Ignoring changes

OK, this one was mildly irritating but happily the solution is dead easy. In short, in this repo I have a file that I need to be committed as an empty file but then locally I want to have it be non-empty.¹ And yet I also don’t want to continually be reminded of this by git as that might lead to me checking in the non-empty version by mistake.

Adding it to .gitignore would be the usual thing to do—but unfortunately, having ignored it I then had to forcibly add and commit the empty version:

touch FILENAME # create the file, empty
echo FILENAME >> .gitignore # ignore the file
git add -f FILENAME # add the ignored file
git commit -m "adding the empty ignored file" # yeah, exactly that

And that mean that git status and friends kept showing it as modified when I put back the non-empty content I want to keep locally:

...
# [edit and save the ignored FILENAME]
...
git status # now shows me FILENAME as modified even though it's ignored :(

What to do? Well, it turns out there’s a command for that:²

git update-index --assume-unchanged FILENAME
git status # no longer whines at me that FILENAME is modified :)

…and now the committed (empty) version remains unchanged, the local (non-empty) version is different, and git doesn’t keep trying to trick me into committing the changes to the ignored file. Happy days.