1PERL5120DELTA(1)       Perl Programmers Reference Guide       PERL5120DELTA(1)
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NAME

6       perl5120delta - what is new for perl v5.12.0
7

DESCRIPTION

9       This document describes differences between the 5.10.0 release and the
10       5.12.0 release.
11
12       Many of the bug fixes in 5.12.0 are already included in the 5.10.1
13       maintenance release.
14
15       You can see the list of those changes in the 5.10.1 release notes
16       (perl5101delta).
17

Core Enhancements

19   New "package NAME VERSION" syntax
20       This new syntax allows a module author to set the $VERSION of a
21       namespace when the namespace is declared with 'package'. It eliminates
22       the need for "our $VERSION = ..." and similar constructs. E.g.
23
24             package Foo::Bar 1.23;
25             # $Foo::Bar::VERSION == 1.23
26
27       There are several advantages to this:
28
29       •   $VERSION is parsed in exactly the same way as "use NAME VERSION"
30
31       •   $VERSION is set at compile time
32
33       •   $VERSION is a version object that provides proper overloading of
34           comparison operators so comparing $VERSION to decimal (1.23) or
35           dotted-decimal (v1.2.3) version numbers works correctly.
36
37       •   Eliminates "$VERSION = ..." and "eval $VERSION" clutter
38
39       •   As it requires VERSION to be a numeric literal or v-string literal,
40           it can be statically parsed by toolchain modules without "eval" the
41           way MM->parse_version does for "$VERSION = ..."
42
43       It does not break old code with only "package NAME", but code that uses
44       "package NAME VERSION" will need to be restricted to perl 5.12.0 or
45       newer This is analogous to the change to "open" from two-args to three-
46       args.  Users requiring the latest Perl will benefit, and perhaps after
47       several years, it will become a standard practice.
48
49       However, "package NAME VERSION" requires a new, 'strict' version number
50       format. See "Version number formats" for details.
51
52   The "..." operator
53       A new operator, "...", nicknamed the Yada Yada operator, has been
54       added.  It is intended to mark placeholder code that is not yet
55       implemented.  See "Yada Yada Operator" in perlop.
56
57   Implicit strictures
58       Using the "use VERSION" syntax with a version number greater or equal
59       to 5.11.0 will lexically enable strictures just like "use strict" would
60       do (in addition to enabling features.) The following:
61
62           use 5.12.0;
63
64       means:
65
66           use strict;
67           use feature ':5.12';
68
69   Unicode improvements
70       Perl 5.12 comes with Unicode 5.2, the latest version available to us at
71       the time of release.  This version of Unicode was released in October
72       2009. See <http://www.unicode.org/versions/Unicode5.2.0> for further
73       details about what's changed in this version of the standard.  See
74       perlunicode for instructions on installing and using other versions of
75       Unicode.
76
77       Additionally, Perl's developers have significantly improved Perl's
78       Unicode implementation. For full details, see "Unicode overhaul" below.
79
80   Y2038 compliance
81       Perl's core time-related functions are now Y2038 compliant. (It may not
82       mean much to you, but your kids will love it!)
83
84   qr overloading
85       It is now possible to overload the "qr//" operator, that is, conversion
86       to regexp, like it was already possible to overload conversion to
87       boolean, string or number of objects. It is invoked when an object
88       appears on the right hand side of the "=~" operator or when it is
89       interpolated into a regexp. See overload.
90
91   Pluggable keywords
92       Extension modules can now cleanly hook into the Perl parser to define
93       new kinds of keyword-headed expression and compound statement. The
94       syntax following the keyword is defined entirely by the extension. This
95       allows a completely non-Perl sublanguage to be parsed inline, with the
96       correct ops cleanly generated.
97
98       See "PL_keyword_plugin" in perlapi for the mechanism. The Perl core
99       source distribution also includes a new module XS::APItest::KeywordRPN,
100       which implements reverse Polish notation arithmetic via pluggable
101       keywords. This module is mainly used for test purposes, and is not
102       normally installed, but also serves as an example of how to use the new
103       mechanism.
104
105       Perl's developers consider this feature to be experimental. We may
106       remove it or change it in a backwards-incompatible way in Perl 5.14.
107
108   APIs for more internals
109       The lowest layers of the lexer and parts of the pad system now have C
110       APIs available to XS extensions. These are necessary to support proper
111       use of pluggable keywords, but have other uses too. The new APIs are
112       experimental, and only cover a small proportion of what would be
113       necessary to take full advantage of the core's facilities in these
114       areas. It is intended that the Perl 5.13 development cycle will see the
115       addition of a full range of clean, supported interfaces.
116
117       Perl's developers consider this feature to be experimental. We may
118       remove it or change it in a backwards-incompatible way in Perl 5.14.
119
120   Overridable function lookup
121       Where an extension module hooks the creation of rv2cv ops to modify the
122       subroutine lookup process, this now works correctly for bareword
123       subroutine calls. This means that prototypes on subroutines referenced
124       this way will be processed correctly. (Previously bareword subroutine
125       names were initially looked up, for parsing purposes, by an unhookable
126       mechanism, so extensions could only properly influence subroutine names
127       that appeared with an "&" sigil.)
128
129   A proper interface for pluggable Method Resolution Orders
130       As of Perl 5.12.0 there is a new interface for plugging and using
131       method resolution orders other than the default linear depth first
132       search.  The C3 method resolution order added in 5.10.0 has been re-
133       implemented as a plugin, without changing its Perl-space interface. See
134       perlmroapi for more information.
135
136   "\N" experimental regex escape
137       Perl now supports "\N", a new regex escape which you can think of as
138       the inverse of "\n". It will match any character that is not a newline,
139       independently from the presence or absence of the single line match
140       modifier "/s". It is not usable within a character class.  "\N{3}"
141       means to match 3 non-newlines; "\N{5,}" means to match at least 5.
142       "\N{NAME}" still means the character or sequence named "NAME", but
143       "NAME" no longer can be things like 3, or "5,".
144
145       This will break a custom charnames translator which allows numbers for
146       character names, as "\N{3}" will now mean to match 3 non-newline
147       characters, and not the character whose name is 3. (No name defined by
148       the Unicode standard is a number, so only custom translators might be
149       affected.)
150
151       Perl's developers are somewhat concerned about possible user confusion
152       with the existing "\N{...}" construct which matches characters by their
153       Unicode name. Consequently, this feature is experimental. We may remove
154       it or change it in a backwards-incompatible way in Perl 5.14.
155
156   DTrace support
157       Perl now has some support for DTrace. See "DTrace support" in INSTALL.
158
159   Support for "configure_requires" in CPAN module metadata
160       Both "CPAN" and "CPANPLUS" now support the "configure_requires" keyword
161       in the META.yml metadata file included in most recent CPAN
162       distributions.  This allows distribution authors to specify
163       configuration prerequisites that must be installed before running
164       Makefile.PL or Build.PL.
165
166       See the documentation for "ExtUtils::MakeMaker" or "Module::Build" for
167       more on how to specify "configure_requires" when creating a
168       distribution for CPAN.
169
170   "each", "keys", "values" are now more flexible
171       The "each", "keys", "values" function can now operate on arrays.
172
173   "when" as a statement modifier
174       "when" is now allowed to be used as a statement modifier.
175
176   $, flexibility
177       The variable $, may now be tied.
178
179   // in when clauses
180       // now behaves like || in when clauses
181
182   Enabling warnings from your shell environment
183       You can now set "-W" from the "PERL5OPT" environment variable
184
185   "delete local"
186       "delete local" now allows you to locally delete a hash entry.
187
188   New support for Abstract namespace sockets
189       Abstract namespace sockets are Linux-specific socket type that live in
190       AF_UNIX family, slightly abusing it to be able to use arbitrary
191       character arrays as addresses: They start with nul byte and are not
192       terminated by nul byte, but with the length passed to the socket()
193       system call.
194
195   32-bit limit on substr arguments removed
196       The 32-bit limit on "substr" arguments has now been removed. The full
197       range of the system's signed and unsigned integers is now available for
198       the "pos" and "len" arguments.
199

