man > PERL5240DELTA(1)

PERL5240DELTA(1)                  Perl Programmers Reference Guide                  PERL5240DELTA(1)

NAME
       perl5240delta - what is new for perl v5.24.0

DESCRIPTION
       This document describes the differences between the 5.22.0 release and the 5.24.0 release.

Core Enhancements
   Postfix dereferencing is no longer experimental
       Using the "postderef" and "postderef_qq" features no longer emits a warning. Existing code
       that disables the "experimental::postderef" warning category that they previously used will
       continue to work. The "postderef" feature has no effect; all Perl code can use postfix
       dereferencing, regardless of what feature declarations are in scope. The 5.24 feature bundle
       now includes the "postderef_qq" feature.

   Unicode 8.0 is now supported
       For details on what is in this release, see <http://www.unicode.org/versions/Unicode8.0.0/>.

   perl will now croak when closing an in-place output file fails
       Until now, failure to close the output file for an in-place edit was not detected, meaning
       that the input file could be clobbered without the edit being successfully completed.  Now,
       when the output file cannot be closed successfully, an exception is raised.

   New "\b{lb}" boundary in regular expressions
       "lb" stands for Line Break.  It is a Unicode property that determines where a line of text is
       suitable to break (typically so that it can be output without overflowing the available
       horizontal space).  This capability has long been furnished by the Unicode::LineBreak module,
       but now a light-weight, non-customizable version that is suitable for many purposes is in
       core Perl.

   "qr/(?[ ])/" now works in UTF-8 locales
       Extended Bracketed Character Classes now will successfully compile when "use locale" is in
       effect.  The compiled pattern will use standard Unicode rules.  If the runtime locale is not
       a UTF-8 one, a warning is raised and standard Unicode rules are used anyway.  No tainting is
       done since the outcome does not actually depend on the locale.

   Integer shift ("<<" and ">>") now more explicitly defined
       Negative shifts are reverse shifts: left shift becomes right shift, and right shift becomes
       left shift.

       Shifting by the number of bits in a native integer (or more) is zero, except when the
       "overshift" is right shifting a negative value under "use integer", in which case the result
       is -1 (arithmetic shift).

       Until now negative shifting and overshifting have been undefined because they have relied on
       whatever the C implementation happens to do.  For example, for the overshift a common C
       behavior is "modulo shift":

         1 >> 64 == 1 >> (64 % 64) == 1 >> 0 == 1  # Common C behavior.

         # And the same for <<, while Perl now produces 0 for both.

       Now these behaviors are well-defined under Perl, regardless of what the underlying C
       implementation does.  Note, however, that you are still constrained by the native integer
       width: you need to know how far left you can go.  You can use for example:

         use Config;
         my $wordbits = $Config{uvsize} * 8;  # Or $Config{uvsize} << 3.

       If you need a more bits on the left shift, you can use for example the "bigint" pragma, or
       the "Bit::Vector" module from CPAN.

   printf and sprintf now allow reordered precision arguments
       That is, "sprintf '|%.*2$d|', 2, 3" now returns "|002|". This extends the existing reordering
       mechanism (which allows reordering for arguments that are used as format fields, widths, and
       vector separators).

   More fields provided to "sigaction" callback with "SA_SIGINFO"
       When passing the "SA_SIGINFO" flag to sigaction, the "errno", "status", "uid", "pid", "addr"
       and "band" fields are now included in the hash passed to the handler, if supported by the
       platform.

   Hashbang redirection to Perl 6
       Previously perl would redirect to another interpreter if it found a hashbang path unless the
       path contains "perl" (see perlrun). To improve compatibility with Perl 6 this behavior has
       been extended to also redirect if "perl" is followed by "6".

Security
   Set proper umask before calling mkstemp(3)
       In 5.22 perl started setting umask to 0600 before calling mkstemp(3) and restoring it
       afterwards. This wrongfully tells open(2) to strip the owner read and write bits from the
       given mode before applying it, rather than the intended negation of leaving only those bits
       in place.

       Systems that use mode 0666 in mkstemp(3) (like old versions of glibc) create a file with
       permissions 0066, leaving world read and write permissions regardless of current umask.

       This has been fixed by using umask 0177 instead. [perl #127322]

   Fix out of boundary access in Win32 path handling
       This is CVE-2015-8608.  For more information see [GH #15067]
       <https://github.com/Perl/perl5/issues/15067>

   Fix loss of taint in canonpath
       This is CVE-2015-8607.  For more information see [GH #15084]
       <https://github.com/Perl/perl5/issues/15084>

   Avoid accessing uninitialized memory in win32 crypt()
       Added validation that will detect both a short salt and invalid characters in the salt.  [GH
       #15091] <https://github.com/Perl/perl5/issues/15091>

   Remove duplicate environment variables from "environ"
       Previously, if an environment variable appeared more than once in "environ[]", %ENV would
       contain the last entry for that name, while a typical getenv() would return the first entry.
       We now make sure %ENV contains the same as what "getenv" returns.

       Second, we remove duplicates from "environ[]", so if a setting with that name is set in %ENV,
       we won't pass an unsafe value to a child process.

       [CVE-2016-2381]

Incompatible Changes
   The "autoderef" feature has been removed
       The experimental "autoderef" feature (which allowed calling "push", "pop", "shift",
       "unshift", "splice", "keys", "values", and "each" on a scalar argument) has been deemed
       unsuccessful. It has now been removed; trying to use the feature (or to disable the
       "experimental::autoderef" warning it previously triggered) now yields an exception.

   Lexical $_ has been removed
       "my $_" was introduced in Perl 5.10, and subsequently caused much confusion with no obvious
       solution.  In Perl 5.18.0, it was made experimental on the theory that it would either be
       removed or redesigned in a less confusing (but backward-incompatible) way.  Over the
       following years, no alternatives were proposed.  The feature has now been removed and will
       fail to compile.

   "qr/\b{wb}/" is now tailored to Perl expectations
       This is now more suited to be a drop-in replacement for plain "\b", but giving better results
       for parsing natural language.  Previously it strictly followed the current Unicode rules
       which calls for it to match between each white space character.  Now it doesn't generally
       match within spans of white space, behaving like "\b" does.  See "\b{wb}" in perlrebackslash

   Regular expression compilation errors
       Some regular expression patterns that had runtime errors now don't compile at all.

       Almost all Unicode properties using the "\p{}" and "\P{}" regular expression pattern
       constructs are now checked for validity at pattern compilation time, and invalid ones will
       cause the program to not compile.  In earlier releases, this check was often deferred until
       run time.  Whenever an error check is moved from run- to compile time, erroneous code is
       caught 100% of the time, whereas before it would only get caught if and when the offending
       portion actually gets executed, which for unreachable code might be never.

   "qr/\N{}/" now disallowed under "use re "strict""
       An empty "\N{}" makes no sense, but for backwards compatibility is accepted as doing nothing,
       though a deprecation warning is raised by default.  But now this is a fatal error under the
       experimental feature "'strict' mode" in re.

   Nested declarations are now disallowed
       A "my", "our", or "state" declaration is no longer allowed inside of another "my", "our", or
       "state" declaration.

       For example, these are now fatal:

          my ($x, my($y));
          our (my $x);

       [GH #14799] <https://github.com/Perl/perl5/issues/14799>

       [GH #13548] <https://github.com/Perl/perl5/issues/13548>

   The "/\C/" character class has been removed.
       This regular expression character class was deprecated in v5.20.0 and has produced a
       deprecation warning since v5.22.0. It is now a compile-time error. If you need to examine the
       individual bytes that make up a UTF8-encoded character, then use utf8::encode() on the string
       (or a copy) first.

   chdir('') no longer chdirs home
       Using chdir('') or chdir(undef) to chdir home has been deprecated since perl v5.8, and will
       now fail.  Use chdir() instead.

