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perl5191delta - what is new for perl v5.19.1


This document describes differences between the 5.19.0 release and the 5.19.1 release.

Core Enhancements

No new features have been added.


There are no new security issues.

Incompatible Changes

Most regex engine global state eliminated

As part of this series of fixes it was necessary to change the API of Perl_re_intuit_start(). See "Internal Changes" for more.

Locale decimal point character no longer leaks outside of use locale scope

This is actually a bug fix, but some code has come to rely on the bug being present, so this change is listed here. The current locale that the program is running under is not supposed to be visible to Perl code except within the scope of a use locale. However, until now under certain circumstances, the character used for a decimal point (often a comma) leaked outside the scope. If your code is affected by this change, simply add a use locale.

Performance Enhancements

  • Perl has a new copy-on-write mechanism that avoids the need to copy the internal string buffer when assigning from one scalar to another. This makes copying large strings appear much faster. Modifying one of the two (or more) strings after an assignment will force a copy internally. This makes it unnecessary to pass strings by reference for efficiency.

    This feature was already available in 5.18.0, but wasn't enabled by default. It is the default now, and so you no longer need build perl with the Configure argument:


    It can be disabled (for now) in a perl build with:


Modules and Pragmata

Updated Modules and Pragmata

  • Archive::Tar has been upgraded from version 1.90 to 1.92.

  • Attribute::Handlers has been upgraded from version 0.94 to 0.95.

  • autodie has been upgraded from version 2.13 to 2.19.

  • B has been upgraded from version 1.42 to 1.43.

  • B::Concise has been upgraded from version 0.95 to 0.96.

  • B::Deparse has been upgraded from version 1.20 to 1.21.

    foreach my $lexical is now deparsed correctly with the -p option. [RT #117081]

    The -l option no longer puts form feeds in the middle of a line when outputting map and grep blocks. [RT #117311]

    Elements of %#, such as $# {foo} and ${#}{foo} are now deparsed correctly. [RT #117531]

  • Benchmark has been upgraded from version 1.15 to 1.16.

  • Carp has been upgraded from version 1.29 to 1.30.

  • Compress::Raw::Bzip2 has been upgraded from version 2.060 to 2.061.

  • Compress::Raw::Zlib has been upgraded from version 2.060 to 2.061.

  • Config::Perl::V has been upgraded from version 0.17 to 0.18.

  • CPAN::Meta has been upgraded from version 2.120921 to 2.131560.

  • Data::Dumper has been upgraded from version 2.145 to 2.146.

  • DB has been updated from 1.05 to 1.06 and perl5db.pl from 1.39_10 to 1.40.

    The call depth allowed by default in the debugger is now 1000 rather than 100.

  • DB_File has been upgraded from version 1.827 to 1.828.

  • Encode has been upgraded from version 2.49 to 2.51.

  • ExtUtils::Install has been upgraded from version 1.59 to 1.60.

  • ExtUtils::MakeMaker has been upgraded from version 6.66 to 6.68.

  • ExtUtils::ParseXS has been upgraded from version 3.18 to 3.19.

  • File::Copy has been upgraded from version 2.26 to 2.27.

  • File::DosGlob has been upgraded from version 1.10 to 1.11.

  • File::Fetch has been upgraded from version 0.38 to 0.42.

  • File::Find has been upgraded from version 1.23 to 1.24.

  • File::Spec has been upgraded from version 3.40 to 3.41.

    tmpdir now respects changes to environment variables from which the temporary directory is derived. [RT #88940]

  • File::Temp has been upgraded from version 0.23 to 0.2301.

  • Filter::Simple has been upgraded from version 0.89 to 0.90.

  • Filter::Util::Call has been upgraded from version 1.45 to 1.49.

  • Getopt::Long has been upgraded from version 2.39 to 2.4.

  • Hash::Util::FieldHash has been upgraded from version 1.10 to 1.11.

  • HTTP::Tiny has been upgraded from version 0.025 to 0.031.

  • IPC::Open3 has been upgraded from version 1.13 to 1.14.

  • Locale::Maketext has been upgraded from version 1.23 to 1.24.

