hostmac

#!/usr/bin/awk -f
# HostMAC.awk - append hardware MAC address to hostname
#
# Copyright Feb 2018 peter at gamache dot us
# Licence: 
# Unlimited distribution/use is allowed, including distribution of derivative works.
# All reproductions must include this license text and the copyright statement above.
# NO WARRANTY expressed or implied, including but not limited to fitness for purpose.

BEGIN { 
  # Use the rightmost X characters of the MAC address (hexedecimal form)
  UseChars=6; # 6 or 12 are common choices
  getline defhost < "/etc/hostname"; # grab default
  newhost=defhost;
  "ip -o link show eth0" | getline;
  if ($0 ~ / link.ether /) { setHost("eth0", tolower($(NF-2))); }
  exit(1); # Exit with error if we do not see expected ip link output.
}

function setHost(interface, macaddr) {
  macpart=gensub(/^([0-9a-f]{2}):([0-9a-f]{2}):([0-9a-f]{2}):([0-9a-f]{2}):([0-9a-f]{2}):([0-9a-f]{2})$/,"\\1\\2\\3\\4\\5\\6",1,macaddr);
  macpart=substr(macpart, (length(macpart) - UseChars));
  newhost=defhost "-" macpart;
  printf("HostMAC: Using %s MAC address for hostname: %s\n", interface, newhost);
  myrc=system("hostname " newhost); # pass on the return code to the caller
  exit(myrc);
}