PERL5180DELTA(1) Perl Programmers Reference Guide PERL5180DELTA(1)

PERL5180DELTA(1) Perl Programmers Reference Guide PERL5180DELTA(1) #

PERL5180DELTA(1) Perl Programmers Reference Guide PERL5180DELTA(1)

NNAAMMEE #

 perl5180delta - what is new for perl v5.18.0

DDEESSCCRRIIPPTTIIOONN #

 This document describes differences between the v5.16.0 release and the
 v5.18.0 release.

 If you are upgrading from an earlier release such as v5.14.0, first read
 perl5160delta, which describes differences between v5.14.0 and v5.16.0.

CCoorree EEnnhhaanncceemmeennttss NNeeww mmeecchhaanniissmm ffoorr eexxppeerriimmeennttaall ffeeaattuurreess Newly-added experimental features will now require this incantation:

     no warnings "experimental::feature_name";
     use feature "feature_name";  # would warn without the prev line

 There is a new warnings category, called "experimental", containing
 warnings that the feature pragma emits when enabling experimental
 features.

 Newly-added experimental features will also be given special warning IDs,
 which consist of "experimental::" followed by the name of the feature.
 (The plan is to extend this mechanism eventually to all warnings, to
 allow them to be enabled or disabled individually, and not just by
 category.)

 By saying

     no warnings "experimental::feature_name";

 you are taking responsibility for any breakage that future changes to, or
 removal of, the feature may cause.

 Since some features (like "~~" or "my $_") now emit experimental
 warnings, and you may want to disable them in code that is also run on
 perls that do not recognize these warning categories, consider using the
 "if" pragma like this:

     no if $] >= 5.018, warnings => "experimental::feature_name";

 Existing experimental features may begin emitting these warnings, too.
 Please consult perlexperiment for information on which features are
 considered experimental.

HHaasshh oovveerrhhaauull Changes to the implementation of hashes in perl v5.18.0 will be one of the most visible changes to the behavior of existing code.

 By default, two distinct hash variables with identical keys and values
 may now provide their contents in a different order where it was
 previously identical.

 When encountering these changes, the key to cleaning up from them is to
 accept that hhaasshheess aarree uunnoorrddeerreedd ccoolllleeccttiioonnss and to act accordingly.

 _H_a_s_h _r_a_n_d_o_m_i_z_a_t_i_o_n

 The seed used by Perl's hash function is now random.  This means that the
 order which keys/values will be returned from functions like "keys()",
 "values()", and "each()" will differ from run to run.

 This change was introduced to make Perl's hashes more robust to
 algorithmic complexity attacks, and also because we discovered that it
 exposes hash ordering dependency bugs and makes them easier to track
 down.

 Toolchain maintainers might want to invest in additional infrastructure
 to test for things like this.  Running tests several times in a row and
 then comparing results will make it easier to spot hash order
 dependencies in code.  Authors are strongly encouraged not to expose the
 key order of Perl's hashes to insecure audiences.

 Further, every hash has its own iteration order, which should make it
 much more difficult to determine what the current hash seed is.

 _N_e_w _h_a_s_h _f_u_n_c_t_i_o_n_s

 Perl v5.18 includes support for multiple hash functions, and changed the
 default (to ONE_AT_A_TIME_HARD), you can choose a different algorithm by
 defining a symbol at compile time.  For a current list, consult the
 _I_N_S_T_A_L_L document.  Note that as of Perl v5.18 we can only recommend use
 of the default or SIPHASH. All the others are known to have security
 issues and are for research purposes only.

 _P_E_R_L___H_A_S_H___S_E_E_D _e_n_v_i_r_o_n_m_e_n_t _v_a_r_i_a_b_l_e _n_o_w _t_a_k_e_s _a _h_e_x _v_a_l_u_e

 "PERL_HASH_SEED" no longer accepts an integer as a parameter; instead the
 value is expected to be a binary value encoded in a hex string, such as
 "0xf5867c55039dc724".  This is to make the infrastructure support hash
 seeds of arbitrary lengths, which might exceed that of an integer.
 (SipHash uses a 16 byte seed.)

 _P_E_R_L___P_E_R_T_U_R_B___K_E_Y_S _e_n_v_i_r_o_n_m_e_n_t _v_a_r_i_a_b_l_e _a_d_d_e_d

 The "PERL_PERTURB_KEYS" environment variable allows one to control the
 level of randomization applied to "keys" and friends.

 When "PERL_PERTURB_KEYS" is 0, perl will not randomize the key order at
 all. The chance that "keys" changes due to an insert will be the same as
 in previous perls, basically only when the bucket size is changed.

 When "PERL_PERTURB_KEYS" is 1, perl will randomize keys in a non-
 repeatable way. The chance that "keys" changes due to an insert will be
 very high.  This is the most secure and default mode.

 When "PERL_PERTURB_KEYS" is 2, perl will randomize keys in a repeatable
 way.  Repeated runs of the same program should produce the same output
 every time.

 "PERL_HASH_SEED" implies a non-default "PERL_PERTURB_KEYS" setting.
 Setting "PERL_HASH_SEED=0" (exactly one 0) implies "PERL_PERTURB_KEYS=0"
 (hash key randomization disabled); setting "PERL_HASH_SEED" to any other
 value implies "PERL_PERTURB_KEYS=2" (deterministic and repeatable hash
 key randomization).  Specifying "PERL_PERTURB_KEYS" explicitly to a
 different level overrides this behavior.

 _HH_aa_ss_hh_::_::_UU_tt_ii_ll_::_::_hh_aa_ss_hh____ss_ee_ee_dd_((_)) _n_o_w _r_e_t_u_r_n_s _a _s_t_r_i_n_g

 HHaasshh::::UUttiill::::hhaasshh__sseeeedd(()) now returns a string instead of an integer.  This
 is to make the infrastructure support hash seeds of arbitrary lengths
 which might exceed that of an integer.  (SipHash uses a 16 byte seed.)

 _O_u_t_p_u_t _o_f _P_E_R_L___H_A_S_H___S_E_E_D___D_E_B_U_G _h_a_s _b_e_e_n _c_h_a_n_g_e_d

 The environment variable PERL_HASH_SEED_DEBUG now makes perl show both
 the hash function perl was built with, _a_n_d the seed, in hex, in use for
 that process. Code parsing this output, should it exist, must change to
 accommodate the new format.  Example of the new format:

     $ PERL_HASH_SEED_DEBUG=1 ./perl -e1
     HASH_FUNCTION = MURMUR3 HASH_SEED = 0x1476bb9f

UUppggrraaddee ttoo UUnniiccooddee 66..22 Perl now supports Unicode 6.2. A list of changes from Unicode 6.1 is at http://www.unicode.org/versions/Unicode6.2.0.

CChhaarraacctteerr nnaammee aalliiaasseess mmaayy nnooww iinncclluuddee nnoonn--LLaattiinn11--rraannggee cchhaarraacctteerrss It is possible to define your own names for characters for use in “\N{…}”, “charnames::vianame()”, etc. These names can now be comprised of characters from the whole Unicode range. This allows for names to be in your native language, and not just English. Certain restrictions apply to the characters that may be used (you can’t define a name that has punctuation in it, for example). See “CUSTOM ALIASES” in charnames.

NNeeww DDTTrraaccee pprroobbeess The following new DTrace probes have been added:

 •   "op-entry"

 •   "loading-file"

 •   "loaded-file"

“”$${{^^LLAASSTT__FFHH}}“” #

 This new variable provides access to the filehandle that was last read.
 This is the handle used by $. and by "tell" and "eof" without arguments.

RReegguullaarr EExxpprreessssiioonn SSeett OOppeerraattiioonnss This is an eexxppeerriimmeennttaall feature to allow matching against the union, intersection, etc., of sets of code points, similar to Unicode::Regex::Set. It can also be used to extend “/x” processing to [bracketed] character classes, and as a replacement of user-defined properties, allowing more complex expressions than they do. See “Extended Bracketed Character Classes” in perlrecharclass.

LLeexxiiccaall ssuubbrroouuttiinneess This new feature is still considered eexxppeerriimmeennttaall. To enable it:

     use 5.018;
     no warnings "experimental::lexical_subs";
     use feature "lexical_subs";

 You can now declare subroutines with "state sub foo", "my sub foo", and
 "our sub foo".  ("state sub" requires that the "state" feature be
 enabled, unless you write it as "CORE::state sub foo".)

 "state sub" creates a subroutine visible within the lexical scope in
 which it is declared.  The subroutine is shared between calls to the
 outer sub.

 "my sub" declares a lexical subroutine that is created each time the
 enclosing block is entered.  "state sub" is generally slightly faster
 than "my sub".

 "our sub" declares a lexical alias to the package subroutine of the same
 name.

 For more information, see "Lexical Subroutines" in perlsub.

CCoommppuutteedd LLaabbeellss The loop controls “next”, “last” and “redo”, and the special “dump” operator, now allow arbitrary expressions to be used to compute labels at run time. Previously, any argument that was not a constant was treated as the empty string.

MMoorree CCOORREE:::: ssuubbss Several more built-in functions have been added as subroutines to the CORE:: namespace - namely, those non-overridable keywords that can be implemented without custom parsers: “defined”, “delete”, “exists”, “glob”, “pos”, “prototype”, “scalar”, “split”, “study”, and “undef”.

 As some of these have prototypes, "prototype('CORE::...')" has been
 changed to not make a distinction between overridable and non-overridable
 keywords.  This is to make "prototype('CORE::pos')" consistent with
 "prototype(&CORE::pos)".

“"kkiillll"” wwiitthh nneeggaattiivvee ssiiggnnaall nnaammeess “kill” has always allowed a negative signal number, which kills the process group instead of a single process. It has also allowed signal names. But it did not behave consistently, because negative signal names were treated as 0. Now negative signals names like “-INT” are supported and treated the same way as -2 [perl #112990].

SSeeccuurriittyy SSeeee aallssoo:: hhaasshh oovveerrhhaauull Some of the changes in the hash overhaul were made to enhance security. Please read that section.

“"SSttoorraabbllee"” sseeccuurriittyy wwaarrnniinngg iinn ddooccuummeennttaattiioonn The documentation for “Storable” now includes a section which warns readers of the danger of accepting Storable documents from untrusted sources. The short version is that deserializing certain types of data can lead to loading modules and other code execution. This is documented behavior and wanted behavior, but this opens an attack vector for malicious entities.

“"LLooccaallee::::MMaakkeetteexxtt"” aalllloowweedd ccooddee iinnjjeeccttiioonn vviiaa aa mmaalliicciioouuss tteemmppllaattee If users could provide a translation string to Locale::Maketext, this could be used to invoke arbitrary Perl subroutines available in the current process.

 This has been fixed, but it is still possible to invoke any method
 provided by "Locale::Maketext" itself or a subclass that you are using.
 One of these methods in turn will invoke the Perl core's "sprintf"
 subroutine.

 In summary, allowing users to provide translation strings without
 auditing them is a bad idea.

 This vulnerability is documented in CVE-2012-6329.

AAvvooiidd ccaalllliinngg mmeemmsseett wwiitthh aa nneeggaattiivvee ccoouunntt Poorly written perl code that allows an attacker to specify the count to perl’s “x” string repeat operator can already cause a memory exhaustion denial-of-service attack. A flaw in versions of perl before v5.15.5 can escalate that into a heap buffer overrun; coupled with versions of glibc before 2.16, it possibly allows the execution of arbitrary code.

 The flaw addressed to this commit has been assigned identifier
 CVE-2012-5195 and was researched by Tim Brown.

IInnccoommppaattiibbllee CChhaannggeess SSeeee aallssoo:: hhaasshh oovveerrhhaauull Some of the changes in the hash overhaul are not fully compatible with previous versions of perl. Please read that section.

AAnn uunnkknnoowwnn cchhaarraacctteerr nnaammee iinn “”\\NN{{......}}“” iiss nnooww aa ssyynnttaaxx eerrrroorr Previously, it warned, and the Unicode REPLACEMENT CHARACTER was substituted. Unicode now recommends that this situation be a syntax error. Also, the previous behavior led to some confusing warnings and behaviors, and since the REPLACEMENT CHARACTER has no use other than as a stand-in for some unknown character, any code that has this problem is buggy.

FFoorrmmeerrllyy ddeepprreeccaatteedd cchhaarraacctteerrss iinn “”\\NN{{}}“” cchhaarraacctteerr nnaammee aalliiaasseess aarree nnooww eerrrroorrss.. Since v5.12.0, it has been deprecated to use certain characters in user- defined “\N{…}” character names. These now cause a syntax error. For example, it is now an error to begin a name with a digit, such as in

  my $undraftable = "\N{4F}";    # Syntax error!

 or to have commas anywhere in the name.  See "CUSTOM ALIASES" in
 charnames.

“”\\NN{{BBEELLLL}}“” nnooww rreeffeerrss ttoo UU++11FF551144 iinnsstteeaadd ooff UU++00000077 Unicode 6.0 reused the name “BELL” for a different code point than it traditionally had meant. Since Perl v5.14, use of this name still referred to U+0007, but would raise a deprecation warning. Now, “BELL” refers to U+1F514, and the name for U+0007 is “ALERT”. All the functions in charnames have been correspondingly updated.

NNeeww RReessttrriiccttiioonnss iinn MMuullttii--CChhaarraacctteerr CCaassee--IInnsseennssiittiivvee MMaattcchhiinngg iinn RReegguullaarr EExxpprreessssiioonn BBrraacckkeetteedd CChhaarraacctteerr CCllaasssseess Unicode has now withdrawn their previous recommendation for regular expressions to automatically handle cases where a single character can match multiple characters case-insensitively, for example, the letter LATIN SMALL LETTER SHARP S and the sequence “ss”. This is because it turns out to be impracticable to do this correctly in all circumstances. Because Perl has tried to do this as best it can, it will continue to do so. (We are considering an option to turn it off.) However, a new restriction is being added on such matches when they occur in [bracketed] character classes. People were specifying things such as “/[\0-\xff]/i”, and being surprised that it matches the two character sequence “ss” (since LATIN SMALL LETTER SHARP S occurs in this range). This behavior is also inconsistent with using a property instead of a range: “\p{Block=Latin1}” also includes LATIN SMALL LETTER SHARP S, but “/[\p{Block=Latin1}]/i” does not match “ss”. The new rule is that for there to be a multi-character case-insensitive match within a bracketed character class, the character must be explicitly listed, and not as an end point of a range. This more closely obeys the Principle of Least Astonishment. See “Bracketed Character Classes” in perlrecharclass. Note that a bug [perl #89774], now fixed as part of this change, prevented the previous behavior from working fully.

