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
       "uselocale" 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
       compatability 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 [perl #126755]
       <https://rt.perl.org/Ticket/Display.html?id=126755>

   Fix loss of taint in canonpath
       This is CVE-2015-8607.  For more information see [perl #126862]
       <https://rt.perl.org/Ticket/Display.html?id=126862>

   Avoid accessing uninitialized memory in win32 "crypt()"
       Added validation that will detect both a short salt and invalid
       characters in the salt.  [perl #126922]
       <https://rt.perl.org/Ticket/Display.html?id=126922>

   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);

       [perl #125587] <https://rt.perl.org/Ticket/Display.html?id=125587>

       [perl #121058] <https://rt.perl.org/Ticket/Display.html?id=121058>

   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 "useutf8".  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
       o   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();

       o   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.

       o   "/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.

       o   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.

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

       o   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

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

       o   Single arguments in list assign are now slightly faster:

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

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

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

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

       o   autodie has been upgraded from version 2.26 to 2.29.

       o   autouse has been upgraded from version 1.08 to 1.11.

       o   B has been upgraded from version 1.58 to 1.62.

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

       o   base has been upgraded from version 2.22 to 2.23.

       o   Benchmark has been upgraded from version 1.2 to 1.22.

       o   bignum has been upgraded from version 0.39 to 0.42.

       o   bytes has been upgraded from version 1.04 to 1.05.

       o   Carp has been upgraded from version 1.36 to 1.40.

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

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

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

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

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

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

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

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

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

       o   Dumpvalue has been upgraded from version 1.17 to 1.18.

       o   DynaLoader has been upgraded from version 1.32 to 1.38.

       o   Encode has been upgraded from version 2.72 to 2.80.

       o   encoding has been upgraded from version 2.14 to 2.17.

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

       o   English has been upgraded from version 1.09 to 1.10.

       o   Errno has been upgraded from version 1.23 to 1.25.

       o   experimental has been upgraded from version 0.013 to 0.016.

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

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

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

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

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

       o   feature has been upgraded from version 1.40 to 1.42.

       o   fields has been upgraded from version 2.17 to 2.23.

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

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

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

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

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

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

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

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

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

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

       o   if has been upgraded from version 0.0604 to 0.0606.

       o   IO has been upgraded from version 1.35 to 1.36.

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

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

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

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

       o   locale has been upgraded from version 1.06 to 1.08.

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

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

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

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

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

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

       o   mro has been upgraded from version 1.17 to 1.18.

       o   ODBM_File has been upgraded from version 1.12 to 1.14.

       o   Opcode has been upgraded from version 1.32 to 1.34.

       o   parent has been upgraded from version 0.232 to 0.234.

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

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

       o   perlfaq has been upgraded from version 5.021009 to 5.021010.

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

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

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

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

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

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

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

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

       o   POSIX has been upgraded from version 1.53 to 1.65.

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

       o   SDBM_File has been upgraded from version 1.13 to 1.14.

       o   SelfLoader has been upgraded from version 1.22 to 1.23.

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

       o   Storable has been upgraded from version 2.53 to 2.56.

       o   strict has been upgraded from version 1.09 to 1.11.

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

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

       o   Test has been upgraded from version 1.26 to 1.28.

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

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

       o   threads has been upgraded from version 2.01 to 2.06.

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

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

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

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

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

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

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

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

       o   UNIVERSAL has been upgraded from version 1.12 to 1.13.

       o   utf8 has been upgraded from version 1.17 to 1.19.

       o   version has been upgraded from version 0.9909 to 0.9916.

       o   warnings has been upgraded from version 1.32 to 1.36.

       o   Win32 has been upgraded from version 0.51 to 0.52.

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

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

       o   XSLoader has been upgraded from version 0.20 to 0.21.

