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SH(1)			  BSD General Commands Manual			 SH(1)

     sh	-- command interpreter (shell)

     sh	[-/+abCEefhIimnPpTuVvx]	[-/+o longname]	[script	[arg ...]]
     sh	[-/+abCEefhIimnPpTuVvx]	[-/+o longname]	-c string [name	[arg ...]]
     sh	[-/+abCEefhIimnPpTuVvx]	[-/+o longname]	-s [arg	...]

     The sh utility is the standard command interpreter	for the	system.	 The
     current version of	sh is close to the IEEE	Std 1003.1 ("POSIX.1") speci-
     fication 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.

     The shell is a command that reads lines from either a file	or the termi-
     nal, 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 chsh(1) command.  The shell imple-
     ments 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 interpre-
     tative 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

     If	no arguments are present and if	the standard input of the shell	is
     connected to a terminal (or if the	-i option is set), the shell is	con-
     sidered an	interactive shell.  An interactive shell generally prompts be-
     fore 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 (`-'), the	shell is also considered a lo-
     gin shell.	 This is normally done automatically by	the system when	the
     user first	logs in.  A login shell	first reads commands from the files
     /etc/profile and then .profile in a user's	home directory,	if they	exist.
     If	the environment	variable ENV is	set on entry to	a shell, or is set in
     the .profile of a login shell, the	shell then subjects its	value to pa-
     rameter expansion and arithmetic expansion	and reads commands from	the
     named file.  Therefore, a user should place commands that are to be exe-
     cuted only	at login time in the .profile file, and	commands that are exe-
     cuted for every shell inside the ENV file.	 The user can set the ENV
     variable to some file by placing the following line in the	file .profile
     in	the home directory, substituting for .shrc the filename	desired:

	   ENV=$HOME/.shrc; export ENV

     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 ($1, $2, etc.).  Otherwise, the shell	reads commands from
     its standard input.

     Unlike older versions of sh the 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 ENV scripts.

   Argument List Processing
     All of the	single letter options to sh have a corresponding long name,
     with the exception	of -c and -/+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 -/+o option of sh.  Once
     the shell is running, the long name for an	option may be specified	as an
     argument to the -/+o option of the	set built-in command (described	later
     in	the section called Built-in Commands).	Introducing an option with a
     dash (`-')	enables	the option, while using	a plus (`+') disables the op-
     tion.  A "--" or plain `-'	will stop option processing and	will force the
     remaining words on	the command line to be treated as arguments.  The -/+o
     and -c options do not have	long names.  They take arguments and are de-
     scribed after the single letter options.

     -a	allexport
	     Flag variables for	export when assignments	are made to them.

     -b	notify
	     Enable asynchronous notification of background job	completion.

     -C	noclobber
	     Do	not overwrite existing files with `>'.

     -E	emacs
	     Enable the	built-in emacs(1) command line editor (disables	the -V
	     option if it has been set;	set automatically when interactive on

     -e	errexit
	     Exit immediately if any untested command fails in non-interactive
	     mode.  The	exit status of a command is considered to be explic-
	     itly tested if the	command	is part	of the list used to control an
	     if, elif, while, or until;	if the command is the left hand	oper-
	     and of an "&&" or "||" operator; or if the	command	is a pipeline
	     preceded by the ! keyword.	 If a shell function is	executed and
	     its exit status is	explicitly tested, all commands	of the func-
	     tion are considered to be tested as well.

	     It	is recommended to check	for failures explicitly	instead	of re-
	     lying on -e because it tends to behave in unexpected ways,	par-
	     ticularly in larger scripts.

     -f	noglob
	     Disable pathname expansion.

     -h	trackall
	     A do-nothing option for POSIX compliance.

     -I	ignoreeof
	     Ignore EOF's from input when in interactive mode.

     -i	interactive
	     Force the shell to	behave interactively.

     -m	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.

     -n	noexec
	     If	not interactive, read commands but do not execute them.	 This
	     is	useful for checking the	syntax of shell	scripts.

     -P	physical
	     Change the	default	for the	cd and pwd commands from -L (logical
	     directory layout) to -P (physical directory layout).

     -p	privileged
	     Turn on privileged	mode.  This mode is enabled on startup if ei-
	     ther 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 en-
	     abled for interactive shells, the file /etc/suid_profile is
	     sourced instead of	~/.profile after /etc/profile is sourced, and
	     the contents of the ENV variable are ignored.

     -s	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
	     set command).

     -T	trapsasync
	     When waiting for a	child, execute traps immediately.  If this op-
	     tion is not set, traps are	executed after the child exits,	as
	     specified in IEEE Std 1003.2 ("POSIX.2").	This nonstandard op-
	     tion 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:

		   sh -T -c "trap 'exit	1' 2 ; some-blocking-program"

     -u	nounset
	     Write a message to	standard error when attempting to expand a
	     variable, a positional parameter or the special parameter ! that
	     is	not set, and if	the shell is not interactive, exit immedi-

     -V	vi   Enable the	built-in vi(1) command line editor (disables -E	if it
	     has been set).

     -v	verbose
	     The shell writes its input	to standard error as it	is read.  Use-
	     ful for debugging.

     -x	xtrace
	     Write each	command	(preceded by the value of the PS4 variable
	     subjected to parameter expansion and arithmetic expansion)	to
	     standard error before it is executed.  Useful for debugging.

     nolog   Another do-nothing	option for POSIX compliance.  It only has a
	     long name.

	     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	SIGPIPE	counts as a non-zero exit status, this option may
	     cause non-zero exit status	for successful pipelines if a command
	     such as head(1) in	the pipeline terminates	with status 0 without
	     reading its input completely.  This option	only has a long	name.

     The -c option causes the commands to be read from the string operand in-
     stead of from the standard	input.	Keep in	mind that this option only ac-
     cepts a single string as its argument, hence multi-word strings must be

     The -/+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 sh
     both enable the built-in emacs(1) command line editor:

	   set -E
	   set -o emacs

     If	used without an	argument, the -o option	displays the current option
     settings in a human-readable format.  If +o is used without an argument,
     the current option	settings are output in a format	suitable for re-input
     into the shell.

