theshell.ch/site/pages/scripts/1-variables.html

---
layout: page
category-page: scripts
category-title: Scripting
tags: variables defining deleting naming
author: Dario Rasic
title: Script Variables
previous-page: pages/scripts/0-base-commands.html
next-page: pages/scripts/2-special-variables.html
---
<!-- Intro -->
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.<br>

<!-- How to name a variable - text -->
<h3>Naming a variable</h3>

<!-- Explaination -->
To name a variable in Unix we can only use letters, numbers or
the underscore character (_).<br>
Other characters can't be used because they have a special meaning in Unix Shell.<br>

Some simple examples are:

<pre>
VAR_1
VAR_2
NAME_3
name_4
</pre>

<!-- How to define a variable - text -->
<h3>Defining a variable</h3>

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

<pre>
variable_name=variable_value
</pre>

<!-- Examples of defining -->
Let me show you a simple example:

<pre>
VAR_1=Strawberry
</pre>

<!-- How to access the variables - text -->
To access a variable we have to use the dollar sign ($). So if I want to
access VAR_1, I have to write:
<!-- Examples of accessing -->
<pre>
VAR_1="Strawberry"
echo $VAR_1
    Strawberry
</pre>

<!-- How to delete a variable - text -->
<h3>Deleting a variable</h3>

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

<pre>
unset variable_name
</pre>

which in our case would be:

<pre>
unset VAR_1
</pre>

<!-- How to protect a variable - text -->
<h3>Protecting variables</h3>

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

<pre>
VAR_1="Strawberry"
readonly VAR_1
VAR_1="Blueberry"
    VAR_1: This variable is read only.
</pre>

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

<pre>
VAR_1="Strawberry"
unset VAR_1
    VAR_1: This variable is read only.
</pre>