PERL5220DELTA(1) Perl Programmers Reference Guide PERL5220DELTA(1)

PERL5220DELTA(1) Perl Programmers Reference Guide PERL5220DELTA(1) #

PERL5220DELTA(1) Perl Programmers Reference Guide PERL5220DELTA(1)

NNAAMMEE #

 perl5220delta - what is new for perl v5.22.0

DDEESSCCRRIIPPTTIIOONN #

 This document describes differences between the 5.20.0 release and the
 5.22.0 release.

 If you are upgrading from an earlier release such as 5.18.0, first read
 perl5200delta, which describes differences between 5.18.0 and 5.20.0.

CCoorree EEnnhhaanncceemmeennttss NNeeww bbiittwwiissee ooppeerraattoorrss A new experimental facility has been added that makes the four standard bitwise operators ("& | ^ ~") treat their operands consistently as numbers, and introduces four new dotted operators ("&. |. ^. ~.") that treat their operands consistently as strings. The same applies to the assignment variants ("&= |= ^= &.= |.= ^.=").

 To use this, enable the "bitwise" feature and disable the
 "experimental::bitwise" warnings category.  See "Bitwise String
 Operators" in perlop for details.  [GH #14348]
 <https://github.com/Perl/perl5/issues/14348>.

NNeeww ddoouubbllee--ddiiaammoonndd ooppeerraattoorr “«»” is like “<>” but uses three-argument “open” to open each file in @ARGV. This means that each element of @ARGV will be treated as an actual file name, and “|foo” won’t be treated as a pipe open.

NNeeww “”\\bb"" bboouunnddaarriieess iinn rreegguullaarr eexxpprreessssiioonnss _"_q_r_/__b_{_g_c_b_}_/_"

 "gcb" stands for Grapheme Cluster Boundary.  It is a Unicode property
 that finds the boundary between sequences of characters that look like a
 single character to a native speaker of a language.  Perl has long had
 the ability to deal with these through the "\X" regular escape sequence.
 Now, there is an alternative way of handling these.  See "\b{}, \b, \B{},
 \B" in perlrebackslash for details.

 _"_q_r_/_\_b_{_w_b_}_/_"

 "wb" stands for Word Boundary.  It is a Unicode property that finds the
 boundary between words.  This is similar to the plain "\b" (without
 braces) but is more suitable for natural language processing.  It knows,
 for example, that apostrophes can occur in the middle of words.  See
 "\b{}, \b, \B{}, \B" in perlrebackslash for details.

 _"_q_r_/_\_b_{_s_b_}_/_"

 "sb" stands for Sentence Boundary.  It is a Unicode property to aid in
 parsing natural language sentences.  See "\b{}, \b, \B{}, \B" in
 perlrebackslash for details.

NNoonn--CCaappttuurriinngg RReegguullaarr EExxpprreessssiioonn FFllaagg Regular expressions now support a “/n” flag that disables capturing and filling in $1, $2, etc inside of groups:

   "hello" =~ /(hi|hello)/n; # $1 is not set

 This is equivalent to putting "?:" at the beginning of every capturing
 group.

 See "n" in perlre for more information.

“"uussee rree ‘’ssttrriicctt’’“” This applies stricter syntax rules to regular expression patterns compiled within its scope. This will hopefully alert you to typos and other unintentional behavior that backwards-compatibility issues prevent us from reporting in normal regular expression compilations. Because the behavior of this is subject to change in future Perl releases as we gain experience, using this pragma will raise a warning of category “experimental::re_strict”. See ‘strict’ in re.

UUnniiccooddee 77..00 ((wwiitthh ccoorrrreeccttiioonn)) iiss nnooww ssuuppppoorrtteedd For details on what is in this release, see http://www.unicode.org/versions/Unicode7.0.0/. The version of Unicode 7.0 that comes with Perl includes a correction dealing with glyph shaping in Arabic (see http://www.unicode.org/errata/#current_errata).

“"uussee  llooccaallee"” ccaann rreessttrriicctt wwhhiicchh llooccaallee ccaatteeggoorriieess aarree aaffffeecctteedd It is now possible to pass a parameter to “use locale” to specify a subset of locale categories to be locale-aware, with the remaining ones unaffected. See “The “use locale” pragma” in perllocale for details.

PPeerrll nnooww ssuuppppoorrttss PPOOSSIIXX 22000088 llooccaallee ccuurrrreennccyy aaddddiittiioonnss On platforms that are able to handle POSIX.1-2008, the hash returned by “POSIX::localeconv()” includes the international currency fields added by that version of the POSIX standard. These are “int_n_cs_precedes”, “int_n_sep_by_space”, “int_n_sign_posn”, “int_p_cs_precedes”, “int_p_sep_by_space”, and “int_p_sign_posn”.

BBeetttteerr hheeuurriissttiiccss oonn oollddeerr ppllaattffoorrmmss ffoorr ddeetteerrmmiinniinngg llooccaallee UUTTFF--88nneessss On platforms that implement neither the C99 standard nor the POSIX 2001 standard, determining if the current locale is UTF-8 or not depends on heuristics. These are improved in this release.

AAlliiaassiinngg vviiaa rreeffeerreennccee Variables and subroutines can now be aliased by assigning to a reference:

     \$c = \$d;
     \&x = \&y;

 Aliasing can also be accomplished by using a backslash before a "foreach"
 iterator variable; this is perhaps the most useful idiom this feature
 provides:

     foreach \%hash (@array_of_hash_refs) { ... }

 This feature is experimental and must be enabled via
 "use feature 'refaliasing'".  It will warn unless the
 "experimental::refaliasing" warnings category is disabled.

 See "Assigning to References" in perlref

“"pprroottoottyyppee"” wwiitthh nnoo aarrgguummeennttss “prototype()” with no arguments now infers $_. [GH #14376] https://github.com/Perl/perl5/issues/14376.

NNeeww “”::ccoonnsstt"” ssuubbrroouuttiinnee aattttrriibbuuttee The “const” attribute can be applied to an anonymous subroutine. It causes the new sub to be executed immediately whenever one is created (_i_._e_. when the “sub” expression is evaluated). Its value is captured and used to create a new constant subroutine that is returned. This feature is experimental. See “Constant Functions” in perlsub.

“"ffiilleennoo"” nnooww wwoorrkkss oonn ddiirreeccttoorryy hhaannddlleess When the relevant support is available in the operating system, the “fileno” builtin now works on directory handles, yielding the underlying file descriptor in the same way as for filehandles. On operating systems without such support, “fileno” on a directory handle continues to return the undefined value, as before, but also sets $! to indicate that the operation is not supported.

 Currently, this uses either a "dd_fd" member in the OS "DIR" structure,
 or a dirfd(3) function as specified by POSIX.1-2008.

LLiisstt ffoorrmm ooff ppiippee ooppeenn iimmpplleemmeenntteedd ffoorr WWiinn3322 The list form of pipe:

   open my $fh, "-|", "program", @arguments;

 is now implemented on Win32.  It has the same limitations as "system
 LIST" on Win32, since the Win32 API doesn't accept program arguments as a
 list.

AAssssiiggnnmmeenntt ttoo lliisstt rreeppeettiittiioonn “(…) x …” can now be used within a list that is assigned to, as long as the left-hand side is a valid lvalue. This allows “(undef,undef,$foo) = that_function()” to be written as “((undef)x2, $foo) = that_function()”.

IInnffiinniittyy aanndd NNaaNN ((nnoott--aa--nnuummbbeerr)) hhaannddlliinngg iimmpprroovveedd Floating point values are able to hold the special values infinity, negative infinity, and NaN (not-a-number). Now we more robustly recognize and propagate the value in computations, and on output normalize them to the strings “Inf”, “-Inf”, and “NaN”.

 See also the POSIX enhancements.

FFllooaattiinngg ppooiinntt ppaarrssiinngg hhaass bbeeeenn iimmpprroovveedd Parsing and printing of floating point values has been improved.

 As a completely new feature, hexadecimal floating point literals (like
 "0x1.23p-4")  are now supported, and they can be output with
 "printf "%a"". See "Scalar value constructors" in perldata for more
 details.

PPaacckkiinngg iinnffiinniittyy oorr nnoott--aa--nnuummbbeerr iinnttoo aa cchhaarraacctteerr iiss nnooww ffaattaall Before, when trying to pack infinity or not-a-number into a (signed) character, Perl would warn, and assumed you tried to pack 0xFF; if you gave it as an argument to “chr”, “U+FFFD” was returned.

 But now, all such actions ("pack", "chr", and "print '%c'") result in a
 fatal error.

EExxppeerriimmeennttaall CC BBaacckkttrraaccee AAPPII Perl now supports (via a C level API) retrieving the C level backtrace (similar to what symbolic debuggers like gdb do).

 The backtrace returns the stack trace of the C call frames, with the
 symbol names (function names), the object names (like "perl"), and if it
 can, also the source code locations (file:line).

 The supported platforms are Linux and OS X (some *BSD might work at least
 partly, but they have not yet been tested).

 The feature needs to be enabled with "Configure -Dusecbacktrace".

 See "C backtrace" in perlhacktips for more information.

SSeeccuurriittyy PPeerrll iiss nnooww ccoommppiilleedd wwiitthh “”--ffssttaacckk--pprrootteeccttoorr--ssttrroonngg"" iiff aavvaaiillaabbllee Perl has been compiled with the anti-stack-smashing option “-fstack-protector” since 5.10.1. Now Perl uses the newer variant called “-fstack-protector-strong”, if available.

TThhee SSaaffee mmoodduullee ccoouulldd aallllooww oouuttssiiddee ppaacckkaaggeess ttoo bbee rreeppllaacceedd Critical bugfix: outside packages could be replaced. Safe has been patched to 2.38 to address this.

PPeerrll iiss nnooww aallwwaayyss ccoommppiilleedd wwiitthh “”--DD__FFOORRTTIIFFYY__SSOOUURRCCEE==22"" iiff aavvaaiillaabbllee The ‘code hardening’ option called “_FORTIFY_SOURCE”, available in gcc 4.*, is now always used for compiling Perl, if available.

 Note that this isn't necessarily a huge step since in many platforms the
 step had already been taken several years ago: many Linux distributions
 (like Fedora) have been using this option for Perl, and OS X has enforced
 the same for many years.

IInnccoommppaattiibbllee CChhaannggeess SSuubbrroouuttiinnee ssiiggnnaattuurreess mmoovveedd bbeeffoorree aattttrriibbuutteess The experimental sub signatures feature, as introduced in 5.20, parsed signatures after attributes. In this release, following feedback from users of the experimental feature, the positioning has been moved such that signatures occur after the subroutine name (if any) and before the attribute list (if any).

“”&&“” aanndd “”\&&“” pprroottoottyyppeess aacccceeppttss oonnllyy ssuubbss The “&” prototype character now accepts only anonymous subs (“sub {…}”), things beginning with “&”, or an explicit “undef”. Formerly it erroneously also allowed references to arrays, hashes, and lists. [GH #2776] https://github.com/Perl/perl5/issues/2776. [GH #14186] https://github.com/Perl/perl5/issues/14186. [GH #14353] https://github.com/Perl/perl5/issues/14353.

 In addition, the "\&" prototype was allowing subroutine calls, whereas
 now it only allows subroutines: &foo is still permitted as an argument,
 while "&foo()" and "foo()" no longer are.  [GH #10633]
 <https://github.com/Perl/perl5/issues/10633>.

“"uussee eennccooddiinngg"” iiss nnooww lleexxiiccaall The encoding pragma’s effect is now limited to lexical scope. This pragma is deprecated, but in the meantime, it could adversely affect unrelated modules that are included in the same program; this change fixes that.

LLiisstt sslliicceess rreettuurrnniinngg eemmppttyy lliissttss List slices now return an empty list only if the original list was empty (or if there are no indices). Formerly, a list slice would return an empty list if all indices fell outside the original list; now it returns a list of “undef” values in that case. [GH #12335] https://github.com/Perl/perl5/issues/12335.

“”\\NN{{}}“” wwiitthh aa sseeqquueennccee ooff mmuullttiippllee ssppaacceess iiss nnooww aa ffaattaall eerrrroorr E.g. “\N{TOO  MANY SPACES}” or “\N{TRAILING SPACE }”. This has been deprecated since v5.18.

“"uussee  UUNNIIVVEERRSSAALL  ‘’......‘’“” iiss nnooww aa ffaattaall eerrrroorr Importing functions from “UNIVERSAL” has been deprecated since v5.12, and is now a fatal error. “use UNIVERSAL” without any arguments is still allowed.

IInn ddoouubbllee--qquuoottiisshh “”\\cc_X"”,, _X mmuusstt nnooww bbee aa pprriinnttaabbllee AASSCCIIII cchhaarraacctteerr In prior releases, failure to do this raised a deprecation warning.

SSpplliittttiinngg tthhee ttookkeennss “”((??“” aanndd “”((“” iinn rreegguullaarr eexxpprreessssiioonnss iiss nnooww aa ffaattaall ccoommppiillaattiioonn eerrrroorr.. These had been deprecated since v5.18.

“"qqrr//ffoooo//xx"” nnooww iiggnnoorreess aallll UUnniiccooddee ppaatttteerrnn wwhhiittee ssppaaccee The “/x” regular expression modifier allows the pattern to contain white space and comments (both of which are ignored) for improved readability. Until now, not all the white space characters that Unicode designates for this purpose were handled. The additional ones now recognized are:

U+0085 NEXT LINE #

U+200E LEFT-TO-RIGHT MARK #

U+200F RIGHT-TO-LEFT MARK #

U+2028 LINE SEPARATOR #

U+2029 PARAGRAPH SEPARATOR #

 The use of these characters with "/x" outside bracketed character classes
 and when not preceded by a backslash has raised a deprecation warning
 since v5.18.  Now they will be ignored.

CCoommmmeenntt lliinneess wwiitthhiinn “”((??[[  ]]))“” aarree nnooww eennddeedd oonnllyy bbyy aa “”\\nn"" “(?[ ])” is an experimental feature, introduced in v5.18. It operates as if “/x” is always enabled. But there was a difference: comment lines (following a “#” character) were terminated by anything matching “\R” which includes all vertical whitespace, such as form feeds. For consistency, this is now changed to match what terminates comment lines outside “(?[ ])”, namely a “\n” (even if escaped), which is the same as what terminates a heredoc string and formats.

“”((??[[......]]))“” ooppeerraattoorrss nnooww ffoollllooww ssttaannddaarrdd PPeerrll pprreecceeddeennccee This experimental feature allows set operations in regular expression patterns. Prior to this, the intersection operator had the same precedence as the other binary operators. Now it has higher precedence. This could lead to different outcomes than existing code expects (though the documentation has always noted that this change might happen, recommending fully parenthesizing the expressions). See “Extended Bracketed Character Classes” in perlrecharclass.

OOmmiittttiinngg “”%%“” aanndd “”@@“” oonn hhaasshh aanndd aarrrraayy nnaammeess iiss nnoo lloonnggeerr ppeerrmmiitttteedd Really old Perl let you omit the “@” on array names and the “%” on hash names in some spots. This has issued a deprecation warning since Perl 5.000, and is no longer permitted.

