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
For a listing of these variables, please see the section on
Reserved Predefined Variables.
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 $_ENV['HOME'] instead of
Using the available PHP Reserved Predefined Variables, like the
From version 4.1.0 onward, PHP provides an additional set of predefined arrays
containing variables from the web server (if applicable), the
environment, and user input. These new arrays are rather special
in that they are automatically global--i.e., automatically
available in every scope. For this reason, they are often known as
'autoglobals' or 'superglobals'. (There is no mechanism in PHP for
user-defined superglobals.) The superglobals are listed below;
however, for a listing of their contents and further discussion on
PHP predefined variables and their natures, please see the section
Reserved Predefined Variables.
Also, you'll notice how the older predefined variables
($HTTP_*_VARS) still exist.
As of PHP 5.0.0, the long PHP
arrays may be disabled with the
Superglobals cannot be used as
inside functions or class methods.
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.
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.
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).
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
configuration directive. This array has no direct analogue in versions
of PHP prior to 4.1.0. See also
Since PHP 4.3.0, FILE information from $_FILES does
not exist in $_REQUEST.
When running on the command line
, this will not include the
argv and argc entries; these are
present in the $_SERVER array.
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.