PERL5420DELTA(1)

📦

version 5.42.3 · 8 versions

5.42.3 · fedora 43, fedora 44 (latest)
5.42.0 · opensuse-leap 16.0
5.42.3 · nixpkgs unstable
5.42.2 · alpine 3.23
5.42.3 · alpine 3.24
5.42.3 · ubuntu stonking
5.42.0 · fedora 43
5.42.1 · fedora 44

🎀 perl5420delta — NAME 🎀

okay so this whole page is perl5420delta — literally just "what is new for perl v5.42.0". that's the assignment bestie 💖

🌸 DESCRIPTION 🌸

this doc spills the tea on what changed between the 5.42.0 release and the 5.40.0 release. differences. that's it. that's the vibe. ✨

👑 Core Enhancements 👑

💅 More `CORE::` subs

chdir has been added as a subroutine to the CORE:: namespace. slay.

before this? code like &CORE::chdir($dir) or my $ref = \&CORE::chdir; $ref->($dir) would just throw an error being like "&CORE::chdir cannot be called directly". rude. those cases are now fully supported. periodt. 🫶

🦋 New pragma `source::encoding`

this one lets you declare that the part of a program for the rest of the lexical scope of this pragma is encoded entirely in ASCII (that's use source::encoding 'ascii') or that UTF-8 is allowed too (that's use source::encoding 'utf8'). no other encodings accepted, sorry bestie, we don't do that here. and the second form is entirely equivalent to use utf8 — you can use them interchangeably.

the whole point of this pragma? catching the case early where you forgot to write use utf8. it's giving personal assistant energy ngl.

use source::encoding 'ascii' is automatically enabled within the lexical scope of a use v5.41.0 or higher.

no source::encoding turns off all this checking for the remainder of its lexical scope. and then the meaning of non-ASCII characters is undefined. 😭 so like. don't.

✨ New `:writer` attribute on field variables

classes defined using use feature 'class' can now automatically create writer accessors for scalar fields, using the :writer attribute — same way :reader already creates reader accessors. iconic.

class Point {
    field $x :reader :writer :param;
    field $y :reader :writer :param;
}

my $p = Point->new( x => 20, y => 40 );
$p->set_x(60);

🔥 New `any` and `all` operators

two new experimental features just dropped, introducing the list-processing operators any and all.

use v5.42;
use feature 'keyword_all';
no warnings 'experimental::keyword_all';

my @numbers = ...

if ( all { $_ % 2 == 0 } @numbers ) {
    say "All the numbers are even";
}

these keywords operate similarly to grep except they only ever return true or false — testing if any (or all) of the elements in the list make the testing block yield true. and because of that they can short-circuit, so they don't have to test any further elements once a given element has already determined the eventual result. efficiency queen. 👑

they're inspired by the same-named functions in the List::Util module, except these are implemented as direct core operators, so they perform faster and don't produce an additional subroutine call stack frame for invoking the code block. no cap.

the feature flags enabling these keywords are named keyword_any and keyword_all — named that way to avoid confusion with the ability of the feature module to refer to all of its features by using the :all export tag. [GH #23104](https://github.com/Perl/perl5/issues/23104)

the related experimental warning flags are consequently named experimental::keyword_any and experimental::keyword_all. consistent. we love to see it.

🧚 Apostrophe as a global name separator can be disabled

so this was deprecated in Perl 5.38 and removed as scheduled in perl 5.41.3, but after some discussion it has been reinstated by default. the comeback tour fr fr.

this can be controlled with the apostrophe_as_package_separator feature, which is enabled by default, but is disabled from the 5.41 feature bundle onwards.

if you wanna disable use within your own code you can explicitly disable the feature:

no feature "apostrophe_as_package_separator";

heads up bestie: disabling this feature only prevents use of apostrophe as a package separator within code. symbolic references still treat ' as :: with the feature disabled:

my $symref = "My'Module'Var";
# default features
my $x = $My'Module'Var; # fine
no feature "apostrophe_as_package_separator";
no strict "refs";
my $y = $$symref;       # like $My::Module::Var
my $z = $My'Module'Var; # syntax error

[GH #22644](https://github.com/Perl/perl5/issues/22644)

💜 Lexical method declaration using `my method`

like sub since Perl version 5.18, method can now be prefixed with the my keyword. this declares a subroutine that has lexical visibility rather than package visibility. see perlclass for more detail. 🫶

🌈 Lexical method invocation operator `->&`

along with being able to declare methods lexically, this release also permits invoking a lexical subroutine as if it were a method — bypassing the usual name-based method resolution. the audacity. the power.

combined with lexical method declaration, these two new abilities create the effect of having private methods. main character energy honestly.

⭐ Switch and Smart Match operator kept, behind a feature

the switch feature and the smartmatch operator, ~~, were introduced in v5.10. their behavior was significantly changed in v5.10.1. when the experiment system was added in v5.18.0, switch and smartmatch were retroactively declared experimental. and over the years, proposals to fix or supplement the features have come and gone. the drama.

they were deprecated in Perl v5.38.0 and scheduled for removal in Perl v5.42.0. but after extensive discussion their removal has been indefinitely postponed. and using them no longer produces a deprecation warning. ✨

switch itself still requires the switch feature, which is enabled by default for feature bundles from v5.9.5 through to v5.34. switch remains disabled in feature bundles 5.35 and later, but can be separately enabled:

# no switch here
use v5.10;
# switch here
use v5.36;
# no switch here
use feature "switch";
# switch here

smart match now requires the smartmatch feature, which is enabled by default and included in all feature bundles up to 5.40. it's disabled for the 5.41 feature bundle and later, but can be separately enabled:

# smartmatch here
use v5.41;
# no smartmatch here
use feature "smartmatch";
# smartmatch here

[GH #22752](https://github.com/Perl/perl5/issues/22752)

🌸 Unicode 16.0 supported

Perl now supports Unicode 16.0 <https://www.unicode.org/versions/Unicode16.0.0/> — including the changes introduced in 15.1 <https://www.unicode.org/versions/Unicode15.1.0/>. the glow up is real. 🦋

💅 Assigning logical xor `^^=` operator

Perl 5.40.0 introduced the logical medium-precedence exclusive-or operator ^^. it was not noticed at the time that the assigning variant ^^= was also missing. 🙈 this is now added. better late than never bestie.

