git: ignoring a file which *is* version controlled

Question

A .gitignore file allows to ignore files from version controlling them at all.

We have a different situation: we want to place in the repository some config

Answer 1

I know this kind of dodges the issue, but I would have a ".defaults" file for each, and then change this. This helps with the configuration energy anyway - what if someone who has a custom configuration wants to change the defaults?

Don't ignore the .defaults, ignore the actual thing. Maybe have a script that copies the .defaults to the regular ones if they don't already exist.

Answer 2

I define the following aliases in my .gitconfig file:

[alias]
  ignore = update-index --assume-unchanged
  unignore = update-index --no-assume-unchanged

That should do exactly what you want: running git ignore some-file will treat the file as unchanged no matter what you do to it, until you run git unignore some-file.