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 { $nothing = 1; }
74 A more complete description of how Perl matches the switch variable
75 against the C<when> conditions is given in L<perlsyn/"Switch statements">.
77 This kind of match is called I<smart match>, and it's also possible to use
78 it outside of switch statements, via the new C<~~> operator. See
79 L<perlsyn/"Smart matching in detail">.
81 This feature was contributed by Robin Houston.
83 =head2 Regular expressions
87 =item Recursive Patterns
89 It is now possible to write recursive patterns without using the C<(??{})>
90 construct. This new way is more efficient, and in many cases easier to
93 Each capturing parenthesis can now be treated as an independent pattern
94 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
95 "parenthesis number"). For example, the following pattern will match
96 nested balanced angle brackets:
100 ( # start capture buffer 1
101 < # match an opening angle bracket
103 (?> # don't backtrack over the inside of this group
104 [^<>]+ # one or more non angle brackets
105 ) # end non backtracking group
107 (?1) # recurse to bracket 1 and try it again
108 )* # 0 or more times.
109 > # match a closing angle bracket
110 ) # end capture buffer one
114 PCRE users should note that Perl's recursive regex feature allows
115 backtracking into a recursed pattern, whereas in PCRE the recursion is
116 atomic or "possessive" in nature. As in the example above, you can
117 add (?>) to control this selectively. (Yves Orton)
119 =item Named Capture Buffers
121 It is now possible to name capturing parenthesis in a pattern and refer to
122 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
123 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
124 syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
125 access the contents of the capture buffers.
127 Thus, to replace all doubled chars with a single copy, one could write
129 s/(?<letter>.)\k<letter>/$+{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 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 )" >>.
308 Formats were improved in several ways. A new field, C<^*>, can be used for
309 variable-width, one-line-at-a-time text. Null characters are now handled
310 correctly in picture lines. Using C<@#> and C<~~> together will now
311 produce a compile-time error, as those format fields are incompatible.
312 L<perlform> has been improved, and miscellaneous bugs fixed.
314 =head2 Byte-order modifiers for pack() and unpack()
316 There are two new byte-order modifiers, C<E<gt>> (big-endian) and C<E<lt>>
317 (little-endian), that can be appended to most pack() and unpack() template
318 characters and groups to force a certain byte-order for that type or group.
319 See L<perlfunc/pack> and L<perlpacktut> for details.
323 You can now use C<no> followed by a version number to specify that you
324 want to use a version of perl older than the specified one.
326 =head2 C<chdir>, C<chmod> and C<chown> on filehandles
328 C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
329 filenames, if the system supports respectively C<fchdir>, C<fchmod> and
330 C<fchown>, thanks to a patch provided by Gisle Aas.
334 C<$(> and C<$)> now return groups in the order where the OS returns them,
335 thanks to Gisle Aas. This wasn't previously the case.
337 =head2 Recursive sort subs
339 You can now use recursive subroutines with sort(), thanks to Robin Houston.
341 =head2 Exceptions in constant folding
343 The constant folding routine is now wrapped in an exception handler, and
344 if folding throws an exception (such as attempting to evaluate 0/0), perl
345 now retains the current optree, rather than aborting the whole program.
346 Without this change, programs would not compile if they had expressions that
347 happened to generate exceptions, even though those expressions were in code
348 that could never be reached at runtime. (Nicholas Clark, Dave Mitchell)
350 =head2 Source filters in @INC
352 It's possible to enhance the mechanism of subroutine hooks in @INC by
353 adding a source filter on top of the filehandle opened and returned by the
354 hook. This feature was planned a long time ago, but wasn't quite working
355 until now. See L<perlfunc/require> for details. (Nicholas Clark)
357 =head2 New internal variables
361 =item C<${^RE_DEBUG_FLAGS}>
363 This variable controls what debug flags are in effect for the regular
364 expression engine when running under C<use re "debug">. See L<re> for
367 =item C<${^CHILD_ERROR_NATIVE}>
369 This variable gives the native status returned by the last pipe close,
370 backtick command, successful call to wait() or waitpid(), or from the
371 system() operator. See L<perlrun> for details. (Contributed by Gisle Aas.)
