3 perldelta - what is new for perl 5.10.0
7 This document describes the differences between the 5.8.8 release and
10 Many of the bug fixes in 5.10.0 were already seen in the 5.8.X maintenance
11 releases; they are not duplicated here and are documented in the set of
12 man pages named perl58[1-8]?delta.
14 =head1 Core Enhancements
16 =head2 The C<feature> pragma
18 The C<feature> pragma is used to enable new syntax that would break Perl's
19 backwards-compatibility with older releases of the language. It's a lexical
20 pragma, like C<strict> or C<warnings>.
22 Currently the following new features are available: C<switch> (adds a
23 switch statement), C<say> (adds a C<say> built-in function), and C<state>
24 (adds an C<state> keyword for declaring "static" variables). Those
25 features are described in their own sections of this document.
27 The C<feature> pragma is also implicitly loaded when you require a minimal
28 perl version (with the C<use VERSION> construct) greater than, or equal
29 to, 5.9.5. See L<feature> for details.
31 =head2 New B<-E> command-line switch
33 B<-E> is equivalent to B<-e>, but it implicitly enables all
34 optional features (like C<use feature ":5.10">).
36 =head2 Defined-or operator
38 A new operator C<//> (defined-or) has been implemented.
39 The following expression:
43 is merely equivalent to
51 can now be used instead of
53 $c = $d unless defined $c;
55 The C<//> operator has the same precedence and associativity as C<||>.
56 Special care has been taken to ensure that this operator Do What You Mean
57 while not breaking old code, but some edge cases involving the empty
58 regular expression may now parse differently. See L<perlop> for
61 =head2 Switch and Smart Match operator
63 Perl 5 now has a switch statement. It's available when C<use feature
64 'switch'> is in effect. This feature introduces three new keywords,
65 C<given>, C<when>, and C<default>:
68 when (/^abc/) { $abc = 1; }
69 when (/^def/) { $def = 1; }
70 when (/^xyz/) { $xyz = 1; }
71 default { $nothing = 1; }
74 A more complete description of how Perl matches the switch variable
75 against the C<when> conditions is given in L<perlsyn/"Switch statements">.
77 This kind of match is called I<smart match>, and it's also possible to use
78 it outside of switch statements, via the new C<~~> operator. See
79 L<perlsyn/"Smart matching in detail">.
81 This feature was contributed by Robin Houston.
83 =head2 Regular expressions
87 =item Recursive Patterns
89 It is now possible to write recursive patterns without using the C<(??{})>
90 construct. This new way is more efficient, and in many cases easier to
93 Each capturing parenthesis can now be treated as an independent pattern
94 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
95 "parenthesis number"). For example, the following pattern will match
96 nested balanced angle brackets:
100 ( # start capture buffer 1
101 < # match an opening angle bracket
103 (?> # don't backtrack over the inside of this group
104 [^<>]+ # one or more non angle brackets
105 ) # end non backtracking group
107 (?1) # recurse to bracket 1 and try it again
108 )* # 0 or more times.
109 > # match a closing angle bracket
110 ) # end capture buffer one
114 Note, users experienced with PCRE will find that the Perl implementation
115 of this feature differs from the PCRE one in that it is possible to
116 backtrack into a recursed pattern, whereas in PCRE the recursion is
117 atomic or "possessive" in nature. (Yves Orton)
119 =item Named Capture Buffers
121 It is now possible to name capturing parenthesis in a pattern and refer to
122 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
123 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
124 syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
125 access the contents of the capture buffers.
127 Thus, to replace all doubled chars, one could write
129 s/(?<letter>.)\k<letter>/$+{letter}/g
131 Only buffers with defined contents will be "visible" in the C<%+> hash, so
132 it's possible to do something like
134 foreach my $name (keys %+) {
135 print "content of buffer '$name' is $+{$name}\n";
138 The C<%-> hash is a bit more complete, since it will contain array refs
139 holding values from all capture buffers similarly named, if there should
142 C<%+> and C<%-> are implemented as tied hashes through the new module
143 C<Tie::Hash::NamedCapture>.
145 Users exposed to the .NET regex engine will find that the perl
146 implementation differs in that the numerical ordering of the buffers
147 is sequential, and not "unnamed first, then named". Thus in the pattern
149 /(A)(?<B>B)(C)(?<D>D)/
151 $1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
152 $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
153 would expect. This is considered a feature. :-) (Yves Orton)
155 =item Possessive Quantifiers
157 Perl now supports the "possessive quantifier" syntax of the "atomic match"
158 pattern. Basically a possessive quantifier matches as much as it can and never
159 gives any back. Thus it can be used to control backtracking. The syntax is
160 similar to non-greedy matching, except instead of using a '?' as the modifier
161 the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
162 quantifiers. (Yves Orton)
164 =item Backtracking control verbs
166 The regex engine now supports a number of special-purpose backtrack
167 control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
168 and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
170 =item Relative backreferences
172 A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
173 safer form of back-reference notation as well as allowing relative
174 backreferences. This should make it easier to generate and embed patterns
175 that contain backreferences. See L<perlre/"Capture buffers">. (Yves Orton)
179 The functionality of Jeff Pinyan's module Regexp::Keep has been added to
180 the core. You can now use in regular expressions the special escape C<\K>
181 as a way to do something like floating length positive lookbehind. It is
182 also useful in substitutions like:
186 that can now be converted to
190 which is much more efficient. (Yves Orton)
192 =item Vertical and horizontal whitespace, and linebreak
194 Regular expressions now recognize the C<\v> and C<\h> escapes, that match
195 vertical and horizontal whitespace, respectively. C<\V> and C<\H>
196 logically match their complements.
