--- 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 --- There are certain strings that we can not use in the variable-naming process.
In this page we will see what actually are those strings, and what's their purpose.

$$

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.
echo $$
    11480

$0

This variable will simply give us the filename of the current script.

$n

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.

$#

This variable gives us the number of arguments supplied to a script.

$!

This variable gives us the process number of the last background command.