If you have stripped away the TLD, the last non-dot characters are the domain name. Most likely, a regular expression is enough:

my $tld = public_suffix($hostname)
    or die "Invalid TLD found in '$hostname'";
$hostname =~ /([^.]+).\Q$tld\E$/
    or die "Couldn't find domain name in '$hostname'";
my $domainname= $1;
print "Domain name is $domainname.$tld\n";

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In reply to Re^3: Module to get domain name from hostname by Corion
in thread Module to get domain name from hostname by gatkins

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