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 variables, in the global scope, such as $argv.
The set of predefined variables changes with PHP versions: for example, in version 8.0, $phperrormsg was definitely removed.
The set of predefined variables also depended on PHP directives. $HTTP_RAW_POST_DATA depended upon the always_populate_raw_post_data directive.
<?php
print_r($_GET);
print_r($argv); // when in CLI
print_r($GLOBALS);
function foo() {
global $argc;
}
?>