You are viewing the version of this documentation from Perl 5.37.9. This is a development version of Perl.



perl5378delta - what is new for perl v5.37.8


This document describes differences between the 5.37.7 release and the 5.37.8 release.

If you are upgrading from an earlier release such as 5.37.6, first read perl5377delta, which describes differences between 5.37.6 and 5.37.7.

Core Enhancements

Optimistic Eval in Patterns

The use of (?{ ... }) and (??{ ... }) in a pattern disables various optimisations globally in that pattern. This may or may not be desired by the programmer. This release adds the (*{ ... }) and (**{ ... }) equivalents. The only difference is that they do not and will never disable any optimisations in the regex engine. This may make them more unstable in the sense that they may be called more or less times in the future, however the number of times they execute will truly match how the regex engine functions. For example, certain types of optimisation are disabled when (?{ ... }) is included in a pattern, so that patterns which are O(N) in normal use become O(N*N) with a (?{ ... }) pattern in them. Switching to (*{ ... }) means the pattern will stay O(N).

NOTE the (**{ ... }) was removed in 5.37.9 as it didn't quite work out as planned.

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, open an issue at

Platform Support

Platform-Specific Notes

  • lstat() on Windows now returns the length of the link target as the size of the file, as it does on POSIX systems. [github #20476]

  • symlink() on Windows now replaces any / in the target with \, since Windows does not recognise / in symbolic links. The reverse translation is not done by readlink(). [github #20506]

  • symlink() where the target was an absolute path to a directory was incorrectly created as a file symbolic link. [github #20533]

Internal Changes


Perl 5.37.8 represents approximately 4 weeks of development since Perl 5.37.7 and contains approximately 42,000 lines of changes across 350 files from 25 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 29,000 lines of changes to 220 .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 5.37.8:

Andrew Ruthven, Andy Lester, Benjamin Smith, Bram, Chris 'BinGOs' Williams, Dagfinn Ilmari Mannsåker, David Cantrell, David Mitchell, Elvin Aslanov, Ferenc Erki, Florian Weimer, James E Keenan, Karen Etheridge, Karl Williamson, Li Linjie, Max Maischein, Nicolas R, Paul Evans, Peter John Acklam, Peter Levine, Renee Baecker, Richard Leach, Tomasz Konojacki, Tony Cook, Yves Orton.

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.