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PERL5280DELTA(1pm)     Perl Programmers Reference Guide     PERL5280DELTA(1pm)


       perl5280delta - what is new for perl v5.28.0


       This document describes differences between the 5.26.0 release and the
       5.28.0 release.

       If you are upgrading from an earlier release such as 5.24.0, first read
       perl5260delta, which describes differences between 5.24.0 and 5.26.0.

Core Enhancements

   Unicode 10.0 is supported
       A list of changes is at

   "delete" on key/value hash slices
       "delete" can now be used on key/value hash slices, returning the keys
       along with the deleted values.  [GH #15982]

   Experimentally, there are now alphabetic synonyms for some regular
       expression assertions
       If you find it difficult to remember how to write certain of the
       pattern assertions, there are now alphabetic synonyms.

        CURRENT                NEW SYNONYMS
        ------                 ------------
        (?=...)        (*pla:...) or (*positive_lookahead:...)
        (?!...)        (*nla:...) or (*negative_lookahead:...)
        (?<=...)       (*plb:...) or (*positive_lookbehind:...)
        (?<!...)       (*nlb:...) or (*negative_lookbehind:...)
        (?>...)        (*atomic:...)

       These are considered experimental, so using any of these will raise
       (unless turned off) a warning in the "experimental::alpha_assertions"

   Mixed Unicode scripts are now detectable
       A mixture of scripts, such as Cyrillic and Latin, in a string is often
       the sign of a spoofing attack.  A new regular expression construct now
       allows for easy detection of these.  For example, you can say

        qr/(*script_run: \d+ \b )/x

       And the digits matched will all be from the same set of 10.  You won't
       get a look-alike digit from a different script that has a different
       value than what it appears to be.


        qr/(*sr: \b \w+ \b )/x

       makes sure that all the characters come from the same script.

       You can also combine script runs with "(?>...)" (or "*atomic:...)").

       Instead of writing:


       you can now run:

           # or

       This is considered experimental, so using it will raise (unless turned
       off) a warning in the "experimental::script_run" category.

       See "Script Runs" in perlre.

   In-place editing with "perl -i" is now safer
       Previously in-place editing ("perl -i") would delete or rename the
       input file as soon as you started working on a new file.

       Without backups this would result in loss of data if there was an
       error, such as a full disk, when writing to the output file.

       This has changed so that the input file isn't replaced until the output
       file has been completely written and successfully closed.

       This works by creating a work file in the same directory, which is
       renamed over the input file once the output file is complete.


       o   Since this renaming needs to only happen once, if you create a
           thread or child process, that renaming will only happen in the
           original thread or process.

       o   If you change directories while processing a file, and your
           operating system doesn't provide the "unlinkat()", "renameat()" and
           "fchmodat()" functions, the final rename step may fail.

       [GH #15216] <>

   Initialisation of aggregate state variables
       A persistent lexical array or hash variable can now be initialized, by
       an expression such as "state @a = qw(x y z)".  Initialization of a list
       of persistent lexical variables is still not possible.

   Full-size inode numbers
       On platforms where inode numbers are of a type larger than perl's
       native integer numerical types, stat will preserve the full content of
       large inode numbers by returning them in the form of strings of decimal
       digits.  Exact comparison of inode numbers can thus be achieved by
       comparing with "eq" rather than "==".  Comparison with "==", and other
       numerical operations (which are usually meaningless on inode numbers),
       work as well as they did before, which is to say they fall back to
       floating point, and ultimately operate on a fairly useless rounded
       inode number if the real inode number is too big for the floating point

   The "sprintf" %j format size modifier is now available with pre-C99
       The actual size used depends on the platform, so remains unportable.

   Close-on-exec flag set atomically
       When opening a file descriptor, perl now generally opens it with its
       close-on-exec flag already set, on platforms that support doing so.
       This improves thread safety, because it means that an "exec" initiated
       by one thread can no longer cause a file descriptor in the process of
       being opened by another thread to be accidentally passed to the
       executed program.

       Additionally, perl now sets the close-on-exec flag more reliably,
       whether it does so atomically or not.  Most file descriptors were
       getting the flag set, but some were being missed.

   String- and number-specific bitwise ops are no longer experimental
       The new string-specific ("&. |. ^. ~.") and number-specific ("& | ^ ~")
       bitwise operators introduced in Perl 5.22 that are available within the
       scope of "use feature 'bitwise'" are no longer experimental.  Because
       the number-specific ops are spelled the same way as the existing
       operators that choose their behaviour based on their operands, these
       operators must still be enabled via the "bitwise" feature, in either of
       these two ways:

           use feature "bitwise";

           use v5.28; # "bitwise" now included

       They are also now enabled by the -E command-line switch.

       The "bitwise" feature no longer emits a warning.  Existing code that
       disables the "experimental::bitwise" warning category that the feature
       previously used will continue to work.

       One caveat that module authors ought to be aware of is that the numeric
       operators now pass a fifth TRUE argument to overload methods.  Any
       methods that check the number of operands may croak if they do not
       expect so many.  XS authors in particular should be aware that this:

           SV *
           bitop_handler (lobj, robj, swap)

       may need to be changed to this:

           SV *
           bitop_handler (lobj, robj, swap, ...)

   Locales are now thread-safe on systems that support them
       These systems include Windows starting with Visual Studio 2005, and in
       POSIX 2008 systems.

       The implication is that you are now free to use locales and change them
       in a threaded environment.  Your changes affect only your thread.  See
       "Multi-threaded operation" in perllocale

   New read-only predefined variable "${^SAFE_LOCALES}"
       This variable is 1 if the Perl interpreter is operating in an
       environment where it is safe to use and change locales (see
       perllocale.)  This variable is true when the perl is unthreaded, or
       compiled in a platform that supports thread-safe locale operation (see
       previous item).


   [CVE-2017-12837] Heap buffer overflow in regular expression compiler
       Compiling certain regular expression patterns with the case-insensitive
       modifier could cause a heap buffer overflow and crash perl.  This has
       now been fixed.  [GH #16021]

   [CVE-2017-12883] Buffer over-read in regular expression parser
       For certain types of syntax error in a regular expression pattern, the
       error message could either contain the contents of a random, possibly
       large, chunk of memory, or could crash perl.  This has now been fixed.
       [GH #16025] <>

   [CVE-2017-12814] $ENV{$key} stack buffer overflow on Windows
       A possible stack buffer overflow in the %ENV code on Windows has been
       fixed by removing the buffer completely since it was superfluous
       anyway.  [GH #16051] <>

   Default Hash Function Change
       Perl 5.28.0 retires various older hash functions which are not viewed
       as sufficiently secure for use in Perl. We now support four general
       purpose hash functions, Siphash (2-4 and 1-3 variants), and  Zaphod32,
       and StadtX hash. In addition we support SBOX32 (a form of tabular
       hashing) for hashing short strings, in conjunction with any of the
       other hash functions provided.

       By default Perl is configured to support SBOX hashing of strings up to
       24 characters, in conjunction with StadtX hashing on 64 bit builds, and
       Zaphod32 hashing for 32 bit builds.

       You may control these settings with the following options to Configure:


       To disable SBOX hashing you can use


       And to set the maximum length to use SBOX32 hashing on with:


       The maximum length allowed is 256. There probably isn't much point in
       setting it higher than the default.

