greatest common divisor x and y

divisor.coffee

[x, y] = process.argv.slice 2, 4

unless x and y
  console.log 'Usage [cmd] [x] [y]'
  console.log 'return greatest common divisor x and y'
  process.exit 1

while 0 isnt r = x%y
  x = y; y = r

console.log y