iam-policy-diff.rb

#!/usr/bin/env ruby

require 'json'

def read_json(file_name)
  JSON.parse(File.read(file_name))
end

def parse(iam)
  result = []
  iam["Statement"].each do |statement|
    action = statement["Action"]
    if !action.respond_to?(:each)
      action = [action]
    end
    res = statement["Resource"]
    if !res.respond_to?(:each)
      res = [res]
    end
    res.each do |r|
      action.each do |a|
        result << "#{statement['Effect']} #{a} to #{r}"
      end
    end
  end
  result
end

from = read_json(ARGV[0])
to = read_json(ARGV[1])
from_set = parse(from)
to_set = parse(to)

minus = from_set - to_set
plus = to_set - from_set

if minus.empty? and plus.empty?
  exit 0
else
  puts "--- #{ARGV[0]}"
  puts "+++ #{ARGV[1]}"
  puts
end

minus.each do |diff|
  puts "- #{diff}"
end
plus.each  do |diff|
  puts "+ #{diff}"
end