When I posted my Perl plans for 2011, Robert asked me why Mastering Perl might not have another print edition. It’s mostly due to the sales for advanced books. I don’t think this is really about Perl or the topic involved. Take any topic and specialize it more and more. You cut down on your audience each time because fewer and fewer people want to follow you along. Most people get by just fine with the basics in Learning Perl.
All the numbers are normalized to the Learning Perl sales in the last quarter of 2009, and the Y axis is logarithmic.
Most authors would like to have the sales of Intermediate Perl. We’re fortunate to have the sales of Learning Perl that let it go on to a fifth edition.