#!/usr/bin/perl
# clockdrift - compare another system's clock with this one
use strict;
use Socket;

my ($host, $him, $src, $port, $ipaddr, $ptime, $delta);
my $SECS_of_70_YEARS      = 2_208_988_800;

socket(MsgBox, PF_INET, SOCK_DGRAM, getprotobyname("udp"))
    or die "socket: $!";
$him = sockaddr_in(scalar(getservbyname("time", "udp")), 
    inet_aton(shift || '127.1'));
defined(send(MsgBox, 0, 0, $him))
    or die "send: $!";
defined($src = recv(MsgBox, $ptime, 4, 0))
    or die "recv: $!";
($port, $ipaddr) = sockaddr_in($src);
$host = gethostbyaddr($ipaddr, AF_INET);
my $delta = (unpack("N", $ptime) - $SECS_of_70_YEARS) - time();
print "Clock on $host is $delta seconds ahead of this one.\n";