the programmable completion functions force Readline to append a slash to completed names which are symbolic links to directories, subject to the value of the mark-directories Readline variable, regardless of the setting of the mark-symlinked-directories Readline variable.
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8.7 Programmable Completion Builtins
Two builtin commands are available to manipulate the programmable completion facilities.
compgen-
compgen [option] [word]Generate possible completion matches for word according to the options, which may be any option accepted by the
completebuiltin with the exception of `-p' and `-r', and write the matches to the standard output. When using the `-F' or `-C' options, the various shell variables set by the programmable completion facilities, while available, will not have useful values.The matches will be generated in the same way as if the programmable completion code had generated them directly from a completion specification with the same flags. If word is specified, only those completions matching word will be displayed.
The return value is true unless an invalid option is supplied, or no matches were generated.
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, existing completion specifications are printed in a way that allows them to be reused as input. The `-r' option removes a completion specification for each name, or, if no names are supplied, all completion specifications.
The process of applying these completion specifications when word completion is 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 the
completebuiltin is invoked.-o comp-option- The comp-option controls several aspects of the compspec's behavior
beyond the simple generation of completions.
comp-option may be one of:
bashdefault- Perform the rest of the default Bash completions if the compspec
generates no matches.
default- Use Readline's default filename completion if the compspec generates
no matches.
dirnames- Perform directory name completion if the compspec generates no matches.
filenames- Tell Readline that the compspec generates filenames, so it can perform any
filename-specific processing (like adding a slash to directory names or
suppressing trailing spaces). This option is intended to be used with
shell functions specified with `-F'.
nospace- Tell Readline not to append a space (the default) to words completed at
the end of the line.
plusdirs- After any matches defined by the compspec are generated,
directory name completion is attempted and any
matches are added to the results of the other actions.
-A action- The action may be one of the following to generate a list of possible
completions:
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
helpbuiltin (see section 4.2 Bash Builtin Commands). hostname- Hostnames, as taken from the file specified by the
HOSTFILEshell 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
setbuiltin (see section 4.3 The Set Builtin). shopt- Shell option names as accepted by the
shoptbuiltin (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 generate
the possible completions.
-W wordlist- The wordlist is split using the characters in the
IFSspecial variable as delimiters, and each resultant word is expanded. The possible completions are the members of the resultant list which match the word being completed. -C command- command is executed in a subshell environment, and its output is
used as the possible completions.
-F function- The shell function function is executed in the current shell
environment.
When it finishes, the possible completions are retrieved from the value
of the
COMPREPLYarray variable. -X filterpat- filterpat is a pattern as used for filename expansion.
It is applied to the list of possible completions generated by the
preceding options and arguments, and each completion matching
filterpat is removed from the list.
A leading `!' in filterpat negates the pattern; in this
case, any completion not matching filterpat is removed.
-P prefix- prefix is added at the beginning of each possible completion
after all other options have been applied.
-S suffix- suffix is appended to each possible completion after all other options have been applied.
The return value is true unless an invalid option is supplied, an option other than `-p' or `-r' is supplied without a name argument, an attempt is made to remove a completion specification for a name for which no specification exists, or an error occurs adding a completion specification.
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9. Using History Interactively
This chapter describes how to use the GNU History Library interactively, from a user's standpoint. It should be considered a user's guide. For information on using the GNU History Library in other programs, see the GNU Readline Library Manual.
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 builtin
is 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 the
number of commands to save in a history list.
The text of the last $HISTSIZE
commands (default 500) is saved.
The shell stores each command in the history list prior to
parameter and variable expansion
but after history expansion is performed, subject to the
values of the shell variables
HISTIGNORE and HISTCONTROL.
When the shell starts up, the history is initialized from the
file named by the HISTFILE variable (default `~/.bash_history').
The file named by the value of HISTFILE is truncated, if
necessary, to contain no more than the number of lines specified by
the value of the HISTFILESIZE variable.
When an interactive shell exits, the last
$HISTSIZE lines are copied from the history list to the file
named by $HISTFILE.
If the histappend shell option is set (see section 4.2 Bash Builtin Commands),
the lines are appended to the history file,
otherwise the history file is overwritten.
