diff --git a/bin/sh/sh.1 b/bin/sh/sh.1
index 9903508d6381..a34f7676fffa 100644
--- a/bin/sh/sh.1
+++ b/bin/sh/sh.1
@@ -1,2938 +1,2941 @@
 .\"-
+.\" SPDX-License-Identifier: BSD-3-Clause
+.\"
 .\" 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.
 .\"
 .Dd November 20, 2024
 .Dt SH 1
 .Os
 .Sh NAME
 .Nm sh
 .Nd command interpreter (shell)
 .Sh SYNOPSIS
 .Nm
 .Op Fl /+abCEefhIilmnPpTuVvx
 .Op Fl /+o Ar longname
 .Oo
 .Ar script
 .Op Ar arg ...
 .Oc
 .Nm
 .Op Fl /+abCEefhIilmnPpTuVvx
 .Op Fl /+o Ar longname
 .Fl c Ar string
 .Oo
 .Ar name
 .Op Ar arg ...
 .Oc
 .Nm
 .Op Fl /+abCEefhIilmnPpTuVvx
 .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 Pq Pa ports/editors/emacs
 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 l
 Force the shell to act as if it has been invoked as a login shell.
 .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.
 .It Li pipefail
 Change the exit status of a pipeline to the last non-zero exit status of
 any command in the pipeline, if any.
 Since an exit due to
 .Dv SIGPIPE
 counts as a non-zero exit status,
 this option may cause non-zero exit status for successful pipelines
 if a command such as
 .Xr head 1
 in the pipeline terminates with status 0 without reading its
 input completely.
 This option only has a long name.
 .It Li verify
 Set
 .Dv O_VERIFY
 when sourcing files or loading profiles.
 .\" See also
 .\" .Xr mac_veriexec 4 . TODO Does not exist; write it.
 .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 Pq Pa ports/editors/emacs
 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 if the
 .Cm pipefail
 option is not set or all commands returned zero,
 or the last non-zero exit status of any command in the pipeline otherwise.
 Otherwise, the exit status is the logical
 NOT of that exit status.
 That is, if
 that status is zero, the exit status is 1; if
 that status is 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 indent
 .Po Ar list Pc
 .Ed
 .Sm on
 .Pp
 or
 .Bd -literal -offset indent
 .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 HISTFILE
 File used for persistent history storage.
 If unset
 .Pa ~/.sh_history
 will be used.
 If set but empty or
 .Va HISTSIZE
 is set to 0
 the shell will not load and save the history.
 .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 \eD{format}
 The current time in
 .Xr strftime 3
 .Ar format .
 The braces are required.
 Empty
 .Ar format
 is equivalent to
 \&%X,
 national representation of the time.
 .It Li \eH
 This system's fully-qualified hostname (FQDN).
 .It Li \eh
 This system's hostname.
 .It Li \eu
 User name.
 .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.
 .It Li \e[
 Start of a sequence of non-printing characters (used, for example,
 to embed ANSI CSI sequences into the prompt).
 .It Li \e]
 End of a sequence of non-printing characters.
 .El
 .Pp
 The following special and non-printing characters are supported
 within the sequence of non-printing characters:
 .Bl -tag -width indent
 .It Li \ea
 Emits ASCII BEL (0x07, 007) character.
 .It Li \ee
 Emits ASCII ESC (0x1b, 033) character.
 .It Li \er
 Emits ASCII CR (0x0d, 015) character.
 .It Li \en
 Emits CRLF sequence.
 .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 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
 If the
 .Ar script
 cannot be found, the exit status will be 127;
 if it cannot be opened for another reason, the exit status will be 126.
 Other 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 Pq Pa ports/editors/emacs ,
 .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 .
+.At V.4
+and first appeared in
+.Bx 4.3 Net/2 .
 .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.