373 =item C<${^RE_TRIE_MAXBUF}>
375 See L</"Trie optimisation of literal string alternations">.
377 =item C<${^WIN32_SLOPPY_STAT}>
379 See L</"Sloppy stat on Windows">.
385 C<unpack()> now defaults to unpacking the C<$_> variable.
387 C<mkdir()> without arguments now defaults to C<$_>.
389 The internal dump output has been improved, so that non-printable characters
390 such as newline and backspace are output in C<\x> notation, rather than
393 The B<-C> option can no longer be used on the C<#!> line. It wasn't
394 working there anyway.
398 The copy of the Unicode Character Database included in Perl 5 has
399 been updated to version 5.0.0.
403 MAD, which stands for I<Miscellaneous Attribute Decoration>, is a
404 still-in-development work leading to a Perl 5 to Perl 6 converter. To
405 enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
406 obtained perl isn't binary compatible with a regular perl 5.10, and has
407 space and speed penalties; moreover not all regression tests still pass
408 with it. (Larry Wall, Nicholas Clark)
410 =head2 kill() on Windows
412 On Windows platforms, C<kill(-9, $pid)> now kills a process tree.
413 (On UNIX, this delivers the signal to all processes in the same process
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 $string. Packed strings can also get upgraded
427 during processing when you store upgraded characters. You can get the old
428 behaviour by using C<use bytes>.
430 To be consistent with pack(), the C<C0> in unpack() templates indicates
431 that the data is to be processed in character mode, i.e. character by
432 character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
433 the packed string is processed in its UTF-8-encoded Unicode form on a byte
434 by byte basis. This is reversed with regard to perl 5.8.X, but now consistent
435 between pack() and unpack().
437 Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
438 respectively character and byte modes.
440 C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
441 specified encoding mode, honoring parens grouping. Previously, parens were
444 Also, there is a new pack() character format, C<W>, which is intended to
445 replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
446 the strings internal representation. C<W> represents unsigned (logical)
447 character values, which can be greater than 255. It is therefore more
448 robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
449 values outside the range 0..255, and not respect the string encoding).
451 In practice, that means that pack formats are now encoding-neutral, except
454 For consistency, C<A> in unpack() format now trims all Unicode whitespace
455 from the end of the string. Before perl 5.9.2, it used to strip only the
456 classical ASCII space characters.
458 =head2 Byte/character count feature in unpack()
460 A new unpack() template character, C<".">, returns the number of bytes or
461 characters (depending on the selected encoding mode, see above) read so far.
463 =head2 The C<$*> and C<$#> variables have been removed
465 C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
466 modifiers, has been removed.
468 The deprecated C<$#> variable (output format for numbers) has been
471 Two new severe warnings, C<$#/$* is no longer supported>, have been added.
473 =head2 substr() lvalues are no longer fixed-length
475 The lvalues returned by the three argument form of substr() used to be a
476 "fixed length window" on the original string. In some cases this could
477 cause surprising action at distance or other undefined behaviour. Now the
478 length of the window adjusts itself to the length of the string assigned to
481 =head2 Parsing of C<-f _>
483 The identifier C<_> is now forced to be a bareword after a filetest
484 operator. This solves a number of misparsing issues when a global C<_>
485 subroutine is defined.
489 The C<:unique> attribute has been made a no-op, since its current
490 implementation was fundamentally flawed and not threadsafe.
492 =head2 Effect of pragmas in eval
494 The compile-time value of the C<%^H> hint variable can now propagate into
495 eval("")uated code. This makes it more useful to implement lexical
498 As a side-effect of this, the overloaded-ness of constants now propagates
503 A bareword argument to chdir() is now recognized as a file handle.
504 Earlier releases interpreted the bareword as a directory name.
507 =head2 Handling of .pmc files
509 An old feature of perl was that before C<require> or C<use> look for a
510 file with a F<.pm> extension, they will first look for a similar filename
511 with a F<.pmc> extension. If this file is found, it will be loaded in
512 place of any potentially existing file ending in a F<.pm> extension.
514 Previously, F<.pmc> files were loaded only if more recent than the
515 matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
518 =head2 @- and @+ in patterns
520 The special arrays C<@-> and C<@+> are no longer interpolated in regular
521 expressions. (Sadahiro Tomoyuki)
523 =head2 $AUTOLOAD can now be tainted
525 If you call a subroutine by a tainted name, and if it defers to an
526 AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
529 =head2 Tainting and printf
531 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
532 reject any tainted format argument. (Rafael Garcia-Suarez)
534 =head2 undef and signal handlers
536 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
537 equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
539 =head2 strictures and dereferencing in defined()
541 C<use strict 'refs'> was ignoring taking a hard reference in an argument
542 to defined(), as in :
546 if (defined $$x) {...}
548 This now correctly produces the run-time error C<Can't use string as a
549 SCALAR ref while "strict refs" in use>.
551 C<defined @$foo> and C<defined %$bar> are now also subject to C<strict
552 'refs'> (that is, C<$foo> and C<$bar> shall be proper references there.)
