knoppix@Microknoppix:~$ perl -E '
> $mac = q{525400eb8b36};
> substr $mac, $_, 0, q{:}
>    for reverse grep { ! ( $_ % 2 ) } 2 .. 10;
> say $mac;'
52:54:00:eb:8b:36
knoppix@Microknoppix:~$