I understand. But apparently, b hasn't read your book, and you shouldn't assume everyone who wants to/knows perl has. Since it's such a short, useful program, I'd think you wouldn't mind explainning it to those who don't understand it. After all, it's not like he was asking about a Shwartzian Transfom (though I doubt you'd mind explainning that).
Humans have a wonderful love for "Do What I mean, Not What I say".
This applies both to programming languages (Perl) and
general conversations. I'm pretty sure he didn't want a
role call of who knew the answer to the question, even though
that's how it's phrased. Since we rely on a programming
language that goes out of its way to be nice to us, perhaps
we should go out of our way to be nice to other people. :)