All posts by Dave Cross

About Dave Cross

Dave Cross runs Magnum Solutions Ltd., a London Perl consultancy. In 1998 he started London Perl Mongers, the first Perl Mongers group outside of Northern America.

Pebble and Perl

I’ve been wearing a Pebble watch for a couple of months now. I really like it but, to be honest, it’s the potential that has me most excited. The number of apps currently available is a bit disappointing and the API is taking its time appearing.

But even when the API is published, I wonder if I’ll have the time to learn all the necessary technologies in order to write Pebble-aware apps. All I want is to have some way to send a notification that pops up on the phone. Surely there must be an easy way to achieve that. Preferably one that I can use from Perl.

Of course, it turns out that there is. The secret is an app called Pushover. Pushover is a web service that sends notifications to your Android (or iOS if you’re that way inclined) device. There’s an app that you install on your device (it’s not free – I think it cost me £3.30) and you need to sign up for a free account. Then you can send notifications to your device either from their web site or using their API. The API is a simple HTTP request-based system. There’s an example on the Pushover web site that uses LWP::UserAgent, but you can make it even simpler using WebService::Pushover.

That’s all well and good. We can now send arbitrary notification from to our phone. How do we get from there to the watch?

The standard Pebble Android app is currently a little disappointing. In particular, it only supports pushing notifications from a tiny number of apps from the phone to the watch. But there’s another alternative. There’s an app called Pebble Notifier which will forward notifications from any app on the phone to the watch. When you install Pebble Notifier you can choose which apps you want to forward notifications for.

So, in summary, sign up for a Pushover account and install Pushover and Pebble Notifier on your phone. Then install WebService::Pushover on your computer. Then you can write code like this:

use WebService::Pushover;

my $push = WebService::Pushover->new
or die( "Can't create Pushover interface.\n" );

my $status = $push->message(
message => 'Hello Pebble',
# Signing up to Pushover gives you these tokens

And that will send a message to your Pebble.

Now all I need is something useful to do with it.

Update: I’ve just noticed that there’s also an IFTTT channel for Pushover. It has nothing to do with Perl, obviously, but would be an easy way to trigger Pebble notifications for certain triggers.

Removing Modules from Core

I was on holiday last week and missed most of the discussions about removing Module::Build and CGI from the Perl core in the next few years. I hope you won’t mind if I chime in a little late with my thoughts.


I’m a little bemused by the Module::Build story. Well, perhaps “bemused” isn’t quite the right word. Perhaps I should say “embarrassed”. Embarrassed because the discussions around Module::Build just show how out of touch I am with important parts of the Perl ecosystem.

I remember seeing Schwern’s MakeMaker Is DOOMED! talk ten years ago. What he said made a lot of sense to me and I switched all of my CPAN modules to Module::Build over the next few years. And then I rather took my eye off the ball. I was vaguely aware that people were complaining about Module::Build and were switching to things like Module::Install and Dist::Zilla. But I was happy with Module::Build and just stuck with it.

Now I’m hearing people saying that Module::Build is fundamentally flawed. Someone whose opinion I value mentioned that he lowers his estimate of the IQ of any CPAN author who uses Module::Build. That, presumably, includes me. But when I ask people what the problems are with Module::Build, I can’t get anyone to give me a detailed and dispassionate answer.

I’m quite prepared to believe that there are problems with Module::Build. Given the calibre of the people who are telling me that these problems exist, it would be astonishing if it wasn’t true. But it would be nice if there was a good explanation available somewhere of just what these problems are.

And I think that this is indicative of a deeper problem that the Perl community has. I like to think that I’m pretty much in touch with what is going on in the Perl community. I read the blogs. I’m subscribed to (too many) mailing lists. But it appears I’m not following discussions of the CPAN toolchain closely enough. I guess it’s something that I just expect to work. And I guess I expect that if there are important discussions going on, then I’ll hear about them through other channels – blog posts, for example. But that doesn’t seem to have happened here. Of course I can subscribe myself to another mailing list or two to correct that, but I don’t think I’m unusual in not trying to follow every single Perl discussion. There are surely many people like me who would like information like this to be disseminated better. This is part of the reason why Leo and I set up the Perl News site. But we have a tiny number of editors and we can’t know everything that is worth publishing. If you think we’ve missed an interesting story then please let us know about it.

So I’m not going to object to Module::Build leaving the core. I’m sure there are good reasons, I just wish I knew what they are. I am, however, slightly disappointed to find that Schwern was wrong ten years ago and that ExtUtils::MakeMaker wasn’t doomed.

