PERL5260DELTA(1) Perl Programmers Reference Guide PERL5260DELTA(1)

PERL5260DELTA(1) Perl Programmers Reference Guide PERL5260DELTA(1) #

PERL5260DELTA(1) Perl Programmers Reference Guide PERL5260DELTA(1)

NNAAMMEE #

 perl5260delta - what is new for perl v5.26.0

DDEESSCCRRIIPPTTIIOONN #

 This document describes the differences between the 5.24.0 release and
 the 5.26.0 release.

NNoottiiccee This release includes three updates with widespread effects:

 •   "." no longer in @INC

     For security reasons, the current directory (".") is no longer
     included by default at the end of the module search path (@INC). This
     may have widespread implications for the building, testing and
     installing of modules, and for the execution of scripts.  See the
     section "Removal of the current directory (".") from @INC" for the
     full details.

 •   "do" may now warn

     "do" now gives a deprecation warning when it fails to load a file
     which it would have loaded had "." been in @INC.

 •   In regular expression patterns, a literal left brace "{" should be
     escaped

     See "Unescaped literal "{" characters in regular expression patterns
     are no longer permissible".

CCoorree EEnnhhaanncceemmeennttss LLeexxiiccaall ssuubbrroouuttiinneess aarree nnoo lloonnggeerr eexxppeerriimmeennttaall Using the “lexical_subs” feature introduced in v5.18 no longer emits a warning. Existing code that disables the “experimental::lexical_subs” warning category that the feature previously used will continue to work. The “lexical_subs” feature has no effect; all Perl code can use lexical subroutines, regardless of what feature declarations are in scope.

IInnddeenntteedd HHeerree--ddooccuummeennttss This adds a new modifier “~” to here-docs that tells the parser that it should look for “/^\s*$DELIM\n/” as the closing delimiter.

 These syntaxes are all supported:

«~EOF; #

«~\EOF; #

«~‘EOF’; #

«~“EOF”; #

«~EOF; #

«~ ‘EOF’; #

«~ “EOF”; #

«~ EOF; #

 The "~" modifier will strip, from each line in the here-doc, the same
 whitespace that appears before the delimiter.

 Newlines will be copied as-is, and lines that don't include the proper
 beginning whitespace will cause perl to croak.

 For example:

     if (1) {
       print <<~EOF;
         Hello there

EOF #

     }

 prints "Hello there\n" with no leading whitespace.

NNeeww rreegguullaarr eexxpprreessssiioonn mmooddiiffiieerr “”//xxxx"" Specifying two “x” characters to modify a regular expression pattern does everything that a single one does, but additionally TAB and SPACE characters within a bracketed character class are generally ignored and can be added to improve readability, like “/[ ^ A-Z d-f p-x ]/xx”. Details are at “/x and /xx” in perlre.

“”@@{{^^CCAAPPTTUURREE}}“”,, “”%%{{^^CCAAPPTTUURREE}}“”,, aanndd “”%%{{^^CCAAPPTTUURREE__AALLLL}}“” “@{^CAPTURE}” exposes the capture buffers of the last match as an array. So $1 is “${^CAPTURE}[0]”. This is a more efficient equivalent to code like “substr($matched_string,$-[0],$+[0]-$-[0])”, and you don’t have to keep track of the $matched_string either. This variable has no single character equivalent. Note that, like the other regex magic variables, the contents of this variable is dynamic; if you wish to store it beyond the lifetime of the match you must copy it to another array.

 "%{^CAPTURE}" is equivalent to "%+" (_i_._e_., named captures).  Other than
 being more self-documenting there is no difference between the two forms.

 "%{^CAPTURE_ALL}" is equivalent to "%-" (_i_._e_., all named captures).
 Other than being more self-documenting there is no difference between the
 two forms.

DDeeccllaarriinngg aa rreeffeerreennccee ttoo aa vvaarriiaabbllee As an experimental feature, Perl now allows the referencing operator to come after “my()”, “state()”, “our()”, or “local()”. This syntax must be enabled with “use feature ‘declared_refs’”. It is experimental, and will warn by default unless “no warnings ’experimental::refaliasing’” is in effect. It is intended mainly for use in assignments to references. For example:

     use experimental 'refaliasing', 'declared_refs';
     my \$a = \$b;

 See "Assigning to References" in perlref for more details.

UUnniiccooddee 99..00 iiss nnooww ssuuppppoorrtteedd A list of changes is at http://www.unicode.org/versions/Unicode9.0.0/. Modules that are shipped with core Perl but not maintained by p5p do not necessarily support Unicode 9.0. Unicode::Normalize does work on 9.0.

UUssee ooff “”\\pp{{_s_c_r_i_p_t}}“” uusseess tthhee iimmpprroovveedd SSccrriipptt__EExxtteennssiioonnss pprrooppeerrttyy Unicode 6.0 introduced an improved form of the Script (“sc”) property, and called it Script_Extensions (“scx”). Perl now uses this improved version when a property is specified as just “\p{_s_c_r_i_p_t}”. This should make programs more accurate when determining if a character is used in a given script, but there is a slight chance of breakage for programs that very specifically needed the old behavior. The meaning of compound forms, like “\p{sc=_s_c_r_i_p_t}” are unchanged. See “Scripts” in perlunicode.

PPeerrll ccaann nnooww ddoo ddeeffaauulltt ccoollllaattiioonn iinn UUTTFF--88 llooccaalleess oonn ppllaattffoorrmmss tthhaatt ssuuppppoorrtt iitt Some platforms natively do a reasonable job of collating and sorting in UTF-8 locales. Perl now works with those. For portability and full control, Unicode::Collate is still recommended, but now you may not need to do anything special to get good-enough results, depending on your application. See “Category “LC_COLLATE”: Collation: Text Comparisons and Sorting” in perllocale.

BBeetttteerr llooccaallee ccoollllaattiioonn ooff ssttrriinnggss ccoonnttaaiinniinngg eemmbbeeddddeedd “"NNUULL"” cchhaarraacctteerrss In locales that have multi-level character weights, “NUL"s are now ignored at the higher priority ones. There are still some gotchas in some strings, though. See “Collation of strings containing embedded “NUL” characters” in perllocale.

“"CCOORREE"” ssuubbrroouuttiinneess ffoorr hhaasshh aanndd aarrrraayy ffuunnccttiioonnss ccaallllaabbllee vviiaa rreeffeerreennccee The hash and array functions in the “CORE” namespace (“keys”, “each”, “values”, “push”, “pop”, “shift”, “unshift” and “splice”) can now be called with ampersand syntax ("&CORE::keys(%hash”) and via reference (“my $k = &CORE::keys; $k->(%hash)”). Previously they could only be used when inlined.

NNeeww HHaasshh FFuunnccttiioonn FFoorr 6644--bbiitt BBuuiillddss We have switched to a hybrid hash function to better balance performance for short and long keys.

 For short keys, 16 bytes and under, we use an optimised variant of One At
 A Time Hard, and for longer keys we use Siphash 1-3.  For very long keys
 this is a big improvement in performance.  For shorter keys there is a
 modest improvement.

SSeeccuurriittyy RReemmoovvaall ooff tthhee ccuurrrreenntt ddiirreeccttoorryy ((“”..“”)) ffrroomm @@IINNCC The perl binary includes a default set of paths in @INC. Historically it has also included the current directory (".") as the final entry, unless run with taint mode enabled (“perl -T”). While convenient, this has security implications: for example, where a script attempts to load an optional module when its current directory is untrusted (such as _/_t_m_p), it could load and execute code from under that directory.

 Starting with v5.26, "." is always removed by default, not just under
 tainting.  This has major implications for installing modules and
 executing scripts.

 The following new features have been added to help ameliorate these
 issues.

 •   _C_o_n_f_i_g_u_r_e _-_U_d_e_f_a_u_l_t___i_n_c___e_x_c_l_u_d_e_s___d_o_t

     There is a new _C_o_n_f_i_g_u_r_e option, "default_inc_excludes_dot" (enabled
     by default) which builds a perl executable without "."; unsetting
     this option using "-U" reverts perl to the old behaviour.  This may
     fix your path issues but will reintroduce all the security concerns,
     so don't build a perl executable like this unless you're _r_e_a_l_l_y
     confident that such issues are not a concern in your environment.

• “PERL_USE_UNSAFE_INC” #

     There is a new environment variable recognised by the perl
     interpreter.  If this variable has the value 1 when the perl
     interpreter starts up, then "." will be automatically appended to
     @INC (except under tainting).

     This allows you restore the old perl interpreter behaviour on a case-
     by-case basis.  But note that this is intended to be a temporary
     crutch, and this feature will likely be removed in some future perl
     version.  It is currently set by the "cpan" utility and
     "Test::Harness" to ease installation of CPAN modules which have not
     been updated to handle the lack of dot.  Once again, don't use this
     unless you are sure that this will not reintroduce any security
     concerns.

 •   A new deprecation warning issued by "do".

     While it is well-known that "use" and "require" use @INC to search
     for the file to load, many people don't realise that "do "file"" also
     searches @INC if the file is a relative path.  With the removal of
     ".", a simple "do "file.pl"" will fail to read in and execute
     "file.pl" from the current directory.  Since this is commonly
     expected behaviour, a new deprecation warning is now issued whenever
     "do" fails to load a file which it otherwise would have found if a
     dot had been in @INC.

 Here are some things script and module authors may need to do to make
 their software work in the new regime.

 •   Script authors

     If the issue is within your own code (rather than within included
     modules), then you have two main options.  Firstly, if you are
     confident that your script will only be run within a trusted
     directory (under which you expect to find trusted files and modules),
     then add "." back into the path; _e_._g_.:

BEGIN { #

             my $dir = "/some/trusted/directory";
             chdir $dir or die "Can't chdir to $dir: $!\n";
             # safe now
             push @INC, '.';
         }

         use "Foo::Bar"; # may load /some/trusted/directory/Foo/Bar.pm
         do "config.pl"; # may load /some/trusted/directory/config.pl

     On the other hand, if your script is intended to be run from within
     untrusted directories (such as _/_t_m_p), then your script suddenly
     failing to load files may be indicative of a security issue.  You
     most likely want to replace any relative paths with full paths; for
     example,

         do "foo_config.pl"

     might become

         do "$ENV{HOME}/foo_config.pl"

     If you are absolutely certain that you want your script to load and
     execute a file from the current directory, then use a "./" prefix;
     for example:

         do "./foo_config.pl"

 •   Installing and using CPAN modules

     If you install a CPAN module using an automatic tool like "cpan",
     then this tool will itself set the "PERL_USE_UNSAFE_INC" environment
     variable while building and testing the module, which may be
     sufficient to install a distribution which hasn't been updated to be
     dot-aware.  If you want to install such a module manually, then
     you'll need to replace the traditional invocation:

         perl Makefile.PL && make && make test && make install

     with something like

         (export PERL_USE_UNSAFE_INC=1; \
          perl Makefile.PL && make && make test && make install)

     Note that this only helps build and install an unfixed module.  It's
     possible for the tests to pass (since they were run under
     "PERL_USE_UNSAFE_INC=1"), but for the module itself to fail to
     perform correctly in production.  In this case, you may have to
     temporarily modify your script until a fixed version of the module is
     released.  For example:

         use Foo::Bar;
         {
             local @INC = (@INC, '.');
             # assuming read_config() needs '.' in @INC
             $config = Foo::Bar->read_config();
         }

     This is only rarely expected to be necessary.  Again, if doing this,
     assess the resultant risks first.