198 C<\R> matches a generic linebreak, that is, vertical whitespace, plus
199 the multi-character sequence C<"\x0D\x0A">.
205 say() is a new built-in, only available when C<use feature 'say'> is in
206 effect, that is similar to print(), but that implicitly appends a newline
207 to the printed string. See L<perlfunc/say>. (Robin Houston)
211 The default variable C<$_> can now be lexicalized, by declaring it like
212 any other lexical variable, with a simple
216 The operations that default on C<$_> will use the lexically-scoped
217 version of C<$_> when it exists, instead of the global C<$_>.
219 In a C<map> or a C<grep> block, if C<$_> was previously my'ed, then the
220 C<$_> inside the block is lexical as well (and scoped to the block).
222 In a scope where C<$_> has been lexicalized, you can still have access to
223 the global version of C<$_> by using C<$::_>, or, more simply, by
224 overriding the lexical declaration with C<our $_>. (Rafael Garcia-Suarez)
226 =head2 The C<_> prototype
228 A new prototype character has been added. C<_> is equivalent to C<$> (it
229 denotes a scalar), but defaults to C<$_> if the corresponding argument
230 isn't supplied. Due to the optional nature of the argument, you can only
231 use it at the end of a prototype, or before a semicolon.
233 This has a small incompatible consequence: the prototype() function has
234 been adjusted to return C<_> for some built-ins in appropriate cases (for
235 example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
237 =head2 UNITCHECK blocks
239 C<UNITCHECK>, a new special code block has been introduced, in addition to
240 C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
242 C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
243 are always executed at the transition between the compilation and the
244 execution of the main program, and thus are useless whenever code is
245 loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
246 just after the unit which defined them has been compiled. See L<perlmod>
247 for more information. (Alex Gough)
249 =head2 New Pragma, C<mro>
251 A new pragma, C<mro> (for Method Resolution Order) has been added. It
252 permits to switch, on a per-class basis, the algorithm that perl uses to
253 find inherited methods in case of a multiple inheritance hierarchy. The
254 default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
255 available: the C3 algorithm. See L<mro> for more information.
258 Note that, due to changes in the implementation of class hierarchy search,
259 code that used to undef the C<*ISA> glob will most probably break. Anyway,
260 undef'ing C<*ISA> had the side-effect of removing the magic on the @ISA
261 array and should not have been done in the first place.
263 =head2 readpipe() is now overridable
265 The built-in function readpipe() is now overridable. Overriding it permits
266 also to override its operator counterpart, C<qx//> (a.k.a. C<``>).
267 Moreover, it now defaults to C<$_> if no argument is provided. (Rafael
270 =head2 Default argument for readline()
272 readline() now defaults to C<*ARGV> if no argument is provided. (Rafael
275 =head2 state() variables
277 A new class of variables has been introduced. State variables are similar
278 to C<my> variables, but are declared with the C<state> keyword in place of
279 C<my>. They're visible only in their lexical scope, but their value is
280 persistent: unlike C<my> variables, they're not undefined at scope entry,
281 but retain their previous value. (Rafael Garcia-Suarez, Nicholas Clark)
283 To use state variables, one needs to enable them by using
287 or by using the C<-E> command-line switch in one-liners.
288 See L<perlsub/"Persistent variables via state()">.
290 =head2 Stacked filetest operators
292 As a new form of syntactic sugar, it's now possible to stack up filetest
293 operators. You can now write C<-f -w -x $file> in a row to mean
294 C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
296 =head2 UNIVERSAL::DOES()
298 The C<UNIVERSAL> class has a new method, C<DOES()>. It has been added to
299 solve semantic problems with the C<isa()> method. C<isa()> checks for
300 inheritance, while C<DOES()> has been designed to be overridden when
301 module authors use other types of relations between classes (in addition
302 to inheritance). (chromatic)
304 See L<< UNIVERSAL/"$obj->DOES( ROLE )" >>.
306 =head2 C<CLONE_SKIP()>
308 Perl has now support for the C<CLONE_SKIP> special subroutine. Like
309 C<CLONE>, C<CLONE_SKIP> is called once per package; however, it is called
310 just before cloning starts, and in the context of the parent thread. If it
311 returns a true value, then no objects of that class will be cloned. See
312 L<perlmod> for details. (Contributed by Dave Mitchell.)
316 Formats were improved in several ways. A new field, C<^*>, can be used for
317 variable-width, one-line-at-a-time text. Null characters are now handled
318 correctly in picture lines. Using C<@#> and C<~~> together will now
319 produce a compile-time error, as those format fields are incompatible.
320 L<perlform> has been improved, and miscellaneous bugs fixed.
322 =head2 Byte-order modifiers for pack() and unpack()
324 There are two new byte-order modifiers, C<E<gt>> (big-endian) and C<E<lt>>
325 (little-endian), that can be appended to most pack() and unpack() template
326 characters and groups to force a certain byte-order for that type or group.
327 See L<perlfunc/pack> and L<perlpacktut> for details.
331 You can now use C<no> followed by a version number to specify that you
332 want to use a version of perl older than the specified one.