If HISTFILE
is unset, or if the history file is unwritable, the history is
not saved. After saving the history, the history file is truncated
to contain no more than $HISTFILESIZE
lines. If HISTFILESIZE is not set, no truncation is performed.
If the HISTTIMEFORMAT is set, the time stamp information
associated with each history entry is written to the history file.
The builtin command fc may be used to list or edit and re-execute
a portion of the history list.
The history builtin may be used to display or modify the history
list and manipulate the history file.
When using command-line editing, search commands
are available in each editing mode that provide access to the
history list (see section 8.4.2 Commands For Manipulating The History).
The shell allows control over which commands are saved on the history
list. The HISTCONTROL and HISTIGNORE
variables may be set to cause the shell to save only a subset of the
commands entered.
The cmdhist
shell option, if enabled, causes the shell to attempt to save each
line of a multi-line command in the same history entry, adding
semicolons where necessary to preserve syntactic correctness.
The lithist
shell option causes the shell to save the command with embedded newlines
instead of semicolons.
The shopt builtin is used to set these options.
See 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 the history 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 to last is selected from the history list. Both first and last may be specified as a string (to locate the most recent command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). If last is not specified it is set to first. If first is not specified it is set to the previous command for editing and -16 for listing. If the `-l' flag is given, the commands are listed on standard output. The `-n' flag suppresses the command numbers when listing. The `-r' flag reverses the order of the listing. Otherwise, the editor given by ename is invoked on a file containing those commands. If ename is not given, the value of the following variable expansion is used:
${FCEDIT:-${EDITOR:-vi}}. This says to use the value of theFCEDITvariable if set, or the value of theEDITORvariable if that is set, orviif neither is set. When editing is complete, the edited commands are echoed and executed.In the second form, command is re-executed after each instance of pat in the selected command is replaced by rep.
A useful alias to use with the
fccommand isr='fc -s', so that typing `r cc' runs the last command beginning withccand 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. If the shell variable
HISTTIMEFORMATis set and not null, it is used as a format string for strftime to display the time stamp associated with each displayed history entry. No intervening blank is printed between the formatted time stamp and the history line.Options, if supplied, have the following meanings:
-c- Clear the history list. This may be combined
with 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 is
displayed.
-a- Append the new
history lines (history lines entered since the beginning of the
current Bash session) to the history file.
-n- Append the history lines not already read from the history file
to the current history list. These are lines appended to the history
file since the beginning of the current Bash session.
-r- Read the current history file and append its contents to
the history list.
-w- Write out the current history to the history file.
-p- Perform history substitution on the args and display the result
on the standard output, without storing the results in the history list.
-s- The args are added to the end of
the history list as a single entry.
When any of the `-w', `-r', `-a', or `-n' options is used, if filename is given, then it is used as the history file. If not, then the value of the
HISTFILEvariable is used.
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9.3 History Expansion
The History library provides a history expansion feature that is similar
to the history expansion provided by csh. This section
describes the syntax used to manipulate the history information.
History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current input line, or fix errors in previous commands quickly.
History expansion takes place in two parts. The first is to determine which line from the history list should be used during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is called the event, and the portions of that line that are acted upon are called words. Various modifiers are available to manipulate the selected words. The line is broken into words in the same fashion that Bash does, so that several words surrounded by quotes are considered one word. History expansions are introduced by the appearance of the history expansion character, which is `!' by default. Only `\' and `'' may be used to escape the history expansion character.
Several shell options settable with the shopt
builtin (see section 4.2 Bash Builtin Commands) may be used to tailor
the behavior of history expansion. If the
histverify shell option is enabled, and Readline
is being used, history substitutions are not immediately passed to
the shell parser.
Instead, the expanded line is reloaded into the Readline
editing buffer for further modification.
If Readline is being used, and the histreedit
shell option is enabled, a failed history expansion will be
reloaded into the Readline editing buffer for correction.
The `-p' option to the history builtin command
may be used to see what a history expansion will do before using it.
The `-s' option to the history builtin may be used to
add commands to the end of the history list without actually executing
them, so that they are available for subsequent recall.
This is most useful in conjunction with Readline.
The shell allows control of the various characters used by the
history expansion mechanism with the histchars variable.