 •   Module Authors

     If you maintain a CPAN distribution, it may need updating to run in a
     dotless environment.  Although "cpan" and other such tools will
     currently set the "PERL_USE_UNSAFE_INC" during module build, this is
     a temporary workaround for the set of modules which rely on "." being
     in @INC for installation and testing, and this may mask deeper
     issues.  It could result in a module which passes tests and installs,
     but which fails at run time.

     During build, test, and install, it will normally be the case that
     any perl processes will be executing directly within the root
     directory of the untarred distribution, or a known subdirectory of
     that, such as _t_/.  It may well be that _M_a_k_e_f_i_l_e_._P_L or _t_/_f_o_o_._t will
     attempt to include local modules and configuration files using their
     direct relative filenames, which will now fail.

     However, as described above, automatic tools like _c_p_a_n will (for now)
     set the "PERL_USE_UNSAFE_INC" environment variable, which introduces
     dot during a build.

     This makes it likely that your existing build and test code will
     work, but this may mask issues with your code which only manifest
     when used after install.  It is prudent to try and run your build
     process with that variable explicitly disabled:

         (export PERL_USE_UNSAFE_INC=0; \
          perl Makefile.PL && make && make test && make install)

     This is more likely to show up any potential problems with your
     module's build process, or even with the module itself.  Fixing such
     issues will ensure both that your module can again be installed
     manually, and that it will still build once the "PERL_USE_UNSAFE_INC"
     crutch goes away.

     When fixing issues in tests due to the removal of dot from @INC,
     reinsertion of dot into @INC should be performed with caution, for
     this too may suppress real errors in your runtime code.  You are
     encouraged wherever possible to apply the aforementioned approaches
     with explicit absolute/relative paths, or to relocate your needed
     files into a subdirectory and insert that subdirectory into @INC
     instead.

     If your runtime code has problems under the dotless @INC, then the
     comments above on how to fix for script authors will mostly apply
     here too.  Bear in mind though that it is considered bad form for a
     module to globally add a dot to @INC, since it introduces both a
     security risk and hides issues of accidentally requiring dot in @INC,
     as explained above.

EEssccaappeedd ccoolloonnss aanndd rreellaattiivvee ppaatthhss iinn PPAATTHH On Unix systems, Perl treats any relative paths in the “PATH” environment variable as tainted when starting a new process. Previously, it was allowing a backslash to escape a colon (unlike the OS), consequently allowing relative paths to be considered safe if the PATH was set to something like “/:.”. The check has been fixed to treat “.” as tainted in that example.

NNeeww “”--DDii"" sswwiittcchh iiss nnooww rreeqquuiirreedd ffoorr PPeerrllIIOO ddeebbuuggggiinngg oouuttppuutt This is used for debugging of code within PerlIO to avoid recursive calls. Previously this output would be sent to the file specified by the “PERLIO_DEBUG” environment variable if perl wasn’t running setuid and the “-T” or “-t” switches hadn’t been parsed yet.

 If perl performed output at a point where it hadn't yet parsed its
 switches this could result in perl creating or overwriting the file named
 by "PERLIO_DEBUG" even when the "-T" switch had been supplied.

 Perl now requires the "-Di" switch to be present before it will produce
 PerlIO debugging output.  By default this is written to "stderr", but can
 optionally be redirected to a file by setting the "PERLIO_DEBUG"
 environment variable.

 If perl is running setuid or the "-T" switch was supplied, "PERLIO_DEBUG"
 is ignored and the debugging output is sent to "stderr" as for any other
 "-D" switch.

IInnccoommppaattiibbllee CChhaannggeess UUnneessccaappeedd lliitteerraall “”{{“” cchhaarraacctteerrss iinn rreegguullaarr eexxpprreessssiioonn ppaatttteerrnnss aarree nnoo lloonnggeerr ppeerrmmiissssiibbllee You have to now say something like “{” or “[{]” to specify to match a LEFT CURLY BRACKET; otherwise, it is a fatal pattern compilation error. This change will allow future extensions to the language.

 These have been deprecated since v5.16, with a deprecation message raised
 for some uses starting in v5.22.  Unfortunately, the code added to raise
 the message was buggy and failed to warn in some cases where it should
 have.  Therefore, enforcement of this ban for these cases is deferred
 until Perl 5.30, but the code has been fixed to raise a default-on
 deprecation message for them in the meantime.

 Some uses of literal "{" occur in contexts where we do not foresee the
 meaning ever being anything but the literal, such as the very first
 character in the pattern, or after a "|" meaning alternation.  Thus

  qr/{fee|{fie/

 matches either of the strings "{fee" or "{fie".  To avoid forcing
 unnecessary code changes, these uses do not need to be escaped, and no
 warning is raised about them, and there are no current plans to change
 this.

 But it is always correct to escape "{", and the simple rule to remember
 is to always do so.

 See Unescaped left brace in regex is illegal here.

“"ssccaallaarr((%%hhaasshh))“” rreettuurrnn ssiiggnnaattuurree cchhaannggeedd The value returned for “scalar(%hash)” will no longer show information about the buckets allocated in the hash. It will simply return the count of used keys. It is thus equivalent to “0+keys(%hash)”.

 A form of backward compatibility is provided via
 "Hash::Util::bucket_ratio()" which provides the same behavior as
 "scalar(%hash)" provided in Perl 5.24 and earlier.

“"kkeeyyss"” rreettuurrnneedd ffrroomm aann llvvaalluuee ssuubbrroouuttiinnee “keys” returned from an lvalue subroutine can no longer be assigned to in list context.

     sub foo : lvalue { keys(%INC) }
     (foo) = 3; # death
     sub bar : lvalue { keys(@_) }
     (bar) = 3; # also an error

 This makes the lvalue sub case consistent with "(keys %hash) = ..." and
 "(keys @_) = ...", which are also errors.  [GH #15339]
 <https://github.com/Perl/perl5/issues/15339>

TThhee “”$${{^^EENNCCOODDIINNGG}}“” ffaacciilliittyy hhaass bbeeeenn rreemmoovveedd The special behaviour associated with assigning a value to this variable has been removed. As a consequence, the encoding pragma’s default mode is no longer supported. If you still need to write your source code in encodings other than UTF-8, use a source filter such as Filter::Encoding on CPAN or encoding’s “Filter” option.

“"PPOOSSIIXX::::ttmmppnnaamm(())“” hhaass bbeeeenn rreemmoovveedd The fundamentally unsafe “tmpnam()” interface was deprecated in Perl 5.22 and has now been removed. In its place, you can use, for example, the File::Temp interfaces.

rreeqquuiirree ::::FFoooo::::BBaarr iiss nnooww iilllleeggaall.. Formerly, “require ::Foo::Bar” would try to read _/_F_o_o_/_B_a_r_._p_m. Now any bareword require which starts with a double colon dies instead.

LLiitteerraall ccoonnttrrooll cchhaarraacctteerr vvaarriiaabbllee nnaammeess aarree nnoo lloonnggeerr ppeerrmmiissssiibbllee A variable name may no longer contain a literal control character under any circumstances. These previously were allowed in single-character names on ASCII platforms, but have been deprecated there since Perl 5.20. This affects things like “$__c_T”, where __c_T is a literal control (such as a “NAK” or “NEGATIVE ACKNOWLEDGE” character) in the source code.

“"NNBBSSPP"” iiss nnoo lloonnggeerr ppeerrmmiissssiibbllee iinn “”\\NN{{......}}“” The name of a character may no longer contain non-breaking spaces. It has been deprecated to do so since Perl 5.22.

DDeepprreeccaattiioonnss SSttrriinngg ddeelliimmiitteerrss tthhaatt aarreenn’’tt ssttaanndd--aalloonnee ggrraapphheemmeess aarree nnooww ddeepprreeccaatteedd For Perl to eventually allow string delimiters to be Unicode grapheme clusters (which look like a single character, but may be a sequence of several ones), we have to stop allowing a single character delimiter that isn’t a grapheme by itself. These are unlikely to exist in actual code, as they would typically display as attached to the character in front of them.

“”\\cc_X"” tthhaatt mmaappss ttoo aa pprriinnttaabbllee iiss nnoo lloonnggeerr ddeepprreeccaatteedd This means we have no plans to remove this feature. It still raises a warning, but only if syntax warnings are enabled. The feature was originally intended to be a way to express non-printable characters that don’t have a mnemonic ("\t” and “\n” are mnemonics for two non-printable characters, but most non-printables don’t have a mnemonic.) But the feature can be used to specify a few printable characters, though those are more clearly expressed as the printable itself. See http://www.nntp.perl.org/group/perl.perl5.porters/2017/02/msg242944.html.

PPeerrffoorrmmaannccee EEnnhhaanncceemmeennttss • A hash in boolean context is now sometimes faster, _e_._g_.

         if (!%h) { ... }

     This was already special-cased, but some cases were missed (such as
     "grep %$_, @AoH"), and even the ones which weren't have been
     improved.

 •   New Faster Hash Function on 64 bit builds

     We use a different hash function for short and long keys.  This
     should improve performance and security, especially for long keys.

 •   readline is faster

     Reading from a file line-by-line with "readline()" or "<>" should now
     typically be faster due to a better implementation of the code that
     searches for the next newline character.

 •   Assigning one reference to another, _e_._g_. "$ref1 = $ref2" has been
     optimized in some cases.

 •   Remove some exceptions to creating Copy-on-Write strings. The string
     buffer growth algorithm has been slightly altered so that you're less
     likely to encounter a string which can't be COWed.

 •   Better optimise array and hash assignment: where an array or hash
     appears in the LHS of a list assignment, such as "(..., @a) =
     (...);", it's likely to be considerably faster, especially if it
     involves emptying the array/hash. For example, this code runs about a
     third faster compared to Perl 5.24.0:

         my @a;
         for my $i (1..10_000_000) {
             @a = (1,2,3);
             @a = ();
         }

 •   Converting a single-digit string to a number is now substantially
     faster.

 •   The "split" builtin is now slightly faster in many cases: in
     particular for the two specially-handled forms

         my    @a = split ...;
         local @a = split ...;

 •   The rather slow implementation for the experimental subroutine
     signatures feature has been made much faster; it is now comparable in
     speed with the traditional "my ($a, $b, @c) = @_".

 •   Bareword constant strings are now permitted to take part in constant
     folding.  They were originally exempted from constant folding in
     August 1999, during the development of Perl 5.6, to ensure that "use
     strict "subs"" would still apply to bareword constants.  That has now
     been accomplished a different way, so barewords, like other
     constants, now gain the performance benefits of constant folding.

     This also means that void-context warnings on constant expressions of
     barewords now report the folded constant operand, rather than the
     operation; this matches the behaviour for non-bareword constants.

MMoodduulleess aanndd PPrraaggmmaattaa UUppddaatteedd MMoodduulleess aanndd PPrraaggmmaattaa • IO::Compress has been upgraded from version 2.069 to 2.074.

 •   Archive::Tar has been upgraded from version 2.04 to 2.24.

 •   arybase has been upgraded from version 0.11 to 0.12.

 •   attributes has been upgraded from version 0.27 to 0.29.

     The deprecation message for the ":unique" and ":locked" attributes
     now mention that they will disappear in Perl 5.28.

 •   B has been upgraded from version 1.62 to 1.68.

 •   B::Concise has been upgraded from version 0.996 to 0.999.

     Its output is now more descriptive for "op_private" flags.

 •   B::Debug has been upgraded from version 1.23 to 1.24.

 •   B::Deparse has been upgraded from version 1.37 to 1.40.

 •   B::Xref has been upgraded from version 1.05 to 1.06.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   base has been upgraded from version 2.23 to 2.25.

 •   bignum has been upgraded from version 0.42 to 0.47.