Potentially Incompatible Changes

201   Deprecations warn by default
202       Over the years, Perl's developers have deprecated a number of language
203       features for a variety of reasons.  Perl now defaults to issuing a
204       warning if a deprecated language feature is used. Many of the
205       deprecations Perl now warns you about have been deprecated for many
206       years.  You can find a list of what was deprecated in a given release
207       of Perl in the "perl5xxdelta.pod" file for that release.
208
209       To disable this feature in a given lexical scope, you should use "no
210       warnings 'deprecated';" For information about which language features
211       are deprecated and explanations of various deprecation warnings, please
212       see perldiag. See "Deprecations" below for the list of features and
213       modules Perl's developers have deprecated as part of this release.
214
215   Version number formats
216       Acceptable version number formats have been formalized into "strict"
217       and "lax" rules. "package NAME VERSION" takes a strict version number.
218       "UNIVERSAL::VERSION" and the version object constructors take lax
219       version numbers. Providing an invalid version will result in a fatal
220       error. The version argument in "use NAME VERSION" is first parsed as a
221       numeric literal or v-string and then passed to "UNIVERSAL::VERSION"
222       (and must then pass the "lax" format test).
223
224       These formats are documented fully in the version module. To a first
225       approximation, a "strict" version number is a positive decimal number
226       (integer or decimal-fraction) without exponentiation or else a dotted-
227       decimal v-string with a leading 'v' character and at least three
228       components. A "lax" version number allows v-strings with fewer than
229       three components or without a leading 'v'. Under "lax" rules, both
230       decimal and dotted-decimal versions may have a trailing "alpha"
231       component separated by an underscore character after a fractional or
232       dotted-decimal component.
233
234       The version module adds "version::is_strict" and "version::is_lax"
235       functions to check a scalar against these rules.
236
237   @INC reorganization
238       In @INC, "ARCHLIB" and "PRIVLIB" now occur after the current version's
239       "site_perl" and "vendor_perl".  Modules installed into "site_perl" and
240       "vendor_perl" will now be loaded in preference to those installed in
241       "ARCHLIB" and "PRIVLIB".
242
243   REGEXPs are now first class
244       Internally, Perl now treats compiled regular expressions (such as those
245       created with "qr//") as first class entities. Perl modules which
246       serialize, deserialize or otherwise have deep interaction with Perl's
247       internal data structures need to be updated for this change.  Most
248       affected CPAN modules have already been updated as of this writing.
249
250   Switch statement changes
251       The "given"/"when" switch statement handles complex statements better
252       than Perl 5.10.0 did (These enhancements are also available in 5.10.1
253       and subsequent 5.10 releases.) There are two new cases where "when" now
254       interprets its argument as a boolean, instead of an expression to be
255       used in a smart match:
256
257       flip-flop operators
258           The ".." and "..." flip-flop operators are now evaluated in boolean
259           context, following their usual semantics; see "Range Operators" in
260           perlop.
261
262           Note that, as in perl 5.10.0, "when (1..10)" will not work to test
263           whether a given value is an integer between 1 and 10; you should
264           use "when ([1..10])" instead (note the array reference).
265
266           However, contrary to 5.10.0, evaluating the flip-flop operators in
267           boolean context ensures it can now be useful in a when(), notably
268           for implementing bistable conditions, like in:
269
270               when (/^=begin/ .. /^=end/) {
271                 # do something
272               }
273
274       defined-or operator
275           A compound expression involving the defined-or operator, as in
276           "when (expr1 // expr2)", will be treated as boolean if the first
277           expression is boolean. (This just extends the existing rule that
278           applies to the regular or operator, as in "when (expr1 || expr2)".)
279
280   Smart match changes
281       Since Perl 5.10.0, Perl's developers have made a number of changes to
282       the smart match operator. These, of course, also alter the behaviour of
283       the switch statements where smart matching is implicitly used.  These
284       changes were also made for the 5.10.1 release, and will remain in
285       subsequent 5.10 releases.
286
287       Changes to type-based dispatch
288
289       The smart match operator "~~" is no longer commutative. The behaviour
290       of a smart match now depends primarily on the type of its right hand
291       argument. Moreover, its semantics have been adjusted for greater
292       consistency or usefulness in several cases. While the general backwards
293       compatibility is maintained, several changes must be noted:
294
295       •   Code references with an empty prototype are no longer treated
296           specially.  They are passed an argument like the other code
297           references (even if they choose to ignore it).
298
299       •   "%hash ~~ sub {}" and "@array ~~ sub {}" now test that the
300           subroutine returns a true value for each key of the hash (or
301           element of the array), instead of passing the whole hash or array
302           as a reference to the subroutine.
303
304       •   Due to the commutativity breakage, code references are no longer
305           treated specially when appearing on the left of the "~~" operator,
306           but like any vulgar scalar.
307
308       •   "undef ~~ %hash" is always false (since "undef" can't be a key in a
309           hash). No implicit conversion to "" is done (as was the case in
310           perl 5.10.0).
311
312       •   "$scalar ~~ @array" now always distributes the smart match across
313           the elements of the array. It's true if one element in @array
314           verifies "$scalar ~~ $element". This is a generalization of the old
315           behaviour that tested whether the array contained the scalar.
316
317       The full dispatch table for the smart match operator is given in "Smart
318       matching in detail" in perlsyn.
319
320       Smart match and overloading
321
322       According to the rule of dispatch based on the rightmost argument type,
323       when an object overloading "~~" appears on the right side of the
324       operator, the overload routine will always be called (with a 3rd
325       argument set to a true value, see overload.) However, when the object
326       will appear on the left, the overload routine will be called only when
327       the rightmost argument is a simple scalar. This way, distributivity of
328       smart match across arrays is not broken, as well as the other
329       behaviours with complex types (coderefs, hashes, regexes). Thus,
330       writers of overloading routines for smart match mostly need to worry
331       only with comparing against a scalar, and possibly with stringification
332       overloading; the other common cases will be automatically handled
333       consistently.
334
335       "~~" will now refuse to work on objects that do not overload it (in
336       order to avoid relying on the object's underlying structure). (However,
337       if the object overloads the stringification or the numification
338       operators, and if overload fallback is active, it will be used instead,
339       as usual.)
340
341   Other potentially incompatible changes
342       •   The definitions of a number of Unicode properties have changed to
343           match those of the current Unicode standard. These are listed above
344           under "Unicode overhaul". This change may break code that expects
345           the old definitions.
346
347       •   The boolkeys op has moved to the group of hash ops. This breaks
348           binary compatibility.
349
350       •   Filehandles are now always blessed into "IO::File".
351
352           The previous behaviour was to bless Filehandles into FileHandle (an
353           empty proxy class) if it was loaded into memory and otherwise to
354           bless them into "IO::Handle".
355
356       •   The semantics of "use feature :5.10*" have changed slightly.  See
357           "Modules and Pragmata" for more information.
358
359       •   Perl's developers now use git, rather than Perforce.  This should
360           be a purely internal change only relevant to people actively
361           working on the core.  However, you may see minor difference in perl
362           as a consequence of the change.  For example in some of details of
363           the output of "perl -V". See perlrepository for more information.
364
365       •   As part of the "Test::Harness" 2.x to 3.x upgrade, the experimental
366           "Test::Harness::Straps" module has been removed.  See "Modules and
367           Pragmata" for more details.
368
369       •   As part of the "ExtUtils::MakeMaker" upgrade, the
370           "ExtUtils::MakeMaker::bytes" and "ExtUtils::MakeMaker::vmsish"
371           modules have been removed from this distribution.
372
373       •   "Module::CoreList" no longer contains the %:patchlevel hash.
374
375       •   "length undef" now returns undef.
376
377       •   Unsupported private C API functions are now declared "static" to
378           prevent leakage to Perl's public API.
379
380       •   To support the bootstrapping process, miniperl no longer builds
381           with UTF-8 support in the regexp engine.
382
383           This allows a build to complete with PERL_UNICODE set and a UTF-8
384           locale.  Without this there's a bootstrapping problem, as miniperl
385           can't load the UTF-8 components of the regexp engine, because
386           they're not yet built.
387
388miniperl's @INC is now restricted to just "-I...", the split of
389           $ENV{PERL5LIB}, and "".""
390
391       •   A space or a newline is now required after a "#line XXX" directive.
392
393       •   Tied filehandles now have an additional method EOF which provides
394           the EOF type.
395
396       •   To better match all other flow control statements, "foreach" may no
397           longer be used as an attribute.
398
399       •   Perl's command-line switch "-P", which was deprecated in version
400           5.10.0, has now been removed. The CPAN module "Filter::cpp" can be
401           used as an alternative.
402

Deprecations

404       From time to time, Perl's developers find it necessary to deprecate
405       features or modules we've previously shipped as part of the core
406       distribution. We are well aware of the pain and frustration that a
407       backwards-incompatible change to Perl can cause for developers building
408       or maintaining software in Perl. You can be sure that when we deprecate
409       a functionality or syntax, it isn't a choice we make lightly.
410       Sometimes, we choose to deprecate functionality or syntax because it
411       was found to be poorly designed or implemented. Sometimes, this is
412       because they're holding back other features or causing performance
413       problems. Sometimes, the reasons are more complex. Wherever possible,
414       we try to keep deprecated functionality available to developers in its
415       previous form for at least one major release. So long as a deprecated
416       feature isn't actively disrupting our ability to maintain and extend
417       Perl, we'll try to leave it in place as long as possible.
418
419       The following items are now deprecated:
420
421       suidperl
422           "suidperl" is no longer part of Perl. It used to provide a
423           mechanism to emulate setuid permission bits on systems that don't
424           support it properly.
425
426       Use of ":=" to mean an empty attribute list
427           An accident of Perl's parser meant that these constructions were
428           all equivalent:
429
430               my $pi := 4;
431               my $pi : = 4;
432               my $pi :  = 4;
433
434           with the ":" being treated as the start of an attribute list, which
435           ends before the "=". As whitespace is not significant here, all are
436           parsed as an empty attribute list, hence all the above are
437           equivalent to, and better written as
438
439               my $pi = 4;
440
441           because no attribute processing is done for an empty list.
442
443           As is, this meant that ":=" cannot be used as a new token, without
444           silently changing the meaning of existing code. Hence that
445           particular form is now deprecated, and will become a syntax error.
446           If it is absolutely necessary to have empty attribute lists (for
447           example, because of a code generator) then avoid the warning by
448           adding a space before the "=".
449
450       "UNIVERSAL->import()"
451           The method "UNIVERSAL->import()" is now deprecated. Attempting to
452           pass import arguments to a "use UNIVERSAL" statement will result in
453           a deprecation warning.
454
455       Use of "goto" to jump into a construct
456           Using "goto" to jump from an outer scope into an inner scope is now
457           deprecated. This rare use case was causing problems in the
458           implementation of scopes.
459
460       Custom character names in \N{name} that don't look like names
461           In "\N{name}", name can be just about anything. The standard
462           Unicode names have a very limited domain, but a custom name
463           translator could create names that are, for example, made up
464           entirely of punctuation symbols. It is now deprecated to make names
465           that don't begin with an alphabetic character, and aren't
466           alphanumeric or contain other than a very few other characters,
467           namely spaces, dashes, parentheses and colons. Because of the added
468           meaning of "\N" (See ""\N" experimental regex escape"), names that
469           look like curly brace -enclosed quantifiers won't work. For
470           example, "\N{3,4}" now means to match 3 to 4 non-newlines; before a
471           custom name "3,4" could have been created.
472
473       Deprecated Modules
474           The following modules will be removed from the core distribution in
475           a future release, and should be installed from CPAN instead.
476           Distributions on CPAN which require these should add them to their
477           prerequisites. The core versions of these modules warnings will
478           issue a deprecation warning.
479
480           If you ship a packaged version of Perl, either alone or as part of
481           a larger system, then you should carefully consider the
482           repercussions of core module deprecations. You may want to consider
483           shipping your default build of Perl with packages for some or all
484           deprecated modules which install into "vendor" or "site" perl
485           library directories. This will inhibit the deprecation warnings.
486
487           Alternatively, you may want to consider patching lib/deprecate.pm
488           to provide deprecation warnings specific to your packaging system
489           or distribution of Perl, consistent with how your packaging system
490           or distribution manages a staged transition from a release where
491           the installation of a single package provides the given
492           functionality, to a later release where the system administrator
493           needs to know to install multiple packages to get that same
494           functionality.
495
496           You can silence these deprecation warnings by installing the
497           modules in question from CPAN.  To install the latest version of
498           all of them, just install "Task::Deprecations::5_12".
499
500           Class::ISA
501           Pod::Plainer
502           Shell
503           Switch
504               Switch is buggy and should be avoided. You may find Perl's new
505               "given"/"when" feature a suitable replacement.  See "Switch
506               statements" in perlsyn for more information.
507
508       Assignment to $[
509       Use of the attribute :locked on subroutines
510       Use of "locked" with the attributes pragma
511       Use of "unique" with the attributes pragma
512       Perl_pmflag
513           "Perl_pmflag" is no longer part of Perl's public API. Calling it
514           now generates a deprecation warning, and it will be removed in a
515           future release. Although listed as part of the API, it was never
516           documented, and only ever used in toke.c, and prior to 5.10,
517           regcomp.c. In core, it has been replaced by a static function.
518
519       Numerous Perl 4-era libraries
520           termcap.pl, tainted.pl, stat.pl, shellwords.pl, pwd.pl, open3.pl,
521           open2.pl, newgetopt.pl, look.pl, find.pl, finddepth.pl,
522           importenv.pl, hostname.pl, getopts.pl, getopt.pl, getcwd.pl,
523           flush.pl, fastcwd.pl, exceptions.pl, ctime.pl, complete.pl,
524           cacheout.pl, bigrat.pl, bigint.pl, bigfloat.pl, assert.pl,
525           abbrev.pl, dotsh.pl, and timelocal.pl are all now deprecated.
526           Earlier, Perl's developers intended to remove these libraries from
527           Perl's core for the 5.14.0 release.
528
529           During final testing before the release of 5.12.0, several
530           developers discovered current production code using these ancient
531           libraries, some inside the Perl core itself.  Accordingly, the
532           pumpking granted them a stay of execution. They will begin to warn
533           about their deprecation in the 5.14.0 release and will be removed
534           in the 5.16.0 release.
535

