PERL5220DELTA(1)

💖 PERL5220DELTA(1) 💖

okay bestie, so this is the Perl Programmers Reference Guide page for perl5220delta and it's literally the tea on what's new for perl v5.22.0. no cap. 🫶

🌸 NAME 🌸

perl5220delta — what is new for perl v5.22.0

✨ DESCRIPTION ✨

This doc spills all the differences between the 5.20.0 release and the 5.22.0 release. fr fr.

If you're upgrading from an earlier release like 5.18.0, bestie you gotta read perl5200delta first, because that one describes the glow-up from 5.18.0 to 5.20.0. 💅

👑 Core Enhancements 👑

⚡ New bitwise operators ⚡

A brand-new experimental facility just dropped, and it makes the four standard bitwise operators (& | ^ ~) treat their operands consistently as numbers, and it introduces four new dotted operators (&. |. ^. ~.) that treat their operands consistently as strings. The same energy applies to the assignment variants (&= |= ^= &.= |.= ^.=). periodt.

To use this, enable the bitwise feature and disable the experimental::bitwise warnings category. See "Bitwise String Operators" in perlop for details. [GH #14348] <https://github.com/Perl/perl5/issues/14348>. 🦋

💎 New double-diamond operator 💎

<<>> is like <> but uses three-argument open to open each file in @ARGV. This means that each element of @ARGV will be treated as an actual file name, and |foo won't be treated as a pipe open. lowkey iconic.

🌈 New `\b` boundaries in regular expressions 🌈

qr/\b{gcb}/

gcb stands for Grapheme Cluster Boundary. It's a Unicode property that finds the boundary between sequences of characters that look like a single character to a native speaker of a language. Perl has long had the ability to deal with these through the \X regular escape sequence. Now, there's an alternative way of handling these. See \b{}, \b, \B{}, \B in perlrebackslash for details. ✨

qr/\b{wb}/

wb stands for Word Boundary. It's a Unicode property that finds the boundary between words. This is similar to the plain \b (without braces) but is more suitable for natural language processing. It knows, for example, that apostrophes can occur in the middle of words. See \b{}, \b, \B{}, \B in perlrebackslash for details. 💖

qr/\b{sb}/

sb stands for Sentence Boundary. It's a Unicode property to aid in parsing natural language sentences. See \b{}, \b, \B{}, \B in perlrebackslash for details. 🎀

🚫 Non-Capturing Regular Expression Flag 🚫

Regular expressions now support a /n flag that disables capturing and filling in $1, $2, etc inside of groups:

"hello" =~ /(hi|hello)/n; # $1 is not set

This is equivalent to putting ?: at the beginning of every capturing group.

See "n" in perlre for more information. 💅

🔒 `use re 'strict'` 🔒

This applies stricter syntax rules to regular expression patterns compiled within its scope. This will hopefully alert you to typos and other unintentional behavior that backwards-compatibility issues prevent us from reporting in normal regular expression compilations. Because the behavior of this is subject to change in future Perl releases as we gain experience, using this pragma will raise a warning of category experimental::re_strict. See 'strict' in re. 😭

🌍 Unicode 7.0 (with correction) is now supported 🌍

For details on what is in this release, see <http://www.unicode.org/versions/Unicode7.0.0/>. The version of Unicode 7.0 that comes with Perl includes a correction dealing with glyph shaping in Arabic (see <http://www.unicode.org/errata/#current_errata>). 🧚

🗺️ `use locale` can restrict which locale categories are affected 🗺️

It is now possible to pass a parameter to use locale to specify a subset of locale categories to be locale-aware, with the remaining ones unaffected. See "The "use locale" pragma" in perllocale for details. 💜

💰 Perl now supports POSIX 2008 locale currency additions 💰

On platforms that are able to handle POSIX.1-2008, the hash returned by POSIX::localeconv() includes the international currency fields added by that version of the POSIX standard. These are int_n_cs_precedes, int_n_sep_by_space, int_n_sign_posn, int_p_cs_precedes, int_p_sep_by_space, and int_p_sign_posn. slay.

🧠 Better heuristics on older platforms for determining locale UTF-8ness 🧠

On platforms that implement neither the C99 standard nor the POSIX 2001 standard, determining if the current locale is UTF-8 or not depends on heuristics. These are improved in this release. 🌸

🔗 Aliasing via reference 🔗

Variables and subroutines can now be aliased by assigning to a reference:

\$c = \$d;
\&x = \&y;

Aliasing can also be accomplished by using a backslash before a foreach iterator variable; this is perhaps the most useful idiom this feature provides:

foreach \%hash (@array_of_hash_refs) { ... }

This feature is experimental and must be enabled via use feature 'refaliasing'. It will warn unless the experimental::refaliasing warnings category is disabled.

See "Assigning to References" in perlref 🫶

🕵️ `prototype` with no arguments 🕵️

prototype() with no arguments now infers $_. [GH #14376] <https://github.com/Perl/perl5/issues/14376>. 💀

🧊 New `:const` subroutine attribute 🧊

The const attribute can be applied to an anonymous subroutine. It causes the new sub to be executed immediately whenever one is created (i.e. when the sub expression is evaluated). Its value is captured and used to create a new constant subroutine that is returned. This feature is experimental. See "Constant Functions" in perlsub. ⭐

📂 `fileno` now works on directory handles 📂

When the relevant support is available in the operating system, the fileno builtin now works on directory handles, yielding the underlying file descriptor in the same way as for filehandles. On operating systems without such support, fileno on a directory handle continues to return the undefined value, as before, but also sets $! to indicate that the operation is not supported.

Currently, this uses either a dd_fd member in the OS DIR structure, or a dirfd(3) function as specified by POSIX.1-2008. 🔥

🪟 List form of pipe open implemented for Win32 🪟

The list form of pipe:

open my $fh, "-|", "program", @arguments;

is now implemented on Win32. It has the same limitations as system LIST on Win32, since the Win32 API doesn't accept program arguments as a list. 🦋

🔁 Assignment to list repetition 🔁

(...) x ... can now be used within a list that is assigned to, as long as the left-hand side is a valid lvalue. This allows (undef,undef,$foo) = that_function() to be written as ((undef)x2, $foo) = that_function(). periodt. 💅

♾️ Infinity and NaN (not-a-number) handling improved ♾️

Floating point values are able to hold the special values infinity, negative infinity, and NaN (not-a-number). Now we more robustly recognize and propagate the value in computations, and on output normalize them to the strings Inf, -Inf, and NaN.

🔢 Floating point parsing has been improved 🔢

Parsing and printing of floating point values has been improved.

As a completely new feature, hexadecimal floating point literals (like 0x1.23p-4) are now supported, and they can be output with printf "%a". See "Scalar value constructors" in perldata for more details. 💜

💀 Packing infinity or not-a-number into a character is now fatal 💀

Before, when trying to pack infinity or not-a-number into a (signed) character, Perl would warn, and assumed you tried to pack 0xFF; if you gave it as an argument to chr, U+FFFD was returned.

But now, all such actions (pack, chr, and print '%c') result in a fatal error. no cap. 🚨

🧬 Experimental C Backtrace API 🧬

Perl now supports (via a C level API) retrieving the C level backtrace (similar to what symbolic debuggers like gdb do).

The backtrace returns the stack trace of the C call frames, with the symbol names (function names), the object names (like perl), and if it can, also the source code locations (file:line).

The supported platforms are Linux and OS X (some *BSD might work at least partly, but they have not yet been tested).

The feature needs to be enabled with Configure -Dusecbacktrace.

See "C backtrace" in perlhacktips for more information. 🌈

🛡️ Security 🛡️

🛡️ Perl is now compiled with `-fstack-protector-strong` if available 🛡️

Perl has been compiled with the anti-stack-smashing option -fstack-protector since 5.10.1. Now Perl uses the newer variant called -fstack-protector-strong, if available. 💪

🚨 The Safe module could allow outside packages to be replaced 🚨

Critical bugfix: outside packages could be replaced. Safe has been patched to 2.38 to address this. bestie this one is serious. 😭

🧱 Perl is now always compiled with `-D_FORTIFY_SOURCE=2` if available 🧱

The 'code hardening' option called _FORTIFY_SOURCE, available in gcc 4.*, is now always used for compiling Perl, if available.

Note that this isn't necessarily a huge step since in many platforms the step had already been taken several years ago: many Linux distributions (like Fedora) have been using this option for Perl, and OS X has enforced the same for many years. 🔥

💖 INCOMPATIBLE CHANGES 💖

okay bestie, vibe check 🚨 these are the changes that will absolutely break your old code if you're not paying attention. no cap, read carefully. 💅

✨ Subroutine signatures moved before attributes ✨

So the experimental sub signatures feature? When it first showed up in 5.20, it parsed signatures after attributes. But users gave feedback, and now the positioning is moved: signatures happen after the subroutine name (if any) and before the attribute list (if any). It's giving glow-up, fr fr. 🦋

💀 `&` and `\&` prototypes accepts only subs 💀

The & prototype character now accepts only:

anonymous subs (sub {...})
things beginning with \&
an explicit undef

Before, it lowkey also allowed references to arrays, hashes, and lists — which was a whole buggy mess. [GH #2776] <https://github.com/Perl/perl5/issues/2776>. [GH #14186] <https://github.com/Perl/perl5/issues/14186>. [GH #14353] <https://github.com/Perl/perl5/issues/14353>.

Also, the \& prototype used to allow subroutine calls, but now it only allows subroutines: &foo is still permitted as an argument, while &foo() and foo() no longer are. [GH #10633] <https://github.com/Perl/perl5/issues/10633>.

🌸 `use encoding` is now lexical 🌸

The encoding pragma's effect is now limited to lexical scope. This pragma is deprecated, but in the meantime, it could adversely affect unrelated modules that are included in the same program; this change fixes that. iconic behavior tbh.

🍓 List slices returning empty lists 🍓

List slices now return an empty list only if the original list was empty (or if there are no indices). Formerly, a list slice would return an empty list if all indices fell outside the original list; now it returns a list of undef values in that case. [GH #12335] <https://github.com/Perl/perl5/issues/12335>.

🚨 `\N{}` with a sequence of multiple spaces is now a fatal error 🚨

E.g. \N{TOO MANY SPACES} or \N{TRAILING SPACE }. This has been deprecated since v5.18. so yeah, no more extra spaces bestie, it's fatal now. 💀

💅 `use UNIVERSAL '...'` is now a fatal error 💅

Importing functions from UNIVERSAL has been deprecated since v5.12, and is now a fatal error. use UNIVERSAL without any arguments is still allowed. so if you were doing the import thing, it's over. periodt.

🎀 In double-quotish `\cX`, X must now be a printable ASCII character 🎀

In prior releases, failure to do this raised a deprecation warning. now it's a hard requirement, bestie.

🔥 Splitting the tokens `(?` and `(*` in regular expressions is now a fatal compilation error 🔥

These had been deprecated since v5.18. so don't split them, okay? it's giving fatal.

🌈 `qr/foo/x` now ignores all Unicode pattern white space 🌈

The /x regular expression modifier lets the pattern contain white space and comments (both ignored) for readability. Until now, not all the white space characters that Unicode designates for this purpose were handled. The additional ones now recognized are:

U+0085 NEXT LINE
U+200E LEFT-TO-RIGHT MARK
U+200F RIGHT-TO-LEFT MARK
U+2028 LINE SEPARATOR
U+2029 PARAGRAPH SEPARATOR

The use of these characters with /x outside bracketed character classes and when not preceded by a backslash has raised a deprecation warning since v5.18. Now they will be ignored. slay, more readable regexes.

🦋 Comment lines within `(?[ ])` are now ended only by a `\n` 🦋

(?[ ]) is an experimental feature, introduced in v5.18. It operates as if /x is always enabled. But there was a difference: comment lines (following a # character) were terminated by anything matching \R which includes all vertical whitespace, such as form feeds. For consistency, this is now changed to match what terminates comment lines outside (?[ ]), namely a \n (even if escaped), which is the same as what terminates a heredoc string and formats. consistency is key, bestie.

💜 `(?[...])` operators now follow standard Perl precedence 💜

This experimental feature allows set operations in regular expression patterns. Prior to this, the intersection operator had the same precedence as the other binary operators. Now it has higher precedence. This could lead to different outcomes than existing code expects (though the documentation has always noted that this change might happen, recommending fully parenthesizing the expressions). See "Extended Bracketed Character Classes" in perlrecharclass. so parenthesize, bestie, or risk the vibe shift.

👑 Omitting `%` and `@` on hash and array names is no longer permitted 👑

Really old Perl let you omit the @ on array names and the % on hash names in some spots. This has issued a deprecation warning since Perl 5.000, and is no longer permitted. like, ancient behavior, finally gone. 💀

💖 `$!` text is now in English outside the scope of `use locale` 💖

Previously, the text, unlike almost everything else, always came out based on the current underlying locale of the program. (Also affected on some systems is $^E.) For programs that are unprepared to handle locale differences, this can cause garbage text to be displayed. It's better to display text that is translatable via some tool than garbage text which is much harder to figure out. so now it's English by default, iconic.

⭐ `$!` text will be returned in UTF-8 when appropriate ⭐

The stringification of $! and $^E will have the UTF-8 flag set when the text is actually non-ASCII UTF-8. This will enable programs that are set up to be locale-aware to properly output messages in the user's native language. Code that needs to continue the 5.20 and earlier behavior can do the stringification within the scopes of both use bytes and use locale ":messages". Within these two scopes, no other Perl operations will be affected by locale; only $! and $^E stringification. The bytes pragma causes the UTF-8 flag to not be set, just as in previous Perl releases. This resolves [GH #12035] <https://github.com/Perl/perl5/issues/12035>. so if you need the old vibe, use those scopes, iykyk.

