[git] git: How to ignore all present untracked files?

I came here trying to solve a slightly different problem. Maybe this will be useful to someone else:

I create a new branch feature-a. as part of this branch I create new directories and need to modify .gitignore to suppress some of them. This happens a lot when adding new tools to a project that create various cache folders. .serverless, .terraform, etc.

Before I'm ready to merge that back to master I have something else come up, so I checkout master again, but now git status picks up those suppressed folders again, since the .gitignore hasn't been merged yet.

The answer here is actually simple, though I had to find this blog to figure it out:

Just checkout the .gitignore file from feature-a branch

git checkout feature-a -- feature-a/.gitignore
git add .
git commit -m "update .gitignore from feature-a branch"