my @cmd = ('tshark','-r',$PCAPFILE,
	qw# -R tcp.options.mss -T fields -e ip.src -e tcp.srcport
	-e ip.dst -e tcp.dstport -e tcp.options.mss_val #);
open my $ts, '-|', @cmd or die "Error opening pipe: $!";
while(<$ts>) {
	chomp;
	my ($src_addr,$src_port,$dst_addr,$dst_port,$mss) = split /\t/;
	print "$src_addr:$src_port -> $dst_addr:$dst_port  MSS=$mss\n";
}
close $ts or die $! ? "Error closing pipe: $!"
	: "Exit status \$?=$? from pipe";