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

Maybe you want to "pretend" that the file hasn't changed when actually it did? You can do that like this:

git update-index --assume-unchanged file.txt

To undo this later:

git update-index --no-assume-unchanged file.txt

To view a list of files that are marked this way:

git ls-files -v | grep '^[a-z]'

UPDATE

As comments have pointed out, this is most probably NOT what you want to do. A better answer has been posted by @Tom Auger, use that instead.