Perl脚本怎么检测域名是否有效？

#!/usr/bin/perl
use strict;
use Net::Ping;
use Net::DNS;
use Time::HiRes qw();
$| = 1;

my $DEFAULT_TIMEOUT = 2;
my $PING_TIMEOUT = 2;
my $DNS_TIMEOUT = 3;

### 查询域名是否有效
sub queryDomain {

  my $domain = shift();
  my $query = '';
  my $dns  = Net::DNS::Resolver->new(
    tcp_timeout => $DNS_TIMEOUT, udp_timeout => $DNS_TIMEOUT, retry => 1
  );
  my @nameservers = qw/8.8.8.8 114.114.114.114/;
  $dns->nameservers(@nameservers);
  eval {
 $query = $dns->search($domain,'A');
  };
  if ($@ or ! $query) {
    my $err = $dns->errorstring ;
    print "ERR: query $domain failed: $errn";
    return if ($err =~ /NXDOMAIN/);
  }
  return 'OK';
}

### return nothing is FAILED, other is OK
sub pingHost {
  my $arg = shift();

  return 1 if (ref $arg ne 'HASH');

  my $p;
  eval { $p = Net::Ping->new($arg->{'proto'},$DEFAULT_TIMEOUT,0) };

  if ($@) {
 warn "ERR to create Net::Ping object: $@n";
    return;
  }
 
  $p->hires();
  my ($host,$duration,$hip,$rep,$ret);

  ### tcp/syn ping
  if ($arg->{'proto'} eq "syn") {
 $p->{port_num} = $arg->{'port'};
 $p->ping($arg->{'host'},$PING_TIMEOUT);
 if (($host,$duration,$hip) = $p->ack()) {
   printf("ACK Reply from $arg->{'host'}[%s] time=%.2f msn", $hip, $duration * 1000);
      $ret = 'OK';
    } else {
      warn "SYN Request for $arg->{'host'} timed out.n";
 }
  } 

  ### icmp ping
  else {
    ($rep,$duration,$hip) = $p->ping($arg->{'host'},$PING_TIMEOUT);
    if ($rep) {
      printf("Echo Reply from $arg->{'host'}[%s] time=%.2f msn", $hip, $duration * 1000);
      $ret = 'OK';
    }
 else {
      warn "PING Request for $arg->{'host'} timed out.n";
   }
  }
  $p->close;
  undef($p);
  return $ret;
}

my $ARG = { proto => 'syn', port => 80 };
my $host = $ARGV[0];
my $proto = $ARGV[1];

die "Usage: $0 [icmp]n" if (! $host);
$ARG->{'host'} = $host;
$ARG->{'proto'} = $proto if ($proto);

my $code;
if (&queryDomain($host) eq 'OK' and $code = &pingHost($ARG)) {
  print "$host is online !n";
}
else {
  print "$host is DOWN !n";
}

测试例子：
# ./check.host.pl 2013.jb200.com
ERR: query 2013.jb200.com failed: NXDOMAIN
2013.jb200.com is DOWN !

# ./check.host.pl www.jb200.com
ACK Reply from www.jb200.com[173.255.214.254] time=307.04 ms
www.jb200.com is online !

# ./check.host.pl jb200.com icmp
Echo Reply from jb200.com[173.255.214.254] time=205.61 ms
jb200.com is online !

# ./check.host.pl chinagfw.com icmp
PING Request for chinagfw.com timed out.
chinagfw.com is DOWN !