553 (C<defined(@foo)> and C<defined(%bar)> are discouraged constructs anyway.)
556 =head2 C<(?p{})> has been removed
558 The regular expression construct C<(?p{})>, which was deprecated in perl
559 5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
561 =head2 Pseudo-hashes have been removed
563 Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
564 pragma remains here, but uses an alternate implementation.)
566 =head2 Removal of the bytecode compiler and of perlcc
568 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
569 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
570 experimental tools have never worked reliably, and, due to the lack of
571 volunteers to keep them in line with the perl interpreter developments, it
572 was decided to remove them instead of shipping a broken version of those.
573 The last version of those modules can be found with perl 5.9.4.
575 However the B compiler framework stays supported in the perl core, as with
576 the more useful modules it has permitted (among others, B::Deparse and
579 =head2 Removal of the JPL
581 The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.
583 =head2 Recursive inheritance detected earlier
585 Perl will now immediately throw an exception if you modify any package's
586 C<@ISA> in such a way that it would cause recursive inheritance.
588 Previously, the exception would not occur until Perl attempted to make
589 use of the recursive inheritance while resolving a method or doing a
590 C<$foo-E<gt>isa($bar)> lookup.
592 =head1 Modules and Pragmata
594 =head2 Pragmata Changes
600 The new pragma C<feature> is used to enable new features that might break
601 old code. See L</"The C<feature> pragma"> above.
605 This new pragma enables to change the algorithm used to resolve inherited
606 methods. See L</"New Pragma, C<mro>"> above.
608 =item Scoping of the C<sort> pragma
610 The C<sort> pragma is now lexically scoped. Its effect used to be global.
612 =item Scoping of C<bignum>, C<bigint>, C<bigrat>
614 The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
615 lexically scoped. (Tels)
619 The C<base> pragma now warns if a class tries to inherit from itself.
622 =item C<strict> and C<warnings>
624 C<strict> and C<warnings> will now complain loudly if they are loaded via
625 incorrect casing (as in C<use Strict;>). (Johan Vromans)
629 The C<version> module provides support for version objects.
633 The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
634 that used C<Carp> routines without having loaded it at compile time might
635 need to be adjusted; typically, the following (faulty) code won't work
636 anymore, and will require parentheses to be added after the function name:
640 Carp::confess 'argh';
644 C<less> now does something useful (or at least it tries to). In fact, it
645 has been turned into a lexical pragma. So, in your modules, you can now
646 test whether your users have requested to use less CPU, or less memory,
647 less magic, or maybe even less fat. See L<less> for more. (Joshua ben
658 C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
659 whenever an ASCII character string containing high-bit bytes is implicitly
660 converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
661 perls, its effect is global.
665 C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
666 you what versions of core modules ship with any versions of Perl 5. It
667 comes with a command-line frontend, C<corelist>.
671 C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
672 C<Math::BigInt::Calc>.
676 C<Compress::Zlib> is an interface to the zlib compression library. It
677 comes with a bundled version of zlib, so having a working zlib is not a
678 prerequisite to install it. It's used by C<Archive::Tar> (see below).
682 C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
686 C<Archive::Tar> is a module to manipulate C<tar> archives.
690 C<Digest::SHA> is a module used to calculate many types of SHA digests,
691 has been included for SHA support in the CPAN module.
695 C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
699 C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
700 provides support for I<field hashes>: hashes that maintain an association
701 of a reference with a value, in a thread-safe garbage-collected way.
702 Such hashes are useful to implement inside-out objects.
706 C<Module::Build>, by Ken Williams, has been added. It's an alternative to
707 C<ExtUtils::MakeMaker> to build and install perl modules.
711 C<Module::Load>, by Jos Boumans, has been added. It provides a single
712 interface to load Perl modules and F<.pl> files.
716 C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
717 modules as loaded or unloaded.
721 C<Package::Constants>, by Jos Boumans, has been added. It's a simple
722 helper to list all constants declared in a given package.
