Sometimes you want to view a file on another branch (without switching
branches). That is, you want to view the version of that file as it exists
on that branch. git show can help. If the other branch is named some_branch and
the file you want to see is app/models/users.rb, then your command should
look like this:
$ git show some_branch:app/models/users.rb
You can even tab-complete the filename as you type it out.
See man git-show for more details.