Month: January 2011

Updates to Chapter 6, “Hashes”

[This post notes differences between the fifth and sixth editions.]

I didn’t have much to update in the hashes chapter, so when you get to Perl 5.14, you’ll find that Perl’s hash features are the same things you had in previous versions of Perl.

However, I did move the “fat arrow”, => stuff from Chapter 17, “Advanced Perl Features”, to the hash chapter. Why have it so far away? It’s just a couple of paragraphs, so it’s moved up to the first half of the book.

Updates to Chapter 13, “Directory Operations”

[This post notes differences between the fifth and sixth editions.]

Our updates to Chapter 13 aren’t that exciting. There’s not much that has changed in the world of Perl and directories. It’s almost dull, even.

  • Use variables as directory handles: opendir my $dir, $directory.
  • Mention a couple more modules incidental to some of the examples, including File::Spec::Functions, Path::Class, and File::Temp
  • Show a find2perl example. We mentioned File::Find only to say that we weren’t going to say anything about it. Also mention the improved interfaces of File::Finder and File::Find::Rule

Updates to Chapter 7, “In the World of Regular Expressions”

[This post notes differences between the fifth and sixth editions.]

I just committed the new Chapter 7, “In the World of Regular Expressions”. It was quite an education, even for me, because the character class stuff has changed so much since Perl 5.6, and, since Learning Perl had been ignoring Unicode, we didn’t face the hard problems.

  • The \w character class is almost dangerous now. By default, it represents over 100,000 characters that can match at that position. The \d and \s character classes have the same problem on a smaller scale. It’s unlikely that anyone actually wants these shortcuts anymore, but there are still in older programs. I did cover this over at The Effective Perler, too.
  • Since we’re covering Unicode, this is the right chapter to cover the Unicode properties, such as \p{Space}. Those don’t completely solve the character class shortcut problem because they still match many characters. The perluniprops documentation lists how many characters match each property, which is kinda cool.
  • Perl 5.13.9 includes Karl Williamson’s work to add the /a adverb to enforce ASCII semantics, so we use that
    too even though we don’t really get into options into the next chapter.

This is all rather painful to update because I didn’t want to go through everything assuming ASCII semantics (so, very few changes) then tack on an “if you are using Unicode” section that then invalidates everything. We just have to bite the bullet and make the switch to thinking of Unicode as the default and ASCII as the backward-compatibility special case.

Learning Perl in Works in Progress

Want a sneak peek at Learning Perl, Sixth Edition? Over at The Perl Review, subscribers have access to early versions of the books that I’m working on. I call it “Works in Progress”. It’s available to the sort of people that can help make the books as good as they can be without being easily available to all the people who will just add the content to their own websites.

Since I’m working on Learning Perl this week, I’ve uploaded the output of O’Reilly’s automated DocBook build system. To be sure, it’s a work in progress. You’ll see a lot of mistakes, unfinished bits, and so on, but feel free to point out anything weirdness that you find. I’m especially interested in stuff that’s missing that you think I should cover.

Here’s a sample, which you’ll recognize as O’Reilly Nutshell format:

To follow what’s changing, watch the updates category.