 •   Carp has been upgraded from version 1.40 to 1.42.

 •   charnames has been upgraded from version 1.43 to 1.44.

 •   Compress::Raw::Bzip2 has been upgraded from version 2.069 to 2.074.

 •   Compress::Raw::Zlib has been upgraded from version 2.069 to 2.074.

 •   Config::Perl::V has been upgraded from version 0.25 to 0.28.

 •   CPAN has been upgraded from version 2.11 to 2.18.

 •   CPAN::Meta has been upgraded from version 2.150005 to 2.150010.

 •   Data::Dumper has been upgraded from version 2.160 to 2.167.

     The XS implementation now supports Deparse.

 •   DB_File has been upgraded from version 1.835 to 1.840.

 •   Devel::Peek has been upgraded from version 1.23 to 1.26.

 •   Devel::PPPort has been upgraded from version 3.32 to 3.35.

 •   Devel::SelfStubber has been upgraded from version 1.05 to 1.06.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   diagnostics has been upgraded from version 1.34 to 1.36.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   Digest has been upgraded from version 1.17 to 1.17_01.

 •   Digest::MD5 has been upgraded from version 2.54 to 2.55.

 •   Digest::SHA has been upgraded from version 5.95 to 5.96.

 •   DynaLoader has been upgraded from version 1.38 to 1.42.

 •   Encode has been upgraded from version 2.80 to 2.88.

 •   encoding has been upgraded from version 2.17 to 2.19.

     This module's default mode is no longer supported.  It now dies when
     imported, unless the "Filter" option is being used.

 •   encoding::warnings has been upgraded from version 0.12 to 0.13.

     This module is no longer supported.  It emits a warning to that
     effect and then does nothing.

 •   Errno has been upgraded from version 1.25 to 1.28.

     It now documents that using "%!" automatically loads Errno for you.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   ExtUtils::Embed has been upgraded from version 1.33 to 1.34.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   ExtUtils::MakeMaker has been upgraded from version 7.10_01 to 7.24.

 •   ExtUtils::Miniperl has been upgraded from version 1.05 to 1.06.

 •   ExtUtils::ParseXS has been upgraded from version 3.31 to 3.34.

 •   ExtUtils::Typemaps has been upgraded from version 3.31 to 3.34.

 •   feature has been upgraded from version 1.42 to 1.47.

 •   File::Copy has been upgraded from version 2.31 to 2.32.

 •   File::Fetch has been upgraded from version 0.48 to 0.52.

 •   File::Glob has been upgraded from version 1.26 to 1.28.

     It now Issues a deprecation message for "File::Glob::glob()".

 •   File::Spec has been upgraded from version 3.63 to 3.67.

 •   FileHandle has been upgraded from version 2.02 to 2.03.

 •   Filter::Simple has been upgraded from version 0.92 to 0.93.

     It no longer treats "no MyFilter" immediately following "use
     MyFilter" as end-of-file.  [GH #11853]
     <https://github.com/Perl/perl5/issues/11853>

 •   Getopt::Long has been upgraded from version 2.48 to 2.49.

 •   Getopt::Std has been upgraded from version 1.11 to 1.12.

 •   Hash::Util has been upgraded from version 0.19 to 0.22.

 •   HTTP::Tiny has been upgraded from version 0.056 to 0.070.

     Internal 599-series errors now include the redirect history.

 •   I18N::LangTags has been upgraded from version 0.40 to 0.42.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   IO has been upgraded from version 1.36 to 1.38.

 •   IO::Socket::IP has been upgraded from version 0.37 to 0.38.

 •   IPC::Cmd has been upgraded from version 0.92 to 0.96.

 •   IPC::SysV has been upgraded from version 2.06_01 to 2.07.

 •   JSON::PP has been upgraded from version 2.27300 to 2.27400_02.

 •   lib has been upgraded from version 0.63 to 0.64.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   List::Util has been upgraded from version 1.42_02 to 1.46_02.

 •   Locale::Codes has been upgraded from version 3.37 to 3.42.

 •   Locale::Maketext has been upgraded from version 1.26 to 1.28.

 •   Locale::Maketext::Simple has been upgraded from version 0.21 to
     0.21_01.

 •   Math::BigInt has been upgraded from version 1.999715 to 1.999806.

 •   Math::BigInt::FastCalc has been upgraded from version 0.40 to 0.5005.

 •   Math::BigRat has been upgraded from version 0.260802 to 0.2611.

 •   Math::Complex has been upgraded from version 1.59 to 1.5901.

 •   Memoize has been upgraded from version 1.03 to 1.03_01.

 •   Module::CoreList has been upgraded from version 5.20170420 to
     5.20170530.

 •   Module::Load::Conditional has been upgraded from version 0.64 to
     0.68.

 •   Module::Metadata has been upgraded from version 1.000031 to 1.000033.

 •   mro has been upgraded from version 1.18 to 1.20.

 •   Net::Ping has been upgraded from version 2.43 to 2.55.

     IPv6 addresses and "AF_INET6" sockets are now supported, along with
     several other enhancements.

 •   NEXT has been upgraded from version 0.65 to 0.67.

 •   Opcode has been upgraded from version 1.34 to 1.39.

 •   open has been upgraded from version 1.10 to 1.11.

 •   OS2::Process has been upgraded from version 1.11 to 1.12.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   overload has been upgraded from version 1.26 to 1.28.

     Its compilation speed has been improved slightly.

 •   parent has been upgraded from version 0.234 to 0.236.

 •   perl5db.pl has been upgraded from version 1.50 to 1.51.

     It now ignores _/_d_e_v_/_t_t_y on non-Unix systems.  [GH #12244]
     <https://github.com/Perl/perl5/issues/12244>

 •   Perl::OSType has been upgraded from version 1.009 to 1.010.

 •   perlfaq has been upgraded from version 5.021010 to 5.021011.

 •   PerlIO has been upgraded from version 1.09 to 1.10.

 •   PerlIO::encoding has been upgraded from version 0.24 to 0.25.

 •   PerlIO::scalar has been upgraded from version 0.24 to 0.26.

 •   Pod::Checker has been upgraded from version 1.60 to 1.73.

 •   Pod::Functions has been upgraded from version 1.10 to 1.11.

 •   Pod::Html has been upgraded from version 1.22 to 1.2202.

 •   Pod::Perldoc has been upgraded from version 3.25_02 to 3.28.

 •   Pod::Simple has been upgraded from version 3.32 to 3.35.

 •   Pod::Usage has been upgraded from version 1.68 to 1.69.

 •   POSIX has been upgraded from version 1.65 to 1.76.

     This remedies several defects in making its symbols exportable.  [GH
     #15260] <https://github.com/Perl/perl5/issues/15260>

     The "POSIX::tmpnam()" interface has been removed, see
     "PPOOSSIIXX::::ttmmppnnaamm(()) has been removed".

     The following deprecated functions have been removed:

         POSIX::isalnum
         POSIX::isalpha
         POSIX::iscntrl
         POSIX::isdigit
         POSIX::isgraph
         POSIX::islower
         POSIX::isprint
         POSIX::ispunct
         POSIX::isspace
         POSIX::isupper
         POSIX::isxdigit
         POSIX::tolower
         POSIX::toupper

     Trying to import POSIX subs that have no real implementations (like
     "POSIX::atend()") now fails at import time, instead of waiting until
     runtime.

 •   re has been upgraded from version 0.32 to 0.34

     This adds support for the new "/xx" regular expression pattern
     modifier, and a change to the "use re 'strict'" experimental feature.
     When "re 'strict'" is enabled, a warning now will be generated for
     all unescaped uses of the two characters "}" and "]" in regular
     expression patterns (outside bracketed character classes) that are
     taken literally.  This brings them more in line with the ")"
     character which is always a metacharacter unless escaped.  Being a
     metacharacter only sometimes, depending on an action at a distance,
     can lead to silently having the pattern mean something quite
     different than was intended, which the "re 'strict'" mode is intended
     to minimize.

 •   Safe has been upgraded from version 2.39 to 2.40.

 •   Scalar::Util has been upgraded from version 1.42_02 to 1.46_02.

 •   Storable has been upgraded from version 2.56 to 2.62.

     Fixes [GH #15714] <https://github.com/Perl/perl5/issues/15714>.

 •   Symbol has been upgraded from version 1.07 to 1.08.

 •   Sys::Syslog has been upgraded from version 0.33 to 0.35.

 •   Term::ANSIColor has been upgraded from version 4.04 to 4.06.

 •   Term::ReadLine has been upgraded from version 1.15 to 1.16.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   Test has been upgraded from version 1.28 to 1.30.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   Test::Harness has been upgraded from version 3.36 to 3.38.

 •   Test::Simple has been upgraded from version 1.001014 to 1.302073.

 •   Thread::Queue has been upgraded from version 3.09 to 3.12.

 •   Thread::Semaphore has been upgraded from 2.12 to 2.13.

     Added the "down_timed" method.

 •   threads has been upgraded from version 2.07 to 2.15.

 •   threads::shared has been upgraded from version 1.51 to 1.56.

 •   Tie::Hash::NamedCapture has been upgraded from version 0.09 to 0.10.

 •   Time::HiRes has been upgraded from version 1.9733 to 1.9741.

     It now builds on systems with C++11 compilers (such as G++ 6 and
     Clang++ 3.9).

     Now uses "clockid_t".

 •   Time::Local has been upgraded from version 1.2300 to 1.25.

 •   Unicode::Collate has been upgraded from version 1.14 to 1.19.

 •   Unicode::UCD has been upgraded from version 0.64 to 0.68.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   version has been upgraded from version 0.9916 to 0.9917.

 •   VMS::DCLsym has been upgraded from version 1.06 to 1.08.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

 •   warnings has been upgraded from version 1.36 to 1.37.

 •   XS::Typemap has been upgraded from version 0.14 to 0.15.

 •   XSLoader has been upgraded from version 0.21 to 0.27.

     Fixed a security hole in which binary files could be loaded from a
     path outside of @INC.

     It now uses 3-arg "open()" instead of 2-arg "open()".  [GH #15721]
     <https://github.com/Perl/perl5/issues/15721>

DDooccuummeennttaattiioonn NNeeww DDooccuummeennttaattiioonn _p_e_r_l_d_e_p_r_e_c_a_t_i_o_n

 This file documents all upcoming deprecations, and some of the
 deprecations which already have been removed.  The purpose of this
 documentation is two-fold: document what will disappear, and by which
 version, and serve as a guide for people dealing with code which has
 features that no longer work after an upgrade of their perl.

CChhaannggeess ttoo EExxiissttiinngg DDooccuummeennttaattiioonn 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 perlbug@perl.org mailto:perlbug@perl.org.

 Additionally, all references to Usenet have been removed, and the
 following selected changes have been made:

 _p_e_r_l_f_u_n_c

 •   Removed obsolete text about "defined()" on aggregates that should
     have been deleted earlier, when the feature was removed.

 •   Corrected documentation of "eval()", and "evalbytes()".

 •   Clarified documentation of "seek()", "tell()" and "sysseek()"
     emphasizing that positions are in bytes and not characters.  [GH
     #15438] <https://github.com/Perl/perl5/issues/15438>

 •   Clarified documentation of "sort()" concerning the variables $a and
     $b.

 •   In "split()" noted that certain pattern modifiers are legal, and
     added a caution about its use in Perls before v5.11.

 •   Removed obsolete documentation of "study()", noting that it is now a
     no-op.

 •   Noted that "vec()" doesn't work well when the string contains
     characters whose code points are above 255.