   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	char-
     acters called "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:

     Control operators:
		   &	 &&    (     )	   \n
		   ;;	 ;&    ;     |	   ||

     Redirection operators:
		   <	 >     <<    >>	   <>
		   <&	 >&    <<-   >|

     The character `#' introduces a comment if used at the beginning of	a
     word.  The	word starting with `#' and the rest of the line	are ignored.

     ASCII NUL characters (character code 0) are not allowed in	shell input.

     Quoting is	used to	remove the special meaning of certain characters or
     words to the shell, such as operators, whitespace,	keywords, or alias

     There are four types of quoting: matched single quotes, dollar-single
     quotes, matched double quotes, and	backslash.

     Single Quotes
	     Enclosing characters in single quotes preserves the literal mean-
	     ing of all	the characters (except single quotes, making it	impos-
	     sible to put single-quotes	in a single-quoted string).

     Dollar-Single Quotes
	     Enclosing characters between $' and ' preserves the literal mean-
	     ing of all	characters except backslashes and single quotes.  A
	     backslash introduces a C-style escape sequence:

	     \a		 Alert (ring the terminal bell)

	     \b		 Backspace

	     \cc	 The control character denoted by ^c in	stty(1).  If c
			 is a backslash, it must be doubled.

	     \e		 The ESC character (ASCII 0x1b)

	     \f		 Formfeed

	     \n		 Newline

	     \r		 Carriage return

	     \t		 Horizontal tab

	     \v		 Vertical tab

	     \\		 Literal backslash

	     \'		 Literal single-quote

	     \"		 Literal double-quote

	     \nnn	 The byte whose	octal value is nnn (one	to three dig-

	     \xnn	 The byte whose	hexadecimal value is nn	(one or	more
			 digits	only the last two of which are used)

	     \unnnn	 The Unicode code point	nnnn (four hexadecimal digits)

	     \Unnnnnnnn	 The Unicode code point	nnnnnnnn (eight	hexadecimal

	     The sequences for Unicode code points are currently only useful
	     with UTF-8	locales.  They reject code point 0 and UTF-16 surro-

	     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.

	     Any other string starting with a backslash	is an error.

     Double Quotes
	     Enclosing characters within double	quotes preserves the literal
	     meaning of	all characters except dollar sign (`$'), backquote
	     (``'), and	backslash (`\').  The backslash	inside double quotes
	     is	historically weird.  It	remains	literal	unless it precedes the
	     following characters, which it serves to quote:

		   $	 `     "     \	   \n

	     A backslash preserves the literal meaning of the following	char-
	     acter, with the exception of the newline character	(`\n').	 A
	     backslash preceding a newline is treated as a line	continuation.

     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:

	   !	    {	     }	      case	do
	   done	    elif     else     esac	fi
	   for	    if	     then     until	while

     An	alias is a name	and corresponding value	set using the 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
     "lf" with the value "ls -F", then the input

	   lf foobar

     would become

	   ls -F foobar

     Aliases are also recognized after an alias	whose value ends with a	space
     or	tab.  For example, if there is also an alias called "nohup" with the
     value "nohup ", then the input

	   nohup lf foobar

     would become

	   nohup ls -F foobar

     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.

     An	alias name may be escaped in a command line, so	that it	is not re-
     placed 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 Quoting subsection.

     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 IEEE Std 1003.2 ("POSIX.2")	document).  Essentially
     though, a line is read and	if the first word of the line (or after	a con-
     trol 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.

   Simple Commands
     If	a simple command has been recognized, the shell	performs the following

     1.	  Leading words	of the form "name=value" are stripped off and assigned
	  to the environment of	the simple command (they do not	affect expan-
	  sions).  Redirection operators and their arguments (as described be-
	  low) are stripped off	and saved for processing.

     2.	  The remaining	words are expanded as described	in the section called
	  Word Expansions, and the first remaining word	is considered the com-
	  mand name and	the command is located.	 The remaining words are con-
	  sidered the arguments	of the command.	 If no command name resulted,
	  then the "name=value"	variable assignments recognized	in 1) affect
	  the current shell.

     3.	  Redirections are performed as	described in the next section.

     Redirections are used to change where a command reads its input or	sends
     its output.  In general, redirections open, close,	or duplicate an	exist-
     ing reference to a	file.  The overall format used for redirection is:

	   [n] redir-op	file

     The 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.

	   [n]>	file	 redirect stdout (or file descriptor n)	to file

	   [n]>| file	 same as above,	but override the -C option

	   [n]>> file	 append	stdout (or file	descriptor n) to file

	   [n]<	file	 redirect stdin	(or file descriptor n) from file

	   [n]<> file	 redirect stdin	(or file descriptor n) to and from

	   [n1]<&n2	 duplicate stdin (or file descriptor n1) from file de-
			 scriptor n2

	   [n]<&-	 close stdin (or file descriptor n)

	   [n1]>&n2	 duplicate stdout (or file descriptor n1) to file de-
			 scriptor n2

	   [n]>&-	 close stdout (or file descriptor n)

     The following redirection is often	called a "here-document".

	   [n]<< delimiter

     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 n if
     it	is specified.  If the delimiter	as specified on	the initial line is
     quoted, then the 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 Word Expansions).  If the oper-
     ator is "<<-" instead of "<<", then leading tabs in the here-doc-text are

   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 or-
     der.  The three types of commands are all executed	in a different way.

     When a shell function is executed,	all of the shell positional parameters
     (except $0, which remains unchanged) are set to the arguments of the
     shell function.  The variables which are explicitly placed	in the envi-
     ronment of	the command (by	placing	assignments to them before the func-
     tion 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.

     Shell built-in commands are executed internally to	the shell, without
     spawning a	new process.  There are	two kinds of built-in commands:	regu-
     lar 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.

