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perl5192delta - what is new for perl v5.19.2


This document describes differences between the 5.19.1 release and the 5.19.2 release.

If you are upgrading from an earlier release such as 5.19.0, first read perl5191delta, which describes differences between 5.19.0 and 5.19.1.

Core Enhancements

More consistent prototype parsing

Multiple semicolons in subroutine prototypes have long been tolerated and treated as a single semicolon. There was one case where this did not happen. A subroutine whose prototype begins with "*" or ";*" can affect whether a bareword is considered a method name or sub call. This now applies also to ";;;*".

Whitespace has long been allowed inside subroutine prototypes, so sub( $ $ ) is equivalent to sub($$), but until now it was stripped when the subroutine was parsed. Hence, whitespace was not allowed in prototypes set by Scalar::Util::set_prototype. Now it is permitted, and the parser no longer strips whitespace. This means prototype &mysub returns the original prototype, whitespace and all.

Performance Enhancements

  • Precomputed hash values are now used in more places during method lookup.

Modules and Pragmata

Updated Modules and Pragmata

  • autodie has been upgraded from version 2.19 to 2.20.

  • B has been upgraded from version 1.43 to 1.44.

  • B::Concise has been upgraded from version 0.96 to 0.98.

  • B::Deparse has been upgraded from version 1.21 to 1.22.

  • base has been upgraded from version 2.18 to 2.19.

  • Benchmark has been upgraded from version 1.16 to 1.17.

  • Class::Struct has been upgraded from version 0.64 to 0.65.

  • Data::Dumper has been upgraded from version 2.146 to 2.147.

  • DB_File has been upgraded from version 1.828 to 1.829.

  • DBM_Filter has been upgraded from version 0.05 to 0.06.

  • Devel::Peek has been upgraded from version 1.11 to 1.12.

  • Digest::MD5 has been upgraded from version 2.52 to 2.53.

  • Digest::SHA has been upgraded from version 5.84 to 5.85.

  • English has been upgraded from version 1.06 to 1.07.

  • Errno has been upgraded from version 1.18 to 1.19.

  • ExtUtils::Embed has been upgraded from version 1.30 to 1.31

    The generated C code now incorporates bug fixes present in miniperlmain.c, and has whitespace changes. It now uses #include "..." for header files instead of #include <...>. This should not make any difference, unless programs embedding libperl happen to have local and incompatible files named EXTERN.h, XSUB.h or perl.h, as these will now be picked up instead of the installed Perl headers.

    The canon() function now correctly handles packages with multiple :: separators when the $as parameter is not /. Given that it used to generate strings which would likely be syntax errors or pathnames instead of filenames, we infer that from the complete lack of bug reports no-one was using this functionality. (ExtUtils::Miniperl is now using it.)

  • ExtUtils::Miniperl has been upgraded and given a version of 1. Previously it did not have a version number.

    writemain() now takes an optional first argument. A reference to a scalar is treated as a filename to be opened and written to. Any other reference is used as the filehandle to write to. Otherwise the existing default remains, to write to STDOUT.

    writemain() has been refactored to use functions from ExtUtils::Embed, reducing code size and duplication. The internal function canon() has been deleted.

  • ExtUtils::ParseXS has been upgraded from version 3.19 to 3.21.

  • File::Basename has been upgraded from version 2.84 to 2.85.

  • Getopt::Long has been upgraded from version 2.4 to 2.41.

  • Getopt::Std has been upgraded from version 1.08 to 1.09.

  • Hash::Util::FieldHash has been upgraded from version 1.11 to 1.12.

  • HTTP::Tiny has been upgraded from version 0.031 to 0.034.

  • I18N::Langinfo has been upgraded from version 0.10 to 0.11.

  • if has been upgraded from version 0.0602 to 0.0603.

  • IPC::Cmd has been upgraded from version 0.80 to 0.82.

  • MIME::Base64 has been upgraded from version 3.13 to 3.14.

  • Module::CoreList has been upgraded from version 2.92 to 2.94.

  • Params::Check has been upgraded from version 0.36 to 0.38.

  • Parse::CPAN::Meta has been upgraded from version 1.4404 to 1.4405.

  • Pod::Functions has been upgraded from version 1.06 to 1.07.

  • Pod::Html has been upgraded from version 1.19 to 1.2.

  • POSIX has been upgraded from version 1.33 to 1.34.

    POSIX::AUTOLOAD will no longer infinitely recurse if the shared object fails to load.

  • Safe has been upgraded from version 2.36 to 2.37.

  • Socket has been upgraded from version 2.009 to 2.010.

  • Storable has been upgraded from version 2.43 to 2.45.

