foo.rb

desc "Remove branches that are merged to master"
task :grm do
  branch_string = `git branch --merged master`
  branches = branch_string.strip.split("\n")
  branches.each do |branch_name|
    branch_name.strip!
    unless branch_name =~ /master/
      print "Deleting branch #{branch_name} y/n: "
      char = STDIN.gets()
      if char.is_a?(Fixnum)
        if char == 121
          system("git branch -D #{branch_name}")
        end
      else
        if char.strip == 'y'
          system("git branch -D #{branch_name}")
        end
      end
    end
  end
end