EExxpplliicciitt rruulleess ffoorr vvaarriiaabbllee nnaammeess aanndd iiddeennttiiffiieerrss Due to an oversight, single character variable names in v5.16 were completely unrestricted. This opened the door to several kinds of insanity. As of v5.18, these now follow the rules of other identifiers, in addition to accepting characters that match the “\p{POSIX_Punct}” property.

 There is no longer any difference in the parsing of identifiers specified
 by using braces versus without braces.  For instance, perl used to allow
 "${foo:bar}" (with a single colon) but not $foo:bar.  Now that both are
 handled by a single code path, they are both treated the same way: both
 are forbidden.  Note that this change is about the range of permissible
 literal identifiers, not other expressions.

VVeerrttiiccaall ttaabbss aarree nnooww wwhhiitteessppaaccee No one could recall why “\s” didn’t match “\cK”, the vertical tab. Now it does. Given the extreme rarity of that character, very little breakage is expected. That said, here’s what it means:

 "\s" in a regex now matches a vertical tab in all circumstances.

 Literal vertical tabs in a regex literal are ignored when the "/x"
 modifier is used.

 Leading vertical tabs, alone or mixed with other whitespace, are now
 ignored when interpreting a string as a number.  For example:

   $dec = " \cK \t 123";
   $hex = " \cK \t 0xF";

   say 0 + $dec;   # was 0 with warning, now 123
   say int $dec;   # was 0, now 123
   say oct $hex;   # was 0, now  15

“”//((??{{}}))//“” aanndd “”//((????{{}}))//“” hhaavvee bbeeeenn hheeaavviillyy rreewwoorrkkeedd The implementation of this feature has been almost completely rewritten. Although its main intent is to fix bugs, some behaviors, especially related to the scope of lexical variables, will have changed. This is described more fully in the “Selected Bug Fixes” section.

SSttrriicctteerr ppaarrssiinngg ooff ssuubbssttiittuuttiioonn rreeppllaacceemmeenntt It is no longer possible to abuse the way the parser parses “s///e” like this:

     %_=(_,"Just another ");
     $_="Perl hacker,\n";
     s//_}->{_/e;print

“"ggiivveenn"” nnooww aalliiaasseess tthhee gglloobbaall $$ Instead of assigning to an implicit lexical $, “given” now makes the global $ an alias for its argument, just like “foreach”. However, it still uses lexical $_ if there is lexical $_ in scope (again, just like “foreach”) [perl #114020].

TThhee ssmmaarrttmmaattcchh ffaammiillyy ooff ffeeaattuurreess aarree nnooww eexxppeerriimmeennttaall Smart match, added in v5.10.0 and significantly revised in v5.10.1, has been a regular point of complaint. Although there are a number of ways in which it is useful, it has also proven problematic and confusing for both users and implementors of Perl. There have been a number of proposals on how to best address the problem. It is clear that smartmatch is almost certainly either going to change or go away in the future. Relying on its current behavior is not recommended.

 Warnings will now be issued when the parser sees "~~", "given", or
 "when".  To disable these warnings, you can add this line to the
 appropriate scope:

   no if $] >= 5.018, warnings => "experimental::smartmatch";

 Consider, though, replacing the use of these features, as they may change
 behavior again before becoming stable.

LLeexxiiccaall $$ iiss nnooww eexxppeerriimmeennttaall Since it was introduced in Perl v5.10, it has caused much confusion with no obvious solution:

 •   Various modules (e.g., List::Util) expect callback routines to use
     the global $_.  "use List::Util 'first'; my $_; first { $_ == 1 }
     @list" does not work as one would expect.

 •   A "my $_" declaration earlier in the same file can cause confusing
     closure warnings.

 •   The "_" subroutine prototype character allows called subroutines to
     access your lexical $_, so it is not really private after all.

 •   Nevertheless, subroutines with a "(@)" prototype and methods cannot
     access the caller's lexical $_, unless they are written in XS.

 •   But even XS routines cannot access a lexical $_ declared, not in the
     calling subroutine, but in an outer scope, iff that subroutine
     happened not to mention $_ or use any operators that default to $_.

 It is our hope that lexical $_ can be rehabilitated, but this may cause
 changes in its behavior.  Please use it with caution until it becomes
 stable.

rreeaaddlliinnee(()) wwiitthh “”$$// == \\NN"" nnooww rreeaaddss NN cchhaarraacctteerrss,, nnoott NN bbyytteess Previously, when reading from a stream with I/O layers such as “encoding”, the rreeaaddlliinnee(()) function, otherwise known as the “<>” operator, would read _N bytes from the top-most layer. [perl #79960]

 Now, _N characters are read instead.

 There is no change in behaviour when reading from streams with no extra
 layers, since bytes map exactly to characters.

OOvveerrrriiddddeenn “"gglloobb"” iiss nnooww ppaasssseedd oonnee aarrgguummeenntt “glob” overrides used to be passed a magical undocumented second argument that identified the caller. Nothing on CPAN was using this, and it got in the way of a bug fix, so it was removed. If you really need to identify the caller, see Devel::Callsite on CPAN.

HHeerree ddoocc ppaarrssiinngg The body of a here document inside a quote-like operator now always begins on the line after the “«foo” marker. Previously, it was documented to begin on the line following the containing quote-like operator, but that was only sometimes the case [perl #114040].

AAllpphhaannuummeerriicc ooppeerraattoorrss mmuusstt nnooww bbee sseeppaarraatteedd ffrroomm tthhee cclloossiinngg ddeelliimmiitteerr ooff rreegguullaarr eexxpprreessssiioonnss You may no longer write something like:

  m/a/and 1

 Instead you must write

  m/a/ and 1

 with whitespace separating the operator from the closing delimiter of the
 regular expression.  Not having whitespace has resulted in a deprecation
 warning since Perl v5.14.0.

qqww((......)) ccaann nnoo lloonnggeerr bbee uusseedd aass ppaarreenntthheesseess “qw” lists used to fool the parser into thinking they were always surrounded by parentheses. This permitted some surprising constructions such as “foreach $x qw(a b c) {…}”, which should really be written “foreach $x (qw(a b c)) {…}”. These would sometimes get the lexer into the wrong state, so they didn’t fully work, and the similar “foreach qw(a b c) {…}” that one might expect to be permitted never worked at all.

 This side effect of "qw" has now been abolished.  It has been deprecated
 since Perl v5.13.11.  It is now necessary to use real parentheses
 everywhere that the grammar calls for them.

IInntteerraaccttiioonn ooff lleexxiiccaall aanndd ddeeffaauulltt wwaarrnniinnggss Turning on any lexical warnings used first to disable all default warnings if lexical warnings were not already enabled:

     $*; # deprecation warning
     use warnings "void";
     $#; # void warning; no deprecation warning

 Now, the "debugging", "deprecated", "glob", "inplace" and "malloc"
 warnings categories are left on when turning on lexical warnings (unless
 they are turned off by "no warnings", of course).

 This may cause deprecation warnings to occur in code that used to be free
 of warnings.

 Those are the only categories consisting only of default warnings.
 Default warnings in other categories are still disabled by "use warnings
 "category"", as we do not yet have the infrastructure for controlling
 individual warnings.

“"ssttaattee ssuubb"” aanndd “"oouurr ssuubb"” Due to an accident of history, “state sub” and “our sub” were equivalent to a plain “sub”, so one could even create an anonymous sub with “our sub { … }”. These are now disallowed outside of the “lexical_subs” feature. Under the “lexical_subs” feature they have new meanings described in “Lexical Subroutines” in perlsub.

DDeeffiinneedd vvaalluueess ssttoorreedd iinn eennvviirroonnmmeenntt aarree ffoorrcceedd ttoo bbyyttee ssttrriinnggss A value stored in an environment variable has always been stringified when inherited by child processes.

 In this release, when assigning to %ENV, values are immediately
 stringified, and converted to be only a byte string.

 First, it is forced to be only a string.  Then if the string is utf8 and
 the equivalent of "utf8::downgrade()" works, that result is used;
 otherwise, the equivalent of "utf8::encode()" is used, and a warning is
 issued about wide characters ("Diagnostics").

“"rreeqquuiirree"” ddiieess ffoorr uunnrreeaaddaabbllee ffiilleess When “require” encounters an unreadable file, it now dies. It used to ignore the file and continue searching the directories in @INC [perl #113422].

“"ggvv__ffeettcchhmmeetthh__“” aanndd SSUUPPEERR The various “gv_fetchmeth_*” XS functions used to treat a package whose named ended with “::SUPER” specially. A method lookup on the “Foo::SUPER” package would be treated as a “SUPER” method lookup on the “Foo” package. This is no longer the case. To do a “SUPER” lookup, pass the “Foo” stash and the “GV_SUPER” flag.

“"sspplliitt"”‘’ss ffiirrsstt aarrgguummeenntt iiss mmoorree ccoonnssiisstteennttllyy iinntteerrpprreetteedd After some changes earlier in v5.17, “split”’s behavior has been simplified: if the PATTERN argument evaluates to a string containing one space, it is treated the way that a _l_i_t_e_r_a_l string containing one space once was.

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

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

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

 encoding
     The use of this pragma is now strongly discouraged. It conflates the
     encoding of source text with the encoding of I/O data, reinterprets
     escape sequences in source text (a questionable choice), and
     introduces the UTF-8 bug to all runtime handling of character
     strings. It is broken as designed and beyond repair.

     For using non-ASCII literal characters in source text, please refer
     to utf8.  For dealing with textual I/O data, please refer to Encode
     and open.

 Archive::Extract
 B::Lint
 B::Lint::Debug
 CPANPLUS and all included "CPANPLUS::*" modules
 Devel::InnerPackage
 Log::Message
 Log::Message::Config
 Log::Message::Handlers
 Log::Message::Item
 Log::Message::Simple
 Module::Pluggable
 Module::Pluggable::Object
 Object::Accessor
 Pod::LaTeX
 Term::UI
 Term::UI::History

DDeepprreeccaatteedd UUttiilliittiieess The following utilities will be removed from the core distribution in a future release as their associated modules have been deprecated. They will remain available with the applicable CPAN distribution.

 cpanp
 "cpanp-run-perl"
 cpan2dist
     These items are part of the "CPANPLUS" distribution.

 pod2latex
     This item is part of the "Pod::LaTeX" distribution.

PPLL__ssvv__oobbjjccoouunntt This interpreter-global variable used to track the total number of Perl objects in the interpreter. It is no longer maintained and will be removed altogether in Perl v5.20.

FFiivvee aaddddiittiioonnaall cchhaarraacctteerrss sshhoouulldd bbee eessccaappeedd iinn ppaatttteerrnnss wwiitthh “”//xx"” When a regular expression pattern is compiled with “/x”, Perl treats 6 characters as white space to ignore, such as SPACE and TAB. However, Unicode recommends 11 characters be treated thusly. We will conform with this in a future Perl version. In the meantime, use of any of the missing characters will raise a deprecation warning, unless turned off. The five characters 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 #

UUsseerr--ddeeffiinneedd cchhaarrnnaammeess wwiitthh ssuurrpprriissiinngg wwhhiitteessppaaccee A user-defined character name with trailing or multiple spaces in a row is likely a typo. This now generates a warning when defined, on the assumption that uses of it will be unlikely to include the excess whitespace.

VVaarriioouuss XXSS--ccaallllaabbllee ffuunnccttiioonnss aarree nnooww ddeepprreeccaatteedd All the functions used to classify characters will be removed from a future version of Perl, and should not be used. With participating C compilers (e.g., gcc), compiling any file that uses any of these will generate a warning. These were not intended for public use; there are equivalent, faster, macros for most of them.

 See "Character classes" in perlapi.  The complete list is:

 "is_uni_alnum", "is_uni_alnumc", "is_uni_alnumc_lc", "is_uni_alnum_lc",
 "is_uni_alpha", "is_uni_alpha_lc", "is_uni_ascii", "is_uni_ascii_lc",
 "is_uni_blank", "is_uni_blank_lc", "is_uni_cntrl", "is_uni_cntrl_lc",
 "is_uni_digit", "is_uni_digit_lc", "is_uni_graph", "is_uni_graph_lc",
 "is_uni_idfirst", "is_uni_idfirst_lc", "is_uni_lower", "is_uni_lower_lc",
 "is_uni_print", "is_uni_print_lc", "is_uni_punct", "is_uni_punct_lc",
 "is_uni_space", "is_uni_space_lc", "is_uni_upper", "is_uni_upper_lc",
 "is_uni_xdigit", "is_uni_xdigit_lc", "is_utf8_alnum", "is_utf8_alnumc",
 "is_utf8_alpha", "is_utf8_ascii", "is_utf8_blank", "is_utf8_char",
 "is_utf8_cntrl", "is_utf8_digit", "is_utf8_graph", "is_utf8_idcont",
 "is_utf8_idfirst", "is_utf8_lower", "is_utf8_mark", "is_utf8_perl_space",
 "is_utf8_perl_word", "is_utf8_posix_digit", "is_utf8_print",
 "is_utf8_punct", "is_utf8_space", "is_utf8_upper", "is_utf8_xdigit",
 "is_utf8_xidcont", "is_utf8_xidfirst".

 In addition these three functions that have never worked properly are
 deprecated: "to_uni_lower_lc", "to_uni_title_lc", and "to_uni_upper_lc".

