#! /usr/bin/perl

my $tcpdump = '/usr/sbin/tcpdump -n'; # path and options
my $timeout = 5; # time to listen
my $fileout = 'out.tcpdump';
open(OUT, "> $fileout") || die $!;
open(CMD, "$tcpdump |") || die $!;

eval 
{
    local $SIG{ALRM}= sub { die('done') };
    alarm( $timeout );

    while (<CMD>)
    {
    my $line = $_;
    print OUT $line;
    }

    alarm(0);
};

print $@ if $@;
close OUT || die $!;
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