How to use variables in shell scripting

In this article I will show you how to create variables and set values to variables. This is an easy thing to do, but very important in shell scripting.

I will use echo to display the variable values.

How to create variables in bash scripting

Variable syntax: variable=value

Example 1:
OS=Linux

Some things you should know:

1: Do not use any space in the left and the right of equal “=” !!!

OS =Linux , OS= Linux, OS = Linux will all generate command not found errors.

2: Variable names are case sensitive !!! OS=Linux is not the same as Os=Linux

Example 2:
Kernel_vers=3.0

3: The assigned value must be placed in the right of the equal “=” sign!!! 3.0=Kernel_vers is will generate an error.

4: In your variable names, use only uppen and lower letters, numbers and underscores _ , the rest of the special characters may have different roles and mess up your commands.

How to display variable values with echo:

Syntax: echo $variable_name

The variables can also be displayed with printf, just like in C, but we will discuss about it in another tutorial.

No spaces before and after the equal “=” sign:

$ OS=Linux
$ echo $OS
Linux
$ OS =Linux

#the space placed in the left of the = causes errors
OS: command not found

The shell is case sensitive:

$ user=mike #only low cases
$ User=root #the first case is an upper
$ echo $user
mike
$ echo $User
root

Place the variable value only in the right side of the “=” sign:

$ Kernel_vers=3.0
echo $Kernel_vers=3.0
3.0

$ 3.0=kernel_vers
3.0=kernel_vers: command not found
#error generated by the misplacement of the value

Special characters in the variable names:

$ mike?=11
mike?=11: command not found # ? created this error
mike*=12
mike*=12: command not found # also * created an error
mike_id=1001
$ echo $mike_id
1001 #the underscore can be used in variable names

To remove the variable’s value use: echo variable_name=”” or unset variable_name.

The next shell scripting article is about the usage of the echo command in shell scripting.

Related reading about Linux / Unix environment variables:

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