Net::Pcap::dump_open($pcap_t, $filename);
               Open a savefile for writing and return a descriptor for doing so.  If $filename is "-" data is written to standard output.

##</code><code>##

  ...
  my $result = Net::Pcap::loop($pcap_desc, $args{NUMPACKETS}, \&sniffit, args{USERDATA});
  ...
  sub sniffit {
    my ($args,$header,$packet) = @_;
    my $pcap_dumper_t = Net::Pcap::dump_open($pcap_desc, "/tmp/andy.pcap");
    Net::Pcap::dump($pcap_dumper_t, $header, $packet);
    Net::Pcap::dump_close($pcap_dumper_t);
    open(FH,"tethereal -V -r /tmp/andy.pcap |");
    print <FH>;
    close(FH); 
    unlink("/tmp/andy.pcap");
  }

##</code><code>##

  $pid = open2(*Reader, *Writer, "tethereal -V -i -" ); # open tethereal reading on STDIN
  my $pcap_dumper_t = Net::Pcap::dump_open($pcap_desc, *Writer); # write to Writer FH
  Net::Pcap::dump($pcap_dumper_t, $header, $packet);
  Net::Pcap::dump_close($pcap_dumper_t);
  $got = <Reader>;
  print $got;