726 C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
727 This module provides low-level access to Win32 system API calls for
732 C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
733 C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
734 included in the perl core; the behaviour of C<Locale::Maketext::Simple>
735 gracefully degrades when the later isn't present.
739 C<Params::Check> implements a generic input parsing/checking mechanism. It
744 C<Term::UI> simplifies the task to ask questions at a terminal prompt.
748 C<Object::Accessor> provides an interface to create per-object accessors.
752 C<Module::Pluggable> is a simple framework to create modules that accept
753 pluggable sub-modules.
757 C<Module::Load::Conditional> provides simple ways to query and possibly
758 load installed modules.
762 C<Time::Piece> provides an object oriented interface to time functions,
763 overriding the built-ins localtime() and gmtime().
767 C<IPC::Cmd> helps to find and run external commands, possibly
772 C<File::Fetch> provide a simple generic file fetching mechanism.
776 C<Log::Message> and C<Log::Message::Simple> are used by the log facility
781 C<Archive::Extract> is a generic archive extraction mechanism
782 for F<.tar> (plain, gziped or bzipped) or F<.zip> files.
786 C<CPANPLUS> provides an API and a command-line tool to access the CPAN
791 =head2 Selected Changes to Core Modules
795 =item C<Attribute::Handlers>
797 C<Attribute::Handlers> can now report the caller's file and line number.
802 C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
803 with plugins. (Joshua ben Jore)
807 It's now possible to access the lexical pragma hints (C<%^H>) by using the
808 method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
809 can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
814 As the old 5005thread threading model has been removed, in favor of the
815 ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
816 be used in old code only. It has been removed from the default list of
821 =head1 Utility Changes
827 The Perl debugger can now save all debugger commands for sourcing later;
828 notably, it can now emulate stepping backwards, by restarting and
829 rerunning all bar the last command from a saved command history.
831 It can also display the parent inheritance tree of a given class, with the
836 C<ptar> is a pure perl implementation of C<tar>, that comes with
841 C<ptardiff> is a small utility used to generate a diff between the contents
842 of a tar archive and a directory tree. Like C<ptar>, it comes with
847 C<shasum> is a command-line utility, used to print or to check SHA
848 digests. It comes with the new C<Digest::SHA> module.
852 The C<corelist> utility is now installed with perl (see L</"New modules">
857 C<h2ph> and C<h2xs> have been made more robust with regard to
860 C<h2xs> implements a new option C<--use-xsloader> to force use of
861 C<XSLoader> even in backwards compatible modules.
863 The handling of authors' names that had apostrophes has been fixed.
865 Any enums with negative values are now skipped.
869 C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
870 option to run I<all> tests.
874 C<find2perl> now assumes C<-print> as a default action. Previously, it
875 needed to be specified explicitly.
877 Several bugs have been fixed in C<find2perl>, regarding C<-exec> and
878 C<-eval>. Also the options C<-path>, C<-ipath> and C<-iname> have been
883 C<config_data> is a new utility that comes with C<Module::Build>. It
884 provides a command-line interface to the configuration of Perl modules
885 that use Module::Build's framework of configurability (that is,
886 C<*::ConfigData> modules that contain local configuration information for
887 their parent modules.)
891 C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, a
892 helper for CPANPLUS operation, has been added too, but isn't intended for
897 C<cpan2dist> is a new utility, that comes with CPANPLUS. It's a tool to
898 create distributions (or packages) from CPAN modules.
902 The output of C<pod2html> has been enhanced to be more customizable via
903 CSS. Some formatting problems were also corrected. (Jari Aalto)
907 =head1 New Documentation
909 The L<perlpragma> manpage documents how to write one's own lexical
910 pragmas in pure Perl (something that is possible starting with 5.9.4).
912 The new L<perlglossary> manpage is a glossary of terms used in the Perl
913 documentation, technical and otherwise, kindly provided by O'Reilly Media,
916 The L<perlreguts> manpage, courtesy of Yves Orton, describes internals of the
917 Perl regular expression engine.
919 The L<perlreapi> manpage describes the interface to the perl interpreter
920 used to write pluggable regular expression engines (by Ævar Arnfjörð
923 The L<perlunitut> manpage is an tutorial for programming with Unicode and
924 string encodings in Perl, courtesy of Juerd Waalboer.
