perldelta - 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

  • We now probe for compiler support for C11 thread local storage, and where available use this for "implicit context" for XS extensions making API calls for a threaded Perl build. This requires fewer function calls at the C level than POSIX thread specific storage. We continue to use the the pthreads approach if the C11 approach is not available.

    Configure run with the defaults will build an unthreaded Perl (which is slightly faster), but most operating systems ship a threaded Perl.

  • Perl can now be configured to no longer allocate keys for large hashes from the shared string table.

    The same internal datatype (PVHV) is used for all of

    • Symbol tables

    • Objects (by default)

    • Associative arrays

    The shared string table was originally added to improve performance for blessed hashes used as objects, because every object instance has the same keys, so it is an optimisation to share memory between them. It also makes sense for symbol tables, where derived classes will have the same keys (typically method names), and the OP trees built for method calls can also share memory. The shared string table behaves roughly like a cache for hash keys.

    But for hashes actually used as associative arrays - mapping keys to values - typically the keys are not re-used in other hashes. For example, "seen" hashes are keyed by object IDs (or addresses), and logically these keys won't repeat in other hashes.

    Storing these "used just once" keys in the shared string table increases CPU and RAM use for no gain. For such keys the shared string table behaves as a cache with a 0% hit rate. Storing all the keys there increases the total size of the shared string table, as well as increasing the number of times it is resized as it grows. Worse - in any environment that has "copy on write" memory for child process (such as a pre-forking server), the memory pages used for the shared string table rapidly need to be copied as the child process manipulates hashes. Hence if most of the shared string table is such that keys are used only in one place, there is no benefit from re-use within the perl interpreter, but a high cost due to more pages for the OS to copy.

    The perl interpreter can now be Configured to disable shared hash keys for "large" hashes (that are neither objects nor symbol tables). To do so, add -Accflags='-DPERL_USE_UNSHARED_KEYS_IN_LARGE_HASHES' to your Configure options. "Large" is a heuristic -- currently the heuristic is that sharing is disabled when adding a key to a hash triggers allocation of more storage, and the hash has more than 42 keys.

    This might cause slightly increased memory usage for programs that create (unblessed) data structures that contain multiple large hashes that share the same keys. But generally our testing suggests that for the specific cases described it is a win, and other code is unaffected.

  • In certain scenarios, creation of new scalars is now noticeably faster.

    For example, the following code is now executing ~30% faster:

        $str = "A" x 64;
        for (0..1_000_000) {
            @svs = split //, $str

    (You can read more about this one in [perl #19414].)

Modules and Pragmata

Updated Modules and Pragmata

  • Archive::Tar has been upgraded from version 2.38 to 2.40.

  • Attribute::Handlers has been upgraded from version 1.01 to 1.02.

  • attributes has been upgraded from version 0.33 to 0.34.

  • B has been upgraded from version 1.82 to 1.83.

  • B::Concise has been upgraded from version 1.004 to 1.006.

  • B::Deparse has been upgraded from version 1.56 to 1.64.

  • bignum has been upgraded from version 0.51 to 0.65.

  • charnames has been upgraded from version 1.48 to 1.50.

  • Compress::Raw::Bzip2 has been upgraded from version 2.101 to 2.103.

  • Compress::Raw::Zlib has been upgraded from version 2.101 to 2.105.

  • CPAN has been upgraded from version 2.28 to 2.33.

  • Data::Dumper has been upgraded from version 2.179 to 2.184.

  • DB_File has been upgraded from version 1.855 to 1.857.

  • Devel::Peek has been upgraded from version 1.30 to 1.32.

  • Devel::PPPort has been upgraded from version 3.62 to 3.68.

  • diagnostics has been upgraded from version 1.37 to 1.39.

  • Digest has been upgraded from version 1.19 to 1.20.

  • DynaLoader has been upgraded from version 1.50 to 1.52.

  • Encode has been upgraded from version 3.08 to 3.17.

  • Errno has been upgraded from version 1.33 to 1.36.

  • experimental has been upgraded from version 0.024 to 0.028.

  • Exporter has been upgraded from version 5.76 to 5.77.

