How do I delete all Git branches which have been merged?

How do I delete branches which have already been merged? Can I delete them all at once, instead of deleting each branch one-by-one?

[delphinus35]

master にマージ済みのブランチを全部消す（github 上のものも含む）

[nabinno]

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

[mikesorae]

スーパーお便利コマンドだ “git branch --merged | grep -v "\*" | grep -v master | grep -v dev | xargs -n 1 git branch -d ”

[kanno_kanno]

マージ済みのブランチ(ローカル/リモート共に)消すスクリプト