“”$$!!“” tteexxtt iiss nnooww iinn EEnngglliisshh oouuttssiiddee tthhee ssccooppee ooff “"uussee llooccaallee"” Previously, the text, unlike almost everything else, always came out based on the current underlying locale of the program. (Also affected on some systems is “$^E”.) For programs that are unprepared to handle locale differences, this can cause garbage text to be displayed. It’s better to display text that is translatable via some tool than garbage text which is much harder to figure out.

“”$$!!“” tteexxtt wwiillll bbee rreettuurrnneedd iinn UUTTFF--88 wwhheenn aapppprroopprriiaattee The stringification of $! and $^E will have the UTF-8 flag set when the text is actually non-ASCII UTF-8. This will enable programs that are set up to be locale-aware to properly output messages in the user’s native language. Code that needs to continue the 5.20 and earlier behavior can do the stringification within the scopes of both “use bytes” and “use locale “:messages””. Within these two scopes, no other Perl operations will be affected by locale; only $! and $^E stringification. The “bytes” pragma causes the UTF-8 flag to not be set, just as in previous Perl releases. This resolves [GH #12035] https://github.com/Perl/perl5/issues/12035.

SSuuppppoorrtt ffoorr “”??PPAATTTTEERRNN??“” wwiitthhoouutt eexxpplliicciitt ooppeerraattoorr hhaass bbeeeenn rreemmoovveedd The “m?PATTERN?” construct, which allows matching a regex only once, previously had an alternative form that was written directly with a question mark delimiter, omitting the explicit “m” operator. This usage has produced a deprecation warning since 5.14.0. It is now a syntax error, so that the question mark can be available for use in new operators.

“"ddeeffiinneedd((@@aarrrraayy))“” aanndd “"ddeeffiinneedd((%%hhaasshh))“” aarree nnooww ffaattaall eerrrroorrss These have been deprecated since v5.6.1 and have raised deprecation warnings since v5.16.

UUssiinngg aa hhaasshh oorr aann aarrrraayy aass aa rreeffeerreennccee aarree nnooww ffaattaall eerrrroorrss For example, “%foo->{“bar”}” now causes a fatal compilation error. These have been deprecated since before v5.8, and have raised deprecation warnings since then.

CChhaannggeess ttoo tthhee “”“” pprroottoottyyppee The “*” character in a subroutine’s prototype used to allow barewords to take precedence over most, but not all, subroutine names. It was never consistent and exhibited buggy behavior.

 Now it has been changed, so subroutines always take precedence over
 barewords, which brings it into conformity with similarly prototyped
 built-in functions:

     sub splat(*) { ... }
     sub foo { ... }
     splat(foo); # now always splat(foo())
     splat(bar); # still splat('bar') as before
     close(foo); # close(foo())
     close(bar); # close('bar')

DDeepprreeccaattiioonnss SSeettttiinngg “”$${{^^EENNCCOODDIINNGG}}“” ttoo aannyytthhiinngg bbuutt “"uunnddeeff"” This variable allows Perl scripts to be written in an encoding other than ASCII or UTF-8. However, it affects all modules globally, leading to wrong answers and segmentation faults. New scripts should be written in UTF-8; old scripts should be converted to UTF-8, which is easily done with the piconv utility.

UUssee ooff nnoonn--ggrraapphhiicc cchhaarraacctteerrss iinn ssiinnggllee--cchhaarraacctteerr vvaarriiaabbllee nnaammeess The syntax for single-character variable names is more lenient than for longer variable names, allowing the one-character name to be a punctuation character or even invisible (a non-graphic). Perl v5.20 deprecated the ASCII-range controls as such a name. Now, all non-graphic characters that formerly were allowed are deprecated. The practical effect of this occurs only when not under “use utf8”, and affects just the C1 controls (code points 0x80 through 0xFF), NO-BREAK SPACE, and SOFT

HYPHEN. #

IInnlliinniinngg ooff “"ssuubb (()) {{ $$vvaarr }}“” wwiitthh oobbsseerrvvaabbllee ssiiddee--eeffffeeccttss In many cases Perl makes “sub () { $var }” into an inlinable constant subroutine, capturing the value of $var at the time the “sub” expression is evaluated. This can break the closure behavior in those cases where $var is subsequently modified, since the subroutine won’t return the changed value. (Note that this all only applies to anonymous subroutines with an empty prototype (“sub ()”).)

 This usage is now deprecated in those cases where the variable could be
 modified elsewhere.  Perl detects those cases and emits a deprecation
 warning.  Such code will likely change in the future and stop producing a
 constant.

 If your variable is only modified in the place where it is declared, then
 Perl will continue to make the sub inlinable with no warnings.

     sub make_constant {
         my $var = shift;
         return sub () { $var }; # fine
     }

     sub make_constant_deprecated {
         my $var;
         $var = shift;
         return sub () { $var }; # deprecated
     }

     sub make_constant_deprecated2 {
         my $var = shift;
         log_that_value($var); # could modify $var
         return sub () { $var }; # deprecated
     }

 In the second example above, detecting that $var is assigned to only once
 is too hard to detect.  That it happens in a spot other than the "my"
 declaration is enough for Perl to find it suspicious.

 This deprecation warning happens only for a simple variable for the body
 of the sub.  (A "BEGIN" block or "use" statement inside the sub is
 ignored, because it does not become part of the sub's body.)  For more
 complex cases, such as "sub () { do_something() if 0; $var }" the
 behavior has changed such that inlining does not happen if the variable
 is modifiable elsewhere.  Such cases should be rare.

UUssee ooff mmuullttiippllee “”//xx"” rreeggeexxpp mmooddiiffiieerrss It is now deprecated to say something like any of the following:

     qr/foo/xx;
     /(?xax:foo)/;
     use re qw(/amxx);

 That is, now "x" should only occur once in any string of contiguous
 regular expression pattern modifiers.  We do not believe there are any
 occurrences of this in all of CPAN.  This is in preparation for a future
 Perl release having "/xx" permit white-space for readability in bracketed
 character classes (those enclosed in square brackets: "[...]").

UUssiinngg aa NNOO--BBRREEAAKK ssppaaccee iinn aa cchhaarraacctteerr aalliiaass ffoorr “”\\NN{{......}}“” iiss nnooww ddeepprreeccaatteedd This non-graphic character is essentially indistinguishable from a regular space, and so should not be allowed. See “CUSTOM ALIASES” in charnames.

AA lliitteerraall “”{{“” sshhoouulldd nnooww bbee eessccaappeedd iinn aa ppaatttteerrnn If you want a literal left curly bracket (also called a left brace) in a regular expression pattern, you should now escape it by either preceding it with a backslash (”{”) or enclosing it within square brackets “[{]”, or by using “\Q”; otherwise a deprecation warning will be raised. This was first announced as forthcoming in the v5.16 release; it will allow future extensions to the language to happen.

MMaakkiinngg aallll wwaarrnniinnggss ffaattaall iiss ddiissccoouurraaggeedd The documentation for fatal warnings notes that “use warnings FATAL => ‘all’” is discouraged, and provides stronger language about the risks of fatal warnings in general.

PPeerrffoorrmmaannccee EEnnhhaanncceemmeennttss • If a method or class name is known at compile time, a hash is precomputed to speed up run-time method lookup. Also, compound method names like “SUPER::new” are parsed at compile time, to save having to parse them at run time.

 •   Array and hash lookups (especially nested ones) that use only
     constants or simple variables as keys, are now considerably faster.
     See "Internal Changes" for more details.

 •   "(...)x1", "("constant")x0" and "($scalar)x0" are now optimised in
     list context.  If the right-hand argument is a constant 1, the
     repetition operator disappears.  If the right-hand argument is a
     constant 0, the whole expression is optimised to the empty list, so
     long as the left-hand argument is a simple scalar or constant.  (That
     is, "(foo())x0" is not subject to this optimisation.)

 •   "substr" assignment is now optimised into 4-argument "substr" at the
     end of a subroutine (or as the argument to "return").  Previously,
     this optimisation only happened in void context.

 •   In "\L...", "\Q...", etc., the extra "stringify" op is now optimised
     away, making these just as fast as "lcfirst", "quotemeta", etc.

 •   Assignment to an empty list is now sometimes faster.  In particular,
     it never calls "FETCH" on tied arguments on the right-hand side,
     whereas it used to sometimes.

 •   There is a performance improvement of up to 20% when "length" is
     applied to a non-magical, non-tied string, and either "use bytes" is
     in scope or the string doesn't use UTF-8 internally.

 •   On most perl builds with 64-bit integers, memory usage for non-
     magical, non-tied scalars containing only a floating point value has
     been reduced by between 8 and 32 bytes, depending on OS.

 •   In "@array = split", the assignment can be optimized away, so that
     "split" writes directly to the array.  This optimisation was
     happening only for package arrays other than @_, and only sometimes.
     Now this optimisation happens almost all the time.

 •   "join" is now subject to constant folding.  So for example
     "join "-", "a", "b"" is converted at compile-time to "a-b".
     Moreover, "join" with a scalar or constant for the separator and a
     single-item list to join is simplified to a stringification, and the
     separator doesn't even get evaluated.

 •   "qq(@array)" is implemented using two ops: a stringify op and a join
     op.  If the "qq" contains nothing but a single array, the
     stringification is optimized away.

 •   "our $var" and "our($s,@a,%h)" in void context are no longer
     evaluated at run time.  Even a whole sequence of "our $foo;"
     statements will simply be skipped over.  The same applies to "state"
     variables.

 •   Many internal functions have been refactored to improve performance
     and reduce their memory footprints.  [GH #13659]
     <https://github.com/Perl/perl5/issues/13659> [GH #13856]
     <https://github.com/Perl/perl5/issues/13856> [GH #13874]
     <https://github.com/Perl/perl5/issues/13874>

 •   "-T" and "-B" filetests will return sooner when an empty file is
     detected.  [GH #13686] <https://github.com/Perl/perl5/issues/13686>

 •   Hash lookups where the key is a constant are faster.

 •   Subroutines with an empty prototype and a body containing just
     "undef" are now eligible for inlining.  [GH #14077]
     <https://github.com/Perl/perl5/issues/14077>

 •   Subroutines in packages no longer need to be stored in typeglobs:
     declaring a subroutine will now put a simple sub reference directly
     in the stash if possible, saving memory.  The typeglob still
     notionally exists, so accessing it will cause the stash entry to be
     upgraded to a typeglob (_i_._e_. this is just an internal implementation
     detail).  This optimization does not currently apply to XSUBs or
     exported subroutines, and method calls will undo it, since they cache
     things in typeglobs.  [GH #13392]
     <https://github.com/Perl/perl5/issues/13392>

 •   The functions "utf8::native_to_unicode()" and
     "utf8::unicode_to_native()" (see utf8) are now optimized out on ASCII
     platforms.  There is now not even a minimal performance hit in
     writing code portable between ASCII and EBCDIC platforms.

 •   Win32 Perl uses 8 KB less of per-process memory than before for every
     perl process, because some data is now memory mapped from disk and
     shared between processes from the same perl binary.

MMoodduulleess aanndd PPrraaggmmaattaa UUppddaatteedd MMoodduulleess aanndd PPrraaggmmaattaa Many of the libraries distributed with perl have been upgraded since v5.20.0. For a complete list of changes, run:

   corelist --diff 5.20.0 5.22.0

 You can substitute your favorite version in place of 5.20.0, too.

 Some notable changes include:

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

     Tests can now be run in parallel.

 •   attributes has been upgraded to version 0.27.

     The usage of "memEQs" in the XS has been corrected.  [GH #14072]
     <https://github.com/Perl/perl5/issues/14072>

     Avoid reading beyond the end of a buffer. [perl #122629]

 •   B has been upgraded to version 1.58.

     It provides a new "B::safename" function, based on the existing
     "B::GV->SAFENAME", that converts "\cOPEN" to "^OPEN".

     Nulled COPs are now of class "B::COP", rather than "B::OP".

     "B::REGEXP" objects now provide a "qr_anoncv" method for accessing
     the implicit CV associated with "qr//" things containing code blocks,
     and a "compflags" method that returns the pertinent flags originating
     from the "qr//blahblah" op.

     "B::PMOP" now provides a "pmregexp" method returning a "B::REGEXP"
     object.  Two new classes, "B::PADNAME" and "B::PADNAMELIST", have
     been introduced.

     A bug where, after an ithread creation or pseudofork,
     special/immortal SVs in the child ithread/pseudoprocess did not have
     the correct class of "B::SPECIAL", has been fixed.  The "id" and
     "outid" PADLIST methods have been added.

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

     Null ops that are part of the execution chain are now given sequence
     numbers.

     Private flags for nulled ops are now dumped with mnemonics as they
     would be for the non-nulled counterparts.

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

     It now deparses "+sub : attr { ... }" correctly at the start of a
     statement.  Without the initial "+", "sub" would be a statement
     label.

     "BEGIN" blocks are now emitted in the right place most of the time,
     but the change unfortunately introduced a regression, in that "BEGIN"
     blocks occurring just before the end of the enclosing block may
     appear below it instead.

     "B::Deparse" no longer puts erroneous "local" here and there, such as
     for "LIST = tr/a//d".  [perl #119815]

     Adjacent "use" statements are no longer accidentally nested if one
     contains a "do" block.  [perl #115066]

     Parenthesised arrays in lists passed to "\" are now correctly
     deparsed with parentheses (_e_._g_., "\(@a, (@b), @c)" now retains the
     parentheses around @b), thus preserving the flattening behavior of
     referenced parenthesised arrays.  Formerly, it only worked for one
     array: "\(@a)".

     "local our" is now deparsed correctly, with the "our" included.

     "for($foo; !$bar; $baz) {...}" was deparsed without the "!" (or
     "not").  This has been fixed.

     Core keywords that conflict with lexical subroutines are now deparsed
     with the "CORE::" prefix.

     "foreach state $x (...) {...}" now deparses correctly with "state"
     and not "my".

     "our @array = split(...)" now deparses correctly with "our" in those
     cases where the assignment is optimized away.

     It now deparses "our(_L_I_S_T)" and typed lexical ("my Dog $spot")
     correctly.

     Deparse $#_ as that instead of as $#{_}.  [GH #14545]
     <https://github.com/Perl/perl5/issues/14545>

     BEGIN blocks at the end of the enclosing scope are now deparsed in
     the right place.  [perl #77452]

     BEGIN blocks were sometimes deparsed as __ANON__, but are now always
     called BEGIN.

     Lexical subroutines are now fully deparsed.  [perl #116553]

     "Anything =~ y///r" with "/r" no longer omits the left-hand operand.

     The op trees that make up regexp code blocks are now deparsed for
     real.  Formerly, the original string that made up the regular
     expression was used.  That caused problems with "qr/(?{<<heredoc})/"
     and multiline code blocks, which were deparsed incorrectly.  [perl
     #123217] [perl #115256]

     $; at the end of a statement no longer loses its semicolon.  [perl
     #123357]

     Some cases of subroutine declarations stored in the stash in
     shorthand form were being omitted.