334 =head2 C<chdir>, C<chmod> and C<chown> on filehandles
336 C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
337 filenames, if the system supports respectively C<fchdir>, C<fchmod> and
338 C<fchown>, thanks to a patch provided by Gisle Aas.
342 C<$(> and C<$)> now return groups in the order where the OS returns them,
343 thanks to Gisle Aas. This wasn't previously the case.
345 =head2 Recursive sort subs
347 You can now use recursive subroutines with sort(), thanks to Robin Houston.
349 =head2 Exceptions in constant folding
351 The constant folding routine is now wrapped in an exception handler, and
352 if folding throws an exception (such as attempting to evaluate 0/0), perl
353 now retains the current optree, rather than aborting the whole program.
354 (Nicholas Clark, Dave Mitchell)
356 =head2 Source filters in @INC
358 It's possible to enhance the mechanism of subroutine hooks in @INC by
359 adding a source filter on top of the filehandle opened and returned by the
360 hook. This feature was planned a long time ago, but wasn't quite working
361 until now. See L<perlfunc/require> for details. (Nicholas Clark)
363 =head2 New internal variables
367 =item C<${^RE_DEBUG_FLAGS}>
369 This variable controls what debug flags are in effect for the regular
370 expression engine when running under C<use re "debug">. See L<re> for
373 =item C<${^CHILD_ERROR_NATIVE}>
375 This variable gives the native status returned by the last pipe close,
376 backtick command, successful call to wait() or waitpid(), or from the
377 system() operator. See L<perlrun> for details. (Contributed by Gisle Aas.)
379 =item C<${^RE_TRIE_MAXBUF}>
381 See L</"Trie optimisation of literal string alternations">.
383 =item C<${^WIN32_SLOPPY_STAT}>
385 See L</"Sloppy stat on Windows">.
391 C<unpack()> now defaults to unpacking the C<$_> variable.
393 C<mkdir()> without arguments now defaults to C<$_>.
395 The internal dump output has been improved, so that non-printable characters
396 such as newline and backspace are output in C<\x> notation, rather than
399 The B<-C> option can no longer be used on the C<#!> line. It wasn't
400 working there anyway.
404 The copy of the Unicode Character Database included in Perl 5 has
405 been updated to version 5.0.0.
409 MAD, which stands for I<Misc Attribute Decoration>, is a
410 still-in-development work leading to a Perl 5 to Perl 6 converter. To
411 enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
412 obtained perl isn't binary compatible with a regular perl 5.9.4, and has
413 space and speed penalties; moreover not all regression tests still pass
414 with it. (Larry Wall, Nicholas Clark)
416 =head1 Incompatible Changes
418 =head2 Packing and UTF-8 strings
422 The semantics of pack() and unpack() regarding UTF-8-encoded data has been
423 changed. Processing is now by default character per character instead of
424 byte per byte on the underlying encoding. Notably, code that used things
425 like C<pack("a*", $string)> to see through the encoding of string will now
426 simply get back the original $string. Packed strings can also get upgraded
427 during processing when you store upgraded characters. You can get the old
428 behaviour by using C<use bytes>.
430 To be consistent with pack(), the C<C0> in unpack() templates indicates
431 that the data is to be processed in character mode, i.e. character by
432 character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
433 the packed string is processed in its UTF-8-encoded Unicode form on a byte
434 by byte basis. This is reversed with regard to perl 5.8.X.
436 Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
437 respectively character and byte modes.
439 C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
440 specified encoding mode, honoring parens grouping. Previously, parens were
443 Also, there is a new pack() character format, C<W>, which is intended to
444 replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
445 the strings internal representation. C<W> represents unsigned (logical)
446 character values, which can be greater than 255. It is therefore more
447 robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
448 values outside the range 0..255, and not respect the string encoding).
450 In practice, that means that pack formats are now encoding-neutral, except
453 For consistency, C<A> in unpack() format now trims all Unicode whitespace
454 from the end of the string. Before perl 5.9.2, it used to strip only the
455 classical ASCII space characters.
457 =head2 Byte/character count feature in unpack()
459 A new unpack() template character, C<".">, returns the number of bytes or
460 characters (depending on the selected encoding mode, see above) read so far.
462 =head2 The C<$*> and C<$#> variables have been removed
464 C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
465 modifiers, has been removed.
467 The deprecated C<$#> variable (output format for numbers) has been
470 Two new severe warnings, C<$#/$* is no longer supported>, have been added.
472 =head2 substr() lvalues are no longer fixed-length
474 The lvalues returned by the three argument form of substr() used to be a
475 "fixed length window" on the original string. In some cases this could
476 cause surprising action at distance or other undefined behaviour. Now the
477 length of the window adjusts itself to the length of the string assigned to
480 =head2 Parsing of C<-f _>
482 The identifier C<_> is now forced to be a bareword after a filetest
483 operator. This solves a number of misparsing issues when a global C<_>
484 subroutine is defined.
488 The C<:unique> attribute has been made a no-op, since its current
489 implementation was fundamentally flawed and not threadsafe.