🚫 Support for `?PATTERN?` without explicit operator has been removed 🚫

The m?PATTERN? construct, which allows matching a regex only once, previously had an alternative form that was written directly with a question mark delimiter, omitting the explicit m operator. This usage has produced a deprecation warning since 5.14.0. It is now a syntax error, so that the question mark can be available for use in new operators. so the old shortcut? gone. periodt.

💀 defined(@array) and defined(%hash) are now fatal errors 💀

These have been deprecated since v5.6.1 and have raised deprecation warnings since v5.16. now they're fatal, bestie.

🔥 Using a hash or an array as a reference are now fatal errors 🔥

For example, %foo->{"bar"} now causes a fatal compilation error. These have been deprecated since before v5.8, and have raised deprecation warnings since then. so don't do it, it's giving fatal.

💅 Changes to the `*` prototype 💅

The * character in a subroutine's prototype used to allow barewords to take precedence over most, but not all, subroutine names. It was never consistent and exhibited buggy behavior.

Now it has been changed, so subroutines always take precedence over barewords, which brings it into conformity with similarly prototyped built-in functions:

sub splat(*) { ... }
sub foo { ... }
splat(foo); # now always splat(foo())
splat(bar); # still splat('bar') as before
close(foo); # close(foo())
close(bar); # close('bar')

💅 Deprecations 💅

✨ Setting `"${^ENCODING}"` to anything but `"undef"` ✨

okay bestie, so this variable lets Perl scripts be written in an encoding that's not ASCII or UTF-8. no cap, it's giving global chaos: it affects all modules globally, which leads to wrong answers and segmentation faults. New scripts should be written in UTF-8; old scripts should be converted to UTF-8, which is easily done with the piconv utility. periodt.

👀 Use of non-graphic characters in single-character variable names 👀

The syntax for single-character variable names is more lenient than for longer variable names, so the one-character name can be a punctuation character or even invisible (a non-graphic). Perl v5.20 deprecated the ASCII-range controls as such a name. Now, all non-graphic characters that formerly were allowed are deprecated. The practical effect of this occurs only when not under use utf8, and affects just the C1 controls (code points 0x80 through 0xFF), NO-BREAK SPACE, and SOFT HYPHEN.

🧠 Inlining of `"sub () { $var }"` with observable side-effects 🧠

In many cases Perl makes "sub () { $var }" into an inlinable constant subroutine, capturing the value of $var at the time the "sub" expression is evaluated. This can break the closure behavior in those cases where $var is subsequently modified, since the subroutine won't return the changed value. (Note that this all only applies to anonymous subroutines with an empty prototype ("sub ()").)

This usage is now deprecated in those cases where the variable could be modified elsewhere. Perl detects those cases and emits a deprecation warning. Such code will likely change in the future and stop producing a constant.

If your variable is only modified in the place where it is declared, then Perl will continue to make the sub inlinable with no warnings.

sub make_constant {
    my $var = shift;
    return sub () { $var }; # fine
}

sub make_constant_deprecated {
    my $var;
    $var = shift;
    return sub () { $var }; # deprecated
}

sub make_constant_deprecated2 {
    my $var = shift;
    log_that_value($var); # could modify $var
    return sub () { $var }; # deprecated
}

In the second example above, detecting that $var is assigned to only once is too hard to detect. That it happens in a spot other than the "my" declaration is enough for Perl to find it suspicious.

This deprecation warning happens only for a simple variable for the body of the sub. (A "BEGIN" block or "use" statement inside the sub is ignored, because it does not become part of the sub's body.) For more complex cases, such as "sub () { do_something() if 0; $var }" the behavior has changed such that inlining does not happen if the variable is modifiable elsewhere. Such cases should be rare.

✂️ Use of multiple `"/x"` regexp modifiers ✂️

It is now deprecated to say something like any of the following:

qr/foo/xx;
/(?xax:foo)/;
use re qw(/amxx);

That is, now "x" should only occur once in any string of contiguous regular expression pattern modifiers. We do not believe there are any occurrences of this in all of CPAN. This is in preparation for a future Perl release having "/xx" permit white-space for readability in bracketed character classes (those enclosed in square brackets: "[...]").

🚫 Using a NO-BREAK space in a character alias for `"\N{...}"` is now deprecated 🚫

This non-graphic character is essentially indistinguishable from a regular space, and so should not be allowed. See "CUSTOM ALIASES" in charnames.

🌀 A literal `"{"` should now be escaped in a pattern 🌀

If you want a literal left curly bracket (also called a left brace) in a regular expression pattern, you should now escape it by either preceding it with a backslash ("\{") or enclosing it within square brackets "[{]", or by using "\Q"; otherwise a deprecation warning will be raised. This was first announced as forthcoming in the v5.16 release; it will allow future extensions to the language to happen.

💀 Making all warnings fatal is discouraged 💀

The documentation for fatal warnings notes that "use warnings FATAL => 'all'" is discouraged, and provides stronger language about the risks of fatal warnings in general.

🚀 Performance Enhancements 🚀

✨ okay the performance glow-up is real, bestie. lowkey obsessed. here's the tea: ✨

If a method or class name is known at compile time, a hash is precomputed to speed up run-time method lookup. Also, compound method names like "SUPER::new" are parsed at compile time, to save having to parse them at run time.
Array and hash lookups (especially nested ones) that use only constants or simple variables as keys, are now considerably faster. See "Internal Changes" for more details.
"(...)x1", "("constant")x0" and "($scalar)x0" are now optimised in list context. If the right-hand argument is a constant 1, the repetition operator disappears. If the right-hand argument is a constant 0, the whole expression is optimised to the empty list, so long as the left-hand argument is a simple scalar or constant. (That is, "(foo())x0" is not subject to this optimisation.)
"substr" assignment is now optimised into 4-argument "substr" at the end of a subroutine (or as the argument to "return"). Previously, this optimisation only happened in void context.
In "\L...", "\Q...", etc., the extra "stringify" op is now optimised away, making these just as fast as "lcfirst", "quotemeta", etc.
Assignment to an empty list is now sometimes faster. In particular, it never calls "FETCH" on tied arguments on the right-hand side, whereas it used to sometimes.
There is a performance improvement of up to 20% when "length" is applied to a non-magical, non-tied string, and either "use bytes" is in scope or the string doesn't use UTF-8 internally.
On most perl builds with 64-bit integers, memory usage for non-magical, non-tied scalars containing only a floating point value has been reduced by between 8 and 32 bytes, depending on OS.
In "@array = split", the assignment can be optimized away, so that "split" writes directly to the array. This optimisation was happening only for package arrays other than @_, and only sometimes. Now this optimisation happens almost all the time.
"join" is now subject to constant folding. So for example "join "-", "a", "b"" is converted at compile-time to "a-b". Moreover, "join" with a scalar or constant for the separator and a single-item list to join is simplified to a stringification, and the separator doesn't even get evaluated.
qq(@array) is implemented using two ops: a stringify op and a join op. If the "qq" contains nothing but a single array, the stringification is optimized away.
"our $var" and "our($s,@a,%h)" in void context are no longer evaluated at run time. Even a whole sequence of "our $foo;" statements will simply be skipped over. The same applies to "state" variables.
Many internal functions have been refactored to improve performance and reduce their memory footprints. [GH #13659] <https://github.com/Perl/perl5/issues/13659> [GH #13856] <https://github.com/Perl/perl5/issues/13856> [GH #13874] <https://github.com/Perl/perl5/issues/13874>
"-T" and "-B" filetests will return sooner when an empty file is detected. [GH #13686] <https://github.com/Perl/perl5/issues/13686>
Hash lookups where the key is a constant are faster.
Subroutines with an empty prototype and a body containing just "undef" are now eligible for inlining. [GH #14077] <https://github.com/Perl/perl5/issues/14077>
Subroutines in packages no longer need to be stored in typeglobs: declaring a subroutine will now put a simple sub reference directly in the stash if possible, saving memory. The typeglob still notionally exists, so accessing it will cause the stash entry to be upgraded to a typeglob (i.e. this is just an internal implementation detail). This optimization does not currently apply to XSUBs or exported subroutines, and method calls will undo it, since they cache things in typeglobs. [GH #13392] <https://github.com/Perl/perl5/issues/13392>
The functions utf8::native_to_unicode() and utf8::unicode_to_native() (see utf8) are now optimized out on ASCII platforms. There is now not even a minimal performance hit in writing code portable between ASCII and EBCDIC platforms.
Win32 Perl uses 8 KB less of per-process memory than before for every perl process, because some data is now memory mapped from disk and shared between processes from the same perl binary.

📦 Modules and Pragmata 📦

🆙 Updated Modules and Pragmata 🆙

Many of the libraries distributed with perl have been upgraded since v5.20.0. For a complete list of changes, run:

corelist --diff 5.20.0 5.22.0

You can substitute your favorite version in place of 5.20.0, too.

Some notable changes include:

Archive::Tar has been upgraded to version 2.04.

Tests can now be run in parallel.

attributes has been upgraded to version 0.27.

The usage of "memEQs" in the XS has been corrected. [GH #14072] <https://github.com/Perl/perl5/issues/14072>

Avoid reading beyond the end of a buffer. [perl #122629]

B has been upgraded to version 1.58.

It provides a new "B::safename" function, based on the existing "B::GV->SAFENAME", that converts "\cOPEN" to "^OPEN".

Nulled COPs are now of class "B::COP", rather than "B::OP".

"B::REGEXP" objects now provide a "qr_anoncv" method for accessing the implicit CV associated with "qr//" things containing code blocks, and a "compflags" method that returns the pertinent flags originating from the "qr//blahblah" op.

"B::PMOP" now provides a "pmregexp" method returning a "B::REGEXP" object. Two new classes, "B::PADNAME" and "B::PADNAMELIST", have been introduced.

A bug where, after an ithread creation or pseudofork, special/immortal SVs in the child ithread/pseudoprocess did not have the correct class of "B::SPECIAL", has been fixed. The "id" and "outid" PADLIST methods have been added.

B::Concise has been upgraded to version 0.996.

Null ops that are part of the execution chain are now given sequence numbers.

Private flags for nulled ops are now dumped with mnemonics as they would be for the non-nulled counterparts.

B::Deparse has been upgraded to version 1.35.

It now deparses "+sub : attr { ... }" correctly at the start of a statement. Without the initial "+", "sub" would be a statement label.

"BEGIN" blocks are now emitted in the right place like, <em>most</em> of the time bestie — but the change lowkey introduced a regression, so "BEGIN" blocks that show up right before the end of the enclosing block might pop up below it instead. 🙈
- B::Deparse no longer sprinkles bogus local everywhere, like for LIST = tr/a//d. [perl #119815]
- Adjacent use statements don't get accidentally nested anymore when one of them contains a do block. [perl #115066]
- Parenthesised arrays inside lists passed to \ now deparse with their parentheses intact (so \(@a, (@b), @c) keeps the parens around @b), which preserves the flattening behavior of referenced parenthesised arrays. Before this it only worked for a single array: \(@a).
- local our now deparses correctly, our included and everything. ✨
- for($foo; !$bar; $baz) {...} used to deparse without the ! (or not). Fixed, slay.
- Core keywords that clash with lexical subroutines now deparse with the CORE:: prefix.
- foreach state $x (...) {...} now deparses correctly with state and not my.
- our @array = split(...) now deparses correctly with our in the cases where the assignment gets optimized away.
- It now deparses our(LIST) and typed lexical (my Dog $spot) correctly.
- Deparses $#_ as $#_ instead of $#{_}. [GH #14545] https://github.com/Perl/perl5/issues/14545
- BEGIN blocks at the end of the enclosing scope are now deparsed in the right place. [perl #77452]
- BEGIN blocks used to sometimes deparse as __ANON__, but now they're always called BEGIN.
- Lexical subroutines are now fully deparsed. [perl #116553]
- Anything =~ y///r with /r no longer drops the left-hand operand.
- The op trees that make up regexp code blocks are now deparsed for real. Before, it just reused the original string that made up the regular expression — which broke qr/(?{<<heredoc})/ and multiline code blocks, deparsing them wrong. [perl #123217] [perl #115256]
- $; at the end of a statement no longer loses its semicolon. [perl #123357]
- Some cases of subroutine declarations stored in the stash in shorthand form were getting omitted. Not anymore.
- Non-ASCII characters are now consistently escaped in strings instead of only some of the time. (There are still outstanding problems with regular expressions and identifiers that haven't been fixed — so heads up.)
- When prototype sub calls are deparsed with & (like under the -P option), scalar is now added where appropriate, to force the scalar context the prototype implies.
- require(foo()), do(foo()), goto(foo()) and similar constructs with loop controls now deparse correctly. The outer parentheses are not optional.
- Whitespace is no longer escaped in regular expressions, because it was getting wrongly escaped inside (?x:...) sections.
- sub foo { foo() } now deparses with those mandatory parentheses.
- /@array/ now deparses as a regular expression, not just @array.
- /@{-}/, /@{+}/ and $#{1} now deparse with the braces, which are mandatory in these cases.
- When deparsing feature bundles, B::Deparse was emitting no feature; first instead of no feature ':all';. Fixed. 💅
- chdir FH now deparses without quotation marks.
- \my @a now deparses without parentheses. (Parens would flatten the array, bestie, that's the whole thing.)
- system and exec followed by a block now deparse correctly. Before there was a bogus do before the block.
- use constant QR => qr/.../flags followed by "" =~ QR is no longer missing the flags.
- Deparsing BEGIN { undef &foo } with the -w switch enabled started throwing 'uninitialized' warnings back in Perl 5.14. That's fixed now.
- Deparsing calls to subs with a (;+) prototype caused an infinite loop. The (;$ (_) and (;_) prototypes were given the wrong precedence, making foo($a<$b) deparse without the parentheses.
- Deparse now provides a defined state sub in inner subs.
B::Op_private has been added.