     Non-ASCII characters are now consistently escaped in strings, instead
     of some of the time.  (There are still outstanding problems with
     regular expressions and identifiers that have not been fixed.)

     When prototype sub calls are deparsed with "&" (_e_._g_., under the --PP
     option), "scalar" is now added where appropriate, to force the scalar
     context implied by the prototype.

     "require(foo())", "do(foo())", "goto(foo())" and similar constructs
     with loop controls are now deparsed correctly.  The outer parentheses
     are not optional.

     Whitespace is no longer escaped in regular expressions, because it
     was getting erroneously escaped within "(?x:...)" sections.

     "sub foo { foo() }" is now deparsed with those mandatory parentheses.

     "/@array/" is now deparsed as a regular expression, and not just
     @array.

     "/@{-}/", "/@{+}/" and $#{1} are now deparsed with the braces, which
     are mandatory in these cases.

     In deparsing feature bundles, "B::Deparse" was emitting "no feature;"
     first instead of "no feature ':all';".  This has been fixed.

     "chdir FH" is now deparsed without quotation marks.

     "\my @a" is now deparsed without parentheses.  (Parenthese would
     flatten the array.)

     "system" and "exec" followed by a block are now deparsed correctly.
     Formerly there was an erroneous "do" before the block.

     "use constant QR => qr/.../flags" followed by """ =~ QR" is no longer
     without the flags.

     Deparsing "BEGIN { undef &foo }" with the --ww switch enabled started
     to emit 'uninitialized' warnings in Perl 5.14.  This has been fixed.

     Deparsing calls to subs with a "(;+)" prototype resulted in an
     infinite loop.  The "(;$") "(_)" and "(;_)" prototypes were given the
     wrong precedence, causing "foo($a<$b)" to be deparsed without the
     parentheses.

     Deparse now provides a defined state sub in inner subs.

 •   B::Op_private has been added.

     B::Op_private provides detailed information about the flags used in
     the "op_private" field of perl opcodes.

 •   bigint, bignum, bigrat have been upgraded to version 0.39.

     Document in CAVEATS that using strings as numbers won't always invoke
     the big number overloading, and how to invoke it.  [rt.perl.org
     #123064]

 •   Carp has been upgraded to version 1.36.

     "Carp::Heavy" now ignores version mismatches with Carp if Carp is
     newer than 1.12, since "Carp::Heavy"'s guts were merged into Carp at
     that point.  [GH #13708] <https://github.com/Perl/perl5/issues/13708>

     Carp now handles non-ASCII platforms better.

     Off-by-one error fix for Perl < 5.14.

 •   constant has been upgraded to version 1.33.

     It now accepts fully-qualified constant names, allowing constants to
     be defined in packages other than the caller.

 •   CPAN has been upgraded to version 2.11.

     Add support for "Cwd::getdcwd()" and introduce workaround for a
     misbehavior seen on Strawberry Perl 5.20.1.

     Fix "chdir()" after building dependencies bug.

     Introduce experimental support for plugins/hooks.

     Integrate the "App::Cpan" sources.

     Do not check recursion on optional dependencies.

     Sanity check _M_E_T_A_._y_m_l to contain a hash.  [cpan #95271]
     <https://rt.cpan.org/Ticket/Display.html?id=95271>

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

     Works around limitations in "version::vpp" detecting v-string magic
     and adds support for forthcoming ExtUtils::MakeMaker bootstrap
     _v_e_r_s_i_o_n_._p_m for Perls older than 5.10.0.

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

     Fixes CVE-2014-4330 by adding a configuration variable/option to
     limit recursion when dumping deep data structures.

     Changes to resolve Coverity issues.  XS dumps incorrectly stored the
     name of code references stored in a GLOB. [GH #13911]
     <https://github.com/Perl/perl5/issues/13911>

 •   DynaLoader has been upgraded to version 1.32.

     Remove "dl_nonlazy" global if unused in Dynaloader. [perl #122926]

 •   Encode has been upgraded to version 2.72.

     "piconv" now has better error handling when the encoding name is
     nonexistent, and a build breakage when upgrading Encode in perl-5.8.2
     and earlier has been fixed.

     Building in C++ mode on Windows now works.

 •   Errno has been upgraded to version 1.23.

     Add "-P" to the preprocessor command-line on GCC 5.  GCC added extra
     line directives, breaking parsing of error code definitions.
     [rt.perl.org #123784]

 •   experimental has been upgraded to version 0.013.

     Hardcodes features for Perls older than 5.15.7.

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

     Fixes a regression on Android.  [GH #14064]
     <https://github.com/Perl/perl5/issues/14064>

 •   ExtUtils::Manifest has been upgraded to version 1.70.

     Fixes a bug with "maniread()"'s handling of quoted filenames and
     improves "manifind()" to follow symlinks.  [GH #14003]
     <https://github.com/Perl/perl5/issues/14003>

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

     Only declare "file" unused if we actually define it.  Improve
     generated "RETVAL" code generation to avoid repeated references to
     ST(0).  [perl #123278] Broaden and document the "/OBJ$/" to "/REF$/"
     typemap optimization for the "DESTROY" method.  [perl #123418]

 •   Fcntl has been upgraded to version 1.13.

     Add support for the Linux pipe buffer size "fcntl()" commands.

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

     "find()" and "finddepth()" will now warn if passed inappropriate or
     misspelled options.

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

     Avoid "SvIV()" expanding to call "get_sv()" three times in a few
     places. [perl #123606]

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

     "keep_alive" is now fork-safe and thread-safe.

 •   IO has been upgraded to version 1.35.

     The XS implementation has been fixed for the sake of older Perls.

 •   IO::Socket has been upgraded to version 1.38.

     Document the limitations of the "connected()" method.  [perl #123096]

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

     A better fix for subclassing "connect()".  [cpan #95983]
     <https://rt.cpan.org/Ticket/Display.html?id=95983> [cpan #97050]
     <https://rt.cpan.org/Ticket/Display.html?id=97050>

     Implements Timeout for "connect()".  [cpan #92075]
     <https://rt.cpan.org/Ticket/Display.html?id=92075>

 •   The libnet collection of modules has been upgraded to version 3.05.

     Support for IPv6 and SSL to "Net::FTP", "Net::NNTP", "Net::POP3" and
     "Net::SMTP".  Improvements in "Net::SMTP" authentication.

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

     Fixed a bug in the scripts used to extract data from spreadsheets
     that prevented the SHP currency code from being found.  [cpan #94229]
     <https://rt.cpan.org/Ticket/Display.html?id=94229>

     New codes have been added.

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

     Synchronize POD changes from the CPAN release.
     "Math::BigFloat->blog(x)" would sometimes return "blog(2*x)" when the
     accuracy was greater than 70 digits.  The result of
     "Math::BigFloat->bdiv()" in list context now satisfies "x = quotient
     * divisor + remainder".

     Correct handling of subclasses.  [cpan #96254]
     <https://rt.cpan.org/Ticket/Display.html?id=96254> [cpan #96329]
     <https://rt.cpan.org/Ticket/Display.html?id=96329>

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

     Support installations on older perls with an ExtUtils::MakeMaker
     earlier than 6.63_03

 •   overload has been upgraded to version 1.26.

     A redundant "ref $sub" check has been removed.

 •   The PathTools module collection has been upgraded to version 3.56.

     A warning from the ggcccc compiler is now avoided when building the XS.

     Don't turn leading "//" into "/" on Cygwin. [perl #122635]

 •   perl5db.pl has been upgraded to version 1.49.

     The debugger would cause an assertion failure.  [GH #14605]
     <https://github.com/Perl/perl5/issues/14605>

     "fork()" in the debugger under "tmux" will now create a new window
     for the forked process. [GH #13602]
     <https://github.com/Perl/perl5/issues/13602>

     The debugger now saves the current working directory on startup and
     restores it when you restart your program with "R" or "rerun".  [GH
     #13691] <https://github.com/Perl/perl5/issues/13691>

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

     Reading from a position well past the end of the scalar now correctly
     returns end of file.  [perl #123443]

     Seeking to a negative position still fails, but no longer leaves the
     file position set to a negation location.

     "eof()" on a "PerlIO::scalar" handle now properly returns true when
     the file position is past the 2GB mark on 32-bit systems.

     Attempting to write at file positions impossible for the platform now
     fail early rather than wrapping at 4GB.

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

     Filehandles opened for reading or writing now have ":encoding(UTF-8)"
     set.  [cpan #98019]
     <https://rt.cpan.org/Ticket/Display.html?id=98019>

 •   POSIX has been upgraded to version 1.53.

     The C99 math functions and constants (for example "acosh", "isinf",
     "isnan", "round", "trunc"; "M_E", "M_SQRT2", "M_PI") have been added.

     "POSIX::tmpnam()" now produces a deprecation warning.  [perl #122005]

 •   Safe has been upgraded to version 2.39.

     "reval" was not propagating void context properly.

 •   Scalar-List-Utils has been upgraded to version 1.41.

     A new module, Sub::Util, has been added, containing functions related
     to CODE refs, including "subname" (inspired by "Sub::Identity") and
     "set_subname" (copied and renamed from "Sub::Name").  The use of
     "GetMagic" in "List::Util::reduce()" has also been fixed.  [cpan
     #63211] <https://rt.cpan.org/Ticket/Display.html?id=63211>

 •   SDBM_File has been upgraded to version 1.13.

     Simplified the build process.  [perl #123413]

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

     When pretty printing negative "Time::Seconds", the "minus" is no
     longer lost.

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

     Version 0.67's improved discontiguous contractions is invalidated by
     default and is supported as a parameter "long_contraction".

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

     The XSUB implementation has been removed in favor of pure Perl.

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

     A new function pprrooppeerrttyy__vvaalluueess(()) has been added to return a given
     property's possible values.

     A new function cchhaarrpprroopp(()) has been added to return the value of a
     given property for a given code point.

     A new function cchhaarrpprrooppss__aallll(()) has been added to return the values of
     all Unicode properties for a given code point.

     A bug has been fixed so that pprrooppaalliiaasseess(()) returns the correct short
     and long names for the Perl extensions where it was incorrect.

     A bug has been fixed so that pprroopp__vvaalluuee__aalliiaasseess(()) returns "undef"
     instead of a wrong result for properties that are Perl extensions.

     This module now works on EBCDIC platforms.

 •   utf8 has been upgraded to version 1.17

     A mismatch between the documentation and the code in
     "utf8::downgrade()" was fixed in favor of the documentation. The
     optional second argument is now correctly treated as a perl boolean
     (true/false semantics) and not as an integer.

 •   version has been upgraded to version 0.9909.

     Numerous changes.  See the _C_h_a_n_g_e_s file in the CPAN distribution for
     details.

 •   Win32 has been upgraded to version 0.51.

     "GetOSName()" now supports Windows 8.1, and building in C++ mode now
     works.

 •   Win32API::File has been upgraded to version 0.1202

     Building in C++ mode now works.

 •   XSLoader has been upgraded to version 0.20.

     Allow XSLoader to load modules from a different namespace.  [perl
     #122455]

RReemmoovveedd MMoodduulleess aanndd PPrraaggmmaattaa The following modules (and associated modules) have been removed from the core perl distribution:

• CGI #

 •   Module::Build

DDooccuummeennttaattiioonn NNeeww DDooccuummeennttaattiioonn _p_e_r_l_u_n_i_c_o_o_k

 This document, by Tom Christiansen, provides examples of handling Unicode
 in Perl.

CChhaannggeess ttoo EExxiissttiinngg DDooccuummeennttaattiioonn _p_e_r_l_a_i_x

 •   A note on long doubles has been added.

 _p_e_r_l_a_p_i

 •   Note that "SvSetSV" doesn't do set magic.

 •   "sv_usepvn_flags" - fix documentation to mention the use of "Newx"
     instead of "malloc".

     [GH #13835] <https://github.com/Perl/perl5/issues/13835>

 •   Clarify where "NUL" may be embedded or is required to terminate a
     string.

 •   Some documentation that was previously missing due to formatting
     errors is now included.

 •   Entries are now organized into groups rather than by the file where
     they are found.

 •   Alphabetical sorting of entries is now done consistently
     (automatically by the POD generator) to make entries easier to find
     when scanning.

 _p_e_r_l_d_a_t_a

 •   The syntax of single-character variable names has been brought up-to-
     date and more fully explained.

 •   Hexadecimal floating point numbers are described, as are infinity and
     NaN.

 _p_e_r_l_e_b_c_d_i_c

 •   This document has been significantly updated in the light of recent
     improvements to EBCDIC support.

 _p_e_r_l_f_i_l_t_e_r

 •   Added a LIMITATIONS section.

 _p_e_r_l_f_u_n_c

 •   Mention that "study()" is currently a no-op.

 •   Calling "delete" or "exists" on array values is now described as
     "strongly discouraged" rather than "deprecated".

 •   Improve documentation of "our".

 •   "-l" now notes that it will return false if symlinks aren't supported
     by the file system.  [GH #13695]
     <https://github.com/Perl/perl5/issues/13695>

 •   Note that "exec LIST" and "system LIST" may fall back to the shell on
     Win32. Only the indirect-object syntax "exec PROGRAM LIST" and
     "system PROGRAM LIST" will reliably avoid using the shell.

     This has also been noted in perlport.

     [GH #13907] <https://github.com/Perl/perl5/issues/13907>

 _p_e_r_l_g_u_t_s

 •   The OOK example has been updated to account for COW changes and a
     change in the storage of the offset.

 •   Details on C level symbols and libperl.t added.

 •   Information on Unicode handling has been added

 •   Information on EBCDIC handling has been added

 _p_e_r_l_h_a_c_k

 •   A note has been added about running on platforms with non-ASCII
     character sets

 •   A note has been added about performance testing

 _p_e_r_l_h_a_c_k_t_i_p_s

 •   Documentation has been added illustrating the perils of assuming that
     there is no change to the contents of static memory pointed to by the
     return values of Perl's wrappers for C library functions.

 •   Replacements for "tmpfile", "atoi", "strtol", and "strtoul" are now
     recommended.

 •   Updated documentation for the "test.valgrind" "make" target.  [GH
     #13658] <https://github.com/Perl/perl5/issues/13658>

 •   Information is given about writing test files portably to non-ASCII
     platforms.

 •   A note has been added about how to get a C language stack backtrace.

 _p_e_r_l_h_p_u_x

 •   Note that the message "Redeclaration of "sendpath" with a different
     storage class specifier" is harmless.

 _p_e_r_l_l_o_c_a_l_e

 •   Updated for the enhancements in v5.22, along with some
     clarifications.

 _p_e_r_l_m_o_d_s_t_y_l_e

 •   Instead of pointing to the module list, we are now pointing to PrePAN
     <http://prepan.org/>.

 _p_e_r_l_o_p

 •   Updated for the enhancements in v5.22, along with some
     clarifications.

 _p_e_r_l_p_o_d_s_p_e_c

 •   The specification of the pod language is changing so that the default
     encoding of pods that aren't in UTF-8 (unless otherwise indicated) is
     CP1252 instead of ISO 8859-1 (Latin1).

 _p_e_r_l_p_o_l_i_c_y

 •   We now have a code of conduct for the _p_5_p mailing list, as documented
     in "STANDARDS OF CONDUCT" in perlpolicy.

