Provided by: yash_2.35-2_amd64 
NAME
yash - a POSIX-compliant command line shell
SYNOPSIS
yash [options...] [--] [operands...]
INTRODUCTION
Yet anther shell (yash) is a command line shell for UNIX-like operating systems. The shell
conforms to the POSIX.1-2008 standard (for the most parts), and actually is more
conforming than other POSIX-conforming shells. Moreover, it has many features that are
used for interactive use, such as command history and command line editing.
This program can be freely modified and redistributed under the terms of GNU General
Public License (Version 2). Use of this program is all at your own risk. There is no
warranty and the author is not responsible for any consequences caused by use of this
program.
This manual can be freely modified and redistributed under the terms of Creative Commons
Attribution-ShareAlike 2.1 Japan.
Yash is developed and maintained by 渡邊裕貴 (WATANABE Yuki) aka Magicant. Yash
development project and Yash’s homepage are hosted by SourceForge.jp.
INVOCATION
When invoked as a program, yash performs the predefined initialization steps and
repeatedly reads and executed commands. Command line arguments given in the invocation
determines how the shell initializes itself and executes commands.
Command line arguments
The syntax of command line arguments for yash conforms to POSIX. As defined in POSIX,
arguments are separated into options and operands. For more detailed explanation about
options and operands, see Command argument syntax. All options must come before operands.
The interpretation of operands depends on options specified.
When you specify the -c (--cmdline) option, you must give at least one operand. The shell
interprets and executes the first operand as a command string. The second operand, if any,
is used to initialize the 0 special parameter. The other operands, if any, are used to
initialize the positional parameters. When the -c (--cmdline) option is specified, the
shell does not read any file or the standard input (unless the dot built-in is used).
If you specify the -s (--stdin) option, the shell reads the standard input, interprets the
input as commands, and executes them. All the operands given are used to initialize the
positional parameters. The 0 special parameter is initialized to the name the shell is
invoked as.
If you specify neither the -c (--cmdline) nor -s (--stdin) option, the shell reads a file,
interprets the file contents as commands, and executes them. The first operand specifies
the pathname of the file. The remaining operands are used to initialize the positional
parameters. If you do not give any operands, the shell reads the standard input as if the
-s (--stdin) option is specified.
You cannot use both the -c (--cmdline) and -s (--stdin) options at a time.
If you specify either the --help or --version option, the shell never performs the usual
initialization or command execution. Instead, it just prints brief usage (for --help) or
version information (for --version). If the --version option is accompanied by the -v
(--verbose) option, the shell prints a list of the available optional features as well.
If you specify the -i (--interactive) option, the shell goes into the interactive mode. If
you specify the +i (++interactive) option, conversely, the shell never goes into the
interactive mode.
If you specify the -l (--login) option, the shell behaves as a login shell.
The --noprofile, --norcfile, --profile, and --rcfile options determine how the shell is
initialized (see below for details).
In addition to the options described above, you can specify options that can be specified
to the set built-in.
If the first operand is - and the options and the operands are not separated by --, the
first operand is ignored.
Initialization of yash
Yash initializes itself as follows:
1. Yash first parses the name it was invoked as. If the name starts with -, the shell
behaves as a login shell. If the name is sh (including names such as /bin/sh), the
shell goes into the POSIXly-correct mode.
2. If no operands are given and the standard input and standard error are both connected
to a terminal, the shell goes into the interactive mode unless the +i (++interactive)
option is specified.
3. Job control is automatically enabled in an interactive shell unless the +m (++monitor)
option is specified.
4. Yash reads and executes commands from the following files (unless the real and
effective user IDs of the shell process are different or the real and effective group
IDs of the shell process are different):
1. If it is behaving as a login shell, the shell reads the file specified by the
--profile=filename option unless the --noprofile option is specified or the shell
is in the POSIXly-correct mode.
If the --profile=filename option is not specified, the shell reads ~/.yash_profile
as a default.
2. If in the interactive mode, the shell reads the file specified by the
--rcfile=filename option unless the --norcfile option is specified.
If the --rcfile=filename option is not specified, the shell
• reads ~/.yashrc as a default if not in the POSIXly-correct mode; or
• performs parameter expansion on the value of the ENV environment variable and
treats the expansion result as the name of the file to read if in the
POSIXly-correct mode.
Note
Yash never automatically reads /etc/profile, /etc/yashrc, nor ~/.profile.
SYNTAX
The shell reads, parses, and executes command line by line. If there is more than one
command on a line, all the commands are parsed before executed. If a command is continued
to next lines, the shell reads more enough lines to complete the command. On a syntax
error, the shell neither reads nor executes any more commands.
Tokens and keywords
A command is composed of one or more tokens. In the shell syntax, a token is a word that
is part of a command. Normally, tokens are separated by whitespaces, that is, the space or
tab character. Whitespaces inside a command substitution or a parameter expansion,
however, do not separate tokens.
The following symbols have special meanings in the shell syntax and in most cases separate
tokens:
; & | < > ( ) [newline]
The following symbols do not separate tokens, but have syntactic meanings:
$ ` \ " ' * ? [ # ~ = %
The following tokens are treated as keywords depending on the context in which they
appear:
! { } case do done elif else esac fi
for function if in then until while
A token is treated as a keyword when:
• it is the first token of a command,
• it follows another keyword (except case, for, and in), or
• it is a non-first token of a command and is supposed to be a keyword to compose a
composite command.
If a token begins with #, then the # and any following characters up to the end of the
line are treated as a comment, which is completely ignored in syntax parsing.
Quotations
If you want whitespaces, separator characters, or keywords described above to be treated
as a normal characters, you must quote the characters using appropriate quotation marks.
Quotation marks are not treated as normal characters unless they are themselves quoted.
You can use the following three quotation marks:
• A backslash (\) quotes a character that immediately follows.
The only exception about a backslash is the case where a backslash is followed by a
newline. In this case, the two characters are treated as a line continuation rather
than a newline being quoted. The two characters are removed from the input and the two
lines surrounding the line continuation are concatenated into a single line.
• A pair of single-quotation marks (') quote any characters between them except another
single-quotation. Note that newlines can be quoted using single-quotations.
• Double-quotation marks (") are like single-quotations, but they have a few exceptions:
Parameter expansion, command substitution, and arithmetic expansion are interpreted as
usual even between double-quotations. A backslash between double-quotations is treated
as a quotation mark only when it is followed by $, `, ", \, or a newline; other
backslashes are treated as normal characters.
Aliases
Tokens that compose a command are subject to alias substitution. A token that matches the
name of an alias that has already been defined is substituted with the value of the alias
before the command is parsed.
Tokens that contain quotations are not alias-substituted since an alias name cannot
contain quotation marks. Keywords and command separator characters are not
alias-substituted either.
There are two kinds of aliases: normal aliases and global aliases. A normal alias can only
substitute the first token of a command while a global alias can substitute any part of a
command. Global aliases are yash extension that is not defined in POSIX.
If a token is alias-substituted with the value of a normal alias that ends with a
whitespace, the next token is exceptionally subject to alias substitution for normal
aliases.
The results of alias substitution are again subject to alias substitution for other
aliases (but not for the aliases that have been already applied).
You can define aliases using the alias built-in and remove using the unalias built-in.
Simple commands
A command that does not start with a keyword token is a simple command. Simple commands
are executed as defined in Execution of simple commands.
If the first and any number of following tokens of a simple command have the form
name=value, they are interpreted as variable assignments. A variable name must consist of
one or more alphabets, digits and/or underlines (_) and must not start with a digit. The
first token that is not a variable assignment is considered as a command name and all the
following tokens (whether or not they have the form name=value) as command arguments.
A variable assignment of the form var=(tokens) is interpreted as assignment to an array.
You can write any number of tokens between a pair of parentheses. Tokens can be separated
by not only spaces and tabs but also newlines.
Pipelines
A pipeline is a sequence of one or more simple commands, compound commands, and/or
function definitions that are separated by |.
A pipeline that has more than one subcommand is executed by executing each subcommand of
the pipeline in a subshell simultaneously. The standard output of each subcommand except
the last one is redirected to the standard input of the next subcommand. The standard
input of the first subcommand and the standard output of the last subcommand are not
redirected. The exit status of the pipeline is that of the last subcommand.
A pipeline can be prefixed by !, in which case the exit status of the pipeline is
reversed: the exit status of the pipeline is 1 if that of the last subcommand is 0, and 0
otherwise.
Note
When the execution of a pipeline finishes, at least the execution of the last
subcommand has finished since the exit status of the last subcommand defines that of
the whole pipeline. The execution of other subcommands, however, may not have finished
then. On the other hand, the execution of the pipeline may not finish soon after that
of the last subcommand finished because the shell may choose to wait for the execution
of other subcommands to finish.
Note
The POSIX standard allows executing any of subcommands in the current shell rather
than subshells, though yash does not do so.
And/or lists
An and/or list is a sequence of one or more pipelines separated by && or ||.
An and/or list is executed by executing some of the pipelines conditionally. The first
pipeline is always executed. The other pipelines are either executed or not executed
according to the exit status of the previous pipelines.
• If two pipelines are separated by && and the exit status of the first pipeline is
zero, the second pipeline is executed.
• If two pipelines are separated by || and the exit status of the first pipeline is not
zero, the second pipeline is executed.
• In other cases, the execution of the and/or list ends: the second and any remaining
pipelines are not executed.
The exit status of an and/or list is that of the last pipeline that was executed.
Normally, an and/or list must be terminated by a semicolon, ampersand, or newline. See
Command separators and asynchronous commands.
Command separators and asynchronous commands
The whole input to the shell must be composed of any number of and/or lists separated by a
semicolon or ampersand. A terminating semicolon can be omitted if it is followed by ;;, ),
or a newline. Otherwise, an and/or list must be terminated by a semicolon or ampersand.
If an and/or list is terminated by a semicolon, it is executed synchronously: the shell
waits for the and/or list to finish before executing the next and/or list. If an and/or
list is terminated by an ampersand, it is executed asynchronously: after the execution of
the and/or list is started, the next and/or list is executed immediately. An asynchronous
and/or list is always executed in a subshell and its exit status is zero.
If the shell is not doing job control, the standard input of an asynchronous and/or list
is automatically redirected to /dev/null. Signal handlers of the and/or list for the
SIGINT and SIGQUIT signals are set to “ignore” the signal so that the execution of the
and/or list cannot be stopped by those signals. (In the POSIXly-correct mode, the standard
input is redirected if and only if the shell is interactive, regardless of whether job
control is on. Moreover, the SIGINT and SIGQUIT signals are ignored even if job control is
on.)
When the execution of an asynchronous and/or list is started, the shell remembers its
process ID. You can obtain the ID by referencing the ! special parameter. You can obtain
the current and exit status of the asynchronous list as well by using the jobs and wait
built-ins.
Compound commands
Compound commands provide you with programmatic control of shell command execution.
Grouping
A grouping is a list of commands that is treated as a simple command.
Normal grouping syntax
{ command...; }
Subshell grouping syntax
(command...)
The { and } tokens are keywords, which must be separated from other tokens. The ( and
) tokens, however, are special separators that need not to be separated.
In the normal grouping syntax, the commands in a grouping are executed in the current
shell. In the subshell grouping syntax, the commands are executed in a new subshell.
In the POSIXly-correct mode, a grouping must contain at least one command. If the
shell is not in the POSIXly-correct mode, a grouping may contain no commands.
The exit status of a grouping is that of the last command in the grouping. If the
grouping contains no commands, its exit status is that of the last executed command
before the grouping.
If command
The if command performs a conditional branch.
Basic if command syntax
if condition...; then body...; fi
Syntax with the else clause
if condition...; then body...; else body...; fi
Syntax with the elif clause
if condition...; then body...; elif condition...; then body...; fi
Syntax with the elif clause
if condition...; then body...; elif condition...; then body...; else body...; fi
For all the syntaxes, the execution of an if command starts with the execution of the
condition commands that follows the if token. If the exit status of the condition
commands is zero, the condition is considered as “true”. In this case, the body
commands that follows the then token are executed and the execution of the if command
finishes. If the exit status of the condition commands is non-zero, the condition is
considered as “false”. In this case, the condition commands for the next elif clause
are executed and the exit status is tested in the same manner as above. If there is no
elif clause, the body commands that follow the else token are executed and the
execution of the if command finishes. If there is no else clause either, the execution
of the if command just ends.
An if command may have more than one elif-then clause.
The exit status of an if command is that of the body commands that were executed. The
exit status is zero if no body commands were executed, that is, all the conditions
were false and there was no else clause.
While and until loops
The while loop and until loop are simple loops with condition.
While loop syntax
while condition...; do body...; done
Until loop syntax
until condition...; do body...; done
If the shell is not in the POSIXly-correct mode, you can omit the condition and/or
body commands of a while/until loop.
The execution of a while loop is started by executing the condition commands. If the
exit status of the condition commands is zero, the shell executes the body commands
and returns to the execution of the condition commands. The condition and body
commands are repeatedly executed until the exit status of the condition commands is
non-zero.
Note
The body commands are not executed at all if the first execution of the condition
commands yields a non-zero exit status.
An until loop is executed in the same manner as a while loop except that the condition
to repeat the loop is reversed: the body commands are executed when the exit status of
the condition commands is non-zero.
The exit status of a while/until loop is that of the last executed body command. The
exit status is zero if the body commands are empty or were not executed at all.
For loop
The for loop repeats commands with a variable assigned one of given values in each
round.
For loop syntax
for varname in word...; do command...; donefor varname do command...; done
The word list after the in token may be empty, but the semicolon (or newline) before
the do token is required even in that case. The words are not treated as keywords, but
you need to quote separator characters (such as & and |) to include them as part of a
word. If you omit the in token and the following words, you must also omit the
semicolon before the do token. However, the shell does not complain about the
existence of the semicolon if not in the POSIXly-correct mode. The command list may be
empty if not in the POSIXly-correct mode.
The execution of a for loop is started by expanding the words in the same manner as in
the execution of a simple command. If the in and word tokens are omitted, the shell
assumes the word tokens to be "$@". Next, the following steps are taken for each word
expanded (in the order the words were expanded):
1. Assign the word to the variable whose name is varname.
2. Execute the commands.
Each word is assigned as a local variable except in the POSIXly-correct mode. If the
expansion of the words yielded no words as a result, the commands are not executed at
all.
The exit status of a for loop is that of the last executed command. The exit status is
zero if the commands are not empty and not executed at all. If the commands are empty,
the exit status is that of the last executed command before the for loop.
Case command
The case command performs a pattern matching to select commands to execute.
Case command syntax
case word in caseitem... esac
Case item syntax
(patterns) command...;;
The word between the case and in tokens must be exactly one word. The word is not
treated as a keyword, but you need to quote separator characters (such as & and |) to
include them as part of the word. Between the in and esac tokens you can put any
number of case items (may be none). You can omit the first ( token of a case item and
the last ;; token before the esac token. If the last command of a case item is
terminated by a semicolon, you can omit the semicolon as well. The commands in a case
item may be empty.
The patterns in a case item are one or more tokens each separated by a | token.
The execution of a case command starts with subjecting the word to the four
expansions. Next, the following steps are taken for each case item (in the order of
appearance):
1. For each word in the patterns, expand the word in the same manner as the word and
test if the expanded pattern matches the expanded word. (If a pattern is found
that matches the word, the remaining patterns are not expanded nor tested, so some
of the patterns may not be expanded. Yash expands and tests the patterns in the
order of appearance, but it may not be the case for other shells.)
2. If one of the patterns was found to match the word in the previous step, the
commands in this case item are executed and the execution of the whole case item
ends. Otherwise, proceed to the next case item.
The exit status of a case command is that of the commands executed. The exit status is
zero if no commands were executed, that is, there were no case items, no matching
pattern was found, or no commands were associated with the matching pattern.
In the POSIXly-correct mode, the first pattern in a case item cannot be esac (even if
you do not omit the ( token).
Function definition
The function definition command defines a function.
Function definition syntax
funcname ( ) compound_commandfunction funcname compound_commandfunction funcname ( )
compound_command
In the first syntax without the function keyword, funcname cannot contain any special
characters such as semicolons and quotation marks. In the second and third syntax, which
cannot be used in the POSIXly-correct mode, funcname is subjected to the four expansions
when executed.
When a function definition command is executed, a function whose name is funcname is
defined with its body being compound_command.
A function definition command cannot be directly redirected. Any redirections that follow
a function definition are associated with compound_command rather than the whole function
definition command. In func() { cat; } >/dev/null, for example, it is not func() { cat; }
but { cat; } that is redirected.
The exit status of a function definition is zero if the function was defined without
errors, and non-zero otherwise.
PARAMETERS AND VARIABLES
Parameters are string values that are expanded in parameter expansion. There are three
types of parameters: positional parameters, special parameters and variables.
Positional parameters
Positional parameters are parameters that are identified by natural numbers. If there are
three positional parameters, for example, they are identified as 1, 2, and 3. You can
obtain the number of positional parameters by the # special parameter. The * and @ special
parameters are expanded to all positional parameters.
Positional parameters are initialized from the shell’s command line arguments when the
shell is started (see Command line arguments). In the initialization, the order of the
operands are preserved as the order of the positional parameters.
When the shell executes a function call, positional parameters are changed to the
arguments to the function call so that you can access the arguments while the function is
being executed. Positional parameters are restored to the original values when the
execution of the function is finished.
Positional parameters can be manipulated by built-in commands like set and shift.
Note that 0 is not a positional parameter but a special parameter.
Special parameters
Special parameters are parameters each identified by a single symbol. They cannot be
directly assigned to by the user.
Yash provides the following special parameters:
0
The name of the shell executable file or the script file that was specified in the
invocation of the shell.
#
The number of current positional parameters. The value is a non-negative integer.
$
The process ID of the shell. The value is a positive integer and is never changed even
in subshells.
-
Currently enabled shell options. The value is a concatenation of alphabet characters
that are the names of currently enabled single-character options that can be specified
in shell invocation. The value reflects changes of enabled options when you enable or
disable options using the set built-in.
?
The exit status of the last executed pipeline. The value is a non-negative integer.
!
The process ID of the last executed asynchronous list.
*
This special parameter represents the whole positional parameters. When there is no
positional parameters, the value of this special parameter is the empty string. When
there is more than one positional parameter, the value is a concatenation of all the
positional parameters, each of which is separated as follows:
• If the IFS variable exists and its value is not empty, positional parameters are
each separated by the first character of the value of the IFS variable.
• If the IFS variable exists and has an empty value, positional parameters are just
concatenated without any separator.
• If the IFS variable does not exist, positional parameters are each separated by a
space character.
@
This special parameter represents the whole positional parameters like the * special
parameter above. The difference between the two is the results of expansion that
occurs between a pair of double-quotation marks. If the @ special parameter is
expanded inside double-quotations, positional parameters are field-split rather than
concatenated (in spite of the quotation). If there are no positional parameters, the
expansion yields no word rather than an empty word.
• When there are no positional parameters, the command words echo 1 "$@" 2 is
expanded to the three words echo, 1, and 2.
• When positional parameters are the three words 1, 2 2, and 3, the command words
echo "$@" is expanded to the four words echo, 1, 2 2, and 3, and the words echo
"a$@b" to the four words echo, a1, 2 2, and 3b.
Variables
Variables are parameters the user can assign values to. Each variable has a name that
identifies it and a value that defines the results of expansion.
A variable name is composed of one or more alphanumeric characters and underscores (_). A
name cannot start with a digit. Other characters may be used in a name depending on
internationalization support of your environment.
Variables that are exported to external commands are called environment variables. They
are passed to all external commands the shell invokes. Variables passed to the shell in
invocation will be automatically exported.
You can assign to variables by a simple command as well as the typeset built-in. You can
remove variables by using the unset built-in.
Variables used by the shell
The following variables are used by the shell for special purposes.
CDPATH
This variable is used by the cd built-in to find a destination directory.
COLUMNS
This variable specifies the width (the number of character columns) of the
terminal screen. The value affects the display of line-editing.
COMMAND_NOT_FOUND_HANDLER
When the shell cannot find a command to be executed, the value of this variable is
interpreted and executed instead. You can override the shell’s error handling
behavior with this variable. See Execution of simple commands for detail.
This feature is disabled in the POSIXly-correct mode.
DIRSTACK
This array variable is used by the shell to store the directory stack contents. If
you modify the value of this variable, the directory stack may be corrupted.
ECHO_STYLE
This variable specifies the behavior of the echo built-in.
ENV
When an interactive shell is started in the POSIXly-correct mode, the value of
this variable is used to find the initialization file. See Initialization of yash.
FCEDIT
This variable specifies an editor program used to edit command lines during
execution of the fc built-in.
HANDLED
This variable can be set in the command-not-found handler to tell the shell not to
produce a further error message. See Execution of simple commands for detail.
HISTFILE
This variable specifies the pathname of the file to save the command history in.
HISTRMDUP
This variable specifies the number of command history items to be checked for
duplication. When the shell is adding a new history item to the command history,
if some of the most recent n items have the same contents as the new one, then the
duplicate existing items are removed from the history before the new one is added,
where n is the value of this variable.
If the value of this variable is 1, for example, the most recent item is removed
when a new item that have the same contents is added.
Items older than the nth recent item are not removed. No items are removed if the
value of this variable is 0. All items are subject to removal if the variable
value is greater than or equal to the value of the HISTSIZE variable.
HISTSIZE
This variable specifies the maximum number of items in the command history.
HOME
This variable specifies the pathname of the user’s home directory and affects
results of tilde expansion and cd built-in.
IFS
This variable specifies separators used in field splitting. The variable value is
initialized to the three characters of a space, a tab, and a newline when the
shell is started.
LANG, LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES, LC_MONETARY, LC_NUMERIC, LC_TIME
These variables specify a locale in which the shell runs. The shell chooses the
file input/output encoding, the error message language, etc. according to the
locale specified.
Unless the shell is interactive and not in the POSIXly-correct mode, the value of
the LC_CTYPE variable is considered only when the shell is started. Once the shell
has been initialized, changing the value of LC_CTYPE will have no effect on the
shell’s behavior.
LINENO
The value of this variable is automatically set to the line number in which the
currently executed command appears in the file.
In the interactive shell, the line number is reset to 1 each time the shell reads
and executes a command.
If you assign to or remove this variable, it will no longer provide line numbers.