 _p_e_r_l_g_u_t_s

 •   Added advice on formatted printing of operands of "Size_t" and
     "SSize_t"

 _p_e_r_l_h_a_c_k

 •   Clarify what editor tab stop rules to use, and note that we are
     migrating away from using tabs, replacing them with sequences of
     SPACE characters.

 _p_e_r_l_h_a_c_k_t_i_p_s

 •   Give another reason to use "cBOOL" to cast an expression to boolean.

 •   Note that the macros "TRUE" and "FALSE" are available to express
     boolean values.

 _p_e_r_l_i_n_t_e_r_p

 •   perlinterp has been expanded to give a more detailed example of how
     to hunt around in the parser for how a given operator is handled.

 _p_e_r_l_l_o_c_a_l_e

 •   Some locales aren't compatible with Perl.  Note that these can cause
     core dumps.

 _p_e_r_l_m_o_d

 •   Various clarifications have been added.

 _p_e_r_l_m_o_d_l_i_b

 •   Updated the site mirror list.

 _p_e_r_l_o_b_j

 •   Added a section on calling methods using their fully qualified names.

 •   Do not discourage manual @ISA.

 _p_e_r_l_o_o_t_u_t

 •   Mention "Moo" more.

 _p_e_r_l_o_p

 •   Note that white space must be used for quoting operators if the
     delimiter is a word character (_i_._e_., matches "\w").

 •   Clarify that in regular expression patterns delimited by single
     quotes, no variable interpolation is done.

 _p_e_r_l_r_e

 •   The first part was extensively rewritten to incorporate various basic
     points, that in earlier versions were mentioned in sort of an
     appendix on Version 8 regular expressions.

 •   Note that it is common to have the "/x" modifier and forget that this
     means that "#" has to be escaped.

 _p_e_r_l_r_e_t_u_t

 •   Add introductory material.

 •   Note that a metacharacter occurring in a context where it can't mean
     that, silently loses its meta-ness and matches literally.  "use re
     'strict'" can catch some of these.

 _p_e_r_l_u_n_i_c_o_d_e

 •   Corrected the text about Unicode BYTE ORDER MARK handling.

 •   Updated the text to correspond with changes in Unicode UTS#18,
     concerning regular expressions, and Perl compatibility with what it
     says.

 _p_e_r_l_v_a_r

 •   Document @ISA.  It was documented in other places, but not in
     perlvar.

DDiiaaggnnoossttiiccss NNeeww DDiiaaggnnoossttiiccss _N_e_w _E_r_r_o_r_s

 •   A signature parameter must start with '$', '@' or '%'

 •   Bareword in require contains "%s"

 •   Bareword in require maps to empty filename

 •   Bareword in require maps to disallowed filename "%s"

 •   Bareword in require must not start with a double-colon: "%s"

 •   %s: command not found

     (A) You've accidentally run your script through bbaasshh or another shell
     instead of Perl.  Check the "#!" line, or manually feed your script
     into Perl yourself.  The "#!" line at the top of your file could look
     like:

       #!/usr/bin/perl

 •   %s: command not found: %s

     (A) You've accidentally run your script through zzsshh or another shell
     instead of Perl.  Check the "#!" line, or manually feed your script
     into Perl yourself.  The "#!" line at the top of your file could look
     like:

       #!/usr/bin/perl

 •   The experimental declared_refs feature is not enabled

     (F) To declare references to variables, as in "my \%x", you must
     first enable the feature:

         no warnings "experimental::declared_refs";
         use feature "declared_refs";

     See "Declaring a reference to a variable".

 •   Illegal character following sigil in a subroutine signature

 •   Indentation on line %d of here-doc doesn't match delimiter

 •   Infinite recursion via empty pattern.

     Using the empty pattern (which re-executes the last successfully-
     matched pattern) inside a code block in another regex, as in "/(?{
     s!!new! })/", has always previously yielded a segfault.  It now
     produces this error.

 •   Malformed UTF-8 string in "%s"

 •   Multiple slurpy parameters not allowed

 •   '#' not allowed immediately following a sigil in a subroutine
     signature

 •   panic: unknown OA_*: %x

 •   Unescaped left brace in regex is illegal here

     Unescaped left braces are now illegal in some contexts in regular
     expression patterns.  In other contexts, they are still just
     deprecated; they will be illegal in Perl 5.30.

 •   Version control conflict marker

     (F) The parser found a line starting with "<<<<<<<", ">>>>>>>", or
     "=======".  These may be left by a version control system to mark
     conflicts after a failed merge operation.

 _N_e_w _W_a_r_n_i_n_g_s

 •   Can't determine class of operator %s, assuming "BASEOP"

 •   Declaring references is experimental

     (S experimental::declared_refs) This warning is emitted if you use a
     reference constructor on the right-hand side of "my()", "state()",
     "our()", or "local()".  Simply suppress the warning if you want to
     use the feature, but know that in doing so you are taking the risk of
     using an experimental feature which may change or be removed in a
     future Perl version:

         no warnings "experimental::declared_refs";
         use feature "declared_refs";
         $fooref = my \$foo;

     See "Declaring a reference to a variable".

 •   do "%s" failed, '.' is no longer in @INC

     Since "." is now removed from @INC by default, "do" will now trigger
     a warning recommending to fix the "do" statement.

 •   "File::Glob::glob()" will disappear in perl 5.30. Use
     "File::Glob::bsd_glob()" instead.

 •   Unescaped literal '%c' in regex; marked by <-- HERE in m/%s/

 •   Use of unassigned code point or non-standalone grapheme for a
     delimiter will be a fatal error starting in Perl 5.30

     See "Deprecations"

CChhaannggeess ttoo EExxiissttiinngg DDiiaaggnnoossttiiccss • When a “require” fails, we now do not provide @INC when the “require” is for a file instead of a module.

 •   When @INC is not scanned for a "require" call, we no longer display
     @INC to avoid confusion.

 •   Attribute "locked" is deprecated, and will disappear in Perl 5.28

     This existing warning has had the _a_n_d _w_i_l_l _d_i_s_a_p_p_e_a_r text added in
     this release.

 •   Attribute "unique" is deprecated, and will disappear in Perl 5.28

     This existing warning has had the _a_n_d _w_i_l_l _d_i_s_a_p_p_e_a_r text added in
     this release.

 •   Calling POSIX::%s() is deprecated

     This warning has been removed, as the deprecated functions have been
     removed from POSIX.

 •   Constants from lexical variables potentially modified elsewhere are
     deprecated. This will not be allowed in Perl 5.32

     This existing warning has had the _t_h_i_s _w_i_l_l _n_o_t _b_e _a_l_l_o_w_e_d text added
     in this release.

 •   Deprecated use of "my()" in false conditional. This will be a fatal
     error in Perl 5.30

     This existing warning has had the _t_h_i_s _w_i_l_l _b_e _a _f_a_t_a_l _e_r_r_o_r text
     added in this release.

 •   "dump()" better written as "CORE::dump()". "dump()" will no longer be
     available in Perl 5.30

     This existing warning has had the _n_o _l_o_n_g_e_r _b_e _a_v_a_i_l_a_b_l_e text added
     in this release.

 •   Experimental %s on scalar is now forbidden

     This message is now followed by more helpful text.  [GH #15291]
     <https://github.com/Perl/perl5/issues/15291>

 •   Experimental "%s" subs not enabled

     This warning was been removed, as lexical subs are no longer
     experimental.

 •   Having more than one /%c regexp modifier is deprecated

     This deprecation warning has been removed, since "/xx" now has a new
     meaning.

 •   %s() is deprecated on ":utf8" handles. This will be a fatal error in
     Perl 5.30 .

     where "%s" is one of "sysread", "recv", "syswrite", or "send".

     This existing warning has had the _t_h_i_s _w_i_l_l _b_e _a _f_a_t_a_l _e_r_r_o_r text
     added in this release.

     This warning is now enabled by default, as all "deprecated" category
     warnings should be.

 •   $* is no longer supported. Its use will be fatal in Perl 5.30

     This existing warning has had the _i_t_s _u_s_e _w_i_l_l _b_e _f_a_t_a_l text added in
     this release.

 •   $# is no longer supported. Its use will be fatal in Perl 5.30

     This existing warning has had the _i_t_s _u_s_e _w_i_l_l _b_e _f_a_t_a_l text added in
     this release.

 •   Malformed UTF-8 character%s

     Details as to the exact problem have been added at the end of this
     message

 •   Missing or undefined argument to %s

     This warning used to warn about "require", even if it was actually
     "do" which being executed. It now gets the operation name right.

 •   NO-BREAK SPACE in a charnames alias definition is deprecated

     This warning has been removed as the behavior is now an error.

 •   Odd name/value argument for subroutine '%s'

     This warning now includes the name of the offending subroutine.

 •   Opening dirhandle %s also as a file. This will be a fatal error in
     Perl 5.28

     This existing warning has had the _t_h_i_s _w_i_l_l _b_e _a _f_a_t_a_l _e_r_r_o_r text
     added in this release.

 •   Opening filehandle %s also as a directory. This will be a fatal error
     in Perl 5.28

     This existing warning has had the _t_h_i_s _w_i_l_l _b_e _a _f_a_t_a_l _e_r_r_o_r text
     added in this release.

 •   panic: ck_split, type=%u

     panic: pp_split, pm=%p, s=%p

     These panic errors have been removed.

 •   Passing malformed UTF-8 to "%s" is deprecated

     This warning has been changed to the fatal Malformed UTF-8 string in
     "%s"

 •   Setting $/ to a reference to %s as a form of slurp is deprecated,
     treating as undef. This will be fatal in Perl 5.28

     This existing warning has had the _t_h_i_s _w_i_l_l _b_e _f_a_t_a_l text added in
     this release.

 •   "${^ENCODING}" is no longer supported. Its use will be fatal in Perl
     5.28

     This warning used to be: "Setting "${^ENCODING}" is deprecated".

     The special action of the variable "${^ENCODING}" was formerly used
     to implement the "encoding" pragma. As of Perl 5.26, rather than
     being deprecated, assigning to this variable now has no effect except
     to issue the warning.

 •   Too few arguments for subroutine '%s'

     This warning now includes the name of the offending subroutine.

 •   Too many arguments for subroutine '%s'

     This warning now includes the name of the offending subroutine.

 •   Unescaped left brace in regex is deprecated here (and will be fatal
     in Perl 5.30), passed through in regex; marked by <-- HERE in m/%s/

     This existing warning has had the _h_e_r_e _(_a_n_d _w_i_l_l _b_e _f_a_t_a_l_._._._) text
     added in this release.

 •   Unknown charname '' is deprecated. Its use will be fatal in Perl 5.28

     This existing warning has had the _i_t_s _u_s_e _w_i_l_l _b_e _f_a_t_a_l text added in
     this release.

 •   Use of bare << to mean <<"" is deprecated. Its use will be fatal in
     Perl 5.28

     This existing warning has had the _i_t_s _u_s_e _w_i_l_l _b_e _f_a_t_a_l text added in
     this release.

 •   Use of code point 0x%s is deprecated; the permissible max is 0x%s.
     This will be fatal in Perl 5.28

     This existing warning has had the _t_h_i_s _w_i_l_l _b_e _f_a_t_a_l text added in
     this release.

 •   Use of comma-less variable list is deprecated. Its use will be fatal
     in Perl 5.28

     This existing warning has had the _i_t_s _u_s_e _w_i_l_l _b_e _f_a_t_a_l text added in
     this release.

 •   Use of inherited "AUTOLOAD" for non-method %s() is deprecated. This
     will be fatal in Perl 5.28

     This existing warning has had the _t_h_i_s _w_i_l_l _b_e _f_a_t_a_l text added in
     this release.

