my $pid = open TRAFFIC, "-|",  "/usr/sbin/tcpdump", "-i", "eth0" or die $!;

##</code><code>##

my ($rin,$rout);
vec( $rin, fileno( TRAFFIC), 1) = 1;
while( ($num,$sleep) = select($rout=$rin,undef,undef,$sleep)) {
    last if $sleep <= 0;
 # read TRAFFIC and process
}