PHP Variables

PHP provides a set of predefined variables. They may be super-global, and available in any context, such as $_GET; they may also be classic variable, in the global scope, such as $argv.

<?php

print_r($_GET);
print_r($argv);
print_r($GLOBALS);

function foo() {
    global $argc;
}

?>

Documentation

Related : Superglobal Variables, Variables, Native