Script Variables

A variable is simply a string to which we assign a certain type of data, which could be some text, a number, a filename or other types of data.

Naming a variable

To name a variable in Unix we can only use letters, numbers or the underscore character (_).
Other characters can't be used because they have a special meaning in Unix Shell.
Some simple examples are:

VAR_1
VAR_2
NAME_3
name_4

Defining a variable

To define a certain variable, we use the following base case:

variable_name=variable_value

Let me show you a simple example:

VAR_1=Strawberry

To access a variable we have to use the dollar sign ($). So if I want to access VAR_1, I have to write:

VAR_1="Strawberry"
echo $VAR_1
    Strawberry

Deleting a variable

Deleting a variable means that the shell will remove a certain variable from the list of those that it tracks.
To delete a variable we use the following command:

unset variable_name

which in our case would be:

unset VAR_1

Protecting variables

To protect a certain variable, we can set it as read-only so that it can't be changed or deleted.
So, if we try to change the value of VAR_1, the result will be the following:

VAR_1="Strawberry"
readonly VAR_1
VAR_1="Blueberry"
    VAR_1: This variable is read only.

If we try to delete the variable, the shell will give us the following error:

VAR_1="Strawberry"
unset VAR_1
    VAR_1: This variable is read only.

theshell