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UNIX in a Nutshell: System V Edition

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The Bourne Shell and Korn Shell
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set



set

 [

options arg1 arg2 ...

]

With no arguments, set prints the values of all variables known to the current shell. Options can be enabled (- option ) or disabled (+ option ). Options can also be set when the shell is invoked, via ksh or sh . (See "Invoking the Shell" at the end of this section.) Arguments are assigned in order to $1 , $2 , etc.

Options

+A name

Assign remaining arguments as elements of array name . Korn shell only.

-A name

Same as +A , but unset name before making assignments. Korn shell only.

-a

From now on, automatically mark variables for export after defining or changing them.

-e

Exit if a command yields a nonzero exit status. In the Korn shell, the ERR trap is issued before the command exits.

-f

Ignore filename metacharacters (e.g., * ? [ ] ).

-h

Locate commands as they are defined. The Korn shell creates tracked aliases, whereas the Bourne shell hashes function names. See hash .

-k

Assignment of environment variables ( var = value ) will take effect regardless of where they appear on the command line. Normally, assignments must follow the command name.

-m

Enable job control; background jobs will execute in a separate process group. -m is usually set automatically. Korn shell only.

-n

Read commands but don't execute; useful for checking errors.

-o [ m ]

List Korn shell modes, or turn on mode m . Many modes can be set by other options. Modes are:

allexport

Same as -a .

bgnice

Run background jobs at lower priority.

emacs

Set command-line editor to emacs .

errexit

Same as -e .

ignoreeof

Don't process EOF signals. To exit the shell, type exit .

keyword

Same as -k .

markdirs

Append / to directory names.

monitor

Same as -m .

noclobber

Prevent overwriting via > redirection; use >| to overwrite files.

noexec

Same as -n .

noglob

Same as -f .

nolog

Omit function definitions from history file.

nounset

Same as -u .

privileged

Same as -p .

trackall

Same as -h .

verbose

Same as -v .

vi

Set command-line editor to vi .

viraw

Same as vi , but process each character when it's typed.

xtrace

Same as -x .

-p

Start up as a privileged user (i.e., don't process $HOME/.profile ).

-s

Sort the positional parameters. Korn shell only.

-t

Exit after one command is executed.

-u

In substitutions, treat unset variables as errors.

-v

Show each shell command line when read.

-x

Show commands and arguments when executed, preceded by a + . This provides step-by-step debugging of shell scripts. (Same as -o xtrace .)

-

Turn off -v and -x , and turn off option processing. Included in Korn shell for compatibility with older versions of Bourne shell.

--

Used as the last option; -- turns off option processing so that arguments beginning with - are not misinterpreted as options. (For example, you can set $1 to -1.) If no arguments are given after -- , unset the positional parameters.

Examples

set - "$num" -20 -30	
Set 

$1
 to 
$num
, 
$2
 to -20, 
$3
 to -30.
set -vx	
Read each command line; show it;

	
execute it; show it again (with arguments).

set +x	
Stop command tracing.

set -o noclobber	
Prevent file overwriting.

set +o noclobber	
Allow file overwriting again.


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