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1=head1 NAME
2
3perldelta - what is new for perl v5.9.5
4
5=head1 DESCRIPTION
6
7This document describes differences between the 5.9.4 and the 5.9.5
8development releases. See L<perl590delta>, L<perl591delta>,
9L<perl592delta>, L<perl593delta> and L<perl594delta> for the differences
10between 5.8.0 and 5.9.4.
11
12=head1 Incompatible Changes
13
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14=head2 Tainting and printf
15
16When perl is run under taint mode, C<printf()> and C<sprintf()> will now
3f10c77a 17reject any tainted format argument. (Rafael Garcia-Suarez)
20ee07fb 18
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19=head2 undef and signal handlers
20
21Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
22equivalent to setting it to C<'DEFAULT'>.
23
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24=head2 Removal of the bytecode compiler and of perlcc
25
26C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
27B::Bytecode, etc.) are no longer distributed with the perl sources. Those
28experimental tools have never worked reliably, and, due to the lack of
29volunteers to keep them in line with the perl interpreter developments, it
30was decided to remove them instead of shipping a broken version of those.
31The last version of those modules can be found with perl 5.9.4.
32
33However the B compiler framework stays supported in the perl core, as with
34the more useful modules it has permitted (among others, B::Deparse and
35B::Concise).
36
37=head2 Removal of the JPL
38
39The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
40
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41=head1 Core Enhancements
42
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43=head2 Regular expressions
44
45=over 4
46
47=item Recursive Patterns
48
49It is now possible to write recursive patterns without using the C<(??{})>
50construct. This new way is more efficient, and in many cases easier to
51read.
52
53Each capturing parenthesis can now be treated as an independent pattern
54that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
55"parenthesis number"). For example, the following pattern will match
56nested balanced angle brackets:
57
58 /
59 ^ # start of line
60 ( # start capture buffer 1
61 < # match an opening angle bracket
62 (?: # match one of:
63 (?> # don't backtrack over the inside of this group
64 [^<>]+ # one or more non angle brackets
65 ) # end non backtracking group
66 | # ... or ...
67 (?1) # recurse to bracket 1 and try it again
68 )* # 0 or more times.
69 > # match a closing angle bracket
70 ) # end capture buffer one
71 $ # end of line
72 /x
73
74Note, users experienced with PCRE will find that the Perl implementation
75of this feature differs from the PCRE one in that it is possible to
76backtrack into a recursed pattern, whereas in PCRE the recursion is
73966613 77atomic or "possessive" in nature. (Yves Orton)
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78
79=item Named Capture Buffers
80
81It is now possible to name capturing parenthesis in a pattern and refer to
82the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
83It's possible to backreference to a named buffer with the C<< \k<NAME> >>
84syntax. In code, the new magical hash C<%+> can be used to access the
85contents of the buffers.
86
87Thus, to replace all doubled chars, one could write
88
89 s/(?<letter>.)\k<letter>/$+{letter}/g
90
91Only buffers with defined contents will be "visible" in the hash, so
92it's possible to do something like
93
94 foreach my $name (keys %+) {
95 print "content of buffer '$name' is $+{$name}\n";
96 }
97
98Users exposed to the .NET regex engine will find that the perl
99implementation differs in that the numerical ordering of the buffers
100is sequential, and not "unnamed first, then named". Thus in the pattern
101
102 /(A)(?<B>B)(C)(?<D>D)/
103
104$1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
105$1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
73966613 106would expect. This is considered a feature. :-) (Yves Orton)
072f65b4 107
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108=item Possessive Quantifiers
109
ee9b8eae 110Perl now supports the "possessive quantifier" syntax of the "atomic match"
b9b4dddf 111pattern. Basically a possessive quantifier matches as much as it can and never
ee9b8eae 112gives any back. Thus it can be used to control backtracking. The syntax is
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113similar to non-greedy matching, except instead of using a '?' as the modifier
114the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
73966613 115quantifiers. (Yves Orton)
b9b4dddf 116
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117=item Backtracking control verbs
118
3f10c77a 119The regex engine now supports a number of special-purpose backtrack
5d458dd8 120control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
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121and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
122
123=item Relative backreferences
124
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125A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
126safer form of back-reference notation as well as allowing relative
127backreferences. This should make it easier to generate and embed patterns
3f10c77a 128that contain backreferences. See L<perlre/"Capture buffers">. (Yves Orton)
24b23f37 129
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130=item Regexp::Keep internalized
131
132The functionality of Jeff Pinyan's module Regexp::Keep has been added to
133the core. You can now use in regular expressions the special escape C<\K>
134as a way to do something like floating length positive lookbehind. It is
135also useful in substitutions like:
136
137 s/(foo)bar/$1/g
138
139that can now be converted to
140
141 s/foo\Kbar//g
142
143which is much more efficient.