🚨 Security 🚨

💀 [CVE-2024-56406] Heap buffer overflow vulnerability with `tr//`

a heap buffer overflow vulnerability was discovered in Perl. 😭

when there are non-ASCII bytes in the left-hand-side of the tr operator, S_do_trans_invmap() can overflow the destination pointer d.

$ perl -e '$_ = "\x{FF}" x 1000000; tr/\xFF/\x{100}/;'
Segmentation fault (core dumped)

it is believed that this vulnerability can enable Denial of Service or Arbitrary Code Execution attacks on platforms that lack sufficient defenses.

this problem was discovered by Nathan Mills and assigned [CVE-2024-56406](https://lists.security.metacpan.org/cve-announce/msg/28708725/) by the [CPAN Security Group](https://security.metacpan.org/).

the patch to fix this issue (87f42aa0e0096e9a346c9672aa3a0bd3bef8c1dd <https://github.com/Perl/perl5/commit/87f42aa0e0096e9a346c9672aa3a0bd3bef8c1dd>) is applicable to all perls that are vulnerable — including those out-of-support. so like, patch it. pls.

🔥 [CVE-2025-40909] Perl threads have a working directory race condition where file operations may target unintended paths

Perl thread cloning had a working directory race condition where file operations may target unintended paths. Perl 5.42 will no longer chdir to each handle. fixed and functioning. 💅

this problem was discovered by Vincent Lefèvre via [GH #23010](https://github.com/Perl/perl5/issues/23010) and assigned [CVE-2025-40909](https://lists.security.metacpan.org/cve-announce/msg/30017499/) by the [CPAN Security Group](https://security.metacpan.org/).

fixes were provided via [GH #23019](https://github.com/Perl/perl5/pull/23019) and [GH #23361](https://github.com/Perl/perl5/pull/23361).

😭 Incompatible Changes 😭

🫶 Removed containing function references for functions without `eval`

Perl 5.40 reintroduced unconditional references from functions to their containing functions — to fix a bug introduced in Perl 5.18 that broke the special behaviour of eval EXPR in package DB, which is what the debugger uses.

but in some cases this change led to circular reference chains between closures and other existing references, resulting in memory leaks. not the vibe.

this change has been reverted — fixing [GH #22547](https://github.com/Perl/perl5/issues/22547) but re-breaking [GH #19370](https://github.com/Perl/perl5/issues/19370). we can't have everything bestie.

this means the reference loops won't occur, and that lexical variables and functions from enclosing functions may not be visible in the debugger.

note: calling eval EXPR in a function unconditionally causes a function to reference its enclosing functions — as it always has. that part didn't change. 🫶

✨ Performance Enhancements ✨

okay bestie, let's talk about the speed upgrades because this release is literally glowing up 💅✨

Constant-folded strings are now shareable via the Copy-on-Write mechanism. [GH #22163 <https://github.com/Perl/perl5/pull/22163>]

The following code would previously have allocated eleven string buffers, each containing one million "A"s:

my @scalars; push @scalars, ("A" x 1_000_000) for 0..9;

Now a single buffer is allocated and shared between a CONST OP and the ten scalar elements of @scalars. It's giving efficiency, periodt 🫶

Note that any code using this sort of constant to simulate memory leaks (perhaps in test files) must now permute the string in order to trigger a string copy and the allocation of separate buffers. For example, ("A" x 1_000_000).time might be a suitable small change. So if your leak tests are suddenly not leaking, that's why, bestie 😭

tr/// now runs at the same speed regardless of the internal representation of its operand, as long as the only characters being translated are ASCII-range, for example tr/A-Z/a-z/. Previously, if the internal encoding was UTF-8, a slower, more general implementation was used. Now it's the same speed either way, no cap 🏎️💨
Code that uses the indexed function from the builtin module to generate a list of index/value pairs out of an array or list which is then passed into a two-variable foreach list to unpack those again is now optimised to be more efficient.

my @array = (...);

foreach my ($idx, $val) (builtin::indexed @array) {
    ...
}

foreach my ($idx, $val) (builtin::indexed LIST...) {
    ...
}

In particular, a temporary list twice the size of the original is no longer generated. Instead, the loop iterates down the original array or list in-place directly, in the same way that foreach (@array) or foreach (LIST) would do. Lowkey saving so much memory, we love to see it 🎀

The peephole optimizer recognises the following zero-offset substr patterns and swaps in a new dedicated operator (OP_SUBSTR_LEFT). [GH #22785 <https://github.com/Perl/perl5/issues/22785>]

substr($x, 0, ...)
substr($x, 0, ..., '')

The stringification of integers by print in perlfunc and say in perlfunc, when coming from an SVt_IV, is now more efficient. [GH #22927 <https://github.com/Perl/perl5/issues/22927>] — faster printing, we love that for us 💅
String reversal from a single argument, when the string buffer is not swiped, is now done in a single pass and is noticeably faster. The extent of the improvement is compiler & hardware dependent. [GH #23012 <https://github.com/Perl/perl5/issues/23012>] — your reverse() is now speedier, but your mileage may vary, bestie 🧚

📦 Modules and Pragmata 📦

Updated Modules and Pragmata

okay so a whole bunch of modules got glow-ups, and we're obsessed. Here's the full list, no cap:

