Quick fix: Generate random MAC-address in bash

If you need too generate a random MAC address for whatever reason - say assigning them to virtual machines or when setting up bridge interfaces - you cay simply do this with bash only.

function genranmac() {
    out=""
    for i in 0 1 2 3 4
    do
        out=${out}$(printf %01X $((RANDOM % 256))):
    done
    out=${out}$(printf %01X $((RANDOM % 256)))
    echo -n $out
} 

Example:

alex@picobeast:~$ sudo ip link show dev virbr0
4: virbr0: <BROADCAST,MULTICAST> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:45:04:74 brd ff:ff:ff:ff:ff:ff
alex@picobeast:~$ sudo ip link set addr $(genranmac) dev virbr0
alex@picobeast:~$ sudo ip link show dev virbr0
4: virbr0: <BROADCAST,MULTICAST> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
    link/ether 4c:a5:fb:4c:dd:ed brd ff:ff:ff:ff:ff:ff

Bonus information: If you want to do it proper, use MAC-addresses from the experimental/private ranges, such that the 2nd byte of the MAC-address is in 2,6,a,e, e.g.:

x2:xx:xx:xx:xx:xx
x6:xx:xx:xx:xx:xx
xa:xx:xx:xx:xx:xx
xe:xx:xx:xx:xx:xx