#!/usr/bin/perl
use strict;

my $dev = shift || 'eth0';

my $traf1 = get_curr_traf();
select(undef, undef, undef, 2);
my $traf2 = get_curr_traf();

my ($conn) = grep {/connections established/} `netstat -ts`;
$conn = (split/\s+/,$conn)[1];


my $trafavg = ($traf2 - $traf1) / (2*1024);
printf "%s%10.2f%14s\n","Average traffic on $dev is:", $trafavg, "kbytes/second";

my $traf_per_conn = $trafavg / $conn;
printf "%s%7.2f%14s\n","Average traffic per connection on $dev is:", $traf_per_conn, "kbytes/second";

sub get_curr_traf
{
open DEV,'/proc/net/dev' or die $!;
my ($in,$out);
while(<DEV>) {
next unless /$dev:\d+/;
($in,$out) = (split)[0,8];
$in = (split/:/,$in)[1];

}
close DEV;
return $in+$out;
}