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perl5135delta - what is new for perl v5.13.5


This document describes differences between the 5.13.4 release and the 5.13.5 release.

If you are upgrading from an earlier release such as 5.13.3, first read perl5134delta, which describes differences between 5.13.3 and 5.13.4.

Core Enhancements

Adjacent pairs of nextstate opcodes are now optimized away

Previously, in code such as

use constant DEBUG => 0;

sub GAK {
    warn if DEBUG;
    print "stuff\n";

the ops for warn if DEBUG; would be folded to a null op (ex-const), but the nextstate op would remain, resulting in a runtime op dispatch of nextstate, nextstate, ...

The execution of a sequence of nextstate ops is indistinguishable from just the last nextstate op so the peephole optimizer now eliminates the first of a pair of nextstate ops, except where the first carries a label, since labels must not be eliminated by the optimizer and label usage isn't conclusively known at compile time.

API function to parse statements

The parse_fullstmt function has been added to allow parsing of a single complete Perl statement. See perlapi for details.

API functions for accessing the runtime hinthash

A new C API for introspecting the hinthash %^H at runtime has been added. See cop_hints_2hv, cop_hints_fetchpvn, cop_hints_fetchpvs, cop_hints_fetchsv, and hv_copy_hints_hv in perlapi for details.

C interface to caller()

The caller_cx function has been added as an XSUB-writer's equivalent of caller(). See perlapi for details.

Incompatible Changes

Magic variables outside the main package

In previous versions of Perl, magic variables like $!, %SIG, etc. would 'leak' into other packages. So %foo::SIG could be used to access signals, ${"foo::!"} (with strict mode off) to access C's errno, etc.

This was a bug, or an 'unintentional' feature, which caused various ill effects, such as signal handlers being wiped when modules were loaded, etc.

This has been fixed (or the feature has been removed, depending on how you see it).

Smart-matching against array slices

Previously, the following code resulted in a successful match:

my @a = qw(a y0 z);
my @b = qw(a x0 z);
@a[0 .. $#b] ~~ @b;

This odd behaviour has now been fixed [perl #77468].

C API changes

The first argument of the C API function Perl_fetch_cop_label has changed from struct refcounted he * to COP *, to better insulate the user from implementation details.

This API function was marked as "may change", and likely isn't in use outside the core. (Neither an unpacked CPAN, nor Google's codesearch, finds any other references to it.)


Use of qw(...) as parentheses

Historically the parser fooled itself into thinking that qw(...) literals were always enclosed in parentheses, and as a result you could sometimes omit parentheses around them:

for $x qw(a b c) { ... }

The parser no longer lies to itself in this way. Wrap the list literal in parentheses, like:

for $x (qw(a b c)) { ... }

Performance Enhancements

Modules and Pragmata

Updated Modules and Pragmata


Upgraded from version 0.23 to 0.25.


Upgraded from version 1.05 to 1.06.


Upgraded from version 1.07 to 1.08.


Upgraded from version 1.33_02 to 1.33_03.

warnings and warnings::register

Upgraded from version 1.10 to 1.11 and from version 1.01 to 1.02 respectively.

It is now possible to register warning categories other than the names of packages using warnings::register. See perllexwarn for more information.


Upgraded from version 1.12 to 1.16.


Upgraded from version 0.46 to 0.48.


Upgraded from version 2.126 to 2.128.

This fixes a crash when using custom sort functions that might cause the stack to change.


Upgraded from version 2.39 to 2.40.


Upgraded from version 1.12 to 1.13.

On some platforms with unusual header files, like Win32/gcc using mingw64 headers, some constants which weren't actually error numbers have been exposed by Errno. This has been fixed [perl #77416].


Upgraded from version 6.5601 to 6.57_05.


Upgraded from version 0.84 to 0.85.


Upgraded from version 0.08 to 0.09.


Upgraded from version 1.89_01 to 1.95.

This fixes, among other things, incorrect results when computing binomial coefficients [perl #77640].


Upgraded from version 0.19 to 0.22.


Upgraded from version 0.24 to 0.26.


Upgraded from version 2.37 to 2.38.


Upgraded from version 0.08 to 0.09.


Upgraded from version 1.19 to 1.20.

It now includes constants for POSIX signal constants.


Upgraded from version 2.27 to 2.28.

This fixes a possible infinite loop when looking for coderefs.


Upgraded from version 0.96 to 0.97_01.


Upgraded from version 1.03 to 1.04.

Calling Tie::Hash->TIEHASH() used to loop forever. Now it croaks.


Upgraded from version 0.56 to 0.59.


Upgraded from version 0.10 to 0.11.


Changes to Existing Documentation





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

Changes to Existing Diagnostics

Utility Changes



Platform Support

Platform-Specific Notes

  • Make PerlIOUnix_open honour default permissions on VMS.

    When perlio became the default and unixio became the default bottom layer, the most common path for creating files from Perl became PerlIOUnix_open, which has always explicitly used 0666 as the permission mask.

    To avoid this, 0777 is now passed as the permissions to open(). In the VMS CRTL, 0777 has a special meaning over and above intersecting with the current umask; specifically, it allows Unix syscalls to preserve native default permissions.

Internal Changes

Selected Bug Fixes

Known Problems


Perl 5.13.5 represents approximately one month of development since Perl 5.13.4 and contains 74558 lines of changes across 549 files from 45 authors and committers:

Abigail, Alexander Alekseev, Aristotle Pagaltzis, Ben Morrow, Bram, brian d foy, Chas. Owens, Chris 'BinGOs' Williams, Craig A. Berry, Curtis Jewell, Dagfinn Ilmari Mannsåker, David Golden, David Leadbeater, David Mitchell, Eric Brine, Father Chrysostomos, Florian Ragwitz, Gisle Aas, Jan Dubois, Jerry D. Hedden, Jesse Vincent, Jim Cromie, Jirka Hruška, Karl Williamson, Michael G. Schwern, Nicholas Clark, Paul Johnson, Philippe Bruhat (BooK), Piotr Fusik, Rafael Garcia-Suarez, Rainer Tammer, Reini Urban, Ricardo Signes, Rob Hoelz, Robin Barker, Steffen Mueller, Steve Hay, Steve Peters, Todd Rinaldo, Tony Cook, Vincent Pit, Yves Orton, Zefram, Zsbán Ambrus, Ævar Arnfjörð Bjarmason.

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.

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 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.