262 lines
6.9 KiB
Groff
262 lines
6.9 KiB
Groff
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.TH SH 1
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.SH NAME
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sh, ., break, case, cd, continue, eval, exec, exit, export, for, if, read, readonly, set, shift, trap, umask, wait, while \- shell
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.SH SYNOPSIS
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\fBsh\fR [\fB\-eiknqstvxu\fR] [\fB\-c \fIstr\fR] \fB[\fIfile\fR]\fR
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.br
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.de FL
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.TP
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\\fB\\$1\\fR
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\\$2
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..
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.de EX
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.TP 20
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\\fB\\$1\\fR
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# \\$2
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..
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.SH OPTIONS
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.FL "\-c" "Execute the commands in \fIstr\fR"
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.FL "\-e" "Quit on error"
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.FL "\-i" "Interactive mode; ignore QUIT, TERMINATE, INTERRUPT"
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.FL "\-k" "Look for name=value everywhere on command line"
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.FL "\-n" "Do not execute commands"
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.FL "\-q" "Change qflag from sig_ign to sig_del"
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.FL "\-s" "Read commands from standard input"
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.FL "\-t" "Exit after reading and executing one command"
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.FL "\-v" "Echo input lines as they are read"
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.FL "\-x" "Trace"
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.FL "\-u" "Unset variables"
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.SH EXAMPLES
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.EX "sh script" "Run a shell script"
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.SH DESCRIPTION
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.PP
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.I Sh
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is the shell, which forms the user's main interface with the system.
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On startup, the shell reads /etc/profile and $HOME/.profile, if they exist,
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and executes any commands they contain. The Minix shell has most of the
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features of the V7 (Bourne) shell, including redirection of input and output,
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pipes, magic characters, background processes, and shell scripts. A brief
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summary follows, but whole books have been written on shell programming alone.
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.LP
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Some of the more common notations are:
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.PP
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.in +2.45i
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.ta 2i 2.2i
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.ti -2.2i
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date # Regular command
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.ti -2.2i
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sort <file # Redirect \fIstdin\fR (standard input)
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.ti -2.2i
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sort <file1 >file2 # Redirect \fIstdin\fR and \fIstdout\fR
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.ti -2.2i
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cc file.c 2>error # Redirect \fIstderr\fR
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.ti -2.2i
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a.out >f 2>&1 # Combine standard output and standard error
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.ti -2.2i
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sort <file1 >>file2 # Append output to \fIfile2\fR
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.ti -2.2i
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sort <file1 >file2 & # Background job
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.ti -2.2i
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(ls \-l; a.out) & # Run two background commands sequentially
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.ti -2.2i
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sort <file | wc # Two-process pipeline
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.ti -2.2i
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sort <f | uniq | wc # Three-process pipeline
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.ti -2.2i
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ls \-l *.c # List all files ending in \fI.c\fR
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.ti -2.2i
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ls \-l [\fIa-c\fR]* # List all files beginning with \fIa\fR, \fIb\fR, or \fIc\fR
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.ti -2.2i
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ls \-l ? # List all one-character file names
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.ti -2.2i
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ls \e? # List the file whose name is question mark
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.ti -2.2i
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ls \(fm???\(fm # List the file whose name is three question marks
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.ti -2.2i
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v=/usr/ast # Set shell variable \fIv\fR
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.ti -2.2i
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ls \-l $v # Use shell variable \fIv\fR
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.ti -2.2i
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PS1=\(fmHi! \(fm # Change the primary prompt to \fIHi!\fR
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.ti -2.2i
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PS2=\(fmMore: \(fm # Change the secondary prompt to \fIMore:\fR
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.ti -2.2i
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ls \-l $HOME # List the home directory
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.ti -2.2i
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echo $PATH # Echo the search path
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.ti -2.2i
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echo $? # Echo exit status of previous command in decimal
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.ti -2.2i
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echo $$ # Echo shell's pid in decimal
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.ti -2.2i
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echo $! # Echo PID of last background process
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.ti -2.2i
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echo $# # Echo number of parameters (shell script)
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.ti -2.2i
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echo $2 # Echo second parameter (shell script)
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.ti -2.2i
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echo "$2" # Echo second parameter without expanding spaces
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.ti -2.2i
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echo $* # Echo all parameters (shell script)
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.ti -2.2i
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echo $@ # Echo all parameters (shell script)
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.ti -2.2i
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echo "$@" # Echo all parameters without expanding spaces
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.in -2.45i
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.LP
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The shell uses the following variables for specific purposes:
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.PP
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.in +2.25i
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.ta 2i
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.ti -2i
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SHELL the path of the current shell
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.ti -2i
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HOME the default value for the cd(1) command
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.ti -2i
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PATH the directories to be searched to find commands
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.ti -2i
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IFS the internal field separators for command strings
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.ti -2i
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PS1 the primary shell prompt
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.ti -2i
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PS2 the secondary shell prompt
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.in -2.25i
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.LP
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There are various forms of substitution on the shell command line:
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.PP
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.in +2.25i
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.ta 2i
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.ti -2i
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`...` Command string between back-quotes is replaced by its output
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.ti -2i
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"..." Permits variable substitution between quotes
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.ti -2i
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\&'...' Inhibits variable substitution between quotes
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.ti -2i
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$VAR Replaced by contents of variable VAR
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.ti -2i
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${VAR} Delimits variable VAR from any following string
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.in -2.25i
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.LP
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The expressions below depend on whether or not VAR has ever been set.