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 the history list.
!- Start a history substitution, except when followed by a space, tab,
the end of the line, `=' or `(' (when the
extglobshell option is enabled using theshoptbuiltin). !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 by
a newline.
^string1^string2^- Quick Substitution. Repeat the last command, replacing string1
with 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. It may be omitted if the word designator begins with a `^', `$', `*', `-', or `%'. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.
For example,
!!- designates the preceding command. When you type this, the preceding
command is repeated in toto.
!!:$- designates the last argument of the preceding command. This may be
shortened to
!$. !fi:2- designates the second argument of the most recent command starting with
the 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, the previous 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 more of 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', leaving
the 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 the
event line. Any delimiter may be used in place of `/'.
The delimiter may be quoted in old and new
with a single backslash. If `&' appears in new,
it is replaced by old. A single backslash will quote
the `&'. The final delimiter is optional if it is the last
character on the input line.
&- Repeat the previous substitution.
ga- Cause changes to be applied over the entire event line. Used in
conjunction with `s', as in
gs/old/new/, or with `&'. G- Apply the following `s' modifier once to each word in the event.
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10. Installing Bash
This chapter provides basic instructions for installing Bash on the various supported platforms. The distribution supports the GNU operating systems, nearly every version of Unix, and several non-Unix systems such as BeOS and Interix. Other independent ports exist for MS-DOS, OS/2, and Windows platforms.
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:
-
cdto the directory containing the source code and type `./configure' to configure Bash for your system. If you're usingcshon an old version of System V, you might need to type `sh ./configure' instead to preventcshfrom trying to executeconfigureitself.Running
configuretakes some time. While running, it prints messages telling which features it is checking for. -
Type `make' to compile Bash and build the
bashbugbug reporting script. -
Optionally, type `make tests' to run the Bash test suite.
-
Type `make install' to install
bashandbashbug. This will also install the manual pages and Info file.
The configure shell script attempts to guess correct
values for various system-dependent variables used during
compilation. It uses those values to create a `Makefile' in
each directory of the package (the top directory, the
`builtins', `doc', and `support' directories,
each directory under `lib', and several others). It also creates a
`config.h' file containing system-dependent definitions.
Finally, it creates a shell script named config.status that you
can run in the future to recreate the current configuration, a
file `config.cache' that saves the results of its tests to
speed up reconfiguring, and a file `config.log' containing
compiler output (useful mainly for debugging configure).
If at some point
`config.cache' contains results you don't want to keep, you
may remove or edit it.
To find out more about the options and arguments that the
configure script understands, type
bash-2.04$ ./configure --help |
at the Bash prompt in your Bash source directory.
If you need to do unusual things to compile Bash, please
try to figure out how configure could check whether or not
to do them, and mail diffs or instructions to
bash-maintainers@gnu.org so they can be
considered for the next release.
The file `configure.in' is used to create configure
by a program called Autoconf. You only need
`configure.in' if you want to change it or regenerate
configure using a newer version of Autoconf. If
you do this, make sure you are using Autoconf version 2.50 or
newer.
You can remove the program binaries and object files from the
source code directory by typing `make clean'. To also remove the
files that configure created (so you can compile Bash for
a different kind of computer), type `make distclean'.
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10.2 Compilers and Options
Some systems require unusual options for compilation or linking
that the configure script does not know about. You can
give configure initial values for variables by setting
them in the environment. Using a Bourne-compatible shell, you
can do that on the command line like this:
CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure |
On systems that have the env program, you can do it like this:
env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure |
The configuration process uses GCC to build Bash if it is available.
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10.3 Compiling For Multiple Architectures
You can compile Bash for more than one kind of computer at the
same time, by placing the object files for each architecture in their
own directory. To do this, you must use a version of make that
supports the VPATH variable, such as GNU make.
cd to the
directory where you want the object files and executables to go and run
the configure script from the source directory. You may need to
supply the `--srcdir=PATH' argument to tell configure where the
source files are. configure automatically checks for the
source code in the directory that configure is in and in `..'.
If you have to use a make that does not supports the VPATH
variable, you can compile Bash for one architecture at a
time in the source code directory. After you have installed
Bash for one architecture, use `make distclean' before
reconfiguring for another architecture.