Incompatible Changes

   Subroutine attribute and signature order
       The experimental subroutine signatures feature has been changed so that
       subroutine attributes must now come before the signature rather than
       after. This is because attributes like ":lvalue" can affect the
       compilation of code within the signature, for example:

           sub f :lvalue ($a = do { $x = "abc"; return substr($x,0,1)}) { ...}

       Note that this the second time they have been flipped:

           sub f :lvalue ($a, $b) { ... }; # 5.20; 5.28 onwards
           sub f ($a, $b) :lvalue { ... }; # 5.22 - 5.26

   Comma-less variable lists in formats are no longer allowed
       Omitting the commas between variables passed to formats is no longer
       allowed.  This has been deprecated since Perl 5.000.

   The ":locked" and ":unique" attributes have been removed
       These have been no-ops and deprecated since Perl 5.12 and 5.10,

   "\N{}" with nothing between the braces is now illegal
       This has been deprecated since Perl 5.24.

   Opening the same symbol as both a file and directory handle is no longer
       Using "open()" and "opendir()" to associate both a filehandle and a
       dirhandle to the same symbol (glob or scalar) has been deprecated since
       Perl 5.10.

   Use of bare "<<" to mean "<<""" is no longer allowed
       Use of a bare terminator has been deprecated since Perl 5.000.

   Setting $/ to a reference to a non-positive integer no longer allowed
       This used to work like setting it to "undef", but has been deprecated
       since Perl 5.20.

   Unicode code points with values exceeding "IV_MAX" are now fatal
       This was deprecated since Perl 5.24.

   The "B::OP::terse" method has been removed
       Use "B::Concise::b_terse" instead.

   Use of inherited AUTOLOAD for non-methods is no longer allowed
       This was deprecated in Perl 5.004.

   Use of strings with code points over 0xFF is not allowed for bitwise string
       Code points over 0xFF do not make sense for bitwise operators and such
       an operation will now croak, except for a few remaining cases. See

       This was deprecated in Perl 5.24.

   Setting "${^ENCODING}" to a defined value is now illegal
       This has been deprecated since Perl 5.22 and a no-op since Perl 5.26.

   Backslash no longer escapes colon in PATH for the "-S" switch
       Previously the "-S" switch incorrectly treated backslash ("\") as an
       escape for colon when traversing the "PATH" environment variable.  [GH
       #15584] <>

   the -DH (DEBUG_H) misfeature has been removed
       On a perl built with debugging support, the "H" flag to the "-D"
       debugging option has been removed. This was supposed to dump hash
       values, but has been broken for many years.

   Yada-yada is now strictly a statement
       By the time of its initial stable release in Perl 5.12, the "..."
       (yada-yada) operator was explicitly intended to serve as a statement,
       not an expression.  However, the original implementation was confused
       on this point, leading to inconsistent parsing.  The operator was
       accidentally accepted in a few situations where it did not serve as a
       complete statement, such as

           ... . "foo";
           ... if $a < $b;

       The parsing has now been made consistent, permitting yada-yada only as
       a statement.  Affected code can use "do{...}" to put a yada-yada into
       an arbitrary expression context.

   Sort algorithm can no longer be specified
       Since Perl 5.8, the sort pragma has had subpragmata "_mergesort",
       "_quicksort", and "_qsort" that can be used to specify which algorithm
       perl should use to implement the sort builtin.  This was always
       considered a dubious feature that might not last, hence the underscore
       spellings, and they were documented as not being portable beyond Perl
       5.8.  These subpragmata have now been deleted, and any attempt to use
       them is an error.  The sort pragma otherwise remains, and the
       algorithm-neutral "stable" subpragma can be used to control sorting
       behaviour.  [GH #13234] <>

   Over-radix digits in floating point literals
       Octal and binary floating point literals used to permit any hexadecimal
       digit to appear after the radix point.  The digits are now restricted
       to those appropriate for the radix, as digits before the radix point
       always were.

   Return type of "unpackstring()"
       The return types of the C API functions "unpackstring()" and
       "unpack_str()" have changed from "I32" to "SSize_t", in order to
       accommodate datasets of more than two billion items.


   Use of "vec" on strings with code points above 0xFF is deprecated
       Such strings are represented internally in UTF-8, and "vec" is a bit-
       oriented operation that will likely give unexpected results on those

   Some uses of unescaped "{" in regexes are no longer fatal
       Perl 5.26.0 fatalized some uses of an unescaped left brace, but an
       exception was made at the last minute, specifically crafted to be a
       minimal change to allow GNU Autoconf to work.  That tool is heavily
       depended upon, and continues to use the deprecated usage.  Its use of
       an unescaped left brace is one where we have no intention of
       repurposing "{" to be something other than itself.

       That exception is now generalized to include various other such cases
       where the "{" will not be repurposed.

       Note that these uses continue to raise a deprecation message.

   Use of unescaped "{" immediately after a "(" in regular expression patterns
       is deprecated
       Using unescaped left braces is officially deprecated everywhere, but it
       is not enforced in contexts where their use does not interfere with
       expected extensions to the language.  A deprecation is added in this
       release when the brace appears immediately after an opening
       parenthesis.  Before this, even if the brace was part of a legal
       quantifier, it was not interpreted as such, but as the literal
       characters, unlike other quantifiers that follow a "(" which are
       considered errors.  Now, their use will raise a deprecation message,
       unless turned off.

   Assignment to $[ will be fatal in Perl 5.30
       Assigning a non-zero value to $[ has been deprecated since Perl 5.12,
       but was never given a deadline for removal.  This has now been
       scheduled for Perl 5.30.

   hostname() won't accept arguments in Perl 5.32
       Passing arguments to "Sys::Hostname::hostname()" was already
       deprecated, but didn't have a removal date.  This has now been
       scheduled for Perl 5.32.  [GH #14662]

   Module removals
       The following modules will be removed from the core distribution in a
       future release, and will at that time need to be installed from CPAN.
       Distributions on CPAN which require these modules will need to list
       them as prerequisites.

       The core versions of these modules will now issue "deprecated"-category
       warnings to alert you to this fact.  To silence these deprecation
       warnings, install the modules in question from CPAN.

       Note that these are (with rare exceptions) fine modules that you are
       encouraged to continue to use.  Their disinclusion from core primarily
       hinges on their necessity to bootstrapping a fully functional, CPAN-
       capable Perl installation, not usually on concerns over their design.

       Locale::Codes and its associated Country, Currency and Language modules

Performance Enhancements

       o   The start up overhead for creating regular expression patterns with
           Unicode properties ("\p{...}") has been greatly reduced in most

       o   Many string concatenation expressions are now considerably faster,
           due to the introduction internally of a "multiconcat" opcode which
           combines multiple concatenations, and optionally a "=" or ".=",
           into a single action. For example, apart from retrieving $s, $a and
           $b, this whole expression is now handled as a single op:

               $s .= "a=$a b=$b\n"

           As a special case, if the LHS of an assignment is a lexical
           variable or "my $s", the op itself handles retrieving the lexical
           variable, which is faster.

