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