   ASCII characters in variable names must now be all visible
       It was legal until now on ASCII platforms for variable names to contain non-graphical ASCII
       control characters (ordinals 0 through 31, and 127, which are the C0 controls and "DELETE").
       This usage has been deprecated since v5.20, and as of now causes a syntax error.  The
       variables these names referred to are special, reserved by Perl for whatever use it may
       choose, now, or in the future.  Each such variable has an alternative way of spelling it.
       Instead of the single non-graphic control character, a two character sequence beginning with
       a caret is used, like $^] and "${^GLOBAL_PHASE}".  Details are at perlvar.   It remains
       legal, though unwise and deprecated (raising a deprecation warning), to use certain non-
       graphic non-ASCII characters in variables names when not under "use utf8".  No code should do
       this, as all such variables are reserved by Perl, and Perl doesn't currently define any of
       them (but could at any time, without notice).

   An off by one issue in $Carp::MaxArgNums has been fixed
       $Carp::MaxArgNums is supposed to be the number of arguments to display.  Prior to this
       version, it was instead showing $Carp::MaxArgNums + 1 arguments, contrary to the
       documentation.

   Only blanks and tabs are now allowed within "[...]" within "(?[...])".
       The experimental Extended Bracketed Character Classes can contain regular bracketed character
       classes within them.  These differ from regular ones in that white space is generally
       ignored, unless escaped by preceding it with a backslash.  The white space that is ignored is
       now limited to just tab "\t" and SPACE characters.  Previously, it was any white space.  See
       "Extended Bracketed Character Classes" in perlrecharclass.

Deprecations
   Using code points above the platform's "IV_MAX" is now deprecated
       Unicode defines code points in the range "0..0x10FFFF".  Some standards at one time defined
       them up to 2**31 - 1, but Perl has allowed them to be as high as anything that will fit in a
       word on the platform being used.  However, use of those above the platform's "IV_MAX" is
       broken in some constructs, notably "tr///", regular expression patterns involving
       quantifiers, and in some arithmetic and comparison operations, such as being the upper limit
       of a loop.  Now the use of such code points raises a deprecation warning, unless that warning
       category is turned off.  "IV_MAX" is typically 2**31 -1 on 32-bit platforms, and 2**63-1 on
       64-bit ones.

   Doing bitwise operations on strings containing code points above 0xFF is deprecated
       The string bitwise operators treat their operands as strings of bytes, and values beyond 0xFF
       are nonsensical in this context.  To operate on encoded bytes, first encode the strings.  To
       operate on code points' numeric values, use "split" and "map ord".  In the future, this
       warning will be replaced by an exception.

   sysread(), syswrite(), recv() and send() are deprecated on :utf8 handles
       The sysread(), recv(), syswrite() and send() operators are deprecated on handles that have
       the ":utf8" layer, either explicitly, or implicitly, eg., with the :encoding(UTF-16LE) layer.

       Both sysread() and recv() currently use only the ":utf8" flag for the stream, ignoring the
       actual layers.  Since sysread() and recv() do no UTF-8 validation they can end up creating
       invalidly encoded scalars.

       Similarly, syswrite() and send() use only the ":utf8" flag, otherwise ignoring any layers.
       If the flag is set, both write the value UTF-8 encoded, even if the layer is some different
       encoding, such as the example above.

       Ideally, all of these operators would completely ignore the ":utf8" state, working only with
       bytes, but this would result in silently breaking existing code.  To avoid this a future
       version of perl will throw an exception when any of sysread(), recv(), syswrite() or send()
       are called on handle with the ":utf8" layer.

Performance Enhancements
       •   The  overhead  of  scope  entry  and  exit  has been considerably reduced, so for example
           subroutine calls, loops and basic blocks are all faster now.  This  empty  function  call
           now takes about a third less time to execute:

               sub f{} f();

       •   Many  languages,  such  as Chinese, are caseless.  Perl now knows about most common ones,
           and skips much of the work when a program tries to change case in them  (like  ucfirst())
           or  match caselessly ("qr//i").  This will speed up a program, such as a web server, that
           can operate on multiple languages, while it is operating on a caseless one.

       •   "/fixed-substr/" has been made much faster.

           On platforms with a libc memchr() implementation  which  makes  good  use  of  underlying
           hardware  support, patterns which include fixed substrings will now often be much faster;
           for example with glibc on a recent x86_64 CPU, this:

               $s = "a" x 1000 . "wxyz";
               $s =~ /wxyz/ for 1..30000

           is now about 7 times faster.  On systems with slow memchr(), e.g.  32-bit  ARM  Raspberry
           Pi,  there  will be a small or little speedup.  Conversely, some pathological cases, such
           as ""ab" x 1000 =~ /aa/" will be slower now; up to 3 times slower on the rPi, 1.5x slower
           on x86_64.

       •   Faster addition, subtraction and multiplication.

           Since 5.8.0, arithmetic became slower due to the need to support 64-bit integers. To deal
           with 64-bit integers, a lot more corner cases need to be checked, which adds time. We now
           detect common cases where there is no need to check for those corner cases, and  special-
           case them.

       •   Preincrement,  predecrement,  postincrement,  and  postdecrement have been made faster by
           internally splitting the functions which handled multiple cases into different functions.

       •   Creating Perl debugger data structures (see  "Debugger  Internals"  in  perldebguts)  for
           XSUBs  and  const  subs  has  been  removed.  This removed one glob/scalar combo for each
           unique ".c" file that XSUBs and const subs came from.  On startup  ("perl  -e"0"")  about
           half  a  dozen glob/scalar debugger combos were created.  Loading XS modules created more
           glob/scalar combos.  These things were being  created  regardless  of  whether  the  perl
           debugger was being used, and despite the fact that it can't debug C code anyway

       •   On  Win32,  "stat"ing  or "-X"ing a path, if the file or directory does not exist, is now
           3.5x faster than before.

       •   Single arguments in list assign are now slightly faster:

             ($x) = (...);
             (...) = ($x);

       •   Less peak memory is now used when compiling regular expression patterns.

Modules and Pragmata
   Updated Modules and Pragmata
       •   arybase has been upgraded from version 0.10 to 0.11.

       •   Attribute::Handlers has been upgraded from version 0.97 to 0.99.

       •   autodie has been upgraded from version 2.26 to 2.29.

       •   autouse has been upgraded from version 1.08 to 1.11.

       •   B has been upgraded from version 1.58 to 1.62.

       •   B::Deparse has been upgraded from version 1.35 to 1.37.

       •   base has been upgraded from version 2.22 to 2.23.

       •   Benchmark has been upgraded from version 1.2 to 1.22.

       •   bignum has been upgraded from version 0.39 to 0.42.

       •   bytes has been upgraded from version 1.04 to 1.05.

       •   Carp has been upgraded from version 1.36 to 1.40.

       •   Compress::Raw::Bzip2 has been upgraded from version 2.068 to 2.069.

       •   Compress::Raw::Zlib has been upgraded from version 2.068 to 2.069.

       •   Config::Perl::V has been upgraded from version 0.24 to 0.25.

       •   CPAN::Meta has been upgraded from version 2.150001 to 2.150005.

       •   CPAN::Meta::Requirements has been upgraded from version 2.132 to 2.140.

