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-.\"-
-.\" Copyright (c) 1991, 1993
-.\"	The Regents of the University of California.  All rights reserved.
-.\"
-.\" This code is derived from software contributed to Berkeley by
-.\" Kenneth Almquist.
-.\"
-.\" Redistribution and use in source and binary forms, with or without
-.\" modification, are permitted provided that the following conditions
-.\" are met:
-.\" 1. Redistributions of source code must retain the above copyright
-.\"    notice, this list of conditions and the following disclaimer.
-.\" 2. Redistributions in binary form must reproduce the above copyright
-.\"    notice, this list of conditions and the following disclaimer in the
-.\"    documentation and/or other materials provided with the distribution.
-.\" 3. Neither the name of the University nor the names of its contributors
-.\"    may be used to endorse or promote products derived from this software
-.\"    without specific prior written permission.
-.\"
-.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
-.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
-.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
-.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
-.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
-.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
-.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
-.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
-.\" SUCH DAMAGE.
-.\"
-.\"	from: @(#)sh.1	8.6 (Berkeley) 5/4/95
-.\" $FreeBSD: releng/12.0/bin/sh/sh.1 336483 2018-07-19 13:09:29Z 0mp $
-.\"
-.Dd July 19, 2018
-.Dt SH 1
-.Os
-.Sh NAME
-.Nm sh
-.Nd command interpreter (shell)
-.Sh SYNOPSIS
-.Nm
-.Op Fl /+abCEefhIimnPpTuVvx
-.Op Fl /+o Ar longname
-.Oo
-.Ar script
-.Op Ar arg ...
-.Oc
-.Nm
-.Op Fl /+abCEefhIimnPpTuVvx
-.Op Fl /+o Ar longname
-.Fl c Ar string
-.Oo
-.Ar name
-.Op Ar arg ...
-.Oc
-.Nm
-.Op Fl /+abCEefhIimnPpTuVvx
-.Op Fl /+o Ar longname
-.Fl s
-.Op Ar arg ...
-.Sh DESCRIPTION
-The
-.Nm
-utility is the standard command interpreter for the system.
-The current version of
-.Nm
-is close to the
-.St -p1003.1
-specification for the shell.
-It only supports features
-designated by POSIX,
-plus a few Berkeley extensions.
-This man page is not intended to be a tutorial nor a complete
-specification of the shell.
-.Ss Overview
-The shell is a command that reads lines from
-either a file or the terminal, interprets them, and
-generally executes other commands.
-It is the program that is started when a user logs into the system,
-although a user can select a different shell with the
-.Xr chsh 1
-command.
-The shell
-implements a language that has flow control constructs,
-a macro facility that provides a variety of features in
-addition to data storage, along with built-in history and line
-editing capabilities.
-It incorporates many features to
-aid interactive use and has the advantage that the interpretative
-language is common to both interactive and non-interactive
-use (shell scripts).
-That is, commands can be typed directly
-to the running shell or can be put into a file,
-which can be executed directly by the shell.
-.Ss Invocation
-.\"
-.\" XXX This next sentence is incredibly confusing.
-.\"
-If no arguments are present and if the standard input of the shell
-is connected to a terminal
-(or if the
-.Fl i
-option is set),
-the shell is considered an interactive shell.
-An interactive shell
-generally prompts before each command and handles programming
-and command errors differently (as described below).
-When first starting, the shell inspects argument 0, and
-if it begins with a dash
-.Pq Ql - ,
-the shell is also considered a login shell.
-This is normally done automatically by the system
-when the user first logs in.
-A login shell first reads commands
-from the files
-.Pa /etc/profile
-and then
-.Pa .profile
-in a user's home directory,
-if they exist.
-If the environment variable
-.Ev ENV
-is set on entry to a shell, or is set in the
-.Pa .profile
-of a login shell, the shell then subjects its value to parameter expansion
-and arithmetic expansion and reads commands from the named file.
-Therefore, a user should place commands that are to be executed only
-at login time in the
-.Pa .profile
-file, and commands that are executed for every shell inside the
-.Ev ENV
-file.
-The user can set the
-.Ev ENV
-variable to some file by placing the following line in the file
-.Pa .profile
-in the home directory,
-substituting for
-.Pa .shrc
-the filename desired:
-.Pp
-.Dl "ENV=$HOME/.shrc; export ENV"
-.Pp
-The first non-option argument specified on the command line
-will be treated as the
-name of a file from which to read commands (a shell script), and
-the remaining arguments are set as the positional parameters
-of the shell
-.Li ( $1 , $2 ,
-etc.).
-Otherwise, the shell reads commands
-from its standard input.
-.Pp
-Unlike older versions of
-.Nm
-the
-.Ev ENV
-script is only sourced on invocation of interactive shells.
-This
-closes a well-known, and sometimes easily exploitable security
-hole related to poorly thought out
-.Ev ENV
-scripts.
-.Ss Argument List Processing
-All of the single letter options to
-.Nm
-have a corresponding long name,
-with the exception of
-.Fl c
-and
-.Fl /+o .
-These long names are provided next to the single letter options
-in the descriptions below.
-The long name for an option may be specified as an argument to the
-.Fl /+o
-option of
-.Nm .
-Once the shell is running,
-the long name for an option may be specified as an argument to the
-.Fl /+o
-option of the
-.Ic set
-built-in command
-(described later in the section called
-.Sx Built-in Commands ) .
-Introducing an option with a dash
-.Pq Ql -
-enables the option,
-while using a plus
-.Pq Ql +
-disables the option.
-A
-.Dq Li --
-or plain
-.Ql -
-will stop option processing and will force the remaining
-words on the command line to be treated as arguments.
-The
-.Fl /+o
-and
-.Fl c
-options do not have long names.
-They take arguments and are described after the single letter options.
-.Bl -tag -width indent
-.It Fl a Li allexport
-Flag variables for export when assignments are made to them.
-.It Fl b Li notify
-Enable asynchronous notification of background job
-completion.
-(UNIMPLEMENTED)
-.It Fl C Li noclobber
-Do not overwrite existing files with
-.Ql > .
-.It Fl E Li emacs
-Enable the built-in
-.Xr emacs 1
-command line editor (disables the
-.Fl V
-option if it has been set;
-set automatically when interactive on terminals).
-.It Fl e Li errexit
-Exit immediately if any untested command fails in non-interactive mode.
-The exit status of a command is considered to be
-explicitly tested if the command is part of the list used to control
-an
-.Ic if , elif , while ,
-or
-.Ic until ;
-if the command is the left
-hand operand of an
-.Dq Li &&
-or
-.Dq Li ||
-operator; or if the command is a pipeline preceded by the
-.Ic !\&
-keyword.
-If a shell function is executed and its exit status is explicitly
-tested, all commands of the function are considered to be tested as
-well.
-.Pp
-It is recommended to check for failures explicitly
-instead of relying on
-.Fl e
-because it tends to behave in unexpected ways,
-particularly in larger scripts.
-.It Fl f Li noglob
-Disable pathname expansion.
-.It Fl h Li trackall
-A do-nothing option for POSIX compliance.
-.It Fl I Li ignoreeof
-Ignore
-.Dv EOF Ap s
-from input when in interactive mode.
-.It Fl i Li interactive
-Force the shell to behave interactively.
-.It Fl m Li monitor
-Turn on job control (set automatically when interactive).
-A new process group is created for each pipeline (called a job).
-It is possible to suspend jobs or to have them run in the foreground or
-in the background.
-In a non-interactive shell,
-this option can be set even if no terminal is available
-and is useful to place processes in separate process groups.
-.It Fl n Li noexec
-If not interactive, read commands but do not
-execute them.
-This is useful for checking the
-syntax of shell scripts.
-.It Fl P Li physical
-Change the default for the
-.Ic cd
-and
-.Ic pwd
-commands from
-.Fl L
-(logical directory layout)
-to
-.Fl P
-(physical directory layout).
-.It Fl p Li privileged
-Turn on privileged mode.
-This mode is enabled on startup
-if either the effective user or group ID is not equal to the
-real user or group ID.
-Turning this mode off sets the
-effective user and group IDs to the real user and group IDs.
-When this mode is enabled for interactive shells, the file
-.Pa /etc/suid_profile
-is sourced instead of
-.Pa ~/.profile
-after
-.Pa /etc/profile
-is sourced, and the contents of the
-.Ev ENV
-variable are ignored.
-.It Fl s Li stdin
-Read commands from standard input (set automatically
-if no file arguments are present).
-This option has
-no effect when set after the shell has already started
-running (i.e., when set with the
-.Ic set
-command).
-.It Fl T Li trapsasync
-When waiting for a child, execute traps immediately.
-If this option is not set,
-traps are executed after the child exits,
-as specified in
-.St -p1003.2 .
-This nonstandard option is useful for putting guarding shells around
-children that block signals.
-The surrounding shell may kill the child
-or it may just return control to the tty and leave the child alone,
-like this:
-.Bd -literal -offset indent
-sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
-.Ed
-.It Fl u Li nounset
-Write a message to standard error when attempting
-to expand a variable, a positional parameter or
-the special parameter
-.Va \&!
-that is not set, and if the
-shell is not interactive, exit immediately.
-.It Fl V Li vi
-Enable the built-in
-.Xr vi 1
-command line editor (disables
-.Fl E
-if it has been set).
-.It Fl v Li verbose
-The shell writes its input to standard error
-as it is read.
-Useful for debugging.
-.It Fl x Li xtrace
-Write each command
-(preceded by the value of the
-.Va PS4
-variable subjected to parameter expansion and arithmetic expansion)
-to standard error before it is executed.