           In general, the more the expression includes a mix of constant
           strings and variable expressions, the longer the expression, and
           the more it mixes together non-utf8 and utf8 strings, the more
           marked the performance improvement. For example on a "x86_64"
           system, this code has been benchmarked running four times faster:

               my $s;
               my $a = "ab\x{100}cde";
               my $b = "fghij";
               my $c = "\x{101}klmn";

               for my $i (1..10_000_000) {
                   $s = "\x{100}wxyz";
                   $s .= "foo=$a bar=$b baz=$c";

           In addition, "sprintf" expressions which have a constant format
           containing only %s and "%%" format elements, and which have a fixed
           number of arguments, are now also optimised into a "multiconcat"

       o   The "ref()" builtin is now much faster in boolean context, since it
           no longer bothers to construct a temporary string like

       o   "keys()" in void and scalar contexts is now more efficient.

       o   The common idiom of comparing the result of index() with -1 is now
           specifically optimised,  e.g.

               if (index(...) != -1) { ... }

       o   "for()" loops and similar constructs are now more efficient in most

       o   File::Glob has been modified to remove unnecessary backtracking and
           recursion, thanks to Russ Cox. See
           <> for more details.

       o   The XS-level "SvTRUE()" API function is now more efficient.

       o   Various integer-returning ops are now more efficient in
           scalar/boolean context.

       o   Slightly improved performance when parsing stash names.  [GH
           #15689] <>

       o   Calls to "require" for an already loaded module are now slightly
           faster.  [GH #16175] <>

       o   The performance of pattern matching "[[:ascii:]]" and
           "[[:^ascii:]]" has been improved significantly except on EBCDIC

       o   Various optimizations have been applied to matching regular
           expression patterns, so under the right circumstances, significant
           performance gains may be noticed.  But in an application with many
           varied patterns, little overall improvement likely will be seen.

       o   Other optimizations have been applied to UTF-8 handling, but these
           are not typically a major factor in most applications.

Modules and Pragmata

       Key highlights in this release across several modules:

   Removal of use vars
       The usage of "use vars" has been discouraged since the introduction of
       "our" in Perl 5.6.0. Where possible the usage of this pragma has now
       been removed from the Perl source code.

       This had a slight effect (for the better) on the output of WARNING_BITS
       in B::Deparse.

   Use of DynaLoader changed to XSLoader in many modules
       XSLoader is more modern, and most modules already require perl 5.6 or
       greater, so no functionality is lost by switching. In some cases, we
       have also made changes to the local implementation that may not be
       reflected in the version on CPAN due to a desire to maintain more
       backwards compatibility.

   Updated Modules and Pragmata
       o   Archive::Tar has been upgraded from version 2.24 to 2.30.

           This update also handled CVE-2018-12015: directory traversal
           vulnerability.  [cpan #125523]

       o   arybase has been upgraded from version 0.12 to 0.15.

       o   Attribute::Handlers has been upgraded from version 0.99 to 1.01.

       o   attributes has been upgraded from version 0.29 to 0.33.

       o   B has been upgraded from version 1.68 to 1.74.

       o   B::Concise has been upgraded from version 0.999 to 1.003.

       o   B::Debug has been upgraded from version 1.24 to 1.26.

           NOTE: B::Debug is deprecated and may be removed from a future
           version of Perl.

       o   B::Deparse has been upgraded from version 1.40 to 1.48.

           It includes many bug fixes, and in particular, it now deparses
           variable attributes correctly:

               my $x :foo;  # used to deparse as
                            # 'attributes'->import('main', \$x, 'foo'), my $x;

       o   base has been upgraded from version 2.25 to 2.27.

       o   bignum has been upgraded from version 0.47 to 0.49.

       o   blib has been upgraded from version 1.06 to 1.07.

       o   bytes has been upgraded from version 1.05 to 1.06.

       o   Carp has been upgraded from version 1.42 to 1.50.

           If a package on the call stack contains a constant named "ISA",
           Carp no longer throws a "Not a GLOB reference" error.

           Carp, when generating stack traces, now attempts to work around
           longstanding bugs resulting from Perl's non-reference-counted
           stack.  [GH #9282] <>

           Carp has been modified to avoid assuming that objects cannot be
           overloaded without the overload module loaded (this can happen with
           objects created by XS modules).  Previously, infinite recursion
           would result if an XS-defined overload method itself called Carp.
           [GH #16407] <>

           Carp now avoids using "overload::StrVal", partly because older
           versions of overload (included with perl 5.14 and earlier) load
           Scalar::Util at run time, which will fail if Carp has been invoked
           after a syntax error.

       o   charnames has been upgraded from version 1.44 to 1.45.

       o   Compress::Raw::Zlib has been upgraded from version 2.074 to 2.076.

           This addresses a security vulnerability in older versions of the
           'zlib' library (which is bundled with Compress-Raw-Zlib).

       o   Config::Extensions has been upgraded from version 0.01 to 0.02.

       o   Config::Perl::V has been upgraded from version 0.28 to 0.29.

       o   CPAN has been upgraded from version 2.18 to 2.20.

       o   Data::Dumper has been upgraded from version 2.167 to 2.170.

           Quoting of glob names now obeys the Useqq option [GH #13274]

           Attempts to set an option to "undef" through a combined
           getter/setter method are no longer mistaken for getter calls [GH
           #12135] <>.

       o   Devel::Peek has been upgraded from version 1.26 to 1.27.

       o   Devel::PPPort has been upgraded from version 3.35 to 3.40.

           Devel::PPPort has moved from cpan-first to perl-first maintenance

           Primary responsibility for the code in Devel::PPPort has moved into
           core perl.  In a practical sense there should be no change except
           that hopefully it will stay more up to date with changes made to
           symbols in perl, rather than needing to be updated after the fact.

       o   Digest::SHA has been upgraded from version 5.96 to 6.01.

       o   DirHandle has been upgraded from version 1.04 to 1.05.

       o   DynaLoader has been upgraded from version 1.42 to 1.45.

           Its documentation now shows the use of "__PACKAGE__" and direct
           object syntax [GH #16190]

       o   Encode has been upgraded from version 2.88 to 2.97.

       o   encoding has been upgraded from version 2.19 to 2.22.

       o   Errno has been upgraded from version 1.28 to 1.29.

       o   experimental has been upgraded from version 0.016 to 0.019.

       o   Exporter has been upgraded from version 5.72 to 5.73.

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

       o   ExtUtils::Constant has been upgraded from version 0.23 to 0.25.

       o   ExtUtils::Embed has been upgraded from version 1.34 to 1.35.

       o   ExtUtils::Install has been upgraded from version 2.04 to 2.14.

       o   ExtUtils::MakeMaker has been upgraded from version 7.24 to 7.34.

       o   ExtUtils::Miniperl has been upgraded from version 1.06 to 1.08.

       o   ExtUtils::ParseXS has been upgraded from version 3.34 to 3.39.

       o   ExtUtils::Typemaps has been upgraded from version 3.34 to 3.38.

       o   ExtUtils::XSSymSet has been upgraded from version 1.3 to 1.4.

       o   feature has been upgraded from version 1.47 to 1.52.

       o   fields has been upgraded from version 2.23 to 2.24.

       o   File::Copy has been upgraded from version 2.32 to 2.33.