 •   Use of strings with code points over 0xFF as arguments to %s operator
     is deprecated. This will be a fatal error in Perl 5.28

     This existing warning has had the _t_h_i_s _w_i_l_l _b_e _a _f_a_t_a_l _e_r_r_o_r text
     added in this release.

UUttiilliittyy CChhaannggeess _c_2_p_h aanndd _p_s_t_r_u_c_t • These old utilities have long since superceded by h2xs, and are now gone from the distribution.

_P_o_r_t_i_n_g_/_p_o_d___l_i_b_._p_l • Removed spurious executable bit.

 •   Account for the possibility of DOS file endings.

_P_o_r_t_i_n_g_/_s_y_n_c_-_w_i_t_h_-_c_p_a_n • Many improvements.

_p_e_r_f_/_b_e_n_c_h_m_a_r_k_s • Tidy file, rename some symbols.

_P_o_r_t_i_n_g_/_c_h_e_c_k_A_U_T_H_O_R_S_._p_l • Replace obscure character range with “\w”.

_t_/_p_o_r_t_i_n_g_/_r_e_g_e_n_._t • Try to be more helpful when tests fail.

_u_t_i_l_s_/_h_2_x_s_._P_L • Avoid infinite loop for enums.

ppeerrllbbuugg • Long lines in the message body are now wrapped at 900 characters, to stay well within the 1000-character limit imposed by SMTP mail transfer agents. This is particularly likely to be important for the list of arguments to _C_o_n_f_i_g_u_r_e, which can readily exceed the limit if, for example, it names several non-default installation paths. This change also adds the first unit tests for perlbug. [perl #128020] https://rt.perl.org/Public/Bug/Display.html?id=128020

CCoonnffiigguurraattiioonn aanndd CCoommppiillaattiioonn • “-Ddefault_inc_excludes_dot” has added, and enabled by default.

 •   The "dtrace" build process has further changes [GH #15718]
     <https://github.com/Perl/perl5/issues/15718>:

     •   If the "-xnolibs" is available, use that so a _d_t_r_a_c_e perl can be
         built within a FreeBSD jail.

     •   On systems that build a _d_t_r_a_c_e object file (FreeBSD, Solaris, and
         SystemTap's dtrace emulation), copy the input objects to a
         separate directory and process them there, and use those objects
         in the link, since "dtrace -G" also modifies these objects.

     •   Add _l_i_b_e_l_f to the build on FreeBSD 10.x, since _d_t_r_a_c_e adds
         references to _l_i_b_e_l_f symbols.

     •   Generate a dummy _d_t_r_a_c_e___m_a_i_n_._o if "dtrace -G" fails to build it.
         A default build on Solaris generates probes from the unused
         inline functions, while they don't on FreeBSD, which causes
         "dtrace -G" to fail.

 •   You can now disable perl's use of the "PERL_HASH_SEED" and
     "PERL_PERTURB_KEYS" environment variables by configuring perl with
     "-Accflags=NO_PERL_HASH_ENV".

 •   You can now disable perl's use of the "PERL_HASH_SEED_DEBUG"
     environment variable by configuring perl with
     "-Accflags=-DNO_PERL_HASH_SEED_DEBUG".

 •   _C_o_n_f_i_g_u_r_e now zeroes out the alignment bytes when calculating the
     bytes for 80-bit "NaN" and "Inf" to make builds more reproducible.
     [GH #15725] <https://github.com/Perl/perl5/issues/15725>

 •   Since v5.18, for testing purposes we have included support for
     building perl with a variety of non-standard, and non-recommended
     hash functions.  Since we do not recommend the use of these
     functions, we have removed them and their corresponding build
     options.  Specifically this includes the following build options:

PERL_HASH_FUNC_SDBM #

PERL_HASH_FUNC_DJB2 #

PERL_HASH_FUNC_SUPERFAST #

PERL_HASH_FUNC_MURMUR3 #

PERL_HASH_FUNC_ONE_AT_A_TIME #

PERL_HASH_FUNC_ONE_AT_A_TIME_OLD #

PERL_HASH_FUNC_MURMUR_HASH_64A #

PERL_HASH_FUNC_MURMUR_HASH_64B #

 •   Remove "Warning: perl appears in your path"

     This install warning is more or less obsolete, since most platforms
     already wwiillll have a _/_u_s_r_/_b_i_n_/_p_e_r_l or similar provided by the OS.

 •   Reduce verbosity of "make install.man"

     Previously, two progress messages were emitted for each manpage: one
     by installman itself, and one by the function in _i_n_s_t_a_l_l___l_i_b_._p_l that
     it calls to actually install the file.  Disabling the second of those
     in each case saves over 750 lines of unhelpful output.

 •   Cleanup for "clang -Weverything" support.  [GH #15683]
     <https://github.com/Perl/perl5/issues/15683>

 •   _C_o_n_f_i_g_u_r_e: signbit scan was assuming too much, stop assuming negative
     0.

 •   Various compiler warnings have been silenced.

 •   Several smaller changes have been made to remove impediments to
     compiling under C++11.

 •   Builds using "USE_PAD_RESET" now work again; this configuration had
     bit-rotted.

 •   A probe for "gai_strerror" was added to _C_o_n_f_i_g_u_r_e that checks if the
     "gai_strerror()" routine is available and can be used to translate
     error codes returned by "getaddrinfo()" into human readable strings.

 •   _C_o_n_f_i_g_u_r_e now aborts if both "-Duselongdouble" and "-Dusequadmath"
     are requested.  [GH #14944]
     <https://github.com/Perl/perl5/issues/14944>

 •   Fixed a bug in which _C_o_n_f_i_g_u_r_e could append "-quadmath" to the
     archname even if it was already present.  [GH #15423]
     <https://github.com/Perl/perl5/issues/15423>

 •   Clang builds with "-DPERL_GLOBAL_STRUCT" or
     "-DPERL_GLOBAL_STRUCT_PRIVATE" have been fixed (by disabling Thread
     Safety Analysis for these configurations).

 •   _m_a_k_e___e_x_t_._p_l no longer updates a module's _p_m___t_o___b_l_i_b file when no
     files require updates.  This could cause dependencies, _p_e_r_l_m_a_i_n_._c in
     particular, to be rebuilt unnecessarily.  [GH #15060]
     <https://github.com/Perl/perl5/issues/15060>

 •   The output of "perl -V" has been reformatted so that each
     configuration and compile-time option is now listed one per line, to
     improve readability.

 •   _C_o_n_f_i_g_u_r_e now builds "miniperl" and "generate_uudmap" if you invoke
     it with "-Dusecrosscompiler" but not "-Dtargethost=somehost".  This
     means you can supply your target platform "config.sh", generate the
     headers and proceed to build your cross-target perl.  [GH #15126]
     <https://github.com/Perl/perl5/issues/15126>

 •   Perl built with "-Accflags=-DPERL_TRACE_OPS" now only dumps the
     operator counts when the environment variable "PERL_TRACE_OPS" is set
     to a non-zero integer.  This allows "make test" to pass on such a
     build.

 •   When building with GCC 6 and link-time optimization (the "-flto"
     option to "gcc"), _C_o_n_f_i_g_u_r_e was treating all probed symbols as
     present on the system, regardless of whether they actually exist.
     This has been fixed.  [GH #15322]
     <https://github.com/Perl/perl5/issues/15322>

 •   The _t_/_t_e_s_t_._p_l library is used for internal testing of Perl itself,
     and also copied by several CPAN modules.  Some of those modules must
     work on older versions of Perl, so _t_/_t_e_s_t_._p_l must in turn avoid newer
     Perl features.  Compatibility with Perl 5.8 was inadvertently removed
     some time ago; it has now been restored.  [GH #15302]
     <https://github.com/Perl/perl5/issues/15302>

 •   The build process no longer emits an extra blank line before building
     each "simple" extension (those with only _*_._p_m and _*_._p_o_d files).

TTeessttiinngg Tests were added and changed to reflect the other additions and changes in this release. Furthermore, these substantive changes were made:

 •   A new test script, _c_o_m_p_/_p_a_r_s_e_r___r_u_n_._t, has been added that is like
     _c_o_m_p_/_p_a_r_s_e_r_._t but with _t_e_s_t_._p_l included so that "runperl()" and the
     like are available for use.

 •   Tests for locales were erroneously using locales incompatible with
     Perl.

 •   Some parts of the test suite that try to exhaustively test edge cases
     in the regex implementation have been restricted to running for a
     maximum of five minutes.  On slow systems they could otherwise take
     several hours, without significantly improving our understanding of
     the correctness of the code under test.

 •   A new internal facility allows analysing the time taken by the
     individual tests in Perl's own test suite; see
     _P_o_r_t_i_n_g_/_h_a_r_n_e_s_s_-_t_i_m_e_r_-_r_e_p_o_r_t_._p_l.

 •   _t_/_r_e_/_r_e_g_e_x_p___n_o_n_u_l_l_._t has been added to test that the regular
     expression engine can handle scalars that do not have a null byte
     just past the end of the string.

 •   A new test script, _t_/_o_p_/_d_e_c_l_-_r_e_f_s_._t, has been added to test the new
     feature "Declaring a reference to a variable".

 •   A new test script, _t_/_r_e_/_k_e_e_p___t_a_b_s_._t has been added to contain tests
     where "\t" characters should not be expanded into spaces.

 •   A new test script, _t_/_r_e_/_a_n_y_o_f_._t, has been added to test that the
     ANYOF nodes generated by bracketed character classes are as expected.

 •   There is now more extensive testing of the Unicode-related API macros
     and functions.

 •   Several of the longer running API test files have been split into
     multiple test files so that they can be run in parallel.

 •   _t_/_h_a_r_n_e_s_s now tries really hard not to run tests which are located
     outside of the Perl source tree.  [GH #14578]
     <https://github.com/Perl/perl5/issues/14578>

 •   Prevent debugger tests (_l_i_b_/_p_e_r_l_5_d_b_._t) from failing due to the
     contents of $ENV{PERLDB_OPTS}.  [GH #15782]
     <https://github.com/Perl/perl5/issues/15782>

PPllaattffoorrmm SSuuppppoorrtt NNeeww PPllaattffoorrmmss NetBSD/VAX Perl now compiles under NetBSD on VAX machines. However, it’s not possible for that platform to implement floating-point infinities and NaNs compatible with most modern systems, which implement the IEEE-754 floating point standard. The hexadecimal floating point (“0x…p[+-]n” literals, “printf %a”) is not implemented, either. The “make test” passes 98% of tests.

     •   Test fixes and minor updates.

     •   Account for lack of "inf", "nan", and "-0.0" support.

PPllaattffoorrmm--SSppeecciiffiicc NNootteess Darwin • Don’t treat “-Dprefix=/usr” as special: instead require an extra option “-Ddarwin_distribution” to produce the same results.

     •   OS X El Capitan doesn't implement the "clock_gettime()" or
         "clock_getres()" APIs; emulate them as necessary.

     •   Deprecated syscall(2) on macOS 10.12.

EBCDIC #

     Several tests have been updated to work (or be skipped) on EBCDIC
     platforms.

HP-UX #

     The Net::Ping UDP test is now skipped on HP-UX.

 Hurd
     The hints for Hurd have been improved, enabling malloc wrap and
     reporting the GNU libc used (previously it was an empty string when
     reported).

 VAX VAX floating point formats are now supported on NetBSD.

VMS #

     •   The path separator for the "PERL5LIB" and "PERLLIB" environment
         entries is now a colon (":") when running under a Unix shell.
         There is no change when running under DCL (it's still "|").