     Otherwise,	if the command name does not match a function or built-in com-
     mand, 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 "magic number" whose ASCII	representation is
     "#!", resulting in	an ENOEXEC return value	from execve(2))	but appears to
     be	a text file, the shell will run	a new instance of sh to	interpret it.

     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 "shell	procedure".

   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:

     1.	  Command names	containing a slash are simply executed without per-
	  forming any searches.

     2.	  The shell searches each entry	in the PATH variable in	turn for the
	  command.  The	value of the PATH variable should be a series of en-
	  tries	separated by colons.  Each entry consists of a directory name.
	  The current directory	may be indicated implicitly by an empty	direc-
	  tory name, or	explicitly by a	single period.

   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 nor-
     mal 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.

     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 kill -l.

     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 con-
     tain any command substitutions.

   Complex Commands
     Complex commands are combinations of simple commands with control opera-
     tors or keywords, together	creating a larger complex command.  More gen-
     erally, a command is one of the following:

	   simple command


	   list	or compound-list

	   compound command

	   function definition

     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

     A pipeline	is a sequence of one or	more commands separated	by the control
     operator `|'.  The	standard output	of all but the last command is con-
     nected to the standard input of the next command.	The standard output of
     the last command is inherited from	the shell, as usual.

     The format	for a pipeline is:

	   [!] command1	[| command2 ...]

     The standard output of command1 is	connected to the standard input	of
     command2.	The standard input, standard output, or	both of	a command is
     considered	to be assigned by the pipeline before any redirection speci-
     fied by redirection operators that	are part of the	command.

     Note that unlike some other shells, sh executes each process in a pipe-
     line with more than one command in	a subshell environment and as a	child
     of	the sh process.

     If	the pipeline is	not in the background (discussed later), the shell
     waits for all commands to complete.

     If	the keyword ! does not precede the pipeline, the exit status is	the
     exit status of the	last command specified in the pipeline if the 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.

     Because pipeline assignment of standard input or standard output or both
     takes place before	redirection, it	can be modified	by redirection.	 For

	   command1 2>&1 | command2

     sends both	the standard output and	standard error of command1 to the
     standard input of command2.

     A `;' or newline terminator causes	the preceding AND-OR-list (described
     below in the section called Short-Circuit List Operators) to be executed
     sequentially; an `&' causes asynchronous execution	of the preceding AND-

   Background Commands (&)
     If	a command is terminated	by the control operator	ampersand (`&'), the
     shell executes the	command	in a subshell environment (see Grouping
     Commands Together below) and asynchronously; the shell does not wait for
     the command to finish before executing the	next command.

     The format	for running a command in background is:

	   command1 & [command2	& ...]

     If	the shell is not interactive, the standard input of an asynchronous
     command is	set to /dev/null.

     The exit status is	zero.

   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.

   Short-Circuit List Operators
     "&&" and "||" are AND-OR list operators.  "&&" executes the first com-
     mand, and then executes the second	command	if the exit status of the
     first command is zero.  "||" is similar, but executes the second command
     if	the exit status	of the first command is	nonzero.  "&&" and "||"	both
     have the same priority.

   Flow-Control	Constructs (if,	while, for, case)
     The syntax	of the if command is:
	   if list
	   then	list
	   [elif list
	   then	list] ...
	   [else list]

     The exit status is	that of	selected then or else list, or zero if no list
     was selected.

     The syntax	of the while command is:
	   while list
	   do list

     The two lists are executed	repeatedly while the exit status of the	first
     list is zero.  The	until command is similar, but has the word until in
     place of while, which causes it to	repeat until the exit status of	the
     first list	is zero.

     The exit status is	that of	the last execution of the second list, or zero
     if	it was never executed.

     The syntax	of the for command is:
	   for variable	[in word ...]
	   do list

     If	in and the following words are omitted,	in "$@"	is used	instead.  The
     words are expanded, and then the list is executed repeatedly with the
     variable set to each word in turn.	 The do	and done commands may be re-
     placed with `{' and `}'.

     The syntax	of the break and continue commands is:
	   break [num]
	   continue [num]

     The break command terminates the num innermost for	or while loops.	 The
     continue command continues	with the next iteration	of the innermost loop.
     These are implemented as special built-in commands.

     The syntax	of the case command is:
	   case	word in
	   pattern) list ;;

     The pattern can actually be one or	more patterns (see Shell Patterns de-
     scribed later), separated by `|' 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 `;&'	instead	of `;;', execution
     continues with the	next list, continuing until a list terminated with
     `;;' or the end of	the case command.

   Grouping Commands Together
     Commands may be grouped by	writing	either



	   { list; }

     The first form executes the commands in a subshell	environment.  A	sub-
     shell environment has its own copy	of:

     1.	  The current working directory	as set by cd.

     2.	  The file creation mask as set	by umask.

     3.	  Resource limits as set by ulimit.

     4.	  References to	open files.

     5.	  Traps	as set by trap.

     6.	  Known	jobs.

     7.	  Positional parameters	and variables.

     8.	  Shell	options.

     9.	  Shell	functions.

     10.  Shell	aliases.

     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.

     A subshell	environment may	be implemented as a child process or differ-
     ently.  If	job control is enabled in an interactive shell,	commands
     grouped in	parentheses can	be suspended and continued as a	unit.

     For compatibility with other shells, two open parentheses in sequence
     should be separated by whitespace.

     The second	form never forks another shell,	so it is slightly more effi-
     cient.  Grouping commands together	this way allows	the user to redirect
     their output as though they were one program:

	   { echo -n "hello"; echo " world"; } > greeting

     The syntax	of a function definition is

	   name	( ) command

     A function	definition is an executable statement; when executed it	in-
     stalls a function named name and returns an exit status of	zero.  The
     command is	normally a list	enclosed between `{' and `}'.

     Variables may be declared to be local to a	function by using the local
     command.  This should appear as the first statement of a function,	and
     the syntax	is:

	   local [variable ...]	[-]

     The 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 in-

     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 surround-
     ing scope,	if there is one.  Otherwise, the variable is initially unset.
     The shell uses dynamic scoping, so	that if	the variable x is made local
     to	function f, which then calls function g, references to the variable x
     made inside g will	refer to the variable x	declared inside	f, not to the
     global variable named x.

