Depends on money.js, nodejs, coffeescript and request

currency_converter.coffee

request = require('request')
money = require('money')
fs = require('fs')

arguments = process.argv.splice(2)
amount = arguments.shift()

try
  loop
    base = arguments.shift()
    break if base.length == 3

  loop
    target = arguments.shift()
    break if target.length == 3
catch error
  console.log 'Wrong arguments'
  process.exit()

request 'http://openexchangerates.org/latest.json', (error, response, body) ->
  data = JSON.parse(body)
  money.rates = data.rates
  money.base = data.base

  base = base.toUpperCase()
  target = target.toUpperCase()

  console.log "#{amount} #{base} in #{target} is: #{money(amount).from(base).to(target)} #{target}"