3 perldelta - what is new for perl v5.9.5
7 This document describes differences between the 5.9.4 and the 5.9.5
8 development releases. See L<perl590delta>, L<perl591delta>,
9 L<perl592delta>, L<perl593delta> and L<perl594delta> for the differences
10 between 5.8.0 and 5.9.4.
12 =head1 Incompatible Changes
14 =head2 Tainting and printf
16 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
17 reject any tainted format argument. (Rafael Garcia-SUarez)
19 =head2 undef and signal handlers
21 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
22 equivalent to setting it to C<'DEFAULT'>.
24 =head2 Removal of the bytecode compiler and of perlcc
26 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
27 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
28 experimental tools have never worked reliably, and, due to the lack of
29 volunteers to keep them in line with the perl interpreter developments, it
30 was decided to remove them instead of shipping a broken version of those.
31 The last version of those modules can be found with perl 5.9.4.
33 However the B compiler framework stays supported in the perl core, as with
34 the more useful modules it has permitted (among others, B::Deparse and
37 =head2 Removal of the JPL
39 The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
41 =head1 Core Enhancements
43 =head2 Regular expressions
47 =item Recursive Patterns
49 It is now possible to write recursive patterns without using the C<(??{})>
50 construct. This new way is more efficient, and in many cases easier to
53 Each capturing parenthesis can now be treated as an independent pattern
54 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
55 "parenthesis number"). For example, the following pattern will match
56 nested balanced angle brackets:
60 ( # start capture buffer 1
61 < # match an opening angle bracket
63 (?> # don't backtrack over the inside of this group
64 [^<>]+ # one or more non angle brackets
65 ) # end non backtracking group
67 (?1) # recurse to bracket 1 and try it again
69 > # match a closing angle bracket
70 ) # end capture buffer one
74 Note, users experienced with PCRE will find that the Perl implementation
75 of this feature differs from the PCRE one in that it is possible to
76 backtrack into a recursed pattern, whereas in PCRE the recursion is
77 atomic or "possessive" in nature. (Yves Orton)
79 =item Named Capture Buffers
81 It is now possible to name capturing parenthesis in a pattern and refer to
82 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
83 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
84 syntax. In code, the new magical hash C<%+> can be used to access the
85 contents of the buffers.
87 Thus, to replace all doubled chars, one could write
89 s/(?<letter>.)\k<letter>/$+{letter}/g
91 Only buffers with defined contents will be "visible" in the hash, so
92 it's possible to do something like
94 foreach my $name (keys %+) {
95 print "content of buffer '$name' is $+{$name}\n";
98 Users exposed to the .NET regex engine will find that the perl
99 implementation differs in that the numerical ordering of the buffers
100 is sequential, and not "unnamed first, then named". Thus in the pattern
102 /(A)(?<B>B)(C)(?<D>D)/
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 $4 is 'D' that a .NET programmer
106 would expect. This is considered a feature. :-) (Yves Orton)
108 =item Possessive Quantifiers
110 Perl now supports the "possessive quantifier" syntax of the "atomic match"
111 pattern. Basically a possessive quantifier matches as much as it can and never
112 gives any back. Thus it can be used to control backtracking. The syntax is
113 similar to non-greedy matching, except instead of using a '?' as the modifier
114 the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
115 quantifiers. (Yves Orton)
117 =item Backtracking control verbs
119 The regex engine now supports a number of special purpose backtrack
120 control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
121 and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
123 =item Relative backreferences
125 A new syntax C<\R1> ("1" being any positive decimal integer) allows
126 relative backreferencing. This should make it easier to embed patterns
127 that contain backreferences. (Yves Orton)
131 =head2 The C<_> prototype
133 A new prototype character has been added. C<_> is equivalent to C<$> (it
134 denotes a scalar), but defaults to C<$_> if the corresponding argument
135 isn't supplied. Due to the optional nature of the argument, you can only
136 use it at the end of a prototype, or before a semicolon.