     The only special parameter	that can be made local is `-'.	Making `-' lo-
     cal causes	any shell options (including those that	only have long names)
     that are changed via the set command inside the function to be restored
     to	their original values when the function	returns.

     The syntax	of the return command is

	   return [exitstatus]

     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 return command is im-
     plemented as a special built-in command.

   Variables and Parameters
     The shell maintains a set of parameters.  A parameter denoted by a	name
     (consisting solely	of alphabetics,	numerics, and underscores, and start-
     ing 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


     A parameter can also be denoted by	a number or a special character	as ex-
     plained below.

     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.

     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 export, local or readonly built-in commands	that have this form.
     For this, the builtin's name must be literal (not the result of an	expan-
     sion) and may optionally be preceded by one or more literal instances of
     command without options.

   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 set built-in
     command can also be used to set or	reset them.

   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

     $*	     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 IFS	variable, or by	a space	if IFS is un-

     $@	     Expands to	the positional parameters, starting from one.  When
	     the expansion occurs within double-quotes,	each positional	param-
	     eter expands as a separate	argument.  If there are	no positional
	     parameters, the expansion of @ generates zero arguments, even
	     when @ is double-quoted.  What this basically means, for example,
	     is	if $1 is "abc" and $2 is "def ghi", then "$@" expands to the
	     two arguments:

		   "abc"   "def	ghi"

     $#	     Expands to	the number of positional parameters.

     $?	     Expands to	the exit status	of the most recent pipeline.

     $-	     (hyphen) Expands to the current option flags (the single-letter
	     option names concatenated into a string) as specified on invoca-
	     tion, by the set built-in command,	or implicitly by the shell.

     $$	     Expands to	the process ID of the invoked shell.  A	subshell re-
	     tains the same value of $ as its parent.

     $!	     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 wait	built-in command reports completion of
	     the process.

     $0	     (zero) Expands to the name	of the shell script if passed on the
	     command line, the name operand if given (with -c) or otherwise
	     argument 0	passed to the shell.

   Special Variables
     The following variables are set by	the shell or have special meaning to

     CDPATH    The search path used with the cd	built-in.

     EDITOR    The fallback editor used	with the fc built-in.  If not set, the
	       default editor is ed(1).

     FCEDIT    The default editor used with the	fc built-in.

     HISTSIZE  The number of previous commands that are	accessible.

     HOME      The user's home directory, used in tilde	expansion and as a de-
	       fault directory for the cd built-in.

     IFS       Input Field Separators.	This is	initialized at startup to
	       <space>,	<tab>, and <newline> in	that order.  This value	also
	       applies if IFS is unset,	but not	if it is set to	the empty
	       string.	See the	White Space Splitting section for more de-

     LINENO    The current line	number in the script or	function.

     MAIL      The name	of a mail file,	that will be checked for the arrival
	       of new mail.  Overridden	by MAILPATH.

     MAILPATH  A colon (`:') separated list of file names, for the shell to
	       check for incoming mail.	 This variable overrides the MAIL set-
	       ting.  There is a maximum of 10 mailboxes that can be monitored
	       at once.

     OPTIND    The index of the	next argument to be processed by getopts.
	       This is initialized to 1	at startup.

     PATH      The default search path for executables.	 See the Path Search
	       section for details.

     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 re-
	       tains the same value of PPID.

     PS1       The primary prompt string, which	defaults to "$ ", unless you
	       are the superuser, in which case	it defaults to "# ".  PS1 may
	       include any of the following formatting sequences, which	are
	       replaced	by the given information:

	       \H      This system's fully-qualified hostname (FQDN).

	       \h      This system's hostname.

	       \u      User name.

	       \W      The final component of the current working directory.

	       \w      The entire path of the current working directory.

	       \$      Superuser status.  "$" for normal users and "#" for su-

	       \\      A literal backslash.

     PS2       The secondary prompt string, which defaults to "> ".  PS2 may
	       include any of the formatting sequences from PS1.

     PS4       The prefix for the trace	output (if -x is active).  The default
	       is "+ ".

   Word	Expansions
     This clause describes the various expansions that are performed on	words.
     Not all expansions	are performed on every word, as	explained later.

     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 @ within double-
     quotes, as	was described above.

     The order of word expansion is:

     1.	  Tilde	Expansion, Parameter Expansion,	Command	Substitution, Arith-
	  metic	Expansion (these all occur at the same time).

     2.	  Field	Splitting is performed on fields generated by step (1) unless
	  the IFS variable is null.

     3.	  Pathname Expansion (unless the -f option is in effect).

     4.	  Quote	Removal.

     The `$' character is used to introduce parameter expansion, command sub-
     stitution,	or arithmetic expansion.

   Tilde Expansion (substituting a user's home directory)
     A word beginning with an unquoted tilde character (`~') is	subjected to
     tilde expansion.  All the characters up to	a slash	(`/') 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 ~/foobar), the tilde	is re-
     placed with the value of the HOME variable	(the current user's home di-

   Parameter Expansion
     The format	for parameter expansion	is as follows:


     where expression consists of all characters until the matching `}'.  Any
     `}' escaped by a backslash	or within a single-quoted or double-quoted
     string, and characters in embedded	arithmetic expansions, command substi-
     tutions, and variable expansions, are not examined	in determining the
     matching `}'.  If the variants with `+', `-', `=' or `?' occur within a
     double-quoted string, as an extension there may be	unquoted parts (via
     double-quotes inside the expansion); `}' within such parts	are also not
     examined in determining the matching `}'.

     The simplest form for parameter expansion is:


     The value,	if any,	of parameter is	substituted.

     The parameter name	or symbol can be enclosed in braces, which are op-
     tional 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:

     1.	  Field	splitting is not performed on the results of the expansion,
	  with the exception of	the special parameter @.

     2.	  Pathname expansion is	not performed on the results of	the expansion.

     In	addition, a parameter expansion	can be modified	by using one of	the
     following formats.