LINES
This variable specifies the height (the number of character lines) of the terminal
screen. The value affects the display of line-editing.
MAIL
This variable specifies the pathname of a file that is checked in mail checking.
MAILCHECK
This variable specifies how often the shell should do mail checking. The value has
to be specified as a positive integer in seconds. The value is initialized to the
default value of 600 when the shell is started.
MAILPATH
This variable specifies the pathnames of files that are checked in mail checking.
NLSPATH
The POSIX standard prescribes that the value of this variable specifies pathname
templates of locale-dependent message data files, but yash does not use it.
OLDPWD
This variable is set to the previous working directory path when you change the
working directory by using the cd or other built-ins. This variable is exported by
default.
OPTARG
When the getopts built-in parses an option that takes an argument, the argument
value is assigned to this variable.
OPTIND
The value of this variable specifies the index of an option that is to be parsed
by the next getopts built-in execution. This variable is initialized to 1 when the
shell is started.
PATH
This variable specifies paths that are searched for a command in command search.
PPID
The value of this variable is the process ID of the shell’s parent process, which
is a positive integer. This variable is initialized when the shell is started. The
value is not changed when the shell makes a new subshell.
PROMPT_COMMAND
The shell interprets and executes the value of this variable before printing each
command prompt if the shell is interactive and not in the POSIXly-correct mode.
This behavior is equivalent to executing the command eval -i --
"${PROMPT_COMMAND-}" before each command prompt, but its exit status does not
affect the expansion of the ? special parameter in the next command.
PS1
This variable specifies the main command prompt string printed by an interactive
shell. See Prompts for the format of the variable value. The value is initialized
to \$ when the shell is started. (In the POSIXly-correct mode, the initial value
is either $ or # depending on whether the effective user ID of the shell process
is zero or not.)
PS1R
This variable specifies the auxiliary prompt string printed to the right of the
cursor when you input a command line to an interactive shell. See Prompts for the
format of the variable value.
PS1S
This variable specifies the font style of command strings you enter to an
interactive shell. See Prompts for the format of the variable value.
PS2
This variable is like the PS1 variable, but it is used for the second and
following lines of a command that is longer than one line. See Prompts for the
format of the variable value. The value is initialized to > when the shell is
started.
PS2R
This variable is like the PS1R variable, but it is used when PS2 is used. See
Prompts for the format of the variable value.
PS2S
This variable is like the PS1S variable, but it is used when PS2 is used. See
Prompts for the format of the variable value.
PS4
The value of this variable is printed before each command trace output when the
xtrace option is enabled. The value is subject to parameter expansion, command
substitution, arithmetic expansion. You can also use backslash notations if the
shell is not in the POSIXly-correct mode. The value is initialized to + when the
shell is started.
PS4S
This variable is like the PS1S variable, but it is used when PS4 is used. You can
use this variable to modify font style of command trace output.
PWD
The value of this variable is the pathname of the current working directory. The
value is set when the shell is started and reset each time the working directory
is changed by the cd or other built-ins. This variable is exported by default.
RANDOM
You can use this variable to get random numbers. The value of this variable is a
uniformly distributed random integer between 0 and 32767 (inclusive). You will get
a different number each time the variable is expanded.
You can set the “seed” of random numbers by assigning a non-negative integer to
the variable.
If you remove this variable, it will no longer work as a random number generator.
If the shell was invoked in the POSIXly-correct mode, this variable does not work
as a random number generator.
TERM
This variable specifies the type of the terminal in which the shell is running.
The value affects the behavior of line-editing.
YASH_AFTER_CD
The shell interprets and executes the value of this variable after each time the
shell’s working directory is changed by the cd or other built-ins. This behavior
is equivalent to executing the command eval -i -- "${YASH_AFTER_CD-}" after the
directory was changed.
YASH_LOADPATH
This variable specifies directories the dot built-in searches for a script file.
More than one directory can be specified by separating them by colons like the
PATH variable. When the shell is started, this variable is initialized to the
pathname of the directory where common script files are installed.
YASH_LE_TIMEOUT
This variable specifies how long the shell should wait for a next possible input
from the terminal when it encountered an ambiguous control sequence while
line-editing. The value must be specified in milliseconds. If you do not define
this variable, the default value of 100 milliseconds is assumed.
YASH_VERSION
The value is initialized to the version number of the shell when the shell is
started.
Arrays
An array is a variable that contains zero or more strings. The string values of an
array are identified by natural numbers (like positional parameters).
You can assign values to an array by using a simple command as well as the array
built-in. You can use the unset built-in to remove arrays.
Arrays cannot be exported as arrays. When an array is exported, it is treated as a
normal variable whose value is a concatenation of all the array values, each separated
by a colon.
Arrays are not supported in the POSIXly-correct mode.
WORD EXPANSIONS
Word expansion is substitution of part of a word with another particular string. There are
seven types of word expansions:
1. Tilde expansion
2. Parameter expansion
3. Command substitution
4. Arithmetic expansion
5. Brace expansion
6. Field splitting
7. Pathname expansion (globbing)
These types of expansions are performed in the order specified above.
Tilde expansion, parameter expansion, command substitution, and arithmetic expansion are
called the four expansions.
Tilde expansion
In tilde expansion, parts of words that start with a tilde (~) are substituted with
particular pathnames. The part of each word that gets substituted is from the beginning of
the word, which is a tilde, up to (but not including) the first slash (/) in the word. If
the word does not contain a slash, the whole word is substituted. If any character in the
substituted part is quoted, tilde expansion is not performed on the word.
The results of expansion are determined by the format of the substituted part:
~
A single tilde is substituted with the value of the HOME variable.
~username
A tilde followed by a user name is substituted with the pathname of the user’s home
directory.
~+
~+ is substituted with the value of the PWD variable.
~-
~- is substituted with the value of the OLDPWD variable.
~+n, ~-n
where n is a non-negative integer. This type of tilde expansion yields the pathname of
a directory of which ~+n or ~-n is the index in the directory stack.
When tilde expansion is performed on the value of a variable assignment that occurs during
execution of a simple command, the value is considered as a colon-separated list of words
and those words are each subject to tilde expansion. For example, the variable assignment
VAR=~/a:~/b:~/c
is equivalent to
VAR=/home/foo/a:/home/foo/b:/home/foo/c
if the value of HOME variable is /home/foo.
The POSIX standard does not prescribe how the shell should behave when it encounters an
error during tilde expansion (e.g., when the HOME variable is not defined). Yash silently
ignores any errors during tilde expansion; the part of the word that would be substituted
is left intact.
In the POSIXly-correct mode, tilde expansion supports the formats of ~ and ~username only.
Parameter expansion
Parameter expansion expands to the value of a parameter.
The syntax of typical, simple parameter expansion is ${parameter}, which expands to the
value of the parameter whose name is parameter. You can omit the braces (e.g., $parameter)
if
• parameter is a special parameter,
• parameter is a positional parameter whose index is a one-digit integer, or
• parameter is a variable and the parameter expansion is not followed by a character
that can be used as part of a variable name. For example, ${path}-name is equivalent
to $path-name, but ${path}name and $pathname are different.
If parameter is none of a special parameter, positional parameter, and variable, it is a
syntax error. (Some shells other than yash may treat such a case as an expansion error.)
If the unset option is disabled and the parameter is an undefined variable, it is an
expansion error. If the unset option is enabled, an undefined variable expands to the
empty string.
More complex syntax of parameter expansion allows modifying the value of a parameter.
Parameter expansion
${ prefix parameter index modifier }
The spaces in the syntax definition above are for readability only and must be omitted.
You can omit prefix, index, and/or modifier.
Prefix
The prefix, if any, must be a hash sign (#). If a parameter expansion has the prefix,
the result of expansion is the number of characters in the value this expansion would
be expanded to without the prefix.
Parameter name
The parameter name (parameter) must be either
• a name of a special parameter, positional parameter, or variable; or
• another parameter expansion, command substitution, or arithmetic expansion.
The parameter expansion is expanded to the value of the parameter. If parameter is an
array variable, the values of the array are field-split like the @ special parameter
unless the index [*] is specified.
If parameter is another expansion, it is called a nested expansion. Nested expansion
cannot be used in the POSIXly-correct mode. The braces ({ }) of a nested parameter
expansion cannot be omitted.
Index.sp An index allows extracting part of the parameter value (or some of array values).
Index
[word1]
[word1,word2]
where word1 and word2 are parsed in the same manner as normal tokens except that they are
always delimited by , or ] and can contain whitespace characters.
If there is an index in a parameter expansion, it is interpreted as follows:
1. Words word1 and word2 are subjected to parameter expansion, command substitution, and
arithmetic expansion.
2. If there is no word2 and if word1 expands to one of *, @, and #, then that is the
interpretation of index and the next step is not taken.
3. The results of the previous steps (the expanded word1 and word2) are interpreted and
evaluated as an arithmetic expression in the same manner as in arithmetic expansion.
The resulting integers are the interpretation of index. If the results are not
integers, it is an expansion error. If there is no word2, it is assumed that word2 is
equal to word1.
If parameter is an array variable, the index specifies the part of the array. If parameter
is either the * or @ special parameter, the index specifies the index range of positional
parameters. In other cases, the index specifies the index range of a substring of the
parameter value that is being expanded. In all cases, the specified range of the array
values, positional parameters, or parameter value remains in the results of the expansion
and other values are dropped.
If the interpretation of index is one or two integers, the following rules apply:
• If the interpreted index value is negative, it wraps around. For example, the index
value of -1 corresponds to the last value/character.
• It is not an error when the index value is out of range. Existing values/characters
within the range are just selected.
• If the interpretation of either word1 or word2 is 0, the range is assumed empty and
the expansion results in nothing.
If the interpretation of index is one of *, @, and #, it is treated as follows:
*
If parameter is an array, all values of the array are concatenated into a single
string. If parameter is the * or @ special parameter, all positional parameters are
concatenated into a string. See the description of the * special parameter for how the
values/positional parameters are separated in the result string. In other cases, the
interpretation of index is treated as if the interpretation is the two integers 1 and
-1.
@
The interpretation of index is treated as if the interpretation is the two integers 1
and -1.
#
The interpretation of the #index is special in that it does not simply specify a
range. Instead, the expanded values are substituted with the count.
If parameter is an array, the result of this parameter expansion will be the number of
values in the array being expanded. If parameter is the * or @ special parameter, the
result will be the number of current positional parameters. Otherwise, the result will
be the number of characters in the value that is being expanded.
If a parameter expansion does not contain an index, it is assumed to be [@]. In the
POSIXly-correct mode, index cannot be specified.
Example 1. Expansion of a normal variable
The following commands will print the string ABC:
var='123ABC789'
echo "${var[4,6]}"
Example 2. Expansion of positional parameters
The following commands will print the string 2 3 4:
set 1 2 3 4 5
echo "${*[2,-2]}"
Example 3. Expansion of an array
The following commands will print the string 2 3 4:
array=(1 2 3 4 5)
echo "${array[2,-2]}"
Modifier
You can modify the value to be expanded by using modifiers:
-word
If the parameter name (parameter) is an undefined variable, the parameter
expansion is expanded to word. It is not treated as an error if the unset option
is disabled.
+word
If the parameter name (parameter) is an existing variable, the parameter expansion
is expanded to word. It is not treated as an error if the unset option is
disabled.
=word
If the parameter name (parameter) is an undefined variable, word is assigned to
the variable and the parameter expansion is expanded to word. It is not treated as
an error if the unset option is disabled.
?word
If the parameter name (parameter) is an undefined variable, word is printed as an
error message to the standard error. If word is empty, the default error message
is printed instead.
:-word, :+word, :=word, :?word
These are similar to the four types of modifiers above. The only difference is
that, if parameter exists and has an empty value, it is also treated as an
undefined variable.
#word
The shell performs pattern matching against the value that is being expanded,
using word as a pattern. If word matches the beginning of the value, the matching
part is removed from the value and the other part remains as expansion results.
The shortest matching is used if more than one matching is possible.
##word
This is similar to #word above. The only difference is that the longest matching
is used if more than one matching is possible.
%word
This is similar to #word above. The only difference is that matching is tried at
the end of the value rather than at the beginning: if word matches the end of the
value, the matching part is removed from the value and the other part remains as
expansion results.
%%word
This is similar to %word above. The only difference is that the longest matching
is used if more than one matching is possible.
/word1/word2
The shell performs pattern matching against the value that is being expanded,
using word1 as a pattern. If word1 matches any part of the value, the matching
part is replaced with word2 and the whole value after the replacement remains as
expansion results. If word1 matches more than one part of the value, only the
first part is replaced. The shortest matching is replaced if more than one
matching is possible for the same starting point in the value.
This modifier cannot be used in the POSIXly-correct mode.
/#word1/word2
This is similar to /word1/word2 above. The only difference is that word1 matches
only at the beginning of the value being expanded.
/%word1/word2
This is similar to /word1/word2 above. The only difference is that word1 matches
only at the end of the value being expanded.
//word1/word2
This is similar to /word1/word2 above. The only difference is that all matched
parts are replaced if word1 matches more than one part of the value.
:/word1/word2
This is similar to /word1/word2 above. The only difference is that the value is
replaced only when word1 matches the whole value.
In all types of modifiers above, words are subjected to the four expansions when (and
only when) they are used.
If parameter is an array variable or the @ or * special parameter, modifiers affect
each value of the array or all positional parameters.
Command substitution
Command substitution expands to output of commands specified.
Command substitution
$(commands)
`commands`
When command substitution is evaluated, commands are executed by a subshell with output
pipelined to the shell. When the commands finished, command substitution is substituted
with the output of the commands. Any trailing newline characters in the output are
ignored.
When command substitution of the form $(commands) is parsed, the commands are parsed
carefully so that complex commands such as nested command substitution are parsed
correctly. If commands start with (, you should put a space before commands so that the
whole command substitution is not confused with arithmetic expansion. If the shell is in
the POSIXly-correctly mode, the commands are parsed each time the command substitution is
expanded; otherwise, commands are parsed only when the command substitution is parsed.
If command substitution is of the form `commands`, the commands are not parsed when the
command substitution is parsed. The end of commands is detected by the first backquote
character (`) after the beginning of commands that is not quoted by a backslash.
Backquotes that are part of commands (typically used for nested command substitution) must
be quoted by backslashes. The commands are parsed each time the command substitution is
expanded.
Arithmetic expansion
Arithmetic expansion evaluates an arithmetic expression and expands to the value of the
expression.
Arithmetic expansion
$((expression))
When arithmetic expansion is expanded, the expression is subject to parameter expansion,
command substitution, and (nested) arithmetic expansion. The expression is parsed in
(almost) same manner as an expression of the C programming language.
Yash allows an expression to be either an integer (of the long type in C) or a
floating-point number (of the double type in C). An operation on integers yields an
integer and an operation involving a floating-point number yields a floating-point number.
In the POSIXly-correct mode, you can use integers only.
The following operators are available (in the order of precedence):
1. ( )
2. ++-- (postfix operators)
3. ++--+-~! (prefix operators)
4. */%
5. +- (binary operators)
6. <<>>
7. <<=>>=
8. ==!=
9. &
10. ^
11. |
12. &&
13. ||
14. ? :
15. =*=/=%=+=-=<<=>>=&=^=|=
The ++ and -- operators cannot be used in the POSIXly-correct mode.
An atomic expression can be one of an integer literal, a floating-point number literal,
and a variable. Literals are parsed in the same manner as in C. An octal integer literal
starts with 0, and hexadecimal with 0x. A floating-point number literal may have an
exponent (i.e. 1.23e+6). A variable with a non-numeric value will result in an error.
Brace expansion
Brace expansion expands to several split words with preceding and succeeding portions
duplicated to each split words. Brace expansion is expanded only when the brace-expand
option is enabled.
Comma-separated brace expansion
{word1,word2,...,wordn}
Range brace expansion
{start..end}
{start..end..delta}
Comma-separated brace expansion is expanded to each comma-separated word. For example,
a{1,2,3}b is expanded to the three words a1b, a2b, and a3b.
Range brace expansion is expanded to integers in the range defined by start and end. The
difference between each integer can be defined by delta. If start is larger than end, the
results will be in descending order. When ..delta is omitted, it defaults to 1 or -1. For
example, a{1..3}b is expanded to the three words a1b, a2b, and a3b; and a{1..7..2}b to the
four words a1b, a3b, a5b, and a7b.
Multiple brace expansions can be used in one word. Brace expansions can also be nested.
You can quote braces and/or commas to prevent them from being treated as brace expansion.
Any errors in brace expansion are silently ignored.
Field splitting
In field splitting, words are split at predefined separators.
Field splitting can occur only within parts of words that resulted from parameter
expansion, command substitution, and arithmetic expansion that are not between
double-quotation marks. Expansion results of the @ special parameter are exceptionally
split even between double-quotation marks.
Separators used in field splitting are defined by the value of the IFS variable. If the
variable does not exist, the value is assumed to be the three characters of space, tab,
and newline.
Characters included in the value of the IFS variable are called IFS characters. IFS
characters that are any of space, tab, and newline are called IFS whitespace and other IFS
characters are called IFS non-whitespace.
Field splitting is performed as follows:
1. The shell searches words for split points. A split point is one or more adjacent IFS
characters within the word portions that are subject to field splitting. The following
steps are taken for each split point found.
2. If the split point includes one or more IFS non-whitespaces, any IFS whitespaces in
the split point are ignored and the word is split at each IFS non-whitespace in the
split point.
3. If the split point includes no IFS non-whitespaces, the word is split at the split
point unless it is at the beginning or end of the word.
4. The split points are removed from the results.
Note
Words are not split at all when the value of the IFS variable is empty.
Pathname expansion
Pathname expansion performs pattern matching and expands to pathnames matched by the
pattern.
A word subjected to pathname expansion is treated as a pattern. If one or more pathnames
are found that are matched by the pattern, the pathnames become the results of the
pathname expansion.
Pathname expansion is not performed when the glob option is disabled.
The shell searches readable directories for matching pathnames. Unreadable directories are
silently ignored.
The following options affect the behavior of pathname expansion:
null-glob
This option affects the result of pathname expansion when no matching pathnames are
found. If enabled, the result is no word. If disabled, the result is the original
pattern word.
case-glob
This option specifies case-sensitivity in matching. If enabled, pattern matching is
done case-sensitively.
dot-glob
This option affects matching of filenames that start with a period (.). If disabled, a
period at the beginning of a filename does not match wildcard patterns (? and *) or
bracket expressions. If enabled, there is no such special treatment of periods.
mark-dirs
If enabled, each resulting pathname that is a directory name is suffixed by a slash
(/).
extended-glob
This option enables the extension. (See below)
Any errors in pathname expansion are silently ignored. If the word is an invalid pattern,
it just becomes the result. The results depend on the null-glob option when no matching
pathnames are found.
Pattern matching is done for each filename (or pathname component) of pathnames. The shell
skips matching for literal patterns that contain no wildcards or bracket expressions. As a
result, the patterns /*/foo and /*/fo[o] may yield different expansion results when the
case-glob option is disabled; for example, the pattern /*/fo[o] matches the pathname
/bar/FOO but the pattern /*/foo does not because matching is skipped for foo.
Extension in pathname expansion
The following patterns can be used when the extended-glob option is enabled.
**
The directory is searched recursively and the pattern matches any number of
directory filenames (each separated by a slash). Any directory whose name begins
with a period is excluded from search. For example, the pattern dir/**/file can
match the pathnames dir/file, dir/foo/file, dir/a/b/c/file, etc.
This pattern is not effective when appearing at the end of the whole pattern (i.e.
foo/bar/**).
.**
This pattern is like **, but all directories are searched including ones with a
name starting with a period.
***
This pattern is like **, but if a symbolic link to a directory is found during
recursive search, the directory is searched recursively as well.
.***
This pattern is like ***, but all directories are searched including ones with a
name starting with a period.
PATTERN MATCHING NOTATION
Pattern matching notation is a syntax of patterns that represent particular sets of
strings. When a string is included in the set of strings a pattern represents, the pattern
is said to match the string. Whether a pattern matches a string or not is defined as
follows.
Normal characters
A character that is not quoted or any of special characters defined below is a normal
character, which matches the character itself.
For example, the pattern abc matches the string abc, and not any other strings.
Single-character wildcard
The character ? matches any single character.
For example, the pattern a?c matches any three-character strings that starts with a and
ends with c, such as aac, abc, and a;c.
Multi-character wildcard
The character * matches any strings (of any length, including the empty string).
For example, the pattern a*c matches any string that starts with a and ends with c, such
as ac, abc, and a;xyz;c.
Bracket expression
A pattern that is enclosed by brackets ([ and ]) is a bracket expression. A bracket
expression must have at least one character between the brackets. The characters between
the brackets are interpreted as a bracket expression pattern, which is a below-defined
special notation for bracket expression. A bracket expression pattern represents a set of
characters. The bracket expression matches any one of the characters in the set the
bracket expression pattern represents.
If the opening bracket ([) is followed by an exclamation mark (!), the exclamation is not
treated as part of the bracket expression pattern and the whole bracket expression instead
matches a character that is not included in the set the bracket expression pattern
represents. If the opening bracket is followed by a caret (^), it is treated like an
exclamation mark as above (but shells other than yash may treat the caret differently).
If the opening bracket (or the following exclamation or caret, if any) is followed by a
closing bracket (]), it is treated as part of the bracket expression pattern rather than
the end of the bracket expression. You cannot quote characters in the bracket expression
pattern because quotation is treated before bracket expression.
An opening bracket in a pattern is treated as a normal character if it is not the
beginning of a valid bracket expression.
Normal characters (in bracket expression pattern)
A character that is not any of special characters defined below is a normal character,
which represents the character itself.
For example, the bracket expression pattern abc represents the set of the three characters
a, b, and c. The bracket expression [abc] therefore matches any of the three characters.
Range expressions
A hyphen preceded and followed by a character (or collating symbol) is a range expression,
which represents the set of the two characters and all characters between the two in the
collation order. A collation order is an order of characters that is defined in the locale
data.
If a hyphen is followed by a closing bracket (]), the bracket is treated as the end of the
bracket expression and the hyphen as a normal character.
For example, the range expression 3-5 represents the set of the three characters 3, 4, and
5. The bracket expression [3-5-] therefore matches one of the four characters 3, 4, 5, and
-.
