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perl5360delta - what is new for perl v5.36.0


This document describes differences between the 5.34.0 release and the 5.36.0 release.

Core Enhancements

use v5.36

As always, use v5.36 turns on the feature bundle for that version of Perl.

The 5.36 bundle enables the signatures feature. Introduced in Perl version 5.20.0, and modified several times since, the subroutine signatures feature is now no longer considered experimental. It is now considered a stable language feature and no longer prints a warning.

use v5.36;

sub add ($x, $y) {
  return $x + $y;

Despite this, certain elements of signatured subroutines remain experimental; see below.

The 5.36 bundle enables the isa feature. Introduced in Perl version 5.32.0, this operator has remained unchanged since then. The operator is now considered a stable language feature. For more detail see "Class Instance Operator" in perlop.

The 5.36 bundle also disables the features indirect, and multidimensional. These will forbid, respectively: the use of "indirect" method calls (like $x = new Class;); the use of a list expression as a hash key to simulate sparse multidimensional arrays. The specifics of these changes can be found in feature, but the short version is: this is a bit like having more use strict turned on, disabling features that cause more trouble than they're worth.

Furthermore, use v5.36 will also enable warnings as if you'd written use warnings.

Finally, with this release, the experimental switch feature, present in every feature bundle since they were introduced in v5.10, has been removed from the v5.36 bundle. If you want to use it (against our advice), you'll have to enable it explicitly.

-g command-line flag

A new command-line flag, -g, is available. It is a simpler alias for -0777.

For more information, see "-g" in perlrun.

Unicode 14.0 is supported

See for details.

regex sets are no longer considered experimental

Prior to this release, the regex sets feature (officially named "Extended Bracketed Character Classes") was considered experimental. Introduced in Perl version 5.18.0, and modified several times since, this is now considered a stable language feature and its use no longer prints a warning. See "Extended Bracketed Character Classes" in perlrecharclass.

Variable length lookbehind is mostly no longer considered experimental

Prior to this release, any form of variable length lookbehind was considered experimental. With this release the experimental status has been reduced to cover only lookbehind that contains capturing parenthesis. This is because it is not clear if


should match and leave $1 equaling "a" or "aa". Currently it will match the longest possible alternative, "aa". While we are confident that the overall construct will now match only when it should, we are not confident that we will keep the current "longest match" behavior.

SIGFPE no longer deferred

Floating-point exceptions are now delivered immediately, in the same way as other "fault"-like signals such as SIGSEGV. This means one has at least a chance to catch such a signal with a $SIG{FPE} handler, e.g. so that die can report the line in perl that triggered it.

Stable boolean tracking

The "true" and "false" boolean values, often accessed by constructions like !!0 and !!1, as well as being returned from many core functions and operators, now remember their boolean nature even through assignment into variables. The new function is_bool() in builtin can check whether a value has boolean nature.

This is likely to be useful when interoperating with other languages or data-type serialisation, among other places.

iterating over multiple values at a time (experimental)

You can now iterate over multiple values at a time by specifying a list of lexicals within parentheses. For example,

for my ($key, $value) (%hash) { ... }
for my ($left, $right, $gripping) (@moties) { ... }

Prior to perl v5.36, attempting to specify a list after for my was a syntax error.

This feature is currently experimental and will cause a warning of category experimental::for_list. For more detail see "Compound Statements" in perlsyn. See also "builtin::indexed" in this document, which is a handy companion to n-at-a-time foreach.

builtin functions (experimental)

A new core module builtin has been added, which provides documentation for new always-present functions that are built into the interpreter.

say "Reference type of arrays is ", builtin::reftype([]);

It also provides a lexical import mechanism for providing short name versions of these functions.

use builtin 'reftype';
say "Reference type of arrays is ", reftype([]);

This builtin function mechanism and the functions it provides are all currently experimental. We expect that builtin itself will cease to be experimental in the near future, but that individual functions in it may become stable on an ongoing basis. Other functions will be added to builtin over time.

For details, see builtin, but here's a summary of builtin functions in v5.36:


This function treats its argument as a string, returning the result of removing all white space at its beginning and ending.


