18.7.1. Problem

18.7.2. Solution

use Net::Ping;

$p = Net::Ping->new( )
    or die "Can't create new ping object: $!\n";
print "$host is alive" if $p->ping($host);
$p->close;

18.7.3. Discussion

Testing whether a machine is up isn't as easy as it sounds. It's not only possible but also unpleasantly common for machines to respond to the ping command when they have no working services. It's better to think of ping as testing whether a machine is reachable, rather than whether the machine is doing its job. To check the latter, you must try its services (Telnet, FTP, web, NFS, etc.).

In the form shown in the Solution, Net::Ping attempts to connect to the TCP echo port (port number 7) on the remote machine. The ping method returns true if the connection could be made, false otherwise.

You can also ping using other protocols by passing the protocol name to new. Valid protocols are tcp, udp, syn, and icmp (all lowercase). A UDP ping attempts to connect to the echo port (port 7) on the remote machine, sends a datagram, and attempts to read the response. The machine is considered unreachable if it can't connect, if the reply datagram isn't received, or if the reply differs from the original datagram. An ICMP ping uses the ICMP protocol, just like the ping(8) command. On Unix machines, you must be the superuser to use the ICMP protocol:

# use TCP if we're not root, ICMP if we are
$pong = Net::Ping->new( $> ? "tcp" : "icmp" );

(defined $pong)
    or die "Couldn't create Net::Ping object: $!\n";

if ($pong->ping("kingkong.com")) {
    print "The giant ape lives!\n";
} else {
    print "All hail mighty Gamera, friend of children!\n";
}

A SYN ping is asynchronous: you first send out many ping s and then receive responses by repeatedly invoking the ack method. This method returns a list containing the hostname, round-trip time, and the IP address that responded:

$net = Net::Ping->new('syn');
foreach $host (@hosts) {
  $net->ping($host);
}
while (($host, $rtt, $ip) = $net->ack( )) {
  printf "Response from %s (%s) in %d\n", $host, $ip, $rtt;
}