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1=head1 NAME
2
3perldelta - what's new for perl v5.6.x
4
5=head1 DESCRIPTION
6
7This document describes differences between the 5.005 release and the 5.6.1
8release.
9
10=head1 Summary of changes between 5.6.0 and 5.6.1
11
12This section contains a summary of the changes between the 5.6.0 release
13and the 5.6.1 release. More details about the changes mentioned here
14may be found in the F<Changes> files that accompany the Perl source
15distribution. See L<perlhack> for pointers to online resources where you
16can inspect the individual patches described by these changes.
17
18=head2 Security Issues
19
20suidperl will not run /bin/mail anymore, because some platforms have
21a /bin/mail that is vulnerable to buffer overflow attacks.
22
23Note that suidperl is neither built nor installed by default in
24any recent version of perl. Use of suidperl is highly discouraged.
25If you think you need it, try alternatives such as sudo first.
26See http://www.courtesan.com/sudo/.
27
28=head2 Core bug fixes
29
30This is not an exhaustive list. It is intended to cover only the
31significant user-visible changes.
32
33=over
34
35=item C<UNIVERSAL::isa()>
36
37A bug in the caching mechanism used by C<UNIVERSAL::isa()> that affected
38base.pm has been fixed. The bug has existed since the 5.005 releases,
39but wasn't tickled by base.pm in those releases.
40
41=item Memory leaks
42
43Various cases of memory leaks and attempts to access uninitialized memory
44have been cured. See L</"Known Problems"> below for further issues.
45
46=item Numeric conversions
47
48Numeric conversions did not recognize changes in the string value
49properly in certain circumstances.
50
51In other situations, large unsigned numbers (those above 2**31) could
52sometimes lose their unsignedness, causing bogus results in arithmetic
53operations.
54
55Integer modulus on large unsigned integers sometimes returned
56incorrect values.
57
58Perl 5.6.0 generated "not a number" warnings on certain conversions where
59previous versions didn't.
60
61These problems have all been rectified.
62
63Infinity is now recognized as a number.
64
65=item qw(a\\b)
66
67In Perl 5.6.0, qw(a\\b) produced a string with two backslashes instead
68of one, in a departure from the behavior in previous versions. The
69older behavior has been reinstated.
70
71=item caller()
72
73caller() could cause core dumps in certain situations. Carp was sometimes
74affected by this problem.
75
76=item Bugs in regular expressions
77
78Pattern matches on overloaded values are now handled correctly.
79
80Perl 5.6.0 parsed m/\x{ab}/ incorrectly, leading to spurious warnings.
81This has been corrected.
82
83The RE engine found in Perl 5.6.0 accidentally pessimised certain kinds
84of simple pattern matches. These are now handled better.
85
86Regular expression debug output (whether through C<use re 'debug'>
87or via C<-Dr>) now looks better.
88
89Multi-line matches like C<"a\nxb\n" =~ /(?!\A)x/m> were flawed. The
90bug has been fixed.
91
92Use of $& could trigger a core dump under some situations. This
93is now avoided.
94
95Match variables $1 et al., weren't being unset when a pattern match
96was backtracking, and the anomaly showed up inside C</...(?{ ... }).../>
97etc. These variables are now tracked correctly.
98
99pos() did not return the correct value within s///ge in earlier
100versions. This is now handled correctly.
101
102=item "slurp" mode
103
104readline() on files opened in "slurp" mode could return an extra "" at
105the end in certain situations. This has been corrected.
106
107=item Autovivification of symbolic references to special variables
108
109Autovivification of symbolic references of special variables described
110in L<perlvar> (as in C<${$num}>) was accidentally disabled. This works
111again now.
112
113=item Lexical warnings
114
115Lexical warnings now propagate correctly into C<eval "...">.
116
117C<use warnings qw(FATAL all)> did not work as intended. This has been
118corrected.
119
120Lexical warnings could leak into other scopes in some situations.
121This is now fixed.
122
123warnings::enabled() now reports the state of $^W correctly if the caller
124isn't using lexical warnings.
125
126=item Spurious warnings and errors
127
128Perl 5.6.0 could emit spurious warnings about redefinition of dl_error()
129when statically building extensions into perl. This has been corrected.
130
131"our" variables could result in bogus "Variable will not stay shared"
132warnings. This is now fixed.
133
134"our" variables of the same name declared in two sibling blocks
135resulted in bogus warnings about "redeclaration" of the variables.
136The problem has been corrected.
137
138=item glob()
139
140Compatibility of the builtin glob() with old csh-based glob has been
141improved with the addition of GLOB_ALPHASORT option. See C<File::Glob>.
142
143File::Glob::glob() has been renamed to File::Glob::bsd_glob()
144because the name clashes with the builtin glob(). The older
145name is still available for compatibility, but is deprecated.
146
147Spurious syntax errors generated in certain situations, when glob()
148caused File::Glob to be loaded for the first time, have been fixed.
149
150=item Tainting
151
152Some cases of inconsistent taint propagation (such as within hash
153values) have been fixed.
154
155The tainting behavior of sprintf() has been rationalized. It does
156not taint the result of floating point formats anymore, making the
157behavior consistent with that of string interpolation.
158
159=item sort()
160
161Arguments to sort() weren't being provided the right wantarray() context.
162The comparison block is now run in scalar context, and the arguments to
163be sorted are always provided list context.
164
165sort() is also fully reentrant, in the sense that the sort function
166can itself call sort(). This did not work reliably in previous releases.
167
168=item #line directives
169
170#line directives now work correctly when they appear at the very
171beginning of C<eval "...">.
172
173=item Subroutine prototypes
174
175The (\&) prototype now works properly.
176
177=item map()
178
179map() could get pathologically slow when the result list it generates
180is larger than the source list. The performance has been improved for
181common scenarios.
182
183=item Debugger
184
185Debugger exit code now reflects the script exit code.
186
187Condition C<"0"> in breakpoints is now treated correctly.
188
189The C<d> command now checks the line number.
190
191C<$.> is no longer corrupted by the debugger.
192
193All debugger output now correctly goes to the socket if RemotePort
194is set.
195
196=item PERL5OPT
197
198PERL5OPT can be set to more than one switch group. Previously,
199it used to be limited to one group of options only.
200
201=item chop()
202
203chop(@list) in list context returned the characters chopped in reverse
204order. This has been reversed to be in the right order.
205
206=item Unicode support
207
208Unicode support has seen a large number of incremental improvements,
209but continues to be highly experimental. It is not expected to be
210fully supported in the 5.6.x maintenance releases.
211
212substr(), join(), repeat(), reverse(), quotemeta() and string
213concatenation were all handling Unicode strings incorrectly in
214Perl 5.6.0. This has been corrected.
215
216Support for C<tr///CU> and C<tr///UC> etc., have been removed since
217we realized the interface is broken. For similar functionality,
218see L<perlfunc/pack>.
219
220The Unicode Character Database has been updated to version 3.0.1
221with additions made available to the public as of August 30, 2000.
222
223The Unicode character classes \p{Blank} and \p{SpacePerl} have been
224added. "Blank" is like C isblank(), that is, it contains only
225"horizontal whitespace" (the space character is, the newline isn't),
226and the "SpacePerl" is the Unicode equivalent of C<\s> (\p{Space}
227isn't, since that includes the vertical tabulator character, whereas
228C<\s> doesn't.)
229
230If you are experimenting with Unicode support in perl, the development
231versions of Perl may have more to offer. In particular, I/O layers
232are now available in the development track, but not in the maintenance
233track, primarily to do backward compatibility issues. Unicode support
234is also evolving rapidly on a daily basis in the development track--the
235maintenance track only reflects the most conservative of these changes.
236
237=item 64-bit support
238
239Support for 64-bit platforms has been improved, but continues to be
240experimental. The level of support varies greatly among platforms.
241
242=item Compiler
243
244The B Compiler and its various backends have had many incremental
245improvements, but they continue to remain highly experimental. Use in
246production environments is discouraged.
247
248The perlcc tool has been rewritten so that the user interface is much
249more like that of a C compiler.
250
251The perlbc tools has been removed. Use C<perlcc -B> instead.
252
253=item Lvalue subroutines
254
255There have been various bugfixes to support lvalue subroutines better.
256However, the feature still remains experimental.
257
258=item IO::Socket
259
260IO::Socket::INET failed to open the specified port if the service
261name was not known. It now correctly uses the supplied port number
262as is.
263
264=item File::Find
265
266File::Find now chdir()s correctly when chasing symbolic links.
267
268=item xsubpp
269
270xsubpp now tolerates embedded POD sections.
271
272=item C<no Module;>
273
274C<no Module;> does not produce an error even if Module does not have an
275unimport() method. This parallels the behavior of C<use> vis-a-vis
276C<import>.
277
278=item Tests
279
280A large number of tests have been added.
281
282=back
283
284=head2 Core features
285
286untie() will now call an UNTIE() hook if it exists. See L<perltie>
287for details.
288
289The C<-DT> command line switch outputs copious tokenizing information.
290See L<perlrun>.
291
292Arrays are now always interpolated in double-quotish strings. Previously,
293C<"foo@bar.com"> used to be a fatal error at compile time, if an array
294C<@bar> was not used or declared. This transitional behavior was
295intended to help migrate perl4 code, and is deemed to be no longer useful.
296See L</"Arrays now always interpolate into double-quoted strings">.
297
298keys(), each(), pop(), push(), shift(), splice() and unshift()
299can all be overridden now.
300
301C<my __PACKAGE__ $obj> now does the expected thing.
