Thanks for your detailed reply, much of which I'm now beginning to grasp, which should put me in good stead for making other patches. I found many examples like yours, along the way.

My 'idea'; bigger systems fonts throughout the UI (already installed files manually on my device, looks pretty good to me).

I'm trying to create an RPM so I can install different font files (into /usr/share/fonts) for better readability in the general UI

I want to remove the 'sail-sans-pro' folder and its 2 font files (a+b) and replace with a 'fira-sans-pro' folder and its new font files (a+b).

Then, I would like to change the 2 font files (a+b) existing in the 'roboto' font folder for new font files (a+b). That's it.

Obviously it needs to uninstall cleanly and leave or restore the original font files.

I also do understand now that, diff tool is for files as you say, not folders, this is quite apparent through my hundreds of attempts at getting the right output from 'diffing' folders. (barking and tree, springs to mind)

Hope that's clear enough. Also, here's what I had made so far (RPM) and relevant files, except working unified_diff.patch (which may now be irrelevant); https://www.dropbox.com/s/teyb67xhvq...fonts.rar?dl=0

...oO(Now, where's my quill sharpener gone?)Oo...