Which method, getenv or $_SERVER, is recommended for retrieving the referer in PHP?

When retrieving the referer in PHP, it is recommended to use the $_SERVER superglobal over the getenv function. This is because $_SERVER is a predefined array that contains server and execution environment information, including the HTTP referer. Using $_SERVER['HTTP_REFERER'] is a more straightforward and reliable way to access the referer information.

$referer = isset($_SERVER['HTTP_REFERER']) ? $_SERVER['HTTP_REFERER'] : '';
echo $referer;