Isolates the second- and top-level domain from the rest

domain_from_hostname.sh

#!/usr/bin/env awk -f
# returns "google.com" when called on "www.google.com"
# returns "google.com" when called on "foo.bar.zot.www.google.com"
BEGIN {
    string=ARGV[1];
    search=".";
    n=split(string,array,search);
	printf("%s%s%s\n",array[n-1],search,array[n]);
    exit;
}