SH(1)							      General Commands Manual							     SH(1)

NAME

       sh, ., break, case, cd, continue, eval, exec, exit, export, for, if, read, readonly, set, shift, trap, umask, wait, while - shell

SYNOPSIS

       sh [-eiknqstvxu] [-c str] [file]

OPTIONS

       -c     Execute the commands in str

       -e     Quit on error

       -i     Interactive mode; ignore QUIT, TERMINATE, INTERRUPT

       -k     Look for name=value everywhere on command line

       -n     Do not execute commands

       -q     Change qflag from sig_ign to sig_del

       -s     Read commands from standard input

       -t     Exit after reading and executing one command

       -v     Echo input lines as they are read

       -x     Trace

       -u     Unset variables

EXAMPLES

       sh script	   # Run a shell script

DESCRIPTION

       Sh  is  the  shell, which forms the user's main interface with the system.  On startup, the shell reads /etc/profile and $HOME/.profile, if
       they exist, and executes any commands they contain.  The Minix shell has most of the features of the V7 (Bourne) shell, including redirect-
       ion  of	input and output, pipes, magic characters, background processes, and shell scripts.  A brief summary follows, but whole books have
       been written on shell programming alone.

       Some of the more common notations are:

	 date		     # Regular command
	 sort <file	     # Redirect stdin (standard input)
	 sort <file1  >file2 # Redirect stdin and stdout
	 cc file.c  2>error  # Redirect stderr
	 a.out >f  2>&1      # Combine standard output and standard error
	 sort <file1  >>file2  #Append output to file2
	 sort <file1  >file2 & #Background job
	 (ls -l; a.out) &    # Run two background commands sequentially
	 sort <file | wc     # Two-process pipeline
	 sort <f | uniq | wc # Three-process pipeline
	 ls -l *.c	     # List all files ending in .c
	 ls -l [a-c]*	     # List all files beginning with a, b, or c
	 ls -l ?	     # List all one-character file names
	 ls ?		     # List the file whose name is question mark
	 ls '???'	     # List the file whose name is three question marks
	 v=/usr/ast	     # Set shell variable v
	 ls -l $v	     # Use shell variable v
	 PS1='Hi! '	     # Change the primary prompt to Hi!
	 PS2='More: '	     # Change the secondary prompt to More:
	 ls -l $HOME	     # List the home directory
	 echo $PATH	     # Echo the search path
	 echo $?	     # Echo exit status of previous command in decimal
	 echo $$	     # Echo shell's pid in decimal
	 echo $!	     # Echo PID of last background process
	 echo $#	     # Echo number of parameters (shell script)
	 echo $2	     # Echo second parameter (shell script)
	 echo "$2"	     # Echo second parameter without expanding spaces
	 echo $*	     # Echo all parameters (shell script)
	 echo $@	     # Echo all parameters (shell script)
	 echo "$@"	     # Echo all parameters without expanding spaces

       The shell uses the following variables for specific purposes:

	 SHELL		     the path of the current shell
	 HOME		     the default value for the cd(1) command
	 PATH		     the directories to be searched to find commands
	 IFS		     the internal field separators for command strings
	 PS1		     the primary shell prompt
	 PS2		     the secondary shell prompt

       There are various forms of substitution on the shell command line:

	 `...`		     Command string between back-quotes is replaced by its output
	 "..."		     Permits variable substitution between quotes
	 '...'		     Inhibits variable substitution between quotes
	 $VAR		     Replaced by contents of variable VAR
	 ${VAR} 	     Delimits variable VAR from any following string

       The expressions below depend on whether or not VAR has ever been set.  If VAR has been set, they give:

	 ${VAR-str}	     Replace expression by VAR, else by str
	 ${VAR=str}	     Replace expression by VAR, else by str and set VAR to str
	 ${VAR?str}	     Replace expression by VAR, else print str and exit shell
	 ${VAR+str}	     Replace expression by str, else by null string

       If a colon is placed after VAR, the expressions depend on whether or not VAR is currently set and non-null.

       The shell has a number of built-in commands:

	 :		     return true status
	 . fn		     execute shell script fn on current path
	 break [n]	     break from a for, until or while loop; exit n levels
	 continue [n]	     continue a for, until or while loop; resume nth loop
	 cd [dir]	     change current working directory; move to $HOME
	 eval cmd	     rescan cmd, performing substitutions
	 eval		     rescan the current command line
	 exec cmd	     execute cmd without creating a new process
	 exec <|>	     with no command name, modify shell I/O
	 exit [n]	     exit a shell program, with exit value n
	 export [var]	     export var to shell's children; list exported variables
	 pwd		     print the name of the current working directory
	 read var	     read a line from stdin and assign to var
	 readonly [var]      make var readonly; list readonly variables
	 set -f 	     set shell flag (+f unsets flag)
	 set str	     set positional parameter to str
	 set		     show the current shell variables
	 shift		     reassign positional parameters (except ${0}) one left
	 times		     print accumulated user and system times for processes
	 trap arg sigs	     trap signals sigs and run arg on receipt
	 trap		     list trapped signals
	 umask [n]	     set the user file creation mask; show the current umask
	 wait [n]	     wait for process pid n; wait for all processes

       The shell also contains a programming language, which has the following operators and flow control statements:

	  #		      Comment	  The rest of the line is ignored
	  =		      Assignment  Set a shell variable
	  &&		      Logical AND Execute second command only if first succeeds
	  ||		      Logical OR  Execute second command only if first fails
	  (...) 	      Group	  Execute enclosed commands before continuing

	 for		     For loop (for ... in ... do ... done)
	 case		     Case statement ((case ... ) ... ;; ... esac)
	 esac		     Case statement end
	 while		     While loop (while ... do ... done)
	 do		     Do/For/While loop start (do ... until ...)
	 done		     For/While loop end
	 if		     Conditional statement (if ... else ... elif ... fi)
	 in		     For loop selection
	 then		     Conditional statement start
	 else		     Conditional statement alternative
	 elif		     Conditional statement end
	 until		     Do loop end
	 fi		     Conditional statement end

SEE ALSO

       echo(1), expr(1), pwd(1), true(1).

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