926 A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
929 The L<perlcommunity> manpage gives a description of the Perl community
930 on the Internet and in real life. (Edgar "Trizor" Bering)
932 The L<CORE> manual page documents the C<CORE::> namespace. (Tels)
934 The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
937 =head1 Performance Enhancements
939 =head2 In-place sorting
941 Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
942 making a temporary copy of the array.
944 Likewise, C<reverse sort ...> is now optimized to sort in reverse,
945 avoiding the generation of a temporary intermediate list.
947 =head2 Lexical array access
949 Access to elements of lexical arrays via a numeric constant between 0 and
950 255 is now faster. (This used to be only the case for global arrays.)
952 =head2 XS-assisted SWASHGET
954 Some pure-perl code that perl was using to retrieve Unicode properties and
955 transliteration mappings has been reimplemented in XS.
957 =head2 Constant subroutines
959 The interpreter internals now support a far more memory efficient form of
960 inlineable constants. Storing a reference to a constant value in a symbol
961 table is equivalent to a full typeglob referencing a constant subroutine,
962 but using about 400 bytes less memory. This proxy constant subroutine is
963 automatically upgraded to a real typeglob with subroutine if necessary.
964 The approach taken is analogous to the existing space optimisation for
965 subroutine stub declarations, which are stored as plain scalars in place
966 of the full typeglob.
968 Several of the core modules have been converted to use this feature for
969 their system dependent constants - as a result C<use POSIX;> now takes about
972 =head2 C<PERL_DONT_CREATE_GVSV>
974 The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
975 in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
976 from creating an empty scalar with every new typeglob. See L<perl588delta>
979 =head2 Weak references are cheaper
981 Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
982 Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
983 happens at program exit, it may be skipped completely.
985 =head2 sort() enhancements
987 Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
988 and to speed up some cases.
990 =head2 Memory optimisations
992 Several internal data structures (typeglobs, GVs, CVs, formats) have been
993 restructured to use less memory. (Nicholas Clark)
995 =head2 UTF-8 cache optimisation
997 The UTF-8 caching code is now more efficient, and used more often.
1000 =head2 Sloppy stat on Windows
1002 On Windows, perl's stat() function normally opens the file to determine
1003 the link count and update attributes that may have been changed through
1004 hard links. Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up
1005 stat() by not performing this operation. (Jan Dubois)
1007 =head2 Regular expressions optimisations
1011 =item Engine de-recursivised
1013 The regular expression engine is no longer recursive, meaning that
1014 patterns that used to overflow the stack will either die with useful
1015 explanations, or run to completion, which, since they were able to blow
1016 the stack before, will likely take a very long time to happen. If you were
1017 experiencing the occasional stack overflow (or segfault) and upgrade to
1018 discover that now perl apparently hangs instead, look for a degenerate
1019 regex. (Dave Mitchell)
1021 =item Single char char-classes treated as literals
1023 Classes of a single character are now treated the same as if the character
1024 had been used as a literal, meaning that code that uses char-classes as an
1025 escaping mechanism will see a speedup. (Yves Orton)
1027 =item Trie optimisation of literal string alternations
1029 Alternations, where possible, are optimised into more efficient matching
1030 structures. String literal alternations are merged into a trie and are
1031 matched simultaneously. This means that instead of O(N) time for matching
1032 N alternations at a given point, the new code performs in O(1) time.
1033 A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune
1034 this optimization. (Yves Orton)
1036 B<Note:> Much code exists that works around perl's historic poor
1037 performance on alternations. Often the tricks used to do so will disable
1038 the new optimisations. Hopefully the utility modules used for this purpose
1039 will be educated about these new optimisations by the time 5.10 is
1042 =item Aho-Corasick start-point optimisation
1044 When a pattern starts with a trie-able alternation and there aren't
1045 better optimisations available, the regex engine will use Aho-Corasick
1046 matching to find the start point. (Yves Orton)
1050 =head1 Installation and Configuration Improvements
1052 =head2 Configuration improvements
1056 =item C<-Dusesitecustomize>
1058 Run-time customization of @INC can be enabled by passing the
1059 C<-Dusesitecustomize> flag to Configure. When enabled, this will make perl
1060 run F<$sitelibexp/sitecustomize.pl> before anything else. This script can
1061 then be set up to add additional entries to @INC.
