本文共 1009 字，大约阅读时间需要 3 分钟。

1. #!/usr/bin/perl -w
2. strict;
3. Socket;
4. Sys::Hostname;
6. ( $count, $hisiaddr, $hispaddr, $histime,
7. $host, $iaddr, $paddr, $port, $proto,
8. $rin, $rout, $rtime, $SECS_OF_70_YEARS);
10. $SECS_OF_70_YEARS = 2_208_988_800;
12. $iaddr = (hostname());
13. $proto = ("udp");
14. $port = ("time", "udp");
15. $paddr = sockaddr_in(0, $iaddr); # 0 means let kernel pick
17. (SOCKET, PF_INET, SOCK_DGRAM, $proto) || "socket: $!";
18. (SOCKET, $paddr) || "bind: $!";
20. $| = 1;
21. "%-12s %8s %s\n", "localhost", 0, ();
22. $count = 0;
23. for $host (@ARGV) {
24. $count++;
25. $hisiaddr = inet_aton($host) || "unknown host";
26. $hispaddr = sockaddr_in($port, $hisiaddr);
27. ((SOCKET, 0, 0, $hispaddr)) || "send $host: $!";
28. }
30. $rin = "";
31. ($rin, (SOCKET), 1) = 1;
33. # timeout after 10.0 seconds
34. while ($count && ($rout = $rin, , , 10.0)) {
35. $rtime = "";
36. $hispaddr = (SOCKET, $rtime, 4, 0) || "recv: $!";
37. ($port, $hisiaddr) = sockaddr_in($hispaddr);
38. $host = ($hisiaddr, AF_INET);
39. $histime = ("N", $rtime) - $SECS_OF_70_YEARS;
40. "%-12s ", $host;
41. "%8d %s\n", $histime - (), ($histime);
42. $count--;
43. }

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