I found a good answer here: stackoverflow Q332528
It uses ideas taken from here: Pro-Git merge strategies
Here is a copy of it:
Let’s say you want to exclude the file
config.php
On branch A:
Create a file named ‘.gitattributes’ in the same dir, with this
line:config.php merge=ours
. This tells git what strategy to use
when mergin the file. In this case it always keep your version, ie.
the version on the branch you are merging into.Add the .gitattributes file and commit
On branch B: repeat steps 1-2
Try merging now. Your file should be left untouched.
Edit:
From the git book regarding merge=ours
, “One very useful option is to tell Git to not try to merge specific files when they have conflicts, but rather to use your side of the merge over someone else’s.”
So, this answer doesn’t apply as well as it might to the question. pjmorse’s answer regarding using submodules is good.
Another option would be to use a sub-tree merge, which may have added benefits.