sh.1

Unix操作系统minix 2.0源码

.TH SH 1
.SH NAME
sh, ., break, case, cd, continue, eval, exec, exit, export, for, if, read, readonly, set, shift, trap, umask, wait, while \- shell
.SH SYNOPSIS
\fBsh\fR [\fB\-eiknqstvxu\fR] [\fB\-c \fIstr\fR] \fB[\fIfile\fR]\fR
.br
.de FL
.TP
\\fB\\$1\\fR
\\$2
..
.de EX
.TP 20
\\fB\\$1\\fR
# \\$2
..
.SH OPTIONS
.FL "\-c" "Execute the commands in \fIstr\fR"
.FL "\-e" "Quit on error"
.FL "\-i" "Interactive mode; ignore QUIT, TERMINATE, INTERRUPT"
.FL "\-k" "Look for name=value everywhere on command line"
.FL "\-n" "Do not execute commands"
.FL "\-q" "Change qflag from sig_ign to sig_del"
.FL "\-s" "Read commands from standard input"
.FL "\-t" "Exit after reading and executing one command"
.FL "\-v" "Echo input lines as they are read"
.FL "\-x" "Trace"
.FL "\-u" "Unset variables"
.SH EXAMPLES
.EX "sh script" "Run a shell script"
.SH DESCRIPTION
.PP
.I 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 redirection 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.
.LP
Some of the more common notations are:
.PP
.in +2.45i
.ta 2i 2.2i
.ti -2.2i
date	#	Regular command
.ti -2.2i
sort <file	#	Redirect \fIstdin\fR (standard input)
.ti -2.2i
sort <file1  >file2	#	Redirect \fIstdin\fR and \fIstdout\fR
.ti -2.2i
cc file.c  2>error	#	Redirect \fIstderr\fR
.ti -2.2i
a.out >f  2>&1	#	Combine standard output and standard error
.ti -2.2i
sort <file1  >>file2	#	Append output to \fIfile2\fR
.ti -2.2i
sort <file1  >file2 &	#	Background job
.ti -2.2i
(ls \-l; a.out) &	#	Run two background commands sequentially
.ti -2.2i
sort <file | wc	#	Two-process pipeline
.ti -2.2i
sort <f | uniq | wc	#	Three-process pipeline
.ti -2.2i
ls \-l *.c	#	List all files ending in \fI.c\fR
.ti -2.2i
ls \-l [\fIa-c\fR]*	#	List all files beginning with \fIa\fR, \fIb\fR, or \fIc\fR
.ti -2.2i
ls \-l ?	#	List all one-character file names
.ti -2.2i
ls \e?	#	List the file whose name is question mark
.ti -2.2i
ls \(fm???\(fm	#	List the file whose name is three question marks
.ti -2.2i
v=/usr/ast	#	Set shell variable \fIv\fR
.ti -2.2i
ls \-l $v	#	Use shell variable \fIv\fR
.ti -2.2i
PS1=\(fmHi! \(fm	#	Change the primary prompt to \fIHi!\fR
.ti -2.2i
PS2=\(fmMore: \(fm	#	Change the secondary prompt to \fIMore:\fR
.ti -2.2i
ls \-l $HOME	#	List the home directory
.ti -2.2i
echo $PATH	#	Echo the search path
.ti -2.2i
echo $?	#	Echo exit status of previous command in decimal
.ti -2.2i
echo $$	#	Echo shell's pid in decimal
.ti -2.2i
echo $!	#	Echo PID of last background process
.ti -2.2i
echo $#	#	Echo number of parameters (shell script)
.ti -2.2i
echo $2	#	Echo second parameter (shell script)
.ti -2.2i
echo "$2"	#	Echo second parameter without expanding spaces
.ti -2.2i
echo $*	#	Echo all parameters (shell script)
.ti -2.2i
echo $@	#	Echo all parameters (shell script)
.ti -2.2i
echo "$@"	#	Echo all parameters without expanding spaces
.in -2.45i
.LP
The shell uses the following variables for specific purposes:
.PP
.in +2.25i
.ta 2i
.ti -2i
SHELL	the path of the current shell
.ti -2i
HOME	the default value for the cd(1) command
.ti -2i
PATH	the directories to be searched to find commands
.ti -2i
IFS	the internal field separators for command strings
.ti -2i
PS1	the primary shell prompt
.ti -2i
PS2	the secondary shell prompt
.in -2.25i
.LP
There are various forms of substitution on the shell command line:
.PP
.in +2.25i
.ta 2i
.ti -2i
`...`	Command string between back-quotes is replaced by its output
.ti -2i
"..."	Permits variable substitution between quotes
.ti -2i
\&'...'	Inhibits variable substitution between quotes
.ti -2i
$VAR	Replaced by contents of variable VAR
.ti -2i
${VAR}	Delimits variable VAR from any following string
.in -2.25i
.LP
The expressions below depend on whether or not VAR has ever been set.
