PHP : Super Global Variables
$GLOBALS
$_SERVER
$_REQUEST
$_POST
$_GET
$_FILES
$_ENV
$_COOKIE
$_SESSION
// a few examples for just $_SERVER
echo $_SERVER['PHP_SELF'];
echo $_SERVER['SERVER_NAME'];
echo $_SERVER['HTTP_HOST'];
echo $_SERVER['HTTP_REFERER'];
echo $_SERVER['HTTP_USER_AGENT'];
echo $_SERVER['SCRIPT_NAME'];