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If VAR has been set, they give:
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.PP
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.in +2.25i
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.ta 2i
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.ti -2i
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${VAR-str} Replace expression by VAR, else by str
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.ti -2i
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${VAR=str} Replace expression by VAR, else by str and set VAR to str
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.ti -2i
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${VAR?str} Replace expression by VAR, else print str and exit shell
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.ti -2i
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${VAR+str} Replace expression by str, else by null string
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.in -2.25i
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.LP
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If a colon is placed after VAR, the expressions depend on whether or not
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VAR is currently set and non-null.
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.LP
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The shell has a number of built-in commands:
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.PP
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.in +2.25i
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.ta 2i
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.ti -2i
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: return true status
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.ti -2i
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\&. fn execute shell script fn on current path
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.ti -2i
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break [n] break from a for, until or while loop; exit n levels
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.ti -2i
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continue [n] continue a for, until or while loop; resume nth loop
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.ti -2i
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cd [dir] change current working directory; move to $HOME
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.ti -2i
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eval cmd rescan cmd, performing substitutions
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.ti -2i
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eval rescan the current command line
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.ti -2i
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exec cmd execute cmd without creating a new process
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.ti -2i
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exec <|> with no command name, modify shell I/O
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.ti -2i
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exit [n] exit a shell program, with exit value n
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.ti -2i
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export [var] export var to shell's children; list exported variables
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.ti -2i
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pwd print the name of the current working directory
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.ti -2i
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read var read a line from stdin and assign to var
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.ti -2i
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readonly [var] make var readonly; list readonly variables
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.ti -2i
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set -f set shell flag (+f unsets flag)
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.ti -2i
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set str set positional parameter to str
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.ti -2i
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set show the current shell variables
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.ti -2i
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shift reassign positional parameters (except ${0}) one left
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.ti -2i
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times print accumulated user and system times for processes
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.ti -2i
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trap arg sigs trap signals sigs and run arg on receipt
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.ti -2i
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trap list trapped signals
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.ti -2i
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umask [n] set the user file creation mask; show the current umask
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.ti -2i
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wait [n] wait for process pid n; wait for all processes
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.in -2.25i
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.LP
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The shell also contains a programming language, which has the following
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operators and flow control statements:
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.PP
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.in +3.50i
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.ta 2i 3.25i
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.ti -3.25i
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# Comment The rest of the line is ignored
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.ti -3.25i
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= Assignment Set a shell variable
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.ti -3.25i
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&& Logical AND Execute second command only if first succeeds
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.ti -3.25i
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|| Logical OR Execute second command only if first fails
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.ti -3.25i
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(...) Group Execute enclosed commands before continuing
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.in -3.50i
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.PP
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.in +2.25i
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.ta 2i
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.ti -2i
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for For loop (for ... in ... do ... done)
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.ti -2i
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case Case statement ((case ... ) ... ;; ... esac)
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.ti -2i
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esac Case statement end
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.ti -2i
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while While loop (while ... do ... done)
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.ti -2i
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do Do/For/While loop start (do ... until ...)
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.ti -2i
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done For/While loop end
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.ti -2i
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if Conditional statement (if ... else ... elif ... fi)
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.ti -2i
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in For loop selection
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.ti -2i
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then Conditional statement start
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.ti -2i
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else Conditional statement alternative
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.ti -2i
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elif Conditional statement end
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.ti -2i
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until Do loop end
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.ti -2i
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fi Conditional statement end
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.in -2.25i
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.SH "SEE ALSO"
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.BR echo (1),
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.BR expr (1),
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.BR pwd (1),
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.BR true (1).
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