1063 =item Relocatable installations
1065 There is now Configure support for creating a relocatable perl tree. If
1066 you Configure with C<-Duserelocatableinc>, then the paths in @INC (and
1067 everything else in %Config) can be optionally located via the path of the
1070 That means that, if the string C<".../"> is found at the start of any
1071 path, it's substituted with the directory of $^X. So, the relocation can
1072 be configured on a per-directory basis, although the default with
1073 C<-Duserelocatableinc> is that everything is relocated. The initial
1074 install is done to the original configured prefix.
1076 =item strlcat() and strlcpy()
1078 The configuration process now detects whether strlcat() and strlcpy() are
1079 available. When they are not available, perl's own version is used (from
1080 Russ Allbery's public domain implementation). Various places in the perl
1081 interpreter now use them. (Steve Peters)
1083 =item C<d_pseudofork> and C<d_printf_format_null>
1085 A new configuration variable, available as C<$Config{d_pseudofork}> in
1086 the L<Config> module, has been added, to distinguish real fork() support
1087 from fake pseudofork used on Windows platforms.
1089 A new configuration variable, C<d_printf_format_null>, has been added,
1090 to see if printf-like formats are allowed to be NULL.
1092 =item Configure help
1094 C<Configure -h> has been extended with the most commonly used options.
1098 =head2 Compilation improvements
1102 =item Parallel build
1104 Parallel makes should work properly now, although there may still be problems
1105 if C<make test> is instructed to run in parallel.
1107 =item Borland's compilers support
1109 Building with Borland's compilers on Win32 should work more smoothly. In
1110 particular Steve Hay has worked to side step many warnings emitted by their
1111 compilers and at least one C compiler internal error.
1113 =item Static build on Windows
1115 Perl extensions on Windows now can be statically built into the Perl DLL.
1117 Also, it's now possible to build a C<perl-static.exe> that doesn't depend
1118 on the Perl DLL on Win32. See the Win32 makefiles for details.
1121 =item ppport.h files
1123 All F<ppport.h> files in the XS modules bundled with perl are now
1124 autogenerated at build time. (Marcus Holland-Moritz)
1126 =item C++ compatibility
1128 Efforts have been made to make perl and the core XS modules compilable
1129 with various C++ compilers (although the situation is not perfect with
1130 some of the compilers on some of the platforms tested.)
1132 =item Support for Microsoft 64-bit compiler
1134 Support for building perl with Microsoft's 64-bit compiler has been
1135 improved. (ActiveState)
1139 Perl can now be compiled with Microsoft Visual C++ 2005 (and 2008 Beta 2).
1143 All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
1147 =head2 Installation improvements
1151 =item Module auxiliary files
1153 README files and changelogs for CPAN modules bundled with perl are no
1158 =head2 New Or Improved Platforms
1160 Perl has been reported to work on Symbian OS. See L<perlsymbian> for more
1163 Many improvements have been made towards making Perl work correctly on
1166 Perl has been reported to work on DragonFlyBSD and MidnightBSD.
1168 The VMS port has been improved. See L<perlvms>.
1170 Support for Cray XT4 Catamount/Qk has been added. See
1171 F<hints/catamount.sh> in the source code distribution for more
1174 Vendor patches have been merged for RedHat and Gentoo.
1176 DynaLoader::dl_unload_file() now works on Windows.
1178 =head1 Selected Bug Fixes
1182 =item strictures in regexp-eval blocks
1184 C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
1186 =item Calling CORE::require()
1188 CORE::require() and CORE::do() were always parsed as require() and do()
1189 when they were overridden. This is now fixed.
1191 =item Subscripts of slices
1193 You can now use a non-arrowed form for chained subscripts after a list
1196 ({foo => "bar"})[0]{foo}
1198 This used to be a syntax error; a C<< -> >> was required.
1200 =item C<no warnings 'category'> works correctly with -w
1202 Previously when running with warnings enabled globally via C<-w>, selective
1203 disabling of specific warning categories would actually turn off all warnings.
1204 This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
1205 C<io> class. Previously it would erroneously turn off all warnings.
1207 =item threads improvements
1209 Several memory leaks in ithreads were closed. Also, ithreads were made
1210 less memory-intensive.
1212 C<threads> is now a dual-life module, also available on CPAN. It has been
1213 expanded in many ways. A kill() method is available for thread signalling.
