blogs.perl.org

1. Confusing output order:

   use warnings; use strict; use 5.010;

   print 'OK'; my $x; say $x; $x = 42; say $x;

This code prints statements before the line generating the warning, the result might be confusing:

Use of uninitialized value $x in say at perl_warning_1.pl line 7.
OK
42

The reason is that by default Perl buffers STDOUT, while not buffer STDERR.

Turn off the buffering of STDOUT by: $| = 1; at the beginning of the script.

1. Second most common warning: Use of uninitialized value:

Usually means variables have no value: either it never got a value, or at some point undef was assigned to it.

1. Unknown warning category 'xxxx':

   use strict; use warnings

   print "Hello World";

Missing semicolon after using warnings statement. Perl is executing the print function and returns 1 indicating that is was successfull. changed to:

use warnings 1

Some time ago I was on a team that was rewriting a very large legacy system. We wanted to use a more maintainable OO style (rather then just a huge global hash-ref ) but unfortunately the team was restricted by using only perl 5.6.0. By the time I joined the project work was well underway and I was still stuck doing accessors by hand. So I came up with this little beastly Orignal to solve that problem.

It fixed things up nicely as we could have nice 5.14 style accessors with some silly other little bits that came in very handy at least to us.

Hao Wu provided a great comment showing how I could solve exercise one using sum from List::Util and grep. I'd considered sum but utilzed false laziness and didn't use it. I'd also considered grep, but did not immediately hit upon the elegant solution that Hao suggested and so went with a more verbose solution.

So, here are some new solutions.

Perl 5:

Not Perl related, but I suspect some folks may appreciate this.

Today after a nasty mistake on the command line involving find and rm, I discovered that I deleted a number of files I didn't mean to delete, including some hidden files. Oops! I opened my Time Machine backup, only to discover that it doesn't show hidden files. However, it turns out that you can use that to show hidden files so long as your main system shows hidden files. I'm using OS X Mavericks, so I dropped the following bash script into my bin folder and named it togglehidden. Running this from the command line will toggle showing hidden files in the Finder on or off.

Hi!

Today I'd like to show you my testing setup which involves database testing. Hopefully it can help someone out or maybe someone could suggest me better ways of doing things.

First of all, having all the tests in the root of the 't/' directory got too messy, so I'm using mostly the same directory structure in my 't/' directory, as I have in my 'lib/' directory for the ease of navigation. Let's say this is the 'lib/' tree:

- lib/
-     MyApp.pm
-     MyApp/
-         MyModule.pm

then my 't/' directory would have the following layout:
- t/
-     MyApp/
-         0001-MyApp_first_test.t
-         0002-MyApp_second_test.t
-         MyModule/
-             0001-MyModule_first_test.t
-             0002-MyModule_second_test.t

Because of the nested structure it would be messy to add the 'use lib' statement into the testfiles themselves to use my 'lib/' directory, so I give it as a parameter to prove. I run all my tests from the 't/' directory, so for the ease of use I created a 't/prove'

Well a good day today. Had an interesting though come by my desk. Was debugging a problem with a colleague and in our back and forth he came up with the little jape'

'I prefer to never return anything from a perl subroutine!'

I could of course dive into the often fought and confusing battle of the difference between a function or a subroutine, but that dead horse has been done over like yesterday's poutine gravy. We could of course take a vote on it but I think it would be this sort of reaction in the community? Anyway on with my story I did a little digging and was surprise to discover that in perl a subroutine always returns a value. This goes back to day 1 when Larry

My starting problem is easy. Coming from Project Euler:

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

Perl 5:

Timm Murray will be giving a talk on using Perl on a Raspberry Pi to control an Arduino to make drones and robots. 

[From my blog.]

I officially join Fruit Protectors R Us:

The pix of the tricks.

Well looks like old fiend smartypants was up to her old tricks again.

You know the type, spends the day at work in some IRC, never forgets the minutia of page 67 of the help file of a sys-admin command, has memorized and and has a better version every regex ever written, knows she is always right and in the bosses eyes can never make a poor choice when designing code.

Anyway let's get on with the code example. Sometimes the ugly way to do
things is the best. In this case processing a large array where lets say the following has to be extracted,

1. The maximum value
2. The minimum value
3. Clean out any duplicates
4. Group the data into 3 sets

Simple enough really. But then I saw the code (changed to protect the guilty and save space)

This challenge is a stencil quest on questhub: in each calendar month of 2014 you have to release a distribution that you haven't released before, and write a blog post about it. This might be an entirely new distribution, one that you've adopted, or one that you're helping with. The rules so far are:

• You have to release at least one such dist within each calendar month. You can't catch up, by releasing 12 in December.
• You must blog about the dist and link to the blog post in a comment on your quest. It doesn't matter if the blog post is in a following month.
• Renaming one of your existing dists doesn't count :-)

Come and join us!

I blame Jeff Thalhammer. He is the one who directed me to The ChangeLog, and that's where I've heard the interview with Katrina Owen, the creator of Exercism.io.

