Set a random mac address on Snow Leopard (only until next reboot)

mac_rand_mac_addr.rb

#!/usr/bin/env ruby

#
# Script to change to a random mac address
#   Usage: ruby random_mac_address
#
# Modeled after instructions at:
#   http://www.iclarified.com/entry/index.php?enid=7673
#
# Author:: Marc Siegel <wowstrongdrink@yahoo.com>
# Date::   2011-02-11
#

def cur_mac_addr
  `ifconfig en1 | grep ether`.gsub('ether', '').strip
end

def set_mac_addr(new_addr)
  `sudo ifconfig -v en1 lladdr #{new_addr}`
  `sudo ifconfig -v en1 ether #{new_addr}` 
end

def generate_mac_addr
  random_48bit_int = rand(2**48)
  padded_hex = "%012x" % random_48bit_int
  digit_pairs = padded_hex.split('').inject([]) do |arr, d|
    if arr.last && arr.last.size == 1
      arr.last << d
    else
      arr << d
    end
    arr
  end
  new_addr = digit_pairs.join(':')  
end

def disconnect_from_wireless_networks
  `sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -z`
end


##
# Main logic here
##
puts "\n(Disconnecting from any wireless network...)"
disconnect_from_wireless_networks

old_addr = cur_mac_addr
puts "\nOld mac address:\t #{old_addr}"

new_addr = generate_mac_addr
puts "Generated new address:\t #{new_addr}\n\n"

(1..10).each do |attempt|
  puts "Attempting to set new address (try ##{attempt})..."
  set_mac_addr(new_addr)
  break if cur_mac_addr == new_addr
  sleep 1
end

puts ""

if cur_mac_addr == new_addr
  puts "New mac address: #{new_addr}\n\n"
else
  puts "Unable to set new mac address. "
  puts "Try turning airport off and then back on, and running again."
end

puts ""

Ok, updated to try up to 10 times, to use lladdr as well as ether, and to advice power-cycling airport after failure, which does seem to work.