5 perldelta - what is new for perl 5.10.0
9 This document describes the differences between the 5.8.8 release and
12 Many of the bug fixes in 5.10.0 were already seen in the 5.8.X maintenance
13 releases; they are not duplicated here and are documented in the set of
14 man pages named perl58[1-8]?delta.
16 =head1 Core Enhancements
18 =head2 The C<feature> pragma
20 The C<feature> pragma is used to enable new syntax that would break Perl's
21 backwards-compatibility with older releases of the language. It's a lexical
22 pragma, like C<strict> or C<warnings>.
24 Currently the following new features are available: C<switch> (adds a
25 switch statement), C<say> (adds a C<say> built-in function), and C<state>
26 (adds a C<state> keyword for declaring "static" variables). Those
27 features are described in their own sections of this document.
29 The C<feature> pragma is also implicitly loaded when you require a minimal
30 perl version (with the C<use VERSION> construct) greater than, or equal
31 to, 5.9.5. See L<feature> for details.
33 =head2 New B<-E> command-line switch
35 B<-E> is equivalent to B<-e>, but it implicitly enables all
36 optional features (like C<use feature ":5.10">).
38 =head2 Defined-or operator
40 A new operator C<//> (defined-or) has been implemented.
41 The following expression:
45 is merely equivalent to
53 can now be used instead of
55 $c = $d unless defined $c;
57 The C<//> operator has the same precedence and associativity as C<||>.
58 Special care has been taken to ensure that this operator Do What You Mean
59 while not breaking old code, but some edge cases involving the empty
60 regular expression may now parse differently. See L<perlop> for
63 =head2 Switch and Smart Match operator
65 Perl 5 now has a switch statement. It's available when C<use feature
66 'switch'> is in effect. This feature introduces three new keywords,
67 C<given>, C<when>, and C<default>:
70 when (/^abc/) { $abc = 1; }
71 when (/^def/) { $def = 1; }
72 when (/^xyz/) { $xyz = 1; }
73 default { $nothing = 1; }
76 A more complete description of how Perl matches the switch variable
77 against the C<when> conditions is given in L<perlsyn/"Switch statements">.
79 This kind of match is called I<smart match>, and it's also possible to use
80 it outside of switch statements, via the new C<~~> operator. See
81 L<perlsyn/"Smart matching in detail">.
83 This feature was contributed by Robin Houston.
85 =head2 Regular expressions
89 =item Recursive Patterns
91 It is now possible to write recursive patterns without using the C<(??{})>
92 construct. This new way is more efficient, and in many cases easier to
95 Each capturing parenthesis can now be treated as an independent pattern
96 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
97 "parenthesis number"). For example, the following pattern will match
98 nested balanced angle brackets:
102 ( # start capture buffer 1
103 < # match an opening angle bracket
105 (?> # don't backtrack over the inside of this group
106 [^<>]+ # one or more non angle brackets
107 ) # end non backtracking group
109 (?1) # recurse to bracket 1 and try it again
110 )* # 0 or more times.
111 > # match a closing angle bracket
112 ) # end capture buffer one
116 PCRE users should note that Perl's recursive regex feature allows
117 backtracking into a recursed pattern, whereas in PCRE the recursion is
118 atomic or "possessive" in nature. As in the example above, you can
119 add (?>) to control this selectively. (Yves Orton)
121 =item Named Capture Buffers
123 It is now possible to name capturing parenthesis in a pattern and refer to
124 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
125 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
126 syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
127 access the contents of the capture buffers.
129 Thus, to replace all doubled chars with a single copy, one could write
131 s/(?<letter>.)\k<letter>/$+{letter}/g
133 Only buffers with defined contents will be "visible" in the C<%+> hash, so
134 it's possible to do something like
136 foreach my $name (keys %+) {
137 print "content of buffer '$name' is $+{$name}\n";
140 The C<%-> hash is a bit more complete, since it will contain array refs
141 holding values from all capture buffers similarly named, if there should
144 C<%+> and C<%-> are implemented as tied hashes through the new module
145 C<Tie::Hash::NamedCapture>.
147 Users exposed to the .NET regex engine will find that the perl
148 implementation differs in that the numerical ordering of the buffers
149 is sequential, and not "unnamed first, then named". Thus in the pattern
151 /(A)(?<B>B)(C)(?<D>D)/
153 $1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
154 $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
155 would expect. This is considered a feature. :-) (Yves Orton)
157 =item Possessive Quantifiers
159 Perl now supports the "possessive quantifier" syntax of the "atomic match"
160 pattern. Basically a possessive quantifier matches as much as it can and never
161 gives any back. Thus it can be used to control backtracking. The syntax is
162 similar to non-greedy matching, except instead of using a '?' as the modifier
163 the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
164 quantifiers. (Yves Orton)
166 =item Backtracking control verbs
168 The regex engine now supports a number of special-purpose backtrack
169 control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
170 and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
172 =item Relative backreferences
174 A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
175 safer form of back-reference notation as well as allowing relative
176 backreferences. This should make it easier to generate and embed patterns
177 that contain backreferences. See L<perlre/"Capture buffers">. (Yves Orton)
181 The functionality of Jeff Pinyan's module Regexp::Keep has been added to
182 the core. In regular expressions you can now use the special escape C<\K>
183 as a way to do something like floating length positive lookbehind. It is
184 also useful in substitutions like:
188 that can now be converted to
192 which is much more efficient. (Yves Orton)
194 =item Vertical and horizontal whitespace, and linebreak
196 Regular expressions now recognize the C<\v> and C<\h> escapes that match
197 vertical and horizontal whitespace, respectively. C<\V> and C<\H>
198 logically match their complements.