Alternatively, if your system supports symbolic links, you can use the `support/mkclone' script to create a build tree which has symbolic links back to each file in the source directory. Here's an example that creates a build directory in the current directory from a source directory `/usr/gnu/src/bash-2.0':
bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 . |
The mkclone script requires Bash, so you must have already built
Bash for at least one architecture before you can create build
directories for other architectures.
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10.4 Installation Names
By default, `make install' will install into
`/usr/local/bin', `/usr/local/man', etc. You can
specify an installation prefix other than `/usr/local' by
giving configure the option `--prefix=PATH',
or by specifying a value for the DESTDIR `make'
variable when running `make install'.
You can specify separate installation prefixes for
architecture-specific files and architecture-independent files.
If you give configure the option
`--exec-prefix=PATH', `make install' will use
PATH as the prefix for installing programs and libraries.
Documentation and other data files will still use the regular prefix.
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10.5 Specifying the System Type
There may be some features configure can not figure out
automatically, but need to determine by the type of host Bash
will run on. Usually configure can figure that
out, but if it prints a message saying it can not guess the host
type, give it the `--host=TYPE' option. `TYPE' can
either be a short name for the system type, such as `sun4',
or a canonical name with three fields: `CPU-COMPANY-SYSTEM'
(e.g., `i386-unknown-freebsd4.2').
See the file `support/config.sub' for the possible values of each field.
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10.6 Sharing Defaults
If you want to set default values for configure scripts to
share, you can create a site shell script called
config.site that gives default values for variables like
CC, cache_file, and prefix. configure
looks for `PREFIX/share/config.site' if it exists, then
`PREFIX/etc/config.site' if it exists. Or, you can set the
CONFIG_SITE environment variable to the location of the site
script. A warning: the Bash configure looks for a site script,
but not all configure scripts do.
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10.7 Operation Controls
configure recognizes the following options to control how it
operates.
--cache-file=file- Use and save the results of the tests in
file instead of `./config.cache'. Set file to
`/dev/null' to disable caching, for debugging
configure. --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. Usually
configurecan 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, boilerplate
options. `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 feature
that is enabled by default, use `--disable-feature'.
Here is a complete list of the `--enable-' and
`--with-' options that the Bash configure recognizes.
--with-afs- Define if you are using the Andrew File System from Transarc.
--with-bash-malloc- Use the Bash version of
mallocin the directory `lib/malloc'. This is not the samemallocthat appears in GNU libc, but an older version originally derived from the 4.2 BSDmalloc. Thismallocis very fast, but wastes some space on each allocation. This option is enabled by default. The `NOTES' file contains a list of systems for which this should be turned off, andconfiguredisables this option automatically for a number of systems. --with-curses- Use the curses library instead of the termcap library. This should
be supplied if your system has an inadequate or incomplete termcap
database.
--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 Readline
rather than the version in `lib/readline'. This works only with
Readline 5.0 and later versions. If PREFIX is
yesor not supplied,configureuses the values of the make variablesincludedirandlibdir, which are subdirectories ofprefixby default, to find the installed version of Readline if it is not in the standard system include and library directories. If PREFIX isno, Bash links with the version in `lib/readline'. If PREFIX is set to any other value,configuretreats it as a directory pathname and looks for the installed version of Readline in subdirectories of that directory (include files in PREFIX/includeand the library in PREFIX/lib). --with-purify- Define this to use the Purify memory allocation checker from Rational
Software.
--enable-minimal-config- This produces a shell with minimal features, close to the historical Bourne shell.
There are several `--enable-' options that alter how Bash is compiled and linked, rather than changing run-time features.
--enable-largefile- Enable support for large files if the operating system requires special compiler options
to build programs which can access large files. This is enabled by
default, if the operating system provides large file support.
--enable-profiling- This builds a Bash binary that produces profiling information to be
processed by
gprofeach time it is executed. --enable-static-link- This causes Bash to be linked statically, if
gccis being used. This could be used to build a version to use as root's shell.
The `minimal-config' option can be used to disable all of the following options, but it is processed first, so individual options may be enabled using `enable-feature'.