Unicode overhaul

537       Perl's developers have made a concerted effort to update Perl to be in
538       sync with the latest Unicode standard. Changes for this include:
539
540       Perl can now handle every Unicode character property. New
541       documentation, perluniprops, lists all available non-Unihan character
542       properties. By default, perl does not expose Unihan, deprecated or
543       Unicode-internal properties.  See below for more details on these;
544       there is also a section in the pod listing them, and explaining why
545       they are not exposed.
546
547       Perl now fully supports the Unicode compound-style of using "=" and ":"
548       in writing regular expressions: "\p{property=value}" and
549       "\p{property:value}" (both of which mean the same thing).
550
551       Perl now fully supports the Unicode loose matching rules for text
552       between the braces in "\p{...}" constructs. In addition, Perl allows
553       underscores between digits of numbers.
554
555       Perl now accepts all the Unicode-defined synonyms for properties and
556       property values.
557
558       "qr/\X/", which matches a Unicode logical character, has been expanded
559       to work better with various Asian languages. It now is defined as an
560       extended grapheme cluster. (See
561       <http://www.unicode.org/reports/tr29/>).  Anything matched previously
562       and that made sense will continue to be accepted.   Additionally:
563
564       •   "\X" will not break apart a "CR LF" sequence.
565
566       •   "\X" will now match a sequence which includes the "ZWJ" and "ZWNJ"
567           characters.
568
569       •   "\X" will now always match at least one character, including an
570           initial mark.  Marks generally come after a base character, but it
571           is possible in Unicode to have them in isolation, and "\X" will now
572           handle that case, for example at the beginning of a line, or after
573           a "ZWSP". And this is the part where "\X" doesn't match the things
574           that it used to that don't make sense. Formerly, for example, you
575           could have the nonsensical case of an accented LF.
576
577       •   "\X" will now match a (Korean) Hangul syllable sequence, and the
578           Thai and Lao exception cases.
579
580       Otherwise, this change should be transparent for the non-affected
581       languages.
582
583       "\p{...}" matches using the Canonical_Combining_Class property were
584       completely broken in previous releases of Perl.  They should now work
585       correctly.
586
587       Before Perl 5.12, the Unicode "Decomposition_Type=Compat" property and
588       a Perl extension had the same name, which led to neither matching all
589       the correct values (with more than 100 mistakes in one, and several
590       thousand in the other). The Perl extension has now been renamed to be
591       "Decomposition_Type=Noncanonical" (short: "dt=noncanon"). It has the
592       same meaning as was previously intended, namely the union of all the
593       non-canonical Decomposition types, with Unicode "Compat" being just one
594       of those.
595
596       "\p{Decomposition_Type=Canonical}" now includes the Hangul syllables.
597
598       "\p{Uppercase}" and "\p{Lowercase}" now work as the Unicode standard
599       says they should.  This means they each match a few more characters
600       than they used to.
601
602       "\p{Cntrl}" now matches the same characters as "\p{Control}". This
603       means it no longer will match Private Use (gc=co), Surrogates (gc=cs),
604       nor Format (gc=cf) code points. The Format code points represent the
605       biggest possible problem. All but 36 of them are either officially
606       deprecated or strongly discouraged from being used. Of those 36, likely
607       the most widely used are the soft hyphen (U+00AD), and BOM, ZWSP, ZWNJ,
608       WJ, and similar characters, plus bidirectional controls.
609
610       "\p{Alpha}" now matches the same characters as "\p{Alphabetic}". Before
611       5.12, Perl's definition included a number of things that aren't really
612       alpha (all marks) while omitting many that were. The definitions of
613       "\p{Alnum}" and "\p{Word}" depend on Alpha's definition and have
614       changed accordingly.
615
616       "\p{Word}" no longer incorrectly matches non-word characters such as
617       fractions.
618
619       "\p{Print}" no longer matches the line control characters: Tab, LF, CR,
620       FF, VT, and NEL. This brings it in line with standards and the
621       documentation.
622
623       "\p{XDigit}" now matches the same characters as "\p{Hex_Digit}". This
624       means that in addition to the characters it currently matches,
625       "[A-Fa-f0-9]", it will also match the 22 fullwidth equivalents, for
626       example U+FF10: FULLWIDTH DIGIT ZERO.
627
628       The Numeric type property has been extended to include the Unihan
629       characters.
630
631       There is a new Perl extension, the 'Present_In', or simply 'In',
632       property. This is an extension of the Unicode Age property, but
633       "\p{In=5.0}" matches any code point whose usage has been determined as
634       of Unicode version 5.0. The "\p{Age=5.0}" only matches code points
635       added in precisely version 5.0.
636
637       A number of properties now have the correct values for unassigned code
638       points. The affected properties are Bidi_Class, East_Asian_Width,
639       Joining_Type, Decomposition_Type, Hangul_Syllable_Type, Numeric_Type,
640       and Line_Break.
641
642       The Default_Ignorable_Code_Point, ID_Continue, and ID_Start properties
643       are now up to date with current Unicode definitions.
644
645       Earlier versions of Perl erroneously exposed certain properties that
646       are supposed to be Unicode internal-only.  Use of these in regular
647       expressions will now generate, if enabled, a deprecation warning
648       message.  The properties are: Other_Alphabetic,
649       Other_Default_Ignorable_Code_Point, Other_Grapheme_Extend,
650       Other_ID_Continue, Other_ID_Start, Other_Lowercase, Other_Math, and
651       Other_Uppercase.
652
653       It is now possible to change which Unicode properties Perl understands
654       on a per-installation basis. As mentioned above, certain properties are
655       turned off by default.  These include all the Unihan properties (which
656       should be accessible via the CPAN module Unicode::Unihan) and any
657       deprecated or Unicode internal-only property that Perl has never
658       exposed.
659
660       The generated files in the "lib/unicore/To" directory are now more
661       clearly marked as being stable, directly usable by applications.  New
662       hash entries in them give the format of the normal entries, which
663       allows for easier machine parsing. Perl can generate files in this
664       directory for any property, though most are suppressed.  You can find
665       instructions for changing which are written in perluniprops.
666

