Originally published at Perl Weekly 760

Hi there,

Perl's asynchronous ecosystem continues to grow, enabling developers to build non-blocking, responsive applications with ease. Modules like IO::Async, async features in Mojolicious, and helpers for asynchronous database operations (such as DBIx::Class::Async) allow event-driven designs, background tasks, and futures/promises, making high-throughput web services, real time APIs, and streaming pipelines straightforward to implement.

Projects like PAGI and PAGI::Server, now with HTTP/2 support, and Thunderhorse showcase how Perl can handle multiple connections efficiently while keeping code clear and maintainable. Together, these tools make it easier to build responsive, scalable, and maintainable applications, all while retaining the expressive, pragmatic style that continues to define Perl.

With each new module and project, Perl's potential in the modern, concurrent world keeps expanding, the best is yet to come.

A small milestone reached with this issue, my 200th edition. Enjoy rest of the newsletter and stay safe.

--
Your editor: Mohammad Sajid Anwar.

Announcements

Join us for TPRC 2026 in Greenville, SC!

It’s great to see the announcement for The Perl and Raku Conference 2026 (TPRC) taking shape, with registration opening and plans underway for a vibrant community gathering in Greenville, SC this June. The post reinforces the value of bringing Perl and Raku developers together for talks, workshops, and networking. A highlight on the opensource calendar that strengthens the ecosystem and connects contributors across projects.

This week in PSC (215) | 2026-02-11

In This week in PSC 215, the Perl Steering Council covered a deep discussion around legal identifier name restrictions for security without reaching consensus and planning to broaden the conversation beyond p5p, tackled the challenge of an absent maintainer for the dual‑life Encode module, and decided to hold off on merging larger PRs like magic v2 and attributes v2 due to the upcoming freeze in this release cycle. These updates give a clear snapshot of ongoing governance and core maintenance decisions within the Perl project.

Articles

Poplar Decisions

The post reflects on the challenge of rational decision‑making with a quirky, human‑centred anecdote, weaving in the idea that structured data models, like decision trees, can help bring objectivity to complex choices. The post’s blend of storytelling and commentary on data structures adds a thoughtful and entertaining perspective for programmers thinking about reasoning and modeling in code.

Mojo with WebSocket

A practical real‑world example of using Mojolicious’ built‑in WebSocket support to build an interactive online chat app in Perl, complete with multiple server variants and integration options like Redis or PostgreSQL. The repository showcases how easily Mojolicious can handle real‑time bidirectional communication with WebSockets, making it a solid reference for Perl developers exploring event‑driven web apps.

Coding Agents using Anthropic and z.ai - presentation at the German Perl Workshop 2026

The post previews Max's talk at the German Perl Workshop 2026, exploring how modern AI coding agents from Anthropic and z.ai can assist with Perl development, what differences exist between the models, and tips for getting them to write good code. It’s an engaging look at practical uses of agentic AI in real world programming contexts, a timely topic for anyone curious about AI‑assisted development.

Beautiful Perl feature: 'local', for temporary changes to global variables

This article highlights one of Perl’s unique strengths, the local keyword, showing how it enables temporary, dynamic changes to global variables without permanent side effects. With clear examples manipulating %ENV, special Perl variables and even symbol table entries, it makes a compelling case for using local judiciously to solve real world problems that lexical scoping alone can’t.

CPAN

PAGI::Server, now with HTTP/2!

The announcement of PAGI::Server 0.001017 highlights experimental HTTP/2 support built on nghttp2, bringing both cleartext h2c and TLS‑based HTTP/2 to Perl web services with automatic protocol detection and solid h2spec compliance. The write‑up explains why HTTP/2 matters for backend performance and modern use cases like gRPC and multiplexed APIs, and it also outlines other quality‑of‑life improvements and operational fixes in the release.

Black box test generator version 0.28 released

Version 0.28 of App::Test::Generator, the black‑box test case generator, has just been released with improved schema extraction and test generation accuracy, tightening detection of getter/setter methods and better typing in generated tests. These enhancements make it easier to produce honest, robust fuzz and corpus driven test harnesses from your Perl modules.

Run::WeeklyChallenge

Run::WeeklyChallenge is a small but useful CPAN module that helps you automate running solutions to challenges from The Weekly Challenge site by passing one or more sets of JSON‑formatted inputs to your code. It cleanly wraps your solution logic and input schema validation, making it easier to test and reuse challenge solutions programmatically.

DBIx::Class::Async

DBIx::Class::Async is a modern asynchronous wrapper for DBIx::Class that allows non‑blocking database operations in Perl, keeping the familiar DBIC interface while running queries in the background via futures. The latest update brings several improvements: caching is now disabled by default (TTL 0), automatic detection of non-deterministic SQL functions (like NOW() and RAND()) ensures safe bypass of caching, cache invalidation on update/delete operations is more precise using primary keys, and count() queries are no longer cached to guarantee accurate row counts. These enhancements make asynchronous DBIC usage both safer and more reliable.

