Whoops :( My implementation of the example found in "perldoc -f seek" was incomplete. This one seems to work:

    for (;;) {
        for ($curpos = tell(FILE); $_ = <FILE>;
             $curpos = tell(FILE)) {
            # search for some stuff and put it into files
        }
        sleep($for_a_while);
        seek(FILE, $curpos, 0);
    }
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I'm really not that much of an idiot. really.