-Useful for debugging.
-.It Li nolog
-Another do-nothing option for POSIX compliance.
-It only has a long name.
-.El
-.Pp
-The
-.Fl c
-option causes the commands to be read from the
-.Ar string
-operand instead of from the standard input.
-Keep in mind that this option only accepts a single string as its
-argument, hence multi-word strings must be quoted.
-.Pp
-The
-.Fl /+o
-option takes as its only argument the long name of an option
-to be enabled or disabled.
-For example, the following two invocations of
-.Nm
-both enable the built-in
-.Xr emacs 1
-command line editor:
-.Bd -literal -offset indent
-set -E
-set -o emacs
-.Ed
-.Pp
-If used without an argument, the
-.Fl o
-option displays the current option settings in a human-readable format.
-If
-.Cm +o
-is used without an argument, the current option settings are output
-in a format suitable for re-input into the shell.
-.Ss Lexical Structure
-The shell reads input in terms of lines from a file and breaks
-it up into words at whitespace (blanks and tabs), and at
-certain sequences of
-characters called
-.Dq operators ,
-which are special to the shell.
-There are two types of operators: control operators and
-redirection operators (their meaning is discussed later).
-The following is a list of valid operators:
-.Bl -tag -width indent
-.It Control operators:
-.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
-.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
-.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
-.El
-.It Redirection operators:
-.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
-.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
-.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
-.El
-.El
-.Pp
-The character
-.Ql #
-introduces a comment if used at the beginning of a word.
-The word starting with
-.Ql #
-and the rest of the line are ignored.
-.Pp
-ASCII
-.Dv NUL
-characters (character code 0) are not allowed in shell input.
-.Ss Quoting
-Quoting is used to remove the special meaning of certain characters
-or words to the shell, such as operators, whitespace, keywords,
-or alias names.
-.Pp
-There are four types of quoting: matched single quotes,
-dollar-single quotes,
-matched double quotes, and backslash.
-.Bl -tag -width indent
-.It Single Quotes
-Enclosing characters in single quotes preserves the literal
-meaning of all the characters (except single quotes, making
-it impossible to put single-quotes in a single-quoted string).
-.It Dollar-Single Quotes
-Enclosing characters between
-.Li $'
-and
-.Li '
-preserves the literal meaning of all characters
-except backslashes and single quotes.
-A backslash introduces a C-style escape sequence:
-.Bl -tag -width xUnnnnnnnn
-.It \ea
-Alert (ring the terminal bell)
-.It \eb
-Backspace
-.It \ec Ns Ar c
-The control character denoted by
-.Li ^ Ns Ar c
-in
-.Xr stty 1 .
-If
-.Ar c
-is a backslash, it must be doubled.
-.It \ee
-The ESC character (ASCII 0x1b)
-.It \ef
-Formfeed
-.It \en
-Newline
-.It \er
-Carriage return
-.It \et
-Horizontal tab
-.It \ev
-Vertical tab
-.It \e\e
-Literal backslash
-.It \e\&'
-Literal single-quote
-.It \e\&"
-Literal double-quote
-.It \e Ns Ar nnn
-The byte whose octal value is
-.Ar nnn
-(one to three digits)
-.It \ex Ns Ar nn
-The byte whose hexadecimal value is
-.Ar nn
-(one or more digits only the last two of which are used)
-.It \eu Ns Ar nnnn
-The Unicode code point
-.Ar nnnn
-(four hexadecimal digits)
-.It \eU Ns Ar nnnnnnnn
-The Unicode code point
-.Ar nnnnnnnn
-(eight hexadecimal digits)
-.El
-.Pp
-The sequences for Unicode code points are currently only useful with
-UTF-8 locales.
-They reject code point 0 and UTF-16 surrogates.
-.Pp
-If an escape sequence would produce a byte with value 0,
-that byte and the rest of the string until the matching single-quote
-are ignored.
-.Pp
-Any other string starting with a backslash is an error.
-.It Double Quotes
-Enclosing characters within double quotes preserves the literal
-meaning of all characters except dollar sign
-.Pq Ql $ ,
-backquote
-.Pq Ql ` ,
-and backslash
-.Pq Ql \e .
-The backslash inside double quotes is historically weird.
-It remains literal unless it precedes the following characters,
-which it serves to quote:
-.Pp
-.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
-.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
-.El
-.It Backslash
-A backslash preserves the literal meaning of the following
-character, with the exception of the newline character
-.Pq Ql \en .
-A backslash preceding a newline is treated as a line continuation.
-.El
-.Ss Keywords
-Keywords or reserved words are words that have special meaning to the
-shell and are recognized at the beginning of a line and
-after a control operator.
-The following are keywords:
-.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
-.It Li \&! Ta { Ta } Ta Ic case Ta Ic do
-.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
-.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
-.El
-.Ss Aliases
-An alias is a name and corresponding value set using the
-.Ic alias
-built-in command.
-Wherever the command word of a simple command may occur,
-and after checking for keywords if a keyword may occur, the shell
-checks the word to see if it matches an alias.
-If it does, it replaces it in the input stream with its value.
-For example, if there is an alias called
-.Dq Li lf
-with the value
-.Dq Li "ls -F" ,
-then the input
-.Pp
-.Dl "lf foobar"
-.Pp
-would become
-.Pp
-.Dl "ls -F foobar"
-.Pp
-Aliases are also recognized after an alias
-whose value ends with a space or tab.
-For example, if there is also an alias called
-.Dq Li nohup
-with the value
-.Dq Li "nohup " ,
-then the input
-.Pp
-.Dl "nohup lf foobar"
-.Pp
-would become
-.Pp
-.Dl "nohup ls -F foobar"
-.Pp
-Aliases provide a convenient way for naive users to
-create shorthands for commands without having to learn how
-to create functions with arguments.
-Using aliases in scripts is discouraged
-because the command that defines them must be executed
-before the code that uses them is parsed.
-This is fragile and not portable.
-.Pp
-An alias name may be escaped in a command line, so that it is not
-replaced by its alias value, by using quoting characters within or
-adjacent to the alias name.
-This is most often done by prefixing
-an alias name with a backslash to execute a function, built-in, or
-normal program with the same name.
-See the
-.Sx Quoting
-subsection.
-.Ss Commands
-The shell interprets the words it reads according to a
-language, the specification of which is outside the scope
-of this man page (refer to the BNF in the
-.St -p1003.2
-document).
-Essentially though, a line is read and if
-the first word of the line (or after a control operator)
-is not a keyword, then the shell has recognized a
-simple command.
-Otherwise, a complex command or some
-other special construct may have been recognized.
-.Ss Simple Commands
-If a simple command has been recognized, the shell performs
-the following actions:
-.Bl -enum
-.It
-Leading words of the form
-.Dq Li name=value
-are stripped off and assigned to the environment of
-the simple command
-(they do not affect expansions).
-Redirection operators and
-their arguments (as described below) are stripped
-off and saved for processing.
-.It
-The remaining words are expanded as described in
-the section called
-.Sx Word Expansions ,
-and the first remaining word is considered the command
-name and the command is located.
-The remaining
-words are considered the arguments of the command.
-If no command name resulted, then the
-.Dq Li name=value
-variable assignments recognized in 1) affect the
-current shell.
-.It
-Redirections are performed as described in
-the next section.
-.El
-.Ss Redirections
-Redirections are used to change where a command reads its input
-or sends its output.
-In general, redirections open, close, or
-duplicate an existing reference to a file.
-The overall format
-used for redirection is:
-.Pp
-.D1 Oo Ar n Oc Ar redir-op file
-.Pp
-The
-.Ar redir-op
-is one of the redirection operators mentioned
-previously.
-The following gives some examples of how these
-operators can be used.
-Note that stdin and stdout are commonly used abbreviations
-for standard input and standard output respectively.
-.Bl -tag -width "1234567890XX" -offset indent
-.It Oo Ar n Oc Ns Li > Ar file
-redirect stdout (or file descriptor
-.Ar n )
-to
-.Ar file
-.It Oo Ar n Oc Ns Li >| Ar file
-same as above, but override the
-.Fl C
-option
-.It Oo Ar n Oc Ns Li >> Ar file
-append stdout (or file descriptor
-.Ar n )
-to
-.Ar file
-.It Oo Ar n Oc Ns Li < Ar file
-redirect stdin (or file descriptor
-.Ar n )
-from
-.Ar file
-.It Oo Ar n Oc Ns Li <> Ar file
-redirect stdin (or file descriptor
-.Ar n )
-to and from
-.Ar file
-.It Oo Ar n1 Oc Ns Li <& Ns Ar n2
-duplicate stdin (or file descriptor
-.Ar n1 )
-from file descriptor
-.Ar n2
-.It Oo Ar n Oc Ns Li <&-
-close stdin (or file descriptor
-.Ar n )
-.It Oo Ar n1 Oc Ns Li >& Ns Ar n2
-duplicate stdout (or file descriptor
-.Ar n1 )
-to file descriptor
-.Ar n2
-.It Oo Ar n Oc Ns Li >&-
-close stdout (or file descriptor
-.Ar n )
-.El
-.Pp
-The following redirection is often called a
-.Dq here-document .
-.Bd -unfilled -offset indent
-.Oo Ar n Oc Ns Li << Ar delimiter
-.Ar here-doc-text
-.Ar ...
-.Ar delimiter
-.Ed
-.Pp
-All the text on successive lines up to the delimiter is
-saved away and made available to the command on standard
-input, or file descriptor
-.Ar n
-if it is specified.