Modules and Pragmata

668   New Modules and Pragmata
669       "autodie"
670           "autodie" is a new lexically-scoped alternative for the "Fatal"
671           module.  The bundled version is 2.06_01. Note that in this release,
672           using a string eval when "autodie" is in effect can cause the
673           autodie behaviour to leak into the surrounding scope. See "BUGS" in
674           autodie for more details.
675
676           Version 2.06_01 has been added to the Perl core.
677
678       "Compress::Raw::Bzip2"
679           Version 2.024 has been added to the Perl core.
680
681       "overloading"
682           "overloading" allows you to lexically disable or enable overloading
683           for some or all operations.
684
685           Version 0.001 has been added to the Perl core.
686
687       "parent"
688           "parent" establishes an ISA relationship with base classes at
689           compile time. It provides the key feature of "base" without further
690           unwanted behaviors.
691
692           Version 0.223 has been added to the Perl core.
693
694       "Parse::CPAN::Meta"
695           Version 1.40 has been added to the Perl core.
696
697       "VMS::DCLsym"
698           Version 1.03 has been added to the Perl core.
699
700       "VMS::Stdio"
701           Version 2.4 has been added to the Perl core.
702
703       "XS::APItest::KeywordRPN"
704           Version 0.003 has been added to the Perl core.
705
706   Updated Pragmata
707       "base"
708           Upgraded from version 2.13 to 2.15.
709
710       "bignum"
711           Upgraded from version 0.22 to 0.23.
712
713       "charnames"
714           "charnames" now contains the Unicode NameAliases.txt database file.
715           This has the effect of adding some extra "\N" character names that
716           formerly wouldn't have been recognised; for example, "\N{LATIN
717           CAPITAL LETTER GHA}".
718
719           Upgraded from version 1.06 to 1.07.
720
721       "constant"
722           Upgraded from version 1.13 to 1.20.
723
724       "diagnostics"
725           "diagnostics" now supports %.0f formatting internally.
726
727           "diagnostics" no longer suppresses "Use of uninitialized value in
728           range (or flip)" warnings. [perl #71204]
729
730           Upgraded from version 1.17 to 1.19.
731
732       "feature"
733           In "feature", the meaning of the ":5.10" and ":5.10.X" feature
734           bundles has changed slightly. The last component, if any (i.e. "X")
735           is simply ignored.  This is predicated on the assumption that new
736           features will not, in general, be added to maintenance releases. So
737           ":5.10" and ":5.10.X" have identical effect. This is a change to
738           the behaviour documented for 5.10.0.
739
740           "feature" now includes the "unicode_strings" feature:
741
742               use feature "unicode_strings";
743
744           This pragma turns on Unicode semantics for the case-changing
745           operations ("uc", "lc", "ucfirst", "lcfirst") on strings that don't
746           have the internal UTF-8 flag set, but that contain single-byte
747           characters between 128 and 255.
748
749           Upgraded from version 1.11 to 1.16.
750
751       "less"
752           "less" now includes the "stash_name" method to allow subclasses of
753           "less" to pick where in %^H to store their stash.
754
755           Upgraded from version 0.02 to 0.03.
756
757       "lib"
758           Upgraded from version 0.5565 to 0.62.
759
760       "mro"
761           "mro" is now implemented as an XS extension. The documented
762           interface has not changed. Code relying on the implementation
763           detail that some "mro::" methods happened to be available at all
764           times gets to "keep both pieces".
765
766           Upgraded from version 1.00 to 1.02.
767
768       "overload"
769           "overload" now allow overloading of 'qr'.
770
771           Upgraded from version 1.06 to 1.10.
772
773       "threads"
774           Upgraded from version 1.67 to 1.75.
775
776       "threads::shared"
777           Upgraded from version 1.14 to 1.32.
778
779       "version"
780           "version" now has support for "Version number formats" as described
781           earlier in this document and in its own documentation.
782
783           Upgraded from version 0.74 to 0.82.
784
785       "warnings"
786           "warnings" has a new warnings::fatal_enabled() function.  It also
787           includes a new "illegalproto" warning category. See also "New or
788           Changed Diagnostics" for this change.
789
790           Upgraded from version 1.06 to 1.09.
791
792   Updated Modules
793       "Archive::Extract"
794           Upgraded from version 0.24 to 0.38.
795
796       "Archive::Tar"
797           Upgraded from version 1.38 to 1.54.
798
799       "Attribute::Handlers"
800           Upgraded from version 0.79 to 0.87.
801
802       "AutoLoader"
803           Upgraded from version 5.63 to 5.70.
804
805       "B::Concise"
806           Upgraded from version 0.74 to 0.78.
807
808       "B::Debug"
809           Upgraded from version 1.05 to 1.12.
810
811       "B::Deparse"
812           Upgraded from version 0.83 to 0.96.
813
814       "B::Lint"
815           Upgraded from version 1.09 to 1.11_01.
816
817       "CGI"
818           Upgraded from version 3.29 to 3.48.
819
820       "Class::ISA"
821           Upgraded from version 0.33 to 0.36.
822
823           NOTE: "Class::ISA" is deprecated and may be removed from a future
824           version of Perl.
825
826       "Compress::Raw::Zlib"
827           Upgraded from version 2.008 to 2.024.
828
829       "CPAN"
830           Upgraded from version 1.9205 to 1.94_56.
831
832       "CPANPLUS"
833           Upgraded from version 0.84 to 0.90.
834
835       "CPANPLUS::Dist::Build"
836           Upgraded from version 0.06_02 to 0.46.
837
838       "Data::Dumper"
839           Upgraded from version 2.121_14 to 2.125.
840
841       "DB_File"
842           Upgraded from version 1.816_1 to 1.820.
843
844       "Devel::PPPort"
845           Upgraded from version 3.13 to 3.19.
846
847       "Digest"
848           Upgraded from version 1.15 to 1.16.
849
850       "Digest::MD5"
851           Upgraded from version 2.36_01 to 2.39.
852
853       "Digest::SHA"
854           Upgraded from version 5.45 to 5.47.
855
856       "Encode"
857           Upgraded from version 2.23 to 2.39.
858
859       "Exporter"
860           Upgraded from version 5.62 to 5.64_01.
861
862       "ExtUtils::CBuilder"
863           Upgraded from version 0.21 to 0.27.
864
865       "ExtUtils::Command"
866           Upgraded from version 1.13 to 1.16.
867
868       "ExtUtils::Constant"
869           Upgraded from version 0.2 to 0.22.
870
871       "ExtUtils::Install"
872           Upgraded from version 1.44 to 1.55.
873
874       "ExtUtils::MakeMaker"
875           Upgraded from version 6.42 to 6.56.
876
877       "ExtUtils::Manifest"
878           Upgraded from version 1.51_01 to 1.57.
879
880       "ExtUtils::ParseXS"
881           Upgraded from version 2.18_02 to 2.21.
882
883       "File::Fetch"
884           Upgraded from version 0.14 to 0.24.
885
886       "File::Path"
887           Upgraded from version 2.04 to 2.08_01.
888
889       "File::Temp"
890           Upgraded from version 0.18 to 0.22.
891
892       "Filter::Simple"
893           Upgraded from version 0.82 to 0.84.
894
895       "Filter::Util::Call"
896           Upgraded from version 1.07 to 1.08.
897
898       "Getopt::Long"
899           Upgraded from version 2.37 to 2.38.
900
901       "IO"
902           Upgraded from version 1.23_01 to 1.25_02.
903
904       "IO::Zlib"
905           Upgraded from version 1.07 to 1.10.
906
907       "IPC::Cmd"
908           Upgraded from version 0.40_1 to 0.54.
909
910       "IPC::SysV"
911           Upgraded from version 1.05 to 2.01.
912
913       "Locale::Maketext"
914           Upgraded from version 1.12 to 1.14.
915
916       "Locale::Maketext::Simple"
917           Upgraded from version 0.18 to 0.21.
918
919       "Log::Message"
920           Upgraded from version 0.01 to 0.02.
921
922       "Log::Message::Simple"
923           Upgraded from version 0.04 to 0.06.
924
925       "Math::BigInt"
926           Upgraded from version 1.88 to 1.89_01.
927
928       "Math::BigInt::FastCalc"
929           Upgraded from version 0.16 to 0.19.
930
931       "Math::BigRat"
932           Upgraded from version 0.21 to 0.24.
933
934       "Math::Complex"
935           Upgraded from version 1.37 to 1.56.
936
937       "Memoize"
938           Upgraded from version 1.01_02 to 1.01_03.
939
940       "MIME::Base64"
941           Upgraded from version 3.07_01 to 3.08.
942
943       "Module::Build"
944           Upgraded from version 0.2808_01 to 0.3603.
945
946       "Module::CoreList"
947           Upgraded from version 2.12 to 2.29.
948
949       "Module::Load"
950           Upgraded from version 0.12 to 0.16.
951
952       "Module::Load::Conditional"
953           Upgraded from version 0.22 to 0.34.
954
955       "Module::Loaded"
956           Upgraded from version 0.01 to 0.06.
957
958       "Module::Pluggable"
959           Upgraded from version 3.6 to 3.9.
960
961       "Net::Ping"
962           Upgraded from version 2.33 to 2.36.
963
964       "NEXT"
965           Upgraded from version 0.60_01 to 0.64.
966
967       "Object::Accessor"
968           Upgraded from version 0.32 to 0.36.
969
970       "Package::Constants"
971           Upgraded from version 0.01 to 0.02.
972
973       "PerlIO"
974           Upgraded from version 1.04 to 1.06.
975
976       "Pod::Parser"
977           Upgraded from version 1.35 to 1.37.
978
979       "Pod::Perldoc"
980           Upgraded from version 3.14_02 to 3.15_02.
981
982       "Pod::Plainer"
983           Upgraded from version 0.01 to 1.02.
984
985           NOTE: "Pod::Plainer" is deprecated and may be removed from a future
986           version of Perl.
987
988       "Pod::Simple"
989           Upgraded from version 3.05 to 3.13.
990
991       "Safe"
992           Upgraded from version 2.12 to 2.22.
993
994       "SelfLoader"
995           Upgraded from version 1.11 to 1.17.
996
997       "Storable"
998           Upgraded from version 2.18 to 2.22.
999
1000       "Switch"
1001           Upgraded from version 2.13 to 2.16.
1002
1003           NOTE: "Switch" is deprecated and may be removed from a future
1004           version of Perl.
1005
1006       "Sys::Syslog"
1007           Upgraded from version 0.22 to 0.27.
1008
1009       "Term::ANSIColor"
1010           Upgraded from version 1.12 to 2.02.
1011
1012       "Term::UI"
1013           Upgraded from version 0.18 to 0.20.
1014
1015       "Test"
1016           Upgraded from version 1.25 to 1.25_02.
1017
1018       "Test::Harness"
1019           Upgraded from version 2.64 to 3.17.
1020
1021       "Test::Simple"
1022           Upgraded from version 0.72 to 0.94.
1023
1024       "Text::Balanced"
1025           Upgraded from version 2.0.0 to 2.02.
1026
1027       "Text::ParseWords"
1028           Upgraded from version 3.26 to 3.27.
1029
1030       "Text::Soundex"
1031           Upgraded from version 3.03 to 3.03_01.
1032
1033       "Thread::Queue"
1034           Upgraded from version 2.00 to 2.11.
1035
1036       "Thread::Semaphore"
1037           Upgraded from version 2.01 to 2.09.
1038
1039       "Tie::RefHash"
1040           Upgraded from version 1.37 to 1.38.
1041
1042       "Time::HiRes"
1043           Upgraded from version 1.9711 to 1.9719.
1044
1045       "Time::Local"
1046           Upgraded from version 1.18 to 1.1901_01.
1047
1048       "Time::Piece"
1049           Upgraded from version 1.12 to 1.15.
1050
1051       "Unicode::Collate"
1052           Upgraded from version 0.52 to 0.52_01.
1053
1054       "Unicode::Normalize"
1055           Upgraded from version 1.02 to 1.03.
1056
1057       "Win32"
1058           Upgraded from version 0.34 to 0.39.
1059
1060       "Win32API::File"
1061           Upgraded from version 0.1001_01 to 0.1101.
1062
1063       "XSLoader"
1064           Upgraded from version 0.08 to 0.10.
1065
1066   Removed Modules and Pragmata
1067       "attrs"
1068           Removed from the Perl core.  Prior version was 1.02.
1069
1070       "CPAN::API::HOWTO"
1071           Removed from the Perl core.  Prior version was 'undef'.
1072
1073       "CPAN::DeferedCode"
1074           Removed from the Perl core.  Prior version was 5.50.
1075
1076       "CPANPLUS::inc"
1077           Removed from the Perl core.  Prior version was 'undef'.
1078
1079       "DCLsym"
1080           Removed from the Perl core.  Prior version was 1.03.
1081
1082       "ExtUtils::MakeMaker::bytes"
1083           Removed from the Perl core.  Prior version was 6.42.
1084
1085       "ExtUtils::MakeMaker::vmsish"
1086           Removed from the Perl core.  Prior version was 6.42.
1087
1088       "Stdio"
1089           Removed from the Perl core.  Prior version was 2.3.
1090
1091       "Test::Harness::Assert"
1092           Removed from the Perl core.  Prior version was 0.02.
1093
1094       "Test::Harness::Iterator"
1095           Removed from the Perl core.  Prior version was 0.02.
1096
1097       "Test::Harness::Point"
1098           Removed from the Perl core.  Prior version was 0.01.
1099
1100       "Test::Harness::Results"
1101           Removed from the Perl core.  Prior version was 0.01.
1102
1103       "Test::Harness::Straps"
1104           Removed from the Perl core.  Prior version was 0.26_01.
1105
1106       "Test::Harness::Util"
1107           Removed from the Perl core.  Prior version was 0.01.
1108
1109       "XSSymSet"
1110           Removed from the Perl core.  Prior version was 1.1.
1111
1112   Deprecated Modules and Pragmata
1113       See "Deprecated Modules" above.
1114

Documentation

1116   New Documentation
1117       •   perlhaiku contains instructions on how to build perl for the Haiku
1118           platform.
1119
1120       •   perlmroapi describes the new interface for pluggable Method
1121           Resolution Orders.
1122
1123       •   perlperf, by Richard Foley, provides an introduction to the use of
1124           performance and optimization techniques which can be used with
1125           particular reference to perl programs.
1126
1127       •   perlrepository describes how to access the perl source using the
1128           git version control system.
1129
1130       •   perlpolicy extends the "Social contract about contributed modules"
1131           into the beginnings of a document on Perl porting policies.
1132
1133   Changes to Existing Documentation
1134       •   The various large Changes* files (which listed every change made to
1135           perl over the last 18 years) have been removed, and replaced by a
1136           small file, also called Changes, which just explains how that same
1137           information may be extracted from the git version control system.
1138
1139Porting/patching.pod has been deleted, as it mainly described
1140           interacting with the old Perforce-based repository, which is now
1141           obsolete.  Information still relevant has been moved to
1142           perlrepository.
1143
1144       •   The syntax "unless (EXPR) BLOCK else BLOCK" is now documented as
1145           valid, as is the syntax "unless (EXPR) BLOCK elsif (EXPR) BLOCK ...
1146           else BLOCK", although actually using the latter may not be the best
1147           idea for the readability of your source code.
1148
1149       •   Documented -X overloading.
1150
1151       •   Documented that when() treats specially most of the filetest
1152           operators
1153
1154       •   Documented "when" as a syntax modifier.
1155
1156       •   Eliminated "Old Perl threads tutorial", which described 5005
1157           threads.
1158
1159           pod/perlthrtut.pod is the same material reworked for ithreads.
1160
1161       •   Correct previous documentation: v-strings are not deprecated
1162
1163           With version objects, we need them to use MODULE VERSION syntax.
1164           This patch removes the deprecation notice.
1165
1166       •   Security contact information is now part of perlsec.
1167
1168       •   A significant fraction of the core documentation has been updated
1169           to clarify the behavior of Perl's Unicode handling.
1170
1171           Much of the remaining core documentation has been reviewed and
1172           edited for clarity, consistent use of language, and to fix the
1173           spelling of Tom Christiansen's name.
1174
1175       •   The Pod specification (perlpodspec) has been updated to bring the
1176           specification in line with modern usage already supported by most
1177           Pod systems. A parameter string may now follow the format name in a
1178           "begin/end" region. Links to URIs with a text description are now
1179           allowed. The usage of "L<"section">" has been marked as deprecated.
1180
1181       •   if.pm has been documented in "use" in perlfunc as a means to get
1182           conditional loading of modules despite the implicit BEGIN block
1183           around "use".
1184
1185       •   The documentation for $1 in perlvar.pod has been clarified.
1186
1187       •   "\N{U+code point}" is now documented.
1188

Selected Performance Enhancements

1190       •   A new internal cache means that isa() will often be faster.
1191
1192       •   The implementation of "C3" Method Resolution Order has been
1193           optimised - linearisation for classes with single inheritance is
1194           40% faster. Performance for multiple inheritance is unchanged.
1195
1196       •   Under "use locale", the locale-relevant information is now cached
1197           on read-only values, such as the list returned by "keys %hash".
1198           This makes operations such as "sort keys %hash" in the scope of
1199           "use locale" much faster.
1200
1201       •   Empty "DESTROY" methods are no longer called.
1202
1203       •   Perl_sv_utf8_upgrade() is now faster.
1204
1205       •   "keys" on empty hash is now faster.
1206
1207       •   "if (%foo)" has been optimized to be faster than "if (keys %foo)".
1208
1209       •   The string repetition operator ("$str x $num") is now several times
1210           faster when $str has length one or $num is large.
1211
1212       •   Reversing an array to itself (as in "@a = reverse @a") in void
1213           context now happens in-place and is several orders of magnitude
1214           faster than it used to be. It will also preserve non-existent
1215           elements whenever possible, i.e. for non magical arrays or tied
1216           arrays with "EXISTS" and "DELETE" methods.
1217

