5 perldelta - what is new for perl 5.10.0
9 This document describes the differences between the 5.8.8 release and
12 Many of the bug fixes in 5.10.0 were already seen in the 5.8.X maintenance
13 releases; they are not duplicated here and are documented in the set of
14 man pages named perl58[1-8]?delta.
16 =head1 Core Enhancements
18 =head2 The C<feature> pragma
20 The C<feature> pragma is used to enable new syntax that would break Perl's
21 backwards-compatibility with older releases of the language. It's a lexical
22 pragma, like C<strict> or C<warnings>.
24 Currently the following new features are available: C<switch> (adds a
25 switch statement), C<say> (adds a C<say> built-in function), and C<state>
26 (adds a C<state> keyword for declaring "static" variables). Those
27 features are described in their own sections of this document.
29 The C<feature> pragma is also implicitly loaded when you require a minimal
30 perl version (with the C<use VERSION> construct) greater than, or equal
31 to, 5.9.5. See L<feature> for details.
33 =head2 New B<-E> command-line switch
35 B<-E> is equivalent to B<-e>, but it implicitly enables all
36 optional features (like C<use feature ":5.10">).
38 =head2 Defined-or operator
40 A new operator C<//> (defined-or) has been implemented.
41 The following expression:
45 is merely equivalent to
53 can now be used instead of
55 $c = $d unless defined $c;
57 The C<//> operator has the same precedence and associativity as C<||>.
58 Special care has been taken to ensure that this operator Do What You Mean
59 while not breaking old code, but some edge cases involving the empty
60 regular expression may now parse differently. See L<perlop> for
63 =head2 Switch and Smart Match operator
65 Perl 5 now has a switch statement. It's available when C<use feature
66 'switch'> is in effect. This feature introduces three new keywords,
67 C<given>, C<when>, and C<default>:
70 when (/^abc/) { $abc = 1; }
71 when (/^def/) { $def = 1; }
72 when (/^xyz/) { $xyz = 1; }
73 default { $nothing = 1; }
76 A more complete description of how Perl matches the switch variable
77 against the C<when> conditions is given in L<perlsyn/"Switch statements">.
79 This kind of match is called I<smart match>, and it's also possible to use
80 it outside of switch statements, via the new C<~~> operator. See
81 L<perlsyn/"Smart matching in detail">.
83 This feature was contributed by Robin Houston.
85 =head2 Regular expressions
89 =item Recursive Patterns
91 It is now possible to write recursive patterns without using the C<(??{})>
92 construct. This new way is more efficient, and in many cases easier to
95 Each capturing parenthesis can now be treated as an independent pattern
96 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
97 "parenthesis number"). For example, the following pattern will match
98 nested balanced angle brackets:
102 ( # start capture buffer 1
103 < # match an opening angle bracket
105 (?> # don't backtrack over the inside of this group
106 [^<>]+ # one or more non angle brackets
107 ) # end non backtracking group
109 (?1) # recurse to bracket 1 and try it again
110 )* # 0 or more times.
111 > # match a closing angle bracket
112 ) # end capture buffer one
116 PCRE users should note that Perl's recursive regex feature allows
117 backtracking into a recursed pattern, whereas in PCRE the recursion is
118 atomic or "possessive" in nature. As in the example above, you can
119 add (?>) to control this selectively. (Yves Orton)
121 =item Named Capture Buffers
123 It is now possible to name capturing parenthesis in a pattern and refer to
124 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
125 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
126 syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
127 access the contents of the capture buffers.
129 Thus, to replace all doubled chars with a single copy, one could write
131 s/(?<letter>.)\k<letter>/$+{letter}/g
133 Only buffers with defined contents will be "visible" in the C<%+> hash, so
134 it's possible to do something like
136 foreach my $name (keys %+) {
137 print "content of buffer '$name' is $+{$name}\n";
140 The C<%-> hash is a bit more complete, since it will contain array refs
141 holding values from all capture buffers similarly named, if there should
144 C<%+> and C<%-> are implemented as tied hashes through the new module
145 C<Tie::Hash::NamedCapture>.
147 Users exposed to the .NET regex engine will find that the perl
148 implementation differs in that the numerical ordering of the buffers
149 is sequential, and not "unnamed first, then named". Thus in the pattern
151 /(A)(?<B>B)(C)(?<D>D)/
153 $1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
154 $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
155 would expect. This is considered a feature. :-) (Yves Orton)
157 =item Possessive Quantifiers
159 Perl now supports the "possessive quantifier" syntax of the "atomic match"
160 pattern. Basically a possessive quantifier matches as much as it can and never
161 gives any back. Thus it can be used to control backtracking. The syntax is
162 similar to non-greedy matching, except instead of using a '?' as the modifier
163 the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
164 quantifiers. (Yves Orton)
166 =item Backtracking control verbs
168 The regex engine now supports a number of special-purpose backtrack
169 control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
170 and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
172 =item Relative backreferences
174 A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
175 safer form of back-reference notation as well as allowing relative
176 backreferences. This should make it easier to generate and embed patterns
177 that contain backreferences. See L<perlre/"Capture buffers">. (Yves Orton)
181 The functionality of Jeff Pinyan's module Regexp::Keep has been added to
182 the core. In regular expressions you can now use the special escape C<\K>
183 as a way to do something like floating length positive lookbehind. It is
184 also useful in substitutions like:
188 that can now be converted to
192 which is much more efficient. (Yves Orton)
194 =item Vertical and horizontal whitespace, and linebreak
196 Regular expressions now recognize the C<\v> and C<\h> escapes that match
197 vertical and horizontal whitespace, respectively. C<\V> and C<\H>
198 logically match their complements.
200 C<\R> matches a generic linebreak, that is, vertical whitespace, plus
201 the multi-character sequence C<"\x0D\x0A">.