All of the following options except for `disabled-builtins' and `xpg-echo-default' are enabled by default, unless the operating system does not provide the necessary support.
--enable-alias- Allow alias expansion and include the
aliasandunaliasbuiltins (see section 6.6 Aliases). --enable-arith-for-command- Include support for the alternate form of the
forcommand that behaves like the C languageforstatement (see section 3.2.4.1 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
timeas a reserved word and for displaying timing statistics for the pipeline followingtime(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 3.2.4.2 Conditional Constructs). --enable-cond-regexp- Include support for matching POSIX regular expressions using the
`=~' binary operator in the
[[conditional command. (see section 3.2.4.2 Conditional Constructs). --enable-debugger- Include support for the bash debugger (distributed separately).
--enable-directory-stack- Include support for a
csh-like directory stack and thepushd,popd, anddirsbuiltins (see section 6.8 The Directory Stack). --enable-disabled-builtins- Allow builtin commands to be invoked via `builtin xxx'
even after
xxxhas been disabled using `enable -n xxx'. See 4.2 Bash Builtin Commands, for details of thebuiltinandenablebuiltin commands. --enable-dparen-arithmetic- Include support for the
((...))command (see section 3.2.4.2 Conditional Constructs). --enable-extended-glob- Include support for the extended pattern matching features described
above under 3.5.8.1 Pattern Matching.
--enable-help-builtin- Include the
helpbuiltin, which displays help on shell builtins and variables (see section 4.2 Bash Builtin Commands). --enable-history- Include command history and the
fcandhistorybuiltin 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-multibyte- This enables support for multibyte characters if the operating
system provides the necessary support.
--enable-net-redirections- This enables the special handling of filenames of the form
/dev/tcp/host/portand/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) if
the operating system provides the necessary support.
--enable-progcomp- Enable the programmable completion facilities
(see section 8.6 Programmable Completion).
If Readline is not enabled, this option has no effect.
--enable-prompt-string-decoding- Turn on the interpretation of a number of backslash-escaped characters
in the
$PS1,$PS2,$PS3, and$PS4prompt strings. See 6.9 Controlling the Prompt, for a complete list of prompt string escape sequences. --enable-readline- Include support for command-line editing and history with the Bash
version 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. See 6.10 The Restricted Shell, for a description of restricted mode. --enable-select- Include the
selectbuiltin, which allows the generation of simple menus (see section 3.2.4.2 Conditional Constructs). --enable-separate-helpfiles- Use external files for the documentation displayed by the
helpbuiltin instead of storing the text internally. --enable-single-help-strings- Store the text displayed by the
helpbuiltin as a single string for each help topic. This aids in translating the text to different languages. You may need to disable this if your compiler cannot handle very long string literals. --enable-strict-posix-default- Make Bash POSIX-conformant by default (see section 6.11 Bash POSIX Mode).
--enable-usg-echo-default- A synonym for
--enable-xpg-echo-default. --enable-xpg-echo-default- Make the
echobuiltin expand backslash-escaped characters by default, without requiring the `-e' option. This sets the default value of thexpg_echoshell option toon, which makes the Bashechobehave more like the version specified in the Single Unix Specification, version 3. See section 4.2 Bash Builtin Commands, for a description of the escape sequences thatechorecognizes.
The file `config-top.h' contains C Preprocessor
`#define' statements for options which are not settable from
configure.
Some of these are not meant to be changed; beware of the consequences if
you do.
Read the comments associated with each definition for more
information about its effect.
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A. Reporting Bugs
Please report all bugs you find in Bash. But first, you should make sure that it really is a bug, and that it appears in the latest version of Bash. The latest version of Bash is always available for FTP from ftp://ftp.gnu.org/pub/bash/.
Once you have determined that a bug actually exists, use the
bashbug command to submit a bug report.
If you have a fix, you are encouraged to mail that as well!
Suggestions and `philosophical' bug reports may be mailed
to bug-bash@gnu.org or posted to the Usenet
newsgroup gnu.bash.bug.
All bug reports should include:
- 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 into
the template it provides for filing a bug report.
Please send all reports concerning this manual to chet@po.CWRU.Edu.