	     Use Default Values.  If parameter is unset	or null, the expansion
	     of	word is	substituted; otherwise,	the value of parameter is sub-

	     Assign Default Values.  If	parameter is unset or null, the	expan-
	     sion of word is assigned to parameter.  In	all cases, the final
	     value of parameter	is substituted.	 Quoting inside	word does not
	     prevent field splitting or	pathname expansion.  Only variables,
	     not positional parameters or special parameters, can be assigned
	     in	this way.

	     Indicate Error if Null or Unset.  If parameter is unset or	null,
	     the expansion of word (or a message indicating it is unset	if
	     word is omitted) is written to standard error and the shell exits
	     with a nonzero exit status.  Otherwise, the value of parameter is
	     substituted.  An interactive shell	need not exit.

	     Use Alternate Value.  If parameter	is unset or null, null is sub-
	     stituted; otherwise, the expansion	of word	is substituted.

     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.

     The 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.

	     String Length.  The length	in characters of the value of

     The following four	varieties of parameter expansion provide for substring
     processing.  In each case,	pattern	matching notation (see Shell
     Patterns),	rather than regular expression notation, is used to evaluate
     the patterns.  If parameter is one	of the special parameters * or @, the
     result of the expansion is	unspecified.  Enclosing	the full parameter ex-
     pansion string in double-quotes does not cause the	following four vari-
     eties of pattern characters to be quoted, whereas quoting characters
     within the	braces has this	effect.

	     Remove Smallest Suffix Pattern.  The word is expanded to produce
	     a pattern.	 The parameter expansion then results in parameter,
	     with the smallest portion of the suffix matched by	the pattern

	     Remove Largest Suffix Pattern.  The word is expanded to produce a
	     pattern.  The parameter expansion then results in parameter, with
	     the largest portion of the	suffix matched by the pattern deleted.

	     Remove Smallest Prefix Pattern.  The word is expanded to produce
	     a pattern.	 The parameter expansion then results in parameter,
	     with the smallest portion of the prefix matched by	the pattern

	     Remove Largest Prefix Pattern.  The word is expanded to produce a
	     pattern.  The parameter expansion then results in parameter, with
	     the largest portion of the	prefix matched by the pattern deleted.

   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:


     or	the backquoted version:


     The shell expands the command substitution	by executing command and re-
     placing the command substitution with the standard	output of the command,
     removing sequences	of one or more newlines	at the end of the substitu-
     tion.  Embedded newlines before the end of	the output are not removed;
     however, during field splitting, they may be translated into spaces de-
     pending on	the value of IFS and the quoting that is in effect.  The com-
     mand is executed in a subshell environment, except	that the built-in com-
     mands jobid, jobs,	and trap return	information about the parent shell en-
     vironment and times returns information about the same process if they
     are the only command in a command substitution.

     If	a command substitution of the $( form begins with a subshell, the $(
     and ( must	be separated by	whitespace to avoid ambiguity with arithmetic

   Arithmetic Expansion
     Arithmetic	expansion provides a mechanism for evaluating an arithmetic
     expression	and substituting its value.  The format	for arithmetic expan-
     sion is as	follows:


     The 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 expression for parameter	expansion, command
     substitution, arithmetic expansion	and quote removal.

     The allowed expressions are a subset of C expressions, summarized below.

	   Values     All values are of	type intmax_t.

	   Constants  Decimal, octal (starting with 0) and hexadecimal (start-
		      ing with 0x) integer constants.

	   Variables  Shell variables can be read and written and contain in-
		      teger constants.

	   Unary operators
		      !	~ + -

	   Binary operators
		      *	/ % + -	<< >> <	<= > >=	== != &	^ | && ||

	   Assignment operators
		      =	+= -= *= /= %= <<= >>= &= ^= |=

	   Conditional operator
		      ?	:

     The result	of the expression is substituted in decimal.

   White Space Splitting (Field	Splitting)
     In	certain	contexts, after	parameter expansion, command substitution, and
     arithmetic	expansion the shell scans the results of expansions and	sub-
     stitutions	that did not occur in double-quotes for	field splitting	and
     multiple fields can result.

     Characters	in IFS that are	whitespace (<space>, <tab>, and	<newline>) are
     treated differently from other characters in IFS.

     Whitespace	in IFS at the beginning	or end of a word is discarded.

     Subsequently, a field is delimited	by either

     1.	  a non-whitespace character in	IFS with any whitespace	in IFS sur-
	  rounding it, or

     2.	  one or more whitespace characters in IFS.

     If	a word ends with a non-whitespace character in IFS, there is no	empty
     field after this character.

     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 IFS	is

   Pathname Expansion (File Name Generation)
     Unless the	-f option is set, file name generation is performed after word
     splitting is complete.  Each word is viewed as a series of	patterns, sep-
     arated 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 case command.

   Shell Patterns
     A pattern consists	of normal characters, which match themselves, and
     meta-characters.  The meta-characters are `*', `?', and `['.  These char-
     acters 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.

     An	asterisk (`*') matches any string of characters.  A question mark
     (`?') matches any single character.  A left bracket (`[') introduces a
     character class.  The end of the character	class is indicated by a	`]';
     if	the `]'	is missing then	the `['	matches	a `[' rather than introducing
     a character class.	 A character class matches any of the characters be-
     tween the square brackets.	 A locale-dependent range of characters	may be
     specified using a minus sign.  A named class of characters	(see
     wctype(3))	may be specified by surrounding	the name with `[:' and `:]'.
     For example, `[[:alpha:]]'	is a shell pattern that	matches	a single let-
     ter.  The character class may be complemented by making an	exclamation
     point (`!') the first character of	the character class.  A	caret (`^')
     has the same effect but is	non-standard.

     To	include	a `]' in a character class, make it the	first character	listed
     (after the	`!' or `^', if any).  To include a `-',	make it	the first or
     last character listed.

