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perl52110delta - what is new for perl v5.21.10


This document describes differences between the 5.21.9 release and the 5.21.10 release.

If you are upgrading from an earlier release such as 5.21.8, first read perl5219delta, which describes differences between 5.21.8 and 5.21.9.

Incompatible Changes

(?[...]) operators now follow standard Perl precedence

This experimental feature allows set operations in regular expression patterns. Prior to this, the intersection operator had the same precedence as the other binary operators. Now it has higher precedence. This could lead to different outcomes than existing code expects (though the documentation has always noted that this change might happen, recommending fully parenthesizing the expressions). See Extended Bracketed Character Classes in perlrecharclass.

Performance Enhancements

  • The functions utf8::native_to_unicode() and utf8::unicode_to_native() (see utf8) are now optimized out on ASCII platforms. There is now not even a minimal performance hit in writing code portable between ASCII and EBCDIC platforms.

Modules and Pragmata

Updated Modules and Pragmata

  • B has been upgraded from version 1.56 to 1.57.

  • B::Deparse has been upgraded from version 1.33 to 1.34.

    Deparse $#_ as that instead of as $#{_} . [perl #123947]

  • Carp has been upgraded from version 1.35 to 1.36.

  • CPAN has been upgraded from version 2.05 to 2.10.

    • Add support for Cwd::getdcwd() and introduce workaround for a misbehaviour seen on Strawberry Perl 5.20.1.

    • Fix chdir() after building dependencies bug.

    • Introduce experimental support for plugins/hooks.

    • Integrate the App::Cpan sources.

    • Do not check recursion on optional dependencies.

    • Sanity check META.yml to contain a hash. [cpan #95271]

  • CPAN::Meta has been upgraded from version 2.143240 to 2.150001.

  • Data::Dumper has been upgraded from version 2.157 to 2.158.

  • DB has been upgraded from version 1.07 to 1.08.

  • Devel::PPPort has been upgraded from version 3.28 to 3.31.

  • DynaLoader has been upgraded from version 1.31 to 1.32.

  • Encode has been upgraded from version 2.70 to 2.72.

  • encoding has been upgraded from version 2.13 to 2.14.

  • Getopt::Long has been upgraded from version 2.43 to 2.45.

  • locale has been upgraded from version 1.05 to 1.06.

  • Locale::Codes has been upgraded from version 3.33 to 3.34.

  • Module::CoreList has been upgraded from version 5.20150220 to 5.20150320.

  • parent has been upgraded from version 0.228 to 0.232.

    No changes to installed files other than the version bump.

  • The PathTools modules have been upgraded from version 3.54 to 3.55.

  • Pod::Functions has been upgraded from version 1.08 to 1.09.

  • POSIX has been upgraded from version 1.51 to 1.52.

  • re has been upgraded from version 0.31 to 0.32.

  • sigtrap has been upgraded from version 1.07 to 1.08.

  • Term::Complete has been upgraded from version 1.402 to 1.403.

  • Test::Simple has been reverted from version 1.301001_098 to 1.001014.

  • Text::Balanced has been upgraded from version 2.02 to 2.03.

    No changes to installed files other than the version bump.

  • Text::ParseWords has been upgraded from version 3.29 to 3.30.

  • threads has been upgraded from version 1.96_001 to 2.01.

  • Unicode::Collate has been upgraded from version 1.11 to 1.12.

  • utf8 has been upgraded from version 1.14 to 1.15.


Changes to Existing Documentation


  • Documentation has been added regarding the special floating point values Inf and NaN .


  • Removed note about \s matching VT now that it is no longer experimental.

  • Added note that use re 'strict' has been introduced experimentally.


  • The documentation of what to expect to see in future maintenance releases has been updated. Essentially the same types of changes will be included as before but with fewer changes that don't affect the installation or execution of perl.


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


  • Tests for performance issues have been added in the file t/perf/taint.t.

Platform Support

New Platforms

  • z/OS running EBCDIC Code Page 1047

    Core perl now works on this EBCDIC platform. Early perls also worked, but, even though support wasn't officially withdrawn, recent perls would not compile and run well. Perl 5.20 would work, but had many bugs which have now been fixed. Many CPAN modules that ship with Perl still fail tests, including Pod::Simple. However the version of Pod::Simple currently on CPAN should work; it was fixed too late to include in Perl 5.22. Work is under way to fix many of the still-broken CPAN modules, which likely will be installed on CPAN when completed, so that you may not have to wait until Perl 5.24 to get a working version.

Platform-Specific Notes

  • HP-UX

    The archname now distinguishes use64bitint from use64bitall.

Internal Changes

  • Macros have been created to allow XS code to better manipulate the POSIX locale category LC_NUMERIC . See Locale-related functions and macros in perlapi.

  • The previous atoi et al replacement function, grok_atou , has now been superseded by grok_atoUV . See perlclib for details.

Selected Bug Fixes

  • Repeated global pattern matches in scalar context on large tainted strings were exponentially slow depending on the current match position in the string. [perl #123202]

  • Various crashes due to the parser getting confused by syntax errors have been fixed. [perl #123801] [perl #123802] [perl #123955] [perl #123995]

  • split in the scope of lexical $_ has been fixed not to fail assertions. [perl #123763]

  • my $x : attr syntax inside various list operators no longer fails assertions. [perl #123817]

  • An @ sign in quotes followed by a non-ASCII digit (which is not a valid identifier) would cause the parser to crash, instead of simply trying the @ as literal. This has been fixed. [perl #123963]

  • *bar::=*foo::=*glob_with_hash has been crashing since Perl 5.14, but no longer does. [perl #123847]

  • foreach in scalar context was not pushing an item on to the stack, resulting in bugs. (print 4, scalar do { foreach(@x){} } + 1 would print 5.) It has been fixed to return undef. [perl #124004]

  • A memory leak introduced in Perl 5.21.6 has been fixed. [perl #123922]

  • A regression in the behaviour of the readline built-in function, caused by the introduction of the <<>> operator, has been fixed. [perl #123990]

  • Several cases of data used to store environment variable contents in core C code being potentially overwritten before being used have been fixed. [perl #123748]

Known Problems

  • A goal is for Perl to be able to be recompiled to work reasonably well on any Unicode version. In Perl 5.22, though, the earliest such version is Unicode 5.1 (current is 7.0).

  • EBCDIC platforms

    • Encode and encoding are mostly broken.

    • Many cpan modules that are shipped with core show failing tests.

    • pack/unpack with "U0" format may not work properly.


Perl 5.21.10 represents approximately 4 weeks of development since Perl 5.21.9 and contains approximately 170,000 lines of changes across 860 files from 27 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 170,000 lines of changes to 610 .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 5.21.10:

Chris 'BinGOs' Williams, David Golden, David Mitchell, David Wheeler, Father Chrysostomos, H.Merijn Brand, Hugo van der Sanden, James E Keenan, Jarkko Hietaniemi, Jasmine Ngan, Jerry D. Hedden, John Goodyear, Karen Etheridge, Karl Williamson, Lukas Mai, Matthew Horsfall, Nicholas Clark, Petr Písař, Rafael Garcia-Suarez, Reini Urban, Ricardo Signes, Sawyer X, Steffen Müller, Steve Hay, Sullivan Beck, Tony Cook, Vincent Pit.

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.