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[perl5.git] / pod / perl595delta.pod
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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
5a093634 17reject any tainted format argument. (Rafael Garcia-SUarez)
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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 $4 is 'D' that a .NET programmer
73966613 106would expect. This is considered a feature. :-) (Yves Orton)
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108=item Possessive Quantifiers
109
110Perl now supports the "possessive quantifier" syntax of the "atomic match"
111pattern. Basically a possessive quantifier matches as much as it can and never
112gives any back. Thus it can be used to control backtracking. The syntax is
113similar to non-greedy matching, except instead of using a '?' as the modifier
114the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
73966613 115quantifiers. (Yves Orton)
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117=item Backtracking control verbs
118
119The regex engine now supports a number of special purpose backtrack
5d458dd8 120control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
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121and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
122
123=item Relative backreferences
124
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125A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
126safer form of back-reference notation as well as allowing relative
127backreferences. This should make it easier to generate and embed patterns
c74340f9 128that contain backreferences. (Yves Orton)
24b23f37 129
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130=back
131
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132=head2 The C<_> prototype
133
134A new prototype character has been added. C<_> is equivalent to C<$> (it
135denotes a scalar), but defaults to C<$_> if the corresponding argument
136isn't supplied. Due to the optional nature of the argument, you can only
137use it at the end of a prototype, or before a semicolon.
138
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139This has a small incompatible consequence: the prototype() function has
140been adjusted to return C<_> for some built-ins in appropriate cases (for
141example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
142
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143=head2 UNITCHECK blocks
144
145C<UNITCHECK>, a new special code block has been introduced, in addition to
146C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
147
148C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
149are always executed at the transition between the compilation and the
150execution of the main program, and thus are useless whenever code is
151loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
152just after the unit which defined them has been compiled. See L<perlmod>
153for more information. (Alex Gough)
154
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155=head2 readpipe() is now overridable
156
157The built-in function readpipe() is now overridable. Overriding it permits
158also to override its operator counterpart, C<qx//> (a.k.a. C<``>). (Rafael
159Garcia-Suarez)
160
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161=head2 UCD 5.0.0
162
163The copy of the Unicode Character Database included in Perl 5.9 has
164been updated to version 5.0.0.
165
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166=head1 Modules and Pragmas
167
168=head2 New Core Modules
169
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170=over 4
171
172=item *
173
174C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
175C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
176included in the perl core; the behaviour of C<Locale::Maketext::Simple>
177gracefully degrades when the later isn't present.
178
179=item *
180
181C<Params::Check> implements a generic input parsing/checking mechanism. It
182is used by CPANPLUS.
183
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184=item *
185
186C<Term::UI> simplifies the task to ask questions at a terminal prompt.
187
188=item *
189
190C<Object::Accessor> provides an interface to create per-object accessors.
191
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192=back
193
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194=head2 Module changes
195
196=over 4
197
198=item C<base>
199
200The C<base> pragma now warns if a class tries to inherit from itself.
201
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202=item C<warnings>
203
204The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
205that used C<Carp> routines without having loaded it at compile time might
206need to be adjusted; typically, the following (faulty) code won't work
207anymore, and will require parentheses to be added after the function name:
208
209 use warnings;
210 require Carp;
211 Carp::confess "argh";
212
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213=back
214
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215=head1 Utility Changes
216
217=head1 Documentation
218
219=head1 Performance Enhancements
220
221=head1 Installation and Configuration Improvements
222
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223=head2 C++ compatibility
224
225Efforts have been made to make perl and the core XS modules compilable
226with various C++ compilers (although the situation is not perfect with
227some of the compilers on some of the platforms tested.)
228
229=head2 Ports
230
231Perl has been reported to work on MidnightBSD.
232
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233=head1 Selected Bug Fixes
234
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235PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
236seek() is now supported with PerlIO::scalar-based filehandles, the
237underlying string being zero-filled as needed.
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238
239study() never worked for UTF-8 strings, but could lead to false results.
240It's now a no-op on UTF-8 data. (Yves Orton)
241
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242The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
243"unsafe" manner (contrary to other signals, that are deferred until the
244perl interpreter reaches a reasonably stable state; see
245L<perlipc/"Deferred Signals (Safe Signals)">).
246
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247When a module or a file is loaded through an @INC-hook, and when this hook
248has set a filename entry in %INC, __FILE__ is now set for this module
249accordingly to the contents of that %INC entry.
250
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251=head1 New or Changed Diagnostics
252
253=head1 Changed Internals
254
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255The anonymous hash and array constructors now take 1 op in the optree
256instead of 3, now that pp_anonhash and pp_anonlist return a reference to
257an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
258
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259=head1 Known Problems
260
261=head2 Platform Specific Problems
262
263=head1 Reporting Bugs
264
265If you find what you think is a bug, you might check the articles
266recently posted to the comp.lang.perl.misc newsgroup and the perl
267bug database at http://rt.perl.org/rt3/ . There may also be
268information at http://www.perl.org/ , the Perl Home Page.
269
270If you believe you have an unreported bug, please run the B<perlbug>
271program included with your release. Be sure to trim your bug down
272to a tiny but sufficient test case. Your bug report, along with the
273output of C<perl -V>, will be sent off to perlbug@perl.org to be
274analysed by the Perl porting team.
275
276=head1 SEE ALSO
277
278The F<Changes> file for exhaustive details on what changed.
279
280The F<INSTALL> file for how to build Perl.
281
282The F<README> file for general stuff.
283
284The F<Artistic> and F<Copying> files for copyright information.
285
286=cut