B::Op_private gives you the detailed tea ☕ on the flags used in the op_private field of perl opcodes.

bigint, bignum, bigrat have been upgraded to version 0.39.

Documented in CAVEATS that using strings as numbers won't always invoke the big number overloading, plus how to actually invoke it. [rt.perl.org #123064]

Carp has been upgraded to version 1.36.

Carp::Heavy now ignores version mismatches with Carp if Carp is newer than 1.12, since Carp::Heavy's guts got merged into Carp at that point. [GH #13708] https://github.com/Perl/perl5/issues/13708

Carp now handles non-ASCII platforms better.

Off-by-one error fix for Perl < 5.14.

constant has been upgraded to version 1.33.

It now accepts fully-qualified constant names, so you can define constants in packages other than the caller. iconic.

CPAN has been upgraded to version 2.11.

Added support for Cwd::getdcwd() and introduced a workaround for a misbehavior seen on Strawberry Perl 5.20.1.

Fixed the chdir() after building dependencies bug.

Introduced experimental support for plugins/hooks.

Integrated the App::Cpan sources.

Doesn't check recursion on optional dependencies anymore.

Sanity checks META.yml to make sure it contains a hash. [cpan #95271] https://rt.cpan.org/Ticket/Display.html?id=95271

CPAN::Meta::Requirements has been upgraded to version 2.132.

Works around limitations in version::vpp detecting v-string magic, and adds support for the forthcoming ExtUtils::MakeMaker bootstrap version.pm for Perls older than 5.10.0.

Data::Dumper has been upgraded to version 2.158.

Fixes CVE-2014-4330 by adding a configuration variable/option to limit recursion when dumping deep data structures. (Yeah, that's a security thing, take it seriously bestie.)

Changes to resolve Coverity issues. XS dumps incorrectly stored the name of code references stored in a GLOB. [GH #13911] https://github.com/Perl/perl5/issues/13911

DynaLoader has been upgraded to version 1.32.

Removed the dl_nonlazy global if it's unused in Dynaloader. [perl #122926]

Encode has been upgraded to version 2.72.

piconv now has better error handling when the encoding name doesn't exist, and a build breakage when upgrading Encode in perl-5.8.2 and earlier has been fixed.

Building in C++ mode on Windows now works.

Errno has been upgraded to version 1.23.

Added -P to the preprocessor command-line on GCC 5. GCC added extra line directives, which broke parsing of error code definitions. [rt.perl.org #123784]

experimental has been upgraded to version 0.013.

Hardcodes features for Perls older than 5.15.7.

ExtUtils::CBuilder has been upgraded to version 0.280221.

Fixes a regression on Android. [GH #14064] https://github.com/Perl/perl5/issues/14064

ExtUtils::Manifest has been upgraded to version 1.70.

Fixes a bug with maniread()'s handling of quoted filenames and improves manifind() to follow symlinks. [GH #14003] https://github.com/Perl/perl5/issues/14003

ExtUtils::ParseXS has been upgraded to version 3.28.

Only declares file unused if we actually define it. Improves generated RETVAL code generation to avoid repeated references to ST(0). [perl #123278] Broadens and documents the /OBJ$/ to /REF$/ typemap optimization for the DESTROY method. [perl #123418]

Fcntl has been upgraded to version 1.13.

Added support for the Linux pipe buffer size fcntl() commands.

File::Find has been upgraded to version 1.29.

find() and finddepth() will now warn if you pass them inappropriate or misspelled options. (ty bestie 🫶)

File::Glob has been upgraded to version 1.24.

Avoids SvIV() expanding to call get_sv() three times in a few places. [perl #123606]

HTTP::Tiny has been upgraded to version 0.054.

keep_alive is now fork-safe and thread-safe.

IO has been upgraded to version 1.35.

The XS implementation has been fixed for the sake of older Perls.

IO::Socket has been upgraded to version 1.38.

Documents the limitations of the connected() method. [perl #123096]

IO::Socket::IP has been upgraded to version 0.37.

A better fix for subclassing connect(). [cpan #95983] https://rt.cpan.org/Ticket/Display.html?id=95983 [cpan #97050] https://rt.cpan.org/Ticket/Display.html?id=97050

Implements Timeout for connect(). [cpan #92075] https://rt.cpan.org/Ticket/Display.html?id=92075

The libnet collection of modules has been upgraded to version 3.05.

Support for IPv6 and SSL to Net::FTP, Net::NNTP, Net::POP3 and Net::SMTP. Improvements in Net::SMTP authentication.

Locale::Codes has been upgraded to version 3.34.

Fixed a bug in the scripts used to extract data from spreadsheets that stopped the SHP currency code from being found. [cpan #94229] https://rt.cpan.org/Ticket/Display.html?id=94229

New codes have been added. ✨

Math::BigInt has been upgraded to version 1.9997.

Synchronized POD changes from the CPAN release. Math::BigFloat->blog(x) would sometimes return blog(2*x) when the accuracy was greater than 70 digits. The result of Math::BigFloat->bdiv() in list context now satisfies x = quotient * divisor + remainder.

Correct handling of subclasses. [cpan #96254] https://rt.cpan.org/Ticket/Display.html?id=96254 [cpan #96329] https://rt.cpan.org/Ticket/Display.html?id=96329

Module::Metadata has been upgraded to version 1.000026.

Support installations on older perls with an ExtUtils::MakeMaker earlier than 6.63_03.

overload has been upgraded to version 1.26.

A redundant ref $sub check has been removed.

The PathTools module collection has been upgraded to version 3.56.

A warning from the gcc compiler is now avoided when building the XS.

Don't turn leading // into / on Cygwin. [perl #122635]

perl5db.pl has been upgraded to version 1.49.

The debugger would cause an assertion failure. [GH #14605] https://github.com/Perl/perl5/issues/14605

fork() in the debugger under tmux will now create a new window for the forked process. [GH #13602] https://github.com/Perl/perl5/issues/13602

The debugger now saves the current working directory on startup and restores it when you restart your program with R or rerun. bestie it remembers where you were 💖 [GH #13691] <https://github.com/Perl/perl5/issues/13691>
PerlIO::scalar has been upgraded to version 0.22. ✨
- Reading from a position well past the end of the scalar now correctly returns end of file. [perl #123443] no more nonsense past the edge fr
- Seeking to a negative position still fails, but no longer leaves the file position set to a negation location. it still says no, it just doesn't leave your stuff in a weird spot after
- eof() on a PerlIO::scalar handle now properly returns true when the file position is past the 2GB mark on 32-bit systems. 🎀
- Attempting to write at file positions impossible for the platform now fail early rather than wrapping at 4GB. fail early > fail silently at 4GB, periodt
Pod::Perldoc has been upgraded to version 3.25. 💅
- Filehandles opened for reading or writing now have :encoding(UTF-8) set. unicode girlies stay winning [cpan #98019] <https://rt.cpan.org/Ticket/Display.html?id=98019>
POSIX has been upgraded to version 1.53. 🌸
- The C99 math functions and constants (for example acosh, isinf, isnan, round, trunc; M_E, M_SQRT2, M_PI) have been added. math ate
- POSIX::tmpnam() now produces a deprecation warning. ⚠️ it's giving deprecated [perl #122005]
Safe has been upgraded to version 2.39. 🔥
- reval was not propagating void context properly. lowkey a bug, now fixed
Scalar-List-Utils has been upgraded to version 1.41. 🦋
- A new module, Sub::Util, has been added, containing functions related to CODE refs, including subname (inspired by Sub::Identity) and set_subname (copied and renamed from Sub::Name). The use of GetMagic in List::Util::reduce() has also been fixed. [cpan #63211] <https://rt.cpan.org/Ticket/Display.html?id=63211>
SDBM_File has been upgraded to version 1.13. 🍓
- Simplified the build process. [perl #123413] build go brrr
Time::Piece has been upgraded to version 1.29. ⭐
- When pretty printing negative Time::Seconds, the minus is no longer lost. the minus is the main character, we do NOT lose her
Unicode::Collate has been upgraded to version 1.12. 🌈
- Version 0.67's improved discontiguous contractions is invalidated by default and is supported as a parameter long_contraction. iykyk
Unicode::Normalize has been upgraded to version 1.18. ✨
- The XSUB implementation has been removed in favor of pure Perl.
Unicode::UCD has been upgraded to version 0.61. 👑
- A new function property_values() has been added to return a given property's possible values.
- A new function charprop() has been added to return the value of a given property for a given code point.
- A new function charprops_all() has been added to return the values of all Unicode properties for a given code point.
- A bug has been fixed so that propaliases() returns the correct short and long names for the Perl extensions where it was incorrect.
- A bug has been fixed so that prop_value_aliases() returns undef instead of a wrong result for properties that are Perl extensions.
- This module now works on EBCDIC platforms. EBCDIC besties we see you 🫶
utf8 has been upgraded to version 1.17. 💜
- A mismatch between the documentation and the code in utf8::downgrade() was fixed in favor of the documentation. The optional second argument is now correctly treated as a perl boolean (true/false semantics) and not as an integer. docs said one thing, code did another, docs won, slay
version has been upgraded to version 0.9909. 🎀
- Numerous changes. See the Changes file in the CPAN distribution for details.
Win32 has been upgraded to version 0.51. 🦋
- GetOSName() now supports Windows 8.1, and building in C++ mode now works.
Win32API::File has been upgraded to version 0.1202. 🔥
- Building in C++ mode now works.
XSLoader has been upgraded to version 0.20. ✨
- Allow XSLoader to load modules from a different namespace. [perl #122455]

🗑️ Removed Modules and Pragmata 💀

The following modules (and associated modules) have been removed from the core perl distribution: they're gone bestie, not deprecated, GONE

CGI
Module::Build

if you were relying on those, that's a you-and-CPAN situation now 🙈

📖 Documentation 📖

okay bestie, the docs got so much attention in this release, like genuinely a glow-up. let's go through it 💖

✨ New Documentation ✨

perlunicook

this doc, written by Tom Christiansen, is literally a whole cookbook of examples for handling Unicode in Perl. chef's kiss 👑

💖 Changes to Existing Documentation 💖

perlaix

a note on long doubles has been added.

perlapi

note that SvSetSV doesn't do set magic.
sv_usepvn_flags — the docs got fixed up to mention using Newx instead of malloc.

[GH #13835] <https://github.com/Perl/perl5/issues/13835>

clarified where NUL may be embedded or is required to terminate a string.
some documentation that was previously missing (because of formatting errors, embarrassing) is now included.
entries are now organized into groups instead of by the file where they're found.
alphabetical sorting of entries is now done consistently (automatically, by the POD generator) so scanning through them is actually findable now. slay.

perldata

the syntax of single-character variable names has been brought up-to-date and explained way more fully.
hexadecimal floating point numbers are described, and so are infinity and NaN.

perlebcdic

this document has been significantly updated in light of recent improvements to EBCDIC support.

perlfilter

a LIMITATIONS section was added.

perlfunc

mention that study() is currently a no-op. yes bestie, it does nothing. it's giving decorative.
calling delete or exists on array values is now described as "strongly discouraged" rather than "deprecated".
improved the documentation of our.
-l now notes that it will return false if symlinks aren't supported by the file system. [GH #13695] <https://github.com/Perl/perl5/issues/13695>
note that exec LIST and system LIST may fall back to the shell on Win32. only the indirect-object syntax exec PROGRAM LIST and system PROGRAM LIST will reliably avoid using the shell.

this has also been noted in perlport.

[GH #13907] <https://github.com/Perl/perl5/issues/13907>

perlguts

the OOK example has been updated to account for COW changes and a change in the storage of the offset.
details on C level symbols and libperl.t added.
information on Unicode handling has been added.
information on EBCDIC handling has been added.

perlhack

a note has been added about running on platforms with non-ASCII character sets.
a note has been added about performance testing.

perlhacktips

documentation has been added illustrating the perils of assuming that there's no change to the contents of static memory pointed to by the return values of Perl's wrappers for C library functions. 🚩
replacements for tmpfile, atoi, strtol, and strtoul are now recommended.
updated documentation for the test.valgrind make target. [GH #13658] <https://github.com/Perl/perl5/issues/13658>
information is given about writing test files portably to non-ASCII platforms.
a note has been added about how to get a C language stack backtrace.

perlhpux

note that the message Redeclaration of "sendpath" with a different storage class specifier is harmless. it's just talking. let it talk.

perllocale

updated for the enhancements in v5.22, along with some clarifications.

perlmodstyle

instead of pointing to the module list, we're now pointing to PrePAN <http://prepan.org/>.

perlop

updated for the enhancements in v5.22, along with some clarifications.

perlpodspec

the specification of the pod language is changing, so that the default encoding of pods that aren't in UTF-8 (unless otherwise indicated) is CP1252 instead of ISO 8859-1 (Latin1).

perlpolicy

we now have a code of conduct for the p5p mailing list, as documented in "STANDARDS OF CONDUCT" in perlpolicy. 🫶
the conditions for marking an experimental feature as non-experimental are now set out.
clarification has been made as to what sorts of changes are permissible in maintenance releases.

perlport

out-of-date VMS-specific information has been fixed and/or simplified.
notes about EBCDIC have been added.

perlre

the description of the /x modifier has been clarified to note that comments cannot be continued onto the next line by escaping them; and there is now a list of all the characters that are considered whitespace by this modifier.
the new /n modifier is described.
a note has been added on how to make bracketed character class ranges portable to non-ASCII machines.

perlrebackslash

added documentation of \b{sb}, \b{wb}, \b{gcb}, and \b{g}.

perlrecharclass

clarifications have been added to "Character Ranges" in perlrecharclass to the effect that [A-Z], [a-z], [0-9] and any subranges thereof in regular expression bracketed character classes are guaranteed to match exactly what a naive English speaker would expect them to match, even on platforms (such as EBCDIC) where perl has to do extra work to accomplish this. bestie, it's guaranteed.
the documentation of Bracketed Character Classes has been expanded to cover the improvements in qr/[\N{named sequence}]/ (see under "Selected Bug Fixes").

perlref

a new section has been added: Assigning to References.

perlsec

comments added on algorithmic complexity and tied hashes.

perlsyn

an ambiguity in the documentation of the ... statement has been corrected. [GH #14054] <https://github.com/Perl/perl5/issues/14054>
the empty conditional in for and while is now documented in perlsyn.

perlunicode

this has had extensive revisions to bring it up-to-date with current Unicode support and to make it more readable. notable is that Unicode 7.0 changed what it should do with non-characters. Perl retains the old way of handling for reasons of backward compatibility. see "Noncharacter code points" in perlunicode.

perluniintro

advice for how to make sure your strings and regular expression patterns are interpreted as Unicode has been updated.

perlvar

$] is no longer listed as being deprecated. instead, discussion has been added on the advantages and disadvantages of using it versus $^V. $OLD_PERL_VERSION was re-added to the documentation as the long form of $].
${^ENCODING} is now marked as deprecated.
the entry for %^H has been clarified to indicate it can only handle simple values.

perlvms

out-of-date and/or incorrect material has been removed.
updated documentation on environment and shell interaction in VMS.

perlxs

added a discussion of locale issues in XS code.