138 This has a small incompatible consequence: the prototype() function has
139 been adjusted to return C<_> for some built-ins in appropriate cases (for
140 example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
142 =head2 UNITCHECK blocks
144 C<UNITCHECK>, a new special code block has been introduced, in addition to
145 C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
147 C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
148 are always executed at the transition between the compilation and the
149 execution of the main program, and thus are useless whenever code is
150 loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
151 just after the unit which defined them has been compiled. See L<perlmod>
152 for more information. (Alex Gough)
154 =head2 readpipe() is now overridable
156 The built-in function readpipe() is now overridable. Overriding it permits
157 also to override its operator counterpart, C<qx//> (a.k.a. C<``>). (Rafael
162 The copy of the Unicode Character Database included in Perl 5.9 has
163 been updated to version 5.0.0.
165 =head1 Modules and Pragmas
167 =head2 New Core Modules
173 C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
174 C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
175 included in the perl core; the behaviour of C<Locale::Maketext::Simple>
176 gracefully degrades when the later isn't present.
180 C<Params::Check> implements a generic input parsing/checking mechanism. It
185 C<Term::UI> simplifies the task to ask questions at a terminal prompt.
189 C<Object::Accessor> provides an interface to create per-object accessors.
193 =head2 Module changes
199 The C<base> pragma now warns if a class tries to inherit from itself.
203 The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
204 that used C<Carp> routines without having loaded it at compile time might
205 need to be adjusted; typically, the following (faulty) code won't work
206 anymore, and will require parentheses to be added after the function name:
210 Carp::confess "argh";
214 =head1 Utility Changes
218 =head1 Performance Enhancements
220 =head1 Installation and Configuration Improvements
222 =head2 C++ compatibility
224 Efforts have been made to make perl and the core XS modules compilable
225 with various C++ compilers (although the situation is not perfect with
226 some of the compilers on some of the platforms tested.)
230 Perl has been reported to work on MidnightBSD.
232 =head1 Selected Bug Fixes
234 PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
235 seek() is now supported with PerlIO::scalar-based filehandles, the
236 underlying string being zero-filled as needed.
238 study() never worked for UTF-8 strings, but could lead to false results.
239 It's now a no-op on UTF-8 data. (Yves Orton)
241 The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
242 "unsafe" manner (contrary to other signals, that are deferred until the
243 perl interpreter reaches a reasonably stable state; see
244 L<perlipc/"Deferred Signals (Safe Signals)">).
246 When a module or a file is loaded through an @INC-hook, and when this hook
247 has set a filename entry in %INC, __FILE__ is now set for this module
248 accordingly to the contents of that %INC entry.
250 =head1 New or Changed Diagnostics
252 =head2 Variable length character upgraded in print
254 This new UTF-8 warning indicates a situation where a non-Unicode string is
255 sent to a UTF-8 output layer, but given what the string contains, encoding
256 problems such as double UTF-8 encoding might arise. See L<perldiag>.
258 =head1 Changed Internals
260 The anonymous hash and array constructors now take 1 op in the optree
261 instead of 3, now that pp_anonhash and pp_anonlist return a reference to
262 an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
264 =head1 Known Problems
266 =head2 Platform Specific Problems
268 =head1 Reporting Bugs
270 If you find what you think is a bug, you might check the articles
271 recently posted to the comp.lang.perl.misc newsgroup and the perl
272 bug database at http://rt.perl.org/rt3/ . There may also be
273 information at http://www.perl.org/ , the Perl Home Page.
275 If you believe you have an unreported bug, please run the B<perlbug>
276 program included with your release. Be sure to trim your bug down
277 to a tiny but sufficient test case. Your bug report, along with the
278 output of C<perl -V>, will be sent off to perlbug@perl.org to be
279 analysed by the Perl porting team.
283 The F<Changes> file for exhaustive details on what changed.
285 The F<INSTALL> file for how to build Perl.
287 The F<README> file for general stuff.
289 The F<Artistic> and F<Copying> files for copyright information.