100 lines
2.3 KiB
HTML
100 lines
2.3 KiB
HTML
|
---
|
||
|
|
layout: page
|
||
|
|
category-page: scripts
|
||
|
|
category-title: Scripting
|
||
|
|
tags: variables, defining, deleting, naming
|
||
|
|
author: Dario Rasic
|
||
|
|
title: Script Variables
|
||
|
|
---
|
||
|
|
<!-- Intro -->
|
||
|
|
<p>
|
||
|
|
A variable is simply a string to which we assign a certain type of data, which could be a text, a number, a filename and other types of data.
|
||
|
|
<br>
|
||
|
|
<!-- How to name a variable - text -->
|
||
|
|
<h3>Naming a variable</h3>
|
||
|
|
<!-- Explaination -->
|
||
|
|
To name a variable in Unix we have to use only letters, numbers or the underscore character (_).<br>
|
||
|
|
Other characters can't be used because they have a special meaning in Unix Shell.<br>
|
||
|
|
<br>
|
||
|
|
<!-- Examples of naming -->
|
||
|
|
Some simple examples are:
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
VAR_1
|
||
|
|
VAR_2
|
||
|
|
NAME_3
|
||
|
|
name_4
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<!-- How to define a variable - text -->
|
||
|
|
<h3>Defining a variable</h3>
|
||
|
|
|
||
|
|
To define a certain variable, we could use the following basecase:
|
||
|
|
|
||
|
|
<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
|
||
|
|
</pre>
|
||
|
|
And shell will give us the following result:
|
||
|
|
<pre>
|
||
|
|
Strawberry
|
||
|
|
</pre>
|
||
|
|
<br>
|
||
|
|
<!-- How to delete a variable - text -->
|
||
|
|
<h3>Deleting a variable</h3>
|
||
|
|
<!-- Explaination -->
|
||
|
|
Deleting a variable means that shell will remove a certain variable from the list of those that it tracks.<br>
|
||
|
|
To delete a variable we use the following command:
|
||
|
|
<!-- Examples of deleting -->
|
||
|
|
<pre>
|
||
|
|
unset variable_name
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
which in our case would be:
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
unset VAR_1
|
||
|
|
</pre>
|
||
|
|
<br>
|
||
|
|
<!-- How to protect a variable - text -->
|
||
|
|
<h3>Protecting variables</h3>
|
||
|
|
<!-- Explaination -->
|
||
|
|
To protect a certain variable, we can set them 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:
|
||
|
|
<!-- Examples of protection -->
|
||
|
|
<pre>
|
||
|
|
VAR_1=Strawberry
|
||
|
|
readonly VAR_1
|
||
|
|
VAR_1=Blueberry
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
which will give us:
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
VAR_1: This variable is read only.
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
If we try to delete the variable, shell will give us the following value:
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
VAR_1=Strawberry
|
||
|
|
unset VAR_1
|
||
|
|
echo $VAR_1
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
As VAR_1 is read-only, shell will not give us any output, as you can't use the unset command with read-only files.
|
||
|
|
</p>
|