CGI and I go back a long way. In fact I think was added to the Perl core at about the same time as I started using Perl.

It’s obvious why it was added to the core. Back in 1997, Perl and CGI were tightly bound together in many people’s minds. I had people telling me that Perl could only be used to write CGI programs and other people telling me that CGI programs could only be written in Perl. Both sets of people were, of course, wrong; but it’s easy to see how they reached both of those conclusions.

Before was added to the Perl core, people used to parse CGI parameters using horribly broken code copied from Matt Wright (code which he had originally copied from Reuven Lerner). Of course, adding the module to the Perl core didn’t magically rewrite all those horrible CGI programs to use CGI::params, but at least it meant that the option was there.

This became important to me when I started the nms project. This project rewrote Matt Wright’s scripts using a better standard of Perl code. The problem was that many people started by installing one of Matt’s scripts on their server and later, when they wanted to move on from using other people’s code, they would use Matt’s code as a template for their own first steps into Perl. This is partly what made Perl so popular. But it’s also what lead to the preponderance of terrible Perl code that you still find on the web today.

We wrote the nms programs to work, as far as possible, in the same environment as Matt’s scripts. Matt said that his scripts would work fine on Perl 4 (back then, there were still many cheap hosting plans that came with Perl 4). We decided not to put ourselves through that pain and to target Perl 5.004 – because that was the first version to include Remember, we were targeting Matt Wright’s users. And they were people who used cheap hosting plans with basic FTP access and little or no chance of installing anything from CPAN. We had to rely on core modules. If hadn’t been in the Perl core, then the nms programs would have been far harder to write and the project may have never been started.

The nms project was started over ten years ago. What is the situation like now? Those cheap hosting plans still exist. People still use them for simple web sites. Some of those people still use Matt’s scripts or the nms alternatives. But the numbers of people using those programs are far smaller than they used to be. These days, people wanting to add simple dynamic functionality to a web site are far more likely to use a PHP program. And those cheap web hosts are far more likely to want to support PHP.

Of course, these days, no serious Perl developer uses to write web programs. We’d be far more likely to use something based on PSGI. And even if we did want to use, we’d know how to get it installed from CPAN. The only people who are going to suffer from the removal of are the people using something like the nms programs on a cheap hosting plan. I worry a little about the influx of support email we will get when some cheap hosting company updates from Perl 5.18 to Perl 5.21 and suddenly all the nms programs stop working. It’s slightly galling to realise that Matt’s scripts will continue to work at that point. Of course, the kinds of companies that we’re talking about tend to lag well behind the bleeding edge of Perl versions, so this might not happen for eight or more years. So I think it might well be someone else’s problem.

All in all, I think it will be sad to see removed from the core. It will effectively see the end of even half-decent Perl code being used on bottom of the range hosting plans. But Perl has been losing that market for years and, speaking as someone who spent a lot of time helping out on support forums for basic Perl/CGI code, I’m far from convinced that I’ll miss those users. So my sadness at seeing CGI,pm go, will be purely historical.

But I’d really like to see some cut-down version of PSGI take its place!

Perl School: DBIx::Class

Update: I’m sorry to have to announce that this course has been cancelled. I hope to reschedule for later in the year.

Tempus fugit and another Perl School rolls around.

Next Saturday (June 8th) I’ll be running my one-day course on Database Programming with Perl and DBIx::Class. As always the course will take place at Google Campus in London and tickets for the course cost £30.

The course is aimed at people who know Perl but would like an introduction to modern database programming using DBIx::Class. Full details of the topics covered are on the Perl School web site, where you’ll also find a booking form.

What New(ish) Perl features Do You Use?

Over on LinkedIn, someone asked me “What core PERL[sic] features do you use regularly that are new since 95?” It’s hard to be sure as the perldelta files only seem to go back to 1997 (for example, when were qw(...), q(...) and qq(...) added?), but here’s a quick list off the top of my head.

  • my was, of course, added in 5.0. But 5.004 added the ability to use it in control expressions – while (my $foo = <>) – and in foreach loops – foreach my $foo (@foos)
  • use VERSION
  • Regex extensions – (?<=RE) and similar. Oh, and qr/.../
  • Data::Dumper (added in 5.005)
  • Unicode support – first added in 5.6.0 and improved in every release since
  • our
  • Three-argument open
  • Omission of intermediate arrows in data structure lookups – $foo[$x][$y] instead of $foo[$x]->[$y]
  • use warnings
  • Memoize
  • Test::More and Test::Simple
  • say
  • defined-or
  • use base (or, more recently, use parent)
  • yada-yada operator

Have I missed anything obvious? What new Perl features do you use most?