1214 One can get thread status, or the list of running or joinable threads.
1216 A new C<< threads->exit() >> method is used to exit from the application
1217 (this is the default for the main thread) or from the current thread only
1218 (this is the default for all other threads). On the other hand, the exit()
1219 built-in now always causes the whole application to terminate. (Jerry
1222 =item chr() and negative values
1224 chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
1225 character, unless when the C<bytes> pragma is in effect, where the low
1226 eight bytes of the value are used.
1228 =item PERL5SHELL and tainting
1230 On Windows, the PERL5SHELL environment variable is now checked for
1231 taintedness. (Rafael Garcia-Suarez)
1233 =item Using *FILE{IO}
1235 C<stat()> and C<-X> filetests now treat *FILE{IO} filehandles like *FILE
1236 filehandles. (Steve Peters)
1238 =item Overloading and reblessing
1240 Overloading now works when references are reblessed into another class.
1241 Internally, this has been implemented by moving the flag for "overloading"
1242 from the reference to the referent, which logically is where it should
1243 always have been. (Nicholas Clark)
1245 =item Overloading and UTF-8
1247 A few bugs related to UTF-8 handling with objects that have
1248 stringification overloaded have been fixed. (Nicholas Clark)
1250 =item eval memory leaks fixed
1252 Traditionally, C<eval 'syntax error'> has leaked badly. Many (but not all)
1253 of these leaks have now been eliminated or reduced. (Dave Mitchell)
1255 =item Random device on Windows
1257 In previous versions, perl would read the file F</dev/urandom> if it
1258 existed when seeding its random number generator. That file is unlikely
1259 to exist on Windows, and if it did would probably not contain appropriate
1260 data, so perl no longer tries to read it on Windows. (Alex Davies)
1264 The C<PERLIO_DEBUG> environment variable no longer has any effect for
1265 setuid scripts and for scripts run with B<-T>.
1267 Moreover, with a thread-enabled perl, using C<PERLIO_DEBUG> could lead to
1268 an internal buffer overflow. This has been fixed.
1270 =item PerlIO::scalar and read-only scalars
1272 PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
1273 seek() is now supported with PerlIO::scalar-based filehandles, the
1274 underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
1276 =item study() and UTF-8
1278 study() never worked for UTF-8 strings, but could lead to false results.
1279 It's now a no-op on UTF-8 data. (Yves Orton)
1281 =item Critical signals
1283 The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
1284 "unsafe" manner (contrary to other signals, that are deferred until the
1285 perl interpreter reaches a reasonably stable state; see
1286 L<perlipc/"Deferred Signals (Safe Signals)">). (Rafael)
1290 When a module or a file is loaded through an @INC-hook, and when this hook
1291 has set a filename entry in %INC, __FILE__ is now set for this module
1292 accordingly to the contents of that %INC entry. (Rafael)
1294 =item C<-t> switch fix
1296 The C<-w> and C<-t> switches can now be used together without messing
1297 up which categories of warnings are activated. (Rafael)
1299 =item Duping UTF-8 filehandles
1301 Duping a filehandle which has the C<:utf8> PerlIO layer set will now
1302 properly carry that layer on the duped filehandle. (Rafael)
1304 =item Localisation of hash elements
1306 Localizing an hash element whose key was given as a variable didn't work
1307 correctly if the variable was changed while the local() was in effect (as
1308 in C<local $h{$x}; ++$x>). (Bo Lindbergh)
1312 =head1 New or Changed Diagnostics
1316 =item Use of uninitialized value
1318 Perl will now try to tell you the name of the variable (if any) that was
1321 =item Deprecated use of my() in false conditional
1323 A new deprecation warning, I<Deprecated use of my() in false conditional>,
1324 has been added, to warn against the use of the dubious and deprecated
1329 See L<perldiag>. Use C<state> variables instead.
1331 =item !=~ should be !~
1333 A new warning, C<!=~ should be !~>, is emitted to prevent this misspelling
1334 of the non-matching operator.
1336 =item Newline in left-justified string
1338 The warning I<Newline in left-justified string> has been removed.
1340 =item Too late for "-T" option
1342 The error I<Too late for "-T" option> has been reformulated to be more
1345 =item "%s" variable %s masks earlier declaration
1347 This warning is now emitted in more consistent cases; in short, when one
1348 of the declarations involved is a C<my> variable:
1350 my $x; my $x; # warns
1351 my $x; our $x; # warns
1352 our $x; my $x; # warns
1354 On the other hand, the following:
1358 now gives a C<"our" variable %s redeclared> warning.