       •   CPAN::Meta::YAML has been upgraded from version 0.012 to 0.018.

       •   Data::Dumper has been upgraded from version 2.158 to 2.160.

       •   Devel::Peek has been upgraded from version 1.22 to 1.23.

       •   Devel::PPPort has been upgraded from version 3.31 to 3.32.

       •   Dumpvalue has been upgraded from version 1.17 to 1.18.

       •   DynaLoader has been upgraded from version 1.32 to 1.38.

       •   Encode has been upgraded from version 2.72 to 2.80.

       •   encoding has been upgraded from version 2.14 to 2.17.

       •   encoding::warnings has been upgraded from version 0.11 to 0.12.

       •   English has been upgraded from version 1.09 to 1.10.

       •   Errno has been upgraded from version 1.23 to 1.25.

       •   experimental has been upgraded from version 0.013 to 0.016.

       •   ExtUtils::CBuilder has been upgraded from version 0.280221 to 0.280225.

       •   ExtUtils::Embed has been upgraded from version 1.32 to 1.33.

       •   ExtUtils::MakeMaker has been upgraded from version 7.04_01 to 7.10_01.

       •   ExtUtils::ParseXS has been upgraded from version 3.28 to 3.31.

       •   ExtUtils::Typemaps has been upgraded from version 3.28 to 3.31.

       •   feature has been upgraded from version 1.40 to 1.42.

       •   fields has been upgraded from version 2.17 to 2.23.

       •   File::Find has been upgraded from version 1.29 to 1.34.

       •   File::Glob has been upgraded from version 1.24 to 1.26.

       •   File::Path has been upgraded from version 2.09 to 2.12_01.

       •   File::Spec has been upgraded from version 3.56 to 3.63.

       •   Filter::Util::Call has been upgraded from version 1.54 to 1.55.

       •   Getopt::Long has been upgraded from version 2.45 to 2.48.

       •   Hash::Util has been upgraded from version 0.18 to 0.19.

       •   Hash::Util::FieldHash has been upgraded from version 1.15 to 1.19.

       •   HTTP::Tiny has been upgraded from version 0.054 to 0.056.

       •   I18N::Langinfo has been upgraded from version 0.12 to 0.13.

       •   if has been upgraded from version 0.0604 to 0.0606.

       •   IO has been upgraded from version 1.35 to 1.36.

       •   IO-Compress has been upgraded from version 2.068 to 2.069.

       •   IPC::Open3 has been upgraded from version 1.18 to 1.20.

       •   IPC::SysV has been upgraded from version 2.04 to 2.06_01.

       •   List::Util has been upgraded from version 1.41 to 1.42_02.

       •   locale has been upgraded from version 1.06 to 1.08.

       •   Locale::Codes has been upgraded from version 3.34 to 3.37.

       •   Math::BigInt has been upgraded from version 1.9997 to 1.999715.

       •   Math::BigInt::FastCalc has been upgraded from version 0.31 to 0.40.

       •   Math::BigRat has been upgraded from version 0.2608 to 0.260802.

       •   Module::CoreList has been upgraded from version 5.20150520 to 5.20160320.

       •   Module::Metadata has been upgraded from version 1.000026 to 1.000031.

       •   mro has been upgraded from version 1.17 to 1.18.

       •   ODBM_File has been upgraded from version 1.12 to 1.14.

       •   Opcode has been upgraded from version 1.32 to 1.34.

       •   parent has been upgraded from version 0.232 to 0.234.

       •   Parse::CPAN::Meta has been upgraded from version 1.4414 to 1.4417.

       •   Perl::OSType has been upgraded from version 1.008 to 1.009.

       •   perlfaq has been upgraded from version 5.021009 to 5.021010.

       •   PerlIO::encoding has been upgraded from version 0.21 to 0.24.

       •   PerlIO::mmap has been upgraded from version 0.014 to 0.016.

       •   PerlIO::scalar has been upgraded from version 0.22 to 0.24.

       •   PerlIO::via has been upgraded from version 0.15 to 0.16.

       •   Pod::Functions has been upgraded from version 1.09 to 1.10.

       •   Pod::Perldoc has been upgraded from version 3.25 to 3.25_02.

       •   Pod::Simple has been upgraded from version 3.29 to 3.32.

       •   Pod::Usage has been upgraded from version 1.64 to 1.68.

       •   POSIX has been upgraded from version 1.53 to 1.65.

       •   Scalar::Util has been upgraded from version 1.41 to 1.42_02.

       •   SDBM_File has been upgraded from version 1.13 to 1.14.

       •   SelfLoader has been upgraded from version 1.22 to 1.23.

       •   Socket has been upgraded from version 2.018 to 2.020_03.

       •   Storable has been upgraded from version 2.53 to 2.56.

       •   strict has been upgraded from version 1.09 to 1.11.

       •   Term::ANSIColor has been upgraded from version 4.03 to 4.04.

       •   Term::Cap has been upgraded from version 1.15 to 1.17.

       •   Test has been upgraded from version 1.26 to 1.28.

       •   Test::Harness has been upgraded from version 3.35 to 3.36.

       •   Thread::Queue has been upgraded from version 3.05 to 3.08.

       •   threads has been upgraded from version 2.01 to 2.06.

       •   threads::shared has been upgraded from version 1.48 to 1.50.

       •   Tie::File has been upgraded from version 1.01 to 1.02.

       •   Tie::Scalar has been upgraded from version 1.03 to 1.04.

       •   Time::HiRes has been upgraded from version 1.9726 to 1.9732.

       •   Time::Piece has been upgraded from version 1.29 to 1.31.

       •   Unicode::Collate has been upgraded from version 1.12 to 1.14.

       •   Unicode::Normalize has been upgraded from version 1.18 to 1.25.

       •   Unicode::UCD has been upgraded from version 0.61 to 0.64.

       •   UNIVERSAL has been upgraded from version 1.12 to 1.13.

       •   utf8 has been upgraded from version 1.17 to 1.19.

       •   version has been upgraded from version 0.9909 to 0.9916.

       •   warnings has been upgraded from version 1.32 to 1.36.

       •   Win32 has been upgraded from version 0.51 to 0.52.

       •   Win32API::File has been upgraded from version 0.1202 to 0.1203.

       •   XS::Typemap has been upgraded from version 0.13 to 0.14.

       •   XSLoader has been upgraded from version 0.20 to 0.21.

Documentation
   Changes to Existing Documentation
       perlapi

       •   The process of using undocumented globals has been documented, namely,  that  one  should
           send email to perl5-porters AT perl.org <mailto:perl5-porters AT perl.org> first to get the go-
           ahead for documenting and using an undocumented function or global variable.

       perlcall

       •   A number of cleanups have been made to perlcall, including:

           •   use "EXTEND(SP, n)" and PUSHs() instead of XPUSHs() where applicable and update prose
               to match

           •   add  POPu,  POPul  and POPpbytex to the "complete list of POP macros" and clarify the
               documentation for some of the existing entries, and a note about side-effects

           •   add API documentation for POPu and POPul

           •   use ERRSV more efficiently

           •   approaches to thread-safety storage of SVs.

       perlfunc

       •   The documentation of "hex" has been revised to clarify valid inputs.