Collating symbols
A collating symbol allows more than one character to be treated as a single character in
matching. A collating symbol is made up of one or more characters enclosed by the special
brackets [. and .].
One or more characters that are treated as a single character in matching are called a
collating element. Precisely, a bracket expression pattern represents a set of collating
elements and a bracket expression matches a collating element rather than a character, but
we do not differentiate them for brevity here.
For example, the character combination “ch” was treated as a single character in the
traditional Spanish language. If this character combination is registered as a collating
element in the locale data, the bracket expression [[.ch.]df] matches one of ch, d, and f.
Equivalence classes
An equivalence class represents a set of characters that are considered equivalent. A
equivalence class is made up of a character (or more precisely, a collating element)
enclosed by the special brackets [= and =].
An equivalence class represents the set of characters that consists of the character
enclosed by the brackets and the characters that are in the same primary equivalence class
as the enclosed character. The shell consults the locale data for the definition of
equivalence classes in the current locale.
For example, if the six characters a, à, á, â, ã, ä are defined to be in the same primary
equivalence class, the bracket expressions [[=a=]], [[=à=]], and [[=á=]] match one of the
six.
Character classes
A character class represents a predefined set of characters. A character class is made up
of a class name enclosed by the special brackets [: and :]. The shell consults the locale
data for which class a character belongs to.
The following character classes can be used in all locales:
[:lower:]
set of lowercase letters
[:upper:]
set of uppercase letters
[:alpha:]
set of letters, including the [:lower:] and [:upper:] classes.
[:digit:]
set of decimal digits
[:xdigit:]
set of hexadecimal digits
[:alnum:]
set of letters and digits, including the [:alpha:] and [:digit:] classes.
[:blank:]
set of blank characters, not including the newline character
[:space:]
set of space characters, including the newline character
[:punct:]
set of punctuations
[:print:]
set of printable characters
[:cntrl:]
set of control characters
For example, the bracket expression [[:lower:][:upper:]] matches a lower or upper case
character. In addition to the classes listed above, other classes may be used depending on
the definition of the current locale.
REDIRECTION
Redirection is a feature you can use to modify file descriptors of commands. By using
redirection, you can execute commands with their standard input/output connected with
files or devices other than the terminal.
You can do redirection by adding redirection operators to a command (simple command or
compound command) In a simple command, redirection operators may appear anywhere in the
command as long as operator tokens are separated from other tokens. In a compound command,
redirection operators must appear at the end of the command.
Redirection operators are processed before the command body is executed. More than one
redirection operator in a command are processed in the order of appearance. Redirection
operators affect only the command in which they appear, except when they appear in an exec
built-in without command operands. That is, file descriptors modified by redirection are
restored after the command has finished.
A redirection operator starts with < or >. Redirection operators starting with < affects
the standard input (file descriptor 0) by default. Redirection operators starting with >
affects the standard output (file descriptor 1) by default. To affect another file
descriptor, you can prefix a redirection operator with a non-negative integer; the
operator will affect the file descriptor specified by the integer. The integer must
immediately precede the < or > without any whitespaces in between. The integer must not be
quoted, either.
Redirection to files
The most common type of redirection is redirection to files.
Redirection of input
< token
Redirection of output
> token
>| token
>> token
Redirection of input and output
<> token
The token is subject to the four expansions. It is also subject to pathname expansion if
the shell is interactive. The expansion result is treated as the pathname of the file to
which redirection is performed. If the pathname expansion does not result in a single
pathname, it is an error.
In redirection of input, the standard input is replaced with a file descriptor which is
open for read-only access to the target file. If the target file cannot be opened for
read-only access, it is an error.
In redirection of output, the standard output is replaced with a file descriptor which is
open for write-only access to the target file. If the target file cannot be opened for
write-only access, it is an error. If the target file does not exist, a new empty file is
created and opened. If the target file already exists, the file is opened as follows:
• For the >| operator, the file is emptied when opened if it is a regular file.
• For the > operator, the behavior is the same as the >| operator if the clobber option
is enabled. If the option is disabled and the file is a regular file, it is treated as
an error.
• For the >> operator, the file is opened for appending; any output to the file
descriptor is appended to the end of the file.
In redirection of input and output, the standard input is replaced with a file descriptor
which is open for read-and-write access to the target file. If the file does not exist, a
new empty file is created and opened.
Socket redirection
If the pathname of the target file is of the form /dev/tcp/host/port or
/dev/udp/host/port and the file cannot be opened in the usual manner, a new socket is
opened for communication with the port of the host. The redirection replaces the
standard input or output with the file descriptor to the socket.
A stream socket is opened for the form /dev/tcp/host/port and a datagram socket for
the form /dev/udp/host/port. The protocol actually used for communication is
determined by the socket library the shell uses. Typically, stream sockets use TCP and
datagram sockets UDP.
In socket redirection, the file descriptor is both readable and writable regardless of
the type of the redirection operator used.
Socket redirection is yash’s extension that is not defined in POSIX. Bash as well has
socket redirection as extension.
Duplication of file descriptors
Redirection allows duplicating or closing existing file descriptors.
Duplication of file descriptor
<& token
>& token
The token is subject to expansion as in redirection to files, but it is treated as a file
descriptor rather than a pathname. Thus the expanded token must be a non-negative integer.
The <& and >& operators duplicate the file descriptor specified by token to the standard
input and output, respectively. (The operators can be prefixed with a non-negative integer
so that the file descriptor is duplicated to a file descriptor other than the standard
input or output.)
If the expanded token is a single hyphen rather than a non-negative integer, the file
descriptor is closed rather than duplicated. By default, the <& and >& operators close the
standard input and output, respectively, but the operators can be prefixed with a
non-negative integer so that another file descriptor is closed.
In the POSIXly-correct mode, a file descriptor must be readable when duplicated by the <&
operator and writable when duplicated by the >& operator.
Here documents and here strings
Here document and here string allow redirection to file descriptors that reads strings
directly specified in shell commands.
Here document
<< token
<<- token
Here string
<<< token
In a here document or here string, the standard input is replaced with a readable file
descriptor. When the command reads from the file descriptor, it will read the contents of
the here document/string, which is defined below.
When a here document operator (<< or <<-) appears in a command, the shell reads the
contents of the here document starting from the next line. The contents of here documents
are not parsed nor executed as commands. The token after the operand specifies a delimiter
that indicates the end of the contents. (The token is not subject to any expansion, but
quotation is processed.) The contents of the here document is terminated just before the
first line containing the token only. When using the <<- operator, all tab characters at
the beginning of each line in the here document contents are removed and the delimiter
token may be preceded by tab characters.
If there are more than one here document operator on one line, the contents of the here
documents are parsed in order: The contents of the first here document starts from the
next line and ends before the first line containing the token that followed the first
operator. Just after that line, the contents of the second here document starts, and so
on.
The contents of here documents are treated literally: whitespaces, tabs, etc. remain as
is. The exception is that, when the token is not quoted at all:
• the contents are subject to parameter expansion, command substitution, arithmetic
expansion.
• a backslash in the contents is treated as quotation if and only if it precedes $, `,
", or another backslash.
• a backslash followed by a newline is treated as line continuation.
In here string, the token after the operator is subject to expansion as in redirection to
files. The expansion result becomes the contents of the here string. A newline character
is automatically appended to the end of here string contents.
Here string is yash’s extension that is not defined in POSIX. Other shells like bash, ksh,
and zsh have the same feature.
Pipeline redirection
Pipeline redirection allows opening pipelines that can be used for arbitrary purposes.
Pipeline redirection
>>| token
The token is subject to expansion as in redirection to files, but it is treated as a file
descriptor rather than a pathname. Thus the expanded token must be a non-negative integer.
Pipeline redirection opens a new pipeline. The standard output (or the file descriptor
specified before the operator, if any) is replaced with the file descriptor open for
writing to the pipeline. The file descriptor specified by token is replaced with the file
descriptor open for reading from the pipeline.
Pipeline redirection is yash’s extension that is not defined in POSIX.
Process redirection
Process redirection creates a pipeline connected to another command.
Process redirection
<(command...)
>(command...)
In process redirection, the command specified is executed in a subshell. If the process
redirection is of the form <(command...), the standard output of command is connected with
a pipeline to the standard input of the command the redirection is associated with. If the
process redirection is of the form >(command...), the standard input of command is
connected with a pipeline to the standard output of the command the redirection is
associated with.
Process redirection is yash’s extension that is not defined in POSIX. Bash and zsh have a
feature called process substitution, which uses the same syntax as yash’s process
redirection, but incompatibly differs in behavior.
COMMAND EXECUTION
This section describes how commands are executed.
Execution of simple commands
A simple command is executed as follows:
1. All tokens in the simple command are expanded except for assignment and redirection
tokens. If an error occurs during expansion, the execution of the simple command is
aborted with a non-zero exit status.
In the following steps, the first word of the expansion results is referred to as
command name, and the other words as command arguments. If there is only one word of
the expansion results, there are no command argument words. If there are none of the
expansion results, there is no command name either.
2. Redirection specified in the command, if any, is processed. The word token after each
redirection operator is expanded. If an error occurs during processing redirection
(including when expanding the word token), the execution of this simple command is
aborted with a non-zero exit status.
3. Assignments specified in the command, if any, are processed. For each assignment
token, the value is expanded and assigned to the specified variable. If an error
occurs during assignments (including when expanding the values to be assigned), the
execution of this simple command is aborted with a non-zero exit status.
• If there is no command name or the name denotes a special built-in or function,
the assignments are permanent: the assigned values remain after the command has
finished (until the variable is reassigned).
• Otherwise, the assignments are temporary: the assigned values only last during the
execution of this simple command.
The assigned variables are automatically exported when the command name is specified
or the all-export option is enabled.
4. If there is no command name, the command execution ends with the exit status of zero
(unless there are any command substitutions in the command, in which case the exit
status of the simple command is that of the last executed command substitution).
5. A command to be executed is determined using the command search algorithm and the
command is executed.
• If the command is an external command, the command is executed by creating a new
subshell and calling the “exec” system call in the subshell. The command name and
arguments are passed to the executed command. Exported variables are passed to the
executed command as environment variables.
• If the command is a built-in, the built-in is executed with the command arguments
passed to the built-in.
• If the command is a function, the contents of the function are executed with the
command arguments as function arguments.
If the command was executed, the exit status of this simple command is that of the
executed command. If the algorithm failed to determine a command, no command is
executed and the exit status is 127. If the shell failed to execute the determined
command, the exit status is 126. If the executed command was killed by a signal, the
exit status is the signal number plus 384.
Note
In shells other than yash, the exit status may be different when the command was
killed by a signal, because the POSIX standard only requires that the exit status
be "greater than 128."
If the shell is not in the POSIXly-correct mode and the algorithm failed to determine
a command, the command eval -i -- "${COMMAND_NOT_FOUND_HANDLER-}" is evaluated. During
the command execution, positional parameters are temporarily set to the command name
and arguments that resulted in the first step. Any local variables defined during the
execution are removed when the execution is finished. The HANDLED local variable is
automatically defined with the initial value being the empty string. If the HANDLED
variable has a non-empty value when the execution of the command string is finished,
the shell pretends that the command was successfully determined and executed. The exit
status of the simple command is that of the command string in this case.
Command search
A command that is executed in a simple command is determined by the command name using
the following algorithm:
1. If the command name contains a slash (/), the whole name is treated as the
pathname of an external command. The external command is determined as the
executed command.
2. If the command name is a special built-in, the built-in is determined as the
executed command.
3. If the command name is the name of an existing function, the function is
determined as the executed command.
4. If the command name is a semi-special built-in, the built-in is determined as the
executed command.
5. If the command name is a regular built-in, the built-in is determined as the
executed command unless the shell is in the POSIXly-correct mode.
6. The shell searches the PATH for a executed command:
The value of the PATH variable is separated by colons. Each separated part is
considered as a directory pathname (an empty pathname denotes the current working
directory). The shell searches the directories (in the order of appearance) and
checks if any directory directly contains an executable regular file whose name is
equal to the command name. If such a file is found:
• If the command name is the name of a built-in, the built-in is determined as
the executed command.
• Otherwise, the file is determined as the executed command. (The file will be
executed as an external command.)
If no such file is found, no command is determined as the executed command.
When the shell finds a file that matches the command name during the search above, the
shell remembers the pathname of the file if it is an absolute path. When the algorithm
above is used for the same command name again, the shell skips searching and directly
determines the command to be executed. If an executable regular file no longer exists
at the remembered pathname, however, the shell searches again to update the remembered
pathname. You can manage remembered pathnames using the hash built-in.
Termination of the shell
The shell exits when it reached the end of input and has parsed and executed all input
commands or when the exit built-in is executed. The exit status of the shell is that of
the last command the shell executed (or zero if no commands were executed). The exit
status of the shell is always between 0 and 255 (inclusive). If the exit status of the
last command is 256 or larger, the exit status of the shell will be the remainder of the
exit status divided by 256.
If an exit handler has been registered by the trap built-in, the handler is executed just
before the shell exits. The exit status of the commands executed in the handler does not
affect the exit status of the shell.
If a non-interactive shell encountered one of the following errors, the shell immediately
exits with a non-zero exit status:
• A command cannot be parsed due to an syntax error (except during shell
initialization).
• A special built-in is executed in the POSIXly-correct mode and the command arguments
do not meet the syntax of the built-in’s arguments.
• An error occurs during redirection or assignment in a simple command whose command
name is a special built-in and the shell is in the POSIXly-correct mode.
• An error occurs during expansion (except during shell initialization).
Note
Some shells other than yash exit when they fail to find a command to execute in
command search.
Functions
Functions allow executing a compound command as a simple command. A function can be
defined by the function definition command and executed by a simple command. You can use
the unset built-in to remove function definitions.
There are no functions predefined when yash is started.
A function is executed by executing its body, which is a compound command. While the
function is being executed, positional parameters are set to the arguments given to the
function. The old positional parameters are restored when the function execution finishes.
Local variables
Local variables are temporary variables that are defined in a function and exist
during the function execution only. They can be defined by the typeset built-in. They
are removed when the function execution finishes.
Local variables may hide variables that have already been defined before the function
execution had started. An existing variable becomes inaccessible if a local variable
of the same name is defined in a function. The old variable becomes accessible again
when the function execution finishes.
You cannot create a local variable when not executing a function. A normal variable is
created if you try to do so.
Command execution environment
The shell holds following properties during execution.
• The working directory
• Open file descriptors
• The file creation mask (umask)
• The set of signals whose handler is set to “ignore” (trap)
• Environment variables
• Resource limits (ulimit)
Those properties are inherited from the invoker of the shell to the shell, and from the
shell to each external command executed by the shell.
The properties can be changed during the execution of the shell by built-in commands,
variable assignments, etc.
Subshells
A subshell is a copy of the shell process. Subshells are used in execution of
groupings, pipelines, etc.
Subshells inherit functions, aliases, etc. defined in the shell as well as the
properties above since subshells are copies of the shell process. Notable exceptions
are:
• Signal handlers registered by the trap built-in are all reset in subshells except
for ones whose action is set to “ignore”.
• The interactive mode and job control are disabled in subshells. Jobs are not
inherited by subshells.
Subshells are executed independently of the original shell, so changes of any
properties above do not affect those of the original shell.
INTERACTIVE MODE
The interactive mode is a mode of the shell intended for direct interaction with a user.
If yash is in the interactive mode, it is called an interactive shell.
Whether a shell runs in the interactive mode or not is determined in the invocation of the
shell. After the shell has started up, the interactive mode cannot be switched on or off.
When the shell is interactive:
• Initialization scripts are executed during invocation.
• The shell checks for mail and prints a command prompt when it reads a command. Job
status changes are also reported if job control is active. Line-editing may be used
depending on the capability of the terminal.
• Commands executed are automatically registered in command history.
• If a command executed by the shell is killed by a signal other than SIGINT and
SIGPIPE, the shell reports the fact to the standard error.
• The filename token is subject to pathname expansion in file redirection.
• The standard input of an asynchronous command is not automatically redirected to
/dev/null (in the POSIXly-correct mode only).
• The shell does not exit when it encounters a syntax or expansion error during command
execution. (cf. Termination of the shell)
• The shell does not exit when it receives the SIGINT, SIGTERM, or SIGQUIT signal.
• A signal handler can be changed by the trap built-in even if the handler had been set
to “ignore” when the shell was invoked.
• The value of the - special parameter contains i.
• The shell’s locale reflects the value of the LC_CTYPE variable whenever the value is
changed (if the shell is not in the POSIXly-correct mode).
• Commands are executed even when the exec option is off.
• The ignore-eof option takes effect when enabled.
• When the shell reaches the end of input or the exit built-in is executed, the shell
checks if there is any stopped job. If so, the shell prints a warning and does not
actually exit.
• The suspend built-in by default cannot stop the shell if it is a session leader.
• The shell does not exit when the dot built-in fails to find a script file to read.
• The shell does not exit when the exec built-in fails to execute a command (if not in
the POSIXly-correct mode).
• When a job finished for which the wait built-in has been waiting, the fact is reported
(only if job control is active and not in the POSIXly-correct mode).
• A prompt is printed when the read built-in reads a second or following line.
Prompts
The interactive shell prints a prompt just before it reads a command. The contents of the
prompt is specified by the value of the PS1 and PS2 variables. The former is used for
reading the first line of the command and the latter for other lines.
When the prompt is printed, the variable value is subjected to parameter expansion,
command substitution, and arithmetic expansion (but note that the POSIX standard requires
parameter expansion only). The result of the expansion is parsed by the rules below to
make the actual prompt string, which is printed to the standard error.
In the POSIXly-correct mode, each exclamation mark (!) in the string is substituted with
the command history number of the command that is being input. Two adjacent exclamation
marks (!!) are printed as a single exclamation. Other characters are printed intact.
If the shell is not in the POSIXly-command mode, the following notations can be used to
format the prompt string. Notations are replaced with the strings designated in the list
below. Characters that are not interpreted as notations are printed intact.
\a
Bell character (ASCII code: 7)
\e
Escape character (ASCII code: 27)
\j
The number of jobs in the shell.
\n
Newline character (ASCII code: 10)
\r
Carriage return character (ASCII code: 13)
\!
The command history number of the command that is being input
\$
# if the shell’s effective user ID is 0; $ otherwise.
\\
Backslash
\[, \]
These two notations can surround part of the prompt string that is not visible on the
terminal. The surrounded part is ignored when the shell counts the number of
characters that is displayed on the terminal, thus making characters correctly aligned
on the terminal when the prompt string contains special invisible characters.
\ffontspecs.
When line-editing is active, this notation is replaced with special characters to
change font styles on the terminal if the terminal is capable of it. If line-editing
is inactive or the terminal is incapable of changing font styles, this notation is
silently ignored. One or more of the following can be used for fontspecs:
k
Change font color to black
r
Change font color to red
g
Change font color to green
y
Change font color to yellow
b
Change font color to blue
m
Change font color to magenta
c
Change font color to cyan
w
Change font color to white
K
Change background color to black
R
Change background color to red
G
Change background color to green
Y
Change background color to yellow
B
Change background color to blue
M
Change background color to magenta
C
Change background color to cyan
W
Change background color to white
t
Make font color or background brighter (can only be used just after one of the
characters above)
d
Change font and background colors to normal
s
Make font standout
u
Make font underlined
v
Make font and background colors reversed
b
Make font blink
i
Make font dim
o
Make font bold
x
Make font invisible
D
Make color and style normal
The actual colors of font and background are defined by the terminal. Different
terminals may use different colors.
In addition to the normal prompt, a prompt string can be displayed to the right of the
cursor if line-editing is active. Those prompts are called right prompts. The contents of
right prompts are defined by the value of the PS1R and PS2R variables, each corresponding
to the PS1 and PS2 variables.
Using the above-said notations, the font style of command strings the user inputs can be
changed as well as that of prompts. The font style of command strings is defined by the
value of the PS1S and PS2S variables, each corresponding to the PS1 and PS2 variables. The
value can contain the \ffontspecs. notation only.
When the shell is not in the POSIXly-correct mode, the value of the PROMPT_COMMAND
variable is executed before each prompt.
Command history
Command history is a feature of the shell that remembers executed commands to allow
re-executing them later. Commands executed in the interactive mode are automatically saved
in the command history. Saved commands can be edited and re-executed using line-editing
and the fc and history built-ins.
Commands are saved line by line. Lines that do not contain any non-whitespace characters
are not saved in the history. Lines that start with whitespaces are not saved when the
hist-space option is on.
Command history is saved in a file. When history is first used after an interactive shell
was started, the shell opens a file to save history in. The filename is specified by the
value of the HISTFILE variable. If the file contains history data when opened, the data is
restored to the shell’s history. The file contents are updated in real time as the user
inputs commands into the shell. If the HISTFILE variable is not set or the file cannot be
opened successfully, history is not saved in the file, but the history feature will be
functional in all other respects.
The number of commands saved in history is specified by the value of the HISTSIZE
variable. The shell automatically removes old history data so that the number of saved
commands does not exceed the value. If the HISTSIZE variable is not set or its value is
not a natural number, 500 items will be saved in history.
The shell looks at the value of the HISTFILE and HISTSIZE variables only when the history
feature is first used after the shell was started. “The history feature is used” when:
• the fc or history built-in is executed,
• line-editing is used (regardless of whether or not history data is recalled in
line-editing), or
• a command is input to the shell
Therefore, the variables should be set in initialization scripts.
When more than one instance of yash shares a single history file, all the shells use the
same history data. As a result, commands that have been executed by a shell instance can
be recalled on another shell instance. Shells sharing the same history should have the
same HISTSIZE value so that they manipulate history data properly.
Yash’s history data file has its own format that is incompatible with other kinds of
shells.
The HISTRMDUP variable can be set to remove duplicate history items.
Mail checking
An interactive shell can notify receipt of email. The shell periodically checks the
modification date/time of a file specified by the user. If the file has been modified
since the previous check, the shell prints a notification message (except when the shell
is not in the POSIXly-correct mode and the file is empty). By specifying a mailbox file to
be checked, the shell will print a message when the file has been modified, that is, some
mail has been received.
Check is done just before the shell prints a command line prompt. The interval of checks
can be specified by the MAILCHECK variable in seconds. If the variable value is 0, check
is done before every prompt. If the variable value is not a non-negative integer, no
checks are done.
