If you don’t want the file going into your repo, then the standard .gitignore instructions work.
However, suppose you work on a team where you want only one person every checking changes to db/schema.rb?
You can use this command to have git ignore this file in regards to the git “index”:
git update-index --assume-unchanged db/schema.rb
You can undo that later with this command:
git update-index --no-assume-unchanged db/schema.rb
To find out what files you’re ignoring:
git ls-files -v | grep "^[a-z]"