  • ExtUtils::MakeMaker has been upgraded from version 7.62 to 7.64.

  • ExtUtils::Miniperl has been upgraded from version 1.10 to 1.11.

  • ExtUtils::ParseXS has been upgraded from version 3.43 to 3.45.

  • ExtUtils::Typemaps has been upgraded from version 3.43 to 3.45.

  • Fcntl has been upgraded from version 1.14 to 1.15.

  • feature has been upgraded from version 1.64 to 1.72.

  • File::Compare has been upgraded from version 1.1006 to 1.1007.

  • File::Copy has been upgraded from version 2.35 to 2.39.

  • File::Fetch has been upgraded from version 1.00 to 1.04.

  • File::Find has been upgraded from version 1.39 to 1.40.

  • File::Glob has been upgraded from version 1.33 to 1.37.

  • File::Spec has been upgraded from version 3.80 to 3.84.

  • File::stat has been upgraded from version 1.09 to 1.12.

  • FindBin has been upgraded from version 1.52 to 1.53.

  • GDBM_File has been upgraded from version 1.19 to 1.23.

  • Hash::Util has been upgraded from version 0.25 to 0.28.

  • Hash::Util::FieldHash has been upgraded from version 1.21 to 1.26.

  • HTTP::Tiny has been upgraded from version 0.076 to 0.080.

  • I18N::Langinfo has been upgraded from version 0.19 to 0.21.

  • if has been upgraded from version 0.0609 to 0.0610.

  • IO has been upgraded from version 1.46 to 1.50.

  • IO-Compress has been upgraded from version 2.102 to 2.106.

  • IPC::Open3 has been upgraded from version 1.21 to 1.22.

  • JSON::PP has been upgraded from version 4.06 to 4.07.

  • libnet has been upgraded from version 3.13 to 3.14.

  • Locale::Maketext has been upgraded from version 1.29 to 1.31.

  • Math::BigInt has been upgraded from version 1.999818 to 1.999830.

  • Math::BigInt::FastCalc has been upgraded from version 0.5009 to 0.5012.

  • Math::BigRat has been upgraded from version 0.2614 to 0.2621.

  • Module::CoreList has been upgraded from version 5.20210520 to 5.20220520.

  • mro has been upgraded from version 1.25_001 to 1.26.

  • NEXT has been upgraded from version 0.68 to 0.69.

  • Opcode has been upgraded from version 1.50 to 1.57.

  • open has been upgraded from version 1.12 to 1.13.

  • overload has been upgraded from version 1.33 to 1.35.

  • perlfaq has been upgraded from version 5.20210411 to 5.20210520.

  • PerlIO has been upgraded from version 1.11 to 1.12.

  • Pod::Functions has been upgraded from version 1.13 to 1.14.

  • Pod::Html has been upgraded from version 1.27 to 1.33.

  • Pod::Simple has been upgraded from version 3.42 to 3.43.

  • POSIX has been upgraded from version 1.97 to 2.03.

  • re has been upgraded from version 0.41 to 0.43.

  • Scalar::Util has been upgraded from version 1.55 to 1.62.

  • sigtrap has been upgraded from version 1.09 to 1.10.

  • Socket has been upgraded from version 2.031 to 2.033.

  • sort has been upgraded from version 2.04 to 2.05.

  • Storable has been upgraded from version 3.23 to 3.26.

  • Sys::Hostname has been upgraded from version 1.23 to 1.24.

  • Test::Harness has been upgraded from version 3.43 to 3.44.

  • Test::Simple has been upgraded from version 1.302183 to 1.302190.

  • Text::ParseWords has been upgraded from version 3.30 to 3.31.

  • Text::Tabs has been upgraded from version 2013.0523 to 2021.0814.

  • Text::Wrap has been upgraded from version 2013.0523 to 2021.0814.

  • threads has been upgraded from version 2.26 to 2.27.

  • threads::shared has been upgraded from version 1.62 to 1.64.

  • Tie::Handle has been upgraded from version 4.2 to 4.3.

  • Tie::Hash has been upgraded from version 1.05 to 1.06.

