It's not spam. It's a relevant mention of how to obtain the book that is the subject of this thread at a 50% discount from the publisher (or any other Perl book from that manufacturer). Mention that these sorts of discounts come up again from time to time, and you have a post that is still of value after the sale expires in a few days. Seriously, people need to lighten up if they consider you helping people reading this thread to obtain the book at half the price to be spamy behavior.

O'Reilly also offers discounts to members of Perl Monger groups by virtue of PM's affiliation with OSCON, if I'm not mistaken.

The Monastery is about enhancing peoples' education with respect to Perl. Let's not prohibit the mention of a book sale in a thread that talks about a book aimed at achieving a compatible goal.

If you were a blog owner, and you got a random comment that said "What amazing timing! The ebook just went on sale today for 50% off (and the sale lasts for the week)." you would hit the spam button too. The link is perl related, but if you do not check the link it looks 100% like comment bot spam. Some monks would do -- vote in a blink of an eye on the post without bothering to hover over it or checking the poster's profile to see they are not a spam account registration. No offensive to user frozenwithjoy. The original post would greatly have needed the word "perl" in its text but the poster already fixed it so it doesn't look like comment spam.