    Calling STORABLE_attach hooks no longer leaks memory. [perl #118829]

  • Text::ParseWords has been upgraded from version 3.28 to 3.29.

  • Tie::Hash has been upgraded from version 1.04 to 1.05.

  • Time::Piece has been upgraded from version 1.2002 to 1.21.


Changes to Existing Documentation


  • Code in regular expressions, regular expression backtracking verbs, and lvalue subroutines are no longer listed as experimental. (This also affects perlre and perlsub.)


  • Since Perl v5.10, it has been possible for subroutines in @INC to return a reference to a scalar holding initial source code to prepend to the file. This is now documented.


  • The language design of Perl has always called for monomorphic operators. This is now mentioned explicitly.


  • The fact that the regexp engine makes no effort to call (?{}) and (??{}) constructs any specified number of times (although it will basically DWIM in case of a successful match) has been documented.


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

Changes to Existing Diagnostics

  • Under rare circumstances, one could get a "Can't coerce readonly REF to string" instead of the customary "Modification of a read-only value". This alternate error message has been removed.

  • "Ambiguous use of * resolved as operator *": This and similar warnings about "%" and "&" used to occur in some circumstances where there was no operator of the type cited, so the warning was completely wrong. This has been fixed [perl #117535, #76910].

  • Warnings about malformed subroutine prototypes are now more consistent in how the prototypes are rendered. Some of these warnings would truncate prototypes containing nulls. In other cases one warning would suppress another. The warning about illegal characters in prototypes no longer says "after '_'" if the bad character came before the underscore.

  • Perl folding rules are not up-to-date for 0x%X; please use the perlbug utility to report; in regex; marked by <-- HERE in m/%s/

    This message is now only in the regexp category, and not in the deprecated category. It is still a default (i.e., severe) warning [perl #89648].

  • The debugger's "n" command now respects lvalue subroutines and steps over them [perl #118839].

Configuration and Compilation

  • installperl and installman's option handling has been refactored to use Getopt::Long. Both are used by the Makefile install targets, and are not installed, so these changes are only likely to affect custom installation scripts.

    • single letter options now also have long names

    • invalid options are now rejected

    • command line arguments that are not options are now rejected

    • Each now has a --help option to display the usage message.

    The behaviour for all valid documented invocations is unchanged.

Platform Support

Platform-Specific Notes


objformat was removed from version 0.4-RELEASE of MidnightBSD and had been deprecated on earlier versions. This caused the build environment to be erroneously configured for a.out rather than elf. This has been now been corrected.

Internal Changes

  • The Makefile shortcut targets for many rarely (or never) used testing and profiling targets have been removed, or merged into the only other Makefile target that uses them. Specifically, these targets are gone, along with documentation that referenced them or explained how to use them:

        check.third check.utf16 check.utf8 coretest minitest.prep
        minitest.utf16 perl.config.dashg perl.config.dashpg
        perl.config.gcov perl.gcov perl.gprof perl.gprof.config
        perl.pixie perl.pixie.atom perl.pixie.config perl.pixie.irix
        perl.third perl.third.config perl.valgrind.config purecovperl
        pureperl quantperl test.deparse test.taintwarn test.third
        test.torture test.utf16 test.utf8 test_notty.deparse
        test_notty.third test_notty.valgrind test_prep.third
        test_prep.valgrind torturetest ucheck ucheck.third ucheck.utf16
        ucheck.valgrind utest utest.third utest.utf16 utest.valgrind

    It's still possible to run the relevant commands by "hand" - no underlying functionality has been removed.

  • It is now possible to keep Perl from initializing locale handling. For the most part, Perl doesn't pay attention to locale. (See perllocale.) Nonetheless, until now, on startup, it has always initialized locale handling to the system default, just in case the program being executed ends up using locales. (This is one of the first things a locale-aware program should do, long before Perl knows if it will actually be needed or not.) This works well except when Perl is embedded in another application which wants a locale that isn't the system default. Now, if the environment variable PERL_SKIP_LOCALE_INIT is set at the time Perl is started, this initialization step is skipped. Prior to this, on Windows platforms, the only workaround for this deficiency was to use a hacked-up copy of internal Perl code. Applications that need to use older Perls can discover if the embedded Perl they are using needs the workaround by testing that the C preprocessor symbol HAS_SKIP_LOCALE_INIT is not defined. (RT #38193)

  • BmRARE and BmPREVIOUS have been removed. They were not used anywhere and are not part of the API. For XS modules, they are now #defined as 0.