Archive::Tar has been upgraded from version 3.02_001 to 3.04.
B::Deparse has been upgraded from version 1.76 to 1.85.
Benchmark has been upgraded from version 1.25 to 1.27.
builtin has been upgraded from version 0.014 to 0.019.
Compress::Raw::Bzip2 has been upgraded from version 2.212 to 2.213.
Compress::Raw::Zlib has been upgraded from version 2.212 to 2.213.
Config::Perl::V has been upgraded from version 0.36 to 0.38.
CPAN has been upgraded from version 2.36 to 2.38.
CPAN::Meta::YAML has been upgraded from version 0.018 to 0.020.
Data::Dumper has been upgraded from version 2.189 to 2.192.
DB has been upgraded from version 1.08 to 1.09.
DBM_Filter has been upgraded from version 0.06 to 0.07.
Devel::Peek has been upgraded from version 1.34 to 1.36.
Devel::PPPort has been upgraded from version 3.72 to 3.73.
Digest::MD5 has been upgraded from version 2.58_01 to 2.59.
DynaLoader has been upgraded from version 1.56 to 1.57.
experimental has been upgraded from version 0.032 to 0.035.
Exporter has been upgraded from version 5.78 to 5.79.
ExtUtils::CBuilder has been upgraded from version 0.280240 to 0.280242.
ExtUtils::MakeMaker has been upgraded from version 7.70 to 7.76.
ExtUtils::ParseXS has been upgraded from version 3.51 to 3.57.
ExtUtils::Typemaps has been upgraded from version 3.51 to 3.57.
Fcntl has been upgraded from version 1.18 to 1.20.
feature has been upgraded from version 1.89 to 1.97.
fields has been upgraded from version 2.25 to 2.27.
File::Spec has been upgraded from version 3.90 to 3.94.
Getopt::Long has been upgraded from version 2.57 to 2.58.
HTTP::Tiny has been upgraded from version 0.088 to 0.090.
IO::Compress has been upgraded from version 2.212 to 2.213.
IO::Socket::IP has been upgraded from version 0.42 to 0.43.
IPC::Open3 has been upgraded from version 1.22 to 1.24.
locale has been upgraded from version 1.12 to 1.13.
Math::BigInt has been upgraded from version 2.003002 to 2.005002.
Math::BigInt::FastCalc has been upgraded from version 0.5018 to 0.5020.
Math::Complex has been upgraded from version 1.62 to 1.63.
Memoize has been upgraded from version 1.16 to 1.17.
Module::CoreList has been upgraded from version 5.20240609 to 5.20250702.
NDBM_File has been upgraded from version 1.17 to 1.18.
ODBM_File has been upgraded from version 1.18 to 1.20.
Opcode has been upgraded from version 1.65 to 1.69.
overload has been upgraded from version 1.37 to 1.40.
parent has been upgraded from version 0.241 to 0.244.
perlfaq has been upgraded from version 5.20240218 to 5.20250619.
Pod::Usage has been upgraded from version 2.03 to 2.05.
podlators has been upgraded from version 5.01_02 to v6.0.2.
POSIX has been upgraded from version 2.20 to 2.23.
re has been upgraded from version 0.47 to 0.48.
Safe has been upgraded from version 2.46 to 2.47.
Scalar::Util has been upgraded from version 1.63 to 1.68_01.
Search::Dict has been upgraded from version 1.07 to 1.08.
SelfLoader has been upgraded from version 1.27 to 1.28.
sort has been upgraded from version 2.05 to 2.06.
Storable has been upgraded from version 3.32 to 3.37.
strict has been upgraded from version 1.13 to 1.14.
Term::Table has been upgraded from version 0.018 to 0.024.
Test::Harness has been upgraded from version 3.48 to 3.50.
Test::Simple has been upgraded from version 1.302199 to 1.302210.
Thread has been upgraded from version 3.05 to 3.06.
threads has been upgraded from version 2.40 to 2.43.
threads::shared has been upgraded from version 1.69 to 1.70.
Tie::File has been upgraded from version 1.09 to 1.10.
Tie::RefHash has been upgraded from version 1.40 to 1.41.
Time::HiRes has been upgraded from version 1.9777 to 1.9778.
Time::Piece has been upgraded from version 1.3401_01 to 1.36.
Unicode::UCD has been upgraded from version 0.78 to 0.81.
utf8 has been upgraded from version 1.25 to 1.27.
version has been upgraded from version 0.9930 to 0.9933.
VMS::Filespec has been upgraded from version 1.13 to 1.15.
warnings has been upgraded from version 1.69 to 1.74.
Win32 has been upgraded from version 0.59 to 0.59_01.
XS::APItest has been upgraded from version 1.36 to 1.43.

📚 Documentation 📚

Changes to Existing Documentation

We have attempted to update the documentation to reflect the changes listed in this document. If you find any we have missed, open an issue at <https://github.com/Perl/perl5/issues>. Bestie, if you spot something we missed, please tell us, we're not perfect 💖

Additionally, the following selected changes have been made:

perlapi

Combined the documentation for several groups of related functions into single entries.
All forms of gv_fetchmeth() are now documented together.
gv_autoload4 is now documented with gv_autoload_pv and additional notes added. The long Perl_ forms are now listed when available.

perldata

Binary and octal floating-point constants (such as 012.345p-2 and 0b101.11p-1) are now documented. This feature was first introduced in perl 5.22.0 together with hexadecimal floating-point constants and had a few bug fixes in perl 5.28.0, but it was never formally documented. [GH #18664 <https://github.com/Perl/perl5/issues/18664>] — finally documented, we been knew, but now it's official ✨

perlfunc

Clarified the description of ref and reftype in relation to built-in types and class names.
Clarified that perl sort is stable (and has been since v5.8.0).
The recommended alternatives to the rand() function were updated to modern modules recommended by the CPAN Security Group <https://security.metacpan.org/>. [GH #22873 <https://github.com/Perl/perl5/pull/22873>] — rand() is not your bestie for crypto, use these instead 💅

perlgov

The list of Steering Council and Core Team members have been updated, following the conclusion of the latest election on 2024-07-17.