207 say() is a new built-in, only available when C<use feature 'say'> is in
208 effect, that is similar to print(), but that implicitly appends a newline
209 to the printed string. See L<perlfunc/say>. (Robin Houston)
213 The default variable C<$_> can now be lexicalized, by declaring it like
214 any other lexical variable, with a simple
218 The operations that default on C<$_> will use the lexically-scoped
219 version of C<$_> when it exists, instead of the global C<$_>.
221 In a C<map> or a C<grep> block, if C<$_> was previously my'ed, then the
222 C<$_> inside the block is lexical as well (and scoped to the block).
224 In a scope where C<$_> has been lexicalized, you can still have access to
225 the global version of C<$_> by using C<$::_>, or, more simply, by
226 overriding the lexical declaration with C<our $_>. (Rafael Garcia-Suarez)
228 =head2 The C<_> prototype
230 A new prototype character has been added. C<_> is equivalent to C<$> but
231 defaults to C<$_> if the corresponding argument isn't supplied. (both C<$>
232 and C<_> denote a scalar). Due to the optional nature of the argument, you
233 can only use it at the end of a prototype, or before a semicolon.
235 This has a small incompatible consequence: the prototype() function has
236 been adjusted to return C<_> for some built-ins in appropriate cases (for
237 example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
239 =head2 UNITCHECK blocks
241 C<UNITCHECK>, a new special code block has been introduced, in addition to
242 C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
244 C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
245 are always executed at the transition between the compilation and the
246 execution of the main program, and thus are useless whenever code is
247 loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
248 just after the unit which defined them has been compiled. See L<perlmod>
249 for more information. (Alex Gough)
251 =head2 New Pragma, C<mro>
253 A new pragma, C<mro> (for Method Resolution Order) has been added. It
254 permits to switch, on a per-class basis, the algorithm that perl uses to
255 find inherited methods in case of a multiple inheritance hierarchy. The
256 default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
257 available: the C3 algorithm. See L<mro> for more information.
260 Note that, due to changes in the implementation of class hierarchy search,
261 code that used to undef the C<*ISA> glob will most probably break. Anyway,
262 undef'ing C<*ISA> had the side-effect of removing the magic on the @ISA
263 array and should not have been done in the first place.
265 =head2 readdir() may return a "short filename" on Windows
267 The readdir() function may return a "short filename" when the long
268 filename contains characters outside the ANSI codepage. Similarly
269 Cwd::cwd() may return a short directory name, and glob() may return short
270 names as well. On the NTFS file system these short names can always be
271 represented in the ANSI codepage. This will not be true for all other file
272 system drivers; e.g. the FAT filesystem stores short filenames in the OEM
273 codepage, so some files on FAT volumes remain unaccessible through the
276 Similarly, $^X, @INC, and $ENV{PATH} are preprocessed at startup to make
277 sure all paths are valid in the ANSI codepage (if possible).
279 The Win32::GetLongPathName() function now returns the UTF-8 encoded
280 correct long file name instead of using replacement characters to force
281 the name into the ANSI codepage. The new Win32::GetANSIPathName()
282 function can be used to turn a long pathname into a short one only if the
283 long one cannot be represented in the ANSI codepage.
285 Many other functions in the C<Win32> module have been improved to accept
286 UTF-8 encoded arguments. Please see L<Win32> for details.
288 =head2 readpipe() is now overridable
290 The built-in function readpipe() is now overridable. Overriding it permits
291 also to override its operator counterpart, C<qx//> (a.k.a. C<``>).
292 Moreover, it now defaults to C<$_> if no argument is provided. (Rafael
295 =head2 Default argument for readline()
297 readline() now defaults to C<*ARGV> if no argument is provided. (Rafael
300 =head2 state() variables
302 A new class of variables has been introduced. State variables are similar
303 to C<my> variables, but are declared with the C<state> keyword in place of
304 C<my>. They're visible only in their lexical scope, but their value is
305 persistent: unlike C<my> variables, they're not undefined at scope entry,
306 but retain their previous value. (Rafael Garcia-Suarez, Nicholas Clark)
308 To use state variables, one needs to enable them by using
312 or by using the C<-E> command-line switch in one-liners.
313 See L<perlsub/"Persistent variables via state()">.
315 =head2 Stacked filetest operators
317 As a new form of syntactic sugar, it's now possible to stack up filetest
318 operators. You can now write C<-f -w -x $file> in a row to mean
319 C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
321 =head2 UNIVERSAL::DOES()
323 The C<UNIVERSAL> class has a new method, C<DOES()>. It has been added to
324 solve semantic problems with the C<isa()> method. C<isa()> checks for
325 inheritance, while C<DOES()> has been designed to be overridden when
326 module authors use other types of relations between classes (in addition
327 to inheritance). (chromatic)
329 See L<< UNIVERSAL/"$obj->DOES( ROLE )" >>.
333 Formats were improved in several ways. A new field, C<^*>, can be used for
334 variable-width, one-line-at-a-time text. Null characters are now handled
335 correctly in picture lines. Using C<@#> and C<~~> together will now
336 produce a compile-time error, as those format fields are incompatible.
337 L<perlform> has been improved, and miscellaneous bugs fixed.
339 =head2 Byte-order modifiers for pack() and unpack()
341 There are two new byte-order modifiers, C<E<gt>> (big-endian) and C<E<lt>>
342 (little-endian), that can be appended to most pack() and unpack() template
343 characters and groups to force a certain byte-order for that type or group.
344 See L<perlfunc/pack> and L<perlpacktut> for details.
348 You can now use C<no> followed by a version number to specify that you
349 want to use a version of perl older than the specified one.
351 =head2 C<chdir>, C<chmod> and C<chown> on filehandles
353 C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
354 filenames, if the system supports respectively C<fchdir>, C<fchmod> and
355 C<fchown>, thanks to a patch provided by Gisle Aas.
359 C<$(> and C<$)> now return groups in the order where the OS returns them,
360 thanks to Gisle Aas. This wasn't previously the case.