302
303=head2 Configuration issues
304
305On some systems (IRIX and Solaris among them) the system malloc is demonstrably
306better. While the defaults haven't been changed in order to retain binary
307compatibility with earlier releases, you may be better off building perl
308with C<Configure -Uusemymalloc ...> as discussed in the F<INSTALL> file.
309
310C<Configure> has been enhanced in various ways:
311
312=over
313
314=item *
315
316Minimizes use of temporary files.
317
318=item *
319
320By default, does not link perl with libraries not used by it, such as
321the various dbm libraries. SunOS 4.x hints preserve behavior on that
322platform.
323
324=item *
325
326Support for pdp11-style memory models has been removed due to obsolescence.
327
328=item *
329
330Building outside the source tree is supported on systems that have
331symbolic links. This is done by running
332
333 sh /path/to/source/Configure -Dmksymlinks ...
334 make all test install
335
336in a directory other than the perl source directory. See F<INSTALL>.
337
338=item *
339
340C<Configure -S> can be run non-interactively.
341
342=back
343
344=head2 Documentation
345
346README.aix, README.solaris and README.macos have been added. README.posix-bc
347has been renamed to README.bs2000. These are installed as L<perlaix>,
348L<perlsolaris>, L<perlmacos>, and L<perlbs2000> respectively.
349
350The following pod documents are brand new:
351
352 perlclib Internal replacements for standard C library functions
353 perldebtut Perl debugging tutorial
354 perlebcdic Considerations for running Perl on EBCDIC platforms
355 perlnewmod Perl modules: preparing a new module for distribution
356 perlrequick Perl regular expressions quick start
357 perlretut Perl regular expressions tutorial
358 perlutil utilities packaged with the Perl distribution
359
360The F<INSTALL> file has been expanded to cover various issues, such as
36164-bit support.
362
363A longer list of contributors has been added to the source distribution.
364See the file C<AUTHORS>.
365
366Numerous other changes have been made to the included documentation and FAQs.
367
368=head2 Bundled modules
369
370The following modules have been added.
371
372=over
373
374=item B::Concise
375
376Walks Perl syntax tree, printing concise info about ops. See L<B::Concise>.
377
378=item File::Temp
379
380Returns name and handle of a temporary file safely. See L<File::Temp>.
381
382=item Pod::LaTeX
383
384Converts Pod data to formatted LaTeX. See L<Pod::LaTeX>.
385
386=item Pod::Text::Overstrike
387
388Converts POD data to formatted overstrike text. See L<Pod::Text::Overstrike>.
389
390=back
391
392The following modules have been upgraded.
393
394=over
395
396=item CGI
397
398CGI v2.752 is now included.
399
400=item CPAN
401
402CPAN v1.59_54 is now included.
403
404=item Class::Struct
405
406Various bugfixes have been added.
407
408=item DB_File
409
410DB_File v1.75 supports newer Berkeley DB versions, among other
411improvements.
412
413=item Devel::Peek
414
415Devel::Peek has been enhanced to support dumping of memory statistics,
416when perl is built with the included malloc().
417
418=item File::Find
419
420File::Find now supports pre and post-processing of the files in order
421to sort() them, etc.
422
423=item Getopt::Long
424
425Getopt::Long v2.25 is included.
426
427=item IO::Poll
428
429Various bug fixes have been included.
430
431=item IPC::Open3
432
433IPC::Open3 allows use of numeric file descriptors.
434
435=item Math::BigFloat
436
437The fmod() function supports modulus operations. Various bug fixes
438have also been included.
439
440=item Math::Complex
441
442Math::Complex handles inf, NaN etc., better.
443
444=item Net::Ping
445
446ping() could fail on odd number of data bytes, and when the echo service
447isn't running. This has been corrected.
448
449=item Opcode
450
451A memory leak has been fixed.
452
453=item Pod::Parser
454
455Version 1.13 of the Pod::Parser suite is included.
456
457=item Pod::Text
458
459Pod::Text and related modules have been upgraded to the versions
460in podlators suite v2.08.
461
462=item SDBM_File
463
464On dosish platforms, some keys went missing because of lack of support for
465files with "holes". A workaround for the problem has been added.
466
467=item Sys::Syslog
468
469Various bug fixes have been included.
470
471=item Tie::RefHash
472
473Now supports Tie::RefHash::Nestable to automagically tie hashref values.
474
475=item Tie::SubstrHash
476
477Various bug fixes have been included.
478
479=back
480
481=head2 Platform-specific improvements
482
483The following new ports are now available.
484
485=over
486
487=item NCR MP-RAS
488
489=item NonStop-UX
490
491=back
492
493Perl now builds under Amdahl UTS.
494
495Perl has also been verified to build under Amiga OS.
496
497Support for EPOC has been much improved. See README.epoc.
498
499Building perl with -Duseithreads or -Duse5005threads now works
500under HP-UX 10.20 (previously it only worked under 10.30 or later).
501You will need a thread library package installed. See README.hpux.
502
503Long doubles should now work under Linux.
504
505MacOS Classic is now supported in the mainstream source package.
506See README.macos.
507
508Support for MPE/iX has been updated. See README.mpeix.
509
510Support for OS/2 has been improved. See C<os2/Changes> and README.os2.
511
512Dynamic loading on z/OS (formerly OS/390) has been improved. See
513README.os390.
514
515Support for VMS has seen many incremental improvements, including
516better support for operators like backticks and system(), and better
517%ENV handling. See C<README.vms> and L<perlvms>.
518
519Support for Stratus VOS has been improved. See C<vos/Changes> and README.vos.
520
521Support for Windows has been improved.
522
523=over
524
525=item *
526
527fork() emulation has been improved in various ways, but still continues
528to be experimental. See L<perlfork> for known bugs and caveats.
529
530=item *
531
532%SIG has been enabled under USE_ITHREADS, but its use is completely
533unsupported under all configurations.
534
535=item *
536
537Borland C++ v5.5 is now a supported compiler that can build Perl.
538However, the generated binaries continue to be incompatible with those
539generated by the other supported compilers (GCC and Visual C++).
540
541=item *
542
543Non-blocking waits for child processes (or pseudo-processes) are
544supported via C<waitpid($pid, &POSIX::WNOHANG)>.
545
546=item *
547
548A memory leak in accept() has been fixed.
549
550=item *
551
552wait(), waitpid() and backticks now return the correct exit status under
553Windows 9x.
554
555=item *
556
557Trailing new %ENV entries weren't propagated to child processes. This
558is now fixed.
559
560=item *
561
562Current directory entries in %ENV are now correctly propagated to child
563processes.
564
565=item *
566
567Duping socket handles with open(F, ">&MYSOCK") now works under Windows 9x.
568
569=item *
570
571The makefiles now provide a single switch to bulk-enable all the features
572enabled in ActiveState ActivePerl (a popular binary distribution).
573
574=item *
575
576Win32::GetCwd() correctly returns C:\ instead of C: when at the drive root.
577Other bugs in chdir() and Cwd::cwd() have also been fixed.
578
579=item *
580
581fork() correctly returns undef and sets EAGAIN when it runs out of
582pseudo-process handles.
583
584=item *
585
586ExtUtils::MakeMaker now uses $ENV{LIB} to search for libraries.
587
588=item *
589
590UNC path handling is better when perl is built to support fork().
591
592=item *
593
594A handle leak in socket handling has been fixed.
595
596=item *
597
598send() works from within a pseudo-process.
599
600=back
601
602Unless specifically qualified otherwise, the remainder of this document
603covers changes between the 5.005 and 5.6.0 releases.
604
605=head1 Core Enhancements
606
607=head2 Interpreter cloning, threads, and concurrency
608
609Perl 5.6.0 introduces the beginnings of support for running multiple
610interpreters concurrently in different threads. In conjunction with
611the perl_clone() API call, which can be used to selectively duplicate
612the state of any given interpreter, it is possible to compile a
613piece of code once in an interpreter, clone that interpreter
614one or more times, and run all the resulting interpreters in distinct
615threads.
616
617On the Windows platform, this feature is used to emulate fork() at the
618interpreter level. See L<perlfork> for details about that.
619
620This feature is still in evolution. It is eventually meant to be used
621to selectively clone a subroutine and data reachable from that
622subroutine in a separate interpreter and run the cloned subroutine
623in a separate thread. Since there is no shared data between the
624interpreters, little or no locking will be needed (unless parts of
625the symbol table are explicitly shared). This is obviously intended
626to be an easy-to-use replacement for the existing threads support.
627
628Support for cloning interpreters and interpreter concurrency can be
629enabled using the -Dusethreads Configure option (see win32/Makefile for
630how to enable it on Windows.) The resulting perl executable will be
631functionally identical to one that was built with -Dmultiplicity, but
632the perl_clone() API call will only be available in the former.
633
634-Dusethreads enables the cpp macro USE_ITHREADS by default, which in turn
635enables Perl source code changes that provide a clear separation between
636the op tree and the data it operates with. The former is immutable, and
637can therefore be shared between an interpreter and all of its clones,
638while the latter is considered local to each interpreter, and is therefore
639copied for each clone.
640
641Note that building Perl with the -Dusemultiplicity Configure option
642is adequate if you wish to run multiple B<independent> interpreters
643concurrently in different threads. -Dusethreads only provides the
644additional functionality of the perl_clone() API call and other
645support for running B<cloned> interpreters concurrently.
646
647 NOTE: This is an experimental feature. Implementation details are
648 subject to change.
