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 a 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 { $nothing = 1; }
74 A more complete description of how Perl matches the switch variable
75 against the C<when> conditions is given in L<perlsyn/"Switch statements">.
77 This kind of match is called I<smart match>, and it's also possible to use
78 it outside of switch statements, via the new C<~~> operator. See
79 L<perlsyn/"Smart matching in detail">.
81 This feature was contributed by Robin Houston.
83 =head2 Regular expressions
87 =item Recursive Patterns
89 It is now possible to write recursive patterns without using the C<(??{})>
90 construct. This new way is more efficient, and in many cases easier to
93 Each capturing parenthesis can now be treated as an independent pattern
94 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
95 "parenthesis number"). For example, the following pattern will match
96 nested balanced angle brackets:
100 ( # start capture buffer 1
101 < # match an opening angle bracket
103 (?> # don't backtrack over the inside of this group
104 [^<>]+ # one or more non angle brackets
105 ) # end non backtracking group
107 (?1) # recurse to bracket 1 and try it again
108 )* # 0 or more times.
109 > # match a closing angle bracket
110 ) # end capture buffer one
114 PCRE users should note that Perl's recursive regex feature allows
115 backtracking into a recursed pattern, whereas in PCRE the recursion is
116 atomic or "possessive" in nature. As in the example above, you can
117 add (?>) to control this selectively. (Yves Orton)
119 =item Named Capture Buffers
121 It is now possible to name capturing parenthesis in a pattern and refer to
122 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
123 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
124 syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
125 access the contents of the capture buffers.
127 Thus, to replace all doubled chars with a single copy, one could write
129 s/(?<letter>.)\k<letter>/$+{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. In regular expressions you can now use 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 $_>. (Rafael Garcia-Suarez)
226 =head2 The C<_> prototype
228 A new prototype character has been added. C<_> is equivalent to C<$> but
229 defaults to C<$_> if the corresponding argument isn't supplied. (both C<$>
230 and C<_> denote a scalar). Due to the optional nature of the argument, you
231 can only 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 readdir() may return a "short filename" on Windows
265 The readdir() function may return a "short filename" when the long
266 filename contains characters outside the ANSI codepage. Similarly
267 Cwd::cwd() may return a short directory name, and glob() may return short
268 names as well. On the NTFS file system these short names can always be
269 represented in the ANSI codepage. This will not be true for all other file
270 system drivers; e.g. the FAT filesystem stores short filenames in the OEM
271 codepage, so some files on FAT volumes remain unaccessible through the
274 Similarly, $^X, @INC, and $ENV{PATH} are preprocessed at startup to make
275 sure all paths are valid in the ANSI codepage (if possible).
277 The Win32::GetLongPathName() function now returns the UTF-8 encoded
278 correct long file name instead of using replacement characters to force
279 the name into the ANSI codepage. The new Win32::GetANSIPathName()
280 function can be used to turn a long pathname into a short one only if the
281 long one cannot be represented in the ANSI codepage.
283 Many other functions in the C<Win32> module have been improved to accept
284 UTF-8 encoded arguments. Please see L<Win32> for details.
286 =head2 readpipe() is now overridable
288 The built-in function readpipe() is now overridable. Overriding it permits
289 also to override its operator counterpart, C<qx//> (a.k.a. C<``>).
290 Moreover, it now defaults to C<$_> if no argument is provided. (Rafael
293 =head2 Default argument for readline()
295 readline() now defaults to C<*ARGV> if no argument is provided. (Rafael
298 =head2 state() variables
300 A new class of variables has been introduced. State variables are similar
301 to C<my> variables, but are declared with the C<state> keyword in place of
302 C<my>. They're visible only in their lexical scope, but their value is
303 persistent: unlike C<my> variables, they're not undefined at scope entry,
304 but retain their previous value. (Rafael Garcia-Suarez, Nicholas Clark)
306 To use state variables, one needs to enable them by using
310 or by using the C<-E> command-line switch in one-liners.
311 See L<perlsub/"Persistent variables via state()">.
313 =head2 Stacked filetest operators
315 As a new form of syntactic sugar, it's now possible to stack up filetest
316 operators. You can now write C<-f -w -x $file> in a row to mean
317 C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
319 =head2 UNIVERSAL::DOES()
321 The C<UNIVERSAL> class has a new method, C<DOES()>. It has been added to
322 solve semantic problems with the C<isa()> method. C<isa()> checks for
323 inheritance, while C<DOES()> has been designed to be overridden when
324 module authors use other types of relations between classes (in addition
325 to inheritance). (chromatic)
327 See L<< UNIVERSAL/"$obj->DOES( ROLE )" >>.
331 Formats were improved in several ways. A new field, C<^*>, can be used for
332 variable-width, one-line-at-a-time text. Null characters are now handled
333 correctly in picture lines. Using C<@#> and C<~~> together will now
334 produce a compile-time error, as those format fields are incompatible.