200 C<\R> matches a generic linebreak, that is, vertical whitespace, plus
201 the multi-character sequence C<"\x0D\x0A">.
207 say() is a new built-in, only available when C<use feature 'say'> is in
208 effect, that is similar to print(), but that implicitly appends a newline
209 to the printed string. See L<perlfunc/say>. (Robin Houston)
213 The default variable C<$_> can now be lexicalized, by declaring it like
214 any other lexical variable, with a simple
218 The operations that default on C<$_> will use the lexically-scoped
219 version of C<$_> when it exists, instead of the global C<$_>.
221 In a C<map> or a C<grep> block, if C<$_> was previously my'ed, then the
222 C<$_> inside the block is lexical as well (and scoped to the block).
224 In a scope where C<$_> has been lexicalized, you can still have access to
225 the global version of C<$_> by using C<$::_>, or, more simply, by
226 overriding the lexical declaration with C<our $_>. (Rafael Garcia-Suarez)
228 =head2 The C<_> prototype
230 A new prototype character has been added. C<_> is equivalent to C<$> but
231 defaults to C<$_> if the corresponding argument isn't supplied. (both C<$>
232 and C<_> denote a scalar). Due to the optional nature of the argument, you
233 can only use it at the end of a prototype, or before a semicolon.
235 This has a small incompatible consequence: the prototype() function has
236 been adjusted to return C<_> for some built-ins in appropriate cases (for
237 example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
239 =head2 UNITCHECK blocks
241 C<UNITCHECK>, a new special code block has been introduced, in addition to
242 C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
244 C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
245 are always executed at the transition between the compilation and the
246 execution of the main program, and thus are useless whenever code is
247 loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
248 just after the unit which defined them has been compiled. See L<perlmod>
249 for more information. (Alex Gough)
251 =head2 New Pragma, C<mro>
253 A new pragma, C<mro> (for Method Resolution Order) has been added. It
254 permits to switch, on a per-class basis, the algorithm that perl uses to
255 find inherited methods in case of a multiple inheritance hierarchy. The
256 default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
257 available: the C3 algorithm. See L<mro> for more information.
260 Note that, due to changes in the implementation of class hierarchy search,
261 code that used to undef the C<*ISA> glob will most probably break. Anyway,
262 undef'ing C<*ISA> had the side-effect of removing the magic on the @ISA
263 array and should not have been done in the first place.
265 =head2 readdir() may return a "short filename" on Windows
267 The readdir() function may return a "short filename" when the long
268 filename contains characters outside the ANSI codepage. Similarly
269 Cwd::cwd() may return a short directory name, and glob() may return short
270 names as well. On the NTFS file system these short names can always be
271 represented in the ANSI codepage. This will not be true for all other file
272 system drivers; e.g. the FAT filesystem stores short filenames in the OEM
273 codepage, so some files on FAT volumes remain unaccessible through the
276 Similarly, $^X, @INC, and $ENV{PATH} are preprocessed at startup to make
277 sure all paths are valid in the ANSI codepage (if possible).
279 The Win32::GetLongPathName() function now returns the UTF-8 encoded
280 correct long file name instead of using replacement characters to force
281 the name into the ANSI codepage. The new Win32::GetANSIPathName()
282 function can be used to turn a long pathname into a short one only if the
283 long one cannot be represented in the ANSI codepage.
285 Many other functions in the C<Win32> module have been improved to accept
286 UTF-8 encoded arguments. Please see L<Win32> for details.
288 =head2 readpipe() is now overridable
290 The built-in function readpipe() is now overridable. Overriding it permits
291 also to override its operator counterpart, C<qx//> (a.k.a. C<``>).
292 Moreover, it now defaults to C<$_> if no argument is provided. (Rafael
295 =head2 Default argument for readline()
297 readline() now defaults to C<*ARGV> if no argument is provided. (Rafael
300 =head2 state() variables
302 A new class of variables has been introduced. State variables are similar
303 to C<my> variables, but are declared with the C<state> keyword in place of
304 C<my>. They're visible only in their lexical scope, but their value is
305 persistent: unlike C<my> variables, they're not undefined at scope entry,
306 but retain their previous value. (Rafael Garcia-Suarez, Nicholas Clark)
308 To use state variables, one needs to enable them by using
312 or by using the C<-E> command-line switch in one-liners.
313 See L<perlsub/"Persistent variables via state()">.
315 =head2 Stacked filetest operators
317 As a new form of syntactic sugar, it's now possible to stack up filetest
318 operators. You can now write C<-f -w -x $file> in a row to mean
319 C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
321 =head2 UNIVERSAL::DOES()
323 The C<UNIVERSAL> class has a new method, C<DOES()>. It has been added to
324 solve semantic problems with the C<isa()> method. C<isa()> checks for
325 inheritance, while C<DOES()> has been designed to be overridden when
326 module authors use other types of relations between classes (in addition
327 to inheritance). (chromatic)
329 See L<< UNIVERSAL/"$obj->DOES( ROLE )" >>.
333 Formats were improved in several ways. A new field, C<^*>, can be used for
334 variable-width, one-line-at-a-time text. Null characters are now handled
335 correctly in picture lines. Using C<@#> and C<~~> together will now
336 produce a compile-time error, as those format fields are incompatible.
337 L<perlform> has been improved, and miscellaneous bugs fixed.
339 =head2 Byte-order modifiers for pack() and unpack()
341 There are two new byte-order modifiers, C<E<gt>> (big-endian) and C<E<lt>>
342 (little-endian), that can be appended to most pack() and unpack() template
343 characters and groups to force a certain byte-order for that type or group.