perlguts

Added some description of real AVs compared to fake AVs.
Documentation was updated to reflect that mixing Newx, Renew, and Safefree vs malloc, realloc, and free are not allowed, and mixing pointers between the 2 classes of APIs is not allowed. Updates made in perlguts and perlclib.
Additional caveats have been added to the description of TARG.

perlop

Portions of perlop are supposed to be ordered so that all the operators wth the same precedence are in a single section, and the sections are ordered so that the highest precedence operators appear first. This ordering has now been restored. Other reorganization was done to improve clarity, with more basic operations described before ones that depend on them.
The documentation for here-docs has been cleaned up and reorganized. Indented here-docs were formerly documented separately, now the two types have interwoven documentation which is more compact, and easier to understand.
The documentation of the xor operator has been expanded.
Outdated advice about using relational string operators in UTF-8 locales has been removed. Use Unicode::Collate for the best results, but these operators will give adequate results on many platforms.
Normalized alignment of verbatim sections, fixing how they are displayed by some Pod viewers that strip indentation.

perlvar

Entries for $# and $* have been amended to note that use of them result in a compilation error, not a warning.

🩺 Diagnostics 💅

okay so the tea on diagnostic output — that's warnings AND fatal error messages btw — is that it got some additions and changes. for the complete list of every diagnostic message ever, go peek at perldiag, bestie. 🫶

New Diagnostics ✨

New Errors 🚨

Use of non-ASCII character 0x%X illegal when 'use source::encoding "ascii"' is in effect

(F) this pragma literally just forbids non-ASCII characters inside its scope. that's it, that's the whole vibe. no non-ASCII for you. 💀

Undefined subroutine &%s called, close to label '%s'

(F) the sub you're calling hasn't been defined, or it was defined and then got undefined since. rude of it, honestly.

this error can also mean you typo'd your package separator — like you typed a single colon when you needed two. for example, Foo:bar() would get parsed as the label "Foo" followed by an unqualified function name: foo: bar(). [GH #22860 <https://github.com/Perl/perl5/issues/22860>]

New Warnings ⚠️

__CLASS__ is experimental

(S experimental::class) this one pops off if you use the "__CLASS__" keyword from "use feature 'class'". it's experimental rn and its behaviour may genuinely change in future releases of Perl. living on the edge, we love to see it. 🌈

%s() attempted on handle %s opened with open()

(W io) bestie you called readdir(), telldir(), seekdir(), rewinddir() or closedir() on a handle that was opened with open(). if you wanna traverse a directory's contents with these functions, you gotta open that handle with opendir() instead. periodt. [GH #22394 <https://github.com/Perl/perl5/issues/22394>]

Possible precedence problem between ! and %s

(W precedence) so you wrote something like

    !$x < $y               # parsed as: (!$x) < $y
    !$x eq $y              # parsed as: (!$x) eq $y
    !$x =~ /regex/         # parsed as: (!$x) =~ /regex/
    !$obj isa Some::Class  # parsed as: (!$obj) isa Some::Class

but bc "!" has higher precedence than comparison operators, "=~", and "isa", Perl reads this as comparing/matching the logical negation of the first operand — instead of negating the result of the comparison/match. not the same thing at all, and it's giving subtle-bug energy. 😭

to disambiguate, either use a negated comparison/binding operator:

    $x >= $y
    $x ne $y
    $x !~ /regex/

... or parentheses:

    !($x < $y)
    !($x eq $y)
    !($x =~ /regex/)
    !($obj isa Some::Class)

... or the low-precedence "not" operator:

    not $x < $y
    not $x eq $y
    not $x =~ /regex/
    not $obj isa Some::Class

(if you did mean to compare the boolean result of negating the first operand, parenthesize as "(!$x) < $y", "(!$x) eq $y", etc.) 🎀

note: this warning does not trigger for code like "!!$x == $y" — i.e. where double negation ("!!") is being used as a convert-to-boolean operator. iconic exception, no notes. 💅

Changes to Existing Diagnostics 🔁

%s() attempted on invalid dirhandle %s

this got consolidated from separate messages for readdir(), telldir(), seekdir(), rewinddir() and closedir() as part of the refactoring for [GH #22394 <https://github.com/Perl/perl5/issues/22394>]. glow-up fr. ✨

Useless use of %s in void context

this warning now triggers for use of a chained comparison like "0 < $x < 1". [GH #22969 <https://github.com/Perl/perl5/issues/22969>]

Use of uninitialized value%s

this no longer fires when you access a function parameter in @_ that's an lvalue reference to an untied hash element where the key was undefined. the warning still gets produced at the point of call, tho. [GH #22423 <https://github.com/Perl/perl5/issues/22423>]

🛠️ Utility Changes 🛠️

`Porting/test-dist-modules.pl` 📦

separate installation (like, without overwriting installed modules) is now the default. 🎀
documentation got significantly enhanced. she's got lore now. 👑

⚙️ Configuration and Compilation ⚙️

fixed compilation on platforms (e.g. "Gentoo Prefix") that only have a C locale [GH #22569 <https://github.com/Perl/perl5/issues/22569>] — bug first reported downstream at bugs.gentoo.org/939014 <https://bugs.gentoo.org/939014> 🐧
the (mostly undocumented) configuration macro "PERL_STRICT_CR" has been removed. when it was enabled (e.g. with "./Configure -A ccflags=-DPERL_STRICT_CR"), it would make the perl parser throw a fatal error whenever it hit a CR (carriage return) character in source files. the default — and now the only — behavior of the perl parser is to strip CRs that are paired with newline characters, and otherwise treat them as whitespace. bye bestie 🫶