Installation and Configuration Improvements

1219       •   perlapi, perlintern, perlmodlib and perltoc are now all generated
1220           at build time, rather than being shipped as part of the release.
1221
1222       •   If "vendorlib" and "vendorarch" are the same, then they are only
1223           added to @INC once.
1224
1225       •   $Config{usedevel} and the C-level "PERL_USE_DEVEL" are now defined
1226           if perl is built with  "-Dusedevel".
1227
1228Configure will enable use of "-fstack-protector", to provide
1229           protection against stack-smashing attacks, if the compiler supports
1230           it.
1231
1232Configure will now determine the correct prototypes for re-entrant
1233           functions and for "gconvert" if you are using a C++ compiler rather
1234           than a C compiler.
1235
1236       •   On Unix, if you build from a tree containing a git repository, the
1237           configuration process will note the commit hash you have checked
1238           out, for display in the output of "perl -v" and "perl -V". Unpushed
1239           local commits are automatically added to the list of local patches
1240           displayed by "perl -V".
1241
1242       •   Perl now supports SystemTap's "dtrace" compatibility layer and an
1243           issue with linking "miniperl" has been fixed in the process.
1244
1245       •   perldoc now uses "less -R" instead of "less" for improved behaviour
1246           in the face of "groff"'s new usage of ANSI escape codes.
1247
1248       •   "perl -V" now reports use of the compile-time options
1249           "USE_PERL_ATOF" and "USE_ATTRIBUTES_FOR_PERLIO".
1250
1251       •   As part of the flattening of ext, all extensions on all platforms
1252           are built by make_ext.pl. This replaces the Unix-specific
1253           ext/util/make_ext, VMS-specific make_ext.com and Win32-specific
1254           win32/buildext.pl.
1255

Internal Changes

1257       Each release of Perl sees numerous internal changes which shouldn't
1258       affect day to day usage but may still be notable for developers working
1259       with Perl's source code.
1260
1261       •   The J.R.R. Tolkien quotes at the head of C source file have been
1262           checked and proper citations added, thanks to a patch from Tom
1263           Christiansen.
1264
1265       •   The internal structure of the dual-life modules traditionally found
1266           in the lib/ and ext/ directories in the perl source has changed
1267           significantly. Where possible, dual-lifed modules have been
1268           extracted from lib/ and ext/.
1269
1270           Dual-lifed modules maintained by Perl's developers as part of the
1271           Perl core now live in dist/.  Dual-lifed modules maintained
1272           primarily on CPAN now live in cpan/.  When reporting a bug in a
1273           module located under cpan/, please send your bug report directly to
1274           the module's bug tracker or author, rather than Perl's bug tracker.
1275
1276       •   "\N{...}" now compiles better, always forces UTF-8 internal
1277           representation
1278
1279           Perl's developers have fixed several problems with the recognition
1280           of "\N{...}" constructs.  As part of this, perl will store any
1281           scalar or regex containing "\N{name}" or "\N{U+code point}" in its
1282           definition in UTF-8 format. (This was true previously for all
1283           occurrences of "\N{name}" that did not use a custom translator, but
1284           now it's always true.)
1285
1286       •   Perl_magic_setmglob now knows about globs, fixing RT #71254.
1287
1288       •   "SVt_RV" no longer exists. RVs are now stored in IVs.
1289
1290       •   Perl_vcroak() now accepts a null first argument. In addition, a
1291           full audit was made of the "not NULL" compiler annotations, and
1292           those for several other internal functions were corrected.
1293
1294       •   New macros "dSAVEDERRNO", "dSAVE_ERRNO", "SAVE_ERRNO",
1295           "RESTORE_ERRNO" have been added to formalise the temporary saving
1296           of the "errno" variable.
1297
1298       •   The function "Perl_sv_insert_flags" has been added to augment
1299           "Perl_sv_insert".
1300
1301       •   The function Perl_newSV_type(type) has been added, equivalent to
1302           Perl_newSV() followed by Perl_sv_upgrade(type).
1303
1304       •   The function Perl_newSVpvn_flags() has been added, equivalent to
1305           Perl_newSVpvn() and then performing the action relevant to the
1306           flag.
1307
1308           Two flag bits are currently supported.
1309
1310           •   "SVf_UTF8" will call SvUTF8_on() for you. (Note that this does
1311               not convert a sequence of ISO 8859-1 characters to UTF-8). A
1312               wrapper, newSVpvn_utf8() is available for this.
1313
1314           •   "SVs_TEMP" now calls Perl_sv_2mortal() on the new SV.
1315
1316           There is also a wrapper that takes constant strings,
1317           newSVpvs_flags().
1318
1319       •   The function "Perl_croak_xs_usage" has been added as a wrapper to
1320           "Perl_croak".
1321
1322       •   Perl now exports the functions "PerlIO_find_layer" and
1323           "PerlIO_list_alloc".
1324
1325       •   "PL_na" has been exterminated from the core code, replaced by local
1326           STRLEN temporaries, or *_nolen() calls. Either approach is faster
1327           than "PL_na", which is a pointer dereference into the interpreter
1328           structure under ithreads, and a global variable otherwise.
1329
1330       •   Perl_mg_free() used to leave freed memory accessible via SvMAGIC()
1331           on the scalar. It now updates the linked list to remove each piece
1332           of magic as it is freed.
1333
1334       •   Under ithreads, the regex in "PL_reg_curpm" is now reference
1335           counted. This eliminates a lot of hackish workarounds to cope with
1336           it not being reference counted.
1337
1338       •   Perl_mg_magical() would sometimes incorrectly turn on SvRMAGICAL().
1339           This has been fixed.
1340
1341       •   The public IV and NV flags are now not set if the string value has
1342           trailing "garbage". This behaviour is consistent with not setting
1343           the public IV or NV flags if the value is out of range for the
1344           type.
1345
1346       •   Uses of "Nullav", "Nullcv", "Nullhv", "Nullop", "Nullsv" etc have
1347           been replaced by "NULL" in the core code, and non-dual-life
1348           modules, as "NULL" is clearer to those unfamiliar with the core
1349           code.
1350
1351       •   A macro MUTABLE_PTR(p) has been added, which on (non-pedantic) gcc
1352           will not cast away "const", returning a "void *". Macros
1353           MUTABLE_SV(av), MUTABLE_SV(cv) etc build on this, casting to "AV *"
1354           etc without casting away "const". This allows proper compile-time
1355           auditing of "const" correctness in the core, and helped picked up
1356           some errors (now fixed).
1357
1358       •   Macros mPUSHs() and mXPUSHs() have been added, for pushing SVs on
1359           the stack and mortalizing them.
1360
1361       •   Use of the private structure "mro_meta" has changed slightly.
1362           Nothing outside the core should be accessing this directly anyway.
1363
1364       •   A new tool, Porting/expand-macro.pl has been added, that allows you
1365           to view how a C preprocessor macro would be expanded when compiled.
1366           This is handy when trying to decode the macro hell that is the perl
1367           guts.
1368

Testing

1370   Testing improvements
1371       Parallel tests
1372           The core distribution can now run its regression tests in parallel
1373           on Unix-like platforms. Instead of running "make test", set
1374           "TEST_JOBS" in your environment to the number of tests to run in
1375           parallel, and run "make test_harness". On a Bourne-like shell, this
1376           can be done as
1377
1378               TEST_JOBS=3 make test_harness  # Run 3 tests in parallel
1379
1380           An environment variable is used, rather than parallel make itself,
1381           because TAP::Harness needs to be able to schedule individual non-
1382           conflicting test scripts itself, and there is no standard interface
1383           to "make" utilities to interact with their job schedulers.
1384
1385           Note that currently some test scripts may fail when run in parallel
1386           (most notably "ext/IO/t/io_dir.t"). If necessary run just the
1387           failing scripts again sequentially and see if the failures go away.
1388
1389       Test harness flexibility
1390           It's now possible to override "PERL5OPT" and friends in t/TEST
1391
1392       Test watchdog
1393           Several tests that have the potential to hang forever if they fail
1394           now incorporate a "watchdog" functionality that will kill them
1395           after a timeout, which helps ensure that "make test" and "make
1396           test_harness" run to completion automatically.
1397
1398   New Tests
1399       Perl's developers have added a number of new tests to the core.  In
1400       addition to the items listed below, many modules updated from CPAN
1401       incorporate new tests.
1402
1403       •   Significant cleanups to core tests to ensure that language and
1404           interpreter features are not used before they're tested.
1405
1406       •   "make test_porting" now runs a number of important pre-commit
1407           checks which might be of use to anyone working on the Perl core.
1408
1409t/porting/podcheck.t automatically checks the well-formedness of
1410           POD found in all .pl, .pm and .pod files in the MANIFEST, other
1411           than in dual-lifed modules which are primarily maintained outside
1412           the Perl core.
1413
1414t/porting/manifest.t now tests that all files listed in MANIFEST
1415           are present.
1416
1417t/op/while_readdir.t tests that a bare readdir in while loop sets
1418           $_.
1419
1420t/comp/retainedlines.t checks that the debugger can retain source
1421           lines from "eval".
1422
1423t/io/perlio_fail.t checks that bad layers fail.
1424
1425t/io/perlio_leaks.t checks that PerlIO layers are not leaking.
1426
1427t/io/perlio_open.t checks that certain special forms of open work.
1428
1429t/io/perlio.t includes general PerlIO tests.
1430
1431t/io/pvbm.t checks that there is no unexpected interaction between
1432           the internal types "PVBM" and "PVGV".
1433
1434t/mro/package_aliases.t checks that mro works properly in the
1435           presence of aliased packages.
1436
1437t/op/dbm.t tests "dbmopen" and "dbmclose".
1438
1439t/op/index_thr.t tests the interaction of "index" and threads.
1440
1441t/op/pat_thr.t tests the interaction of esoteric patterns and
1442           threads.
1443
1444t/op/qr_gc.t tests that "qr" doesn't leak.
1445
1446t/op/reg_email_thr.t tests the interaction of regex recursion and
1447           threads.
1448
1449t/op/regexp_qr_embed_thr.t tests the interaction of patterns with
1450           embedded "qr//" and threads.
1451
1452t/op/regexp_unicode_prop.t tests Unicode properties in regular
1453           expressions.
1454
1455t/op/regexp_unicode_prop_thr.t tests the interaction of Unicode
1456           properties and threads.
1457
1458t/op/reg_nc_tie.t tests the tied methods of
1459           "Tie::Hash::NamedCapture".
1460
1461t/op/reg_posixcc.t checks that POSIX character classes behave
1462           consistently.
1463
1464t/op/re.t checks that exportable "re" functions in universal.c
1465           work.
1466
1467t/op/setpgrpstack.t checks that "setpgrp" works.
1468
1469t/op/substr_thr.t tests the interaction of "substr" and threads.
1470
1471t/op/upgrade.t checks that upgrading and assigning scalars works.
1472
1473t/uni/lex_utf8.t checks that Unicode in the lexer works.
1474
1475t/uni/tie.t checks that Unicode and "tie" work.
1476
1477t/comp/final_line_num.t tests whether line numbers are correct at
1478           EOF
1479
1480t/comp/form_scope.t tests format scoping.
1481
1482t/comp/line_debug.t tests whether "@{"_<$file"}" works.
1483
1484t/op/filetest_t.t tests if -t file test works.
1485
1486t/op/qr.t tests "qr".
1487
1488t/op/utf8cache.t tests malfunctions of the utf8 cache.
1489
1490t/re/uniprops.t test unicodes "\p{}" regex constructs.
1491
1492t/op/filehandle.t tests some suitably portable filetest operators
1493           to check that they work as expected, particularly in the light of
1494           some internal changes made in how filehandles are blessed.
1495
1496t/op/time_loop.t tests that unix times greater than "2**63", which
1497           can now be handed to "gmtime" and "localtime", do not cause an
1498           internal overflow or an excessively long loop.
1499