344 See L<perlfunc/pack> and L<perlpacktut> for details.
348 You can now use C<no> followed by a version number to specify that you
349 want to use a version of perl older than the specified one.
351 =head2 C<chdir>, C<chmod> and C<chown> on filehandles
353 C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
354 filenames, if the system supports respectively C<fchdir>, C<fchmod> and
355 C<fchown>, thanks to a patch provided by Gisle Aas.
359 C<$(> and C<$)> now return groups in the order where the OS returns them,
360 thanks to Gisle Aas. This wasn't previously the case.
362 =head2 Recursive sort subs
364 You can now use recursive subroutines with sort(), thanks to Robin Houston.
366 =head2 Exceptions in constant folding
368 The constant folding routine is now wrapped in an exception handler, and
369 if folding throws an exception (such as attempting to evaluate 0/0), perl
370 now retains the current optree, rather than aborting the whole program.
371 Without this change, programs would not compile if they had expressions that
372 happened to generate exceptions, even though those expressions were in code
373 that could never be reached at runtime. (Nicholas Clark, Dave Mitchell)
375 =head2 Source filters in @INC
377 It's possible to enhance the mechanism of subroutine hooks in @INC by
378 adding a source filter on top of the filehandle opened and returned by the
379 hook. This feature was planned a long time ago, but wasn't quite working
380 until now. See L<perlfunc/require> for details. (Nicholas Clark)
382 =head2 New internal variables
386 =item C<${^RE_DEBUG_FLAGS}>
388 This variable controls what debug flags are in effect for the regular
389 expression engine when running under C<use re "debug">. See L<re> for
392 =item C<${^CHILD_ERROR_NATIVE}>
394 This variable gives the native status returned by the last pipe close,
395 backtick command, successful call to wait() or waitpid(), or from the
396 system() operator. See L<perlrun> for details. (Contributed by Gisle Aas.)
398 =item C<${^RE_TRIE_MAXBUF}>
400 See L</"Trie optimisation of literal string alternations">.
402 =item C<${^WIN32_SLOPPY_STAT}>
404 See L</"Sloppy stat on Windows">.
410 C<unpack()> now defaults to unpacking the C<$_> variable.
412 C<mkdir()> without arguments now defaults to C<$_>.
414 The internal dump output has been improved, so that non-printable characters
415 such as newline and backspace are output in C<\x> notation, rather than
418 The B<-C> option can no longer be used on the C<#!> line. It wasn't
419 working there anyway, since the standard streams are already set up
420 at this point in the execution of the perl interpreter. You can use
421 binmode() instead to get the desired behaviour.
425 The copy of the Unicode Character Database included in Perl 5 has
426 been updated to version 5.0.0.
430 MAD, which stands for I<Miscellaneous Attribute Decoration>, is a
431 still-in-development work leading to a Perl 5 to Perl 6 converter. To
432 enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
433 obtained perl isn't binary compatible with a regular perl 5.10, and has
434 space and speed penalties; moreover not all regression tests still pass
435 with it. (Larry Wall, Nicholas Clark)
437 =head2 kill() on Windows
439 On Windows platforms, C<kill(-9, $pid)> now kills a process tree.
440 (On UNIX, this delivers the signal to all processes in the same process
443 =head1 Incompatible Changes
445 =head2 Packing and UTF-8 strings
449 The semantics of pack() and unpack() regarding UTF-8-encoded data has been
450 changed. Processing is now by default character per character instead of
451 byte per byte on the underlying encoding. Notably, code that used things
452 like C<pack("a*", $string)> to see through the encoding of string will now
453 simply get back the original $string. Packed strings can also get upgraded
454 during processing when you store upgraded characters. You can get the old
455 behaviour by using C<use bytes>.
457 To be consistent with pack(), the C<C0> in unpack() templates indicates
458 that the data is to be processed in character mode, i.e. character by
459 character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
460 the packed string is processed in its UTF-8-encoded Unicode form on a byte
461 by byte basis. This is reversed with regard to perl 5.8.X, but now consistent
462 between pack() and unpack().
464 Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
465 respectively character and byte modes.
467 C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
468 specified encoding mode, honoring parens grouping. Previously, parens were
471 Also, there is a new pack() character format, C<W>, which is intended to
472 replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
473 the strings internal representation. C<W> represents unsigned (logical)
474 character values, which can be greater than 255. It is therefore more
475 robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
476 values outside the range 0..255, and not respect the string encoding).
478 In practice, that means that pack formats are now encoding-neutral, except
481 For consistency, C<A> in unpack() format now trims all Unicode whitespace
482 from the end of the string. Before perl 5.9.2, it used to strip only the
483 classical ASCII space characters.
485 =head2 Byte/character count feature in unpack()
487 A new unpack() template character, C<".">, returns the number of bytes or
488 characters (depending on the selected encoding mode, see above) read so far.
490 =head2 The C<$*> and C<$#> variables have been removed
492 C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
493 modifiers, has been removed.
495 The deprecated C<$#> variable (output format for numbers) has been
498 Two new severe warnings, C<$#/$* is no longer supported>, have been added.
500 =head2 substr() lvalues are no longer fixed-length
502 The lvalues returned by the three argument form of substr() used to be a
503 "fixed length window" on the original string. In some cases this could
504 cause surprising action at distance or other undefined behaviour. Now the
505 length of the window adjusts itself to the length of the string assigned to
508 =head2 Parsing of C<-f _>
510 The identifier C<_> is now forced to be a bareword after a filetest
511 operator. This solves a number of misparsing issues when a global C<_>
512 subroutine is defined.
