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

You're trying to compare your working tree with a particular branch name, so you want this:

git diff master -- foo

Which is from this form of git-diff (see the git-diff manpage)

   git diff [--options]  [--] [...]
       This form is to view the changes you have in your working tree
       relative to the named . You can use HEAD to compare it with
       the latest commit, or a branch name to compare with the tip of a
       different branch.

FYI, there is also a --cached (aka --staged) option for viewing the diff of what you've staged, rather than everything in your working tree:

   git diff [--options] --cached [] [--] [...]
       This form is to view the changes you staged for the next commit
       relative to the named .
       ...
       --staged is a synonym of --cached.