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B. Major Differences From The Bourne Shell
Bash implements essentially the same grammar, parameter and
variable expansion, redirection, and quoting as the Bourne Shell.
Bash uses the POSIX standard as the specification of
how these features are to be implemented. There are some
differences between the traditional Bourne shell and Bash; this
section quickly details the differences of significance. A
number of these differences are explained in greater depth in
previous sections.
This section uses the version of sh included in SVR4.2 (the
last version of the historical Bourne shell) as the baseline reference.
-
Bash is POSIX-conformant, even where the POSIX specification
differs from traditional
shbehavior (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
bindbuiltin. -
Bash provides a programmable word completion mechanism
(see section 8.6 Programmable Completion), and two builtin commands,
completeandcompgen, to manipulate it. -
Bash has command history (see section 9.1 Bash History Facilities) and the
historyandfcbuiltins to manipulate it. The Bash history list maintains timestamp information and uses the value of theHISTTIMEFORMATvariable to display 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 anifstatement needs to act only if a test fails. The Bash `-o pipefail' option tosetwill cause a pipeline to return a failure status if any command fails. -
Bash has the
timereserved word and command timing (see section 3.2.2 Pipelines). The display of the timing statistics may be controlled with theTIMEFORMATvariable. -
Bash implements the
for (( expr1 ; expr2 ; expr3 ))arithmetic for command, similar to the C language (see section 3.2.4.1 Looping Constructs). -
Bash includes the
selectcompound command, which allows the generation of simple menus (see section 3.2.4.2 Conditional Constructs). -
Bash includes the
[[compound command, which makes conditional testing part of the shell grammar (see section 3.2.4.2 Conditional Constructs), including optional regular expression matching. -
Bash provides optional case-insensitive matching for the
caseand[[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
aliasandunaliasbuiltins (see section 6.6 Aliases). -
Bash provides shell arithmetic, the
((compound command (see section 3.2.4.2 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
exportcommand. -
Bash supports the `+=' assignment operator, which appends to the value
of the variable named on the left hand side.
-
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 ofvar'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 ofvar, 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
$9using${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, andGROUPS), the current host (HOSTTYPE,OSTYPE,MACHTYPE, andHOSTNAME), and the instance of Bash that is running (BASH,BASH_VERSION, andBASH_VERSINFO). See section 5.2 Bash Variables, for details. -
The
IFSvariable 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 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
extglobshell 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;
shdoes not separate the two name spaces. -
Bash functions are permitted to have local variables using the
localbuiltin, 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 includes the `<<<' redirection operator, allowing a string to
be used as the standard input to a command.
-
Bash implements the `[n]<&word' and `[n]>&word'
redirection operators, which move one file descriptor to another.
-
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
noclobberoption is available to avoid overwriting existing files with output redirection (see section 4.3 The Set Builtin). The `>|' redirection operator may be used to overridenoclobber. -
The Bash
cdandpwdbuiltins (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
builtinandcommandbuiltins (see section 4.2 Bash Builtin Commands). -
The
commandbuiltin 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
enablebuiltin (see section 4.2 Bash Builtin Commands). -
The Bash
execbuiltin 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, anddeclarebuiltins 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
hashbuiltin 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
helpbuiltin for quick reference to shell facilities (see section 4.2 Bash Builtin Commands). -
The
printfbuiltin is available to display formatted output (see section 4.2 Bash Builtin Commands). -
The Bash
readbuiltin (see section 4.2 Bash Builtin Commands) will read a line ending in `\' with the `-r' option, and will use theREPLYvariable as a default if no non-option arguments are supplied. The Bashreadbuiltin also accepts a prompt string with the `-p' option and will use Readline to obtain the line when given the `-e' option. Thereadbuiltin 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 allowreadto 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
returnbuiltin may be used to abort execution of scripts executed with the.orsourcebuiltins (see section 4.1 Bourne Shell Builtins). -
Bash includes the
shoptbuiltin, 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
setbuiltin (see section 4.3 The Set Builtin). -
The `-x' (
xtrace) option displays commands other than simple commands when performing an execution trace (see section 4.3 The Set Builtin). -
The
testbuiltin (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. -
Bash includes the
callerbuiltin, which displays the context of any active subroutine call (a shell function or a script executed with the.orsourcebuiltins). This supports the bash debugger. -
The
trapbuiltin (see section 4.1 Bourne Shell Builtins) allows aDEBUGpseudo-signal specification, similar toEXIT. Commands specified with aDEBUGtrap are executed before every simple command,forcommand,casecommand,selectcommand, every arithmeticforcommand, and before the first command executes in a shell function. TheDEBUGtrap is not inherited by shell functions unless the function has been given thetraceattribute or thefunctraceoption has been enabled using theshoptbuiltin. Theextdebugshell option has additional effects on theDEBUGtrap.The