516 The C<:unique> attribute has been made a no-op, since its current
517 implementation was fundamentally flawed and not threadsafe.
519 =head2 Effect of pragmas in eval
521 The compile-time value of the C<%^H> hint variable can now propagate into
522 eval("")uated code. This makes it more useful to implement lexical
525 As a side-effect of this, the overloaded-ness of constants now propagates
530 A bareword argument to chdir() is now recognized as a file handle.
531 Earlier releases interpreted the bareword as a directory name.
534 =head2 Handling of .pmc files
536 An old feature of perl was that before C<require> or C<use> look for a
537 file with a F<.pm> extension, they will first look for a similar filename
538 with a F<.pmc> extension. If this file is found, it will be loaded in
539 place of any potentially existing file ending in a F<.pm> extension.
541 Previously, F<.pmc> files were loaded only if more recent than the
542 matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
545 =head2 @- and @+ in patterns
547 The special arrays C<@-> and C<@+> are no longer interpolated in regular
548 expressions. (Sadahiro Tomoyuki)
550 =head2 $AUTOLOAD can now be tainted
552 If you call a subroutine by a tainted name, and if it defers to an
553 AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
556 =head2 Tainting and printf
558 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
559 reject any tainted format argument. (Rafael Garcia-Suarez)
561 =head2 undef and signal handlers
563 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
564 equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
566 =head2 strictures and dereferencing in defined()
568 C<use strict 'refs'> was ignoring taking a hard reference in an argument
569 to defined(), as in :
573 if (defined $$x) {...}
575 This now correctly produces the run-time error C<Can't use string as a
576 SCALAR ref while "strict refs" in use>.
578 C<defined @$foo> and C<defined %$bar> are now also subject to C<strict
579 'refs'> (that is, C<$foo> and C<$bar> shall be proper references there.)
580 (C<defined(@foo)> and C<defined(%bar)> are discouraged constructs anyway.)
583 =head2 C<(?p{})> has been removed
585 The regular expression construct C<(?p{})>, which was deprecated in perl
586 5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
588 =head2 Pseudo-hashes have been removed
590 Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
591 pragma remains here, but uses an alternate implementation.)
593 =head2 Removal of the bytecode compiler and of perlcc
595 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
596 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
597 experimental tools have never worked reliably, and, due to the lack of
598 volunteers to keep them in line with the perl interpreter developments, it
599 was decided to remove them instead of shipping a broken version of those.
600 The last version of those modules can be found with perl 5.9.4.
602 However the B compiler framework stays supported in the perl core, as with
603 the more useful modules it has permitted (among others, B::Deparse and
606 =head2 Removal of the JPL
608 The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.
610 =head2 Recursive inheritance detected earlier
612 Perl will now immediately throw an exception if you modify any package's
613 C<@ISA> in such a way that it would cause recursive inheritance.
615 Previously, the exception would not occur until Perl attempted to make
616 use of the recursive inheritance while resolving a method or doing a
617 C<$foo-E<gt>isa($bar)> lookup.
619 =head1 Modules and Pragmata
621 =head2 Pragmata Changes
627 The new pragma C<feature> is used to enable new features that might break
628 old code. See L</"The C<feature> pragma"> above.
632 This new pragma enables to change the algorithm used to resolve inherited
633 methods. See L</"New Pragma, C<mro>"> above.
635 =item Scoping of the C<sort> pragma
637 The C<sort> pragma is now lexically scoped. Its effect used to be global.
639 =item Scoping of C<bignum>, C<bigint>, C<bigrat>
641 The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
642 lexically scoped. (Tels)
646 The C<base> pragma now warns if a class tries to inherit from itself.
649 =item C<strict> and C<warnings>
651 C<strict> and C<warnings> will now complain loudly if they are loaded via
652 incorrect casing (as in C<use Strict;>). (Johan Vromans)
656 The C<version> module provides support for version objects.
660 The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
661 that used C<Carp> routines without having loaded it at compile time might
662 need to be adjusted; typically, the following (faulty) code won't work
663 anymore, and will require parentheses to be added after the function name:
667 Carp::confess 'argh';
671 C<less> now does something useful (or at least it tries to). In fact, it
672 has been turned into a lexical pragma. So, in your modules, you can now
673 test whether your users have requested to use less CPU, or less memory,
674 less magic, or maybe even less fat. See L<less> for more. (Joshua ben
685 C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
686 whenever an ASCII character string containing high-bit bytes is implicitly
687 converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
688 perls, its effect is global.
692 C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
693 you what versions of core modules ship with any versions of Perl 5. It
694 comes with a command-line frontend, C<corelist>.
698 C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
699 C<Math::BigInt::Calc>.
703 C<Compress::Zlib> is an interface to the zlib compression library. It
704 comes with a bundled version of zlib, so having a working zlib is not a
705 prerequisite to install it. It's used by C<Archive::Tar> (see below).
709 C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
713 C<Archive::Tar> is a module to manipulate C<tar> archives.
717 C<Digest::SHA> is a module used to calculate many types of SHA digests,
718 has been included for SHA support in the CPAN module.
722 C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
726 C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
727 provides support for I<field hashes>: hashes that maintain an association
728 of a reference with a value, in a thread-safe garbage-collected way.
729 Such hashes are useful to implement inside-out objects.
733 C<Module::Build>, by Ken Williams, has been added. It's an alternative to
734 C<ExtUtils::MakeMaker> to build and install perl modules.
738 C<Module::Load>, by Jos Boumans, has been added. It provides a single
739 interface to load Perl modules and F<.pl> files.
743 C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
744 modules as loaded or unloaded.
