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perldelta - what is new for perl v5.17.9


This document describes differences between the 5.17.8 release and the 5.17.9 release.

If you are upgrading from an earlier release such as 5.17.7, first read perl5178delta, which describes differences between 5.17.7 and 5.17.8.

Core Enhancements

Interpolations now Accepted in Regular Expression Set Operations

Perl v5.17.8 introduced regular expression set operations. They have now been expanded to allow the interpolation of a previously-compiled set into a bigger set, like this:

 my $thai_or_lao = qr/\p{Thai} + \p{Lao}/;
 qr/(?[ \p{Digit} & $thai_or_lao ])/;

Incompatible Changes

$ENV{foo} = undef no longer deletes value from environ

5.17.3 Introduced a change where assiging undef to an %ENV key was equivalent to delete $ENV{foo}.

This release reverts that change.


The deprecation of lexical $_ in 5.17.7 has been commuted. The feature is now marked experimental.

Deprecated pragma


This module is deprecated under perl 5.18. It uses a mechanism provided by perl that is deprecated under 5.18 and higher, and may be removed in a future version.

Deprecated Modules

The following modules will be removed from the core distribution in a future release, and should be installed from CPAN instead. Distributions on CPAN which require these should add them to their prerequisites. The core versions of these modules warnings will issue a deprecation warning.

You can silence these deprecation warnings by installing the modules in question from CPAN.


Deprecated Utilities

The following utilities will be removed from the core distribution in a future release as their associated modules have been deprecated. They will remain available with the applicable CPAN distribution.


Included with CPANPLUS.


Included with CPANPLUS.


Included with CPANPLUS.


The Pod::LaTeX module was deprecated with 5.17.8.

Five additional characters should be escaped in patterns with /x

When a regular expression pattern is compiled with /x, Perl treats 6 characters as white space to ignore, such as SPACE and TAB. However, Unicode recommends 11 characters be treated thusly. In preparation to conforming with this in a future Perl version, in the meantime, use of any of the missing characters will raise a deprecation warning, unless turned off. The five characters are: U+0085 NEXT LINE, U+200E LEFT-TO-RIGHT MARK, U+200F RIGHT-TO-LEFT MARK, U+2028 LINE SEPARATOR, and U+2029 PARAGRAPH SEPARATOR.

Modules and Pragmata

New Modules and Pragmata

  • Config::Perl::V version 0.16 has been added as a dual-lifed module. It provides structured data retrieval of perl -V output including information only known to the perl binary and not available via Config.

Updated Modules and Pragmata

  • Archive::Extract has been upgraded from version 0.62 to 0.68.

    NOTE: Archive::Extract is deprecated and may be removed from a future version of Perl.

  • Attribute::Handlers has been upgraded from version 0.93 to 0.94.

  • B::Lint has been upgraded from version 1.14 to 1.17.

    NOTE: B::Lint is deprecated and may be removed from a future version of Perl.

  • Benchmark has been upgraded from version 1.13 to 1.14.

    The "too few iterations" message is now a warning on STDERR instead of being output on STDOUT.

  • bignum has been upgraded from version 0.31 to 0.32.

  • CPAN has been upgraded from version 1.99_51 to 2.00.

  • CPANPLUS has been upgraded from version 0.9133 to 0.9135.

    NOTE: CPANPLUS is deprecated and may be removed from a future version of Perl.

  • CPANPLUS::Dist::Build has been upgraded from version 0.68 to 0.70.

    NOTE: CPANPLUS::Dist::Build is deprecated and may be removed from a future version of Perl.

  • Data::Dumper has been upgraded from version 2.141 to 2.142.

    Additional tests were added in order to improve statement, branch, condition and subroutine coverage. On the basis of the coverage analysis, some of the internals of Dumper.pm were refactored. Almost all methods are now documented.

  • DBM_Filter has been upgraded from version 0.04 to 0.05.

  • Digest::SHA has been upgraded from version 5.81 to 5.82.

  • Encode has been upgraded from version 2.47 to 2.48.

  • ExtUtils::Manifest has been upgraded from version 1.62 to 1.63.

  • File::CheckTree has been upgraded from version 4.41 to 4.42.

  • File::DosGlob has been upgraded from version 1.09 to 1.10.

  • File::Temp has been upgraded from version 0.22 to 0.22_90

    Fixes various bugs involving directory removal. Defers unlinking tempfiles if the initial unlink fails, which fixes problems on NFS.

  • Filter::Simple has been upgraded from version 0.88 to 0.89.

  • IO has been upgraded from version 1.26 to 1.27.

  • Log::Message has been upgraded from version 0.04 to 0.06.

    NOTE: Log::Message is deprecated and may be removed from a future version of Perl.

  • Log::Message::Simple has been upgraded from version 0.08 to 0.10.

    NOTE: Log::Message::Simple is deprecated and may be removed from a future version of Perl.

  • Math::BigInt has been upgraded from version 1.998 to 1.999.

  • Module::CoreList has been upgraded from version 2.80 to 2.82.

  • Module::Load has been upgraded from version 0.22 to 0.24.

  • Module::Pluggable has been upgraded from version 4.5 to 4.6.

    NOTE: Module::Pluggable is deprecated and may be removed from a future version of Perl.

