perl5315delta - 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


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


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.

Changes to Existing Diagnostics

Configuration and Compilation


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


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 There may also be information at, 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 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.