335 L<perlform> has been improved, and miscellaneous bugs fixed.
337 =head2 Byte-order modifiers for pack() and unpack()
339 There are two new byte-order modifiers, C<E<gt>> (big-endian) and C<E<lt>>
340 (little-endian), that can be appended to most pack() and unpack() template
341 characters and groups to force a certain byte-order for that type or group.
342 See L<perlfunc/pack> and L<perlpacktut> for details.
346 You can now use C<no> followed by a version number to specify that you
347 want to use a version of perl older than the specified one.
349 =head2 C<chdir>, C<chmod> and C<chown> on filehandles
351 C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
352 filenames, if the system supports respectively C<fchdir>, C<fchmod> and
353 C<fchown>, thanks to a patch provided by Gisle Aas.
357 C<$(> and C<$)> now return groups in the order where the OS returns them,
358 thanks to Gisle Aas. This wasn't previously the case.
360 =head2 Recursive sort subs
362 You can now use recursive subroutines with sort(), thanks to Robin Houston.
364 =head2 Exceptions in constant folding
366 The constant folding routine is now wrapped in an exception handler, and
367 if folding throws an exception (such as attempting to evaluate 0/0), perl
368 now retains the current optree, rather than aborting the whole program.
369 Without this change, programs would not compile if they had expressions that
370 happened to generate exceptions, even though those expressions were in code
371 that could never be reached at runtime. (Nicholas Clark, Dave Mitchell)
373 =head2 Source filters in @INC
375 It's possible to enhance the mechanism of subroutine hooks in @INC by
376 adding a source filter on top of the filehandle opened and returned by the
377 hook. This feature was planned a long time ago, but wasn't quite working
378 until now. See L<perlfunc/require> for details. (Nicholas Clark)
380 =head2 New internal variables
384 =item C<${^RE_DEBUG_FLAGS}>
386 This variable controls what debug flags are in effect for the regular
387 expression engine when running under C<use re "debug">. See L<re> for
390 =item C<${^CHILD_ERROR_NATIVE}>
392 This variable gives the native status returned by the last pipe close,
393 backtick command, successful call to wait() or waitpid(), or from the
394 system() operator. See L<perlrun> for details. (Contributed by Gisle Aas.)
396 =item C<${^RE_TRIE_MAXBUF}>
398 See L</"Trie optimisation of literal string alternations">.
400 =item C<${^WIN32_SLOPPY_STAT}>
402 See L</"Sloppy stat on Windows">.
408 C<unpack()> now defaults to unpacking the C<$_> variable.
410 C<mkdir()> without arguments now defaults to C<$_>.
412 The internal dump output has been improved, so that non-printable characters
413 such as newline and backspace are output in C<\x> notation, rather than
416 The B<-C> option can no longer be used on the C<#!> line. It wasn't
417 working there anyway.
421 The copy of the Unicode Character Database included in Perl 5 has
422 been updated to version 5.0.0.
426 MAD, which stands for I<Miscellaneous Attribute Decoration>, is a
427 still-in-development work leading to a Perl 5 to Perl 6 converter. To
428 enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
429 obtained perl isn't binary compatible with a regular perl 5.10, and has
430 space and speed penalties; moreover not all regression tests still pass
431 with it. (Larry Wall, Nicholas Clark)
433 =head2 kill() on Windows
435 On Windows platforms, C<kill(-9, $pid)> now kills a process tree.
436 (On UNIX, this delivers the signal to all processes in the same process
439 =head1 Incompatible Changes
441 =head2 Packing and UTF-8 strings
445 The semantics of pack() and unpack() regarding UTF-8-encoded data has been
446 changed. Processing is now by default character per character instead of
447 byte per byte on the underlying encoding. Notably, code that used things
448 like C<pack("a*", $string)> to see through the encoding of string will now
449 simply get back the original $string. Packed strings can also get upgraded
450 during processing when you store upgraded characters. You can get the old
451 behaviour by using C<use bytes>.
453 To be consistent with pack(), the C<C0> in unpack() templates indicates
454 that the data is to be processed in character mode, i.e. character by
455 character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
456 the packed string is processed in its UTF-8-encoded Unicode form on a byte
457 by byte basis. This is reversed with regard to perl 5.8.X, but now consistent
458 between pack() and unpack().
460 Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
461 respectively character and byte modes.
463 C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
464 specified encoding mode, honoring parens grouping. Previously, parens were
467 Also, there is a new pack() character format, C<W>, which is intended to
468 replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
469 the strings internal representation. C<W> represents unsigned (logical)
470 character values, which can be greater than 255. It is therefore more
471 robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
472 values outside the range 0..255, and not respect the string encoding).
