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

     sh	-- command interpreter (shell)

     sh	[-/+abCEefIimnpsTuVvx] [-/+o longname] [-c string] [arg	...]

     sh	is the standard	command	interpreter for	the system.  The current ver-
     sion of sh	is in the process of being changed to conform with the IEEE
     Std 1003.2	("POSIX.2") specification for the shell.  This version has
     many features which make it appear	similar	in some	respects to the	Korn
     shell, but	it is not a Korn shell clone (run GNU's	bash if	you want
     that).  Only features designated by POSIX,	plus a few Berkeley exten-
     sions, are	being incorporated into	this shell.  This man page is not in-
     tended to be a tutorial or	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 running 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 and the file can be executed directly by
     the shell.

     If	no args	are present and	if the standard	input of the shell is con-
     nected to a terminal (or if the -i	flag 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	de-
     scribed below).  When first starting, the shell inspects argument 0, and
     if	it begins with a dash '-', 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 /etc/profile
     and .profile 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
     next reads	commands from the file named in	ENV.  Therefore, a user	should
     place commands that are to	be executed only at login time in the .profile
     file, and commands	that are executed for every shell inside the ENV file.
     To	set the	ENV variable to	some file, place the following line in your
     .profile of your home directory

	   ENV=$HOME/.shinit; export ENV

     substituting for .shinit any filename you wish.  If commandline arguments
     besides the options have been specified, then the shell treats the	first
     argument 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 name that can
     be	used as	an argument to the set(1) builtin (described later).  These
     names are provided	next to	the single letter option in the	descriptions
     below.  Specifying	a dash "-" enables the option, while using a plus "+"
     disables the option.  A "--" or plain "-" will stop option	processing and
     will force	the remaining words on the command line	to be treated as argu-

     -a	allexport
	     Export all	variables assigned to.

     -b	notify
	     Enable asynchronous notification of background job	completion.

     -C	noclobber
	     Don't overwrite existing files with ">." (UNIMPLEMENTED)

     -E	emacs
	     Enable the	built-in emacs(1) commandline editor (disables -V if
	     it	has been set).

     -e	errexit
	     If	not interactive, exit immediately if any untested command
	     fails.  The exit status of	a command is considered	to be explic-
	     itly tested if the	command	is used	to control an if, elif,	while,
	     or	until; or if the command is the	left hand operand of an	"&&"
	     or	"||" operator.

     -f	noglob
	     Disable pathname expansion.

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

     -i	interactive
	     Force the shell to	behave interactively.

     -m	monitor
	     Turn on job control (set automatically when interactive).

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

     -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.	Also on	interactive
	     shells and	when enabled, this mode	sources	/etc/suid_profile (in-
	     stead of ~/.profile) after	/etc/profile and ignores the contents
	     of	the ENV	variable.

     -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. with set(1)).

     -T	asynctraps
	     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 option
	     is	useful to put guarding shells around childs that block sig-
	     nals. The surrounding shell may kill the child or it may just re-
	     turn 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 that is not set, and if the shell	is not interactive,
	     exit immediately.	(UNIMPLEMENTED)

     -V	vi   Enable the	built-in vi(1) commandline 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	to standard error (preceded by a '+ ') before
	     it	is executed.  Useful for debugging.

     -c	string
	     Pass the string argument to the shell to be interpreted as	input.
	     Keep in mind that this option only	accepts	a single string	as its
	     argument, hence multi-word	strings	must be	quoted.

   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 that are special to	the shell called ``operators''.	 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:
	     <	>  >|  <<  >>  <&  >&  <<-

     Quoting is	used to	remove the special meaning of certain characters or
     words to the shell, such as operators, whitespace,	or keywords.  There
     are three types of	quoting: matched 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).

     Double Quotes
	     Enclosing characters within double	quotes preserves the literal
	     meaning of	all characters except dollarsign ($), backquote	(`),
	     and backslash (\).	 The backslash inside double quotes is histor-
	     ically weird, and serves to quote only the	following characters:
	     $	`  "  \	\n.  Otherwise it remains literal.

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

   Reserved Words
     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 reserved words:

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

     An	alias is a name	and corresponding value	set using the alias(1) builtin
     command.  Whenever	a reserved word	may occur (see above), and after
     checking for reserved words, 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 <return>

     would become

	   ls -F foobar	<return>

     Aliases provide a convenient way for naive	users to create	shorthands for
     commands without having to	learn how to create functions with arguments.
     They can also be used to create lexically obscure code.  This use is dis-

     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 reserved word, then the shell has recognized a
     simple command.  Otherwise, a complex command or some other special con-
     struct 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	as-
	  signed to the	environment of the simple command.  Redirection	opera-
	  tors and their arguments (as described below)	are stripped off and
	  saved	for processing.

