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Source   Latest Release: perl-5.17.11


perl5170delta - what is new for perl v5.17.0


This document describes differences between the 5.16.0 release and the 5.17.0 release.

If you are upgrading from an earlier release such as 5.16.0, first read perl5160delta, which describes differences between 5.14.0 and 5.16.0.

Incompatible Changes ^

qw(...) can no longer be used as parentheses

qw lists used to fool the parser into thinking they were always surrounded by parentheses. This permitted some surprising constructions such as foreach $x qw(a b c) {...}, which should really be written foreach $x (qw(a b c)) {...}. These would sometimes get the lexer into the wrong state, so they didn't fully work, and the similar foreach qw(a b c) {...} that one might expect to be permitted never worked at all.

This side effect of qw has now been abolished. It has been deprecated since Perl 5.13.11. It is now necessary to use real parentheses everywhere that the grammar calls for them.

\s in regular expressions now matches a Vertical Tab (experimental)

This is an experiment early in the development cycle to see what repercussions arise from this change. It may well be that we decide to require a "use feature" to activate this behavior. Because of the experimental nature of this, which may be reversed, the documentation has not been changed to reflect it.

Deprecations ^

Unescaped braces in regexps

Literal unescaped { in regular expressions is now deprecated. Every brace character should be either escaped (by a preceding backslash) or part of a construct where it's a metacharacter. This catches likely typos such as /f{,3}/. It will also allow braces to be used in the future to delimit parameters to metacharacters that currently take no parameters.

Performance Enhancements ^

Modules and Pragmata ^

Updated Modules and Pragmata

Removed Modules and Pragmata

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

Testing ^

Platform Support ^

Platform-Specific Notes


There is now a workaround for a compiler bug that prevented compiling with clang++ since Perl 5.15.7 [perl #112786].


When compiling the Perl core as C++ (which is only semi-supported), the mathom functions are now compiled as extern "C", to ensure proper binary compatibility. (However, binary compatibility isn't generally guaranteed anyway in the situations where this would matter.)


It should now be possible to compile Perl as C++ on VMS.

Internal Changes ^

Selected Bug Fixes ^

Acknowledgements ^

Perl 5.17.0 represents approximately 1 week of development since Perl 5.16.0 and contains approximately 17,000 lines of changes across 180 files from 26 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 5.16.1:

Alan Haggai Alavi, Aristotle Pagaltzis, Brian Fraser, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker, Eric Brine, Father Chrysostomos, Igor Zaytsev, James E Keenan, Karl Williamson, Leon Timmermans, Lukas Mai, Marcus Holland-Moritz, Matthew Horsfall, Moritz Lenz, Rafael Garcia-Suarez, Reini Urban, Ricardo Signes, Robin Barker, Ronald J. Kimball, Smylers, Steffen Müller, Steve Hay, Tony Cook, Zefram.

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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