catatester/puppet/cast_builder/lib/facter/devices.rb

def ls(dir)
  if File.directory?(dir)
    Dir.entries(dir).reject { |entry| entry == '.' || entry == '..' }
  else
    Array.new
  end
end

Facter.add('usb_devices') do
  confine :kernel => 'Linux'

  # udev rules configure the system to generate symlinks in this directory
  # when devices are connected to the machine (see: 60-persistent-serial.rules)
  setcode do
    ls('/dev/serial/by-path/')
  end
end