Ok so if anyone can help even a tiny bit, that would be awesome:
I host for many clients and they all use a custom CMS that I created for their site so they can login and edit stuff. For many of these clients, various files are the exact same(like the login screen, traffic page, etc) and since I have 30+ clients, when I make changes to one of those common pages, the current method is to ftp connect to all 30 sites individually and upload the new file. As you may know, that's a huge pain. All of these sites are on my server(shared server) but the domains are all different.
Based on what I described, is there a way that these common php files can be accessed from one central file and then I can update 1 file and each client would see the changes to the corresponding file on their domain?