-If the
-.Ar delimiter
-as specified on the initial line is quoted, then the
-.Ar here-doc-text
-is treated literally, otherwise the text is subjected to
-parameter expansion, command substitution, and arithmetic
-expansion (as described in the section on
-.Sx Word Expansions ) .
-If the operator is
-.Dq Li <<-
-instead of
-.Dq Li << ,
-then leading tabs
-in the
-.Ar here-doc-text
-are stripped.
-.Ss Search and Execution
-There are three types of commands: shell functions,
-built-in commands, and normal programs.
-The command is searched for (by name) in that order.
-The three types of commands are all executed in a different way.
-.Pp
-When a shell function is executed, all of the shell positional
-parameters (except
-.Li $0 ,
-which remains unchanged) are
-set to the arguments of the shell function.
-The variables which are explicitly placed in the environment of
-the command (by placing assignments to them before the
-function name) are made local to the function and are set
-to the values given.
-Then the command given in the function definition is executed.
-The positional parameters are restored to their original values
-when the command completes.
-This all occurs within the current shell.
-.Pp
-Shell built-in commands are executed internally to the shell, without
-spawning a new process.
-There are two kinds of built-in commands: regular and special.
-Assignments before special builtins persist after they finish
-executing and assignment errors, redirection errors and certain
-operand errors cause a script to be aborted.
-Special builtins cannot be overridden with a function.
-Both regular and special builtins can affect the shell in ways
-normal programs cannot.
-.Pp
-Otherwise, if the command name does not match a function
-or built-in command, the command is searched for as a normal
-program in the file system (as described in the next section).
-When a normal program is executed, the shell runs the program,
-passing the arguments and the environment to the program.
-If the program is not a normal executable file
-(i.e., if it does not begin with the
-.Dq "magic number"
-whose ASCII representation is
-.Dq Li #! ,
-resulting in an
-.Er ENOEXEC
-return value from
-.Xr execve 2 )
-but appears to be a text file,
-the shell will run a new instance of
-.Nm
-to interpret it.
-.Pp
-Note that previous versions of this document
-and the source code itself misleadingly and sporadically
-refer to a shell script without a magic number
-as a
-.Dq "shell procedure" .
-.Ss Path Search
-When locating a command, the shell first looks to see if
-it has a shell function by that name.
-Then it looks for a
-built-in command by that name.
-If a built-in command is not found,
-one of two things happen:
-.Bl -enum
-.It
-Command names containing a slash are simply executed without
-performing any searches.
-.It
-The shell searches each entry in the
-.Va PATH
-variable
-in turn for the command.
-The value of the
-.Va PATH
-variable should be a series of
-entries separated by colons.
-Each entry consists of a
-directory name.
-The current directory
-may be indicated implicitly by an empty directory name,
-or explicitly by a single period.
-.El
-.Ss Command Exit Status
-Each command has an exit status that can influence the behavior
-of other shell commands.
-The paradigm is that a command exits
-with zero for normal or success, and non-zero for failure,
-error, or a false indication.
-The man page for each command
-should indicate the various exit codes and what they mean.
-Additionally, the built-in commands return exit codes, as does
-an executed shell function.
-.Pp
-If a command is terminated by a signal, its exit status is greater than 128.
-The signal name can be found by passing the exit status to
-.Li kill -l .
-.Pp
-If there is no command word,
-the exit status is the exit status of the last command substitution executed,
-or zero if the command does not contain any command substitutions.
-.Ss Complex Commands
-Complex commands are combinations of simple commands
-with control operators or keywords, together creating a larger complex
-command.
-More generally, a command is one of the following:
-.Bl -item -offset indent
-.It
-simple command
-.It
-pipeline
-.It
-list or compound-list
-.It
-compound command
-.It
-function definition
-.El
-.Pp
-Unless otherwise stated, the exit status of a command is
-that of the last simple command executed by the command,
-or zero if no simple command was executed.
-.Ss Pipelines
-A pipeline is a sequence of one or more commands separated
-by the control operator
-.Ql \&| .
-The standard output of all but
-the last command is connected to the standard input
-of the next command.
-The standard output of the last
-command is inherited from the shell, as usual.
-.Pp
-The format for a pipeline is:
-.Pp
-.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
-.Pp
-The standard output of
-.Ar command1
-is connected to the standard input of
-.Ar command2 .
-The standard input, standard output, or
-both of a command is considered to be assigned by the
-pipeline before any redirection specified by redirection
-operators that are part of the command.
-.Pp
-Note that unlike some other shells,
-.Nm
-executes each process in a pipeline with more than one command
-in a subshell environment and as a child of the
-.Nm
-process.
-.Pp
-If the pipeline is not in the background (discussed later),
-the shell waits for all commands to complete.
-.Pp
-If the keyword
-.Ic !\&
-does not precede the pipeline, the
-exit status is the exit status of the last command specified
-in the pipeline.
-Otherwise, the exit status is the logical
-NOT of the exit status of the last command.
-That is, if
-the last command returns zero, the exit status is 1; if
-the last command returns greater than zero, the exit status
-is zero.
-.Pp
-Because pipeline assignment of standard input or standard
-output or both takes place before redirection, it can be
-modified by redirection.
-For example:
-.Pp
-.Dl "command1 2>&1 | command2"
-.Pp
-sends both the standard output and standard error of
-.Ar command1
-to the standard input of
-.Ar command2 .
-.Pp
-A
-.Ql \&;
-or newline terminator causes the preceding
-AND-OR-list
-(described below in the section called
-.Sx Short-Circuit List Operators )
-to be executed sequentially;
-an
-.Ql &
-causes asynchronous execution of the preceding AND-OR-list.
-.Ss Background Commands (&)
-If a command is terminated by the control operator ampersand
-.Pq Ql & ,
-the shell executes the command in a subshell environment (see
-.Sx Grouping Commands Together
-below) and asynchronously;
-the shell does not wait for the command to finish
-before executing the next command.
-.Pp
-The format for running a command in background is:
-.Pp
-.D1 Ar command1 Li & Op Ar command2 Li & Ar ...
-.Pp
-If the shell is not interactive, the standard input of an
-asynchronous command is set to
-.Pa /dev/null .
-.Pp
-The exit status is zero.
-.Ss Lists (Generally Speaking)
-A list is a sequence of zero or more commands separated by
-newlines, semicolons, or ampersands,
-and optionally terminated by one of these three characters.
-The commands in a
-list are executed in the order they are written.
-If command is followed by an ampersand, the shell starts the
-command and immediately proceeds onto the next command;
-otherwise it waits for the command to terminate before
-proceeding to the next one.
-.Ss Short-Circuit List Operators
-.Dq Li &&
-and
-.Dq Li ||
-are AND-OR list operators.
-.Dq Li &&
-executes the first command, and then executes the second command
-if the exit status of the first command is zero.
-.Dq Li ||
-is similar, but executes the second command if the exit
-status of the first command is nonzero.
-.Dq Li &&
-and
-.Dq Li ||
-both have the same priority.
-.Ss Flow-Control Constructs (if, while, for, case)
-The syntax of the
-.Ic if
-command is:
-.Bd -unfilled -offset indent -compact
-.Ic if Ar list
-.Ic then Ar list
-.Oo Ic elif Ar list
-.Ic then Ar list Oc Ar ...
-.Op Ic else Ar list
-.Ic fi
-.Ed
-.Pp
-The exit status is that of selected
-.Ic then
-or
-.Ic else
-list,
-or zero if no list was selected.
-.Pp
-The syntax of the
-.Ic while
-command is:
-.Bd -unfilled -offset indent -compact
-.Ic while Ar list
-.Ic do Ar list
-.Ic done
-.Ed
-.Pp
-The two lists are executed repeatedly while the exit status of the
-first list is zero.
-The
-.Ic until
-command is similar, but has the word
-.Ic until
-in place of
-.Ic while ,
-which causes it to
-repeat until the exit status of the first list is zero.
-.Pp
-The exit status is that of the last execution of the second list,
-or zero if it was never executed.
-.Pp
-The syntax of the
-.Ic for
-command is:
-.Bd -unfilled -offset indent -compact
-.Ic for Ar variable Op Ic in Ar word ...
-.Ic do Ar list
-.Ic done
-.Ed
-.Pp
-If
-.Ic in
-and the following words are omitted,
-.Ic in Li \&"$@\&"
-is used instead.
-The words are expanded, and then the list is executed
-repeatedly with the variable set to each word in turn.
-The
-.Ic do
-and
-.Ic done
-commands may be replaced with
-.Ql {
-and
-.Ql } .
-.Pp
-The syntax of the
-.Ic break
-and
-.Ic continue
-commands is:
-.D1 Ic break Op Ar num
-.D1 Ic continue Op Ar num
-.Pp
-The
-.Ic break
-command terminates the
-.Ar num
-innermost
-.Ic for
-or
-.Ic while
-loops.
-The
-.Ic continue
-command continues with the next iteration of the innermost loop.
-These are implemented as special built-in commands.
-.Pp
-The syntax of the
-.Ic case
-command is:
-.Bd -unfilled -offset indent -compact
-.Ic case Ar word Ic in
-.Ar pattern ) Ar list Li ;;
-.Ar ...
-.Ic esac
-.Ed
-.Pp
-The pattern can actually be one or more patterns
-(see
-.Sx Shell Patterns
-described later),
-separated by
-.Ql \&|
-characters.
-Tilde expansion, parameter expansion, command substitution,
-arithmetic expansion and quote removal are applied to the word.
-Then, each pattern is expanded in turn using tilde expansion,
-parameter expansion, command substitution and arithmetic expansion and
-the expanded form of the word is checked against it.
