After branches are merged, and GitHub no longer show difference when I try to make a pull request, but git diff
will still show differences.
For example:
Now GitHub pull request from H to D shows no difference but git diff H D show differences.
What I am trying to do is to create a command-line tool to see which old branches (there can be a lot) don't have code differences to develop. right now I have to go to GitHub, do a pull request and select each branch to see if there are difference.
You probably want the "triple-dot" syntax:
git diff D...H
See also What are the differences between double-dot ".." and triple-dot "..." in Git diff commit ranges?