🚨 Diagnostics 🚨

the following additions or changes have been made to diagnostic output, including warnings and fatal error messages. for the complete list of diagnostic messages, see perldiag.

🆕 New Diagnostics 🆕

💀 New Errors 💀

Bad symbol for scalar

(P) an internal request asked to add a scalar entry to something that wasn't a symbol table entry.

Can't use a hash as a reference

(F) you tried to use a hash as a reference, as in %foo->{"bar"} or %$ref->{"hello"}. versions of perl <= 5.6.1 used to allow this syntax, but shouldn't have.

Can't use an array as a reference

(F) you tried to use an array as a reference, as in @foo->[23] or @$ref->[99]. versions of perl <= 5.6.1 used to allow this syntax, but shouldn't have.

Can't use 'defined(@array)' (Maybe you should just omit the defined()?)

(F) defined() is not useful on arrays because it checks for an undefined scalar value. if you want to see if the array is empty, just use if (@array) { # not empty } for example.

Can't use 'defined(%hash)' (Maybe you should just omit the defined()?)

(F) defined() is not usually right on hashes.

although defined %hash is false on a plain not-yet-used hash, it becomes true in several non-obvious circumstances, including iterators, weak references, stash names, even remaining true after undef %hash. these things make defined %hash fairly useless in practice, so it now generates a fatal error.

if a check for non-empty is what you wanted then just put it in boolean context (see "Scalar values" in perldata):

if (%hash) {
   # not empty
}

if you had defined %Foo::Bar::QUUX to check whether such a package variable exists then that's never really been reliable, and isn't a good way to enquire about the features of a package, or whether it's loaded, etc.

Cannot chr %f

(F) you passed an invalid number (like an infinity or not-a-number) to chr.

Cannot compress %f in pack

(F) you tried converting an infinity or not-a-number to an unsigned character, which makes no sense. 🫠

Cannot pack %f with '%c'

(F) you tried converting an infinity or not-a-number to a character, which makes no sense.

Cannot print %f with '%c'

(F) you tried printing an infinity or not-a-number as a character (%c), which makes no sense. maybe you meant '%s', or just stringifying it?

charnames alias definitions may not contain a sequence of multiple spaces

(F) you defined a character name which had multiple space characters in a row. change them to single spaces. usually these names are defined in the ":alias" import argument to use charnames, but they could be defined by a translator installed into $^H{charnames}. see "CUSTOM ALIASES" in charnames.

charnames alias definitions may not contain trailing white-space

(F) you defined a character name which ended in a space character. remove the trailing space(s). usually these names are defined in the ":alias" import argument to use charnames, but they could be defined by a translator installed into $^H{charnames}. see "CUSTOM ALIASES" in charnames.

:const is not permitted on named subroutines

(F) the "const" attribute causes an anonymous subroutine to be run and its value captured at the time that it is cloned. named subroutines are not cloned like this, so the attribute does not make sense on them.

Hexadecimal float: internal error

(F) something went horribly bad in hexadecimal float handling. 😭

Hexadecimal float: unsupported long double format
(F) You have configured Perl to use long doubles but the internals of the long double format are unknown, therefore the hexadecimal float output is impossible.
Illegal suidscript — (F) The script run under suidperl was somehow illegal. 💀
In '(?...)', the '(' and '?' must be adjacent in regex; marked by <-- HERE in m/%s/ — (F) So the two-character sequence (? in this context in a regular expression pattern should be one indivisible token, with nothing wedged in between the ( and the ?, but bestie… you separated them. 🙈
In '(*VERB...)', the '(' and '*' must be adjacent in regex; marked by <-- HERE in m/%s/ — (F) Same energy, different characters: the two-character sequence (* in this context in a regular expression pattern should be an indivisible token, with nothing between the ( and the *, but you went and separated them. 😭
Invalid quantifier in {,} in regex; marked by <-- HERE in m/%s/ — (F) The pattern looks like a {min,max} quantifier, but the min or max couldn't be parsed as a valid number: either it's got leading zeroes, or it's just too big a number to cope with. That <-- HERE shows you where in the regular expression the problem was discovered. Peep perlre. 👑
'%s' is an unknown bound type in regex — (F) You used \b{...} or \B{...} and the ... is not a thing Perl knows about. The currently valid ones are listed in "\b{}, \b, \B{}, \B" in perlrebackslash. 📚
Missing or undefined argument to require — (F) You tried to call require with no argument, or with an undefined value as the argument. require expects either a package name or a file-specification as its argument. Check "require" in perlfunc. Fun fact: formerly, require with no argument or undef just warned about a Null filename. Glow-up era fr fr. ✨

✨ New Warnings ✨ 🎀

\C is deprecated in regex — (D deprecated) The /\C/ character class got deprecated back in v5.20, and now it emits a warning. The plan is for it to become an error in v5.24. This character class matches a single byte even when it's sitting inside a multi-byte character, it breaks encapsulation, and it can straight-up corrupt UTF-8 strings. Not cute, not slay. 💅
"%s" is more clearly written simply as "%s" in regex; marked by <-- HERE in m/%s/ — (W regexp) (only under use re 'strict' or within (?[...])) You specified a character that has the given plainer way of writing it, and which is also portable to platforms running with different character sets. 🌈
Argument "%s" treated as 0 in increment (++) — (W numeric) The indicated string got fed as an argument to the ++ operator, which expects either a number or a string matching /^[a-zA-Z]*[0-9]*\z/. Details in "Auto-increment and Auto-decrement" in perlop. 🔢
Both or neither range ends should be Unicode in regex; marked by <-- HERE in m/%s/ — (W regexp) (only under use re 'strict' or within (?[...])) In a bracketed character class in a regular expression pattern, you had a range where exactly one end is specified using \N{} and the other end uses a non-portable mechanism. Perl treats the range as a Unicode range — meaning all the characters in it are considered the Unicode characters, and those may be different code points on some platforms Perl runs on. For example, [\N{U+06}-\x08] is treated as if you'd instead said [\N{U+06}-\N{U+08}], i.e. it matches the characters whose code points in Unicode are 6, 7, and 8. But that \x08 might mean you meant something different, so the warning gets raised. 👀
Can't do %s("%s") on non-UTF-8 locale; resolved to "%s". — (W locale) Okay so: 1) you're running under "use locale"; 2) the current locale is not a UTF-8 one; 3) you tried to do the designated case-change operation on the specified Unicode character; and 4) the result of this operation would mix Unicode and locale rules, which likely conflict. The warnings category locale is new. 🦋
:const is experimental — (S experimental::const_attr) The const attribute is experimental. If you wanna use the feature, disable the warning with no warnings 'experimental::const_attr' — but know that in doing so you are taking the risk that your code may break in a future Perl version. Your call, bestie. ⚠️
gmtime(%f) failed — (W overflow) You called gmtime with a number it couldn't handle: too large, too small, or NaN. The returned value is undef. 😭
Hexadecimal float: exponent overflow — (W overflow) The hexadecimal floating point has a larger exponent than the floating point supports. 📈
Hexadecimal float: exponent underflow — (W overflow) The hexadecimal floating point has a smaller exponent than the floating point supports. 📉
Hexadecimal float: mantissa overflow — (W overflow) The hexadecimal floating point literal had more bits in the mantissa (that's the part between the 0x and the exponent, also known as the fraction or the significand) than the floating point supports. 💀
Hexadecimal float: precision loss — (W overflow) The hexadecimal floating point had internally more digits than could be output. This can be caused by unsupported long double formats, or by 64-bit integers not being available (needed to retrieve the digits under some configurations). 🙈
Locale '%s' may not work well.%s — (W locale) You're using the named locale, which is a non-UTF-8 one, and which perl has determined is not fully compatible with what it can handle. That second %s gives a reason. The warnings category locale is new. 🌸
localtime(%f) failed — (W overflow) You called localtime with a number it couldn't handle: too large, too small, or NaN. The returned value is undef. ⏰
Negative repeat count does nothing — (W numeric) You tried to execute the x repetition operator fewer than 0 times, which… doesn't make sense, bestie. 🤨
NO-BREAK SPACE in a charnames alias definition is deprecated — (D deprecated) You defined a character name that contained a no-break space character. Change it to a regular space. Usually these names are defined in the :alias import argument to use charnames, but they could be defined by a translator installed into $^H{charnames}. See "CUSTOM ALIASES" in charnames. 🎀
Non-finite repeat count does nothing — (W numeric) You tried to execute the x repetition operator Inf (or -Inf) or NaN times, which doesn't make sense. 🔥
PerlIO layer ':win32' is experimental — (S experimental::win32_perlio) The :win32 PerlIO layer is experimental. If you wanna take the risk of using this layer, simply disable this warning:

    no warnings "experimental::win32_perlio";

Ranges of ASCII printables should be some subset of "0-9", "A-Z", or "a-z" in regex; marked by <-- HERE in m/%s/ — (W regexp) (only under use re 'strict' or within (?[...])) Stricter rules help to find typos and other errors. Maybe you didn't even intend a range here — like if the - was meant to be some other character, or should've been escaped (like \-). If you did intend a range, the one that got used is not portable between ASCII and EBCDIC platforms, and doesn't have an obvious meaning to a casual reader. 👇

 [3-7]    # OK; Obvious and portable
 [d-g]    # OK; Obvious and portable
 [A-Y]    # OK; Obvious and portable
 [A-z]    # WRONG; Not portable; not clear what is meant
 [a-Z]    # WRONG; Not portable; not clear what is meant
 [%-.]    # WRONG; Not portable; not clear what is meant
 [\x41-Z] # WRONG; Not portable; not obvious to non-geek

(You can force portability by specifying a Unicode range, which means the endpoints are specified by \N{...}, but the meaning may still not be obvious.) The stricter rules require that ranges starting or stopping with an ASCII character that is not a control have all their endpoints be a literal character, and not some escape sequence (like \x41), and the ranges must be all digits, or all uppercase letters, or all lowercase letters. 🧚

Ranges of digits should be from the same group in regex; marked by <-- HERE in m/%s/ — (W regexp) (only under use re 'strict' or within (?[...])) Stricter rules help to find typos and other errors. You included a range, and at least one of the end points is a decimal digit. Under the stricter rules, when this happens, both end points should be digits in the same group of 10 consecutive digits. 🔢
Redundant argument in %s — (W redundant) You called a function with more arguments than were needed, as indicated by information within other arguments you supplied (e.g. a printf format). Currently only emitted when a printf-type format required fewer arguments than were supplied, but it might be used in the future for e.g. "pack" in perlfunc. The warnings category redundant is new. See also [GH #13534] https://github.com/Perl/perl5/issues/13534. 👑
Replacement list is longer than search list — Not a new diagnostic, but in earlier releases it was accidentally not displayed if the transliteration contained wide characters. That's now fixed, so you may see this diagnostic in places where you previously didn't (but should have). 💅
Use of \b{} for non-UTF-8 locale is wrong. Assuming a UTF-8 locale — (W locale) You're matching a regular expression using locale rules, and a Unicode boundary is being matched, but the locale is not a Unicode one. That doesn't make sense. Perl will continue, assuming a Unicode (UTF-8) locale, but the results could well be wrong — except if the locale happens to be ISO-8859-1 (Latin1), where this message is spurious and can be ignored. The warnings category locale is new. 🦋
Using /u for '%s' instead of /%s in regex; marked by <-- HERE in m/%s/ — (W regexp) You used a Unicode boundary (\b{...} or \B{...}) in a portion of a regular expression where the character set modifiers /a or /aa are in effect. Those two modifiers indicate an ASCII interpretation, and that doesn't make sense for a Unicode definition. The generated regular expression will compile so that the boundary uses all of Unicode. No other portion of the regular expression is affected. 🌈
The bitwise feature is experimental
experimental::bitwise — okay so this one's (S experimental::bitwise). It fires when you use the bitwise operators (& | ^ ~ &. |. ^. ~.) while the bitwise feature is turned on. You can just hush it if you're committed to the feature, but bestie, be so for real: doing that means you're signing up to use an experimental feature that might change or get deleted in a future Perl version. Your call 💅

no warnings "experimental::bitwise";
use feature "bitwise";
$x |.= $y;

Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/%s/ — (D deprecated, regexp) deprecated alert! You dropped a literal { into a regex pattern. Switch to \{ instead, because a future version of Perl (tentatively v5.26) is gonna treat the bare brace as a syntax error. And if your pattern delimiters are braces too, then any matching right brace (}) should also be escaped so the parser doesn't get its wig all twisted, like this:

qr{abc\{def\}ghi}

Use of literal non-graphic characters in variable names is deprecated — (D deprecated) Using literal non-graphic characters (control characters included 🫣) in your source to refer to the ^FOO variables — think $^X and ${^GLOBAL_PHASE} — is now deprecated.
Useless use of attribute "const" — (W misc) The const attribute literally does nothing except on anonymous closure prototypes. You slapped it on a subroutine via attributes.pm, and it's only ever useful inside an attribute handler for an anonymous subroutine. So yeah, useless 😭
Useless use of /d modifier in transliteration operator — Not a new diagnostic, but plot twist: in earlier releases it was accidentally never displayed if the transliteration had wide characters in it. That's fixed now, so you may start seeing this diagnostic in places you previously didn't (but lowkey should have) 💀
"use re 'strict'" is experimental — (S experimental::re_strict) Everything that behaves differently when a regex pattern is compiled under 'strict' is subject to change in future Perl releases in incompatible ways. There are also proposals floating around about changing how you enable strict checking instead of using this subpragma. Translation: a pattern that compiles today might not compile in a future Perl release. This warning exists to keep you aware of that risk 🧚
Warning: unable to close filehandle properly: %s and Warning: unable to close filehandle %s properly: %s — (S io) Back in the day, perl would silently ignore any errors from an implicit close of a filehandle — meaning the moment the filehandle's reference count hit zero and your code had never actually called close() itself. Like this:

{
    open my $fh, '>', $file  or die "open: '$file': $!\n";
    print $fh, $data  or die;
} # implicit close here

In a situation like a full disk, buffering means the error might only get detected during that final close — so not checking the result of the close is genuinely dangerous. Which is why perl now warns you in these situations 🔥

Wide character (U+%X) in %s — (W locale) You were in a single-byte locale (so, a non-UTF-8 one) and a multi-byte character showed up. Perl treats that character as the Unicode code point it says on the tin. Mixing non-UTF-8 locales and Unicode is dangerous, no cap — almost certainly some characters are gonna end up with two different representations. For example, in the ISO 8859-7 (Greek) locale, the code point 0xC3 represents a Capital Gamma. But so does 0x393. That makes string comparisons unreliable 😭

You probably need to work out how this multi-byte character got tangled up with your single-byte locale — or maybe you thought you had a UTF-8 locale, but Perl respectfully disagrees 🙈

The warnings category locale is new.

Changes to Existing Diagnostics

<> should be quotes — This warning got a glow-up and now reads <> at require-statement should be quotes, so the actual issue is way easier to clock.
Argument "%s" isn't numeric%s — The perldiag entry for this warning picked up this clarifying note:

Note that for the Inf and NaN (infinity and not-a-number) the definition of "numeric" is somewhat unusual: the strings themselves (like "Inf") are considered numeric, and anything following them is considered non-numeric.

Global symbol "%s" requires explicit package name — This message now has (did you forget to declare "my %s"?) tacked onto the end, because it's giving helpful-to-new-Perl-programmers energy. [GH #13732] <https://github.com/Perl/perl5/issues/13732>
'"my" variable &foo::bar can't be in a package' — Got reworded to say 'subroutine' instead of 'variable'. Words matter bestie 💅
\N{} in character class restricted to one character in regex; marked by <-- HERE in m/%s/ — This message had character class swapped out for inverted character class or as a range end-point, to reflect the improvements in qr/[\N{named sequence}]/ (peep under "Selected Bug Fixes").
panic: frexp — This message now has : %f appended, so it can show you exactly which offending floating point number caused the drama.
Possible precedence problem on bitwise %c operator — Reworded as Possible precedence problem on bitwise %s operator.
Unsuccessful %s on filename containing newline — This warning is now only produced when the newline is at the very end of the filename.
"Variable %s will not stay shared" — Now says "Subroutine" when it's actually a lexical sub that won't stay shared, which, iconic accuracy ✨
Variable length lookbehind not implemented in regex m/%s/ — The perldiag entry for this warning got info about Unicode behavior added to it.

Diagnostic Removals

"Ambiguous use of -foo resolved as -&foo()" — Removed, because there's genuinely no ambiguity here, and it was blocking the use of negated constants — e.g., -Inf. Bye 👋
"Constant is not a FOO reference" — Removed. Compile-time checking of constant dereferencing (e.g., my_constant->()) has been taken out, since it wasn't taking overloading into account. [GH #9891] <https://github.com/Perl/perl5/issues/9891> [GH #14044] <https://github.com/Perl/perl5/issues/14044>

Utility Changes

find2perl, s2p and a2p removal

The x2p/ directory has been removed from the Perl core. 🌸

That takes find2perl, s2p and a2p with it. All three have been released to CPAN as separate distributions (App::find2perl, App::s2p, App::a2p), so like, they're not gone-gone, they just moved out 🫶

h2ph

h2ph now handles hexadecimal constants in the compiler's predefined macro definitions, as visible in $Config{cppsymbols}. [GH #14491] <https://github.com/Perl/perl5/issues/14491>.

encguess

No longer depends on non-core modules. Self-sufficient queen 👑

Configuration and Compilation

Configure now checks for lrintl(), lroundl(), llrintl(), and llroundl().
Configure with -Dmksymlinks should now be faster. [GH #13890] <https://github.com/Perl/perl5/issues/13890>.
The pthreads and cl libraries will be linked by default if they're present. This lets XS modules that require threading work on non-threaded perls. Note though: you still have to pass -Dusethreads if you actually want a threaded perl. Don't skip that part bestie 🙈
Wanna get more precision and range out of your floating point numbers? You can now use the GCC quadmath library, which implements quadruple precision floating point numbers on x86 and IA-64 platforms. See INSTALL for the deets.
MurmurHash64A and MurmurHash64B can now be configured as the internal hash function.
make test.valgrind now supports parallel testing. For example:

TEST_JOBS=9 make test.valgrind

See "valgrind" in perlhacktips for more information. [GH #13658] <https://github.com/Perl/perl5/issues/13658>

The MAD (Misc Attribute Decoration) build option has been removed 💀

It was an unmaintained attempt at preserving the Perl parse tree more faithfully, so that automatic conversion of Perl 5 to Perl 6 would be easier. This build-time configuration option had been unmaintained for years, and had probably seriously diverged on both the Perl 5 and Perl 6 sides.

A new compilation flag, -DPERL_OP_PARENT, is available. For details, see the discussion below at "Internal Changes".
Pathtools no longer tries to load XS on miniperl. This speeds up building perl slightly. Tiny wins are still wins ✨

Testing

t/porting/re_context.t has been added, to test that utf8 and its dependencies only use the subset of the $1..$n capture vars that Perl_save_re_context() is hard-coded to localize — because that function has no efficient way of figuring out at runtime which vars to localize.
Tests for performance issues have been added in the file t/perf/taint.t.
Some regular expression tests are written in such a way that they'll run very slowly if certain optimizations break. Those tests have been moved into new files, t/re/speed.t and t/re/speed_thr.t, and are run with a watchdog().
test.pl now allows plan skip_all => $reason, which makes it more compatible with Test::More.
A new test script, op/infnan.t, has been added to test whether infinity and NaN are working correctly. See "Infinity and NaN (not-a-number) handling improved". ⭐

🌸 Platform Support 🌸

💖 Regained Platforms 💖

IRIX and Tru64 platforms are working again. 🎉 Some make test failures remain: [GH #14557] <https://github.com/Perl/perl5/issues/14557> and [GH #14727] <https://github.com/Perl/perl5/issues/14727> for IRIX; [GH #14629] <https://github.com/Perl/perl5/issues/14629>, [cpan #99605] <https://rt.cpan.org/Public/Bug/Display.html?id=99605>, and [cpan #104836] <https://rt.cpan.org/Ticket/Display.html?id=104836> for Tru64.
z/OS running EBCDIC Code Page 1047 — bestie, core perl now works on this EBCDIC platform 💜 Earlier perls also worked, but even though support wasn't officially withdrawn, recent perls would not compile and run well. Perl 5.20 would work, but had many bugs which have now been fixed. Many CPAN modules that ship with Perl still fail tests, including Pod::Simple. However the version of Pod::Simple currently on CPAN should work; it was fixed too late to include in Perl 5.22. Work is under way to fix many of the still-broken CPAN modules, which likely will be installed on CPAN when completed, so that you may not have to wait until Perl 5.24 to get a working version. 🫶

🦋 Discontinued Platforms 🦋

NeXTSTEP/OPENSTEP — NeXTSTEP was a proprietary operating system bundled with NeXT's workstations in the early to mid 90s; OPENSTEP was an API specification that provided a NeXTSTEP-like environment on a non-NeXTSTEP system. Both are now long dead 💀 so support for building Perl on them has been removed.

✨ Platform-Specific Notes ✨

🌈 EBCDIC

Special handling is required of the perl interpreter on EBCDIC platforms to get qr/[i-j]/ to match only i and j, since there are 7 characters between the code points for i and j. This special handling had only been invoked when both ends of the range are literals. Now it is also invoked if any of the \N{...} forms for specifying a character by name or Unicode code point is used instead of a literal. See "Character Ranges" in perlrecharclass.

🌸 HP-UX

The archname now distinguishes use64bitint from use64bitall.

🎀 Android

Build support has been improved for cross-compiling in general and for Android in particular. 💅

💜 VMS

When spawning a subprocess without waiting, the return value is now the correct PID. 👑
Fix a prototype so linking doesn't fail under the VMS C++ compiler.
finite, finitel, and isfinite detection has been added to configure.com, environment handling has had some minor changes, and a fix for legacy feature checking status.

🦋 Win32

miniperl.exe is now built with -fno-strict-aliasing, allowing 64-bit builds to complete on GCC 4.8. [GH #14556] <https://github.com/Perl/perl5/issues/14556>
nmake minitest now works on Win32. Due to dependency issues you need to build nmake test-prep first, and a small number of the tests fail. [GH #14318] <https://github.com/Perl/perl5/issues/14318>
Perl can now be built in C++ mode on Windows by setting the makefile macro USE_CPLUSPLUS to the value define.
The list form of piped open has been implemented for Win32. Note: unlike system LIST this does not fall back to the shell. [GH #13574] <https://github.com/Perl/perl5/issues/13574>
New DebugSymbols and DebugFull configuration options added to Windows makefiles.
Previously, compiling XS modules (including CPAN ones) using Visual C++ for Win64 resulted in around a dozen warnings per file from hv_func.h. These warnings have been silenced. 🤫
Support for building without PerlIO has been removed from the Windows makefiles. Non-PerlIO builds were all but deprecated in Perl 5.18.0 and are already not supported by Configure on POSIX systems.
Between 2 and 6 milliseconds and seven I/O calls have been saved per attempt to open a perl module for each path in @INC. ⚡
Intel C builds are now always built with C99 mode on.
%I64d is now being used instead of %lld for MinGW.
In the experimental :win32 layer, a crash in open was fixed. Also opening /dev/null (which works under Win32 Perl's default :unix layer) was implemented for :win32. [GH #13968] <https://github.com/Perl/perl5/issues/13968>
A new makefile option, USE_LONG_DOUBLE, has been added to the Windows dmake makefile for gcc builds only. Set this to define if you want perl to use long doubles to give more accuracy and range for floating point numbers.

🐚 OpenBSD

On OpenBSD, Perl will now default to using the system malloc due to the security features it provides. Perl's own malloc wrapper has been in use since v5.14 due to performance reasons, but the OpenBSD project believes the tradeoff is worth it and would prefer that users who need the speed specifically ask for it.

[GH #13888] <https://github.com/Perl/perl5/issues/13888>.

☀️ Solaris

We now look for the Sun Studio compiler in both /opt/solstudio* and /opt/solarisstudio*.
Builds on Solaris 10 with -Dusedtrace would fail early since make didn't follow implied dependencies to build perldtrace.h. Added an explicit dependency to depend. [GH #13334] <https://github.com/Perl/perl5/issues/13334>
C99 options have been cleaned up; hints look for solstudio as well as SUNWspro; and support for native setenv has been added.

👑 Internal Changes 👑

Experimental support has been added to allow ops in the optree to locate their parent, if any. This is enabled by the non-default build option -DPERL_OP_PARENT. It is envisaged that this will eventually become enabled by default, so XS code which directly accesses the op_sibling field of ops should be updated to be future-proofed. 🔮

On PERL_OP_PARENT builds, the op_sibling field has been renamed op_sibparent and a new flag, op_moresib, added. On the last op in a sibling chain, op_moresib is false and op_sibparent points to the parent (if any) rather than being NULL.

To make existing code work transparently whether using PERL_OP_PARENT or not, a number of new macros and functions have been added that should be used, rather than directly manipulating op_sibling.

