How to ignore existing file in Git?

Question

I need to work on file.txt locally and in Git, with different content. I want Git not to tell me that there have been changes to that file.

Is this possible

Answer 1

SOURCETREE Terminal codes

Add ignore file:

git update-index --skip-worktree index.php

Extract ignore file:

git update-index --no-skip-worktree index.php

List ignore files:

git ls-files . --ignored --exclude-standard --others