++ed by:

179 PAUSE users
173 non-PAUSE users.

Steve Hay
and 1 contributors


perldelta - what is new for perl v5.31.5


This document describes differences between the 5.31.4 release and the 5.31.5 release.

If you are upgrading from an earlier release such as 5.31.3, first read perl5314delta, which describes differences between 5.31.3 and 5.31.4.

Incompatible Changes

Modifiable variables are no longer permitted in constants

Code like:

    my $var;
    $sub = sub () { $var };

where $var is referenced elsewhere in some sort of modifiable context now produces an exception when the sub is defined.

This error can be avoided by adding a return to the sub definition:

    $sub = sub () { return $var };

This has been deprecated since Perl 5.22.

[perl #131138].

Modules and Pragmata

Updated Modules and Pragmata

  • B has been upgraded from version 1.76 to 1.77.

  • B::Deparse has been upgraded from version 1.49 to 1.50.

  • Devel::PPPort has been upgraded from version 3.55 to 3.54.

  • Digest::MD5 has been upgraded from version 2.55 to 2.55_01.

  • Dumpvalue has been upgraded from version 1.18 to 1.21.

    Previously, when dumping elements of an array and encountering an undefined value, the string printed would have been empty array. This has been changed to what was apparently originally intended: empty slot.

  • ExtUtils::CBuilder has been upgraded from version 0.280232 to 0.280233.

  • Math::BigInt has been upgraded from version 1.999816 to 1.999817_01.

  • Math::BigInt::FastCalc has been upgraded from version 0.5008 to 0.5009.

  • Module::CoreList has been upgraded from version 5.20190920 to 5.20191020.

  • Safe has been upgraded from version 2.40 to 2.41.

  • threads has been upgraded from version 2.22 to 2.23.

  • Time::HiRes has been upgraded from version 1.9763 to 1.9764.

  • XS::APItest has been upgraded from version 1.03 to 1.04.


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, send email to perlbug@perl.org.


  • Details of the various stacks within the perl interpreter are now explained here.

Additionally, the following selected changes have been made:

  • Where applicable, the URLs in the documentation have been moved from using the http:// protocol to https:// . This also affects the location of the bug tracker at https://rt.perl.org.

  • Some links to OS/2 libraries, Address Sanitizer and other system tools had gone stale. These have been updated with working links.

  • Some links to old mails on perl5-porters had gone stale. These have been updated with working links.


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.

Changes to Existing Diagnostics

  • Can't use global %s in %s

    This error message has been slightly reformatted from the original Can't use global %s in "%s", and in particular misleading error messages like Can't use global $_ in "my" are now rendered as Can't use global $_ in subroutine signature.

  • Constants from lexical variables potentially modified elsewhere are no longer permitted

    This error message replaces the former Constants from lexical variables potentially modified elsewhere are deprecated. This will not be allowed in Perl 5.32 to reflect the fact that this previously deprecated usage has now been transformed into an exception. The message's classification has also been updated from D (deprecated) to F (fatal).

    See also "Incompatible Changes".

Configuration and Compilation

  • Perl now no longer probes for d_u32align, defaulting to define on all platforms. This check was error prone when it was done, which was on 32-bit platforms only. [perl #133495].

  • Documentation and hints for building perl on Z/OS (native EBCDIC) have been updated. Still work in progress.

  • A new probe for malloc_usable_size has been added.


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

Platform Support

Platform-Specific Notes

  • Support for building perl with Visual C++ 6.0 has now been removed.

  • Building perl with Visual C++ 2013 and earlier was broken in the previous release but has now been fixed.

Internal Changes

  • Added the <PL_curstackinfo-si_cxsubix>> field. This records the stack index of the most recently pushed sub/format/eval context. It is set and restored automatically by cx_pushsub(), cx_popsub() etc., but would need to be manually managed if you do any unusual manipulation of the context stack.

  • Various macros dealing with character type classification and changing case where the input is encoded in UTF-8 now require an extra parameter to prevent potential reads beyond the end of the buffer. Use of these has generated a deprecation warning since Perl 5.26. Details are in "In XS code, use of various macros dealing with UTF-8." in perldeprecation


Perl 5.31.5 represents approximately 4 weeks of development since Perl 5.31.4 and contains approximately 27,000 lines of changes across 610 files from 15 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 9,500 lines of changes to 150 .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 5.31.5:

Dagfinn Ilmari Mannsåker, David Mitchell, H.Merijn Brand, James E Keenan, Karl Williamson, Matt Turner, Max Maischein, Nicolas R., Pali, Paul Evans, Paul Marquess, Peter Eisentraut, Steve Hay, Tomasz Konojacki, Tony Cook.

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

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

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

Reporting Bugs

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

If you believe you have an unreported bug, please run the perlbug program included with your release. Be sure to trim your bug down to a tiny but sufficient test case. Your bug report, along with the output of perl -V, will be sent off to perlbug@perl.org to be analysed by the Perl porting team.

If the bug you are reporting has security implications which make it inappropriate to send to a publicly archived mailing list, 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.