Month: March 2011

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

I didn’t have to make many changes to this chapter. I wanted to put in at least one Perl 5.14 feature, but the only new thing that the substitution operator gets is the /r modifier.

While working through this chapter though, I started to wonder if our terms in the previous editions were the same in the Perl documentation. We called the modifiers “option modifiers”, and sometimes “flags”, perlre just says “modifier”. Personally, I’m used to saying “flag” all the time and I like that term just fine, but for regular people, there’s nothing to connect the everyday use of “flag” to the thing after the match operators. So, “modifier” it is. I’d much rather use “adverb”, which is popular in Perl 6 land, but it’s a bit late for Perl 5 to change terms. When I made the switch in this chapter, I had to go back to Chapters 7 and 8 and do the same thing.

This chapter is also curious in that it ends with a long example the builds up to a perl one-liner. One of the things the reviewers noted about a new edition was a new chapter devoted to one-liners. That’s still possible, I guess.

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

There are a couple of interesting updates for Chapter 8. The small change is the slight modification of a footnote. We mentioned that the performance problem of the match variables $& and friends wouldn’t be solved before Perl 6. However, with Perl 5.10’s introduction of the /p match operator flag, problem solved!

Chapter 8 also has a subtle shift in thinking about anchors. Perl 5 introduced the \A, \Z, and \z regular expression anchors. Somehow, never made the shift from the Perl 4 anchors ^ and $. Even after Perl Best Practices pointed out the problem, we failed to update the Llama

I’d never really bothered to check when Perl introduced \A until today. That’s a task I do quite frequently: when did some feature show up in Perl? I could just go through all the tarballs, unpack them, and look at the documentation, but there’s an easier way. Since I have a clone of the perl repository, I have access to the entire perl development history. Each release has a tag, and I can list all the tags:

$ git tag
perl-1.0
perl-1.0.15
perl-1.0.16
perl-2.0
perl-2.001
perl-3.000
perl-3.044
perl-4.0.00
perl-4.0.36
perl-5.000
perl-5.000o
perl-5.001
perl-5.001n
perl-5.002
perl-5.002_01
perl-5.003
...

If I want to see what was going on in a particular release, I checkout the appropriate tag:

git checkout perl-5.000

Now I can see the state of the repo at the point of that release. Sure enough, C<\A>, C<\Z>, and C<\z> are in the documentation back then.