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Perl 5 version 22.0 documentation
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perl5213delta - what is new for perl v5.21.3


This document describes differences between the 5.21.2 release and the 5.21.3 release.

If you are upgrading from an earlier release such as 5.21.1, first read perl5212delta, which describes differences between 5.21.1 and 5.21.2.

Core Enhancements

defined(@array = LIST) is no longer fatal

In 5.21.1, defined(@array) was made fatal. This has been relaxed to not die if the argument is assigning to an array.

Floating point parsing has been improved

Parsing and printing of floating point values has been improved.

As a completely new feature, hexadecimal floating point literals (like 0x1.23p-4) are now supported, and they can be output with printf %a .


The Safe module could allow outside packages to be replaced

Critical bugfix: outside packages could be replaced. Safe has been patched to 2.38 to address this.

Incompatible Changes

use UNIVERSAL '...' is now a fatal error

Importing functions from UNIVERSAL has been deprecated since v5.12, and is now a fatal error. "use UNIVERSAL" without any arguments is still allowed.

Modules and Pragmata

Updated Modules and Pragmata

  • B::Debug has been upgraded from version 1.19 to 1.21.

  • Config::Perl::V has been upgraded from version 0.20 to 0.22.

  • CPAN::Meta has been upgraded from version 2.141520 to 2.142060.

  • CPAN::Meta::Requirements has been upgraded from version 2.125 to 2.126.

  • ExtUtils::CBuilder was moved from dist to cpan.

  • ExtUtils::CBuilder has been upgraded from version 0.280216 to 0.280217.

  • ExtUtils::Install was moved from dist to cpan.

  • ExtUtils::Manifest has been upgraded from version 1.64 to 1.65. It was also moved from dist to cpan.

  • HTTP::Tiny has been upgraded from version 0.043 to 0.047.

  • IPC::Open3 has been upgraded from version 1.17 to 1.18.

  • Module::CoreList has been upgraded from version 5.021002 to 5.021003.

  • Opcode has been upgraded from version 1.27 to 1.28.

  • has been upgraded from version 1.45 to 1.46.

  • perlfaq has been upgraded from version 5.0150044 to 5.0150045.

  • POSIX has been upgraded from version 1.41 to 1.42.

  • Safe has been upgraded from version 2.37 to 2.38.

  • Socket has been upgraded from version 2.014 to 2.015.

  • Sys::Hostname has been upgraded from version 1.18 to 1.19

  • UNIVERSAL has been upgraded from version 1.11 to 1.12.


Changes to Existing Documentation



  • Details on C level symbols and libperl.t added.


  • Recommended replacements for tmpfile, atoi, strtol, and strtoul added.


  • ASCII v. EBCDIC clarifications added.


  • Comments added on algorithmic complexity and tied hashes.


  • Updated documentation on environment and shell interaction in VMS.


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

  • Hexadecimal float: exponent overflow

    (W overflow) The hexadecimal floating point has larger exponent than the floating point supports.

  • Hexadecimal float: exponent underflow

    (W overflow) The hexadecimal floating point has smaller exponent than the floating point supports.

  • Hexadecimal float: mantissa overflow

    (W overflow) The hexadecimal floating point literal had more bits in the mantissa (the part between the 0x and the exponent, also known as the fraction or the significand) than the floating point supports.

  • Hexadecimal float: precision loss

    (W overflow) The hexadecimal floating point had internally more digits than could be output. This can be caused by unsupported long double formats, or by 64-bit integers not being available (needed to retrieve the digits under some configurations).

Changes to Existing Diagnostics

  • require with no argument or undef used to warn about a Null filename; now it dies with Missing or undefined argument to require .

Configuration and Compilation

  • MurmurHash64A and MurmurHash64B can now be configured as the internal hash function.

Platform Support

Platform-Specific Notes

  • Android

    Build support has been improved for cross-compiling in general and for Android in particular.

  • Solaris

    c99 options have been cleaned up, hints look for solstudio as well as SUNWspro , and support for native setenv has been added.

  • VMS

    finite , finitel , and isfinite detection has been added to , environment handling has had some minor changes, and a fix for legacy feature checking status.

  • Windows

    %I64d is now being used instead of %lld for MinGW.

Internal Changes

  • Added sync_locale in perlapi. Changing the program's locale should be avoided by XS code. Nevertheless, certain non-Perl libraries called from XS, such as Gtk do so. When this happens, Perl needs to be told that the locale has changed. Use this function to do so, before returning to Perl.

  • Added grok_atou in perlapi as a safer replacement for atoi and strtol.

Selected Bug Fixes

  • Failing to compile use Foo in an eval could leave a spurious BEGIN subroutine definition, which would produce a "Subroutine BEGIN redefined" warning on the next use of use, or other BEGIN block. [perl #122107]

  • method { BLOCK } ARGS syntax now correctly parses the arguments if they begin with an opening brace. [perl #46947]

  • External libraries and Perl may have different ideas of what the locale is. This is problematic when parsing version strings if the locale's numeric separator has been changed. Version parsing has been patched to ensure it handles the locales correctly. [perl #121930]

  • A bug has been fixed where zero-length assertions and code blocks inside of a regex could cause pos to see an incorrect value. [perl #122460]


Perl 5.21.3 represents approximately 4 weeks of development since Perl 5.21.2 and contains approximately 21,000 lines of changes across 250 files from 25 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 18,000 lines of changes to 160 .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 5.21.3:

Aaron Crane, Abigail, Alberto Simões, Andy Dougherty, Brian Fraser, Chad Granum, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, David Mitchell, Father Chrysostomos, H.Merijn Brand, James E Keenan, Jan Dubois, Jarkko Hietaniemi, Karen Etheridge, Karl Williamson, Lukas Mai, Peter Martini, Rafael Garcia-Suarez, syber, Tony Cook, Vladimir Marek, 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 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.