Accessing variables/ etc out of functions in a php file

I have this

index.php:

<?PHP
require('config.php');

function readAppSettings(){
    return $sql->readAppSettings();
}
?>





//
config.php
<?php
include('mysql.php');  // mysql class

$sql = new mysql();
?>


I mean.. that is a very cut down version without the technical variables to make it work, but thats the idea.
When i try to access $sql outside of the function, its fine.. but inside the function,its calling a non object..


Is there a way to do like

function readAppSettings(){

return parent->$sql->readAppSettings();
}


(you can tell i'm an actionscript guy)

How do i access the $sql without redefining it in every function?
I dont wanna reconnect every time i wanna use the function