       •   Better   explain   meaning   of   negative    PIDs    in    "waitpid".     [GH    #15108]
           <https://github.com/Perl/perl5/issues/15108>

       •   General  cleanup:  there's  more  consistency now (in POD usage, grammar, code examples),
           better practices in code examples (use of "my", removal of bareword filehandles,  dropped
           usage of "&" when calling subroutines, ...), etc.

       perlguts

       •   A  new  section  has been added, "Dynamic Scope and the Context Stack" in perlguts, which
           explains how the perl context stack works.

       perllocale

       •   A stronger caution about using locales in threaded applications is  given.   Locales  are
           not thread-safe, and you can get wrong results or even segfaults if you use them there.

       perlmodlib

       •   We  now  recommend contacting the module-authors list or PAUSE in seeking guidance on the
           naming of modules.

       perlop

       •   The documentation of "qx//" now describes how $? is affected.

       perlpolicy

       •   This note has been added to perlpolicy:

            While civility is required, kindness is encouraged; if you have any
            doubt about whether you are being civil, simply ask yourself, "Am I
            being kind?" and aspire to that.

       perlreftut

       •   Fix some examples to be strict clean.

       perlrebackslash

       •   Clarify that in languages like Japanese  and  Thai,  dictionary  lookup  is  required  to
           determine word boundaries.

       perlsub

       •   Updated to note that anonymous subroutines can have signatures.

       perlsyn

       •   Fixed  a  broken  example  where  "=" was used instead of "==" in conditional in do/while
           example.

       perltie

       •   The usage of "FIRSTKEY" and "NEXTKEY" has been clarified.

       perlunicode

       •   Discourage use of 'In' as a prefix signifying the Unicode Block property.

       perlvar

       •   The documentation of $@ was reworded to clarify that it is not just for syntax errors  in
           "eval".  [GH #14572] <https://github.com/Perl/perl5/issues/14572>

       •   The  specific  true  value  of  $!{E...}  is now documented, noting that it is subject to
           change and not guaranteed.

       •   Use of $OLD_PERL_VERSION is now discouraged.

       perlxs

       •   The documentation of "PROTOTYPES" has been corrected; they are disabled by  default,  not
           enabled.

Diagnostics
       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

       •   %s must not be a named sequence in transliteration operator

       •   Can't find Unicode property definition "%s" in regex;

       •   Can't redeclare "%s" in "%s"

       •   Character following \p must be '{' or a single-character Unicode property name in regex;

       •   Empty \%c in regex; marked by <-- HERE in m/%s/

       •   Illegal user-defined property name

       •   Invalid number '%s' for -C option.

       •   Sequence (?... not terminated in regex; marked by <-- HERE in m/%s/

       •   Sequence (?P<... not terminated in regex; marked by <-- HERE in m/%s/

       •   Sequence (?P>... not terminated in regex; marked by <-- HERE in m/%s/

       New Warnings

       •   Assuming NOT a POSIX class since %s in regex; marked by <-- HERE in m/%s/

       •   %s() is deprecated on :utf8 handles

   Changes to Existing Diagnostics
       •   Accessing the "IO" part  of  a  glob  as  "FILEHANDLE"  instead  of  "IO"  is  no  longer
           deprecated.   It  is  discouraged  to encourage uniformity (so that, for example, one can
           grep    more    easily)    but    it    will    not    be    removed.     [GH     #15105]
           <https://github.com/Perl/perl5/issues/15105>

       •   The  diagnostic  "Hexadecimal  float:  internal  error"  has been changed to "Hexadecimal
           float: internal error (%s)" to include more information.

       •   Can't modify non-lvalue subroutine call of &%s

           This error now reports the name of the non-lvalue subroutine you attempted to use  as  an
           lvalue.

       •   When  running  out  of  memory during an attempt the increase the stack size, previously,
           perl would  die  using  the  cryptic  message  "panic:  av_extend_guts()  negative  count
           (-9223372036854775681)".  This has been fixed to show the prettier message: Out of memory
           during stack extend

Configuration and Compilation
       •   "Configure"  now  acts  as  if  the  "-O"  option is always passed, allowing command line
           options to override saved configuration.  This should eliminate  confusion  when  command
           line options are ignored for no obvious reason.  "-O" is now permitted, but ignored.

       •   Bison 3.0 is now supported.

       •   Configure  no  longer  probes  for  libnm by default.  Originally this was the "New Math"
           library, but the name  has  been  re-used  by  the  GNOME  NetworkManager.   [GH  #15115]
           <https://github.com/Perl/perl5/issues/15115>

       •   Added Configure probes for "newlocale", "freelocale", and "uselocale".

       •   "PPPort.so/PPPort.dll" no longer get installed, as they are not used by "PPPort.pm", only
           by its test files.

       •   It  is  now  possible  to  specify which compilation date to show on "perl -V" output, by
           setting the macro "PERL_BUILD_DATE".

       •   Using  the  "NO_HASH_SEED"  define  in  combination  with  the  default  hash   algorithm
           "PERL_HASH_FUNC_ONE_AT_A_TIME_HARD"  resulted  in  a  fatal  error  while  compiling  the
           interpreter, since Perl 5.17.10.  This has been fixed.

       •   Configure should handle spaces in paths a little better.

       •   No longer generate EBCDIC POSIX-BC tables.  We don't believe anyone  is  using  Perl  and
           POSIX-BC  at  this  time,  and  by  not  generating  these  tables  it  saves time during
           development, and makes the resulting tar ball smaller.

       •   The GNU Make makefile for Win32 now supports parallel builds.  [perl #126632]

       •   You can now build perl with MSVC++ on Win32 using GNU Make.  [perl #126632]

       •   The Win32 miniperl now has a real "getcwd" which increases build performance resulting in
           getcwd() being 605x faster in Win32 miniperl.

       •   Configure now takes  "-Dusequadmath"  into  account  when  calculating  the  "alignbytes"
           configuration variable.  Previously the mis-calculated "alignbytes" could cause alignment
           errors on debugging builds. [perl #127894]

Testing
       •   A  new  test  (t/op/aassign.t)  has  been  added  to  test  the  list assignment operator
           "OP_AASSIGN".

       •   Parallel building has been added to the dmake "makefile.mk" makefile. All Win32 compilers
           are supported.

Platform Support
   Platform-Specific Notes
       AmigaOS
           •   The AmigaOS port has been reintegrated into the main tree, based off of Perl 5.22.1.

       Cygwin
           •   Tests  are  more   robust   against   unusual   cygdrive   prefixes.    [GH   #15076]
               <https://github.com/Perl/perl5/issues/15076>

       EBCDIC
           UTF-EBCDIC extended
               UTF-EBCDIC is like UTF-8, but for EBCDIC platforms.  It now has been extended so that
               it  can represent code points up to 2 ** 64 - 1 on platforms with 64-bit words.  This
               brings it into parity with UTF-8.  This enhancement requires an  incompatible  change
               to  the  representation of code points in the range 2 ** 30 to 2 ** 31 -1 (the latter
               was the previous maximum representable code point).  This  means  that  a  file  that
               contains  one of these code points, written out with previous versions of perl cannot
               be read in, without conversion, by a perl containing this change.  We do not  believe
               any  such  files  are  in  existence,  but  if  you  do  have one, submit a ticket at
               perlbug AT perl.org <mailto:perlbug AT perl.org>, and we will write a conversion script for
               you.

           EBCDIC cmp() and sort() fixed for UTF-EBCDIC strings
               Comparing two strings that were both encoded in UTF-8 (or more precisely, UTF-EBCDIC)
               did not work properly until now.  Since sort() uses cmp(), this fixes that as well.

           EBCDIC "tr///" and "y///" fixed for "\N{}", and "use utf8" ranges
               Perl v5.22 introduced the concept of portable ranges to regular expression  patterns.
               A  portable range matches the same set of characters no matter what platform is being
               run on.  This concept is now extended to "tr///".  See "tr///".

