set file to executable and drop in /usr/local/bin/

remove_old_branches.rb

#!/usr/bin/env ruby
require 'date'
commit_branches_and_dates = `git for-each-ref --sort=-committerdate refs/heads/ --format='%(refname) %(committerdate)'`.split("\n").map {|e| e[11..-1] }.map {|e| e.split(' ', 2) }

one_month_in_seconds = 60*60*24*30
parsable_time = (Time.now - one_month_in_seconds).to_s
one_month_before_now = Date.parse(parsable_time)
deleted_branch_count = 0
commit_branches_and_dates.each do |branch, date|
  date = Date.parse date
  # delete branches that haven't had a commit in more than a month
  if date < one_month_before_now
    deleted_branch_count += 1
    puts "deleting #{branch} from #{date}"
    `git branch -D #{branch}`
  end
end

puts "finished deleting branches", "#{deleted_branch_count} removed"