Append SUB-ID tracking variable to the link provided

Recently I have hired several affiliate marketing companies to bring lots of traffic to our site, However I need to append SUB-ID tracking variable to the link provided (in order to keep track of subids, keyword, etc..) e.g our current site is [login to view URL] we need to look something like this to keep track of which affiliate/keyword the traffic is coming from => [login to view URL] I think this can be done using PHP???