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

---
layout: page
category-page: scripts
category-title: Scripting
tags: variables special $ !
author: Dario Rasic
title: Script Special Variables
---
<!-- Intro -->
There are certain strings that we can not use in the variable-naming process.<br>
In this page we will see what actually are those strings, and what's their purpose.<br>

<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.