trapbuiltin (see section 4.1 Bourne Shell Builtins) allows anERRpseudo-signal specification, similar toEXITandDEBUG. Commands specified with anERRtrap are executed after a simple command fails, with a few exceptions. TheERRtrap is not inherited by shell functions unless the-o errtraceoption to thesetbuiltin is enabled.The
trapbuiltin (see section 4.1 Bourne Shell Builtins) allows aRETURNpseudo-signal specification, similar toEXITandDEBUG. Commands specified with anRETURNtrap are executed before execution resumes after a shell function or a shell script executed with.orsourcereturns. TheRETURNtrap is not inherited by shell functions unless the function has been given thetraceattribute or thefunctraceoption has been enabled using theshoptbuiltin. -
The Bash
typebuiltin is more extensive and gives more information about the names it finds (see section 4.2 Bash Builtin Commands). -
The Bash
umaskbuiltin permits a `-p' option to cause the output to be displayed in the form of aumaskcommand that may be reused as input (see section 4.1 Bourne Shell Builtins). -
Bash implements a
csh-like directory stack, and provides thepushd,popd, anddirsbuiltins to manipulate it (see section 6.8 The Directory Stack). Bash also makes the directory stack visible as the value of theDIRSTACKshell 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
disownbuiltin can remove a job from the internal shell job table (see section 7.2 Job Control Builtins) or suppress the sending ofSIGHUPto a job when the shell exits as the result of aSIGHUP. -
Bash includes a number of features to support a separate debugger for
shell scripts.
-
The SVR4.2 shell has two privilege-related builtins
(
mldmodeandpriv) not present in Bash. -
Bash does not have the
stopornewgrpbuiltins. -
Bash does not use the
SHACCTvariable or perform shell accounting. -
The SVR4.2
shuses aTIMEOUTvariable like Bash usesTMOUT.
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 from many 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
iforwhilestatement. -
Bash does not allow unbalanced quotes. The SVR4.2 shell will silently
insert a needed closing quote at
EOFunder 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 withSIGSEGVblocked (e.g., by using thesystem()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, orSIGCHLD. -
The SVR4.2 shell does not allow the
IFS,MAILCHECK,PATH,PS1, orPS2variables 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 special builtins fails, and
only for certain failures, as enumerated in the POSIX standard.
-
The SVR4.2 shell behaves differently when invoked as
jsh(it turns on job control).
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C. Copying This Manual
C.1 GNU Free Documentation License License for copying this manual.
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C.1 GNU Free Documentation License
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. |
-
PREAMBLE
The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
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This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.
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VERBATIM COPYING
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MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
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Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document). You may use the same title as a previous version
if the original publisher of that version gives permission.
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List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has fewer than five),
unless they release you from this requirement.
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State on the Title page the name of the publisher of the
Modified Version, as the publisher.
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Preserve all the copyright notices of the Document.
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Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
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Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.
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Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.
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Include an unaltered copy of this License.
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Preserve the section Entitled "History", Preserve its Title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page. If
there is no section Entitled "History" in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.
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Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on. These may be placed in the "History" section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.
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For any section Entitled "Acknowledgements" or "Dedications", Preserve
the Title of the section, and preserve in the section all the
substance and tone of each of the contributor acknowledgements and/or
dedications given therein.
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Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section titles.
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Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
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Do not retitle any existing section to be Entitled "Endorsements" or
to conflict in title with any Invariant Section.
- Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.
You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.
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Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document). You may use the same title as a previous version
if the original publisher of that version gives permission.
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COMBINING DOCUMENTS
You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements."
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COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
-
AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.