491 =head2 Effect of pragmas in eval
493 The compile-time value of the C<%^H> hint variable can now propagate into
494 eval("")uated code. This makes it more useful to implement lexical
497 As a side-effect of this, the overloaded-ness of constants now propagates
502 A bareword argument to chdir() is now recognized as a file handle.
503 Earlier releases interpreted the bareword as a directory name.
506 =head2 Handling of .pmc files
508 An old feature of perl was that before C<require> or C<use> look for a
509 file with a F<.pm> extension, they will first look for a similar filename
510 with a F<.pmc> extension. If this file is found, it will be loaded in
511 place of any potentially existing file ending in a F<.pm> extension.
513 Previously, F<.pmc> files were loaded only if more recent than the
514 matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
517 =head2 @- and @+ in patterns
519 The special arrays C<@-> and C<@+> are no longer interpolated in regular
520 expressions. (Sadahiro Tomoyuki)
522 =head2 $AUTOLOAD can now be tainted
524 If you call a subroutine by a tainted name, and if it defers to an
525 AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
528 =head2 Tainting and printf
530 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
531 reject any tainted format argument. (Rafael Garcia-Suarez)
533 =head2 undef and signal handlers
535 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
536 equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
538 =head2 strictures and dereferencing in defined()
540 C<use strict "refs"> was ignoring taking a hard reference in an argument
541 to defined(), as in :
545 if (defined $$x) {...}
547 This now correctly produces the run-time error C<Can't use string as a
548 SCALAR ref while "strict refs" in use>.
550 C<defined @$foo> and C<defined %$bar> are now also subject to C<strict
551 'refs'> (that is, C<$foo> and C<$bar> shall be proper references there.)
552 (C<defined(@foo)> and C<defined(%bar)> are discouraged constructs anyway.)
555 =head2 C<(?p{})> has been removed
557 The regular expression construct C<(?p{})>, which was deprecated in perl
558 5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
560 =head2 Pseudo-hashes have been removed
562 Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
563 pragma remains here, but uses an alternate implementation.)
565 =head2 Removal of the bytecode compiler and of perlcc
567 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
568 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
569 experimental tools have never worked reliably, and, due to the lack of
570 volunteers to keep them in line with the perl interpreter developments, it
571 was decided to remove them instead of shipping a broken version of those.
572 The last version of those modules can be found with perl 5.9.4.
574 However the B compiler framework stays supported in the perl core, as with
575 the more useful modules it has permitted (among others, B::Deparse and
578 =head2 Removal of the JPL
580 The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
582 =head2 Recursive inheritance detected earlier
584 Perl will now immediately throw an exception if you modify any package's
585 C<@ISA> in such a way that it would cause recursive inheritance.
587 Previously, the exception would not occur until Perl attempted to make
588 use of the recursive inheritance while resolving a method or doing a
589 C<$foo-E<gt>isa($bar)> lookup.
591 =head1 Modules and Pragmata
593 =head2 Pragmata Changes
599 The new pragma C<feature> is used to enable new features that might break
600 old code. See L</"The C<feature> pragma"> above.
604 This new pragma enables to change the algorithm used to resolve inherited
605 methods. See L</"New Pragma, C<mro>"> above.
607 =item Scoping of the C<sort> pragma
609 The C<sort> pragma is now lexically scoped. Its effect used to be global.
611 =item Scoping of C<bignum>, C<bigint>, C<bigrat>
613 The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
614 lexically scoped. (Tels)
618 The C<base> pragma now warns if a class tries to inherit from itself.
621 =item C<strict> and C<warnings>
623 C<strict> and C<warnings> will now complain loudly if they are loaded via
624 incorrect casing (as in C<use Strict;>). (Johan Vromans)
628 The C<version> module provides support for version objects.
632 The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
633 that used C<Carp> routines without having loaded it at compile time might
634 need to be adjusted; typically, the following (faulty) code won't work
635 anymore, and will require parentheses to be added after the function name:
639 Carp::confess "argh";
643 C<less> now does something useful (or at least it tries to). In fact, it
644 has been turned into a lexical pragma. So, in your modules, you can now
645 test whether your users have requested to use less CPU, or less memory,
646 less magic, or maybe even less fat. See L<less> for more. (Joshua ben
657 C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
658 whenever an ASCII character string containing high-bit bytes is implicitly
659 converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
660 perls, its effect is global.
664 C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
665 you what versions of core modules ship with any versions of Perl 5. It
666 comes with a command-line frontend, C<corelist>.
670 C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
671 C<Math::BigInt::Calc>.
675 C<Compress::Zlib> is an interface to the zlib compression library. It
676 comes with a bundled version of zlib, so having a working zlib is not a
677 prerequisite to install it. It's used by C<Archive::Tar> (see below).
681 C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
685 C<Archive::Tar> is a module to manipulate C<tar> archives.
689 C<Digest::SHA> is a module used to calculate many types of SHA digests,
690 has been included for SHA support in the CPAN module.
694 C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
698 C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
699 provides support for I<field hashes>: hashes that maintain an association
700 of a reference with a value, in a thread-safe garbage-collected way.
701 Such hashes are useful to implement inside-out objects.
705 C<Module::Build>, by Ken Williams, has been added. It's an alternative to
706 C<ExtUtils::MakeMaker> to build and install perl modules.
710 C<Module::Load>, by Jos Boumans, has been added. It provides a single
711 interface to load Perl modules and F<.pl> files.
715 C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
716 modules as loaded or unloaded.
720 C<Package::Constants>, by Jos Boumans, has been added. It's a simple
721 helper to list all constants declared in a given package.