362 =head2 Recursive sort subs
364 You can now use recursive subroutines with sort(), thanks to Robin Houston.
366 =head2 Exceptions in constant folding
368 The constant folding routine is now wrapped in an exception handler, and
369 if folding throws an exception (such as attempting to evaluate 0/0), perl
370 now retains the current optree, rather than aborting the whole program.
371 Without this change, programs would not compile if they had expressions that
372 happened to generate exceptions, even though those expressions were in code
373 that could never be reached at runtime. (Nicholas Clark, Dave Mitchell)
375 =head2 Source filters in @INC
377 It's possible to enhance the mechanism of subroutine hooks in @INC by
378 adding a source filter on top of the filehandle opened and returned by the
379 hook. This feature was planned a long time ago, but wasn't quite working
380 until now. See L<perlfunc/require> for details. (Nicholas Clark)
382 =head2 New internal variables
386 =item C<${^RE_DEBUG_FLAGS}>
388 This variable controls what debug flags are in effect for the regular
389 expression engine when running under C<use re "debug">. See L<re> for
392 =item C<${^CHILD_ERROR_NATIVE}>
394 This variable gives the native status returned by the last pipe close,
395 backtick command, successful call to wait() or waitpid(), or from the
396 system() operator. See L<perlrun> for details. (Contributed by Gisle Aas.)
398 =item C<${^RE_TRIE_MAXBUF}>
400 See L</"Trie optimisation of literal string alternations">.
402 =item C<${^WIN32_SLOPPY_STAT}>
404 See L</"Sloppy stat on Windows">.
410 C<unpack()> now defaults to unpacking the C<$_> variable.
412 C<mkdir()> without arguments now defaults to C<$_>.
414 The internal dump output has been improved, so that non-printable characters
415 such as newline and backspace are output in C<\x> notation, rather than
418 The B<-C> option can no longer be used on the C<#!> line. It wasn't
419 working there anyway, since the standard streams are already set up
420 at this point in the execution of the perl interpreter. You can use
421 binmode() instead to get the desired behaviour.
425 The copy of the Unicode Character Database included in Perl 5 has
426 been updated to version 5.0.0.
430 MAD, which stands for I<Miscellaneous Attribute Decoration>, is a
431 still-in-development work leading to a Perl 5 to Perl 6 converter. To
432 enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
433 obtained perl isn't binary compatible with a regular perl 5.10, and has
434 space and speed penalties; moreover not all regression tests still pass
435 with it. (Larry Wall, Nicholas Clark)
437 =head2 kill() on Windows
439 On Windows platforms, C<kill(-9, $pid)> now kills a process tree.
440 (On UNIX, this delivers the signal to all processes in the same process
443 =head1 Incompatible Changes
445 =head2 Packing and UTF-8 strings
447 The semantics of pack() and unpack() regarding UTF-8-encoded data has been
448 changed. Processing is now by default character per character instead of
449 byte per byte on the underlying encoding. Notably, code that used things
450 like C<pack("a*", $string)> to see through the encoding of string will now
451 simply get back the original $string. Packed strings can also get upgraded
452 during processing when you store upgraded characters. You can get the old
453 behaviour by using C<use bytes>.
455 To be consistent with pack(), the C<C0> in unpack() templates indicates
456 that the data is to be processed in character mode, i.e. character by
457 character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
458 the packed string is processed in its UTF-8-encoded Unicode form on a byte
459 by byte basis. This is reversed with regard to perl 5.8.X, but now consistent
460 between pack() and unpack().
462 Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
463 respectively character and byte modes.
465 C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
466 specified encoding mode, honoring parens grouping. Previously, parens were
469 Also, there is a new pack() character format, C<W>, which is intended to
470 replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
471 the strings internal representation. C<W> represents unsigned (logical)
472 character values, which can be greater than 255. It is therefore more
473 robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
474 values outside the range 0..255, and not respect the string encoding).
476 In practice, that means that pack formats are now encoding-neutral, except
479 For consistency, C<A> in unpack() format now trims all Unicode whitespace
480 from the end of the string. Before perl 5.9.2, it used to strip only the
481 classical ASCII space characters.
483 =head2 Byte/character count feature in unpack()
485 A new unpack() template character, C<".">, returns the number of bytes or
486 characters (depending on the selected encoding mode, see above) read so far.
488 =head2 The C<$*> and C<$#> variables have been removed
490 C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
491 modifiers, has been removed.
493 The deprecated C<$#> variable (output format for numbers) has been
496 Two new severe warnings, C<$#/$* is no longer supported>, have been added.
498 =head2 substr() lvalues are no longer fixed-length
500 The lvalues returned by the three argument form of substr() used to be a
501 "fixed length window" on the original string. In some cases this could
502 cause surprising action at distance or other undefined behaviour. Now the
503 length of the window adjusts itself to the length of the string assigned to
506 =head2 Parsing of C<-f _>
508 The identifier C<_> is now forced to be a bareword after a filetest
509 operator. This solves a number of misparsing issues when a global C<_>
510 subroutine is defined.
514 The C<:unique> attribute has been made a no-op, since its current
515 implementation was fundamentally flawed and not threadsafe.
517 =head2 Effect of pragmas in eval
519 The compile-time value of the C<%^H> hint variable can now propagate into
520 eval("")uated code. This makes it more useful to implement lexical
523 As a side-effect of this, the overloaded-ness of constants now propagates
528 A bareword argument to chdir() is now recognized as a file handle.
529 Earlier releases interpreted the bareword as a directory name.
532 =head2 Handling of .pmc files
534 An old feature of perl was that before C<require> or C<use> look for a
535 file with a F<.pm> extension, they will first look for a similar filename
536 with a F<.pmc> extension. If this file is found, it will be loaded in
537 place of any potentially existing file ending in a F<.pm> extension.