  • Tie::Scalar has been upgraded from version 1.05 to 1.06.

  • Tie::SubstrHash has been upgraded from version 1.00 to 1.01.

  • Time::HiRes has been upgraded from version 1.9767 to 1.9770.

  • Unicode::Collate has been upgraded from version 1.29 to 1.31.

  • Unicode::Normalize has been upgraded from version 1.28 to 1.31.

  • Unicode::UCD has been upgraded from version 0.75 to 0.78.

  • UNIVERSAL has been upgraded from version 1.13 to 1.14.

  • version has been upgraded from version 0.9928 to 0.9929.

  • VMS::Filespec has been upgraded from version 1.12 to 1.13.

  • VMS::Stdio has been upgraded from version 2.45 to 2.46.

  • warnings has been upgraded from version 1.51 to 1.58.

  • Win32 has been upgraded from version 0.57 to 0.59.

  • XS::APItest has been upgraded from version 1.16 to 1.22.

  • XS::Typemap has been upgraded from version 0.18 to 0.19.

  • XSLoader has been upgraded from version 0.30 to 0.31.


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:


  • This has been cleaned up some, and more than 80% of the (previously many) undocumented functions have now either been documented or deemed to have been inappropriately marked as API.

    As always, Patches Welcome!


  • notes the new location for functions moved from Pod::Html to Pod::Html::Util that are no longer intended to be used outside of core.


  • notes the :win32 IO pseudolayer is removed (this happened in 5.35.2).


  • The election process has been finetuned to allow the vote to be skipped if there are no more candidates than open seats.

  • A special election is now allowed to be postponed for up to twelve weeks, for example until a normal election.


  • now notes that an invocant only needs to be an object or class name for method calls, not for subroutine references.


  • Updated to discourage the use of the /d regexp modifier.


  • -? is now a synonym for -h

  • -g is now a synonym for -0777


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

  • Can't "%s" out of a "defer" block

    (F) An attempt was made to jump out of the scope of a defer block by using a control-flow statement such as return, goto or a loop control. This is not permitted.

  • Can't modify %s in %s (for scalar assignment to undef)

    Attempting to perform a scalar assignment to undef, for example via undef = $foo;, previously triggered a fatal runtime error with the message "Modification of a read-only value attempted." It is more helpful to detect such attempted assignments prior to runtime, so they are now compile time errors, resulting in the message "Can't modify undef operator in scalar assignment".

  • panic: newFORLOOP, %s

    The parser failed an internal consistency check while trying to parse a foreach loop.

New Warnings

Changes to Existing Diagnostics

  • '/' does not take a repeat count in %s

    This warning used to not include the in %s.

  • Subroutine %s redefined

    Localized subroutine redefinitions no longer trigger this warning.

  • unexpected constant lvalue entersub entry via type/targ %d:%d" now has a panic prefix

    This makes it consistent with other checks of internal consistency when compiling a subroutine.

  • Useless use of sort in scalar context is now in the new scalar category.

    When sort is used in scalar context, it provokes a warning that doing this is not useful. This warning used to be in the void category. A new category for warnings about scalar context has now been added, called scalar.

  • Removed a number of diagnostics

    Many diagnostics that have been removed from the perl core across many years have now also been removed from the documentation.

Configuration and Compilation

  • The Perl C source code now uses some C99 features, which we have verified are supported by all compilers we target. This means that Perl's headers now contain some code that is legal in C99 but not C89.

    This may cause problems for some XS modules that unconditionally add -Werror=declaration-after-statement to their C compiler flags if compiling with gcc or clang. Earlier versions of Perl support long obsolete compilers that are strict in rejecting certain C99 features, particularly mixed declarations and code, and hence it makes sense for XS module authors to audit that their code does not violate this. However, doing this is now only possible on these earlier versions of Perl, hence these modules need to be changed to only add this flag for <$] < 5.035005>.

