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

       If you are upgrading from an earlier release such as 5.13.4, first read
       perl5135delta, which describes differences between 5.13.4 and 5.13.5.

Core Enhancements
   "(?^...)" regex construct added to signify default modifiers
       A caret (also called a "circumflex accent") "^" immediately following a
       "(?" in a regular expression now means that the subexpression is to not
       inherit the surrounding modifiers such as "/i", but to revert to the
       Perl defaults.  Any modifiers following the caret override the

       The stringification of regular expressions now uses this notation.
       E.g., before, "qr/hlagh/i" would be stringified as "(?i-xsm:hlagh)",
       but now it's stringified as "(?^i:hlagh)".

       The main purpose of this is to allow tests that rely on the
       stringification to not have to change when new modifiers are added.
       See "Extended Patterns" in perlre.

   "d", "l", and "u" regex modifiers added
       These modifiers are currently only available within a "(?...)"

       The "l" modifier says to compile the regular expression as if it were
       in the scope of "use locale", even if it is not.

       The "u" modifier says to compile the regular expression as if it were
       in the scope of a "use feature "unicode_strings"" pragma.

       The "d" modifier is used to override any "use locale" and "use feature
       "unicode_strings"" pragmas that are in effect at the time of compiling
       the regular expression.

       See just below and "(?dlupimsx-imsx)" in perlre.

   "use feature "unicode_strings"" now applies to some regex matching
       Another chunk of the "The "Unicode Bug"" in perlunicode is fixed in
       this release.  Now, regular expressions compiled within the scope of
       the "unicode_strings" feature will match the same whether or not the
       target string is encoded in utf8, with regard to "\s", "\w", "\b", and
       their complements.  Work is underway to add the "[[:posix:]]" character
       classes and case sensitive matching to the control of this feature, but
       was not complete in time for this dot release.

   "\N{...}" now handles Unicode named character sequences
       Unicode has a number of named character sequences, in which particular
       sequences of code points are given names.  "\N{...}" now recognizes
       these.  See charnames.

       with lexical ("my") variables, lexical pragmata and abnormal exiting.

   Custom per-subroutine check hooks
       XS code in an extension module can now annotate a subroutine (whether
       implemented in XS or in Perl) so that nominated XS code will be called
       at compile time (specifically as part of op checking) to change the op
       tree of that subroutine.  The compile-time check function (supplied by
       the extension module) can implement argument processing that can't be
       expressed as a prototype, generate customised compile-time warnings,
       perform constant folding for a pure function, inline a subroutine
       consisting of sufficiently simple ops, replace the whole call with a
       custom op, and so on.  This was previously all possible by hooking the
       "entersub" op checker, but the new mechanism makes it easy to tie the
       hook to a specific subroutine.  See "cv_set_call_checker" in perlapi.

       To help in writing custom check hooks, several subtasks within standard
       "entersub" op checking have been separated out and exposed in the API.

   Return value of "delete $+{...}"
       Custom regular expression engines can now determine the return value of
       "delete" on an entry of "%+" or "%-".

   "keys", "values" work on arrays
       You can now use the "keys", "values", "each" builtin functions on
       arrays (previously you could only use them on hashes).  See perlfunc
       for details.  This is actually a change introduced in perl 5.12.0, but
       it was missed from that release's perldelta.

Incompatible Changes
   Stringification of regexes has changed
       Default regular expression modifiers are now notated by using
       "(?^...)".  Code relying on the old stringification will fail.  The
       purpose of this is so that when new modifiers are added, such code will
       not have to change (after this one time), as the stringification will
       automatically incorporate the new modifiers.