649
650=head2 Lexically scoped warning categories
651
652You can now control the granularity of warnings emitted by perl at a finer
653level using the C<use warnings> pragma. L<warnings> and L<perllexwarn>
654have copious documentation on this feature.
655
656=head2 Unicode and UTF-8 support
657
658Perl now uses UTF-8 as its internal representation for character
659strings. The C<utf8> and C<bytes> pragmas are used to control this support
660in the current lexical scope. See L<perlunicode>, L<utf8> and L<bytes> for
661more information.
662
663This feature is expected to evolve quickly to support some form of I/O
664disciplines that can be used to specify the kind of input and output data
665(bytes or characters). Until that happens, additional modules from CPAN
666will be needed to complete the toolkit for dealing with Unicode.
667
668 NOTE: This should be considered an experimental feature. Implementation
669 details are subject to change.
670
671=head2 Support for interpolating named characters
672
673The new C<\N> escape interpolates named characters within strings.
674For example, C<"Hi! \N{WHITE SMILING FACE}"> evaluates to a string
675with a Unicode smiley face at the end.
676
677=head2 "our" declarations
678
679An "our" declaration introduces a value that can be best understood
680as a lexically scoped symbolic alias to a global variable in the
681package that was current where the variable was declared. This is
682mostly useful as an alternative to the C<vars> pragma, but also provides
683the opportunity to introduce typing and other attributes for such
684variables. See L<perlfunc/our>.
685
686=head2 Support for strings represented as a vector of ordinals
687
688Literals of the form C<v1.2.3.4> are now parsed as a string composed
689of characters with the specified ordinals. This is an alternative, more
690readable way to construct (possibly Unicode) strings instead of
691interpolating characters, as in C<"\x{1}\x{2}\x{3}\x{4}">. The leading
692C<v> may be omitted if there are more than two ordinals, so C<1.2.3> is
693parsed the same as C<v1.2.3>.
694
695Strings written in this form are also useful to represent version "numbers".
696It is easy to compare such version "numbers" (which are really just plain
697strings) using any of the usual string comparison operators C<eq>, C<ne>,
698C<lt>, C<gt>, etc., or perform bitwise string operations on them using C<|>,
699C<&>, etc.
700
701In conjunction with the new C<$^V> magic variable (which contains
702the perl version as a string), such literals can be used as a readable way
703to check if you're running a particular version of Perl:
704
705 # this will parse in older versions of Perl also
706 if ($^V and $^V gt v5.6.0) {
707 # new features supported
708 }
709
710C<require> and C<use> also have some special magic to support such literals.
711They will be interpreted as a version rather than as a module name:
712
713 require v5.6.0; # croak if $^V lt v5.6.0
714 use v5.6.0; # same, but croaks at compile-time
715
716Alternatively, the C<v> may be omitted if there is more than one dot:
717
718 require 5.6.0;
719 use 5.6.0;
720
721Also, C<sprintf> and C<printf> support the Perl-specific format flag C<%v>
722to print ordinals of characters in arbitrary strings:
723
724 printf "v%vd", $^V; # prints current version, such as "v5.5.650"
725 printf "%*vX", ":", $addr; # formats IPv6 address
726 printf "%*vb", " ", $bits; # displays bitstring
727
728See L<perldata/"Scalar value constructors"> for additional information.
729
730=head2 Improved Perl version numbering system
731
732Beginning with Perl version 5.6.0, the version number convention has been
733changed to a "dotted integer" scheme that is more commonly found in open
734source projects.
735
736Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc.
737The next development series following v5.6.0 will be numbered v5.7.x,
738beginning with v5.7.0, and the next major production release following
739v5.6.0 will be v5.8.0.
740
741The English module now sets $PERL_VERSION to $^V (a string value) rather
742than C<$]> (a numeric value). (This is a potential incompatibility.
743Send us a report via perlbug if you are affected by this.)
744
745The v1.2.3 syntax is also now legal in Perl.
746See L<Support for strings represented as a vector of ordinals> for more on that.
747
748To cope with the new versioning system's use of at least three significant
749digits for each version component, the method used for incrementing the
750subversion number has also changed slightly. We assume that versions older
751than v5.6.0 have been incrementing the subversion component in multiples of
75210. Versions after v5.6.0 will increment them by 1. Thus, using the new
753notation, 5.005_03 is the "same" as v5.5.30, and the first maintenance
754version following v5.6.0 will be v5.6.1 (which should be read as being
755equivalent to a floating point value of 5.006_001 in the older format,
756stored in C<$]>).
757
758=head2 New syntax for declaring subroutine attributes
759
760Formerly, if you wanted to mark a subroutine as being a method call or
761as requiring an automatic lock() when it is entered, you had to declare
762that with a C<use attrs> pragma in the body of the subroutine.
763That can now be accomplished with declaration syntax, like this:
764
765 sub mymethod : locked method ;
766 ...
767 sub mymethod : locked method {
768 ...
769 }
770
771 sub othermethod :locked :method ;
772 ...
773 sub othermethod :locked :method {
774 ...
775 }
776
777
778(Note how only the first C<:> is mandatory, and whitespace surrounding
779the C<:> is optional.)
780
781F<AutoSplit.pm> and F<SelfLoader.pm> have been updated to keep the attributes
782with the stubs they provide. See L<attributes>.
783
784=head2 File and directory handles can be autovivified
785
786Similar to how constructs such as C<< $x->[0] >> autovivify a reference,
787handle constructors (open(), opendir(), pipe(), socketpair(), sysopen(),
788socket(), and accept()) now autovivify a file or directory handle
789if the handle passed to them is an uninitialized scalar variable. This
790allows the constructs such as C<open(my $fh, ...)> and C<open(local $fh,...)>
791to be used to create filehandles that will conveniently be closed
792automatically when the scope ends, provided there are no other references
793to them. This largely eliminates the need for typeglobs when opening
794filehandles that must be passed around, as in the following example:
795
796 sub myopen {
797 open my $fh, "@_"
798 or die "Can't open '@_': $!";
799 return $fh;
800 }
801
802 {
803 my $f = myopen("</etc/motd");
804 print <$f>;
805 # $f implicitly closed here
806 }
807
808=head2 open() with more than two arguments
809
810If open() is passed three arguments instead of two, the second argument
811is used as the mode and the third argument is taken to be the file name.
812This is primarily useful for protecting against unintended magic behavior
813of the traditional two-argument form. See L<perlfunc/open>.
814
815=head2 64-bit support
816
817Any platform that has 64-bit integers either
818
819 (1) natively as longs or ints
820 (2) via special compiler flags
821 (3) using long long or int64_t
822
823is able to use "quads" (64-bit integers) as follows:
824
825=over 4
826
827=item *
828
829constants (decimal, hexadecimal, octal, binary) in the code
830
831=item *
832
833arguments to oct() and hex()
834
835=item *
836
837arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)
838
839=item *
840
841printed as such
842
843=item *
844
845pack() and unpack() "q" and "Q" formats
846
847=item *
848
849in basic arithmetics: + - * / % (NOTE: operating close to the limits
850of the integer values may produce surprising results)
851
852=item *
853
854in bit arithmetics: & | ^ ~ << >> (NOTE: these used to be forced
855to be 32 bits wide but now operate on the full native width.)
856
857=item *
858
859vec()
860
861=back
862
863Note that unless you have the case (a) you will have to configure
864and compile Perl using the -Duse64bitint Configure flag.
865
866 NOTE: The Configure flags -Duselonglong and -Duse64bits have been
867 deprecated. Use -Duse64bitint instead.
868
869There are actually two modes of 64-bitness: the first one is achieved
870using Configure -Duse64bitint and the second one using Configure
871-Duse64bitall. The difference is that the first one is minimal and
872the second one maximal. The first works in more places than the second.
873
874The C<use64bitint> does only as much as is required to get 64-bit
875integers into Perl (this may mean, for example, using "long longs")
876while your memory may still be limited to 2 gigabytes (because your
877pointers could still be 32-bit). Note that the name C<64bitint> does
878not imply that your C compiler will be using 64-bit C<int>s (it might,
879but it doesn't have to): the C<use64bitint> means that you will be
880able to have 64 bits wide scalar values.
881
882The C<use64bitall> goes all the way by attempting to switch also
883integers (if it can), longs (and pointers) to being 64-bit. This may
884create an even more binary incompatible Perl than -Duse64bitint: the
885resulting executable may not run at all in a 32-bit box, or you may
886have to reboot/reconfigure/rebuild your operating system to be 64-bit
887aware.
888
889Natively 64-bit systems like Alpha and Cray need neither -Duse64bitint
890nor -Duse64bitall.
891
892Last but not least: note that due to Perl's habit of always using
893floating point numbers, the quads are still not true integers.
894When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
895-9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
896are silently promoted to floating point numbers, after which they will
897start losing precision (in their lower digits).
898
899 NOTE: 64-bit support is still experimental on most platforms.
900 Existing support only covers the LP64 data model. In particular, the
901 LLP64 data model is not yet supported. 64-bit libraries and system
902 APIs on many platforms have not stabilized--your mileage may vary.
903
904=head2 Large file support
905
906If you have filesystems that support "large files" (files larger than
9072 gigabytes), you may now also be able to create and access them from
908Perl.
909
910 NOTE: The default action is to enable large file support, if
911 available on the platform.
912
913If the large file support is on, and you have a Fcntl constant
914O_LARGEFILE, the O_LARGEFILE is automatically added to the flags
915of sysopen().
916
917Beware that unless your filesystem also supports "sparse files" seeking
918to umpteen petabytes may be inadvisable.