725 C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
726 This module provides low-level access to Win32 system API calls for
731 C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
732 C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
733 included in the perl core; the behaviour of C<Locale::Maketext::Simple>
734 gracefully degrades when the later isn't present.
738 C<Params::Check> implements a generic input parsing/checking mechanism. It
743 C<Term::UI> simplifies the task to ask questions at a terminal prompt.
747 C<Object::Accessor> provides an interface to create per-object accessors.
751 C<Module::Pluggable> is a simple framework to create modules that accept
752 pluggable sub-modules.
756 C<Module::Load::Conditional> provides simple ways to query and possibly
757 load installed modules.
761 C<Time::Piece> provides an object oriented interface to time functions,
762 overriding the built-ins localtime() and gmtime().
766 C<IPC::Cmd> helps to find and run external commands, possibly
771 C<File::Fetch> provide a simple generic file fetching mechanism.
775 C<Log::Message> and C<Log::Message::Simple> are used by the log facility
780 C<Archive::Extract> is a generic archive extraction mechanism
781 for F<.tar> (plain, gziped or bzipped) or F<.zip> files.
785 C<CPANPLUS> provides an API and a command-line tool to access the CPAN
790 =head2 Selected Changes to Core Modules
794 =item C<Attribute::Handlers>
796 C<Attribute::Handlers> can now report the caller's file and line number.
801 C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
802 with plugins. (Joshua ben Jore)
806 It's now possible to access the lexical pragma hints (C<%^H>) by using the
807 method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
808 can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
813 As the old 5005thread threading model has been removed, in favor of the
814 ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
815 be used in old code only. It has been removed from the default list of
820 =head1 Utility Changes
826 The Perl debugger can now save all debugger commands for sourcing later;
827 notably, it can now emulate stepping backwards, by restarting and
828 rerunning all bar the last command from a saved command history.
830 It can also display the parent inheritance tree of a given class, with the
833 Perl has a new -dt command-line flag, which enables threads support in the
838 C<ptar> is a pure perl implementation of C<tar>, that comes with
843 C<ptardiff> is a small script used to generate a diff between the contents
844 of a tar archive and a directory tree. Like C<ptar>, it comes with
849 C<shasum> is a command-line utility, used to print or to check SHA
850 digests. It comes with the new C<Digest::SHA> module.
854 The C<corelist> utility is now installed with perl (see L</"New modules">
859 C<h2ph> and C<h2xs> have been made a bit more robust with regard to
862 C<h2xs> implements a new option C<--use-xsloader> to force use of
863 C<XSLoader> even in backwards compatible modules.
865 The handling of authors' names that had apostrophes has been fixed.
867 Any enums with negative values are now skipped.
871 C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
872 option to run I<all> tests.
876 C<find2perl> now assumes C<-print> as a default action. Previously, it
877 needed to be specified explicitly.
879 Several bugs have been fixed in C<find2perl>, regarding C<-exec> and
880 C<-eval>. Also the options C<-path>, C<-ipath> and C<-iname> have been
885 C<config_data> is a new utility that comes with C<Module::Build>. It
886 provides a command-line interface to the configuration of Perl modules
887 that use Module::Build's framework of configurability (that is,
888 C<*::ConfigData> modules that contain local configuration information for
889 their parent modules.)
893 C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, an
894 helper for CPANPLUS operation, has been added too, but isn't intended for
899 C<cpan2dist> is a new utility, that comes with CPANPLUS. It's a tool to
900 create distributions (or packages) from CPAN modules.
904 The output of C<pod2html> has been enhanced to be more customizable via
905 CSS. Some formatting problems were also corrected. (Jari Aalto)
909 =head1 New Documentation
911 The L<perlpragma> manpage documents how to write one's own lexical
912 pragmas in pure Perl (something that is possible starting with 5.9.4).
914 The new L<perlglossary> manpage is a glossary of terms used in the Perl
915 documentation, technical and otherwise, kindly provided by O'Reilly Media,
918 The L<perlreguts> manpage, courtesy of Yves Orton, describes internals of the
919 Perl regular expression engine.
921 The L<perlunitut> manpage is an tutorial for programming with Unicode and
922 string encodings in Perl, courtesy of Juerd Waalboer.
924 A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
927 The L<perlcommunity> manpage gives a description of the Perl community
928 on the Internet and in real life. (Edgar "Trizor" Bering)
930 The L<CORE> manual page documents the C<CORE::> namespace. (Tels)
932 The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
935 =head1 Performance Enhancements
937 =head2 In-place sorting
939 Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
940 making a temporary copy of the array.
942 Likewise, C<reverse sort ...> is now optimized to sort in reverse,
943 avoiding the generation of a temporary intermediate list.
945 =head2 Lexical array access
947 Access to elements of lexical arrays via a numeric constant between 0 and
948 255 is now faster. (This used to be only the case for global arrays.)
950 =head2 XS-assisted SWASHGET
952 Some pure-perl code that perl was using to retrieve Unicode properties and
953 transliteration mappings has been reimplemented in XS.
955 =head2 Constant subroutines
957 The interpreter internals now support a far more memory efficient form of
958 inlineable constants. Storing a reference to a constant value in a symbol
959 table is equivalent to a full typeglob referencing a constant subroutine,
960 but using about 400 bytes less memory. This proxy constant subroutine is
961 automatically upgraded to a real typeglob with subroutine if necessary.