           It will now use the sub-second precision variant of utime()
           supplied by Time::HiRes where available.  [GH #16225]

       o   File::Fetch has been upgraded from version 0.52 to 0.56.

       o   File::Glob has been upgraded from version 1.28 to 1.31.

       o   File::Path has been upgraded from version 2.12_01 to 2.15.

       o   File::Spec and Cwd have been upgraded from version 3.67 to 3.74.

       o   File::stat has been upgraded from version 1.07 to 1.08.

       o   FileCache has been upgraded from version 1.09 to 1.10.

       o   Filter::Simple has been upgraded from version 0.93 to 0.95.

       o   Filter::Util::Call has been upgraded from version 1.55 to 1.58.

       o   GDBM_File has been upgraded from version 1.15 to 1.17.

           Its documentation now explains that "each" and "delete" don't mix
           in hashes tied to this module [GH #12894]

           It will now retry opening with an acceptable block size if asking
           gdbm to default the block size failed [GH #13232]

       o   Getopt::Long has been upgraded from version 2.49 to 2.5.

       o   Hash::Util::FieldHash has been upgraded from version 1.19 to 1.20.

       o   I18N::Langinfo has been upgraded from version 0.13 to 0.17.

           This module is now available on all platforms, emulating the system
           nl_langinfo(3) on systems that lack it.  Some caveats apply, as
           detailed in its documentation, the most severe being that, except
           for MS Windows, the "CODESET" item is not implemented on those
           systems, always returning "".

           It now sets the UTF-8 flag in its returned scalar if the string
           contains legal non-ASCII UTF-8, and the locale is UTF-8 [GH #15131]

           This update also fixes a bug in which the underlying locale was
           ignored for the "RADIXCHAR" (always was returned as a dot) and the
           "THOUSEP" (always empty).  Now the locale-appropriate values are

       o   I18N::LangTags has been upgraded from version 0.42 to 0.43.

       o   if has been upgraded from version 0.0606 to 0.0608.

       o   IO has been upgraded from version 1.38 to 1.39.

       o   IO::Socket::IP has been upgraded from version 0.38 to 0.39.

       o   IPC::Cmd has been upgraded from version 0.96 to 1.00.

       o   JSON::PP has been upgraded from version 2.27400_02 to 2.97001.

       o   The "libnet" distribution has been upgraded from version 3.10 to

       o   List::Util has been upgraded from version 1.46_02 to 1.49.

       o   Locale::Codes has been upgraded from version 3.42 to 3.56.

           NOTE: Locale::Codes scheduled to be removed from core in Perl 5.30.

       o   Locale::Maketext has been upgraded from version 1.28 to 1.29.

       o   Math::BigInt has been upgraded from version 1.999806 to 1.999811.

       o   Math::BigInt::FastCalc has been upgraded from version 0.5005 to

       o   Math::BigRat has been upgraded from version 0.2611 to 0.2613.

       o   Module::CoreList has been upgraded from version 5.20170530 to

       o   mro has been upgraded from version 1.20 to 1.22.

       o   Net::Ping has been upgraded from version 2.55 to 2.62.

       o   NEXT has been upgraded from version 0.67 to 0.67_01.

       o   ODBM_File has been upgraded from version 1.14 to 1.15.

       o   Opcode has been upgraded from version 1.39 to 1.43.

       o   overload has been upgraded from version 1.28 to 1.30.

       o   PerlIO::encoding has been upgraded from version 0.25 to 0.26.

       o   PerlIO::scalar has been upgraded from version 0.26 to 0.29.

       o   PerlIO::via has been upgraded from version 0.16 to 0.17.

       o   Pod::Functions has been upgraded from version 1.11 to 1.13.

       o   Pod::Html has been upgraded from version 1.2202 to 1.24.

           A title for the HTML document will now be automatically generated
           by default from a "NAME" section in the POD document, as it used to
           be before the module was rewritten to use Pod::Simple::XHTML to do
           the core of its job [GH #11954]

       o   Pod::Perldoc has been upgraded from version 3.28 to 3.2801.

       o   The "podlators" distribution has been upgraded from version 4.09 to

           Man page references and function names now follow the Linux man
           page formatting standards, instead of the Solaris standard.

       o   POSIX has been upgraded from version 1.76 to 1.84.

           Some more cautions were added about using locale-specific functions
           in threaded applications.

       o   re has been upgraded from version 0.34 to 0.36.

       o   Scalar::Util has been upgraded from version 1.46_02 to 1.50.

       o   SelfLoader has been upgraded from version 1.23 to 1.25.

       o   Socket has been upgraded from version 2.020_03 to 2.027.

       o   sort has been upgraded from version 2.02 to 2.04.

       o   Storable has been upgraded from version 2.62 to 3.08.

       o   Sub::Util has been upgraded from version 1.48 to 1.49.

       o   subs has been upgraded from version 1.02 to 1.03.

       o   Sys::Hostname has been upgraded from version 1.20 to 1.22.

       o   Term::ReadLine has been upgraded from version 1.16 to 1.17.

       o   Test has been upgraded from version 1.30 to 1.31.

       o   Test::Harness has been upgraded from version 3.38 to 3.42.

       o   Test::Simple has been upgraded from version 1.302073 to 1.302133.

       o   threads has been upgraded from version 2.15 to 2.22.

           The documentation now better describes the problems that arise when
           returning values from threads, and no longer warns about creating
           threads in "BEGIN" blocks.  [GH #11563]

       o   threads::shared has been upgraded from version 1.56 to 1.58.

       o   Tie::Array has been upgraded from version 1.06 to 1.07.

       o   Tie::StdHandle has been upgraded from version 4.4 to 4.5.

       o   Time::gmtime has been upgraded from version 1.03 to 1.04.

       o   Time::HiRes has been upgraded from version 1.9741 to 1.9759.

       o   Time::localtime has been upgraded from version 1.02 to 1.03.

       o   Time::Piece has been upgraded from version 1.31 to 1.3204.

       o   Unicode::Collate has been upgraded from version 1.19 to 1.25.

       o   Unicode::Normalize has been upgraded from version 1.25 to 1.26.

       o   Unicode::UCD has been upgraded from version 0.68 to 0.70.

           The function "num" now accepts an optional parameter to help in
           diagnosing error returns.

       o   User::grent has been upgraded from version 1.01 to 1.02.

       o   User::pwent has been upgraded from version 1.00 to 1.01.

       o   utf8 has been upgraded from version 1.19 to 1.21.

       o   vars has been upgraded from version 1.03 to 1.04.

       o   version has been upgraded from version 0.9917 to 0.9923.

       o   VMS::DCLsym has been upgraded from version 1.08 to 1.09.

       o   VMS::Stdio has been upgraded from version 2.41 to 2.44.

       o   warnings has been upgraded from version 1.37 to 1.42.

           It now includes new functions with names ending in "_at_level",
           allowing callers to specify the exact call frame.  [GH #16257]

       o   XS::Typemap has been upgraded from version 0.15 to 0.16.

       o   XSLoader has been upgraded from version 0.27 to 0.30.