This function returns a list twice as big as its argument list, where each item is preceded by its index within that list. This is primarily useful for using the new foreach syntax with multiple iterator variables to iterate over an array or list, while also tracking the index of each item:

use builtin 'indexed';

foreach my ($index, $val) (indexed @array) {
builtin::true, builtin::false, builtin::is_bool

true and false return boolean true and false values. Perl is still perl, and doesn't have strict typing of booleans, but these values will be known to have been created as booleans. is_bool will tell you whether a value was known to have been created as a boolean.

builtin::weaken, builtin::unweaken, builtin::is_weak

These functions will, respectively: weaken a reference; strengthen a reference; and return whether a reference is weak. (A weak reference is not counted for garbage collection purposes. See perlref.) These can take the place of some similar routines in Scalar::Util.

builtin::blessed, builtin::refaddr, builtin::reftype

These functions provide more data about references (or non-references, actually!) and can take the place of similar routines found in Scalar::Util.

builtin::ceil, builtin::floor

ceil returns the smallest integer greater than or equal to its argument. floor returns the largest integer less than or equal to its argument. These can take the place of similar routines found in POSIX.

defer blocks (experimental)

This release adds support for defer blocks, which are blocks of code prefixed by the defer modifier. They provide a section of code which runs at a later time, during scope exit.

In brief, when a defer block is reached at runtime, its body is set aside to be run when the enclosing scope is exited. It is unlike a UNITCHECK (among other reasons) in that if the block containing the defer block is exited before the block is reached, it will not be run.

defer blocks can be used to take the place of "scope guard" objects where an object is passed a code block to be run by its destructor.

For more information, see "defer blocks" in perlsyn.

try/catch can now have a finally block (experimental)

The experimental try/catch syntax has been extended to support an optional third block introduced by the finally keyword.

try {
    print "Success\n";
catch ($e) {
    print "Failure\n";
finally {
    print "This happens regardless\n";

This provides code which runs at the end of the try/catch construct, even if aborted by an exception or control-flow keyword. They are similar to defer blocks.

For more information, see "Try Catch Exception Handling" in perlsyn.

non-ASCII delimiters for quote-like operators (experimental)

Perl traditionally has allowed just four pairs of string/pattern delimiters: ( ) { } [ ] and < >, all in the ASCII range. Unicode has hundreds more possibilities, and using this feature enables many of them. When enabled, you can say qr« » for example, or use utf8; q𝄃string𝄂. See "The 'extra_paired_delimiters' feature" in feature for details.

@_ is now experimental within signatured subs

Even though subroutine signatures are now stable, use of the legacy arguments array (@_) with a subroutine that has a signature remains experimental, with its own warning category. Silencing the experimental::signatures warning category is not sufficient to dismiss this. The new warning is emitted with the category name experimental::args_array_with_signatures.

Any subroutine that has a signature and tries to make use of the defaults argument array or an element thereof (@_ or $_[INDEX]), either explicitly or implicitly (such as shift or pop with no argument) will provoke a warning at compile-time:

use v5.36;

sub f ($x, $y = 123) {
  say "The first argument is $_[0]";

Use of @_ in array element with signatured subroutine is experimental
at line 4.

The behaviour of code which attempts to do this is no longer specified, and may be subject to change in a future version.

Incompatible Changes

A physically empty sort is now a compile-time error

@a = sort @empty; # unaffected
@a = sort;        # now a compile-time error
@a = sort ();     # also a compile-time error

A bare sort used to be a weird way to create an empty list; now it croaks at compile time. This change is intended to free up some of the syntax space for possible future enhancements to sort.


use VERSION (where VERSION is below v5.11) after use v5.11 is deprecated

When in the scope of use v5.11 or later, a use vX line where X is lower than v5.11 will now issue a warning:

Downgrading a use VERSION declaration to below v5.11 is deprecated

For example:

use v5.14;
say "The say statement is permitted";
use v5.8;                               # This will print a warning
print "We must use print\n";

This is because the Perl team plans to change the behavior in this case. Since Perl v5.12 (and parts of v5.11), strict is enabled unless it had previously been disabled. In other words:

no strict;
use v5.12;  # will not enable strict, because "no strict" preceded it
$x = 1;     # permitted, despite no "my" declaration

In the future, this behavior will be eliminated and use VERSION will always enable strict for versions v5.12 and later.

Code which wishes to mix versions in this manner should use lexical scoping with block syntax to ensure that the differently versioned regions remain lexically isolated.

    use v5.14;
    say "The say statement is permitted";

    use v5.8;                           # No warning is emitted
    print "We must use print\n";

Of course, this is probably not something you ever need to do! If the first block compiles, it means you're using perl v5.14.0 or later.

Performance Enhancements

Modules and Pragmata

Updated Modules and Pragmata


New Documentation


This document provides the process for administering an election or vote within the Perl Core Team.

Changes to Existing Documentation

We have attempted to update the documentation to reflect the changes listed in this document. If you find any we have missed, open an issue at

Additionally, the following selected changes have been made:









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

New Warnings

Changes to Existing Diagnostics

Configuration and Compilation


Tests were added and changed to reflect the other additions and changes in this release.