CCeerrttaaiinn rraarree uusseess ooff bbaacckkssllaasshheess wwiitthhiinn rreeggeexxeess aarree nnooww ddeepprreeccaatteedd There are three pairs of characters that Perl recognizes as metacharacters in regular expression patterns: “{}”, “[]”, and “()”. These can be used as well to delimit patterns, as in:

   m{foo}
   s(foo)(bar)

 Since they are metacharacters, they have special meaning to regular
 expression patterns, and it turns out that you can't turn off that
 special meaning by the normal means of preceding them with a backslash,
 if you use them, paired, within a pattern delimited by them.  For
 example, in

   m{foo\{1,3\}}

 the backslashes do not change the behavior, and this matches "f o"
 followed by one to three more occurrences of "o".

 Usages like this, where they are interpreted as metacharacters, are
 exceedingly rare; we think there are none, for example, in all of CPAN.
 Hence, this deprecation should affect very little code.  It does give
 notice, however, that any such code needs to change, which will in turn
 allow us to change the behavior in future Perl versions so that the
 backslashes do have an effect, and without fear that we are silently
 breaking any existing code.

SSpplliittttiinngg tthhee ttookkeennss “”((??“” aanndd “”((“” iinn rreegguullaarr eexxpprreessssiioonnss A deprecation warning is now raised if the “(” and “?” are separated by white space or comments in “(?…)” regular expression constructs. Similarly, if the “(” and “*” are separated in “(*VERB…)” constructs.

PPrree--PPeerrllIIOO IIOO iimmpplleemmeennttaattiioonnss In theory, you can currently build perl without PerlIO. Instead, you’d use a wrapper around stdio or sfio. In practice, this isn’t very useful. It’s not well tested, and without any support for IO layers or (thus) Unicode, it’s not much of a perl. Building without PerlIO will most likely be removed in the next version of perl.

 PerlIO supports a "stdio" layer if stdio use is desired.  Similarly a
 sfio layer could be produced in the future, if needed.

FFuuttuurree DDeepprreeccaattiioonnss • Platforms without support infrastructure

     Both Windows CE and z/OS have been historically under-maintained, and
     are currently neither successfully building nor regularly being smoke
     tested.  Efforts are underway to change this situation, but it should
     not be taken for granted that the platforms are safe and supported.
     If they do not become buildable and regularly smoked, support for
     them may be actively removed in future releases.  If you have an
     interest in these platforms and you can lend your time, expertise, or
     hardware to help support these platforms, please let the perl
     development effort know by emailing "perl5-porters@perl.org".

     Some platforms that appear otherwise entirely dead are also on the
     short list for removal between now and v5.20.0:

DG/UX #

     NeXT

     We also think it likely that current versions of Perl will no longer
     build AmigaOS, DJGPP, NetWare (natively), OS/2 and Plan 9. If you are
     using Perl on such a platform and have an interest in ensuring Perl's
     future on them, please contact us.

     We believe that Perl has long been unable to build on mixed endian
     architectures (such as PDP-11s), and intend to remove any remaining
     support code. Similarly, code supporting the long unmaintained GNU
     dld will be removed soon if no-one makes themselves known as an
     active user.

 •   Swapping of $< and $>

     Perl has supported the idiom of swapping $< and $> (and likewise $(
     and $)) to temporarily drop permissions since 5.0, like this:

         ($<, $>) = ($>, $<);

     However, this idiom modifies the real user/group id, which can have
     undesirable side-effects, is no longer useful on any platform perl
     supports and complicates the implementation of these variables and
     list assignment in general.

     As an alternative, assignment only to $> is recommended:

         local $> = $<;

     See also: Setuid Demystified
     <http://www.cs.berkeley.edu/~daw/papers/setuid-usenix02.pdf>.

 •   "microperl", long broken and of unclear present purpose, will be
     removed.

 •   Revamping "\Q" semantics in double-quotish strings when combined with
     other escapes.

     There are several bugs and inconsistencies involving combinations of
     "\Q" and escapes like "\x", "\L", etc., within a "\Q...\E" pair.
     These need to be fixed, and doing so will necessarily change current
     behavior.  The changes have not yet been settled.

 •   Use of $x, where "x" stands for any actual (non-printing) C0 control
     character will be disallowed in a future Perl version.  Use "${x}"
     instead (where again "x" stands for a control character), or better,
     $^A , where "^" is a caret (CIRCUMFLEX ACCENT), and "A" stands for
     any of the characters listed at the end of "OPERATOR DIFFERENCES" in
     perlebcdic.

PPeerrffoorrmmaannccee EEnnhhaanncceemmeennttss • Lists of lexical variable declarations (“my($x, $y)”) are now optimised down to a single op and are hence faster than before.

 •   A new C preprocessor define "NO_TAINT_SUPPORT" was added that, if
     set, disables Perl's taint support altogether.  Using the -T or -t
     command line flags will cause a fatal error.  Beware that both core
     tests as well as many a CPAN distribution's tests will fail with this
     change.  On the upside, it provides a small performance benefit due
     to reduced branching.

     DDoo nnoott eennaabbllee tthhiiss uunnlleessss yyoouu kknnooww eexxaaccttllyy wwhhaatt yyoouu aarree ggeettttiinngg
     yyoouurrsseellff iinnttoo..

 •   "pack" with constant arguments is now constant folded in most cases
     [perl #113470].

 •   Speed up in regular expression matching against Unicode properties.
     The largest gain is for "\X", the Unicode "extended grapheme
     cluster."  The gain for it is about 35% - 40%.  Bracketed character
     classes, e.g., "[0-9\x{100}]" containing code points above 255 are
     also now faster.

 •   On platforms supporting it, several former macros are now implemented
     as static inline functions. This should speed things up slightly on
     non-GCC platforms.

 •   The optimisation of hashes in boolean context has been extended to
     affect "scalar(%hash)", "%hash ? ... : ...", and "sub { %hash || ...
     }".

 •   Filetest operators manage the stack in a fractionally more efficient
     manner.

 •   Globs used in a numeric context are now numified directly in most
     cases, rather than being numified via stringification.

 •   The "x" repetition operator is now folded to a single constant at
     compile time if called in scalar context with constant operands and
     no parentheses around the left operand.

MMoodduulleess aanndd PPrraaggmmaattaa NNeeww MMoodduulleess aanndd PPrraaggmmaattaa • Config::Perl::V version 0.16 has been added as a dual-lifed module. It provides structured data retrieval of “perl -V” output including information only known to the “perl” binary and not available via Config.

UUppddaatteedd MMoodduulleess aanndd PPrraaggmmaattaa For a complete list of updates, run:

   $ corelist --diff 5.16.0 5.18.0

 You can substitute your favorite version in place of 5.16.0, too.

 •   Archive::Extract has been upgraded to 0.68.

     Work around an edge case on Linux with Busybox's unzip.

 •   Archive::Tar has been upgraded to 1.90.

     ptar now supports the -T option as well as dashless options
     [rt.cpan.org #75473], [rt.cpan.org #75475].

     Auto-encode filenames marked as UTF-8 [rt.cpan.org #75474].

     Don't use "tell" on IO::Zlib handles [rt.cpan.org #64339].

     Don't try to "chown" on symlinks.

 •   autodie has been upgraded to 2.13.

     "autodie" now plays nicely with the 'open' pragma.

 •   B has been upgraded to 1.42.

     The "stashoff" method of COPs has been added.   This provides access
     to an internal field added in perl 5.16 under threaded builds [perl
     #113034].

     "B::COP::stashpv" now supports UTF-8 package names and embedded NULs.

     All "CVf_*" and "GVf_*" and more SV-related flag values are now
     provided as constants in the "B::" namespace and available for
     export.  The default export list has not changed.

     This makes the module work with the new pad API.

 •   B::Concise has been upgraded to 0.95.

     The "-nobanner" option has been fixed, and "format"s can now be
     dumped.  When passed a sub name to dump, it will check also to see
     whether it is the name of a format.  If a sub and a format share the
     same name, it will dump both.

     This adds support for the new "OpMAYBE_TRUEBOOL" and "OPpTRUEBOOL"
     flags.

 •   B::Debug has been upgraded to 1.18.

     This adds support (experimentally) for "B::PADLIST", which was added
     in Perl 5.17.4.

 •   B::Deparse has been upgraded to 1.20.

     Avoid warning when run under "perl -w".

     It now deparses loop controls with the correct precedence, and
     multiple statements in a "format" line are also now deparsed
     correctly.

     This release suppresses trailing semicolons in formats.

     This release adds stub deparsing for lexical subroutines.

     It no longer dies when deparsing "sort" without arguments.  It now
     correctly omits the comma for "system $prog @args" and "exec $prog
     @args".

 •   bignum, bigint and bigrat have been upgraded to 0.33.

     The overrides for "hex" and "oct" have been rewritten, eliminating
     several problems, and making one incompatible change:

     •   Formerly, whichever of "use bigint" or "use bigrat" was compiled
         later would take precedence over the other, causing "hex" and
         "oct" not to respect the other pragma when in scope.

     •   Using any of these three pragmata would cause "hex" and "oct"
         anywhere else in the program to evaluate their arguments in list
         context and prevent them from inferring $_ when called without
         arguments.

     •   Using any of these three pragmata would make "oct("1234")" return
         1234 (for any number not beginning with 0) anywhere in the
         program.  Now "1234" is translated from octal to decimal, whether
         within the pragma's scope or not.

     •   The global overrides that facilitate lexical use of "hex" and
         "oct" now respect any existing overrides that were in place
         before the new overrides were installed, falling back to them
         outside of the scope of "use bignum".

     •   "use bignum "hex"", "use bignum "oct"" and similar invocations
         for bigint and bigrat now export a "hex" or "oct" function,
         instead of providing a global override.

 •   Carp has been upgraded to 1.29.

     Carp is no longer confused when "caller" returns undef for a package
     that has been deleted.

     The "longmess()" and "shortmess()" functions are now documented.

 •   CGI has been upgraded to 3.63.

     Unrecognized HTML escape sequences are now handled better,
     problematic trailing newlines are no longer inserted after <form>
     tags by "startform()" or "start_form()", and bogus "Insecure
     Dependency" warnings appearing with some versions of perl are now
     worked around.

 •   Class::Struct has been upgraded to 0.64.

     The constructor now respects overridden accessor methods [perl
     #29230].

 •   Compress::Raw::Bzip2 has been upgraded to 2.060.

     The misuse of Perl's "magic" API has been fixed.

 •   Compress::Raw::Zlib has been upgraded to 2.060.

     Upgrade bundled zlib to version 1.2.7.

     Fix build failures on Irix, Solaris, and Win32, and also when
     building as C++ [rt.cpan.org #69985], [rt.cpan.org #77030],
     [rt.cpan.org #75222].

     The misuse of Perl's "magic" API has been fixed.

     "compress()", "uncompress()", "memGzip()" and "memGunzip()" have been
     speeded up by making parameter validation more efficient.

 •   CPAN::Meta::Requirements has been upgraded to 2.122.

     Treat undef requirements to "from_string_hash" as 0 (with a warning).

     Added "requirements_for_module" method.

 •   CPANPLUS has been upgraded to 0.9135.

     Allow adding _b_l_i_b_/_s_c_r_i_p_t to PATH.

     Save the history between invocations of the shell.

     Handle multiple "makemakerargs" and "makeflags" arguments better.

     This resolves issues with the SQLite source engine.

 •   Data::Dumper has been upgraded to 2.145.

     It has been optimized to only build a seen-scalar hash as necessary,
     thereby speeding up serialization drastically.

     Additional tests were added in order to improve statement, branch,
     condition and subroutine coverage.  On the basis of the coverage
     analysis, some of the internals of Dumper.pm were refactored.  Almost
     all methods are now documented.

 •   DB_File has been upgraded to 1.827.

     The main Perl module no longer uses the "@_" construct.

 •   Devel::Peek has been upgraded to 1.11.

     This fixes compilation with C++ compilers and makes the module work
     with the new pad API.

 •   Digest::MD5 has been upgraded to 2.52.

     Fix "Digest::Perl::MD5" OO fallback [rt.cpan.org #66634].

 •   Digest::SHA has been upgraded to 5.84.

     This fixes a double-free bug, which might have caused vulnerabilities
     in some cases.

 •   DynaLoader has been upgraded to 1.18.

     This is due to a minor code change in the XS for the VMS
     implementation.

     This fixes warnings about using "CODE" sections without an "OUTPUT"
     section.

 •   Encode has been upgraded to 2.49.

     The Mac alias x-mac-ce has been added, and various bugs have been
     fixed in Encode::Unicode, Encode::UTF7 and Encode::GSM0338.

 •   Env has been upgraded to 1.04.

     Its SPLICE implementation no longer misbehaves in list context.

 •   ExtUtils::CBuilder has been upgraded to 0.280210.

     Manifest files are now correctly embedded for those versions of VC++
     which make use of them. [perl #111782, #111798].

     A list of symbols to export can now be passed to "link()" when on
     Windows, as on other OSes [perl #115100].

 •   ExtUtils::ParseXS has been upgraded to 3.18.

     The generated C code now avoids unnecessarily incrementing
     "PL_amagic_generation" on Perl versions where it's done automatically
     (or on current Perl where the variable no longer exists).

     This avoids a bogus warning for initialised XSUB non-parameters [perl
     #112776].

 •   File::Copy has been upgraded to 2.26.

     "copy()" no longer zeros files when copying into the same directory,
     and also now fails (as it has long been documented to do) when
     attempting to copy a file over itself.

 •   File::DosGlob has been upgraded to 1.10.

     The internal cache of file names that it keeps for each caller is now
     freed when that caller is freed.  This means "use File::DosGlob
     'glob'; eval 'scalar <*>'" no longer leaks memory.

 •   File::Fetch has been upgraded to 0.38.

     Added the 'file_default' option for URLs that do not have a file
     component.

     Use "File::HomeDir" when available, and provide "PERL5_CPANPLUS_HOME"
     to override the autodetection.