474 In practice, that means that pack formats are now encoding-neutral, except
477 For consistency, C<A> in unpack() format now trims all Unicode whitespace
478 from the end of the string. Before perl 5.9.2, it used to strip only the
479 classical ASCII space characters.
481 =head2 Byte/character count feature in unpack()
483 A new unpack() template character, C<".">, returns the number of bytes or
484 characters (depending on the selected encoding mode, see above) read so far.
486 =head2 The C<$*> and C<$#> variables have been removed
488 C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
489 modifiers, has been removed.
491 The deprecated C<$#> variable (output format for numbers) has been
494 Two new severe warnings, C<$#/$* is no longer supported>, have been added.
496 =head2 substr() lvalues are no longer fixed-length
498 The lvalues returned by the three argument form of substr() used to be a
499 "fixed length window" on the original string. In some cases this could
500 cause surprising action at distance or other undefined behaviour. Now the
501 length of the window adjusts itself to the length of the string assigned to
504 =head2 Parsing of C<-f _>
506 The identifier C<_> is now forced to be a bareword after a filetest
507 operator. This solves a number of misparsing issues when a global C<_>
508 subroutine is defined.
512 The C<:unique> attribute has been made a no-op, since its current
513 implementation was fundamentally flawed and not threadsafe.
515 =head2 Effect of pragmas in eval
517 The compile-time value of the C<%^H> hint variable can now propagate into
518 eval("")uated code. This makes it more useful to implement lexical
521 As a side-effect of this, the overloaded-ness of constants now propagates
526 A bareword argument to chdir() is now recognized as a file handle.
527 Earlier releases interpreted the bareword as a directory name.
530 =head2 Handling of .pmc files
532 An old feature of perl was that before C<require> or C<use> look for a
533 file with a F<.pm> extension, they will first look for a similar filename
534 with a F<.pmc> extension. If this file is found, it will be loaded in
535 place of any potentially existing file ending in a F<.pm> extension.
537 Previously, F<.pmc> files were loaded only if more recent than the
538 matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
541 =head2 @- and @+ in patterns
543 The special arrays C<@-> and C<@+> are no longer interpolated in regular
544 expressions. (Sadahiro Tomoyuki)
546 =head2 $AUTOLOAD can now be tainted
548 If you call a subroutine by a tainted name, and if it defers to an
549 AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
552 =head2 Tainting and printf
554 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
555 reject any tainted format argument. (Rafael Garcia-Suarez)
557 =head2 undef and signal handlers
559 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
560 equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
562 =head2 strictures and dereferencing in defined()
564 C<use strict 'refs'> was ignoring taking a hard reference in an argument
565 to defined(), as in :
569 if (defined $$x) {...}
571 This now correctly produces the run-time error C<Can't use string as a
572 SCALAR ref while "strict refs" in use>.
574 C<defined @$foo> and C<defined %$bar> are now also subject to C<strict
575 'refs'> (that is, C<$foo> and C<$bar> shall be proper references there.)
576 (C<defined(@foo)> and C<defined(%bar)> are discouraged constructs anyway.)
579 =head2 C<(?p{})> has been removed
581 The regular expression construct C<(?p{})>, which was deprecated in perl
582 5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
584 =head2 Pseudo-hashes have been removed
586 Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
587 pragma remains here, but uses an alternate implementation.)
589 =head2 Removal of the bytecode compiler and of perlcc
591 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
592 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
593 experimental tools have never worked reliably, and, due to the lack of
594 volunteers to keep them in line with the perl interpreter developments, it
595 was decided to remove them instead of shipping a broken version of those.
596 The last version of those modules can be found with perl 5.9.4.
598 However the B compiler framework stays supported in the perl core, as with
599 the more useful modules it has permitted (among others, B::Deparse and
602 =head2 Removal of the JPL
604 The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.
606 =head2 Recursive inheritance detected earlier
608 Perl will now immediately throw an exception if you modify any package's
609 C<@ISA> in such a way that it would cause recursive inheritance.
611 Previously, the exception would not occur until Perl attempted to make
612 use of the recursive inheritance while resolving a method or doing a
613 C<$foo-E<gt>isa($bar)> lookup.
615 =head1 Modules and Pragmata
617 =head2 Pragmata Changes
623 The new pragma C<feature> is used to enable new features that might break
624 old code. See L</"The C<feature> pragma"> above.
628 This new pragma enables to change the algorithm used to resolve inherited
629 methods. See L</"New Pragma, C<mro>"> above.