               There were also some problems with these operations under "use utf8", which  are  now
               fixed

       FreeBSD
           •   Use   the   fdclose()  function  from  FreeBSD  if  it  is  available.   [GH  #15082]
               <https://github.com/Perl/perl5/issues/15082>

       IRIX
           •   Under some circumstances IRIX stdio fgetc() and fread() set the  errno  to  "ENOENT",
               which  made no sense according to either IRIX or POSIX docs.  Errno is now cleared in
               such cases.  [GH #14557] <https://github.com/Perl/perl5/issues/14557>

           •   Problems when multiplying long doubles by infinity  have  been  fixed.   [GH  #14993]
               <https://github.com/Perl/perl5/issues/14993>

       MacOS X
           •   Until  now  OS  X builds of perl have specified a link target of 10.3 (Panther, 2003)
               but have not specified a compiler target.  From now on, builds of perl on OS  X  10.6
               or later (Snow Leopard, 2008) by default capture the current OS X version and specify
               that  as the explicit build target in both compiler and linker flags, thus preserving
               binary compatibility for extensions built later regardless of changes in OS  X,  SDK,
               or compiler and linker versions.  To override the default value used in the build and
               preserved   in  the  flags,  specify  "export  MACOSX_DEPLOYMENT_TARGET=10.N"  before
               configuring and building perl, where 10.N is the version of OS X you wish to  target.
               In OS X 10.5 or earlier there is no change to the behavior present when those systems
               were  current;  the  link target is still OS X 10.3 and there is no explicit compiler
               target.

           •   Builds with both -DDEBUGGING and threading enabled would fail  with  a  "panic:  free
               from  wrong  pool" error when built or tested from Terminal on OS X.  This was caused
               by perl's internal management of the environment conflicting with an  atfork  handler
               using the libc setenv() function to update the environment.

               Perl  now  uses  setenv()/unsetenv()  to update the environment on OS X.  [GH #14955]
               <https://github.com/Perl/perl5/issues/14955>

       Solaris
           •   All Solaris variants now build a shared libperl

               Solaris and variants like OpenIndiana now always build with the shared  Perl  library
               (Configure -Duseshrplib).  This was required for the OpenIndiana builds, but this has
               also been the setting for Oracle/Sun Perl builds for several years.

       Tru64
           •   Workaround  where Tru64 balks when prototypes are listed as "PERL_STATIC_INLINE", but
               where the test is build with "-DPERL_NO_INLINE_FUNCTIONS".

       VMS
           •   On VMS, the math function prototypes in "math.h" are  now  visible  under  C++.   Now
               building the POSIX extension with C++ will no longer crash.

           •   VMS  has  had "setenv"/"unsetenv" since v7.0 (released in 1996), "Perl_vmssetenv" now
               always uses "setenv"/"unsetenv".

           •   Perl now implements its own "killpg" by  scanning  for  processes  in  the  specified
               process group, which may not mean exactly the same thing as a Unix process group, but
               allows  us  to  send  a  signal  to  a parent (or master) process and all of its sub-
               processes.  At the perl level, this means we can now send a negative pid like so:

                   kill SIGKILL, -$pid;

               to signal all processes in the same group as $pid.

           •   For those %ENV elements based on the CRTL environ array, we've always preserved  case
               when  setting  them  but  did  look-ups only after upcasing the key first, which made
               lower- or mixed-case entries go missing. This problem has been  corrected  by  making
               %ENV  elements  derived  from  the environ array case-sensitive on look-up as well as
               case-preserving on store.

           •   Environment look-ups for "PERL5LIB" and "PERLLIB" previously only considered  logical
               names, but now consider all sources of %ENV as determined by "PERL_ENV_TABLES" and as
               documented in "%ENV" in perlvms.

           •   The  minimum  supported  version  of  VMS is now v7.3-2, released in 2003.  As a side
               effect of this change, VAX is no longer supported as the terminal release of  OpenVMS
               VAX was v7.3 in 2001.

       Win32
           •   A new build option "USE_NO_REGISTRY" has been added to the makefiles.  This option is
               off  by  default, meaning the default is to do Windows registry lookups.  This option
               stops Perl from looking inside the registry for anything.  For what values are looked
               up in the registry see perlwin32.  Internally, in C,  the  name  of  this  option  is
               "WIN32_NO_REGISTRY".

           •   The     behavior     of     Perl    using    "HKEY_CURRENT_USER\Software\Perl"    and
               "HKEY_LOCAL_MACHINE\Software\Perl" to lookup  certain  values,  including  %ENV  vars
               starting with "PERL" has changed.  Previously, the 2 keys were checked for entries at
               all  times  through  the  perl  process's  life time even if they did not exist.  For
               performance reasons, now, if the root key (i.e.  "HKEY_CURRENT_USER\Software\Perl" or
               "HKEY_LOCAL_MACHINE\Software\Perl") does not exist at process start time, it will not
               be checked again for %ENV override entries for the remainder of  the  perl  process's
               life.   This  more closely matches Unix behavior in that the environment is copied or
               inherited on startup and changing the variable  in  the  parent  process  or  another
               process  or  editing  .bashrc  will  not  change  the environmental variable in other
               existing, running, processes.

           •   One glob fetch was removed for each "-X" or "stat" call whether done from  Perl  code
               or   internally   from   Perl's   C   code.    The   glob   being   looked   up   was
               "${^WIN32_SLOPPY_STAT}" which is a special variable.   This  makes  "-X"  and  "stat"
               slightly faster.

           •   During  miniperl's process startup, during the build process, 4 to 8 IO calls related
               to the process starting .pl and the buildcustomize.pl file were removed from the code
               opening and executing the first 1 or 2 .pl files.

           •   Builds using Microsoft Visual C++ 2003 and earlier no  longer  produce  an  "INTERNAL
               COMPILER ERROR" message.  [perl #126045]

           •   Visual  C++ 2013 builds will now execute on XP and higher. Previously they would only
               execute on Vista and higher.

           •   You can now build perl with GNU Make and GCC.  [perl #123440]

           •   "truncate($filename, $size)" now works for files over 4GB in size.  [perl #125347]

           •   Parallel building has been added to  the  dmake  "makefile.mk"  makefile.  All  Win32
               compilers are supported.

           •   Building  a  64-bit  perl  with  a  64-bit  GCC but a 32-bit gmake would result in an
               invalid $Config{archname} for the resulting perl.  [perl #127584]

           •   Errors set by Winsock functions are now put  directly  into  $^E,  and  the  relevant
               "WSAE*"  error  codes  are  now exported from the Errno and POSIX modules for testing
               this against.

               The previous behavior of putting the errors  (converted  to  POSIX-style  "E*"  error
               codes  since  Perl 5.20.0) into $! was buggy due to the non-equivalence of like-named
               Winsock and POSIX error constants, a relationship  between  which  has  unfortunately
               been established in one way or another since Perl 5.8.0.

               The  new behavior provides a much more robust solution for checking Winsock errors in
               portable software without accidentally matching POSIX tests that  were  intended  for
               other OSes and may have different meanings for Winsock.

               The  old  behavior is currently retained, warts and all, for backwards compatibility,
               but users are encouraged to change any code that tests $!  against "E*" constants for
               Winsock errors to instead test $^E  against  "WSAE*"  constants.   After  a  suitable
               deprecation  period,  the  old  behavior  may  be removed, leaving $! unchanged after
               Winsock function calls, to avoid any possible confusion over which error variable  to
               check.

       ppc64el
           floating point
               The floating point format of ppc64el (Debian naming for little-endian PowerPC) is now
               detected correctly.

