Variable are used to store data in script. variable starts with '$' symbol If the variables are not defined will be empty or blank. There are two types of variable :
1.  system variable
2.  user defined variable
System variable :
Variables who are already defined by system.
It gives the detail of bash shell varsion
Gives name of your computer
Give the address of history file of command
Gives size of file of history file
Defines path which shell must search in order to execute any command or file
Stores default working directory of user
Stores login name of user
defines file where mail of user is stored
defines duration after shell checks checks for new mail
defines internal fiels separator, which is a space, tab or newline
defines name of your default working shell
defines name of terminal on which user is working
defines timezone of user is working
stands for system prompt1 in shell
system prompt 2 , default value is '>'
User defined variable
User variable generally consist of only alphabets[a-zA-Z]. there shouldnot be any space between variable , = and data.
Read keyword is used to take data to variable from input .