 •   The conditions for marking an experimental feature as non-
     experimental are now set out.

 •   Clarification has been made as to what sorts of changes are
     permissible in maintenance releases.

 _p_e_r_l_p_o_r_t

 •   Out-of-date VMS-specific information has been fixed and/or
     simplified.

 •   Notes about EBCDIC have been added.

 _p_e_r_l_r_e

 •   The description of the "/x" modifier has been clarified to note that
     comments cannot be continued onto the next line by escaping them; and
     there is now a list of all the characters that are considered
     whitespace by this modifier.

 •   The new "/n" modifier is described.

 •   A note has been added on how to make bracketed character class ranges
     portable to non-ASCII machines.

 _p_e_r_l_r_e_b_a_c_k_s_l_a_s_h

 •   Added documentation of "\b{sb}", "\b{wb}", "\b{gcb}", and "\b{g}".

 _p_e_r_l_r_e_c_h_a_r_c_l_a_s_s

 •   Clarifications have been added to "Character Ranges" in
     perlrecharclass to the effect "[A-Z]", "[a-z]", "[0-9]" and any
     subranges thereof in regular expression bracketed character classes
     are guaranteed to match exactly what a naive English speaker would
     expect them to match, even on platforms (such as EBCDIC) where perl
     has to do extra work to accomplish this.

 •   The documentation of Bracketed Character Classes has been expanded to
     cover the improvements in "qr/[\N{named sequence}]/" (see under
     "Selected Bug Fixes").

 _p_e_r_l_r_e_f

 •   A new section has been added Assigning to References

 _p_e_r_l_s_e_c

 •   Comments added on algorithmic complexity and tied hashes.

 _p_e_r_l_s_y_n

 •   An ambiguity in the documentation of the "..." statement has been
     corrected.  [GH #14054] <https://github.com/Perl/perl5/issues/14054>

 •   The empty conditional in "for" and "while" is now documented in
     perlsyn.

 _p_e_r_l_u_n_i_c_o_d_e

 •   This has had extensive revisions to bring it up-to-date with current
     Unicode support and to make it more readable.  Notable is that
     Unicode 7.0 changed what it should do with non-characters.  Perl
     retains the old way of handling for reasons of backward
     compatibility.  See "Noncharacter code points" in perlunicode.

 _p_e_r_l_u_n_i_i_n_t_r_o

 •   Advice for how to make sure your strings and regular expression
     patterns are interpreted as Unicode has been updated.

 _p_e_r_l_v_a_r

 •   $] is no longer listed as being deprecated.  Instead, discussion has
     been added on the advantages and disadvantages of using it versus
     $^V.  $OLD_PERL_VERSION was re-added to the documentation as the long
     form of $].

 •   "${^ENCODING}" is now marked as deprecated.

 •   The entry for "%^H" has been clarified to indicate it can only handle
     simple values.

 _p_e_r_l_v_m_s

 •   Out-of-date and/or incorrect material has been removed.

 •   Updated documentation on environment and shell interaction in VMS.

 _p_e_r_l_x_s

 •   Added a discussion of locale issues in XS code.

DDiiaaggnnoossttiiccss The following additions or changes have been made to diagnostic output, including warnings and fatal error messages. For the complete list of diagnostic messages, see perldiag.

NNeeww DDiiaaggnnoossttiiccss _N_e_w _E_r_r_o_r_s

 •   Bad symbol for scalar

     (P) An internal request asked to add a scalar entry to something that
     wasn't a symbol table entry.

 •   Can't use a hash as a reference

     (F) You tried to use a hash as a reference, as in "%foo->{"bar"}" or
     "%$ref->{"hello"}".  Versions of perl <= 5.6.1 used to allow this
     syntax, but shouldn't have.

 •   Can't use an array as a reference

     (F) You tried to use an array as a reference, as in "@foo->[23]" or
     "@$ref->[99]".  Versions of perl <= 5.6.1 used to allow this syntax,
     but shouldn't have.

 •   Can't use 'defined(@array)' (Maybe you should just omit the
     ddeeffiinneedd(())?)

     (F) "defined()" is not useful on arrays because it checks for an
     undefined _s_c_a_l_a_r value.  If you want to see if the array is empty,
     just use "if (@array) { # not empty }" for example.

 •   Can't use 'defined(%hash)' (Maybe you should just omit the
     ddeeffiinneedd(())?)

     (F) "defined()" is not usually right on hashes.

     Although "defined %hash" is false on a plain not-yet-used hash, it
     becomes true in several non-obvious circumstances, including
     iterators, weak references, stash names, even remaining true after
     "undef %hash".  These things make "defined %hash" fairly useless in
     practice, so it now generates a fatal error.

     If a check for non-empty is what you wanted then just put it in
     boolean context (see "Scalar values" in perldata):

         if (%hash) {
            # not empty
         }

     If you had "defined %Foo::Bar::QUUX" to check whether such a package
     variable exists then that's never really been reliable, and isn't a
     good way to enquire about the features of a package, or whether it's
     loaded, etc.

 •   Cannot chr %f

     (F) You passed an invalid number (like an infinity or not-a-number)
     to "chr".

 •   Cannot compress %f in pack

     (F) You tried converting an infinity or not-a-number to an unsigned
     character, which makes no sense.

 •   Cannot pack %f with '%c'

     (F) You tried converting an infinity or not-a-number to a character,
     which makes no sense.

 •   Cannot print %f with '%c'

     (F) You tried printing an infinity or not-a-number as a character
     (%c), which makes no sense.  Maybe you meant '%s', or just
     stringifying it?

 •   charnames alias definitions may not contain a sequence of multiple
     spaces

     (F) You defined a character name which had multiple space characters
     in a row.  Change them to single spaces.  Usually these names are
     defined in the ":alias" import argument to "use charnames", but they
     could be defined by a translator installed into $^H{charnames}.  See
     "CUSTOM ALIASES" in charnames.

 •   charnames alias definitions may not contain trailing white-space

     (F) You defined a character name which ended in a space character.
     Remove the trailing space(s).  Usually these names are defined in the
     ":alias" import argument to "use charnames", but they could be
     defined by a translator installed into $^H{charnames}.  See "CUSTOM
     ALIASES" in charnames.

 •   :const is not permitted on named subroutines

     (F) The "const" attribute causes an anonymous subroutine to be run
     and its value captured at the time that it is cloned.  Named
     subroutines are not cloned like this, so the attribute does not make
     sense on them.

 •   Hexadecimal float: internal error

     (F) Something went horribly bad in hexadecimal float handling.

 •   Hexadecimal float: unsupported long double format

     (F) You have configured Perl to use long doubles but the internals of
     the long double format are unknown, therefore the hexadecimal float
     output is impossible.

 •   Illegal suidscript

     (F) The script run under suidperl was somehow illegal.

 •   In '(?...)', the '(' and '?' must be adjacent in regex; marked by
     <-- HERE in m/%s/

     (F) The two-character sequence "(?" in this context in a regular
     expression pattern should be an indivisible token, with nothing
     intervening between the "(" and the "?", but you separated them.

 •   In '(*VERB...)', the '(' and '*' must be adjacent in regex; marked by
     <-- HERE in m/%s/

     (F) The two-character sequence "(*" in this context in a regular
     expression pattern should be an indivisible token, with nothing
     intervening between the "(" and the "*", but you separated them.

 •   Invalid quantifier in {,} in regex; marked by <-- HERE in m/%s/

     (F) The pattern looks like a {min,max} quantifier, but the min or max
     could not be parsed as a valid number: either it has leading zeroes,
     or it represents too big a number to cope with.  The <-- HERE shows
     where in the regular expression the problem was discovered.  See
     perlre.

 •   '%s' is an unknown bound type in regex

     (F) You used "\b{...}" or "\B{...}" and the "..." is not known to
     Perl.  The current valid ones are given in "\b{}, \b, \B{}, \B" in
     perlrebackslash.

 •   Missing or undefined argument to require

     (F) You tried to call "require" with no argument or with an undefined
     value as an argument.  "require" expects either a package name or a
     file-specification as an argument.  See "require" in perlfunc.

     Formerly, "require" with no argument or "undef" warned about a Null
     filename.

 _N_e_w _W_a_r_n_i_n_g_s

 •   \C is deprecated in regex

     (D deprecated) The "/\C/" character class was deprecated in v5.20,
     and now emits a warning. It is intended that it will become an error
     in v5.24.  This character class matches a single byte even if it
     appears within a multi-byte character, breaks encapsulation, and can
     corrupt UTF-8 strings.

 •   "%s" is more clearly written simply as "%s" in regex; marked by <--
     HERE in m/%s/

     (W regexp) (only under "use re 'strict'" or within "(?[...])")

     You specified a character that has the given plainer way of writing
     it, and which is also portable to platforms running with different
     character sets.

 •   Argument "%s" treated as 0 in increment (++)

     (W numeric) The indicated string was fed as an argument to the "++"
     operator which expects either a number or a string matching
     "/^[a-zA-Z]*[0-9]*\z/".  See "Auto-increment and Auto-decrement" in
     perlop for details.

 •   Both or neither range ends should be Unicode in regex; marked by <--
     HERE in m/%s/

     (W regexp) (only under "use re 'strict'" or within "(?[...])")

     In a bracketed character class in a regular expression pattern, you
     had a range which has exactly one end of it specified using "\N{}",
     and the other end is specified using a non-portable mechanism.  Perl
     treats the range as a Unicode range, that is, all the characters in
     it are considered to be the Unicode characters, and which may be
     different code points on some platforms Perl runs on.  For example,
     "[\N{U+06}-\x08]" is treated as if you had instead said
     "[\N{U+06}-\N{U+08}]", that is it matches the characters whose code
     points in Unicode are 6, 7, and 8.  But that "\x08" might indicate
     that you meant something different, so the warning gets raised.

 •   Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".

     (W locale) You are 1) running under ""use locale""; 2) the current
     locale is not a UTF-8 one; 3) you tried to do the designated case-
     change operation on the specified Unicode character; and 4) the
     result of this operation would mix Unicode and locale rules, which
     likely conflict.

     The warnings category "locale" is new.

 •   :const is experimental

     (S experimental::const_attr) The "const" attribute is experimental.
     If you want to use the feature, disable the warning with "no warnings
     'experimental::const_attr'", but know that in doing so you are taking
     the risk that your code may break in a future Perl version.

 •   gmtime(%f) failed

     (W overflow) You called "gmtime" with a number that it could not
     handle: too large, too small, or NaN.  The returned value is "undef".

 •   Hexadecimal float: exponent overflow

     (W overflow) The hexadecimal floating point has larger exponent than
     the floating point supports.

 •   Hexadecimal float: exponent underflow

     (W overflow) The hexadecimal floating point has smaller exponent than
     the floating point supports.

 •   Hexadecimal float: mantissa overflow

     (W overflow) The hexadecimal floating point literal had more bits in
     the mantissa (the part between the "0x" and the exponent, also known
     as the fraction or the significand) than the floating point supports.

 •   Hexadecimal float: precision loss

     (W overflow) The hexadecimal floating point had internally more
     digits than could be output.  This can be caused by unsupported long
     double formats, or by 64-bit integers not being available (needed to
     retrieve the digits under some configurations).

 •   Locale '%s' may not work well.%s

     (W locale) You are using the named locale, which is a non-UTF-8 one,
     and which perl has determined is not fully compatible with what it
     can handle.  The second %s gives a reason.

     The warnings category "locale" is new.

 •   localtime(%f) failed

     (W overflow) You called "localtime" with a number that it could not
     handle: too large, too small, or NaN.  The returned value is "undef".

 •   Negative repeat count does nothing

     (W numeric) You tried to execute the "x" repetition operator fewer
     than 0 times, which doesn't make sense.

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

     (D deprecated) You defined a character name which contained a no-
     break space character.  Change it to a regular space.  Usually these
     names are defined in the ":alias" import argument to "use charnames",
     but they could be defined by a translator installed into
     $^H{charnames}.  See "CUSTOM ALIASES" in charnames.

 •   Non-finite repeat count does nothing

     (W numeric) You tried to execute the "x" repetition operator "Inf"
     (or "-Inf") or NaN times, which doesn't make sense.

 •   PerlIO layer ':win32' is experimental

     (S experimental::win32_perlio) The ":win32" PerlIO layer is
     experimental.  If you want to take the risk of using this layer,
     simply disable this warning:

         no warnings "experimental::win32_perlio";

 •   Ranges of ASCII printables should be some subset of "0-9", "A-Z", or
     "a-z" in regex; marked by <-- HERE in m/%s/

     (W regexp) (only under "use re 'strict'" or within "(?[...])")

     Stricter rules help to find typos and other errors.  Perhaps you
     didn't even intend a range here, if the "-" was meant to be some
     other character, or should have been escaped (like "\-").  If you did
     intend a range, the one that was used is not portable between ASCII
     and EBCDIC platforms, and doesn't have an obvious meaning to a casual
     reader.

      [3-7]    # OK; Obvious and portable
      [d-g]    # OK; Obvious and portable
      [A-Y]    # OK; Obvious and portable
      [A-z]    # WRONG; Not portable; not clear what is meant
      [a-Z]    # WRONG; Not portable; not clear what is meant
      [%-.]    # WRONG; Not portable; not clear what is meant
      [\x41-Z] # WRONG; Not portable; not obvious to non-geek

     (You can force portability by specifying a Unicode range, which means
     that the endpoints are specified by "\N{...}", but the meaning may
     still not be obvious.)  The stricter rules require that ranges that
     start or stop with an ASCII character that is not a control have all
     their endpoints be a literal character, and not some escape sequence
     (like "\x41"), and the ranges must be all digits, or all uppercase
     letters, or all lowercase letters.

 •   Ranges of digits should be from the same group in regex; marked by
     <-- HERE in m/%s/

     (W regexp) (only under "use re 'strict'" or within "(?[...])")

     Stricter rules help to find typos and other errors.  You included a
     range, and at least one of the end points is a decimal digit.  Under
     the stricter rules, when this happens, both end points should be
     digits in the same group of 10 consecutive digits.

 •   Redundant argument in %s

     (W redundant) You called a function with more arguments than were
     needed, as indicated by information within other arguments you
     supplied (_e_._g. a printf format). Currently only emitted when a
     printf-type format required fewer arguments than were supplied, but
     might be used in the future for _e_._g_. "pack" in perlfunc.

     The warnings category "redundant" is new. See also [GH #13534]
     <https://github.com/Perl/perl5/issues/13534>.

 •   Replacement list is longer than search list

     This is not a new diagnostic, but in earlier releases was
     accidentally not displayed if the transliteration contained wide
     characters.  This is now fixed, so that you may see this diagnostic
     in places where you previously didn't (but should have).

 •   Use of \b{} for non-UTF-8 locale is wrong.  Assuming a UTF-8 locale

     (W locale) You are matching a regular expression using locale rules,
     and a Unicode boundary is being matched, but the locale is not a
     Unicode one.  This doesn't make sense.  Perl will continue, assuming
     a Unicode (UTF-8) locale, but the results could well be wrong except
     if the locale happens to be ISO-8859-1 (Latin1) where this message is
     spurious and can be ignored.