919
920Note that in addition to requiring a proper file system to do large
921files you may also need to adjust your per-process (or your
922per-system, or per-process-group, or per-user-group) maximum filesize
923limits before running Perl scripts that try to handle large files,
924especially if you intend to write such files.
925
926Finally, in addition to your process/process group maximum filesize
927limits, you may have quota limits on your filesystems that stop you
928(your user id or your user group id) from using large files.
929
930Adjusting your process/user/group/file system/operating system limits
931is outside the scope of Perl core language. For process limits, you
932may try increasing the limits using your shell's limits/limit/ulimit
933command before running Perl. The BSD::Resource extension (not
934included with the standard Perl distribution) may also be of use, it
935offers the getrlimit/setrlimit interface that can be used to adjust
936process resource usage limits, including the maximum filesize limit.
937
938=head2 Long doubles
939
940In some systems you may be able to use long doubles to enhance the
941range and precision of your double precision floating point numbers
942(that is, Perl's numbers). Use Configure -Duselongdouble to enable
943this support (if it is available).
944
945=head2 "more bits"
946
947You can "Configure -Dusemorebits" to turn on both the 64-bit support
948and the long double support.
949
950=head2 Enhanced support for sort() subroutines
951
952Perl subroutines with a prototype of C<($$)>, and XSUBs in general, can
953now be used as sort subroutines. In either case, the two elements to
954be compared are passed as normal parameters in @_. See L<perlfunc/sort>.
955
956For unprototyped sort subroutines, the historical behavior of passing
957the elements to be compared as the global variables $a and $b remains
958unchanged.
959
960=head2 C<sort $coderef @foo> allowed
961
962sort() did not accept a subroutine reference as the comparison
963function in earlier versions. This is now permitted.
964
965=head2 File globbing implemented internally
966
967Perl now uses the File::Glob implementation of the glob() operator
968automatically. This avoids using an external csh process and the
969problems associated with it.
970
971 NOTE: This is currently an experimental feature. Interfaces and
972 implementation are subject to change.
973
974=head2 Support for CHECK blocks
975
976In addition to C<BEGIN>, C<INIT>, C<END>, C<DESTROY> and C<AUTOLOAD>,
977subroutines named C<CHECK> are now special. These are queued up during
978compilation and behave similar to END blocks, except they are called at
979the end of compilation rather than at the end of execution. They cannot
980be called directly.
981
982=head2 POSIX character class syntax [: :] supported
983
984For example to match alphabetic characters use /[[:alpha:]]/.
985See L<perlre> for details.
986
987=head2 Better pseudo-random number generator
988
989In 5.005_0x and earlier, perl's rand() function used the C library
990rand(3) function. As of 5.005_52, Configure tests for drand48(),
991random(), and rand() (in that order) and picks the first one it finds.
992
993These changes should result in better random numbers from rand().
994
995=head2 Improved C<qw//> operator
996
997The C<qw//> operator is now evaluated at compile time into a true list
998instead of being replaced with a run time call to C<split()>. This
999removes the confusing misbehaviour of C<qw//> in scalar context, which
1000had inherited that behaviour from split().
1001
1002Thus:
1003
1004 $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
1005
1006now correctly prints "3|a", instead of "2|a".
1007
1008=head2 Better worst-case behavior of hashes
1009
1010Small changes in the hashing algorithm have been implemented in
1011order to improve the distribution of lower order bits in the
1012hashed value. This is expected to yield better performance on
1013keys that are repeated sequences.
1014
1015=head2 pack() format 'Z' supported
1016
1017The new format type 'Z' is useful for packing and unpacking null-terminated
1018strings. See L<perlfunc/"pack">.
1019
1020=head2 pack() format modifier '!' supported
1021
1022The new format type modifier '!' is useful for packing and unpacking
1023native shorts, ints, and longs. See L<perlfunc/"pack">.
1024
1025=head2 pack() and unpack() support counted strings
1026
1027The template character '/' can be used to specify a counted string
1028type to be packed or unpacked. See L<perlfunc/"pack">.
1029
1030=head2 Comments in pack() templates
1031
1032The '#' character in a template introduces a comment up to
1033end of the line. This facilitates documentation of pack()
1034templates.
1035
1036=head2 Weak references
1037
1038In previous versions of Perl, you couldn't cache objects so as
1039to allow them to be deleted if the last reference from outside
1040the cache is deleted. The reference in the cache would hold a
1041reference count on the object and the objects would never be
1042destroyed.
1043
1044Another familiar problem is with circular references. When an
1045object references itself, its reference count would never go
1046down to zero, and it would not get destroyed until the program
1047is about to exit.
1048
1049Weak references solve this by allowing you to "weaken" any
1050reference, that is, make it not count towards the reference count.
1051When the last non-weak reference to an object is deleted, the object
1052is destroyed and all the weak references to the object are
1053automatically undef-ed.
1054
1055To use this feature, you need the WeakRef package from CPAN, which
1056contains additional documentation.
1057
1058 NOTE: This is an experimental feature. Details are subject to change.
1059
1060=head2 Binary numbers supported
1061
1062Binary numbers are now supported as literals, in s?printf formats, and
1063C<oct()>:
1064
1065 $answer = 0b101010;
1066 printf "The answer is: %b\n", oct("0b101010");
1067
1068=head2 Lvalue subroutines
1069
1070Subroutines can now return modifiable lvalues.
1071See L<perlsub/"Lvalue subroutines">.
1072
1073 NOTE: This is an experimental feature. Details are subject to change.
1074
1075=head2 Some arrows may be omitted in calls through references
1076
1077Perl now allows the arrow to be omitted in many constructs
1078involving subroutine calls through references. For example,
1079C<< $foo[10]->('foo') >> may now be written C<$foo[10]('foo')>.
1080This is rather similar to how the arrow may be omitted from
1081C<< $foo[10]->{'foo'} >>. Note however, that the arrow is still
1082required for C<< foo(10)->('bar') >>.
1083
1084=head2 Boolean assignment operators are legal lvalues
1085
1086Constructs such as C<($a ||= 2) += 1> are now allowed.
1087
1088=head2 exists() is supported on subroutine names
1089
1090The exists() builtin now works on subroutine names. A subroutine
1091is considered to exist if it has been declared (even if implicitly).
1092See L<perlfunc/exists> for examples.
1093
1094=head2 exists() and delete() are supported on array elements
1095
1096The exists() and delete() builtins now work on simple arrays as well.
1097The behavior is similar to that on hash elements.
1098
1099exists() can be used to check whether an array element has been
1100initialized. This avoids autovivifying array elements that don't exist.
1101If the array is tied, the EXISTS() method in the corresponding tied
1102package will be invoked.
1103
1104delete() may be used to remove an element from the array and return
1105it. The array element at that position returns to its uninitialized
1106state, so that testing for the same element with exists() will return
1107false. If the element happens to be the one at the end, the size of
1108the array also shrinks up to the highest element that tests true for
1109exists(), or 0 if none such is found. If the array is tied, the DELETE()
1110method in the corresponding tied package will be invoked.
1111
1112See L<perlfunc/exists> and L<perlfunc/delete> for examples.
1113
1114=head2 Pseudo-hashes work better
1115
1116Dereferencing some types of reference values in a pseudo-hash,
1117such as C<< $ph->{foo}[1] >>, was accidentally disallowed. This has
1118been corrected.
1119
1120When applied to a pseudo-hash element, exists() now reports whether
1121the specified value exists, not merely if the key is valid.
1122
1123delete() now works on pseudo-hashes. When given a pseudo-hash element
1124or slice it deletes the values corresponding to the keys (but not the keys
1125themselves). See L<perlref/"Pseudo-hashes: Using an array as a hash">.
1126
1127Pseudo-hash slices with constant keys are now optimized to array lookups
1128at compile-time.
1129
1130List assignments to pseudo-hash slices are now supported.
1131
1132The C<fields> pragma now provides ways to create pseudo-hashes, via
1133fields::new() and fields::phash(). See L<fields>.
1134
1135 NOTE: The pseudo-hash data type continues to be experimental.
1136 Limiting oneself to the interface elements provided by the
1137 fields pragma will provide protection from any future changes.
1138
1139=head2 Automatic flushing of output buffers
1140
1141fork(), exec(), system(), qx//, and pipe open()s now flush buffers
1142of all files opened for output when the operation was attempted. This
1143mostly eliminates confusing buffering mishaps suffered by users unaware
1144of how Perl internally handles I/O.
1145
1146This is not supported on some platforms like Solaris where a suitably
1147correct implementation of fflush(NULL) isn't available.
1148
1149=head2 Better diagnostics on meaningless filehandle operations
1150
1151Constructs such as C<< open(<FH>) >> and C<< close(<FH>) >>
1152are compile time errors. Attempting to read from filehandles that
1153were opened only for writing will now produce warnings (just as
1154writing to read-only filehandles does).
1155
1156=head2 Where possible, buffered data discarded from duped input filehandle
1157
1158C<< open(NEW, "<&OLD") >> now attempts to discard any data that
1159was previously read and buffered in C<OLD> before duping the handle.
1160On platforms where doing this is allowed, the next read operation
1161on C<NEW> will return the same data as the corresponding operation
1162on C<OLD>. Formerly, it would have returned the data from the start
1163of the following disk block instead.
1164
1165=head2 eof() has the same old magic as <>
1166
1167C<eof()> would return true if no attempt to read from C<< <> >> had
1168yet been made. C<eof()> has been changed to have a little magic of its
1169own, it now opens the C<< <> >> files.
