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.

The set of predefined variables changes with PHP versions: for example, in PHP 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;
    }

?>

Documentation

See also Predefined Variables in PHP: For complete beginners.

Related : Superglobal Variables, Variables, Native, $argc, $argv