You are viewing the version of this documentation from Perl 5.37.4. This is a development version of Perl.



perldelta - what is new for perl v5.37.4


This document describes differences between the 5.37.3 release and the 5.37.4 release.

If you are upgrading from an earlier release such as 5.37.2, first read perl5373delta, which describes differences between 5.37.2 and 5.37.3.

Incompatible Changes

readline() no longer clears the stream error flag

readline(), also spelled <>, would clear the handle's error flag after an error occurred on the stream.

The error flag is now only cleared when an error occurs when reading from the child process for glob() in miniperl. This allows it to correctly report errors from the child process on close().

Since the error flag is no longer cleared calling close() on the stream may fail and if the stream was not explicitly closed, the implicit close of the stream may produce a warning.

[GH #20060]

INIT blocks no longer run after an exit() in BEGIN

INIT blocks will no longer run after an exit() performed inside of a BEGIN. This means that the combination of the -v option and the -c option no longer executes a compile check as well as showing the perl version. The -v option executes an exit(0) after printing the version information inside of a BEGIN block, and the -c check is implemented by using INIT hooks, resulting in the -v option taking precedence.

[GH #1537] [GH #20181]

Syntax errors will no longer produce "phantom error messages".

Generally perl will continue parsing the source code even after encountering a compile error. In many cases this is helpful, for instance with misspelled variable names it is helpful to show as many examples of the error as possible. But in the case of syntax errors continuing often produces bizarre error messages, and may even cause segmentation faults during the compile process. In this release the compiler will halt at the first syntax error encountered. This means that any code expecting to see the specific error messages we used to produce will be broken. The error that is emitted will be one of the diagnostics that used to be produced, but in some cases some messages that used to be produced will no longer be displayed.

See "Changes to Existing Diagnostics" for more details.

Performance Enhancements

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

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.

New Diagnostics

New Errors

New Warnings

Changes to Existing Diagnostics


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

Internal Changes

Known Problems


Perl 5.37.4 represents approximately 4 weeks of development since Perl 5.37.3 and contains approximately 20,000 lines of changes across 270 files from 21 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 12,000 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 5.37.4:

Bram, Dagfinn Ilmari Mannsåker, danielnachun, E. Choroba, Ed J, Elvin Aslanov, H.Merijn Brand, James E Keenan, Karen Etheridge, Karl Williamson, Kenneth Ölwing, Leon Timmermans, Neil Bowers, Nicolas R, Paul Evans, Richard Leach, Sisyphus, Todd Rinaldo, 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.