If VAR has been set, they give:
.PP
.in +2.25i
.ta 2i
.ti -2i
${VAR-str}	Replace expression by VAR, else by str
.ti -2i
${VAR=str}	Replace expression by VAR, else by str and set VAR to str
.ti -2i
${VAR?str}	Replace expression by VAR, else print str and exit shell
.ti -2i
${VAR+str}	Replace expression by str, else by null string
.in -2.25i
.LP
If a colon is placed after VAR, the expressions depend on whether or not
VAR is currently set and non-null.
.LP
The shell has a number of built-in commands:
.PP
.in +2.25i
.ta 2i
.ti -2i
:	return true status
.ti -2i
\&. fn	execute shell script fn on current path
.ti -2i
break [n]	break from a for, until or while loop; exit n levels
.ti -2i
continue [n]	continue a for, until or while loop; resume nth loop
.ti -2i
cd [dir]	change current working directory; move to $HOME
.ti -2i
eval cmd	rescan cmd, performing substitutions
.ti -2i
eval	rescan the current command line
.ti -2i
exec cmd	execute cmd without creating a new process
.ti -2i
exec <|>	with no command name, modify shell I/O
.ti -2i
exit [n]	exit a shell program, with exit value n
.ti -2i
export [var]	export var to shell's children; list exported variables
.ti -2i
pwd	print the name of the current working directory
.ti -2i
read var	read a line from stdin and assign to var
.ti -2i
readonly [var]	make var readonly; list readonly variables
.ti -2i
set -f	set shell flag (+f unsets flag)
.ti -2i
set str	set positional parameter to str
.ti -2i
set	show the current shell variables
.ti -2i
shift	reassign positional parameters (except ${0}) one left
.ti -2i
times	print accumulated user and system times for processes
.ti -2i
trap arg sigs	trap signals sigs and run arg on receipt
.ti -2i
trap	list trapped signals
.ti -2i
umask [n]	set the user file creation mask; show the current umask
.ti -2i
wait [n]	wait for process pid n; wait for all processes
.in -2.25i
.LP
The shell also contains a programming language, which has the following
operators and flow control statements:
.PP
.in +3.50i
.ta 2i 3.25i
.ti -3.25i
#	Comment	The rest of the line is ignored
.ti -3.25i
=	Assignment	Set a shell variable
.ti -3.25i
&&	Logical AND	Execute second command only if first succeeds
.ti -3.25i
||	Logical OR	Execute second command only if first fails
.ti -3.25i
(...)	Group	Execute enclosed commands before continuing
.in -3.50i
.PP
.in +2.25i
.ta 2i
.ti -2i
for	For loop (for ... in ... do ... done)
.ti -2i
case	Case statement ((case ... ) ... ;; ... esac)
.ti -2i
esac	Case statement end
.ti -2i
while	While loop (while ... do ... done)
.ti -2i
do	Do/For/While loop start (do ... until ...)
.ti -2i
done	For/While loop end
.ti -2i
if	Conditional statement (if ... else ... elif ... fi)
.ti -2i
in	For loop selection
.ti -2i
then	Conditional statement start
.ti -2i
else	Conditional statement alternative
.ti -2i
elif	Conditional statement end
.ti -2i
until	Do loop end
.ti -2i
fi	Conditional statement end
.in -2.25i
.SH "SEE ALSO"
.BR echo (1),
.BR expr (1),
.BR pwd (1),
.BR true (1).