-If a match is found, the corresponding list is executed.
-If the selected list is terminated by the control operator
-.Ql ;&
-instead of
-.Ql ;; ,
-execution continues with the next list,
-continuing until a list terminated with
-.Ql ;;
-or the end of the
-.Ic case
-command.
-.Ss Grouping Commands Together
-Commands may be grouped by writing either
-.Pp
-.Sm off
-.Bd -literal -offset -ident
-.Po Ar list Pc
-.Ed
-.Sm on
-.Pp
-or
-.Bd -literal -offset -ident
-.No { Ar list ; }
-.Ed
-.Pp
-The first form executes the commands in a subshell environment.
-A subshell environment has its own copy of:
-.Bl -enum
-.It
-The current working directory as set by
-.Ic cd .
-.It
-The file creation mask as set by
-.Ic umask .
-.It
-Resource limits as set by
-.Ic ulimit .
-.It
-References to open files.
-.It
-Traps as set by
-.Ic trap .
-.It
-Known jobs.
-.It
-Positional parameters and variables.
-.It
-Shell options.
-.It
-Shell functions.
-.It
-Shell aliases.
-.El
-.Pp
-These are copied from the parent shell environment,
-except that trapped (but not ignored) signals are reset to the default action
-and known jobs are cleared.
-Any changes do not affect the parent shell environment.
-.Pp
-A subshell environment may be implemented as a child process or differently.
-If job control is enabled in an interactive shell,
-commands grouped in parentheses can be suspended and continued as a unit.
-.Pp
-For compatibility with other shells,
-two open parentheses in sequence should be separated by whitespace.
-.Pp
-The second form never forks another shell,
-so it is slightly more efficient.
-Grouping commands together this way allows the user to
-redirect their output as though they were one program:
-.Bd -literal -offset indent
-{ echo -n "hello"; echo " world"; } > greeting
-.Ed
-.Ss Functions
-The syntax of a function definition is
-.Pp
-.D1 Ar name Li \&( \&) Ar command
-.Pp
-A function definition is an executable statement; when
-executed it installs a function named
-.Ar name
-and returns an
-exit status of zero.
-The
-.Ar command
-is normally a list
-enclosed between
-.Ql {
-and
-.Ql } .
-.Pp
-Variables may be declared to be local to a function by
-using the
-.Ic local
-command.
-This should appear as the first statement of a function,
-and the syntax is:
-.Pp
-.D1 Ic local Oo Ar variable ... Oc Op Fl
-.Pp
-The
-.Ic local
-command is implemented as a built-in command.
-The exit status is zero
-unless the command is not in a function or a variable name is invalid.
-.Pp
-When a variable is made local, it inherits the initial
-value and exported and readonly flags from the variable
-with the same name in the surrounding scope, if there is
-one.
-Otherwise, the variable is initially unset.
-The shell
-uses dynamic scoping, so that if the variable
-.Va x
-is made local to function
-.Em f ,
-which then calls function
-.Em g ,
-references to the variable
-.Va x
-made inside
-.Em g
-will refer to the variable
-.Va x
-declared inside
-.Em f ,
-not to the global variable named
-.Va x .
-.Pp
-The only special parameter that can be made local is
-.Ql - .
-Making
-.Ql -
-local causes any shell options
-(including those that only have long names)
-that are
-changed via the
-.Ic set
-command inside the function to be
-restored to their original values when the function
-returns.
-.Pp
-The syntax of the
-.Ic return
-command is
-.Pp
-.D1 Ic return Op Ar exitstatus
-.Pp
-It terminates the current executional scope, returning from the closest
-nested function or sourced script;
-if no function or sourced script is being executed,
-it exits the shell instance.
-The
-.Ic return
-command is implemented as a special built-in command.
-.Ss Variables and Parameters
-The shell maintains a set of parameters.
-A parameter
-denoted by a name
-(consisting solely
-of alphabetics, numerics, and underscores,
-and starting with an alphabetic or an underscore)
-is called a variable.
-When starting up,
-the shell turns all environment variables with valid names into shell
-variables.
-New variables can be set using the form
-.Pp
-.D1 Ar name Ns = Ns Ar value
-.Pp
-A parameter can also be denoted by a number
-or a special character as explained below.
-.Pp
-Assignments are expanded differently from other words:
-tilde expansion is also performed after the equals sign and after any colon
-and usernames are also terminated by colons,
-and field splitting and pathname expansion are not performed.
-.Pp
-This special expansion applies not only to assignments that form a simple
-command by themselves or precede a command word,
-but also to words passed to the
-.Ic export ,
-.Ic local
-or
-.Ic readonly
-built-in commands that have this form.
-For this, the builtin's name must be literal
-(not the result of an expansion)
-and may optionally be preceded by one or more literal instances of
-.Ic command
-without options.
-.Ss Positional Parameters
-A positional parameter is a parameter denoted by a number greater than zero.
-The shell sets these initially to the values of its command line
-arguments that follow the name of the shell script.
-The
-.Ic set
-built-in command can also be used to set or reset them.
-.Ss Special Parameters
-Special parameters are parameters denoted by a single special character
-or the digit zero.
-They are shown in the following list, exactly as they would appear in input
-typed by the user or in the source of a shell script.
-.Bl -hang
-.It Li $*
-Expands to the positional parameters, starting from one.
-When
-the expansion occurs within a double-quoted string
-it expands to a single field with the value of each parameter
-separated by the first character of the
-.Va IFS
-variable,
-or by a space if
-.Va IFS
-is unset.
-.It Li $@
-Expands to the positional parameters, starting from one.
-When
-the expansion occurs within double-quotes, each positional
-parameter expands as a separate argument.
-If there are no positional parameters, the
-expansion of
-.Li @
-generates zero arguments, even when
-.Li @
-is double-quoted.
-What this basically means, for example, is
-if
-.Li $1
-is
-.Dq Li abc
-and
-.Li $2
-is
-.Dq Li "def ghi" ,
-then
-.Li \&"$@\&"
-expands to
-the two arguments:
-.Bd -literal -offset indent
-"abc"   "def ghi"
-.Ed
-.It Li $#
-Expands to the number of positional parameters.
-.It Li $?
-Expands to the exit status of the most recent pipeline.
-.It Li $-
-(hyphen) Expands to the current option flags (the single-letter
-option names concatenated into a string) as specified on
-invocation, by the
-.Ic set
-built-in command, or implicitly
-by the shell.
-.It Li $$
-Expands to the process ID of the invoked shell.
-A subshell
-retains the same value of
-.Va $
-as its parent.
-.It Li $!
-Expands to the process ID of the most recent background
-command executed from the current shell.
-For a
-pipeline, the process ID is that of the last command in the
-pipeline.
-If this parameter is referenced, the shell will remember
-the process ID and its exit status until the
-.Ic wait
-built-in command reports completion of the process.
-.It Li $0
-(zero) Expands to the name of the shell script if passed on the command line,
-the
-.Ar name
-operand if given (with
-.Fl c )
-or otherwise argument 0 passed to the shell.
-.El
-.Ss Special Variables
-The following variables are set by the shell or
-have special meaning to it:
-.Bl -tag -width ".Va HISTSIZE"
-.It Va CDPATH
-The search path used with the
-.Ic cd
-built-in.
-.It Va EDITOR
-The fallback editor used with the
-.Ic fc
-built-in.
-If not set, the default editor is
-.Xr ed 1 .
-.It Va FCEDIT
-The default editor used with the
-.Ic fc
-built-in.
-.It Va HISTSIZE
-The number of previous commands that are accessible.
-.It Va HOME
-The user's home directory,
-used in tilde expansion and as a default directory for the
-.Ic cd
-built-in.
-.It Va IFS
-Input Field Separators.
-This is initialized at startup to
-.Aq space ,
-.Aq tab ,
-and
-.Aq newline
-in that order.
-This value also applies if
-.Va IFS
-is unset, but not if it is set to the empty string.
-See the
-.Sx White Space Splitting
-section for more details.
-.It Va LINENO
-The current line number in the script or function.
-.It Va MAIL
-The name of a mail file, that will be checked for the arrival of new
-mail.
-Overridden by
-.Va MAILPATH .
-.It Va MAILPATH
-A colon
-.Pq Ql \&:
-separated list of file names, for the shell to check for incoming
-mail.
-This variable overrides the
-.Va MAIL
-setting.
-There is a maximum of 10 mailboxes that can be monitored at once.
-.It Va OPTIND
-The index of the next argument to be processed by
-.Ic getopts .
-This is initialized to 1 at startup.
-.It Va PATH
-The default search path for executables.
-See the
-.Sx Path Search
-section for details.
-.It Va PPID
-The parent process ID of the invoked shell.
-This is set at startup
-unless this variable is in the environment.
-A later change of parent process ID is not reflected.
-A subshell retains the same value of
-.Va PPID .
-.It Va PS1
-The primary prompt string, which defaults to
-.Dq Li "$ " ,
-unless you are the superuser, in which case it defaults to
-.Dq Li "# " .
-.Va PS1
-may include any of the following formatting sequences,
-which are replaced by the given information:
-.Bl -tag -width indent
-.It Li \eH
-This system's fully-qualified hostname (FQDN).
-.It Li \eh
-This system's hostname.
-.It Li \eW
-The final component of the current working directory.
-.It Li \ew
-The entire path of the current working directory.
-.It Li \e$
-Superuser status.
-.Dq Li "$ "
-for normal users and
-.Dq Li "# "
-for superusers.
-.It Li \e\e
-A literal backslash.
