|BASH=/bin/bash||Our shell name|
|BASH_VERSION=1.14.7(1)||Our shell version name|
|COLUMNS=80||No. of columns for our screen|
|HOME=/home/vivek||Our home directory|
|LINES=25||No. of columns for our screen|
|LOGNAME=students||students Our logging name|
|OSTYPE=Linux||Our Os type|
|PATH=/usr/bin:/sbin:/bin:/usr/sbin||Our path settings|
|PS1=[\u@\h \W]\$||Our prompt settings|
|PWD=/home/students/Common||Our current working directory|
|SHELL=/bin/bash||Our shell name|
|USERNAME=vivek||User name who is currently login to this PC|
User defined Variable
To define UDV use following syntax
'value' is assigned to given 'variable name' and Value must be on right side = sign.
$ no=10# this is ok
$ 10=no# Error, NOT Ok, Value must be on right side of = sign.
To define variable called 'vech' having value Bus
To define variable called n having value 10
(1) Variable name must begin with Alphanumeric character or underscore character (_), followed by one or more Alphanumeric character. For e.g. Valid shell variable are as follows
(2) Don't put spaces on either side of the equal sign when assigning value to variable. For e.g. In following variable declaration there will be no error
But there will be problem for any of the following variable declaration:
$ no =10
$ no= 10
$ no = 10
(3) Variables are case-sensitive, just like filename in Linux. For e.g.
Above all are different variable name, so to print value 20 we have to use $ echo $NO and not any of the following
$ echo $no # will print 10 but not 20
$ echo $No# will print 11 but not 20
$ echo $nO# will print 2 but not 20
(4) You can define NULL variable as follows (NULL variable is variable which has no value at the time of definition) For e.g.
Try to print it's value by issuing following command
$ echo $vech
Nothing will be shown because variable has no value i.e. NULL variable.
(5) Do not use ?,* etc, to name your variable names