For the case of just reading op_sibling to determine the next sibling, two new macros have been added. A simple scan through a sibling chain like this:

for (; kid->op_sibling; kid = kid->op_sibling) { ... }

should now be written as:

for (; OpHAS_SIBLING(kid); kid = OpSIBLING(kid)) { ... }

For altering optrees, a general-purpose function op_sibling_splice() has been added, which allows for manipulation of a chain of sibling ops. By analogy with the Perl function splice(), it allows you to cut out zero or more ops from a sibling chain and replace them with zero or more new ops. It transparently handles all the updating of sibling, parent, op_last pointers etc. ✂️

If you need to manipulate ops at a lower level, then three new macros, OpMORESIB_set, OpLASTSIB_set and OpMAYBESIB_set are intended to be a low-level portable way to set op_sibling / op_sibparent while also updating op_moresib. The first sets the sibling pointer to a new sibling, the second makes the op the last sibling, and the third conditionally does the first or second action. Note that unlike op_sibling_splice() these macros won't maintain consistency in the parent at the same time (e.g. by updating op_first and op_last where appropriate). ⚠️

A C-level Perl_op_parent() function and a Perl-level B::OP::parent() method have been added. The C function only exists under PERL_OP_PARENT builds (using it is build-time error on vanilla perls). B::OP::parent() exists always, but on a vanilla build it always returns NULL. Under PERL_OP_PARENT, they return the parent of the current op, if any. The variable $B::OP::does_parent allows you to determine whether B supports retrieving an op's parent. 🫶

PERL_OP_PARENT was introduced in 5.21.2, but the interface was changed considerably in 5.21.11. If you updated your code before the 5.21.11 changes, it may require further revision. The main changes after 5.21.2 were:

The OP_SIBLING and OP_HAS_SIBLING macros have been renamed OpSIBLING and OpHAS_SIBLING for consistency with other op-manipulating macros.
The op_lastsib field has been renamed op_moresib, and its meaning inverted.
The macro OpSIBLING_set has been removed, and has been superseded by OpMORESIB_set et al.
The op_sibling_splice() function now accepts a null parent argument where the splicing doesn't affect the first or last ops in the sibling chain

Macros have been created to allow XS code to better manipulate the POSIX locale category LC_NUMERIC. See "Locale-related functions and macros" in perlapi.
The previous atoi et al replacement function, grok_atou, has now been superseded by grok_atoUV. See perlclib for details.
A new function, Perl_sv_get_backrefs(), has been added which allows you retrieve the weak references, if any, which point at an SV.
The screaminstr() function has been removed. Although marked as public API, it was undocumented and had no usage in CPAN modules. Calling it has been fatal since 5.17.0. 💀
The newDEFSVOP(), block_start(), block_end() and intro_my() functions have been added to the API.
The internal convert function in op.c has been renamed op_convert_list and added to the API.
The sv_magic() function no longer forbids ext magic on read-only values. After all, perl can't know whether the custom magic will modify the SV or not. [GH #14202] <https://github.com/Perl/perl5/issues/14202>. 💅
Accessing CvPADLIST in perlapi on an XSUB is now forbidden.

The CvPADLIST field has been reused for a different internal purpose for XSUBs. So in particular, you can no longer rely on it being NULL as a test of whether a CV is an XSUB. Use CvISXSUB() instead. ⭐

SVs of type SVt_NV are now sometimes bodiless when the build config and the platform allow it — specifically, when sizeof(NV) <= sizeof(IV). "Bodiless" meaning the NV value lives directly in the head of an SV, no separate body allocation needed 💅. This trick has already been used for IVs since 5.9.2 (tho for IVs it's always used, no matter the platform or build configuration — she's committed).
The $DB::single, $DB::signal and $DB::trace variables now have set- and get-magic that stores their values as IVs, and those IVs are what gets used when testing their values in pp_dbstate(). This stops perl from recursing infinitely if an overloaded object gets assigned to any of those variables. [GH #14013] https://github.com/Perl/perl5/issues/14013 🌀
Perl_tmps_grow(), which is marked as public API but is undocumented, has been removed from the public API. This change does not affect XS code that uses the EXTEND_MORTAL macro to pre-extend the mortal stack. (so like, if that's you, you're fine bestie 🫶)
Perl's internals no longer sets or uses the SVs_PADMY flag. SvPADMY() now returns a true value for anything not marked PADTMP, and SVs_PADMY is now defined as 0.
The macros SETsv and SETsvUN have been removed. They hadn't been used in the core since commit 6f1401dc2a five years ago, and they haven't been found present on CPAN. gone girl 💀
The SvFAKE bit (unused on HVs) got informally reserved by David Mitchell for future work on vtables.
The sv_catpvn_flags() function accepts SV_CATBYTES and SV_CATUTF8 flags, which say whether the appended string is bytes or UTF-8, respectively. (These flags have actually been present since 5.16.0, but were formerly not regarded as part of the API — retroactively iconic ✨)
A new opcode class, METHOP, has been introduced 👑. It holds info used at runtime to improve the performance of class/object method calls.

OP_METHOD and OP_METHOD_NAMED have changed from being UNOP/SVOP to being METHOP.

cv_name() is a new API function that can be passed a CV or a GV. It returns an SV containing the name of the subroutine, for use in diagnostics.

[GH #12767] https://github.com/Perl/perl5/issues/12767 [GH #13392] https://github.com/Perl/perl5/issues/13392

cv_set_call_checker_flags() is a new API function that works like cv_set_call_checker(), except it lets the caller specify whether the call checker requires a full GV for reporting the subroutine's name, or whether it could be passed a CV instead. Whatever value gets passed will be acceptable to cv_name(). cv_set_call_checker() guarantees there will be a GV, but it may have to create one on the fly, which is inefficient. [GH #12767] https://github.com/Perl/perl5/issues/12767
CvGV (which is not part of the API) is now a more complex macro, which may call a function and reify a GV. For those cases where it's been used as a boolean, CvHASGV has been added, which returns true for CVs that notionally have GVs, but without reifying the GV. CvGV also returns a GV now for lexical subs. [GH #13392] https://github.com/Perl/perl5/issues/13392
The sync_locale in perlapi function has been added to the public API. Changing the program's locale should be avoided by XS code. That said, certain non-Perl libraries called from XS need to do it, like Gtk. When that happens, Perl needs to be told that the locale has changed — use this function to do so, before returning to Perl. 🧚
The defines and labels for the flags in the op_private field of OPs are now auto-generated from data in regen/op_private. The noticeable effect: some of the flag output of Concise might differ slightly, and the flag output of perl -Dx may differ considerably (they both use the same set of labels now). Also, debugging builds now have a new assertion in op_free() to make sure the op doesn't have any unrecognized flags set in op_private. vibe check passed 🔥
The deprecated variable PL_sv_objcount has been removed.
Perl now tries to keep the locale category LC_NUMERIC set to C except around operations that need it set to the program's underlying locale. This protects the many XS modules that cannot cope with the decimal radix character not being a dot. Before this release, Perl initialized this category to C, but a call to POSIX::setlocale() would change it. Now such a call will change the underlying locale of the LC_NUMERIC category for the program, but the locale exposed to XS code stays C. There are new macros to manipulate the LC_NUMERIC locale, including STORE_LC_NUMERIC_SET_TO_NEEDED and STORE_LC_NUMERIC_FORCE_TO_UNDERLYING. See "Locale-related functions and macros" in perlapi. 🌸
A new macro isUTF8_CHAR has been written which efficiently determines if the string given by its parameters begins with a well-formed UTF-8 encoded character. no cap, it's fast ⚡
The following private API functions had their context parameter removed: Perl_cast_ulong, Perl_cast_i32, Perl_cast_iv, Perl_cast_uv, Perl_cv_const_sv, Perl_mg_find, Perl_mg_findext, Perl_mg_magical, Perl_mini_mktime, Perl_my_dirfd, Perl_sv_backoff, Perl_utf8_hop.

Note that the prefix-less versions of those functions that are part of the public API, such as cast_i32(), remain unaffected. 💖

The PADNAME and PADNAMELIST types are now separate types, and no longer just aliases for SV and AV. [GH #14250] https://github.com/Perl/perl5/issues/14250
Pad names are now always UTF-8. The PadnameUTF8 macro always returns true. Previously this was effectively the case already, but any support for two different internal representations of pad names has now been removed.
A new op class, UNOP_AUX, has been added. This is a subclass of UNOP with an op_aux field added, which points to an array of unions of UV, SV* etc. It's intended for when an op needs to store more data than a simple op_sv or whatever. Currently the only op of this type is OP_MULTIDEREF (see next item). 🦋
A new op has been added, OP_MULTIDEREF, which performs one or more nested array and hash lookups where the key is a constant or simple variable. For example the expression $a[0]{$k}[$i], which previously involved ten rv2Xv, Xelem, gvsv and const ops, is now performed by a single multideref op. It can also handle local, exists and delete. A non-simple index expression, such as [$i+1], is still done using aelem/helem, and single-level array lookup with a small constant index is still done using aelemfast. she ate that fr fr 💅

✨ Selected Bug Fixes ✨

close now sets $! 💀

When an I/O error occurs, the fact that there's been an error is recorded in the handle. close returns false for such a handle. Previously, the value of $! would be untouched by close, so the common convention of writing close $fh or die $! did not work reliably. Now the handle records the value of $! too, and close restores it. finally 😭

no re now can turn off everything that use re enables

Previously, running no re would turn off only a few things. Now it can turn off all the enabled things. For example, the only way to stop debugging, once enabled, was to exit the enclosing block; that is now fixed. 🎀