144
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145=back
146
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147=head2 The C<_> prototype
148
149A new prototype character has been added. C<_> is equivalent to C<$> (it
150denotes a scalar), but defaults to C<$_> if the corresponding argument
151isn't supplied. Due to the optional nature of the argument, you can only
152use it at the end of a prototype, or before a semicolon.
153
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154This has a small incompatible consequence: the prototype() function has
155been adjusted to return C<_> for some built-ins in appropriate cases (for
156example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
157
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158=head2 UNITCHECK blocks
159
160C<UNITCHECK>, a new special code block has been introduced, in addition to
161C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
162
163C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
164are always executed at the transition between the compilation and the
165execution of the main program, and thus are useless whenever code is
166loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
167just after the unit which defined them has been compiled. See L<perlmod>
168for more information. (Alex Gough)
169
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170=head2 readpipe() is now overridable
171
172The built-in function readpipe() is now overridable. Overriding it permits
173also to override its operator counterpart, C<qx//> (a.k.a. C<``>). (Rafael
174Garcia-Suarez)
175
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176=head2 UCD 5.0.0
177
178The copy of the Unicode Character Database included in Perl 5.9 has
179been updated to version 5.0.0.
180
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181=head1 Modules and Pragmas
182
183=head2 New Core Modules
184
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185=over 4
186
187=item *
188
189C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
190C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
191included in the perl core; the behaviour of C<Locale::Maketext::Simple>
192gracefully degrades when the later isn't present.
193
194=item *
195
196C<Params::Check> implements a generic input parsing/checking mechanism. It
197is used by CPANPLUS.
198
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199=item *
200
201C<Term::UI> simplifies the task to ask questions at a terminal prompt.
202
203=item *
204
205C<Object::Accessor> provides an interface to create per-object accessors.
206
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207=back
208
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209=head2 Module changes
210
211=over 4
212
213=item C<base>
214
215The C<base> pragma now warns if a class tries to inherit from itself.
216
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217=item C<warnings>
218
219The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
220that used C<Carp> routines without having loaded it at compile time might
221need to be adjusted; typically, the following (faulty) code won't work
222anymore, and will require parentheses to be added after the function name:
223
224 use warnings;
225 require Carp;
226 Carp::confess "argh";
227
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228=item C<Attribute::Handlers>
229
230C<Attribute::Handlers> can now report the caller's file and line number.
231(David Feldman)
232
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233=back
234
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235=head1 Utility Changes
236
237=head1 Documentation
238
239=head1 Performance Enhancements
240
241=head1 Installation and Configuration Improvements
242
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243=head2 C++ compatibility
244
245Efforts have been made to make perl and the core XS modules compilable
246with various C++ compilers (although the situation is not perfect with
247some of the compilers on some of the platforms tested.)
248
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249=head2 Static build on Win32
250
251It's now possible to build a C<perl-static.exe> that doesn't depend
252on C<perl59.dll> on Win32. See the Win32 makefiles for details.
253(Steve Hay)
254
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255=head2 Ports
256
257Perl has been reported to work on MidnightBSD.
258
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259=head1 Selected Bug Fixes
260
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261PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
262seek() is now supported with PerlIO::scalar-based filehandles, the
263underlying string being zero-filled as needed.
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264
265study() never worked for UTF-8 strings, but could lead to false results.
266It's now a no-op on UTF-8 data. (Yves Orton)
267
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268The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
269"unsafe" manner (contrary to other signals, that are deferred until the
270perl interpreter reaches a reasonably stable state; see
271L<perlipc/"Deferred Signals (Safe Signals)">).
272
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273When a module or a file is loaded through an @INC-hook, and when this hook
274has set a filename entry in %INC, __FILE__ is now set for this module
275accordingly to the contents of that %INC entry.
276
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277=head1 New or Changed Diagnostics
278
279=head1 Changed Internals
280
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281The anonymous hash and array constructors now take 1 op in the optree
282instead of 3, now that pp_anonhash and pp_anonlist return a reference to
283an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
284
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285=head1 Known Problems
286
287=head2 Platform Specific Problems
288
289=head1 Reporting Bugs
290
291If you find what you think is a bug, you might check the articles
292recently posted to the comp.lang.perl.misc newsgroup and the perl
293bug database at http://rt.perl.org/rt3/ . There may also be
294information at http://www.perl.org/ , the Perl Home Page.
295
296If you believe you have an unreported bug, please run the B<perlbug>
297program included with your release. Be sure to trim your bug down
298to a tiny but sufficient test case. Your bug report, along with the
299output of C<perl -V>, will be sent off to perlbug@perl.org to be
300analysed by the Perl porting team.
301
302=head1 SEE ALSO
303
304The F<Changes> file for exhaustive details on what changed.
305
306The F<INSTALL> file for how to build Perl.
307
308The F<README> file for general stuff.
309
310The F<Artistic> and F<Copying> files for copyright information.
311
312=cut