("PERL_STRICT_CR" was originally introduced in perl 5.005 to optionally restore backward compatibility with perl 5.004, which had made CR in source files an error. before that, CR was accepted, but retained literally in quoted multi-line constructs such as here-documents — even at the end of a line. the history is giving deep lore. 📜)

similarly, the (even less documented) configuration macro "PERL_CR_FILTER" has been removed. when enabled, it would install a default source filter to strip carriage returns from source code before the parser proper even got to see it. gone, but not forgotten. 💀

🧪 Testing 🧪

tests were added and changed to reflect all the other additions and changes in this release. furthermore, these significant changes were made:

a new t/run/todo.t test script was added as a place for TODO tests for known unfixed bugs. patches are welcome to add to this file — come thru, contributors! 🫶
added testing of the perl headers against the C++ compiler corresponding to the C compiler perl is being built with. [GH #22232 <https://github.com/Perl/perl5/issues/22232>] 🔥

🌍 Platform Support 🌍

Platform-Specific Notes 📝

arm64 Darwin 🍎

fix arm64 darwin hints when using use64bitall with Configure [GH #22672 <https://github.com/Perl/perl5/issues/22672>]

Android 🤖

changes to perl_langinfo.h for Android [GH #22650 <https://github.com/Perl/perl5/issues/22650>] related to [GH #22627 <https://github.com/Perl/perl5/issues/22627>].

Cygwin 🐧

cygwin.c: fix several silly/terrible C errors. [GH #22724 <https://github.com/Perl/perl5/issues/22724>] we love a bug-fix moment 💅
supply an explicit base address for "cygperl*.dll" that cannot conflict with those generated by "--enable-auto-image-base". [GH #22695 <https://github.com/Perl/perl5/issues/22695>][GH #22104 <https://github.com/Perl/perl5/issues/22104>]

MacOS (Darwin) 🍏

collation of strings using locales on MacOS 15 (Darwin 24) and up has been turned off due to a failed assertion in its libc. 😭

if earlier versions are also experiencing issues (such as failures in locale.t), you can explicitly disable locale collation by adding the "-Accflags=-DNO_LOCALE_COLLATE" option to your invocation of "./Configure", or just "-DNO_LOCALE_COLLATE" to the "ccflags" and "cppflags" variables in config.sh.

🛠️ INTERNAL CHANGES 🛠️

okay this section is the behind-the-scenes lore bestie, the stuff core hackers and XS devs live for 💅 strap in, it's long but it's so worth it.

"sv_strftime_ints" in perlapi is brand new ✨ — it's a glow-up version of "my_strftime" in perlapi, which is still hanging around for backwards compatibility 🫶. Both of them are meant to call strftime(3) when you've got the year, month, hour, etc. The new one handles UTF8ness for you, and it lets you specify whether you want the possibility of daylight savings time to be considered. my_strftime never considers DST, periodt.
bytes_to_utf8, bytes_from_utf8, and bytes_from_utf8_loc are no longer experimental 🎉 they graduated, they're iconic now.
Calls to call_argv() with the G_DISCARD flag set also make sure the SV parameters constructed from the argv parameter get released before call_argv() returns. Before this, they were released on the next FREETMPS 🙈. [GH #22255 https://github.com/Perl/perl5/issues/22255]
When perl is built with the -DDEBUGGING compile option, perl API functions that take pointers to distinct types of SVs (AVs, HVs or CVs) will check the SvTYPE() of the passed values to make sure they're valid 👀. Also, internal code within core functions that attempts to extract AVs, HVs or CVs from reference values passed in will also perform such checks.

While this has been entirely tested by normal Perl CI testing, there may still be some corner-cases where these constraints are violated in otherwise-valid calls 😭. These may require further investigation if they are found, and specific code to be adjusted to account for it.

op_dump() has been expanded to include additional information about the recent OP_METHSTART and OP_INITFIELD ops, as well as for OP_ARGCHECK and OP_ARGELEM, which had not been done previously 💅.
op_dump() now also has the facility to print extra debugging information about custom operators, if those operators register a helper function via the new xop_dump element of the XOP structure. For more information, see the relevant additions to perlguts 📚.
New API functions are introduced to convert strings encoded in UTF-8 to their ordinal code point equivalent 🦋. These are safe to use by default, and generally more convenient to use than the existing ones.
- "utf8_to_uv" in perlapi and "utf8_to_uv_or_die" in perlapi replace "utf8_to_uvchr" in perlapi (which is retained for backwards compatibility), but you should convert to use the new forms, as likely you aren't using the old one safely 😬.
- To convert in the opposite direction, you can now use "uv_to_utf8" in perlapi. This is not a new function, but a new synonym for "uvchr_to_utf8" in perlapi. It is added so you don't have to learn two sets of names 🧠.
- There are also two new functions, "strict_utf8_to_uv" in perlapi and "c9strict_utf8_to_uv" in perlapi, which do the same thing except when the input string represents a code point that Unicode doesn't accept as legal for interchange, using either the strict original definition (strict_utf8_to_uv), or the looser one given by Unicode Corrigendum #9 (https://www.unicode.org/versions/corrigendum9.html) (c9strict_utf8_to_uv). When the input string represents one of the restricted code points, these functions return the Unicode "REPLACEMENT CHARACTER" instead.
- Also "extended_utf8_to_uv" in perlapi is a synonym for utf8_to_uv, for use when you want to emphasize that the entire range of Perl extended UTF-8 is acceptable ✨.
- There are also replacement functions for the three more specialized conversion functions that you are unlikely to need to use. Again, the old forms are kept for backwards compatibility, but you should convert to use the new forms.
  - "utf8_to_uv_flags" in perlapi replaces "utf8n_to_uvchr" in perlapi.
  - "utf8_to_uv_errors" in perlapi replaces "utf8n_to_uvchr_error" in perlapi.
  - "utf8_to_uv_msgs" in perlapi replaces "utf8n_to_uvchr_msgs" in perlapi.
- Also added are the inverse functions "uv_to_utf8_flags" in perlapi and "uv_to_utf8_msgs" in perlapi, which are synonyms for the existing functions, "uvchr_to_utf8_flags" in perlapi and "uvchr_to_utf8_flags_msgs" in perlapi respectively. These are provided only so you don't have to learn two sets of names 🫶.
Three new API functions are introduced to convert strings encoded in UTF-8 to native bytes format (if possible) 🔄. These are easier to use than the existing ones, and they avoid unnecessary memory allocations. The functions are "utf8_to_bytes_overwrite" in perlapi, which is used when it is ok for the input string to be overwritten with the converted result; and "utf8_to_bytes_new_pv" in perlapi and "utf8_to_bytes_temp_pv" in perlapi, for when the original string must be preserved intact. "utf8_to_bytes_temp_pv" returns the result in a temporary using perlapi/"SAVEFREEPV" that will automatically be destroyed 🧚. With utf8_to_bytes_new_pv, you are responsible for freeing the newly allocated memory that is returned if the conversion is successful.