     2.	  The remaining	words are expanded as described	in the section called
	  ``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

     where redir-op is one of the redirection operators	mentioned previously.
     The following gives some examples of how these operators can be used.
     NOTE: stdin and stdout are	commonly used abbreviations for	standard input
     and standard output, respectively.

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

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

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

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

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

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

	   [n1]>&n2    duplicate stdout	(or n1)	to n2.

	   [n]>&-      close stdout (or	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 ``Expansions'').	 If the	opera-
     tor is ``<<-'' instead of ``<<'', then leading tabs in the	here-doc-text
     are stripped.

   Search and Execution
     There are three types of commands:	shell functions, builtin commands, and
     normal programs --	and the	command	is searched for	(by name) in that or-
     der.  They	each are 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 builtins are	executed internally to the shell, without spawning a
     new process.

     Otherwise,	if the command name doesn't match a function or	builtin, the
     command is	searched for as	a normal program in the	filesystem (as de-
     scribed 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 "#!", so
     execve() returns ENOEXEC then) the	shell will interpret the program in a
     subshell.	The child shell	will reinitialize itself in this case, so that
     the effect	will be	as if a	new shell had been invoked to handle the ad-
     hoc shell script, except that the location	of hashed commands located in
     the parent	shell will be remembered by the	child.

     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 builtin command by that name.
     If	a builtin 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 PATH	in turn	for the	command.  The
	  value	of the 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.

   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	builtin	commands return	exit codes, as
     does an executed shell function.

     If	a command is terminated	by a signal, its exit status is	128 plus the
     signal number.  Signal numbers are	defined	in the header file

   Complex Commands
     Complex commands are combinations of simple commands with control opera-
     tors or reserved words, together creating a larger	complex	command.  More
     generally,	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.

     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 connected
     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.

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

     If	the reserved word ! does not precede the pipeline, the exit status is
     the exit status of	the last command specified in the pipeline.  Other-
     wise, the exit status is the logical NOT of the exit status of the	last
     command.  That is,	if the last command returns zero, the exit status is
     1;	if the last command returns greater than zero, the exit	status is

     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
     next) to be executed sequentially;	a & causes asynchronous	execution of
     the preceding AND-OR-list.

     Note that unlike some other shells, each process in the pipeline is a
     child of the invoking shell (unless it is a shell builtin,	in which case
     it	executes in the	current	shell -- but any effect	it has on the environ-
     ment is wiped).

   Background Commands -- &
     If	a command is terminated	by the control operator	ampersand (&), the
     shell executes the	command	asynchronously -- that is, 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.

   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 proceed 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
     command, and then executes	the second command if the exit status of the
     first command is zero.  ``||'' is similar,	but executes the second	com-
     mand 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 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 syntax	of the for command is

	   for variable	in word...
	   do	list

     The words are expanded, and then the list is executed repeatedly with the
     variable set to each word in turn.	 do and	done may be replaced with
     ``{'' and ``}''.

     The syntax	of the break and continue command is

	   break [ num ]
	   continue [ num ]

     Break terminates the num innermost	for or while loops.  Continue contin-
     ues with the next iteration of the	innermost loop.	 These are implemented
     as	builtin	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.

   Grouping Commands Together
     Commands may be grouped by	writing	either



	   { list; }

     The first of these	executes the commands in a subshell.  Builtin commands
     grouped into a (list) will	not affect the current shell.  The second form
     does not fork another shell so is slightly	more efficient.	 Grouping com-
     mands together this way allows you	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 a local com-
     mand.  This should	appear as the first statement of a function, and the
     syntax is

	   local [ variable | -	] ...

     Local is implemented as a builtin command.

     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	you make the variable x	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	than can be made local is ``-''.  Making ``-''
     local any shell options that are changed via the set command inside the
     function to be restored to	their original values when the function	re-

     The syntax	of the return command is

	   return [ exitstatus ]

     It	terminates the currently executing function.  Return is	implemented as
     a builtin command.

   Variables and Parameters
     The shell maintains a set of parameters.  A parameter denoted by a	name
     is	called a variable.  When starting up, the shell	turns all the environ-
     ment variables into shell variables.  New variables can be	set using the


     Variables set by the user must have a name	consisting solely of alphabet-
     ics, numerics, and	underscores - the first	of which must not be numeric.
     A parameter can also be denoted by	a number or a special character	as ex-
     plained below.