Syntax::Highlight::Engine::Kate

Syntax::Highlight::Engine::Kate provides Perl programs with robust syntax highlighting using the same engine as the Kate editor. The latest update fixes Issue #23 in Template.pm: the testDetectSpaces() regex was corrected, ensuring only spaces and tabs are matched and improving number highlighting in Perl and other languages. The test suite expected outputs were also updated to reflect the corrected highlighting behavior.

The Weekly Challenge

The Weekly Challenge by Mohammad Sajid Anwar will help you step out of your comfort-zone. You can even win prize money of $50 by participating in the weekly challenge. We pick one champion at the end of the month from among all of the contributors during the month, thanks to the sponsor Lance Wicks.

The Weekly Challenge - 361

Welcome to a new week with a couple of fun tasks "Zeckendorf Representation" and "Find Celebrity". If you are new to the weekly challenge then why not join us and have fun every week. For more information, please read the FAQ.

RECAP - The Weekly Challenge - 360

Enjoy a quick recap of last week's contributions by Team PWC dealing with the "Text Justifier" and "Word Sorter" tasks in Perl and Raku. You will find plenty of solutions to keep you busy.

TWC360

This write-up delivers straightforward, idiomatic Perl solutions for both text justification and word sorting, showing practical use of fc for case-insensitive comparisons and clear subroutine design. The concise code examples make the challenge solutions easy to follow and apply.

Full Circle

In this post, an effective solution to The Weekly Challenge #360 is given, with beautiful examples showing how Raku can be implemented for text justification and sorting as the output. Most of the explanations are fairly short, but they are clearly defined, giving lots of examples; and, they consider the idiomatic usage of Raku's features to make the output readable and helpful.

Pertaining to a subtlety of sorting

This article offers a thoughtful take on the Word Sorter task from PWC 360, with a clear explanation of the case-insensitive sort and an efficient Perl solution using a Schwartzian transform. The benchmarking insight and attention to Unicode case folding nuance show both practical coding skill and depth of understanding.

Perl Weekly Challenge: Week 360

This write-up clearly presents both Text Justifier and Word Sorter tasks with simple, idiomatic Perl and Raku solutions that showcase practical string manipulation and sorting techniques. The inclusion of multiple examples and cross-language snippets makes the challenge approachable and highlights the expressive power of each language.

Perl Weekly Challenge 360

This post showcases clear, idiomatic Perl solutions for both the Text Justifier and Word Sorter tasks, with one‑liner examples and concise logic that demonstrate practical use of integer arithmetic and case‑preserving sorting. The included sample inputs and outputs make the behavior easy to follow and verify.

This is exactly the sort of justification that I was looking for

This post methodically implements both Text Justifier and Word Sorter solutions for PWC 360 in clear Perl code, showing careful step-by-step padding logic and idiomatic sorting. The explanations of how the examples are handled make the approach easy to follow and instructive for readers.

Justifying TIMTOWTDI

The post offers well‑structured Perl solutions that clearly implement both text justification and alphabetical word sorting with idiomatic constructs and practical tests. The use of case‑preserving sorting and centered padding logic demonstrates good command of Perl’s core features and makes the solutions easy to follow and reuse.

Word Crimes are Justified

An excellent and clear walk-through of the Perl Weekly Challenge tasks, with well-structured multi-language solutions and thoughtful explanations that make the text justification and word sorting problems easy to follow. The blend of Perl, Raku, Python, and Elixir examples shows both depth and versatility of approach.

Padding and sorting

The post presents the Text Justifier and Word Sorter tasks clearly with well-explained inputs and desired outputs, giving readers a solid grounding in the problem definitions. The examples are practical and show the expected string centering and alphabetical ordering behavior in a way that supports straightforward implementation.

The Weekly Challenge - 360: Text Justifier

This post demonstrates a practical and idiomatic Perl solution by leveraging String::Pad for Text Justifier, showcasing how using existing modules can simplify challenge tasks. The concise examples with clear input/output make it easy to grasp the task mechanics and verify correctness.

The Weekly Challenge - 360: Word Sorter

This write-up delivers a succinct and idiomatic Perl solution to the Word Sorter task, using a case-insensitive sort and clean split/grep logic that keeps words unchanged while ordering them alphabetically. The included test cases make the behavior clear and easy to verify.

Justify the Words

This post delivers clear and well-commented solutions to both Text Justifier and Word Sorter tasks from The Weekly Challenge 360, using concise Lua, Raku, Perl and other language examples with practical explanations of key steps like centered padding and case-insensitive sorting. The author’s discussion of different implementation strategies highlights thoughtful coding decisions that make the techniques accessible and educational for readers.