The file whose modification time is checked is specified by the MAIL variable. The
variable value should be set to the pathname of the file.
If you want to check more than one file or customize the notification message, you can set
the MAILPATH variable instead of the MAIL variable. When the MAILPATH variable is set, the
MAIL variable is ignored. The value of the MAILPATH variable should be set to one or more
colon-separated pathnames of files to be checked. Each pathname can be followed by a
percent sign (%) and a custom notification message, which is printed when the
corresponding file has been modified. If the pathname contains a percent sign, it should
be quoted by a backslash. The specified message is subject to parameter expansion. For
example, if the value of the MAILPATH variable is /foo/mail%New mail!:/bar/mailbox%You've
got mail:/baz/mail\%data, the shell will print
• New mail! when the file /foo/mail has been modified
• You've got mail when the file /bar/mailbox has been modified
• the default message when the file /baz/mail%data has been modified.
JOB CONTROL
Job control is a function of the shell that executes multiple commands simultaneously and
suspends/resumes the commands.
When control is active:
• Every pipeline executed by the shell becomes a job. A job has its unique process group
ID that is shared among all processes in the job.
• If the processes of a job are suspended while the shell is waiting for the processes
to finish, the shell continues to the next command as if the process have finished.
The shell remembers the job as suspended so that it can be resumed later.
• If a job is executed synchronously, the shell sets the foreground process group of the
terminal to the process group of the job. When the job is finished (or suspended), the
shell gets back to the foreground.
• The subshell executing a command substitution has its own unique process group ID like
a job. However, the shell does not remember the subshell as a job, so it cannot be
suspended or resumed.
• If the shell is interactive, job status is reported before every command line prompt
as if the command jobs -n is executed.
• The standard input of an asynchronous command is not automatically redirected to
/dev/null (unless in the POSIXly-correct mode).
• The shell does not exit when it receives the SIGTSTP signal.
• The value of the - special parameter contains m.
• When a job finished for which the wait built-in has been waiting, the fact is reported
(only if the shell is interactive and not in the POSIXly-correct mode).
When job control is inactive, processes executed by the shell have the same process group
ID as the shell. The shell treats asynchronous commands as an uncontrolled job.
You can use the following built-ins to manipulate jobs:
jobs
prints existing jobs
fg and bg
run jobs in the foreground or background
wait
waits for jobs to be finished (or suspended)
disown
forgets jobs
kill
sends a signal to jobs
An interactive job-controlling shell reports jobs status before every prompt by default.
You can set the following options to make the shell report status at other timings:
notify
the shell reports immediately whenever job status changes.
notify-le
the shell reports immediately when job status changes while line-editing.
A job is removed from the shell’s job list when:
• it has finished and the “finished” status is reported,
• the wait built-in successfully waited for the job to finish, or
• the disown built-in removed the job.
Note
The word “stop” is synonymous to “suspend” in the context of job control.
Job ID
Some built-ins use the following notation, which is called job ID, to specify a job to
operate on:
%, %%, %+
the current job
%-
the previous job
%n
the job that has job number n, where n is a positive integer
%string
the job whose name begins with string
%?string
the job whose name contains string
The current job and previous job are jobs selected by the shell according to the following
rules:
• When there is one or more suspended jobs, the current job is selected from them.
• When there is one or more suspended jobs other than the current job, the previous job
is selected from them.
• The current and previous jobs are always different. When the shell has only one job,
it is the current job and there is no previous job.
• When the current job finished, the previous job becomes the current job.
• When the current job is changed, the old current job becomes the previous job except
when the old job finished.
• When the foreground job is suspended, the job becomes the current job.
Yash has some options to modify the rules of the current/previous job selection. (The
rules above have priority over the options below.)
cur-async
When a new asynchronous command is started, it becomes the current job.
cur-bg
When a job is resumed by the bg built-in, the job becomes the current job.
cur-stop
When a job is suspended, it becomes the current job.
The current and previous jobs are not changed as long as the rules above are met.
The rules of the current/previous job selection defined in the POSIX standard are looser
than yash’s rules above. Other POSIX-compliant shells may select the current and previous
jobs differently.
BUILT-IN COMMANDS
Built-in commands are commands that are implemented in the shell and are executed by the
shell without external programs.
Types of built-in commands
There are three types of built-in commands in yash: special built-in commands,
semi-special built-in commands and regular built-in commands.
Special built-in commands are much more important commands than others. They are executed
regardless of whether the corresponding external commands exist or not. Results of
variable assignments that occur in a simple command that invokes a special built-in last
after the command has finished. Moreover, in the POSIXly-correct mode, a non-interactive
shell immediately exits with a non-zero exit status when a redirect error, assignment
error, or misuse of option or operand occurs in a special built-in command.
Semi special built-in commands are the second important built-in commands. They are
executed regardless of whether the corresponding external commands exist or not. In other
parts they are the same as regular built-in commands.
Regular built-in commands are less important built-in commands including commands that can
be implemented as external commands or are not listed in POSIX. In the POSIXly-correct
mode, a regular built-in is executed only when a corresponding external command is found
in PATH.
Syntax of command arguments
In this section we explain common rules about command arguments. The built-in commands of
yash follow the rules unless otherwise stated.
There are two types of command arguments. One is options and the other is operands. An
option is an argument that starts with a hyphen (-) and changes the way the command
behaves. Some options take arguments. An operand is an argument that is not an option and
specifies objects the command operates on.
If you specify more than one option to a command, the order of the options are normally
not significant. The order of operands, however, affects the command behavior.
An option is either a single-character option or a long option. A single-character option
is identified by one alphabetic character. A long option is identified by multiple
alphabetic characters. The POSIX standard only prescribes single-character options, so in
the POSIXly-correct mode you cannot use long options.
A single-character option is composed of a hyphen followed by a letter. For example, -a is
a single-character option. A single-character option that takes an argument requires the
argument to be just after the option name.
Example 4. The set built-in and single-character options
For the set built-in, -m is a single-character option that does not take an argument and
-o is one that takes an argument.
• set -o errexit -m
• set -oerrexit -m
In these two command lines, errexit is the argument to the -o option.
In the second example above, the -o option and its argument are combined into a single
command line argument. The POSIX standard deprecates that style and any POSIX-conforming
applications must specify options and their arguments as separate command line arguments,
although yash accepts both styles.
You can combine single-character options that do not take arguments into a single command
line argument. For example, the three options -a, -b and -c can be combined into -abc.
A long option is composed of two hyphens followed by an option name. For example,
--long-option is a long option. You can omit some last characters of a long option name as
long as it is not ambiguous. For example, you can use --long instead of --long-option if
there is no other options beginning with --long. Like a single-character option, a long
option that takes an argument requires the argument to be a command line argument just
after the option name or to be specified in the same command line argument as the option
name, separated by an equal sign (=).
Example 5. The fc built-in and long options
For the fc built-in, --quiet is a long option that does not take an argument and --editor
is one that takes an argument.
• fc --editor vi --quiet
• fc --editor=vi --quiet
In these command lines, vi is the argument to the --editor option.
Arguments that are not options (nor arguments to them) are interpreted as operands. The
POSIX standard requires all options should be specified before any operands. Therefore, in
the POSIXly-correct mode, any arguments that come after the first operand are interpreted
as operands (even if they look like options). If not in the POSIXly-correct mode, you can
specify options after operand.
Regardless of whether the shell is in the POSIXly-correct mode or not, an argument that is
just composed of two hyphens (--) can be used as a separator between options and operands.
All command line arguments after the -- separator are interpreted as operands, so you can
specify operands that start with a hyphen correctly using the separator.
Example 6. Options and operands to the set built-in
• set -a -b -- -c -d
In this example, -a and -b are options and -c and -d are operands. The -- separator itself
is neither an option nor an operand.
Regardless of whether the shell is in the POSIXly-correct mode or not, an argument that is
just composed of a single hyphen (-) is interpreted as an operand.
LINE-EDITING
With the line-editing feature, you can edit the command text when you input a command to
an interactive shell. It not only works as a simple visual-interface editor, but also is
integrated with the command history. You can recall, edit, and execute commands in the
history with line-editing instead of using the fc built-in.
Line-editing has two editing modes, the vi and emacs modes, which each have their own key
binding settings. By switching editing modes, you can change key bindings used in
line-editing. Each mode has a corresponding shell option, which determines whether the
mode is currently active or not. No more than one mode can be active at a time, so the
options for the other modes are automatically turned off when you turn on the option for
one mode. The whole line-editing feature is deactivated when those options are off.
When an interactive shell is started, the vi mode is automatically activated if the
standard input and error are both connected to a terminal.
Line-editing can be used only when the standard input and error are both connected to a
terminal. If not, the shell silently falls back to the normal input mechanism. While
line-editing is being used, the shell uses the termios interface to change I/O settings of
the terminal and the terminfo interface to parse input key sequences.
Shell options on line-editing
The following options can be set by the set built-in to enable line-editing and choose an
editing mode to activate:
vi
activates the vi mode.
emacs
activates the emacs mode.
The other line-editing-related options are:
le-always-rp
When this options is enabled, the right prompt is always visible: when the cursor
reaches the right prompt, it moves to the next line from the original position, which
would otherwise be overwritten by input text.
le-comp-debug
When enabled, internal information is printed during completion, which will help
debugging completion scripts.
le-conv-meta
When enabled, the 8th bit of each input byte is always treated as a meta-key flag,
regardless of terminfo data.
le-no-conv-meta
When enabled, the 8th bit of each input byte is never treated as a meta-key flag,
regardless of terminfo data.
The le-conv-meta and le-no-conv-meta options cannot be both enabled at a time. When
either is enabled, the other is automatically disabled. When neither is enabled, the
8th bit may be treated as a meta-key flag depending on terminfo data.
le-prompt-sp
When enabled, the shell prints a special character sequence before printing each
prompt so that every prompt is printed at the beginning of a line.
This option is enabled by default.
le-visible-bell
When enabled, the shell flashes the terminal instead of sounding an alarm when an
alert is required.
Editing modes
The vi mode is an editing mode that offers key bindings similar to that of the vi editor.
The vi mode has two sub-modes that are switched during editing: the insert and command
modes. The sub-mode is always reset to the insert mode when line-editing is started for a
new command line. In the insert mode, most characters are inserted to the buffer as typed.
In the command mode, input characters are treated as commands that move the cursor,
insert/delete text, etc.
The emacs mode offers key bindings similar to the emacs editor. Most characters are
inserted to the buffer as typed, but more characters are treated as commands than the vi
insert mode.
Another sub-mode is used while you enter search keywords. The sub-mode is called the
search mode, which offers slightly different key bindings depending on the active editing
mode.
Line-editing commands
All characters the user enters while line-editing is active are treated as line-editing
commands listed below. The bindkey built-in allows customizing the key bindings of each
mode (except for the search mode).
The list below shows not only the functions of commands but also the default key bindings.
The keywords “vi-insert”, “vi-command”, “vi-search”, “emacs”, “emacs-search” means the vi
insert mode, the vi command mode, the search mode for the vi mode (the vi search mode),
the emacs mode, and the search mode for the emacs mode (the emacs search mode),
respectively.
Some commands take an argument that affects the function of the commands. For example, the
forward-char command moves the cursor by as many characters as specified by the argument.
To specify an argument, use the digit-argument command just before another command that
takes an argument.
Basic editing commands
noop
Do nothing.
vi-command
\^[
alert
Alert.
self-insert
Insert the input character at the current cursor position. Characters escaped by
escape sequences cannot be inserted.
vi-insert, emacs
\\
insert-tab
Insert a tab character at the current cursor position.
emacs
\^[\^I
expect-verbatim
Insert a character that is entered just after this command at the current cursor
position. This command can input a character that cannot be input by the
self-insert command, except a null character ('\0').
vi-insert, vi-search, emacs-search
\^V
emacs
\^Q, \^V
digit-argument
Pass the input digit to the next command as an argument.
This command can be bound to a digit or hyphen. To pass “12” as an argument to the
forward-char command in the vi mode, for example, enter 12l.
vi-command
1, 2, 3, 4, 5, 6, 7, 8, 9
emacs
\^[0, \^[1, \^[2, \^[3, \^[4, \^[5, \^[6, \^[7, \^[8, \^[9, \^[-,
bol-or-digit
Like the beginning-of-line command if there is no argument; like the
digit-argument command otherwise.
vi-command
0
accept-line
Finish editing the current line. A newline is automatically appended to the line.
The line will be executed by the shell.
vi-insert, vi-command, emacs, emacs-search
\^J, \^M
abort-line
Abandon the current buffer and finish editing as if an empty line was input.
vi-insert, vi-command, vi-search, emacs, emacs-search
\!, \^C
eof
Abandon the current buffer and finish editing as if the shell reached the end of
input. This normally makes the shell exit.
eof-if-empty
Like the eof command if the buffer is empty; like the alert command otherwise.
vi-insert, vi-command
\#, \^D
eof-or-delete
Like the eof command if the buffer is empty; like the delete-char command
otherwise.
emacs
\#, \^D
accept-with-hash
Like the accept-line command, but:
• A hash sign (#) is inserted at the beginning of the line if there is none.
• Otherwise, the hash sign is removed from the beginning of the line.
vi-command
#
emacs
\^[#
setmode-viinsert
Switch to the vi insert mode.
vi-command
i, \I
setmode-vicommand
Switch to the vi command mode.
vi-insert
\^[
setmode-emacs
Switch to the emacs mode.
expect-char, abort-expect-char
These commands are not meant for use by the user. They are used by the shell to
implement some other commands.
redraw-all
Reprint the prompt and the current line to the terminal.
vi-insert, vi-command, vi-search, emacs, emacs-search
\^L
clear-and-redraw-all
Clear the terminal and reprint the prompt and the current line.
Motion commands
Motion commands move the cursor on the line. Most motion commands accept an argument.
When passed an argument, they repeat the cursor motion as many times as specified by
the argument. Passing “4” as an argument to the forward-char command, for example,
advances the cursor by four characters.
The shell has several definitions of words as units of distance: A bigword is one or
more adjacent non-whitespace characters. A semiword is one or more adjacent characters
that contain no whitespaces or punctuations. An emacsword is one or more adjacent
alphanumeric characters. A viword is either:
• one or more adjacent alphanumeric characters and/or underscores (_), or
• one or more adjacent characters that contain none of alphanumeric characters,
underscores, and whitespaces.
forward-char
Move the cursor to the next character.
vi-insert
\R
vi-command
l, (space), \R
emacs
\R, \^F
backward-char
Move the cursor to the previous character.
vi-insert
\L
vi-command
h, \B, \L, \?, \^H
emacs
\L, \^B
forward-bigword
Move the cursor to the next bigword.
vi-command
W
end-of-bigword
Move the cursor to the next end of a bigword.
vi-command
E
backward-bigword
Move the cursor to the previous bigword.
vi-command
B
forward-semiword
Move the cursor to the next semiword.
end-of-semiword
Move the cursor to the next end of a semiword.
backward-semiword
Move the cursor to the previous semiword.
forward-viword
Move the cursor to the next viword.
vi-command
w
end-of-viword
Move the cursor to the next end of a viword.
vi-command
e
backward-viword
Move the cursor to the previous viword.
vi-command
b
forward-emacsword
Move the cursor to the next emacsword.
emacs
\^[f, \^[F
backward-emacsword
Move the cursor to the previous emacsword.
emacs
\^[b, \^[B
beginning-of-line
Move the cursor to the beginning of the line.
vi-insert, vi-command
\H
emacs
\H, \^A
end-of-line
Move the cursor to the end of the line.
vi-insert
\E
vi-command
$, \E
emacs
\E, \^E
go-to-column
Move the cursor to the nth character on the line, where n is the argument. Assume
n = 1 when no argument.
vi-command
|
first-nonblank
Move the cursor to the first non-blank character on the line.
vi-command
^
find-char
Move the cursor to the first position where a character that is entered just after
this command appears after the current cursor position.
vi-command
f
emacs
\^]
find-char-rev
Move the cursor to the last position where a character that is entered just after
this command appears before the current cursor position.
vi-command
F
emacs
\^[\^]
till-char
Move the cursor to the first position just before a character that is entered just
after this command appears after the current cursor position.
vi-command
t
till-char-rev
Move the cursor to the last position just after a character that is entered just
after this command appears before the current cursor position.
vi-command
T
refind-char
Redo the last find-char, find-char-rev, till-char, till-char-rev command.
vi-command
;
refind-char-rev
Redo the last find-char, find-char-rev, till-char, till-char-rev command in the
reverse direction.
vi-command
,
Editing commands
Editing commands modify contents of the buffer. Most editing commands accept an
argument. When passed an argument, they repeat the modification as many times as
specified by the argument.
Texts deleted by commands whose name starts with “kill” are saved in kill ring, from
which deleted contents can be restored to the buffer. The most recent 32 texts are
kept in the kill ring.
delete-char
Delete a character at the current cursor position if no argument is passed; like
the kill-char command otherwise.
vi-insert, emacs
\X
delete-bigword
Delete a bigword at the current cursor position if no argument is passed; like the
kill-bigword command otherwise.
delete-semiword
Delete a semiword at the current cursor position if no argument is passed; like
the kill-semiword command otherwise.
delete-viword
Delete a viword at the current cursor position if no argument is passed; like the
kill-viword command otherwise.
delete-emacsword
Delete a emacsword at the current cursor position if no argument is passed; like
the kill-emacsword command otherwise.
backward-delete-char
Delete a character just before the current cursor position if no argument is
passed; like the backward-kill-char command otherwise.
vi-insert, emacs
\B, \?, \^H
backward-delete-bigword
Delete a bigword just before the current cursor position if no argument is passed;
like the backward-kill-bigword command otherwise.
backward-delete-semiword
Delete a semiword just before the current cursor position if no argument is
passed; like the backward-kill-semiword command otherwise.
vi-insert
\^W
backward-delete-viword
Delete a viword just before the current cursor position if no argument is passed;
like the backward-kill-viword command otherwise.
backward-delete-emacsword
Delete a emacsword just before the current cursor position if no argument is
passed; like the backward-kill-emacsword command otherwise.
delete-line
Delete the whole buffer contents.
forward-delete-line
Delete all characters from the current cursor position to the end of the buffer.
backward-delete-line
Delete all characters before the current cursor position.
vi-insert
\$, \^U
kill-char
Delete a character at the current cursor position and add it to the kill ring.
vi-command
x, \X
kill-bigword
Delete a bigword at the current cursor position and add it to the kill ring.
kill-semiword
Delete a semiword at the current cursor position and add it to the kill ring.
kill-viword
Delete a viword at the current cursor position and add it to the kill ring.
kill-emacsword
Delete a emacsword at the current cursor position and add it to the kill ring.
emacs
\^[d, \^[D
backward-kill-char
Delete a character just before the current cursor position and add it to the kill
ring.
vi-command
X
backward-kill-bigword
Delete a bigword just before the current cursor position and add it to the kill
ring.
emacs
\^W
backward-kill-semiword
Delete a semiword just before the current cursor position and add it to the kill
ring.
backward-kill-viword
Delete a viword just before the current cursor position and add it to the kill
ring.
backward-kill-emacsword
Delete a emacsword just before the current cursor position and add it to the kill
ring.
emacs
\^[\B, \^[\?, \^[\^H
kill-line
Delete the whole buffer contents and add it to the kill ring.
forward-kill-line
Delete all characters from the current cursor position to the end of the buffer
and add it to the kill ring.
emacs
\^K
backward-kill-line
Delete all characters before the current cursor position and add it to the kill
ring.
emacs
\$, \^U, \^X\B, \^X\?
put-before
Insert the last-killed text before the current cursor position and move the cursor
to the last character that was inserted.
vi-command
P
put
Insert the last-killed text after the current cursor position and move the cursor
to the last character that was inserted.
vi-command
p
put-left
Insert the last-killed text before the current cursor position and move the cursor
to the last character that was inserted.
emacs
\^Y
put-pop
Replace the just put text with the next older killed text.
This command can be used only just after the put-before, put, put-left, or put-pop
command.
emacs
\^[y, \^[Y
undo
Cancel modification by the last editing command.
vi
u
emacs
\^_, \^X\$, \^X\^U
undo-all
Cancel all modification in the current buffer, restoring the initial contents.
vi
U
emacs
\^[\^R, \^[r, \^[R
cancel-undo
Cancel cancellation by the last undo or undo-all command.
vi
\^R
cancel-undo-all
Cancel all cancellation by all most recent undo and undo-all commands.
redo
Repeat modification by the last editing command.
vi-command
.
Completion commands
complete
Complete a word just before the cursor position and, if there is more than one
candidate, show a list of the candidates.
complete-next-candidate
Like the complete command when candidates are not being listed; otherwise, select
the next candidate in the list.
vi-insert, emacs
\^I
complete-prev-candidate
Like the complete command when candidates are not being listed; otherwise, select
the previous candidate in the list.
vi-insert, emacs
\bt
complete-next-column
Like the complete command when candidates are not being listed; otherwise, select
the first candidate in the next column in the list.
complete-prev-column
Like the complete command when candidates are not being listed; otherwise, select
the first candidate in the previous column in the list.
complete-next-page
Like the complete command when candidates are not being listed; otherwise, select
the first candidate in the next page in the list.
complete-prev-page
Like the complete command when candidates are not being listed; otherwise, select
the first candidate in the previous page in the list.
complete-list
Complete a word just before the cursor position.
If you pass no argument, a list of completion candidates is shown. Otherwise, the
word is completed with the nth candidate where n is the argument.
emacs
\^[?, \^[=
complete-all
Replace a word just before the cursor position with all possible completion
candidates, each separated by a space.
emacs
\^[*
complete-max
Complete a word just before the cursor position with the longest prefix of all
possible completion candidates.
clear-candidates
Clear the list of completion candidates.
Vi-specific commands
vi-replace-char
Replace the character at the cursor position with a character that is entered just
after this command.
vi-command
r
vi-insert-beginning
Move the cursor to the beginning of the line and switch to the vi insert mode.
vi-command
I
vi-append
Move the cursor to the next character and switch to the vi insert mode.
vi-command
I
vi-append-to-eol
Move the cursor to the end of the line and switch to the vi insert mode.
vi-command
A
vi-replace
Switch to the vi insert mode and start overwriting. While overwriting, the
self-insert command replaces the character at cursor position rather than
inserting a character. Overwriting ends when the editing mode is changed.
vi-command
R
vi-switch-case
Switch case of characters between the current and next cursor positions. This
command must be followed by a motion command, which determines the next cursor
position.
vi-switch-case-char
Switch case of the character at the current cursor position and move the cursor to
the next character.
vi-command
~
vi-yank
Add to the kill ring the characters between the current and next cursor positions.