Documentation
   Changes to Existing Documentation
       perlapi

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

       perlcall

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

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

           o   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

           o   add API documentation for POPu and POPul

           o   use ERRSV more efficiently

           o   approaches to thread-safety storage of SVs.

       perlfunc

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

       o   Better explain meaning of negative PIDs in "waitpid".  [perl
           #127080] <https://rt.perl.org/Ticket/Display.html?id=127080>

       o   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

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

       perllocale

       o   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

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

       perlop

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

       perlpolicy

       o   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

       o   Fix some examples to be strict clean.

       perlrebackslash

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

       perlsub

       o   Updated to note that anonymous subroutines can have signatures.

       perlsyn

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

       perltie

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

       perlunicode

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

       perlvar

       o   The documentation of $@ was reworded to clarify that it is not just
           for syntax errors in "eval".  [perl #124034]
           <https://rt.perl.org/Ticket/Display.html?id=124034>

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

       o   Use of $OLD_PERL_VERSION is now discouraged.

       perlxs

       o   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

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

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

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

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

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

       o   Illegal user-defined property name

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

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

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

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

       New Warnings

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

       o   %s() is deprecated on :utf8 handles

   Changes to Existing Diagnostics
       o   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.  [perl #127060]
           <https://rt.perl.org/Ticket/Display.html?id=127060>

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

       o   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.

       o   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
       o   "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.

       o   Bison 3.0 is now supported.

       o   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.  [perl #127131]
           <https://rt.perl.org/Ticket/Display.html?id=127131>

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

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

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

       o   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.

       o   Configure should handle spaces in paths a little better.

       o   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.

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

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

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

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

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

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

       Cygwin
           o   Tests are more robust against unusual cygdrive prefixes.  [perl
               #126834] <https://rt.perl.org/Ticket/Display.html?id=126834>

       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@perl.org <mailto:perlbug@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 "useutf8" 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
               "useutf8", which are now fixed

       FreeBSD
           o   Use the "fdclose()" function from FreeBSD if it is available.
               [perl #126847]
               <https://rt.perl.org/Ticket/Display.html?id=126847>

       IRIX
           o   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.  [perl
               #123977] <https://rt.perl.org/Ticket/Display.html?id=123977>

           o   Problems when multiplying long doubles by infinity have been
               fixed.  [perl #126396]
               <https://rt.perl.org/Ticket/Display.html?id=126396>

       MacOS X
           o   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.

           o   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.  [perl #126240]
               <https://rt.perl.org/Ticket/Display.html?id=126240>

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

       VMS
           o   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.

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

           o   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.

           o   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.

           o   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.

           o   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
           o   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".

           o   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.

           o   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.

           o   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.

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

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

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

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

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

           o   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]

           o   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
       o   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:

           o   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.

           o   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()

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

                 ENTER; SAVETMPS; ....; LEAVE

           o   "cx_popblock()" now also restores "PL_curpm".

           o   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).

           o   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()".

           o   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.

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

           o   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()".

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

           o   "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".

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

       o   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.  [perl #121351]
           <https://rt.perl.org/Ticket/Display.html?id=121351>

       o   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.  [perl #126845]
           <https://rt.perl.org/Ticket/Display.html?id=126845>

       o   "::" 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").

       o   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>.)

       o   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.

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

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

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

       o   "sv_ref()" is now part of the API.

       o   "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)".

       o   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).

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

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

Selected Bug Fixes
       o   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.

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

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

       o   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.

       o   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.

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

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

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

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

       o   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]

       o   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]

       o   "untie()" would sometimes return the last value returned by the
           "UNTIE()" handler as well as it's normal value, messing up the
           stack.  [perl #126621]

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

       o   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]

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

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

       o   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]

       o   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]