Padding and sorting

This write‑up walks through both the Text Justifier and Word Sorter tasks from The Weekly Challenge 360 with clear Python and Perl solutions, showing well‑structured logic for string padding and case‑insensitive sorting. The practical examples and side‑by‑side language implementations make the techniques easy to understand and apply.

Perl Power: Two Tiny Scripts, Big Learning!

This write‑up distills both Text Justifier and Word Sorter solutions into clean, minimal Perl scripts with clear logic for padding and sorting, and emphasizes solid test‑driven development and edge‑case handling. The examples and explanation of core techniques make it both beginner‑friendly and technically sound.

Rakudo

2026.06 CÔD YN GYMRAEG

Weekly collections

NICEPERL's lists

Great CPAN modules released last week.

The corner of Gabor

A couple of entries sneaked in by Gabor.

WhatsApp

Do you use WhatsApp? Join the Perl Maven chat group!

Events

Paris.pm monthly meeting

March 11, 2025

German Perl/Raku Workshop 2026 in Berlin

March 16-18, 2025

The Perl and Raku Conference 2026

June 26-29, 2026, Greenville, SC, USA

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(C) Copyright Gabor Szabo
The articles are copyright the respective authors.

Beautiful Perl series

This post is part of the beautiful Perl features series.
See the introduction post for general explanations about the series.

The last post was about BLOCKs and lexical scoping, a feature present in almost all programming languages. By contrast, today's topic is about another feature quite unique to Perl : dynamic scoping, introduced through the 'local' keyword. As we shall see, lexical scoping and dynamic scoping address different needs, and Perl allows us to choose the scoping strategy most appropriate to each situation.

Using local : an appetizer

Let us start with a very simple example:

say "current time here is ", scalar localtime;

foreach my $zone ("Asia/Tokyo", "Africa/Nairobi", "Europe/Athens") {
  local $ENV{TZ} = $zone;
  say "in $zone, time is ", scalar localtime;
}

say "but here current time is still ", scalar localtime;

Perl's localtime builtin function returns the time "in the current timezone". On Unix-like systems, the notion of "current timezone" can be controlled through the TZ environment variable, so here the program temporarily changes that variable to get the local time in various cities around the world. At the end of the program, we get back to the usual local time. Here is the output:

current time here is Sun Feb  8 22:21:41 2026
in Asia/Tokyo, time is Mon Feb  9 06:21:41 2026
in Africa/Nairobi, time is Mon Feb  9 00:21:41 2026
in Europe/Athens, time is Sun Feb  8 23:21:41 2026
but here current time is still Sun Feb  8 22:21:41 2026

The gist of that example is that:

1. we want to call some code not written by us (here: the localtime builtin function);
2. the API of that code does not offer any parameter or option to tune its behaviour according to our needs; instead, it relies on some information in the global state of the running program (here: the local timezone);
3. apart from getting our specific result, we don't want the global state to be durably altered, because this could lead to unwanted side-effects.

Use cases similar to this one are very common, not only in Perl but in every programming language. There is always some kind of implicit global state that controls how the program behaves internally and how it interacts with its operating system: for example environment variables, command-line arguments, open sockets, signal handlers, etc. Each language has its strategies for dealing with the global state, but often the solutions are multi-faceted and domain-specific. Perl shines because its local mechanism covers a very wide range of situations in a consistent way and is extremely simple to activate.

Before going into the details, let us address the bad reputation of dynamic scoping. This mechanism is often described as something that should be absolutely avoided because it implements a kind of action at distance, yielding unpredictable program behaviour. Yes, it is totally true, and therefore languages that only have dynamic scoping are not suited for programming-in-the-large. Yet in specific contexts, dynamic scoping is acceptable or even appropriate. The most notable examples are Unix shells and also Microsoft Powershell for Windows, that still today all rely on dynamic scoping, probably because it's easier to implement.

Perl1 also used dynamic scoping in its initial design, presumably for the same reason of easiness of implementation, and also because it was heavily influenced by shell programming and was addressing the same needs. When later versions of Perl evolved into a general-purpose language, the additional mechanism of lexical scoping was introduced because it was indispensable for larger architectures. Nevertheless, dynamic scoping was not removed, partly for historical reasons, but also because action at distance is precisely what you want in some specific situations. The next chapters will show you why.

The mechanics of local

In the last post we saw that a my declaration declares a new variable, possibly shadowing a previous variable of the same name. By contrast, a local declaration is only possible on a global variable that already exists; the effect of the declaration is to temporarily push aside the current value of that global variable, leaving room for a new value. After that operation, any code anywhere in the program that accesses the global variable will see the new value ... until the effect of local is reverted, namely when exiting the scope in which the local declaration started.

