If you're like me, and like to keep your git tree clean and free of unruly unused branches, you always click "Delete this branch" when merging a pull request on GitHub.

But what about your local machine!!?!?!? How do we keep the homegrounds nice and clean?

To remove the tracking branches (origin/whatever) after you've merged and deleted them use:
git fetch --prune

This fetching command will get the latest changes from your remote repository, while "pruning" your tree of deleted (origin/whatever) branches.

As for the merged local branches, use:
git diff --merged | grep -v master | xargs git branch -d

This command deletes your local branches that have been merged remotely. The grep -v filters out master so that you don't delete your local master branch if it's up to date with origin/master.

I just deleted about 50 excess branches with those two commands. So, needless to say, these are quite useful for me.

As a caution:

Only use those if your team is okay with deleting unused branches. My team isn't okay with that, but for personal projects, I like to keep my branch count to a minimum.

Cheers!