  • Math::BigInt has been upgraded from version 1.9991 to 1.9992.

  • Math::BigRat has been upgraded from version 0.2604 to 0.2606.

  • Module::Build has been upgraded from version 0.4003 to 0.4005.

  • Module::CoreList has been upgraded from version 2.91 to 2.92.

    Adds Module::CoreList::Utils which provides information on which core and dual-life utilities shipped with each version of perl.

  • Module::Metadata has been upgraded from version 1.000011 to 1.000014.

  • mro has been upgraded from version 1.11 to 1.12.

  • Net::Ping has been upgraded from version 2.41 to 2.42.

  • perlfaq has been upgraded from version 5.0150042 to 5.0150043.

  • Pod::Html has been upgraded from version 1.18 to 1.19.

  • Pod::Parser has been upgraded from version 1.60 to 1.61.

  • Pod::Perldoc has been upgraded from version 3.19 to 3.20.

  • Pod::Usage has been upgraded from version 1.61 to 1.63.

  • POSIX has been upgraded from version 1.32 to 1.33.

  • re has been upgraded from version 0.23 to 0.25.

  • Safe has been upgraded from version 2.35 to 2.36.

  • Storable has been upgraded from version 2.42 to 2.43.

  • Sys::Hostname has been upgraded from version 1.17 to 1.18.

  • Sys::Syslog has been upgraded from version 0.32 to 0.33.

  • Term::ReadLine has been upgraded from version 1.12 to 1.13.

  • Test::Harness has been upgraded from version 3.26 to 3.28

    Memory usage is dramatically reduced. t/harness now uses about 10% of the memory used by 3.26 and earlier.

    PERL5LIB is always propagated to a test's @INC, even under -T.

  • threads has been upgraded from version 1.86 to 1.87.

  • threads::shared has been upgraded from version 1.43 to 1.44.

  • Tie::File has been upgraded from version 0.99 to 1.00.

  • Time::Piece has been upgraded from version 1.20_01 to 1.2002.

  • Unicode::Collate has been upgraded from version 0.97 to 0.98.

  • Unicode::UCD has been upgraded from version 0.51 to 0.52.

    A function, "search_invlist()" in Unicode::UCD is now available to do search an inversion list or map for a code point.


Changes to Existing Documentation


  • goto EXPR is now documented to handle an expression that evalutes to a code reference as if it was goto &$coderef. This behavior is at least ten years old.

  • eval EXPR now has caveats about expanding floating point numbers in some locales

  • Noted that chop and chomp can reset the hash iterator

  • Improved fileno example


  • \s matching \cK is marked experimental

  • ithreads were accepted in 5.8.0

  • Long doubles are not experimental


  • Update to mention fc(), \F



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 Warnings

Utility Changes

bisect.pl enhancements

The git bisection tool Porting/bisect.pl has had many enhancements.

  • Can optionally run the test case with a timeout.

  • Can now run in-place in a clean git checkout.

  • Can run the test case under valgrind.

  • Can apply user supplied patches and fixes to the source checkout before building.

  • Now has fixups to enable building several more historical ranges of bleadperl, which can be useful for pinpointing the origins of bugs or behaviour changes.

It is provided as part of the source distribution but not installed because it is not self-contained as it relies on being run from within a git checkout. Note also that it makes no attempt to fix tests, correct runtime bugs or make something useful to install - its purpose is to make minimal changes to get any historical revision of interest to build and run as close as possible to "as-was", and thereby make git bisect easy to use.

Platform Support

Discontinued Platforms


DG/UX was a Unix sold by Data General. The last release was in April 2001. It only runs on Data General's own hardware.

Platform-Specific Notes

Mixed-endian platforms

The code supporting pack and unpack operations on mixed endian platforms has been removed. We believe that Perl has long been unable to build on mixed endian architectures (such as PDP-11s), so we don't think that this change will affect any platforms which are able to build v5.18.0.


The BUILD_STATIC and ALL_STATIC makefile options for linking some or (nearly) all extensions statically (into perl519.dll, and into a separate perl-static.exe too) were broken for MinGW builds. This has now been fixed.