   Built-in Commands
     This section lists	the built-in commands.

     :	     A null command that returns a 0 (true) exit value.

     . file  The commands in the specified file	are read and executed by the
	     shell.  The return	command	may be used to return to the . com-
	     mand's caller.  If	file contains any `/' characters, it is	used
	     as	is.  Otherwise,	the shell searches the PATH for	the file.  If
	     it	is not found in	the PATH, it is	sought in the current working

     [	     A built-in	equivalent of test(1).

     alias [name[=string] ...]
	     If	name=string is specified, the shell defines the	alias name
	     with value	string.	 If just name is specified, the	value of the
	     alias name	is printed.  With no arguments,	the alias built-in
	     command prints the	names and values of all	defined	aliases	(see
	     unalias).	Alias values are written with appropriate quoting so
	     that they are suitable for	re-input to the	shell.	Also see the
	     Aliases subsection.

     bg	[job ...]
	     Continue the specified jobs (or the current job if	no jobs	are
	     given) in the background.

     bind [-aeklrsv] [key [command]]
	     List or alter key bindings	for the	line editor.  This command is
	     documented	in editrc(5).

     break [num]
	     See the Flow-Control Constructs subsection.

     builtin cmd [arg ...]
	     Execute the specified built-in command, cmd.  This	is useful when
	     the user wishes to	override a shell function with the same	name
	     as	a built-in command.

     cd	[-L | -P] [-e] [directory]

     cd	-    Switch to the specified directory,	to the directory specified in
	     the HOME environment variable if no directory is specified	or to
	     the directory specified in	the OLDPWD environment variable	if
	     directory is -.  If directory does	not begin with /, ., or	..,
	     then the directories listed in the	CDPATH variable	will be
	     searched for the specified	directory.  If CDPATH is unset,	the
	     current directory is searched.  The format	of CDPATH is the same
	     as	that of	PATH.  In an interactive shell,	the cd command will
	     print out the name	of the directory that it actually switched to
	     if	the CDPATH mechanism was used or if directory was -.

	     If	the -P option is specified, .. is handled physically and sym-
	     bolic links are resolved before ..	components are processed.  If
	     the -L option is specified, .. is handled logically.  This	is the

	     The -e option causes cd to	return exit status 1 if	the full path-
	     name of the new directory cannot be determined reliably or	at
	     all.  Normally this is not	considered an error, although a	warn-
	     ing is printed.

	     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	-e was given.

     chdir   A synonym for the cd built-in command.

     command [-p] [utility [argument ...]]

     command [-p] -v utility

     command [-p] -V utility
	     The first form of invocation executes the specified utility, ig-
	     noring shell functions in the search.  If utility is a special
	     builtin, it is executed as	if it were a regular builtin.

	     If	the -p option is specified, the	command	search is performed
	     using a default value of PATH that	is guaranteed to find all of
	     the standard utilities.

	     If	the -v option is specified, utility is not executed but	a de-
	     scription of its interpretation by	the shell is printed.  For or-
	     dinary 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 "alias name=value".

	     The -V option is identical	to -v except for the output.  It
	     prints "utility is	description" where description is either the
	     path name to utility, a special shell builtin, a shell builtin, a
	     shell function, a shell keyword or	an alias for value.

     continue [num]
	     See the Flow-Control Constructs subsection.

     echo [-e |	-n] [string ...]
	     Print a space-separated list of the arguments to the standard
	     output and	append a newline character.

	     -n	     Suppress the output of the	trailing newline.

	     -e	     Process C-style backslash escape sequences.  The echo
		     command understands the following character escapes:

		     \a	     Alert (ring the terminal bell)

		     \b	     Backspace

		     \c	     Suppress the trailing newline (this has the side-
			     effect of truncating the line if it is not	the
			     last character)

		     \e	     The ESC character (ASCII 0x1b)

		     \f	     Formfeed

		     \n	     Newline

		     \r	     Carriage return

		     \t	     Horizontal	tab

		     \v	     Vertical tab

		     \\	     Literal backslash

		     \0nnn   (Zero) The	character whose	octal value is nnn

		     If	string is not enclosed in quotes then the backslash
		     itself must be escaped with a backslash to	protect	it
		     from the shell.  For example

			   $ echo -e "a\vb"
			   $ echo -e a\\vb
			   $ echo -e "a\\b"
			   $ echo -e a\\\\b

	     Only one of the -e	and -n options may be specified.

     eval string ...
	     Concatenate all the arguments with	spaces.	 Then re-parse and ex-
	     ecute the command.

     exec [command [arg	...]]
	     Unless 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 exec com-
	     mand are marked as	permanent, so that they	are not	undone when
	     the exec command finishes.

     exit [exitstatus]
	     Terminate the shell process.  If exitstatus is given it is	used
	     as	the exit status	of the shell.  Otherwise, if the shell is exe-
	     cuting an 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 sta-
	     tus should	be an integer between 0	and 255.

     export name ...

     export [-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 unset it.  The shell allows	the value of a vari-
	     able to be	set at the same	time as	it is exported by writing

		   export name=value

	     With no arguments the export command lists	the names of all ex-
	     ported variables.	If the -p option is specified, the exported
	     variables are printed as "export name=value" lines, suitable for
	     re-input to the shell.

     false   A null command that returns a non-zero (false) exit value.

     fc	[-e editor] [first [last]]

     fc	-l [-nr] [first	[last]]

     fc	-s [old=new] [first]
	     The fc built-in command lists, or edits and re-executes, commands
	     previously	entered	to an interactive shell.

	     -e	editor
		     Use the editor named by editor to edit the	commands.  The
		     editor string is a	command	name, subject to search	via
		     the PATH variable.	 The value in the FCEDIT variable is
		     used as a default when -e is not specified.  If FCEDIT is
		     null or unset, the	value of the EDITOR variable is	used.
		     If	EDITOR is null or unset, ed(1) is used as the editor.

	     -l	(ell)
		     List the commands rather than invoking an editor on them.
		     The commands are written in the sequence indicated	by the
		     first and last operands, as affected by -r, with each
		     command preceded by the command number.