I’ve been writing articles about Perl for a number of years. Because I have written for many people, the articles are currently spread out over a lot of different sites. I’ve decided to do something about this.

There’s now a new articles section on the site and over the next few weeks I plan to pull all of my Perl articles together in that section.

Currently, it just contains the seven articles that I wrote for If you read them, please bear in mind the fact that they are all around ten years old and may well no longer reflect current best practices.

This coming weekend is a long weekend in the UK. This means that I may well find the time to republish a lot more articles.

Moose Course This Saturday

I’m running another Perl School this Saturday (6th April). This time the subject is Object Oriented Programming with Perl and Moose. I ran a two-hour taster version of this course at the London Perl Workshop back in November, but this is the full six-hour version. Tickets are £30 each.

The course is run at Google Campus on the outskirts of the City of London. There’s a full list of topics and a booking form over on the Perl School web site.

Texinfo 5.0 in Perl

There was a story on Slashdot on Sunday saying that the new version of Texinfo had replaced the old, C, implementation of makeinfo with one written in Perl.

I thought it would be interesting to look at the Perl they’ve written. This is, after all, a reasonably large example of Perl code that will be getting a bit of attention in the open source[1] world. If you want to look too, you can download the tarball or browse the CVS repository. In both cases, the Perl code is in the directory called ‘tp’.

This first thing to note is that this is obviously code which has been written by programmers who know their craft. This has not been written by script kiddies. There are, however, some rather bizarre touches which imply that the authors don’t know Perl as well as they might hope.

  • The code is nicely partitioned into modules. And many of the modules are really classes. But some of the modules (the ones in the init directory) have no package statement. So they are more like Perl4-style libraries than what we’d recognise as modules.
  • Many (in fact it might be all) of the subroutines in the modules have prototypes. In many cases, that doesn’t do any harm (although Perl prototypes don’t really address the issues that most people assume they address). But many of these subroutines are called as methods. And prototypes have no effect on method calls at all.
  • There is rather more use of package variables (instead of lexical variables) than I’d be comfortable using in my code.
  • I can see no use of CPAN modules. Perhaps there are no CPAN modules that help with this code. But I’d find that surprising in a project of this size.

Then I started to wonder which version of Perl they were targetting. So I searched for “use” statements. And found quite a range. Many of the files insist on 5.006 and most of the rest want 5.00405 – which I consider a scarily old version of Perl to try and support. There was one file that wanted 5.007_003. Then in one file (Texinfo::Parser) I found this:

# We need the unicode stuff.
use 5.006;

Reading the original Slashdot story, it claimed that one of the improvements in this new version was its Unicode support. And suggesting that you need Perl 5.006 for decent Unicode shows some major misunderstanding. Perl 5.006 was probably the point at which the Perl 5 Porters started to take Unicode seriously. It took until 5.12 or 5.14 before they got it right. Trying to support Unicode properly on anything earlier is almost certainly doomed to failure.

It’s great that another heavily-used project has started to use Perl. But it’s a shame that people might mistake this 5.6-era code for state of the art Perl. I can’t help wondering if this is a symptom of the “Perl 5 can’t have a new version number” problem that I’ve been reading about recently

I’ll get in touch with the Texinfo team and make some suggestions to them, of course.

Update: I emailed the Texinfo mailing list with a link to this blog post. I got a reply from Patrick Dumas who wrote most of this Perl code. His reply is available on the mailing list archives.

[1] Sorry, it’s a GNU project so obviously I mean “free”, not “open source”.

Training Debrief

I’ve spent a lot of the last seven days running training courses. It might be interesting to share some thoughts about how they went.

Last Saturday was Perl School 4. A week before the course I was a little worried about ticket sales, but I did a bit of marketing early last week and managed to more than double sales in a few days. In the end I had 27 people signed up.

Perl School is always enjoyable. I think that people often turn up with quite low expectations as it’s so cheap. So it’s fun to overturn those expectations and give them a day of high quality training. People obviously recognise that as I’m getting a lot of repeat business – at least one person has come along to three of the four courses so far.

Many of the courses I give are overviews of Perl at various levels. This one was just about DBIx::Class so it was great to be able to go into a lot more depth on a single topic. Of course, DBIx::Class is a great subject to cover and it was fun explaining its more powerful corners to a room of people who don’t know much about it.

I thought it went well. But don’t just take my word for it. I’ve been asking attendees to fill in feedback forms about all the Perl School courses and I’ve published a page summarising that feedback.