           Its documentation now shows the use of "__PACKAGE__", and direct
           object syntax for example "DynaLoader" usage [GH #16190]

           Platforms that use "mod2fname" to edit the names of loadable
           libraries now look for bootstrap (.bs) files under the correct,
           non-edited name.

   Removed Modules and Pragmata
       o   The "VMS::stdio" compatibility shim has been removed.


   Changes to Existing Documentation
       We have attempted to update the documentation to reflect the changes
       listed in this document.  If you find any we have missed, send email to <>.

       Additionally, the following selected changes have been made:


       o   The API functions "perl_parse()", "perl_run()", and
           "perl_destruct()" are now documented comprehensively, where
           previously the only documentation was a reference to the perlembed

       o   The documentation of "newGIVENOP()" has been belatedly updated to
           account for the removal of lexical $_.

       o   The API functions "newCONSTSUB()" and "newCONSTSUB_flags()" are
           documented much more comprehensively than before.


       o   The section "Truth and Falsehood" in perlsyn has been moved into


       o   The description of the conditions under which "DB::sub()" will be
           called has been clarified.  [GH #16055]


       o   "Variable length lookbehind not implemented in regex m/%s/" in

           This now gives more ideas as to workarounds to the issue that was
           introduced in Perl 5.18 (but not documented explicitly in its
           perldelta) for the fact that some Unicode "/i" rules cause a few
           sequences such as


           to be considered variable length, and hence disallowed.

       o   "Use of state $_ is experimental" in perldiag

           This entry has been removed, as the experimental support of this
           construct was removed in perl 5.24.0.

       o   The diagnostic "Initialization of state variables in list context
           currently forbidden" has changed to "Initialization of state
           variables in list currently forbidden", because list-context
           initialization of single aggregate state variables is now


       o   The examples in perlembed have been made more portable in the way
           they exit, and the example that gets an exit code from the embedded
           Perl interpreter now gets it from the right place.  The examples
           that pass a constructed argv to Perl now show the mandatory null

       o   An example in perlembed used the string value of "ERRSV" as a
           format string when calling croak().  If that string contains format
           codes such as %s this could crash the program.

           This has been changed to a call to croak_sv().

           An alternative could have been to supply a trivial format string:

             croak("%s", SvPV_nolen(ERRSV));

           or as a special case for "ERRSV" simply:



       o   There is now a note that warnings generated by built-in functions
           are documented in perldiag and warnings.  [GH #12642]

       o   The documentation for the "exists" operator no longer says that
           autovivification behaviour "may be fixed in a future release".
           We've determined that we're not going to change the default
           behaviour.  [GH #15231]

       o   A couple of small details in the documentation for the "bless"
           operator have been clarified.  [GH #14684]

       o   The description of @INC hooks in the documentation for "require"
           has been corrected to say that filter subroutines receive a useless
           first argument.  [GH #12569]

       o   The documentation of "ref" has been rewritten for clarity.

       o   The documentation of "use" now explains what syntactically
           qualifies as a version number for its module version checking

       o   The documentation of "warn" has been updated to reflect that since
           Perl 5.14 it has treated complex exception objects in a manner
           equivalent to "die".  [GH #13641]

       o   The documentation of "die" and "warn" has been revised for clarity.

       o   The documentation of "each" has been improved, with a slightly more
           explicit description of the sharing of iterator state, and with
           caveats regarding the fragility of while-each loops.  [GH #16334]

       o   Clarification to "require" was added to explain the differences

               require Foo::Bar;
               require "Foo/";


       o   The precise rules for identifying "smoke-me" branches are now


       o   The section on reference counting in perlguts has been heavily
           revised, to describe references in the way a programmer needs to
           think about them rather than in terms of the physical data

       o   Improve documentation related to UTF-8 multibytes.


       o   The internal functions "newXS_len_flags()" and "newATTRSUB_x()" are
           now documented.


       o   The documentation about "DESTROY" methods has been corrected,
           updated, and revised, especially in regard to how they interact
           with exceptions.  [GH #14083]


       o   The description of the "x" operator in perlop has been clarified.
           [GH #16253] <>

       o   perlop has been updated to note that "qw"'s whitespace rules differ
           from that of "split"'s in that only ASCII whitespace is used.

       o   The general explanation of operator precedence and associativity
           has been corrected and clarified.  [GH #15153]

       o   The documentation for the "\" referencing operator now explains the
           unusual context that it supplies to its operand.  [GH #15932]


       o   Clarifications on metacharacters and character classes


       o   Clarify metacharacters.


       o   Clarify the differences between -M and -m.  [GH #15998]


       o   The documentation about set-id scripts has been updated and
           revised.  [GH #10289] <>

       o   A section about using "sudo" to run Perl scripts has been added.


       o   The section "Truth and Falsehood" in perlsyn has been removed from
           that document, where it didn't belong, and merged into the existing
           paragraph on the same topic in perldata.

       o   The means to disambiguate between code blocks and hash
           constructors, already documented in perlref, are now documented in
           perlsyn too.  [GH #15918]


       o   perluniprops has been updated to note that "\p{Word}" now includes
           code points matching the "\p{Join_Control}" property.  The change
           to the property was made in Perl 5.18, but not documented until
           now.  There are currently only two code points that match this
           property U+200C (ZERO WIDTH NON-JOINER) and U+200D (ZERO WIDTH

       o   For each binary table or property, the documentation now includes
           which characters in the range "\x00-\xFF" it matches, as well as a
           list of the first few ranges of code points matched above that.


       o   The entry for $+ in perlvar has been expanded upon to describe
           handling of multiply-named capturing groups.

       perlfunc, perlop, perlsyn

       o   In various places, improve the documentation of the special cases
           in the condition expression of a while loop, such as implicit
           "defined" and assignment to $_.  [GH #16334]


       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   Can't "goto" into a "given" block

           (F) A "goto" statement was executed to jump into the middle of a
           "given" block.  You can't get there from here.  See "goto" in

       o   Can't "goto" into a binary or list expression

           Use of "goto" to jump into the parameter of a binary or list
           operator has been prohibited, to prevent crashes and stack
           corruption.  [GH #15914]

           You may only enter the first argument of an operator that takes a
           fixed number of arguments, since this is a case that will not cause
           stack corruption.  [GH #16415]

       New Warnings

       o   Old package separator used in string

           (W syntax) You used the old package separator, "'", in a variable
           named inside a double-quoted string; e.g., "In $name's house".
           This is equivalent to "In $name::s house".  If you meant the
           former, put a backslash before the apostrophe ("In $name\'s

       o   "Locale '%s' contains (at least) the following characters which
           have unexpected meanings: %s  The Perl program will use the
           expected meanings" in perldiag

   Changes to Existing Diagnostics
       o   A false-positive warning that was issued when using a numerically-
           quantified sub-pattern in a recursive regex has been silenced. [GH
           #16106] <>

       o   The warning about useless use of a concatenation operator in void
           context is now generated for expressions with multiple
           concatenations, such as "$a.$b.$c", which used to mistakenly not
           warn.  [GH #3990] <>

       o   Warnings that a variable or subroutine "masks earlier declaration
           in same ...", or that an "our" variable has been redeclared, have
           been moved to a new warnings category "shadow".  Previously they
           were in category "misc".

       o   The deprecation warning from "Sys::Hostname::hostname()" saying
           that it doesn't accept arguments now states the Perl version in
           which the warning will be upgraded to an error.  [GH #14662]

       o   The perldiag entry for the error regarding a set-id script has been
           expanded to make clear that the error is reporting a specific
           security vulnerability, and to advise how to fix it.

       o   The "Unable to flush stdout" error message was missing a trailing
           newline. [debian #875361]

Utility Changes

       o   "--help" and "--version" options have been added.

