Alias subdomains to the same php file

ok so this is a really complex situation and if anyone can help it is greatly appreciated.

What needs to be done is I have many subdomains that need to be directed to the same php file in order for that file to confirm what page needs to be brought up (this sounds unusual i know but this is how it has to work for specific reasons). when the subdomain gets directed to the php it also has to keep the entire url in tact so that the php app can tell what site the customer is trying to access by exploding the url. I was thinking of using a redirect but that changes the url. So instead I was trying to use AliasMatch but I cannot get it to work.

Please someone help me!