748 C<Package::Constants>, by Jos Boumans, has been added. It's a simple
749 helper to list all constants declared in a given package.
753 C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
754 This module provides low-level access to Win32 system API calls for
759 C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
760 C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
761 included in the perl core; the behaviour of C<Locale::Maketext::Simple>
762 gracefully degrades when the later isn't present.
766 C<Params::Check> implements a generic input parsing/checking mechanism. It
771 C<Term::UI> simplifies the task to ask questions at a terminal prompt.
775 C<Object::Accessor> provides an interface to create per-object accessors.
779 C<Module::Pluggable> is a simple framework to create modules that accept
780 pluggable sub-modules.
784 C<Module::Load::Conditional> provides simple ways to query and possibly
785 load installed modules.
789 C<Time::Piece> provides an object oriented interface to time functions,
790 overriding the built-ins localtime() and gmtime().
794 C<IPC::Cmd> helps to find and run external commands, possibly
799 C<File::Fetch> provide a simple generic file fetching mechanism.
803 C<Log::Message> and C<Log::Message::Simple> are used by the log facility
808 C<Archive::Extract> is a generic archive extraction mechanism
809 for F<.tar> (plain, gziped or bzipped) or F<.zip> files.
813 C<CPANPLUS> provides an API and a command-line tool to access the CPAN
818 C<Pod::Escapes> provides utilities that are useful in decoding Pod
819 EE<lt>...E<gt> sequences.
823 C<Pod::Simple> is now the backend for several of the Pod-related modules
828 =head2 Selected Changes to Core Modules
832 =item C<Attribute::Handlers>
834 C<Attribute::Handlers> can now report the caller's file and line number.
839 C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
840 with plugins. (Joshua ben Jore)
844 It's now possible to access the lexical pragma hints (C<%^H>) by using the
845 method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
846 can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
851 As the old 5005thread threading model has been removed, in favor of the
852 ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
853 be used in old code only. It has been removed from the default list of
858 =head1 Utility Changes
864 The Perl debugger can now save all debugger commands for sourcing later;
865 notably, it can now emulate stepping backwards, by restarting and
866 rerunning all bar the last command from a saved command history.
868 It can also display the parent inheritance tree of a given class, with the
873 C<ptar> is a pure perl implementation of C<tar> that comes with
878 C<ptardiff> is a small utility used to generate a diff between the contents
879 of a tar archive and a directory tree. Like C<ptar>, it comes with
884 C<shasum> is a command-line utility, used to print or to check SHA
885 digests. It comes with the new C<Digest::SHA> module.
889 The C<corelist> utility is now installed with perl (see L</"New modules">
894 C<h2ph> and C<h2xs> have been made more robust with regard to
897 C<h2xs> implements a new option C<--use-xsloader> to force use of
898 C<XSLoader> even in backwards compatible modules.
900 The handling of authors' names that had apostrophes has been fixed.
902 Any enums with negative values are now skipped.
906 C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
907 option to run I<all> tests.
911 C<find2perl> now assumes C<-print> as a default action. Previously, it
912 needed to be specified explicitly.
914 Several bugs have been fixed in C<find2perl>, regarding C<-exec> and
915 C<-eval>. Also the options C<-path>, C<-ipath> and C<-iname> have been
920 C<config_data> is a new utility that comes with C<Module::Build>. It
921 provides a command-line interface to the configuration of Perl modules
922 that use Module::Build's framework of configurability (that is,
923 C<*::ConfigData> modules that contain local configuration information for
924 their parent modules.)
928 C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, a
929 helper for CPANPLUS operation, has been added too, but isn't intended for
934 C<cpan2dist> is a new utility that comes with CPANPLUS. It's a tool to
935 create distributions (or packages) from CPAN modules.
939 The output of C<pod2html> has been enhanced to be more customizable via
940 CSS. Some formatting problems were also corrected. (Jari Aalto)
944 =head1 New Documentation
946 The L<perlpragma> manpage documents how to write one's own lexical
947 pragmas in pure Perl (something that is possible starting with 5.9.4).
949 The new L<perlglossary> manpage is a glossary of terms used in the Perl
950 documentation, technical and otherwise, kindly provided by O'Reilly Media,
953 The L<perlreguts> manpage, courtesy of Yves Orton, describes internals of the
954 Perl regular expression engine.
956 The L<perlreapi> manpage describes the interface to the perl interpreter
957 used to write pluggable regular expression engines (by Ævar Arnfjörð
960 The L<perlunitut> manpage is an tutorial for programming with Unicode and
961 string encodings in Perl, courtesy of Juerd Waalboer.
963 A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
966 The L<perlcommunity> manpage gives a description of the Perl community
967 on the Internet and in real life. (Edgar "Trizor" Bering)
969 The L<CORE> manual page documents the C<CORE::> namespace. (Tels)
971 The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
974 =head1 Performance Enhancements
976 =head2 In-place sorting
978 Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
979 making a temporary copy of the array.
981 Likewise, C<reverse sort ...> is now optimized to sort in reverse,
982 avoiding the generation of a temporary intermediate list.
984 =head2 Lexical array access
986 Access to elements of lexical arrays via a numeric constant between 0 and
987 255 is now faster. (This used to be only the case for global arrays.)
989 =head2 XS-assisted SWASHGET
991 Some pure-perl code that perl was using to retrieve Unicode properties and
992 transliteration mappings has been reimplemented in XS.
994 =head2 Constant subroutines
996 The interpreter internals now support a far more memory efficient form of
997 inlineable constants. Storing a reference to a constant value in a symbol
998 table is equivalent to a full typeglob referencing a constant subroutine,
999 but using about 400 bytes less memory. This proxy constant subroutine is
1000 automatically upgraded to a real typeglob with subroutine if necessary.
