Assuming you will always get the line you want:

my $pid = open(my $pipe, 'mDNS -L "Service Name" _service._tcp domain 
+|');

my $data;
while (<$pipe>) {
   if (/...is desired line.../) {
      $data = $_;
      last;
   }
}

kill KILL => $pid;

print($data);
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