#!/usr/bin/perl
use strict;
# simple application of two Perl modules: 
use Net::DNS;
use Regexp::Common;
# replace dotted-decimal ip addresses with their DNS names.

my $res = Net::DNS::Resolver->new;

sub h0stname {
	my $arg = shift;
	my $result = $arg;
	my $query = $res->search("$arg");
	if($query){
		for my $rr($query->answer){
			$rr->type eq 'PTR' and $result=$rr->ptrdname
		}
	} 
	return $result;
}

while(<>) {
	#s/$RE{net}{IPv4}{-sep}{-keep}/h0stname($1)/e;
	#print;

	my $changed = $_;
	$changed =~ s/\b$RE{net}{IPv4}{-keep}\b/"[".h0stname($1)."]"/eg;
	print $changed;
}