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SH(1)			    General Commands Manual			 SH(1)

NAME
       sh,  for, case, if, while, :, .,	break, continue, cd, eval, exec, exit,
       export, login, newgrp, read, readonly, set, shift, times, trap,	umask,
       wait - command language

SYNOPSIS
       sh [ -ceiknrstuvx ] [ arg ] ...

DESCRIPTION
       Sh is a command programming language that executes commands read	from a
       terminal	or a file.  See	invocation for the meaning of arguments	to the
       shell.

       Commands.
       A  simple-command  is a sequence	of non blank words separated by	blanks
       (a blank	is a tab or a space).  The first word specifies	 the  name  of
       the  command  to	 be executed.  Except as specified below the remaining
       words are passed	as arguments to	the invoked command.  The command name
       is  passed  as argument 0 (see exec(2)).	 The value of a	simple-command
       is its exit status if it	terminates normally or 200+status if it	termi-
       nates abnormally	(see signal(2) for a list of status values).

       A  pipeline  is a sequence of one or more commands separated by |.  The
       standard	output of each command but the last is connected by a  pipe(2)
       to  the	standard  input	of the next command.  Each command is run as a
       separate	process; the shell waits for the last command to terminate.

       A list is a sequence of one or more pipelines separated by ;, &,	&&  or
       ||  and optionally terminated by	; or &.	 ; and & have equal precedence
       which is	lower than that	of && and ||, && and ||	also have equal	prece-
       dence.	A  semicolon  causes sequential	execution; an ampersand	causes
       the preceding pipeline to be executed without waiting for it to finish.
       The symbol && (||) causes the list following to be executed only	if the
       preceding pipeline returns a zero (non zero) value.  Newlines  may  ap-
       pear in a list, instead of semicolons, to delimit commands.

       A  command  is  either  a  simple-command or one	of the following.  The
       value returned by a command is that of the last simple-command executed
       in the command.

       for name	[in word ...] do list done
	      Each time	a for command is executed name is set to the next word
	      in the for word list If in word ...  is omitted then in "$@"  is
	      assumed.	 Execution  ends  when	there are no more words	in the
	      list.

       case word in [pattern [ | pattern ] ... ) list ;;] ... esac
	      A	case command executes the list associated with the first  pat-
	      tern that	matches	word.  The form	of the patterns	is the same as
	      that used	for file name generation.

       if list then list [elif list then list] ... [else list] fi
	      The list following if is executed	and if	it  returns  zero  the
	      list  following then is executed.	 Otherwise, the	list following
	      elif is executed and if its value	is  zero  the  list  following
	      then is executed.	 Failing that the else list is executed.

       while list [do list] done
	      A	 while	command	 repeatedly executes the while list and	if its
	      value is zero executes the do list; otherwise  the  loop	termi-
	      nates.   The  value  returned  by	a while	command	is that	of the
	      last executed command in the do list.   until  may  be  used  in
	      place of while to	negate the loop	termination test.

       ( list )
	      Execute list in a	subshell.

       { list }
	      list is simply executed.

       The  following words are	only recognized	as the first word of a command
       and when	not quoted.

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

       Command substitution.
       The standard output from	a command enclosed in a	pair of	grave  accents
       (``)  may  be  used as part or all of a word; trailing newlines are re-
       moved.

       Parameter substitution.
       The character $ is used to introduce substitutable  parameters.	 Posi-
       tional  parameters may be assigned values by set.  Variables may	be set
       by writing

	      name=value [ name=value ]	...

       ${parameter}
	      A	parameter is a sequence	of letters, digits or  underscores  (a
	      name),  a	 digit,	 or  any of the	characters * @ # ? - $ !.  The
	      value, if	any, of	the parameter is substituted.  The braces  are
	      required	only when parameter is followed	by a letter, digit, or
	      underscore that is not to	be interpreted as part	of  its	 name.
	      If  parameter  is	a digit	then it	is a positional	parameter.  If
	      parameter	is * or	@ then all the positional parameters, starting
	      with  $1,	 are  substituted separated by spaces.	$0 is set from
	      argument zero when the shell is invoked.

       ${parameter-word}
	      If parameter is set then substitute its value; otherwise substi-
	      tute word.