962 The approach taken is analogous to the existing space optimisation for
963 subroutine stub declarations, which are stored as plain scalars in place
964 of the full typeglob.
966 Several of the core modules have been converted to use this feature for
967 their system dependent constants - as a result C<use POSIX;> now takes about
970 =head2 C<PERL_DONT_CREATE_GVSV>
972 The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
973 in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
974 from creating an empty scalar with every new typeglob. See L<perl588delta>
977 =head2 Weak references are cheaper
979 Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
980 Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
981 happens at program exit, it may be skipped completely.
983 =head2 sort() enhancements
985 Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
986 and to speed up some cases.
988 =head2 Memory optimisations
990 Several internal data structures (typeglobs, GVs, CVs, formats) have been
991 restructured to use less memory. (Nicholas Clark)
993 =head2 UTF-8 cache optimisation
995 The UTF-8 caching code is now more efficient, and used more often.
998 =head2 Sloppy stat on Windows
1000 On Windows, perl's stat() function normally opens the file to determine
1001 the link count and update attributes that may have been changed through
1002 hard links. Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up
1003 stat() by not performing this operation. (Jan Dubois)
1005 =head2 Regular expressions optimisations
1009 =item Engine de-recursivised
1011 The regular expression engine is no longer recursive, meaning that
1012 patterns that used to overflow the stack will either die with useful
1013 explanations, or run to completion, which, since they were able to blow
1014 the stack before, will likely take a very long time to happen. If you were
1015 experiencing the occasional stack overflow (or segfault) and upgrade to
1016 discover that now perl apparently hangs instead, look for a degenerate
1017 regex. (Dave Mitchell)
1019 =item Single char char-classes treated as literals
1021 Classes of a single character are now treated the same as if the character
1022 had been used as a literal, meaning that code that uses char-classes as an
1023 escaping mechanism will see a speedup. (Yves Orton)
1025 =item Trie optimisation of literal string alternations
1027 Alternations, where possible, are optimised into more efficient matching
1028 structures. String literal alternations are merged into a trie and are
1029 matched simultaneously. This means that instead of O(N) time for matching
1030 N alternations at a given point, the new code performs in O(1) time.
1031 A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune
1032 this optimization. (Yves Orton)
1034 B<Note:> Much code exists that works around perl's historic poor
1035 performance on alternations. Often the tricks used to do so will disable
1036 the new optimisations. Hopefully the utility modules used for this purpose
1037 will be educated about these new optimisations by the time 5.10 is
1040 =item Aho-Corasick start-point optimisation
1042 When a pattern starts with a trie-able alternation and there aren't
1043 better optimisations available the regex engine will use Aho-Corasick
1044 matching to find the start point. (Yves Orton)
1048 =head1 Installation and Configuration Improvements
1050 =head2 Configuration improvements
1054 =item C<-Dusesitecustomize>
1056 Run-time customization of @INC can be enabled by passing the
1057 C<-Dusesitecustomize> flag to Configure. When enabled, this will make perl
1058 run F<$sitelibexp/sitecustomize.pl> before anything else. This script can
1059 then be set up to add additional entries to @INC.
1061 =item Relocatable installations
1063 There is now Configure support for creating a relocatable perl tree. If
1064 you Configure with C<-Duserelocatableinc>, then the paths in @INC (and
1065 everything else in %Config) can be optionally located via the path of the
1068 That means that, if the string C<".../"> is found at the start of any
1069 path, it's substituted with the directory of $^X. So, the relocation can
1070 be configured on a per-directory basis, although the default with
1071 C<-Duserelocatableinc> is that everything is relocated. The initial
1072 install is done to the original configured prefix.
1074 =item strlcat() and strlcpy()
1076 The configuration process now detects whether strlcat() and strlcpy() are
1077 available. When they are not available, perl's own version is used (from
1078 Russ Allbery's public domain implementation). Various places in the perl
1079 interpreter now use them. (Steve Peters)
1081 =item C<d_pseudofork> and C<d_printf_format_null>
1083 A new configuration variable, available as C<$Config{d_pseudofork}> in
1084 the L<Config> module, has been added, to distinguish real fork() support
1085 from fake pseudofork used on Windows platforms.
1087 A new configuration variable, C<d_printf_format_null>, has been added,
1088 to see if printf-like formats are allowed to be NULL.
1090 =item Configure help
1092 C<Configure -h> has been extended with the most commonly used options.
1096 =head2 Compilation improvements
1100 =item Parallel build
1102 Parallel makes should work properly now, although there may still be problems
1103 if C<make test> is instructed to run in parallel.
1105 =item Borland's compilers support
1107 Building with Borland's compilers on Win32 should work more smoothly. In
1108 particular Steve Hay has worked to side step many warnings emitted by their
1109 compilers and at least one C compiler internal error.
1111 =item Static build on Windows
1113 Perl extensions on Windows now can be statically built into the Perl DLL.
1115 Also, it's now possible to build a C<perl-static.exe> that doesn't depend
1116 on the Perl DLL on Win32. See the Win32 makefiles for details.
1119 =item ppport.h files
1121 All F<ppport.h> files in the XS modules bundled with perl are now
1122 autogenerated at build time. (Marcus Holland-Moritz)
1124 =item C++ compatibility
1126 Efforts have been made to make perl and the core XS modules compilable
1127 with various C++ compilers (although the situation is not perfect with
1128 some of the compilers on some of the platforms tested.)