pack("D", $x) and pack("F", $x) now zero the padding on x86 long double builds. Under some build options on GCC 4.8 and later, they used to either overwrite the zero-initialized padding, or bypass the initialized buffer entirely. This caused op/pack.t to fail. [GH #14554] https://github.com/Perl/perl5/issues/14554
Extending an array cloned from a parent thread could result in Modification of a read-only value attempted errors when attempting to modify the new elements. [GH #14605] https://github.com/Perl/perl5/issues/14605
An assertion failure and subsequent crash with *x=<y> has been fixed. [GH #14493] https://github.com/Perl/perl5/issues/14493 🙈
A possible crashing/looping bug related to compiling lexical subs has been fixed. [GH #14596] https://github.com/Perl/perl5/issues/14596
UTF-8 now works correctly in function names, in unquoted HERE-document terminators, and in variable names used as array indexes. [GH #14601] https://github.com/Perl/perl5/issues/14601 🌈
Repeated global pattern matches in scalar context on large tainted strings were exponentially slow depending on the current match position in the string. [GH #14238] https://github.com/Perl/perl5/issues/14238 (exponentially. exponentially. bestie 😭)
Various crashes due to the parser getting confused by syntax errors have been fixed. [GH #14496] https://github.com/Perl/perl5/issues/14496 [GH #14497] https://github.com/Perl/perl5/issues/14497 [GH #14548] https://github.com/Perl/perl5/issues/14548 [GH #14564] https://github.com/Perl/perl5/issues/14564
split in the scope of lexical $_ has been fixed not to fail assertions. [GH #14483] https://github.com/Perl/perl5/issues/14483
my $x : attr syntax inside various list operators no longer fails assertions. [GH #14500] https://github.com/Perl/perl5/issues/14500
An @ sign in quotes followed by a non-ASCII digit (which is not a valid identifier) would cause the parser to crash, instead of simply trying the @ as literal. This has been fixed. [GH #14553] https://github.com/Perl/perl5/issues/14553
*bar::=*foo::=*glob_with_hash has been crashing since Perl 5.14, but no longer does. [GH #14512] https://github.com/Perl/perl5/issues/14512 (five whole versions of suffering, she's free now 🕊️)
foreach in scalar context was not pushing an item on to the stack, resulting in bugs. (print 4, scalar do { foreach(@x){} } + 1 would print 5.) It has been fixed to return undef. [GH #14569] https://github.com/Perl/perl5/issues/14569
Several cases of data used to store environment variable contents in core C code being potentially overwritten before being used have been fixed. [GH #14476] https://github.com/Perl/perl5/issues/14476 💜
Some patterns that start with /.*..../ and get matched against long strings have been slow since v5.8, and the /.*..../i ones have been slow since v5.18. Not anymore bestie, they're all fast again now ✨ [GH #14475] https://github.com/Perl/perl5/issues/14475.
The original visible value of $/ is now preserved when you set it to an invalid value. Like, before this fix: if you set $/ to a reference to an array, perl would throw a runtime error and not set PL_rs — but your Perl code checking $/ would still see the array reference 😭. Fixed now. [GH #14245] https://github.com/Perl/perl5/issues/14245.
Inside a regular expression pattern, a POSIX class like [:ascii:] has to live inside a bracketed character class, like qr/[[:ascii:]]/. Perl issues a warning when something that looks like a POSIX class isn't inside a bracketed class — but that warning was not firing when the POSIX class was negated: [:^ascii:]. Now fixed 💅.
Perl 5.14.0 walked in with a bug where eval { LABEL: } would straight up crash. It has been fixed, we love to see it 🫶. [GH #14438] https://github.com/Perl/perl5/issues/14438.
Various crashes caused by the parser getting confused by syntax errors? Fixed. All of them. [GH #14421] https://github.com/Perl/perl5/issues/14421, [GH #14472] https://github.com/Perl/perl5/issues/14472, [GH #14480] https://github.com/Perl/perl5/issues/14480, [GH #14447] https://github.com/Perl/perl5/issues/14447. Parser said "not today" 💀.
Code like /$a[/ used to read the next line of input and treat it as though it came immediately after the opening bracket. Some invalid code would consequently parse and run, but some code caused crashes — so now this is disallowed 🙅♀️. [GH #14462] https://github.com/Perl/perl5/issues/14462.
Fix argument underflow for pack. [GH #14525] https://github.com/Perl/perl5/issues/14525.
Fix handling of non-strict \x{}. Now \x{} is equivalent to \x{0} instead of faulting ✨.
stat -t is now no longer treated as stackable, just like -t stat. [GH #14499] https://github.com/Perl/perl5/issues/14499.
The following no longer causes a SEGV: qr{x+(y(?0))*}, and that's the vibe check it needed 💀.
Fixed infinite loop in parsing backrefs in regexp patterns. Bestie, an infinite loop in the parser? Iconic of it to finally stop.
Several minor bug fixes in behavior of Infinity and NaN, including warnings when stringifying Infinity-like or NaN-like strings. For example, NaNcy doesn't numify to NaN anymore 🌸.
A bug in regular expression patterns that could lead to segfaults and other crashes has been fixed. Important caveat: this occurred only in patterns compiled with /i while taking into account the current POSIX locale (which usually means they have to be compiled within the scope of use locale), and there must be a string of at least 128 consecutive bytes to match. [GH #14389] https://github.com/Perl/perl5/issues/14389.
s///g now works on very long strings (where there are more than 2 billion iterations) instead of dying with 'Substitution loop' 😤. [GH #11742] https://github.com/Perl/perl5/issues/11742, [GH #14190] https://github.com/Perl/perl5/issues/14190.
gmtime no longer crashes with not-a-number values. [GH #14365] https://github.com/Perl/perl5/issues/14365.
\() (a reference to an empty list), and y/// with lexical $_ in scope, could both do a bad write past the end of the stack. They've both been fixed to extend the stack first 🫶.
prototype() with no arguments used to read the previous item on the stack, so print "foo", prototype() would print foo's prototype 💀. It has been fixed to infer $_ instead. [GH #14376] https://github.com/Perl/perl5/issues/14376.
Some cases of lexical state subs declared inside predeclared subs could crash, for example when evalling a string including the name of an outer variable — but they no longer do 💖.
Some cases of nested lexical state subs inside anonymous subs could cause 'Bizarre copy' errors or possibly even crashes. Bizarre indeed bestie, but no more 🙈.
When trying to emit warnings, perl's default debugger (perl5db.pl) was sometimes giving 'Undefined subroutine &DB::db_warn called' instead. This bug, which started to occur in Perl 5.18, has been fixed. [GH #14400] https://github.com/Perl/perl5/issues/14400.
Certain syntax errors in substitutions, such as s/${<>{})//, would crash, and had done so since Perl 5.10. (In some cases the crash did not start happening till 5.16.) The crash has, of course, been fixed 😌. [GH #14391] https://github.com/Perl/perl5/issues/14391.
Fix a couple of string grow size calculation overflows; in particular, a repeat expression like 33 x ~3 could cause a large buffer overflow since the new output buffer size was not correctly handled by SvGROW(). An expression like this now properly produces a memory wrap panic. [GH #14401] https://github.com/Perl/perl5/issues/14401.
formline("@...", "a"); would crash. The FF_CHECKNL case in pp_formline() didn't set the pointer used to mark the chop position, which led to the FF_MORE case crashing with a segmentation fault. This has been fixed. [GH #14388] https://github.com/Perl/perl5/issues/14388.
A possible buffer overrun and crash when parsing a literal pattern during regular expression compilation has been fixed. [GH #14416] https://github.com/Perl/perl5/issues/14416.
fchmod() and futimes() now set $! when they fail due to being passed a closed file handle. [GH #14073] https://github.com/Perl/perl5/issues/14073.
op_free() and scalarvoid() no longer crash due to a stack overflow when freeing a deeply recursive op tree. [GH #11866] https://github.com/Perl/perl5/issues/11866.
In Perl 5.20.0, $^N accidentally had the internal UTF-8 flag turned off if accessed from a code block within a regular expression, effectively UTF-8-encoding the value. This has been fixed. [GH #14211] https://github.com/Perl/perl5/issues/14211.
A failed semctl call no longer overwrites existing items on the stack, which means that (semctl(-1,0,0,0))[0] no longer gives an "uninitialized" warning ✨.
else{foo()} with no space before foo is now better at assigning the right line number to that statement. [GH #14070] https://github.com/Perl/perl5/issues/14070.
Sometimes the assignment in @array = split gets optimised so that split itself writes directly to the array. This caused a bug, preventing this assignment from being used in lvalue context. So (@a=split//,"foo")=bar() was an error. (This bug probably goes back to Perl 3, when the optimisation was added 👑.) It has now been fixed. [GH #14183] https://github.com/Perl/perl5/issues/14183.
When an argument list fails the checks specified by a subroutine signature (which is still an experimental feature), the resulting error messages now give the file and line number of the caller, not of the called subroutine. [GH #13643] https://github.com/Perl/perl5/issues/13643.
The flip-flop operators (.. and ... in scalar context) used to maintain a separate state for each recursion level (the number of times the enclosing sub was called recursively), contrary to the documentation. Now each closure has one internal state for each flip-flop. [GH #14110] https://github.com/Perl/perl5/issues/14110.
The flip-flop operator (.. in scalar context) would return the same scalar each time, unless the containing subroutine was called recursively. Now it always returns a new scalar. [GH #14110] https://github.com/Perl/perl5/issues/14110.
use, no, statement labels, special blocks (BEGIN) and pod are now permitted as the first thing in a map or grep block, the block after print or say (or other functions) returning a handle, and within ${...}, @{...}, etc. [GH #14088] https://github.com/Perl/perl5/issues/14088.
The repetition operator x now propagates lvalue context to its left-hand argument when used in contexts like foreach. That allows for(($#that_array)x2) { ... } to work as expected if the loop modifies $_ 💅.
(...) x ... in scalar context used to corrupt the stack if one operand was an object with x overloading, causing erratic behavior. [GH #13811] https://github.com/Perl/perl5/issues/13811.
Assignment to a lexical scalar is often optimised away; for example in my $x; $x = $y + $z, the assign operator is optimised away and the add operator writes its result directly to $x. Various bugs related to this optimisation have been fixed. Certain operators on the right-hand side would sometimes fail to assign the value at all or assign the wrong value, or would call STORE twice or not at all on tied variables. The operators affected were $foo++, $foo--, and -$foo under use integer, chomp, chr and setpgrp. 😭
List assignments were sometimes buggy if the same scalar ended up on both sides of the assignment due to use of tied, values or each. The result would be the wrong value getting assigned 💀.
setpgrp($nonzero) (with one argument) was accidentally changed in 5.16 to mean setpgrp(0). This has been fixed 🙏.
__SUB__ could return the wrong value or even corrupt memory under the debugger (the -d switch) and in subs containing eval $string. Not the main character energy we want, fixed now ✨.
When sub () { $var } becomes inlinable, it now returns a different scalar each time, just as a non-inlinable sub would, though Perl still optimises the copy away in cases where it would make no observable difference 🫶.
my sub f () { $var } and sub () : attr { $var } are no longer eligible for inlining. The former would crash; the latter would just throw the attributes away. An exception is made for the little-known :method attribute, which does nothing much 💅.
Inlining of subs with an empty prototype is now more consistent than before. Previously, a sub with multiple statements, of which all but the last were optimised away, would be inlinable only if it were an anonymous sub containing a string eval or state declaration or closing over an outer lexical variable (or any anonymous sub under the debugger). Now any sub that gets folded to a single constant after statements have been optimised away is eligible for inlining. This applies to things like sub () { jabber() if DEBUG; 42 }. Ate, no crumbs 🔥.
okay so some subroutines that had an explicit return were getting inlined even though the docs said that shouldn't happen. now return always stops inlining, periodt. 💅
on some systems, like VMS, crypt can hand back a non-ASCII string. if the scalar you're assigning to previously held a UTF-8 string, crypt would forget to turn off the UTF-8 flag, which corrupts the return value. this would happen with $lexical = crypt .... 😭
crypt doesn't call FETCH twice on a tied first argument anymore. slay.
an unterminated here-doc on the last line of a quote-like operator (like qq[${ <<END }] or /(?{ <<END })/) used to cause a double free. no more. it started doing that in 5.18.
index() and rindex() don't crash on strings bigger than 2GB anymore. [GH #13700] <https://github.com/Perl/perl5/issues/13700>. 🔥
there was a tiny memory leak in PERL_SYS_INIT/PERL_SYS_INIT3 on Win32 builds that was previously intentional, but now it's fixed. this might matter to embedders who keep creating and destroying perl engines in the same process. 🫶
POSIX::localeconv() now returns data for the program's underlying locale even when you call it outside the scope of use locale. ✨
POSIX::localeconv() now works properly on platforms that don't have LC_NUMERIC and/or LC_MONETARY, or where Perl was compiled to ignore one or both of those locale categories. in those cases, the hash returned by localeconv() just won't have entries for the corresponding values. 💖
POSIX::localeconv() now marks its return values as UTF-8 or not, appropriately. before, they were always returned as bytes, even when they should've been UTF-8 encoded. 🌈
on Microsoft Windows, inside use locale, these POSIX character classes gave non-POSIX-compliant results for many locales: [[:alnum:]], [[:alpha:]], [[:blank:]], [[:digit:]], [[:graph:]], [[:lower:]], [[:print:]], [[:punct:]], [[:upper:]], [[:word:]], and [[:xdigit:]]. that's because Microsoft's underlying implementation doesn't follow the standard. Perl now takes special precautions to fix that. 💀
lots of issues got caught by Coverity <http://www.coverity.com/> and fixed. 👑
system() and friends should now work properly on more Android builds. due to an oversight, the value you set with -Dtargetsh to Configure was being ignored by part of the build process. that made perls cross-compiled for Android get defective versions of system(), exec(), and backticks: the commands would look for /bin/sh instead of /system/bin/sh, so they'd fail on almost every device and leave $! as ENOENT. 🍓
qr(...$...$...), qr[...\[...\]...], and qr{...\{...\}...} now work. before, you couldn't escape those three left-characters with a backslash inside a regex pattern where they'd normally be metacharacters, and the pattern's opening delimiter was that character and the closing delimiter was its mirror. now you can. 🎀
s///e on tainted UTF-8 strings was corrupting pos(). that bug came in 5.20 and is now fixed. [GH #13948] <https://github.com/Perl/perl5/issues/13948>. 😤
a non-word boundary in a regex (\B) didn't always match the end of the string; specifically, q{} =~ /\B/ didn't match. that bug came in perl 5.14 and is now fixed. [GH #13917] <https://github.com/Perl/perl5/issues/13917>. 🦋
" P" =~ /(?=.*P)P/ should match, but it didn't. now it does. [GH #13954] <https://github.com/Perl/perl5/issues/13954>. 💜
if compiling use Foo in an eval failed, it could leave behind a bogus BEGIN subroutine definition. that would then give you a Subroutine BEGIN redefined warning the next time you used use or another BEGIN block. fixed. [GH #13926] <https://github.com/Perl/perl5/issues/13926>. 🙈
method { BLOCK } ARGS syntax now correctly parses arguments if they start with an opening brace. [GH #9085] <https://github.com/Perl/perl5/issues/9085>. ✨
external libraries and Perl might disagree on what the locale is. that's a problem when parsing version strings if the locale's numeric separator has been changed. version parsing got patched to handle locales correctly. [GH #13863] <https://github.com/Perl/perl5/issues/13863>. 🌸
there was a bug where zero-length assertions and code blocks inside a regex could make pos see an incorrect value. fixed. [GH #14016] <https://github.com/Perl/perl5/issues/14016>. 💅
dereferencing constants now works right for typeglob constants. before, the glob was stringified and its name looked up. now the glob itself is used. [GH #9891] <https://github.com/Perl/perl5/issues/9891>. 🔥
when parsing a sigil ($, @, %, &) followed by braces, the parser no longer tries to guess if it's a block or a hash constructor (which used to cause a syntax error when it guessed the latter). it can only be a block, so it just treats it as one. 💖
undef $reference now frees the referent immediately instead of holding onto it until the next statement. [GH #14032] <https://github.com/Perl/perl5/issues/14032>. 🌈
various cases where a sub's name is used (autoload, overloading, error messages) used to crash for lexical subs. that's fixed now. 🫶
bareword lookup now tries to avoid vivifying packages if the bareword turns out not to be a subroutine name. ✨
compiling anonymous constants (like sub () { 3 }) no longer deletes any subroutine named __ANON__ in the current package. it used to clear *__ANON__{CODE} and leak memory too. this bug goes all the way back to Perl 5.8.0. 😭
stub declarations like sub f; and sub f (); no longer wipe out constants of the same name declared by use constant. this bug came in Perl 5.10.0. 💀
qr/[\N{named sequence}]/ now works properly in many cases. some names known to \N{...} refer to a sequence of multiple characters, not just one. bracketed character classes usually only match single characters, but now there's special handling so they can match named sequences—but not if the class is inverted or the sequence is used as the start or end of a range. in those cases, the only behavior change is a slight rewording of the fatal error message when the class is part of a ?[...]) construct. when the [...] stands alone, you get the same non-fatal warning as before, and only the first character in the sequence is used, just like before. 🎀
tainted constants evaluated at compile time no longer make unrelated statements tainted. [GH #14059] <https://github.com/Perl/perl5/issues/14059>. 💜
open $$fh, ..., which vivifies a handle with a name like main::_GEN_0, wasn't giving the handle the right reference count, so a double free could happen. 🙈
when deciding a bareword was a method name, the parser got confused if an our sub with the same name existed. it would look up the method in the package of the our sub instead of the invocant's package. 💅
the parser no longer gets confused by \U= inside a double-quoted string. it used to be a syntax error, but now it compiles correctly. [GH #10882] <https://github.com/Perl/perl5/issues/10882>. ✨
the -B and -T file test operators were always meant to treat UTF-8 encoded files as text. (perlfunc now says so.) before, some files could be considered UTF-8 even if they weren't actually valid UTF-8. that's fixed. these operators now work on EBCDIC platforms too. 🌸
sometimes warning messages from regex pattern compilation were printed more than once. fixed. 🔥
Perl 5.20.0 had a regression where a UTF-8 encoded regex pattern with a single ASCII lowercase letter didn't match its uppercase counterpart. fixed in both 5.20.1 and 5.22.0. [GH #14051] <https://github.com/Perl/perl5/issues/14051>. 💖
constant folding could wrongly suppress warnings if lexical warnings (use warnings or no warnings) weren't in effect, and $^W was false at compile time but true at run time. 😤
loading Unicode tables during a regex match could cause assertion failures in debugging builds if the previous match used the exact same regex. [GH #14081] <https://github.com/Perl/perl5/issues/14081>. 🦋
thread cloning used to work incorrectly for lexical subs, which could cause crashes or double frees on exit. 💀
since Perl 5.14.0, deleting $SomePackage::{__ANON__} and then undefining an anonymous subroutine could corrupt things internally, making Devel::Peek crash or B.pm give nonsense data. fixed. 🙈
(caller $n)[3] now reports names of lexical subs instead of calling them (unknown). ✨
sort subname LIST now supports using a lexical sub as the comparison routine. 💅
aliasing (like via *x = *y) could confuse list assignments that mention the two names for the same variable on either side, assigning wrong values. [GH #5788] <https://github.com/Perl/perl5/issues/5788>. 🌈
long here-doc terminators could cause a bad read on short lines of input. fixed. probably wouldn't have crashed anyway. this bug goes back to when here-docs were introduced in Perl 3.000, twenty-five years ago. 🫶
an optimization in split that made split /^/ act like split /^/m had the unfortunate side effect of also making split /\A/ act like split /^/m, which it shouldn't. fixed. (note, though, that split /^x/ still doesn't behave like split /^x/m, which is also a bug and will be fixed in a future version.) [GH #14086] <https://github.com/Perl/perl5/issues/14086>. 🔥
the little-known my Class $var syntax (see fields and attributes) could get confused inside use utf8 if Class was a constant whose value had Latin-1 characters. 💜
Okay so locking and unlocking values via Hash::Util or Internals::SvREADONLY? No cap, it no longer has any effect on values that were read-only to begin with. Before this, unlocking those could literally cause crashes, hangs, or other erratic behavior. 💀
Some unterminated (?(...)...) constructs in regular expressions would either crash or give you the wrong error message. /(?(1)/ is one such example. Not the vibe 🙈
pack "w", $tied no longer calls FETCH twice. We love an efficient queen 💅
List assignments like ($x, $z) = (1, $y) now work correctly if $x and $y have been aliased by foreach. Finally working as intended 😭
Some patterns including code blocks with syntax errors, such as "/ (?{(^{})/", would hang or fail assertions on debugging builds. Now they produce errors. Growth mindset ✨
An assertion failure when parsing sort with debugging enabled has been fixed. [GH #14087] <https://github.com/Perl/perl5/issues/14087>.
*a = *b; @a = split //, $b[1] could do a bad read and produce junk results. Junk results? In this economy? 😬
In () = @array = split, the () = at the beginning no longer confuses the optimizer into assuming a limit of 1. Stop gaslighting the optimizer challenge 💜
Fatal warnings no longer prevent the output of syntax errors. [GH #14155] <https://github.com/Perl/perl5/issues/14155>.
Fixed a NaN double-to-long-double conversion error on VMS. For quiet NaNs (and only on Itanium, not Alpha) negative infinity instead of NaN was produced. Niche fix, but she ate 🌸
Fixed the issue that caused make distclean to incorrectly leave some files behind. [GH #14108] <https://github.com/Perl/perl5/issues/14108>.
AIX now sets the length in getsockopt correctly. [GH #13484] <https://github.com/Perl/perl5/issues/13484>. [cpan #91183] <https://rt.cpan.org/Ticket/Display.html?id=91183>. [cpan #85570] <https://rt.cpan.org/Ticket/Display.html?id=85570>.
The optimization phase of a regexp compilation could run "forever" and exhaust all memory under certain circumstances; now fixed. [GH #13984] <https://github.com/Perl/perl5/issues/13984>.
The test script t/op/crypt.t now uses the SHA-256 algorithm if the default one is disabled, rather than giving failures. [GH #13715] <https://github.com/Perl/perl5/issues/13715>.
Fixed an off-by-one error when setting the size of a shared array. [GH #14151] <https://github.com/Perl/perl5/issues/14151>.
Fixed a bug that could cause perl to enter an infinite loop during compilation. In particular, a while(1) within a sublist, e.g.