     The warnings category "locale" is new.

 •   Using /u for '%s' instead of /%s in regex; marked by <-- HERE in
     m/%s/

     (W regexp) You used a Unicode boundary ("\b{...}" or "\B{...}") in a
     portion of a regular expression where the character set modifiers
     "/a" or "/aa" are in effect.  These two modifiers indicate an ASCII
     interpretation, and this doesn't make sense for a Unicode definition.
     The generated regular expression will compile so that the boundary
     uses all of Unicode.  No other portion of the regular expression is
     affected.

 •   The bitwise feature is experimental

     (S experimental::bitwise) This warning is emitted if you use bitwise
     operators ("& | ^ ~ &. |. ^. ~.") with the "bitwise" feature enabled.
     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::bitwise";
         use feature "bitwise";
         $x |.= $y;

 •   Unescaped left brace in regex is deprecated, passed through in regex;
     marked by <-- HERE in m/%s/

     (D deprecated, regexp) You used a literal "{" character in a regular
     expression pattern. You should change to use "\{" instead, because a
     future version of Perl (tentatively v5.26) will consider this to be a
     syntax error.  If the pattern delimiters are also braces, any
     matching right brace ("}") should also be escaped to avoid confusing
     the parser, for example,

         qr{abc\{def\}ghi}

 •   Use of literal non-graphic characters in variable names is deprecated

     (D deprecated) Using literal non-graphic (including control)
     characters in the source to refer to the _^_F_O_O variables, like $^X and
     "${^GLOBAL_PHASE}" is now deprecated.

 •   Useless use of attribute "const"

     (W misc) The "const" attribute has no effect except on anonymous
     closure prototypes.  You applied it to a subroutine via
     attributes.pm.  This is only useful inside an attribute handler for
     an anonymous subroutine.

 •   Useless use of /d modifier in transliteration operator

     This is not a new diagnostic, but in earlier releases was
     accidentally not displayed if the transliteration contained wide
     characters.  This is now fixed, so that you may see this diagnostic
     in places where you previously didn't (but should have).

 •   "use re 'strict'" is experimental

     (S experimental::re_strict) The things that are different when a
     regular expression pattern is compiled under 'strict' are subject to
     change in future Perl releases in incompatible ways; there are also
     proposals to change how to enable strict checking instead of using
     this subpragma.  This means that a pattern that compiles today may
     not in a future Perl release.  This warning is to alert you to that
     risk.

 •   Warning: unable to close filehandle properly: %s

     Warning: unable to close filehandle %s properly: %s

     (S io) Previously, perl silently ignored any errors when doing an
     implicit close of a filehandle, _i_._e_. where the reference count of the
     filehandle reached zero and the user's code hadn't already called
     "close()"; _e_._g_.

         {
             open my $fh, '>', $file  or die "open: '$file': $!\n";
             print $fh, $data  or die;
         } # implicit close here

     In a situation such as disk full, due to buffering, the error may
     only be detected during the final close, so not checking the result
     of the close is dangerous.

     So perl now warns in such situations.

 •   Wide character (U+%X) in %s

     (W locale) While in a single-byte locale (_i_._e_., a non-UTF-8 one), a
     multi-byte character was encountered.   Perl considers this character
     to be the specified Unicode code point.  Combining non-UTF-8 locales
     and Unicode is dangerous.  Almost certainly some characters will have
     two different representations.  For example, in the ISO 8859-7
     (Greek) locale, the code point 0xC3 represents a Capital Gamma.  But
     so also does 0x393.  This will make string comparisons unreliable.

     You likely need to figure out how this multi-byte character got mixed
     up with your single-byte locale (or perhaps you thought you had a
     UTF-8 locale, but Perl disagrees).

     The warnings category "locale" is new.

CChhaannggeess ttoo EExxiissttiinngg DDiiaaggnnoossttiiccss • <> should be quotes

     This warning has been changed to <> at require-statement should be
     quotes to make the issue more identifiable.

 •   Argument "%s" isn't numeric%s

     The perldiag entry for this warning has added this clarifying note:

      Note that for the Inf and NaN (infinity and not-a-number) the
      definition of "numeric" is somewhat unusual: the strings themselves
      (like "Inf") are considered numeric, and anything following them is
      considered non-numeric.

 •   Global symbol "%s" requires explicit package name

     This message has had '(did you forget to declare "my %s"?)' appended
     to it, to make it more helpful to new Perl programmers.  [GH #13732]
     <https://github.com/Perl/perl5/issues/13732>

 •   '"my" variable &foo::bar can't be in a package' has been reworded to
     say 'subroutine' instead of 'variable'.

 •   \N{} in character class restricted to one character in regex; marked
     by <-- HERE in m/%s/

     This message has had _c_h_a_r_a_c_t_e_r _c_l_a_s_s changed to _i_n_v_e_r_t_e_d _c_h_a_r_a_c_t_e_r
     _c_l_a_s_s _o_r _a_s _a _r_a_n_g_e _e_n_d_-_p_o_i_n_t _i_s to reflect improvements in
     "qr/[\N{named sequence}]/" (see under "Selected Bug Fixes").

 •   panic: frexp

     This message has had ': %f' appended to it, to show what the
     offending floating point number is.

 •   _P_o_s_s_i_b_l_e _p_r_e_c_e_d_e_n_c_e _p_r_o_b_l_e_m _o_n _b_i_t_w_i_s_e _%_c _o_p_e_r_a_t_o_r reworded as
     Possible precedence problem on bitwise %s operator.

 •   Unsuccessful %s on filename containing newline

     This warning is now only produced when the newline is at the end of
     the filename.

 •   "Variable %s will not stay shared" has been changed to say
     "Subroutine" when it is actually a lexical sub that will not stay
     shared.

 •   Variable length lookbehind not implemented in regex m/%s/

     The perldiag entry for this warning has had information about Unicode
     behavior added.

DDiiaaggnnoossttiicc RReemmoovvaallss • “Ambiguous use of -foo resolved as -&ffoooo(())”

     There is actually no ambiguity here, and this impedes the use of
     negated constants; _e_._g_., "-Inf".

 •   "Constant is not a FOO reference"

     Compile-time checking of constant dereferencing (_e_._g_.,
     "my_constant->()") has been removed, since it was not taking
     overloading into account.  [GH #9891]
     <https://github.com/Perl/perl5/issues/9891> [GH #14044]
     <https://github.com/Perl/perl5/issues/14044>

UUttiilliittyy CChhaannggeess _f_i_n_d_2_p_e_r_l,, _s_2_p aanndd _a_2_p rreemmoovvaall • The _x_2_p_/ directory has been removed from the Perl core.

     This removes find2perl, s2p and a2p. They have all been released to
     CPAN as separate distributions ("App::find2perl", "App::s2p",
     "App::a2p").

hh22pphh • _h_2_p_h now handles hexadecimal constants in the compiler’s predefined macro definitions, as visible in $Config{cppsymbols}. [GH #14491] https://github.com/Perl/perl5/issues/14491.

eennccgguueessss • No longer depends on non-core modules.

CCoonnffiigguurraattiioonn aanndd CCoommppiillaattiioonn • _C_o_n_f_i_g_u_r_e now checks for “lrintl()”, “lroundl()”, “llrintl()”, and “llroundl()”.

 •   _C_o_n_f_i_g_u_r_e with "-Dmksymlinks" should now be faster.  [GH #13890]
     <https://github.com/Perl/perl5/issues/13890>.

 •   The "pthreads" and "cl" libraries will be linked by default if
     present.  This allows XS modules that require threading to work on
     non-threaded perls. Note that you must still pass "-Dusethreads" if
     you want a threaded perl.

 •   To get more precision and range for floating point numbers one can
     now use the GCC quadmath library which implements the quadruple
     precision floating point numbers on x86 and IA-64 platforms.  See
     _I_N_S_T_A_L_L for details.

 •   MurmurHash64A and MurmurHash64B can now be configured as the internal
     hash function.

 •   "make test.valgrind" now supports parallel testing.

     For example:

         TEST_JOBS=9 make test.valgrind

     See "valgrind" in perlhacktips for more information.

     [GH #13658] <https://github.com/Perl/perl5/issues/13658>

 •   The MAD (Misc Attribute Decoration) build option has been removed

     This was an unmaintained attempt at preserving the Perl parse tree
     more faithfully so that automatic conversion of Perl 5 to Perl 6
     would have been easier.

     This build-time configuration option had been unmaintained for years,
     and had probably seriously diverged on both Perl 5 and Perl 6 sides.

 •   A new compilation flag, "-DPERL_OP_PARENT" is available. For details,
     see the discussion below at "Internal Changes".

 •   Pathtools no longer tries to load XS on miniperl. This speeds up
     building perl slightly.

TTeessttiinngg • _t_/_p_o_r_t_i_n_g_/_r_e___c_o_n_t_e_x_t_._t has been added to test that utf8 and its dependencies only use the subset of the “$1..$n” capture vars that “Perl_save_re_context()” is hard-coded to localize, because that function has no efficient way of determining at runtime what vars to localize.

 •   Tests for performance issues have been added in the file
     _t_/_p_e_r_f_/_t_a_i_n_t_._t.

 •   Some regular expression tests are written in such a way that they
     will run very slowly if certain optimizations break. These tests have
     been moved into new files, _t_/_r_e_/_s_p_e_e_d_._t and _t_/_r_e_/_s_p_e_e_d___t_h_r_._t, and are
     run with a "watchdog()".

 •   "test.pl" now allows "plan skip_all => $reason", to make it more
     compatible with "Test::More".

 •   A new test script, _o_p_/_i_n_f_n_a_n_._t, has been added to test if infinity
     and NaN are working correctly.  See "Infinity and NaN (not-a-number)
     handling improved".

PPllaattffoorrmm SSuuppppoorrtt RReeggaaiinneedd PPllaattffoorrmmss IRIX and Tru64 platforms are working again. Some “make test” failures remain: [GH #14557] https://github.com/Perl/perl5/issues/14557 and [GH #14727] https://github.com/Perl/perl5/issues/14727 for IRIX; [GH #14629] https://github.com/Perl/perl5/issues/14629, [cpan #99605] https://rt.cpan.org/Public/Bug/Display.html?id=99605, and [cpan #104836] https://rt.cpan.org/Ticket/Display.html?id=104836 for Tru64.

 z/OS running EBCDIC Code Page 1047
     Core perl now works on this EBCDIC platform.  Earlier perls also
     worked, but, even though support wasn't officially withdrawn, recent
     perls would not compile and run well.  Perl 5.20 would work, but had
     many bugs which have now been fixed.  Many CPAN modules that ship
     with Perl still fail tests, including "Pod::Simple".  However the
     version of "Pod::Simple" currently on CPAN should work; it was fixed
     too late to include in Perl 5.22.  Work is under way to fix many of
     the still-broken CPAN modules, which likely will be installed on CPAN
     when completed, so that you may not have to wait until Perl 5.24 to
     get a working version.

DDiissccoonnttiinnuueedd PPllaattffoorrmmss NeXTSTEP/OPENSTEP NeXTSTEP was a proprietary operating system bundled with NeXT’s workstations in the early to mid 90s; OPENSTEP was an API specification that provided a NeXTSTEP-like environment on a non- NeXTSTEP system. Both are now long dead, so support for building Perl on them has been removed.

PPllaattffoorrmm--SSppeecciiffiicc NNootteess

EBCDIC #

     Special handling is required of the perl interpreter on EBCDIC
     platforms to get "qr/[i-j]/" to match only "i" and "j", since there
     are 7 characters between the code points for "i" and "j".  This
     special handling had only been invoked when both ends of the range
     are literals.  Now it is also invoked if any of the "\N{...}" forms
     for specifying a character by name or Unicode code point is used
     instead of a literal.  See "Character Ranges" in perlrecharclass.

HP-UX #

     The archname now distinguishes use64bitint from use64bitall.

 Android
     Build support has been improved for cross-compiling in general and
     for Android in particular.

VMS #

     •   When spawning a subprocess without waiting, the return value is
         now the correct PID.

     •   Fix a prototype so linking doesn't fail under the VMS C++
         compiler.

     •   "finite", "finitel", and "isfinite" detection has been added to
         "configure.com", environment handling has had some minor changes,
         and a fix for legacy feature checking status.

 Win32
     •   _m_i_n_i_p_e_r_l_._e_x_e is now built with "-fno-strict-aliasing", allowing
         64-bit builds to complete on GCC 4.8. [GH #14556]
         <https://github.com/Perl/perl5/issues/14556>

     •   "nmake minitest" now works on Win32.  Due to dependency issues
         you need to build "nmake test-prep" first, and a small number of
         the tests fail.  [GH #14318]
         <https://github.com/Perl/perl5/issues/14318>

     •   Perl can now be built in C++ mode on Windows by setting the
         makefile macro "USE_CPLUSPLUS" to the value "define".

     •   The list form of piped open has been implemented for Win32.
         Note: unlike "system LIST" this does not fall back to the shell.
         [GH #13574] <https://github.com/Perl/perl5/issues/13574>

     •   New "DebugSymbols" and "DebugFull" configuration options added to
         Windows makefiles.

     •   Previously, compiling XS modules (including CPAN ones) using
         Visual C++ for Win64 resulted in around a dozen warnings per file
         from _h_v___f_u_n_c_._h.  These warnings have been silenced.

     •   Support for building without PerlIO has been removed from the
         Windows makefiles.  Non-PerlIO builds were all but deprecated in
         Perl 5.18.0 and are already not supported by _C_o_n_f_i_g_u_r_e on POSIX
         systems.

     •   Between 2 and 6 milliseconds and seven I/O calls have been saved
         per attempt to open a perl module for each path in @INC.

     •   Intel C builds are now always built with C99 mode on.

     •   %I64d is now being used instead of %lld for MinGW.

     •   In the experimental ":win32" layer, a crash in "open" was fixed.
         Also opening _/_d_e_v_/_n_u_l_l (which works under Win32 Perl's default
         ":unix" layer) was implemented for ":win32".  [GH #13968]
         <https://github.com/Perl/perl5/issues/13968>

     •   A new makefile option, "USE_LONG_DOUBLE", has been added to the
         Windows dmake makefile for gcc builds only.  Set this to "define"
         if you want perl to use long doubles to give more accuracy and
         range for floating point numbers.

 OpenBSD
     On OpenBSD, Perl will now default to using the system "malloc" due to
     the security features it provides. Perl's own malloc wrapper has been
     in use since v5.14 due to performance reasons, but the OpenBSD
     project believes the tradeoff is worth it and would prefer that users
     who need the speed specifically ask for it.

     [GH #13888] <https://github.com/Perl/perl5/issues/13888>.

 Solaris
     •   We now look for the Sun Studio compiler in both _/_o_p_t_/_s_o_l_s_t_u_d_i_o_*
         and _/_o_p_t_/_s_o_l_a_r_i_s_s_t_u_d_i_o_*.