New or Changed Diagnostics

1501   New Diagnostics
1502       •   SV allocation tracing has been added to the diagnostics enabled by
1503           "-Dm".  The tracing can alternatively output via the "PERL_MEM_LOG"
1504           mechanism, if that was enabled when the perl binary was compiled.
1505
1506       •   Smartmatch resolution tracing has been added as a new diagnostic.
1507           Use "-DM" to enable it.
1508
1509       •   A new debugging flag "-DB" now dumps subroutine definitions,
1510           leaving "-Dx" for its original purpose of dumping syntax trees.
1511
1512       •   Perl 5.12 provides a number of new diagnostic messages to help you
1513           write better code.  See perldiag for details of these new messages.
1514
1515           •   "Bad plugin affecting keyword '%s'"
1516
1517           •   "gmtime(%.0f) too large"
1518
1519           •   "Lexing code attempted to stuff non-Latin-1 character into
1520               Latin-1 input"
1521
1522           •   "Lexing code internal error (%s)"
1523
1524           •   "localtime(%.0f) too large"
1525
1526           •   "Overloaded dereference did not return a reference"
1527
1528           •   "Overloaded qr did not return a REGEXP"
1529
1530           •   "Perl_pmflag() is deprecated, and will be removed from the XS
1531               API"
1532
1533           •   "lvalue attribute ignored after the subroutine has been
1534               defined"
1535
1536               This new warning is issued when one attempts to mark a
1537               subroutine as lvalue after it has been defined.
1538
1539           •   Perl now warns you if "++" or "--" are unable to change the
1540               value because it's beyond the limit of representation.
1541
1542               This uses a new warnings category: "imprecision".
1543
1544           •   "lc", "uc", "lcfirst", and "ucfirst" warn when passed undef.
1545
1546           •   "Show constant in "Useless use of a constant in void context""
1547
1548           •   "Prototype after '%s'"
1549
1550           •   "panic: sv_chop %s"
1551
1552               This new fatal error occurs when the C routine Perl_sv_chop()
1553               was passed a position that is not within the scalar's string
1554               buffer. This could be caused by buggy XS code, and at this
1555               point recovery is not possible.
1556
1557           •   The fatal error "Malformed UTF-8 returned by \N" is now
1558               produced if the "charnames" handler returns malformed UTF-8.
1559
1560           •   If an unresolved named character or sequence was encountered
1561               when compiling a regex pattern then the fatal error "\N{NAME}
1562               must be resolved by the lexer" is now produced. This can
1563               happen, for example, when using a single-quotish context like
1564               "$re = '\N{SPACE}'; /$re/;". See perldiag for more examples of
1565               how the lexer can get bypassed.
1566
1567           •   "Invalid hexadecimal number in \N{U+...}" is a new fatal error
1568               triggered when the character constant represented by "..." is
1569               not a valid hexadecimal number.
1570
1571           •   The new meaning of "\N" as "[^\n]" is not valid in a bracketed
1572               character class, just like "." in a character class loses its
1573               special meaning, and will cause the fatal error "\N in a
1574               character class must be a named character: \N{...}".
1575
1576           •   The rules on what is legal for the "..." in "\N{...}" have been
1577               tightened up so that unless the "..." begins with an alphabetic
1578               character and continues with a combination of alphanumerics,
1579               dashes, spaces, parentheses or colons then the warning
1580               "Deprecated character(s) in \N{...} starting at '%s'" is now
1581               issued.
1582
1583           •   The warning "Using just the first characters returned by \N{}"
1584               will be issued if the "charnames" handler returns a sequence of
1585               characters which exceeds the limit of the number of characters
1586               that can be used. The message will indicate which characters
1587               were used and which were discarded.
1588
1589   Changed Diagnostics
1590       A number of existing diagnostic messages have been improved or
1591       corrected:
1592
1593       •   A new warning category "illegalproto" allows finer-grained control
1594           of warnings around function prototypes.
1595
1596           The two warnings:
1597
1598           "Illegal character in prototype for %s : %s"
1599           "Prototype after '%c' for %s : %s"
1600
1601           have been moved from the "syntax" top-level warnings category into
1602           a new first-level category, "illegalproto". These two warnings are
1603           currently the only ones emitted during parsing of an
1604           invalid/illegal prototype, so one can now use
1605
1606             no warnings 'illegalproto';
1607
1608           to suppress only those, but not other syntax-related warnings.
1609           Warnings where prototypes are changed, ignored, or not met are
1610           still in the "prototype" category as before.
1611
1612       •   "Deep recursion on subroutine "%s""
1613
1614           It is now possible to change the depth threshold for this warning
1615           from the default of 100, by recompiling the perl binary, setting
1616           the C pre-processor macro "PERL_SUB_DEPTH_WARN" to the desired
1617           value.
1618
1619       •   "Illegal character in prototype" warning is now more precise when
1620           reporting illegal characters after _
1621
1622       •   mro merging error messages are now very similar to those produced
1623           by Algorithm::C3.
1624
1625       •   Amelioration of the error message "Unrecognized character %s in
1626           column %d"
1627
1628           Changes the error message to "Unrecognized character %s; marked by
1629           <-- HERE after %s<-- HERE near column %d". This should make it a
1630           little simpler to spot and correct the suspicious character.
1631
1632       •   Perl now explicitly points to $. when it causes an uninitialized
1633           warning for ranges in scalar context.
1634
1635       •   "split" now warns when called in void context.
1636
1637       •   "printf"-style functions called with too few arguments will now
1638           issue the warning "Missing argument in %s" [perl #71000]
1639
1640       •   Perl now properly returns a syntax error instead of segfaulting if
1641           "each", "keys", or "values" is used without an argument.
1642
1643       •   tell() now fails properly if called without an argument and when no
1644           previous file was read.
1645
1646           tell() now returns -1, and sets errno to "EBADF", thus restoring
1647           the 5.8.x behaviour.
1648
1649       •   "overload" no longer implicitly unsets fallback on repeated 'use
1650           overload' lines.
1651
1652POSIX::strftime() can now handle Unicode characters in the format
1653           string.
1654
1655       •   The "syntax" category was removed from 5 warnings that should only
1656           be in "deprecated".
1657
1658       •   Three fatal "pack"/"unpack" error messages have been normalized to
1659           "panic: %s"
1660
1661       •   "Unicode character is illegal" has been rephrased to be more
1662           accurate
1663
1664           It now reads "Unicode non-character is illegal in interchange" and
1665           the perldiag documentation has been expanded a bit.
1666
1667       •   Currently, all but the first of the several characters that the
1668           "charnames" handler may return are discarded when used in a regular
1669           expression pattern bracketed character class. If this happens then
1670           the warning "Using just the first character returned by \N{} in
1671           character class" will be issued.
1672
1673       •   The warning "Missing right brace on \N{} or unescaped left brace
1674           after \N.  Assuming the latter" will be issued if Perl encounters a
1675           "\N{" but doesn't find a matching "}". In this case Perl doesn't
1676           know if it was mistakenly omitted, or if "match non-newline"
1677           followed by "match a "{"" was desired.  It assumes the latter
1678           because that is actually a valid interpretation as written, unlike
1679           the other case.  If you meant the former, you need to add the
1680           matching right brace.  If you did mean the latter, you can silence
1681           this warning by writing instead "\N\{".
1682
1683       •   "gmtime" and "localtime" called with numbers smaller than they can
1684           reliably handle will now issue the warnings "gmtime(%.0f) too
1685           small" and "localtime(%.0f) too small".
1686
1687       The following diagnostic messages have been removed:
1688
1689       •   "Runaway format"
1690
1691       •   "Can't locate package %s for the parents of %s"
1692
1693           In general this warning it only got produced in conjunction with
1694           other warnings, and removing it allowed an ISA lookup optimisation
1695           to be added.
1696
1697       •   "v-string in use/require is non-portable"
1698

Utility Changes

1700h2ph now looks in "include-fixed" too, which is a recent addition
1701           to gcc's search path.
1702
1703h2xs no longer incorrectly treats enum values like macros.  It also
1704           now handles C++ style comments ("//") properly in enums.
1705
1706perl5db.pl now supports "LVALUE" subroutines.  Additionally, the
1707           debugger now correctly handles proxy constant subroutines, and
1708           subroutine stubs.
1709
1710perlbug now uses %Module::CoreList::bug_tracker to print out
1711           upstream bug tracker URLs.  If a user identifies a particular
1712           module as the topic of their bug report and we're able to divine
1713           the URL for its upstream bug tracker, perlbug now provide a message
1714           to the user explaining that the core copies the CPAN version
1715           directly, and provide the URL for reporting the bug directly to the
1716           upstream author.
1717
1718           perlbug no longer reports "Message sent" when it hasn't actually
1719           sent the message
1720
1721perlthanks is a new utility for sending non-bug-reports to the
1722           authors and maintainers of Perl. Getting nothing but bug reports
1723           can become a bit demoralising. If Perl 5.12 works well for you,
1724           please try out perlthanks. It will make the developers smile.
1725
1726       •   Perl's developers have fixed bugs in a2p having to do with the
1727           match() operator in list context.  Additionally, a2p no longer
1728           generates code that uses the $[ variable.
1729