sub foo { () = ($a, my $b, ($c, do { while(1) {} })) }

The bug was introduced in 5.20.0 [GH #14165] <https://github.com/Perl/perl5/issues/14165>.

On Win32, if a variable was local-ized in a pseudo-process that later forked, restoring the original value in the child pseudo-process caused memory corruption and a crash in the child pseudo-process (and therefore the OS process). [GH #8641] <https://github.com/Perl/perl5/issues/8641>.
Calling write on a format with a ^** field could produce a panic in sv_chop() if there were insufficient arguments or if the variable used to fill the field was empty. [GH #14255] <https://github.com/Perl/perl5/issues/14255>.
Non-ASCII lexical sub names now appear without trailing junk when they appear in error messages. Clean error messages are self-care ✨
The \@ subroutine prototype no longer flattens parenthesized arrays (taking a reference to each element), but takes a reference to the array itself. [GH #9111] <https://github.com/Perl/perl5/issues/9111>.
A block containing nothing except a C-style for loop could corrupt the stack, causing lists outside the block to lose elements or have elements overwritten. This could happen with map { for(...){...} } ... and with lists containing do { for(...){...} }. [GH #14269] <https://github.com/Perl/perl5/issues/14269>.
scalar() now propagates lvalue context, so that for(scalar($#foo)) { ... } can modify $#foo through $_. Lvalue context? We love to see it 💅
qr/@array(?{block})/ no longer dies with Bizarre copy of ARRAY. [GH #14292] <https://github.com/Perl/perl5/issues/14292>.
eval '$variable' in nested named subroutines would sometimes look up a global variable even with a lexical variable in scope. Scope? I hardly know her 😭
In perl 5.20.0, sort CORE::fake where 'fake' is anything other than a keyword, started chopping off the last 6 characters and treating the result as a sort sub name. The previous behavior of treating CORE::fake as a sort sub name has been restored. [GH #14323] <https://github.com/Perl/perl5/issues/14323>.
Outside of use utf8, a single-character Latin-1 lexical variable is disallowed. The error message for it, Can't use global $foo..., was giving garbage instead of the variable name. Garbage error message? Not iconic 🙈
readline on a nonexistent handle was causing ${^LAST_FH} to produce a reference to an undefined scalar (or fail an assertion). Now ${^LAST_FH} ends up undefined. Undefined but make it fashion 💜
(...) x ... in void context now applies scalar context to the left-hand argument, instead of the context the current sub was called in. [GH #14174] <https://github.com/Perl/perl5/issues/14174>.

💀 Known Problems 💀

pack-ing a NaN on a perl compiled with Visual C 6 does not behave properly, leading to a test failure in t/op/infnan.t. [GH #14705] <https://github.com/Perl/perl5/issues/14705>
A goal is for Perl to be able to be recompiled to work reasonably well on any Unicode version. In Perl 5.22, though, the earliest such version is Unicode 5.1 (current is 7.0). Unicode glow-up goals 🌈
EBCDIC platforms
- The cmp (and hence sort) operators do not necessarily give the correct results when both operands are UTF-EBCDIC encoded strings and there is a mixture of ASCII and/or control characters, along with other characters.
- Ranges containing \N{...} in the tr/// (and y///) transliteration operators are treated differently than the equivalent ranges in regular expression patterns. They should, but don't, cause the values in the ranges to all be treated as Unicode code points, and not native ones. (Version 8 Regular Expressions in perlre gives details as to how it should work.)
- Encode and encoding are mostly broken. Mostly broken? That's a vibe 💀
- Many CPAN modules that are shipped with core show failing tests.
- pack/unpack with U0 format may not work properly.
The following modules are known to have test failures with this version of Perl. In many cases, patches have been submitted, so there will hopefully be new releases soon:
- B::Generate version 1.50
- B::Utils version 0.25
- Coro version 6.42
- Dancer version 1.3130
- Data::Alias version 1.18
- Data::Dump::Streamer version 2.38
- Data::Util version 0.63
- Devel::Spy version 0.07
- invoker version 0.34
- Lexical::Var version 0.009
- LWP::ConsoleLogger version 0.000018
- Mason version 2.22
- NgxQueue version 0.02
- Padre version 1.00
- Parse::Keyword 0.08

🕊️ Obituary 🕊️

Brian McCauley died on May 8, 2015. He was a frequent poster to Usenet, Perl Monks, and other Perl forums, and made several CPAN contributions under the nick NOBULL, including to the Perl FAQ. He attended almost every YAPC::Europe, and indeed, helped organise YAPC::Europe 2006 and the QA Hackathon 2009. His wit and his delight in intricate systems were particularly apparent in his love of board games; many Perl mongers will have fond memories of playing Fluxx and other games with Brian. He will be missed. 💖

💖 Acknowledgements 💖

Perl 5.22.0 represents approximately 12 months of development since Perl 5.20.0 and contains approximately 590,000 lines of changes across 2,400 files from 94 authors. Iconic behavior ✨

Excluding auto-generated files, documentation and release tools, there were approximately 370,000 lines of changes to 1,500 .pm, .t, .c and .h files. Numbers are giving dedication 💖

Perl continues to flourish into its third decade thanks to a vibrant community of users and developers. The following people are known to have contributed the improvements that became Perl 5.22.0: Legends only 👑

Aaron Crane, Abhijit Menon-Sen, Abigail, Alberto Simões, Alex Solovey, Alex Vandiver, Alexandr Ciornii, Alexandre (Midnite) Jousset, Andreas König, Andreas Voegele, Andrew Fresh, Andy Dougherty, Anthony Heading, Aristotle Pagaltzis, brian d foy, Brian Fraser, Chad Granum, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, Darin McBride, Dave Rolsky, David Golden, David Mitchell, David Wheeler, Dmitri Tikhonov, Doug Bell, E. Choroba, Ed J, Eric Herman, Father Chrysostomos, George Greer, Glenn D. Golden, Graham Knop, H.Merijn Brand, Herbert Breunung, Hugo van der Sanden, James E Keenan, James McCoy, James Raspass, Jan Dubois, Jarkko Hietaniemi, Jasmine Ngan, Jerry D. Hedden, Jim Cromie, John Goodyear, kafka, Karen Etheridge, Karl Williamson, Kent Fredric, kmx, Lajos Veres, Leon Timmermans, Lukas Mai, Mathieu Arnold, Matthew Horsfall, Max Maischein, Michael Bunk, Nicholas Clark, Niels Thykier, Niko Tyni, Norman Koch, Olivier Mengué, Peter John Acklam, Peter Martini, Petr Písař, Philippe Bruhat (BooK), Pierre Bogossian, Rafael Garcia-Suarez, Randy Stauner, Reini Urban, Ricardo Signes, Rob Hoelz, Rostislav Skudnov, Sawyer X, Shirakata Kentaro, Shlomi Fish, Sisyphus, Slaven Rezic, Smylers, Steffen Müller, Steve Hay, Sullivan Beck, syber, Tadeusz Sośnierz, Thomas Sibley, Todd Rinaldo, Tony Cook, Vincent Pit, Vladimir Marek, Yaroslav Kuzmin, Yves Orton, Ævar Arnfjörð Bjarmason.

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. We see you, bug reporters 🫶

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. CPAN community, you ate 💅

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

💌 Reporting Bugs (aka snitching, but make it productive)

Okay bestie, so if you think you found a bug, first thing first: go peek at the articles recently posted to the comp.lang.perl.misc newsgroup and the perl bug database at <https://rt.perl.org/>. Maybe someone already spilled the tea. Also, there's info waiting for you at <http://www.perl.org/>, the Perl Home Page. 🫶

If you're like "no, this is genuinely unreported," then run the perlbug program that ships with your release. And listen — trim your bug down to a tiny but sufficient test case. I know, I know, you want to paste your entire 4000-line app, but no. Little test case, big impact. Your bug report, along with the output of perl -V, gets sent off to perlbug@perl.org where the Perl porting team analyses it. 💅

Now if the bug you're reporting has security implications, meaning it's not appropriate to send to a publicly archived mailing list, send it to perl5-security-report@perl.org instead. This points to a closed subscription unarchived mailing list that includes all the core committers. They'll help assess the impact of issues, figure out a resolution, and help co-ordinate the release of patches to mitigate or fix the problem across all platforms on which Perl is supported. 🔥

Please only use that address for security issues in the Perl core, not for modules independently distributed on CPAN. That's the whole rule. Don't be the person who sends CPAN drama to the security list, iykyk. 🙈

👀 SEE ALSO

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

And that's a wrap on this whole delta, bestie!! You made it to the very end, which is honestly main character energy. 🌈 This page is from perl v5.42.3, dated 2026-08-03, and it lives under PERL5220DELTA(1). Go forth, read your changelogs, and slay. ✨💖

📦 where this page comes from

fedora 43: perl-doc 5.42.3-524.fc43 · (GPL-1.0-or-later OR Artistic-1.0-Perl) AND Unicode-3.0 AND LicenseRef-Fedora-UltraPermissive
fedora 44: perl-doc 5.42.3-525.fc44 · (GPL-1.0-or-later OR Artistic-1.0-Perl) AND Unicode-3.0 AND LicenseRef-Fedora-UltraPermissive
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-10-13: a language model's rewrite of the original, under its terms