The latter two functions are designed to replace "bytes_from_utf8" in perlapi, which creates memory unnecessarily, or unnecessarily large 💀.

New API functions valid_identifier_pve(), valid_identifier_pvn() and valid_identifier_sv() have been added, which test if a string would be considered by Perl to be a valid identifier name ✅.
When assigning from an SVt_IV into a SVt_NV (or vice versa), providing that both are "bodyless" types, Perl_sv_setsv_flags will now just change the destination type to match the source type 🎯. Previously, an SVt_IV would have been upgraded to a SVt_PVNV to store an NV, and an SVt_NV would have been upgraded to a SVt_PVIV to store an IV. This change prevents the need to allocate — and later free — the relevant body struct 🚮.
Two new API functions are introduced to convert strings encoded in native bytes format to UTF-8 🌈. These return the string unchanged if its UTF-8 representation is the same as the original. Otherwise, new memory is allocated to contain the converted string. This is in contrast to the existing "bytes_to_utf8" in perlapi, which always allocates new memory. The new functions are "bytes_to_utf8_free_me" in perlapi and "bytes_to_utf8_temp_pv" in perlapi. "bytes_to_utf8_temp_pv" in perlapi arranges for the new memory to automatically be freed 🧚. With bytes_to_utf8_free_me, you are responsible for freeing any newly allocated memory.
The way that subroutine signatures are parsed by the parser grammar has been changed 👑.

Previously, when parsing individual signature parameters, the parser would accumulate an OP_ARGELEM optree fragment for each parameter on the parser stack, collecting them in an OP_LIST sequence, before finally building the complete argument handling optree itself, in a large action block defined directly in perly.y.

In the new approach, all the optree generation is handled by newly-defined functions in op.c which are called by the action blocks in the parser. These do not keep state on the parser stack, but instead in a dedicated memory structure referenced by the main PL_parser structure. This is intended to be largely opaque to other code, and accessed only via the new functions.

This new arrangement is intended to allow more flexible code generation and additional features to be developed in the future 🔮.

Three new API functions have been added to interact with the regexp global match position stored in an SV 💜. These are sv_regex_global_pos_get(), sv_regex_global_pos_set() and sv_regex_global_pos_clear(). Using these API functions avoids XS modules needing to know about or interact directly with the way this position is currently stored, which involves the PERL_MAGIC_regex_global magic type.
New SvVSTRING API macro 🎀

A new API macro has been added, which is used to obtain the second string buffer out of a vstring SV, in a manner similar to the SvPV macro which obtains the regular string buffer out of a regular SV.

STRLEN len;
const char *vstr_pv = SvVSTRING(sv, vstr_len);

See "SvVSTRING" in perlapi.

✨ Selected Bug Fixes ✨

Fix null pointer dereference in S_SvREFCNT_dec — she was dereferencing nulls like it was a personality trait, but no more bestie 💅 [GH #16627 https://github.com/Perl/perl5/issues/16627].
Fix feature 'class' Segmentation fault in DESTROY — the feature 'class' segfault in DESTROY is gone, periodt ✨ [GH #22278 https://github.com/Perl/perl5/issues/22278].
chdir now returns real booleans (as its documentation describes), not integers. This means the result of a failed chdir now stringifies to '', not '0'. [GH #22365 https://github.com/Perl/perl5/issues/22365]
Compound assignment operators return lvalues that can be further modified:

($x &= $y) += $z;
# Equivalent to:
#  $x &= $y;
#  $x += $z;

However, the separate numeric/string bitwise operators provided by the bitwise feature, &= ^= |= &.= ^.= |.=, did not return such lvalues:

use feature qw(bitwise);
($x &= $y) += $z;
# Used to die:
#  Can't modify numeric bitwise and (&) in addition (+) at ...

This has been corrected. [GH #22412 https://github.com/Perl/perl5/issues/22412]

