#!/usr/bin/env perl
#
# ipnum2name - translate IP addresses in the input to DNS names
#
# $Id: ipnum2name 687 2010-01-19 15:48:56Z rp $

use warnings;
use strict;

use Socket;

my %ipnum2name;

$| = 1;    # force output line flushing

while (<>)
{
  my @line = split(/\b(\d+\.\d+\.\d+\.\d+)\b/, $_);
  @line = map
  {
    my $fld = $line[$_];

    if ($_ % 2 == 0)
    {
      $fld;
    }
    else
    {
      local $_;

      if ((my @fld = grep { $_ >= 0 && $_ < 256 } split(/\./, $fld)) < 4)
      {
        $fld;
      }
      else
      {
        if (!defined $ipnum2name{$fld})
        {
          my $name = gethostbyaddr(inet_aton($fld), AF_INET);
          if (!defined $name)
          {
            $name = $fld;
          }
          $ipnum2name{$fld} = $name;
        }
        $ipnum2name{$fld};
      }
    }
  }
    0 .. $#line;
      
  print join( '', @line );
}