langstats.rb

#!/usr/bin/env ruby

#
# Utility to count the number of lines added to a git repository by month and file extension.
#

require 'csv'
require 'set'

stats = {}
date = nil

open("|git log --numstat", "r").each_line do |line|
  case line
  when /^Date:[[:space:]]+... ([A-Za-z]{3}) [1-3]?[0-9] [0-2][0-9]:[0-5][0-9]:[0-5][0-9] ([0-9]{4})/
    date = $1 + " " + $2
    stats[date] = {} unless stats.has_key?(date)
  when /^Date/
    raise line
  when /^([0-9]+)[[:space:]]+([0-9]+)[[:space:]]+.*?\.([a-z]+)$/
    ext = $3
    added = $1.to_i
    stats[date][ext] = (stats[date][ext] || 0) + added
  end
end

keys = stats.inject(Set.new) { |accum, (k,v)|  accum | v.keys }.to_a.sort

csv = CSV.generate do |csv|
  csv << ["Month"] + keys
  stats.each do |date, data|
      csv << [date] + keys.map{|k| data[k] || 0}
  end
end

puts csv