1360 =item readdir()/closedir()/etc. attempted on invalid dirhandle
1362 These new warnings are now emitted when a dirhandle is used but is
1363 either closed or not really a dirhandle.
1365 =item Opening dirhandle/filehandle %s also as a file/directory
1367 Two deprecation warnings have been added: (Rafael)
1369 Opening dirhandle %s also as a file
1370 Opening filehandle %s also as a directory
1372 =item Use of -P is deprecated
1374 Perl's command-line switch C<-P> is now deprecated.
1376 =item v-string in use/require is non-portable
1378 Perl will warn you against potential backwards compatibility problems with
1379 the C<use VERSION> syntax.
1383 C<perl -V> has several improvements, making it more useable from shell
1384 scripts to get the value of configuration variables. See L<perlrun> for
1389 =head1 Changed Internals
1391 In general, the source code of perl has been refactored, tied up, and
1392 optimized in many places. Also, memory management and allocation has been
1393 improved in a couple of points.
1395 =head2 Reordering of SVt_* constants
1397 The relative ordering of constants that define the various types of C<SV>
1398 have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
1399 C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
1400 difference unless you have code that explicitly makes assumptions about that
1401 ordering. (The inheritance hierarchy of C<B::*> objects has been changed
1404 =head2 Elimination of SVt_PVBM
1406 Related to this, the internal type C<SVt_PVBM> has been been removed. This
1407 dedicated type of C<SV> was used by the C<index> operator and parts of the
1408 regexp engine to facilitate fast Boyer-Moore matches. Its use internally has
1409 been replaced by C<SV>s of type C<SVt_PVGV>.
1411 =head2 New type SVt_BIND
1413 A new type C<SVt_BIND> has been added, in readiness for the project to
1414 implement Perl 6 on 5. There deliberately is no implementation yet, and
1415 they cannot yet be created or destroyed.
1417 =head2 Removal of CPP symbols
1419 The C preprocessor symbols C<PERL_PM_APIVERSION> and
1420 C<PERL_XS_APIVERSION>, which were supposed to give the version number of
1421 the oldest perl binary-compatible (resp. source-compatible) with the
1422 present one, were not used, and sometimes had misleading values. They have
1425 =head2 Less space is used by ops
1427 The C<BASEOP> structure now uses less space. The C<op_seq> field has been
1428 removed and replaced by a single bit bit-field C<op_opt>. C<op_type> is now 9
1429 bits long. (Consequently, the C<B::OP> class doesn't provide an C<seq>
1434 perl's parser is now generated by bison (it used to be generated by
1435 byacc.) As a result, it seems to be a bit more robust.
1437 Also, Dave Mitchell improved the lexer debugging output under C<-DT>.
1439 =head2 Use of C<const>
1441 Andy Lester supplied many improvements to determine which function
1442 parameters and local variables could actually be declared C<const> to the C
1443 compiler. Steve Peters provided new C<*_set> macros and reworked the core to
1444 use these rather than assigning to macros in LVALUE context.
1448 A new file, F<mathoms.c>, has been added. It contains functions that are
1449 no longer used in the perl core, but that remain available for binary or
1450 source compatibility reasons. However, those functions will not be
1451 compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
1453 =head2 C<AvFLAGS> has been removed
1455 The C<AvFLAGS> macro has been removed.
1457 =head2 C<av_*> changes
1459 The C<av_*()> functions, used to manipulate arrays, no longer accept null
1464 The implementation of the special variables $^H and %^H has changed, to
1465 allow implementing lexical pragmas in pure Perl.
1467 =head2 B:: modules inheritance changed
1469 The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
1470 inherits from C<B::SV> (it used to inherit from C<B::IV>).
1472 =head2 Anonymous hash and array constructors
1474 The anonymous hash and array constructors now take 1 op in the optree
1475 instead of 3, now that pp_anonhash and pp_anonlist return a reference to
1476 an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
1478 =head1 Known Problems
1480 There's still a remaining problem in the implementation of the lexical
1481 C<$_>: it doesn't work inside C</(?{...})/> blocks. (See the TODO test in
1484 =head1 Platform Specific Problems
1486 =head1 Reporting Bugs
1490 The F<Changes> file and the perl590delta to perl595delta man pages for
1491 exhaustive details on what changed.
1493 The F<INSTALL> file for how to build Perl.
1495 The F<README> file for general stuff.
1497 The F<Artistic> and F<Copying> files for copyright information.