In PHP, superglobal variables are special variables that are predefined and accessible in all scopes of a PHP script. These variables are called "superglobals" because they are always available, regardless of the scope, and you don't need to use the global keyword to access them. PHP provides several superglobal variables that contain information related to the server, client, and script itself. Here are the most commonly used superglobal variables in PHP:
$_GET: Contains variables passed to the script via the URL parameters (GET method).
$_POST: Contains variables submitted to the script via an HTTP POST request.
$_REQUEST: Combines the contents of $_GET, $_POST, and $_COOKIE arrays.
$_SESSION: Contains variables stored in the user's session.
$_COOKIE: Contains variables stored in HTTP cookies.
$_SERVER: Contains server and execution environment information (as mentioned in the previous response).
$_FILES: Contains information about uploaded files via HTTP POST.
$_ENV: Contains variables from the environment of the server.
$_GLOBALS: A global variable that contains all other global variables.
These superglobal variables are accessible from anywhere in your PHP script. For example, to access a value passed through the URL using the GET method, you can use $_GET['variable_name']. Similarly, to access a value submitted via an HTML form using the POST method, you can use $_POST['variable_name']. The other superglobals can be accessed in a similar manner.
It's important to properly validate and sanitize user input when working with superglobal variables to prevent security vulnerabilities such as SQL injection or cross-site scripting (XSS) attacks.