631 =item Scoping of the C<sort> pragma
633 The C<sort> pragma is now lexically scoped. Its effect used to be global.
635 =item Scoping of C<bignum>, C<bigint>, C<bigrat>
637 The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
638 lexically scoped. (Tels)
642 The C<base> pragma now warns if a class tries to inherit from itself.
645 =item C<strict> and C<warnings>
647 C<strict> and C<warnings> will now complain loudly if they are loaded via
648 incorrect casing (as in C<use Strict;>). (Johan Vromans)
652 The C<version> module provides support for version objects.
656 The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
657 that used C<Carp> routines without having loaded it at compile time might
658 need to be adjusted; typically, the following (faulty) code won't work
659 anymore, and will require parentheses to be added after the function name:
663 Carp::confess 'argh';
667 C<less> now does something useful (or at least it tries to). In fact, it
668 has been turned into a lexical pragma. So, in your modules, you can now
669 test whether your users have requested to use less CPU, or less memory,
670 less magic, or maybe even less fat. See L<less> for more. (Joshua ben
681 C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
682 whenever an ASCII character string containing high-bit bytes is implicitly
683 converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
684 perls, its effect is global.
688 C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
689 you what versions of core modules ship with any versions of Perl 5. It
690 comes with a command-line frontend, C<corelist>.
694 C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
695 C<Math::BigInt::Calc>.
699 C<Compress::Zlib> is an interface to the zlib compression library. It
700 comes with a bundled version of zlib, so having a working zlib is not a
701 prerequisite to install it. It's used by C<Archive::Tar> (see below).
705 C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
709 C<Archive::Tar> is a module to manipulate C<tar> archives.
713 C<Digest::SHA> is a module used to calculate many types of SHA digests,
714 has been included for SHA support in the CPAN module.
718 C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
722 C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
723 provides support for I<field hashes>: hashes that maintain an association
724 of a reference with a value, in a thread-safe garbage-collected way.
725 Such hashes are useful to implement inside-out objects.
729 C<Module::Build>, by Ken Williams, has been added. It's an alternative to
730 C<ExtUtils::MakeMaker> to build and install perl modules.
734 C<Module::Load>, by Jos Boumans, has been added. It provides a single
735 interface to load Perl modules and F<.pl> files.
739 C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
740 modules as loaded or unloaded.
744 C<Package::Constants>, by Jos Boumans, has been added. It's a simple
745 helper to list all constants declared in a given package.
749 C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
750 This module provides low-level access to Win32 system API calls for
755 C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
756 C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
757 included in the perl core; the behaviour of C<Locale::Maketext::Simple>
758 gracefully degrades when the later isn't present.
762 C<Params::Check> implements a generic input parsing/checking mechanism. It
767 C<Term::UI> simplifies the task to ask questions at a terminal prompt.
771 C<Object::Accessor> provides an interface to create per-object accessors.
775 C<Module::Pluggable> is a simple framework to create modules that accept
776 pluggable sub-modules.
780 C<Module::Load::Conditional> provides simple ways to query and possibly
781 load installed modules.
785 C<Time::Piece> provides an object oriented interface to time functions,
786 overriding the built-ins localtime() and gmtime().
790 C<IPC::Cmd> helps to find and run external commands, possibly
795 C<File::Fetch> provide a simple generic file fetching mechanism.
799 C<Log::Message> and C<Log::Message::Simple> are used by the log facility
804 C<Archive::Extract> is a generic archive extraction mechanism
805 for F<.tar> (plain, gziped or bzipped) or F<.zip> files.
809 C<CPANPLUS> provides an API and a command-line tool to access the CPAN
814 =head2 Selected Changes to Core Modules
818 =item C<Attribute::Handlers>
820 C<Attribute::Handlers> can now report the caller's file and line number.
825 C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
826 with plugins. (Joshua ben Jore)
830 It's now possible to access the lexical pragma hints (C<%^H>) by using the
831 method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
832 can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
837 As the old 5005thread threading model has been removed, in favor of the
838 ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
839 be used in old code only. It has been removed from the default list of
844 =head1 Utility Changes
850 The Perl debugger can now save all debugger commands for sourcing later;
851 notably, it can now emulate stepping backwards, by restarting and
852 rerunning all bar the last command from a saved command history.
854 It can also display the parent inheritance tree of a given class, with the
859 C<ptar> is a pure perl implementation of C<tar> that comes with
864 C<ptardiff> is a small utility used to generate a diff between the contents
865 of a tar archive and a directory tree. Like C<ptar>, it comes with
870 C<shasum> is a command-line utility, used to print or to check SHA
871 digests. It comes with the new C<Digest::SHA> module.
875 The C<corelist> utility is now installed with perl (see L</"New modules">
880 C<h2ph> and C<h2xs> have been made more robust with regard to
883 C<h2xs> implements a new option C<--use-xsloader> to force use of
884 C<XSLoader> even in backwards compatible modules.
886 The handling of authors' names that had apostrophes has been fixed.
888 Any enums with negative values are now skipped.
892 C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
893 option to run I<all> tests.
897 C<find2perl> now assumes C<-print> as a default action. Previously, it
898 needed to be specified explicitly.
