This works, assuming you redirect your tcpdump output to a file. Run with your output file as STDIN to this snippet. You could probably use IO::File here as well: 
use strict; 

open (DUMP, "|cat -v");
select(DUMP);
$| = 1;

while (<>) {
        if (/^\s/) {
                chop;
                s/\s//g;
                while ($_) {
                        my $hex;
                        ($hex, $_) = /^(..)(.*)$/;
                        my $byte = hex($hex);
                        print pack("c", $byte);
                }
        } else {
                print "\n", "-"x74, "\n\n";
        }
}
close(DUMP);

[download]

Here's another, which runs tcpdump directly: 

use strict;

my ($pkt, $client, $host);
my $lim         = shift || 999999999;
my $tcpd        = "/usr/sbin/tcpdump";
my $tcpargs     = "-lnx -s 1024 dst host 68.14.142.134|";

$|=1;
open (STDIN, "$tcpd $tcpargs");
while (<>) {
        if (/^\S/) {
                last unless $lim--;
                while ($pkt=~/(.+).+/g)  {
                        print "$client -> $host\t$&\n";
                }

                ($client, $host, $pkt) = ();

                # All on one line please
                ($client, $host) = /(\d+\.\d+\.\d+\.\d+).+ 
                        > (\d+\.\d+\.\d+\.\d+)/ 
                        if /P \d+:\d+\((\d+)\)/ && $1 > 0;
        }
        next unless $client && $host;
        s/\s+//;
        s/([0-9a-f]{2})\s?/chr(hex($1))/eg;
        tr/\x1F-\x7E\r\n//cd;
        $pkt .= $_;
}

[download]

Here's one using Net::Pcap and Net::RawIP. I leave the decoding of the packet stream up to you.. 

use strict;
use Net::Pcap;
use Net::RawIP;

my $errstr;
my $count       = 0;
my $dev         = Net::Pcap::lookupdev(\$errstr);
my $pcap        = Net::Pcap::open_live($dev, 1024, 1, 0, \$errstr);

Net::Pcap::loop($pcap, -1, \&check_tcp, "abc");
Net::Pcap::close($pcap);

sub check_tcp {
        my ($user, $hdr, $pkt) = @_;

        # Add your error checking here
        print "Saw snap of len 
               hdr->{len} $hdr->{caplen} \n";
        $count++;
}

[download]

In reply to Re: converting tcpdump files by hacker
in thread converting tcpdump files by botho

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