1170
1171=head2 binmode() can be used to set :crlf and :raw modes
1172
1173binmode() now accepts a second argument that specifies a discipline
1174for the handle in question. The two pseudo-disciplines ":raw" and
1175":crlf" are currently supported on DOS-derivative platforms.
1176See L<perlfunc/"binmode"> and L<open>.
1177
1178=head2 C<-T> filetest recognizes UTF-8 encoded files as "text"
1179
1180The algorithm used for the C<-T> filetest has been enhanced to
1181correctly identify UTF-8 content as "text".
1182
1183=head2 system(), backticks and pipe open now reflect exec() failure
1184
1185On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
1186etc., are implemented via fork() and exec(). When the underlying
1187exec() fails, earlier versions did not report the error properly,
1188since the exec() happened to be in a different process.
1189
1190The child process now communicates with the parent about the
1191error in launching the external command, which allows these
1192constructs to return with their usual error value and set $!.
1193
1194=head2 Improved diagnostics
1195
1196Line numbers are no longer suppressed (under most likely circumstances)
1197during the global destruction phase.
1198
1199Diagnostics emitted from code running in threads other than the main
1200thread are now accompanied by the thread ID.
1201
1202Embedded null characters in diagnostics now actually show up. They
1203used to truncate the message in prior versions.
1204
1205$foo::a and $foo::b are now exempt from "possible typo" warnings only
1206if sort() is encountered in package C<foo>.
1207
1208Unrecognized alphabetic escapes encountered when parsing quote
1209constructs now generate a warning, since they may take on new
1210semantics in later versions of Perl.
1211
1212Many diagnostics now report the internal operation in which the warning
1213was provoked, like so:
1214
1215 Use of uninitialized value in concatenation (.) at (eval 1) line 1.
1216 Use of uninitialized value in print at (eval 1) line 1.
1217
1218Diagnostics that occur within eval may also report the file and line
1219number where the eval is located, in addition to the eval sequence
1220number and the line number within the evaluated text itself. For
1221example:
1222
1223 Not enough arguments for scalar at (eval 4)[newlib/perl5db.pl:1411] line 2, at EOF
1224
1225=head2 Diagnostics follow STDERR
1226
1227Diagnostic output now goes to whichever file the C<STDERR> handle
1228is pointing at, instead of always going to the underlying C runtime
1229library's C<stderr>.
1230
1231=head2 More consistent close-on-exec behavior
1232
1233On systems that support a close-on-exec flag on filehandles, the
1234flag is now set for any handles created by pipe(), socketpair(),
1235socket(), and accept(), if that is warranted by the value of $^F
1236that may be in effect. Earlier versions neglected to set the flag
1237for handles created with these operators. See L<perlfunc/pipe>,
1238L<perlfunc/socketpair>, L<perlfunc/socket>, L<perlfunc/accept>,
1239and L<perlvar/$^F>.
1240
1241=head2 syswrite() ease-of-use
1242
1243The length argument of C<syswrite()> has become optional.
1244
1245=head2 Better syntax checks on parenthesized unary operators
1246
1247Expressions such as:
1248
1249 print defined(&foo,&bar,&baz);
1250 print uc("foo","bar","baz");
1251 undef($foo,&bar);
1252
1253used to be accidentally allowed in earlier versions, and produced
1254unpredictable behaviour. Some produced ancillary warnings
1255when used in this way; others silently did the wrong thing.
1256
1257The parenthesized forms of most unary operators that expect a single
1258argument now ensure that they are not called with more than one
1259argument, making the cases shown above syntax errors. The usual
1260behaviour of:
1261
1262 print defined &foo, &bar, &baz;
1263 print uc "foo", "bar", "baz";
1264 undef $foo, &bar;
1265
1266remains unchanged. See L<perlop>.
1267
1268=head2 Bit operators support full native integer width
1269
1270The bit operators (& | ^ ~ << >>) now operate on the full native
1271integral width (the exact size of which is available in $Config{ivsize}).
1272For example, if your platform is either natively 64-bit or if Perl
1273has been configured to use 64-bit integers, these operations apply
1274to 8 bytes (as opposed to 4 bytes on 32-bit platforms).
1275For portability, be sure to mask off the excess bits in the result of
1276unary C<~>, e.g., C<~$x & 0xffffffff>.
1277
1278=head2 Improved security features
1279
1280More potentially unsafe operations taint their results for improved
1281security.
1282
1283The C<passwd> and C<shell> fields returned by the getpwent(), getpwnam(),
1284and getpwuid() are now tainted, because the user can affect their own
1285encrypted password and login shell.
1286
1287The variable modified by shmread(), and messages returned by msgrcv()
1288(and its object-oriented interface IPC::SysV::Msg::rcv) are also tainted,
1289because other untrusted processes can modify messages and shared memory
1290segments for their own nefarious purposes.
1291
1292=head2 More functional bareword prototype (*)
1293
1294Bareword prototypes have been rationalized to enable them to be used
1295to override builtins that accept barewords and interpret them in
1296a special way, such as C<require> or C<do>.
1297
1298Arguments prototyped as C<*> will now be visible within the subroutine
1299as either a simple scalar or as a reference to a typeglob.
1300See L<perlsub/Prototypes>.
1301
1302=head2 C<require> and C<do> may be overridden
1303
1304C<require> and C<do 'file'> operations may be overridden locally
1305by importing subroutines of the same name into the current package
1306(or globally by importing them into the CORE::GLOBAL:: namespace).
1307Overriding C<require> will also affect C<use>, provided the override
1308is visible at compile-time.
1309See L<perlsub/"Overriding Built-in Functions">.
1310
1311=head2 $^X variables may now have names longer than one character
1312
1313Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
1314error. Now variable names that begin with a control character may be
1315arbitrarily long. However, for compatibility reasons, these variables
1316I<must> be written with explicit braces, as C<${^XY}> for example.
1317C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more
1318than one control character, such as C<${^XY^Z}>, are illegal.
1319
1320The old syntax has not changed. As before, `^X' may be either a
1321literal control-X character or the two-character sequence `caret' plus
1322`X'. When braces are omitted, the variable name stops after the
1323control character. Thus C<"$^XYZ"> continues to be synonymous with
1324C<$^X . "YZ"> as before.
1325
1326As before, lexical variables may not have names beginning with control
1327characters. As before, variables whose names begin with a control
1328character are always forced to be in package `main'. All such variables
1329are reserved for future extensions, except those that begin with
1330C<^_>, which may be used by user programs and are guaranteed not to
1331acquire special meaning in any future version of Perl.
1332
1333=head2 New variable $^C reflects C<-c> switch
1334
1335C<$^C> has a boolean value that reflects whether perl is being run
1336in compile-only mode (i.e. via the C<-c> switch). Since
1337BEGIN blocks are executed under such conditions, this variable
1338enables perl code to determine whether actions that make sense
1339only during normal running are warranted. See L<perlvar>.
1340
1341=head2 New variable $^V contains Perl version as a string
1342
1343C<$^V> contains the Perl version number as a string composed of
1344characters whose ordinals match the version numbers, i.e. v5.6.0.
1345This may be used in string comparisons.
1346
1347See C<Support for strings represented as a vector of ordinals> for an
1348example.
1349
1350=head2 Optional Y2K warnings
1351
1352If Perl is built with the cpp macro C<PERL_Y2KWARN> defined,
1353it emits optional warnings when concatenating the number 19
1354with another number.
1355
1356This behavior must be specifically enabled when running Configure.
1357See F<INSTALL> and F<README.Y2K>.
1358
1359=head2 Arrays now always interpolate into double-quoted strings
1360
1361In double-quoted strings, arrays now interpolate, no matter what. The
1362behavior in earlier versions of perl 5 was that arrays would interpolate
1363into strings if the array had been mentioned before the string was
1364compiled, and otherwise Perl would raise a fatal compile-time error.
1365In versions 5.000 through 5.003, the error was
1366
1367 Literal @example now requires backslash
1368
1369In versions 5.004_01 through 5.6.0, the error was
1370
1371 In string, @example now must be written as \@example
1372
1373The idea here was to get people into the habit of writing
1374C<"fred\@example.com"> when they wanted a literal C<@> sign, just as
1375they have always written C<"Give me back my \$5"> when they wanted a
1376literal C<$> sign.
1377
1378Starting with 5.6.1, when Perl now sees an C<@> sign in a
1379double-quoted string, it I<always> attempts to interpolate an array,
1380regardless of whether or not the array has been used or declared
1381already. The fatal error has been downgraded to an optional warning:
1382
1383 Possible unintended interpolation of @example in string
1384
1385This warns you that C<"fred@example.com"> is going to turn into
1386C<fred.com> if you don't backslash the C<@>.
1387See http://www.plover.com/~mjd/perl/at-error.html for more details
1388about the history here.
1389
1390=head1 Modules and Pragmata
1391
1392=head2 Modules
1393
1394=over 4
1395
1396=item attributes
1397
1398While used internally by Perl as a pragma, this module also
1399provides a way to fetch subroutine and variable attributes.
1400See L<attributes>.
1401
1402=item B
1403
1404The Perl Compiler suite has been extensively reworked for this
1405release. More of the standard Perl testsuite passes when run
1406under the Compiler, but there is still a significant way to
1407go to achieve production quality compiled executables.
1408
1409 NOTE: The Compiler suite remains highly experimental. The
1410 generated code may not be correct, even when it manages to execute
1411 without errors.