900 Several bugs have been fixed in C<find2perl>, regarding C<-exec> and
901 C<-eval>. Also the options C<-path>, C<-ipath> and C<-iname> have been
906 C<config_data> is a new utility that comes with C<Module::Build>. It
907 provides a command-line interface to the configuration of Perl modules
908 that use Module::Build's framework of configurability (that is,
909 C<*::ConfigData> modules that contain local configuration information for
910 their parent modules.)
914 C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, a
915 helper for CPANPLUS operation, has been added too, but isn't intended for
920 C<cpan2dist> is a new utility that comes with CPANPLUS. It's a tool to
921 create distributions (or packages) from CPAN modules.
925 The output of C<pod2html> has been enhanced to be more customizable via
926 CSS. Some formatting problems were also corrected. (Jari Aalto)
930 =head1 New Documentation
932 The L<perlpragma> manpage documents how to write one's own lexical
933 pragmas in pure Perl (something that is possible starting with 5.9.4).
935 The new L<perlglossary> manpage is a glossary of terms used in the Perl
936 documentation, technical and otherwise, kindly provided by O'Reilly Media,
939 The L<perlreguts> manpage, courtesy of Yves Orton, describes internals of the
940 Perl regular expression engine.
942 The L<perlreapi> manpage describes the interface to the perl interpreter
943 used to write pluggable regular expression engines (by Ævar Arnfjörð
946 The L<perlunitut> manpage is an tutorial for programming with Unicode and
947 string encodings in Perl, courtesy of Juerd Waalboer.
949 A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
952 The L<perlcommunity> manpage gives a description of the Perl community
953 on the Internet and in real life. (Edgar "Trizor" Bering)
955 The L<CORE> manual page documents the C<CORE::> namespace. (Tels)
957 The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
960 =head1 Performance Enhancements
962 =head2 In-place sorting
964 Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
965 making a temporary copy of the array.
967 Likewise, C<reverse sort ...> is now optimized to sort in reverse,
968 avoiding the generation of a temporary intermediate list.
970 =head2 Lexical array access
972 Access to elements of lexical arrays via a numeric constant between 0 and
973 255 is now faster. (This used to be only the case for global arrays.)
975 =head2 XS-assisted SWASHGET
977 Some pure-perl code that perl was using to retrieve Unicode properties and
978 transliteration mappings has been reimplemented in XS.
980 =head2 Constant subroutines
982 The interpreter internals now support a far more memory efficient form of
983 inlineable constants. Storing a reference to a constant value in a symbol
984 table is equivalent to a full typeglob referencing a constant subroutine,
985 but using about 400 bytes less memory. This proxy constant subroutine is
986 automatically upgraded to a real typeglob with subroutine if necessary.
987 The approach taken is analogous to the existing space optimisation for
988 subroutine stub declarations, which are stored as plain scalars in place
989 of the full typeglob.
991 Several of the core modules have been converted to use this feature for
992 their system dependent constants - as a result C<use POSIX;> now takes about
995 =head2 C<PERL_DONT_CREATE_GVSV>
997 The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
998 in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
999 from creating an empty scalar with every new typeglob. See L<perl588delta>
1002 =head2 Weak references are cheaper
1004 Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
1005 Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
1006 happens at program exit, it may be skipped completely.
1008 =head2 sort() enhancements
1010 Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
1011 and to speed up some cases.
1013 =head2 Memory optimisations
1015 Several internal data structures (typeglobs, GVs, CVs, formats) have been
1016 restructured to use less memory. (Nicholas Clark)
1018 =head2 UTF-8 cache optimisation
1020 The UTF-8 caching code is now more efficient, and used more often.
1023 =head2 Sloppy stat on Windows
1025 On Windows, perl's stat() function normally opens the file to determine
1026 the link count and update attributes that may have been changed through
1027 hard links. Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up
1028 stat() by not performing this operation. (Jan Dubois)
1030 =head2 Regular expressions optimisations
1034 =item Engine de-recursivised
1036 The regular expression engine is no longer recursive, meaning that
1037 patterns that used to overflow the stack will either die with useful
1038 explanations, or run to completion, which, since they were able to blow
1039 the stack before, will likely take a very long time to happen. If you were
1040 experiencing the occasional stack overflow (or segfault) and upgrade to
1041 discover that now perl apparently hangs instead, look for a degenerate
1042 regex. (Dave Mitchell)
1044 =item Single char char-classes treated as literals
1046 Classes of a single character are now treated the same as if the character
1047 had been used as a literal, meaning that code that uses char-classes as an
1048 escaping mechanism will see a speedup. (Yves Orton)
1050 =item Trie optimisation of literal string alternations
1052 Alternations, where possible, are optimised into more efficient matching
1053 structures. String literal alternations are merged into a trie and are
1054 matched simultaneously. This means that instead of O(N) time for matching
1055 N alternations at a given point, the new code performs in O(1) time.
1056 A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune
1057 this optimization. (Yves Orton)
1059 B<Note:> Much code exists that works around perl's historic poor
1060 performance on alternations. Often the tricks used to do so will disable
1061 the new optimisations. Hopefully the utility modules used for this purpose
1062 will be educated about these new optimisations.
