You are viewing the version of this documentation from Perl 5.22.0. View the latest version



perl5215delta - what is new for perl v5.21.5


This document describes differences between the 5.21.4 release and the 5.21.5 release.

If you are upgrading from an earlier release such as 5.21.3, first read perl5214delta, which describes differences between 5.21.3 and 5.21.4.

Core Enhancements

New double-diamond operator

<<>> is like <> but uses three-argument open to open each file in @ARGV. So each element of @ARGV is an actual file name, and "|foo" won't be treated as a pipe open.

Aliasing via reference

Variables and subroutines can now be aliased by assigning to a reference:

\$c = \$d;
\&x = \&y;

Or by using a backslash before a foreach iterator variable, which is perhaps the most useful idiom this feature provides:

foreach \%hash (@array_of_hash_refs) { ... }

This feature is experimental and must be enabled via use feature 'refaliasing'. It will warn unless the experimental::refaliasing warnings category is disabled.

See "Assigning to References" in perlref

Perl now supports POSIX 2008 locale currency additions.

On platforms that are able to handle POSIX.1-2008, the hash returned by POSIX::localeconv() includes the international currency fields added by that version of the POSIX standard. These are int_n_cs_precedes, int_n_sep_by_space, int_n_sign_posn, int_p_cs_precedes, int_p_sep_by_space, and int_p_sign_posn.

Packing infinity or not-a-number into a character is now fatal

Before, when trying to pack infinity or not-a-number into a (signed) character, Perl would warn, and assumed you tried to pack 0xFF; if you gave it as an argument to chr, U+FFFD was returned.

But now, all such actions (pack, chr, and print '%c') result in a fatal error.

Inf and NaN

Many small improvements, bug fixes and added test cases for dealing with math related to infinity and not-a-number.


Perl is now compiled with -fstack-protector-strong if available

Perl has been compiled with the anti-stack-smashing option -fstack-protector since 5.10.1. Now Perl uses the newer variant called -fstack-protector-strong, if available. (This was added already in 5.21.4.)


Use of multiple /x regexp modifiers

It is now deprecated to say something like any of the following:

use re qw(/amxx);

That is, now x should only occur once in any string of contiguous regular expression pattern modifiers. We do not believe there are any occurrences of this in all of CPAN. This is in preparation for a future Perl release having /xx mean to allow white-space for readability in bracketed character classes (those enclosed in square brackets: [...]).

Performance Enhancements

Modules and Pragmata

Updated Modules and Pragmata


Changes to Existing Documentation



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

Changes to Existing Diagnostics


Platform Support

Regained Platforms

IRIX and Tru64 platforms are working again. (Some make test failures remain.)

Platform-Specific Notes


Special handling is required on EBCDIC platforms to get qr/[i-j]/ to match only "i" and "j", since there are 7 characters between the code points for "i" and "j". This special handling had only been invoked when both ends of the range are literals. Now it is also invoked if any of the \N{...} forms for specifying a character by name or Unicode code point is used instead of a literal. See "Character Ranges" in perlrecharclass.

Internal Changes

Selected Bug Fixes


Perl 5.21.5 represents approximately 4 weeks of development since Perl 5.21.4 and contains approximately 40,000 lines of changes across 530 files from 33 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 29,000 lines of changes to 390 .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 5.21.5:

Aaron Crane, Abigail, Alberto Simões, Andrew Fresh, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, David Mitchell, Doug Bell, Ed J, Father Chrysostomos, George Greer, Graham Knop, James E Keenan, Jarkko Hietaniemi, Karen Etheridge, Karl Williamson, Leon Timmermans, Lukas Mai, Niko Tyni, Peter Martini, Petr Písař, Rafael Garcia-Suarez, Reini Urban, Ricardo Signes, Shlomi Fish, Steve Hay, syber, Tony Cook, Vincent Pit, Yves Orton, Ævar Arnfjörð Bjarmason.

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.