       Code that needs to work properly with both old- and new-style regexes
       can avoid the whole issue by using (for Perls since 5.9.5):

        use re qw(regexp_pattern);
        my ($pat, $mods) = regexp_pattern($re_ref);

       where $re_ref is a reference to a compiled regular expression.  Upon
       return, $mods will be a string containing all the non-default modifiers
       used when the regular expression was compiled, and $pattern the actual

       If the actual stringification is important, or older Perls need to be
       supported, you can use something like the following:

           # Accept both old and new-style stringification
           my $modifiers = (qr/foobar/ =~ /\Q(?^/) ? '^' : '-xism';

       And then use $modifiers instead of "-xism".
       On systems that do not have a "fchdir" function, newly-created threads
       no longer inherit directory handles from their parent threads. Such
       programs would probably have crashed anyway [perl #75154]

   Negation treats strings differently from before
       The unary negation operator "-" now treats strings that look like
       numbers as numbers [perl #57706]

   Negative zero
       Negative zero (-0.0), when converted to a string, now becomes "0" on
       all platforms. It used to become "-0" on some, but "0" on others.

       If you still need to determine whether a zero is negative, use
       "sprintf("%g", $zero) =~ /^-/" or the Data::Float module on CPAN.

Performance Enhancements
       o   The bulk of the "Tie::Hash::NamedCapture" module used to be in the
           perl core. It has now been moved to an XS module, to reduce the
           overhead for programs that do not use "%+" or "%-".

       o   Eliminate "PL_*" accessor functions under ithreads.

           When "MULTIPLICITY" was first developed, and interpreter state
           moved into an interpreter struct, thread and interpreter local
           "PL_*" variables were defined as macros that called accessor
           functions, returning the address of the value, outside of the perl
           core. The intent was to allow members within the interpreter struct
           to change size without breaking binary compatibility, so that bug
           fixes could be merged to a maintenance branch that necessitated
           such a size change.

           However, some non-core code defines "PERL_CORE", sometimes
           intentionally to bypass this mechanism for speed reasons, sometimes
           for other reasons but with the inadvertent side effect of bypassing
           this mechanism. As some of this code is widespread in production
           use, the result is that the core can't change the size of members
           of the interpreter struct, as it will break such modules compiled
           against a previous release on that maintenance branch. The upshot
           is that this mechanism is redundant, and well-behaved code is
           penalised by it. Hence it can and should be removed.

Modules and Pragmata
   Updated Modules and Pragmata
       o   "Archive::Extract" has been upgraded from version 0.42 to 0.44

       o   "Carp" has been upgraded from version 1.18 to 1.19.

           It no longer autovivifies the *CORE::GLOBAL::caller glob, something
           it started doing in 1.18, which was released with perl 5.13.4 [perl
           #78082] <>

       o   "Compress::Raw::Bzip2" has been upgraded from version 2.030 to

           It is now safe to use this module in combination with threads.

       o   "File::DosGlob" has been upgraded from version 1.02 to 1.03.

           It allows patterns containing literal parentheses (they no longer
           need to be escaped). On Windows, it no longer adds an extra ./ to
           the file names returned when the pattern is a relative glob with a
           drive specification, like c:*.pl [perl #71712]

       o   "File::Find" has been upgraded from version 1.17 to 1.18.

           It improves handling of backslashes on Windows, so that paths such
           as c:\dir\/file are no longer generated [perl #71710]

       o   "if" has been upgraded from version 0.05 to 0.06

       o   "IPC::Cmd" has been upgraded from version 0.60 to 0.64

       o   "IPC::Open3" has been upgraded from version 1.06 to 1.07.

           The internal "xclose" routine now knows how to handle file
           descriptors, as documented, so duplicating STDIN in a child process
           using its file descriptor now works [perl #76474]

       o   "Locale::Codes" has been upgraded from version 3.13 to 3.14.

       o   "Locale::Maketext" has been upgraded from version 1.15 to 1.16.

           It fixes an infinite loop in "Locale::Maketext::Guts::_compile()"
           when working with tainted values (CPAN RT #40727

           "->maketext" calls will now backup and restore $@ so that error
           messages are not suppressed (CPAN RT #34182

       o   "Math::BigInt" has been upgraded from version 1.95 to 1.97.

           This prevents "sqrt($int)" from crashing under "use bigrat;" [perl
           #73534] <>.

       o   "NEXT" has been upgraded from version 0.64 to 0.65.

       o   "overload" has been upgraded from version 1.10 to 1.11.

