Possible to Get the MAC Address?

Is there any way to read the MAC address of the Wifi or Ethernet interface into an Arduino sketch?

If not, is there any other type of globally unique identifier that I can read from a sketch?

Find all MAC address

/sbin/ifconfig -a | /bin/grep HWaddr
eth0      Link encap:Ethernet  HWaddr 90:A2:DA:F0:YY:XX
eth1      Link encap:Ethernet  HWaddr 90:A2:DA:F8:YY:XX
wlan0     Link encap:Ethernet  HWaddr 90:A2:DA:F0:YY:XX

Find WIFI MAC address

/sbin/ifconfig -a | /bin/grep HWaddr |/bin/grep wlan0

Find Ethernet MAC address

/sbin/ifconfig -a | /bin/grep HWaddr |/bin/grep eth1

Use Bridge you could read it from ATmega32u4 .

find Wifi Mac Address only:

/sbin/ifconfig -a | /bin/grep HWaddr |/bin/grep wlan0 | /usr/bin/awk '{print $5}'
90:A2:DA:F0:XX:YY

Thanks sonnyyu!