The open or die idiom is fairly ubiquitous in Perl. To be useful, the exception should say something about what went wrong: open ... or die "Open error: $!", for example.
The $! built-in variable (a.k.a. $ERRNO or $OS_ERROR if use English; is in effect) gives you access to the C language errno variable, which through the magic of Perl interpolates an error message appropriate to the error given.
But there are times when some error analysis is in order. Fortunately, $! is a dualvar, so if you access it in numeric context rather than string context, you get the actual numeric value of the error code. But for both portability and maintainability you don't want to compare $! to a numeric literal. Thus, Errno. For example:
Spoiler Alert: This weekly challenge deadline is due in a few days from now (on March 26, 2023 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.
Task 1: Special Bit Characters
You are given an array of binary bits that ends with 0.
Valid sequences in the bit string are:
[0] -decodes-to-> "a"
[1, 0] -> "b"
[1, 1] -> "c"
Write a script to print 1 if the last character is an “a” otherwise print 0.
Dancer2 0.400000 has been released, and is on its way to CPAN.
We realize that some of you might be curious as to the large version bump. There are a couple of reasons for this:
- Modules we depend on bumped their minimum Perl version to 5.12, requiring us to follow suit.
- As of 2022, Dancer2 has an official deprecation policy. We are implementing this policy effective with this release, and it will help shape and guide future development.
- We’ve officially marked a lot of outdated and unused API as being deprecated.
With that, the following APIs, methods, etc. are now officially deprecated:
Dancer2::Test
request->dispatch_path
push_header
header
headers
context
Named placeholders: splat and capture
In plugins:
plugin_setting
dancer_app
request
var
hook
To discuss any of these, you can find issue for each of the above here.
Around the beginning of 2022 I started noticing a large number of warnings when compiling XS modules under macOS 12 Monterey. These looked like warning: '(' and '{' tokens introducing statement expression appear in different macro expansion contexts [-Wcompound-token-split-by-macro], and appeared to originate fairly deeply in Perl's macro stack.
This week I was moved to address them for my one lone XS distribution, Mac-Pasteboard. Not only are they really annoying, but they would make it difficult or impossible to find anything more serious.
A little web searching seemed to say that this warning was added in clang 12.0, and is enabled by default. Beyond that, I did not find much. A Ruby ticket turned up, but the patch involved rewriting the relevant macros so that the warning was not tickled. A desultory check of a few other XS modules that came to mind did not provide any help -- they all showed the same behavior.
Spoiler Alert: This weekly challenge deadline is due in a few days from now (on March 19, 2023 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.
Task 1: Minimum Index Sum
You are given two arrays of strings.
Write a script to find out all common strings in the given two arrays with minimum index sum. If no common strings found returns an empty list.
As a bystander in the evolution of Object-Oriented Programming in Perl,
and someone who is really only just starting to get the hang of Perl modules and packages
(still not any good at it), I get really quite overwhelmed by ideologies.
There is considerable debate about the right way to program things, the right
style, the right direction that Perl should go. It is Vim vs Emacs, Atari ST
vs Amiga, Mods vs Punks. Really one needs a language to do what one needs it
to do, simply, quickly and consistently. For an amateur, Perl has been able
to do exactly that for me. I code rubbishly, but hey, who's looking?
Last year, impressed with the apparent speed of an M1 Mac Mini I bought to try out, I explored its perl performance and wrote about it in a
blog post
. I used mainly my own benchmarks which were mostly representative of workloads I was interested in.
Spoiler Alert: This weekly challenge deadline is due in a few days from now (on March 12, 2023 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.
Task 1: Keyboard Word
You are given an array of words.
Write a script to print all the words in the given array that can be types using alphabet on only one row of the keyboard.
'It is a capital mistake to theorize before one has data.' -- Sherlock Holmes, "A Scandal in Bohemia"
The mental excursion that led to this blog post started with a report from Olaf Alders that my Perl::Critic::Policy::Variables::ProhibitUnusedVarsStricter was generating a false positive on variables used only as defaults in subroutine signatures. After the first cut at fixing this I thought a regression test was in order. I did this by running both unpatched and patched versions of the policy against my Mini CPAN, and then diff on the outputs.
This has always taken the better part of a day to run, and given that it had to expand all the distributions first and then run a fairly brute-force policy against anything it found, I accepted this as the price of conscientiousness.
Spoiler Alert: This weekly challenge deadline is due in a few days from now (on March 5, 2023 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.
Task 1: Shortest Time
You are given a list of time points, at least 2, in the 24-hour clock format HH:MM.
Write a script to find out the shortest time in minutes between any two time points.
Example 1
Input: @time = ("00:00", "23:55", "20:00")
Output: 5
Since the difference between "00:00" and "23:55" is the shortest (5 minutes).
XS has a reputation of being ugly and cumbersome, but in my experience, it doesn't have to be. Let's take for example this snippet from my Thread::Csp::Promise class:
Spoiler Alert: This weekly challenge deadline is due in a few days from now (on February 26, 2023 at 23:59). This blog post offers some solutions to this challenge. Please don’t read on if you intend to complete the challenge on your own.
Task 1: Third Highest
You are given an array of integers.
Write a script to find out the Third Highest if found otherwise return the maximum.
Example 1
Input: @array = (5,3,4)
Output: 3
First highest is 5. Second highest is 4. Third highest is 3.
'A fair jaw-cracker dwarf-language must be.' -- Samwise Gamgee, The Lord of the Rings, II/iii: "The Ring Goes South", as quoted in regcomp.c, the Perl regular expression compiler.
As you would expect, this category gets you warnings about possibly-problematic regular expression constructions. A couple specific examples are:
Assuming NOT a POSIX class ...
This warning is about things that look kind of like POSIX character classes, but do not parse that way. The full diagnostic gives examples like [[:alnum]] (missing colon) and [[:digit:xyz] (missing right square bracket). These parse like simple character classes ([:[almnu]\] and [:[dgitxyz] respectively), so without the warning you get a hard-to-diagnose bug.
Unescaped left brace in regex is passed through ...
Efforts to eliminate unescaped left braces so that they are available for new syntax have been underway since 5.17.0, released May 2012. As I recall, this effort turned to be much harder than originally anticipated because at least one toolchain external to Perl (autoconf if memory serves) relied on this behavior.
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