   Positional Parameters
     A positional parameter is a parameter denoted by a	number (n > 0).	 The
     shell sets	these initially	to the values of its commandline arguments
     that follow the name of the shell script.	The set(1) builtin can also be
     used to set or reset them.

   Special Parameters
     A special parameter is a parameter	denoted	by one of the following	spe-
     cial characters.  The value of the	parameter is listed next to its	char-

     *	     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

     @	     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 builtin 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.

     0	     (zero) Expands to the name	of the shell or	shell script.

   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 set -f is in effect).

     4.	  Quote	Removal.

     The $ character is	used to	introduce parameter expansion, command substi-
     tution, or	arithmetic evaluation.

   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 di-
     rectory.  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	quoted string, and characters in em-
     bedded arithmetic expansions, command substitutions, and variable expan-
     sions, are	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.	  Pathname expansion is	not performed on the results of	the expansion.

     2.	  Field	splitting is not performed on the results of the expansion,
	  with the exception of	@.

     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.	 Only variables, not posi-
	     tional parameters or special parameters, can be assigned in this

	     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.

	     String Length.  The length	in characters of the value of parame-

	     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 * or @, the re-
	     sult of the expansion is unspecified.  Enclosing the full parame-
	     ter expansion string in double-quotes does	not cause the follow-
	     ing four varieties	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	(``backquoted''	version):


     The shell expands the command substitution	by executing command in	a sub-
     shell environment and replacing the command substitution with the stan-
     dard output of the	command, removing sequences of one or more <newline>s
     at	the end	of the substitution.  (Embedded	<newline>s before the end of
     the output	are not	removed; however, during field splitting, they may be
     translated	into <space>s, depending on the	value of IFS and quoting that
     is	in effect.)

   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, and quote removal.

     Next, the shell treats this as an arithmetic expression and substitutes
     the value of the expression.

   White Space Splitting (Field	Splitting)
     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	re-

     The shell treats each character of	the IFS	as a delimiter and use the de-
     limiters to split the results of parameter	expansion and command substi-
     tution into fields.

   Pathname Expansion (File Name Generation)
     Unless the	-f flag	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 both Pathname Expansion and the case(1)

   Shell Patterns
     A pattern consists	of normal characters, which match themselves, and
     meta-characters.	The meta-characters are	``!'', ``*'', ``?'', and
     ``[''.  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 out-
     put 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 charac-
     ter class.	 The end of the	character class	is indicated by	a ``]''; if
     the ``]'' is missing then the ``['' matches a ``['' rather	than introduc-
     ing a character class.  A character class matches any of the characters
     between the square	brackets.  A range of characters may be	specified us-
     ing a minus sign.	The character class may	be complemented	by making an
     exclamation point the first character of the character class.

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

     This section lists	the builtin commands which are builtin because they
     need to perform some operation that can't be performed by a separate
     process.  In addition to these, there are several other commands that may
     be	builtin	for efficiency (e.g.  printf(1), echo(1), test(1), etc).

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

     . file  The commands in the specified file	are read and executed by the
	     shell.  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	direc-

     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
	     builtin prints the	names and values of all	defined	aliases	(see

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

     command command arg ...
	     Execute the specified builtin command.  (This is useful when you
	     have a shell function with	the same name as a builtin command.)

     cd	[directory]
	     Switch to the specified directory (default	$HOME).	 If an entry
	     for CDPATH	appears	in the environment of the cd command or	the
	     shell variable CDPATH is set and the directory name does not be-
	     gin with a	slash, then the	directories listed in CDPATH will be
	     searched for the specified	directory.  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 this is different from the name that the user
	     gave.  These may be different either because the CDPATH mechanism
	     was used or because a symbolic link was crossed.

     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
	     builtin or	function).  Any	redirections on	the exec command 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	the exit status	of the
	     preceding command is used.

     export name ...
	     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 it	is exported by writing

		   export name=value

	     With no arguments the export command lists	the names of all ex-
	     ported variables.

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

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

     fc	-s [old=new] [first]
	     The fc builtin lists, or edits and	re-executes, commands previ-
	     ously 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:

		     A positive	number representing a command number; command
		     numbers can be displayed with the -l option.

		     A negative	decimal	number representing the	command	that
		     was executed number of commands previously.  For example,
		     -1	is the immediately previous 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 contain an embedded	equal sign.
	     The following environment variables affect	the execution of fc:

	     FCEDIT  Name of the editor	to use.

		     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 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 option is
	     encountered, var is set to	'?'.  It returns a false value (1)
	     when it encounters	the end	of the options.

