perldelta - what is new for perl v5.37.3


This document describes differences between the 5.37.2 release and the 5.37.3 release.

If you are upgrading from an earlier release such as 5.37.1, first read perl5372delta, which describes differences between 5.37.1 and 5.37.2.

Core Enhancements


Added a new environment variable PERL_RAND_SEED which can be used to cause a perl program which uses rand without using srand() explicitly or which uses srand() with no arguments to be repeatable. See perlrun. This feature can be disabled at compile time by passing


to Configure during the build process.

Performance Enhancements

  • Additional optree optimizations for common OP patterns. For example, multiple simple OPs replaced by a single streamlined OP, so as to be more efficient at runtime. [GH #19943].

Modules and Pragmata

Updated Modules and Pragmata

  • attributes has been upgraded from version 0.34 to 0.35.

  • B has been upgraded from version 1.85 to 1.86.

  • B::Deparse has been upgraded from version 1.65 to 1.68.

  • Digest::SHA has been upgraded from version 6.02 to 6.03.

  • DynaLoader has been upgraded from version 1.52 to 1.53.

  • Encode has been upgraded from version 3.18 to 3.19.

  • ExtUtils::PL2Bat has been upgraded from version 0.004 to 0.005.

  • File::Find has been upgraded from version 1.40 to 1.41.

  • Filter::Util::Call has been upgraded from version 1.61 to 1.64.

  • HTTP::Tiny has been upgraded from version 0.080 to 0.082: no longer deletes the 'headers' key from post_form arguments hashref.

  • JSON::PP has been upgraded from version 4.10 to 4.11.

  • Memoize has been upgraded from version 1.03_01 to 1.10.

  • Module::CoreList has been upgraded from version 5.20220720 to 5.20220820.

  • NDBM_File has been upgraded from version 1.15 to 1.16.

  • Opcode has been upgraded from version 1.59 to 1.60.

  • Scalar::Util has been upgraded from version 1.62 to 1.63: fix off-by-one in stack handling of head() / tail() (RT143905).

  • Socket has been upgraded from version 2.035 to 2.036: Avoid putting macros inside arguments to other macros, as it annoys strict C compilers

  • threads has been upgraded from version 2.28 to 2.29.

  • XS::APItest has been upgraded from version 1.24 to 1.25.

Platform Support

Platform-Specific Notes

  • FreeBSD no longer uses thread-safe locale operations, to avoid a bug in FreeBSD

Internal Changes

  • The CVf_METHOD CV flag and associated CvMETHOD macro has been renamed to CVf_NOWARN_AMBIGUOUS and CvNOWARN_AMBIGUOUS. This closer reflects its actual behaviour (it suppresses a warning that would otherwise be generated about ambiguous names), in order to be less confusing with a possible upcoming feature.

  • The OPf_SPECIAL flag is no longer set on the OP_ENTERSUB op constructed to call the VERSION, import and unimport methods as part of a use statement and attribute application, nor when assigning to an :lvalue subroutine.

  • A new CV flag CVf_REFCOUNTED_ANYSV has been added, which indicates that the CV is an XSUB and stores an SV pointer in the CvXSUBANY.any_sv union field. Perl core operations such as cloning or destroying the CV will maintain the reference count of the pointed-to SV, destroying it when required.

Selected Bug Fixes

  • PerlIO::get_layers will now accept IO references too

    Previously it would only take glob references or names of globs. Now it will also accept IO references.


Perl 5.37.3 represents approximately 4 weeks of development since Perl 5.37.2 and contains approximately 13,000 lines of changes across 240 files from 25 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 11,000 lines of changes to 160 .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 5.37.3:

Aristotle Pagaltzis, Bram, Dagfinn Ilmari Mannsåker, Dan Book, Dan Kogai, David Golden, David Mitchell, Elvin Aslanov, Graham Knop, Harald Jörg, James E Keenan, Karl Williamson, Leon Timmermans, Mark Shelor, Neil Bowers, Nicholas Clark, Nicolas R, Paul Evans, Reini Urban, Richard Leach, Sinan Unur, Tomasz Konojacki, Tony Cook, Yves Orton, 小鸡.

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.