	     -n	     Suppress command numbers when listing with	-l.

	     -r	     Reverse the order of the commands listed (with -l)	or
		     edited (with neither -l nor -s).

	     -s	     Re-execute	the command without invoking an	editor.


	     last    Select the	commands to list or edit.  The number of pre-
		     vious commands that can be	accessed are determined	by the
		     value of the HISTSIZE variable.  The value	of first or
		     last or both are one of the following:

		     [+]num  A positive	number representing a command number;
			     command numbers can be displayed with the -l op-

		     -num    A negative	decimal	number representing the	com-
			     mand that was executed num	of commands previ-
			     ously.  For example, -1 is	the immediately	previ-
			     ous command.

		     string  A string indicating the most recently entered
			     command that begins with that string.  If the
			     old=new operand is	not also specified with	-s,
			     the string	form of	the first operand cannot con-
			     tain an embedded equal sign.

	     The following variables affect the	execution of fc:

	     FCEDIT    Name of the editor to use for history editing.

	     HISTSIZE  The number of previous commands that are	accessible.

     fg	[job]
	     Move the specified	job or the current job to the foreground.

     getopts optstring var
	     The POSIX getopts command.	 The getopts command deprecates	the
	     older 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 OPTIND.  If an option takes an argument,
	     it	is placed into the shell variable OPTARG.  If an invalid op-
	     tion is encountered, var is set to	`?'.  It returns a false value
	     (1) when it encounters the	end of the options.  A new set of ar-
	     guments may be parsed by assigning	OPTIND=1.

     hash [-rv]	[command ...]
	     The shell maintains a hash	table which remembers the locations of
	     commands.	With no	arguments whatsoever, the hash command prints
	     out the contents of this table.

	     With arguments, the hash command removes each specified command
	     from the hash table (unless they are functions) and then locates
	     it.  With the -v option, hash prints the locations	of the com-
	     mands as it finds them.  The -r option causes the hash command to
	     delete all	the entries in the hash	table except for functions.

     jobid [job]
	     Print the process IDs of the processes in the specified job.  If
	     the job argument is omitted, use the current job.

     jobs [-lps] [job ...]
	     Print information about the specified jobs, or all	jobs if	no job
	     argument is given.	 The information printed includes job ID, sta-
	     tus and command name.

	     If	the -l option is specified, the	PID of each job	is also
	     printed.  If the -p option	is specified, only the process IDs for
	     the process group leaders are printed, one	per line.  If the -s
	     option is specified, only the PIDs	of the job commands are
	     printed, one per line.

     kill    A built-in	equivalent of kill(1) that additionally	supports send-
	     ing signals to jobs.

     local [variable ...] [-]
	     See the Functions subsection.

     printf  A built-in	equivalent of printf(1).

     pwd [-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 re-
	     computing it each time.  This makes it faster.  However, if the
	     current directory is renamed, the built-in	version	of pwd(1) will
	     continue to print the old name for	the directory.

	     If	the -P option is specified, symbolic links are resolved.  If
	     the -L option is specified, the shell's notion of the current di-
	     rectory is	printed	(symbolic links	are not	resolved).  This is
	     the default.

     read [-p prompt] [-t timeout] [-er] variable ...
	     The prompt	is printed if the -p option is specified and the stan-
	     dard 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 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	IFS that sepa-
	     rated them) are assigned to the last variable.  If	there are more
	     variables than pieces, the	remaining variables are	assigned the
	     null string.

	     Backslashes are treated specially,	unless the -r option is	speci-
	     fied.  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	IFS, even if
	     it	is.

	     If	the -t option is specified and the timeout elapses before a
	     complete line of input is supplied, the read command will return
	     an	exit status as if terminated by	SIGALRM	without	assigning any
	     values.  The timeout value	may optionally be followed by one of
	     `s', `m' or `h' to	explicitly specify seconds, minutes or hours.
	     If	none is	supplied, `s' is assumed.

	     The -e option exists only for backward compatibility with older

	     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	read.

     readonly [-p] [name ...]
	     Each specified 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:

		   readonly name=value

	     With no arguments the readonly command lists the names of all
	     read only variables.  If the -p option is specified, the read-
	     only variables are	printed	as "readonly name=value" lines,	suit-
	     able for re-input to the shell.

     return [exitstatus]
	     See the Functions subsection.

     set [-/+abCEefIimnpTuVvx] [-/+o longname] [-- arg ...]
	     The set command performs three different functions:

	     With no arguments,	it lists the values of all shell variables.

	     If	options	are given, either in short form	or using the long
	     "-/+o longname" form, it sets or clears the specified options as
	     described in the section called Argument List Processing.

	     If	the "--" option	is specified, set will replace the shell's po-
	     sitional parameters with the subsequent arguments.	 If no argu-
	     ments follow the "--" option, all the positional parameters will
	     be	cleared, which is equivalent to	executing the command "shift
	     $#".  The "--" flag may be	omitted	when specifying	arguments to
	     be	used as	positional replacement parameters.  This is not	recom-
	     mended, because the first argument	may begin with a dash (`-') or
	     a plus (`+'), which the set command will interpret	as a request
	     to	enable or disable options.

     setvar variable value
	     Assigns the specified value to the	specified variable.  The
	     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 "variable=value" rather than	using

     shift [n]
	     Shift the positional parameters n times, or once if n is not
	     specified.	 A shift sets the value	of $1 to the value of $2, the
	     value of $2 to the	value of $3, and so on,	decreasing the value
	     of	$# by one.  For	portability, shifting if there are zero	posi-
	     tional parameters should be avoided, since	the shell may abort.

     test    A built-in	equivalent of test(1).