Here is a very simple example, again based on the %ENV global hash. This hash is automatically populated with a copy of the shell environment when perl starts up. We'll suppose that the initial value of $ENV{USERNAME}, as transmitted from the shell, is Alex:

sub greet_user ($salute) {
  say "$salute, $ENV{USERNAME}";
}

greet_user("Hello");                 # Hello, Alex

{ local $ENV{USERNAME} = 'Brigitte';
  greet_user("Hi");                  # Hi, Brigitte

  { local $ENV{USERNAME} = 'Charles';
    greet_user("Good morning");      # Good morning, Charles
  }

  greet_user("Still there");         # Still there, Brigitte
}

greet_user("Good bye");              # Good bye, Alex

The same thing would work with a global package variable:

our $username = 'Alex';             # "our" declares a global package variable

sub greet_user ($salute) {
  say "$salute, $username";
}

greet_user("Hello");
{ local $username = 'Brigitte';
  greet_user("Hi");
  ... etc.

but if the variable is not pre-declared, we get an error:

Global symbol "$username" requires explicit package name (did you forget to declare "my $username"?)

or if the variable is pre-declared as lexical through my $username instead of our $username, we get another error:

Can't localize lexical variable $username

So the local mechanism only applies to global variables. There are three categories of such variables:

1. standard variables of the Perl interpreter;
2. package members (of modules imported from CPAN, or of your own modules). This includes the whole symbol tables of those packages, i.e. not only the global variables, but also the subroutines or methods;
3. what the Perl documentation calls elements of composite types, i.e. individual members of arrays or hashes. Such elements can be localized even if the array or hash is itself a lexical variable, because while the entry point to the array or hash may be on the execution stack, its member elements are always stored in global heap memory. This last category of global variables is perhaps more difficult to understand, but we will give examples later to make it clear.

As we can see, the single and simple mechanism of dynamic scoping covers a vast range of applications! Let us explore the various use cases.

Localizing standard Perl variables

The Perl interpreter has a number of builtin special variables, listed in perlvar. Some of them control the internal behaviour of the interpreter; some other are interfaces to the operating system (environment variables, signal handlers, etc.). These variables have reasonable default values that satisfy most common needs, but they can be changed whenever needed. If the change is for the whole program, a regular assignment instruction is good enough; but if it is for a temporary change in a specific context, localis the perfect tool for the job.

Internal variables of the interpreter

The examples below are typical of idiomatic Perl programming: altering global variables so that builtin functions behave differently from the default.

# input record separator ($/)
my @lines         = <STDIN>;                     # regular mode, separating by newlines
my @paragraphs    = do {local $/ = ""; <STDIN>}; # paragraph mode, separating by 2 or more newlines
my $whole_content = do {local $/; <STDIN>};      # slurp mode, no separation

# output field and output record separators
sub write_csv_file ($rows, $filename) {
  open my $fh, ">:unix", $filename or die "cannot write into $filename: $!";
  local $, = ",";               # output field separator -- inserted between columns
  local $\ = "\r\n";            # output row separator   -- inserted between rows
  print $fh @$_ foreach @$rows; # assuming that each member of @$rows is an arrayref
}

# list separator in interpolated strings
my @perl_files   = <*.pl>; # globbing perl files in the current directory
my @python_files = <*.py>; # idem for python files
{ local $" = ", ";         # lists will be comma-separated when interpolated in a string
  say "I found these perl files: @perl_files and these python files: @python_files";
}

Interface to the operating system

We have already seen two examples involving the %ENV hash of environment variables inherited from the operating system. Likewise, it is possible to tweak the @ARGV array before parsing the command-line arguments. Another interesting variable is the %SIG hash of signal handlers, as documented in perlipc:

{ local $SIG{HUP} = "IGNORE"; # don't want to be disturbed for a while
  do_some_tricky_computation();
}

Predefined handles like STDIN, STDOUT and STDERR can also be localized:

say "printing to regular STDOUT";
{ local *STDOUT;
  open STDOUT, ">", "captured_stdout.txt" or die $!;
  do_some_verbose_computation();
}
say "back to regular STDOUT";

Localizing package members

Package global variables

Global variables are declared with the our keyword. The difference with lexical variables (declared with my) is that such global variables are accessible, not only from within the package, but also from the outside, if prefixed by the package name. So if package Foo::Bar declares our ($x, @a, %h), these variables are accessible from anywhere in the Perl program under $Foo::Bar::x, @Foo::Bar::a or %Foo::Bar::h.

