PHP: variables
Variables in PHP are represented by a dollar sign followed by the variable name. The variable name is case-sensitive.
Variable names follow the same rules as other labels in PHP. The name must start with a letter or underscore, followed by any number of letters, numbers, or underscores. Valid characters for a variable name are ‘[a-zA-Z_x7f-xff][a-zA-Z0-9_x7f-xff]*’ (sans quotes).
There is a new set of powerful predefined arrays that contain variables from the webserver, user-input and the environment. These arrays are known as superglobals. Here is a listing of superglobals:
| $GLOBALS | Contains a reference to every variable that is available within the global scope of the script. |
| $_SERVER | Variables set by the web server and/or otherwise directly related to the execution environment of the script. |
| $_GET | Variables provided to the script via a URL query string. |
| $_POST | Variables provided to the script via the HTTP POST. |
| $_COOKIE | Variables provided to the script via HTTP COOKIES. |
| $_FILES | Variables provided to the script via HTTP POST file uploads. |
| $_ENV | Variables provided to the script via the environment |
| $_REQUEST | Variables provided to the script via the GET, POST, and COOKIE inputs. These variables cannot be trusted. |
| $_SESSION | Variables which are currently registered to a scripts’s session |
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