Convertidor simple

convert.rb

#!/usr/bin/env ruby

require 'open-uri'
require 'json'

FROM = 'USD'
TO   = 'PEN'
URL  = "http://rate-exchange.appspot.com/currency?from=#{ FROM }&to=#{ TO }"

open URL do |rates_file|
  hash = JSON.parse rates_file.string
  puts hash['rate'].to_f * ARGV.first.to_f
end