     Always re-fetch _C_H_E_C_K_S_U_M_S if "fetchdir" is set.

 •   File::Find has been upgraded to 1.23.

     This fixes inconsistent unixy path handling on VMS.

     Individual files may now appear in list of directories to be searched
     [perl #59750].

 •   File::Glob has been upgraded to 1.20.

     File::Glob has had exactly the same fix as File::DosGlob.  Since it
     is what Perl's own "glob" operator itself uses (except on VMS), this
     means "eval 'scalar <*>'" no longer leaks.

     A space-separated list of patterns return long lists of results no
     longer results in memory corruption or crashes.  This bug was
     introduced in Perl 5.16.0.  [perl #114984]

 •   File::Spec::Unix has been upgraded to 3.40.

     "abs2rel" could produce incorrect results when given two relative
     paths or the root directory twice [perl #111510].

 •   File::stat has been upgraded to 1.07.

     "File::stat" ignores the filetest pragma, and warns when used in
     combination therewith.  But it was not warning for "-r".  This has
     been fixed [perl #111640].

     "-p" now works, and does not return false for pipes [perl #111638].

     Previously "File::stat"'s overloaded "-x" and "-X" operators did not
     give the correct results for directories or executable files when
     running as root. They had been treating executable permissions for
     root just like for any other user, performing group membership tests
     _e_t_c for files not owned by root. They now follow the correct Unix
     behaviour - for a directory they are always true, and for a file if
     any of the three execute permission bits are set then they report
     that root can execute the file. Perl's builtin "-x" and "-X"
     operators have always been correct.

 •   File::Temp has been upgraded to 0.23

     Fixes various bugs involving directory removal.  Defers unlinking
     tempfiles if the initial unlink fails, which fixes problems on NFS.

 •   GDBM_File has been upgraded to 1.15.

     The undocumented optional fifth parameter to "TIEHASH" has been
     removed. This was intended to provide control of the callback used by
     "gdbm*" functions in case of fatal errors (such as filesystem
     problems), but did not work (and could never have worked). No code on
     CPAN even attempted to use it. The callback is now always the
     previous default, "croak". Problems on some platforms with how the
     "C" "croak" function is called have also been resolved.

 •   Hash::Util has been upgraded to 0.15.

     "hash_unlocked" and "hashref_unlocked" now returns true if the hash
     is unlocked, instead of always returning false [perl #112126].

     "hash_unlocked", "hashref_unlocked", "lock_hash_recurse" and
     "unlock_hash_recurse" are now exportable [perl #112126].

     Two new functions, "hash_locked" and "hashref_locked", have been
     added.  Oddly enough, these two functions were already exported, even
     though they did not exist [perl #112126].

 •   HTTP::Tiny has been upgraded to 0.025.

     Add SSL verification features [github #6], [github #9].

     Include the final URL in the response hashref.

     Add "local_address" option.

     This improves SSL support.

 •   IO has been upgraded to 1.28.

     "sync()" can now be called on read-only file handles [perl #64772].

     IO::Socket tries harder to cache or otherwise fetch socket
     information.

 •   IPC::Cmd has been upgraded to 0.80.

     Use "POSIX::_exit" instead of "exit" in "run_forked" [rt.cpan.org
     #76901].

 •   IPC::Open3 has been upgraded to 1.13.

     The "open3()" function no longer uses "POSIX::close()" to close file
     descriptors since that breaks the ref-counting of file descriptors
     done by PerlIO in cases where the file descriptors are shared by
     PerlIO streams, leading to attempts to close the file descriptors a
     second time when any such PerlIO streams are closed later on.

 •   Locale::Codes has been upgraded to 3.25.

     It includes some new codes.

 •   Memoize has been upgraded to 1.03.

     Fix the "MERGE" cache option.

 •   Module::Build has been upgraded to 0.4003.

     Fixed bug where modules without $VERSION might have a version of '0'
     listed in 'provides' metadata, which will be rejected by PAUSE.

     Fixed bug in PodParser to allow numerals in module names.

     Fixed bug where giving arguments twice led to them becoming arrays,
     resulting in install paths like _AA_RR_RR_AA_YY_(_0_x_d_e_a_d_b_e_e_f_)_/_l_i_b_/_F_o_o_._p_m.

     A minor bug fix allows markup to be used around the leading "Name" in
     a POD "abstract" line, and some documentation improvements have been
     made.

 •   Module::CoreList has been upgraded to 2.90

     Version information is now stored as a delta, which greatly reduces
     the size of the _C_o_r_e_L_i_s_t_._p_m file.

     This restores compatibility with older versions of perl and cleans up
     the corelist data for various modules.

 •   Module::Load::Conditional has been upgraded to 0.54.

     Fix use of "requires" on perls installed to a path with spaces.

     Various enhancements include the new use of Module::Metadata.

 •   Module::Metadata has been upgraded to 1.000011.

     The creation of a Module::Metadata object for a typical module file
     has been sped up by about 40%, and some spurious warnings about
     $VERSIONs have been suppressed.

 •   Module::Pluggable has been upgraded to 4.7.

     Amongst other changes, triggers are now allowed on events, which
     gives a powerful way to modify behaviour.

 •   Net::Ping has been upgraded to 2.41.

     This fixes some test failures on Windows.

 •   Opcode has been upgraded to 1.25.

     Reflect the removal of the boolkeys opcode and the addition of the
     clonecv, introcv and padcv opcodes.

 •   overload has been upgraded to 1.22.

     "no overload" now warns for invalid arguments, just like "use
     overload".

 •   PerlIO::encoding has been upgraded to 0.16.

     This is the module implementing the ":encoding(...)" I/O layer.  It
     no longer corrupts memory or crashes when the encoding back-end
     reallocates the buffer or gives it a typeglob or shared hash key
     scalar.

 •   PerlIO::scalar has been upgraded to 0.16.

     The buffer scalar supplied may now only contain code points 0xFF or
     lower. [perl #109828]

 •   Perl::OSType has been upgraded to 1.003.

     This fixes a bug detecting the VOS operating system.

 •   Pod::Html has been upgraded to 1.18.

     The option "--libpods" has been reinstated. It is deprecated, and its
     use does nothing other than issue a warning that it is no longer
     supported.

     Since the HTML files generated by pod2html claim to have a UTF-8
     charset, actually write the files out using UTF-8 [perl #111446].

 •   Pod::Simple has been upgraded to 3.28.

     Numerous improvements have been made, mostly to Pod::Simple::XHTML,
     which also has a compatibility change: the "codes_in_verbatim" option
     is now disabled by default.  See _c_p_a_n_/_P_o_d_-_S_i_m_p_l_e_/_C_h_a_n_g_e_L_o_g for the
     full details.

 •   re has been upgraded to 0.23

     Single character [class]es like "/[s]/" or "/[s]/i" are now optimized
     as if they did not have the brackets, i.e. "/s/" or "/s/i".

     See note about "op_comp" in the "Internal Changes" section below.

 •   Safe has been upgraded to 2.35.

     Fix interactions with "Devel::Cover".

     Don't eval code under "no strict".

 •   Scalar::Util has been upgraded to version 1.27.

     Fix an overloading issue with "sum".

     "first" and "reduce" now check the callback first (so &first(1) is
     disallowed).

     Fix "tainted" on magical values [rt.cpan.org #55763].

     Fix "sum" on previously magical values [rt.cpan.org #61118].

     Fix reading past the end of a fixed buffer [rt.cpan.org #72700].

 •   Search::Dict has been upgraded to 1.07.

     No longer require "stat" on filehandles.

     Use "fc" for casefolding.

 •   Socket has been upgraded to 2.009.

     Constants and functions required for IP multicast source group
     membership have been added.

     "unpack_sockaddr_in()" and "unpack_sockaddr_in6()" now return just
     the IP address in scalar context, and "inet_ntop()" now guards
     against incorrect length scalars being passed in.

     This fixes an uninitialized memory read.

 •   Storable has been upgraded to 2.41.

     Modifying $_[0] within "STORABLE_freeze" no longer results in crashes
     [perl #112358].

     An object whose class implements "STORABLE_attach" is now thawed only
     once when there are multiple references to it in the structure being
     thawed [perl #111918].

     Restricted hashes were not always thawed correctly [perl #73972].

     Storable would croak when freezing a blessed REF object with a
     "STORABLE_freeze()" method [perl #113880].

     It can now freeze and thaw vstrings correctly.  This causes a slight
     incompatible change in the storage format, so the format version has
     increased to 2.9.

     This contains various bugfixes, including compatibility fixes for
     older versions of Perl and vstring handling.

 •   Sys::Syslog has been upgraded to 0.32.

     This contains several bug fixes relating to "getservbyname()",
     "setlogsock()"and log levels in "syslog()", together with fixes for
     Windows, Haiku-OS and GNU/kFreeBSD.  See _c_p_a_n_/_S_y_s_-_S_y_s_l_o_g_/_C_h_a_n_g_e_s for
     the full details.

 •   Term::ANSIColor has been upgraded to 4.02.

     Add support for italics.

     Improve error handling.

 •   Term::ReadLine has been upgraded to 1.10.  This fixes the use of the
     ccppaann and ccppaannpp shells on Windows in the event that the current drive
     happens to contain a _\_d_e_v_\_t_t_y file.

 •   Test::Harness has been upgraded to 3.26.

     Fix glob semantics on Win32 [rt.cpan.org #49732].

     Don't use "Win32::GetShortPathName" when calling perl [rt.cpan.org
     #47890].

     Ignore -T when reading shebang [rt.cpan.org #64404].

     Handle the case where we don't know the wait status of the test more
     gracefully.

     Make the test summary 'ok' line overridable so that it can be changed
     to a plugin to make the output of prove idempotent.

     Don't run world-writable files.

 •   Text::Tabs and Text::Wrap have been upgraded to 2012.0818.  Support
     for Unicode combining characters has been added to them both.

 •   threads::shared has been upgraded to 1.31.

     This adds the option to warn about or ignore attempts to clone
     structures that can't be cloned, as opposed to just unconditionally
     dying in that case.

     This adds support for dual-valued values as created by
     Scalar::Util::dualvar.

 •   Tie::StdHandle has been upgraded to 4.3.

     "READ" now respects the offset argument to "read" [perl #112826].

 •   Time::Local has been upgraded to 1.2300.

     Seconds values greater than 59 but less than 60 no longer cause
     "timegm()" and "timelocal()" to croak.

 •   Unicode::UCD has been upgraded to 0.53.

     This adds a function aallll__ccaasseeffoollddss(()) that returns all the casefolds.

 •   Win32 has been upgraded to 0.47.

     New APIs have been added for getting and setting the current code
     page.

RReemmoovveedd MMoodduulleess aanndd PPrraaggmmaattaa • Version::Requirements has been removed from the core distribution. It is available under a different name: CPAN::Meta::Requirements.

DDooccuummeennttaattiioonn CChhaannggeess ttoo EExxiissttiinngg DDooccuummeennttaattiioonn _p_e_r_l_c_h_e_a_t

 •   perlcheat has been reorganized, and a few new sections were added.

 _p_e_r_l_d_a_t_a

 •   Now explicitly documents the behaviour of hash initializer lists that
     contain duplicate keys.

 _p_e_r_l_d_i_a_g

 •   The explanation of symbolic references being prevented by "strict
     refs" now doesn't assume that the reader knows what symbolic
     references are.

 _p_e_r_l_f_a_q

 •   perlfaq has been synchronized with version 5.0150040 from CPAN.

 _p_e_r_l_f_u_n_c

 •   The return value of "pipe" is now documented.

 •   Clarified documentation of "our".

 _p_e_r_l_o_p

 •   Loop control verbs ("dump", "goto", "next", "last" and "redo") have
     always had the same precedence as assignment operators, but this was
     not documented until now.

 _D_i_a_g_n_o_s_t_i_c_s

 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

 •   Unterminated delimiter for here document

     This message now occurs when a here document label has an initial
     quotation mark but the final quotation mark is missing.

     This replaces a bogus and misleading error message about not finding
     the label itself [perl #114104].

 •   panic: child pseudo-process was never scheduled

     This error is thrown when a child pseudo-process in the ithreads
     implementation on Windows was not scheduled within the time period
     allowed and therefore was not able to initialize properly [perl
     #88840].

 •   Group name must start with a non-digit word character in regex;
     marked by <-- HERE in m/%s/

     This error has been added for "(?&0)", which is invalid.  It used to
     produce an incomprehensible error message [perl #101666].

 •   Can't use an undefined value as a subroutine reference

     Calling an undefined value as a subroutine now produces this error
     message.  It used to, but was accidentally disabled, first in Perl
     5.004 for non-magical variables, and then in Perl v5.14 for magical
     (e.g., tied) variables.  It has now been restored.  In the mean time,
     undef was treated as an empty string [perl #113576].

 •   Experimental "%s" subs not enabled

     To use lexical subs, you must first enable them:

         no warnings 'experimental::lexical_subs';
         use feature 'lexical_subs';
         my sub foo { ... }

 _N_e_w _W_a_r_n_i_n_g_s

 •   'Strings with code points over 0xFF may not be mapped into in-memory
     file handles'

 •   '%s' resolved to '\o{%s}%d'

 •   'Trailing white-space in a charnames alias definition is deprecated'

 •   'A sequence of multiple spaces in a charnames alias definition is
     deprecated'

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

 •   Subroutine "&%s" is not available

     (W closure) During compilation, an inner named subroutine or eval is
     attempting to capture an outer lexical subroutine that is not
     currently available.  This can happen for one of two reasons.  First,
     the lexical subroutine may be declared in an outer anonymous
     subroutine that has not yet been created.  (Remember that named subs
     are created at compile time, while anonymous subs are created at run-
     time.)  For example,

         sub { my sub a {...} sub f { \&a } }

     At the time that f is created, it can't capture the current the "a"
     sub, since the anonymous subroutine hasn't been created yet.
     Conversely, the following won't give a warning since the anonymous
     subroutine has by now been created and is live:

         sub { my sub a {...} eval 'sub f { \&a }' }->();

     The second situation is caused by an eval accessing a variable that
     has gone out of scope, for example,

         sub f {
             my sub a {...}
             sub { eval '\&a' }
         }
         f()->();

     Here, when the '\&a' in the eval is being compiled, f() is not
     currently being executed, so its &a is not available for capture.