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TRANSLATION
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.
-
TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
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FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.
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C.1.1 ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:
Copyright (C) year your name. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. |
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with...Texts." line with this:
with the Invariant Sections being list their titles, with
the Front-Cover Texts being list, and with the Back-Cover Texts
being list.
|
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
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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 |
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Index of Shell Reserved Words
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Parameter and Variable Index
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Function Index
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Concept Index
| Jump to: | A B C D E F H I J K L M N O P Q R S T V W Y |
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| Jump to: | A B C D E F H I J K L M N O P Q R S T V W Y |
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| [Top] | [Contents] | [Index] | [ ? ] |
Table of Contents
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1. Introduction
2. Definitions
3. Basic Shell Features
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3.1 Shell Syntax
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3.1.1 Shell Operation
3.1.2 Quoting
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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
3.3 Shell Functions
3.4 Shell Parameters
3.5 Shell Expansions
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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
3.5.9 Quote Removal
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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
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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
5. Shell Variables
6. Bash Features
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6.1 Invoking Bash
6.2 Bash Startup Files
6.3 Interactive Shells
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6.3.1 What is an Interactive Shell?
6.3.2 Is this Shell Interactive?
6.3.3 Interactive Shell Behavior
6.5 Shell Arithmetic
6.6 Aliases
6.7 Arrays
6.8 The Directory Stack
6.9 Controlling the Prompt
6.10 The Restricted Shell
6.11 Bash POSIX Mode
8. Command Line Editing
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8.1 Introduction to Line Editing
8.2 Readline Interaction
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8.2.1 Readline Bare Essentials
8.2.2 Readline Movement Commands
8.2.3 Readline Killing Commands
8.2.4 Readline Arguments
8.2.5 Searching for Commands in the History
8.4 Bindable Readline Commands
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8.4.1 Commands For Moving
8.4.2 Commands For Manipulating The History
8.4.3 Commands For Changing Text
8.4.4 Killing And Yanking
8.4.5 Specifying Numeric Arguments
8.4.6 Letting Readline Type For You
8.4.7 Keyboard Macros
8.4.8 Some Miscellaneous Commands
8.6 Programmable Completion
8.7 Programmable Completion Builtins
10. Installing Bash
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10.1 Basic Installation
10.2 Compilers and Options
10.3 Compiling For Multiple Architectures
10.4 Installation Names
10.5 Specifying the System Type
10.6 Sharing Defaults
10.7 Operation Controls
10.8 Optional Features
B. Major Differences From The Bourne Shell
C. Copying This Manual
Index of Shell Builtin Commands
Index of Shell Reserved Words
Parameter and Variable Index
Function Index
Concept Index
| [Top] | [Contents] | [Index] | [ ? ] |
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
C. Copying This Manual
Index of Shell Builtin Commands
Index of Shell Reserved Words
Parameter and Variable Index
Function Index
Concept Index
| [Top] | [Contents] | [Index] | [ ? ] |
About this document
This document was generated by Chet Ramey on September, 28 2006 using texi2html The buttons in the navigation panels have the following meaning:| Button | Name | Go to | From 1.2.3 go to |
|---|---|---|---|
| [ < ] | Back | previous section in reading order | 1.2.2 |
| [ > ] | Forward | next section in reading order | 1.2.4 |
| [ << ] | FastBack | previous or up-and-previous section | 1.1 |
| [ Up ] | Up | up section | 1.2 |
| [ >> ] | FastForward | next or up-and-next section | 1.3 |
| [Top] | Top | cover (top) of document | |
| [Contents] | Contents | table of contents | |
| [Index] | Index | concept index | |
| [ ? ] | About | this page |
- 1. Section One
- 1.1 Subsection One-One
- ...
- 1.2 Subsection One-Two
- 1.2.1 Subsubsection One-Two-One
- 1.2.2 Subsubsection One-Two-Two
- 1.2.3 Subsubsection One-Two-Three <== Current Position
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This document was generated by Chet Ramey on September, 28 2006 using texi2html
:: Command execute :: | |
:: Shadow's tricks :D :: | |
Useful Commands
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:: Preddy's tricks :D :: | |
Php Safe-Mode Bypass (Read Files)
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