Many CPAN modules use such global variables to expose their public API. For example, the venerable Data::Dumper chooses among various styles for dumping a data structure, depending on the $Data::Dumper::Indent variable. The default (style 2) is optimized for readability, but sometimes the compact style 0 is more appropriate:

print Dumper($data_tree);
print do {local $Data::Dumper::Indent=0; Dumper($other_tree)};

Carp or URI are other examples of well-known modules where global variables are used as a configuration API.

Modules with this kind of architecture are often pretty old; more recent modules tend to prefer an object-oriented style, where the configuration options are given as options to the new() method instead of using global variables. Of course the object-oriented architecture offers better encapsulation, since a large program can work with several instances of the same module, each instance having its own configuration options, without interference between them. This is not to say, however, that object-oriented configuration is always the best solution: when it comes to tracing, debugging or profiling needs, it is often very convenient to be able to tune a global knob and have its effect applied to the whole program: in those situations, what you want is just the opposite of strict encapsulation! Therefore some modules, although written in a modern style, still made the wise choice of leaving some options expressed as global variables; changing these options has a global effect, but thanks to local this effect can be limited to a specific scope. Examples can be found in Type::Tiny or in List::Util.

Subroutines (aka monkey-patching)

Every package has a symbol table that contains not only its global variables, but also the subroutines (or methods) declared in that package. Since the symbol table is writeable, it is possible to overwrite any subroutine, thereby changing the behaviour of the package - an operation called monkey-patching. Of course monkey-patching could easily create chaos, so it should be used with care - but in some circumstances it is extremely powerful and practical. In particular, testing frameworks often use monkey-patching for mocking interactions with the outside world, so that the internal behaviour of a sofware component can be tested in isolation.

The following example is not very realistic, but it's the best I could come up with to convey the idea in just a few lines of code. Consider a big application equipped with a logger object. Here we will use a logger from Log::Dispatch:

use Log::Dispatch;
my $log = Log::Dispatch->new(
  outputs   => [['Screen', min_level => 'info', newline => 1]],
);

The logger has methods debug(), info(), error(), etc. for accepting messages at different levels. Here it is configured to only log messages starting from level info; so when the client code calls info(), the message is printed, while calls to debug() are ignored. As a result, when the following routine is called, we normally only see the messages "start working ..." and "end working ...":

sub work ($phase) {
  $log->info("start working on $phase");
  $log->debug("weird condition while doing $phase"); # normally not seen - level below 'info'
  $log->info("end working on $phase\n");
}

Now suppose that we don't want to change the log level for the whole application, but nevertheless we need to see the debug messages at a given point of execution. One (dirty!) way of achieving this is to temporarily treat calls to debug() as if they were calls to info(). So a scenario like

work("initial setup");
{ local *Log::Dispatch::debug = *Log::Dispatch::info; # temporarily alias the 'debug' method to 'info'
  work("core stuff")}
work("cleanup");

logs the following sequence:

start working on initial setup
end working on initial setup

start working on core stuff
weird condition while doing core stuff
end working on core stuff

start working on cleanup
end working on cleanup

Monkey-patching techniques are not specific to Perl; they are used in all dynamic languages (Python, Javascript, etc.), not for regular programming needs, but rather for testing or profiling tasks. However, since other dynamic languages do not have the local mechanism, temporary changes to the symbol table must be programmed by hand, by storing the initial code reference in a temporary variable, and restoring it when exiting from the monkey-patched scope. This is a bit more work and is more error-prone. Often there are library modules for making the job easier, though: see for example https://docs.pytest.org/en/7.1.x/how-to/monkeypatch.html in Python.

Monkey-patching in a statically-typed language like Java is more acrobatic, as shown in Nicolas Fränkel's blog.

Localizing elements of arrays or hashes

The value of an array at a specific index, or the value of a hash for a specific key, can be localized too. We have already seen some examples with the builtin hashes %ENV or %SIG, but it works as well on user data, even when the data structure is several levels deep. A typical use case for this is when a Web application loads a JSON, YAML or XML config file at startup. The config data becomes a nested tree in memory; if for any reason that config data must be changed at some point, local can override a specific data leaf, or any intermediate subtree, like this:

local $app->config->{logger_file} = '/opt/log/special.log';
local $app->config->{session}     = {storage => '/opt/data/app_session',
                                     expires => 42900,
                                    };

Another example can be seen in my Data::Domain module. The job of that module is to walk through a datatree and check if it meets the conditions expected by a "domain". The inspect() method that does the checking sometimes needs to know at which node it is currently located; so a $context tree is worked upon during the traversal and passed to every method call. With the help of local, temporary changes to the shape of $context are very easy to implement:

  for (my $i = 0; $i < $n_items; $i++) {
    local $context->{path} = [@{$context->{path}}, $i];
    ...

