Korn Shell Variables

What is a shell variables? How do I define and use a variable under korn shell?

A variable is nothing but a symbolic name associated with a value and whose associated value may be changed.

Variables is used by the Korn shell to store values. Setting variables within a script or at a shell prompt is pretty simple. Define a variable called IP and BASE as follows:

IP="foo"
BASE="/nas/backup"

To display variable, use:

echo $IP
echo $BASE

Rules For Naming Korn Shell Variables

Korn shell variable names can begin with an alphabetic (a–Z) or underscore character.
Other variable names that contain only digits (0–9) or special characters (!, @, #, %, *, ?, $) are reserved for special parameters set directly by the Korn shell.

How Do I Create a Null Variable?

Simply use the following syntax:

DIR=

If a value is not given, the variable is set to null.

Common Shell Variable Examples

Set backup directory path:

BACKUPROOT=/iscsi/mysql

Store date and time:

NOW=$(date)

Set file path

HTTPDCONF=/etc/httpd/httpd.conf

A Sample Shell Script Using Variables

#!/bin/ksh
NOW=$(date)
DNSCONF="/etc/resolv.conf"
SERVERNAME=$(hostname)
OS=$(uname)
 
echo "Your OS : $OS"
echo "Server Name : $SERVERNAME"
echo "Current date and time : $NOW"
echo "Client DNS Config file - $DNSCONF"
echo "----------------------"
cat $DNSCONF

typeset Command

Use typeset to define variable attributes. Some common examples:

Set the type of variable to be integer

typeset -i x=10
typeset -i y=10
typeset -i z=$(( $x + $y ))
echo "$x + $y = $z"

Set the type of variable to be float

typeset -F PI=3.14
echo $PI

You can also use it as follows:

typeset -F3 PI=3.14159
echo $PI

How Do I Store Command Output To a Variable?

Variables can be assigned command output using the following format:

variable=$(command)

variable=`command`

For e.g. store hostname to a variable called HOST, enter:

HOST=`hostname`
echo $HOST

HOST=$(hostname)

How Do I Define Read Only Variable?

Set the readonly attribute using typeset command:

typeset -r BASE=/iscsi

If you try to make change, you will be greeted with an error message:

BASE=foo

ksh: BASE: is read only

ksh shell programming, unix ksh variable,ksh positional parameters,ksh variable substitution,bin ksh,ksh shell script

You should follow me on twitter here or grab rss feed to keep track of new changes.