How can you get the HTTP Referrer when redirected from another website, not when they click on a link since it would work for $_SERVER['HTTP_REFERER'], but it doesn't work when a user has been redirected a website and the referrer would be empty.
What will be the method to get the referrer?
How can you get the HTTP Referrer when redirected from another website
You can't. If the redirection takes place under your control, you can add the original referer as a parameter, but if the external redirector doesn't do that, you have no way to get hold of the information.
An example of how I did it. Say we have 3 pages, one calling the next.
page1.com -> page2.com -> page3.com.
in page2.com get the page1.com using:
$referrer = $_SERVER['HTTP_REFERER'];//=page1.com
when redirecting to page3, send $referrer as a GET parameter
page3.com?referrer=$referrer
in page3 read the $referrer from the get.
$initialReferrer = $_GET['referrer'];//=page1.com
来源：https://stackoverflow.com/questions/4043196/get-http-referrer-on-redirection