open(TCPIN, "/usr/sbin/tcpdump -n -p tcp |");
while (1) {
 # Method 1
 die "Aiii! $!" if !sysread(TCPIN, $_, 1024);
 # Method 2
 $_ = <TCPIN>;
 # Of course, both of these methods aren't used at the same time!
 # Parsing stuff here (this is really fast, so the problem isn't here)
}