1064 =item Aho-Corasick start-point optimisation
1066 When a pattern starts with a trie-able alternation and there aren't
1067 better optimisations available, the regex engine will use Aho-Corasick
1068 matching to find the start point. (Yves Orton)
1072 =head1 Installation and Configuration Improvements
1074 =head2 Configuration improvements
1078 =item C<-Dusesitecustomize>
1080 Run-time customization of @INC can be enabled by passing the
1081 C<-Dusesitecustomize> flag to Configure. When enabled, this will make perl
1082 run F<$sitelibexp/sitecustomize.pl> before anything else. This script can
1083 then be set up to add additional entries to @INC.
1085 =item Relocatable installations
1087 There is now Configure support for creating a relocatable perl tree. If
1088 you Configure with C<-Duserelocatableinc>, then the paths in @INC (and
1089 everything else in %Config) can be optionally located via the path of the
1092 That means that, if the string C<".../"> is found at the start of any
1093 path, it's substituted with the directory of $^X. So, the relocation can
1094 be configured on a per-directory basis, although the default with
1095 C<-Duserelocatableinc> is that everything is relocated. The initial
1096 install is done to the original configured prefix.
1098 =item strlcat() and strlcpy()
1100 The configuration process now detects whether strlcat() and strlcpy() are
1101 available. When they are not available, perl's own version is used (from
1102 Russ Allbery's public domain implementation). Various places in the perl
1103 interpreter now use them. (Steve Peters)
1105 =item C<d_pseudofork> and C<d_printf_format_null>
1107 A new configuration variable, available as C<$Config{d_pseudofork}> in
1108 the L<Config> module, has been added, to distinguish real fork() support
1109 from fake pseudofork used on Windows platforms.
1111 A new configuration variable, C<d_printf_format_null>, has been added,
1112 to see if printf-like formats are allowed to be NULL.
1114 =item Configure help
1116 C<Configure -h> has been extended with the most commonly used options.
1120 =head2 Compilation improvements
1124 =item Parallel build
1126 Parallel makes should work properly now, although there may still be problems
1127 if C<make test> is instructed to run in parallel.
1129 =item Borland's compilers support
1131 Building with Borland's compilers on Win32 should work more smoothly. In
1132 particular Steve Hay has worked to side step many warnings emitted by their
1133 compilers and at least one C compiler internal error.
1135 =item Static build on Windows
1137 Perl extensions on Windows now can be statically built into the Perl DLL.
1139 Also, it's now possible to build a C<perl-static.exe> that doesn't depend
1140 on the Perl DLL on Win32. See the Win32 makefiles for details.
1143 =item ppport.h files
1145 All F<ppport.h> files in the XS modules bundled with perl are now
1146 autogenerated at build time. (Marcus Holland-Moritz)
1148 =item C++ compatibility
1150 Efforts have been made to make perl and the core XS modules compilable
1151 with various C++ compilers (although the situation is not perfect with
1152 some of the compilers on some of the platforms tested.)
1154 =item Support for Microsoft 64-bit compiler
1156 Support for building perl with Microsoft's 64-bit compiler has been
1157 improved. (ActiveState)
1161 Perl can now be compiled with Microsoft Visual C++ 2005 (and 2008 Beta 2).
1165 All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
1169 =head2 Installation improvements
1173 =item Module auxiliary files
1175 README files and changelogs for CPAN modules bundled with perl are no
1180 =head2 New Or Improved Platforms
1182 Perl has been reported to work on Symbian OS. See L<perlsymbian> for more
1185 Many improvements have been made towards making Perl work correctly on
1188 Perl has been reported to work on DragonFlyBSD and MidnightBSD.
1190 The VMS port has been improved. See L<perlvms>.
1192 Support for Cray XT4 Catamount/Qk has been added. See
1193 F<hints/catamount.sh> in the source code distribution for more
1196 Vendor patches have been merged for RedHat and Gentoo.
1198 DynaLoader::dl_unload_file() now works on Windows.
1200 =head1 Selected Bug Fixes
1204 =item strictures in regexp-eval blocks
1206 C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
1208 =item Calling CORE::require()
1210 CORE::require() and CORE::do() were always parsed as require() and do()
1211 when they were overridden. This is now fixed.
1213 =item Subscripts of slices
1215 You can now use a non-arrowed form for chained subscripts after a list
1218 ({foo => "bar"})[0]{foo}
1220 This used to be a syntax error; a C<< -> >> was required.
1222 =item C<no warnings 'category'> works correctly with -w
1224 Previously when running with warnings enabled globally via C<-w>, selective
1225 disabling of specific warning categories would actually turn off all warnings.