Starting in v5.39.8, strftime in POSIX would crash or produce odd errors (such as Out of memory in perl:util:safesysmalloc) when given a format string that wasn't actually a string, but a number, undef, or an object (even one with overloaded string conversion). Now strftime stringifies its first argument, as before. [GH #22498 https://github.com/Perl/perl5/issues/22498] Also, fix POSIX::strftime() [GH #22369 https://github.com/Perl/perl5/issues/22369].
pack("p", ...) and pack("P", ...) now SvPV_force() the supplied SV unless it is read only. This will remove CoW from the SV and prevents code that writes through the generated pointer from modifying the value of other SVs that happen the share the same CoWed string buffer. Note: this does not make pack("p",... ) safe, if the SV is magical then any writes to the buffer will likely be discarded on the next read. [GH #22380 https://github.com/Perl/perl5/issues/22380]
Enforce no feature "bareword_filehandles" for bareword file handles that have strictness removed because they are used in open() with a dup mode, such as in open my $fh, ">&", THISHANDLE. [GH #22568 https://github.com/Perl/perl5/issues/22568]
Using goto to tail call, or using the call_sv() and related APIs to call, any of trim(), refaddr(), reftype(), ceil(), floor() or stringify() in the builtin:: package would crash or assert due to a TARG handling bug. [GH #22542 https://github.com/Perl/perl5/issues/22542]
Fix sv_gets() to accept a SSize_t append offset instead of I32. This prevents integer overflows when appending to a large SV for readpipe aka qx// and readline. https://www.perlmonks.org/?node_id=11161665
Fixed an issue where utf8n_to_uvchr failed to correctly identify certain invalid UTF-8 sequences as invalid. Specifically, sequences that start with continuation bytes or unassigned bytes could cause unexpected behavior or a panic. This fix ensures that such invalid sequences are now properly detected and handled. This correction also resolves related issues in modules that handle UTF-8 processing, such as Encode.pm.
The perl parser would erroneously parse some POD directives as if they were =cut. Some other POD directives whose names start with cut, prematurely terminating an embedded POD section. The following cases were affected: cut followed by a digit (e.g. =cut2studio), cut followed by an underscore (e.g. =cut_grass), and in string eval, any identifier starting with cut (e.g. =cute). [GH #22759 https://github.com/Perl/perl5/issues/22759]
Builds with -msse and quadmath on 32-bit x86 systems would crash with a misaligned access early in the build. [GH #22577 https://github.com/Perl/perl5/issues/22577]
On threaded builds on POSIX-like systems, if the perl signal handler receives a signal, we now resend the signal to the main perl thread. Previously this would crash. [GH #22487 https://github.com/Perl/perl5/issues/22487]
Declaring a lexically scoped array or hash using state within a subroutine and then immediately returning no longer triggers a Bizarre copy of HASH/ARRAY in subroutine exit error. [GH #18630 https://github.com/Perl/perl5/issues/18630]
builtin::trim() didn't properly clear TARG which could result in out of date cached numeric versions of the value being used on a second evaluation. Properly clear any cached values. [GH #22784 https://github.com/Perl/perl5/issues/22784]
shmread in perlfunc and shmwrite in perlfunc are no longer limited to 31-bit values and can use all the available bits on a platform for their POS and SIZE arguments. [GH #22895 https://github.com/Perl/perl5/issues/22895]
shmread in perlfunc is now better behaved if VAR is not a plain string. If VAR is a tied variable, it calls STORE once; previously, it would also call FETCH, but without using the result. If VAR is a reference, the referenced entity has its refcount properly decremented when VAR is turned into a string; previously, it would leak memory. [GH #22898 https://github.com/Perl/perl5/issues/22898]
The $SIG{__DIE__} and $SIG{__WARN__} handlers can no longer be invoked recursively, either deliberately or by accident, as described in %SIG in perlvar. That is, when an exception (or warning) triggers a call to a $SIG{__DIE__} (or $SIG{__WARN__}) handler, further exceptions (or warnings) are processed directly, ignoring %SIG until the original $SIG{__DIE__} (or $SIG{__WARN__}) handler call returns. [GH #14527 https://github.com/Perl/perl5/issues/14527], [GH #22984 https://github.com/Perl/perl5/issues/22984], [GH #22987 https://github.com/Perl/perl5/issues/22987]
The ObjectFIELDS() for an object and xhv_class_fields for the object's stash weren't always NULL or not-NULL, confusing sv_dump() (and hence Devel::Peek's Dump()) into crashing on an object with no defined fields in some cases. [GH #22959 https://github.com/Perl/perl5/issues/22959]
When comparing strings when using a UTF-8 locale, the behavior was previously undefined if either or both contained an above-Unicode code point, such as 0x110000. Now all such code points will collate the same as the highest Unicode code point, U+10FFFF. [GH #22989 https://github.com/Perl/perl5/issues/22989]
In regexes, the contents of \g{...} backreferences are now properly validated. Previously, \g{1 FOO} was silently parsed as \g{1}, ignoring everything after the first number. [GH #23050 https://github.com/Perl/perl5/issues/23050]
A run-time pattern which contained a code block which recursed back to the same bit of code which ran that match, could cause a crash. [GH #22869 https://github.com/Perl/perl5/issues/22869] For example:

my $r = qr/... (?{ foo() if ... }) .../;
sub foo { $string =~ $r }
foo()

In some cases an eval would not add integer parts to the source lines saved by the debugger. [GH #23151 https://github.com/Perl/perl5/issues/23151]
In debugging mode, perl saves source lines from all files (plus an indication of whether each line is breakable) for use by the debugger. The internal storage format has been optimized to use less memory. This should save 24 bytes per stored line for 64-bit systems, more for -Duselongdouble or -Dusequadmath builds. Discussed in [GH #23171 https://github.com/Perl/perl5/issues/23171].
Ensure cloning the save stack for fork emulation doesn't duplicate freeing the RExC state. [GH #23022 https://github.com/Perl/perl5/issues/23022]
Smartmatch against a code reference that uses a loop exit such as last would crash perl. [GH #16608 https://github.com/Perl/perl5/issues/16608]
Class initializers and ADJUST blocks, per perlclass, that called last or other loop exits would crash perl. Same cause as for [GH #16608 https://github.com/Perl/perl5/issues/16608].
Exceptions thrown and caught entirely within a defer {} or finally {} block no longer stop the outer run-loop. Code such as the following would stop running the contents of the defer block once the inner exception in the inner try/catch block was caught. This has now been fixed, and runs as expected. ([GH #23064 https://github.com/Perl/perl5/issues/23064]).

defer {
    try { die "It breaks\n"; }
    catch ($e) { warn $e }

    say "This line would never run";
}

readline in perlfunc now clears the error flag if an error occurs when reading and that error is EAGAIN or EWOULDBLOCK. This allows code that depended on readline to clear all errors to ignore these relatively harmless errors. [GH #22883 https://github.com/Perl/perl5/issues/22883]
open automatically creates an anonymous temporary file when passed undef as a filename:

open(my $fh, "+>", undef) or die ...