539 Previously, F<.pmc> files were loaded only if more recent than the
540 matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
543 =head2 @- and @+ in patterns
545 The special arrays C<@-> and C<@+> are no longer interpolated in regular
546 expressions. (Sadahiro Tomoyuki)
548 =head2 $AUTOLOAD can now be tainted
550 If you call a subroutine by a tainted name, and if it defers to an
551 AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
554 =head2 Tainting and printf
556 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
557 reject any tainted format argument. (Rafael Garcia-Suarez)
559 =head2 undef and signal handlers
561 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
562 equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
564 =head2 strictures and dereferencing in defined()
566 C<use strict 'refs'> was ignoring taking a hard reference in an argument
567 to defined(), as in :
571 if (defined $$x) {...}
573 This now correctly produces the run-time error C<Can't use string as a
574 SCALAR ref while "strict refs" in use>.
576 C<defined @$foo> and C<defined %$bar> are now also subject to C<strict
577 'refs'> (that is, C<$foo> and C<$bar> shall be proper references there.)
578 (C<defined(@foo)> and C<defined(%bar)> are discouraged constructs anyway.)
581 =head2 C<(?p{})> has been removed
583 The regular expression construct C<(?p{})>, which was deprecated in perl
584 5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
586 =head2 Pseudo-hashes have been removed
588 Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
589 pragma remains here, but uses an alternate implementation.)
591 =head2 Removal of the bytecode compiler and of perlcc
593 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
594 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
595 experimental tools have never worked reliably, and, due to the lack of
596 volunteers to keep them in line with the perl interpreter developments, it
597 was decided to remove them instead of shipping a broken version of those.
598 The last version of those modules can be found with perl 5.9.4.
600 However the B compiler framework stays supported in the perl core, as with
601 the more useful modules it has permitted (among others, B::Deparse and
604 =head2 Removal of the JPL
606 The JPL (Java-Perl Lingo) has been removed from the perl sources tarball.
608 =head2 Recursive inheritance detected earlier
610 Perl will now immediately throw an exception if you modify any package's
611 C<@ISA> in such a way that it would cause recursive inheritance.
613 Previously, the exception would not occur until Perl attempted to make
614 use of the recursive inheritance while resolving a method or doing a
615 C<$foo-E<gt>isa($bar)> lookup.
617 =head1 Modules and Pragmata
619 =head2 Upgrading individual core modules
621 Even more core modules are now also available separately through the
622 CPAN. If you wish to update one of these modules, you don't need to
623 wait for a new perl release. From within the cpan shell, running the
624 'r' command will report on modules with upgrades available. See
625 C<perldoc CPAN> for more information.
627 =head2 Pragmata Changes
633 The new pragma C<feature> is used to enable new features that might break
634 old code. See L</"The C<feature> pragma"> above.
638 This new pragma enables to change the algorithm used to resolve inherited
639 methods. See L</"New Pragma, C<mro>"> above.
641 =item Scoping of the C<sort> pragma
643 The C<sort> pragma is now lexically scoped. Its effect used to be global.
645 =item Scoping of C<bignum>, C<bigint>, C<bigrat>
647 The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
648 lexically scoped. (Tels)
652 The C<base> pragma now warns if a class tries to inherit from itself.
655 =item C<strict> and C<warnings>
657 C<strict> and C<warnings> will now complain loudly if they are loaded via
658 incorrect casing (as in C<use Strict;>). (Johan Vromans)
662 The C<version> module provides support for version objects.
666 The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
667 that used C<Carp> routines without having loaded it at compile time might
668 need to be adjusted; typically, the following (faulty) code won't work
669 anymore, and will require parentheses to be added after the function name:
673 Carp::confess 'argh';
677 C<less> now does something useful (or at least it tries to). In fact, it
678 has been turned into a lexical pragma. So, in your modules, you can now
679 test whether your users have requested to use less CPU, or less memory,
680 less magic, or maybe even less fat. See L<less> for more. (Joshua ben
691 C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
692 whenever an ASCII character string containing high-bit bytes is implicitly
693 converted into UTF-8. It's a lexical pragma since Perl 5.9.4; on older
694 perls, its effect is global.
698 C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
699 you what versions of core modules ship with any versions of Perl 5. It
700 comes with a command-line frontend, C<corelist>.
704 C<Math::BigInt::FastCalc> is an XS-enabled, and thus faster, version of
705 C<Math::BigInt::Calc>.
709 C<Compress::Zlib> is an interface to the zlib compression library. It
710 comes with a bundled version of zlib, so having a working zlib is not a
711 prerequisite to install it. It's used by C<Archive::Tar> (see below).
715 C<IO::Zlib> is an C<IO::>-style interface to C<Compress::Zlib>.
719 C<Archive::Tar> is a module to manipulate C<tar> archives.
723 C<Digest::SHA> is a module used to calculate many types of SHA digests,
724 has been included for SHA support in the CPAN module.
728 C<ExtUtils::CBuilder> and C<ExtUtils::ParseXS> have been added.
732 C<Hash::Util::FieldHash>, by Anno Siegel, has been added. This module
733 provides support for I<field hashes>: hashes that maintain an association
734 of a reference with a value, in a thread-safe garbage-collected way.
735 Such hashes are useful to implement inside-out objects.
739 C<Module::Build>, by Ken Williams, has been added. It's an alternative to
740 C<ExtUtils::MakeMaker> to build and install perl modules.
744 C<Module::Load>, by Jos Boumans, has been added. It provides a single
745 interface to load Perl modules and F<.pl> files.
749 C<Module::Loaded>, by Jos Boumans, has been added. It's used to mark
750 modules as loaded or unloaded.
754 C<Package::Constants>, by Jos Boumans, has been added. It's a simple
755 helper to list all constants declared in a given package.
759 C<Win32API::File>, by Tye McQueen, has been added (for Windows builds).
760 This module provides low-level access to Win32 system API calls for
765 C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
766 C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
767 included in the perl core; the behaviour of C<Locale::Maketext::Simple>
768 gracefully degrades when the later isn't present.
772 C<Params::Check> implements a generic input parsing/checking mechanism. It
777 C<Term::UI> simplifies the task to ask questions at a terminal prompt.
781 C<Object::Accessor> provides an interface to create per-object accessors.
785 C<Module::Pluggable> is a simple framework to create modules that accept
786 pluggable sub-modules.
