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PERL52510DELTA(1) Perl Programmers Reference Guide PERL52510DELTA(1)


perl52510delta - what is new for perl v5.25.10


This document describes differences between the 5.25.9 release and the 5.25.10 release.

If you are upgrading from an earlier release such as 5.25.8, first read perl5259delta, which describes differences between 5.25.8 and 5.25.9.

Modules and Pragmata

Updated Modules and Pragmata

  • B has been upgraded from version 1.65 to 1.68.
  • CPAN has been upgraded from version 2.16 to 2.17.
  • feature has been upgraded from version 1.46 to 1.47.
  • Getopt::Std has been upgraded from version 1.11 to 1.12.
  • Module::CoreList has been upgraded from version 5.20170120 to 5.20170220.
  • open has been upgraded from version 1.10 to 1.11.
  • PerlIO has been upgraded from version 1.09 to 1.10.
  • Storable has been upgraded from version 2.61 to 2.62.
  • Thread::Queue has been upgraded from version 3.11 to 3.12.
  • threads has been upgraded from version 2.12 to 2.13.


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.

Changes to Existing Diagnostics

  • Use of unassigned code point or non-standalone grapheme for a delimiter will be a fatal error starting in Perl 5.30

    This was changed to drop a leading "v" in "v5.30", so it uses the same style as other deprecation messages.

  • "\c%c" is more clearly written simply as "%s".

    It was decided to undeprecate the use of "\c%c", see <>

Platform Support

Platform-Specific Notes

Support for compiling perl on Windows using Microsoft Visual Studio 2015 (containing Visual C++ 14.0) has been added.

This version of VC++ includes a completely rewritten C run-time library, some of the changes in which mean that work done to resolve a socket close() bug in perl #120091 and perl #118059 is not workable in its current state with this version of VC++. Therefore, we have effectively reverted that bug fix for VS2015 onwards on the basis that being able to build with VS2015 onwards is more important than keeping the bug fix. We may revisit this in the future to attempt to fix the bug again in a way that is compatible with VS2015.

These changes do not affect compilation with GCC or with Visual Studio versions up to and including VS2013, i.e. the bug fix is retained (unchanged) for those compilers.

Note that you may experience compatibility problems if you mix a perl built with GCC or VS <= VS2013 with XS modules built with VS2015, or if you mix a perl built with VS2015 with XS modules built with GCC or VS <= VS2013. Some incompatibility may arise because of the bug fix that has been reverted for VS2015 builds of perl, but there may well be incompatibility anyway because of the rewritten CRT in VS2015 (e.g. see discussion at

Internal Changes

  • The "op_class()" API function has been added. This is like the existing "OP_CLASS()" macro, but can more accurately determine what struct an op has been allocated as. For example "OP_CLASS()" might return "OA_BASEOP_OR_UNOP" indicating that ops of this type are usually allocated as an "OP" or "UNOP"; while "op_class()" will return "OPclass_BASEOP" or "OPclass_UNOP" as appropriate.
  • The output format of the "op_dump()" function (as used by "perl -Dx") has changed: it now displays an "ASCII-art" tree structure, and shows more low-level details about each op, such as its address and class.

Selected Bug Fixes

  • Attempting to use the deprecated variable $# as the object in an indirect object method call could cause a heap use after free or buffer overflow. [perl #129274]
  • When checking for an indirect object method call in some rare cases the parser could reallocate the line buffer but then continue to use pointers to the old buffer. [perl #129190]
  • Supplying a glob as the format argument to "formline" in perlfunc would cause an assertion failure. [perl #130722]
  • Code like " $value1 =~ qr/.../ ~~ $value2 " would have the match converted into a qr// operator, leaving extra elements on the stack to confuse any surrounding expression. [perl #130705]
  • Since 5.24.0 in some obscure cases, a regex which included code blocks from multiple sources (e.g. via embedded via qr// objects) could end up with the wrong current pad and crash or give weird results. [perl #129881]
  • Occasionally "local()"s in a code block within a patterns weren't being undone when the pattern matching backtracked over the code block. [perl #126697]
  • Using "substr()" to modify a magic variable could access freed memory in some cases. [perl #129340]
  • Perl 5.25.9 was fixed so that under "use utf8", the entire Perl program is checked that the UTF-8 is wellformed. It turns out that several edge cases were missed, and are now fixed. [perl #126310] was the original ticket.


Perl 5.25.10 represents approximately 4 weeks of development since Perl 5.25.9 and contains approximately 12,000 lines of changes across 200 files from 25 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 6,700 lines of changes to 130 .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 5.25.10:

Aaron Crane, Abigail, Andreas König, Andy Lester, Chris 'BinGOs' Williams, Christian Millour, Colin Newell, Dagfinn Ilmari Mannsåker, David Mitchell, Hugo van der Sanden, James E Keenan, Jarkko Hietaniemi, Jerry D. Hedden, John Lightsey, Karl Williamson, Neil Bowers, Pali, Renee Baecker, Sawyer X, Sergey Aleynikov, Steffen Müller, Steve Hay, Tony Cook, Yves Orton, 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 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 see "SECURITY VULNERABILITY CONTACT INFORMATION" in perlsec for details of how to report the issue.


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.

2017-05-20 perl v5.26.0