1412
1413=item Benchmark
1414
1415Overall, Benchmark results exhibit lower average error and better timing
1416accuracy.
1417
1418You can now run tests for I<n> seconds instead of guessing the right
1419number of tests to run: e.g., timethese(-5, ...) will run each
1420code for at least 5 CPU seconds. Zero as the "number of repetitions"
1421means "for at least 3 CPU seconds". The output format has also
1422changed. For example:
1423
1424 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
1425
1426will now output something like this:
1427
1428 Benchmark: running a, b, each for at least 5 CPU seconds...
1429 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
1430 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
1431
1432New features: "each for at least N CPU seconds...", "wallclock secs",
1433and the "@ operations/CPU second (n=operations)".
1434
1435timethese() now returns a reference to a hash of Benchmark objects containing
1436the test results, keyed on the names of the tests.
1437
1438timethis() now returns the iterations field in the Benchmark result object
1439instead of 0.
1440
1441timethese(), timethis(), and the new cmpthese() (see below) can also take
1442a format specifier of 'none' to suppress output.
1443
1444A new function countit() is just like timeit() except that it takes a
1445TIME instead of a COUNT.
1446
1447A new function cmpthese() prints a chart comparing the results of each test
1448returned from a timethese() call. For each possible pair of tests, the
1449percentage speed difference (iters/sec or seconds/iter) is shown.
1450
1451For other details, see L<Benchmark>.
1452
1453=item ByteLoader
1454
1455The ByteLoader is a dedicated extension to generate and run
1456Perl bytecode. See L<ByteLoader>.
1457
1458=item constant
1459
1460References can now be used.
1461
1462The new version also allows a leading underscore in constant names, but
1463disallows a double leading underscore (as in "__LINE__"). Some other names
1464are disallowed or warned against, including BEGIN, END, etc. Some names
1465which were forced into main:: used to fail silently in some cases; now they're
1466fatal (outside of main::) and an optional warning (inside of main::).
1467The ability to detect whether a constant had been set with a given name has
1468been added.
1469
1470See L<constant>.
1471
1472=item charnames
1473
1474This pragma implements the C<\N> string escape. See L<charnames>.
1475
1476=item Data::Dumper
1477
1478A C<Maxdepth> setting can be specified to avoid venturing
1479too deeply into deep data structures. See L<Data::Dumper>.
1480
1481The XSUB implementation of Dump() is now automatically called if the
1482C<Useqq> setting is not in use.
1483
1484Dumping C<qr//> objects works correctly.
1485
1486=item DB
1487
1488C<DB> is an experimental module that exposes a clean abstraction
1489to Perl's debugging API.
1490
1491=item DB_File
1492
1493DB_File can now be built with Berkeley DB versions 1, 2 or 3.
1494See C<ext/DB_File/Changes>.
1495
1496=item Devel::DProf
1497
1498Devel::DProf, a Perl source code profiler has been added. See
1499L<Devel::DProf> and L<dprofpp>.
1500
1501=item Devel::Peek
1502
1503The Devel::Peek module provides access to the internal representation
1504of Perl variables and data. It is a data debugging tool for the XS programmer.
1505
1506=item Dumpvalue
1507
1508The Dumpvalue module provides screen dumps of Perl data.
1509
1510=item DynaLoader
1511
1512DynaLoader now supports a dl_unload_file() function on platforms that
1513support unloading shared objects using dlclose().
1514
1515Perl can also optionally arrange to unload all extension shared objects
1516loaded by Perl. To enable this, build Perl with the Configure option
1517C<-Accflags=-DDL_UNLOAD_ALL_AT_EXIT>. (This maybe useful if you are
1518using Apache with mod_perl.)
1519
1520=item English
1521
1522$PERL_VERSION now stands for C<$^V> (a string value) rather than for C<$]>
1523(a numeric value).
1524
1525=item Env
1526
1527Env now supports accessing environment variables like PATH as array
1528variables.
1529
1530=item Fcntl
1531
1532More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
1533large file (more than 4GB) access (NOTE: the O_LARGEFILE is
1534automatically added to sysopen() flags if large file support has been
1535configured, as is the default), Free/Net/OpenBSD locking behaviour
1536flags F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the combined
1537mask of O_RDONLY, O_WRONLY, and O_RDWR. The seek()/sysseek()
1538constants SEEK_SET, SEEK_CUR, and SEEK_END are available via the
1539C<:seek> tag. The chmod()/stat() S_IF* constants and S_IS* functions
1540are available via the C<:mode> tag.
1541
1542=item File::Compare
1543
1544A compare_text() function has been added, which allows custom
1545comparison functions. See L<File::Compare>.
1546
1547=item File::Find
1548
1549File::Find now works correctly when the wanted() function is either
1550autoloaded or is a symbolic reference.
1551
1552A bug that caused File::Find to lose track of the working directory
1553when pruning top-level directories has been fixed.
1554
1555File::Find now also supports several other options to control its
1556behavior. It can follow symbolic links if the C<follow> option is
1557specified. Enabling the C<no_chdir> option will make File::Find skip
1558changing the current directory when walking directories. The C<untaint>
1559flag can be useful when running with taint checks enabled.
1560
1561See L<File::Find>.
1562
1563=item File::Glob
1564
1565This extension implements BSD-style file globbing. By default,
1566it will also be used for the internal implementation of the glob()
1567operator. See L<File::Glob>.
1568
1569=item File::Spec
1570
1571New methods have been added to the File::Spec module: devnull() returns
1572the name of the null device (/dev/null on Unix) and tmpdir() the name of
1573the temp directory (normally /tmp on Unix). There are now also methods
1574to convert between absolute and relative filenames: abs2rel() and
1575rel2abs(). For compatibility with operating systems that specify volume
1576names in file paths, the splitpath(), splitdir(), and catdir() methods
1577have been added.
1578
1579=item File::Spec::Functions
1580
1581The new File::Spec::Functions modules provides a function interface
1582to the File::Spec module. Allows shorthand
1583
1584 $fullname = catfile($dir1, $dir2, $file);
1585
1586instead of
1587
1588 $fullname = File::Spec->catfile($dir1, $dir2, $file);
1589
1590=item Getopt::Long
1591
1592Getopt::Long licensing has changed to allow the Perl Artistic License
1593as well as the GPL. It used to be GPL only, which got in the way of
1594non-GPL applications that wanted to use Getopt::Long.
1595
1596Getopt::Long encourages the use of Pod::Usage to produce help
1597messages. For example:
1598
1599 use Getopt::Long;
1600 use Pod::Usage;
1601 my $man = 0;
1602 my $help = 0;
1603 GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
1604 pod2usage(1) if $help;
1605 pod2usage(-exitstatus => 0, -verbose => 2) if $man;
1606
1607 __END__
1608
1609 =head1 NAME
1610
1611 sample - Using GetOpt::Long and Pod::Usage
1612
1613 =head1 SYNOPSIS
1614
1615 sample [options] [file ...]
1616
1617 Options:
1618 -help brief help message
1619 -man full documentation
1620
1621 =head1 OPTIONS
1622
1623 =over 8
1624
1625 =item B<-help>
1626
1627 Print a brief help message and exits.
1628
1629 =item B<-man>
1630
1631 Prints the manual page and exits.
1632
1633 =back
1634
1635 =head1 DESCRIPTION
1636
1637 B<This program> will read the given input file(s) and do something
1638 useful with the contents thereof.
1639
1640 =cut
1641
1642See L<Pod::Usage> for details.
1643
1644A bug that prevented the non-option call-back <> from being
1645specified as the first argument has been fixed.
1646
1647To specify the characters < and > as option starters, use ><. Note,
1648however, that changing option starters is strongly deprecated.
1649
1650=item IO
1651
1652write() and syswrite() will now accept a single-argument
1653form of the call, for consistency with Perl's syswrite().
1654
1655You can now create a TCP-based IO::Socket::INET without forcing
1656a connect attempt. This allows you to configure its options
1657(like making it non-blocking) and then call connect() manually.
1658
1659A bug that prevented the IO::Socket::protocol() accessor
1660from ever returning the correct value has been corrected.
1661
1662IO::Socket::connect now uses non-blocking IO instead of alarm()
1663to do connect timeouts.
1664
1665IO::Socket::accept now uses select() instead of alarm() for doing
1666timeouts.
1667
1668IO::Socket::INET->new now sets $! correctly on failure. $@ is
1669still set for backwards compatibility.
1670
1671=item JPL
1672
1673Java Perl Lingo is now distributed with Perl. See jpl/README
1674for more information.
1675
1676=item lib
1677
1678C<use lib> now weeds out any trailing duplicate entries.
1679C<no lib> removes all named entries.
1680
1681=item Math::BigInt
1682
1683The bitwise operations C<<< << >>>, C<<< >> >>>, C<&>, C<|>,
1684and C<~> are now supported on bigints.
1685
1686=item Math::Complex
1687
1688The accessor methods Re, Im, arg, abs, rho, and theta can now also
1689act as mutators (accessor $z->Re(), mutator $z->Re(3)).
1690
1691The class method C<display_format> and the corresponding object method
1692C<display_format>, in addition to accepting just one argument, now can
1693also accept a parameter hash. Recognized keys of a parameter hash are
1694C<"style">, which corresponds to the old one parameter case, and two
1695new parameters: C<"format">, which is a printf()-style format string
1696(defaults usually to C<"%.15g">, you can revert to the default by
1697setting the format string to C<undef>) used for both parts of a
1698complex number, and C<"polar_pretty_print"> (defaults to true),
1699which controls whether an attempt is made to try to recognize small
1700multiples and rationals of pi (2pi, pi/2) at the argument (angle) of a
1701polar complex number.
