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 Predefined variables.

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In PHP 4.2.0 and later, the default set of predefined variables which are available in the global scope has changed. Individual input and server variables are by default no longer placed directly into the global scope; rather, they are placed into the following superglobal arrays.

You can still force the old behaviour by setting register_globals to 'On' in your php.ini file.

For more information and background on this change, please see the PHP 4.1.0 Release Announcement.

From version 4.1.0 onward, PHP provides a 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 Predefined variables.

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