clean-zone.sh

#!/bin/sh

# Source:
# https://gist.github.com/pawal/df9444e30eb4d10af0bd1042c0966a4f
# Author: Patrik Wallström

awk '{
  if (match($0,"^$"))     # remove empty lines
    skip = $1
  else if (match($0,"^;"))     # remove comment lines
    skip = $1
  else if ($1 == "se.")        # remove our own zone
    skip = $1
  else if ($1 == "nu.")        # remove our own zone
    skip = $1
  else if ($4 == "NS")         # match on NS
    print $1
}'|sort -u|sed 's/.$//'