#!/usr/bin/perl -w 
$|=1;
use strict;
use Net::Ping;
use Net::Netmask;
use Net::DNS;
use Getopt::Long;

my @blocks=();
my $outfile="";

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

my $res = GetOptions("net=s",\@blocks,
                     "out=s",\$outfile
                     );

$outfile="candidates.txt" unless $outfile;

@blocks=split(",",join(",",@blocks));

foreach my $i(0..$#blocks){
  unless ($blocks[$i] =~ m@^\d+\.\d+\.\d+\.\d+/\d+$@){
    $blocks[$i] = $blocks[$i] . "/24";
  }
}

open FOUT,sprintf("> %s",$outfile) or die "$outfile: $!";

my $p = Net::Ping->new();

foreach my $block(@blocks){
  my $net = Net::Netmask->new($block);
  foreach my $ip($net->enumerate()){
      next if $ip =~ m@\.0$@;
      next if $dns->search($ip);
    printf "%s\r",$ip;
    unless ($p->ping($ip,1)){
      printf FOUT "%s\n",$ip;
    }
  }
}