1130 =item Building XS extensions on Windows
1132 Support for building XS extension modules with the free MinGW compiler has
1133 been improved in the case where perl itself was built with the Microsoft
1134 VC++ compiler. (ActiveState)
1136 =item Support for Microsoft 64-bit compiler
1138 Support for building perl with Microsoft's 64-bit compiler has been
1139 improved. (ActiveState)
1143 Perl now can be compiled with Microsoft Visual C++.
1147 All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
1151 =head2 Installation improvements
1155 =item Module auxiliary files
1157 README files and changelogs for CPAN modules bundled with perl are no
1162 =head2 New Or Improved Platforms
1164 Perl has been reported to work on Symbian OS. See L<perlsymbian> for more
1167 Many improvements have been made towards making Perl work correctly on
1170 Perl has been reported to work on DragonFlyBSD and MidnightBSD.
1172 The VMS port has been improved. See L<perlvms>.
1174 Support for Cray XT4 Catamount/Qk has been added. See
1175 F<hints/catamount.sh> in the source code distribution for more
1178 Vendor patches have been merged for RedHat and Gentoo.
1180 DynaLoader::dl_unload_file() now works on Windows.
1182 =head1 Selected Bug Fixes
1186 =item strictures in regexp-eval blocks
1188 C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
1190 =item Calling CORE::require()
1192 CORE::require() and CORE::do() were always parsed as require() and do()
1193 when they were overridden. This is now fixed.
1195 =item Subscripts of slices
1197 You can now use a non-arrowed form for chained subscripts after a list
1200 ({foo => "bar"})[0]{foo}
1202 This used to be a syntax error; a C<< -> >> was required.
1204 =item C<no warnings 'category'> works correctly with -w
1206 Previously when running with warnings enabled globally via C<-w>, selective
1207 disabling of specific warning categories would actually turn off all warnings.
1208 This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
1209 C<io> class. Previously it would erroneously turn off all warnings.
1211 =item threads improvements
1213 Several memory leaks in ithreads were closed. Also, ithreads were made
1214 less memory-intensive.
1216 C<threads> is now a dual-life module, also available on CPAN. It has been
1217 expanded in many ways. A kill() method is available for thread signalling.
1218 One can get thread status, or the list of running or joinable threads.
1220 A new C<< threads->exit() >> method is used to exit from the application
1221 (this is the default for the main thread) or from the current thread only
1222 (this is the default for all other threads). On the other hand, the exit()
1223 built-in now always causes the whole application to terminate. (Jerry
1226 =item chr() and negative values
1228 chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
1229 character, unless when the C<bytes> pragma is in effect, where the low
1230 eight bytes of the value are used.
1232 =item PERL5SHELL and tainting
1234 On Windows, the PERL5SHELL environment variable is now checked for
1235 taintedness. (Rafael Garcia-Suarez)
1237 =item Using *FILE{IO}
1239 C<stat()> and C<-X> filetests now treat *FILE{IO} filehandles like *FILE
1240 filehandles. (Steve Peters)
1242 =item Overloading and reblessing
1244 Overloading now works when references are reblessed into another class.
1245 Internally, this has been implemented by moving the flag for "overloading"
1246 from the reference to the referent, which logically is where it should
1247 always have been. (Nicholas Clark)
1249 =item Overloading and UTF-8
1251 A few bugs related to UTF-8 handling with objects that have
1252 stringification overloaded have been fixed. (Nicholas Clark)
1254 =item eval memory leaks fixed
1256 Traditionally, C<eval 'syntax error'> has leaked badly. Many (but not all)
1257 of these leaks have now been eliminated or reduced. (Dave Mitchell)
1259 =item Random device on Windows
1261 In previous versions, perl would read the file F</dev/urandom> if it
1262 existed when seeding its random number generator. That file is unlikely
1263 to exist on Windows, and if it did would probably not contain appropriate
1264 data, so perl no longer tries to read it on Windows. (Alex Davies)
1268 The C<PERLIO_DEBUG> environment variable has no longer any effect for
1269 setuid scripts and for scripts run with B<-T>.
1271 Moreover, with a thread-enabled perl, using C<PERLIO_DEBUG> could lead to
1272 an internal buffer overflow. This has been fixed.
1274 =item PerlIO::scalar and read-only scalars
1276 PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
1277 seek() is now supported with PerlIO::scalar-based filehandles, the
1278 underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
1280 =item study() and UTF-8
1282 study() never worked for UTF-8 strings, but could lead to false results.
1283 It's now a no-op on UTF-8 data. (Yves Orton)
1285 =item Critical signals
1287 The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
1288 "unsafe" manner (contrary to other signals, that are deferred until the
1289 perl interpreter reaches a reasonably stable state; see
1290 L<perlipc/"Deferred Signals (Safe Signals)">). (Rafael)
1294 When a module or a file is loaded through an @INC-hook, and when this hook
1295 has set a filename entry in %INC, __FILE__ is now set for this module
1296 accordingly to the contents of that %INC entry. (Rafael)
1298 =item C<-t> switch fix
1300 The C<-w> and C<-t> switches can now be used together without messing
1301 up what categories of warnings are activated or not. (Rafael)
1303 =item Duping UTF-8 filehandles
1305 Duping a filehandle which has the C<:utf8> PerlIO layer set will now
1306 properly carry that layer on the duped filehandle. (Rafael)
1308 =item Localisation of hash elements
1310 Localizing an hash element whose key was given as a variable didn't work
1311 correctly if the variable was changed while the local() was in effect (as
1312 in C<local $h{$x}; ++$x>). (Bo Lindbergh)
1316 =head1 New or Changed Diagnostics
1320 =item Use of uninitialized value
1322 Perl will now try to tell you the name of the variable (if any) that was
1325 =item Deprecated use of my() in false conditional
1327 A new deprecation warning, I<Deprecated use of my() in false conditional>,
1328 has been added, to warn against the use of the dubious and deprecated
1333 See L<perldiag>. Use C<state> variables instead.
1335 =item !=~ should be !~
1337 A new warning, C<!=~ should be !~>, is emitted to prevent this misspelling
1338 of the non-matching operator.