1001 The approach taken is analogous to the existing space optimisation for
1002 subroutine stub declarations, which are stored as plain scalars in place
1003 of the full typeglob.
1005 Several of the core modules have been converted to use this feature for
1006 their system dependent constants - as a result C<use POSIX;> now takes about
1009 =head2 C<PERL_DONT_CREATE_GVSV>
1011 The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
1012 in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
1013 from creating an empty scalar with every new typeglob. See L<perl588delta>
1016 =head2 Weak references are cheaper
1018 Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
1019 Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
1020 happens at program exit, it may be skipped completely.
1022 =head2 sort() enhancements
1024 Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
1025 and to speed up some cases.
1027 =head2 Memory optimisations
1029 Several internal data structures (typeglobs, GVs, CVs, formats) have been
1030 restructured to use less memory. (Nicholas Clark)
1032 =head2 UTF-8 cache optimisation
1034 The UTF-8 caching code is now more efficient, and used more often.
1037 =head2 Sloppy stat on Windows
1039 On Windows, perl's stat() function normally opens the file to determine
1040 the link count and update attributes that may have been changed through
1041 hard links. Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up
1042 stat() by not performing this operation. (Jan Dubois)
1044 =head2 Regular expressions optimisations
1048 =item Engine de-recursivised
1050 The regular expression engine is no longer recursive, meaning that
1051 patterns that used to overflow the stack will either die with useful
1052 explanations, or run to completion, which, since they were able to blow
1053 the stack before, will likely take a very long time to happen. If you were
1054 experiencing the occasional stack overflow (or segfault) and upgrade to
1055 discover that now perl apparently hangs instead, look for a degenerate
1056 regex. (Dave Mitchell)
1058 =item Single char char-classes treated as literals
1060 Classes of a single character are now treated the same as if the character
1061 had been used as a literal, meaning that code that uses char-classes as an
1062 escaping mechanism will see a speedup. (Yves Orton)
1064 =item Trie optimisation of literal string alternations
1066 Alternations, where possible, are optimised into more efficient matching
1067 structures. String literal alternations are merged into a trie and are
1068 matched simultaneously. This means that instead of O(N) time for matching
1069 N alternations at a given point, the new code performs in O(1) time.
1070 A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune
1071 this optimization. (Yves Orton)
1073 B<Note:> Much code exists that works around perl's historic poor
1074 performance on alternations. Often the tricks used to do so will disable
1075 the new optimisations. Hopefully the utility modules used for this purpose
1076 will be educated about these new optimisations.
1078 =item Aho-Corasick start-point optimisation
1080 When a pattern starts with a trie-able alternation and there aren't
1081 better optimisations available, the regex engine will use Aho-Corasick
1082 matching to find the start point. (Yves Orton)
1086 =head1 Installation and Configuration Improvements
1088 =head2 Configuration improvements
1092 =item C<-Dusesitecustomize>
1094 Run-time customization of @INC can be enabled by passing the
1095 C<-Dusesitecustomize> flag to Configure. When enabled, this will make perl
1096 run F<$sitelibexp/sitecustomize.pl> before anything else. This script can
1097 then be set up to add additional entries to @INC.
1099 =item Relocatable installations
1101 There is now Configure support for creating a relocatable perl tree. If
1102 you Configure with C<-Duserelocatableinc>, then the paths in @INC (and
1103 everything else in %Config) can be optionally located via the path of the
1106 That means that, if the string C<".../"> is found at the start of any
1107 path, it's substituted with the directory of $^X. So, the relocation can
1108 be configured on a per-directory basis, although the default with
1109 C<-Duserelocatableinc> is that everything is relocated. The initial
1110 install is done to the original configured prefix.
1112 =item strlcat() and strlcpy()
1114 The configuration process now detects whether strlcat() and strlcpy() are
1115 available. When they are not available, perl's own version is used (from
1116 Russ Allbery's public domain implementation). Various places in the perl
1117 interpreter now use them. (Steve Peters)
1119 =item C<d_pseudofork> and C<d_printf_format_null>
1121 A new configuration variable, available as C<$Config{d_pseudofork}> in
1122 the L<Config> module, has been added, to distinguish real fork() support
1123 from fake pseudofork used on Windows platforms.
1125 A new configuration variable, C<d_printf_format_null>, has been added,
1126 to see if printf-like formats are allowed to be NULL.
1128 =item Configure help
1130 C<Configure -h> has been extended with the most commonly used options.
1134 =head2 Compilation improvements
1138 =item Parallel build
1140 Parallel makes should work properly now, although there may still be problems
1141 if C<make test> is instructed to run in parallel.
1143 =item Borland's compilers support
1145 Building with Borland's compilers on Win32 should work more smoothly. In
1146 particular Steve Hay has worked to side step many warnings emitted by their
1147 compilers and at least one C compiler internal error.
1149 =item Static build on Windows
1151 Perl extensions on Windows now can be statically built into the Perl DLL.
1153 Also, it's now possible to build a C<perl-static.exe> that doesn't depend
1154 on the Perl DLL on Win32. See the Win32 makefiles for details.
1157 =item ppport.h files
1159 All F<ppport.h> files in the XS modules bundled with perl are now
1160 autogenerated at build time. (Marcus Holland-Moritz)
1162 =item C++ compatibility
1164 Efforts have been made to make perl and the core XS modules compilable
1165 with various C++ compilers (although the situation is not perfect with
1166 some of the compilers on some of the platforms tested.)