     •   _c_o_n_f_i_g_u_r_e_._c_o_m now recognizes the VSI-branded C compiler and no
         longer recognizes the "DEC"-branded C compiler (as there hasn't
         been such a thing for 15 or more years).

 Windows
     •   Support for compiling perl on Windows using Microsoft Visual
         Studio 2015 (containing Visual C++ 14.0) has been added.

         This version of VC++ includes a completely rewritten C run-time
         library, some of the changes in which mean that work done to
         resolve a socket "close()" bug in perl #120091 and perl #118059
         is not workable in its current state with this version of VC++.
         Therefore, we have effectively reverted that bug fix for VS2015
         onwards on the basis that being able to build with VS2015 onwards
         is more important than keeping the bug fix.  We may revisit this
         in the future to attempt to fix the bug again in a way that is
         compatible with VS2015.

         These changes do not affect compilation with GCC or with Visual
         Studio versions up to and including VS2013, _i_._e_., the bug fix is
         retained (unchanged) for those compilers.

         Note that you may experience compatibility problems if you mix a
         perl built with GCC or VS <= VS2013 with XS modules built with
         VS2015, or if you mix a perl built with VS2015 with XS modules
         built with GCC or VS <= VS2013. Some incompatibility may arise
         because of the bug fix that has been reverted for VS2015 builds
         of perl, but there may well be incompatibility anyway because of
         the rewritten CRT in VS2015 (_e_._g_., see discussion at
         <http://stackoverflow.com/questions/30412951>).

     •   It now automatically detects GCC versus Visual C and sets the VC
         version number on Win32.

 Linux
     Drop support for Linux _a_._o_u_t executable format. Linux has used ELF
     for over twenty years.

 OpenBSD 6
     OpenBSD 6 still does not support returning "pid", "gid", or "uid"
     with "SA_SIGINFO".  Make sure to account for it.

 FreeBSD
     _t_/_u_n_i_/_o_v_e_r_l_o_a_d_._t: Skip hanging test on FreeBSD.

 DragonFly BSD
     DragonFly BSD now has support for "setproctitle()".  [GH #15703]
     <https://github.com/Perl/perl5/issues/15703>.

IInntteerrnnaall CChhaannggeess • A new API function “sv_setpv_bufsize()” allows simultaneously setting the length and the allocated size of the buffer in an “SV”, growing the buffer if necessary.

 •   A new API macro "SvPVCLEAR()" sets its "SV" argument to an empty
     string, like Perl-space "$x = ''", but with several optimisations.

 •   Several new macros and functions for dealing with Unicode and
     UTF-8-encoded strings have been added to the API, as well as some
     changes in the functionality of existing functions (see "Unicode
     Support" in perlapi for more details):

     •   New versions of the API macros like "isALPHA_utf8" and
         "toLOWER_utf8" have been added, each with the suffix "_safe",
         like "isSPACE_utf8_safe".  These take an extra parameter, giving
         an upper limit of how far into the string it is safe to read.
         Using the old versions could cause attempts to read beyond the
         end of the input buffer if the UTF-8 is not well-formed, and
         their use now raises a deprecation warning.  Details are at
         "Character classification" in perlapi.

     •   Macros like "isALPHA_utf8" and "toLOWER_utf8" now die if they
         detect that their input UTF-8 is malformed.  A deprecation
         warning had been issued since Perl 5.18.

     •   Several new macros for analysing the validity of utf8 sequences.
         These are:

“UTF8_GOT_ABOVE_31_BIT” “UTF8_GOT_CONTINUATION” “UTF8_GOT_EMPTY” #

“UTF8_GOT_LONG” “UTF8_GOT_NONCHAR” “UTF8_GOT_NON_CONTINUATION” #

“UTF8_GOT_OVERFLOW” “UTF8_GOT_SHORT” “UTF8_GOT_SUPER” #

“UTF8_GOT_SURROGATE” “UTF8_IS_INVARIANT” “UTF8_IS_NONCHAR” #

“UTF8_IS_SUPER” “UTF8_IS_SURROGATE” “UVCHR_IS_INVARIANT” #

         "isUTF8_CHAR_flags" "isSTRICT_UTF8_CHAR" "isC9_STRICT_UTF8_CHAR"

     •   Functions that are all extensions of the "is_utf8_string__*()"
         functions, that apply various restrictions to the UTF-8
         recognized as valid:

         "is_strict_utf8_string", "is_strict_utf8_string_loc",
         "is_strict_utf8_string_loclen",

         "is_c9strict_utf8_string", "is_c9strict_utf8_string_loc",
         "is_c9strict_utf8_string_loclen",

         "is_utf8_string_flags", "is_utf8_string_loc_flags",
         "is_utf8_string_loclen_flags",

         "is_utf8_fixed_width_buf_flags",
         "is_utf8_fixed_width_buf_loc_flags",
         "is_utf8_fixed_width_buf_loclen_flags".

         "is_utf8_invariant_string".  "is_utf8_valid_partial_char".
         "is_utf8_valid_partial_char_flags".

     •   The functions "utf8n_to_uvchr" and its derivatives have had
         several changes of behaviour.

         Calling them, while passing a string length of 0 is now asserted
         against in DEBUGGING builds, and otherwise, returns the Unicode
         REPLACEMENT CHARACTER.   If you have nothing to decode, you
         shouldn't call the decode function.

         They now return the Unicode REPLACEMENT CHARACTER if called with
         UTF-8 that has the overlong malformation and that malformation is
         allowed by the input parameters.  This malformation is where the
         UTF-8 looks valid syntactically, but there is a shorter sequence
         that yields the same code point.  This has been forbidden since
         Unicode version 3.1.

         They now accept an input flag to allow the overflow malformation.
         This malformation is when the UTF-8 may be syntactically valid,
         but the code point it represents is not capable of being
         represented in the word length on the platform.  What "allowed"
         means, in this case, is that the function doesn't return an
         error, and it advances the parse pointer to beyond the UTF-8 in
         question, but it returns the Unicode REPLACEMENT CHARACTER as the
         value of the code point (since the real value is not
         representable).

         They no longer abandon searching for other malformations when the
         first one is encountered.  A call to one of these functions thus
         can generate multiple diagnostics, instead of just one.

     •   "valid_utf8_to_uvchr()" has been added to the API (although it
         was present in core earlier). Like "utf8_to_uvchr_buf()", but
         assumes that the next character is well-formed.  Use with
         caution.

     •   A new function, "utf8n_to_uvchr_error", has been added for use by
         modules that need to know the details of UTF-8 malformations
         beyond pass/fail.  Previously, the only ways to know why a
         sequence was ill-formed was to capture and parse the generated
         diagnostics or to do your own analysis.

     •   There is now a safer version of uuttff88__hhoopp(()), called
         "utf8_hop_safe()".  Unlike uuttff88__hhoopp(()), uuttff88__hhoopp__ssaaffee(()) won't
         navigate before the beginning or after the end of the supplied
         buffer.

     •   Two new functions, "utf8_hop_forward()" and "utf8_hop_back()" are
         similar to "utf8_hop_safe()" but are for when you know which
         direction you wish to travel.

     •   Two new macros which return useful utf8 byte sequences:

“BOM_UTF8” #

“REPLACEMENT_CHARACTER_UTF8” #

 •   Perl is now built with the "PERL_OP_PARENT" compiler define enabled
     by default.  To disable it, use the "PERL_NO_OP_PARENT" compiler
     define.  This flag alters how the "op_sibling" field is used in "OP"
     structures, and has been available optionally since perl 5.22.

     See "Internal Changes" in perl5220delta for more details of what this
     build option does.

 •   Three new ops, "OP_ARGELEM", "OP_ARGDEFELEM", and "OP_ARGCHECK" have
     been added.  These are intended principally to implement the
     individual elements of a subroutine signature, plus any overall
     checking required.

 •   The "OP_PUSHRE" op has been eliminated and the "OP_SPLIT" op has been
     changed from class "LISTOP" to "PMOP".

     Formerly the first child of a split would be a "pushre", which would
     have the "split"'s regex attached to it. Now the regex is attached
     directly to the "split" op, and the "pushre" has been eliminated.

 •   The "op_class()" API function has been added.  This is like the
     existing "OP_CLASS()" macro, but can more accurately determine what
     struct an op has been allocated as.  For example "OP_CLASS()" might
     return "OA_BASEOP_OR_UNOP" indicating that ops of this type are
     usually allocated as an "OP" or "UNOP"; while "op_class()" will
     return "OPclass_BASEOP" or "OPclass_UNOP" as appropriate.

 •   All parts of the internals now agree that the "sassign" op is a
     "BINOP"; previously it was listed as a "BASEOP" in _r_e_g_e_n_/_o_p_c_o_d_e_s,
     which meant that several parts of the internals had to be special-
     cased to accommodate it.  This oddity's original motivation was to
     handle code like "$x ||= 1"; that is now handled in a simpler way.

 •   The output format of the "op_dump()" function (as used by "perl -Dx")
     has changed: it now displays an "ASCII-art" tree structure, and shows
     more low-level details about each op, such as its address and class.

 •   The "PADOFFSET" type has changed from being unsigned to signed, and
     several pad-related variables such as "PL_padix" have changed from
     being of type "I32" to type "PADOFFSET".

 •   The "DEBUGGING"-mode output for regex compilation and execution has
     been enhanced.

 •   Several obscure SV flags have been eliminated, sometimes along with
     the macros which manipulate them: "SVpbm_VALID", "SVpbm_TAIL",
     "SvTAIL_on", "SvTAIL_off", "SVrepl_EVAL", "SvEVALED".

 •   An OP "op_private" flag has been eliminated: "OPpRUNTIME". This used
     to often get set on "PMOP" ops, but had become meaningless over time.

SSeelleecctteedd BBuugg FFiixxeess • Perl no longer panics when switching into some locales on machines with buggy “strxfrm()” implementations in their _l_i_b_c. [GH #13768] https://github.com/Perl/perl5/issues/13768

 •   " $-{$name} " would leak an "AV" on each access if the regular
     expression had no named captures.  The same applies to access to any
     hash tied with Tie::Hash::NamedCapture and "all => 1".  [GH #15882]
     <https://github.com/Perl/perl5/issues/15882>

 •   Attempting to use the deprecated variable $# as the object in an
     indirect object method call could cause a heap use after free or
     buffer overflow.  [GH #15599]
     <https://github.com/Perl/perl5/issues/15599>

 •   When checking for an indirect object method call, in some rare cases
     the parser could reallocate the line buffer but then continue to use
     pointers to the old buffer.  [GH #15585]
     <https://github.com/Perl/perl5/issues/15585>

 •   Supplying a glob as the format argument to "formline" would cause an
     assertion failure.  [GH #15862]
     <https://github.com/Perl/perl5/issues/15862>

 •   Code like " $value1 =~ qr/.../ ~~ $value2 " would have the match
     converted into a "qr//" operator, leaving extra elements on the stack
     to confuse any surrounding expression.  [GH #15859]
     <https://github.com/Perl/perl5/issues/15859>

 •   Since v5.24 in some obscure cases, a regex which included code blocks
     from multiple sources (_e_._g_., via embedded via "qr//" objects) could
     end up with the wrong current pad and crash or give weird results.
     [GH #15657] <https://github.com/Perl/perl5/issues/15657>

 •   Occasionally "local()"s in a code block within a patterns weren't
     being undone when the pattern matching backtracked over the code
     block.  [GH #15056] <https://github.com/Perl/perl5/issues/15056>

 •   Using "substr()" to modify a magic variable could access freed memory
     in some cases.  [GH #15871]
     <https://github.com/Perl/perl5/issues/15871>

 •   Under "use utf8", the entire source code is now checked for being
     UTF-8 well formed, not just quoted strings as before.  [GH #14973]
     <https://github.com/Perl/perl5/issues/14973>.

