Module 118 setunset

Previous Table of Contents Next


Module 118
set/unset

DESCRIPTION

The internal set command is used to control the current shell environment. It can perform three basic functions:

   Set options to control how the shell functions.
   Set positional parameters.
   List local environment; the name and value of variables .

C Shell
The C shell utilizes the set command differently from the Bourne or Korn shells . It assigns a value to a variable and displays the name and value of all variables.

The internal unset command removes variables and functions from the shell environment. It does not set them to NUL (\0) but removes the name from the variable table of the shell. Setting a variable to NUL leaves the variable name in the shell variable table with a value of NUL.

COMMAND FORMAT

Following is the general format of the set command.

 set [ -aefhkmnopstuvx ] [ -o opt_arg ] [ -A name ] [ args ]      set [ +aefhkmnopstuvx ] [ +o opt_arg ] [ +A name ] [ args ]      unset [ variables ]      unset [ -f ] [ functions ] 

C Shell

 set variable      set variable=value      set variable=variable[index]      set variable=(wordlist)      set variable=$<      unset variable 

Options

The following list describes the options and their arguments that may be used with the set command.

-- If arguments follow, do not interpret as options. Prevents a -opt in $1 from being interpreted as an option. If no arguments follow then unset all positional parameters.
-a Automatically export all variables as they are assigned values. Implies that an export variable is performed after each variable is assigned a value.
-e Exit the shell immediately if running a shell script and an error occurs.
-f Filename generation is disabled. The shell no longer expands wildcard characters .
-h Causes each command that you enter on the command line to become a tracked alias.
-k Place all keyword arguments in the environment for a command. By default, only the keyword arguments preceding the command are exported to the environment.
-m Enable the job monitor. A line will be displayed upon completion of each background job. The exit status of each background job is displayed with the completion message.
-n Read but do not execute commands. Useful to check for syntax errors in shell scripts.
-o optargs        Allows you to set other and special options.
allexport Same as -a
bgnice Run all background jobs at a lower priority.
emacs The emacs style in-line editor is used for command reentry. See In-line Command Editing in the ksh command, Module 71.
errexit Same as -e
gmacs The gmacs style in-line editor is used for command reentry.
ignoreeof If the shell is the login shell, it will not exit on end-of-file (Ctrl-D). The exit command must be entered.
keyword Same as -k
markdirs A / is appended to all directory names resulting from pathname expansion.
mapesc value Map the escape character (033) to a new value.
noclobber Redirection will not overwrite an existing file. You must use the > symbol to overwrite an existing file.
noexec Same as -n
noglob Same as -f
nolog Function definitions are not stored in the history file.
nounset Same as -u
privileged Same as -p
protected Same as -p, except PATH is reset.
verbose Same as -v
vi The vi style in-line editor is used for command entry. See In-line Command Editing.
viraw Specifies vi character-by-character input.
xtrace Same as -x
-p Toggles the privileged mode on and off. If on, the effective user and group IDs are set to the real ones. If off, the effective IDs are restored to their values when the shell was initially invoked. Thus privileged is on when the effective ID does not match a real ID. When privileged mode is on, the shell
Disables processing of the $HOME/.profile file.
Uses the /etc/suid_profile instead of your ENV file.
-s Sorts the positional parameters.
-t Read and execute one command then exit the shell.
-u Unset variables cause an error when substitution is performed. If a variable has not been assigned a value and it is referenced, then an error will occur.
-v Verbose; echo (display) each shell input line as read.
-x Debug; display command lines as they are executed, each command line is preceded by a +.
-A Assign arguments arg to array name in sequential order beginning with element 0.
+opt If any of the above options are preceded by a + (plus sign) instead of a - (hyphen), the option will be disabled or turned off.
If no options or arguments are given, set displays the local environment.

NOTE:    

The set command can be used to change or set options and arguments once a shell has begun execution. Set cannot change or set the -c, -i, -r, and -s options from within the current shell.


The following list describes the options and their arguments that may be used to control how unset functions.

-f The shell unsets only functions that you list on the command line. Variables are not affected.


Previous Table of Contents Next

Copyright Wordware Publishing, Inc.


Illustrated UNIX System V
Illustrated Unix System V/Bsd
ISBN: 1556221878
EAN: 2147483647
Year: N/A
Pages: 144
Authors: Robert Felps

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net