Remove merged branches from a git remote

Bunches of branches cluttering up Github? Here's an easy one-liner to delete branches that are already merged to master:

git branch -r --merged origin/master | grep origin | grep -v master | cut -f2- -d/ | xargs -I% git push origin :%

Bonus! Deleting merged local branches is much the same:

git branch --merged master | grep -v master | xargs -n1 git branch -d