Updates to Chapter 5, “Input/Output”

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

With the added emphasis on Unicode, we had to update the chapter on input and output a bit. If we are going to talk about Unicode, we need to talk about encodings, which expands the material on three argument open and brings in binmode too.

For this update, we also introduced filehandle references, although we did not call them references, really. We still present most of the chapter using bareword filehandles, and once we have covered everything we show how you can do the same things with filehandles in variables. However, we still save the meat of filehandle referencs to Intermediate Perl.

Some people think everyone should be using lexical filehandles all of the time, but even if you want to do that for new code, you still have to understand what people did in old code so we have to cover the legacy syntax (and some people would even object to calling it “legacy”).

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.