PHP - Super Global Variables

PHP uses special variables called super globals to provide information about the PHP script's environment. These variables don't need to be declared as global. They are automatically available, and they provide important information beyond the script's code itself, such as values from a user's input.

Since PHP 4.01, the super globals are defined in arrays. Arrays are special collections of values. The older super global variables such as those starting with $HTTP_* that were not in arrays still exist, but their use is not recommended, as they are deprecated.

Variable Array Name

Contents
$GLOBALS Contains any global variables that are accessible for the local script. The variable names are used to select which part of the array to access.
$_SERVER Contains information about the web server environment.
$_GET Contains information from GET requests (a form submission). These values should be checked before use.
$_POST Contains information from POST requests (another type of form submission). These values should be checked before use.
$_COOKIE Contains information from HTTP cookies.
$_FILES Contains information from POST file uploads
$_ENV Contains information about the scripts environment
$_REQUEST Contains information from user inputs. These values should be checked before use. $_GET or $_POST should be used instead of $_REQUEST as they are more specific.
$_SESSION Contains information from any variables registered in a session.

Super global variables are used for many PHP web scripts and services. If you are planning on creating a web site based on a PHP script, or are writing your own PHP script, this is a must know.