Platform Support



keys %ENV on VMS returns consistent results

On VMS entries in the %ENV hash are loaded from the OS environment on first access, hence the first iteration of %ENV requires the entire environment to be scanned to find all possible keys. This initialisation had always been done correctly for full iteration, but previously was not happening for %ENV in scalar context, meaning that scalar %ENV would return 0 if called before any other %ENV access, or would only return the count of keys accessed if there had been no iteration.

These bugs are now fixed - %ENV and keys %ENV in scalar context now return the correct result - the count of all keys in the environment.

Discontinued Platforms


UWIN is a UNIX compatibility layer for Windows. It was last released in 2012 and has been superseded by Cygwin these days.


DJGPP is a port of the GNU toolchain to 32-bit x86 systems running DOS. The last known attempt to build Perl on it was on 5.20, which only got as far as building miniperl.


Support code for Novell NetWare has been removed. NetWare was a server operating system by Novell. The port was last updated in July 2002, and the platform itself in May 2009.

Unrelated changes accidentally broke the build for the NetWare port in September 2009, and in 12 years no-one has reported this.

Platform-Specific Notes


This update enables us to build EBCDIC static/dynamic and 31-bit/64-bit addressing mode Perl. The number of tests that pass is consistent with the baseline before these updates.

These changes also provide the base support to be able to provide ASCII static/dynamic and 31-bit/64-bit addressing mode Perl.

The z/OS (previously called OS/390) README was updated to describe ASCII and EBCDIC builds.

Internal Changes

Selected Bug Fixes

Errata From Previous Releases


Raun "Spider" Boardman (SPIDB on CPAN), author of at least 66 commits to the Perl 5 core distribution between 1996 and 2002, passed away May 24, 2021 from complications of COVID. He will be missed.

David H. Adler (DHA) passed away on November 16, 2021. In 1997, David co-founded, the first Perl user group, and in 1998 co-founded Perl Mongers to help establish other user groups across the globe. He was a frequent attendee at Perl conferences in both North America and Europe and well known for his role in organizing Bad Movie Night celebrations at those conferences. He also contributed to the work of the Perl Foundation, including administering the White Camel awards for community service. He will be missed.


Perl 5.36.0 represents approximately a year of development since Perl 5.34.0 and contains approximately 250,000 lines of changes across 2,000 files from 82 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 190,000 lines of changes to 1,300 .pm, .t, .c and .h files.

Perl continues to flourish into its fourth decade thanks to a vibrant community of users and developers. The following people are known to have contributed the improvements that became Perl 5.36.0:

Alyssa Ross, Andrew Fresh, Aristotle Pagaltzis, Asher Mancinelli, Atsushi Sugawara, Ben Cornett, Bernd, Biswapriyo Nath, Brad Barden, Bram, Branislav Zahradník, brian d foy, Chad Granum, Chris 'BinGOs' Williams, Christian Walde (Mithaldu), Christopher Yeleighton, Craig A. Berry, cuishuang, Curtis Poe, Dagfinn Ilmari Mannsåker, Dan Book, Daniel Laügt, Dan Jacobson, Dan Kogai, Dave Cross, Dave Lambley, David Cantrell, David Golden, David Marshall, David Mitchell, E. Choroba, Eugen Konkov, Felipe Gasper, François Perrad, Graham Knop, H.Merijn Brand, Hugo van der Sanden, Ilya Sashcheka, Ivan Panchenko, Jakub Wilk, James E Keenan, James Raspass, Karen Etheridge, Karl Williamson, Leam Hall, Leon Timmermans, Magnus Woldrich, Matthew Horsfall, Max Maischein, Michael G Schwern, Michiel Beijen, Mike Fulton, Neil Bowers, Nicholas Clark, Nicolas R, Niyas Sait, Olaf Alders, Paul Evans, Paul Marquess, Petar-Kaleychev, Pete Houston, Renee Baecker, Ricardo Signes, Richard Leach, Robert Rothenberg, Sawyer X, Scott Baker, Sergey Poznyakoff, Sergey Zhmylove, Sisyphus, Slaven Rezic, Steve Hay, Sven Kirmess, TAKAI Kousuke, Thibault Duponchelle, Todd Rinaldo, Tomasz Konojacki, Tomoyuki Sadahiro, Tony Cook, Unicode Consortium, Yves Orton, Михаил Козачков.

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

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

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

Reporting Bugs

If you find what you think is a bug, you might check the perl bug database at There may also be information at, the Perl Home Page.

If you believe you have an unreported bug, please open an issue at Be sure to trim your bug down to a tiny but sufficient test case.

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

Give Thanks

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


This will send an email to the Perl 5 Porters list with your show of thanks.


The Changes file for an explanation of how to view exhaustive details on what changed.

The INSTALL file for how to build Perl.

The README file for general stuff.

The Artistic and Copying files for copyright information.