  • Object::Accessor has been upgraded from version 0.44 to 0.46.

    NOTE: Object::Accessor is deprecated and may be removed from a future version of Perl.

  • overload has been upgraded from version 1.20 to 1.21.

  • PerlIO::scalar has been upgraded from version 0.15 to 0.16.

    The buffer scalar supplied may now only contain code pounts 0xFF or lower. [perl #109828]

  • Pod::Checker has been upgraded from version 1.51 to 1.60.

  • Pod::Html has been upgraded from version 1.17 to 1.18.

  • Pod::Parser has been upgraded from version 1.51 to 1.60.

  • Pod::Perldoc has been upgraded from version 3.17 to 3.19.

  • Pod::Usage has been upgraded from version 1.51 to 1.61.

  • SelfLoader has been upgraded from version 1.20 to 1.21.

  • Term::UI has been upgraded from version 0.32 to 0.34.

    NOTE: Term::UI is deprecated and may be removed from a future version of Perl.

  • Test::Harness has been upgraded from version 3.25_01 to 3.26.

  • Text::Soundex has been upgraded from version 3.03_01 to 3.04.

  • Thread::Queue has been upgraded from version 3.01 to 3.02.

  • Unicode::UCD has been upgraded from version 0.47 to 0.50.

  • warnings has been upgraded from version 1.16 to 1.17.

  • Win32 has been upgraded from version 0.45 to 0.46.

  • Win32API::File has been upgraded from version 0.1200 to 0.1201.


Changes to Existing Documentation


  • A syntax error was fixed in one of illustrative examples.


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

  • Strings with code points over 0xFF may not be mapped into in-memory file handles

Changes to Existing Diagnostics

  • The warnings for \b{ and \B{ were added in the 5.17 series; they are a deprecation warning which should be turned off by that category. One should not have to turn off regular regexp warnings as well to get rid of these.

Utility Changes


  • Added --feature switch which lists the first version bundle of each named feature given.

  • Added --upstream switch which shows if the given module is primarily maintained in perl core or on CPAN and bug tracker URL.

Configuration and Compilation

  • Added useversionedarchname option to Configure

    When set, it includes 'api_versionstring' in 'archname'. E.g. x86_64-linux-5.13.6-thread-multi. It is unset by default.

    This feature was requested by Tim Bunce, who observed that INSTALL_BASE creates a library structure that does not differentiate by perl version. Instead, it places architecture specific files in "$install_base/lib/perl5/$archname". This makes it difficult to use a common INSTALL_BASE library path with multiple versions of perl.

    By setting -Duseversionedarchname, the $archname will be distinct for architecture *and* API version, allowing mixed use of INSTALL_BASE.

  • Configure will honour the external MAILDOMAIN environment variable, if set.

  • installman no longer ignores the silent option

  • Both META.yml and META.json files are now included in the distribution.


  • Enable perl core tests to pass when locale support is not available.

    use locale - this will now die if $Config{d_setlocale} is not true. All tests that use locale will skip if $Config{d_setlocale} is not true. This enables us to pass tests on Android which uses ICU instead of locales.

Platform Support

Platform-Specific Notes


The character set for Extended Filename Syntax (EFS) is now enabled by default on VMS. Among other things, this provides better handling of dots in directory names, multiple dots in filenames,and spaces in filenames. To obtain the old behavior, set the logical name DECC$EFS_CHARSET to DISABLE.


libc_r was removed from recent versions of MidnightBSD and older versions work better with pthread. Threading is now enabled using pthread which corrects build errors with threading enabled on 0.4-CURRENT.

Internal Changes

  • Synonyms for the misleadingly named av_len() has been created: av_top_index() and av_tindex. All three of these return the number of the highest index in the array, not the number of elements it contains. (The name av_top which was introduced in Perl v.5.17.8 has been removed.)

Selected Bug Fixes

  • -DPERL_GLOBAL_STRUCT builds now free the global struct after they've finished using it.

  • A trailing '/' on a path in @INC will no longer have an additional '/' appended.

  • The :crlf layer now works when unread data doesn't fit into its own buffer. [perl #112244].

  • ungetc() now handles UTF-8 encoded data. [perl #116322].


Perl 5.17.9 represents approximately 4 weeks of development since Perl 5.17.8 and contains approximately 42,000 lines of changes across 510 files from 35 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 5.17.9:

Aaron Crane, Alan Haggai Alavi, Alexandr Ciornii, Andy Dougherty, Brad Gilbert, Chris 'BinGOs' Williams, Christian Hansen, Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, Dave Rolsky, David Golden, David Mitchell, Father Chrysostomos, H.Merijn Brand, James E Keenan, Jan Dubois, Jerry D. Hedden, Jess Robinson, Karl Williamson, Kent Fredric, Leon Timmermans, Lucas Holt, Matthew Horsfall, Nicholas Clark, Peter Martini, Rafael Garcia-Suarez, Ricardo Signes, Smylers, Steffen Müller, Steve Hay, Thomas Sibley, Tobias Leich, Tony Cook.

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 http://rt.perl.org/perlbug/ . There may also be information at http://www.perl.org/ , 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 perlbug@perl.org 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 perl5-security-report@perl.org. 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.