-.El
-.It Va PS2
-The secondary prompt string, which defaults to
-.Dq Li "> " .
-.Va PS2
-may include any of the formatting sequences from
-.Va PS1 .
-.It Va PS4
-The prefix for the trace output (if
-.Fl x
-is active).
-The default is
-.Dq Li "+ " .
-.El
-.Ss Word Expansions
-This clause describes the various expansions that are
-performed on words.
-Not all expansions are performed on
-every word, as explained later.
-.Pp
-Tilde expansions, parameter expansions, command substitutions,
-arithmetic expansions, and quote removals that occur within
-a single word expand to a single field.
-It is only field
-splitting or pathname expansion that can create multiple
-fields from a single word.
-The single exception to this rule is
-the expansion of the special parameter
-.Va @
-within double-quotes,
-as was described above.
-.Pp
-The order of word expansion is:
-.Bl -enum
-.It
-Tilde Expansion, Parameter Expansion, Command Substitution,
-Arithmetic Expansion (these all occur at the same time).
-.It
-Field Splitting is performed on fields generated by step (1)
-unless the
-.Va IFS
-variable is null.
-.It
-Pathname Expansion (unless the
-.Fl f
-option is in effect).
-.It
-Quote Removal.
-.El
-.Pp
-The
-.Ql $
-character is used to introduce parameter expansion, command
-substitution, or arithmetic expansion.
-.Ss Tilde Expansion (substituting a user's home directory)
-A word beginning with an unquoted tilde character
-.Pq Ql ~
-is
-subjected to tilde expansion.
-All the characters up to a slash
-.Pq Ql /
-or the end of the word are treated as a username
-and are replaced with the user's home directory.
-If the
-username is missing (as in
-.Pa ~/foobar ) ,
-the tilde is replaced with the value of the
-.Va HOME
-variable (the current user's home directory).
-.Ss Parameter Expansion
-The format for parameter expansion is as follows:
-.Pp
-.D1 Li ${ Ns Ar expression Ns Li }
-.Pp
-where
-.Ar expression
-consists of all characters until the matching
-.Ql } .
-Any
-.Ql }
-escaped by a backslash or within a single-quoted or double-quoted
-string, and characters in
-embedded arithmetic expansions, command substitutions, and variable
-expansions, are not examined in determining the matching
-.Ql } .
-If the variants with
-.Ql + ,
-.Ql - ,
-.Ql =
-or
-.Ql ?\&
-occur within a double-quoted string,
-as an extension there may be unquoted parts
-(via double-quotes inside the expansion);
-.Ql }
-within such parts are also not examined in determining the matching
-.Ql } .
-.Pp
-The simplest form for parameter expansion is:
-.Pp
-.D1 Li ${ Ns Ar parameter Ns Li }
-.Pp
-The value, if any, of
-.Ar parameter
-is substituted.
-.Pp
-The parameter name or symbol can be enclosed in braces, which are
-optional except for positional parameters with more than one digit or
-when parameter is followed by a character that could be interpreted as
-part of the name.
-If a parameter expansion occurs inside double-quotes:
-.Bl -enum
-.It
-Field splitting is not performed on the results of the
-expansion, with the exception of the special parameter
-.Va @ .
-.It
-Pathname expansion is not performed on the results of the
-expansion.
-.El
-.Pp
-In addition, a parameter expansion can be modified by using one of the
-following formats.
-.Bl -tag -width indent
-.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
-Use Default Values.
-If
-.Ar parameter
-is unset or null, the expansion of
-.Ar word
-is substituted; otherwise, the value of
-.Ar parameter
-is substituted.
-.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
-Assign Default Values.
-If
-.Ar parameter
-is unset or null, the expansion of
-.Ar word
-is assigned to
-.Ar parameter .
-In all cases, the
-final value of
-.Ar parameter
-is substituted.
-Quoting inside
-.Ar word
-does not prevent field splitting or pathname expansion.
-Only variables, not positional
-parameters or special parameters, can be
-assigned in this way.
-.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
-Indicate Error if Null or Unset.
-If
-.Ar parameter
-is unset or null, the expansion of
-.Ar word
-(or a message indicating it is unset if
-.Ar word
-is omitted) is written to standard
-error and the shell exits with a nonzero
-exit status.
-Otherwise, the value of
-.Ar parameter
-is substituted.
-An
-interactive shell need not exit.
-.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
-Use Alternate Value.
-If
-.Ar parameter
-is unset or null, null is substituted;
-otherwise, the expansion of
-.Ar word
-is substituted.
-.El
-.Pp
-In the parameter expansions shown previously, use of the colon in the
-format results in a test for a parameter that is unset or null; omission
-of the colon results in a test for a parameter that is only unset.
-.Pp
-The
-.Ar word
-inherits the type of quoting
-(unquoted, double-quoted or here-document)
-from the surroundings,
-with the exception that a backslash that quotes a closing brace is removed
-during quote removal.
-.Bl -tag -width indent
-.It Li ${# Ns Ar parameter Ns Li }
-String Length.
-The length in characters of
-the value of
-.Ar parameter .
-.El
-.Pp
-The following four varieties of parameter expansion provide for substring
-processing.
-In each case, pattern matching notation
-(see
-.Sx Shell Patterns ) ,
-rather than regular expression notation,
-is used to evaluate the patterns.
-If parameter is one of the special parameters
-.Va *
-or
-.Va @ ,
-the result of the expansion is unspecified.
-Enclosing the full parameter expansion string in double-quotes does not
-cause the following four varieties of pattern characters to be quoted,
-whereas quoting characters within the braces has this effect.
-.Bl -tag -width indent
-.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
-Remove Smallest Suffix Pattern.
-The
-.Ar word
-is expanded to produce a pattern.
-The
-parameter expansion then results in
-.Ar parameter ,
-with the smallest portion of the
-suffix matched by the pattern deleted.
-.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
-Remove Largest Suffix Pattern.
-The
-.Ar word
-is expanded to produce a pattern.
-The
-parameter expansion then results in
-.Ar parameter ,
-with the largest portion of the
-suffix matched by the pattern deleted.
-.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
-Remove Smallest Prefix Pattern.
-The
-.Ar word
-is expanded to produce a pattern.
-The
-parameter expansion then results in
-.Ar parameter ,
-with the smallest portion of the
-prefix matched by the pattern deleted.
-.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
-Remove Largest Prefix Pattern.
-The
-.Ar word
-is expanded to produce a pattern.
-The
-parameter expansion then results in
-.Ar parameter ,
-with the largest portion of the
-prefix matched by the pattern deleted.
-.El
-.Ss Command Substitution
-Command substitution allows the output of a command to be substituted in
-place of the command name itself.
-Command substitution occurs when
-the command is enclosed as follows:
-.Pp
-.D1 Li $( Ns Ar command Ns Li )\&
-.Pp
-or the backquoted version:
-.Pp
-.D1 Li ` Ns Ar command Ns Li `
-.Pp
-The shell expands the command substitution by executing command
-and replacing the command substitution
-with the standard output of the command,
-removing sequences of one or more newlines at the end of the substitution.
-Embedded newlines before the end of the output are not removed;
-however, during field splitting, they may be translated into spaces
-depending on the value of
-.Va IFS
-and the quoting that is in effect.
-The command is executed in a subshell environment,
-except that the built-in commands
-.Ic jobid ,
-.Ic jobs ,
-and
-.Ic trap
-return information about the parent shell environment
-and
-.Ic times
-returns information about the same process
-if they are the only command in a command substitution.
-.Pp
-If a command substitution of the
-.Li $(
-form begins with a subshell,
-the
-.Li $(
-and
-.Li (\&
-must be separated by whitespace
-to avoid ambiguity with arithmetic expansion.
-.Ss Arithmetic Expansion
-Arithmetic expansion provides a mechanism for evaluating an arithmetic
-expression and substituting its value.
-The format for arithmetic expansion is as follows:
-.Pp
-.D1 Li $(( Ns Ar expression Ns Li ))
-.Pp
-The
-.Ar expression
-is treated as if it were in double-quotes, except
-that a double-quote inside the expression is not treated specially.
-The
-shell expands all tokens in the
-.Ar expression
-for parameter expansion,
-command substitution,
-arithmetic expansion
-and quote removal.
-.Pp
-The allowed expressions are a subset of C expressions,
-summarized below.
-.Bl -tag -width "Variables" -offset indent
-.It Values
-All values are of type
-.Ft intmax_t .
-.It Constants
-Decimal, octal (starting with
-.Li 0 )
-and hexadecimal (starting with
-.Li 0x )
-integer constants.
-.It Variables
-Shell variables can be read and written
-and contain integer constants.
-.It Unary operators
-.Li "! ~ + -"
-.It Binary operators
-.Li "* / % + - << >> < <= > >= == != & ^ | && ||"\&
-.It Assignment operators
-.Li "= += -= *= /= %= <<= >>= &= ^= |="
-.It Conditional operator
-.Li "? :"\&
-.El
-.Pp
-The result of the expression is substituted in decimal.
-.Ss White Space Splitting (Field Splitting)
-In certain contexts,
-after parameter expansion, command substitution, and
-arithmetic expansion the shell scans the results of
-expansions and substitutions that did not occur in double-quotes for
-field splitting and multiple fields can result.
-.Pp
-Characters in
-.Va IFS
-that are whitespace
-.Po
-.Aq space ,
-.Aq tab ,
-and
-.Aq newline
-.Pc
-are treated differently from other characters in
-.Va IFS .
-.Pp
-Whitespace in
-.Va IFS
-at the beginning or end of a word is discarded.