 •   "%s" subroutine &%s masks earlier declaration in same %s

     (W misc) A "my" or "state" subroutine has been redeclared in the
     current scope or statement, effectively eliminating all access to the
     previous instance.  This is almost always a typographical error.
     Note that the earlier subroutine will still exist until the end of
     the scope or until all closure references to it are destroyed.

 •   The %s feature is experimental

     (S experimental) This warning is emitted if you enable an
     experimental feature via "use feature".  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::lexical_subs";
         use feature "lexical_subs";

 •   sleep(%u) too large

     (W overflow) You called "sleep" with a number that was larger than it
     can reliably handle and "sleep" probably slept for less time than
     requested.

 •   Wide character in setenv

     Attempts to put wide characters into environment variables via %ENV
     now provoke this warning.

 •   "Invalid negative number (%s) in chr"

     "chr()" now warns when passed a negative value [perl #83048].

 •   "Integer overflow in srand"

     "srand()" now warns when passed a value that doesn't fit in a "UV"
     (since the value will be truncated rather than overflowing) [perl
     #40605].

 •   "-i used with no filenames on the command line, reading from STDIN"

     Running perl with the "-i" flag now warns if no input files are
     provided on the command line [perl #113410].

CChhaannggeess ttoo EExxiissttiinngg DDiiaaggnnoossttiiccss • $* is no longer supported

     The warning that use of $* and $# is no longer supported is now
     generated for every location that references them.  Previously it
     would fail to be generated if another variable using the same
     typeglob was seen first (e.g. "@*" before $*), and would not be
     generated for the second and subsequent uses.  (It's hard to fix the
     failure to generate warnings at all without also generating them
     every time, and warning every time is consistent with the warnings
     that $[ used to generate.)

 •   The warnings for "\b{" and "\B{" were added.  They are a deprecation
     warning which should be turned off by that category.  One should not
     have to turn off regular regexp warnings as well to get rid of these.

 •   Constant(%s): Call to &{$^H{%s}} did not return a defined value

     Constant overloading that returns "undef" results in this error
     message.  For numeric constants, it used to say "Constant(undef)".
     "undef" has been replaced with the number itself.

 •   The error produced when a module cannot be loaded now includes a hint
     that the module may need to be installed: "Can't locate hopping.pm in
     @INC (you may need to install the hopping module) (@INC contains:
     ...)"

 •   vector argument not supported with alpha versions

     This warning was not suppressible, even with "no warnings".  Now it
     is suppressible, and has been moved from the "internal" category to
     the "printf" category.

 •   "Can't do {n,m} with n > m in regex; marked by <-- HERE in m/%s/"

     This fatal error has been turned into a warning that reads:

     Quantifier {n,m} with n > m can't match in regex

     (W regexp) Minima should be less than or equal to maxima.  If you
     really want your regexp to match something 0 times, just put {0}.

 •   The "Runaway prototype" warning that occurs in bizarre cases has been
     removed as being unhelpful and inconsistent.

 •   The "Not a format reference" error has been removed, as the only case
     in which it could be triggered was a bug.

 •   The "Unable to create sub named %s" error has been removed for the
     same reason.

 •   The 'Can't use "my %s" in sort comparison' error has been downgraded
     to a warning, '"my %s" used in sort comparison' (with 'state' instead
     of 'my' for state variables).  In addition, the heuristics for
     guessing whether lexical $a or $b has been misused have been improved
     to generate fewer false positives.  Lexical $a and $b are no longer
     disallowed if they are outside the sort block.  Also, a named unary
     or list operator inside the sort block no longer causes the $a or $b
     to be ignored [perl #86136].

UUttiilliittyy CChhaannggeess _h_2_x_s

 •   _h_2_x_s no longer produces invalid code for empty defines.  [perl
     #20636]

CCoonnffiigguurraattiioonn aanndd CCoommppiillaattiioonn • Added “useversionedarchname” option to Configure

     When set, it includes 'api_versionstring' in 'archname'. E.g.
     x86_64-linux-5.13.6-thread-multi.  It is unset by default.

     This feature was requested by Tim Bunce, who observed that
     "INSTALL_BASE" creates a library structure that does not
     differentiate by perl version.  Instead, it places architecture
     specific files in "$install_base/lib/perl5/$archname".  This makes it
     difficult to use a common "INSTALL_BASE" library path with multiple
     versions of perl.

     By setting "-Duseversionedarchname", the $archname will be distinct
     for architecture _a_n_d API version, allowing mixed use of

“INSTALL_BASE”. #

 •   Add a "PERL_NO_INLINE_FUNCTIONS" option

     If "PERL_NO_INLINE_FUNCTIONS" is defined, don't include "inline.h"

     This permits test code to include the perl headers for definitions
     without creating a link dependency on the perl library (which may not
     exist yet).

 •   Configure will honour the external "MAILDOMAIN" environment variable,
     if set.

 •   "installman" no longer ignores the silent option

 •   Both "META.yml" and "META.json" files are now included in the
     distribution.

 •   _C_o_n_f_i_g_u_r_e will now correctly detect "isblank()" when compiling with a
     C++ compiler.

 •   The pager detection in _C_o_n_f_i_g_u_r_e has been improved to allow responses
     which specify options after the program name, e.g. //uussrr//bbiinn//lleessss --RR,
     if the user accepts the default value.  This helps ppeerrllddoocc when
     handling ANSI escapes [perl #72156].

TTeessttiinngg • The test suite now has a section for tests that require very large amounts of memory. These tests won’t run by default; they can be enabled by setting the “PERL_TEST_MEMORY” environment variable to the number of gibibytes of memory that may be safely used.

PPllaattffoorrmm SSuuppppoorrtt DDiissccoonnttiinnuueedd PPllaattffoorrmmss BeOS BeOS was an operating system for personal computers developed by Be Inc, initially for their BeBox hardware. The OS Haiku was written as an open source replacement for/continuation of BeOS, and its perl port is current and actively maintained.

 UTS Global
     Support code relating to UTS global has been removed.  UTS was a
     mainframe version of System V created by Amdahl, subsequently sold to
     UTS Global.  The port has not been touched since before Perl v5.8.0,
     and UTS Global is now defunct.

VM/ESA #

     Support for VM/ESA has been removed. The port was tested on 2.3.0,
     which IBM ended service on in March 2002. 2.4.0 ended service in June
     2003, and was superseded by Z/VM. The current version of Z/VM is
     V6.2.0, and scheduled for end of service on 2015/04/30.

MPE/IX #

     Support for MPE/IX has been removed.

EPOC #

     Support code relating to EPOC has been removed.  EPOC was a family of
     operating systems developed by Psion for mobile devices.  It was the
     predecessor of Symbian.  The port was last updated in April 2002.

 Rhapsody
     Support for Rhapsody has been removed.

PPllaattffoorrmm--SSppeecciiffiicc NNootteess

_A_I_X #

 Configure now always adds "-qlanglvl=extc99" to the CC flags on AIX when
 using xlC.  This will make it easier to compile a number of XS-based
 modules that assume C99 [perl #113778].

 _c_l_a_n_g_+_+

 There is now a workaround for a compiler bug that prevented compiling
 with clang++ since Perl v5.15.7 [perl #112786].

_C_+_+ #

 When compiling the Perl core as C++ (which is only semi-supported), the
 mathom functions are now compiled as "extern "C"", to ensure proper
 binary compatibility.  (However, binary compatibility isn't generally
 guaranteed anyway in the situations where this would matter.)

 _D_a_r_w_i_n

 Stop hardcoding an alignment on 8 byte boundaries to fix builds using
 -Dusemorebits.

 _H_a_i_k_u

 Perl should now work out of the box on Haiku R1 Alpha 4.

 _M_i_d_n_i_g_h_t_B_S_D

 "libc_r" was removed from recent versions of MidnightBSD and older
 versions work better with "pthread". Threading is now enabled using
 "pthread" which corrects build errors with threading enabled on

0.4-CURRENT. #

 _S_o_l_a_r_i_s

 In Configure, avoid running sed commands with flags not supported on
 Solaris.

_V_M_S #

 •   Where possible, the case of filenames and command-line arguments is
     now preserved by enabling the CRTL features "DECC$EFS_CASE_PRESERVE"
     and "DECC$ARGV_PARSE_STYLE" at start-up time.  The latter only takes
     effect when extended parse is enabled in the process from which Perl
     is run.

 •   The character set for Extended Filename Syntax (EFS) is now enabled
     by default on VMS.  Among other things, this provides better handling
     of dots in directory names, multiple dots in filenames, and spaces in
     filenames.  To obtain the old behavior, set the logical name
     "DECC$EFS_CHARSET" to "DISABLE".

 •   Fixed linking on builds configured with "-Dusemymalloc=y".

 •   Experimental support for building Perl with the HP C++ compiler is
     available by configuring with "-Dusecxx".

 •   All C header files from the top-level directory of the distribution
     are now installed on VMS, providing consistency with a long-standing
     practice on other platforms. Previously only a subset were installed,
     which broke non-core extension builds for extensions that depended on
     the missing include files.

 •   Quotes are now removed from the command verb (but not the parameters)
     for commands spawned via "system", backticks, or a piped "open".
     Previously, quotes on the verb were passed through to DCL, which
     would fail to recognize the command.  Also, if the verb is actually a
     path to an image or command procedure on an ODS-5 volume, quoting it
     now allows the path to contain spaces.

 •   The aa22pp build has been fixed for the HP C++ compiler on OpenVMS.

 _W_i_n_3_2

 •   Perl can now be built using Microsoft's Visual C++ 2012 compiler by
     specifying CCTYPE=MSVC110 (or MSVC110FREE if you are using the free
     Express edition for Windows Desktop) in _w_i_n_3_2_/_M_a_k_e_f_i_l_e.

 •   The option to build without "USE_SOCKETS_AS_HANDLES" has been
     removed.

 •   Fixed a problem where perl could crash while cleaning up threads
     (including the main thread) in threaded debugging builds on Win32 and
     possibly other platforms [perl #114496].

 •   A rare race condition that would lead to sleep taking more time than
     requested, and possibly even hanging, has been fixed [perl #33096].

 •   "link" on Win32 now attempts to set $! to more appropriate values
     based on the Win32 API error code. [perl #112272]

     Perl no longer mangles the environment block, e.g. when launching a
     new sub-process, when the environment contains non-ASCII characters.
     Known problems still remain, however, when the environment contains
     characters outside of the current ANSI codepage (e.g. see the item
     about Unicode in %ENV in
     <http://perl5.git.perl.org/perl.git/blob/HEAD:/Porting/todo.pod>).
     [perl #113536]

 •   Building perl with some Windows compilers used to fail due to a
     problem with miniperl's "glob" operator (which uses the "perlglob"
     program) deleting the PATH environment variable [perl #113798].

 •   A new makefile option, "USE_64_BIT_INT", has been added to the
     Windows makefiles.  Set this to "define" when building a 32-bit perl
     if you want it to use 64-bit integers.

     Machine code size reductions, already made to the DLLs of XS modules
     in Perl v5.17.2, have now been extended to the perl DLL itself.

     Building with VC++ 6.0 was inadvertently broken in Perl v5.17.2 but
     has now been fixed again.

 _W_i_n_C_E

 Building on WinCE is now possible once again, although more work is
 required to fully restore a clean build.

IInntteerrnnaall CChhaannggeess • Synonyms for the misleadingly named “av_len()” have been created: “av_top_index()” and “av_tindex”. All three of these return the number of the highest index in the array, not the number of elements it contains.

 •   SSvvUUPPGGRRAADDEE(()) is no longer an expression. Originally this macro (and
     its underlying function, ssvv__uuppggrraaddee(())) were documented as boolean,
     although in reality they always croaked on error and never returned
     false. In 2005 the documentation was updated to specify a void return
     value, but SSvvUUPPGGRRAADDEE(()) was left always returning 1 for backwards
     compatibility. This has now been removed, and SSvvUUPPGGRRAADDEE(()) is now a
     statement with no return value.

     So this is now a syntax error:

         if (!SvUPGRADE(sv)) { croak(...); }

     If you have code like that, simply replace it with

         SvUPGRADE(sv);

     or to avoid compiler warnings with older perls, possibly

         (void)SvUPGRADE(sv);

 •   Perl has a new copy-on-write mechanism that allows any SvPOK scalar
     to be upgraded to a copy-on-write scalar.  A reference count on the
     string buffer is stored in the string buffer itself.  This feature is
     nnoott eennaabblleedd bbyy ddeeffaauulltt.

     It can be enabled in a perl build by running _C_o_n_f_i_g_u_r_e with
     --AAccccffllaaggss==--DDPPEERRLL__NNEEWW__CCOOPPYY__OONN__WWRRIITTEE, and we would encourage XS authors
     to try their code with such an enabled perl, and provide feedback.
     Unfortunately, there is not yet a good guide to updating XS code to
     cope with COW.  Until such a document is available, consult the
     perl5-porters mailing list.

     It breaks a few XS modules by allowing copy-on-write scalars to go
     through code paths that never encountered them before.

 •   Copy-on-write no longer uses the SvFAKE and SvREADONLY flags.  Hence,
     SvREADONLY indicates a true read-only SV.

     Use the SvIsCOW macro (as before) to identify a copy-on-write scalar.

 •   "PL_glob_index" is gone.

 •   The private Perl_croak_no_modify has had its context parameter
     removed.  It is now has a void prototype.  Users of the public API
     croak_no_modify remain unaffected.

 •   Copy-on-write (shared hash key) scalars are no longer marked read-
     only.  "SvREADONLY" returns false on such an SV, but "SvIsCOW" still
     returns true.

