Couple hours of searching and googling have not helped me
If you have multiple domain names pointing to the same host:
Is there a way to determine which URL was used to access the site?
I know I can get this if there is an HTTP_REFERER but of course that does not help when the URL is typed into the address bar.
I tried REQUEST_URI but that did not work.
What about SCRIPT_URI?
When I look at SCRIPT_URI it seems to echo what I type in the browsers address bar to access it, but I don't currently have another domain name pointing at it to test, I suspect it will not change.