     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.

     trap [action] signal ...

     trap -l
	     Cause the shell to	parse and execute action when any specified
	     signal is received.  The signals are specified by name or number.
	     In	addition, the pseudo-signal EXIT may be	used to	specify	an
	     action that is performed when the shell terminates.  The action
	     may be an empty string or a dash (`-'); the former	causes the
	     specified signal to be ignored and	the latter causes the default
	     action to be taken.  Omitting the action and using	only signal
	     numbers is	another	way to request the default action.  In a sub-
	     shell or utility environment, the shell resets trapped (but not
	     ignored) signals to the default action.  The trap command has no
	     effect on signals that were ignored on entry to the shell.

	     Option -l causes the trap command to display a list of valid sig-
	     nal names.

     true    A null command that returns a 0 (true) exit value.

     type [name	...]
	     Interpret each 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 com-
	     mands and tracked aliases the complete pathname of	the command is

     ulimit [-HSabcdfklmnopstuvw] [limit]
	     Set or display resource limits (see getrlimit(2)).	 If limit is
	     specified,	the named resource will	be set;	otherwise the current
	     resource value will be displayed.

	     If	-H is specified, the hard limits will be set or	displayed.
	     While everybody is	allowed	to reduce a hard limit,	only the supe-
	     ruser can increase	it.  The -S option specifies the soft limits
	     instead.  When displaying limits, only one	of -S or -H can	be
	     given.  The default is to display the soft	limits,	and to set
	     both the hard and the soft	limits.

	     Option -a causes the ulimit command to display all	resources.
	     The parameter limit is not	acceptable in this mode.

	     The remaining options specify which resource value	is to be dis-
	     played or modified.  They are mutually exclusive.

	     -b	sbsize
		     The maximum size of socket	buffer usage, in bytes.

	     -c	coredumpsize
		     The maximal size of core dump files, in 512-byte blocks.
		     Setting coredumpsize to 0 prevents	core dump files	from
		     being created.

	     -d	datasize
		     The maximal size of the data segment of a process,	in

	     -f	filesize
		     The maximal size of a file, in 512-byte blocks.

	     -k	kqueues
		     The maximal number	of kqueues (see	kqueue(2)) for this
		     user ID.

	     -l	lockedmem
		     The maximal size of memory	that can be locked by a
		     process, in kilobytes.

	     -m	memoryuse
		     The maximal resident set size of a	process, in kilobytes.

	     -n	nofiles
		     The maximal number	of descriptors that could be opened by
		     a process.

	     -o	umtxp
		     The maximal number	of process-shared locks	(see
		     pthread(3)) for this user ID.

	     -p	pseudoterminals
		     The maximal number	of pseudo-terminals for	this user ID.

	     -s	stacksize
		     The maximal size of the stack segment, in kilobytes.

	     -t	time
		     The maximal amount	of CPU time to be used by each
		     process, in seconds.

	     -u	userproc
		     The maximal number	of simultaneous	processes for this
		     user ID.

	     -v	virtualmem
		     The maximal virtual size of a process, in kilobytes.

	     -w	swapuse
		     The maximum amount	of swap	space reserved or used for
		     this user ID, in kilobytes.

     umask [-S]	[mask]
	     Set the file creation mask	(see umask(2)) to the octal or sym-
	     bolic (see	chmod(1)) value	specified by mask.  If the argument is
	     omitted, the current mask value is	printed.  If the -S option is
	     specified,	the output is symbolic,	otherwise the output is	octal.

     unalias [-a] [name	...]
	     The specified alias names are removed.  If	-a is specified, all
	     aliases are removed.

     unset [-fv] name ...
	     The specified variables or	functions are unset and	unexported.
	     If	the -v option is specified or no options are given, the	name
	     arguments are treated as variable names.  If the -f option	is
	     specified,	the name arguments are treated as function names.

     wait [job ...]
	     Wait for each specified job to complete and return	the exit sta-
	     tus of the	last process in	the last specified job.	 If any	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

   Command Line	Editing
     When sh is	being used interactively from a	terminal, the current command
     and the command history (see fc in	Built-in Commands) can be edited using
     vi-mode command line editing.  This mode uses commands similar to a sub-
     set of those described in the vi(1) man page.  The	command	"set -o	vi"
     (or "set -V") enables vi-mode editing and places sh into vi insert	mode.
     With vi-mode enabled, sh can be switched between insert mode and command
     mode by typing <ESC>.  Hitting <return> while in command mode will	pass
     the line to the shell.

     Similarly,	the "set -o emacs" (or "set -E") command can be	used to	enable
     a subset of emacs-style command line editing features.

     The following environment variables affect	the execution of sh:

     ENV	 Initialization	file for interactive shells.

     LANG, LC_*	 Locale	settings.  These are inherited by children of the
		 shell,	and is used in a limited manner	by the shell itself.

     OLDPWD	 The previous current directory.  This is used and updated by

     PWD	 An absolute pathname for the current directory, possibly con-
		 taining symbolic links.  This is used and updated by the

     TERM	 The default terminal setting for the shell.  This is inher-
		 ited by children of the shell,	and is used in the history
		 editing modes.

     Additionally, environment variables are turned into shell variables at
     startup, which may	affect the shell as described under Special Variables.

     ~/.profile		  User's login profile.
     /etc/profile	  System login profile.
     /etc/shells	  Shell	database.
     /etc/suid_profile	  Privileged shell profile.

     If	the 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	inter-
     active 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 exit builtin is used with a numeric argument, it will return the ar-

     builtin(1), chsh(1), echo(1), ed(1), emacs(1), kill(1), printf(1),
     pwd(1), test(1), vi(1), execve(2),	getrlimit(2), umask(2),	wctype(3),
     editrc(5),	shells(5)

     A sh command, the Thompson	shell, appeared	in Version 1 AT&T UNIX.	 It
     was superseded in Version 7 AT&T UNIX by the Bourne shell,	which inher-
     ited the name sh.

     This version of sh	was rewritten in 1989 under the	BSD license after the
     Bourne shell from AT&T System V Release 4 UNIX.

     This version of sh	was originally written by Kenneth Almquist.

     The sh utility does not recognize multibyte characters other than UTF-8.
     Splitting using IFS does not recognize multibyte characters.

BSD				 July 6, 2020				   BSD


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