Simple Ruby Credit Card Validator

This code below is a ruby implementation of Luhn Algorithm to validate credit cards numbers.

#!/usr/bin/env ruby

def is_valid(number)
  x = number.split("")

  i = 0

  a = Array.new()

  while (i < x.size) do
    a.push(x[i].to_i*2)
    i = i + 1
    a.push(x[i].to_i)
    i = i + 1
  end
  if (a.join("").split("").inject(0){|sum,item| sum + item.to_i} % 10 == 0)
    return true
  else
    return false
  end
end

puts is_valid(ARGV[0])

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