An alternative could have been to just push $i on top of the @{$context->{path}} array, and then pop it back at the end of the block. But since this code may call subclasses written by other people, with little guarantee on how they would behave with respect to $context->{path}, it is safer to localize it and be sure that $context->{path} is in a clean state when starting the next iteration of the loop. Interested readers can skim through the source code to see the full story. A similar technique can also be observed in Catalyst::Dispatcher.

A final example is the well-known DBI module, whose rich API exploits several Perl mechanisms simultaneously. DBI is principally object-oriented, except that the objects are called "handles"; but in addition to methods, handles also have "attributes" accessible as hash members. The DBI documentation explicitly recommends to use local for temporary modifications to the values of attributes, for example for the RaiseError attribute. This is interesting because it shows a dichotomy between API styles: if DBI had a purely object-oriented style, with usual getter and setter methods, it would be impossible to use the benefits of local - temporary changes to an attribute followed by a revert to the previous value would have to be programmed by hand.

How other languages handle temporary changes to global state

As argued earlier, the need for temporary changes to global state occurs in every programming language, in particular for testing, tracing or profiling tasks. When dynamic scoping is not present, the most common solution is to write specific code for storing the old state in a temporary variable, implement the change for the duration of a given computation, and then restore the old state. A common best practice for such situations is to use a try ... finally ... construct, where restoration to the old state is implemented in the finally clause: this guarantees that even if exceptions occur, the code exits with a clean state. Most languages do possess such constructs - this is definitely the case for Java, JavaScript and Python.

Python context managers

Python has a mechanism more specifically targeted at temporary changes of context : this is called context manager, triggered through a with statement. A context manager implements special methods __enter__() and __exit__() that can be programmed to operate changes into the global context. This technique offers more precision than Perl's local construct, since the enter and exit methods are free to implement any kind of computation; however it is less general, because each context manager is specialized for a specific task. Python's contextlib library provides a collection of context managers for common needs.

Wrapping up

Perl's local mechanism is often misunderstood. It is frowned upon because it breaks encapsulation - and this criticism is perfectly legitimate as far as regular programming tasks are concerned; but on the other hand, it is a powerful and clean mechanism for temporary changes to the global execution state. It solves real problems with surprising grace, and it’s one of the features that makes Perl uniquely expressive among modern languages. So do not follow the common advice to avoid local at all costs, but learn to identify the situations where local will be a helpful tool to you!

Beyond the mere mechanism, the question is more at the level of philosophy of programming: to which extent should we enforce strict encapsulation of components? In an ideal world, each component has a well-defined interface, and interactions are only allowed to go through the official interfaces. But in a big assembly of components, we may encounter situations that were not foreseen by the designers of the individual components, and require inserting some additional screws, or drilling some additional holes, so that the global assembly works satisfactorily. This is where Perl's local is a beautiful device.

About the cover picture

The cover picture¹ represents a violin with a modified global state: the two intermediate strings are crossed! This is the most spectacular example of scordatura in Heirich Biber's Rosary sonatas (sometimes also called "Mystery sonatas"). Each sonata in the collection requires to tune the violin in a specific way, different from the standard tuning in fifths, resulting in very different atmospheres. It requires some intellectual gymnastics from the player, because the notes written in the score no longer represent the actual sounds heard, but merely refer to the locations of fingers on a normal violin; in other words, this operation is like monkey-patching a violin!

1. CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=110521795 ↩

This week, I challenged myself to write small but meaningful Perl programs for Weekly Challenge — focusing on clean logic, edge cases, and test-driven validation.

Sometimes, the simplest problems teach the strongest lessons.

Challenge 1: Text Justifier (Centering Text with Custom Padding)

Problem Statement
Write a script to return the string that centers the text within that width using asterisks * as padding.

If the string length is greater than or equal to the width, return the string as-is.

Example
Input:

("Hi", 5)

Output:

*Hi**

Implementation Highlights

• Calculated total padding required.
• Split padding evenly left and right.
• Handled odd padding differences correctly.
• Covered edge cases like:
  • Empty string
  • Width equal to string length
  • Width smaller than string length

Key Logic

my $pad_total = $width - $len;
my $left_pad = int($pad_total / 2);
my $right_pad = $pad_total - $left_pad;

This ensures perfect centering even when padding is odd.

What I Learned

• Importance of integer division in layout formatting
• Handling edge cases makes logic robust
• Writing test cases increases confidence immediately

Challenge 2: Word Sorter (Alphabetical Word Sorting)

Problem Statement
Write a script to order words in the given sentence alphabetically but keeps the words themselves unchanged.

Example
Input:

"I have 2 apples and 3 bananas!"

Output:

2 3 and apples bananas! have I

Implementation Highlights

• Split words using whitespace regex
• Used Perl’s built-in sort
• Rejoined words with single spaces
• Managed multiple spaces correctly

Core Logic

my @words = split /\s+/, $str;
return join ' ', sort @words;

Simple. Elegant. Effective.

