Notes On: Git
Overview of repos, branches, forks, merges, and clones
Comparing versions of a file between 2 Git branches
git diff branch1 branch2 path/to/myfile.ext
or
git difftool branch1 branch2 path/to/myfile.ext`
Note: If the files are identical, the command will silently return, show no output, and not start any external tool.