superglobals

In PHP, superglobals are a set of built-in variables that are automatically available in every scope throughout a script. They do not require global declarations to be accessed, and they are provided by the PHP runtime. Superglobals are typically arrays or special variables, and they contrast with user-defined globals because they are always accessible without explicit propagation.

The most commonly used superglobals include:

- $_GET and $_POST, which contain query string and form data sent by the client.

- $_REQUEST, which merges data from $_GET, $_POST, and $_COOKIE.

- $_COOKIE, which stores cookies sent by the client.

- $_FILES, which contains information about uploaded files.

- $_SERVER, which provides server and execution environment information (request method, script name, headers, etc.).

- $_ENV, which holds environment variables.

- $_SESSION, which stores session data (requires session_start()).

- $GLOBALS, a reference to all global variables in the script.

Usage typically involves indexing these arrays by a key, with checks for existence. For example, using input data safely can look like: if (isset($_GET['page'])) { $page = (string) $_GET['page']; } and then sanitizing the value before use. Functions like htmlspecialchars or filter_input provide additional protection. When handling file uploads, $_FILES contains details such as name, type, size, and temporary path.

Security and best practices emphasize validating and sanitizing all user-supplied data obtained from these superglobals. Prefer using the specific superglobals ($_GET, $_POST) over $_REQUEST to avoid mixing sources. For session data, always start the session with session_start() and implement proper session security measures.