Configuration and Compilation

       o   C89 requirement

           Perl has been documented as requiring a C89 compiler to build since
           October 1998.  A variety of simplifications have now been made to
           Perl's internals to rely on the features specified by the C89
           standard. We believe that this internal change hasn't altered the
           set of platforms that Perl builds on, but please report a bug if
           Perl now has new problems building on your platform.

       o   On GCC, "-Werror=pointer-arith" is now enabled by default,
           disallowing arithmetic on void and function pointers.

       o   Where an HTML version of the documentation is installed, the HTML
           documents now use relative links to refer to each other.  Links
           from the index page of perlipc to the individual section documents
           are now correct.  [GH #11941]

       o   lib/unicore/mktables now correctly canonicalizes the names of the
           dependencies stored in the files it generates.

           regen/, unlike the other regen/*.pl scripts, used $0
           to name itself in the dependencies stored in the files it
           generates.  It now uses a literal so that the path stored in the
           generated files doesn't depend on how regen/ is

           This lack of canonical names could cause test failures in
           t/porting/regen.t.  [GH #16446]

       o   New probes



       o   Testing of the XS-APItest directory is now done in parallel, where

       o   Perl now includes a default .travis.yml file for Travis CI testing
           on github mirrors.  [GH #14558]

       o   The watchdog timer count in re/pat_psycho.t can now be overridden.

           This test can take a long time to run, so there is a timer to keep
           this in check (currently, 5 minutes). This commit adds checking the
           environment variable "PERL_TEST_TIME_OUT_FACTOR"; if set, the time
           out setting is multiplied by its value.

       o   harness no longer waits for 30 seconds when running t/io/openpid.t.
           [GH #13535] <> [GH
           #16420] <>


       For the past few years we have released perl using three different
       archive formats: bzip (".bz2"), LZMA2 (".xz") and gzip (".gz"). Since
       xz compresses better and decompresses faster, and gzip is more
       compatible and uses less memory, we have dropped the ".bz2" archive
       format with this release.  (If this poses a problem, do let us know;
       see "Reporting Bugs", below.)

Platform Support

   Discontinued Platforms
       PowerUX / Power MAX OS
           Compiler hints and other support for these apparently long-defunct
           platforms has been removed.

   Platform-Specific Notes
           Compilation on CentOS 5 is now fixed.

           A build with the quadmath library can now be done on Cygwin.

           Perl now correctly uses reentrant functions, like "asctime_r", on
           versions of Darwin that have support for them.

           FreeBSD's /usr/share/mk/ specifies "-O2" for architectures
           other than ARM and MIPS. By default, perl is now compiled with the
           same optimization levels.

       VMS Several fix-ups for, marking function VMS has (or
           doesn't have).

           CRTL features can now be set by embedders before invoking Perl by
           using the "decc$feature_set" and "decc$feature_set_value"
           functions.  Previously any attempt to set features after image
           initialization were ignored.

           o   Support for compiling perl on Windows using Microsoft Visual
               Studio 2017 (containing Visual C++ 14.1) has been added.

           o   Visual C++ compiler version detection has been improved to work
               on non-English language systems.

           o   We now set $Config{libpth} correctly for 64-bit builds using
               Visual C++ versions earlier than 14.1.

Internal Changes

       o   A new optimisation phase has been added to the compiler,
           "optimize_optree()", which does a top-down scan of a complete
           optree just before the peephole optimiser is run. This phase is not
           currently hookable.

       o   An "OP_MULTICONCAT" op has been added. At "optimize_optree()" time,
           a chain of "OP_CONCAT" and "OP_CONST" ops, together optionally with
           an "OP_STRINGIFY" and/or "OP_SASSIGN", are combined into a single
           "OP_MULTICONCAT" op. The op is of type "UNOP_AUX", and the aux
           array contains the argument count, plus a pointer to a constant
           string and a set of segment lengths. For example with

               my $x = "foo=$foo, bar=$bar\n";

           the constant string would be "foo=, bar=\n" and the segment lengths
           would be (4,6,1). If the string contains characters such as "\x80",
           whose representation changes under utf8, two sets of strings plus
           lengths are precomputed and stored.

       o   Direct access to "PL_keyword_plugin" is not safe in the presence of
           multithreading. A new "wrap_keyword_plugin" function has been added
           to allow XS modules to safely define custom keywords even when
           loaded from a thread, analogous to "PL_check" / "wrap_op_checker".

       o   The "PL_statbuf" interpreter variable has been removed.

       o   The deprecated function "to_utf8_case()", accessible from XS code,
           has been removed.

       o   A new function "is_utf8_invariant_string_loc()" has been added that
           is like "is_utf8_invariant_string()" but takes an extra pointer
           parameter into which is stored the location of the first variant
           character, if any are found.

       o   A new function, "Perl_langinfo()" has been added.  It is an
           (almost) drop-in replacement for the system nl_langinfo(3), but
           works on platforms that lack that; as well as being more thread-
           safe, and hiding some gotchas with locale handling from the caller.
           Code that uses this, needn't use localeconv(3) (and be affected by
           the gotchas) to find the decimal point, thousands separator, or
           currency symbol.  See "Perl_langinfo" in perlapi.

       o   A new API function "sv_rvunweaken()" has been added to complement
           "sv_rvweaken()".  The implementation was taken from "unweaken" in

       o   A new flag, "SORTf_UNSTABLE", has been added. This will allow a
           future commit to make mergesort unstable when the user specifies
           Xno sort stableX, since it has been decided that mergesort should
           remain stable by default.

       o   XS modules can now automatically get reentrant versions of system
           functions on threaded perls.

           By adding

               #define PERL_REENTRANT

           near the beginning of an "XS" file, it will be compiled so that
           whatever reentrant functions perl knows about on that system will
           automatically and invisibly be used instead of the plain, non-
           reentrant versions.  For example, if you write "getpwnam()" in your
           code, on a system that has "getpwnam_r()" all calls to the former
           will be translated invisibly into the latter.  This does not happen
           except on threaded perls, as they aren't needed otherwise.  Be
           aware that which functions have reentrant versions varies from
           system to system.

       o   The "PERL_NO_OP_PARENT" build define is no longer supported, which
           means that perl is now always built with "PERL_OP_PARENT" enabled.

       o   The format and content of the non-utf8 transliteration table
           attached to the "op_pv" field of "OP_TRANS"/"OP_TRANSR" ops has
           changed. It's now a "struct OPtrans_map".

       o   A new compiler "#define", "dTHX_DEBUGGING". has been added.  This
           is useful for XS or C code that only need the thread context
           because their debugging statements that get compiled only under
           "-DDEBUGGING" need one.

       o   A new API function "Perl_setlocale" in perlapi has been added.

       o   "sync_locale" in perlapi has been revised to return a boolean as to
           whether the system was using the global locale or not.

       o   A new kind of magic scalar, called a "nonelem" scalar, has been
           introduced.  It is stored in an array to denote a non-existent
           element, whenever such an element is accessed in a potential lvalue
           context.  It replaces the existing "defelem" (deferred element)
           magic wherever this is possible, being significantly more
           efficient.  This means that "some_sub($sparse_array[$nonelem])" no
           longer has to create a new magic defelem scalar each time, as long
           as the element is within the array.