The ALL_STATIC option has also been improved to include the Encode and Win32 extensions (for both VC++ and MinGW builds).

Internal Changes

  • Perl's new copy-on-write mechanism (which is now enabled by default), allows any SvPOK scalar to be automatically upgraded to a copy-on-write scalar when copied. A reference count on the string buffer is stored in the string buffer itself.

    For example:

        $ perl -MDevel::Peek -e'$a="abc"; $b = $a; Dump $a; Dump $b'
        SV = PV(0x260cd80) at 0x2620ad8
          REFCNT = 1
          FLAGS = (POK,IsCOW,pPOK)
          PV = 0x2619bc0 "abc"\0
          CUR = 3
          LEN = 16
          COW_REFCNT = 1
        SV = PV(0x260ce30) at 0x2620b20
          REFCNT = 1
          FLAGS = (POK,IsCOW,pPOK)
          PV = 0x2619bc0 "abc"\0
          CUR = 3
          LEN = 16
          COW_REFCNT = 1

    Note that both scalars share the same PV buffer and have a COW_REFCNT greater than zero.

    This means that XS code which wishes to modify the SvPVX() buffer of an SV should call SvPV_force() or similar first, to ensure a valid (and unshared) buffer, and to call SvSETMAGIC() afterwards. This in fact has always been the case (for example hash keys were already copy-on-write); this change just spreads the COW behaviour to a wider variety of SVs.

    One important difference is that before 5.18.0, shared hash-key scalars used to have the SvREADONLY flag set; this is no longer the case.

    This new behaviour can still be disabled by running Configure with -Accflags=-DPERL_NO_COW. This option will probably be removed in Perl 5.22.

  • PL_sawampersand is now a constant. The switch this variable provided (to enable/disable the pre-match copy depending on whether $& had been seen) has been removed and replaced with copy-on-write, eliminating a few bugs.

    The previous behaviour can still be enabled by running Configure with -Accflags=-DPERL_SAWAMPERSAND.

  • The functions my_swap, my_htonl and my_ntohl have been removed. It is unclear why these functions were ever marked as A, part of the API. XS code can't call them directly, as it can't rely on them being compiled. Unsurprisingly, no code on CPAN references them.

  • The signature of the Perl_re_intuit_start() regex function has changed; the function pointer intuit in the regex engine plugin structure has also changed accordingly. A new parameter, strbeg has been added; this has the same meaning as the same-named parameter in Perl_regexec_flags. Previously intuit would try to guess the start of the string from the passed SV (if any), and would sometimes get it wrong (e.g. with an overloaded SV).

  • XS code may use various macros to change the case of a character or code point (for example toLOWER_utf8()). Only a couple of these were documented until now; and now they should be used in preference to calling the underlying functions. See "Character case changing" in perlapi.

  • The code dealt rather inconsistently with uids and gids. Some places assumed that they could be safely stored in UVs, others in IVs, others in ints. Four new macros are introduced: SvUID(), sv_setuid(), SvGID(), and sv_setgid()

Selected Bug Fixes

  • The OP allocation code now returns correctly aligned memory in all cases for struct pmop. Previously it could return memory only aligned to a 4-byte boundary, which is not correct for an ithreads build with 64 bit IVs on some 32 bit platforms. Notably, this caused the build to fail completely on sparc GNU/Linux. [RT #118055]

  • The debugger's man command been fixed. It was broken in the v5.18.0 release. The man command is aliased to the names doc and perldoc - all now work again.

  • @_ is now correctly visible in the debugger, fixing a regression introduced in v5.18.0's debugger. [RT #118169]

  • Evaluating large hashes in scalar context is now much faster, as the number of used chains in the hash is now cached for larger hashes. Smaller hashes continue not to store it and calculate it when needed, as this saves one IV. That would be 1 IV overhead for every object built from a hash. [RT #114576]

  • Fixed a small number of regexp constructions that could either fail to match or crash perl when the string being matched against was allocated above the 2GB line on 32-bit systems. [RT #118175]

  • Perl v5.16 inadvertently introduced a bug whereby calls to XSUBs that were not visible at compile time were treated as lvalues and could be assigned to, even when the subroutine was not an lvalue sub. This has been fixed. [RT #117947]

  • In Perl v5.18.0 dualvars that had an empty string for the string part but a non-zero number for the number part starting being treated as true. In previous versions they were treated as false, the string representation taking precedeence. The old behaviour has been restored. [RT #118159]

  • Since Perl v5.12, inlining of constants that override built-in keywords of the same name had countermanded use subs, causing subsequent mentions of the constant to use the built-in keyword instead. This has been fixed.