     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.  Entries which have not been
	     looked at since the last cd command are marked with an asterisk;
	     it	is possible for	these entries to be invalid.

	     With arguments, the hash command removes the specified commands
	     from the hash table (unless they are functions) and then locates
	     them.   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 id's of the processes in	the job.  If the job
	     argument is omitted, use the current job.

     jobs    This command lists	out all	the background processes which are
	     children of the current shell process.

     pwd     Print the current directory.  The builtin command may differ from
	     the program of the	same name because the builtin command remem-
	     bers what the current directory is	rather than recomputing	it
	     each time.	 This makes it faster.	However, if the	current	direc-
	     tory is renamed, the builtin version of pwd will continue to
	     print the old name	for the	directory.

     read [ -p prompt ]	[ -t timeout ] [ -e ] 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 word 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 separated them) are assigned to
	     the last variable.	 If there are more variables than pieces, the
	     remaining variables are assigned the null string.

	     If	the -t option is specified the timeout elapses before any in-
	     put is supplied, the read command will return without assigning
	     any values.  The timeout value may	optionally be followed by one
	     of	's', 'm' or 'h'	to explicitly specify seconds, minutes or or
	     hours.  If	none is	supplied, 's' is assumed.

	     The -e option causes any backslashes in the input to be treated
	     specially.	 If a backslash	is followed by a newline, the back-
	     slash and the newline will	be deleted.   If a backslash is	fol-
	     lowed 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.

     readonly name ...
	     The specified names are marked as read only, so that they cannot
	     be	subsequently modified or unset.	 The shell allows the value of
	     a variable	to be set at the same time it is marked	read only by
	     writing using the following form

		   readonly name=value

	     With no arguments the readonly command lists the names of all
	     read only variables.

     set [ { -options |	+options | -- }	] arg ...
	     The set command performs three different functions.

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

	     If	options	are given, it sets the specified option	flags, or
	     clears them as described in the section called ``Argument List

	     The third use of the set command is to set	the values of the
	     shell's positional	parameters to the specified args.  To change
	     the positional parameters without changing	any options, use
	     ``--'' as the first argument to set.  If no args are present, the
	     set command will clear all	the positional parameters (equivalent
	     to	executing ``shift $#''.

     setvar variable value
	     Assigns value to variable.	(In general it is better to write
	     variable=value rather than	using setvar.  Setvar is intended to
	     be	used in	functions that assign values to	variables whose	names
	     are passed	as parameters.)

     shift [n]
	     Shift the positional parameters n times.  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.	If there are zero po-
	     sitional parameters, shifting doesn't do anything.

     trap [action] signal ...
	     Cause the shell to	parse and execute action when any of the spec-
	     ified signals are received.  The signals are specified by signal
	     number.  Action may be null or omitted; the former	causes the
	     specified signal to be ignored and	the latter causes the default
	     action to be taken.  When the shell forks off a subshell, it re-
	     sets 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.

     type [name] ...
	     Interpret each name as a command and print	the resolution of the
	     command search. Possible resolutions are: shell keyword, alias,
	     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.

     ulimit [-HSacdflmnust] [limit]
	     Set or display resource limits (see getrlimit(2) ). If ``limit''
	     is	specified, the named resource will be set; otherwise the cur-
	     rent 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.  Option ``-S'' 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'' requests 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.

	     -c	coredumpsize
		     The maximal size of core dump files, in 512-byte blocks.

	     -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.  This is
		     the default.

	     -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.

	     -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.

     umask [mask]
	     Set the value of umask (see umask(2)) to the specified octal
	     value. If the argument is omitted,	the umask value	is printed.

     unalias [-a] [name]
	     If	``name'' is specified, the shell removes that alias.  If
	     ``-a'' is specified, all aliases are removed.

     unset name	...
	     The specified variables and functions are unset and unexported.
	     If	a given	name corresponds to both a variable and	a function,
	     both the variable and the function	are unset.

     wait [job]
	     Wait for the specified job	to complete and	return the exit	status
	     of	the last process in the	job. If	the argument is	omitted, wait
	     for all jobs to complete and the return an	exit status of zero.

   Commandline Editing
     When sh is	being used interactively from a	terminal, the current command
     and the command history (see fc in	Builtins) can be edited	using vi-mode
     commandline editing.  This	mode uses commands similar to a	subset of
     those described in	the vi man page.  The command 'set -o vi' 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' command can be used to enable a subset of
     emacs-style commandline editing features.

     expr(1), test(1)

     A sh command appeared in AT&T System V Release 1 UNIX.

4th Berkeley Distribution	  May 5, 1995	     4th Berkeley Distribution


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