This command must be followed by a motion command, which determines the next
cursor position.
vi-command
y
vi-yank-to-eol
Add to the kill ring the characters from the current cursor position to the end of
the line.
vi-command
Y
vi-delete
Delete characters between the current and next cursor positions and add it to the
kill ring. This command must be followed by a motion command, which determines the
next cursor position.
vi-command
d
vi-delete-to-eol
Delete the characters from the current cursor position to the end of the line and
add it to the kill ring.
vi-command
D
vi-change
Delete characters between the current and next cursor positions and switch to the
vi insert mode. This command must be followed by a motion command, which
determines the next cursor position.
vi-command
c
vi-change-to-eol
Delete the characters from the current cursor position to the end of the line and
switch to the vi insert mode.
vi-command
C
vi-change-line
Delete the whole buffer contents and switch to the vi insert mode.
vi-command
S
vi-yank-and-change
Like the vi-change command, but the deleted text is added to the kill ring.
vi-yank-and-change-to-eol
Like the vi-change-to-eol command, but the deleted text is added to the kill ring.
vi-yank-and-change-line
Like the vi-change-line command, but the deleted text is added to the kill ring.
vi-substitute
Delete a character at the current cursor position, add it to the kill ring, and
switch to the vi insert mode.
vi-command
s
vi-append-last-bigword
Insert a space and the last bigword in the most recent command history entry just
after the current cursor position and switch to the vi insert mode. If argument n
is passed, the nth bigword in the entry is inserted instead of the last.
vi-command
_
vi-exec-alias
Execute the value of an alias named _c as editing commands where c is a character
input just after this command.
vi-command
@
vi-edit-and-accept
Start the vi editor to edit the current buffer contents. When the editor finished,
the edited buffer contents is accepted like the accept-line command unless the
exit status of the editor is non-zero.
vi-command
v
vi-complete-list
Like the complete-list command, but also switch to the vi insert mode.
vi-command
=
vi-complete-all
Like the complete-all command, but also switch to the vi insert mode.
vi-command
*
vi-complete-max
Like the complete-max command, but also switch to the vi insert mode.
vi-command
\\
vi-search-forward
Switch to the vi search mode and start forward history search.
vi-command
?
vi-search-backward
Switch to the vi search mode and start backward history search.
vi-command
/
Emacs-specific commands
emacs-transpose-chars
Move a character just before the cursor to the right.
emacs
\^T
emacs-transpose-words
Move an emacsword just before the cursor to the right.
emacs
\^[t, \^[T
emacs-downcase-word
Make an emacsword just after the cursor lowercase.
emacs
\^[l, \^[L
emacs-upcase-word
Make an emacsword just after the cursor uppercase.
emacs
\^[u, \^[U
emacs-capitalize-word
Capitalize the first letter of an emacsword just after the cursor.
emacs
\^[c, \^[u
emacs-delete-horizontal-space
Delete spaces around the cursor. If any argument was passed, delete spaces just
before the cursor only.
emacs
\^[\\
emacs-just-one-space
Delete spaces around the cursor and leave one space. If an argument is specified,
leave as many spaces as the argument.
emacs
\^[ (Escape followed by a space)
emacs-search-forward
Switch to the emacs search mode and start forward history search.
emacs
\^S
emacs-search-backward
Switch to the emacs search mode and start backward history search.
emacs
\^R
History-related commands
oldest-history
Recall the oldest entry in the history. If argument n is passed, the entry whose
number is n is recalled instead. The cursor position remains unchanged.
newest-history
Recall the newest entry in the history. If argument n is passed, the entry whose
number is n is recalled instead. The cursor position remains unchanged.
return-history
Return to the initial buffer corresponding to none of existing history entries. If
argument n is passed, the entry whose number is n is recalled instead. The cursor
position remains unchanged.
oldest-history-bol
Recall the oldest entry in the history and move the cursor to the beginning of the
line. If argument n is passed, the entry whose number is n is recalled instead.
vi-command
G
newest-history-bol
Recall the newest entry in the history and move the cursor to the beginning of the
line. If argument n is passed, the entry whose number is n is recalled instead.
return-history-bol
Return to the initial buffer corresponding to none of existing history entries and
move the cursor to the beginning of the line. If argument n is passed, the entry
whose number is n is recalled instead.
vi-command
g
oldest-history-eol
Recall the oldest entry in the history and move the cursor to the end of the line.
If argument n is passed, the entry whose number is n is recalled instead.
emacs
\^[<
newest-history-eol
Recall the newest entry in the history and move the cursor to the end of the line.
If argument n is passed, the entry whose number is n is recalled instead.
return-history-eol
Return to the initial buffer corresponding to none of existing history entries and
move the cursor to the end of the line. If argument n is passed, the entry whose
number is n is recalled instead.
emacs
\^[>
next-history
Recall the next history entry. The cursor position remains unchanged.
prev-history
Recall the previous history entry. The cursor position remains unchanged.
next-history-bol
Recall the next history entry and move the cursor to the beginning of the line.
vi-command
j, +, \D, \^N
prev-history-bol
Recall the previous history entry and move the cursor to the beginning of the
line.
vi-command
k, -, \U, \^P
next-history-eol
Recall the next history entry and move the cursor to the end of the line.
vi-insert, emacs
\D, \^N
prev-history-eol
Recall the previous history entry and move the cursor to the end of the line.
vi-insert, emacs
\U, \^P
search-again
Repeat the last command history search.
vi-command
n
search-again-rev
Repeat the last command history search in the reverse direction.
vi-command
N
search-again-forward
Repeat the last command history search in the forward direction.
search-again-backward
Repeat the last command history search in the backward direction.
beginning-search-forward
Recall the next history entry that starts with the same text as the text from the
beginning of the line up to the current cursor position. The cursor position
remains unchanged.
beginning-search-backward
Recall the previous history entry that starts with the same text as the text from
the beginning of the line up to the current cursor position. The cursor position
remains unchanged.
Search mode commands
srch-self-insert
Insert the input character at the current cursor position. Characters escaped by
escape sequences cannot be inserted.
vi-search, emacs-search
\\
srch-backward-delete-char
Delete the last character in the search text. If the text is empty:
• like the srch-abort-search command when in the vi search mode, or
• like the alert command when in the emacs search mode.
vi-search, emacs-search
\B, \?, \^H
srch-backward-delete-line
Delete the whole search text.
vi-search, emacs-search
\$, \^U
srch-continue-forward
Find the next matching history entry.
emacs-search
\^S
srch-continue-backward
Find the previous matching history entry.
emacs-search
\^R
srch-accept-search
Finish the search mode, accepting the result being shown.
vi-search
\^J, \^M
emacs-search
\^J, \^[
srch-abort-search
Abort search and restore the previous buffer contents.
vi-search
\^[
emacs-search
\^G
Escape sequences
In the bindkey built-in, escape sequences are used to represent special keys such as
function keys and arrow keys. Every escape sequence starts with a backslash (\) and thus
there is also an escape sequence for a backslash itself.
Below are available escape sequences:
\\
Backslash (\)
\B
Backspace
\D
Down arrow
\E
End
\H
Home
\I
Insert (Insert-char, Enter-insert-mode)
\L
Left arrow
\N
Page-down (Next-page)
\P
Page-up (Previous-page)
\R
Right arrow
\U
Up arrow
\X
Delete
\!
INTR
\#
EOF
\$
KILL
\?
ERASE
\^@
Ctrl + @
\^A, \^B, ..., \^Z
Ctrl + A, Ctrl + B, ..., Ctrl + Z
Note that Ctrl + I, Ctrl + J, and Ctrl + M are tab, newline, and carriage return,
respectively.
\^[
Ctrl + [ (Escape)
\^\
Ctrl + \
\^]
Ctrl + ]
\^^
Ctrl + ^
\^_
Ctrl + _
\^?
Ctrl + ? (Delete)
\F00, \F01, ..., \F63
F0, F1, ..., F63
\a1
Top-left on keypad
\a3
Top-right on keypad
\b2
Center on keypad
\bg
Beginning
\bt
Back-tab
\c1
Bottom-left on keypad
\c3
Bottom-right on keypad
\ca
Clear-all-tabs
\cl
Close
\cn
Cancel
\co
Command
\cp
Copy
\cr
Create
\cs
Clear-screen or erase
\ct
Clear-tab
\dl
Delete-line
\ei
Exit-insert-mode
\el
Clear-to-end-of-line
\es
Clear-to-end-of-screen
\et
Enter (Send)
\ex
Exit
\fd
Find
\hp
Help
\il
Insert-line
\ll
Home-down
\me
Message
\mk
Mark
\ms
Mouse event
\mv
Move
\nx
Next-object
\on
Open
\op
Options
\pr
Print (Copy)
\pv
Previous-object
\rd
Redo
\re
Resume
\rf
Ref (Reference)
\rh
Refresh
\rp
Replace
\rs
Restart
\sf
Scroll-forward (Scroll-down)
\sl
Select
\sr
Scroll-backward (Scroll-up)
\st
Set-tab
\su
Suspend
\sv
Save
\ud
Undo
\SE
Shift + End
\SH
Shift + Home
\SI
Shift + Insert
\SL
Shift + Left arrow
\SR
Shift + Right arrow
\SX
Shift + Delete
\Sbg
Shift + Beginning
\Scn
Shift + Cancel
\Sco
Shift + Command
\Scp
Shift + Copy
\Scr
Shift + Create
\Sdl
Shift + Delete-line
\Sel
Shift + End-of-line
\Sex
Shift + Exit
\Sfd
Shift + Find
\Shp
Shift + Help
\Smg
Shift + Message
\Smv
Shift + Move
\Snx
Shift + Next
\Sop
Shift + Options
\Spr
Shift + Print
\Spv
Shift + Previous
\Srd
Shift + Redo
\Sre
Shift + Resume
\Srp
Shift + Replace
\Ssu
Shift + Suspend
\Ssv
Shift + Save
\Sud
Shift + Undo
INTR, EOF, KILL, and ERASE are special characters configured by the stty command. In a
typical configuration, they are sent by typing Ctrl+C, Ctrl+D, Ctrl+U, and Ctrl+H,
respectively, but some configuration uses Ctrl+? instead of Ctrl+H for ERASE.
Command line completion
By using the complete and complete-next-candidate commands, etc., you can complete command
names, options, and operands. By default, the complete-next-candidate command is bound
with the Tab key in the vi insert and emacs modes.
Type a few first letters of a command name or pathname and hit the Tab key, and a list of
matching names will be shown. You can choose a candidate from the list to complete the
name by hitting the Tab key again. If there is only one matching name, no list will be
shown and the name will directly be completed.
If the name to be completed contains characters like * and ?, it is treated as a pattern.
The name on the command line will be directly substituted with all possible names matching
the pattern (you cannot choose from a list).
Normally, command names are completed with command names and command arguments with
pathnames. However, completion functions can be defined to refine completion results.
Completion details
When doing completion for the first time after the shell has been started, the INIT
file is loaded as if the command string . -AL completion/INIT is executed. If the file
is not found, it is silently ignored. This automatic loading is mainly intended for
loading completion functions bundled with the shell, but you can let the shell load
your own functions by putting a file in the load path.
When completing a command name, the shell executes the completion//command function
and when completing a command argument, the completion//argument function. If those
completion functions are not defined, the shell just completes with command names or
pathnames. When completing other names, such as the user name in tilde expansion and
the parameter name in parameter expansion, completion functions are never used: the
shell just completes with user names, parameter names, or whatever applicable.
Completion functions are executed without any arguments. The following local variables
are automatically defined while executing completion functions:
IFS
The value is the three characters of a space, a tab, and a newline, which are the
default value of the variable.
WORDS
This variable is an array whose elements are a command name and arguments that
have already been entered before the argument being completed. When completing a
command name, the array has no elements.
TARGETWORD
The value is the partially entered command name or argument that is being
completed.
Completion candidates are generated by executing the complete built-in during a
completion function.
Completion functions must not perform I/O to the terminal, or displayed text will be
corrupted. Completion functions should run as quickly as possible for better user
experience.
While a completion function is being executed:
• the POSIXly-correct mode is temporarily disabled,
• the err-exit option is temporarily disabled, and
• traps are not executed.
POSIXLY-CORRECT MODE
Yash behaves as defined in POSIX.1-2008, Shell & Utilities for the most part, but some
functionalities disobey POSIX for usability. When full POSIX-conformance is needed, you
can enable the POSIXly-correct mode to make yash obey POSIX as mush as possible.
If yash is started with the name “sh”, the POSIXly-correct mode is automatically enabled.
The -o posixly-correct command-line option also enables the POSIXly-correct mode. After
yash has been started, the POSIXly-correct mode can be enabled by executing the command
string set -o posixly-correct.
When the POSIXly-correct mode is on, yash not only tries to obey the requirements by
POSIX, but also treats as errors most conditions where the behavior is undefined or
unspecified by POSIX. As a result, most yash-specific functionalities are disabled in the
POSIXly-correct mode.
Below is the complete list of the behavioral differences between when yash is in the
POSIXly-correct mode and when not. When the POSIXly-correct mode is enabled:
• Different initialization scripts are used.
• Global aliases are not substituted.
• Nested commands in a compound command must not be empty.
• Words expanded in a for loop are assigned as a global variable rather than a local.
• The first pattern in a case command cannot be esac.
• The function keyword cannot be used for function definition.
• Simple commands cannot assign to arrays.
• Changing the value of the LC_CTYPE variable after the shell has been initialized does
not affect the shell’s locale.
• The RANDOM variable cannot be used to generate random numbers.
• Tilde expansion only expands ~ and ~username.
• Parameter expansion cannot be nested. No indexes are allowed.
• The commands in a command substitution of the form $(commands) are parsed every time
the substitution is executed.
• Fractional numbers and the ++ and -- operators cannot be used in arithmetic expansion.
• In a redirection to a file, if the pathname expansion yielded more than one or no
pathname, it is not immediately treated as an error. Instead, the shell tries to treat
the word before the expansion as a pathname.
• Socket redirection, here strings, pipe redirection, and process redirection cannot be
used.
• When executing a simple command, failure in command search does not trigger execution
of the COMMAND_NOT_FOUND_HANDLER variable.
• In command search, a regular built-in needs to have a corresponding external command
for the built-in to be found.
• asynchronous commands ignore the SIGINT and SIGQUIT signals even when job control is
active. The standard input of asynchronous commands is redirected to /dev/null if the
shell is not interactive, regardless of whether job control is active or not.
• Some built-ins behave differently. Especially, some command-line options cannot be
used.
• A non-interactive shell exits when a special built-in is given a syntactically wrong
arguments or when an error occurs in assignment or redirection with a special
built-in.
• An interactive shell does not execute the PROMPT_COMMAND variable before printing a
prompt. The values of the PS1, PS2, and PS4 variables are parsed differently.
• In mail checking, a notification message is printed if the file has been modified,
regardless of whether the file is empty.
FORMAL DEFINITION OF COMMAND SYNTAX
This chapter defines the syntax of shell commands as a parsing expression grammar.
The set of terminals of the grammar is the set of characters that can be handled on the
environment in which the shell is run (a.k.a. execution character set), with the exception
that the set does not contain the null character ('\0').
Below is a list of nonterminals of the grammar with corresponding parsing expressions. The
list does not include rules for parsing contents and ends of here documents. In the
POSIXly-correct mode, the grammar varies from the list below to disable non-POSIX
functionalities.
CompleteCommand
SequenceEOF
Sequence
N* List*
List
Pipeline ((&& / ||) N* Pipeline)* ListSeparator
Pipeline
Bang? Command (|N* Command)*
Command
CompoundCommandRedirection* /
!RFunctionDefinition /
!R SimpleCommand
CompoundCommand
Subshell / Grouping / IfCommand / ForCommand / WhileCommand / CaseCommand /
FunctionCommand
Subshell
(Sequence)S*
Grouping
LeftBraceSequenceRightBrace
IfCommand
IfSequenceThen Sequence (Elif Sequence Then Sequence)* (Else Sequence)? Fi
ForCommand
ForNameS* Separator? (InWord* Separator)? DoSequenceDone
WhileCommand
(While / Until) SequenceDo Sequence Done
CaseCommand
CaseWordN* In N* CaseItem* Esac
CaseItem
!Esac ((S*)? Word (| S* Word)* )Sequence (;; / &Esac)
FunctionCommand
FunctionWord ((S* ))? N* CompoundCommandRedirection*
FunctionDefinition
NameS* ( S* )N* CompoundCommandRedirection*
SimpleCommand
&(Word / Redirection) (Assignment / Redirection)* (Word / Redirection)*
Assignment
Name=Word /
Name =(N* (Word N*)* )
Name
![[:digit:]] [[:alnum:] _]+
PortableName
![0-9] [0-9ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_]+
Word
(WordElement / !SpecialChar .)+ S*
WordElement
\ . / ' (!' .)* ' / "QuoteElement* " / Parameter / Arithmetic / CommandSubstitution
QuoteElement
\ ([$`"\] / NL) / Parameter / Arithmetic / CommandSubstitution /
![`"\] .
Parameter
$ [@*#?-$! [:digit:]] / $PortableName / $ParameterBody
ParameterBody
{ParameterNumber? (ParameterName / ParameterBody / Parameter) ParameterIndex?
ParameterMatch? }
ParameterNumber
# ![+=:/%] !([-?#] })
ParameterName
[@*#?-$!] /
[[:alnum:] _]+
ParameterIndex
[ParameterIndexWord (, ParameterIndexWord)? ]
ParameterIndexWord
(WordElement / !["'],] .)+
ParameterMatch
:? [-+=?] ParameterMatchWord /
(# / ## / % / %%) ParameterMatchWord /
(:/ / / [#%/]?) ParameterMatchWordNoSlash (/ ParameterMatchWord)?
ParameterMatchWord
(WordElement / !["'}] .)*
ParameterMatchWordNoSlash
(WordElement / !["'/}] .)*
Arithmetic
$((ArithmeticBody* ))
ArithmeticBody
\ . / Parameter / Arithmetic / CommandSubstitution / ( ArithmeticBody ) /
![`()] .
CommandSubstitution
$(Sequence) / `CommandSubstitutionBody* `
CommandSubstitutionBody
\ [$`\] /
!` .
Redirection
RedirectionFDRedirectionOperatorS* Word /
RedirectionFD <(Sequence) /
RedirectionFD >( Sequence )
RedirectionFD
[[:digit:]]*
RedirectionOperator
< / <> / > / >| / >> / >>| / <& / >& / << / <<- / <<<
ListSeparator
Separator / &N* /
&) /
&;;
Separator
;N* / N+ / EOF
N
S* NL
S
[[:blank:]] / Comment
Comment
# (!NL .)*
R
Bang / LeftBrace / RightBrace / Case / Do / Done / Elif / Else / Esac / Fi / For / If
/ In / Then / Until / While
Bang
!D
LeftBrace
{D
RightBrace
}D
Case
caseD
Do
doD
Done
doneD
Elif
elifD
Else
elseD
Esac
esacD
Fi
fiD
For
forD
Function
functionD
If
ifD
In
inD
Then
thenD
Until
untilD
While
whileD
D
!WordS*
SpecialChar
[|&;<>()`\"' [:blank:]] / NL
NL
<newline>
EOF
!.
ALIAS BUILT-IN
The alias built-in defines and/or prints aliases.
Syntax
• alias [-gp] [name[=value]...]
Description
The alias built-in defines and/or prints aliases as specified by operands. The printed
aliases can be used as (part of) shell commands. The built-in prints all currently defined
aliases when given no operands.
Options
-g, --global
With this option, aliases are defined as global aliases; without this option, as
normal aliases.
-p, --prefix
With this option, aliases are printed in a full command form like alias -g foo='bar'.
Without this option, only command operands are printed like foo='bar'.
Operands
name
The name of an alias that should be printed.
name=value
The name and value of an alias that is being defined.
Exit status
The exit status of the alias built-in is zero unless there is any error.
Notes
The characters that cannot be used in an alias name are the space, tab, newline, and any
of =$<>\'"`;&|()#. You can use any characters in an alias value.
The alias built-in is a semi-special built-in.
The POSIX standard defines no options for the alias built-in, thus no options are
available in the POSIXly correct mode.
ARRAY BUILT-IN
The array built-in prints or modifies arrays.
Syntax
• array
• array name [value...]
• array -d name [index...]
• array -i name index [value...]
• array -s name index value
Description
When executed without any option or operands, the built-in prints all array definitions to
the standard output in a form that can be parsed as commands.
When executed with name and values (but without an option), the built-in sets the values
as the values of the array named name.
With the -d (--delete) option, the built-in removes the indexth values of the array named
name. The number of values in the array will be decreased by the number of the indexes
specified. If the indexth value does not exist, it is silently ignored.
With the -i (--insert) option, the built-in inserts values into the array named name. The
number of values in the array will be increased by the number of the values specified. The
values are inserted between the indexth and next values. If index is zero, the values are
inserted before the first value. If index is larger than the number of values in the
array, the values are appended after the last element.
With the -s (--set) option, the built-in sets value as the indexth value of the array
named name. The array must have at least index values.
Options
-d, --delete
Delete array values.
-i, --insert
Insert array values.
-s, --set
Set an array value.
Operands
name
The name of an array to operate on.
index
The index to an array element. The first element has the index of 1.
value
A string to which the array element is set.
Exit status
The exit status of the array built-in is zero unless there is any error.
Notes
The array built-in is not defined in the POSIX standard.
The command array name value... is equivalent to the assignment name=(value...).
BG BUILT-IN
The bg built-in resumes a job in the background.
Syntax
• bg [job...]
Description
The bg built-in sends the SIGCONT signal to the specified job. As a result, the job is
resumed in the background (if it has been suspended).
The name of the job is printed when the job is resumed.
The built-in can be used only when job control is enabled.
Operands
job
The job ID of the job to be resumed.
More than one job can be specified at a time. The current job is resumed if none is
specified.
