64f1910f34
git-svn-id: svn+ssh://atelier.inf.usi.ch/home/bevilj/group-1@280 a672b425-5310-4d7a-af5c-997e18724b81
35 lines
1,019 B
HTML
35 lines
1,019 B
HTML
---
|
|
layout: page
|
|
category-page: scripts
|
|
category-title: Scripting
|
|
tags: variables special $ !
|
|
author: Dario Rasic
|
|
title: Script Special Variables
|
|
previous-page: pages/scripts/1-variables.html
|
|
next-page: pages/scripts/3-parameter_expansion.html
|
|
---
|
|
<!-- Intro -->
|
|
There are certain strings that we can't use in the variable-naming process.<br>
|
|
In this page we will see what those strings are, and what their purpose is.<br>
|
|
|
|
<h4>$$</h4>
|
|
To begin, we look at the simplest variable, which is the dollar sign ($).
|
|
This command simply gives us the process ID of the current shell.<br>
|
|
|
|
<pre>
|
|
echo $$
|
|
11480
|
|
</pre>
|
|
|
|
<h4>$0</h4>
|
|
This variable simply gives us the filename of the current script.
|
|
|
|
<h4>$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 ID of the last background command.
|