Then this week has been two two-day courses for flossUK. Two day courses give us time to include practical sessions so that people go home having actually tried out the techniques that I’ve taught – which nicely reinforces the lessons. I really enjoy those sessions as you really see lightbulb moments as people see how easy it is to use these tools. This afternoon, for example, it was great to see people getting a simple Catalyst application up and running in less than an hour. An hour later people were really impressed as I introduced them to Plack::Middleware::Debug and showed them how I could get detailed DBIC_TRACE output on the web page by making tiny changes to the application code. At least one person went away determined to reimplement a number of key applications in Catalyst as soon as possible.

And that, to me, is the joy of running training courses. It’s great to open people’s eyes to the possibilities that these new tools give them. I love to see them leave filled with renewed enthusiasm for the language.

Perl Books

The Perl community on LinkedIn is fascinating. It’s a great way to see how Perl is perceived and used outside of the echo chamber. And that’s a real eye-opener.

Here’s an example. Every few weeks (it seems) someone asks for advice on Perl books.At that point a few people will jump in with sensible suggestions. But for every reasonable suggestion, you’ll get three or four people suggesting something from this list:

  • Something horribly out of date. A lot of publishers stopped updating their Perl books about ten years ago. The most recent version of Perl Black Book that I can find is from 2001. Teach Yourself Perl in 21 Days was last updated in 2002. Perl By Example dates from 2007. I haven’t read any of these books, so I can’t comment on their quality, but I’d be really wary of suggesting that someone learns Perl from a book that is so out of date. Before the days of Amazon, these books would quietly disappear from bookshops, but now they always seem to be available.
  • Something out of date, but that used to be great. There are plenty of books that I would have recommended when they were current, but that I wouldn’t really want to recommend now. A lot of these are O’Reilly books that haven’t been updated recently – Advanced Perl Programming and The Perl Cookbook, for example. I’m sure there’s lots of good stuff in those books. But I really wouldn’t want anyone to read them if they didn’t already have enough experience to update the Perl to current best practices. I sometimes recommend these books myself, but only in specific circumstances. Whenever I run a course on OO Perl I mention Damian’s book. But I also point out that there have been a lot of advances in the area since the book was published. And, I have to confess, my own Data Munging with Perl fits firmly in this category.
  • Something of dubious provenance.  Most of these discussions will, at some point, attract a link to some dubious web site in Eastern Europe that contains the full text of O’Reilly’s various CD bookshelves. I know that these sites exist and I know that there’s nothing that O’Reilly can do about them, But I’d rather not see them mentioned on a professional site like LinkedIn. And quite apart from the copyright issues, there’s the fact that most of the books on these sites fall firmly into the first category above. They’re all over ten years old.
  • Some great tutorial on the internet. I’ve talked about the problems of old and dodgy tutorials before. And things definitely seem to be looking up. We are getting more good tutorials out there. But people still insist on sharing links to the tutorial that they learned from. Even if it’s appalling.

In a recent discussion someone said (and I’m paraphrasing) “just go to Amazon and look for the highest rated books”. I think there are two problems with that:

  1. The people who are rating beginner’s programming books on Amazon are usually the least qualified people to do that. Sure, they can tell how easy the book was to read and how well they picked up what the author taught them. But they have noway of knowing whether what they learned was accurate or useful.
  2. Amazon ratings last forever. But, as noted above, the quality of a technical book in fast-moving subject like programming falls over time. Perhaps Amazon ratings on programming books should have a half-life.

Here are some examples of things that you’re going to miss out on by using outdated Perl references.

  • say – We all love say, don’t we?
  • Lexical filehandles – Storing filehandles in lexical variables is great. I no longer have to worry about bareword filehandles being reused elsewhere in the code.
  • Defined or operator – There’s now no excuse for the $val ||= $default bug.
  • given/when – Perl has a switch statement. And it’s better than anyone else’s :)
  • Unicode support – Perl’s Unicode support is second to none. Except, if you’re using an old version of Perl in which case it’s a bit rubbish. And if you’re reading about Perl in an old book, then you won’t know about it.
  • State variables – Ok, I don’t use those every day. But when I need them, they make my code cleaner.

And then there are all the great CPAN modules that aren’t covered in books that were written before they were released. Would you really want to introduce someone to OO Perl without mentioning Moose?

My rules for recommending books are pretty simple. They should be books that I’ve found useful and they should have been published in the last few years. And given the falling numbers of Perl books that are published each year, that’s now a rather small number of books. Perhaps a dozen or so.

Am I being too harsh? Can beginners get something useful out of older Perl books? How do you decide whether to recommend a book to a colleague?