 •   The range operator ".." on strings now handles its arguments
     correctly when in the scope of the "unicode_strings" feature.  The
     previous behaviour was sufficiently unexpected that we believe no
     correct program could have made use of it.

 •   The "split" operator did not ensure enough space was allocated for
     its return value in scalar context.  It could then write a single
     pointer immediately beyond the end of the memory block allocated for
     the stack.  [GH #15749] <https://github.com/Perl/perl5/issues/15749>

 •   Using a large code point with the "W" pack template character with
     the current output position aligned at just the right point could
     cause a write of a single zero byte immediately beyond the end of an
     allocated buffer.  [GH #15572]
     <https://github.com/Perl/perl5/issues/15572>

 •   Supplying a format's picture argument as part of the format argument
     list where the picture specifies modifying the argument could cause
     an access to the new freed compiled format.  [GH #15566]
     <https://github.com/Perl/perl5/issues/15566>

 •   The ssoorrtt(()) operator's built-in numeric comparison function didn't
     handle large integers that weren't exactly representable by a double.
     This now uses the same code used to implement the "<=>" operator.
     [GH #15768] <https://github.com/Perl/perl5/issues/15768>

 •   Fix issues with "/(?{ ... <<EOF })/" that broke Method::Signatures.
     [GH #15779] <https://github.com/Perl/perl5/issues/15779>

 •   Fixed an assertion failure with "chop" and "chomp", which could be
     triggered by "chop(@x =~ tr/1/1/)".  [GH #15738]
     <https://github.com/Perl/perl5/issues/15738>.

 •   Fixed a comment skipping error in patterns under "/x"; it could stop
     skipping a byte early, which could be in the middle of a UTF-8
     character.  [GH #15790] <https://github.com/Perl/perl5/issues/15790>.

 •   _p_e_r_l_d_b now ignores _/_d_e_v_/_t_t_y on non-Unix systems.  [GH #12244]
     <https://github.com/Perl/perl5/issues/12244>;

 •   Fix assertion failure for "{}->$x" when $x isn't defined.  [GH
     #15791] <https://github.com/Perl/perl5/issues/15791>.

 •   Fix an assertion error which could be triggered when a lookahead
     string in patterns exceeded a minimum length.  [GH #15796]
     <https://github.com/Perl/perl5/issues/15796>.

 •   Only warn once per literal number about a misplaced "_".  [GH #9989]
     <https://github.com/Perl/perl5/issues/9989>.

 •   The "tr///" parse code could be looking at uninitialized data after a
     perse error.  [GH #15624]
     <https://github.com/Perl/perl5/issues/15624>.

 •   In a pattern match, a back-reference ("\1") to an unmatched capture
     could read back beyond the start of the string being matched.  [GH
     #15634] <https://github.com/Perl/perl5/issues/15634>.

 •   "use re 'strict'" is supposed to warn if you use a range (such as
     "/(?[ [ X-Y ] ])/") whose start and end digit aren't from the same
     group of 10.  It didn't do that for five groups of mathematical
     digits starting at "U+1D7E".

 •   A sub containing a "forward" declaration with the same name (_e_._g_.,
     "sub c { sub c; }") could sometimes crash or loop infinitely.  [GH
     #15557] <https://github.com/Perl/perl5/issues/15557>

 •   A crash in executing a regex with a non-anchored UTF-8 substring
     against a target string that also used UTF-8 has been fixed.  [GH
     #15628] <https://github.com/Perl/perl5/issues/15628>

 •   Previously, a shebang line like "#!perl -i u" could be erroneously
     interpreted as requesting the "-u" option.  This has been fixed.  [GH
     #15623] <https://github.com/Perl/perl5/issues/15623>

 •   The regex engine was previously producing incorrect results in some
     rare situations when backtracking past an alternation that matches
     only one thing; this showed up as capture buffers ($1, $2, _e_t_c_.)
     erroneously containing data from regex execution paths that weren't
     actually executed for the final match.  [GH #15666]
     <https://github.com/Perl/perl5/issues/15666>

 •   Certain regexes making use of the experimental "regex_sets" feature
     could trigger an assertion failure.  This has been fixed.  [GH
     #15620] <https://github.com/Perl/perl5/issues/15620>

 •   Invalid assignments to a reference constructor (_e_._g_., "\eval=time")
     could sometimes crash in addition to giving a syntax error.  [GH
     #14815] <https://github.com/Perl/perl5/issues/14815>

 •   The parser could sometimes crash if a bareword came after
     "evalbytes".  [GH #15586]
     <https://github.com/Perl/perl5/issues/15586>

 •   Autoloading via a method call would warn erroneously ("Use of
     inherited AUTOLOAD for non-method") if there was a stub present in
     the package into which the invocant had been blessed.  The warning is
     no longer emitted in such circumstances.  [GH #9094]
     <https://github.com/Perl/perl5/issues/9094>

 •   The use of "splice" on arrays with non-existent elements could cause
     other operators to crash.  [GH #15577]
     <https://github.com/Perl/perl5/issues/15577>

 •   A possible buffer overrun when a pattern contains a fixed utf8
     substring.  [GH #15534] <https://github.com/Perl/perl5/issues/15534>

 •   Fixed two possible use-after-free bugs in perl's lexer.  [GH #15549]
     <https://github.com/Perl/perl5/issues/15549>

 •   Fixed a crash with "s///l" where it thought it was dealing with UTF-8
     when it wasn't.  [GH #15543]
     <https://github.com/Perl/perl5/issues/15543>

 •   Fixed a place where the regex parser was not setting the syntax error
     correctly on a syntactically incorrect pattern.  [GH #15565]
     <https://github.com/Perl/perl5/issues/15565>

 •   The "&." operator (and the "&" operator, when it treats its arguments
     as strings) were failing to append a trailing null byte if at least
     one string was marked as utf8 internally.  Many code paths (system
     calls, regexp compilation) still expect there to be a null byte in
     the string buffer just past the end of the logical string.  An
     assertion failure was the result.  [GH #15606]
     <https://github.com/Perl/perl5/issues/15606>

 •   Avoid a heap-after-use error in the parser when creating an error
     messge for a syntactically invalid heredoc.  [GH #15527]
     <https://github.com/Perl/perl5/issues/15527>

 •   Fix a segfault when run with "-DC" options on DEBUGGING builds.  [GH
     #15563] <https://github.com/Perl/perl5/issues/15563>

 •   Fixed the parser error handling in subroutine attributes for an
     '":attr(foo"' that does not have an ending '")"'.

 •   Fix the perl lexer to correctly handle a backslash as the last char
     in quoted-string context. This actually fixed two bugs, [GH #15546]
     <https://github.com/Perl/perl5/issues/15546> and [GH #15582]
     <https://github.com/Perl/perl5/issues/15582>.

 •   In the API function "gv_fetchmethod_pvn_flags", rework separator
     parsing to prevent possible string overrun with an invalid "len"
     argument.  [GH #15598] <https://github.com/Perl/perl5/issues/15598>

 •   Problems with in-place array sorts: code like "@a = sort { ... } @a",
     where the source and destination of the sort are the same plain
     array, are optimised to do less copying around.  Two side-effects of
     this optimisation were that the contents of @a as seen by sort
     routines were partially sorted; and under some circumstances
     accessing @a during the sort could crash the interpreter.  Both these
     issues have been fixed, and Sort functions see the original value of
     @a.  [GH #15387] <https://github.com/Perl/perl5/issues/15387>

 •   Non-ASCII string delimiters are now reported correctly in error
     messages for unterminated strings.  [GH #15469]
     <https://github.com/Perl/perl5/issues/15469>

 •   "pack("p", ...)" used to emit its warning ("Attempt to pack pointer
     to temporary value") erroneously in some cases, but has been fixed.

 •   @DB::args is now exempt from "used once" warnings.  The warnings only
     occurred under --ww, because _w_a_r_n_i_n_g_s_._p_m itself uses @DB::args multiple
     times.

 •   The use of built-in arrays or hash slices in a double-quoted string
     no longer issues a warning ("Possible unintended interpolation...")
     if the variable has not been mentioned before.  This affected code
     like "qq|@DB::args|" and "qq|@SIG{'CHLD', 'HUP'}|".  (The special
     variables "@-" and "@+" were already exempt from the warning.)

 •   "gethostent" and similar functions now perform a null check
     internally, to avoid crashing with the torsocks library.  This was a
     regression from v5.22.  [GH #15478]
     <https://github.com/Perl/perl5/issues/15478>

 •   "defined *{'!'}", "defined *{'['}", and "defined *{'-'}" no longer
     leak memory if the typeglob in question has never been accessed
     before.

 •   Mentioning the same constant twice in a row (which is a syntax error)
     no longer fails an assertion under debugging builds.  This was a
     regression from v5.20.  [GH #15017]
     <https://github.com/Perl/perl5/issues/15017>

 •   Many issues relating to "printf "%a"" of hexadecimal floating point
     were fixed.  In addition, the "subnormals" (formerly known as
     "denormals") floating point numbers are now supported both with the
     plain IEEE 754 floating point numbers (64-bit or 128-bit) and the x86
     80-bit "extended precision".  Note that subnormal hexadecimal
     floating point literals will give a warning about "exponent
     underflow".  [GH #15495] <https://github.com/Perl/perl5/issues/15495>
     [GH #15503] <https://github.com/Perl/perl5/issues/15503> [GH #15504]
     <https://github.com/Perl/perl5/issues/15504> [GH #15505]
     <https://github.com/Perl/perl5/issues/15505> [GH #15510]
     <https://github.com/Perl/perl5/issues/15510> [GH #15512]
     <https://github.com/Perl/perl5/issues/15512>

 •   A regression in v5.24 with "tr/\N{U+...}/foo/" when the code point
     was between 128 and 255 has been fixed.  [GH #15475]
     <https://github.com/Perl/perl5/issues/15475>.