     •   Builds on Solaris 10 with "-Dusedtrace" would fail early since
         make didn't follow implied dependencies to build "perldtrace.h".
         Added an explicit dependency to "depend".  [GH #13334]
         <https://github.com/Perl/perl5/issues/13334>

     •   C99 options have been cleaned up; hints look for "solstudio" as
         well as "SUNWspro"; and support for native "setenv" has been
         added.

IInntteerrnnaall CChhaannggeess • Experimental support has been added to allow ops in the optree to locate their parent, if any. This is enabled by the non-default build option “-DPERL_OP_PARENT”. It is envisaged that this will eventually become enabled by default, so XS code which directly accesses the “op_sibling” field of ops should be updated to be future-proofed.

     On "PERL_OP_PARENT" builds, the "op_sibling" field has been renamed
     "op_sibparent" and a new flag, "op_moresib", added. On the last op in
     a sibling chain, "op_moresib" is false and "op_sibparent" points to
     the parent (if any) rather than being "NULL".

     To make existing code work transparently whether using
     "PERL_OP_PARENT" or not, a number of new macros and functions have
     been added that should be used, rather than directly manipulating
     "op_sibling".

     For the case of just reading "op_sibling" to determine the next
     sibling, two new macros have been added. A simple scan through a
     sibling chain like this:

         for (; kid->op_sibling; kid = kid->op_sibling) { ... }

     should now be written as:

         for (; OpHAS_SIBLING(kid); kid = OpSIBLING(kid)) { ... }

     For altering optrees, a general-purpose function
     "op_sibling_splice()" has been added, which allows for manipulation
     of a chain of sibling ops.  By analogy with the Perl function
     "splice()", it allows you to cut out zero or more ops from a sibling
     chain and replace them with zero or more new ops.  It transparently
     handles all the updating of sibling, parent, op_last pointers etc.

     If you need to manipulate ops at a lower level, then three new
     macros, "OpMORESIB_set", "OpLASTSIB_set" and "OpMAYBESIB_set" are
     intended to be a low-level portable way to set "op_sibling" /
     "op_sibparent" while also updating "op_moresib".  The first sets the
     sibling pointer to a new sibling, the second makes the op the last
     sibling, and the third conditionally does the first or second action.
     Note that unlike "op_sibling_splice()" these macros won't maintain
     consistency in the parent at the same time (_e_._g_. by updating
     "op_first" and "op_last" where appropriate).

     A C-level "Perl_op_parent()" function and a Perl-level
     "B::OP::parent()" method have been added. The C function only exists
     under "PERL_OP_PARENT" builds (using it is build-time error on
     vanilla perls).  "B::OP::parent()" exists always, but on a vanilla
     build it always returns "NULL". Under "PERL_OP_PARENT", they return
     the parent of the current op, if any. The variable
     $B::OP::does_parent allows you to determine whether "B" supports
     retrieving an op's parent.

     "PERL_OP_PARENT" was introduced in 5.21.2, but the interface was
     changed considerably in 5.21.11. If you updated your code before the
     5.21.11 changes, it may require further revision. The main changes
     after 5.21.2 were:

     •   The "OP_SIBLING" and "OP_HAS_SIBLING" macros have been renamed
         "OpSIBLING" and "OpHAS_SIBLING" for consistency with other op-
         manipulating macros.

     •   The "op_lastsib" field has been renamed "op_moresib", and its
         meaning inverted.

     •   The macro "OpSIBLING_set" has been removed, and has been
         superseded by "OpMORESIB_set" _e_t _a_l.

     •   The "op_sibling_splice()" function now accepts a null "parent"
         argument where the splicing doesn't affect the first or last ops
         in the sibling chain

 •   Macros have been created to allow XS code to better manipulate the
     POSIX locale category "LC_NUMERIC".  See "Locale-related functions
     and macros" in perlapi.

 •   The previous "atoi" _e_t _a_l replacement function, "grok_atou", has now
     been superseded by "grok_atoUV".  See perlclib for details.

 •   A new function, "Perl_sv_get_backrefs()", has been added which allows
     you retrieve the weak references, if any, which point at an SV.

 •   The "screaminstr()" function has been removed. Although marked as
     public API, it was undocumented and had no usage in CPAN modules.
     Calling it has been fatal since 5.17.0.

 •   The "newDEFSVOP()", "block_start()", "block_end()" and "intro_my()"
     functions have been added to the API.

 •   The internal "convert" function in _o_p_._c has been renamed
     "op_convert_list" and added to the API.

 •   The "sv_magic()" function no longer forbids "ext" magic on read-only
     values.  After all, perl can't know whether the custom magic will
     modify the SV or not.  [GH #14202]
     <https://github.com/Perl/perl5/issues/14202>.

 •   Accessing "CvPADLIST" in perlapi on an XSUB is now forbidden.

     The "CvPADLIST" field has been reused for a different internal
     purpose for XSUBs. So in particular, you can no longer rely on it
     being NULL as a test of whether a CV is an XSUB. Use "CvISXSUB()"
     instead.

 •   SVs of type "SVt_NV" are now sometimes bodiless when the build
     configuration and platform allow it: specifically, when "sizeof(NV)
     <= sizeof(IV)". "Bodiless" means that the NV value is stored directly
     in the head of an SV, without requiring a separate body to be
     allocated. This trick has already been used for IVs since 5.9.2
     (though in the case of IVs, it is always used, regardless of platform
     and build configuration).

 •   The $DB::single, $DB::signal and $DB::trace variables now have set-
     and get-magic that stores their values as IVs, and those IVs are used
     when testing their values in "pp_dbstate()".  This prevents perl from
     recursing infinitely if an overloaded object is assigned to any of
     those variables.  [GH #14013]
     <https://github.com/Perl/perl5/issues/14013>.

 •   "Perl_tmps_grow()", which is marked as public API but is
     undocumented, has been removed from the public API. This change does
     not affect XS code that uses the "EXTEND_MORTAL" macro to pre-extend
     the mortal stack.

 •   Perl's internals no longer sets or uses the "SVs_PADMY" flag.
     "SvPADMY()" now returns a true value for anything not marked "PADTMP"
     and "SVs_PADMY" is now defined as 0.

 •   The macros "SETsv" and "SETsvUN" have been removed. They were no
     longer used in the core since commit 6f1401dc2a five years ago, and
     have not been found present on CPAN.

 •   The "SvFAKE" bit (unused on HVs) got informally reserved by David
     Mitchell for future work on vtables.

 •   The "sv_catpvn_flags()" function accepts "SV_CATBYTES" and
     "SV_CATUTF8" flags, which specify whether the appended string is
     bytes or UTF-8, respectively. (These flags have in fact been present
     since 5.16.0, but were formerly not regarded as part of the API.)

 •   A new opcode class, "METHOP", has been introduced. It holds
     information used at runtime to improve the performance of
     class/object method calls.

     "OP_METHOD" and "OP_METHOD_NAMED" have changed from being "UNOP/SVOP"
     to being "METHOP".

 •   "cv_name()" is a new API function that can be passed a CV or GV.  It
     returns an SV containing the name of the subroutine, for use in
     diagnostics.

     [GH #12767] <https://github.com/Perl/perl5/issues/12767> [GH #13392]
     <https://github.com/Perl/perl5/issues/13392>

 •   "cv_set_call_checker_flags()" is a new API function that works like
     "cv_set_call_checker()", except that it allows the caller to specify
     whether the call checker requires a full GV for reporting the
     subroutine's name, or whether it could be passed a CV instead.
     Whatever value is passed will be acceptable to "cv_name()".
     "cv_set_call_checker()" guarantees there will be a GV, but it may
     have to create one on the fly, which is inefficient.  [GH #12767]
     <https://github.com/Perl/perl5/issues/12767>

 •   "CvGV" (which is not part of the API) is now a more complex macro,
     which may call a function and reify a GV.  For those cases where it
     has been used as a boolean, "CvHASGV" has been added, which will
     return true for CVs that notionally have GVs, but without reifying
     the GV.  "CvGV" also returns a GV now for lexical subs.  [GH #13392]
     <https://github.com/Perl/perl5/issues/13392>

 •   The "sync_locale" in perlapi function has been added to the public
     API. Changing the program's locale should be avoided by XS code.
     Nevertheless, certain non-Perl libraries called from XS need to do
     so, such as "Gtk".  When this happens, Perl needs to be told that the
     locale has changed.  Use this function to do so, before returning to
     Perl.

 •   The defines and labels for the flags in the "op_private" field of OPs
     are now auto-generated from data in _r_e_g_e_n_/_o_p___p_r_i_v_a_t_e.  The noticeable
     effect of this is that some of the flag output of "Concise" might
     differ slightly, and the flag output of "perl -Dx" may differ
     considerably (they both use the same set of labels now).  Also,
     debugging builds now have a new assertion in "op_free()" to ensure
     that the op doesn't have any unrecognized flags set in "op_private".

 •   The deprecated variable "PL_sv_objcount" has been removed.

 •   Perl now tries to keep the locale category "LC_NUMERIC" set to "C"
     except around operations that need it to be set to the program's
     underlying locale.  This protects the many XS modules that cannot
     cope with the decimal radix character not being a dot.  Prior to this
     release, Perl initialized this category to "C", but a call to
     "POSIX::setlocale()" would change it.  Now such a call will change
     the underlying locale of the "LC_NUMERIC" category for the program,
     but the locale exposed to XS code will remain "C".  There are new
     macros to manipulate the LC_NUMERIC locale, including
     "STORE_LC_NUMERIC_SET_TO_NEEDED" and
     "STORE_LC_NUMERIC_FORCE_TO_UNDERLYING".  See "Locale-related
     functions and macros" in perlapi.

 •   A new macro "isUTF8_CHAR" has been written which efficiently
     determines if the string given by its parameters begins with a well-
     formed UTF-8 encoded character.

 •   The following private API functions had their context parameter
     removed: "Perl_cast_ulong",  "Perl_cast_i32", "Perl_cast_iv",
     "Perl_cast_uv", "Perl_cv_const_sv", "Perl_mg_find",
     "Perl_mg_findext", "Perl_mg_magical", "Perl_mini_mktime",
     "Perl_my_dirfd", "Perl_sv_backoff", "Perl_utf8_hop".

     Note that the prefix-less versions of those functions that are part
     of the public API, such as "cast_i32()", remain unaffected.

 •   The "PADNAME" and "PADNAMELIST" types are now separate types, and no
     longer simply aliases for SV and AV. [GH #14250]
     <https://github.com/Perl/perl5/issues/14250>.

 •   Pad names are now always UTF-8.  The "PadnameUTF8" macro always
     returns true.  Previously, this was effectively the case already, but
     any support for two different internal representations of pad names
     has now been removed.

 •   A new op class, "UNOP_AUX", has been added. This is a subclass of
     "UNOP" with an "op_aux" field added, which points to an array of
     unions of UV, SV* etc. It is intended for where an op needs to store
     more data than a simple "op_sv" or whatever. Currently the only op of
     this type is "OP_MULTIDEREF" (see next item).

 •   A new op has been added, "OP_MULTIDEREF", which performs one or more
     nested array and hash lookups where the key is a constant or simple
     variable. For example the expression $a[0]{$k}[$i], which previously
     involved ten "rv2Xv", "Xelem", "gvsv" and "const" ops is now
     performed by a single "multideref" op. It can also handle "local",
     "exists" and "delete". A non-simple index expression, such as
     "[$i+1]" is still done using "aelem"/"helem", and single-level array
     lookup with a small constant index is still done using "aelemfast".

SSeelleecctteedd BBuugg FFiixxeess • “close” now sets $!

     When an I/O error occurs, the fact that there has been an error is
     recorded in the handle.  "close" returns false for such a handle.
     Previously, the value of $! would be untouched by "close", so the
     common convention of writing "close $fh or die $!" did not work
     reliably.  Now the handle records the value of $!, too, and "close"
     restores it.

 •   "no re" now can turn off everything that "use re" enables

     Previously, running "no re" would turn off only a few things. Now it
     can turn off all the enabled things. For example, the only way to
     stop debugging, once enabled, was to exit the enclosing block; that
     is now fixed.

 •   "pack("D", $x)" and "pack("F", $x)" now zero the padding on x86 long
     double builds.  Under some build options on GCC 4.8 and later, they
     used to either overwrite the zero-initialized padding, or bypass the
     initialized buffer entirely.  This caused _o_p_/_p_a_c_k_._t to fail.  [GH
     #14554] <https://github.com/Perl/perl5/issues/14554>

 •   Extending an array cloned from a parent thread could result in
     "Modification of a read-only value attempted" errors when attempting
     to modify the new elements.  [GH #14605]
     <https://github.com/Perl/perl5/issues/14605>

 •   An assertion failure and subsequent crash with "*x=<y>" has been
     fixed.  [GH #14493] <https://github.com/Perl/perl5/issues/14493>

 •   A possible crashing/looping bug related to compiling lexical subs has
     been fixed.  [GH #14596] <https://github.com/Perl/perl5/issues/14596>

 •   UTF-8 now works correctly in function names, in unquoted HERE-
     document terminators, and in variable names used as array indexes.
     [GH #14601] <https://github.com/Perl/perl5/issues/14601>

 •   Repeated global pattern matches in scalar context on large tainted
     strings were exponentially slow depending on the current match
     position in the string.  [GH #14238]
     <https://github.com/Perl/perl5/issues/14238>

 •   Various crashes due to the parser getting confused by syntax errors
     have been fixed.  [GH #14496]
     <https://github.com/Perl/perl5/issues/14496> [GH #14497]
     <https://github.com/Perl/perl5/issues/14497> [GH #14548]
     <https://github.com/Perl/perl5/issues/14548> [GH #14564]
     <https://github.com/Perl/perl5/issues/14564>

 •   "split" in the scope of lexical $_ has been fixed not to fail
     assertions.  [GH #14483] <https://github.com/Perl/perl5/issues/14483>

 •   "my $x : attr" syntax inside various list operators no longer fails
     assertions.  [GH #14500] <https://github.com/Perl/perl5/issues/14500>

 •   An "@" sign in quotes followed by a non-ASCII digit (which is not a
     valid identifier) would cause the parser to crash, instead of simply
     trying the "@" as literal.  This has been fixed.  [GH #14553]
     <https://github.com/Perl/perl5/issues/14553>

 •   "*bar::=*foo::=*glob_with_hash" has been crashing since Perl 5.14,
     but no longer does.  [GH #14512]
     <https://github.com/Perl/perl5/issues/14512>

 •   "foreach" in scalar context was not pushing an item on to the stack,
     resulting in bugs.  ("print 4, scalar do { foreach(@x){} } + 1" would
     print 5.)  It has been fixed to return "undef".  [GH #14569]
     <https://github.com/Perl/perl5/issues/14569>

 •   Several cases of data used to store environment variable contents in
     core C code being potentially overwritten before being used have been
     fixed.  [GH #14476] <https://github.com/Perl/perl5/issues/14476>

 •   Some patterns starting with "/.*..../" matched against long strings
     have been slow since v5.8, and some of the form "/.*..../i" have been
     slow since v5.18. They are now all fast again.  [GH #14475]
     <https://github.com/Perl/perl5/issues/14475>.

