git remove-extraneous-branches

.gitconfig

[alias]
  # Prints merged branches without the current working branch and mainline branches
  extraneous-branches = "!f() { git branch --merged | grep -v -e 'gh-pages' -e 'master' -e 'staging' -e 'production'; }; echo `f`"

  # Deletes the extraneous branches with a soft -d
  remove-extraneous-branches = "!f() { git extraneous-branches; }; git branch -d `f`"
  reb = remove-extraneous-branches