  • The makedepend step is now run in parallel by using make

    When using MAKEFLAGS=-j8, this significantly reduces the time required for:

        sh ./makedepend MAKE=make cflags
  • Configure now tests whether #include <xlocale.h> is required to use the POSIX 1003 thread-safe locale functions or some related extensions. This prevents problems where a non-public xlocale.h is removed in a library update, or xlocale.h isn't intended for public use. (github #18936)


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

Platform Support


  • Support for old MSVC++ (pre-VC12) has been removed

    These did not support C99 and hence can no longer be used to compile perl.

  • Support for compiling perl on Windows using Microsoft Visual Studio 2022 (containing Visual C++ 14.3) has been added.

  • The :win32 IO layer has been removed. This experimental replacement for the :unix layer never reached maturity in its nearly two decades of existence.


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

  • Since the removal of PERL_OBJECT in Perl 5.8, PERL_IMPLICIT_CONTEXT and MULTIPLICITY have been synonymous and they were being used interchangeably. To simplify the code, all instances of PERL_IMPLICIT_CONTEXT have been replaced with MULTIPLICITY.

    PERL_IMPLICIT_CONTEXT will remain defined for compatibility with XS modules.

  • The API constant formerly named G_ARRAY, indicating list context, has now been renamed to a more accurate G_LIST. A compatibilty macro G_ARRAY has been added to allow existing code to work unaffected. New code should be written using the new constant instead. This is supported by Devel::PPPort version 3.63.

  • Macros have been added to perl.h to facilitate version comparisons: PERL_GCC_VERSION_GE, PERL_GCC_VERSION_GT, PERL_GCC_VERSION_LE and PERL_GCC_VERSION_LT.

    Inline functions have been added to embed.h to determine the position of the least significant 1 bit in a word: lsbit_pos32 and lsbit_pos64.

  • Perl_ptr_table_clear has been deleted. This has been marked as deprecated since v5.14.0 (released in 2011), and is not used by any code on CPAN.

  • Added new boolean macros and functions. See "Stable boolean tracking" for related information and perlapi for documentation.

    • sv_setbool

    • sv_setbool_mg

    • SvIsBOOL

  • Added 4 missing functions for dealing with RVs:

    • sv_setrv_noinc

    • sv_setrv_noinc_mg

    • sv_setrv_inc

    • sv_setrv_inc_mg

  • xs_handshake()'s two failure modes now provide distinct messages.

  • Memory for hash iterator state (struct xpvhv_aux) is now allocated as part of the hash body, instead of as part of the block of memory allocated for the main hash array.

  • A new phase_name() interface provides access to the name for each interpreter phase (i.e., PL_phase value).

  • The pack behavior of U has changed for EBCDIC.

  • New equality-test functions sv_numeq and sv_streq have been added, along with ..._flags-suffixed variants. These expose a simple and consistent API to perform numerical or string comparison which is aware of operator overloading.

  • Reading the string form of an integer value no longer sets the flag SVf_POK. The string form is still cached internally, and still re-read directly by the macros SvPV(sv) etc (inline, without calling a C function). XS code that already calls the APIs to get values will not be affected by this change. XS code that accesses flags directly instead of using API calls to express its intent might break, but such code likely is already buggy if passed some other values, such as floating point values or objects with string overloading.

    This small change permits code (such as JSON serializers) to reliably determine between

    • a value that was initially written as an integer, but then read as a string

          my $answer = 42;
          print "The answer is $answer\n";
    • that same value that was initially written as a string, but then read as an integer

          my $answer = "42";
          print "That doesn't look right\n"
              unless $answer == 6 * 9;

    For the first case (originally written as an integer), we now have:

        use Devel::Peek;
        my $answer = 42;
        Dump ($answer);
        my $void = "$answer";
        print STDERR "\n";
        SV = IV(0x562538925778) at 0x562538925788
          REFCNT = 1
          FLAGS = (IOK,pIOK)
          IV = 42
        SV = PVIV(0x5625389263c0) at 0x562538925788
          REFCNT = 1
          FLAGS = (IOK,pIOK,pPOK)
          IV = 42
          PV = 0x562538919b50 "42"\0
          CUR = 2
          LEN = 10