           "overload::Method" can now handle subroutines that are themselves
           blessed into overloaded classes [perl #71998]

       o   "PathTools" has been upgraded from version 3.31_01 to 3.34.

       o   "Unicode::Collate" has been upgraded from version 0.59 to 0.63

           U::C::Locale newly supports locales: ar, be, bg, de__phonebook, hu,
           hy, kk, mk, nso, om, tn, vi, hr, ig, ru, sq, se, sr, to and uk

       o   "Unicode::Normalize" has been upgraded from version 1.06 to 1.07

       o   "B::Deparse" has been upgraded from version 0.98 to 0.99

           B::Deparse now properly handles the code that applies a conditional
           pattern match against implicit $_ as it was fixed in [perl #20444]

       o   "GDBM_File" has been upgraded from version 1.10 to 1.11

   Changes to Existing Documentation

       o   The documentation for the "SvTRUE" macro was simply wrong in
           stating that get-magic is not processed. It has been corrected.

       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
       o   The 'Layer does not match this perl' error message has been
           replaced with these more helpful messages:

           o   PerlIO layer function table size (%d) does not match size
               expected by this perl (%d)

           o   PerlIO layer instance size (%d) does not match size expected by
               this perl (%d)

           [perl #73754]

       o   The script t/op/threads-dirh.t has been added, which tests
           interaction of threads and directory handles.

Platform Support
   Platform-Specific Notes
           Conversion of strings to floating-point numbers is now more
           accurate on IRIX systems [perl #32380]

       Mac OS X
           Early versions of Mac OS X (Darwin) had buggy implementations of

       VMS The shortening of symbols longer than 31 characters in the C
           sources is now done by the compiler rather than by xsubpp (which
           could only do so for generated symbols in XS code).

           $Config{gccversion} is now set correctly when perl is built using
           the mingw64 compiler from <> [perl #73754]

           The build process proceeds more smoothly with mingw and dmake when
           C:\MSYS\bin is in the PATH, due to a "Cwd" fix.

Internal Changes
       o   See "Regular expressions retain their localeness when
           interpolated", above.

       o   The "sv_cmp_flags", "sv_cmp_locale_flags", "sv_eq_flags" and
           "sv_collxfrm_flags" functions have been added. These are like their
           non-_flags counterparts, but allow one to specify whether get-magic
           is processed.

           The "sv_cmp", "sv_cmp_locale", "sv_eq" and "sv_collxfrm" functions
           have been replaced with wrappers around the new functions.

       o   A new "sv_2bool_flags" function has been added.

           This is like "sv_2bool", but it lets the calling code decide
           whether get-magic is handled. "sv_2bool" is now a macro that calls
           the new function.

       o   A new macro, "SvTRUE_nomg", has been added.

           This is like "SvTRUE", except that it does not process magic. It
           uses the new "sv_2bool_flags" function.

       o   "sv_catsv_flags" no longer calls "mg_get" on its second argument
           (the source string) if the flags passed to it do not include
           SV_GMAGIC. So it now matches the documentation.

       o   A new interface has been added for custom check hooks on
           subroutines. See "Custom per-subroutine check hooks", above.

       o   List op building functions have been added to the API.  See
           op_append_elem, op_append_list, and op_prepend_elem.

       o   The LINKLIST macro, part of op building that constructs the
           execution-order op chain, has been added to the API.

       o   Many functions ending with pvn now have equivalent pv/pvs/sv

       o   The "save_freeop", "save_op", "save_pushi32ptr" and
           "save_pushptrptr" functions have been added to the API.

       o   Constant-folding used to cause

             $text =~ ( 1 ? /phoo/ : /bear/)

           to turn into

             $text =~ /phoo/

           at compile time. Now it correctly matches against $_ [perl #20444]

       o   Parsing Perl code (either with string "eval" or by loading modules)
           from within a "UNITCHECK" block no longer causes the interpreter to
           crash [perl #70614]

       o   When "-d" is used on the shebang ("#!") line, the debugger now has
           access to the lines of the main program. In the past, this
           sometimes worked and sometimes did not, depending on what order
           things happened to be arranged in memory [perl #71806]

       o   The "y///" or "tr///" operator now calls get-magic (e.g., the
           "FETCH" method of a tie) on its left-hand side just once, not twice
           [perl #76814]

       o   String comparison ("eq", "ne", "lt", "gt", "le", "ge" and "cmp")
           and logical not ("not" and "!") operators no longer call magic
           (e.g., tie methods) twice on their operands [perl #76814]

           This bug was introduced in an earlier 5.13 release, and does not
           affect perl 5.12.

       o   When a tied (or other magic) variable is used as, or in, a regular
           expression, it no longer has its "FETCH" method called twice [perl
           #76814] <>.

