root@sugzum:~/host# cat b2.pl
 #!/usr/bin/perl
 use feature qw(say);
 use Mozilla::PublicSuffix qw(public_suffix);
 open F, &quot;<host.txt&quot; or die $!;
 while (<F>) {
 $hostname = &quot;$_&quot;;
 }
 close F;
 my $tld = public_suffix($hostname)
 or die &quot;Invalid TLD found in '$hostname'&quot;;
 $hostname =~ /([^.]+).\Q$tld\E$/
 or die &quot;Couldn't find domain name in '$hostname'&quot;;
 my $domainname= $1;
 print &quot;Domain name is $domainname.$tld\n&quot;;
 
root@sugzum:~/ssh2smtp# cat host.txt 
200-206-30-98.customer.tdatabrasil.net.br
root@sugzum:~/ssh2smtp# perl b2.pl
Invalid TLD found in '200-206-30-98.customer.tdatabrasil.net.br
' at b2.pl line 9.