 •   The original visible value of $/ is now preserved when it is set to
     an invalid value.  Previously if you set $/ to a reference to an
     array, for example, perl would produce a runtime error and not set
     "PL_rs", but Perl code that checked $/ would see the array reference.
     [GH #14245] <https://github.com/Perl/perl5/issues/14245>.

 •   In a regular expression pattern, a POSIX class, like "[:ascii:]",
     must be inside a bracketed character class, like "qr/[[:ascii:]]/".
     A warning is issued when something looking like a POSIX class is not
     inside a bracketed class.  That warning wasn't getting generated when
     the POSIX class was negated: "[:^ascii:]".  This is now fixed.

 •   Perl 5.14.0 introduced a bug whereby "eval { LABEL: }" would crash.
     This has been fixed.  [GH #14438]
     <https://github.com/Perl/perl5/issues/14438>.

 •   Various crashes due to the parser getting confused by syntax errors
     have been fixed.  [GH #14421]
     <https://github.com/Perl/perl5/issues/14421>.  [GH #14472]
     <https://github.com/Perl/perl5/issues/14472>.  [GH #14480]
     <https://github.com/Perl/perl5/issues/14480>.  [GH #14447]
     <https://github.com/Perl/perl5/issues/14447>.

 •   Code like "/$a[/" used to read the next line of input and treat it as
     though it came immediately after the opening bracket.  Some invalid
     code consequently would parse and run, but some code caused crashes,
     so this is now disallowed.  [GH #14462]
     <https://github.com/Perl/perl5/issues/14462>.

 •   Fix argument underflow for "pack".  [GH #14525]
     <https://github.com/Perl/perl5/issues/14525>.

 •   Fix handling of non-strict "\x{}". Now "\x{}" is equivalent to
     "\x{0}" instead of faulting.

 •   "stat -t" is now no longer treated as stackable, just like "-t stat".
     [GH #14499] <https://github.com/Perl/perl5/issues/14499>.

 •   The following no longer causes a SEGV: "qr{x+(y(?0))*}".

 •   Fixed infinite loop in parsing backrefs in regexp patterns.

 •   Several minor bug fixes in behavior of Infinity and NaN, including
     warnings when stringifying Infinity-like or NaN-like strings. For
     example, "NaNcy" doesn't numify to NaN anymore.

 •   A bug in regular expression patterns that could lead to segfaults and
     other crashes has been fixed.  This occurred only in patterns
     compiled with "/i" while taking into account the current POSIX locale
     (which usually means they have to be compiled within the scope of
     "use locale"), and there must be a string of at least 128 consecutive
     bytes to match.  [GH #14389]
     <https://github.com/Perl/perl5/issues/14389>.

 •   "s///g" now works on very long strings (where there are more than 2
     billion iterations) instead of dying with 'Substitution loop'.  [GH
     #11742] <https://github.com/Perl/perl5/issues/11742>.  [GH #14190]
     <https://github.com/Perl/perl5/issues/14190>.

 •   "gmtime" no longer crashes with not-a-number values.  [GH #14365]
     <https://github.com/Perl/perl5/issues/14365>.

 •   "\()" (a reference to an empty list), and "y///" with lexical $_ in
     scope, could both do a bad write past the end of the stack.  They
     have both been fixed to extend the stack first.

 •   "prototype()" with no arguments used to read the previous item on the
     stack, so "print "foo", prototype()" would print foo's prototype.  It
     has been fixed to infer $_ instead.  [GH #14376]
     <https://github.com/Perl/perl5/issues/14376>.

 •   Some cases of lexical state subs declared inside predeclared subs
     could crash, for example when evalling a string including the name of
     an outer variable, but no longer do.

 •   Some cases of nested lexical state subs inside anonymous subs could
     cause 'Bizarre copy' errors or possibly even crashes.

 •   When trying to emit warnings, perl's default debugger (_p_e_r_l_5_d_b_._p_l)
     was sometimes giving 'Undefined subroutine &DB::db_warn called'
     instead.  This bug, which started to occur in Perl 5.18, has been
     fixed.  [GH #14400] <https://github.com/Perl/perl5/issues/14400>.

 •   Certain syntax errors in substitutions, such as "s/${<>{})//", would
     crash, and had done so since Perl 5.10.  (In some cases the crash did
     not start happening till 5.16.)  The crash has, of course, been
     fixed.  [GH #14391] <https://github.com/Perl/perl5/issues/14391>.

 •   Fix a couple of string grow size calculation overflows; in
     particular, a repeat expression like "33 x ~3" could cause a large
     buffer overflow since the new output buffer size was not correctly
     handled by "SvGROW()".  An expression like this now properly produces
     a memory wrap panic.  [GH #14401]
     <https://github.com/Perl/perl5/issues/14401>.

 •   "formline("@...", "a");" would crash.  The "FF_CHECKNL" case in
     "pp_formline()" didn't set the pointer used to mark the chop
     position, which led to the "FF_MORE" case crashing with a
     segmentation fault.  This has been fixed.  [GH #14388]
     <https://github.com/Perl/perl5/issues/14388>.

 •   A possible buffer overrun and crash when parsing a literal pattern
     during regular expression compilation has been fixed.  [GH #14416]
     <https://github.com/Perl/perl5/issues/14416>.

 •   "fchmod()" and "futimes()" now set $! when they fail due to being
     passed a closed file handle.  [GH #14073]
     <https://github.com/Perl/perl5/issues/14073>.

 •   "op_free()" and "scalarvoid()" no longer crash due to a stack
     overflow when freeing a deeply recursive op tree.  [GH #11866]
     <https://github.com/Perl/perl5/issues/11866>.

 •   In Perl 5.20.0, $^N accidentally had the internal UTF-8 flag turned
     off if accessed from a code block within a regular expression,
     effectively UTF-8-encoding the value.  This has been fixed.  [GH
     #14211] <https://github.com/Perl/perl5/issues/14211>.

 •   A failed "semctl" call no longer overwrites existing items on the
     stack, which means that "(semctl(-1,0,0,0))[0]" no longer gives an
     "uninitialized" warning.

 •   "else{foo()}" with no space before "foo" is now better at assigning
     the right line number to that statement.  [GH #14070]
     <https://github.com/Perl/perl5/issues/14070>.

 •   Sometimes the assignment in "@array = split" gets optimised so that
     "split" itself writes directly to the array.  This caused a bug,
     preventing this assignment from being used in lvalue context.  So
     "(@a=split//,"foo")=bar()" was an error.  (This bug probably goes
     back to Perl 3, when the optimisation was added.) It has now been
     fixed.  [GH #14183] <https://github.com/Perl/perl5/issues/14183>.

 •   When an argument list fails the checks specified by a subroutine
     signature (which is still an experimental feature), the resulting
     error messages now give the file and line number of the caller, not
     of the called subroutine.  [GH #13643]
     <https://github.com/Perl/perl5/issues/13643>.

 •   The flip-flop operators (".." and "..." in scalar context) used to
     maintain a separate state for each recursion level (the number of
     times the enclosing sub was called recursively), contrary to the
     documentation.  Now each closure has one internal state for each
     flip-flop.  [GH #14110] <https://github.com/Perl/perl5/issues/14110>.

 •   The flip-flop operator (".." in scalar context) would return the same
     scalar each time, unless the containing subroutine was called
     recursively.  Now it always returns a new scalar.  [GH #14110]
     <https://github.com/Perl/perl5/issues/14110>.

 •   "use", "no", statement labels, special blocks ("BEGIN") and pod are
     now permitted as the first thing in a "map" or "grep" block, the
     block after "print" or "say" (or other functions) returning a handle,
     and within "${...}", "@{...}", etc.  [GH #14088]
     <https://github.com/Perl/perl5/issues/14088>.

 •   The repetition operator "x" now propagates lvalue context to its
     left-hand argument when used in contexts like "foreach".  That allows
     "for(($#that_array)x2) { ... }" to work as expected if the loop
     modifies $_.

 •   "(...) x ..." in scalar context used to corrupt the stack if one
     operand was an object with "x" overloading, causing erratic behavior.
     [GH #13811] <https://github.com/Perl/perl5/issues/13811>.

 •   Assignment to a lexical scalar is often optimised away; for example
     in "my $x; $x = $y + $z", the assign operator is optimised away and
     the add operator writes its result directly to $x.  Various bugs
     related to this optimisation have been fixed.  Certain operators on
     the right-hand side would sometimes fail to assign the value at all
     or assign the wrong value, or would call STORE twice or not at all on
     tied variables.  The operators affected were "$foo++", "$foo--", and
     "-$foo" under "use integer", "chomp", "chr" and "setpgrp".

 •   List assignments were sometimes buggy if the same scalar ended up on
     both sides of the assignment due to use of "tied", "values" or
     "each".  The result would be the wrong value getting assigned.

 •   "setpgrp($nonzero)" (with one argument) was accidentally changed in
     5.16 to mean setpgrp(0).  This has been fixed.

 •   "__SUB__" could return the wrong value or even corrupt memory under
     the debugger (the "-d" switch) and in subs containing "eval $string".

 •   When "sub () { $var }" becomes inlinable, it now returns a different
     scalar each time, just as a non-inlinable sub would, though Perl
     still optimises the copy away in cases where it would make no
     observable difference.

 •   "my sub f () { $var }" and "sub () : attr { $var }" are no longer
     eligible for inlining.  The former would crash; the latter would just
     throw the attributes away.  An exception is made for the little-known
     ":method" attribute, which does nothing much.

 •   Inlining of subs with an empty prototype is now more consistent than
     before. Previously, a sub with multiple statements, of which all but
     the last were optimised away, would be inlinable only if it were an
     anonymous sub containing a string "eval" or "state" declaration or
     closing over an outer lexical variable (or any anonymous sub under
     the debugger).  Now any sub that gets folded to a single constant
     after statements have been optimised away is eligible for inlining.
     This applies to things like "sub () { jabber() if DEBUG; 42 }".

     Some subroutines with an explicit "return" were being made inlinable,
     contrary to the documentation,  Now "return" always prevents
     inlining.

 •   On some systems, such as VMS, "crypt" can return a non-ASCII string.
     If a scalar assigned to had contained a UTF-8 string previously, then
     "crypt" would not turn off the UTF-8 flag, thus corrupting the return
     value.  This would happen with "$lexical = crypt ...".

 •   "crypt" no longer calls "FETCH" twice on a tied first argument.

 •   An unterminated here-doc on the last line of a quote-like operator
     ("qq[${ <<END }]", "/(?{ <<END })/") no longer causes a double free.
     It started doing so in 5.18.

 •   "index()" and "rindex()" no longer crash when used on strings over
     2GB in size.  [GH #13700]
     <https://github.com/Perl/perl5/issues/13700>.

 •   A small, previously intentional, memory leak in
     "PERL_SYS_INIT"/"PERL_SYS_INIT3" on Win32 builds was fixed. This
     might affect embedders who repeatedly create and destroy perl engines
     within the same process.

 •   "POSIX::localeconv()" now returns the data for the program's
     underlying locale even when called from outside the scope of
     "use locale".

 •   "POSIX::localeconv()" now works properly on platforms which don't
     have "LC_NUMERIC" and/or "LC_MONETARY", or for which Perl has been
     compiled to disregard either or both of these locale categories.  In
     such circumstances, there are now no entries for the corresponding
     values in the hash returned by "localeconv()".

 •   "POSIX::localeconv()" now marks appropriately the values it returns
     as UTF-8 or not.  Previously they were always returned as bytes, even
     if they were supposed to be encoded as UTF-8.

 •   On Microsoft Windows, within the scope of "use locale", the following
     POSIX character classes gave results for many locales that did not
     conform to the POSIX standard: "[[:alnum:]]", "[[:alpha:]]",
     "[[:blank:]]", "[[:digit:]]", "[[:graph:]]", "[[:lower:]]",
     "[[:print:]]", "[[:punct:]]", "[[:upper:]]", "[[:word:]]", and
     "[[:xdigit:]]".  This was because the underlying Microsoft
     implementation does not follow the standard.  Perl now takes special
     precautions to correct for this.

 •   Many issues have been detected by Coverity <http://www.coverity.com/>
     and fixed.

 •   "system()" and friends should now work properly on more Android
     builds.

     Due to an oversight, the value specified through "-Dtargetsh" to
     _C_o_n_f_i_g_u_r_e would end up being ignored by some of the build process.
     This caused perls cross-compiled for Android to end up with defective
     versions of "system()", "exec()" and backticks: the commands would
     end up looking for "/bin/sh" instead of "/system/bin/sh", and so
     would fail for the vast majority of devices, leaving $! as "ENOENT".

 •   "qr(...\(...\)...)", "qr[...\[...\]...]", and "qr{...\{...\}...}" now
     work.  Previously it was impossible to escape these three left-
     characters with a backslash within a regular expression pattern where
     otherwise they would be considered metacharacters, and the pattern
     opening delimiter was the character, and the closing delimiter was
     its mirror character.

 •   "s///e" on tainted UTF-8 strings corrupted "pos()". This bug,
     introduced in 5.20, is now fixed.  [GH #13948]
     <https://github.com/Perl/perl5/issues/13948>.

 •   A non-word boundary in a regular expression ("\B") did not always
     match the end of the string; in particular "q{} =~ /\B/" did not
     match. This bug, introduced in perl 5.14, is now fixed.  [GH #13917]
     <https://github.com/Perl/perl5/issues/13917>.

 •   "" P" =~ /(?=.*P)P/" should match, but did not. This is now fixed.
     [GH #13954] <https://github.com/Perl/perl5/issues/13954>.

 •   Failing to compile "use Foo" in an "eval" could leave a spurious
     "BEGIN" subroutine definition, which would produce a "Subroutine
     BEGIN redefined" warning on the next use of "use", or other "BEGIN"
     block.  [GH #13926] <https://github.com/Perl/perl5/issues/13926>.

 •   "method { BLOCK } ARGS" syntax now correctly parses the arguments if
     they begin with an opening brace.  [GH #9085]
     <https://github.com/Perl/perl5/issues/9085>.

 •   External libraries and Perl may have different ideas of what the
     locale is.  This is problematic when parsing version strings if the
     locale's numeric separator has been changed.  Version parsing has
     been patched to ensure it handles the locales correctly.  [GH #13863]
     <https://github.com/Perl/perl5/issues/13863>.

 •   A bug has been fixed where zero-length assertions and code blocks
     inside of a regex could cause "pos" to see an incorrect value.  [GH
     #14016] <https://github.com/Perl/perl5/issues/14016>.

 •   Dereferencing of constants now works correctly for typeglob
     constants.  Previously the glob was stringified and its name looked
     up.  Now the glob itself is used.  [GH #9891]
     <https://github.com/Perl/perl5/issues/9891>

 •   When parsing a sigil ("$" "@" "%" "&)" followed by braces, the parser
     no longer tries to guess whether it is a block or a hash constructor
     (causing a syntax error when it guesses the latter), since it can
     only be a block.

 •   "undef $reference" now frees the referent immediately, instead of
     hanging on to it until the next statement.  [GH #14032]
     <https://github.com/Perl/perl5/issues/14032>

 •   Various cases where the name of a sub is used (autoload, overloading,
     error messages) used to crash for lexical subs, but have been fixed.