           This bug was introduced in an earlier 5.13 release, and does not
           affect perl 5.12.

       o   The "-C" command line option can now be followed by other options
           [perl #72434]

       o   Assigning a glob to a PVLV used to convert it to a plain string.
           Now it works correctly, and a PVLV can hold a glob. This would
           happen when a nonexistent hash or array element was passed to a

             sub { $_[0] = *foo }->($hash{key});
             # $_[0] would have been the string "*main::foo"

       o   The regular expression parser no longer hangs when parsing "\18"
           and "\88".

           This bug was introduced in version 5.13.5 and did not affect
           earlier versions [perl #78058]

       o   Subroutine redefinition works once more in the debugger [perl
           #48332] <>.

       o   The "&" "|" "^" bitwise operators no longer coerce read-only
           arguments [perl #20661]

       o   Stringifying a scalar containing -0.0 no longer has the affect of
           turning false into true [perl #45133]

       o   Aliasing packages by assigning to globs or deleting packages by
           deleting their containing stash elements used to have erratic
           effects on method resolution, because the internal 'isa' caches
           were not reset. This has been fixed.

       o   "sort" with a custom sort routine could crash if too many nested
           subroutine calls occurred from within the sort routine [perl
           #77930] <>.

           This bug was introduced in an earlier 5.13 release, and did not
           affect perl 5.12.

       o   The "eval_sv" and "eval_pv" C functions now set $@ correctly when
           there is a syntax error and no "G_KEEPERR" flag, and never set it
           if the "G_KEEPERR" flag is present [perl #3719]

       o   Nested "map" and "grep" blocks no longer leak memory when
           processing large lists [perl #48004]

       o   Malformed "version" objects no longer cause crashes [perl #78286]

       o   The interpreter no longer crashes when freeing deeply-nested arrays
           of arrays. Hashes have not been fixed yet [perl #44225]

       o   The mechanism for freeing objects in globs used to leave dangling
           pointers to freed SVs, meaning Perl users could see corrupted state
           during destruction.

           Perl now only frees the affected slots of the GV, rather than
           freeing the GV itself. This makes sure that there are no dangling
           refs or corrupted state during destruction.
           counts if called via the multicall interface from within those very
           subroutines.  This affects modules like List::Util. Calling one of
           its functions with an active subroutine as the first argument could
           cause a crash [perl #78070]

       o   Fixed a typo in perl5135delta regarding array slices and smart

       Perl 5.13.6 represents approximately one month of development since
       Perl 5.13.5 and contains 67920 lines of changes across 566 files from
       47 authors and committers:

       A. Sinan Unur, Aaron Crane, Alex Davies, Ali Polatel, Allen Smith,
       Andrew Rodland, Andy Dougherty, Ben Morrow, brian d foy, Casey West,
       Chip Salzenberg, Chris 'BinGOs' Williams, Craig A. Berry, David Golden,
       David Mitchell, Eric Brine, Father Chrysostomos, Florian Ragwitz,
       George Greer, gregor herrmann, Jan Dubois, Jerry D. Hedden, Jesse
       Vincent, Joshua Pritikin, Karl Williamson, kmx, Michael G Schwern, Mike
       Kelly, Nicholas Clark, Paul Green, Rafael Garcia-Suarez, Renee Baecker,
       Ricardo Signes, Sisyphus, Slaven Rezic, Steffen Mueller, Steve Hay,
       Sullivan Beck, Tatsuhiko Miyagawa, Todd Rinaldo, Tony Cook, Tye
       McQueen, Vernon Lyon, Walt Mankowski, Zefram, Zsban Ambrus, var
       Arnfjoer` 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.

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