1168 =item Support for Microsoft 64-bit compiler
1170 Support for building perl with Microsoft's 64-bit compiler has been
1171 improved. (ActiveState)
1175 Perl can now be compiled with Microsoft Visual C++ 2005 (and 2008 Beta 2).
1179 All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
1183 =head2 Installation improvements
1187 =item Module auxiliary files
1189 README files and changelogs for CPAN modules bundled with perl are no
1194 =head2 New Or Improved Platforms
1196 Perl has been reported to work on Symbian OS. See L<perlsymbian> for more
1199 Many improvements have been made towards making Perl work correctly on
1202 Perl has been reported to work on DragonFlyBSD and MidnightBSD.
1204 The VMS port has been improved. See L<perlvms>.
1206 Support for Cray XT4 Catamount/Qk has been added. See
1207 F<hints/catamount.sh> in the source code distribution for more
1210 Vendor patches have been merged for RedHat and Gentoo.
1212 DynaLoader::dl_unload_file() now works on Windows.
1214 =head1 Selected Bug Fixes
1218 =item strictures in regexp-eval blocks
1220 C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
1222 =item Calling CORE::require()
1224 CORE::require() and CORE::do() were always parsed as require() and do()
1225 when they were overridden. This is now fixed.
1227 =item Subscripts of slices
1229 You can now use a non-arrowed form for chained subscripts after a list
1232 ({foo => "bar"})[0]{foo}
1234 This used to be a syntax error; a C<< -> >> was required.
1236 =item C<no warnings 'category'> works correctly with -w
1238 Previously when running with warnings enabled globally via C<-w>, selective
1239 disabling of specific warning categories would actually turn off all warnings.
1240 This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
1241 C<io> class. Previously it would erroneously turn off all warnings.
1243 =item threads improvements
1245 Several memory leaks in ithreads were closed. Also, ithreads were made
1246 less memory-intensive.
1248 C<threads> is now a dual-life module, also available on CPAN. It has been
1249 expanded in many ways. A kill() method is available for thread signalling.
1250 One can get thread status, or the list of running or joinable threads.
1252 A new C<< threads->exit() >> method is used to exit from the application
1253 (this is the default for the main thread) or from the current thread only
1254 (this is the default for all other threads). On the other hand, the exit()
1255 built-in now always causes the whole application to terminate. (Jerry
1258 =item chr() and negative values
1260 chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
1261 character, unless when the C<bytes> pragma is in effect, where the low
1262 eight bytes of the value are used.
1264 =item PERL5SHELL and tainting
1266 On Windows, the PERL5SHELL environment variable is now checked for
1267 taintedness. (Rafael Garcia-Suarez)
1269 =item Using *FILE{IO}
1271 C<stat()> and C<-X> filetests now treat *FILE{IO} filehandles like *FILE
1272 filehandles. (Steve Peters)
1274 =item Overloading and reblessing
1276 Overloading now works when references are reblessed into another class.
1277 Internally, this has been implemented by moving the flag for "overloading"
1278 from the reference to the referent, which logically is where it should
1279 always have been. (Nicholas Clark)
1281 =item Overloading and UTF-8
1283 A few bugs related to UTF-8 handling with objects that have
1284 stringification overloaded have been fixed. (Nicholas Clark)
1286 =item eval memory leaks fixed
1288 Traditionally, C<eval 'syntax error'> has leaked badly. Many (but not all)
1289 of these leaks have now been eliminated or reduced. (Dave Mitchell)
1291 =item Random device on Windows
1293 In previous versions, perl would read the file F</dev/urandom> if it
1294 existed when seeding its random number generator. That file is unlikely
1295 to exist on Windows, and if it did would probably not contain appropriate
1296 data, so perl no longer tries to read it on Windows. (Alex Davies)
1300 The C<PERLIO_DEBUG> environment variable no longer has any effect for
1301 setuid scripts and for scripts run with B<-T>.
1303 Moreover, with a thread-enabled perl, using C<PERLIO_DEBUG> could lead to
1304 an internal buffer overflow. This has been fixed.
1306 =item PerlIO::scalar and read-only scalars
1308 PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
1309 seek() is now supported with PerlIO::scalar-based filehandles, the
1310 underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
1312 =item study() and UTF-8
1314 study() never worked for UTF-8 strings, but could lead to false results.
1315 It's now a no-op on UTF-8 data. (Yves Orton)
1317 =item Critical signals
1319 The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
1320 "unsafe" manner (contrary to other signals, that are deferred until the
1321 perl interpreter reaches a reasonably stable state; see
1322 L<perlipc/"Deferred Signals (Safe Signals)">). (Rafael)
1326 When a module or a file is loaded through an @INC-hook, and when this hook
1327 has set a filename entry in %INC, __FILE__ is now set for this module
1328 accordingly to the contents of that %INC entry. (Rafael)
1330 =item C<-t> switch fix
1332 The C<-w> and C<-t> switches can now be used together without messing
1333 up which categories of warnings are activated. (Rafael)
1335 =item Duping UTF-8 filehandles
1337 Duping a filehandle which has the C<:utf8> PerlIO layer set will now
1338 properly carry that layer on the duped filehandle. (Rafael)
1340 =item Localisation of hash elements
1342 Localizing a hash element whose key was given as a variable didn't work
1343 correctly if the variable was changed while the local() was in effect (as
1344 in C<local $h{$x}; ++$x>). (Bo Lindbergh)
1348 =head1 New or Changed Diagnostics
1352 =item Use of uninitialized value
1354 Perl will now try to tell you the name of the variable (if any) that was
1357 =item Deprecated use of my() in false conditional
1359 A new deprecation warning, I<Deprecated use of my() in false conditional>,
1360 has been added, to warn against the use of the dubious and deprecated
1365 See L<perldiag>. Use C<state> variables instead.
1367 =item !=~ should be !~
1369 A new warning, C<!=~ should be !~>, is emitted to prevent this misspelling
1370 of the non-matching operator.