What I Learned

• Perl’s sort is powerful and concise
• Regex-based splitting handles messy input cleanly
• Even small scripts benefit from structured testing

PAGI 0.001017 is on CPAN. The headline feature is HTTP/2 support in PAGI::Server, built on the nghttp2 C library and validated against h2spec's conformance suite. HTTP/2 is marked experimental in this release -- the protocol works, the compliance numbers are solid, and we want production feedback before dropping that label.

This post focuses on why h2c (cleartext HTTP/2) between your reverse proxy and backend matters, and how PAGI::Server implements it.

The Quick Version

# Install the HTTP/2 dependency
cpanm Net::HTTP2::nghttp2

# Run with HTTP/2 over TLS
pagi-server --http2 --ssl-cert cert.pem --ssl-key key.pem app.pl

# Run with cleartext HTTP/2 (h2c) -- behind a proxy
pagi-server --http2 app.pl

Your app code doesn't change. HTTP/2 is a transport concern handled entirely by the server. The same async handlers that serve HTTP/1.1 serve HTTP/2 without modification.

"I Have nginx in Front, Why Do I Care?"

If nginx terminates TLS and speaks HTTP/2 to clients, why does the backend need HTTP/2 too?

The answer is h2c -- cleartext HTTP/2 between your proxy and your application server. No TLS overhead, but all of HTTP/2's protocol benefits on the internal hop: stream multiplexing over a single TCP connection, HPACK header compression (especially effective for repetitive internal headers like auth tokens and tracing IDs), and per-stream flow control so a slow response on one stream doesn't block others.

The practical wins: fewer TCP connections between proxy and backend (one multiplexed h2c connection replaces a pool of HTTP/1.1 connections), less file descriptor and kernel memory pressure, and no TIME_WAIT churn from connection recycling.

Where h2c Matters

gRPC requires HTTP/2 -- it doesn't work over HTTP/1.1 at all. If you're building gRPC services, h2c is mandatory.

API gateway fan-out is where multiplexing shines. When your gateway fans out to 10 backend services per request, h2c means 1-2 connections per backend instead of a pool of 50-100.

Service mesh environments (Envoy/Istio sidecars) default to HTTP/2 between services. A backend that speaks h2c natively means one less protocol translation.

A Note on Proxies

Not all proxies handle h2c equally:

• Envoy has the best h2c upstream support with full multiplexing
• Caddy makes it trivial: reverse_proxy h2c://localhost:8080
• nginx supports h2c via grpc_pass for gRPC workloads, but its generic proxy_pass doesn't support proxy_http_version 2.0

For full multiplexing to backends, Envoy or Caddy are better choices than nginx today.

HTTP/2 Over TLS -- No Proxy Required

h2c isn't the only mode. PAGI::Server also does full HTTP/2 over TLS with ALPN negotiation:

pagi-server --http2 --ssl-cert cert.pem --ssl-key key.pem app.pl

This is useful when you don't want the overhead or complexity of a reverse proxy -- internal tools, admin dashboards, development servers, or any app where the traffic doesn't justify a separate proxy layer. Browsers get HTTP/2 directly, with TLS, no nginx required.

What PAGI::Server Does

Dual-Mode Protocol Detection

With TLS, PAGI::Server uses ALPN negotiation during the handshake -- advertising h2 and http/1.1, letting the client choose. The protocol is decided before the first byte of application data.

Without TLS (h2c mode), PAGI::Server inspects the first 24 bytes of each connection for the HTTP/2 client connection preface. If it matches, the connection upgrades to HTTP/2. If not, it falls through to HTTP/1.1. Both protocols coexist on the same port, same worker -- no configuration needed beyond --http2.

Either way, HTTP/1.1 clients are still served normally. The server handles both protocols on the same port.

WebSocket over HTTP/2 (RFC 8441)

Most HTTP/2 implementations skip this. PAGI::Server supports the Extended CONNECT protocol from RFC 8441, which tunnels WebSocket connections over HTTP/2 streams. Multiple WebSocket connections multiplex over a single TCP connection instead of requiring one TCP connection each.

Compliance

Built on nghttp2 (the same C library behind curl, Firefox, and Apache's mod_http2). PAGI::Server passes 137 of 146 h2spec conformance tests (93.8%). The 9 remaining failures are in nghttp2 itself and shared with every server that uses it. Load tested with h2load at 60,000 requests across 50 concurrent connections with no data loss or protocol violations.

Full test-by-test results are published: HTTP/2 Compliance Results.