1340 =item Newline in left-justified string
1342 The warning I<Newline in left-justified string> has been removed.
1344 =item Too late for "-T" option
1346 The error I<Too late for "-T" option> has been reformulated to be more
1349 =item "%s" variable %s masks earlier declaration
1351 This warning is now emitted in more consistent cases; in short, when one
1352 of the declarations involved is a C<my> variable:
1354 my $x; my $x; # warns
1355 my $x; our $x; # warns
1356 our $x; my $x; # warns
1358 On the other hand, the following:
1362 now gives a C<"our" variable %s redeclared> warning.
1364 =item readdir()/closedir()/etc. attempted on invalid dirhandle
1366 These new warnings are now emitted when a dirhandle is used but is
1367 either closed or not really a dirhandle.
1369 =item Opening dirhandle/filehandle %s also as a file/directory
1371 Two deprecation warnings have been added: (Rafael)
1373 Opening dirhandle %s also as a file
1374 Opening filehandle %s also as a directory
1376 =item Use of -P is deprecated
1378 Perl's command-line switch C<-P> is now deprecated.
1380 =item v-string in use/require is non-portable
1382 Perl will warn you against potential backwards compatibility problems with
1383 the C<use VERSION> syntax.
1387 C<perl -V> has several improvements, making it more useable from shell
1388 scripts to get the value of configuration variables. See L<perlrun> for
1393 =head1 Changed Internals
1395 In general, the source code of perl has been refactored, tied up, and
1396 optimized in many places. Also, memory management and allocation has been
1397 improved in a couple of points.
1399 =head2 Reordering of SVt_* constants
1401 The relative ordering of constants that define the various types of C<SV>
1402 have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
1403 C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
1404 difference unless you have code that explicitly makes assumptions about that
1405 ordering. (The inheritance hierarchy of C<B::*> objects has been changed
1408 =head2 Removal of CPP symbols
1410 The C preprocessor symbols C<PERL_PM_APIVERSION> and
1411 C<PERL_XS_APIVERSION>, which were supposed to give the version number of
1412 the oldest perl binary-compatible (resp. source-compatible) with the
1413 present one, were not used, and sometimes had misleading values. They have
1416 =head2 Less space is used by ops
1418 The C<BASEOP> structure now uses less space. The C<op_seq> field has been
1419 removed and replaced by the one-bit fields C<op_opt>. C<op_type> is now 9
1420 bits long. (Consequently, the C<B::OP> class doesn't provide an C<seq>
1425 perl's parser is now generated by bison (it used to be generated by
1426 byacc.) As a result, it seems to be a bit more robust.
1428 Also, Dave Mitchell improved the lexer debugging output under C<-DT>.
1430 =head2 Use of C<const>
1432 Andy Lester supplied many improvements to determine which function
1433 parameters and local variables could actually be declared C<const> to the C
1434 compiler. Steve Peters provided new C<*_set> macros and reworked the core to
1435 use these rather than assigning to macros in LVALUE context.
1439 A new file, F<mathoms.c>, has been added. It contains functions that are
1440 no longer used in the perl core, but that remain available for binary or
1441 source compatibility reasons. However, those functions will not be
1442 compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
1444 =head2 C<AvFLAGS> has been removed
1446 The C<AvFLAGS> macro has been removed.
1448 =head2 C<av_*> changes
1450 The C<av_*()> functions, used to manipulate arrays, no longer accept null
1455 The implementation of the special variables $^H and %^H has changed, to
1456 allow implementing lexical pragmas in pure perl.
1458 =head2 B:: modules inheritance changed
1460 The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
1461 inherits from C<B::SV> (it used to inherit from C<B::IV>).
1463 =head2 Anonymous hash and array constructors
1465 The anonymous hash and array constructors now take 1 op in the optree
1466 instead of 3, now that pp_anonhash and pp_anonlist return a reference to
1467 an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
1469 =for p5p XXX have we some docs on how to create regexp engine plugins, since that's now possible ? (perlreguts)
1471 =for p5p XXX new BIND SV type, #29544, #29642
1473 =head1 Known Problems
1475 There's still a remaining problem in the implementation of the lexical
1476 C<$_>: it doesn't work inside C</(?{...})/> blocks. (See the TODO test in
1479 =head1 Platform Specific Problems
1481 =head1 Reporting Bugs
1485 The F<Changes> file and the perl590delta to perl595delta man pages for
1486 exhaustive details on what changed.
1488 The F<INSTALL> file for how to build Perl.
1490 The F<README> file for general stuff.
1492 The F<Artistic> and F<Copying> files for copyright information.