  • sv_force_normal, which usually croaks on read-only values, used to allow read-only values to be modified at compile time. This has been changed to croak on read-only values regardless. This change uncovered several core bugs.

Selected Bug Fixes

  • There have been several fixes related to Perl's handling of locales. perl #38193 was described above in "Internal Changes". Also fixed is #112208 in which the error string in $! displayed as garbage in many UTF-8 locales; #118197, where the radix (decimal point) character had to be an ASCII character (which doesn't work for some non-Western languages); and #115808, in which POSIX::setlocale() on failure returned an undef which didn't warn about not being defined even if those warnings were enabled.

  • The dtrace sub-entry probe now works with lexical subs, instead of crashing [perl #118305].

  • Compiling a split operator whose third argument is a named constant evaulating to 0 no longer causes the constant's value to change.

  • A named constant used as the second argument to index no longer gets coerced to a string if it is a reference, regular expression, dualvar, etc.

  • A named constant evaluating to the undefined value used as the second argument to index no longer produces "uninitialized" warnings at compile time. It will still produce them at run time.

  • When a scalar was returned from a subroutine in @INC, the referenced scalar was magically converted into an IO thingy, possibly resulting in "Bizarre copy" errors if that scalar continued to be used elsewhere. Now Perl uses an internal copy of the scalar instead.

  • Undefining an inlinable lexical subroutine (my sub foo() { 42 } undef &foo) would result in a crash if warnings were turned on.

  • Certain uses of the sort operator are optimised to modify an array in place, such as @a = sort @a. During the sorting, the array is made read-only. If a sort block should happen to die, then the array remained read-only even outside the sort. This has been fixed.

  • $a and $b inside a sort block are aliased to the actual arguments to sort, so they can be modified through those two variables. This did not always work, e.g., for lvalue subs and $#ary, and probably many other operators. It works now.

  • The arguments to sort are now all in list context. If the sort itself were called in void or scalar context, then some, but not all, of the arguments used to be in void or scalar context.

  • Subroutine prototypes with Unicode characters above U+00FF were getting mangled during closure cloning. This would happen with subroutines closing over lexical variables declared outside, and with lexical subs.

  • In regular expressions containing multiple code blocks, the values of $1, $2, etc., set by nested regular expression calls would leak from one block to the next. Now these variables always refer to the outer regular expression at the start of an embedded block [perl #117917].

  • UNIVERSAL::can now treats its first argument the same way that method calls do: Typeglobs and glob references with non-empty IO slots are treated as handles, and strings are treated as filehandles, rather than packages, if a handle with that name exists [perl #113932].

  • Method calls on typeglobs (e.g., *ARGV->getline) used to stringify the typeglob and then look it up again. Combined with changes in Perl 5.18.0, this allowed *foo->bar to call methods on the "foo" package (like foo->bar). In some cases it could cause the method to be called on the wrong handle. Now a typeglob argument is treated as a handle (just like (\*foo)->bar), or, if its IO slot is empty, an error is raised.

  • Under copy-on-write builds (the default as of 5.19.1) ${'_<-e'}[0] no longer gets mangled. This is the first line of input saved for the debugger's use for one-liners [perl #118627].

  • Assigning a vstring to a tied variable or to a subroutine argument aliased to a nonexistent hash or array element now works, without flattening the vstring into a regular string.

  • pos, tie, tied and untie did not work properly on subroutine arguments aliased to nonexistent hash and array elements [perl #77814, #27010].

  • The => fat arrow operator can now quote built-in keywords even if it occurs on the next line, making it consistent with how it treats other barewords.

Known Problems

  • One of the bug fixes has accidentally thrown line numbers off in rare cases, causing test failures for some CPAN modules. This will hopefully be fixed soon [perl #118931].


Perl 5.19.2 represents approximately 4 weeks of development since Perl 5.19.1 and contains approximately 15,000 lines of changes across 400 files from 40 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 5.19.2:

Abhijit Menon-Sen, Alexandr Ciornii, Andy Dougherty, Aristotle Pagaltzis, Brian Fraser, Brian Gottreu, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, David Golden, David Mitchell, Ed Avis, Father Chrysostomos, Graham Knop, H.Merijn Brand, Hojung Youn, James E Keenan, Johan Vromans, Karl Williamson, Keedi Kim, Kent Fredric, Lukas Mai, Moritz Lenz, Nathan Trapuzzano, Neil Bowers, Nicholas Clark, Niels Thykier, Niko Tyni, Olivier Mengué, Peter Martini, Petr Písař, Reini Urban, Ricardo Signes, Ruslan Zakirov, Slaven Rezic, Steffen Müller, Tony Cook, Vladimir Timofeev, 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 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.