Internal Changes
       •   The  implementation  of  perl's  context  stack  system,  and its internal API, have been
           heavily reworked. Note that no significant changes have been made to any  external  APIs,
           but  XS code which relies on such internal details may need to be fixed. The main changes
           are:

           •   The PUSHBLOCK(), POPSUB() etc. macros have been replaced with static inline functions
               such as  cx_pushblock(),  cx_popsub()  etc.  These  use  function  args  rather  than
               implicitly  relying  on  local vars such as "gimme" and "newsp" being available. Also
               their functionality has changed: in particular, cx_popblock()  no  longer  decrements
               "cxstack_ix".  The  ordering  of  the  steps  in  the "pp_leave*" functions involving
               cx_popblock(), cx_popsub() etc. has changed.  See  the  new  documentation,  "Dynamic
               Scope and the Context Stack" in perlguts, for details on how to use them.

           •   Various macros, which now consistently have a CX_ prefix, have been added:

                 CX_CUR(), CX_LEAVE_SCOPE(), CX_POP()

               or renamed:

                 CX_POP_SAVEARRAY(), CX_DEBUG(), CX_PUSHSUBST(), CX_POPSUBST()

           •   cx_pushblock()  now  saves  "PL_savestack_ix" and "PL_tmps_floor", so "pp_enter*" and
               "pp_leave*" no longer do

                 ENTER; SAVETMPS; ....; LEAVE

           •   cx_popblock() now also restores "PL_curpm".

           •   In dounwind() for every context type, the current savestack frame  is  now  processed
               before  each  context  is  popped;  formerly  this was only done for sub-like context
               frames. This action has been removed from cx_popsub() and placed into its own  macro,
               CX_LEAVE_SCOPE(cx), which must be called before cx_popsub() etc.

               dounwind()  now  also does a cx_popblock() on the last popped frame (formerly it only
               did the cx_popsub() etc. actions on each frame).

           •   The temps stack is now freed on scope exit; previously, temps created during the last
               statement of a block wouldn't be freed until the next "nextstate" following the block
               (apart from an existing hack that did this for recursive subs in scalar context); and
               in something like "f(g())", the temps created by the  last  statement  in  g()  would
               formerly not be freed until the statement following the return from f().

           •   Most values that were saved on the savestack on scope entry are now saved in suitable
               new fields in the context struct, and saved and restored directly by cx_pushfoo() and
               cx_popfoo(), which is much faster.

           •   Various context struct fields have been added, removed or modified.

           •   The  handling  of @_ in cx_pushsub() and cx_popsub() has been considerably tidied up,
               including removing the "argarray" field from the context struct, and  extracting  out
               some  common (but rarely used) code into a separate function, clear_defarray(). Also,
               useful subsets of cx_popsub() which had been unrolled in places like  "pp_goto"  have
               been gathered into the new functions cx_popsub_args() and cx_popsub_common().

           •   "pp_leavesub"  and  "pp_leavesublv"  now  use  the  same  function as the rest of the
               "pp_leave*"'s to process return args.

           •   "CXp_FOR_PAD" and "CXp_FOR_GV" flags have been added,  and  "CXt_LOOP_FOR"  has  been
               split into "CXt_LOOP_LIST", "CXt_LOOP_ARY".

           •   Some  variables  formerly  declared  by  "dMULTICALL"  (but not documented) have been
               removed.

       •   The obscure "PL_timesbuf" variable, effectively a vestige of Perl 1, has been removed. It
           was documented as deprecated in Perl 5.20, with a statement  that  it  would  be  removed
           early   in   the   5.21.x   series;   that   has   now  finally  happened.   [GH  #13632]
           <https://github.com/Perl/perl5/issues/13632>

       •   An unwarranted assertion in Perl_newATTRSUB_x() has been removed.  If a  stub  subroutine
           definition  with  a  prototype has been seen, then any subsequent stub (or definition) of
           the same subroutine with an attribute was causing an assertion failure because of a  null
           pointer.  [GH #15081] <https://github.com/Perl/perl5/issues/15081>

       •   "::"   has   been   replaced   by   "__"  in  "ExtUtils::ParseXS",  like  it's  done  for
           parameters/return values. This  is  more  consistent,  and  simplifies  writing  XS  code
           wrapping  C++  classes  into  a  nested  Perl  namespace  (it requires only a typedef for
           "Foo__Bar" rather than two, one for "Foo_Bar" and the other for "Foo::Bar").

       •   The  to_utf8_case()  function   is   now   deprecated.    Instead   use   "toUPPER_utf8",
           "toTITLE_utf8",          "toLOWER_utf8",         and         "toFOLD_utf8".          (See
           <http://nntp.perl.org/group/perl.perl5.porters/233287>.)

       •   Perl core code and the threads  extension  have  been  annotated  so  that,  if  Perl  is
           configured  to use threads, then during compile-time clang (3.6 or later) will warn about
           suspicious uses of mutexes.   See  <http://clang.llvm.org/docs/ThreadSafetyAnalysis.html>
           for more information.

       •   The  signbit()  emulation  has  been  enhanced.   This will help older and/or more exotic
           platforms or configurations.

       •   Most EBCDIC-specific code in the core has been unified with  non-EBCDIC  code,  to  avoid
           repetition and make maintenance easier.

       •   MSWin32  code  for $^X has been moved out of the win32 directory to caretx.c, where other
           operating systems set that variable.

       •   sv_ref() is now part of the API.

       •   "sv_backoff" in perlapi had its return type changed from "int" to "void".  It  previously
           has  always  returned  0  since  Perl  5.000  stable but that was undocumented.  Although
           "sv_backoff" is marked as public API, XS code is not expected to be  impacted  since  the
           proper API call would be through public API "sv_setsv(sv, &PL_sv_undef)", or quasi-public
           "SvOOK_off",  or  non-public  "SvOK_off"  calls, and the return value of "sv_backoff" was
           previously a meaningless constant that can be rewritten as "(sv_backoff(sv),0)".

       •   The "EXTEND" and "MEXTEND" macros have been improved to avoid various issues with integer
           truncation and wrapping.  In particular, some casts formerly used within the macros  have
           been  removed.   This  means  for  example  that passing an unsigned "nitems" argument is
           likely to raise a compiler warning now (it's always been documented to require  a  signed
           value; formerly int, lately SSize_t).

       •   "PL_sawalias" and "GPf_ALIASED_SV" have been removed.

       •   "GvASSIGN_GENERATION" and "GvASSIGN_GENERATION_set" have been removed.

Selected Bug Fixes
       •   It now works properly to specify a user-defined property, such as

            qr/\p{mypkg1::IsMyProperty}/i

           with  "/i"  caseless  matching, an explicit package name, and IsMyProperty not defined at
           the time of the pattern compilation.

       •   Perl's memcpy(), memmove(), memset() and memcmp() fallbacks are now more compatible  with
           the originals.  [perl #127619]

       •   Fixed  the  issue  where  a "s///r") with -DPERL_NO_COW attempts to modify the source SV,
           resulting in the program dying. [perl #127635]

       •   Fixed an EBCDIC-platform-only case where a pattern could fail  to  match.  This  occurred
           when  matching  characters from the set of C1 controls when the target matched string was
           in UTF-8.

       •   Narrow the filename check in strict.pm and warnings.pm. Previously, it  assumed  that  if
           the  filename  (without  the  .pmc?  extension)  differed from the package name, if was a
           misspelled use statement (i.e. "use Strict"  instead  of  "use  strict").  We  now  check
           whether there's really a miscapitalization happening, and not some other issue.

