We already discussed variables, but we did not already discuss the variables that come ready-made in PHP. Predefined variables are already defined, as their name implies, and can be used without you having to create them first.

The majority of predefined variables are used to provide information from and about the web server, the web browser, and the user. They are called superglobals.

The following superglobals are available:

Variable Name	Variable Description
$_GET	HTTP GET Variables
$_POST	HTTP POST Variables
$_FILES	HTTP File Upload Variables
$_SERVER	Server And Environment Information
$_COOKIE	HTTP Cookies
$_SESSION	Session Variables
$_REQUEST	HTTP Request Variables
$GLOBALS	References All Variables In A Global Scope
$php_errormsg	The Previous (Last) Error Message

We will discuss many of these superglobals in detail on the following pages, so for now we will only briefly demonstrate how they are used with a demonstration of the $_SERVER superglobal.

<?php
  echo "Your IP Address Is: " . $_SERVER['REMOTE_ADDR'] . "<br>";
  echo "The Current Page Name Is: " . $_SERVER['PHP_SELF'] . "<br>";
  echo "You Came From A Page Called: " . $_SERVER['HTTP_REFERER'] . "<br>";
?>

Superglobals, such as the $_SERVER variable, are arrays, which we have not yet learned about. The are a single variable that contain multiple values, all of which are separate and can be referenced separately. The brackets and single quotes at the end of the variable contain the reference name of the real value that we want. The result of the above example is:

Your IP Address Is: 18.191.234.62
The Current Page Name Is: /php/php-forms-predefined-variables-superglobals.php
You Came From A Page Called:


The $_SERVER variable has over thirty elements available, most of which are actually useful. The most common elements, assuming your server supports them, are:

Variable	Description
$_SERVER['PHP_SELF']	The filename of the currently executing script, relative to the document root.
$_SERVER['SERVER_ADDR']	The IP address of the server under which the current script is executing.
$_SERVER['SERVER_NAME']	The name of the server host under which the current script is executing. If the script is running on a virtual host, this will be the value defined for that virtual host.
$_SERVER['SERVER_SOFTWARE']	Server identification string, given in the headers when responding to requests.
$_SERVER['SERVER_PROTOCOL']	Name and revision of the information protocol via which the page was requested; i.e. 'HTTP/1.0';
$_SERVER['REQUEST_METHOD']	Which request method was used to access the page; i.e. 'GET', 'HEAD', 'POST', 'PUT'.
$_SERVER['REQUEST_TIME']	The timestamp of the start of the request. Available since PHP 5.1.0.
$_SERVER['QUERY_STRING']	The query string, if any, via which the page was accessed.
$_SERVER['DOCUMENT_ROOT']	The document root directory under which the current script is executing, as defined in the server's configuration file.
$_SERVER['HTTP_CONNECTION']	Contents of the Connection: header from the current request, if there is one. Example: 'Keep-Alive'.
$_SERVER['HTTP_HOST']	Contents of the Host: header from the current request, if there is one.
$_SERVER['HTTP_REFERER']	The address of the page (if any) which referred the user agent to the current page.
$_SERVER['HTTP_USER_AGENT']	This is a string denoting the user agent being which is accessing the page. A typical example is: Mozilla/4.5 [en] (X11; U; Linux 2.2.9 i586).
$_SERVER['HTTPS']	Set to a non-empty value if the script was queried through the HTTPS protocol.
$_SERVER['REMOTE_ADDR']	The IP address from which the user is viewing the current page.
$_SERVER['REMOTE_HOST']	The Host name from which the user is viewing the current page. The reverse dns lookup is based off the REMOTE_ADDR of the user.
$_SERVER['REMOTE_PORT']	The port being used on the user's machine to communicate with the web server.
$_SERVER['SCRIPT_FILENAME']	The absolute pathname of the currently executing script.
$_SERVER['SERVER_ADMIN']	The value given to the SERVER_ADMIN (for Apache) directive in the web server configuration file.
$_SERVER['SERVER_PORT']	The port on the server machine being used by the web server for communication. For default setups, this will be '80'.
$_SERVER['SERVER_SIGNATURE']	String containing the server version and virtual host name which are added to server-generated pages, if enabled.
$_SERVER['PATH_TRANSLATED']	Filesystem based path to the current script.
$_SERVER['SCRIPT_NAME']	Contains the current script's path. This is useful for pages which need to point to themselves.
$_SERVER['REQUEST_URI']	The URI which was given in order to access this page; for instance, '/index.html'.
$_SERVER['PHP_AUTH_DIGEST']	When running under Apache as module doing Digest HTTP authentication this variable is set to the 'Authorization' header sent by the client.
$_SERVER['PHP_AUTH_USER']	When running under Apache or IIS (ISAPI on PHP 5) as module doing HTTP authentication this variable is set to the username provided by the user.
$_SERVER['PHP_AUTH_PW']	When running under Apache or IIS (ISAPI on PHP 5) as module doing HTTP authentication this variable is set to the password provided by the user.
$_SERVER['AUTH_TYPE']	When running under Apache as module doing HTTP authenticated this variable is set to the authentication type.