Variables in Linux Shell Script
By: Vivek G.
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:
System Variable
|
Meaning
|
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=[\[email protected]\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
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