This is supposed to work only when the undefined value is the one returned by the undef function.

In perls before 5.41.3, this caused a problem due to the fact that the same undefined value can be generated by lookups of non-existent hash keys or array elements, which can lead to bugs in user-level code (reported as [GH #22385 https://github.com/Perl/perl5/issues/22385]).

In 5.41.3, additional checks based on the syntax tree of the call site were added, which fixed this issue for some number of common cases, though not all of them, at the cost of breaking the ability of APIs that wrap open to expose its anonymous file mode. A notable example of such an API is autodie.

This release reverts to the old problem in preference to the new one for the time being.

🕊️ Obituaries

💜 Abe Timmerman

Abe Timmerman (ABELTJE) passed away on August 15, 2024.

Since 2002, Abe built and maintained the Test::Smoke project: "a set of scripts and modules that try to run the Perl core tests on as many configurations as possible and combine the results into an easy to read report". Smoking Perl on as many platforms and configurations as possible has been instrumental in finding bugs and developing patches for those bugs.

Abe was a regular attendee of the Perl Toolchain Summit (née Perl QA Hackathon), the Dutch Perl Workshop and the Amsterdam.pm user group meetings. With his kindness, his smile and his laugh, he helped make Perl and its community better.

Abeltje's memorial card said "Grab every opportunity to have a drink of bubbly. This is an opportunity". We'll miss you Abe, and we'll have a drink of bubbly in your honor.

💜 Andrew Main

Andrew Main (ZEFRAM) passed away on March 10, 2025.

Zefram was a brilliant person, seemingly knowledgeable in everything and happy to impart his knowledge and share his striking insights with a gentle, technical demeanor that often failed to convey the genuine care with which he communicated.

It would be impossible to overstate the impact that Zefram has had on both the language and culture of Perl over the years. From his countless contributions to the code-base, to his often quirky but always distinctive appearances at conferences and gatherings, his influence and memory are sure to endure long into the future.

Zefram wished to have no designated memorial location in meatspace. His designated memorial location in cyberspace is <http://www.fysh.org/~zefram/personal/>.

🫶 Acknowledgements

Perl 5.42.0 represents approximately 13 months of development since Perl 5.40.0 and contains approximately 280,000 lines of changes across 1,600 files from 65 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 94,000 lines of changes to 860 .pm, .t, .c and .h files.

Perl continues to flourish into its fourth decade thanks to a vibrant community of users and developers. The following people are known to have contributed the improvements that became Perl 5.42.0:

Aaron Dill, Andrei Horodniceanu, Andrew Ruthven, Antanas Vaitkus, Aristotle Pagaltzis, Branislav Zahradník, brian d foy, Chad Granum, Chris 'BinGOs' Williams, Craig A. Berry, Dabrien 'Dabe' Murphy, Dagfinn Ilmari Mannsåker, Dan Book, Daniel Dragan, Dan Jacobson, David Cantrell, David Mitchell, E. Choroba, Ed J, Ed Sabol, Elvin Aslanov, Eric Herman, Erik Huelsmann, Gianni Ceccarelli, Graham Knop, hbmaclean, H.Merijn Brand, iabyn, James E Keenan, James Raspass, Johan Vromans, Karen Etheridge, Karl Williamson, Leon Timmermans, Lukas Mai, Marek Rouchal, Marin Tsanov, Mark Fowler, Masahiro Honma, Max Maischein, Paul Evans, Paul Johnson, Paul Marquess, Peter Eisentraut, Peter John Acklam, Philippe Bruhat (BooK), pyrrhlin, Reini Urban, Richard Leach, Robert Rothenberg, Robin Ragged, Russ Allbery, Scott Baker, Sergei Zhmylev, Sevan Janiyan, Sisyphus, Štěpán Němec, Steve Hay, TAKAI Kousuke, Thibault Duponchelle, Todd Rinaldo, Tony Cook, Unicode Consortium, Vladimír Marek, Yves Orton.

The list above is almost certainly incomplete as it is automatically generated from version control history. In particular, it does not include the names of the (very much appreciated) contributors who reported issues to the Perl bug tracker.

Many of the changes included in this version originated in the CPAN modules included in Perl's core. We're grateful to the entire CPAN community for helping Perl to flourish.

For a more complete list of all of Perl's historical contributors, please see the AUTHORS file in the Perl source distribution.

🐛 Reporting Bugs

If you find what you think is a bug, you might check the perl bug database at <https://github.com/Perl/perl5/issues>. There may also be information at <https://www.perl.org/>, the Perl Home Page.

If you believe you have an unreported bug, please open an issue at <https://github.com/Perl/perl5/issues>. Be sure to trim your bug down to a tiny but sufficient test case.

If the bug you are reporting has security implications which make it inappropriate to send to a public issue tracker, then see "SECURITY VULNERABILITY CONTACT INFORMATION" in perlsec for details of how to report the issue. 🙈

💐 Give Thanks

If you wish to thank the Perl 5 Porters for the work we had done in Perl 5, you can do so by running the perlthanks program:

perlthanks

This will send an email to the Perl 5 Porters list with your show of thanks. the way that this is literally just a little love letter option, iconic 💖

👀 SEE ALSO

The Changes file for an explanation of how to view exhaustive details on what changed.
The INSTALL file for how to build Perl.
The README file for general stuff.
The Artistic and Copying files for copyright information.

okay bestie that's the whole entire page, we made it, we're at the end 🎀 This one's documented as perl v5.42.3, dated 2026-08-03, and it lives at PERL5420DELTA(1). go forth and read your deltas, queen 👑 💅

📦 where this page comes from

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