I am writing a script to grab the output from snoop or tcpdump and decode a Cisco Discovery Protocol packet. I want to have snoop/tcpdump killed after so many seconds if I don't get a packet.

I have tried using alarm in an eval block per the example in the alarm doc and it works great. Only problem is that after the script ends I sometimes have zombie processes of tcpdump hanging around if I die in the eval block. Is there a way around this or is the best way to use fork? From the perlipc manpage is seems that the backticks should take care of any zombies without having to call wait(), but I guess not. TIA for the help! 
 eval {
        local $SIG{ALRM} = sub { die "tcpdump Died\n" };
        alarm 20;
        @captured_data = `$tcpdump -i $nic -c1 -xx -s0 'ether[20:2] ==
+ 0x2000' 2>/dev/null`;
        alarm 0;
    };

    # Check the status of eval to see if we alarmed out
    if ($@) {
        return;
    } else {
        return @captured_data;
    };
};

After the script runs:
grapeape:~# ps -ef |grep tcpdump |grep -v grep
root      3499     1  1 16:26 pts/1    00:00:00 sh -c /usr/sbin/tcpdum
+p -i eth0 -c1 -xx -s0 'ether[20:2] == 0x2000' 2>/dev/null
root      3500  3499  2 16:26 pts/1    00:00:00 /usr/sbin/tcpdump -i e
+th0 -c1 -xx -s0 ether[20:2] == 0x2000

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In reply to Eval leaving zombies when dying with alarm by yogsothoth

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