-.Pp
-Subsequently, a field is delimited by either
-.Bl -enum
-.It
-a non-whitespace character in
-.Va IFS
-with any whitespace in
-.Va IFS
-surrounding it, or
-.It
-one or more whitespace characters in
-.Va IFS .
-.El
-.Pp
-If a word ends with a non-whitespace character in
-.Va IFS ,
-there is no empty field after this character.
-.Pp
-If no field is delimited, the word is discarded.
-In particular, if a word consists solely of an unquoted substitution
-and the result of the substitution is null,
-it is removed by field splitting even if
-.Va IFS
-is null.
-.Ss Pathname Expansion (File Name Generation)
-Unless the
-.Fl f
-option is set,
-file name generation is performed
-after word splitting is complete.
-Each word is
-viewed as a series of patterns, separated by slashes.
-The
-process of expansion replaces the word with the names of
-all existing files whose names can be formed by replacing
-each pattern with a string that matches the specified pattern.
-There are two restrictions on this: first, a pattern cannot match
-a string containing a slash, and second,
-a pattern cannot match a string starting with a period
-unless the first character of the pattern is a period.
-The next section describes the patterns used for
-Pathname Expansion,
-the four varieties of parameter expansion for substring processing and the
-.Ic case
-command.
-.Ss Shell Patterns
-A pattern consists of normal characters, which match themselves,
-and meta-characters.
-The meta-characters are
-.Ql * ,
-.Ql \&? ,
-and
-.Ql \&[ .
-These characters lose their special meanings if they are quoted.
-When command or variable substitution is performed and the dollar sign
-or back quotes are not double-quoted, the value of the
-variable or the output of the command is scanned for these
-characters and they are turned into meta-characters.
-.Pp
-An asterisk
-.Pq Ql *
-matches any string of characters.
-A question mark
-.Pq Ql \&?
-matches any single character.
-A left bracket
-.Pq Ql \&[
-introduces a character class.
-The end of the character class is indicated by a
-.Ql \&] ;
-if the
-.Ql \&]
-is missing then the
-.Ql \&[
-matches a
-.Ql \&[
-rather than introducing a character class.
-A character class matches any of the characters between the square brackets.
-A locale-dependent range of characters may be specified using a minus sign.
-A named class of characters (see
-.Xr wctype 3 )
-may be specified by surrounding the name with
-.Ql \&[:\&
-and
-.Ql :\&] .
-For example,
-.Ql \&[\&[:alpha:\&]\&]
-is a shell pattern that matches a single letter.
-The character class may be complemented by making an exclamation point
-.Pq Ql !\&
-the first character of the character class.
-A caret
-.Pq Ql ^
-has the same effect but is non-standard.
-.Pp
-To include a
-.Ql \&]
-in a character class, make it the first character listed
-(after the
-.Ql \&!
-or
-.Ql ^ ,
-if any).
-To include a
-.Ql - ,
-make it the first or last character listed.
-.Ss Built-in Commands
-This section lists the built-in commands.
-.Bl -tag -width indent
-.It Ic \&:
-A null command that returns a 0 (true) exit value.
-.It Ic \&. Ar file
-The commands in the specified file are read and executed by the shell.
-The
-.Ic return
-command may be used to return to the
-.Ic \&.
-command's caller.
-If
-.Ar file
-contains any
-.Ql /
-characters, it is used as is.
-Otherwise, the shell searches the
-.Va PATH
-for the file.
-If it is not found in the
-.Va PATH ,
-it is sought in the current working directory.
-.It Ic \&[
-A built-in equivalent of
-.Xr test 1 .
-.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
-If
-.Ar name Ns = Ns Ar string
-is specified, the shell defines the alias
-.Ar name
-with value
-.Ar string .
-If just
-.Ar name
-is specified, the value of the alias
-.Ar name
-is printed.
-With no arguments, the
-.Ic alias
-built-in command prints the names and values of all defined aliases
-(see
-.Ic unalias ) .
-Alias values are written with appropriate quoting so that they are
-suitable for re-input to the shell.
-Also see the
-.Sx Aliases
-subsection.
-.It Ic bg Op Ar job ...
-Continue the specified jobs
-(or the current job if no jobs are given)
-in the background.
-.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
-List or alter key bindings for the line editor.
-This command is documented in
-.Xr editrc 5 .
-.It Ic break Op Ar num
-See the
-.Sx Flow-Control Constructs
-subsection.
-.It Ic builtin Ar cmd Op Ar arg ...
-Execute the specified built-in command,
-.Ar cmd .
-This is useful when the user wishes to override a shell function
-with the same name as a built-in command.
-.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
-.It Ic cd Fl
-Switch to the specified
-.Ar directory ,
-to the directory specified in the
-.Va HOME
-environment variable if no
-.Ar directory
-is specified or
-to the directory specified in the
-.Va OLDPWD
-environment variable if
-.Ar directory
-is
-.Fl .
-If
-.Ar directory
-does not begin with
-.Pa / , \&. ,
-or
-.Pa .. ,
-then the directories listed in the
-.Va CDPATH
-variable will be
-searched for the specified
-.Ar directory .
-If
-.Va CDPATH
-is unset, the current directory is searched.
-The format of
-.Va CDPATH
-is the same as that of
-.Va PATH .
-In an interactive shell,
-the
-.Ic cd
-command will print out the name of the directory
-that it actually switched to
-if the
-.Va CDPATH
-mechanism was used or if
-.Ar directory
-was
-.Fl .
-.Pp
-If the
-.Fl P
-option is specified,
-.Pa ..
-is handled physically and symbolic links are resolved before
-.Pa ..
-components are processed.
-If the
-.Fl L
-option is specified,
-.Pa ..
-is handled logically.
-This is the default.
-.Pp
-The
-.Fl e
-option causes
-.Ic cd
-to return exit status 1 if the full pathname of the new directory
-cannot be determined reliably or at all.
-Normally this is not considered an error,
-although a warning is printed.
-.Pp
-If changing the directory fails, the exit status is greater than 1.
-If the directory is changed, the exit status is 0, or also 1 if
-.Fl e
-was given.
-.It Ic chdir
-A synonym for the
-.Ic cd
-built-in command.
-.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
-.It Ic command Oo Fl p Oc Fl v Ar utility
-.It Ic command Oo Fl p Oc Fl V Ar utility
-The first form of invocation executes the specified
-.Ar utility ,
-ignoring shell functions in the search.
-If
-.Ar utility
-is a special builtin,
-it is executed as if it were a regular builtin.
-.Pp
-If the
-.Fl p
-option is specified, the command search is performed using a
-default value of
-.Va PATH
-that is guaranteed to find all of the standard utilities.
-.Pp
-If the
-.Fl v
-option is specified,
-.Ar utility
-is not executed but a description of its interpretation by the shell is
-printed.
-For ordinary commands the output is the path name; for shell built-in
-commands, shell functions and keywords only the name is written.
-Aliases are printed as
-.Dq Ic alias Ar name Ns = Ns Ar value .
-.Pp
-The
-.Fl V
-option is identical to
-.Fl v
-except for the output.
-It prints
-.Dq Ar utility Ic is Ar description
-where
-.Ar description
-is either
-the path name to
-.Ar utility ,
-a special shell builtin,
-a shell builtin,
-a shell function,
-a shell keyword
-or
-an alias for
-.Ar value .
-.It Ic continue Op Ar num
-See the
-.Sx Flow-Control Constructs
-subsection.
-.It Ic echo Oo Fl e | n Oc Op Ar string ...
-Print a space-separated list of the arguments to the standard output
-and append a newline character.
-.Bl -tag -width indent
-.It Fl n
-Suppress the output of the trailing newline.
-.It Fl e
-Process C-style backslash escape sequences.
-The
-.Ic echo
-command understands the following character escapes:
-.Bl -tag -width indent
-.It \ea
-Alert (ring the terminal bell)
-.It \eb
-Backspace
-.It \ec
-Suppress the trailing newline (this has the side-effect of truncating the
-line if it is not the last character)
-.It \ee
-The ESC character (ASCII 0x1b)
-.It \ef
-Formfeed
-.It \en
-Newline
-.It \er
-Carriage return
-.It \et
-Horizontal tab
-.It \ev
-Vertical tab
-.It \e\e
-Literal backslash
-.It \e0nnn
-(Zero) The character whose octal value is
-.Ar nnn
-.El
-.Pp
-If
-.Ar string
-is not enclosed in quotes then the backslash itself must be escaped
-with a backslash to protect it from the shell.
-For example
-.Bd -literal -offset indent
-$ echo -e "a\evb"
-a
- b
-$ echo -e a\e\evb
-a
- b
-$ echo -e "a\e\eb"
-a\eb
-$ echo -e a\e\e\e\eb
-a\eb
-.Ed
-.El
-.Pp
-Only one of the
-.Fl e
-and
-.Fl n
-options may be specified.
-.It Ic eval Ar string ...
-Concatenate all the arguments with spaces.
-Then re-parse and execute the command.
-.It Ic exec Op Ar command Op arg ...
-Unless
-.Ar command
-is omitted,
-the shell process is replaced with the specified program
-(which must be a real program, not a shell built-in command or function).
-Any redirections on the
-.Ic exec
-command are marked as permanent,
-so that they are not undone when the
-.Ic exec
-command finishes.
-.It Ic exit Op Ar exitstatus
-Terminate the shell process.
-If
-.Ar exitstatus
-is given
-it is used as the exit status of the shell.
-Otherwise, if the shell is executing an
-.Cm EXIT
-trap, the exit status of the last command before the trap is used;
-if the shell is executing a trap for a signal,
-the shell exits by resending the signal to itself.