 •   A new op type, "OP_PADRANGE" has been introduced.  The perl peephole
     optimiser will, where possible, substitute a single padrange op for a
     pushmark followed by one or more pad ops, and possibly also skipping
     list and nextstate ops.  In addition, the op can carry out the tasks
     associated with the RHS of a "my(...) = @_" assignment, so those ops
     may be optimised away too.

 •   Case-insensitive matching inside a [bracketed] character class with a
     multi-character fold no longer excludes one of the possibilities in
     the circumstances that it used to. [perl #89774].

 •   "PL_formfeed" has been removed.

 •   The regular expression engine no longer reads one byte past the end
     of the target string.  While for all internally well-formed scalars
     this should never have been a problem, this change facilitates clever
     tricks with string buffers in CPAN modules.  [perl #73542]

 •   Inside a BEGIN block, "PL_compcv" now points to the currently-
     compiling subroutine, rather than the BEGIN block itself.

 •   "mg_length" has been deprecated.

 •   "sv_len" now always returns a byte count and "sv_len_utf8" a
     character count.  Previously, "sv_len" and "sv_len_utf8" were both
     buggy and would sometimes returns bytes and sometimes characters.
     "sv_len_utf8" no longer assumes that its argument is in UTF-8.
     Neither of these creates UTF-8 caches for tied or overloaded values
     or for non-PVs any more.

 •   "sv_mortalcopy" now copies string buffers of shared hash key scalars
     when called from XS modules [perl #79824].

 •   The new "RXf_MODIFIES_VARS" flag can be set by custom regular
     expression engines to indicate that the execution of the regular
     expression may cause variables to be modified.  This lets "s///" know
     to skip certain optimisations.  Perl's own regular expression engine
     sets this flag for the special backtracking verbs that set $REGMARK
     and $REGERROR.

 •   The APIs for accessing lexical pads have changed considerably.

     "PADLIST"s are now longer "AV"s, but their own type instead.
     "PADLIST"s now contain a "PAD" and a "PADNAMELIST" of "PADNAME"s,
     rather than "AV"s for the pad and the list of pad names.  "PAD"s,
     "PADNAMELIST"s, and "PADNAME"s are to be accessed as such through the
     newly added pad API instead of the plain "AV" and "SV" APIs.  See
     perlapi for details.

 •   In the regex API, the numbered capture callbacks are passed an index
     indicating what match variable is being accessed. There are special
     index values for the "$`, $&, $&" variables. Previously the same
     three values were used to retrieve "${^PREMATCH}, ${^MATCH},
     ${^POSTMATCH}" too, but these have now been assigned three separate
     values. See "Numbered capture callbacks" in perlreapi.

 •   "PL_sawampersand" was previously a boolean indicating that any of
     "$`, $&, $&" had been seen; it now contains three one-bit flags
     indicating the presence of each of the variables individually.

 •   The "CV *" typemap entry now supports "&{}" overloading and
     typeglobs, just like "&{...}" [perl #96872].

 •   The "SVf_AMAGIC" flag to indicate overloading is now on the stash,
     not the object.  It is now set automatically whenever a method or
     @ISA changes, so its meaning has changed, too.  It now means
     "potentially overloaded".  When the overload table is calculated, the
     flag is automatically turned off if there is no overloading, so there
     should be no noticeable slowdown.

     The staleness of the overload tables is now checked when overload
     methods are invoked, rather than during "bless".

     "A" magic is gone.  The changes to the handling of the "SVf_AMAGIC"
     flag eliminate the need for it.

     "PL_amagic_generation" has been removed as no longer necessary.  For
     XS modules, it is now a macro alias to "PL_na".

     The fallback overload setting is now stored in a stash entry separate
     from overloadedness itself.

 •   The character-processing code has been cleaned up in places.  The
     changes should be operationally invisible.

 •   The "study" function was made a no-op in v5.16.  It was simply
     disabled via a "return" statement; the code was left in place.  Now
     the code supporting what "study" used to do has been removed.

 •   Under threaded perls, there is no longer a separate PV allocated for
     every COP to store its package name ("cop->stashpv").  Instead, there
     is an offset ("cop->stashoff") into the new "PL_stashpad" array,
     which holds stash pointers.

 •   In the pluggable regex API, the "regexp_engine" struct has acquired a
     new field "op_comp", which is currently just for perl's internal use,
     and should be initialized to NULL by other regex plugin modules.

 •   A new function "alloccopstash" has been added to the API, but is
     considered experimental.  See perlapi.

 •   Perl used to implement get magic in a way that would sometimes hide
     bugs in code that could call mmgg__ggeett(()) too many times on magical
     values.  This hiding of errors no longer occurs, so long-standing
     bugs may become visible now.  If you see magic-related errors in XS
     code, check to make sure it, together with the Perl API functions it
     uses, calls mmgg__ggeett(()) only once on SSvvGGMMAAGGIICCAALL(()) values.

 •   OP allocation for CVs now uses a slab allocator.  This simplifies
     memory management for OPs allocated to a CV, so cleaning up after a
     compilation error is simpler and safer [perl #111462][perl #112312].

 •   "PERL_DEBUG_READONLY_OPS" has been rewritten to work with the new
     slab allocator, allowing it to catch more violations than before.

 •   The old slab allocator for ops, which was only enabled for
     "PERL_IMPLICIT_SYS" and "PERL_DEBUG_READONLY_OPS", has been retired.

SSeelleecctteedd BBuugg FFiixxeess • Here document terminators no longer require a terminating newline character when they occur at the end of a file. This was already the case at the end of a string eval [perl #65838].

 •   "-DPERL_GLOBAL_STRUCT" builds now free the global struct aafftteerr
     they've finished using it.

 •   A trailing '/' on a path in @INC will no longer have an additional
     '/' appended.

 •   The ":crlf" layer now works when unread data doesn't fit into its own
     buffer. [perl #112244].

 •   "ungetc()" now handles UTF-8 encoded data. [perl #116322].

 •   A bug in the core typemap caused any C types that map to the T_BOOL
     core typemap entry to not be set, updated, or modified when the
     T_BOOL variable was used in an OUTPUT: section with an exception for
     RETVAL. T_BOOL in an INPUT: section was not affected. Using a T_BOOL
     return type for an XSUB (RETVAL) was not affected. A side effect of
     fixing this bug is, if a T_BOOL is specified in the OUTPUT: section
     (which previous did nothing to the SV), and a read only SV (literal)
     is passed to the XSUB, croaks like "Modification of a read-only value
     attempted" will happen. [perl #115796]

 •   On many platforms, providing a directory name as the script name
     caused perl to do nothing and report success.  It should now
     universally report an error and exit nonzero. [perl #61362]

 •   "sort {undef} ..." under fatal warnings no longer crashes.  It had
     begun crashing in Perl v5.16.

 •   Stashes blessed into each other ("bless \%Foo::, 'Bar'; bless
     \%Bar::, 'Foo'") no longer result in double frees.  This bug started
     happening in Perl v5.16.

 •   Numerous memory leaks have been fixed, mostly involving fatal
     warnings and syntax errors.

 •   Some failed regular expression matches such as "'f' =~ /../g" were
     not resetting "pos".  Also, "match-once" patterns ("m?...?g") failed
     to reset it, too, when invoked a second time [perl #23180].

 •   Several bugs involving "local *ISA" and "local *Foo::" causing stale
     MRO caches have been fixed.

 •   Defining a subroutine when its typeglob has been aliased no longer
     results in stale method caches.  This bug was introduced in Perl
     v5.10.

 •   Localising a typeglob containing a subroutine when the typeglob's
     package has been deleted from its parent stash no longer produces an
     error.  This bug was introduced in Perl v5.14.

 •   Under some circumstances, "local *method=..." would fail to reset
     method caches upon scope exit.

 •   "/[.foo.]/" is no longer an error, but produces a warning (as before)
     and is treated as "/[.fo]/" [perl #115818].

 •   "goto $tied_var" now calls FETCH before deciding what type of goto
     (subroutine or label) this is.

 •   Renaming packages through glob assignment ("*Foo:: = *Bar::; *Bar:: =
     *Baz::") in combination with "m?...?" and "reset" no longer makes
     threaded builds crash.

 •   A number of bugs related to assigning a list to hash have been fixed.
     Many of these involve lists with repeated keys like "(1, 1, 1, 1)".

     •   The expression "scalar(%h = (1, 1, 1, 1))" now returns 4, not 2.

     •   The return value of "%h = (1, 1, 1)" in list context was wrong.
         Previously this would return "(1, undef, 1)", now it returns "(1,
         undef)".

     •   Perl now issues the same warning on "($s, %h) = (1, {})" as it
         does for "(%h) = ({})", "Reference found where even-sized list
         expected".

     •   A number of additional edge cases in list assignment to hashes
         were corrected. For more details see commit 23b7025ebc.

 •   Attributes applied to lexical variables no longer leak memory.  [perl
     #114764]

 •   "dump", "goto", "last", "next", "redo" or "require" followed by a
     bareword (or version) and then an infix operator is no longer a
     syntax error.  It used to be for those infix operators (like "+")
     that have a different meaning where a term is expected.  [perl
     #105924]

 •   "require a::b . 1" and "require a::b + 1" no longer produce erroneous
     ambiguity warnings.  [perl #107002]

 •   Class method calls are now allowed on any string, and not just
     strings beginning with an alphanumeric character.  [perl #105922]

 •   An empty pattern created with "qr//" used in "m///" no longer
     triggers the "empty pattern reuses last pattern" behaviour.  [perl
     #96230]

 •   Tying a hash during iteration no longer results in a memory leak.

 •   Freeing a tied hash during iteration no longer results in a memory
     leak.

 •   List assignment to a tied array or hash that dies on STORE no longer
     results in a memory leak.

 •   If the hint hash ("%^H") is tied, compile-time scope entry (which
     copies the hint hash) no longer leaks memory if FETCH dies.  [perl
     #107000]

 •   Constant folding no longer inappropriately triggers the special
     "split " "" behaviour.  [perl #94490]

 •   "defined scalar(@array)", "defined do { &foo }", and similar
     constructs now treat the argument to "defined" as a simple scalar.
     [perl #97466]

 •   Running a custom debugging that defines no *DB::DB glob or provides a
     subroutine stub for &DB::DB no longer results in a crash, but an
     error instead.  [perl #114990]

 •   "reset """ now matches its documentation.  "reset" only resets
     "m?...?" patterns when called with no argument.  An empty string for
     an argument now does nothing.  (It used to be treated as no
     argument.)  [perl #97958]

 •   "printf" with an argument returning an empty list no longer reads
     past the end of the stack, resulting in erratic behaviour.  [perl
     #77094]

 •   "--subname" no longer produces erroneous ambiguity warnings.  [perl
     #77240]

 •   "v10" is now allowed as a label or package name.  This was
     inadvertently broken when v-strings were added in Perl v5.6.  [perl
     #56880]

 •   "length", "pos", "substr" and "sprintf" could be confused by ties,
     overloading, references and typeglobs if the stringification of such
     changed the internal representation to or from UTF-8.  [perl #114410]

 •   utf8::encode now calls FETCH and STORE on tied variables.
     utf8::decode now calls STORE (it was already calling FETCH).

 •   "$tied =~ s/$non_utf8/$utf8/" no longer loops infinitely if the tied
     variable returns a Latin-1 string, shared hash key scalar, or
     reference or typeglob that stringifies as ASCII or Latin-1.  This was
     a regression from v5.12.

 •   "s///" without /e is now better at detecting when it needs to forego
     certain optimisations, fixing some buggy cases:

     •   Match variables in certain constructs ("&&", "||", ".." and
         others) in the replacement part; e.g., "s/(.)/$l{$a||$1}/g".
         [perl #26986]

     •   Aliases to match variables in the replacement.

     •   $REGERROR or $REGMARK in the replacement.  [perl #49190]

     •   An empty pattern ("s//$foo/") that causes the last-successful
         pattern to be used, when that pattern contains code blocks that
         modify the variables in the replacement.

 •   The taintedness of the replacement string no longer affects the
     taintedness of the return value of "s///e".

 •   The $| autoflush variable is created on-the-fly when needed.  If this
     happened (e.g., if it was mentioned in a module or eval) when the
     currently-selected filehandle was a typeglob with an empty IO slot,
     it used to crash.  [perl #115206]

 •   Line numbers at the end of a string eval are no longer off by one.
     [perl #114658]

 •   @INC filters (subroutines returned by subroutines in @INC) that set
     $_ to a copy-on-write scalar no longer cause the parser to modify
     that string buffer in place.

 •   "length($object)" no longer returns the undefined value if the object
     has string overloading that returns undef.  [perl #115260]

 •   The use of "PL_stashcache", the stash name lookup cache for method
     calls, has been restored,

     Commit da6b625f78f5f133 in August 2011 inadvertently broke the code
     that looks up values in "PL_stashcache". As it's only a cache, quite
     correctly everything carried on working without it.

 •   The error "Can't localize through a reference" had disappeared in
     v5.16.0 when "local %$ref" appeared on the last line of an lvalue
     subroutine.  This error disappeared for "\local %$ref" in perl
     v5.8.1.  It has now been restored.

 •   The parsing of here-docs has been improved significantly, fixing
     several parsing bugs and crashes and one memory leak, and correcting
     wrong subsequent line numbers under certain conditions.

 •   Inside an eval, the error message for an unterminated here-doc no
     longer has a newline in the middle of it [perl #70836].

 •   A substitution inside a substitution pattern ("s/${s|||}//") no
     longer confuses the parser.

 •   It may be an odd place to allow comments, but "s//"" # hello/e" has
     always worked, _u_n_l_e_s_s there happens to be a null character before the
     first #.  Now it works even in the presence of nulls.

 •   An invalid range in "tr///" or "y///" no longer results in a memory
     leak.

 •   String eval no longer treats a semicolon-delimited quote-like
     operator at the very end ("eval 'q;;'") as a syntax error.

