What was being suggested was creating a script that would execute the tcpdump command for you, parse its output, and display whatever you want, based upon the results - no intermediate files, or anything. Without knowing what you are looking for, I can't specify an actual test for the desired output.

use strict;
use warnings;

open(my $tcp, "/usr/sbin/tcpdump |");
my $ok = undef;
while(<$tcp>) {
   $ok = 1 if m/\w/;   # your test here
}
print "All things groovy\n" if $ok;
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