Remove all merged branch. Be careful if you have merged a branch into the master and continue to work on it and then you haven't merged it yet, this script will remove it.

gistfile1.sh

git checkout master
git fetch
git remote prune origin

#Remove locally 
git branch --merged master | grep -v 'master$' | xargs git branch -d

echo "Branches merged, to delete:"
git branch -r --merged master | sed 's/ *origin\///' | grep -v 'master$'

read -p "Sure about that (y/n)? "
if [ "$REPLY" == "y" ]
then
   #Remove remotely 
   git branch -r --merged master | sed 's/ *origin\///' \
             | grep -v 'master$' | xargs -I% git push origin :%
   echo "Done!"
fi