 •   Use of a string delimiter whose code point is above 2**31 now works
     correctly on platforms that allow this.  Previously, certain
     characters, due to truncation, would be confused with other delimiter
     characters with special meaning (such as "?" in "m?...?"), resulting
     in inconsistent behaviour.  Note that this is non-portable, and is
     based on Perl's extension to UTF-8, and is probably not displayable
     nor enterable by any editor.  [GH #15477]
     <https://github.com/Perl/perl5/issues/15477>

 •   "@{x" followed by a newline where "x" represents a control or non-
     ASCII character no longer produces a garbled syntax error message or
     a crash.  [GH #15518] <https://github.com/Perl/perl5/issues/15518>

 •   An assertion failure with "%: = 0" has been fixed.  [GH #15358]
     <https://github.com/Perl/perl5/issues/15358>

 •   In Perl 5.18, the parsing of "$foo::$bar" was accidentally changed,
     such that it would be treated as "$foo."::".$bar".  The previous
     behavior, which was to parse it as "$foo:: . $bar", has been
     restored.  [GH #15408] <https://github.com/Perl/perl5/issues/15408>

 •   Since Perl 5.20, line numbers have been off by one when perl is
     invoked with the --xx switch.  This has been fixed.  [GH #15413]
     <https://github.com/Perl/perl5/issues/15413>

 •   Vivifying a subroutine stub in a deleted stash (_e_._g_., "delete
     $My::{"Foo::"}; \&My::Foo::foo") no longer crashes.  It had begun
     crashing in Perl 5.18.  [GH #15420]
     <https://github.com/Perl/perl5/issues/15420>

 •   Some obscure cases of subroutines and file handles being freed at the
     same time could result in crashes, but have been fixed.  The crash
     was introduced in Perl 5.22.  [GH #15435]
     <https://github.com/Perl/perl5/issues/15435>

 •   Code that looks for a variable name associated with an uninitialized
     value could cause an assertion failure in cases where magic is
     involved, such as $ISA[0][0].  This has now been fixed.  [GH #15364]
     <https://github.com/Perl/perl5/issues/15364>

 •   A crash caused by code generating the warning "Subroutine STASH::NAME
     redefined" in cases such as "sub P::f{} undef *P::; *P::f =sub{};"
     has been fixed.  In these cases, where the STASH is missing, the
     warning will now appear as "Subroutine NAME redefined".  [GH #15368]
     <https://github.com/Perl/perl5/issues/15368>

 •   Fixed an assertion triggered by some code that handles deprecated
     behavior in formats, _e_._g_., in cases like this:

         format STDOUT =
         @
         0"$x"

     [GH #15366] <https://github.com/Perl/perl5/issues/15366>

 •   A possible divide by zero in string transformation code on Windows
     has been avoided, fixing a crash when collating an empty string.  [GH
     #15439] <https://github.com/Perl/perl5/issues/15439>

 •   Some regular expression parsing glitches could lead to assertion
     failures with regular expressions such as "/(?<=/" and "/(?<!/".
     This has now been fixed.  [GH #15332]
     <https://github.com/Perl/perl5/issues/15332>

 •   " until ($x = 1) { ... } " and " ... until $x = 1 " now properly warn
     when syntax warnings are enabled.  [GH #15138]
     <https://github.com/Perl/perl5/issues/15138>

 •   ssoocckkeett(()) now leaves the error code returned by the system in $! on
     failure.  [GH #15383] <https://github.com/Perl/perl5/issues/15383>

 •   Assignment variants of any bitwise ops under the "bitwise" feature
     would crash if the left-hand side was an array or hash.  [GH #15346]
     <https://github.com/Perl/perl5/issues/15346>

 •   "require" followed by a single colon (as in "foo() ? require : ..."
     is now parsed correctly as "require" with implicit $_, rather than
     "require """.  [GH #15380]
     <https://github.com/Perl/perl5/issues/15380>

 •   Scalar "keys %hash" can now be assigned to consistently in all scalar
     lvalue contexts.  Previously it worked for some contexts but not
     others.

 •   List assignment to "vec" or "substr" with an array or hash for its
     first argument used to result in crashes or "Can't coerce" error
     messages at run time, unlike scalar assignment, which would give an
     error at compile time.  List assignment now gives a compile-time
     error, too.  [GH #15370] <https://github.com/Perl/perl5/issues/15370>

 •   Expressions containing an "&&" or "||" operator (or their synonyms
     "and" and "or") were being compiled incorrectly in some cases.  If
     the left-hand side consisted of either a negated bareword constant or
     a negated "do {}" block containing a constant expression, and the
     right-hand side consisted of a negated non-foldable expression, one
     of the negations was effectively ignored.  The same was true of "if"
     and "unless" statement modifiers, though with the left-hand and
     right-hand sides swapped.  This long-standing bug has now been fixed.
     [GH #15285] <https://github.com/Perl/perl5/issues/15285>

 •   "reset" with an argument no longer crashes when encountering stash
     entries other than globs.  [GH #15314]
     <https://github.com/Perl/perl5/issues/15314>

 •   Assignment of hashes to, and deletion of, typeglobs named *:::::: no
     longer causes crashes.  [GH #15307]
     <https://github.com/Perl/perl5/issues/15307>

 •   Perl wasn't correctly handling true/false values in the LHS of a list
     assign; specifically the truth values returned by boolean operators.
     This could trigger an assertion failure in something like the
     following:

         for ($x > $y) {
             ($_, ...) = (...); # here $_ is aliased to a truth value
         }

     This was a regression from v5.24.  [GH #15690]
     <https://github.com/Perl/perl5/issues/15690>

 •   Assertion failure with user-defined Unicode-like properties.  [GH
     #15696] <https://github.com/Perl/perl5/issues/15696>

 •   Fix error message for unclosed "\N{" in a regex.  An unclosed "\N{"
     could give the wrong error message: "\N{NAME} must be resolved by the
     lexer".

 •   List assignment in list context where the LHS contained aggregates
     and where there were not enough RHS elements, used to skip scalar
     lvalues.  Previously, "(($a,$b,@c,$d) = (1))" in list context
     returned "($a)"; now it returns "($a,$b,$d)".  "(($a,$b,$c) = (1))"
     is unchanged: it still returns "($a,$b,$c)".  This can be seen in the
     following:

         sub inc { $_++ for @_ }
         inc(($a,$b,@c,$d) = (10))

     Formerly, the values of "($a,$b,$d)" would be left as
     "(11,undef,undef)"; now they are "(11,1,1)".

 •   Code like this: "/(?{ s!!! })/" could trigger infinite recursion on
     the C stack (not the normal perl stack) when the last successful
     pattern in scope is itself.  We avoid the segfault by simply
     forbidding the use of the empty pattern when it would resolve to the
     currently executing pattern.  [GH #15669]
     <https://github.com/Perl/perl5/issues/15669>

 •   Avoid reading beyond the end of the line buffer in perl's lexer when
     there's a short UTF-8 character at the end.  [GH #15531]
     <https://github.com/Perl/perl5/issues/15531>

 •   Alternations in regular expressions were sometimes failing to match a
     utf8 string against a utf8 alternate.  [GH #15680]
     <https://github.com/Perl/perl5/issues/15680>

 •   Make "do "a\0b"" fail silently (and return "undef" and set $!)
     instead of throwing an error.  [GH #15676]
     <https://github.com/Perl/perl5/issues/15676>

 •   "chdir" with no argument didn't ensure that there was stack space
     available for returning its result.  [GH #15569]
     <https://github.com/Perl/perl5/issues/15569>

 •   All error messages related to "do" now refer to "do"; some formerly
     claimed to be from "require" instead.

 •   Executing "undef $x" where $x is tied or magical no longer
     incorrectly blames the variable for an uninitialized-value warning
     encountered by the tied/magical code.

 •   Code like "$x = $x . "a"" was incorrectly failing to yield a use of
     uninitialized value warning when $x was a lexical variable with an
     undefined value. That has now been fixed.  [GH #15269]
     <https://github.com/Perl/perl5/issues/15269>

 •   "undef *_; shift" or "undef *_; pop" inside a subroutine, with no
     argument to "shift" or "pop", began crashing in Perl 5.14, but has
     now been fixed.

 •   "string$scalar->$*" now correctly prefers concatenation overloading
     to string overloading if "$scalar->$*" returns an overloaded object,
     bringing it into consistency with $$scalar.

 •   "/@0{0*->@*/*0" and similar contortions used to crash, but no longer
     do, but merely produce a syntax error.  [GH #15333]
     <https://github.com/Perl/perl5/issues/15333>

 •   "do" or "require" with an argument which is a reference or typeglob
     which, when stringified, contains a null character, started crashing
     in Perl 5.20, but has now been fixed.  [GH #15337]
     <https://github.com/Perl/perl5/issues/15337>

 •   Improve the error message for a missing "tie()" package/method. This
     brings the error messages in line with the ones used for normal
     method calls.

 •   Parsing bad POSIX charclasses no longer leaks memory.  [GH #15382]
     <https://github.com/Perl/perl5/issues/15382>

KKnnoowwnn PPrroobblleemmss • G++ 6 handles subnormal (denormal) floating point values differently than gcc 6 or g++ 5 resulting in “flush-to-zero”. The end result is that if you specify very small values using the hexadecimal floating point format, like “0x1.fffffffffffffp-1022”, they become zeros. [GH #15990] https://github.com/Perl/perl5/issues/15990

EErrrraattaa FFrroomm PPrreevviioouuss RReelleeaasseess • Fixed issues with recursive regexes. The behavior was fixed in Perl 5.24. [GH #14935] https://github.com/Perl/perl5/issues/14935

OObbiittuuaarryy Jon Portnoy (AVENJ), a prolific Perl author and admired Gentoo community member, has passed away on August 10, 2016. He will be remembered and missed by all those who he came in contact with, and enriched with his intellect, wit, and spirit.

 It is with great sadness that we also note Kip Hampton's passing.
 Probably best known as the author of the Perl & XML column on XML.com, he
 was a core contributor to AxKit, an XML server platform that became an
 Apache Foundation project.  He was a frequent speaker in the early days
 at OSCON, and most recently at YAPC::NA in Madison.  He was frequently on
 irc.perl.org as ubu, generally in the #axkit-dahut community, the group
 responsible for YAPC::NA Asheville in 2011.

 Kip and his constant contributions to the community will be greatly
 missed.

AAcckknnoowwlleeddggeemmeennttss Perl 5.26.0 represents approximately 13 months of development since Perl 5.24.0 and contains approximately 360,000 lines of changes across 2,600 files from 86 authors.

 Excluding auto-generated files, documentation and release tools, there
 were approximately 230,000 lines of changes to 1,800 .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 5.26.0:

 Aaron Crane, Abigail, Ævar Arnfjörð Bjarmason, Alex Vandiver, Andreas
 König, Andreas Voegele, Andrew Fresh, Andy Lester, Aristotle Pagaltzis,
 Chad Granum, Chase Whitener, Chris 'BinGOs' Williams, Chris Lamb,
 Christian Hansen, Christian Millour, Colin Newell, Craig A. Berry,
 Dagfinn Ilmari Mannsåker, Dan Collins, Daniel Dragan, Dave Cross, Dave
 Rolsky, David Golden, David H.  Gutteridge, David Mitchell, Dominic
 Hargreaves, Doug Bell, E. Choroba, Ed Avis, Father Chrysostomos, François
 Perrad, Hauke D, H.Merijn Brand, Hugo van der Sanden, Ivan Pozdeev, James
 E Keenan, James Raspass, Jarkko Hietaniemi, Jerry D. Hedden, Jim Cromie,
 J. Nick Koston, John Lightsey, Karen Etheridge, Karl Williamson, Leon
 Timmermans, Lukas Mai, Matthew Horsfall, Maxwell Carey, Misty De Meo,
 Neil Bowers, Nicholas Clark, Nicolas R., Niko Tyni, Pali, Paul Marquess,
 Peter Avalos, Petr Písař, Pino Toscano, Rafael Garcia-Suarez, Reini
 Urban, Renee Baecker, Ricardo Signes, Richard Levitte, Rick Delaney,
 Salvador Fandiño, Samuel Thibault, Sawyer X, Sébastien Aperghis-Tramoni,
 Sergey Aleynikov, Shlomi Fish, Smylers, Stefan Seifert, Steffen Müller,
 Stevan Little, Steve Hay, Steven Humphrey, Sullivan Beck, Theo Buehler,
 Thomas Sibley, Todd Rinaldo, Tomasz Konojacki, Tony Cook, Unicode
 Consortium, Yaroslav Kuzmin, 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 _A_U_T_H_O_R_S file in the Perl source distribution.

RReeppoorrttiinngg BBuuggss If you find what you think is a bug, you might check 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.

GGiivvee TThhaannkkss 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:

     perlthanks

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

SSEEEE AALLSSOO #

 The _C_h_a_n_g_e_s file for an explanation of how to view exhaustive details on
 what changed.

 The _I_N_S_T_A_L_L file for how to build Perl.

 The _R_E_A_D_M_E file for general stuff.

 The _A_r_t_i_s_t_i_c and _C_o_p_y_i_n_g files for copyright information.

perl v5.36.3 2023-02-15 PERL5260DELTA(1)