       ${parameter=word}
	      If  parameter  is	 not set then set it to	word; the value	of the
	      parameter	is then	substituted.  Positional parameters may	not be
	      assigned to in this way.

       ${parameter?word}
	      If  parameter is set then	substitute its value; otherwise, print
	      word and exit from the shell.  If	word is	omitted	then  a	 stan-
	      dard message is printed.

       ${parameter+word}
	      If  parameter  is	set then substitute word; otherwise substitute
	      nothing.

       In the above word is not	evaluated unless it is to be used as the  sub-
       stituted	string.	 (So that, for example,	echo ${d-`pwd`}	will only exe-
       cute pwd	if d is	unset.)

       The following parameters	are automatically set by the shell.

	      #	     The number	of positional parameters in decimal.
	      -	     Options supplied to the shell on invocation or by set.
	      ?	     The value returned	by the last executed command in	 deci-
		     mal.
	      $	     The process number	of this	shell.
	      !	     The  process  number  of  the last	background command in-
		     voked.

       The following parameters	are used but not set by	the shell.

	      HOME   The default argument (home	directory) for the cd command.
	      PATH   The search	path for commands (see execution).
	      MAIL   If	this variable is set to	the name of a mail  file  then
		     the  shell	informs	the user of the	arrival	of mail	in the
		     specified file.
	      PS1    Primary prompt string, by default `$ '.
	      PS2    Secondary prompt string, by default `> '.
	      IFS    Internal field separators,	normally space,	tab, and  new-
		     line.

       Blank interpretation.
       After  parameter	 and command substitution, any results of substitution
       are scanned for internal	field separator	 characters  (those  found  in
       $IFS)  and  split  into	distinct  arguments  where such	characters are
       found.  Explicit	null arguments ("" or '') are retained.	 Implicit null
       arguments (those	resulting from parameters that have no values) are re-
       moved.

       File name generation.
       Following substitution, each command word is scanned for	the characters
       *,  ?   and [.  If one of these characters appears then the word	is re-
       garded as a pattern.  The word is replaced with	alphabetically	sorted
       file  names  that  match	 the  pattern.	 If no file name is found that
       matches the pattern then	the word is left unchanged.  The  character  .
       at the start of a file name or immediately following a /, and the char-
       acter /,	must be	matched	explicitly.

       *      Matches any string, including the	null string.
       ?      Matches any single character.
       [...]  Matches any one of the characters	enclosed.  A pair  of  charac-
	      ters  separated by - matches any character lexically between the
	      pair.

       Quoting.
       The following characters	have a special meaning to the shell and	 cause
       termination of a	word unless quoted.

	    ;	&   (	)   |	<   >	newline	  space	  tab

       A  character  may  be quoted by preceding it with a \.  \newline	is ig-
       nored.  All characters enclosed between a pair of quote marks (''), ex-
       cept  a	single quote, are quoted.  Inside double quotes	("") parameter
       and command substitution	occurs and \ quotes the	characters \ `	"  and
       $.

       "$*" is equivalent to "$1 $2 ..."  whereas
       "$@" is equivalent to "$1" "$2" ... .

       Prompting.
       When used interactively,	the shell prompts with the value of PS1	before
       reading a command.  If at any time a newline is typed and further input
       is needed to complete a command then the	secondary prompt ($PS2)	is is-
       sued.

       Input output.
       Before a	command	is executed its	input and output may be	redirected us-
       ing a special notation interpreted by the shell.	 The following may ap-
       pear anywhere in	a simple-command or may	precede	or  follow  a  command
       and  are	not passed on to the invoked command.  Substitution occurs be-
       fore word or digit is used.

       <word  Use file word as standard	input (file descriptor 0).

       >word  Use file word as standard	output (file descriptor	 1).   If  the
	      file  does  not  exist then it is	created; otherwise it is trun-
	      cated to zero length.

       >>word Use file word as standard	output.	 If the	file exists then  out-
	      put  is  appended	(by seeking to the end); otherwise the file is
	      created.

       <<word The shell	input is read up to a line the same as word, or	end of
	      file.   The  resulting  document becomes the standard input.  If
	      any character of word is quoted then no interpretation is	placed
	      upon  the	 characters  of	the document; otherwise, parameter and
	      command substitution occurs, \newline is ignored,	and \ is  used
	      to quote the characters \	$ ` and	the first character of word.