What is Exercism.io?

Lately, I’ve been pondering my relationship with Perl.  Every programmer has a different relationship with their language-of-choice, and it impacts how they approach many different aspects of coding, what features they like and which ones they hate, what they clamor for and what they disparage.  And these choices are always going to be challenged by our friends, our coworkers, and our open-source collaborators.  Which is a good thing, for the most part: being challenged is what keeps us honest, keeps us fresh.  Without constant challenge, we can lapse into dogma and cargo cult coding.  But we can’t properly defend our positions—can’t explain why we feel the way we do about certain things—unless we take the time to understand our relationship with our language.

So this is part 1 of an X-part series (we’ll just have to see how long it takes me to work through it all).  Primarily I want to explore this for my own self-awareness, but I hope it will be interesting to others as well.  And perhaps it will make some of my other blog posts make sense.

I begin at the beginning: how I came to Perl.

So I though it would be just a regular day until with me just doing a little coding, drinking my coffee* and generally enjoying life, But I was wrong.

A Little Vulnerable

So I have been babysitting and ever so slowly migrating a 15+ year old application over to a more manageable and of course we have to keep doing improvements to the code so on a very old part I found something like this. (SQL changed to protect the innocent)

my $usr_ids = join(",",@user_sel);

my $sth = $h->prepare("Select * from a_table where id in ($usr_ids)");

$sth->execute();

Params? We an't got no params. We don't need no stinking params!!

Well the old bug-bear of little Bobby Tables or SQL injection shows it ugly little head again.

But what to do? There is no bind_array, well lets just give 'execute_array' a try

my $sth = $h->prepare("Select * from a_table where id in (?)");
my $tuples = $sth->execute_array(
{ ArrayTupleStatus => \my @tuple_status },
@user_sel,
);

ora_st_execute_array(): SELECT statement not supported for array operation.

Ouch so no luck there!

At the patch -p1 Perl hackathon, I'm working on bits related to my idea for a new sort of CPAN client. One of the features I want is a graphical display of the work to do and the work being done.

Creating the data structure in Perl is easy. Start with a module, figure out it's distribution, then grab that META.{json|yml} to get dependencies (for now, with more discovery later). Put that stuff into a data structure.

Hello, folks. This blog was started to talk about a project of Jess and mine, but before we got around to starting it, I posted a couple of times in my own blog about it, so please read these if you’re interested:

• Past Prologue
• Learning Project 2 Whats Different

Future entries will hopefully be collected on this blog, at least until we pick a name for the project. (So far, I’ve come up with learnthing and {mechano,electro,cyber}didact, all of which kind of suck.)

Thanks,
-=- James "theorbtwo" Mastros

Recently, Packt published a book called Debian 7: System Administration Best Practices.

Some time before they had emailed me asking if I would be a reviewer. I know some readers have in the past been disappointed with Packt's books, and thought that since I had time I might be able to contribute enough suggestions to help make the book better. I explained that I am a Perl programmer, not a Debian administrator, and on that understanding we agreed.

I was not told the name of the author, and from his point of view I would have been one of the anonymous reviewers.

During reviews, I made many suggestions. I have received a paper copy of the book, but have not counted how many were adopted. I did check a couple of chapters, and see a few were, and some (a clear majority :-) weren't. The number doesn't matter - what matters of course is the resultant book.

In an odd turn of fate as I was just about to write today's post. I got this email announcing the release of DBI 1.6.31, normally this causes me little concern as DBI has been stable for a very very long time, but given yesterdays Part 18 and this line in the change file

Changed the handle passed to Callbacks from being an 'inner' handle to being an 'outer' handle.

I though maybe I should look at this change?

Are You an Innie or Outie

I'll start by giving the 25 cent tour of inner and outer handles. DBI has been using Tied Hashes since time immemorial, and all handles in DBI are references to tied hashes so you never really get a $dbh or $sth object just a reference to it.

At this point, I don't have a Perl blog. I do Perl things, but nothing that ever seems worth blogging about. However, I've decided to improve my knowledge of Perl 5i and Perl 6, and generally practice my proramming, so I'm going to work through a bunch of easy through to difficult problems in each language. Hopefully I'll pick up the idiomatic solution ideas as I go along.

Feedback and alternate solutions are also welcome.

At some point I may repeat the problems with Python, but not yet.

Problem sets I'm planning on starting with include:

• Code Katal
• Programming Praxis
• Project Euler
• Python Challenge
• Ruby Quiz archives

The latter two are language-targetted, but I believe that I should be able to gain some benefit from some of them anyway. Suggestions for other problem sets are welcome, but this is certainly enough to get me started.

In this post, I’d like to talk about what’s different between this project and other similar things I’ve seen. I haven’t seen everything (by a long shot), and I certainly would love to see more prior art posts — I’ve now at least glanced at all the ones mentioned in the comments to the last post, though it’s been a while since I looked at the Kahn Academy, and that’s probably the closest to what I’ve got in mind.

Mo’ money, mo problems