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create script variable-page

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git-svn-id: svn+ssh://atelier.inf.usi.ch/home/bevilj/group-1@172 a672b425-5310-4d7a-af5c-997e18724b81
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rasicd 2018-11-14 10:55:05 +00:00
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site/pages/scripts/redirection.html
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@ -8,7 +8,7 @@ title: Redirection
---
<p>
<h3>Output as input</h3>
<h3>output as input</h3>
<br>
To redirect a certain output of the command-line we have to use the symbol "&gt;".<br>
@ -39,7 +39,7 @@ cat hello.txt
</pre>
<!-- Input redirection text -->
<h3>Input as output</h3>
<h3>input as output</h3>
<br>
To redirect an input from a file for a command, the symbol "&lt;" is used.
@ -51,7 +51,7 @@ echo < $(cat hello.txt)
<p>This is particularly useful when chaining commands.</p>
<br>
<!-- Chaining command text -->
<h3>Chaining (or Piping)</h3>
<h3>chaining (or piping)</h3>
<br>
Chaining, also called Piping because it works with the pipe symbol "|", takes the output of a certain command-line and feeds it to another command in a direct way.
<!-- Table for the example of the piping command -->
@ -61,7 +61,7 @@ Moon
</pre>
<!-- A simple example -->
<h3>Simple Example</h3>
<h3>simple example</h3>
<br>
Now let's say that we want to combine those commands in a more complex operation. Let's say we want to take some contents from a certain file and put it into another file.<br>

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site/pages/scripts/variables.html Normal file
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---
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>