The percent sign (%) at the beginning of a job ID can be omitted if the shell is not
in the POSIXly-correct mode.
Exit status
The exit status of the bg built-in is zero unless there is any error.
Notes
The bg built-in is a semi-special built-in.
The POSIX standard provides that the built-in shall have no effect when the job is already
running. The bg built-in of yash, however, always sends the SIGCONT signal to the job.
BINDKEY BUILT-IN
The bindkey built-in prints or modifies key bindings used in line-editing.
Syntax
• bindkey -aev [key [command]]
• bindkey -l
Description
When executed with the -l (--list) option, the built-in lists all available line-editing
commands to the standard output.
When executed with one of the other options, the built-in prints or modifies key bindings
for the editing mode specified by the option:
• Without key or command, all currently defined bindings are printed to the standard
output in a form that can be parsed as commands that restore the current bindings when
executed.
• With key but without command, only the binding for the given key is printed.
• With key and command, key is bound to command.
Options
-a, --vi-command
Print or modify bindings for the vi command mode.
-e, --emacs
Print or modify bindings for the emacs mode.
-v, --vi-insert
Print or modify bindings for the vi insert mode.
Operands
key
A character sequence of one or more keys that is bound to an editing command. The
sequence may include escape sequences.
command
A line-editing command to which key is bound. If command is a single hyphen (-), key
is unbound.
Exit status
The exit status of the bindkey built-in is zero unless there is any error.
Notes
The bindkey built-in is not defined in the POSIX standard.
BREAK BUILT-IN
The break built-in aborts a loop being executed.
Syntax
• break [nest]
• break -i
Description
When executed without the -i (--iteration) option, the built-in aborts a currently
executed for, while, or until loop. When executed in nested loops, it aborts the nestth
innermost loop. The default nest is one. If the number of currently executed nested loops
is less than nest, the built-in aborts the outermost loop.
When executed with the -i (--iteration) option, the built-in aborts the currently executed
(innermost) iterative execution.
Options
-i, --iteration
Abort an iterative execution instead of a loop.
Operands
nest
The number of loops to abort, which must be a positive integer.
Exit status
The exit status of the break built-in is:
• zero if a loop was successfully aborted.
• that of the command that was executed just before the break built-in if an iterative
execution was successfully aborted.
Notes
The break built-in is a special built-in.
The POSIX standard defines no options for the break built-in; the built-in accepts no
options in the POSIXly-correct mode.
CD BUILT-IN
The cd built-in changes the working directory.
Syntax
• cd [-L|-P] [directory]
Description
The cd built-in changes the working directory to the directory specified by the operand.
The pathname of the new working directory is assigned to the PWD variable, whose previous
value is again assigned to the OLDPWD variable.
If directory is a relative path that does not start with ‘.’ or ‘..’, paths in the CDPATH
variable are searched to find a new working directory. The search is done in a manner
similar to the last step of command search, but a directory is sought instead of an
executable regular file. If a new working directory was found from CDPATH, its pathname is
printed to the standard output. If no applicable directory was found in the search,
directory is simply treated as a pathname relative to the current working directory.
If the working directory was successfully changed, the value of the YASH_AFTER_CD variable
is executed as a command unless the shell is in the POSIXly-correct mode. If the variable
is an array, its values are executed iteratively (cf. eval built-in).
Options
-L, --logical
Symbolic links in the pathname of the new working directory are not resolved. The new
value of the PWD may include pathname components that are symbolic links.
-P, --physical
Symbolic links in the pathname of the new working directory are resolved. The new
value of the PWD variable never includes pathname components that are symbolic links.
--default-directory=directory
If this option is specified and the directory operand is omitted, the argument to this
option is used for the directory operand. If the directory operand is specified, this
option is ignored.
The -L (--logical) and -P (--physical) options are mutually exclusive: only the last
specified one is effective. If neither is specified, -L is assumed.
Operands
directory
The pathname of the new working directory.
If directory is a single hyphen (‘-’), the value of the OLDPWD variable is assumed for
the new directory pathname, which is printed to the standard output.
If directory is omitted, the working directory is changed to the directory specified
by the --default-directory=... option. If that option is not specified either, the
default is the home directory.
Exit status
The exit status of the cd built-in is zero if the working directory was successfully
changed and non-zero if there was an error.
Notes
The cd built-in is a semi-special built-in.
The POSIX standard does not define the use of the YASH_AFTER_CD variable or the
--default-directory=... option. The standard does not allow using an option with a single
hyphen operand.
The exit status of the commands in the YASH_AFTER_CD variable does not affect that of the
cd built-in.
COLON BUILT-IN
The colon built-in does nothing.
Syntax
• : [argument...]
Description
The colon built-in does nothing. Any command line arguments are ignored.
Exit status
The exit status of the colon built-in is zero.
Notes
The colon built-in is a special built-in.
Arguments are expanded and redirections are performed as usual. The colon and true
built-ins have the same effect, but colon is a special built-in while true is a
semi-special.
COMMAND BUILT-IN
The command built-in executes or identifies a command.
Syntax
• command [-befp] command [argument...]
• command -v|-V [-abefkp] command...
Description
Without the -v (--identify) or -V (--verbose-identify) option, the built-in executes
command with arguments in the same manner as the last step of execution of simple
commands. The command is treated as a built-in or external command or a function according
to the options specified to the command built-in. The shell does not exit on argument
syntax error etc. even if the command is a special built-in
With the -v (--identify) option, command is identified. If the command is found in $PATH,
its full pathname is printed. If it is a keyword, function, or built-in that is not found
in $PATH, the command name is simply printed. If it is an alias, it is printed in the form
like alias ll='ls -l'. If the command is not found, nothing is printed and the exit status
is non-zero.
The -V (--verbose-identify) option is similar to the -v (--identify) option, but the
output format is more human-friendly.
Options
-a, --alias
Search for the command as an alias. Must be used with the -v (--identify) or -V
(--verbose-identify) option.
-b, --builtin-command
Search for the command as a built-in.
-e, --external-command
Search for the command as an external command.
-f, --function
Search for the command as a function.
-k, --keyword
Search for the command as a keyword. Must be used with the -v (--identify) or -V
(--verbose-identify) option.
-p, --standard-path
Search the system’s default PATH instead of the current $PATH.
-v, --identify
Identify commands and print in the format defined in the POSIX standard.
-V, --verbose-identify
Identify commands and print in a human-friendly format.
If none of the -a (--alias), -b (--builtin-command), -e (--external-command), -f
(--function), and -k (--keyword) options is specified, the following defaults are assumed:
Without the -v (--identify) or -V (--verbose-identify) option
-b -e
With the -v (--identify) or -V (--verbose-identify) option
-a -b -e -f -k
Operands
command
A command to be executed or identified.
argument...
Arguments passed to the executed command.
Exit status
The exit status of the command built-in is:
Without the -v (--identify) or -V (--verbose-identify) option
the exit status of the executed command.
With the -v (--identify) or -V (--verbose-identify) option
zero unless there is any error.
Notes
The command built-in is a semi-special built-in.
In the POSIXly-correct mode, options other than -p, -v, and -V cannot be used and at most
one command can be specified. The POSIX standard does not allow specifying both -v and -V
together, but yash does (only the last specified one is effective).
COMPLETE BUILT-IN
The complete built-in generates completion candidates. This built-in can only be executed
from completion functions during command line completion.
Syntax
• complete [-A pattern] [-R pattern] [-T] [-P prefix] [-S suffix] [-abcdfghjkuv] [[-O]
[-D description] word...]
Description
The built-in generates completion candidates according to the specified arguments. No
matter how candidates are generated, only candidates that match the word being completed
are generated.
Options
-A pattern, --accept=pattern
Only accept candidates that match the pattern specified by this option. When more than
one of this option is specified, only candidates that match all of the patterns are
generated.
-D description, --description=description
Give a description of the word candidates. The description is shown beside the
candidates in the candidate list.
-O, --option
The candidates are treated as command line options. A hyphen is prepended to each
candidate that is treated as an option.
-P prefix, --prefix=prefix
Ignore prefix of the word being completed when generating candidates. The specified
prefix must be initial part of the word.
If the word being completed is file:///home/user/docume for example, the command line
complete -P file:// -f will generate pathname candidates that complete
/home/user/docume.
-R pattern, --reject=pattern
Reject candidates that match the pattern specified by this option. When more than one
of this option is specified, only candidates that match none of the patterns are
generated.
-S suffix, --suffix=suffix
Append suffix to each generated candidate.
-T, --no-termination
Do not append a space after the word is completed. Without this option, a space is
appended to the completed word so that you do not have to enter a space before the
next word.
Options that select candidate types
-a, --alias
Aliases. (same as --normal-alias --global-alias)
--array-variable
Arrays.
--bindkey
Line-editing commands the bindkey built-in accepts.
-b, --builtin-command
Built-in commands. (same as --special-builtin --semi-special-builtin
--regular-builtin)
-c, --command
Commands. (same as --builtin-command --external-command --function)
-d, --directory
Directories.
--dirstack-index
Valid indices of the directory stack.
--executable-file
Executable regular files.
--external-command
External commands.
-f, --file
Files (including directories).
--finished-job
Job IDs of finished jobs.
--function
Functions.
--global-alias
Global aliases.
-g, --group
User groups.
-h, --hostname
Host names.
-j, --job
Job IDs.
-k, --keyword
Keywords.
--normal-alias
Normal aliases.
--regular-builtin
Regular built-in commands.
--running-job
Job IDs of jobs that are being executed.
--scalar-variable
Variables that are not arrays.
--semi-special-builtin
Semi-special built-in commands.
--signal
Signals.
--special-builtin
Special built-in commands.
--stopped-job
Job IDs of jobs that are suspended.
-u, --username
Users' log-in names.
-v, --variable
Variables.
If the -d (--directory) option is specified without the -f (--file) option, the -S /
-T options are assumed.
Generated candidates for job IDs do not have leading percent signs (%). If the word
being completed starts with a percent sign, the -P % option should be specified.
Operands
Operands are treated as completion candidates.
Exit status
The exit status of the built-in is zero if one or more candidates were generated, one if
no candidates were generated, or larger than one if an error occurred.
Notes
The complete built-in is not defined in the POSIX standard.
CONTINUE BUILT-IN
The continue built-in skips an iteration of a loop being executed.
Syntax
• continue [nest]
• continue -i
Description
When executed without the -i (--iteration) option, the built-in aborts the current
iteration of for, while, or until loop and starts the next iteration of the loop. When
executed in nested loops, it affects the nestth innermost loop. The default nest is one.
If the number of currently executed nested loops is less than nest, the built-in affects
the outermost loop.
When executed with the -i (--iteration) option, the built-in aborts the current iteration
of (innermost) iterative execution.
Options
-i, --iteration
Skip an iterative execution instead of a loop.
Operands
nest
The nestth innermost loop is affected. nest must be a positive integer.
Exit status
The exit status of the continue built-in is:
• zero if loop iteration was successfully skipped.
• that of the command that was executed just before the continue built-in if iterative
execution was successfully skipped.
Notes
The continue built-in is a special built-in.
The POSIX standard defines no options for the continue built-in; the built-in accepts no
options in the POSIXly-correct mode.
DIRS BUILT-IN
The dirs built-in prints the contents of the directory stack.
Syntax
• dirs [-cv] [index..]
Description
The directory stack is a feature that records history of working directories. You can use
the pushd built-in to save a working directory in the directory stack, the popd built-in
to recall the saved working directory, and the dirs built-in to see the stack contents.
Those built-ins use the DIRSTACK array and the PWD variable to save the stack contents.
Modifying the array means modifying the stack contents.
Directory stack entries are indexed by signed integers. The entry of index +0 is the
current working directory, +1 is the last saved directory, +2 is the second last, and so
on. Negative indices are in the reverse order: the entry of index -0 is the first saved
directory, -1 is the second, and -n is the current working directory if the stack has n
entries,
When executed without the -c (--clear) option, the dirs built-in prints the current
contents of the directory stack to the standard output. With the -c (--clear) option, the
built-in clears the directory stack.
Options
-c, --clear
Clear the directory stack contents except for the current working directory, which has
index +0.
-v, --verbose
Print indices when printing stack contents.
Operands
index
The index of a stack entry to be printed.
You can specify more than one index. If you do not specify any index, all the entries
are printed.
Exit status
The exit status of the dirs built-in is zero unless there is any error.
Notes
The dirs built-in is not defined in the POSIX standard.
DISOWN BUILT-IN
The disown built-in removes jobs.
Syntax
• disown [-a] [job...}
Description
The disown built-in removes the specified jobs from the job list. The removed jobs will no
longer be job-controlled, but the job processes continue execution (unless they have been
suspended).
Options
-a, --all
Removes all jobs.
Operands
job
The job ID of the job to be removed.
You can specify more than one job ID. If you do not specify any job ID, the current
job is removed. If the shell is not in the POSIXly-correct mode, the %-prefix of the
job ID can be omitted.
Exit status
The exit status of the disown built-in is zero unless there is any error.
Notes
The disown built-in is not defined in the POSIX standard.
DOT BUILT-IN
The dot built-in reads a file and executes commands in it.
Syntax
• . [-AL] file [argument...]
Description
The dot built-in reads the specified file, parses its contents as commands, and executes
them in the current command execution environment.
If arguments are specified, positional parameters are temporarily set to them. The
positional parameters will be restored when the dot built-in finishes. If no arguments are
specified, the positional parameters are not changed.
If file does not contain any slashes, the shell searches $PATH for a readable (but not
necessarily executable) shell script file whose name is file in the same manner as command
search. If no such file was found, the shell searches the current working directory for a
file unless in the POSIXly-correct mode. To ensure that the file in the current working
directory is used, start file with ‘./’.
Options
-A, --no-alias
Disable alias substitution while parsing.
-L, --autoload
Search $YASH_LOADPATH instead of $PATH, regardless of whether file contains slashes.
The file value is not considered relative to the current working directory.
The dot built-in treats as operands any command line arguments after the first operand.
Operands
file
The pathname of a file to be read.
arguments...
Strings to which positional parameters are set while execution.
Exit status
The exit status of the dot built-in is that of the last command executed. The exit status
is zero if the file contains no commands to execute and non-zero if a file was not found
or could not be opened.
Notes
The dot built-in is a special built-in.
A non-interactive shell that is not in the POSIXly-correct mode will immediately exit with
a non-zero exit status if the dot built-in fails to find or open a file to execute.
The POSIX standard defines no options for the dot built-in; the built-in accepts no
options in the POSIXly-correct mode.
The POSIX standard does not define the arguments... operands. It is an error to specify
the arguments... operands in the POSIXly-correct mode.
ECHO BUILT-IN
The echo built-in prints its arguments.
Syntax
• echo [string...]
The built-in treats all command line arguments as operands except for the options
described below. Any word that cannot be parsed as an acceptable option is treated as an
operand. Options must precede all operands. Syntax errors never happen in the echo
built-in.
Description
The echo built-in prints the operand strings followed by a newline to the standard output.
The strings are each separated by a space.
Escape sequences
The ECHO_STYLE variable and the -e option enable escape sequences that are replaced
with corresponding characters:
\a
Bell character (ASCII code: 7)
\b
Backspace (ASCII code: 8)
\c
Nothing. After this escape sequence, no characters are printed at all.
\e
Escape character (ASCII code: 27)
\f
Form feed character (ASCII code: 12)
\n
Newline character (ASCII code: 10)
\r
Carriage return character (ASCII code: 13)
\t
Horizontal tab character (ASCII code: 9)
\v
Vertical tab character (ASCII code: 11)
\\
Backslash
\0xxx
Character whose code is xxx, where xxx is an octal number of at most three digits.
When escape sequences are not enabled, they are just printed intact.
ECHO_STYLE variable
The ECHO_STYLE variable defines which options are accepted and whether escape
sequences are enabled by default. The variable value should be set to one of the
following:
SYSV, XSI
No options are accepted. Escape sequences are always enabled.
BSD
The -n option is accepted. Escape sequences are never enabled.
GNU
The -n, -e, and -E options are accepted. Escape sequences are not enabled by
default, but can be enabled by the -e option.
ZSH
The -n, -e, and -E options are accepted. Escape sequences are enabled by default,
but can be disabled by the -E option.
DASH
The -n option is accepted. Escape sequences are always enabled.
RAW
No options are accepted. Escape sequences are never enabled.
When the ECHO_STYLE variable is not set, it defaults to SYSV.
Options
-n
Do not print a newline at the end.
-e
Enable escape sequences.
-E
Disable escape sequences.
Exit status
The exit status of the echo built-in is zero unless there is any error.
Notes
The POSIX standard does not define the ECHO_STYLE variable nor any options for the
built-in. According to POSIX, the behavior of the built-in is implementation-defined when
the first argument is -n or when any argument contains a backslash. For maximum
portability, the printf built-in should be preferred over the echo built-in.
EVAL BUILT-IN
The eval built-in evaluates operands as commands.
Syntax
• eval [-i] [command...]
The eval built-in requires that all options precede operands. Any command line arguments
after the first operand are all treated as operands.
Description
The eval parses operands as commands and executes them in the current command execution
environment.
When executed without the -i (--iteration) option, all the operands are concatenated into
one string (with a space inserted between each operand) and parsed/executed at once.
With the -i (--iteration) option, the built-in performs iterative execution: operands are
parsed/executed one by one. If the continue built-in is executed with the -i (--iteration)
option during the iterative execution, the execution of the current operand is aborted and
the next operand is parsed/executed immediately. The break built-in with the -i
(--iteration) option is similar but the remaining operands are not parsed/executed.
Options
-i, --iteration
Perform iterative execution.
Operands
command
A string that is parsed and executed as commands.
Exit status
The exit status is zero if no command was specified or command contained no actual command
that can be executed. Otherwise, that is, if the eval built-in executed one or more
commands, the exit status of the eval built-in is that of the last executed command.
Notes
The eval built-in is a special built-in.
The POSIX standard defines no options for the eval built-in; the built-in accepts no
options in the POSIXly-correct mode.
EXEC BUILT-IN
The exec built-in replaces the shell process with another external command.
Syntax
• exec [-cf] [-a name] [command [argument...]]
The exec built-in requires that all options precede operands. It is important so that
options to the exec built-in are not confused with options to command. Any command line
arguments after command are treated as arguments.
Description
When the exec built-in is executed with command, the shell executes command with arguments
in a manner similar to the last step of execution of a simple command. The differences are
that command is always treated as an external command ignoring any existing functions and
built-ins and that the exec system call that starts the external command is called in the
current command execution environment instead of a subshell, replacing the shell process
with the new command process.
If the shell is in the POSIXly-correct mode or not interactive, failure in execution of
command causes the shell to exit immediately.
If an interactive shell that is not in the POSIXly-correct mode has a stopped job, the
shell prints a warning message and refuses to execute command. Once the shell process is
replaced with an external command, information about the shell’s jobs is lost, so you will
have to resume or kill the stopped jobs by sending signals by hand. To force the shell to
execute command regardless, specify the -f (--force) option.
When executed without command, the built-in does nothing. As a side effect, however,
redirection applied to the built-in remains in the current command execution environment
even after the built-in finished.
Options
-a name, --as=name
Pass name, instead of command, to the external command as its name.
-c, --clear
Pass to the external command only variables that are assigned in the simple command in
which the built-in is being executed. Other environment variables are not passed to
the command.
-f, --force
Suppress warnings that would prevent command execution.
Operands
command
An external command to be executed.
argument...
Arguments to be passed to the command.
Exit status
If the shell process was successfully replaced with the external command, there is no exit
status since the shell process no longer exists.
The exit status is:
• 127 if the command was not found,
• 126 if the command was found but could not be executed, and
• zero if no command was specified.
Notes
The exec built-in is a special built-in.
The POSIX standard defines no options for the exec built-in; the built-in accepts no
options in the POSIXly-correct mode.
EXIT BUILT-IN
The exit built-in causes the shell process to exit.
Syntax
• exit [-f] [exit_status]
Description
The exit built-in causes the current shell (or subshell) process to exit.
If an interactive shell has a stopped job, the shell prints a warning message and refuses
to exit. To force the shell to exit regardless, specify the -f (--force) option or execute
the built-in twice in a row.
If an EXIT trap has been set, the shell executes the trap before exiting.
Options
-f, --force
Suppress warnings that would prevent the shell from exiting.
Operands
exit_status
A non-negative integer that will be the exit status of the exiting shell.
If this operand is omitted, the exit status of the shell will be that of the last
command executed before the exit built-in (but, if the built-in is executed during a
trap, the exit status will be that of the last command before the trap is entered).
If exit_status is 256 or larger, the actual exit status will be the remainder of
exit_status divided by 256.
Exit status
Because the built-in causes the shell to exit, there is no exit status of the built-in.
As an exception, if the shell refused to exit, the exit status of the built-in is
non-zero.
Notes
The exit built-in is a special built-in.
The POSIX standard defines no options for the exit built-in; the built-in accepts no
options in the POSIXly-correct mode.
The POSIX standard provides that the exit_status operand should be between 0 and 255
(inclusive). Yash accepts integers larger than 255 as an extension.
If the built-in is executed during an EXIT trap, the shell just exits without executing
the trap again. If exit_status was not specified, the exit status of the shell is what the
exit status would be if the trap had not been set. See also Termination of the shell.
EXPORT BUILT-IN
The export built-in marks variables for export to child processes.
Syntax
• export [-prX] [name[=value]...]
Description
The export built-in is equivalent to the typeset built-in with the -gx option.
Notes
The export built-in is a special built-in.
The POSIX standard defines the -p option only; other options cannot be used in the
POSIXly-correct mode. The POSIX does not allow using the option together with operands.
FALSE BUILT-IN
The false built-in does nothing unsuccessfully.
Syntax
• false
Description
The false built-in does nothing. Any command line arguments are ignored.
Exit status
The exit status of the false built-in is non-zero.
Notes
The false built-in is a semi-special built-in.
FC BUILT-IN
The fc built-in re-executes or prints commands from command history.
Syntax
• fc [-qr] [-e editor] [start [end]]
• fc -s[q] [old=new] [start]
• fc -l[nrv] [start [end]]
Description
When executed without the -l (--list) option, the built-in executes the commands in the
command history range specified by the operands. If the -s (--silent) option is not
specified, the shell invokes an editor which allows you to edit the commands before they
are executed. The commands are executed when you quit the editor. If the -s (--silent)
option is specified, the commands are immediately executed. In either case, the executed
commands are printed to the standard output and added to the history.
