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.
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 "superglobals". (There is no mechanism in PHP for user-defined superglobals.) The superglobals are listed below; Also, you'll notice how the older predefined variables ($HTTP_*_VARS) still exist. As of PHP 5.0.0, the long PHP predefined variable arrays may be disabled with the register_long_arrays directive.
Variable variables: Superglobals cannot be used as variable variables inside functions or class methods.
Note: Even though both the superglobal and HTTP_*_VARS can exist at the same time; they are not identical, so modifying one will not change the other.
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 URL query string. 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).
$_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 the GET, POST, and COOKIE input mechanisms, and which therefore cannot be trusted. The presence and order of variable inclusion in this array is defined according to the PHP variables_order configuration directive.
$_SESSION
Variables which are currently registered to a script's session. Analogous to the old $HTTP_SESSION_VARS array (which is still available, but deprecated).
From version 4.1.0 onward, PHP provides an additional set of predefined arrays containing variables from the web server (if applicable), the environment, and user input. These new arrays are rather special in that they are automatically global--i.e., automatically available in every scope. For this reason, they are often known as "superglobals". (There is no mechanism in PHP for user-defined superglobals.) The superglobals are listed below; Also, you'll notice how the older predefined variables ($HTTP_*_VARS) still exist. As of PHP 5.0.0, the long PHP predefined variable arrays may be disabled with the register_long_arrays directive.
Variable variables: Superglobals cannot be used as variable variables inside functions or class methods.
Note: Even though both the superglobal and HTTP_*_VARS can exist at the same time; they are not identical, so modifying one will not change the other.
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 URL query string. 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).
$_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 the GET, POST, and COOKIE input mechanisms, and which therefore cannot be trusted. The presence and order of variable inclusion in this array is defined according to the PHP variables_order configuration directive.
$_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).
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