use Net::SNMP;
my $host = 'blah';
my $community = 'blah';
#my $in = '1.3.6.1.2.1.2.2.1.10.1';
my $in = '1.3.6.1.2.1.31.1.1.1.6.1';
my $speed = 155000000;
my $speed_oct = $speed /8;
my $session = Net::SNMP->session(
    -hostname=>$host,
    -version => 'v2c',
    -community => $community
);
my $old_time = undef;
my $old_val = undef;
while (1) {
    my $time = time;
    my $result = $session->get_request(
    -varbindlist => [$in]
    );
    print "ifhcinoctets=".$result->{$in}."\n";
    if (defined $old_time) {
    my $tick = $time - $old_time;
    my $dif = $result->{$in} - $old_val;
    my $dif_ps = $dif / $tick;
    my $percent = ($dif_ps * 100) / $speed_oct;
    print "tick=$tick; speed=$speed_oct; dif=$dif; dif_ps=$dif_ps; percent=$percent\n"
    }
    $old_time = $time;
    $old_val = $result->{$in};
    sleep(30);
}