#!/usr/bin/perl -w

use strict;
use English;
use Net::Pcap;
use Time::HiRes qw (alarm time );

my($dev, $pcap_t, $err);

$dev = Net::Pcap::lookupdev(\$err);
$pcap_t = Net::Pcap::open_live($dev, 1500, 1, 0, \$err);

my $count = 0;
sub process_pkt {
    my ( $user_data, $hdr, $pkt ) = @_;
    $count++;
    $SIG{ALRM} = sub { printf ("%16.5f %d\n", time, $count); $count = 0 };
#    setitimer(ITIMER_REAL, 0.5, 0.5);
    alarm(0.5);
}

Net::Pcap::loop( $pcap_t, 0, \&process_pkt, "argument");
Net::Pcap::close($pcap_t);