When executed with the -l (--list) option, the built-in prints the commands in the command
history range specified by the operands. By default, commands are printed with their
history entry numbers, but output format can be changed using the -n (--no-numbers)) and
-v (--verbose) options.
Options
-e editor, --editor=editor
Specify an editor that is used to edit commands.
If this option is not specified, the value of the FCEDIT variable is used. If the
variable is not set either, vi is used.
-l, --list
Print command history entries.
-n, --no-numbers
Don’t print entry numbers when printing history entries.
-q, --quiet
Don’t print commands before executing.
-r, --reverse
Reverse the order of command entries in the range.
-s, --silent
Execute commands without editing them.
-v, --verbose
Print execution time before each history entry when printing.
Operands
start and end
The start and end operands specify a range of command history entries that are
executed or printed. If one of the operands is an integer, it is treated as a history
entry number. A negative integer means the nth most recent entry where n is the
absolute value of the integer. If one of the operands is not an integer, it is treated
as part of a command string: the most recent entry that starts with the string is
selected as the start or end of the range.
If the first entry of the range that is specified by start is newer than the last
entry of the range that is specified by end, the range is reversed as if the -r
(--reverse) option was specified. (If the option is already specified, it is
cancelled.)
The default values for start and end are:
┌──────┬─────────┬───────────────┐
│ │ with -l │ without -l │
├──────┼─────────┼───────────────┤
│start │ -16 │ -1 │
├──────┼─────────┼───────────────┤
│end │ -16 │ same as start │
└──────┴─────────┴───────────────┘
old=new
An operand of this format replaces part of the command string. If the command string
contains old, it is replaced with new and the new string is executed. Only the first
occurrence of old is replaced.
Exit status
If commands was executed, the exit status of the fc built-in is that of the last executed
command. Otherwise, the exit status is zero unless there is any error.
Notes
The fc built-in is a semi-special built-in.
The POSIX standard does not define the -q (--quiet) or -v (--verbose) options, so they
cannot be used in the POSIXly-correct mode.
Command history cannot be modified during line-editing.
FG BUILT-IN
The fg built-in resumes a job in the foreground.
Syntax
• fg [job...]
Description
The fg built-in brings the specified job to the foreground and sends the SIGCONT signal to
the job. As a result, the job is resumed in the foreground (if it has been suspended). The
built-in then waits for the job to finish and returns the exit status of it.
The name of the job is printed when the job is resumed.
The built-in can be used only when job control is enabled.
Operands
job
The job ID of the job to be resumed.
If more than one job is specified, they are resumed in order, one at a time. The
current job is resumed if none is specified.
The percent sign (%) at the beginning of a job ID can be omitted if the shell is not
in the POSIXly-correct mode.
Exit status
The exit status of the fg built-in is that of the (last) job resumed. The exit status is
non-zero when there was some error.
Notes
The fg built-in is a semi-special built-in.
You cannot specify more than one job in the POSIXly-correct mode.
GETOPTS BUILT-IN
The getopts built-in parses command options.
Syntax
• getopts optionlist variable [argument...]
Description
The getopts built-in parses single-character options that appear in arguments. Each time
the built-in is invoked, it parses one option and assigns the option character to
variable.
The optionlist operand is a list of option characters that should be accepted by the
parser. In optionlist, an option that takes an argument should be specified as the option
character followed by a colon. For example, if you want the -a, -b and -c options to be
parsed and the -b option to take an argument, then optionlist should be ab:c.
When an option that takes an argument is parsed, the argument is assigned to the OPTARG
variable.
When an option that is not specified in optionlist is found or when an option argument is
missing, the result depends on the first character of optionlist:
• If optionlist starts with a colon, the option character is assigned to the OPTARG
variable and variable is set to either ? (when the option is not in optionlist) or :
(when the option argument is missing).
• Otherwise, variable is set to ?, the OPTARG variable is unset, and an error message is
printed.
The built-in parses one option for each execution. For all options in a set of command
line arguments to be parsed, the built-in has to be executed repeatedly with the same
arguments. The built-in uses the OPTIND variable to remember which argument should be
parsed next. When the built-in is invoked for the first time, the variable value must be
1, which is the default value. You must not modify the variable until all the options have
been parsed, when the built-in sets the variable to the index of the first operand in
arguments. (If there are no operands, it will be set to the number of arguments plus one.)
When you want to start parsing a new set of arguments, you have to reset the OPTIND
variable to 1 beforehand.
Operands
optionlist
A list of options that should be accepted as valid options in parsing.
variable
The name of a variable the result is to be assigned to.
arguments
Command line arguments that are to be parsed.
When no arguments are given, the positional parameters are parsed.
Exit status
If an option is found, whether or not it is specified in optionlist, the exit status is
zero. If there is no more option to be parsed, the exit status is non-zero.
Example
aopt=false bopt= copt=false
while getopts ab:c opt
do
case $opt in
a) aopt=true ;;
b) bopt=$OPTARG ;;
c) copt=true ;;
\?) return 2 ;;
esac
done
if $aopt; then echo Option -a specified; fi
if [ -n "$bopt" ]; then echo Option -b $bopt specified; fi
if $copt; then echo Option -c specified; fi
shift $((OPTIND - 1))
echo Operands are: $*
Notes
In arguments that are parsed, options must precede operands. The built-in ends parsing
when it encounters the first operand.
The getopts built-in is a semi-special built-in.
The POSIX standard does not specify what will happen when the OPTIND variable is assigned
a value other than 1.
HASH BUILT-IN
The hash built-in remembers, forgets, or reports command locations.
Syntax
• hash command...
• hash -r [command...]
• hash [-a]
• hash -d user...
• hash -dr [user...]
• hash -d
Description
When executed with commands but without options, the built-in immediately performs command
path search and caches commands' full paths.
When executed with the -r (--remove) option, it removes the paths of commands (or all
cached paths if none specified) from the cache.
When executed without options or commands, it prints the currently cached paths to the
standard output.
With the -d (--directory) option, the built-in does the same things to the home directory
cache, rather than the command path cache. Cached home directory paths are used in tilde
expansion.
Options
-a, --all
Print all cached paths.
Without this option, paths for built-ins are not printed.
-d, --directory
Affect the home directory cache instead of the command path cache.
-r, --remove
Remove cached paths.
Operands
command
The name of an external command (that does not contain any slash).
user
A user name.
Exit status
The exit status of the hash built-in is zero unless there is any error.
Notes
The shell automatically caches command and directory paths when executing a command or
performing tilde expansion, so normally there is no need to use this built-in explicitly
to cache paths.
Assigning a value to the PATH variable removes all command paths from the cache as if hash
-r was executed.
The POSIX standard defines the -r option only: other options cannot be used in the
POSIXly-correct mode.
HELP BUILT-IN
The help built-in prints usage of built-ins.
Syntax
• help [built-in...]
Description
The help built-in prints a description of built-ins.
The built-in extracts part of the output of man yash and prints it to the standard output.
Therefore, the manual page of yash must have been installed for the built-in to work.
Depending on the formatting style of the man command, the built-in may not work as
expected.
Operands
built-ins
Names of built-ins.
Exit status
The exit status of the help built-in is zero unless there is any error.
Notes
The help built-in is not defined in the POSIX standard.
Many built-ins of yash accept the --help option that prints the same description.
HISTORY BUILT-IN
The history built-in prints or edits command history.
Syntax
• history [-cF] [-d entry] [-s command] [-r file] [-w file] [count]
Description
The history built-in prints or edits command history.
When executed with an option, the built-in edits history according to the option. If more
than one option is specified, each option is processed in order.
When executed with the count operand, the built-in prints the most recent count history
entries to the standard output in the same manner as the fc built-in.
When executed with neither options nor operands, the built-in prints the whole history.
Options
-c, --clear
Clear all history entries completely.
-d entry, --delete=entry
Delete the specified entry. The entry should be specified in the same manner as the
start and end operands of the fc built-in.
-F, --flush-file
Rebuild the history file. This operation removes unused old data from the file.
-r file, --read=file
Read command lines from file and add them to the history. The file contents are
treated as lines of simple text.
-s command, --set=command
Add command as a new history entry after removing the most recent entry.
-w file, --write=file
Write the whole history to file. Any existing data in the file will be lost. The
output format is lines of simple text, each of which is a command string.
Operands
count
The number of entries to be printed.
Exit status
The exit status of the history built-in is zero unless there is any error.
Notes
The history built-in is not defined in the POSIX standard.
Command history cannot be modified during line-editing.
JOBS BUILT-IN
The jobs built-in reports job status.
Syntax
• jobs [-lnprs] [job...]
Description
The jobs built-in prints information of jobs the shell is currently controlling.
By default, the following information is printed for each job, line by line:
• the job number,
• the + or - symbol if the job is the current or previous job, respectively,
• the status, and
• the command string.
Options
-l, --verbose
Print the process ID, status, and command string for each process in the jobs.
-n, --new
Print new jobs only: jobs whose status has never been reported since the status
changed.
-p, --pgid-only
Print process group IDs of jobs only.
-r, --running-only
Print running jobs only.
-s, --stopped-only
Print stopped jobs only.
Operands
jobs
The job IDs of jobs to be reported. When no job is specified, all jobs under the
shell’s control are reported.
Exit status
The exit status of the jobs built-in is zero unless there is any error.
Notes
The jobs built-in is a semi-special built-in.
The POSIX standard defines the -l and -p options only: other options cannot be used in the
POSIXly-correct mode. In the POSIXly-correct mode, the effect of the -l option is
different in that status is reported for each job rather than for each process.
The process group ID of a job executed by yash is equal to the process ID of the first
command of the pipeline that forms the job.
KILL BUILT-IN
The kill built-in sends a signal to processes.
Syntax
• kill [-signal|-s signal|-n signal] process...
• kill -l [-v] [signal...]
The kill built-in requires that all options precede operands. Any command line arguments
after the first operand are all treated as operands.
Description
When executed without the -l option, the built-in sends a signal to processes. The signal
sent can be specified by option. The SIGTERM signal is sent if no signal is specified.
When executed with the -l option, the built-in prints information of signals to the
standard output. If no signal is specified, information of all signals is printed.
Options
Signal-specifying options
-signal, -s signal, -n signal
A signal-specifying option specifies a signal to be sent to processes. signal can
be specified by name or number. If number 0 is specified, the built-in checks if a
signal could be sent to the processes but no signal is actually sent. Signal names
are case-insensitive.
You can specify at most one signal-specifying option at a time.
Other options
-l
Print signal information instead of sending a signal.
-v
Print more signal information.
Without this option, the built-in prints the signal name only. This option adds
the signal number and a short description.
When the -v option is specified, the -l option can be omitted.
Operands
processes
Specify processes to which a signal is sent.
Processes can be specified by the process ID, the process group ID, or the job ID. The
process group ID must be prefixed with a hyphen (-) so that it is not treated as a
process ID.
When 0 is specified as process, the signal is sent to the process group to which the
shell process belongs. When -1 is specified, the signal is sent to all processes on
the system.
signal
Specify a signal of which information is printed.
The signal can be specified by the name, the number, or the exit status of a command
that was killed by the signal.
Exit status
The exit status of the kill built-in is zero unless there is any error. If the signal was
sent to at least one process, the exit status is zero even if the signal was not sent to
all of the specified processes.
Notes
The kill built-in is a semi-special built-in.
Command arguments that start with a hyphen should be used with care. The command kill -1
-2, for example, sends signal 1 to process group 2 since -1 is treated as a
signal-specifying option and -2 as an operand that specifies a process group. The commands
kill -- -1 -2 and kill -TERM -1 -2, on the other hand, treats both -1 and -2 as operands.
The POSIX standard does not define the -n or -v options, so they cannot be used in the
POSIXly-correct mode. The standard does not allow specifying a signal number as the
argument of the -s option or a signal name as the signal operand.
The standard requires signal names to be specified without the SIG prefix, like INT and
QUIT. If the shell is not in the POSIXly-correct mode, the built-in accepts SIG-prefixed
signal names as well.
POPD BUILT-IN
The popd built-in pops a directory from the directory stack.
Syntax
• popd [index]
Description
The popd built-in removes the last entry from the directory stack, returning to the
previous working directory. If index is given, the entry specified by index is removed
instead of the last one.
Operands
index
The index of a directory stack entry you want to remove.
If omitted, +0 (the last entry) is assumed.
Exit status
The exit status of the popd built-in is zero unless there is any error.
Notes
It is an error to use this built-in when there is only one directory stack entry.
The popd built-in is not defined in the POSIX standard.
PRINTF BUILT-IN
The printf built-in prints formatted values.
Syntax
• printf format [value...]
Description
The printf built-in formats values according to format and prints them to the standard
output. Unlike the echo built-in, the printf built-in does not print a newline
automatically.
The formatting process is very similar to that of the printf function in the C programming
language. You can use conversion specifications (which start with %) and escape sequences
(which start with \) in format. Any other characters that are not part of a conversion
specification or escape sequence are printed literally.
Conversion specifications
A conversion specification starts with a percent sign (%).
A conversion specification except %% consumes a value, which is formatted according to
the specification and printed. Each conversion specification consumes one value in the
order of appearance. If there are more values than conversion specifications, the
entire format is re-processed until all the values are consumed. If a value to be
consumed is missing, it is assumed to be an empty string (if the specification
requires a string) or zero (if a number). If no values are given, format is processed
just once.
Available conversion specifications are:
%d, %i
prints a signed integer in decimal
%u
prints an unsigned integer in decimal
%o
prints an unsigned integer in octal
%x
prints an unsigned integer in lowercase hexadecimal
%X
prints an unsigned integer in uppercase hexadecimal
%f
prints a floating-point number in lowercase
%F
prints a floating-point number in uppercase
%e
prints a floating-point number with exponent in lowercase
%E
prints a floating-point number with exponent in uppercase
%g
the same as %f or %e, automatically selected
%G
the same as %F or %E, automatically selected
%c
prints the first character of string
%s
prints a string
%b
prints a string (recognizing escape sequences like the echo built-in)
%%
prints a percent sign (%)
For %g and %G, the specification that is actually used is %f or %F if the exponent
part is between -5 and the precision (exclusive); %e or %E otherwise.
In a conversion specification except %%, the leading percent sign may be followed by
flags, field width, and/or precision in this order.
The flags are a sequence of any number of the following characters:
Minus sign (-)
With this flag, spaces are appended to the formatted value to fill up to the field
width. Otherwise, spaces are prepended.
Plus sign (+)
A plus or minus sign is always prepended to a number.
Space ( )
A space is prepended to a formatted number if it has no plus or minus sign.
Hash sign (#)
The value is formatted in an alternative form: For %o, the printed octal integer
has at least one leading zero. For %x and %X, a non-zero integer is formatted with
0x and 0X prefixes, respectively. For %e, %E, %f, %F, %g, and %G, a decimal mark
(a.k.a. radix character) is always printed even if the value is an exact integer.
For %g and %G, the printed number has at least one digit in the fractional part.
Zero (0)
Zeros are prepended to a formatted number to fill up to the field width. This flag
is ignored if the minus flag is specified or if the conversion specification is
%d, %i, %u, %o, %x, or %X with a precision.
A field width is specified as a decimal integer that has no leading zeros.
A field width defines a minimum byte count of a formatted value. If the formatted
value does not reach the minimum byte count, so many spaces are prepended that the
printed value has the specified byte count.
A precision is specified as a period (.) followed by a decimal integer. If the integer
is omitted after the period, the precision is assumed to be zero.
For conversion specifications %d, %i, %u, %o, %x, and %X, a precision defines a
minimum digit count. If the formatted integer does not reach the minimum digit count,
so many zeros are prepended that the printed integer has the specified number of
digits. The default precision is one for these conversion specifications.
For conversion specifications %e, %E, %f, and %F, a precision defines the number of
digits after the decimal mark. The default precision is six for these conversion
specifications.
For conversion specifications %g, and %G, a precision defines a maximum number of
significant digits in the printed value. The default precision is six for these
conversion specifications.
For conversion specifications %s, and %b, a precision defines a maximum byte count of
the printed string. The default precision is infinity for these conversion
specifications.
In the conversion specification %08.3f, the zero flag is specified, the field width is
8, and the precision is 3. If this specification is applied to value 12.34, the output
will be 0012.340.
Escape sequences
The following escape sequences are recognized in format:
\a
Bell character (ASCII code: 7)
\b
Backspace (ASCII code: 8)
\f
Form feed character (ASCII code: 12)
\n
Newline character (ASCII code: 10)
\r
Carriage return character (ASCII code: 13)
\t
Horizontal tab character (ASCII code: 9)
\v
Vertical tab character (ASCII code: 11)
\\
Backslash
\"
Double quotation
\'
Single quotation (apostrophe)
\xxx
Character whose code is xxx, where xxx is an octal number of at most three digits.
Operands
format
A string that defines how values should be formatted.
values
Values that are formatted according to format.
A value is either a number or a string.
When a numeric value is required, value can be a single or double quotation followed
by a character, instead of a normal number. For example, the command printf '%d' '"3'
will print 51 on a typical environment where character 3 has character code 51.
Exit status
The exit status of the printf built-in is zero unless there is any error.
Notes
The POSIX standard does not precisely define how multibyte characters should be handled by
the built-in. When you use the %s conversion specification with precision or the %c
conversion specification, you may obtain unexpected results if the formatted value
contains a character that is represented by more than one byte. Yash never prints only
part of the bytes that represent a single multibyte character because all multibyte
characters are converted to wide characters when processed in the shell.
PUSHD BUILT-IN
The pushd built-in pushes a directory into the directory stack.
Syntax
• pushd [-L|-P] [directory]
Description
The pushd built-in changes the working directory to directory in the same manner as the cd
built-in and adds it to the directory stack. If the working directory could not be changed
successfully, the stack is not modified.
Options
The pushd built-in accepts the following option as well as the options that can be used
for the cd built-in:
--remove-duplicates
If the new working directory has already been in the directory stack, the existing
entry is removed from the stack before the new directory is pushed into the stack.
Operands
directory
The pathname of the new working directory.
If directory is a single hyphen (‘-’), the value of the OLDPWD variable is assumed for
the new directory pathname, which is printed to the standard output.
If directory is an integer with a plus or minus sign, it is considered as an entry
index of the directory stack. The entry is removed from the stack and then pushed to
the stack again.
If directory is omitted, the working directory is changed to the directory specified
by the --default-directory=... option. If that option is not specified either, the
default is index +1.
Exit status
The exit status of the pushd built-in is zero unless there is any error.
Notes
The pushd built-in is not defined in the POSIX standard.
PWD BUILT-IN
The pwd built-in prints the current working directory.
Syntax
• pwd [-L|-P]
Description
The pwd built-in prints an absolute path to the shell’s current working directory to the
standard output.
Options
-L, --logical
If the value of the PWD variable is an absolute path to the shell’s working directory
and the path does not contain any . or .. components, then the path is printed.
Otherwise, the printed path is the same as when the -P option is specified.
-P, --physical
The printed path does not contain any . or .. components, symbolic link components,
or redundant slashes.
The -L (--logical) and -P (--physical) options are mutually exclusive: only the last
specified one is effective. If neither is specified, -L is assumed.
Exit status
The exit status of the pwd built-in is zero unless there is any error.
Notes
The pwd built-in is a semi-special built-in.
READ BUILT-IN
The read built-in reads a line from the standard input.
Syntax
• read [-Ar] variable...
Description
The read built-in reads a line of string from the standard input and assigns it to the
specified variables. If the shell is interactive and line-editing is enabled, you can use
line-editing when inputting a line.
If the -r (--raw-mode) option is specified, all characters in the line are treated
literally.
If the -r (--raw-mode) option is not specified, backslashes in the line are treated as
quotations. If a backslash is at the end of the line, it is treated as a line
continuation. When the built-in reads the next line, the PS2 variable is used as a prompt
if the standard input is a terminal.
The input line is subject to field splitting. The resulting words are assigned to
variables in order. If there are more words than variables, the last variable is assigned
all the remaining words (as if the words were not split). If the words are fewer than
variables, the remaining variables are assigned empty strings.
Options
-A, --array
Make the last variable an array. Instead of assigning a concatenation of the remaining
words to a normal variable, the words are assigned to an array.
-r, --raw-mode
Don’t treat backslashes as quotations.
Operands
variables
Names of variables to which input words are assigned.
Exit status
The exit status of the read built-in is zero unless there is any error.
Notes
The read built-in is a semi-special built-in.
The POSIX standard defines the -r option only: other options cannot be used in the
POSIXly-correct mode.
READONLY BUILT-IN
The readonly built-in makes variables and functions read-only.
Syntax
• readonly [-pxX] [name[=value]...]
• readonly -f[p] [name...]
Description
The readonly built-in is equivalent to the typeset built-in with the -gr option.
Notes
The readonly built-in is a special built-in.
The POSIX standard defines the -p option only; other options cannot be used in the
POSIXly-correct mode. The POSIX does not allow using the option together with operands.
RETURN BUILT-IN
The return built-in returns from a function or script.
Syntax
• return [-n] [exit_status]
Description
When executed without the -n (--no-return) option, one of the following happens:
• If the shell is executing a function, the execution of the function is terminated.
• If the dot built-in is executing a script, the execution of the script is terminated.
• If the eval built-in is executing a command string, the execution of the command is
terminated.
• Otherwise, the shell exits unless it is interactive.
When executed with the -n (--no-return) option, the built-in does nothing but return the
specified exit_status.
Options
-n, --no-return
Do not terminate a function, script, evaluated command, or the shell.
Operands
exit_status
The exit status of the built-in.
The value must be a non-negative integer.
If omitted, the exit status of the last executed command is used. (But when the shell
is executing a trap, the exit status of the last command before the trap is used.)
Exit status
The exit status of the return built-in is defined by the exit_status operand. The exit
status is used also as the exit status of the terminated function, script, evaluated
script, or the shell.
Notes
The return built-in is a special built-in.
The POSIX standard provides that the exit_status operand should be between 0 and 255
(inclusive). Yash accepts integers larger than 255 as an extension.
In the POSIX standard, the behavior of the return built-in is defined only when the shell
is executing a function or script.
The POSIX standard defines no options for the return built-in; the built-in accepts no
options in the POSIXly-correct mode.