1702
1703The potentially disruptive change is that in list context both methods
1704now I<return the parameter hash>, instead of only the value of the
1705C<"style"> parameter.
1706
1707=item Math::Trig
1708
1709A little bit of radial trigonometry (cylindrical and spherical),
1710radial coordinate conversions, and the great circle distance were added.
1711
1712=item Pod::Parser, Pod::InputObjects
1713
1714Pod::Parser is a base class for parsing and selecting sections of
1715pod documentation from an input stream. This module takes care of
1716identifying pod paragraphs and commands in the input and hands off the
1717parsed paragraphs and commands to user-defined methods which are free
1718to interpret or translate them as they see fit.
1719
1720Pod::InputObjects defines some input objects needed by Pod::Parser, and
1721for advanced users of Pod::Parser that need more about a command besides
1722its name and text.
1723
1724As of release 5.6.0 of Perl, Pod::Parser is now the officially sanctioned
1725"base parser code" recommended for use by all pod2xxx translators.
1726Pod::Text (pod2text) and Pod::Man (pod2man) have already been converted
1727to use Pod::Parser and efforts to convert Pod::HTML (pod2html) are already
1728underway. For any questions or comments about pod parsing and translating
1729issues and utilities, please use the pod-people@perl.org mailing list.
1730
1731For further information, please see L<Pod::Parser> and L<Pod::InputObjects>.
1732
1733=item Pod::Checker, podchecker
1734
1735This utility checks pod files for correct syntax, according to
1736L<perlpod>. Obvious errors are flagged as such, while warnings are
1737printed for mistakes that can be handled gracefully. The checklist is
1738not complete yet. See L<Pod::Checker>.
1739
1740=item Pod::ParseUtils, Pod::Find
1741
1742These modules provide a set of gizmos that are useful mainly for pod
1743translators. L<Pod::Find|Pod::Find> traverses directory structures and
1744returns found pod files, along with their canonical names (like
1745C<File::Spec::Unix>). L<Pod::ParseUtils|Pod::ParseUtils> contains
1746B<Pod::List> (useful for storing pod list information), B<Pod::Hyperlink>
1747(for parsing the contents of C<LE<lt>E<gt>> sequences) and B<Pod::Cache>
1748(for caching information about pod files, e.g., link nodes).
1749
1750=item Pod::Select, podselect
1751
1752Pod::Select is a subclass of Pod::Parser which provides a function
1753named "podselect()" to filter out user-specified sections of raw pod
1754documentation from an input stream. podselect is a script that provides
1755access to Pod::Select from other scripts to be used as a filter.
1756See L<Pod::Select>.
1757
1758=item Pod::Usage, pod2usage
1759
1760Pod::Usage provides the function "pod2usage()" to print usage messages for
1761a Perl script based on its embedded pod documentation. The pod2usage()
1762function is generally useful to all script authors since it lets them
1763write and maintain a single source (the pods) for documentation, thus
1764removing the need to create and maintain redundant usage message text
1765consisting of information already in the pods.
1766
1767There is also a pod2usage script which can be used from other kinds of
1768scripts to print usage messages from pods (even for non-Perl scripts
1769with pods embedded in comments).
1770
1771For details and examples, please see L<Pod::Usage>.
1772
1773=item Pod::Text and Pod::Man
1774
1775Pod::Text has been rewritten to use Pod::Parser. While pod2text() is
1776still available for backwards compatibility, the module now has a new
1777preferred interface. See L<Pod::Text> for the details. The new Pod::Text
1778module is easily subclassed for tweaks to the output, and two such
1779subclasses (Pod::Text::Termcap for man-page-style bold and underlining
1780using termcap information, and Pod::Text::Color for markup with ANSI color
1781sequences) are now standard.
1782
1783pod2man has been turned into a module, Pod::Man, which also uses
1784Pod::Parser. In the process, several outstanding bugs related to quotes
1785in section headers, quoting of code escapes, and nested lists have been
1786fixed. pod2man is now a wrapper script around this module.
1787
1788=item SDBM_File
1789
1790An EXISTS method has been added to this module (and sdbm_exists() has
1791been added to the underlying sdbm library), so one can now call exists
1792on an SDBM_File tied hash and get the correct result, rather than a
1793runtime error.
1794
1795A bug that may have caused data loss when more than one disk block
1796happens to be read from the database in a single FETCH() has been
1797fixed.
1798
1799=item Sys::Syslog
1800
1801Sys::Syslog now uses XSUBs to access facilities from syslog.h so it
1802no longer requires syslog.ph to exist.
1803
1804=item Sys::Hostname
1805
1806Sys::Hostname now uses XSUBs to call the C library's gethostname() or
1807uname() if they exist.
1808
1809=item Term::ANSIColor
1810
1811Term::ANSIColor is a very simple module to provide easy and readable
1812access to the ANSI color and highlighting escape sequences, supported by
1813most ANSI terminal emulators. It is now included standard.
1814
1815=item Time::Local
1816
1817The timelocal() and timegm() functions used to silently return bogus
1818results when the date fell outside the machine's integer range. They
1819now consistently croak() if the date falls in an unsupported range.
1820
1821=item Win32
1822
1823The error return value in list context has been changed for all functions
1824that return a list of values. Previously these functions returned a list
1825with a single element C<undef> if an error occurred. Now these functions
1826return the empty list in these situations. This applies to the following
1827functions:
1828
1829 Win32::FsType
1830 Win32::GetOSVersion
1831
1832The remaining functions are unchanged and continue to return C<undef> on
1833error even in list context.
1834
1835The Win32::SetLastError(ERROR) function has been added as a complement
1836to the Win32::GetLastError() function.
1837
1838The new Win32::GetFullPathName(FILENAME) returns the full absolute
1839pathname for FILENAME in scalar context. In list context it returns
1840a two-element list containing the fully qualified directory name and
1841the filename. See L<Win32>.
1842
1843=item XSLoader
1844
1845The XSLoader extension is a simpler alternative to DynaLoader.
1846See L<XSLoader>.
1847
1848=item DBM Filters
1849
1850A new feature called "DBM Filters" has been added to all the
1851DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
1852DBM Filters add four new methods to each DBM module:
1853
1854 filter_store_key
1855 filter_store_value
1856 filter_fetch_key
1857 filter_fetch_value
1858
1859These can be used to filter key-value pairs before the pairs are
1860written to the database or just after they are read from the database.
1861See L<perldbmfilter> for further information.
1862
1863=back
1864
1865=head2 Pragmata
1866
1867C<use attrs> is now obsolete, and is only provided for
1868backward-compatibility. It's been replaced by the C<sub : attributes>
1869syntax. See L<perlsub/"Subroutine Attributes"> and L<attributes>.
1870
1871Lexical warnings pragma, C<use warnings;>, to control optional warnings.
1872See L<perllexwarn>.
1873
1874C<use filetest> to control the behaviour of filetests (C<-r> C<-w>
1875...). Currently only one subpragma implemented, "use filetest
1876'access';", that uses access(2) or equivalent to check permissions
1877instead of using stat(2) as usual. This matters in filesystems
1878where there are ACLs (access control lists): the stat(2) might lie,
1879but access(2) knows better.
1880
1881The C<open> pragma can be used to specify default disciplines for
1882handle constructors (e.g. open()) and for qx//. The two
1883pseudo-disciplines C<:raw> and C<:crlf> are currently supported on
1884DOS-derivative platforms (i.e. where binmode is not a no-op).
1885See also L</"binmode() can be used to set :crlf and :raw modes">.
1886
1887=head1 Utility Changes
1888
1889=head2 dprofpp
1890
1891C<dprofpp> is used to display profile data generated using C<Devel::DProf>.
1892See L<dprofpp>.
1893
1894=head2 find2perl
1895
1896The C<find2perl> utility now uses the enhanced features of the File::Find
1897module. The -depth and -follow options are supported. Pod documentation
1898is also included in the script.
1899
1900=head2 h2xs
1901
1902The C<h2xs> tool can now work in conjunction with C<C::Scan> (available
1903from CPAN) to automatically parse real-life header files. The C<-M>,
1904C<-a>, C<-k>, and C<-o> options are new.
1905
1906=head2 perlcc
1907
1908C<perlcc> now supports the C and Bytecode backends. By default,
1909it generates output from the simple C backend rather than the
1910optimized C backend.
1911
1912Support for non-Unix platforms has been improved.
1913
1914=head2 perldoc
1915
1916C<perldoc> has been reworked to avoid possible security holes.
1917It will not by default let itself be run as the superuser, but you
1918may still use the B<-U> switch to try to make it drop privileges
1919first.
1920
1921=head2 The Perl Debugger
1922
1923Many bug fixes and enhancements were added to F<perl5db.pl>, the
1924Perl debugger. The help documentation was rearranged. New commands
1925include C<< < ? >>, C<< > ? >>, and C<< { ? >> to list out current
1926actions, C<man I<docpage>> to run your doc viewer on some perl
1927docset, and support for quoted options. The help information was
1928rearranged, and should be viewable once again if you're using B<less>
1929as your pager. A serious security hole was plugged--you should
1930immediately remove all older versions of the Perl debugger as
1931installed in previous releases, all the way back to perl3, from
1932your system to avoid being bitten by this.
1933
1934=head1 Improved Documentation
1935
1936Many of the platform-specific README files are now part of the perl
1937installation. See L<perl> for the complete list.