       •   Turn an assertion into a more user friendly failure when parsing regexes. [perl #127599]

       •   Correctly  raise  an  error  when  trying to compile patterns with unterminated character
           classes while there are trailing backslashes.  [perl #126141].

       •   Line numbers larger than 2**31-1 but less than 2**32 are no longer returned  by  caller()
           as negative numbers.  [perl #126991]

       •   "unless  (  assignment  )"  now  properly  warns when syntax warnings are enabled.  [perl
           #127122]

       •   Setting an "ISA" glob to an array reference now properly  adds  "isaelem"  magic  to  any
           existing  elements.  Previously modifying such an element would not update the ISA cache,
           so method calls would call the wrong function.  Perl would also crash if the  "ISA"  glob
           was  destroyed,  since  new code added in 5.23.7 would try to release the "isaelem" magic
           from the elements.  [perl #127351]

       •   If a here-doc was found while parsing another operator, the parser had already  read  end
           of  file,  and  the  here-doc  was  not  terminated, perl could produce an assertion or a
           segmentation fault.  This now reliably complains about the unterminated here-doc.   [perl
           #125540]

       •   untie()  would sometimes return the last value returned by the UNTIE() handler as well as
           its normal value, messing up the stack.  [perl #126621]

       •   Fixed an operator precedence problem when " castflags & 2" is true.  [perl #127474]

       •   Caching of DESTROY methods could result in a non-pointer or a  non-STASH  stored  in  the
           SvSTASH()  slot  of  a  stash,  breaking the B STASH() method.  The DESTROY method is now
           cached in the MRO metadata for the stash.  [perl #126410]

       •   The AUTOLOAD method is now called when searching for a DESTROY method, and correctly sets
           $AUTOLOAD too.  [perl #124387]  [perl #127494]

       •   Avoid parsing beyond the end of the buffer when processing a "#line"  directive  with  no
           filename.  [perl #127334]

       •   Perl now raises a warning when a regular expression pattern looks like it was supposed to
           contain  a  POSIX  class, like "qr/[[:alpha:]]/", but there was some slight defect in its
           specification which causes it to instead be treated  as  a  regular  bracketed  character
           class.   An  example  would  be  missing  the  second  colon  in  the  above  like  this:
           "qr/[[:alpha]]/".  This compiles to match a sequence of two characters.   The  second  is
           "]",  and  the first is any of: "[", ":", "a", "h", "l", or "p".   This is unlikely to be
           the intended meaning, and now a warning is raised.   No  warning  is  raised  unless  the
           specification  is very close to one of the 14 legal POSIX classes.  (See "POSIX Character
           Classes" in perlrecharclass.)  [perl #8904]

       •   Certain regex patterns involving a complemented POSIX  class  in  an  inverted  bracketed
           character  class,  and matching something else optionally would improperly fail to match.
           An example of one that could fail  is  "qr/_?[^\Wbar]\x{100}/".   This  has  been  fixed.
           [perl #127537]

       •   Perl  5.22  added  support  to the C99 hexadecimal floating point notation, but sometimes
           misparses hex floats. This has been fixed.  [perl #127183]

       •   A regression that allowed undeclared barewords in hash keys to  work  despite  strictures
           has been fixed.  [GH #15099] <https://github.com/Perl/perl5/issues/15099>

       •   Calls to the placeholder &PL_sv_yes used internally when an import() or unimport() method
           isn't     found     now     correctly     handle    scalar    context.     [GH    #14902]
           <https://github.com/Perl/perl5/issues/14902>

       •   Report more context when we see an array where we expect to see an operator and avoid  an
           assertion failure.  [GH #14472] <https://github.com/Perl/perl5/issues/14472>

       •   Modifying an array that was previously a package @ISA no longer causes assertion failures
           or crashes.  [GH #14492] <https://github.com/Perl/perl5/issues/14492>

       •   Retain  binary  compatibility  across  plain  and  DEBUGGING  perl  builds.   [GH #15122]
           <https://github.com/Perl/perl5/issues/15122>

       •   Avoid   leaking   memory   when   setting   $ENV{foo}    on    darwin.     [GH    #14955]
           <https://github.com/Perl/perl5/issues/14955>

       •   "/...\G/"  no  longer  crashes on utf8 strings. When "\G" is a fixed number of characters
           from the start of the regex, perl needs to count  back  that  many  characters  from  the
           current pos() position and start matching from there. However, it was counting back bytes
           rather than characters, which could lead to panics on utf8 strings.

       •   In  some  cases  operators  that  return integers would return negative integers as large
           positive integers.  [GH #15049] <https://github.com/Perl/perl5/issues/15049>

       •   The pipe() operator would assert for DEBUGGING builds instead of  producing  the  correct
           error  message.   The condition asserted on is detected and reported on correctly without
           the    assertions,    so    the     assertions     were     removed.      [GH     #15015]
           <https://github.com/Perl/perl5/issues/15015>

       •   In  some  cases, failing to parse a here-doc would attempt to use freed memory.  This was
           caused    by    a    pointer    not    being    restored    correctly.     [GH    #15009]
           <https://github.com/Perl/perl5/issues/15009>

       •   "@x  =  sort { *a = 0; $a <=> $b } 0 .. 1" no longer frees the GP for *a before restoring
           its SV slot.  [GH #14595] <https://github.com/Perl/perl5/issues/14595>

       •   Multiple problems with the new hexadecimal floating point printf format  %a  were  fixed:
           [GH      #15032]      <https://github.com/Perl/perl5/issues/15032>,      [GH      #15033]
           <https://github.com/Perl/perl5/issues/15033>,                 [GH                 #15074]
           <https://github.com/Perl/perl5/issues/15074>

       •   Calling mg_set() in leave_scope() no longer leaks.

       •   A  regression  from  Perl v5.20 was fixed in which debugging output of regular expression
           compilation was wrong.  (The pattern was correctly compiled, but what got  displayed  for
           it was wrong.)

       •   "\b{sb}"  works much better.  In Perl v5.22.0, this new construct didn't seem to give the
           expected results, yet passed all the tests in the extensive suite furnished  by  Unicode.
           It  turns out that it was because these were short input strings, and the failures had to
           do with longer inputs.

       •   Certain syntax errors in "Extended Bracketed Character Classes" in perlrecharclass caused
           panics instead of the proper error message.  This has now been fixed. [perl #126481]

       •   Perl 5.20 added a message when a quantifier in a regular expression was useless, but then
           caused the parser to skip it; this caused the surplus quantifier to be silently  ignored,
           instead of throwing an error. This is now fixed. [perl #126253]

       •   The  switch to building non-XS modules last in win32/makefile.mk (introduced by design as
           part of the changes to enable parallel building) caused the build of POSIX to  break  due
           to problems with the version module. This is now fixed.

       •   Improved parsing of hex float constants.

       •   Fixed  an  issue with "pack" where "pack "H"" (and "pack "h"") could read past the source
           when given a non-utf8 source, and a utf8 target.  [perl #126325]

       •   Fixed several cases where perl would abort due to a  segmentation  fault,  or  a  C-level
           assert. [perl #126615], [perl #126602], [perl #126193].