1372 =item Newline in left-justified string
1374 The warning I<Newline in left-justified string> has been removed.
1376 =item Too late for "-T" option
1378 The error I<Too late for "-T" option> has been reformulated to be more
1381 =item "%s" variable %s masks earlier declaration
1383 This warning is now emitted in more consistent cases; in short, when one
1384 of the declarations involved is a C<my> variable:
1386 my $x; my $x; # warns
1387 my $x; our $x; # warns
1388 our $x; my $x; # warns
1390 On the other hand, the following:
1394 now gives a C<"our" variable %s redeclared> warning.
1396 =item readdir()/closedir()/etc. attempted on invalid dirhandle
1398 These new warnings are now emitted when a dirhandle is used but is
1399 either closed or not really a dirhandle.
1401 =item Opening dirhandle/filehandle %s also as a file/directory
1403 Two deprecation warnings have been added: (Rafael)
1405 Opening dirhandle %s also as a file
1406 Opening filehandle %s also as a directory
1408 =item Use of -P is deprecated
1410 Perl's command-line switch C<-P> is now deprecated.
1412 =item v-string in use/require is non-portable
1414 Perl will warn you against potential backwards compatibility problems with
1415 the C<use VERSION> syntax.
1419 C<perl -V> has several improvements, making it more useable from shell
1420 scripts to get the value of configuration variables. See L<perlrun> for
1425 =head1 Changed Internals
1427 In general, the source code of perl has been refactored, tidied up,
1428 and optimized in many places. Also, memory management and allocation
1429 has been improved in several points.
1431 When compiling the perl core with gcc, as many gcc warning flags are
1432 turned on as is possible on the platform. (This quest for cleanliness
1433 doesn't extend to XS code because we cannot guarantee the tidiness of
1434 code we didn't write.) Similar strictness flags have been added or
1435 tightened for various other C compilers.
1437 =head2 Reordering of SVt_* constants
1439 The relative ordering of constants that define the various types of C<SV>
1440 have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
1441 C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
1442 difference unless you have code that explicitly makes assumptions about that
1443 ordering. (The inheritance hierarchy of C<B::*> objects has been changed
1446 =head2 Elimination of SVt_PVBM
1448 Related to this, the internal type C<SVt_PVBM> has been been removed. This
1449 dedicated type of C<SV> was used by the C<index> operator and parts of the
1450 regexp engine to facilitate fast Boyer-Moore matches. Its use internally has
1451 been replaced by C<SV>s of type C<SVt_PVGV>.
1453 =head2 New type SVt_BIND
1455 A new type C<SVt_BIND> has been added, in readiness for the project to
1456 implement Perl 6 on 5. There deliberately is no implementation yet, and
1457 they cannot yet be created or destroyed.
1459 =head2 Removal of CPP symbols
1461 The C preprocessor symbols C<PERL_PM_APIVERSION> and
1462 C<PERL_XS_APIVERSION>, which were supposed to give the version number of
1463 the oldest perl binary-compatible (resp. source-compatible) with the
1464 present one, were not used, and sometimes had misleading values. They have
1467 =head2 Less space is used by ops
1469 The C<BASEOP> structure now uses less space. The C<op_seq> field has been
1470 removed and replaced by a single bit bit-field C<op_opt>. C<op_type> is now 9
1471 bits long. (Consequently, the C<B::OP> class doesn't provide an C<seq>
1476 perl's parser is now generated by bison (it used to be generated by
1477 byacc.) As a result, it seems to be a bit more robust.
1479 Also, Dave Mitchell improved the lexer debugging output under C<-DT>.
1481 =head2 Use of C<const>
1483 Andy Lester supplied many improvements to determine which function
1484 parameters and local variables could actually be declared C<const> to the C
1485 compiler. Steve Peters provided new C<*_set> macros and reworked the core to
1486 use these rather than assigning to macros in LVALUE context.
1490 A new file, F<mathoms.c>, has been added. It contains functions that are
1491 no longer used in the perl core, but that remain available for binary or
1492 source compatibility reasons. However, those functions will not be
1493 compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
1495 =head2 C<AvFLAGS> has been removed
1497 The C<AvFLAGS> macro has been removed.
1499 =head2 C<av_*> changes
1501 The C<av_*()> functions, used to manipulate arrays, no longer accept null
1506 The implementation of the special variables $^H and %^H has changed, to
1507 allow implementing lexical pragmas in pure Perl.
1509 =head2 B:: modules inheritance changed
1511 The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
1512 inherits from C<B::SV> (it used to inherit from C<B::IV>).
1514 =head2 Anonymous hash and array constructors
1516 The anonymous hash and array constructors now take 1 op in the optree
1517 instead of 3, now that pp_anonhash and pp_anonlist return a reference to
1518 an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
1520 =head1 Known Problems
1522 There's still a remaining problem in the implementation of the lexical
1523 C<$_>: it doesn't work inside C</(?{...})/> blocks. (See the TODO test in
1526 =head1 Platform Specific Problems
1528 =head1 Reporting Bugs
1532 The F<Changes> file and the perl590delta to perl595delta man pages for
1533 exhaustive details on what changed.
1535 The F<INSTALL> file for how to build Perl.
1537 The F<README> file for general stuff.
1539 The F<Artistic> and F<Copying> files for copyright information.