diff current working copy of a file with another branch's committed copy

Question

I have a repo with file foo in the master branch. I switched to bar branch and made some changes to foo. How can I now run a git diff

Answer 1

To see local changes compare to your current branch

git diff .

To see local changed compare to any other existing branch

git diff  .

To see changes of a particular file

git diff  -- 

Make sure you run git fetch at the beginning.