       •   There  were  places  in  regular  expression patterns where comments ("(?#...)")  weren't
           allowed,   but   should   have   been.     This    is    now    fixed.     [GH    #12755]
           <https://github.com/Perl/perl5/issues/12755>

       •   Some  regressions  from  Perl  5.20  have  been  fixed,  in  which  some syntax errors in
           "(?[...])" constructs within regular expression patterns could cause a  segfault  instead
           of  a proper error message.  [GH #14933] <https://github.com/Perl/perl5/issues/14933> [GH
           #14996] <https://github.com/Perl/perl5/issues/14996>

       •   Another problem with "(?[...])"  constructs has been  fixed  wherein  things  like  "\c]"
           could cause panics.  [GH #14934] <https://github.com/Perl/perl5/issues/14934>

       •   Some  problems  with  attempting to extend the perl stack to around 2G or 4G entries have
           been fixed.  This was particularly an issue on 32-bit perls built to use 64-bit integers,
           and was easily noticeable with the list repetition operator, e.g.

               @a = (1) x $big_number

           Formerly perl may have crashed, depending on the exact value of $big_number; now it  will
           typically raise an exception.  [GH #14880] <https://github.com/Perl/perl5/issues/14880>

       •   In   a   regex  conditional  expression  "(?(condition)yes-pattern|no-pattern)",  if  the
           condition is "(?!)" then perl failed the match  outright  instead  of  matching  the  no-
           pattern.  This has been fixed.  [GH #14947] <https://github.com/Perl/perl5/issues/14947>

       •   The  special  backtracking control verbs "(*VERB:ARG)" now all allow an optional argument
           and    set    "REGERROR"/"REGMARK"    appropriately     as     well.      [GH     #14937]
           <https://github.com/Perl/perl5/issues/14937>

       •   Several  bugs, including a segmentation fault, have been fixed with the boundary checking
           constructs (introduced in Perl 5.22) "\b{gcb}", "\b{sb}", "\b{wb}", "\B{gcb}",  "\B{sb}",
           and "\B{wb}".  All the "\B{}" ones now match an empty string; none of the "\b{}" ones do.
           [GH #14976] <https://github.com/Perl/perl5/issues/14976>

       •   Duplicating  a  closed  file  handle  for  write no longer creates a filename of the form
           GLOB(0xXXXXXXXX).  [perl #125115]

       •   Warning fatality is now  ignored  when  rewinding  the  stack.   This  prevents  infinite
           recursion when the now fatal error also causes rewinding of the stack.  [perl #123398]

       •   In  perl  v5.22.0,  the  logic changed when parsing a numeric parameter to the -C option,
           such that the successfully parsed number was not saved as the option value if  it  parsed
           to the end of the argument.  [perl #125381]

       •   The PadlistNAMES macro is an lvalue again.

       •   Zero -DPERL_TRACE_OPS memory for sub-threads.

           perl_clone_using() was missing Zero init of PL_op_exec_cnt[].  This caused sub-threads in
           threaded  -DPERL_TRACE_OPS builds to spew exceedingly large op-counts at destruct.  These
           counts would print %x as "ABABABAB", clearly a mem-poison value.

       •   A leak in the XS typemap caused one scalar to be leaked each time a "FILE *" or a "PerlIO
           *" was "OUTPUT:"ed or imported to  Perl,  since  perl  5.000.  These  particular  typemap
           entries are thought to be extremely rarely used by XS modules. [perl #124181]

       •   alarm()  and sleep() will now warn if the argument is a negative number and return undef.
           Previously they would pass the negative value to the underlying C function which may have
           set up a timer with a surprising value.

       •   Perl can again be compiled with any Unicode version.  This used to (mostly) work, but was
           lost in v5.18 through v5.20.  The property "Name_Alias" did not exist  prior  to  Unicode
           5.0.  Unicode::UCD incorrectly said it did.  This has been fixed.

       •   Very  large  code-points (beyond Unicode) in regular expressions no longer cause a buffer
           overflow    in    some    cases    when    converted    to    UTF-8.      [GH     #14858]
           <https://github.com/Perl/perl5/issues/14858>

       •   The  integer  overflow  check  for the range operator (...) in list context now correctly
           handles the case where the size of the range is larger  than  the  address  space.   This
           could      happen      on      32-bits      with      -Duse64bitint.      [GH     #14843]
           <https://github.com/Perl/perl5/issues/14843>

       •   A   crash    with    "%::=();    J->${\"::"}"    has    been    fixed.     [GH    #14790]
           <https://github.com/Perl/perl5/issues/14790>

       •   "qr/(?[  ()  ])/"  no  longer  segfaults,  giving  a syntax error message instead.  [perl
           #125805]

       •   Regular    expression    possessive    quantifier    v5.20    regression    now    fixed.
           "qr/"PAT"{"min,max"}+""/"      is      supposed      to     behave     identically     to
           "qr/(?>"PAT"{"min,max"})/".  Since v5.20, this didn't work if min  and  max  were  equal.
           [perl #125825]

       •   "BEGIN <>" no longer segfaults and properly produces an error message.  [perl #125341]

       •   In  "tr///"  an  illegal  backwards  range  like  "tr/\x{101}-\x{100}//"  was  not always
           detected, giving incorrect results.  This is now fixed.

Acknowledgements
       Perl 5.24.0 represents approximately 11 months of development since Perl 5.24.0 and  contains
       approximately 360,000 lines of changes across 1,800 files from 75 authors.

       Excluding  auto-generated  files,  documentation  and release tools, there were approximately
       250,000 lines of changes to 1,200 .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 5.24.0:

       Aaron Crane, Aaron Priven,  Abigail,  Achim  Gratz,  Alexander  D'Archangel,  Alex  Vandiver,
       Andreas  König, Andy Broad, Andy Dougherty, Aristotle Pagaltzis, Chase Whitener, Chas. Owens,
       Chris 'BinGOs' Williams, Craig A.  Berry,  Dagfinn  Ilmari  Mannsåker,  Dan  Collins,  Daniel
       Dragan, David Golden, David Mitchell, Doug Bell, Dr.Ruud, Ed Avis, Ed J, Father Chrysostomos,
       Herbert  Breunung,  H.Merijn  Brand,  Hugo  van der Sanden, Ivan Pozdeev, James E Keenan, Jan
       Dubois, Jarkko Hietaniemi, Jerry D. Hedden, Jim Cromie, John Peacock, John SJ Anderson, Karen
       Etheridge, Karl Williamson, kmx, Leon Timmermans, Ludovic E. R.  Tolhurst-Cleaver, Lukas Mai,
       Martijn Lievaart, Matthew Horsfall, Mattia Barbon, Max Maischein, Mohammed El-Afifi, Nicholas
       Clark, Nicolas R., Niko Tyni, Peter John Acklam, Peter Martini,  Peter  Rabbitson,  Pip  Cet,
       Rafael Garcia-Suarez, Reini Urban, Ricardo Signes, Sawyer X, Shlomi Fish, Sisyphus, Stanislaw
       Pusep,  Steffen Müller, Stevan Little, Steve Hay, Sullivan Beck, Thomas Sibley, Todd Rinaldo,
       Tom Hukins, Tony Cook, Unicode Consortium, Victor Adam, Vincent Pit, Vladimir Timofeev,  Yves
       Orton, Zachary Storer, Zefram.

       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 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 AT 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.

SEE ALSO
       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.

perl v5.38.2                                 2026-08-18                             PERL5240DELTA(1)
PERL5240DELTA(1) □✕
NAME DESCRIPTION Core Enhancements Security Incompatible Changes Deprecations Performance Enhancements Modules and Pragmata Documentation Diagnostics Configuration and Compilation Testing Platform Support Internal Changes Selected Bug Fixes Acknowledgements Reporting Bugs SEE ALSO

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