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

       o   A regression that allowed undeclared barewords in hash keys to work
           despite strictures has been fixed.  [perl #126981]
           <https://rt.perl.org/Ticket/Display.html?id=126981>

       o   Calls to the placeholder &PL_sv_yes used internally when an
           "import()" or "unimport()" method isn't found now correctly handle
           scalar context.  [perl #126042]
           <https://rt.perl.org/Ticket/Display.html?id=126042>

       o   Report more context when we see an array where we expect to see an
           operator and avoid an assertion failure.  [perl #123737]
           <https://rt.perl.org/Ticket/Display.html?id=123737>

       o   Modifying an array that was previously a package @ISA no longer
           causes assertion failures or crashes.  [perl #123788]
           <https://rt.perl.org/Ticket/Display.html?id=123788>

       o   Retain binary compatibility across plain and DEBUGGING perl builds.
           [perl #127212] <https://rt.perl.org/Ticket/Display.html?id=127212>

       o   Avoid leaking memory when setting $ENV{foo} on darwin.  [perl
           #126240] <https://rt.perl.org/Ticket/Display.html?id=126240>

       o   "/...\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.

       o   In some cases operators that return integers would return negative
           integers as large positive integers.  [perl #126635]
           <https://rt.perl.org/Ticket/Display.html?id=126635>

       o   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.  [perl #126480]
           <https://rt.perl.org/Ticket/Display.html?id=126480>

       o   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.  [perl #126443]
           <https://rt.perl.org/Ticket/Display.html?id=126443>

       o   "@x = sort { *a = 0; $a <=> $b } 0 .. 1" no longer frees the GP for
           *a before restoring its SV slot.  [perl #124097]
           <https://rt.perl.org/Ticket/Display.html?id=124097>

       o   Multiple problems with the new hexadecimal floating point printf
           format %a were fixed: [perl #126582]
           <https://rt.perl.org/Ticket/Display.html?id=126582>, [perl #126586]
           <https://rt.perl.org/Ticket/Display.html?id=126586>, [perl #126822]
           <https://rt.perl.org/Ticket/Display.html?id=126822>

       o   Calling "mg_set()" in "leave_scope()" no longer leaks.

       o   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.)

       o   "\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.

       o   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]

       o   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]

       o   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.

       o   Improved parsing of hex float constants.

       o   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]

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

       o   There were places in regular expression patterns where comments
           ("(?#...)")  weren't allowed, but should have been.  This is now
           fixed.  [perl #116639]
           <https://rt.perl.org/Ticket/Display.html?id=116639>

       o   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.
           [perl #126180] <https://rt.perl.org/Ticket/Display.html?id=126180>
           [perl #126404] <https://rt.perl.org/Ticket/Display.html?id=126404>

       o   Another problem with "(?[...])"  constructs has been fixed wherein
           things like "\c]" could cause panics.  [perl #126181]
           <https://rt.perl.org/Ticket/Display.html?id=126181>

       o   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.  [perl
           #125937] <https://rt.perl.org/Ticket/Display.html?id=125937>

       o   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.  [perl #126222]
           <https://rt.perl.org/Ticket/Display.html?id=126222>

       o   The special backtracking control verbs "(*VERB:ARG)" now all allow
           an optional argument and set "REGERROR"/"REGMARK" appropriately as
           well.  [perl #126186]
           <https://rt.perl.org/Ticket/Display.html?id=126186>

       o   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.  [perl #126319]
           <https://rt.perl.org/Ticket/Display.html?id=126319>

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

       o   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]

       o   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]

       o   The PadlistNAMES macro is an lvalue again.

       o   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.

       o   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]

       o   "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.

       o   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.

       o   Very large code-points (beyond Unicode) in regular expressions no
           longer cause a buffer overflow in some cases when converted to
           UTF-8.  [perl #125826]
           <https://rt.perl.org/Ticket/Display.html?id=125826>

       o   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.  [perl #125781]
           <https://rt.perl.org/Ticket/Display.html?id=125781>

       o   A crash with "%::=(); J->${\"::"}" has been fixed.  [perl #125541]
           <https://rt.perl.org/Ticket/Display.html?id=125541>

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

       o   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]

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

       o   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 Konig, Andy Broad, Andy Dougherty, Aristotle
       Pagaltzis, Chase Whitener, Chas. Owens, Chris 'BinGOs' Williams, Craig
       A. Berry, Dagfinn Ilmari Mannsaker, 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 Muller, 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@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 v5.26.1                      2017-10-25                  PERL5240DELTA(1)

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