Webmaster in a Nutshell, Third Edition

Web-Related Variables

PHP automatically creates variables for all the data it receives in an HTTP request. This can include GET data, POST data, cookie data, and environment variables. The variables are either in PHP’s global symbol table or in one of a number of superglobal arrays, depending on the value of the register_globals setting in your php.ini file.

Beginning with PHP 4.2.0, the default setting for register_globals is off. With register_globals off, all the various variables that are usually available directly in the global symbol table are now available via individual superglobal arrays. There is a limited set of superglobals and they cannot be created from a user-level script. The superglobal array to use depends on the source of the variable. Here is the list:

$_GET

GET-method variables. These are the variables supplied directly in the URL. For example, with http://www.example.com/script.php?a=1&b=2, $_GET['a'] and $_GET['b'] are set to 1 and 2, respectively.

$_POST

POST-method variables. Form field data from regular POST-method forms.

$_COOKIE

Any cookies the browser sends end up in this array. The name of the cookie is the key and the cookie value becomes the array value.

$_REQUEST

This array contains all of the above variables (i.e., GET, POST, and cookie). If a variable appears in multiple sources, the order in which they are imported into $_REQUEST is given by the setting of the variables_order php.ini directive. The default is 'GPC', which means GET-method ...