-Otherwise, the exit status of the preceding command is used.
-The exit status should be an integer between 0 and 255.
-.It Ic export Ar name ...
-.It Ic export Op Fl p
-The specified names are exported so that they will
-appear in the environment of subsequent commands.
-The only way to un-export a variable is to
-.Ic unset
-it.
-The shell allows the value of a variable to be set
-at the same time as it is exported by writing
-.Pp
-.D1 Ic export Ar name Ns = Ns Ar value
-.Pp
-With no arguments the
-.Ic export
-command lists the names
-of all exported variables.
-If the
-.Fl p
-option is specified, the exported variables are printed as
-.Dq Ic export Ar name Ns = Ns Ar value
-lines, suitable for re-input to the shell.
-.It Ic false
-A null command that returns a non-zero (false) exit value.
-.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
-.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
-.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
-The
-.Ic fc
-built-in command lists, or edits and re-executes,
-commands previously entered to an interactive shell.
-.Bl -tag -width indent
-.It Fl e Ar editor
-Use the editor named by
-.Ar editor
-to edit the commands.
-The
-.Ar editor
-string is a command name,
-subject to search via the
-.Va PATH
-variable.
-The value in the
-.Va FCEDIT
-variable is used as a default when
-.Fl e
-is not specified.
-If
-.Va FCEDIT
-is null or unset, the value of the
-.Va EDITOR
-variable is used.
-If
-.Va EDITOR
-is null or unset,
-.Xr ed 1
-is used as the editor.
-.It Fl l No (ell)
-List the commands rather than invoking
-an editor on them.
-The commands are written in the
-sequence indicated by the
-.Ar first
-and
-.Ar last
-operands, as affected by
-.Fl r ,
-with each command preceded by the command number.
-.It Fl n
-Suppress command numbers when listing with
-.Fl l .
-.It Fl r
-Reverse the order of the commands listed
-(with
-.Fl l )
-or edited
-(with neither
-.Fl l
-nor
-.Fl s ) .
-.It Fl s
-Re-execute the command without invoking an editor.
-.It Ar first
-.It Ar last
-Select the commands to list or edit.
-The number of previous commands that can be accessed
-are determined by the value of the
-.Va HISTSIZE
-variable.
-The value of
-.Ar first
-or
-.Ar last
-or both are one of the following:
-.Bl -tag -width indent
-.It Oo Cm + Oc Ns Ar num
-A positive number representing a command number;
-command numbers can be displayed with the
-.Fl l
-option.
-.It Fl Ar num
-A negative decimal number representing the
-command that was executed
-.Ar num
-of
-commands previously.
-For example, \-1 is the immediately previous command.
-.It Ar string
-A string indicating the most recently entered command
-that begins with that string.
-If the
-.Ar old Ns = Ns Ar new
-operand is not also specified with
-.Fl s ,
-the string form of the first operand cannot contain an embedded equal sign.
-.El
-.El
-.Pp
-The following variables affect the execution of
-.Ic fc :
-.Bl -tag -width ".Va HISTSIZE"
-.It Va FCEDIT
-Name of the editor to use for history editing.
-.It Va HISTSIZE
-The number of previous commands that are accessible.
-.El
-.It Ic fg Op Ar job
-Move the specified
-.Ar job
-or the current job to the foreground.
-.It Ic getopts Ar optstring var
-The POSIX
-.Ic getopts
-command.
-The
-.Ic getopts
-command deprecates the older
-.Xr getopt 1
-command.
-The first argument should be a series of letters, each possibly
-followed by a colon which indicates that the option takes an argument.
-The specified variable is set to the parsed option.
-The index of
-the next argument is placed into the shell variable
-.Va OPTIND .
-If an option takes an argument, it is placed into the shell variable
-.Va OPTARG .
-If an invalid option is encountered,
-.Ar var
-is set to
-.Ql \&? .
-It returns a false value (1) when it encounters the end of the options.
-A new set of arguments may be parsed by assigning
-.Li OPTIND=1 .
-.It Ic hash Oo Fl rv Oc Op Ar command ...
-The shell maintains a hash table which remembers the locations of commands.
-With no arguments whatsoever, the
-.Ic hash
-command prints out the contents of this table.
-.Pp
-With arguments, the
-.Ic hash
-command removes each specified
-.Ar command
-from the hash table (unless they are functions) and then locates it.
-With the
-.Fl v
-option,
-.Ic hash
-prints the locations of the commands as it finds them.
-The
-.Fl r
-option causes the
-.Ic hash
-command to delete all the entries in the hash table except for functions.
-.It Ic jobid Op Ar job
-Print the process IDs of the processes in the specified
-.Ar job .
-If the
-.Ar job
-argument is omitted, use the current job.
-.It Ic jobs Oo Fl lps Oc Op Ar job ...
-Print information about the specified jobs, or all jobs if no
-.Ar job
-argument is given.
-The information printed includes job ID, status and command name.
-.Pp
-If the
-.Fl l
-option is specified, the PID of each job is also printed.
-If the
-.Fl p
-option is specified, only the process IDs for the process group leaders
-are printed, one per line.
-If the
-.Fl s
-option is specified, only the PIDs of the job commands are printed, one per
-line.
-.It Ic kill
-A built-in equivalent of
-.Xr kill 1
-that additionally supports sending signals to jobs.
-.It Ic local Oo Ar variable ... Oc Op Fl
-See the
-.Sx Functions
-subsection.
-.It Ic printf
-A built-in equivalent of
-.Xr printf 1 .
-.It Ic pwd Op Fl L | P
-Print the path of the current directory.
-The built-in command may
-differ from the program of the same name because the
-built-in command remembers what the current directory
-is rather than recomputing it each time.
-This makes
-it faster.
-However, if the current directory is
-renamed,
-the built-in version of
-.Xr pwd 1
-will continue to print the old name for the directory.
-.Pp
-If the
-.Fl P
-option is specified, symbolic links are resolved.
-If the
-.Fl L
-option is specified, the shell's notion of the current directory
-is printed (symbolic links are not resolved).
-This is the default.
-.It Ic read Oo Fl p Ar prompt Oc Oo
-.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
-The
-.Ar prompt
-is printed if the
-.Fl p
-option is specified
-and the standard input is a terminal.
-Then a line is
-read from the standard input.
-The trailing newline
-is deleted from the line and the line is split as
-described in the section on
-.Sx White Space Splitting (Field Splitting)\&
-above, and
-the pieces are assigned to the variables in order.
-If there are more pieces than variables, the remaining
-pieces (along with the characters in
-.Va IFS
-that separated them)
-are assigned to the last variable.
-If there are more variables than pieces, the remaining
-variables are assigned the null string.
-.Pp
-Backslashes are treated specially, unless the
-.Fl r
-option is
-specified.
-If a backslash is followed by
-a newline, the backslash and the newline will be
-deleted.
-If a backslash is followed by any other
-character, the backslash will be deleted and the following
-character will be treated as though it were not in
-.Va IFS ,
-even if it is.
-.Pp
-If the
-.Fl t
-option is specified and the
-.Ar timeout
-elapses before a complete line of input is supplied,
-the
-.Ic read
-command will return an exit status as if terminated by
-.Dv SIGALRM
-without assigning any values.
-The
-.Ar timeout
-value may optionally be followed by one of
-.Ql s ,
-.Ql m
-or
-.Ql h
-to explicitly specify seconds, minutes or hours.
-If none is supplied,
-.Ql s
-is assumed.
-.Pp
-The
-.Fl e
-option exists only for backward compatibility with older scripts.
-.Pp
-The exit status is 0 on success, 1 on end of file,
-between 2 and 128 if an error occurs
-and greater than 128 if a trapped signal interrupts
-.Ic read .
-.It Ic readonly Oo Fl p Oc Op Ar name ...
-Each specified
-.Ar name
-is marked as read only,
-so that it cannot be subsequently modified or unset.
-The shell allows the value of a variable to be set
-at the same time as it is marked read only
-by using the following form:
-.Pp
-.D1 Ic readonly Ar name Ns = Ns Ar value
-.Pp
-With no arguments the
-.Ic readonly
-command lists the names of all read only variables.
-If the
-.Fl p
-option is specified, the read-only variables are printed as
-.Dq Ic readonly Ar name Ns = Ns Ar value
-lines, suitable for re-input to the shell.
-.It Ic return Op Ar exitstatus
-See the
-.Sx Functions
-subsection.
-.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
-.Fl c Ar string Oc Op Fl - Ar arg ...
-The
-.Ic set
-command performs three different functions:
-.Bl -item
-.It
-With no arguments, it lists the values of all shell variables.
-.It
-If options are given,
-either in short form or using the long
-.Dq Fl /+o Ar longname
-form,
-it sets or clears the specified options as described in the section called
-.Sx Argument List Processing .
-.It
-If the
-.Dq Fl -
-option is specified,
-.Ic set
-will replace the shell's positional parameters with the subsequent
-arguments.
-If no arguments follow the
-.Dq Fl -
-option,
-all the positional parameters will be cleared,
-which is equivalent to executing the command
-.Dq Li "shift $#" .
-The
-.Dq Fl -
-flag may be omitted when specifying arguments to be used
-as positional replacement parameters.
-This is not recommended,
-because the first argument may begin with a dash
-.Pq Ql -
-or a plus
-.Pq Ql + ,
-which the
-.Ic set
-command will interpret as a request to enable or disable options.
-.El
-.It Ic setvar Ar variable value
-Assigns the specified
-.Ar value
-to the specified
-.Ar variable .