 •   Bareword lookup now tries to avoid vivifying packages if it turns out
     the bareword is not going to be a subroutine name.

 •   Compilation of anonymous constants (_e_._g_., "sub () { 3 }") no longer
     deletes any subroutine named "__ANON__" in the current package.  Not
     only was "*__ANON__{CODE}" cleared, but there was a memory leak, too.
     This bug goes back to Perl 5.8.0.

 •   Stub declarations like "sub f;" and "sub f ();" no longer wipe out
     constants of the same name declared by "use constant".  This bug was
     introduced in Perl 5.10.0.

 •   "qr/[\N{named sequence}]/" now works properly in many instances.

     Some names known to "\N{...}" refer to a sequence of multiple
     characters, instead of the usual single character.  Bracketed
     character classes generally only match single characters, but now
     special handling has been added so that they can match named
     sequences, but not if the class is inverted or the sequence is
     specified as the beginning or end of a range.  In these cases, the
     only behavior change from before is a slight rewording of the fatal
     error message given when this class is part of a "?[...])" construct.
     When the "[...]" stands alone, the same non-fatal warning as before
     is raised, and only the first character in the sequence is used,
     again just as before.

 •   Tainted constants evaluated at compile time no longer cause unrelated
     statements to become tainted.  [GH #14059]
     <https://github.com/Perl/perl5/issues/14059>

 •   "open $$fh, ...", which vivifies a handle with a name like
     "main::_GEN_0", was not giving the handle the right reference count,
     so a double free could happen.

 •   When deciding that a bareword was a method name, the parser would get
     confused if an "our" sub with the same name existed, and look up the
     method in the package of the "our" sub, instead of the package of the
     invocant.

 •   The parser no longer gets confused by "\U=" within a double-quoted
     string.  It used to produce a syntax error, but now compiles it
     correctly.  [GH #10882] <https://github.com/Perl/perl5/issues/10882>

 •   It has always been the intention for the "-B" and "-T" file test
     operators to treat UTF-8 encoded files as text.  (perlfunc has been
     updated to say this.)  Previously, it was possible for some files to
     be considered UTF-8 that actually weren't valid UTF-8.  This is now
     fixed.  The operators now work on EBCDIC platforms as well.

 •   Under some conditions warning messages raised during regular
     expression pattern compilation were being output more than once.
     This has now been fixed.

 •   Perl 5.20.0 introduced a regression in which a UTF-8 encoded regular
     expression pattern that contains a single ASCII lowercase letter did
     not match its uppercase counterpart. That has been fixed in both
     5.20.1 and 5.22.0.  [GH #14051]
     <https://github.com/Perl/perl5/issues/14051>

 •   Constant folding could incorrectly suppress warnings if lexical
     warnings ("use warnings" or "no warnings") were not in effect and $^W
     were false at compile time and true at run time.

 •   Loading Unicode tables during a regular expression match could cause
     assertion failures under debugging builds if the previous match used
     the very same regular expression.  [GH #14081]
     <https://github.com/Perl/perl5/issues/14081>

 •   Thread cloning used to work incorrectly for lexical subs, possibly
     causing crashes or double frees on exit.

 •   Since Perl 5.14.0, deleting $SomePackage::{__ANON__} and then
     undefining an anonymous subroutine could corrupt things internally,
     resulting in Devel::Peek crashing or B.pm giving nonsensical data.
     This has been fixed.

 •   "(caller $n)[3]" now reports names of lexical subs, instead of
     treating them as "(unknown)".

 •   "sort subname LIST" now supports using a lexical sub as the
     comparison routine.

 •   Aliasing (_e_._g_., via "*x = *y") could confuse list assignments that
     mention the two names for the same variable on either side, causing
     wrong values to be assigned.  [GH #5788]
     <https://github.com/Perl/perl5/issues/5788>

 •   Long here-doc terminators could cause a bad read on short lines of
     input.  This has been fixed.  It is doubtful that any crash could
     have occurred.  This bug goes back to when here-docs were introduced
     in Perl 3.000 twenty-five years ago.

 •   An optimization in "split" to treat "split /^/" like "split /^/m" had
     the unfortunate side-effect of also treating "split /\A/" like
     "split /^/m", which it should not.  This has been fixed.  (Note,
     however, that "split /^x/" does not behave like "split /^x/m", which
     is also considered to be a bug and will be fixed in a future
     version.)  [GH #14086] <https://github.com/Perl/perl5/issues/14086>

 •   The little-known "my Class $var" syntax (see fields and attributes)
     could get confused in the scope of "use utf8" if "Class" were a
     constant whose value contained Latin-1 characters.

 •   Locking and unlocking values via Hash::Util or
     "Internals::SvREADONLY" no longer has any effect on values that were
     read-only to begin with.  Previously, unlocking such values could
     result in crashes, hangs or other erratic behavior.

 •   Some unterminated "(?(...)...)" constructs in regular expressions
     would either crash or give erroneous error messages.  "/(?(1)/" is
     one such example.

 •   "pack "w", $tied" no longer calls FETCH twice.

 •   List assignments like "($x, $z) = (1, $y)" now work correctly if $x
     and $y have been aliased by "foreach".

 •   Some patterns including code blocks with syntax errors, such as
     "/ (?{(^{})/", would hang or fail assertions on debugging builds.
     Now they produce errors.

 •   An assertion failure when parsing "sort" with debugging enabled has
     been fixed.  [GH #14087]
     <https://github.com/Perl/perl5/issues/14087>.

 •   "*a = *b; @a = split //, $b[1]" could do a bad read and produce junk
     results.

 •   In "() = @array = split", the "() =" at the beginning no longer
     confuses the optimizer into assuming a limit of 1.

 •   Fatal warnings no longer prevent the output of syntax errors.  [GH
     #14155] <https://github.com/Perl/perl5/issues/14155>.

 •   Fixed a NaN double-to-long-double conversion error on VMS. For quiet
     NaNs (and only on Itanium, not Alpha) negative infinity instead of
     NaN was produced.

 •   Fixed the issue that caused "make distclean" to incorrectly leave
     some files behind.  [GH #14108]
     <https://github.com/Perl/perl5/issues/14108>.

 •   AIX now sets the length in "getsockopt" correctly.  [GH #13484]
     <https://github.com/Perl/perl5/issues/13484>.  [cpan #91183]
     <https://rt.cpan.org/Ticket/Display.html?id=91183>.  [cpan #85570]
     <https://rt.cpan.org/Ticket/Display.html?id=85570>.

 •   The optimization phase of a regexp compilation could run "forever"
     and exhaust all memory under certain circumstances; now fixed.  [GH
     #13984] <https://github.com/Perl/perl5/issues/13984>.

 •   The test script _t_/_o_p_/_c_r_y_p_t_._t now uses the SHA-256 algorithm if the
     default one is disabled, rather than giving failures.  [GH #13715]
     <https://github.com/Perl/perl5/issues/13715>.

 •   Fixed an off-by-one error when setting the size of a shared array.
     [GH #14151] <https://github.com/Perl/perl5/issues/14151>.

 •   Fixed a bug that could cause perl to enter an infinite loop during
     compilation. In particular, a while(1) within a sublist, _e_._g_.

         sub foo { () = ($a, my $b, ($c, do { while(1) {} })) }

     The bug was introduced in 5.20.0 [GH #14165]
     <https://github.com/Perl/perl5/issues/14165>.

 •   On Win32, if a variable was "local"-ized in a pseudo-process that
     later forked, restoring the original value in the child pseudo-
     process caused memory corruption and a crash in the child pseudo-
     process (and therefore the OS process).  [GH #8641]
     <https://github.com/Perl/perl5/issues/8641>.

 •   Calling "write" on a format with a "^**" field could produce a panic
     in "sv_chop()" if there were insufficient arguments or if the
     variable used to fill the field was empty.  [GH #14255]
     <https://github.com/Perl/perl5/issues/14255>.

 •   Non-ASCII lexical sub names now appear without trailing junk when
     they appear in error messages.

 •   The "\@" subroutine prototype no longer flattens parenthesized arrays
     (taking a reference to each element), but takes a reference to the
     array itself.  [GH #9111]
     <https://github.com/Perl/perl5/issues/9111>.

 •   A block containing nothing except a C-style "for" loop could corrupt
     the stack, causing lists outside the block to lose elements or have
     elements overwritten.  This could happen with "map { for(...){...} }
     ..." and with lists containing "do { for(...){...} }".  [GH #14269]
     <https://github.com/Perl/perl5/issues/14269>.

 •   "scalar()" now propagates lvalue context, so that
     "for(scalar($#foo)) { ... }" can modify $#foo through $_.

 •   "qr/@array(?{block})/" no longer dies with "Bizarre copy of ARRAY".
     [GH #14292] <https://github.com/Perl/perl5/issues/14292>.

 •   "eval '$variable'" in nested named subroutines would sometimes look
     up a global variable even with a lexical variable in scope.

 •   In perl 5.20.0, "sort CORE::fake" where 'fake' is anything other than
     a keyword, started chopping off the last 6 characters and treating
     the result as a sort sub name.  The previous behavior of treating
     "CORE::fake" as a sort sub name has been restored.  [GH #14323]
     <https://github.com/Perl/perl5/issues/14323>.

 •   Outside of "use utf8", a single-character Latin-1 lexical variable is
     disallowed.  The error message for it, "Can't use global $foo...",
     was giving garbage instead of the variable name.

 •   "readline" on a nonexistent handle was causing "${^LAST_FH}" to
     produce a reference to an undefined scalar (or fail an assertion).
     Now "${^LAST_FH}" ends up undefined.

 •   "(...) x ..." in void context now applies scalar context to the left-
     hand argument, instead of the context the current sub was called in.
     [GH #14174] <https://github.com/Perl/perl5/issues/14174>.

KKnnoowwnn PPrroobblleemmss • “pack”-ing a NaN on a perl compiled with Visual C 6 does not behave properly, leading to a test failure in _t_/_o_p_/_i_n_f_n_a_n_._t. [GH #14705] https://github.com/Perl/perl5/issues/14705

 •   A goal is for Perl to be able to be recompiled to work reasonably
     well on any Unicode version.  In Perl 5.22, though, the earliest such
     version is Unicode 5.1 (current is 7.0).

 •   EBCDIC platforms

     •   The "cmp" (and hence "sort") operators do not necessarily give
         the correct results when both operands are UTF-EBCDIC encoded
         strings and there is a mixture of ASCII and/or control
         characters, along with other characters.

     •   Ranges containing "\N{...}" in the "tr///" (and "y///")
         transliteration operators are treated differently than the
         equivalent ranges in regular expression patterns.  They should,
         but don't, cause the values in the ranges to all be treated as
         Unicode code points, and not native ones.  ("Version 8 Regular
         Expressions" in perlre gives details as to how it should work.)

     •   Encode and encoding are mostly broken.

     •   Many CPAN modules that are shipped with core show failing tests.

     •   "pack"/"unpack" with "U0" format may not work properly.

 •   The following modules are known to have test failures with this
     version of Perl.  In many cases, patches have been submitted, so
     there will hopefully be new releases soon:

     •   B::Generate version 1.50

     •   B::Utils version 0.25

     •   Coro version 6.42

     •   Dancer version 1.3130

     •   Data::Alias version 1.18

     •   Data::Dump::Streamer version 2.38

     •   Data::Util version 0.63

     •   Devel::Spy version 0.07

     •   invoker version 0.34

     •   Lexical::Var version 0.009

     •   LWP::ConsoleLogger version 0.000018

     •   Mason version 2.22

     •   NgxQueue version 0.02

     •   Padre version 1.00

     •   Parse::Keyword 0.08

OObbiittuuaarryy Brian McCauley died on May 8, 2015. He was a frequent poster to Usenet, Perl Monks, and other Perl forums, and made several CPAN contributions under the nick NOBULL, including to the Perl FAQ. He attended almost every YAPC::Europe, and indeed, helped organise YAPC::Europe 2006 and the QA Hackathon 2009. His wit and his delight in intricate systems were particularly apparent in his love of board games; many Perl mongers will have fond memories of playing Fluxx and other games with Brian. He will be missed.

AAcckknnoowwlleeddggeemmeennttss Perl 5.22.0 represents approximately 12 months of development since Perl 5.20.0 and contains approximately 590,000 lines of changes across 2,400 files from 94 authors.

 Excluding auto-generated files, documentation and release tools, there
 were approximately 370,000 lines of changes to 1,500 .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 5.22.0:

 Aaron Crane, Abhijit Menon-Sen, Abigail, Alberto Simões, Alex Solovey,
 Alex Vandiver, Alexandr Ciornii, Alexandre (Midnite) Jousset, Andreas
 König, Andreas Voegele, Andrew Fresh, Andy Dougherty, Anthony Heading,
 Aristotle Pagaltzis, brian d foy, Brian Fraser, Chad Granum, Chris
 'BinGOs' Williams, Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel
 Dragan, Darin McBride, Dave Rolsky, David Golden, David Mitchell, David
 Wheeler, Dmitri Tikhonov, Doug Bell, E. Choroba, Ed J, Eric Herman,
 Father Chrysostomos, George Greer, Glenn D. Golden, Graham Knop, H.Merijn
 Brand, Herbert Breunung, Hugo van der Sanden, James E Keenan, James
 McCoy, James Raspass, Jan Dubois, Jarkko Hietaniemi, Jasmine Ngan, Jerry
 D. Hedden, Jim Cromie, John Goodyear, kafka, Karen Etheridge, Karl
 Williamson, Kent Fredric, kmx, Lajos Veres, Leon Timmermans, Lukas Mai,
 Mathieu Arnold, Matthew Horsfall, Max Maischein, Michael Bunk, Nicholas
 Clark, Niels Thykier, Niko Tyni, Norman Koch, Olivier Mengué, Peter John
 Acklam, Peter Martini, Petr Písař, Philippe Bruhat (BooK), Pierre
 Bogossian, Rafael Garcia-Suarez, Randy Stauner, Reini Urban, Ricardo
 Signes, Rob Hoelz, Rostislav Skudnov, Sawyer X, Shirakata Kentaro, Shlomi
 Fish, Sisyphus, Slaven Rezic, Smylers, Steffen Müller, Steve Hay,
 Sullivan Beck, syber, Tadeusz Sośnierz, Thomas Sibley, Todd Rinaldo, Tony
 Cook, Vincent Pit, Vladimir Marek, Yaroslav Kuzmin, Yves Orton, Ævar
 Arnfjörð Bjarmason.

 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 articles recently posted to the comp.lang.perl.misc newsgroup and the perl bug database at https://rt.perl.org/. There may also be information at http://www.perl.org/, the Perl Home Page.

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

 If the bug you are reporting has security implications, which make it
 inappropriate to send to a publicly archived mailing list, then please
 send it to perl5-security-report@perl.org.  This points to a closed
 subscription unarchived mailing list, which includes all the core
 committers, who will be able to help assess the impact of issues, figure
 out a resolution, and help co-ordinate the release of patches to mitigate
 or fix the problem across all platforms on which Perl is supported.
 Please only use this address for security issues in the Perl core, not
 for modules independently distributed on CPAN.

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 PERL5220DELTA(1)