 •   "warn {$_ => 1} + 1" is no longer a syntax error.  The parser used to
     get confused with certain list operators followed by an anonymous
     hash and then an infix operator that shares its form with a unary
     operator.

 •   "(caller $n)[6]" (which gives the text of the eval) used to return
     the actual parser buffer.  Modifying it could result in crashes.  Now
     it always returns a copy.  The string returned no longer has "\n;"
     tacked on to the end.  The returned text also includes here-doc
     bodies, which used to be omitted.

 •   The UTF-8 position cache is now reset when accessing magical
     variables, to avoid the string buffer and the UTF-8 position cache
     getting out of sync [perl #114410].

 •   Various cases of get magic being called twice for magical UTF-8
     strings have been fixed.

 •   This code (when not in the presence of $& etc)

         $_ = 'x' x 1_000_000;
         1 while /(.)/;

     used to skip the buffer copy for performance reasons, but suffered
     from $1 etc changing if the original string changed.  That's now been
     fixed.

 •   Perl doesn't use PerlIO anymore to report out of memory messages, as
     PerlIO might attempt to allocate more memory.

 •   In a regular expression, if something is quantified with "{n,m}"
     where "n > m", it can't possibly match.  Previously this was a fatal
     error, but now is merely a warning (and that something won't match).
     [perl #82954].

 •   It used to be possible for formats defined in subroutines that have
     subsequently been undefined and redefined to close over variables in
     the wrong pad (the newly-defined enclosing sub), resulting in crashes
     or "Bizarre copy" errors.

 •   Redefinition of XSUBs at run time could produce warnings with the
     wrong line number.

 •   The %vd sprintf format does not support version objects for alpha
     versions.  It used to output the format itself (%vd) when passed an
     alpha version, and also emit an "Invalid conversion in printf"
     warning.  It no longer does, but produces the empty string in the
     output.  It also no longer leaks memory in this case.

 •   "$obj->SUPER::method" calls in the main package could fail if the
     SUPER package had already been accessed by other means.

 •   Stash aliasing ("*foo:: = *bar::") no longer causes SUPER calls to
     ignore changes to methods or @ISA or use the wrong package.

 •   Method calls on packages whose names end in ::SUPER are no longer
     treated as SUPER method calls, resulting in failure to find the
     method.  Furthermore, defining subroutines in such packages no longer
     causes them to be found by SUPER method calls on the containing
     package [perl #114924].

 •   "\w" now matches the code points U+200C (ZERO WIDTH NON-JOINER) and
     U+200D (ZERO WIDTH JOINER).  "\W" no longer matches these.  This
     change is because Unicode corrected their definition of what "\w"
     should match.

 •   "dump LABEL" no longer leaks its label.

 •   Constant folding no longer changes the behaviour of functions like
     "stat()" and "truncate()" that can take either filenames or handles.
     "stat 1 ? foo : bar" nows treats its argument as a file name (since
     it is an arbitrary expression), rather than the handle "foo".

 •   "truncate FOO, $len" no longer falls back to treating "FOO" as a file
     name if the filehandle has been deleted.  This was broken in Perl
     v5.16.0.

 •   Subroutine redefinitions after sub-to-glob and glob-to-glob
     assignments no longer cause double frees or panic messages.

 •   "s///" now turns vstrings into plain strings when performing a
     substitution, even if the resulting string is the same ("s/a/a/").

 •   Prototype mismatch warnings no longer erroneously treat constant subs
     as having no prototype when they actually have "".

 •   Constant subroutines and forward declarations no longer prevent
     prototype mismatch warnings from omitting the sub name.

 •   "undef" on a subroutine now clears call checkers.

 •   The "ref" operator started leaking memory on blessed objects in Perl
     v5.16.0.  This has been fixed [perl #114340].

 •   "use" no longer tries to parse its arguments as a statement, making
     "use constant { () };" a syntax error [perl #114222].

 •   On debugging builds, "uninitialized" warnings inside formats no
     longer cause assertion failures.

 •   On debugging builds, subroutines nested inside formats no longer
     cause assertion failures [perl #78550].

 •   Formats and "use" statements are now permitted inside formats.

 •   "print $x" and "sub { print $x }->()" now always produce the same
     output.  It was possible for the latter to refuse to close over $x if
     the variable was not active; e.g., if it was defined outside a
     currently-running named subroutine.

 •   Similarly, "print $x" and "print eval '$x'" now produce the same
     output.  This also allows "my $x if 0" variables to be seen in the
     debugger [perl #114018].

 •   Formats called recursively no longer stomp on their own lexical
     variables, but each recursive call has its own set of lexicals.

 •   Attempting to free an active format or the handle associated with it
     no longer results in a crash.

 •   Format parsing no longer gets confused by braces, semicolons and low-
     precedence operators.  It used to be possible to use braces as format
     delimiters (instead of "=" and "."), but only sometimes.  Semicolons
     and low-precedence operators in format argument lines no longer
     confuse the parser into ignoring the line's return value.  In format
     argument lines, braces can now be used for anonymous hashes, instead
     of being treated always as "do" blocks.

 •   Formats can now be nested inside code blocks in regular expressions
     and other quoted constructs ("/(?{...})/" and "qq/${...}/") [perl
     #114040].

 •   Formats are no longer created after compilation errors.

 •   Under debugging builds, the --DDAA command line option started crashing
     in Perl v5.16.0.  It has been fixed [perl #114368].

 •   A potential deadlock scenario involving the premature termination of
     a pseudo- forked child in a Windows build with ithreads enabled has
     been fixed.  This resolves the common problem of the _t_/_o_p_/_f_o_r_k_._t test
     hanging on Windows [perl #88840].

 •   The code which generates errors from "require()" could potentially
     read one or two bytes before the start of the filename for filenames
     less than three bytes long and ending "/\.p?\z/".  This has now been
     fixed.  Note that it could never have happened with module names
     given to "use()" or "require()" anyway.

 •   The handling of pathnames of modules given to "require()" has been
     made thread-safe on VMS.

 •   Non-blocking sockets have been fixed on VMS.

 •   Pod can now be nested in code inside a quoted construct outside of a
     string eval.  This used to work only within string evals [perl
     #114040].

 •   "goto ''" now looks for an empty label, producing the "goto must have
     label" error message, instead of exiting the program [perl #111794].

 •   "goto "\0"" now dies with "Can't find label" instead of "goto must
     have label".

 •   The C function "hv_store" used to result in crashes when used on
     "%^H" [perl #111000].

 •   A call checker attached to a closure prototype via
     "cv_set_call_checker" is now copied to closures cloned from it.  So
     "cv_set_call_checker" now works inside an attribute handler for a
     closure.

 •   Writing to $^N used to have no effect.  Now it croaks with
     "Modification of a read-only value" by default, but that can be
     overridden by a custom regular expression engine, as with $1 [perl
     #112184].

 •   "undef" on a control character glob ("undef *^H") no longer emits an
     erroneous warning about ambiguity [perl #112456].

 •   For efficiency's sake, many operators and built-in functions return
     the same scalar each time.  Lvalue subroutines and subroutines in the
     CORE:: namespace were allowing this implementation detail to leak
     through.  "print &CORE::uc("a"), &CORE::uc("b")" used to print "BB".
     The same thing would happen with an lvalue subroutine returning the
     return value of "uc".  Now the value is copied in such cases.

 •   "method {}" syntax with an empty block or a block returning an empty
     list used to crash or use some random value left on the stack as its
     invocant.  Now it produces an error.

 •   "vec" now works with extremely large offsets (>2 GB) [perl #111730].

 •   Changes to overload settings now take effect immediately, as do
     changes to inheritance that affect overloading.  They used to take
     effect only after "bless".

     Objects that were created before a class had any overloading used to
     remain non-overloaded even if the class gained overloading through
     "use overload" or @ISA changes, and even after "bless".  This has
     been fixed [perl #112708].

 •   Classes with overloading can now inherit fallback values.

 •   Overloading was not respecting a fallback value of 0 if there were
     overloaded objects on both sides of an assignment operator like "+="
     [perl #111856].

 •   "pos" now croaks with hash and array arguments, instead of producing
     erroneous warnings.

 •   "while(each %h)" now implies "while(defined($_ = each %h))", like
     "readline" and "readdir".

 •   Subs in the CORE:: namespace no longer crash after "undef *_" when
     called with no argument list (&CORE::time with no parentheses).

 •   "unpack" no longer produces the "'/' must follow a numeric type in
     unpack" error when it is the data that are at fault [perl #60204].

 •   "join" and "@array" now call FETCH only once on a tied $" [perl
     #8931].

 •   Some subroutine calls generated by compiling core ops affected by a
     "CORE::GLOBAL" override had op checking performed twice.  The
     checking is always idempotent for pure Perl code, but the double
     checking can matter when custom call checkers are involved.

 •   A race condition used to exist around fork that could cause a signal
     sent to the parent to be handled by both parent and child. Signals
     are now blocked briefly around fork to prevent this from happening
     [perl #82580].

 •   The implementation of code blocks in regular expressions, such as
     "(?{})" and "(??{})", has been heavily reworked to eliminate a whole
     slew of bugs.  The main user-visible changes are:

     •   Code blocks within patterns are now parsed in the same pass as
         the surrounding code; in particular it is no longer necessary to
         have balanced braces: this now works:

             /(?{  $x='{'  })/

         This means that this error message is no longer generated:

             Sequence (?{...}) not terminated or not {}-balanced in regex

         but a new error may be seen:

             Sequence (?{...}) not terminated with ')'

         In addition, literal code blocks within run-time patterns are
         only compiled once, at perl compile-time:

             for my $p (...) {
                 # this 'FOO' block of code is compiled once,
                 # at the same time as the surrounding 'for' loop
                 /$p{(?{FOO;})/;
             }

     •   Lexical variables are now sane as regards scope, recursion and
         closure behavior. In particular, "/A(?{B})C/" behaves (from a
         closure viewpoint) exactly like "/A/ && do { B } && /C/", while
         "qr/A(?{B})C/" is like "sub {/A/ && do { B } && /C/}". So this
         code now works how you might expect, creating three regexes that
         match 0, 1, and 2:

             for my $i (0..2) {
                 push @r, qr/^(??{$i})$/;
             }
             "1" =~ $r[1]; # matches

     •   The "use re 'eval'" pragma is now only required for code blocks
         defined at runtime; in particular in the following, the text of
         the $r pattern is still interpolated into the new pattern and
         recompiled, but the individual compiled code-blocks within $r are
         reused rather than being recompiled, and "use re 'eval'" isn't
         needed any more:

             my $r = qr/abc(?{....})def/;
             /xyz$r/;

     •   Flow control operators no longer crash. Each code block runs in a
         new dynamic scope, so "next" etc. will not see any enclosing
         loops. "return" returns a value from the code block, not from any
         enclosing subroutine.

     •   Perl normally caches the compilation of run-time patterns, and
         doesn't recompile if the pattern hasn't changed, but this is now
         disabled if required for the correct behavior of closures. For
         example:

             my $code = '(??{$x})';
             for my $x (1..3) {
                 # recompile to see fresh value of $x each time
                 $x =~ /$code/;
             }

     •   The "/msix" and "(?msix)" etc. flags are now propagated into the
         return value from "(??{})"; this now works:

             "AB" =~ /a(??{'b'})/i;

     •   Warnings and errors will appear to come from the surrounding code
         (or for run-time code blocks, from an eval) rather than from an
         "re_eval":

             use re 'eval'; $c = '(?{ warn "foo" })'; /$c/;
             /(?{ warn "foo" })/;

         formerly gave:

             foo at (re_eval 1) line 1.
             foo at (re_eval 2) line 1.

         and now gives:

             foo at (eval 1) line 1.
             foo at /some/prog line 2.

 •   Perl now can be recompiled to use any Unicode version.  In v5.16, it
     worked on Unicodes 6.0 and 6.1, but there were various bugs if
     earlier releases were used; the older the release the more problems.

 •   "vec" no longer produces "uninitialized" warnings in lvalue context
     [perl #9423].

 •   An optimization involving fixed strings in regular expressions could
     cause a severe performance penalty in edge cases.  This has been
     fixed [perl #76546].

 •   In certain cases, including empty subpatterns within a regular
     expression (such as "(?:)" or "(?:|)") could disable some
     optimizations. This has been fixed.

 •   The "Can't find an opnumber" message that "prototype" produces when
     passed a string like "CORE::nonexistent_keyword" now passes UTF-8 and
     embedded NULs through unchanged [perl #97478].

 •   "prototype" now treats magical variables like $1 the same way as non-
     magical variables when checking for the CORE:: prefix, instead of
     treating them as subroutine names.

 •   Under threaded perls, a runtime code block in a regular expression
     could corrupt the package name stored in the op tree, resulting in
     bad reads in "caller", and possibly crashes [perl #113060].

 •   Referencing a closure prototype ("\&{$_[1]}" in an attribute handler
     for a closure) no longer results in a copy of the subroutine (or
     assertion failures on debugging builds).

 •   "eval '__PACKAGE__'" now returns the right answer on threaded builds
     if the current package has been assigned over (as in "*ThisPackage::
     = *ThatPackage::") [perl #78742].

 •   If a package is deleted by code that it calls, it is possible for
     "caller" to see a stack frame belonging to that deleted package.
     "caller" could crash if the stash's memory address was reused for a
     scalar and a substitution was performed on the same scalar [perl
     #113486].

 •   "UNIVERSAL::can" no longer treats its first argument differently
     depending on whether it is a string or number internally.

 •   "open" with "<&" for the mode checks to see whether the third
     argument is a number, in determining whether to treat it as a file
     descriptor or a handle name.  Magical variables like $1 were always
     failing the numeric check and being treated as handle names.

 •   "warn"'s handling of magical variables ($1, ties) has undergone
     several fixes.  "FETCH" is only called once now on a tied argument or
     a tied $@ [perl #97480].  Tied variables returning objects that
     stringify as "" are no longer ignored.  A tied $@ that happened to
     return a reference the _p_r_e_v_i_o_u_s time it was used is no longer
     ignored.