Multi-Worker and Tunable

HTTP/2 works in multi-worker prefork mode. Each worker independently handles HTTP/2 sessions:

pagi-server --http2 --workers 4 app.pl

Protocol settings are exposed for environments that need fine-tuning:

my $server = PAGI::Server->new(
    app   => $app,
    http2 => 1,
    h2_max_concurrent_streams => 50,   # default: 100
    h2_initial_window_size => 131072,  # default: 65535
    h2_max_frame_size => 32768,        # default: 16384
    h2_max_header_list_size => 32768,  # default: 65536
);

Most deployments won't need to touch these. The defaults follow the RFC recommendations.

Context in the Perl Ecosystem

Perl has had HTTP/2 libraries on CPAN (Protocol::HTTP2, Net::HTTP2), but application servers haven't integrated them with validated compliance testing. PAGI::Server is the first to publish h2spec results and ship h2c with automatic protocol detection alongside HTTP/1.1. If you're currently running Starman, Twiggy, or Hypnotoad, none of them offer HTTP/2.

What Else Is in 0.001017

The rest of the release is operational improvements:

• Worker heartbeat monitoring -- parent process detects workers with blocked event loops and replaces them via SIGKILL + respawn. Default 50s timeout. Only triggers on true event loop starvation; async handlers using await are unaffected.
• Custom access log format -- format strings with atoms like %a (address), %s (status), %D (duration).
• TLS performance fix -- shared SSL context via SSL_reuse_ctx eliminates per-connection CA bundle parsing. 26x throughput improvement at 8+ concurrent TLS connections.
• SSE wire format fix -- now handles CRLF, LF, and bare CR line endings per the SSE specification.
• Multi-worker fixes -- shutdown escalation, parameter pass-through, and various stability improvements.

Getting Started

# Install PAGI
cpanm PAGI

# Install HTTP/2 support (optional)
cpanm Net::HTTP2::nghttp2

# Run your app with HTTP/2
pagi-server --http2 app.pl

Links

• PAGI 0.001017 on CPAN
• HTTP/2 Compliance Results
• PAGI on GitHub
• h2spec -- HTTP/2 conformance testing tool

It's been a while since I commented on a Weekly Challenge solution, but here we are at week 360. Such a useful number. So divisible, so circular. It deserves twenty minutes.

Task 2: Word Sorter

The task

You are given a sentence. Write a script to order words in the given
sentence alphabetically but keep the words themselves unchanged.

# Example 1 Input: $str = "The quick brown fox"
#           Output: "brown fox quick The"
# Example 2 Input: $str = "Hello    World!   How   are you?"
#           Output: "are Hello How World! you?"
# Example 3 Input: $str = "Hello"
#           Output: "Hello"
# Example 4 Input: $str = "Hello, World! How are you?"
#           Output: "are Hello, How World! you?"
# Example 5 Input: $str = "I have 2 apples and 3 bananas!"
#           Output: "2 3 and apples bananas! have I"

The thoughts

This should be quite simple: split the words, sort them, put them back together. The sort should be case-insensitive.

join " ", sort { lc($a) cmp lc($b) } split(" ", $str);

Creeping doubt #1

Is converting to lowercase with lc the right way to do case-insenstive compares? Not really. Perl has the fc -- fold-case -- function to take care of subtleties in Unicode. We won't see those in simple ASCII text, but for the full rabbit hole, start with the documentation of fc.

Creeping doubt #2

Doing the case conversion inside the sort means that we will invoke that every time there's a string comparison, which will be quite redundant. We could (probably?) speed it up by pre-calculating the conversions once.

The solution

sub sorter($str)
{
    return join " ",
        map { $_->[0] }
        sort { $a->[1] cmp $b->[1] }
        map { [$_, fc($_)] }
        split(" ", $str);
}

This solution uses the idiom of Schwartzian transformation. Every word gets turned into a pair of [original_word, case_folded_word]. That array of pairs gets sorted, and then we select the original words out of the sorted pairs. This is best read bottom-up.

• split(" ", $str) -- turns the string into an array of words, where words are loosely defined by being white-space separated.
• map { [$_, fc($_)] } -- every word turns into a pair: the original, and its case-folded variation. The result is a list of array references.
• sort { $a->[1] cmp $b->[1] } -- sort by the case-folded versions. The result is still a list of array references.
• map { $_->[0] } -- select the original word from each pair
• join " " -- Return a single string, where the words are separated by one space.

Does it blend?

A quick benchmark shows that it is indeed faster to pre-calculate the case folding. This example used a text string of about 60 words.

           Rate oneline  pre_lc
oneline 32258/s      --    -45%
pre_lc  58140/s     80%      --

My intuition says that when the strings are much shorter, the overhead of the transform might not offset the gains in the sort, but as is so often true, my intuition is crap. This is the result for a string of five words:

oneline  470588/s      --    -59%
pre_lc  1142857/s    143%      --