PHP: $_SERVER[‘REDIRECT_URL’] vs $_SERVER[‘REQUEST_URI’]

REQUEST_URI is the requested URI path and query as used in the HTTP request line. REDIRECT_URL is created by Apache when an internal redirect happens:

REDIRECT_ environment variables are created from the environment variables which existed prior to the redirect. They are renamed with a REDIRECT_ prefix, i.e., HTTP_USER_AGENT becomes REDIRECT_HTTP_USER_AGENT.

REDIRECT_URL, REDIRECT_STATUS, and REDIRECT_QUERY_STRING are guaranteed to be set, and the other headers will be set only if they existed prior to the error condition.

Note that REDIRECT_URL does only contain the URI path.