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perl5150delta - what is new for perl v5.15.0


This document describes differences between the 5.15.0 release and the 5.14.0 release.

If you are upgrading from an earlier release such as 5.12.0, first read perl5140delta, which describes differences between 5.12.0 and 5.14.0.

Some of the changes have been included in Perl 5.14.1. These are indicated with a "(5.14.1)" marker.

Core Enhancements ^

CORE:: works on all keywords

The CORE:: prefix can now be used on keywords enabled by, even outside the scope of use feature. Relevant documentation files CORE, feature, perlfunc, perlsub, and perlsyn have been updated.

continue no longer requires the "switch" feature

The continue keyword has two meanings. It can introduce a continue block after a loop, or it can exit the current when block. Up till now, the latter meaning was only valid with the "switch" feature enabled, and was a syntax error otherwise. Since the main purpose of is to avoid conflicts with user-defined subroutines, there is no reason for continue to depend on it.

$$ can be assigned to

$$ was made read-only in Perl 5.8.0. But only sometimes: local $$ would make it writable again. Some CPAN modules were using local $$ or XS code to bypass the read-only check, so there is no reason to keep $$ read-only. (This change also allowed a bug to be fixed while maintaining backward compatibility.)

Features inside the debugger

The current Perl's feature bundle is now enabled for commands entered in the interactive debugger.

\N{...} can now have Unicode loose name matching

This is described in the charnames item in "Updated Modules and Pragmata" below.

Breakpoints with file names

The debugger's "b" command for setting breakpoints now allows a line number to be prefixed with a file name. See "b [file]:[line] [condition]" in perldebug.

Security ^

No changes since 5.14.0.

Incompatible Changes ^

Tying scalars that hold typeglobs

Attempting to tie a scalar after a typeglob was assigned to it would instead tie the handle in the typeglob's IO slot. This meant that it was impossible to tie the scalar itself. Similar problems affected tied and untie: tied $scalar would return false on a tied scalar if the last thing returned was a typeglob, and untie $scalar on such a tied scalar would do nothing.

We fixed this problem before Perl 5.14.0, but it caused problems with some CPAN modules, so we put in a deprecation cycle instead.

Now the deprecation has been removed and this bug has been fixed. So tie $scalar will always tie the scalar, not the handle it holds. To tie the handle, use tie *$scalar (with an explicit asterisk). The same applies to tied *$scalar and untie *$scalar.

IPC::Open3 no longer provides xfork(), xclose_on_exec() and xpipe_anon()

All three functions were private, undocumented and unexported. They do not appear to be used by any code on CPAN. Two have been inlined and one deleted entirely.

$$ no longer caches PID

Previously, if one embeds Perl or uses XS and calls fork(3) from C, Perls notion of $$ could go out of sync with what getpid() returns. By always fetching the value of $$ via getpid(), this potential bug is eliminated. Code that depends on the caching behavior will break. As described in "Core Enhancements", $$ is now writable, but it will be reset during a fork.

Deprecations ^

There have been no deprecations since 5.14.0.

Performance Enhancements ^

There are no benchmarked enhancements since 5.14.0.

Modules and Pragmata ^

New Modules and Pragmata


Updated Modules and Pragmata

Removed Modules and Pragmata

As promised in Perl 5.14.0's release notes, the following modules have been removed from the core distribution, and if needed should be installed from CPAN instead.

Documentation ^

New Documentation


Changes to Existing Documentation














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.

New Diagnostics

New Warnings

Useless assignment to a temporary

Assigning to a temporary returned from an XS lvalue subroutine now produces a warning [perl #31946].

Changes to Existing Diagnostics


Utility Changes ^


Configuration and Compilation ^

Testing ^

There have been no significant changes to the process for testing a newly-built perl.

See the source code commit history for changes to individual test files.

Platform Support ^

New Platforms


Discontinued Platforms


Platform-Specific Notes


Mac OS X



Ubuntu Linux

Internal Changes ^

Selected Bug Fixes ^

Regular expressions and character classes


Copy-on-write scalars

Copy-on-write scalars were introduced in 5.8.0, but most Perl code did not encounter them (they were used mostly internally). Perl 5.10.0 extended them, such that assigning __PACKAGE__ or a hash key to a scalar would make it copy-on-write. Several parts of Perl were not updated to account for them, but have now been fixed.

lvalue subroutines

There have been various fixes to lvalue subroutines.

Fixes related to hashes

Other notable fixes

Known Problems ^

Acknowledgements ^

Perl 5.15.0 represents approximately five weeks of development since Perl 5.14.0 and contains approximately 54,000 lines of changes across 618 files from 57 authors.

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 5.15.0:

Alan Haggai Alavi, Bo Johansson, Bo Lindbergh, brian d foy, Chia-liang Kao, Chris 'BinGOs' Williams, Claudio Ramirez, Craig A. Berry, David Golden, David Leadbeater, David Mitchell, Dennis Kaarsemaker, Dominic Hargreaves, Eric Brine, Father Chrysostomos, Florian Ragwitz, George Greer, Gisle Aas, H.Merijn Brand, Hojung Yoon, Ian Goodacre, Jesse Vincent, Jim Cromie, Johan Vromans, John Hawkinson, John P. Linderman, Joshua ben Jore, Karl Williamson, Kevin J. Woolley, Leo Lapworth, Leon Brocard, Leon Timmermans, Louis Strous, Marcel Grünauer, Martin Hasch, Max Maischein, Michael Witten, Moritz Lenz, Nicholas Clark, Niko Tyni, Nuno Carvalho, Pau Amma, Peter John Acklam, Robin Barker, Salvador Fandiño, Samuel Thibault, Shawn M Moore, Shigeya Suzuki, Shlomi Fish, Sisyphus, Steffen Müller, Todd Rinaldo, Tom Christiansen, Tony Cook, Vladimir Timofeev, Zefram and Zsbán Ambrus.

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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