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Source   Latest Release: perl-5.28.0-RC1


perldelta - what is new for perl v5.21.7


This document describes differences between the 5.21.6 release and the 5.21.7 release.

If you are upgrading from an earlier release such as 5.21.5, first read perl5216delta, which describes differences between 5.21.5 and 5.21.6.

Core Enhancements ^

faster array and hash lookups

Array and hash lookups (especially nested ones) that use only constants or simple variables as keys, are now considerably faster. See "Internal Changes" for more details.

fileno now works on directory handles

When the relevant support is available in the operating system, the fileno builtin now works on directory handles, yielding the underlying file descriptor in the same way as for filehandles. On operating systems without such support, fileno on a directory handle continues to return the undefined value, as before, but also sets $! to indicate that the operation is not supported.

Currently, this uses either a dd_fd member in the OS DIR structure, or a dirfd(3) function as specified by POSIX.1-2008.

Incompatible Changes ^

& and \& prototypes accepts only subs

The & prototype character now accepts only anonymous subs (sub {...}) and things beginning with \&. Formerly it erroneously also allowed undef and references to array, hashes, and lists. [perl #4539] [perl #123062]

The \& prototype was allowing subroutine calls, whereas now it only allows subroutines. &foo is permitted. &foo() and foo() are not. [perl #77860]

use encoding is now lexical

The encoding pragma's effect is now limited to lexical scope. This pragma is deprecated, but in the meantime, it could adversely affect unrelated modules that are included in the same program.

List slices returning empty lists

List slices return an empty list now only if the original list was empty (or if there are no indices). Formerly, a list slice would return an empty list if all indices fell outside the original list. [perl #114498]

Deprecations ^

Setting ${^ENCODING} to anything but undef

This variable allows Perl scripts to be written in a non-ASCII, non-UTF-8 encoding. However, it affects all modules globally, leading to wrong answers and segmentation faults. New scripts should be written in UTF-8; old scripts should be converted to UTF-8, which is easily done with the encoding pragma.

Performance Enhancements ^

Modules and Pragmata ^

Updated Modules and Pragmata

Diagnostics ^

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

Platform Support ^

Platform-Specific Notes


Internal Changes ^

Selected Bug Fixes ^

Acknowledgements ^

Perl 5.21.7 represents approximately 4 weeks of development since Perl 5.21.6 and contains approximately 97,000 lines of changes across 640 files from 30 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 26,000 lines of changes to 400 .pm, .t, .c and .h files.

Perl continues to flourish into its third decade thanks to a vibrant community of users and developers. The following people are known to have contributed the improvements that became Perl 5.21.7:

Aaron Crane, Aristotle Pagaltzis, Chad Granum, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, David Mitchell, Eric Herman, Father Chrysostomos, H.Merijn Brand, Hugo van der Sanden, James Raspass, Jarkko Hietaniemi, Jim Cromie, Karen Etheridge, Karl Williamson, kmx, Lukas Mai, Matthew Horsfall, Max Maischein, Petr Písař, Ricardo Signes, Shlomi Fish, Steffen Müller, Steve Hay, Sullivan Beck, syber, Todd Rinaldo, 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 articles recently posted to the comp.lang.perl.misc newsgroup and 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 please send it to This points to a closed subscription unarchived mailing list, which includes all the core committers, who will be able to help assess the impact of issues, figure out a resolution, and help co-ordinate the release of patches to mitigate or fix the problem across all platforms on which Perl is supported. Please only use this address for security issues in the Perl core, not for modules independently distributed on CPAN.


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.

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