790 C<Module::Load::Conditional> provides simple ways to query and possibly
791 load installed modules.
795 C<Time::Piece> provides an object oriented interface to time functions,
796 overriding the built-ins localtime() and gmtime().
800 C<IPC::Cmd> helps to find and run external commands, possibly
805 C<File::Fetch> provide a simple generic file fetching mechanism.
809 C<Log::Message> and C<Log::Message::Simple> are used by the log facility
814 C<Archive::Extract> is a generic archive extraction mechanism
815 for F<.tar> (plain, gziped or bzipped) or F<.zip> files.
819 C<CPANPLUS> provides an API and a command-line tool to access the CPAN
824 C<Pod::Escapes> provides utilities that are useful in decoding Pod
825 EE<lt>...E<gt> sequences.
829 C<Pod::Simple> is now the backend for several of the Pod-related modules
834 =head2 Selected Changes to Core Modules
838 =item C<Attribute::Handlers>
840 C<Attribute::Handlers> can now report the caller's file and line number.
843 All interpreted attributes are now passed as array references. (Damian
848 C<B::Lint> is now based on C<Module::Pluggable>, and so can be extended
849 with plugins. (Joshua ben Jore)
853 It's now possible to access the lexical pragma hints (C<%^H>) by using the
854 method B::COP::hints_hash(). It returns a C<B::RHE> object, which in turn
855 can be used to get a hash reference via the method B::RHE::HASH(). (Joshua
860 As the old 5005thread threading model has been removed, in favor of the
861 ithreads scheme, the C<Thread> module is now a compatibility wrapper, to
862 be used in old code only. It has been removed from the default list of
867 =head1 Utility Changes
873 The Perl debugger can now save all debugger commands for sourcing later;
874 notably, it can now emulate stepping backwards, by restarting and
875 rerunning all bar the last command from a saved command history.
877 It can also display the parent inheritance tree of a given class, with the
882 C<ptar> is a pure perl implementation of C<tar> that comes with
887 C<ptardiff> is a small utility used to generate a diff between the contents
888 of a tar archive and a directory tree. Like C<ptar>, it comes with
893 C<shasum> is a command-line utility, used to print or to check SHA
894 digests. It comes with the new C<Digest::SHA> module.
898 The C<corelist> utility is now installed with perl (see L</"New modules">
903 C<h2ph> and C<h2xs> have been made more robust with regard to
906 C<h2xs> implements a new option C<--use-xsloader> to force use of
907 C<XSLoader> even in backwards compatible modules.
909 The handling of authors' names that had apostrophes has been fixed.
911 Any enums with negative values are now skipped.
915 C<perlivp> no longer checks for F<*.ph> files by default. Use the new C<-a>
916 option to run I<all> tests.
920 C<find2perl> now assumes C<-print> as a default action. Previously, it
921 needed to be specified explicitly.
923 Several bugs have been fixed in C<find2perl>, regarding C<-exec> and
924 C<-eval>. Also the options C<-path>, C<-ipath> and C<-iname> have been
929 C<config_data> is a new utility that comes with C<Module::Build>. It
930 provides a command-line interface to the configuration of Perl modules
931 that use Module::Build's framework of configurability (that is,
932 C<*::ConfigData> modules that contain local configuration information for
933 their parent modules.)
937 C<cpanp>, the CPANPLUS shell, has been added. (C<cpanp-run-perl>, a
938 helper for CPANPLUS operation, has been added too, but isn't intended for
943 C<cpan2dist> is a new utility that comes with CPANPLUS. It's a tool to
944 create distributions (or packages) from CPAN modules.
948 The output of C<pod2html> has been enhanced to be more customizable via
949 CSS. Some formatting problems were also corrected. (Jari Aalto)
953 =head1 New Documentation
955 The L<perlpragma> manpage documents how to write one's own lexical
956 pragmas in pure Perl (something that is possible starting with 5.9.4).
958 The new L<perlglossary> manpage is a glossary of terms used in the Perl
959 documentation, technical and otherwise, kindly provided by O'Reilly Media,
962 The L<perlreguts> manpage, courtesy of Yves Orton, describes internals of the
963 Perl regular expression engine.
965 The L<perlreapi> manpage describes the interface to the perl interpreter
966 used to write pluggable regular expression engines (by Ævar Arnfjörð
969 The L<perlunitut> manpage is an tutorial for programming with Unicode and
970 string encodings in Perl, courtesy of Juerd Waalboer.
972 A new manual page, L<perlunifaq> (the Perl Unicode FAQ), has been added
975 The L<perlcommunity> manpage gives a description of the Perl community
976 on the Internet and in real life. (Edgar "Trizor" Bering)
978 The L<CORE> manual page documents the C<CORE::> namespace. (Tels)
980 The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
983 =head1 Performance Enhancements
985 =head2 In-place sorting
987 Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
988 making a temporary copy of the array.
990 Likewise, C<reverse sort ...> is now optimized to sort in reverse,
991 avoiding the generation of a temporary intermediate list.
993 =head2 Lexical array access
995 Access to elements of lexical arrays via a numeric constant between 0 and
996 255 is now faster. (This used to be only the case for global arrays.)
998 =head2 XS-assisted SWASHGET
1000 Some pure-perl code that perl was using to retrieve Unicode properties and
1001 transliteration mappings has been reimplemented in XS.
1003 =head2 Constant subroutines
1005 The interpreter internals now support a far more memory efficient form of
1006 inlineable constants. Storing a reference to a constant value in a symbol
1007 table is equivalent to a full typeglob referencing a constant subroutine,
1008 but using about 400 bytes less memory. This proxy constant subroutine is
1009 automatically upgraded to a real typeglob with subroutine if necessary.
1010 The approach taken is analogous to the existing space optimisation for
1011 subroutine stub declarations, which are stored as plain scalars in place
1012 of the full typeglob.
