How can session variables be retrieved and loaded after the browser has been closed in PHP?

Session variables can be retrieved and loaded after the browser has been closed by storing them in a database or a file on the server. This way, when a user returns to the website, the session data can be retrieved from the database or file and loaded back into the session.

// Start the session
session_start();

// Save session data to a file
file_put_contents('session_data.txt', serialize($_SESSION));

// Retrieve session data from the file
$_SESSION = unserialize(file_get_contents('session_data.txt'));