Linux Shell Scripting Tutorial (LSST) v1.05r3
Chapter 2: Getting started with Shell Programming
To process our data/information, data must be kept in computers RAM memory. RAM memory is divided into small locations, and each location had unique number called memory location/address, which is used to hold our data. Programmer can give a unique name to this memory location/address called memory variable or variable (Its a named storage location that may take different values, but only one at a time).
In Linux (Shell), there are two types of variable:
(1) System variables - Created and maintained by Linux itself. This type of variable defined in CAPITAL LETTERS.
(2) User defined variables (UDV) - Created and maintained by user. This type of variable defined in lower letters.
You can see system variables by giving command like $ set, some of the important System variables are:
|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|
NOTE that Some of the above settings can be different in your PC/Linux environment. You can print any of the above variables contains as follows:
$ echo $USERNAME
$ echo $HOME
1) If you want to print your home directory location then you give command:
$ echo $HOME
$ echo HOME
Which of the above command is correct & why? Click here for answer.
Caution: Do not modify System variable this can some time create problems.
|How to write shell script|| |
How to define User defined variables (UDV)