1014 Several of the core modules have been converted to use this feature for
1015 their system dependent constants - as a result C<use POSIX;> now takes about
1018 =head2 C<PERL_DONT_CREATE_GVSV>
1020 The new compilation flag C<PERL_DONT_CREATE_GVSV>, introduced as an option
1021 in perl 5.8.8, is turned on by default in perl 5.9.3. It prevents perl
1022 from creating an empty scalar with every new typeglob. See L<perl588delta>
1025 =head2 Weak references are cheaper
1027 Weak reference creation is now I<O(1)> rather than I<O(n)>, courtesy of
1028 Nicholas Clark. Weak reference deletion remains I<O(n)>, but if deletion only
1029 happens at program exit, it may be skipped completely.
1031 =head2 sort() enhancements
1033 Salvador Fandiño provided improvements to reduce the memory usage of C<sort>
1034 and to speed up some cases.
1036 =head2 Memory optimisations
1038 Several internal data structures (typeglobs, GVs, CVs, formats) have been
1039 restructured to use less memory. (Nicholas Clark)
1041 =head2 UTF-8 cache optimisation
1043 The UTF-8 caching code is now more efficient, and used more often.
1046 =head2 Sloppy stat on Windows
1048 On Windows, perl's stat() function normally opens the file to determine
1049 the link count and update attributes that may have been changed through
1050 hard links. Setting ${^WIN32_SLOPPY_STAT} to a true value speeds up
1051 stat() by not performing this operation. (Jan Dubois)
1053 =head2 Regular expressions optimisations
1057 =item Engine de-recursivised
1059 The regular expression engine is no longer recursive, meaning that
1060 patterns that used to overflow the stack will either die with useful
1061 explanations, or run to completion, which, since they were able to blow
1062 the stack before, will likely take a very long time to happen. If you were
1063 experiencing the occasional stack overflow (or segfault) and upgrade to
1064 discover that now perl apparently hangs instead, look for a degenerate
1065 regex. (Dave Mitchell)
1067 =item Single char char-classes treated as literals
1069 Classes of a single character are now treated the same as if the character
1070 had been used as a literal, meaning that code that uses char-classes as an
1071 escaping mechanism will see a speedup. (Yves Orton)
1073 =item Trie optimisation of literal string alternations
1075 Alternations, where possible, are optimised into more efficient matching
1076 structures. String literal alternations are merged into a trie and are
1077 matched simultaneously. This means that instead of O(N) time for matching
1078 N alternations at a given point, the new code performs in O(1) time.
1079 A new special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune
1080 this optimization. (Yves Orton)
1082 B<Note:> Much code exists that works around perl's historic poor
1083 performance on alternations. Often the tricks used to do so will disable
1084 the new optimisations. Hopefully the utility modules used for this purpose
1085 will be educated about these new optimisations.
1087 =item Aho-Corasick start-point optimisation
1089 When a pattern starts with a trie-able alternation and there aren't
1090 better optimisations available, the regex engine will use Aho-Corasick
1091 matching to find the start point. (Yves Orton)
1095 =head1 Installation and Configuration Improvements
1097 =head2 Configuration improvements
1101 =item C<-Dusesitecustomize>
1103 Run-time customization of @INC can be enabled by passing the
1104 C<-Dusesitecustomize> flag to Configure. When enabled, this will make perl
1105 run F<$sitelibexp/sitecustomize.pl> before anything else. This script can
1106 then be set up to add additional entries to @INC.
1108 =item Relocatable installations
1110 There is now Configure support for creating a relocatable perl tree. If
1111 you Configure with C<-Duserelocatableinc>, then the paths in @INC (and
1112 everything else in %Config) can be optionally located via the path of the
1115 That means that, if the string C<".../"> is found at the start of any
1116 path, it's substituted with the directory of $^X. So, the relocation can
1117 be configured on a per-directory basis, although the default with
1118 C<-Duserelocatableinc> is that everything is relocated. The initial
1119 install is done to the original configured prefix.
1121 =item strlcat() and strlcpy()
1123 The configuration process now detects whether strlcat() and strlcpy() are
1124 available. When they are not available, perl's own version is used (from
1125 Russ Allbery's public domain implementation). Various places in the perl
1126 interpreter now use them. (Steve Peters)
1128 =item C<d_pseudofork> and C<d_printf_format_null>
1130 A new configuration variable, available as C<$Config{d_pseudofork}> in
1131 the L<Config> module, has been added, to distinguish real fork() support
1132 from fake pseudofork used on Windows platforms.
1134 A new configuration variable, C<d_printf_format_null>, has been added,
1135 to see if printf-like formats are allowed to be NULL.
1137 =item Configure help
1139 C<Configure -h> has been extended with the most commonly used options.
1143 =head2 Compilation improvements
1147 =item Parallel build
1149 Parallel makes should work properly now, although there may still be problems
1150 if C<make test> is instructed to run in parallel.
1152 =item Borland's compilers support
1154 Building with Borland's compilers on Win32 should work more smoothly. In
1155 particular Steve Hay has worked to side step many warnings emitted by their
1156 compilers and at least one C compiler internal error.
1158 =item Static build on Windows
1160 Perl extensions on Windows now can be statically built into the Perl DLL.
1162 Also, it's now possible to build a C<perl-static.exe> that doesn't depend
1163 on the Perl DLL on Win32. See the Win32 makefiles for details.
1166 =item ppport.h files
1168 All F<ppport.h> files in the XS modules bundled with perl are now
1169 autogenerated at build time. (Marcus Holland-Moritz)
1171 =item C++ compatibility
1173 Efforts have been made to make perl and the core XS modules compilable
1174 with various C++ compilers (although the situation is not perfect with
1175 some of the compilers on some of the platforms tested.)