       <&digit
	      The standard input is duplicated from file descriptor digit; see
	      dup(2).  Similarly for the standard output using >.

       <&-    The standard input is closed.  Similarly for the standard	output
	      using >.

       If  one	of  the	 above is preceded by a	digit then the file descriptor
       created is that specified by the	digit (instead of the default 0	or 1).
       For example,

	    ...	2>&1

       creates file descriptor 2 to be a duplicate of file descriptor 1.

       If  a  command is followed by & then the	default	standard input for the
       command is the empty file (/dev/null).  Otherwise, the environment  for
       the  execution of a command contains the	file descriptors of the	invok-
       ing shell as modified by	input output specifications.

       Environment.
       The environment is a list of name-value pairs that is passed to an exe-
       cuted  program  in  the same way	as a normal argument list; see exec(2)
       and environ(5).	The shell interacts with the  environment  in  several
       ways.  On invocation, the shell scans the environment and creates a pa-
       rameter for each	name found, giving it the corresponding	 value.	  Exe-
       cuted  commands inherit the same	environment.  If the user modifies the
       values of these parameters or creates new ones, none of	these  affects
       the  environment	 unless	the export command is used to bind the shell's
       parameter to the	environment.  The environment  seen  by	 any  executed
       command	is thus	composed of any	unmodified name-value pairs originally
       inherited by the	shell, plus any	modifications  or  additions,  all  of
       which must be noted in export commands.

       The environment for any simple-command may be augmented by prefixing it
       with one	or more	assignments to parameters.  Thus these two  lines  are
       equivalent

	      TERM=450 cmd args
	      (export TERM; TERM=450; cmd args)

       If the -k flag is set, all keyword arguments are	placed in the environ-
       ment, even if the occur after the command name.	The  following	prints
       `a=b c' and `c':
       echo a=b	c
       set -k
       echo a=b	c

       Signals.
       The  INTERRUPT  and  QUIT signals for an	invoked	command	are ignored if
       the command is followed by &; otherwise signals have the	values	inher-
       ited by the shell from its parent.  (But	see also trap.)

       Execution.
       Each  time  a  command  is executed the above substitutions are carried
       out.  Except for	the `special commands' listed below a new  process  is
       created and an attempt is made to execute the command via an exec(2).

       The  shell  parameter  $PATH  defines the search	path for the directory
       containing the command.	Each alternative directory name	 is  separated
       by  a  colon  (:).  The default path is :/bin:/usr/bin.	If the command
       name contains a / then the search path is not  used.   Otherwise,  each
       directory  in the path is searched for an executable file.  If the file
       has execute permission but is not an a.out file,	it is assumed to be  a
       file  containing	shell commands.	 A subshell (i.e., a separate process)
       is spawned to read it.  A parenthesized command is also executed	 in  a
       subshell.

       Special commands.
       The  following  commands	 are  executed in the shell process and	except
       where specified no input	output redirection is permitted	for such  com-
       mands.

       :      No effect; the command does nothing.
       . file Read and execute commands	from file and return.  The search path
	      $PATH is used to find the	directory containing file.
       break [n]
	      Exit from	the enclosing for or while loop,  if  any.   If	 n  is
	      specified	then break n levels.
       continue	[n]
	      Resume  the  next	 iteration of the enclosing for	or while loop.
	      If n is specified	then resume at the n-th	enclosing loop.
       cd [arg]
	      Change the current directory to arg.  The	shell parameter	 $HOME
	      is the default arg.
       eval [arg ...]
	      The  arguments  are read as input	to the shell and the resulting
	      command(s) executed.
       exec [arg ...]
	      The command specified by the arguments is	executed in  place  of
	      this  shell  without creating a new process.  Input output argu-
	      ments may	appear and if no other arguments are given  cause  the
	      shell input output to be modified.
       exit [n]
	      Causes  a	 non  interactive  shell  to exit with the exit	status
	      specified	by n.  If n is omitted then the	exit status is that of
	      the  last	command	executed.  (An end of file will	also exit from
	      the shell.)
       export [name ...]
	      The given	names are marked for automatic export to the  environ-
	      ment  of	subsequently-executed  commands.   If no arguments are
	      given then a list	of exportable names is printed.
       login [arg ...]
	      Equivalent to `exec login	arg ...'.
       newgrp [arg ...]
	      Equivalent to `exec newgrp arg ...'.
       read name ...
	      One line is read from the	standard input;	 successive  words  of
	      the  input  are  assigned	 to  the variables name	in order, with
	      leftover words to	the last variable.  The	return code is	0  un-
	      less the end-of-file is encountered.
       readonly	[name ...]
	      The  given names are marked readonly and the values of the these
	      names may	not be changed by subsequent assignment.  If no	 argu-
	      ments are	given then a list of all readonly names	is printed.
       set [-eknptuvx [arg ...]]
	      -e If non	interactive then exit immediately if a command fails.
	      -k All  keyword  arguments  are  placed in the environment for a
		 command, not just those that precede the command name.
	      -n Read commands but do not execute them.
	      -t Exit after reading and	executing one command.
	      -u Treat unset variables as an error when	substituting.
	      -v Print shell input lines as they are read.
	      -x Print commands	and their arguments as they are	executed.
	      -	 Turn off the -x and -v	options.