-The
-.Ic setvar
-command is intended to be used in functions that
-assign values to variables whose names are passed as parameters.
-In general it is better to write
-.Dq Ar variable Ns = Ns Ar value
-rather than using
-.Ic setvar .
-.It Ic shift Op Ar n
-Shift the positional parameters
-.Ar n
-times, or once if
-.Ar n
-is not specified.
-A shift sets the value of
-.Li $1
-to the value of
-.Li $2 ,
-the value of
-.Li $2
-to the value of
-.Li $3 ,
-and so on,
-decreasing the value of
-.Li $#
-by one.
-For portability, shifting if there are zero positional parameters
-should be avoided, since the shell may abort.
-.It Ic test
-A built-in equivalent of
-.Xr test 1 .
-.It Ic times
-Print the amount of time spent executing the shell process and its children.
-The first output line shows the user and system times for the shell process
-itself, the second one contains the user and system times for the
-children.
-.It Ic trap Oo Ar action Oc Ar signal ...
-.It Ic trap Fl l
-Cause the shell to parse and execute
-.Ar action
-when any specified
-.Ar signal
-is received.
-The signals are specified by name or number.
-In addition, the pseudo-signal
-.Cm EXIT
-may be used to specify an
-.Ar action
-that is performed when the shell terminates.
-The
-.Ar action
-may be an empty string or a dash
-.Pq Ql - ;
-the former causes the specified signal to be ignored
-and the latter causes the default action to be taken.
-Omitting the
-.Ar action
-and using only signal numbers is another way to request the default action.
-In a subshell or utility environment,
-the shell resets trapped (but not ignored) signals to the default action.
-The
-.Ic trap
-command has no effect on signals that were ignored on entry to the shell.
-.Pp
-Option
-.Fl l
-causes the
-.Ic trap
-command to display a list of valid signal names.
-.It Ic true
-A null command that returns a 0 (true) exit value.
-.It Ic type Op Ar name ...
-Interpret each
-.Ar name
-as a command and print the resolution of the command search.
-Possible resolutions are:
-shell keyword, alias, special shell builtin, shell builtin, command,
-tracked alias
-and not found.
-For aliases the alias expansion is printed;
-for commands and tracked aliases
-the complete pathname of the command is printed.
-.It Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit
-Set or display resource limits (see
-.Xr getrlimit 2 ) .
-If
-.Ar limit
-is specified, the named resource will be set;
-otherwise the current resource value will be displayed.
-.Pp
-If
-.Fl H
-is specified, the hard limits will be set or displayed.
-While everybody is allowed to reduce a hard limit,
-only the superuser can increase it.
-The
-.Fl S
-option
-specifies the soft limits instead.
-When displaying limits,
-only one of
-.Fl S
-or
-.Fl H
-can be given.
-The default is to display the soft limits,
-and to set both the hard and the soft limits.
-.Pp
-Option
-.Fl a
-causes the
-.Ic ulimit
-command to display all resources.
-The parameter
-.Ar limit
-is not acceptable in this mode.
-.Pp
-The remaining options specify which resource value is to be
-displayed or modified.
-They are mutually exclusive.
-.Bl -tag -width indent
-.It Fl b Ar sbsize
-The maximum size of socket buffer usage, in bytes.
-.It Fl c Ar coredumpsize
-The maximal size of core dump files, in 512-byte blocks.
-Setting
-.Ar coredumpsize
-to 0 prevents core dump files from being created.
-.It Fl d Ar datasize
-The maximal size of the data segment of a process, in kilobytes.
-.It Fl f Ar filesize
-The maximal size of a file, in 512-byte blocks.
-.It Fl k Ar kqueues
-The maximal number of kqueues
-(see
-.Xr kqueue 2 )
-for this user ID.
-.It Fl l Ar lockedmem
-The maximal size of memory that can be locked by a process, in
-kilobytes.
-.It Fl m Ar memoryuse
-The maximal resident set size of a process, in kilobytes.
-.It Fl n Ar nofiles
-The maximal number of descriptors that could be opened by a process.
-.It Fl o Ar umtxp
-The maximal number of process-shared locks
-(see
-.Xr pthread 3 )
-for this user ID.
-.It Fl p Ar pseudoterminals
-The maximal number of pseudo-terminals for this user ID.
-.It Fl s Ar stacksize
-The maximal size of the stack segment, in kilobytes.
-.It Fl t Ar time
-The maximal amount of CPU time to be used by each process, in seconds.
-.It Fl u Ar userproc
-The maximal number of simultaneous processes for this user ID.
-.It Fl v Ar virtualmem
-The maximal virtual size of a process, in kilobytes.
-.It Fl w Ar swapuse
-The maximum amount of swap space reserved or used for this user ID,
-in kilobytes.
-.El
-.It Ic umask Oo Fl S Oc Op Ar mask
-Set the file creation mask (see
-.Xr umask 2 )
-to the octal or symbolic (see
-.Xr chmod 1 )
-value specified by
-.Ar mask .
-If the argument is omitted, the current mask value is printed.
-If the
-.Fl S
-option is specified, the output is symbolic, otherwise the output is octal.
-.It Ic unalias Oo Fl a Oc Op Ar name ...
-The specified alias names are removed.
-If
-.Fl a
-is specified, all aliases are removed.
-.It Ic unset Oo Fl fv Oc Ar name ...
-The specified variables or functions are unset and unexported.
-If the
-.Fl v
-option is specified or no options are given, the
-.Ar name
-arguments are treated as variable names.
-If the
-.Fl f
-option is specified, the
-.Ar name
-arguments are treated as function names.
-.It Ic wait Op Ar job ...
-Wait for each specified
-.Ar job
-to complete and return the exit status of the last process in the
-last specified
-.Ar job .
-If any
-.Ar job
-specified is unknown to the shell, it is treated as if it
-were a known job that exited with exit status 127.
-If no operands are given, wait for all jobs to complete
-and return an exit status of zero.
-.El
-.Ss Command Line Editing
-When
-.Nm
-is being used interactively from a terminal, the current command
-and the command history
-(see
-.Ic fc
-in
-.Sx Built-in Commands )
-can be edited using
-.Nm vi Ns -mode
-command line editing.
-This mode uses commands similar
-to a subset of those described in the
-.Xr vi 1
-man page.
-The command
-.Dq Li "set -o vi"
-(or
-.Dq Li "set -V" )
-enables
-.Nm vi Ns -mode
-editing and places
-.Nm
-into
-.Nm vi
-insert mode.
-With
-.Nm vi Ns -mode
-enabled,
-.Nm
-can be switched between insert mode and command mode by typing
-.Aq ESC .
-Hitting
-.Aq return
-while in command mode will pass the line to the shell.
-.Pp
-Similarly, the
-.Dq Li "set -o emacs"
-(or
-.Dq Li "set -E" )
-command can be used to enable a subset of
-.Nm emacs Ns -style
-command line editing features.
-.Sh ENVIRONMENT
-The following environment variables affect the execution of
-.Nm :
-.Bl -tag -width ".Ev LANGXXXXXX"
-.It Ev ENV
-Initialization file for interactive shells.
-.It Ev LANG , Ev LC_*
-Locale settings.
-These are inherited by children of the shell,
-and is used in a limited manner by the shell itself.
-.It Ev OLDPWD
-The previous current directory.
-This is used and updated by
-.Ic cd .
-.It Ev PWD
-An absolute pathname for the current directory,
-possibly containing symbolic links.
-This is used and updated by the shell.
-.It Ev TERM
-The default terminal setting for the shell.
-This is inherited by children of the shell, and is used in the history
-editing modes.
-.El
-.Pp
-Additionally, environment variables are turned into shell variables
-at startup,
-which may affect the shell as described under
-.Sx Special Variables .
-.Sh FILES
-.Bl -tag -width "/etc/suid_profileXX" -compact
-.It Pa ~/.profile
-User's login profile.
-.It Pa /etc/profile
-System login profile.
-.It Pa /etc/shells
-Shell database.
-.It Pa /etc/suid_profile
-Privileged shell profile.
-.El
-.Sh EXIT STATUS
-Errors that are detected by the shell, such as a syntax error, will
-cause the shell to exit with a non-zero exit status.
-If the shell is not an interactive shell, the execution of the shell
-file will be aborted.
-Otherwise the shell will return the exit status of the last command
-executed, or if the
-.Ic exit
-builtin is used with a numeric argument, it
-will return the argument.
-.Sh SEE ALSO
-.Xr builtin 1 ,
-.Xr chsh 1 ,
-.Xr echo 1 ,
-.Xr ed 1 ,
-.Xr emacs 1 ,
-.Xr kill 1 ,
-.Xr printf 1 ,
-.Xr pwd 1 ,
-.Xr test 1 ,
-.Xr vi 1 ,
-.Xr execve 2 ,
-.Xr getrlimit 2 ,
-.Xr umask 2 ,
-.Xr wctype 3 ,
-.Xr editrc 5 ,
-.Xr shells 5
-.Sh HISTORY
-A
-.Nm
-command, the Thompson shell, appeared in
-.At v1 .
-It was superseded in
-.At v7
-by the Bourne shell, which inherited the name
-.Nm .
-.Pp
-This version of
-.Nm
-was rewritten in 1989 under the
-.Bx
-license after the Bourne shell from
-.At V.4 .
-.Sh AUTHORS
-This version of
-.Nm
-was originally written by
-.An Kenneth Almquist .
-.Sh BUGS
-The
-.Nm
-utility does not recognize multibyte characters other than UTF-8.
-Splitting using
-.Va IFS
-does not recognize multibyte characters.