1177 =item Support for Microsoft 64-bit compiler
1179 Support for building perl with Microsoft's 64-bit compiler has been
1180 improved. (ActiveState)
1184 Perl can now be compiled with Microsoft Visual C++ 2005 (and 2008 Beta 2).
1188 All win32 builds (MS-Win, WinCE) have been merged and cleaned up.
1192 =head2 Installation improvements
1196 =item Module auxiliary files
1198 README files and changelogs for CPAN modules bundled with perl are no
1203 =head2 New Or Improved Platforms
1205 Perl has been reported to work on Symbian OS. See L<perlsymbian> for more
1208 Many improvements have been made towards making Perl work correctly on
1211 Perl has been reported to work on DragonFlyBSD and MidnightBSD.
1213 Perl has also been reported to work on NexentaOS
1214 ( http://www.gnusolaris.org/ ).
1216 The VMS port has been improved. See L<perlvms>.
1218 Support for Cray XT4 Catamount/Qk has been added. See
1219 F<hints/catamount.sh> in the source code distribution for more
1222 Vendor patches have been merged for RedHat and Gentoo.
1224 DynaLoader::dl_unload_file() now works on Windows.
1226 =head1 Selected Bug Fixes
1230 =item strictures in regexp-eval blocks
1232 C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
1234 =item Calling CORE::require()
1236 CORE::require() and CORE::do() were always parsed as require() and do()
1237 when they were overridden. This is now fixed.
1239 =item Subscripts of slices
1241 You can now use a non-arrowed form for chained subscripts after a list
1244 ({foo => "bar"})[0]{foo}
1246 This used to be a syntax error; a C<< -> >> was required.
1248 =item C<no warnings 'category'> works correctly with -w
1250 Previously when running with warnings enabled globally via C<-w>, selective
1251 disabling of specific warning categories would actually turn off all warnings.
1252 This is now fixed; now C<no warnings 'io';> will only turn off warnings in the
1253 C<io> class. Previously it would erroneously turn off all warnings.
1255 =item threads improvements
1257 Several memory leaks in ithreads were closed. Also, ithreads were made
1258 less memory-intensive.
1260 C<threads> is now a dual-life module, also available on CPAN. It has been
1261 expanded in many ways. A kill() method is available for thread signalling.
1262 One can get thread status, or the list of running or joinable threads.
1264 A new C<< threads->exit() >> method is used to exit from the application
1265 (this is the default for the main thread) or from the current thread only
1266 (this is the default for all other threads). On the other hand, the exit()
1267 built-in now always causes the whole application to terminate. (Jerry
1270 =item chr() and negative values
1272 chr() on a negative value now gives C<\x{FFFD}>, the Unicode replacement
1273 character, unless when the C<bytes> pragma is in effect, where the low
1274 eight bytes of the value are used.
1276 =item PERL5SHELL and tainting
1278 On Windows, the PERL5SHELL environment variable is now checked for
1279 taintedness. (Rafael Garcia-Suarez)
1281 =item Using *FILE{IO}
1283 C<stat()> and C<-X> filetests now treat *FILE{IO} filehandles like *FILE
1284 filehandles. (Steve Peters)
1286 =item Overloading and reblessing
1288 Overloading now works when references are reblessed into another class.
1289 Internally, this has been implemented by moving the flag for "overloading"
1290 from the reference to the referent, which logically is where it should
1291 always have been. (Nicholas Clark)
1293 =item Overloading and UTF-8
1295 A few bugs related to UTF-8 handling with objects that have
1296 stringification overloaded have been fixed. (Nicholas Clark)
1298 =item eval memory leaks fixed
1300 Traditionally, C<eval 'syntax error'> has leaked badly. Many (but not all)
1301 of these leaks have now been eliminated or reduced. (Dave Mitchell)
1303 =item Random device on Windows
1305 In previous versions, perl would read the file F</dev/urandom> if it
1306 existed when seeding its random number generator. That file is unlikely
1307 to exist on Windows, and if it did would probably not contain appropriate
1308 data, so perl no longer tries to read it on Windows. (Alex Davies)
1312 The C<PERLIO_DEBUG> environment variable no longer has any effect for
1313 setuid scripts and for scripts run with B<-T>.
1315 Moreover, with a thread-enabled perl, using C<PERLIO_DEBUG> could lead to
1316 an internal buffer overflow. This has been fixed.
1318 =item PerlIO::scalar and read-only scalars
1320 PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
1321 seek() is now supported with PerlIO::scalar-based filehandles, the
1322 underlying string being zero-filled as needed. (Rafael, Jarkko Hietaniemi)
1324 =item study() and UTF-8
1326 study() never worked for UTF-8 strings, but could lead to false results.
1327 It's now a no-op on UTF-8 data. (Yves Orton)
1329 =item Critical signals
1331 The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
1332 "unsafe" manner (contrary to other signals, that are deferred until the
1333 perl interpreter reaches a reasonably stable state; see
1334 L<perlipc/"Deferred Signals (Safe Signals)">). (Rafael)
1338 When a module or a file is loaded through an @INC-hook, and when this hook
1339 has set a filename entry in %INC, __FILE__ is now set for this module
1340 accordingly to the contents of that %INC entry. (Rafael)
1342 =item C<-t> switch fix
1344 The C<-w> and C<-t> switches can now be used together without messing
1345 up which categories of warnings are activated. (Rafael)
1347 =item Duping UTF-8 filehandles
1349 Duping a filehandle which has the C<:utf8> PerlIO layer set will now
1350 properly carry that layer on the duped filehandle. (Rafael)
1352 =item Localisation of hash elements
1354 Localizing a hash element whose key was given as a variable didn't work
1355 correctly if the variable was changed while the local() was in effect (as
1356 in C<local $h{$x}; ++$x>). (Bo Lindbergh)
1360 =head1 New or Changed Diagnostics
1364 =item Use of uninitialized value
1366 Perl will now try to tell you the name of the variable (if any) that was
1369 =item Deprecated use of my() in false conditional
1371 A new deprecation warning, I<Deprecated use of my() in false conditional>,
1372 has been added, to warn against the use of the dubious and deprecated
1377 See L<perldiag>. Use C<state> variables instead.
1379 =item !=~ should be !~
1381 A new warning, C<!=~ should be !~>, is emitted to prevent this misspelling
1382 of the non-matching operator.