  • Lexical constants (my sub a() { 42 }) no longer crash when inlined.

  • Parameter prototypes attached to lexical subroutines are now respected when compiling sub calls without parentheses. Previously, the prototypes were honoured only for calls with parentheses. [RT #116735]

  • Syntax errors in lexical subroutines in combination with calls to the same subroutines no longer cause crashes at compile time.

  • Deep recursion warnings no longer crash lexical subroutines. [RT #118521]

  • The warning produced by -l $handle now applies to IO refs and globs, not just to glob refs. That warning is also now UTF8-clean. [RT #117595]

  • Various memory leaks involving the parsing of the (?[...]) regular expression construct have been fixed.

  • (?[...]) now allows interpolation of precompiled patterns consisting of (?[...]) with bracketed character classes inside ($pat = qr/(?[ [a] ])/; /(?[ $pat ])/). Formerly, the brackets would confuse the regular expression parser.

  • The "Quantifier unexpected on zero-length expression" warning message could appear twice starting in Perl v5.10 for a regular expression also containing alternations (e.g., "a|b") triggering the trie optimisation.

  • delete local $ENV{nonexistent_env_var} no longer leaks memory.

  • sort and require followed by a keyword prefixed with CORE:: now treat it as a keyword, and not as a subroutine or module name. [RT #24482]

  • Through certain conundrums, it is possible to cause the current package to be freed. Certain operators (bless, reset, open, eval) could not cope and would crash. They have been made more resilient. [RT #117941]

  • Aliasing filehandles through glob-to-glob assignment would not update internal method caches properly if a package of the same name as the filehandle existed, resulting in filehandle method calls going to the package instead. This has been fixed.

  • ./Configure -de -Dusevendorprefix didn't default [RT #64126]

  • The Statement unlikely to be reached warning was listed in perldiag as an exec-category warning, but was enabled and disabled by the syntax category. On the other hand, the exec category controlled its fatal-ness. It is now entirely handled by the exec category.

  • The "Replacement list is longer that search list" warning for tr/// and y/// no longer occurs in the presence of the /c flag. [RT #118047]

  • Perl v5.18 inadvertently introduced a bug whereby interpolating mixed up- and down-graded UTF-8 strings in a regex could result in malformed UTF-8 in the pattern: specifically if a downgraded character in the range \x80..\xff followed a UTF-8 string, e.g.

        utf8::upgrade(  my $u = "\x{e5}");
        utf8::downgrade(my $d = "\x{e5}");

    [RT #118297]

  • Stringification of NVs are not cached so that the lexical locale controls stringification of the decimal point [perl #108378] [perl #115800]


Perl 5.19.1 represents approximately 4 weeks of development since Perl 5.19.0 and contains approximately 26,000 lines of changes across 680 files from 37 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 5.19.1:

Alexandr Ciornii, Brian Fraser, Chris 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, David Golden, David Mitchell, David Steinbrunner, Dominic Hargreaves, Eric Brine, Father Chrysostomos, H.Merijn Brand, Heiko Eissfeldt, James E Keenan, Jerry D. Hedden, Kang-min Liu, Karl Williamson, Leon Timmermans, Lukas Mai, Marcel Grünauer, Mark Jason Dominus, Max Maischein, Mike Doherty, Nicholas Clark, Paul Green, Peter Martini, Petr Písař, Ricardo Signes, Shirakata Kentaro, Shlomi Fish, Steffen Müller, Steve Hay, Sullivan Beck, Tony Cook, Yves Orton, Zsbán Ambrus.

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.