 •   "warn """ now treats $@ with a number in it the same way, regardless
     of whether it happened via "$@=3" or "$@="3"".  It used to ignore the
     former.  Now it appends "\t...caught", as it has always done with
     "$@="3"".

 •   Numeric operators on magical variables (e.g., "$1 + 1") used to use
     floating point operations even where integer operations were more
     appropriate, resulting in loss of accuracy on 64-bit platforms [perl
     #109542].

 •   Unary negation no longer treats a string as a number if the string
     happened to be used as a number at some point.  So, if $x contains
     the string "dogs", "-$x" returns "-dogs" even if "$y=0+$x" has
     happened at some point.

 •   In Perl v5.14, "-'-10'" was fixed to return "10", not "+10".  But
     magical variables ($1, ties) were not fixed till now [perl #57706].

 •   Unary negation now treats strings consistently, regardless of the
     internal "UTF8" flag.

 •   A regression introduced in Perl v5.16.0 involving
     "tr/_S_E_A_R_C_H_L_I_S_T/_R_E_P_L_A_C_E_M_E_N_T_L_I_S_T/" has been fixed.  Only the first
     instance is supposed to be meaningful if a character appears more
     than once in "_S_E_A_R_C_H_L_I_S_T".  Under some circumstances, the final
     instance was overriding all earlier ones.  [perl #113584]

 •   Regular expressions like "qr/\87/" previously silently inserted a NUL
     character, thus matching as if it had been written "qr/\00087/".  Now
     it matches as if it had been written as "qr/87/", with a message that
     the sequence "\8" is unrecognized.

 •   "__SUB__" now works in special blocks ("BEGIN", "END", etc.).

 •   Thread creation on Windows could theoretically result in a crash if
     done inside a "BEGIN" block.  It still does not work properly, but it
     no longer crashes [perl #111610].

 •   "\&{''}" (with the empty string) now autovivifies a stub like any
     other sub name, and no longer produces the "Unable to create sub"
     error [perl #94476].

 •   A regression introduced in v5.14.0 has been fixed, in which some
     calls to the "re" module would clobber $_ [perl #113750].

 •   "do FILE" now always either sets or clears $@, even when the file
     can't be read. This ensures that testing $@ first (as recommended by
     the documentation) always returns the correct result.

 •   The array iterator used for the "each @array" construct is now
     correctly reset when @array is cleared [perl #75596]. This happens,
     for example, when the array is globally assigned to, as in "@array =
     (...)", but not when its vvaalluueess are assigned to. In terms of the XS
     API, it means that "av_clear()" will now reset the iterator.

     This mirrors the behaviour of the hash iterator when the hash is
     cleared.

 •   "$class->can", "$class->isa", and "$class->DOES" now return correct
     results, regardless of whether that package referred to by $class
     exists [perl #47113].

 •   Arriving signals no longer clear $@ [perl #45173].

 •   Allow "my ()" declarations with an empty variable list [perl
     #113554].

 •   During parsing, subs declared after errors no longer leave stubs
     [perl #113712].

 •   Closures containing no string evals no longer hang on to their
     containing subroutines, allowing variables closed over by outer
     subroutines to be freed when the outer sub is freed, even if the
     inner sub still exists [perl #89544].

 •   Duplication of in-memory filehandles by opening with a "<&=" or ">&="
     mode stopped working properly in v5.16.0.  It was causing the new
     handle to reference a different scalar variable.  This has been fixed
     [perl #113764].

 •   "qr//" expressions no longer crash with custom regular expression
     engines that do not set "offs" at regular expression compilation time
     [perl #112962].

 •   "delete local" no longer crashes with certain magical arrays and
     hashes [perl #112966].

 •   "local" on elements of certain magical arrays and hashes used not to
     arrange to have the element deleted on scope exit, even if the
     element did not exist before "local".

 •   "scalar(write)" no longer returns multiple items [perl #73690].

 •   String to floating point conversions no longer misparse certain
     strings under "use locale" [perl #109318].

 •   @INC filters that die no longer leak memory [perl #92252].

 •   The implementations of overloaded operations are now called in the
     correct context. This allows, among other things, being able to
     properly override "<>" [perl #47119].

 •   Specifying only the "fallback" key when calling "use overload" now
     behaves properly [perl #113010].

 •   "sub foo { my $a = 0; while ($a) { ... } }" and "sub foo { while (0)
     { ... } }" now return the same thing [perl #73618].

 •   String negation now behaves the same under "use integer;" as it does
     without [perl #113012].

 •   "chr" now returns the Unicode replacement character (U+FFFD) for -1,
     regardless of the internal representation.  -1 used to wrap if the
     argument was tied or a string internally.

 •   Using a "format" after its enclosing sub was freed could crash as of
     perl v5.12.0, if the format referenced lexical variables from the
     outer sub.

 •   Using a "format" after its enclosing sub was undefined could crash as
     of perl v5.10.0, if the format referenced lexical variables from the
     outer sub.

 •   Using a "format" defined inside a closure, which format references
     lexical variables from outside, never really worked unless the
     "write" call was directly inside the closure.  In v5.10.0 it even
     started crashing.  Now the copy of that closure nearest the top of
     the call stack is used to find those variables.

 •   Formats that close over variables in special blocks no longer crash
     if a stub exists with the same name as the special block before the
     special block is compiled.

 •   The parser no longer gets confused, treating "eval foo ()" as a
     syntax error if preceded by "print;" [perl #16249].

 •   The return value of "syscall" is no longer truncated on 64-bit
     platforms [perl #113980].

 •   Constant folding no longer causes "print 1 ? FOO : BAR" to print to
     the FOO handle [perl #78064].

 •   "do subname" now calls the named subroutine and uses the file name it
     returns, instead of opening a file named "subname".

 •   Subroutines looked up by rv2cv check hooks (registered by XS modules)
     are now taken into consideration when determining whether "foo bar"
     should be the sub call "foo(bar)" or the method call ""bar"->foo".

 •   "CORE::foo::bar" is no longer treated specially, allowing global
     overrides to be called directly via "CORE::GLOBAL::uc(...)" [perl
     #113016].

 •   Calling an undefined sub whose typeglob has been undefined now
     produces the customary "Undefined subroutine called" error, instead
     of "Not a CODE reference".

 •   Two bugs involving @ISA have been fixed.  "*ISA =
     *glob_without_array" and "undef *ISA; @{*ISA}" would prevent future
     modifications to @ISA from updating the internal caches used to look
     up methods.  The *glob_without_array case was a regression from Perl
     v5.12.

 •   Regular expression optimisations sometimes caused "$" with "/m" to
     produce failed or incorrect matches [perl #114068].

 •   "__SUB__" now works in a "sort" block when the enclosing subroutine
     is predeclared with "sub foo;" syntax [perl #113710].

 •   Unicode properties only apply to Unicode code points, which leads to
     some subtleties when regular expressions are matched against above-
     Unicode code points.  There is a warning generated to draw your
     attention to this.  However, this warning was being generated
     inappropriately in some cases, such as when a program was being
     parsed.  Non-Unicode matches such as "\w" and "[:word:]" should not
     generate the warning, as their definitions don't limit them to apply
     to only Unicode code points.  Now the message is only generated when
     matching against "\p{}" and "\P{}".  There remains a bug, [perl
     #114148], for the very few properties in Unicode that match just a
     single code point.  The warning is not generated if they are matched
     against an above-Unicode code point.

 •   Uninitialized warnings mentioning hash elements would only mention
     the element name if it was not in the first bucket of the hash, due
     to an off-by-one error.

 •   A regular expression optimizer bug could cause multiline "^" to
     behave incorrectly in the presence of line breaks, such that ""/\n\n"
     =~ m#\A(?:^/$)#im" would not match [perl #115242].

 •   Failed "fork" in list context no longer corrupts the stack.  "@a =
     (1, 2, fork, 3)" used to gobble up the 2 and assign "(1, undef, 3)"
     if the "fork" call failed.

 •   Numerous memory leaks have been fixed, mostly involving tied
     variables that die, regular expression character classes and code
     blocks, and syntax errors.

 •   Assigning a regular expression ("${qr//}") to a variable that happens
     to hold a floating point number no longer causes assertion failures
     on debugging builds.

 •   Assigning a regular expression to a scalar containing a number no
     longer causes subsequent numification to produce random numbers.

 •   Assigning a regular expression to a magic variable no longer wipes
     away the magic.  This was a regression from v5.10.

 •   Assigning a regular expression to a blessed scalar no longer results
     in crashes.  This was also a regression from v5.10.

 •   Regular expression can now be assigned to tied hash and array
     elements with flattening into strings.

 •   Numifying a regular expression no longer results in an uninitialized
     warning.

 •   Negative array indices no longer cause EXISTS methods of tied
     variables to be ignored.  This was a regression from v5.12.

 •   Negative array indices no longer result in crashes on arrays tied to
     non-objects.

 •   "$byte_overload .= $utf8" no longer results in doubly-encoded UTF-8
     if the left-hand scalar happened to have produced a UTF-8 string the
     last time overloading was invoked.

 •   "goto &sub" now uses the current value of @_, instead of using the
     array the subroutine was originally called with.  This means "local
     @_ = (...); goto &sub" now works [perl #43077].

 •   If a debugger is invoked recursively, it no longer stomps on its own
     lexical variables.  Formerly under recursion all calls would share
     the same set of lexical variables [perl #115742].

 •   *_{ARRAY} returned from a subroutine no longer spontaneously becomes
     empty.

 •   When using "say" to print to a tied filehandle, the value of "$\" is
     correctly localized, even if it was previously undef.  [perl #119927]

KKnnoowwnn PPrroobblleemmss • UTF8-flagged strings in %ENV on HP-UX 11.00 are buggy

     The interaction of UTF8-flagged strings and %ENV on HP-UX 11.00 is
     currently dodgy in some not-yet-fully-diagnosed way.  Expect test
     failures in _t_/_o_p_/_m_a_g_i_c_._t, followed by unknown behavior when storing
     wide characters in the environment.

OObbiittuuaarryy Hojung Yoon (AMORETTE), 24, of Seoul, South Korea, went to his long rest on May 8, 2013 with llama figurine and autographed TIMTOADY card. He was a brilliant young Perl 5 & 6 hacker and a devoted member of Seoul.pm. He programmed Perl, talked Perl, ate Perl, and loved Perl. We believe that he is still programming in Perl with his broken IBM laptop somewhere. He will be missed.

AAcckknnoowwlleeddggeemmeennttss Perl v5.18.0 represents approximately 12 months of development since Perl v5.16.0 and contains approximately 400,000 lines of changes across 2,100 files from 113 authors.

 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 v5.18.0:

 Aaron Crane, Aaron Trevena, Abhijit Menon-Sen, Adrian M. Enache, Alan
 Haggai Alavi, Alexandr Ciornii, Andrew Tam, Andy Dougherty, Anton
 Nikishaev, Aristotle Pagaltzis, Augustina Blair, Bob Ernst, Brad Gilbert,
 Breno G. de Oliveira, Brian Carlson, Brian Fraser, Charlie Gonzalez, Chip
 Salzenberg, Chris 'BinGOs' Williams, Christian Hansen, Colin Kuskie,
 Craig A. Berry, Dagfinn Ilmari Mannsåker, Daniel Dragan, Daniel Perrett,
 Darin McBride, Dave Rolsky, David Golden, David Leadbeater, David
 Mitchell, David Nicol, Dominic Hargreaves, E. Choroba, Eric Brine, Evan
 Miller, Father Chrysostomos, Florian Ragwitz, François Perrad, George
 Greer, Goro Fuji, H.Merijn Brand, Herbert Breunung, Hugo van der Sanden,
 Igor Zaytsev, James E Keenan, Jan Dubois, Jasmine Ahuja, Jerry D. Hedden,
 Jess Robinson, Jesse Luehrs, Joaquin Ferrero, Joel Berger, John Goodyear,
 John Peacock, Karen Etheridge, Karl Williamson, Karthik Rajagopalan, Kent
 Fredric, Leon Timmermans, Lucas Holt, Lukas Mai, Marcus Holland-Moritz,
 Markus Jansen, Martin Hasch, Matthew Horsfall, Max Maischein, Michael G
 Schwern, Michael Schroeder, Moritz Lenz, Nicholas Clark, Niko Tyni, Oleg
 Nesterov, Patrik Hägglund, Paul Green, Paul Johnson, Paul Marquess, Peter
 Martini, Rafael Garcia-Suarez, Reini Urban, Renee Baecker, Rhesa
 Rozendaal, Ricardo Signes, Robin Barker, Ronald J. Kimball, Ruslan
 Zakirov, Salvador Fandiño, Sawyer X, Scott Lanning, Sergey Alekseev,
 Shawn M Moore, Shirakata Kentaro, Shlomi Fish, Sisyphus, Smylers, Steffen
 Müller, Steve Hay, Steve Peters, Steven Schubiger, Sullivan Beck, Sven
 Strickroth, Sébastien Aperghis-Tramoni, Thomas Sibley, Tobias Leich, Tom
 Wyant, Tony Cook, Vadim Konovalov, Vincent Pit, Volker Schatz, Walt
 Mankowski, Yves Orton, Zefram.

 The list above is almost certainly incomplete as it is automatically
 generated from version control history. In particular, it does not
 include the names of the (very much appreciated) contributors who
 reported issues to the Perl bug tracker.

 Many of the changes included in this version originated in the CPAN
 modules included in Perl's core. We're grateful to the entire CPAN
 community for helping Perl to flourish.

 For a more complete list of all of Perl's historical contributors, please
 see the _A_U_T_H_O_R_S file in the Perl source distribution.

RReeppoorrttiinngg BBuuggss If you find what you think is a bug, you might check the articles recently posted to the comp.lang.perl.misc newsgroup and the perl bug database at http://rt.perl.org/perlbug/ . 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 PERL5180DELTA(1)