1226 This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
1227 C<io> class. Previously it would erroneously turn off all warnings.
1229 =item threads improvements
1231 Several memory leaks in ithreads were closed. Also, ithreads were made
1232 less memory-intensive.
1234 C<threads> is now a dual-life module, also available on CPAN. It has been
1235 expanded in many ways. A kill() method is available for thread signalling.
1236 One can get thread status, or the list of running or joinable threads.
1238 A new C<< threads->exit() >> method is used to exit from the application
1239 (this is the default for the main thread) or from the current thread only
1240 (this is the default for all other threads). On the other hand, the exit()
1241 built-in now always causes the whole application to terminate. (Jerry
1244 =item chr() and negative values
1246 chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
1247 character, unless when the C<bytes> pragma is in effect, where the low
1248 eight bytes of the value are used.
1250 =item PERL5SHELL and tainting
1252 On Windows, the PERL5SHELL environment variable is now checked for
1253 taintedness. (Rafael Garcia-Suarez)
1255 =item Using *FILE{IO}
1257 C<stat()> and C<-X> filetests now treat *FILE{IO} filehandles like *FILE
1258 filehandles. (Steve Peters)
1260 =item Overloading and reblessing
1262 Overloading now works when references are reblessed into another class.
1263 Internally, this has been implemented by moving the flag for "overloading"
1264 from the reference to the referent, which logically is where it should
1265 always have been. (Nicholas Clark)
1267 =item Overloading and UTF-8
1269 A few bugs related to UTF-8 handling with objects that have
1270 stringification overloaded have been fixed. (Nicholas Clark)
1272 =item eval memory leaks fixed
1274 Traditionally, C<eval 'syntax error'> has leaked badly. Many (but not all)
1275 of these leaks have now been eliminated or reduced. (Dave Mitchell)
1277 =item Random device on Windows
1279 In previous versions, perl would read the file F</dev/urandom> if it
1280 existed when seeding its random number generator. That file is unlikely
1281 to exist on Windows, and if it did would probably not contain appropriate
1282 data, so perl no longer tries to read it on Windows. (Alex Davies)
1286 The C<PERLIO_DEBUG> environment variable no longer has any effect for
1287 setuid scripts and for scripts run with B<-T>.
1289 Moreover, with a thread-enabled perl, using C<PERLIO_DEBUG> could lead to
1290 an internal buffer overflow. This has been fixed.
1292 =item PerlIO::scalar and read-only scalars
1294 PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
1295 seek() is now supported with PerlIO::scalar-based filehandles, the
1296 underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
1298 =item study() and UTF-8
1300 study() never worked for UTF-8 strings, but could lead to false results.
1301 It's now a no-op on UTF-8 data. (Yves Orton)
1303 =item Critical signals
1305 The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
1306 "unsafe" manner (contrary to other signals, that are deferred until the
1307 perl interpreter reaches a reasonably stable state; see
1308 L<perlipc/"Deferred Signals (Safe Signals)">). (Rafael)
1312 When a module or a file is loaded through an @INC-hook, and when this hook
1313 has set a filename entry in %INC, __FILE__ is now set for this module
1314 accordingly to the contents of that %INC entry. (Rafael)
1316 =item C<-t> switch fix
1318 The C<-w> and C<-t> switches can now be used together without messing
1319 up which categories of warnings are activated. (Rafael)
1321 =item Duping UTF-8 filehandles
1323 Duping a filehandle which has the C<:utf8> PerlIO layer set will now
1324 properly carry that layer on the duped filehandle. (Rafael)
1326 =item Localisation of hash elements
1328 Localizing a hash element whose key was given as a variable didn't work
1329 correctly if the variable was changed while the local() was in effect (as
1330 in C<local $h{$x}; ++$x>). (Bo Lindbergh)
1334 =head1 New or Changed Diagnostics
1338 =item Use of uninitialized value
1340 Perl will now try to tell you the name of the variable (if any) that was
1343 =item Deprecated use of my() in false conditional
1345 A new deprecation warning, I<Deprecated use of my() in false conditional>,
1346 has been added, to warn against the use of the dubious and deprecated
1351 See L<perldiag>. Use C<state> variables instead.
1353 =item !=~ should be !~
1355 A new warning, C<!=~ should be !~>, is emitted to prevent this misspelling
1356 of the non-matching operator.
1358 =item Newline in left-justified string
1360 The warning I<Newline in left-justified string> has been removed.
1362 =item Too late for "-T" option
1364 The error I<Too late for "-T" option> has been reformulated to be more
1367 =item "%s" variable %s masks earlier declaration
1369 This warning is now emitted in more consistent cases; in short, when one
1370 of the declarations involved is a C<my> variable:
1372 my $x; my $x; # warns
1373 my $x; our $x; # warns
1374 our $x; my $x; # warns
1376 On the other hand, the following:
1380 now gives a C<"our" variable %s redeclared> warning.
