commit relative to the named <commit>. Typically you
would want comparison with the latest commit, so if you
do not give <commit>, it defaults to HEAD.
+ If HEAD does not exist (e.g. unborned branches) and
+ <commit> is not given, it shows all staged changes.
--staged is a synonym of --cached.
'git diff' [--options] <commit> [--] [<path>...]::