currency.rb

require 'money'
require 'json'
require 'open-uri'

if ARGV.length == 3
  from  = ARGV[0]
  to    = ARGV[1]
  money = ARGV[2].to_f
else
  from  = 'JPY'
  to    = 'EUR'
  money = ARGV[0].to_f
end

rate = JSON.parse(open("http://rate-exchange.appspot.com/currency?from=#{from}&to=#{to}&q=1").read)['rate'].to_f
Money.add_rate from, to, rate

puts "#{Money.new(money, from).exchange_to(to)} (rate: #{rate.round(4)})"