letters = %w(A T G C)

File.open(ARGV[0], 'w+') do |f|
  (lines = ARGV[1].to_i).times do
    (width = (ARGV[2] || 70).to_i).times do
      f.write letters[rand(4)]
    end
    f.write "\n" unless f.pos == (lines * (width + 1) - 1)
  end
  puts "wrote #{lines} lines to #{ARGV[0]}"
end