Selected Bug Fixes

1731       •   U+0FFFF is now a legal character in regular expressions.
1732
1733       •   pp_qr now always returns a new regexp SV. Resolves RT #69852.
1734
1735           Instead of returning a(nother) reference to the (pre-compiled)
1736           regexp in the optree, use reg_temp_copy() to create a copy of it,
1737           and return a reference to that. This resolves issues about
1738           Regexp::DESTROY not being called in a timely fashion (the original
1739           bug tracked by RT #69852), as well as bugs related to blessing
1740           regexps, and of assigning to regexps, as described in
1741           correspondence added to the ticket.
1742
1743           It transpires that we also need to undo the SvPVX() sharing when
1744           ithreads cloning a Regexp SV, because mother_re is set to NULL,
1745           instead of a cloned copy of the mother_re. This change might fix
1746           bugs with regexps and threads in certain other situations, but as
1747           yet neither tests nor bug reports have indicated any problems, so
1748           it might not actually be an edge case that it's possible to reach.
1749
1750       •   Several compilation errors and segfaults when perl was built with
1751           "-Dmad" were fixed.
1752
1753       •   Fixes for lexer API changes in 5.11.2 which broke NYTProf's savesrc
1754           option.
1755
1756       •   "-t" should only return TRUE for file handles connected to a TTY
1757
1758           The Microsoft C version of isatty() returns TRUE for all character
1759           mode devices, including the /dev/null-style "nul" device and
1760           printers like "lpt1".
1761
1762       •   Fixed a regression caused by commit fafafbaf which caused a panic
1763           during parameter passing [perl #70171]
1764
1765       •   On systems which in-place edits without backup files, -i'*' now
1766           works as the documentation says it does [perl #70802]
1767
1768       •   Saving and restoring magic flags no longer loses readonly flag.
1769
1770       •   The malformed syntax "grep EXPR LIST" (note the missing comma) no
1771           longer causes abrupt and total failure.
1772
1773       •   Regular expressions compiled with "qr{}" literals properly set "$'"
1774           when matching again.
1775
1776       •   Using named subroutines with "sort" should no longer lead to bus
1777           errors [perl #71076]
1778
1779       •   Numerous bugfixes catch small issues caused by the recently-added
1780           Lexer API.
1781
1782       •   Smart match against @_ sometimes gave false negatives. [perl
1783           #71078]
1784
1785       •   $@ may now be assigned a read-only value (without error or busting
1786           the stack).
1787
1788       •   "sort" called recursively from within an active comparison
1789           subroutine no longer causes a bus error if run multiple times.
1790           [perl #71076]
1791
1792       •   Tie::Hash::NamedCapture::* will not abort if passed bad input (RT
1793           #71828)
1794
1795       •   @_ and $_ no longer leak under threads (RT #34342 and #41138, also
1796           #70602, #70974)
1797
1798       •   "-I" on shebang line now adds directories in front of @INC as
1799           documented, and as does "-I" when specified on the command-line.
1800
1801       •   "kill" is now fatal when called on non-numeric process identifiers.
1802           Previously, an "undef" process identifier would be interpreted as a
1803           request to kill process 0, which would terminate the current
1804           process group on POSIX systems. Since process identifiers are
1805           always integers, killing a non-numeric process is now fatal.
1806
1807       •   5.10.0 inadvertently disabled an optimisation, which caused a
1808           measurable performance drop in list assignment, such as is often
1809           used to assign function parameters from @_. The optimisation has
1810           been re-instated, and the performance regression fixed. (This fix
1811           is also present in 5.10.1)
1812
1813       •   Fixed memory leak on "while (1) { map 1, 1 }" [RT #53038].
1814
1815       •   Some potential coredumps in PerlIO fixed [RT #57322,54828].
1816
1817       •   The debugger now works with lvalue subroutines.
1818
1819       •   The debugger's "m" command was broken on modules that defined
1820           constants [RT #61222].
1821
1822       •   "crypt" and string complement could return tainted values for
1823           untainted arguments [RT #59998].
1824
1825       •   The "-i".suffix command-line switch now recreates the file using
1826           restricted permissions, before changing its mode to match the
1827           original file. This eliminates a potential race condition [RT
1828           #60904].
1829
1830       •   On some Unix systems, the value in $? would not have the top bit
1831           set ("$? & 128") even if the child core dumped.
1832
1833       •   Under some circumstances, $^R could incorrectly become undefined
1834           [RT #57042].
1835
1836       •   In the XS API, various hash functions, when passed a pre-computed
1837           hash where the key is UTF-8, might result in an incorrect lookup.
1838
1839       •   XS code including XSUB.h before perl.h gave a compile-time error
1840           [RT #57176].
1841
1842       •   "$object->isa('Foo')" would report false if the package "Foo"
1843           didn't exist, even if the object's @ISA contained "Foo".
1844
1845       •   Various bugs in the new-to 5.10.0 mro code, triggered by
1846           manipulating @ISA, have been found and fixed.
1847
1848       •   Bitwise operations on references could crash the interpreter, e.g.
1849           "$x=\$y; $x |= "foo"" [RT #54956].
1850
1851       •   Patterns including alternation might be sensitive to the internal
1852           UTF-8 representation, e.g.
1853
1854               my $byte = chr(192);
1855               my $utf8 = chr(192); utf8::upgrade($utf8);
1856               $utf8 =~ /$byte|X}/i;       # failed in 5.10.0
1857
1858       •   Within UTF8-encoded Perl source files (i.e. where "use utf8" is in
1859           effect), double-quoted literal strings could be corrupted where a
1860           "\xNN", "\0NNN" or "\N{}" is followed by a literal character with
1861           ordinal value greater than 255 [RT #59908].
1862
1863       •   "B::Deparse" failed to correctly deparse various constructs:
1864           "readpipe STRING" [RT #62428], CORE::require(STRING) [RT #62488],
1865           "sub foo(_)" [RT #62484].
1866
1867       •   Using "setpgrp" with no arguments could corrupt the perl stack.
1868
1869       •   The block form of "eval" is now specifically trappable by "Safe"
1870           and "ops". Previously it was erroneously treated like string
1871           "eval".
1872
1873       •   In 5.10.0, the two characters "[~" were sometimes parsed as the
1874           smart match operator ("~~") [RT #63854].
1875
1876       •   In 5.10.0, the "*" quantifier in patterns was sometimes treated as
1877           "{0,32767}" [RT #60034, #60464]. For example, this match would
1878           fail:
1879
1880               ("ab" x 32768) =~ /^(ab)*$/
1881
1882       •   "shmget" was limited to a 32 bit segment size on a 64 bit OS [RT
1883           #63924].
1884
1885       •   Using "next" or "last" to exit a "given" block no longer produces a
1886           spurious warning like the following:
1887
1888               Exiting given via last at foo.pl line 123
1889
1890       •   Assigning a format to a glob could corrupt the format; e.g.:
1891
1892                *bar=*foo{FORMAT}; # foo format now bad
1893
1894       •   Attempting to coerce a typeglob to a string or number could cause
1895           an assertion failure. The correct error message is now generated,
1896           "Can't coerce GLOB to $type".
1897
1898       •   Under "use filetest 'access'", "-x" was using the wrong access
1899           mode. This has been fixed [RT #49003].
1900
1901       •   "length" on a tied scalar that returned a Unicode value would not
1902           be correct the first time. This has been fixed.
1903
1904       •   Using an array "tie" inside in array "tie" could SEGV. This has
1905           been fixed. [RT #51636]
1906
1907       •   A race condition inside PerlIOStdio_close() has been identified and
1908           fixed. This used to cause various threading issues, including
1909           SEGVs.
1910
1911       •   In "unpack", the use of "()" groups in scalar context was
1912           internally placing a list on the interpreter's stack, which
1913           manifested in various ways, including SEGVs. This is now fixed [RT
1914           #50256].
1915
1916       •   Magic was called twice in "substr", "\&$x", "tie $x, $m" and
1917           "chop".  These have all been fixed.
1918
1919       •   A 5.10.0 optimisation to clear the temporary stack within the
1920           implicit loop of "s///ge" has been reverted, as it turned out to be
1921           the cause of obscure bugs in seemingly unrelated parts of the
1922           interpreter [commit ef0d4e17921ee3de].
1923
1924       •   The line numbers for warnings inside "elsif" are now correct.
1925
1926       •   The ".." operator now works correctly with ranges whose ends are at
1927           or close to the values of the smallest and largest integers.
1928
1929       •   "binmode STDIN, ':raw'" could lead to segmentation faults on some
1930           platforms.  This has been fixed [RT #54828].
1931
1932       •   An off-by-one error meant that "index $str, ..." was effectively
1933           being executed as "index "$str\0", ...". This has been fixed [RT
1934           #53746].
1935
1936       •   Various leaks associated with named captures in regexes have been
1937           fixed [RT #57024].
1938
1939       •   A weak reference to a hash would leak. This was affecting "DBI" [RT
1940           #56908].
1941
1942       •   Using (?|) in a regex could cause a segfault [RT #59734].
1943
1944       •   Use of a UTF-8 "tr//" within a closure could cause a segfault [RT
1945           #61520].
1946
1947       •   Calling Perl_sv_chop() or otherwise upgrading an SV could result in
1948           an unaligned 64-bit access on the SPARC architecture [RT #60574].
1949
1950       •   In the 5.10.0 release, "inc_version_list" would incorrectly list
1951           "5.10.*" after "5.8.*"; this affected the @INC search order [RT
1952           #67628].
1953
1954       •   In 5.10.0, "pack "a*", $tainted_value" returned a non-tainted value
1955           [RT #52552].
1956
1957       •   In 5.10.0, "printf" and "sprintf" could produce the fatal error
1958           "panic: utf8_mg_pos_cache_update" when printing UTF-8 strings [RT
1959           #62666].
1960
1961       •   In the 5.10.0 release, a dynamically created "AUTOLOAD" method
1962           might be missed (method cache issue) [RT #60220,60232].
1963
1964       •   In the 5.10.0 release, a combination of "use feature" and "//ee"
1965           could cause a memory leak [RT #63110].
1966
1967       •   "-C" on the shebang ("#!") line is once more permitted if it is
1968           also specified on the command line. "-C" on the shebang line used
1969           to be a silent no-op if it was not also on the command line, so
1970           perl 5.10.0 disallowed it, which broke some scripts. Now perl
1971           checks whether it is also on the command line and only dies if it
1972           is not [RT #67880].
1973
1974       •   In 5.10.0, certain types of re-entrant regular expression could
1975           crash, or cause the following assertion failure [RT #60508]:
1976
1977               Assertion rx->sublen >= (s - rx->subbeg) + i failed
1978
1979       •   Perl now includes previously missing files from the Unicode
1980           Character Database.
1981
1982       •   Perl now honors "TMPDIR" when opening an anonymous temporary file.
1983

Platform Specific Changes

1985       Perl is incredibly portable. In general, if a platform has a C
1986       compiler, someone has ported Perl to it (or will soon).  We're happy to
1987       announce that Perl 5.12 includes support for several new platforms.  At
1988       the same time, it's time to bid farewell to some (very) old friends.
1989
1990   New Platforms
1991       Haiku
1992           Perl's developers have merged patches from Haiku's maintainers.
1993           Perl should now build on Haiku.
1994
1995       MirOS BSD
1996           Perl should now build on MirOS BSD.
1997
1998   Discontinued Platforms
1999       Domain/OS
2000       MiNT
2001       Tenon MachTen
2002
2003   Updated Platforms
2004       AIX
2005           •   Removed libbsd for AIX 5L and 6.1. Only flock() was used from
2006               libbsd.
2007
2008           •   Removed libgdbm for AIX 5L and 6.1 if libgdbm < 1.8.3-5 is
2009               installed.  The libgdbm is delivered as an optional package
2010               with the AIX Toolbox.  Unfortunately the versions below 1.8.3-5
2011               are broken.
2012
2013           •   Hints changes mean that AIX 4.2 should work again.
2014
2015       Cygwin
2016           •   Perl now supports IPv6 on Cygwin 1.7 and newer.
2017
2018           •   On Cygwin we now strip the last number from the DLL. This has
2019               been the behaviour in the cygwin.com build for years. The hints
2020               files have been updated.
2021
2022       Darwin (Mac OS X)
2023           •   Skip testing the be_BY.CP1131 locale on Darwin 10 (Mac OS X
2024               10.6), as it's still buggy.
2025
2026           •   Correct infelicities in the regexp used to identify buggy
2027               locales on Darwin 8 and 9 (Mac OS X 10.4 and 10.5,
2028               respectively).
2029
2030       DragonFly BSD
2031           •   Fix thread library selection [perl #69686]
2032
2033       FreeBSD
2034           •   The hints files now identify the correct threading libraries on
2035               FreeBSD 7 and later.
2036
2037       Irix
2038           •   We now work around a bizarre preprocessor bug in the Irix 6.5
2039               compiler: "cc -E -" unfortunately goes into K&R mode, but "cc
2040               -E file.c" doesn't.
2041
2042       NetBSD
2043           •   Hints now supports versions 5.*.
2044
2045       OpenVMS
2046           •   "-UDEBUGGING" is now the default on VMS.
2047
2048               Like it has been everywhere else for ages and ages. Also make
2049               command-line selection of -UDEBUGGING and -DDEBUGGING work in
2050               configure.com; before the only way to turn it off was by saying
2051               no in answer to the interactive question.
2052
2053           •   The default pipe buffer size on VMS has been updated to 8192 on
2054               64-bit systems.
2055
2056           •   Reads from the in-memory temporary files of "PerlIO::scalar"
2057               used to fail if $/ was set to a numeric reference (to indicate
2058               record-style reads).  This is now fixed.
2059
2060           •   VMS now supports "getgrgid".
2061
2062           •   Many improvements and cleanups have been made to the VMS file
2063               name handling and conversion code.
2064
2065           •   Enabling the "PERL_VMS_POSIX_EXIT" logical name now encodes a
2066               POSIX exit status in a VMS condition value for better
2067               interaction with GNV's bash shell and other utilities that
2068               depend on POSIX exit values. See "$?" in perlvms for details.
2069
2070           •   "File::Copy" now detects Unix compatibility mode on VMS.
2071
2072       Stratus VOS
2073           •   Various changes from Stratus have been merged in.
2074
2075       Symbian
2076           •   There is now support for Symbian S60 3.2 SDK and S60 5.0 SDK.
2077
2078       Windows
2079           •   Perl 5.12 supports Windows 2000 and later. The supporting code
2080               for legacy versions of Windows is still included, but will be
2081               removed during the next development cycle.
2082
2083           •   Initial support for building Perl with MinGW-w64 is now
2084               available.
2085
2086perl.exe now includes a manifest resource to specify the
2087               "trustInfo" settings for Windows Vista and later. Without this
2088               setting Windows would treat perl.exe as a legacy application
2089               and apply various heuristics like redirecting access to
2090               protected file system areas (like the "Program Files" folder)
2091               to the users "VirtualStore" instead of generating a proper
2092               "permission denied" error.
2093
2094               The manifest resource also requests the Microsoft Common-
2095               Controls version 6.0 (themed controls introduced in Windows
2096               XP).  Check out the Win32::VisualStyles module on CPAN to
2097               switch back to old style unthemed controls for legacy
2098               applications.
2099
2100           •   The "-t" filetest operator now only returns true if the
2101               filehandle is connected to a console window.  In previous
2102               versions of Perl it would return true for all character mode
2103               devices, including NUL and LPT1.
2104
2105           •   The "-p" filetest operator now works correctly, and the
2106               Fcntl::S_IFIFO constant is defined when Perl is compiled with
2107               Microsoft Visual C.  In previous Perl versions "-p" always
2108               returned a false value, and the Fcntl::S_IFIFO constant was not
2109               defined.
2110
2111               This bug is specific to Microsoft Visual C and never affected
2112               Perl binaries built with MinGW.
2113
2114           •   The socket error codes are now more widely supported:  The
2115               POSIX module will define the symbolic names, like
2116               POSIX::EWOULDBLOCK, and stringification of socket error codes
2117               in $! works as well now;
2118
2119                 C:\>perl -MPOSIX -E "$!=POSIX::EWOULDBLOCK; say $!"
2120                 A non-blocking socket operation could not be completed immediately.
2121
2122flock() will now set sensible error codes in $!.  Previous Perl
2123               versions copied the value of $^E into $!, which caused much
2124               confusion.
2125
2126select() now supports all empty "fd_set"s more correctly.
2127
2128           •   '.\foo' and '..\foo'  were treated differently than './foo' and
2129               '../foo' by "do" and "require" [RT #63492].
2130
2131           •   Improved message window handling means that "alarm" and "kill"
2132               messages will no longer be dropped under race conditions.
2133
2134           •   Various bits of Perl's build infrastructure are no longer
2135               converted to win32 line endings at release time. If this hurts
2136               you, please report the problem with the perlbug program
2137               included with perl.
2138

