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created special script variables page

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git-svn-id: svn+ssh://atelier.inf.usi.ch/home/bevilj/group-1@173 a672b425-5310-4d7a-af5c-997e18724b81
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rasicd 2018-11-14 11:36:51 +00:00
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---
layout: page
category-page: scripts
category-title: Scripting
tags: variables, special, $, !
author: Dario Rasic
title: Script Special Variables
---
<!-- Intro -->
<p>
As previously said, there are certain characters that we can not use in the variable-naming process.
<br>
In this page we will see what actually are those characters, and what's their purpose.
<br>
<!-- list of commands-->
<h4>$$</h4>
To begin, we will see the simplest variable, which is the dollar sign ($). This command simply gives us the process ID number of the current shell.<br>
<pre>
echo $$
11480
</pre>
<h4>$0</h4>
This variable will simply give us the filename of the current script.
<h4>$n</h4>
This variable corresponds to the arguments with which a script was invoked. Here n is a positive number corresponding to the position of an argument.
<h4>$#</h4>
This variable gives us the number of arguments supplied to a script.
<h4>$!</h4>
This variable gives us the process number of the last background command.
</p>