What is the role of $_SERVER in PHP?

$_SERVER in PHP is a global variable that contains information such as headers, paths, and script locations in an associative array. It stores information related to the server and execution environment, including but not limited to the following:

1. Information about the server, such as the server name, port number, and server software.
2. Client information such as client IP address, client port number, user agent information, etc.
3. Request information such as request method, request URL, and request time.
4. Information about the script, such as the script name, script path, and script execution time.
5. HTTP request headers: such as Accept, User-Agent, Referer, and so on.
6. Environmental variables information such as DOCUMENT_ROOT and SERVER_NAME.

By accessing elements in the $_SERVER array, you can obtain this information. For example, you can use $_SERVER[‘REMOTE_ADDR’] to get the client’s IP address, and use $_SERVER[‘HTTP_USER_AGENT’] to get user agent information. These details are often used in development to determine the visitor’s source, browser type, etc., for appropriate handling and response.