           It partially fixes the rare bug of deferred elements getting out of
           synch with their arrays when the array is shifted or unshifted.
           [GH #16364] <>

Selected Bug Fixes

       o   List assignment ("aassign") could in some rare cases allocate an
           entry on the mortals stack and leave the entry uninitialized,
           leading to possible crashes.  [GH #16017]

       o   Attempting to apply an attribute to an "our" variable where a
           function of that name already exists could result in a NULL pointer
           being supplied where an SV was expected, crashing perl.  [perl
           #131597] <>

       o   "split ' '" now correctly handles the argument being split when in
           the scope of the "unicode_strings" feature. Previously, when a
           string using the single-byte internal representation contained
           characters that are whitespace by Unicode rules but not by ASCII
           rules, it treated those characters as part of fields rather than as
           field separators.  [GH #15904]

       o   Several built-in functions previously had bugs that could cause
           them to write to the internal stack without allocating room for the
           item being written. In rare situations, this could have led to a
           crash. These bugs have now been fixed, and if any similar bugs are
           introduced in future, they will be detected automatically in
           debugging builds.

           These internal stack usage checks introduced are also done by the
           "entersub" operator when calling XSUBs.  This means we can report
           which XSUB failed to allocate enough stack space.  [GH #16126]

       o   Using a symbolic ref with postderef syntax as the key in a hash
           lookup was yielding an assertion failure on debugging builds.  [GH
           #16029] <>

       o   Array and hash variables whose names begin with a caret now admit
           indexing inside their curlies when interpolated into strings, as in
           "${^CAPTURE[0]}" to index "@{^CAPTURE}".  [GH #16050]

       o   Fetching the name of a glob that was previously UTF-8 but wasn't
           any longer would return that name flagged as UTF-8.  [GH #15971]

       o   The perl "sprintf()" function (via the underlying C function
           "Perl_sv_vcatpvfn_flags()") has been heavily reworked to fix many
           minor bugs, including the integer wrapping of large width and
           precision specifiers and potential buffer overruns. It has also
           been made faster in many cases.

       o   Exiting from an "eval", whether normally or via an exception, now
           always frees temporary values (possibly calling destructors) before
           setting $@. For example:

               sub DESTROY { eval { die "died in DESTROY"; } }
               eval { bless []; };
               # $@ used to be equal to "died in DESTROY" here; it's now "".

       o   Fixed a duplicate symbol failure with "-flto -mieee-fp" builds.
           pp.c defined "_LIB_VERSION" which "-lieee" already defines.  [GH
           #16086] <>

       o   The tokenizer no longer consumes the exponent part of a floating
           point number if it's incomplete.  [GH #16073]

       o   On non-threaded builds, for "m/$null/" where $null is an empty
           string is no longer treated as if the "/o" flag was present when
           the previous matching match operator included the "/o" flag.  The
           rewriting used to implement this behavior could confuse the
           interpreter.  This matches the behaviour of threaded builds.  [GH
           #14668] <>

       o   Parsing a "sub" definition could cause a use after free if the
           "sub" keyword was followed by whitespace including newlines (and
           comments.)  [GH #16097]

       o   The tokenizer now correctly adjusts a parse pointer when skipping
           whitespace in a "${identifier}" construct.  [perl #131949]

       o   Accesses to "${^LAST_FH}" no longer assert after using any of a
           variety of I/O operations on a non-glob.  [GH #15372]

       o   The XS-level "Copy()", "Move()", "Zero()" macros and their variants
           now assert if the pointers supplied are "NULL".  ISO C considers
           supplying NULL pointers to the functions these macros are built
           upon as undefined behaviour even when their count parameters are
           zero.  Based on these assertions and the original bug report three
           macro calls were made conditional.  [GH #16079]
           <> [GH #16112]

       o   Only the "=" operator is permitted for defining defaults for
           parameters in subroutine signatures.  Previously other assignment
           operators, e.g. "+=", were also accidentally permitted.  [GH
           #16084] <>

       o   Package names are now always included in ":prototype" warnings
           [perl #131833]

       o   The "je_old_stack_hwm" field, previously only found in the "jmpenv"
           structure on debugging builds, has been added to non-debug builds
           as well. This fixes an issue with some CPAN modules caused by the
           size of this structure varying between debugging and non-debugging
           builds.  [GH #16122] <>

       o   The arguments to the "ninstr()" macro are now correctly

       o   A NULL pointer dereference in the "S_regmatch()" function has been
           fixed.  [perl #132017]

       o   Calling exec PROGRAM LIST with an empty "LIST" has been fixed.
           This should call "execvp()" with an empty "argv" array (containing
           only the terminating "NULL" pointer), but was instead just
           returning false (and not setting $!).  [GH #16075]

       o   The "gv_fetchmeth_sv" C function stopped working properly in Perl
           5.22 when fetching a constant with a UTF-8 name if that constant
           subroutine was stored in the stash as a simple scalar reference,
           rather than a full typeglob.  This has been corrected.

       o   Single-letter debugger commands followed by an argument which
           starts with punctuation  (e.g. "p$^V" and "x@ARGV") now work again.
           They had been wrongly requiring a space between the command and the
           argument.  [GH #13342] <>

       o   splice now throws an exception ("Modification of a read-only value
           attempted") when modifying a read-only array.  Until now it had
           been silently modifying the array.  The new behaviour is consistent
           with the behaviour of push and unshift.  [GH #15923]

       o   "stat()", "lstat()", and file test operators now fail if given a
           filename containing a nul character, in the same way that "open()"
           already fails.

       o   "stat()", "lstat()", and file test operators now reliably set $!
           when failing due to being applied to a closed or otherwise invalid
           file handle.

       o   File test operators for Unix permission bits that don't exist on a
           particular platform, such as "-k" (sticky bit) on Windows, now
           check that the file being tested exists before returning the
           blanket false result, and yield the appropriate errors if the
           argument doesn't refer to a file.

       o   Fixed a 'read before buffer' overrun when parsing a range starting
           with "\N{}" at the beginning of the character set for the
           transliteration operator.  [GH #16189]

       o   Fixed a leaked scalar when parsing an empty "\N{}" at compile-time.
           [GH #16189] <>

       o   Calling "do $path" on a directory or block device now yields a
           meaningful error code in $!.  [GH #14841]

       o   Regexp substitution using an overloaded replacement value that
           provides a tainted stringification now correctly taints the
           resulting string.  [GH #12495]

       o   Lexical sub declarations in "do" blocks such as "do { my sub lex;
           123 }" could corrupt the stack, erasing items already on the stack
           in the enclosing statement.  This has been fixed.  [GH #16243]

       o   "pack" and "unpack" can now handle repeat counts and lengths that
           exceed two billion.  [GH #13179]

       o   Digits past the radix point in octal and binary floating point
           literals now have the correct weight on platforms where a floating
           point significand doesn't fit into an integer type.

