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# Predefined variables

PHP provides a large number of predefined variables to any script which it runs. Many of these variables, however, cannot be fully documented as they are dependent upon which server is running, the version and setup of the server, and other factors. Some of these variables will not be available when PHP is run on the command line. For a listing of these variables, please see the section on Reserved Predefined Variables.

Warning
In PHP 4.2.0 and later, the default value for the PHP directive register_globals is off. This is a major change in PHP. Having register_globals off affects the set of predefined variables available in the global scope. For example, to get `DOCUMENT_ROOT` you'll use `$_SERVER['DOCUMENT_ROOT']` instead of `$DOCUMENT_ROOT`, or `$_GET['id']` from the URL `http://www.example.com/test.php?id=3` instead of `$id`, or `$_ENV['HOME']` instead of `$HOME`. For related information on this change, read the configuration entry for register_globals, the security chapter on Using Register Globals , as well as the PHP 4.1.0 and 4.2.0 Release Announcements. Using the available PHP Reserved Predefined Variables, like the superglobal arrays, is preferred.

From version 4.1.0 onward, PHP provides an additional set of predefined arrays containing variables from the web server (if applicable), the environment, and user input. These new arrays are rather special in that they are automatically global--i.e., automatically available in every scope. For this reason, they are often known as 'autoglobals' or 'superglobals'. (There is no mechanism in PHP for user-defined superglobals.) The superglobals are listed below; however, for a listing of their contents and further discussion on PHP predefined variables and their natures, please see the section Reserved Predefined Variables. Also, you'll notice how the older predefined variables (`$HTTP_*_VARS`) still exist.

If certain variables in variables_order are not set, their appropriate PHP predefined arrays are also left empty.

PHP Superglobals

$GLOBALS

  Contains a reference to every variable which is currently available within the global scope of the script. The keys of this array are the names of the global variables. `$GLOBALS` has existed since PHP 3.

$_SERVER

  Variables set by the web server or otherwise directly related to the execution environment of the current script. Analogous to the old `$HTTP_SERVER_VARS` array (which is still available, but deprecated).

$_GET

  Variables provided to the script via HTTP GET. Analogous to the old `$HTTP_GET_VARS` array (which is still available, but deprecated).

$_POST

  Variables provided to the script via HTTP POST. Analogous to the old `$HTTP_POST_VARS` array (which is still available, but deprecated).

$_COOKIE

  Variables provided to the script via HTTP cookies. Analogous to the old `$HTTP_COOKIE_VARS` array (which is still available, but deprecated).

$_FILES

  Variables provided to the script via HTTP post file uploads. Analogous to the old `$HTTP_POST_FILES` array (which is still available, but deprecated). See POST method uploads for more information.

$_ENV

  Variables provided to the script via the environment. Analogous to the old `$HTTP_ENV_VARS` array (which is still available, but deprecated).

$_REQUEST

  Variables provided to the script via any user input mechanism, and which therefore cannot be trusted. The presence and order of variable inclusion in this array is defined according to the variables_order configuration directive. This array has no direct analogue in versions of PHP prior to 4.1.0. See also import_request_variables().

  > Note: When running on the command line , this will not include the `argv` and `argc` entries; these are present in the `$_SERVER` array.

$_SESSION

  Variables which are currently registered to a script's session. Analogous to the old `$HTTP_SESSION_VARS` array (which is still available, but deprecated). See the Session handling functions section for more information.

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