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Steve Hay
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perldelta - what is new for perl v5.25.3


This document describes differences between the 5.25.2 release and the 5.25.3 release.

If you are upgrading from an earlier release such as 5.25.1, first read perl5252delta, which describes differences between 5.25.1 and 5.25.2.

Core Enhancements

Unicode 9.0 is now supported

A list of changes is at http://www.unicode.org/versions/Unicode9.0.0/. Modules that are shipped with core Perl but not maintained by p5p do not necessarily support Unicode 9.0. Unicode::Normalize does work on 9.0.

Use of \p{script} uses the improved Script_Extensions property

Unicode 6.0 introduced an improved form of the Script (sc) property, and called it Script_Extensions (scx). As of now, Perl uses this improved version when a property is specified as just \p{script}. The meaning of compound forms, like \p{sc=script} are unchanged. This should make programs be more accurate when determining if a character is used in a given script, but there is a slight chance of breakage for programs that very specifically needed the old behavior. See "Scripts" in perlunicode.

Declaring a reference to a variable

As an experimental feature, Perl now allows the referencing operator to come after my(), state(), our(), or local(). This syntax must be enabled with use feature 'declared_refs'. It is experimental, and will warn by default unless no warnings 'experimental::refaliasing' is in effect. It is intended mainly for use in assignments to references. For example:

    use experimental 'refaliasing', 'declared_refs';
    my \$a = \$b;

See "Assigning to References" in perlref for slightly more detail.

Incompatible Changes

${^ENCODING} has been removed

Consequently, the encoding pragma's default mode is no longer supported. If you still need to write your source code in encodings other than UTF-8, use a source filter such as Filter::Encoding on CPAN or encoding's Filter option.

scalar(%hash) return signature changed

The value returned for scalar(%hash) will no longer show information about the buckets allocated in the hash. It will simply return the count of used keys. It is thus equivalent to 0+keys(%hash).

A form of backwards compatibility is provided via Hash::Util::bucket_ratio() which provides the same behavior as scalar(%hash) provided prior to Perl 5.25.

Modules and Pragmata

Updated Modules and Pragmata

  • bignum has been upgraded from version 0.42 to 0.43.

  • Data::Dumper has been upgraded from version 2.160 to 2.161.

  • Devel::PPPort has been upgraded from version 3.32 to 3.35.

  • Encode has been upgraded from version 2.80 to 2.84.

  • encoding has been upgraded from version 2.17 to 2.17_01.

    This module's default mode is no longer supported as of Perl 5.25.3. It now dies when imported, unless the Filter option is being used.

  • encoding::warnings has been upgraded from version 0.12 to 0.13.

    This module is no longer supported as of Perl 5.25.3. It emits a warning to that effect and then does nothing.

  • ExtUtils::ParseXS has been upgraded from version 3.32 to 3.33.

  • ExtUtils::Typemaps has been upgraded from version 3.32 to 3.33.

  • feature has been upgraded from version 1.44 to 1.45.

  • Hash::Util has been upgraded from version 0.19 to 0.20.

  • Math::BigInt has been upgraded from version 1.999715 to 1.999726.

  • Math::BigInt::FastCalc has been upgraded from version 0.40 to 0.42.

  • Math::BigRat has been upgraded from version 0.260802 to 0.260804.

  • Module::CoreList has been upgraded from version 5.20160620 to 5.20160720.

  • Parse::CPAN::Meta has been upgraded from version 1.4417 to 1.4422.

  • Perl::OSType has been upgraded from version 1.009 to 1.010.

  • Test::Simple has been upgraded from version 1.302026 to 1.302045.

  • Time::HiRes has been upgraded from version 1.9734 to 1.9739.

  • Unicode::UCD has been upgraded from version 0.65 to 0.66.

  • version has been upgraded from version 0.9916 to 0.9917.

  • warnings has been upgraded from version 1.36 to 1.37.

  • XSLoader has been upgraded from version 0.21 to 0.22, fixing a security hole in which binary files could be loaded from a path outside of @INC.