	      These flags can also be used upon	invocation of the shell.   The
	      current set of flags may be found	in $-.

	      Remaining	 arguments are positional parameters and are assigned,
	      in order,	to $1, $2, etc.	 If no arguments are  given  then  the
	      values of	all names are printed.

       shift  The positional parameters	from $2...  are	renamed	$1...

       times  Print  the  accumulated  user and	system times for processes run
	      from the shell.

       trap [arg] [n] ...
	      Arg is a command to be read and executed when the	shell receives
	      signal(s)	 n.   (Note  that arg is scanned once when the trap is
	      set and once when	the trap is taken.)  Trap  commands  are  exe-
	      cuted  in	 order	of  signal  number.  If	arg is absent then all
	      trap(s) n	are reset to their original values.   If  arg  is  the
	      null  string then	this signal is ignored by the shell and	by in-
	      voked commands.  If n is 0 then the command arg is  executed  on
	      exit  from the shell, otherwise upon receipt of signal n as num-
	      bered in signal(2).  Trap	with no	arguments  prints  a  list  of
	      commands associated with each signal number.

       umask [ nnn ]
	      The  user	 file creation mask is set to the octal	value nnn (see
	      umask(2)).  If nnn is omitted, the current value of the mask  is
	      printed.

       wait [n]
	      Wait  for	 the specified process and report its termination sta-
	      tus.  If n is not	given then all	currently  active  child  pro-
	      cesses  are  waited  for.	  The return code from this command is
	      that of the process waited for.

       Invocation.
       If the first character of argument zero is -, commands  are  read  from
       $HOME/.profile,	if  such a file	exists.	 Commands are then read	as de-
       scribed below.  The following flags are interpreted by the  shell  when
       it is invoked.
       -c string  If  the  -c  flag  is	 present  then	commands are read from
		  string.
       -s	  If the -s flag is present or if  no  arguments  remain  then
		  commands  are	read from the standard input.  Shell output is
		  written to file descriptor 2.
       -i	  If the -i flag is present or if the shell input  and	output
		  are attached to a terminal (as told by gtty) then this shell
		  is interactive.  In this case	the terminate  signal  SIGTERM
		  (see	signal(2))  is ignored (so that	`kill 0' does not kill
		  an interactive shell)	and the	 interrupt  signal  SIGINT  is
		  caught  and ignored (so that wait is interruptable).	In all
		  cases	SIGQUIT	is ignored by the shell.

       The remaining flags and arguments are described under the set command.

FILES
       $HOME/.profile
       /tmp/sh*
       /dev/null

SEE ALSO
       test(1),	exec(2),

DIAGNOSTICS
       Errors detected by the shell, such as syntax errors cause the shell  to
       return a	non zero exit status.  If the shell is being used non interac-
       tively then execution of	the shell file is abandoned.   Otherwise,  the
       shell  returns  the  exit status	of the last command executed (see also
       exit).

BUGS
       If << is	used to	provide	standard input to an asynchronous process  in-
       voked by	&, the shell gets mixed	up about naming	the input document.  A
       garbage file /tmp/sh* is	created, and the shell complains about not be-
       ing able	to find	the file by another name.

									 SH(1)

NAME | SYNOPSIS | DESCRIPTION | FILES | SEE ALSO | DIAGNOSTICS | BUGS

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