1384 =item Newline in left-justified string
1386 The warning I<Newline in left-justified string> has been removed.
1388 =item Too late for "-T" option
1390 The error I<Too late for "-T" option> has been reformulated to be more
1393 =item "%s" variable %s masks earlier declaration
1395 This warning is now emitted in more consistent cases; in short, when one
1396 of the declarations involved is a C<my> variable:
1398 my $x; my $x; # warns
1399 my $x; our $x; # warns
1400 our $x; my $x; # warns
1402 On the other hand, the following:
1406 now gives a C<"our" variable %s redeclared> warning.
1408 =item readdir()/closedir()/etc. attempted on invalid dirhandle
1410 These new warnings are now emitted when a dirhandle is used but is
1411 either closed or not really a dirhandle.
1413 =item Opening dirhandle/filehandle %s also as a file/directory
1415 Two deprecation warnings have been added: (Rafael)
1417 Opening dirhandle %s also as a file
1418 Opening filehandle %s also as a directory
1420 =item Use of -P is deprecated
1422 Perl's command-line switch C<-P> is now deprecated.
1424 =item v-string in use/require is non-portable
1426 Perl will warn you against potential backwards compatibility problems with
1427 the C<use VERSION> syntax.
1431 C<perl -V> has several improvements, making it more useable from shell
1432 scripts to get the value of configuration variables. See L<perlrun> for
1437 =head1 Changed Internals
1439 In general, the source code of perl has been refactored, tidied up,
1440 and optimized in many places. Also, memory management and allocation
1441 has been improved in several points.
1443 When compiling the perl core with gcc, as many gcc warning flags are
1444 turned on as is possible on the platform. (This quest for cleanliness
1445 doesn't extend to XS code because we cannot guarantee the tidiness of
1446 code we didn't write.) Similar strictness flags have been added or
1447 tightened for various other C compilers.
1449 =head2 Reordering of SVt_* constants
1451 The relative ordering of constants that define the various types of C<SV>
1452 have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
1453 C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
1454 difference unless you have code that explicitly makes assumptions about that
1455 ordering. (The inheritance hierarchy of C<B::*> objects has been changed
1458 =head2 Elimination of SVt_PVBM
1460 Related to this, the internal type C<SVt_PVBM> has been been removed. This
1461 dedicated type of C<SV> was used by the C<index> operator and parts of the
1462 regexp engine to facilitate fast Boyer-Moore matches. Its use internally has
1463 been replaced by C<SV>s of type C<SVt_PVGV>.
1465 =head2 New type SVt_BIND
1467 A new type C<SVt_BIND> has been added, in readiness for the project to
1468 implement Perl 6 on 5. There deliberately is no implementation yet, and
1469 they cannot yet be created or destroyed.
1471 =head2 Removal of CPP symbols
1473 The C preprocessor symbols C<PERL_PM_APIVERSION> and
1474 C<PERL_XS_APIVERSION>, which were supposed to give the version number of
1475 the oldest perl binary-compatible (resp. source-compatible) with the
1476 present one, were not used, and sometimes had misleading values. They have
1479 =head2 Less space is used by ops
1481 The C<BASEOP> structure now uses less space. The C<op_seq> field has been
1482 removed and replaced by a single bit bit-field C<op_opt>. C<op_type> is now 9
1483 bits long. (Consequently, the C<B::OP> class doesn't provide an C<seq>
1488 perl's parser is now generated by bison (it used to be generated by
1489 byacc.) As a result, it seems to be a bit more robust.
1491 Also, Dave Mitchell improved the lexer debugging output under C<-DT>.
1493 =head2 Use of C<const>
1495 Andy Lester supplied many improvements to determine which function
1496 parameters and local variables could actually be declared C<const> to the C
1497 compiler. Steve Peters provided new C<*_set> macros and reworked the core to
1498 use these rather than assigning to macros in LVALUE context.
1502 A new file, F<mathoms.c>, has been added. It contains functions that are
1503 no longer used in the perl core, but that remain available for binary or
1504 source compatibility reasons. However, those functions will not be
1505 compiled in if you add C<-DNO_MATHOMS> in the compiler flags.
1507 =head2 C<AvFLAGS> has been removed
1509 The C<AvFLAGS> macro has been removed.
1511 =head2 C<av_*> changes
1513 The C<av_*()> functions, used to manipulate arrays, no longer accept null
1518 The implementation of the special variables $^H and %^H has changed, to
1519 allow implementing lexical pragmas in pure Perl.
1521 =head2 B:: modules inheritance changed
1523 The inheritance hierarchy of C<B::> modules has changed; C<B::NV> now
1524 inherits from C<B::SV> (it used to inherit from C<B::IV>).
1526 =head2 Anonymous hash and array constructors
1528 The anonymous hash and array constructors now take 1 op in the optree
1529 instead of 3, now that pp_anonhash and pp_anonlist return a reference to
1530 an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
1532 =head1 Known Problems
1534 There's still a remaining problem in the implementation of the lexical
1535 C<$_>: it doesn't work inside C</(?{...})/> blocks. (See the TODO test in
1538 Stacked filetest operators won't work when the C<filetest> pragma is in
1539 effect, because they rely on the stat() buffer C<_> being populated, and
1540 filetest bypasses stat().
1542 When compiled with g++ and thread support on Linux, it's reported that the
1543 C<$!> stops working correctly. This is related to the fact that the glibc
1544 provides two strerror_r(3) implementation, and perl selects the wrong
1547 =head1 Platform Specific Problems
1549 =head1 Reporting Bugs
1553 The F<Changes> file and the perl590delta to perl595delta man pages for
1554 exhaustive details on what changed.
1556 The F<INSTALL> file for how to build Perl.
1558 The F<README> file for general stuff.
1560 The F<Artistic> and F<Copying> files for copyright information.