PHP predefined variables

PHP can provide some predefined variables. Which can be used global aspect, knowing the environment, session, cookie, etc.
1. Superglobals — Built-in variables that are always available in all scopes are Superglobales.

The following variables are superglobal variables:

$GLOBALS

$_SERVER

$_GET

$_POST

$_FILES

$_COOKIE

$_SESSION

$_REQUEST

$_ENV

2.$php_errormsg — The previous error message.

3. $http_response_header — HTTP response headers

4. $argc — The number of arguments passed to the script

5. $argv — Array of arguments passed to the script

Read Also:-

PHP VARIABLES

PHP Global Variable $_GET

PHP Global Variable $_SERVER

PHP $GLOBALS Variable

How to code a PHP application

For more detail about variables please see manual