       o   The canonical truth value no longer has a spurious special meaning
           as a callable subroutine.  It used to be a magic placeholder for a
           missing "import" or "unimport" method, but is now treated like any
           other string 1.  [GH #14902]

       o   "system" now reduces its arguments to strings in the parent
           process, so any effects of stringifying them (such as overload
           methods being called or warnings being emitted) are visible in the
           way the program expects.  [GH #13561]

       o   The "readpipe()" built-in function now checks at compile time that
           it has only one parameter expression, and puts it in scalar
           context, thus ensuring that it doesn't corrupt the stack at
           runtime.  [GH #2793] <>

       o   "sort" now performs correct reference counting when aliasing $a and
           $b, thus avoiding premature destruction and leakage of scalars if
           they are re-aliased during execution of the sort comparator.  [GH
           #11422] <>

       o   "reverse" with no operand, reversing $_ by default, is no longer in
           danger of corrupting the stack.  [GH #16291]

       o   "exec", "system", et al are no longer liable to have their argument
           lists corrupted by reentrant calls and by magic such as tied
           scalars.  [GH #15660] <>

       o   Perl's own "malloc" no longer gets confused by attempts to allocate
           more than a gigabyte on a 64-bit platform.  [GH #13273]

       o   Stacked file test operators in a sort comparator expression no
           longer cause a crash.  [GH #15626]

       o   An identity "tr///" transformation on a reference is no longer
           mistaken for that reference for the purposes of deciding whether it
           can be assigned to.  [GH #15812]

       o   Lengthy hexadecimal, octal, or binary floating point literals no
           longer cause undefined behaviour when parsing digits that are of
           such low significance that they can't affect the floating point
           value.  [GH #16114] <>

       o   "open $$scalarref..." and similar invocations no longer leak the
           file handle.  [GH #12593]

       o   Some convoluted kinds of regexp no longer cause an arithmetic
           overflow when compiled.  [GH #16113]

       o   The default typemap, by avoiding "newGVgen", now no longer leaks
           when XSUBs return file handles ("PerlIO *" or "FILE *").  [GH
           #12593] <>

       o   Creating a "BEGIN" block as an XS subroutine with a prototype no
           longer crashes because of the early freeing of the subroutine.

       o   The "printf" format specifier "%.0f" no longer rounds incorrectly
           [GH #9125] <>, and now
           shows the correct sign for a negative zero.

       o   Fixed an issue where the error "Scalar value @arrayname[0] better
           written as $arrayname" would give an error "Cannot printf Inf with
           'c'" when arrayname starts with "Inf".  [GH #16335]

       o   The Perl implementation of "getcwd()" in "Cwd" in the PathTools
           distribution now behaves the same as XS implementation on errors:
           it returns an error, and sets $!.  [GH #16338]

       o   Vivify array elements when putting them on the stack.  Fixes [GH
           #5310] <> (reported in
           April 2002).

       o   Fixed parsing of braced subscript after parens. Fixes [GH #4688]
           <> (reported in December

       o   "tr/non_utf8/long_non_utf8/c" could give the wrong results when the
           length of the replacement character list was greater than 0x7fff.

       o   "tr/non_utf8/non_utf8/cd" failed to add the implied
           "\x{100}-\x{7fffffff}" to the search character list.

       o   Compilation failures within "perl-within-perl" constructs, such as
           with string interpolation and the right part of "s///e", now cause
           compilation to abort earlier.

           Previously compilation could continue in order to report other
           errors, but the failed sub-parse could leave partly parsed
           constructs on the parser shift-reduce stack, confusing the parser,
           leading to perl crashes.  [GH #14739]

       o   On threaded perls where the decimal point (radix) character is not
           a dot, it has been possible for a race to occur between threads
           when one needs to use the real radix character (such as with
           "sprintf").  This has now been fixed by use of a mutex on systems
           without thread-safe locales, and the problem just doesn't come up
           on those with thread-safe locales.

       o   Errors while compiling a regex character class could sometime
           trigger an assertion failure.  [GH #16172]


       Perl 5.28.0 represents approximately 13 months of development since
       Perl 5.26.0 and contains approximately 730,000 lines of changes across
       2,200 files from 77 authors.

       Excluding auto-generated files, documentation and release tools, there
       were approximately 580,000 lines of changes to 1,300 .pm, .t, .c and .h

       Perl continues to flourish into its fourth decade thanks to a vibrant
       community of users and developers. The following people are known to
       have contributed the improvements that became Perl 5.28.0:

       Aaron Crane, Abigail, AEvar Arnfjoer` Bjarmason, Alberto Simo~es,
       Alexandr Savca, Andrew Fresh, Andy Dougherty, Andy Lester, Aristotle
       Pagaltzis, Ask Bjorn Hansen, Chris 'BinGOs' Williams, Craig A. Berry,
       Dagfinn Ilmari Mannsaaker, Dan Collins, Daniel Dragan, David Cantrell,
       David Mitchell, Dmitry Ulanov, Dominic Hargreaves, E. Choroba, Eric
       Herman, Eugen Konkov, Father Chrysostomos, Gene Sullivan, George
       Hartzell, Graham Knop, Harald Joerg, H.Merijn Brand, Hugo van der
       Sanden, Jacques Germishuys, James E Keenan, Jarkko Hietaniemi, Jerry D.
       Hedden, J. Nick Koston, John Lightsey, John Peacock, John P. Linderman,
       John SJ Anderson, Karen Etheridge, Karl Williamson, Ken Brown, Ken
       Cotterill, Leon Timmermans, Lukas Mai, Marco Fontani, Marc-Philip
       Werner, Matthew Horsfall, Neil Bowers, Nicholas Clark, Nicolas R., Niko
       Tyni, Pali, Paul Marquess, Peter John Acklam, Reini Urban, Renee
       Baecker, Ricardo Signes, Robin Barker, Sawyer X, Scott Lanning, Sergey
       Aleynikov, Shirakata Kentaro, Shoichi Kaji, Slaven Rezic, Smylers,
       Steffen Mueller, Steve Hay, Sullivan Beck, Thomas Sibley, Todd Rinaldo,
       Tomasz Konojacki, Tom Hukins, Tom Wyant, Tony Cook, Vitali Peil, Yves
       Orton, 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 perl bug
       database at <> .  There may also be information at
       <> , the Perl Home Page.

       If you believe you have an unreported bug, please run the perlbug
       program included with your release.  Be sure to trim your bug down to a
       tiny but sufficient test case.  Your bug report, along with the output
       of "perl -V", will be sent off to to be analysed by
       the Perl porting team.

       If the bug you are reporting has security implications which make it
       inappropriate to send to a publicly archived mailing list, then see
       how to report the issue.

Give Thanks

       If you wish to thank the Perl 5 Porters for the work we had done in
       Perl 5, you can do so by running the "perlthanks" program:


       This will send an email to the Perl 5 Porters list with your show of


       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 v5.34.0                      2021-05-04                PERL5280DELTA(1pm)

perl 5.34.0 - Generated Fri Feb 25 07:39:00 CST 2022
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