gitignore - Git: Ignoring Version-Controlled Files

Question

The .gitignore file is very useful in ignoring some of the files that we don't want to control. Unfortunately, it cannot be used when the file is already under version control. For example, my .gitignore (which is already added to git) file might be different than what my coworker wants it to be (e.g. I want to ignore Vim files). Whenever I make changes to this file, git shows it as a modified file. So my questions:

1. Is there any way to ignore changes for a certain file, which is already controlled by Git?!
2. Is there any way to commit these changes, but keep it for myself only? Obviously, I don't want to use a branch, because I am working on a certain branch.

Answer 1

Use git-update-index to temporarily ignore changes to files that are already under version control:

git update-index --assume-unchanged <files>

To undo that use:

git update-index --no-assume-unchanged <files>

Also have a look at the skip-worktree and no-skip-worktree options for update-index if you need this to persist past a git-reset