SET BUILT-IN
The set built-in sets shell options and positional parameters.
Syntax
• set [options] [operands]
• set -o
• set +o
The set built-in requires that all options precede operands. Any command line arguments
after the first operand are all treated as operands.
Description
When executed without any command arguments, the built-in prints a list of all existing
variables to the standard input in a form that can be reused as commands that will restore
the variable definitions.
When -o is the only command argument, the built-in prints a list of shell options with
their current settings. When +o is the only command argument, the built-in prints commands
that can be reused to restore the current shell option settings.
In other cases, the built-in changes shell option settings and/or positional parameters.
Options
When one or more options are specified, the built-in enables or disables the shell
options. A normal hyphen-prefixed option enables a shell option. An option that is
prefixed with a plus (+) instead of a hyphen disables a shell option. For example, options
-m, -o monitor, and --monitor enable the monitor option and options +m, +o monitor,
++monitor disable it.
The name of a long option is case-insensitive and may include irrelevant non-alphanumeric
characters, which are ignored. For example, options --le-comp-debug and --LeCompDebug are
equivalent. If no is prepended to the name of a long option, the meaning is reversed. For
example, --noallexport is equivalent to ++allexport and ++nonotify to --notify.
An option can be specified in one of the following forms:
• a long option e.g. --allexport
• an -o option with a option name specified as the argument e.g. -o allexport
• a single-character option e.g. -a
Not all options can be specified as single-character options.
The available options are:
all-export (-a)
When enabled, all variables are automatically exported when assigned.
brace-expand
This option enables brace expansion.
case-glob
(Enabled by default) When enabled, pattern matching is case-sensitive in pathname
expansion.
clobber (+C)
(Enabled by default) When enabled, the >redirection behaves the same as the >|
redirection.
cur-async, cur-bg, cur-stop
(Enabled by default) These options affect choice of the current job (cf. job ID).
dot-glob
When enabled, periods at the beginning of filenames are not treated specially in
pathname expansion.
emacs
This option enables line-editing in the emacs mode.
err-exit (-e)
When enabled, if a pipeline ends with a non-zero exit status, the shell immediately
exits unless:
• the pipeline is a condition of an if command or while or until loop;
• the pipeline is prefixed by !; or
• the pipeline is a single compound command other than a subshell grouping.
exec (+n)
(Enabled by default) Commands are actually executed only when this option is enabled.
Otherwise, commands are just parsed and not executed. Disabling this option may be
useful for syntax checking. In an interactive shell, this option is always assumed
enabled.
extended-glob
This option enables extension in pathname expansion.
glob (+f)
(Enabled by default) This option enables pathname expansion.
hash-on-def (-h)
When a function is defined when this option is enabled, the shell immediately performs
command path search for each command that appears in the function and caches the
command’s full path.
hist-space
When enabled, command lines that start with a whitespace are not saved in command
history.
ignore-eof
When enabled, an interactive shell does not exit when EOF (end of file) is input. This
prevents the shell from exiting when you accidentally hit Ctrl-D.
le-always-rp, le-comp-debug, le-conv-meta, le-no-conv-meta, le-prompt-sp, le-visible-bell
See shell options on line-editing.
mark-dirs
When enabled, resulting directory names are suffixed by a slash in pathname expansion.
monitor (-m)
This option enables job control. This option is enabled by default for an interactive
shell.
notify (-b)
When the status of a job changes when this option is enabled, the shell immediately
notifies at any time. This option overrides the notify-le option.
notify-le
This option is similar to the notify option, but the status change is notified only
while the shell is waiting for input with line-editing.
null-glob
When enabled, in pathname expansion, patterns that do not match any pathname are
removed from the command line rather than left as is.
posixly-correct
This option enables the POSIXly-correct mode.
trace-all
(Enabled by default) When this option is disabled, the x-trace option is temporarily
disabled while the shell is executing commands defined in the
COMMAND_NOT_FOUND_HANDLER, PROMPT_COMMAND, or YASH_AFTER_CD variable.
unset (+u)
(Enabled by default) When enabled, undefined parameters are expanded to empty strings
in parameter expansion. When disabled, expansion of undefined parameter results in an
error.
verbose (-v)
When enabled, the shell prints each command line to the standard error before parsing
and executing it.
vi
This option enables line-editing in the vi mode. This option is enabled by default in
an interactive shell if the standard input and error are both terminals.
x-trace (-x)
When enabled, the results of expansion are printed to the standard error for each
simple command being executed. When printed, each line is prepended with an expansion
result of the PS4 variable. See also the trace-all option.
Operands
If one or more operands are passed to the set built-in, current positional parameters are
all removed and the operands are set as new positional parameters. If the -- separator
(cf. syntax of command arguments) is passed, the positional parameters are set even when
there are no operands, in which case new positional parameters will be nothing.
Exit status
The exit status of the set built-in is zero unless there is any error.
Notes
The set built-in is a special built-in.
In the POSIX standard, available shell options are much limited. The standard does not
define:
• long options such as --allexport,
• prepending no to negate an option,
• using uppercase letters and/or non-alphanumeric characters in option names
The options defined in the standard are:
• -a, -o allexport
• -e, -o errexit
• -m, -o monitor
• -C, -o noclobber
• -n, -o noexec
• -f, -o noglob
• -b, -o notify
• -u, -o nounset
• -v, -o verbose
• -x, -o xtrace
• -h
• -o ignoreeof
• -o nolog
• -o vi
Yash does not support the nolog option, which prevents function definitions from being
added to command history.
SHIFT BUILT-IN
The shift built-in removes some positional parameters.
Syntax
• shift [count]
Description
The shift built-in removes the first count positional parameters.
Operands
count
The number of positional parameters to be removed.
It is an error if the actual number of positional parameters is less than count. If
omitted, the default value is one.
Exit status
The exit status of the shift built-in is zero unless there is any error.
Notes
The shift built-in is a special built-in.
The number of positional parameters can be obtained with the # special parameter.
SUSPEND BUILT-IN
The suspend built-in suspends the shell.
Syntax
• suspend [-f]
Description
The suspend built-in sends a SIGSTOP signal to all processes in the process group to which
the shell process belongs. The signal suspends the processes (including the shell). The
suspended processes resume when they receive a SIGCONT signal.
If the shell is interactive and its process group ID is equal to the process ID of the
session leader, the shell prints a warning message and refuses to send a signal unless the
-f (--force) option is specified. (In such a case, there is no other job-controlling shell
that can send a SIGCONT signal to resume the suspended shell, so the shell could never be
resumed.)
Options
-f, --force
Suppress warnings that would prevent the shell from sending a signal.
Exit status
The exit status is zero if the signal was successfully sent and non-zero otherwise.
Notes
The suspend built-in is not defined in the POSIX standard.
TEST BUILT-IN
The test built-in evaluates an expression.
Syntax
• test expression
• [ expression ]
The test built-in does not distinguish options and operands; all command line arguments
are interpreted as expression. If the built-in is executed with the name [, expression
must be followed by ].
Description
The test built-in evaluates expression as a conditional expression that is made up of
operators and operands described below. The exit status is 0 if the condition is true and
1 otherwise.
The unary operators below test a file. If the operand file is a symbolic link, the file
referred to by the link is tested (except for the -h and -L operators).
-b file
file is a block special file
-c file
file is a character special file
-d file
file is a directory
-e file
file exists
-f file
file is a regular file
-G file
file's group ID is same as the shell’s effective group ID
-g file
file's set-group-ID flag is set
-h file
same as -L
-k file
file's sticky bit is set
-L file
file is a symbolic link
-N file
file has not been accessed since last modified
-O file
file's user ID is same as the shell’s effective user ID
-p file
file is a FIFO (named pipe)
-r file
file is readable
-S file
file is a socket
-s file
file is not empty
-u file
file's set-user-ID flag is set
-w file
file is writable
-x file
file is executable
The unary operator below tests a file descriptor:
-t fd
fd is associated with a terminal
The unary operators below test a string:
-n string
string is not empty
-z string
string is empty
The unary operator below tests a shell option:
-o ?option
option is a valid shell option name
-o option
option is a valid shell option name that is enabled
The binary operators below compare files. Non-existing files are considered older than any
existing files.
file1 -nt file2
file1 is newer than file2
file1 -ot file2
file1 is older than file2
file1 -ef file2
file1 is a hard link to file2
The binary operators below compare strings:
string1 = string2
string1 is the same string as string2
string1 != string2
string1 is not the same string as string2
The binary operators below compare strings according to the alphabetic order in the
current locale:
string1 === string2
string1 is equal to string2
string1 !== string2
string1 is not equal to string2
string1 < string2
string1 is less than string2
string1 <= string2
string1 is less than or equal to string2
string1 > string2
string1 is greater than string2
string1 >= string2
string1 is greater than or equal to string2
The binary operator below performs pattern matching:
string =~ pattern
extended regular expression pattern matches string
The binary operators below compare integers:
v1 -eq v2
v1 is equal to v2
v1 -ne v2
v1 is not equal to v2
v1 -gt v2
v1 is greater than v2
v1 -ge v2
v1 is greater than or equal to v2
v1 -lt v2
v1 is less than v2
v1 -le v2
v1 is less than or equal to v2
The binary operators below compare version numbers:
v1 -veq v2
v1 is equal to v2
v1 -vne v2
v1 is not equal to v2
v1 -vgt v2
v1 is greater than v2
v1 -vge v2
v1 is greater than or equal to v2
v1 -vlt v2
v1 is less than v2
v1 -vle v2
v1 is less than or equal to v2
The operators below can be used to make complex expressions:
! expression
negate (reverse) the result
( expression )
change operator precedence
expression1 -a expression2
logical conjunction (and)
expression1 -o expression2
logical disjunction (or)
If the expression is a single word without operators, the -n operator is assumed. An empty
expression evaluates to false.
Comparison of version numbers
Comparison of version numbers is similar to comparison of strings in alphabetic order.
The differences are:
• Adjacent digits are treated as an integer. Integers are compared in mathematical
order rather than alphabetic order.
• Digits are considered larger than any non-digit characters.
For example, version numbers 0.1.2-3 and 00.001.02-3 are equal and 0.2.1 is smaller
than 0.10.0.
Exit status
The exit status of the test built-in is 0 if expression is true and 1 otherwise. The exit
status is 2 if expression cannot be evaluated because of a syntax error or any other
reasons.
Notes
Complex expressions may cause confusion and should be avoided. Use the shell’s compound
commands. For example, [ 1 -eq 1 ] && [ -t = 1 ] && ! [ foo ] is preferred over [ 1 -eq 1
-a -t = 1 -a ! foo ].
The POSIX standard provides that the exit status should be larger than 1 on error. The
POSIX standard does not define the following operators: -nt, -ot, -ef, ==, ===, !==, <,
<=, >, >=, =~, -veq, -vne, -vgt, -vge, -vlt, and -vle. POSIX neither specifies -o as a
unary operator.
TIMES BUILT-IN
The times built-in prints CPU time usage.
Syntax
• times
Description
The times built-in prints the CPU times consumed by the shell process and its child
processes to the standard output.
The built-in prints two lines: the first line shows the CPU time of the shell process and
the second one that of its child processes (not including those which have not
terminated). Each line shows the CPU times consumed in the user and system mode.
Exit status
The exit status of the times built-in is zero unless there is any error.
Notes
The times built-in is a special built-in.
TRAP BUILT-IN
The trap built-in sets or prints signal handlers.
Syntax
• trap
• trap action signal...
• trap signal_number [signal...]
• trap -p [signal...]
Description
The trap built-in sets or prints actions that are taken when the shell receives signals.
(Those actions are called traps.)
When executed with action and one or more signals, the built-in sets the traps for signals
to action. If the shell receives one of the signals, the action will be taken.
If the first operand is signal_number instead of action, the built-in resets the traps for
signal_number and signals as if action was -.
When executed with the -p (--print) option or with no operands, the built-in prints
currently set traps to the standard output in a format that can be executed as commands
that restore the current traps. If one or more signals are specified, only those signals
are printed. Otherwise, all signals with non-default actions are printed.
Options
-p, --print
Print current trap settings.
Operands
action
An action that will be taken when signal is received.
If action is a single hyphen (-), the action is reset to the default action that is
defined by the operating system. If action is an empty string, the signal is ignored
on receipt. Otherwise, action is treated as a command string: the string is parsed and
executed as commands when the signal is received. (If a signal is received while a
command is being executed, the action is taken just after the command finishes.)
signal
The number or name of a signal.
If signal is number 0 or name EXIT, it is treated as a special imaginary signal that
is always received when the shell exits. The action set for this signal is taken when
the shell exits normally.
signal_number
This is like signal, but must be a number.
Exit status
The exit status of the trap built-in is zero unless there is any error.
Notes
The trap built-in is a special built-in.
The POSIX standard requires that signal names must be specified without the SIG-prefix,
like INT and QUIT. As an extension, yash accepts SIG-prefixed names like SIGINT and
SIGQUIT and treats signal names case-insensitively.
TRUE BUILT-IN
The true built-in does nothing successfully.
Syntax
• true
Description
The true built-in does nothing. Any command line arguments are ignored.
Exit status
The exit status of the true built-in is zero.
Notes
The true built-in is a semi-special built-in.
The true and colon built-ins have the same effect, but true is a semi-special built-in
while colon is a special.
TYPE BUILT-IN
The type built-in identifies a command.
Syntax
• type [-abefkp] [command...]
Description
The type built-in is equivalent to the command built-in with the -V option.
Notes
The POSIX standard does not define the relation between the type and command built-ins.
The standard does not define options for the type built-in.
At least one command operand must be specified in the POSIXly-correct mode.
TYPESET BUILT-IN
The typeset built-in prints or sets variables or functions.
Syntax
• typeset [-gprxX] [variable[=value]...]
• typeset -f[pr] [function...]
Description
If executed without the -f (--functions) option, the typeset built-in prints or sets
variables to the standard output. Otherwise, it prints or sets functions.
If executed with the -p (--print) option, the built-in prints the variables or functions
specified by operands. Without the option, it sets variables or functions. If no operands
are specified, it prints all existing variables or functions, regardless of whether the -p
(--print) option is specified.
Options
-f, --functions
Print or set functions rather than variables.
-g, --global
When setting a new variable, the variable will be a global variable if this option is
specified. Without this option, the variable would be a local variable.
When printing variables, all existing variables including global variables are printed
if this option is specified. Without this option, only local variables are printed.
-p, --print
Print variables or functions in a form that can be parsed and executed as commands
that will restore the currently set variables or functions.
-r, --readonly
When setting variables or functions, make them read-only.
When printing variables or functions, print read-only variables or functions only.
-x, --export
When setting variables, mark them for export, so that they will be exported to
external commands.
When printing variables, print exported variables only.
-X, --unexport
When setting variables, cancel exportation of the variables.
Operands
variable (without value)
The name of a variable that is to be set or printed.
Without the -p (--print) option, the variable is defined (if not yet defined) but its
value is not set nor changed. Variables that are defined without values are treated as
unset in parameter expansion.
variable=value
The name of a variable and its new value.
The value is assigned to the variable (regardless of the -p (--print) option).
function
The name of an existing function that is to be set or printed.
Exit status
The exit status of the typeset built-in is zero unless there is any error.
Notes
A global variable cannot be newly defined if a local variable has already been defined
with the same name. The local variable will be set regardless of the -g (--global) option.
The POSIX standard does not define the typeset built-in.
The export and readonly built-ins are equivalent to the typeset built-in with the -gx and
-gr options, respectively.
ULIMIT BUILT-IN
The ulimit built-in sets or prints a resource limit.
Syntax
• ulimit -a [-H|-S]
• ulimit [-H|-S] [-efilnqrstuvx] [limit]
Description
The ulimit built-in sets or prints a resource limit.
If executed with the -a (--all) option, the built-in prints the current limits for all
resource types. Otherwise, it sets or prints the limit of a single resource type. The
resource type can be specified by the options listed below. The resource limits will
affect the current shell process and all commands invoked from the shell.
Each resource type has two limit values: the hard and soft limit. You can change a soft
limit freely as long as it does not exceed the hard limit. You can decrease a hard limit
but cannot increase it without a proper permission.
When the -H (--hard) or -S (--soft) option is specified, the built-in sets or prints the
hard or soft limit, respectively. If neither of the options is specified, the built-in
sets both the hard and soft limit or prints the soft limit.
Options
-H, --hard
Set or print a hard limit.
-S, --soft
Set or print a soft limit.
-a, --all
Print all current limit settings.
The following options specify the type of resources. If none of them is specified, -f is
the default. The types of resources that can be set depend on the operating system.
-c, --core
Maximum size of core files created (in 512-byte blocks)
-d, --data
Maximum size of a process’s data segment (in kilobytes)
-e, --nice
Maximum scheduling priority (‘nice’)
-f, --fsize
Maximum size of files created by a process (in 512-byte blocks)
-i, --sigpending
Maximum number of pending signals
-l, --memlock
Maximum memory size that can be locked into RAM (in kilobytes)
-m, --rss
Maximum size of a process’s resident set (in kilobytes)
-n, --nofile
Maximum file descriptor + 1
-q, --msgqueue
Maximum size of POSIX message queues
-r, --rtprio
Maximum real-time scheduling priority
-s, --stack
Maximum size of a process’s stack (in kilobytes)
-t, --cpu
Maximum CPU time that can be used by a process (in seconds)
-u, --nproc
Maximum number of processes for a user
-v, --as
Maximum size of memory used by a process (in kilobytes)
-x, --locks
Maximum number of file locks
Operands
limit
A limit to be set.
The value must be a non-negative integer or one of hard, soft, and unlimited. If value
is hard or soft, the new limit is set to the current hard or soft limit. If limit is
not specified, the current limit is printed.
Exit status
The exit status of the ulimit built-in is zero unless there is any error.
Notes
The POSIX standard defines no options other than -f. It neither defines hard, soft, or
unlimited for limit values.
UMASK BUILT-IN
The umask built-in sets or prints the file mode creation mask.
Syntax
• umask mask
• umask [-S]
Description
If executed without the mask operand, the built-in prints the current file mode creation
mask of the shell to the standard output in a form that can later be used as mask to
restore the current mask.
Otherwise, the built-in sets the file mode creation mask to mask.
Options
-S, --symbolic
Print in the symbolic form instead of the octal integer form.
Operands
mask
The new file mode creation mask either in the symbolic or octal integer form.
Octal integer form
In the octal integer form, the mask is specified as a non-negative octal integer that
is the sum of the following permissions:
0400
read by owner
0200
write by owner
0100
execute/search by owner
0040
read by group
0020
write by group
0010
execute/search by group
0004
read by others
0002
write by others
0001
execute/search by others
Symbolic form
In the symbolic form, the mask is specified as a symbolic expression that denotes
permissions that are not included in the mask.
The entire expression is one or more clauses separated by comma. A clause is a
sequence of whos followed by one or more actions.
A who is one of:
u
owner
g
group
o
others
a
all of owner, group, and others
An empty sequence of whos is equivalent to who a.
An action is an operator followed by permission. An operator is one of:
=
set who's permission to permission
+
add permission to who's permission
-
remove permission from who's permission
and permission is one of:
r
read
w
write
x
execute/search
X
execute/search (only if some user already has execute/search permission)
s
set-user-ID and set-group-ID
u
user’s current permissions
g
group’s current permissions
o
others' current permissions
but more than one of r, w, x, X, and s can be specified after a single operand.
For example, the command umask u=rwx,go+r-w
• unmasks the user’s read, write, and execute/search permissions;
• unmasks the group’s and others' read permission; and
• masks the group’s and others' write permission.
Exit status
The exit status of the umask built-in is zero unless there is any error.
Notes
The umask built-in is a semi-special built-in.
The POSIX standard does not require the default output format (used when the -S option is
not specified) to be the octal integer form.
UNALIAS BUILT-IN
The unalias built-in undefines aliases.
Syntax
• unalias name...
• unalias -a
Description
The unalias built-in removes the definition of the aliases specified by operands.
Options
-a, --all
Undefine all aliases.
Operands
name
The name of an alias to be undefined.
Exit status
The exit status of the unalias built-in is zero unless there is any error. It is an error
to specify the name of a non-existing alias as name.
Notes
The unalias built-in is a semi-special built-in.
UNSET BUILT-IN
The unset built-in undefines variables or functions.
Syntax
• unset [-fv] [name...]
Description
The unset built-in removes the definition of the variables or functions specified by
operands.
It is not an error if any of the specified variables or functions do not exist; they are
silently ignored.
Options
-f, --functions
Undefine functions.
-v, --variables
Undefine variables.
These options are mutually exclusive: only the last specified one is effective. If neither
is specified, -v is assumed.
Operands
name
The name of a variable or function to be undefined.
Exit status
The exit status of the unset built-in is zero unless there is any error.
Notes
The unset built-in is a special built-in.
Although yash does not do so, the POSIX standard allows removing a function if neither of
the -f and -v options is specified and the specified variable does not exist.
At least one name operand must be specified in the POSIXly-correct mode.
WAIT BUILT-IN
The wait built-in waits for jobs to terminate.
Syntax
• wait [job...]
Description
The wait built-in waits for background jobs to terminate. If job control is enabled,
stopped jobs are considered as terminated.
The built-in can be used to wait for asynchronous commands if job control is disabled.
If the shell receives a signal while the built-in is waiting and if a trap has been set
for the signal, then the trap is executed and the built-in immediately finishes (without
waiting for the jobs). If the shell receives a SIGINT signal when job control is enabled,
the built-in aborts waiting.
Operands
job
The job ID of the job or the process ID of a process in the job.
If no jobs are specified, the built-in waits for all existing jobs.
If the specified job does not exist, the job is considered to have terminated with the
exit status of 127.
Exit status
If no jobs were specified and the built-in successfully waited for all the jobs, the exit
status is zero. If one or more jobs were specified, the exit status is that of the last
job.
If the built-in was aborted by a signal, the exit status is an integer (> 128) that
denotes the signal. If there was any other error, the exit status is between 1 and 126
(inclusive).
Notes
The wait built-in is a semi-special built-in.
The process ID of the last process of a job can be obtained by the ! special parameter.
You can use the jobs built-in as well to obtain process IDs of job processes.
AUTHOR
Yuki Watanabe <magicant@users.sourceforge.jp>
Author.
2.35 2013-06-08 YASH(1)