1382 =item readdir()/closedir()/etc. attempted on invalid dirhandle
1384 These new warnings are now emitted when a dirhandle is used but is
1385 either closed or not really a dirhandle.
1387 =item Opening dirhandle/filehandle %s also as a file/directory
1389 Two deprecation warnings have been added: (Rafael)
1391 Opening dirhandle %s also as a file
1392 Opening filehandle %s also as a directory
1394 =item Use of -P is deprecated
1396 Perl's command-line switch C<-P> is now deprecated.
1398 =item v-string in use/require is non-portable
1400 Perl will warn you against potential backwards compatibility problems with
1401 the C<use VERSION> syntax.
1405 C<perl -V> has several improvements, making it more useable from shell
1406 scripts to get the value of configuration variables. See L<perlrun> for
1411 =head1 Changed Internals
1413 In general, the source code of perl has been refactored, tidied up,
1414 and optimized in many places. Also, memory management and allocation
1415 has been improved in several points.
1417 When compiling the perl core with gcc, as many gcc warning flags are
1418 turned on as is possible on the platform. (This quest for cleanliness
1419 doesn't extend to XS code because we cannot guarantee the tidiness of
1420 code we didn't write.) Similar strictness flags have been added or
1421 tightened for various other C compilers.
1423 =head2 Reordering of SVt_* constants
1425 The relative ordering of constants that define the various types of C<SV>
1426 have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
1427 C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
1428 difference unless you have code that explicitly makes assumptions about that
1429 ordering. (The inheritance hierarchy of C<B::*> objects has been changed
1432 =head2 Elimination of SVt_PVBM
1434 Related to this, the internal type C<SVt_PVBM> has been been removed. This
1435 dedicated type of C<SV> was used by the C<index> operator and parts of the
1436 regexp engine to facilitate fast Boyer-Moore matches. Its use internally has
1437 been replaced by C<SV>s of type C<SVt_PVGV>.
1439 =head2 New type SVt_BIND
1441 A new type C<SVt_BIND> has been added, in readiness for the project to
1442 implement Perl 6 on 5. There deliberately is no implementation yet, and
1443 they cannot yet be created or destroyed.
1445 =head2 Removal of CPP symbols
1447 The C preprocessor symbols C<PERL_PM_APIVERSION> and
1448 C<PERL_XS_APIVERSION>, which were supposed to give the version number of
1449 the oldest perl binary-compatible (resp. source-compatible) with the
1450 present one, were not used, and sometimes had misleading values. They have
1453 =head2 Less space is used by ops
1455 The C<BASEOP> structure now uses less space. The C<op_seq> field has been
1456 removed and replaced by a single bit bit-field C<op_opt>. C<op_type> is now 9
1457 bits long. (Consequently, the C<B::OP> class doesn't provide an C<seq>
1462 perl's parser is now generated by bison (it used to be generated by
1463 byacc.) As a result, it seems to be a bit more robust.
1465 Also, Dave Mitchell improved the lexer debugging output under C<-DT>.
1467 =head2 Use of C<const>
1469 Andy Lester supplied many improvements to determine which function
1470 parameters and local variables could actually be declared C<const> to the C
1471 compiler. Steve Peters provided new C<*_set> macros and reworked the core to
1472 use these rather than assigning to macros in LVALUE context.
1476 A new file, F<mathoms.c>, has been added. It contains functions that are
1477 no longer used in the perl core, but that remain available for binary or
1478 source compatibility reasons. However, those functions will not be
1479 compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
1481 =head2 C<AvFLAGS> has been removed
1483 The C<AvFLAGS> macro has been removed.
1485 =head2 C<av_*> changes
1487 The C<av_*()> functions, used to manipulate arrays, no longer accept null
1492 The implementation of the special variables $^H and %^H has changed, to
1493 allow implementing lexical pragmas in pure Perl.
1495 =head2 B:: modules inheritance changed
1497 The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
1498 inherits from C<B::SV> (it used to inherit from C<B::IV>).
1500 =head2 Anonymous hash and array constructors
1502 The anonymous hash and array constructors now take 1 op in the optree
1503 instead of 3, now that pp_anonhash and pp_anonlist return a reference to
1504 an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
1506 =head1 Known Problems
1508 There's still a remaining problem in the implementation of the lexical
1509 C<$_>: it doesn't work inside C</(?{...})/> blocks. (See the TODO test in
1512 =head1 Platform Specific Problems
1514 =head1 Reporting Bugs
1518 The F<Changes> file and the perl590delta to perl595delta man pages for
1519 exhaustive details on what changed.
1521 The F<INSTALL> file for how to build Perl.
1523 The F<README> file for general stuff.
1525 The F<Artistic> and F<Copying> files for copyright information.