Known Problems

2140       This is a list of some significant unfixed bugs, which are regressions
2141       from either 5.10.x or 5.8.x.
2142
2143       •   Some CPANPLUS tests may fail if there is a functioning file
2144           ../../cpanp-run-perl outside your build directory. The failure
2145           shouldn't imply there's a problem with the actual functional
2146           software. The bug is already fixed in [RT #74188] and is scheduled
2147           for inclusion in perl-v5.12.1.
2148
2149       •   "List::Util::first" misbehaves in the presence of a lexical $_
2150           (typically introduced by "my $_" or implicitly by "given"). The
2151           variable which gets set for each iteration is the package variable
2152           $_, not the lexical $_ [RT #67694].
2153
2154           A similar issue may occur in other modules that provide functions
2155           which take a block as their first argument, like
2156
2157               foo { ... $_ ...} list
2158
2159       •   Some regexes may run much more slowly when run in a child thread
2160           compared with the thread the pattern was compiled into [RT #55600].
2161
2162       •   Things like ""\N{LATIN SMALL LIGATURE FF}" =~ /\N{LATIN SMALL
2163           LETTER F}+/" will appear to hang as they get into a very long
2164           running loop [RT #72998].
2165
2166       •   Several porters have reported mysterious crashes when Perl's entire
2167           test suite is run after a build on certain Windows 2000 systems.
2168           When run by hand, the individual tests reportedly work fine.
2169

Errata

2171       •   This one is actually a change introduced in 5.10.0, but it was
2172           missed from that release's perldelta, so it is mentioned here
2173           instead.
2174
2175           A bugfix related to the handling of the "/m" modifier and "qr"
2176           resulted in a change of behaviour between 5.8.x and 5.10.0:
2177
2178               # matches in 5.8.x, doesn't match in 5.10.0
2179               $re = qr/^bar/; "foo\nbar" =~ /$re/m;
2180

Acknowledgements

2182       Perl 5.12.0 represents approximately two years of development since
2183       Perl 5.10.0 and contains over 750,000 lines of changes across over
2184       3,000 files from over 200 authors and committers.
2185
2186       Perl continues to flourish into its third decade thanks to a vibrant
2187       community of users and developers.  The following people are known to
2188       have contributed the improvements that became Perl 5.12.0:
2189
2190       Aaron Crane, Abe Timmerman, Abhijit Menon-Sen, Abigail, Adam Russell,
2191       Adriano Ferreira, Ævar Arnfjörð Bjarmason, Alan Grover, Alexandr
2192       Ciornii, Alex Davies, Alex Vandiver, Andreas Koenig, Andrew Rodland,
2193       andrew@sundale.net, Andy Armstrong, Andy Dougherty, Jose AUGUSTE-
2194       ETIENNE, Benjamin Smith, Ben Morrow, bharanee rathna, Bo Borgerson, Bo
2195       Lindbergh, Brad Gilbert, Bram, Brendan O'Dea, brian d foy, Charles
2196       Bailey, Chip Salzenberg, Chris 'BinGOs' Williams, Christoph Lamprecht,
2197       Chris Williams, chromatic, Claes Jakobsson, Craig A. Berry, Dan
2198       Dascalescu, Daniel Frederick Crisman, Daniel M. Quinlan, Dan Jacobson,
2199       Dan Kogai, Dave Mitchell, Dave Rolsky, David Cantrell, David Dick,
2200       David Golden, David Mitchell, David M. Syzdek, David Nicol, David
2201       Wheeler, Dennis Kaarsemaker, Dintelmann, Peter, Dominic Dunlop,
2202       Dr.Ruud, Duke Leto, Enrico Sorcinelli, Eric Brine, Father Chrysostomos,
2203       Florian Ragwitz, Frank Wiegand, Gabor Szabo, Gene Sullivan, Geoffrey T.
2204       Dairiki, George Greer, Gerard Goossen, Gisle Aas, Goro Fuji, Graham
2205       Barr, Green, Paul, Hans Dieter Pearcey, Harmen, H. Merijn Brand, Hugo
2206       van der Sanden, Ian Goodacre, Igor Sutton, Ingo Weinhold, James Bence,
2207       James Mastros, Jan Dubois, Jari Aalto, Jarkko Hietaniemi, Jay Hannah,
2208       Jerry Hedden, Jesse Vincent, Jim Cromie, Jody Belka, John E. Malmberg,
2209       John Malmberg, John Peacock, John Peacock via RT, John P. Linderman,
2210       John Wright, Josh ben Jore, Jos I. Boumans, Karl Williamson, Kenichi
2211       Ishigaki, Ken Williams, Kevin Brintnall, Kevin Ryde, Kurt Starsinic,
2212       Leon Brocard, Lubomir Rintel, Luke Ross, Marcel Grünauer, Marcus
2213       Holland-Moritz, Mark Jason Dominus, Marko Asplund, Martin Hasch,
2214       Mashrab Kuvatov, Matt Kraai, Matt S Trout, Max Maischein, Michael
2215       Breen, Michael Cartmell, Michael G Schwern, Michael Witten, Mike
2216       Giroux, Milosz Tanski, Moritz Lenz, Nicholas Clark, Nick Cleaton, Niko
2217       Tyni, Offer Kaye, Osvaldo Villalon, Paul Fenwick, Paul Gaborit, Paul
2218       Green, Paul Johnson, Paul Marquess, Philip Hazel, Philippe Bruhat,
2219       Rafael Garcia-Suarez, Rainer Tammer, Rajesh Mandalemula, Reini Urban,
2220       Renée Bäcker, Ricardo Signes, Ricardo SIGNES, Richard Foley, Rich
2221       Rauenzahn, Rick Delaney, Risto Kankkunen, Robert May, Roberto C.
2222       Sanchez, Robin Barker, SADAHIRO Tomoyuki, Salvador Ortiz Garcia, Sam
2223       Vilain, Scott Lanning, Sébastien Aperghis-Tramoni, Sérgio Durigan
2224       Júnior, Shlomi Fish, Simon 'corecode' Schubert, Sisyphus, Slaven Rezic,
2225       Smylers, Steffen Müller, Steffen Ullrich, Stepan Kasal, Steve Hay,
2226       Steven Schubiger, Steve Peters, Tels, The Doctor, Tim Bunce, Tim
2227       Jenness, Todd Rinaldo, Tom Christiansen, Tom Hukins, Tom Wyant, Tony
2228       Cook, Torsten Schoenfeld, Tye McQueen, Vadim Konovalov, Vincent Pit,
2229       Hio YAMASHINA, Yasuhiro Matsumoto, Yitzchak Scott-Thoennes, Yuval
2230       Kogman, Yves Orton, Zefram, Zsban Ambrus
2231
2232       This is woefully incomplete as it's automatically generated from
2233       version control history.  In particular, it doesn't include the names
2234       of the (very much appreciated) contributors who reported issues in
2235       previous versions of Perl that helped make Perl 5.12.0 better. For a
2236       more complete list of all of Perl's historical contributors, please see
2237       the "AUTHORS" file in the Perl 5.12.0 distribution.
2238
2239       Our "retired" pumpkings Nicholas Clark and Rafael Garcia-Suarez deserve
2240       special thanks for their brilliant and substantive ongoing
2241       contributions. Nicholas personally authored over 30% of the patches
2242       since 5.10.0. Rafael comes in second in patch authorship with 11%, but
2243       is first by a long shot in committing patches authored by others,
2244       pushing 44% of the commits since 5.10.0 in this category, often after
2245       providing considerable coaching to the patch authors. These statistics
2246       in no way comprise all of their contributions, but express in shorthand
2247       that we couldn't have done it without them.
2248
2249       Many of the changes included in this version originated in the CPAN
2250       modules included in Perl's core. We're grateful to the entire CPAN
2251       community for helping Perl to flourish.
2252

Reporting Bugs

2254       If you find what you think is a bug, you might check the articles
2255       recently posted to the comp.lang.perl.misc newsgroup and the perl bug
2256       database at <http://rt.perl.org/perlbug/>. There may also be
2257       information at <http://www.perl.org/>, the Perl Home Page.
2258
2259       If you believe you have an unreported bug, please run the perlbug
2260       program included with your release. Be sure to trim your bug down to a
2261       tiny but sufficient test case. Your bug report, along with the output
2262       of "perl -V", will be sent off to perlbug@perl.org to be analyzed by
2263       the Perl porting team.
2264
2265       If the bug you are reporting has security implications, which make it
2266       inappropriate to send to a publicly archived mailing list, then please
2267       send it to perl5-security-report@perl.org. This points to a closed
2268       subscription unarchived mailing list, which includes all the core
2269       committers, who will be able to help assess the impact of issues,
2270       figure out a resolution, and help co-ordinate the release of patches to
2271       mitigate or fix the problem across all platforms on which Perl is
2272       supported. Please only use this address for security issues in the Perl
2273       core, not for modules independently distributed on CPAN.
2274

SEE ALSO

2276       The Changes file for an explanation of how to view exhaustive details
2277       on what changed.
2278
2279       The INSTALL file for how to build Perl.
2280
2281       The README file for general stuff.
2282
2283       The Artistic and Copying files for copyright information.
2284
2285       <http://dev.perl.org/perl5/errata.html> for a list of issues found
2286       after this release, as well as a list of CPAN modules known to be
2287       incompatible with this release.
2288
2289
2290
2291perl v5.38.2                      2023-11-30                  PERL5120DELTA(1)
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