Changes to Existing Documentation

perldata and perltie

perlexperiment and perlref





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

  • Declaring references is experimental

    (S experimental::declared_refs) This warning is emitted if you use a reference constructor on the right-hand side of my(), state(), our(), or local(). Simply suppress the warning if you want to use the feature, but know that in doing so you are taking the risk of using an experimental feature which may change or be removed in a future Perl version:

        no warnings "experimental::declared_refs";
        use feature "declared_refs";
        $fooref = my \$foo;
  • ${^ENCODING} is no longer supported

    (D deprecated) The special variable ${^ENCODING}, formerly used to implement the encoding pragma, is no longer supported as of Perl 5.26.0.

Configuration and Compilation

  • Configure now aborts if both "-Duselongdouble" and "-Dusequadmath" are requested. [perl #126203]

  • Fixed a bug in which Configure could append "-quadmath" to the archname even if it was already present. [perl #128538]

  • Clang builds with "-DPERL_GLOBAL_STRUCT" or "-DPERL_GLOBAL_STRUCT_PRIVATE" have been fixed (by disabling Thread Safety Analysis for these configurations).


  • A new test script, t/op/decl-refs.t, has been added to test the new feature, "Declaring a reference to a variable".

  • A new test script, t/re/anyof.t, has been added to test that the ANYOF nodes generated by bracketed character classes are as expected.

Platform Support

Platform-Specific Notes


VAX floating point formats are now supported.

Selected Bug Fixes

  • An assertion failure with %: = 0 has been fixed. [perl #128238]

  • In Perl 5.18, the parsing of "$foo::$bar" was accidentally changed, such that it would be treated as $foo."::".$bar. The previous behavior, which was to parse it as $foo:: . $bar, has been restored. [perl #128478]

  • Since Perl 5.20, line numbers have been off by one when perl is invoked with the -x switch. This has been fixed. [perl #128508]

  • Vivifying a subroutine stub in a deleted stash (e.g., delete $My::{"Foo::"}; \&My::Foo::foo) no longer crashes. It had begun crashing in Perl 5.18. [perl #128532]

  • Some obscure cases of subroutines and file handles being freed at the same time could result in crashes, but have been fixed. The crash was introduced in Perl 5.22. [perl #128597]

  • Code that looks for a variable name associated with an uninitialized value could cause an assertion in cases where magic is involved, such as $ISA[0][0]. This has now been fixed. [perl #128253]

  • A crash caused by code generating the warning "Subroutine STASH::NAME redefined" in cases such as sub P::f{} undef *P::; *P::f =sub{}; has been fixed. In these cases, where the STASH is missing, the warning will now appear as "Subroutine NAME redefined". [perl #128257]

  • Fixed an assertion triggered by some code that handles deprecated behavior in formats, e.g. in cases like this:

        format STDOUT =

    [perl #128255]

  • A possible divide by zero in string transformation code on Windows has been avoided, fixing a crash when collating an empty string. [perl #128618]

  • Some regular expression parsing glitches could lead to assertion failures with regular expressions such as /(?<=/ and /(?<!/. This has now been fixed. [perl #128170]

Errata From Previous Releases

  • Parsing bad POSIX charclasses no longer leaks memory. This was fixed in Perl 5.25.2 [perl #128313]

  • Fixed issues with recursive regexes. The behavior was fixed in Perl 5.24.0. [perl #126182]


Perl 5.25.3 represents approximately 4 weeks of development since Perl 5.25.2 and contains approximately 67,000 lines of changes across 510 files from 25 authors.

Excluding auto-generated files, documentation and release tools, there were approximately 40,000 lines of changes to 290 .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 5.25.3:

Aaron Crane, Ævar Arnfjörð Bjarmason, Alex Vandiver, Aristotle Pagaltzis, Chad Granum, Chris 'BinGOs' Williams, Chris Lamb, Craig A. Berry, Dan Collins, David Mitchell, Father Chrysostomos, H.Merijn Brand, Jarkko Hietaniemi, Karl Williamson, Lukas Mai, Matthew Horsfall, Salvador Fandiño, Sawyer X, Sébastien Aperghis-Tramoni, Steffen Müller, Steve Hay, Todd Rinaldo, Tony Cook, Unicode Consortium, 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 perl bug database at https://rt.perl.org/ . 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 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.