    For the second (originally written as a string), we now have:

        use Devel::Peek;
        my $answer = "42";
        Dump ($answer);
        my $void = $answer == 6 * 9;
        print STDERR "\n";
        SV = PV(0x5586ffe9bfb0) at 0x5586ffec0788
          REFCNT = 1
          FLAGS = (POK,IsCOW,pPOK)
          PV = 0x5586ffee7fd0 "42"\0
          CUR = 2
          LEN = 10
          COW_REFCNT = 1
        SV = PVIV(0x5586ffec13c0) at 0x5586ffec0788
          REFCNT = 1
          FLAGS = (IOK,POK,IsCOW,pIOK,pPOK)
          IV = 42
          PV = 0x5586ffee7fd0 "42"\0
          CUR = 2
          LEN = 10
          COW_REFCNT = 1

    (One can't rely on the presence or absence of the flag SVf_IsCOW to determine the history of operations on a scalar.)

    Previously both cases would be indistinguishable, with all 4 flags set:

        SV = PVIV(0x55d4d62edaf0) at 0x55d4d62f0930
          REFCNT = 1
          FLAGS = (IOK,POK,pIOK,pPOK)
          IV = 42
          PV = 0x55d4d62e1740 "42"\0
          CUR = 2
          LEN = 10

    (and possibly SVf_IsCOW, but not always)

    This now means that if XS code really needs to determine which form a value was first written as, it should implement logic roughly

        if (flags & SVf_IOK|SVf_NOK) && !(flags & SVf_POK)
            serialize as number
        else if (flags & SVf_POK)
            serialize as string
            the existing guesswork ...

    Note that this doesn't cover "dualvars" - scalars that report different values when asked for their string form or number form (such as $!). Most serialization formats cannot represent such duplicity.

    The existing guesswork remains because as well as dualvars, values might be undef, references, overloaded references, typeglobs and other things that Perl itself can represent but do not map one-to-one into external formats, so need some amount of approximation or encapsulation.

  • sv_dump (and Devel::Peek’s Dump function) now escapes high-bit octets in the PV as hex rather than octal. Since most folks understand hex more readily than octal, this should make these dumps a bit more legible. This does not affect any other diagnostic interfaces like pv_display.

Selected Bug Fixes

  • utime() now correctly sets errno/$! when called on a closed handle.

  • The flags on the OPTVAL parameter to setsockopt() were previously checked before magic was called, possibly treating a numeric value as a packed buffer or vice versa. It also ignored the UTF-8 flag, potentially treating the internal representation of an upgraded SV as the bytes to supply to the setsockopt() system call. (github #18660)

  • Only set IOKp, not IOK on $) and $(. This was issue #18955: This will prevent serializers from serializing these variables as numbers (which loses the additional groups). This restores behaviour from 5.16

  • Use of the mktables debugging facility would cause perl to croak since v5.31.10; this problem has now been fixed.

  • makedepend logic is now compatible with BSD make (fixes GH #19046).

  • Calling untie on a tied hash that is partway through iteration now frees the iteration state immediately.

    Iterating a tied hash causes perl to store a copy of the current hash key to track the iteration state, with this stored copy passed as the second parameter to NEXTKEY. This internal state is freed immediately when tie hash iteration completes, or if the hash is destroyed, but due to an implementation oversight, it was not freed if the hash was untied. In that case, the internal copy of the key would persist until the earliest of

    1. tie was called again on the same hash

    2. The (now untied) hash was iterated (ie passed to any of keys, values or each)

    3. The hash was destroyed.

    This inconsistency is now fixed - the internal state is now freed immediately by untie.

    As the precise timing of this behaviour can be observed with pure Perl code (the timing of DESTROY on objects returned from FIRSTKEY and NEXTKEY) it's just possible that some code is sensitive to it.

  • The Internals::getcwd() function added for bootstrapping miniperl in perl 5.30.0 is now only available in miniperl. [github #19122]

  • Setting a breakpoint on a BEGIN or equivalently a use statement could cause a memory write to a freed dbstate op. [GH #19198]

  • When bareword filehandles are disabled, the parser was interpreting any bareword as a filehandle, even when immediatey followed by parens.

Errata From Previous Releases

  • perl5300delta mistakenly identified a CVE whose correct identification is CVE-2015-1592.


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

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.