I am searching for a solution to automatically merge files on upload.
To be more precise, we are working in small groups doing web-development, working on the same folder on our Debian Server remotely, so the Problem is of course that if we often have the situation, where up to 3 People need to write in the same php file, at the moment we are trying to coordinate when which person is allowed to work on it.
So my idea was if there is a subversion like solution, to just merge every time we save the file via sshfs.
You should use version control. Here are some options. Which one you should use depends on a variety of factors.
You can then have the server your site is on pull from the repository.