Even though BASH is not a typed language like another programming language, it provides different ways to create variables. Variables in Bash scripts can only contain String or numerical values.

There are some rules when creating the Bash variables.

• Shell script name starts with an underscore or an Alphabet.
• The bash script is case-sensitive. It means my_name and MY_NAME are two different variables.

Types of Bash Variables

There are mainly three types of variables in a Bash script that we can use.

• Local variables
• Environment variables
• Positional Parameters Variable.

Local Variables

This variable exists throughout the session of the script and is not accessible outside of that particular script. It can be declared using equals = sign can be retrieved using dollar $ sign. When you declare a variable in a shell script, you should not have a space between the variable name, = and the value.

Let’s create the shell script with the below local variable.

When the above piece of code runs, we will see the below value.

Instead of this, we can use the local keyword to declare the variable. The main advantage of doing this is that the variable disappears when the function exits.

Environment Variables

Environment variables are accessible to any program or script running the current Shell session. They are global settings that control Shell’s function as well as other Linux-based commands. They are created using the export keyword when declaring in the shell script. Depending upon your flavors of Linux you might have a file called .bashrc or .zshrc in your home location. It will have a list of environment variables that are available in that Linux session.

For Example, the MySql home path is set up in the below location.

So if I use the echo command of Mysql home from a bash script or a terminal, I will be able to get the value of this variable.

There are many environment variables in bash that are already defined. Below are some of the common parameters that you can use after adding a dollar $ sign.

Variable	Description
HOME	Current users Home directory. The value of this variable is the same one when using tilde ~ expansion.
PWD	Current/Present working directory
RANDOM	Generates a Random number between 0 and 32767
PATH	A list of a colon-separated list of Application Paths from the current Shell session
UID	The numeric, Real ID of the current user

Positional Parameters Variables

These variables are allocated when a function is evaluated and are given positionally. When we pass parameters to a shell script, the value of those parameters is read as a positional Variable.

The following tables give a list of positional parameters and other variables which have their special meaning when used inside of Bash script function.

Parameter	Description
$0	Current Scripts Name
$#	Number of Parameters Passed not counting $0
$1 ... $9	Parameter List Elements from 1 to 9
$* or $@	All Positional Parameters except $0

You can check the below command to run this script.