1938
1939=over 4
1940
1941=item perlapi.pod
1942
1943The official list of public Perl API functions.
1944
1945=item perlboot.pod
1946
1947A tutorial for beginners on object-oriented Perl.
1948
1949=item perlcompile.pod
1950
1951An introduction to using the Perl Compiler suite.
1952
1953=item perldbmfilter.pod
1954
1955A howto document on using the DBM filter facility.
1956
1957=item perldebug.pod
1958
1959All material unrelated to running the Perl debugger, plus all
1960low-level guts-like details that risked crushing the casual user
1961of the debugger, have been relocated from the old manpage to the
1962next entry below.
1963
1964=item perldebguts.pod
1965
1966This new manpage contains excessively low-level material not related
1967to the Perl debugger, but slightly related to debugging Perl itself.
1968It also contains some arcane internal details of how the debugging
1969process works that may only be of interest to developers of Perl
1970debuggers.
1971
1972=item perlfork.pod
1973
1974Notes on the fork() emulation currently available for the Windows platform.
1975
1976=item perlfilter.pod
1977
1978An introduction to writing Perl source filters.
1979
1980=item perlhack.pod
1981
1982Some guidelines for hacking the Perl source code.
1983
1984=item perlintern.pod
1985
1986A list of internal functions in the Perl source code.
1987(List is currently empty.)
1988
1989=item perllexwarn.pod
1990
1991Introduction and reference information about lexically scoped
1992warning categories.
1993
1994=item perlnumber.pod
1995
1996Detailed information about numbers as they are represented in Perl.
1997
1998=item perlopentut.pod
1999
2000A tutorial on using open() effectively.
2001
2002=item perlreftut.pod
2003
2004A tutorial that introduces the essentials of references.
2005
2006=item perltootc.pod
2007
2008A tutorial on managing class data for object modules.
2009
2010=item perltodo.pod
2011
2012Discussion of the most often wanted features that may someday be
2013supported in Perl.
2014
2015=item perlunicode.pod
2016
2017An introduction to Unicode support features in Perl.
2018
2019=back
2020
2021=head1 Performance enhancements
2022
2023=head2 Simple sort() using { $a <=> $b } and the like are optimized
2024
2025Many common sort() operations using a simple inlined block are now
2026optimized for faster performance.
2027
2028=head2 Optimized assignments to lexical variables
2029
2030Certain operations in the RHS of assignment statements have been
2031optimized to directly set the lexical variable on the LHS,
2032eliminating redundant copying overheads.
2033
2034=head2 Faster subroutine calls
2035
2036Minor changes in how subroutine calls are handled internally
2037provide marginal improvements in performance.
2038
2039=head2 delete(), each(), values() and hash iteration are faster
2040
2041The hash values returned by delete(), each(), values() and hashes in a
2042list context are the actual values in the hash, instead of copies.
2043This results in significantly better performance, because it eliminates
2044needless copying in most situations.
2045
2046=head1 Installation and Configuration Improvements
2047
2048=head2 -Dusethreads means something different
2049
2050The -Dusethreads flag now enables the experimental interpreter-based thread
2051support by default. To get the flavor of experimental threads that was in
20525.005 instead, you need to run Configure with "-Dusethreads -Duse5005threads".
2053
2054As of v5.6.0, interpreter-threads support is still lacking a way to
2055create new threads from Perl (i.e., C<use Thread;> will not work with
2056interpreter threads). C<use Thread;> continues to be available when you
2057specify the -Duse5005threads option to Configure, bugs and all.
2058
2059 NOTE: Support for threads continues to be an experimental feature.
2060 Interfaces and implementation are subject to sudden and drastic changes.
2061
2062=head2 New Configure flags
2063
2064The following new flags may be enabled on the Configure command line
2065by running Configure with C<-Dflag>.
2066
2067 usemultiplicity
2068 usethreads useithreads (new interpreter threads: no Perl API yet)
2069 usethreads use5005threads (threads as they were in 5.005)
2070
2071 use64bitint (equal to now deprecated 'use64bits')
2072 use64bitall
2073
2074 uselongdouble
2075 usemorebits
2076 uselargefiles
2077 usesocks (only SOCKS v5 supported)
2078
2079=head2 Threadedness and 64-bitness now more daring
2080
2081The Configure options enabling the use of threads and the use of
208264-bitness are now more daring in the sense that they no more have an
2083explicit list of operating systems of known threads/64-bit
2084capabilities. In other words: if your operating system has the
2085necessary APIs and datatypes, you should be able just to go ahead and
2086use them, for threads by Configure -Dusethreads, and for 64 bits
2087either explicitly by Configure -Duse64bitint or implicitly if your
2088system has 64-bit wide datatypes. See also L<"64-bit support">.
2089
2090=head2 Long Doubles
2091
2092Some platforms have "long doubles", floating point numbers of even
2093larger range than ordinary "doubles". To enable using long doubles for
2094Perl's scalars, use -Duselongdouble.
2095
2096=head2 -Dusemorebits
2097
2098You can enable both -Duse64bitint and -Duselongdouble with -Dusemorebits.
2099See also L<"64-bit support">.
2100
2101=head2 -Duselargefiles
2102
2103Some platforms support system APIs that are capable of handling large files
2104(typically, files larger than two gigabytes). Perl will try to use these
2105APIs if you ask for -Duselargefiles.
2106
2107See L<"Large file support"> for more information.
2108
2109=head2 installusrbinperl
2110
2111You can use "Configure -Uinstallusrbinperl" which causes installperl
2112to skip installing perl also as /usr/bin/perl. This is useful if you
2113prefer not to modify /usr/bin for some reason or another but harmful
2114because many scripts assume to find Perl in /usr/bin/perl.
2115
2116=head2 SOCKS support
2117
2118You can use "Configure -Dusesocks" which causes Perl to probe
2119for the SOCKS proxy protocol library (v5, not v4). For more information
2120on SOCKS, see:
2121
2122 http://www.socks.nec.com/
2123
2124=head2 C<-A> flag
2125
2126You can "post-edit" the Configure variables using the Configure C<-A>
2127switch. The editing happens immediately after the platform specific
2128hints files have been processed but before the actual configuration
2129process starts. Run C<Configure -h> to find out the full C<-A> syntax.
2130
2131=head2 Enhanced Installation Directories
2132
2133The installation structure has been enriched to improve the support
2134for maintaining multiple versions of perl, to provide locations for
2135vendor-supplied modules, scripts, and manpages, and to ease maintenance
2136of locally-added modules, scripts, and manpages. See the section on
2137Installation Directories in the INSTALL file for complete details.
2138For most users building and installing from source, the defaults should
2139be fine.
2140
2141If you previously used C<Configure -Dsitelib> or C<-Dsitearch> to set
2142special values for library directories, you might wish to consider using
2143the new C<-Dsiteprefix> setting instead. Also, if you wish to re-use a
2144config.sh file from an earlier version of perl, you should be sure to
2145check that Configure makes sensible choices for the new directories.
2146See INSTALL for complete details.
2147
2148=head2 gcc automatically tried if 'cc' does not seem to be working
2149
2150In many platforms the vendor-supplied 'cc' is too stripped-down to
2151build Perl (basically, the 'cc' doesn't do ANSI C). If this seems
2152to be the case and the 'cc' does not seem to be the GNU C compiler
2153'gcc', an automatic attempt is made to find and use 'gcc' instead.
2154
2155=head1 Platform specific changes
2156
2157=head2 Supported platforms
2158
2159=over 4
2160
2161=item *
2162
2163The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
2164extension.
2165
2166=item *
2167
2168GNU/Hurd is now supported.
2169
2170=item *
2171
2172Rhapsody/Darwin is now supported.
2173
2174=item *
2175
2176EPOC is now supported (on Psion 5).
2177
2178=item *
2179
2180The cygwin port (formerly cygwin32) has been greatly improved.
2181
2182=back
2183
2184=head2 DOS
2185
2186=over 4
2187
2188=item *
2189
2190Perl now works with djgpp 2.02 (and 2.03 alpha).
2191
2192=item *
2193
2194Environment variable names are not converted to uppercase any more.
2195
2196=item *
2197
2198Incorrect exit codes from backticks have been fixed.
2199
2200=item *
2201
2202This port continues to use its own builtin globbing (not File::Glob).
2203
2204=back
2205
2206=head2 OS390 (OpenEdition MVS)
2207
2208Support for this EBCDIC platform has not been renewed in this release.
2209There are difficulties in reconciling Perl's standardization on UTF-8
2210as its internal representation for characters with the EBCDIC character
2211set, because the two are incompatible.
2212
2213It is unclear whether future versions will renew support for this
2214platform, but the possibility exists.
2215
2216=head2 VMS
2217
2218Numerous revisions and extensions to configuration, build, testing, and
2219installation process to accommodate core changes and VMS-specific options.
2220
2221Expand %ENV-handling code to allow runtime mapping to logical names,
2222CLI symbols, and CRTL environ array.
2223
2224Extension of subprocess invocation code to accept filespecs as command
2225"verbs".
2226
2227Add to Perl command line processing the ability to use default file types and
2228to recognize Unix-style C<2E<gt>&1>.
2229
2230Expansion of File::Spec::VMS routines, and integration into ExtUtils::MM_VMS.
2231
2232Extension of ExtUtils::MM_VMS to handle complex extensions more flexibly.
2233
2234Barewords at start of Unix-syntax paths may be treated as text rather than
2235only as logical names.
2236
2237Optional secure translation of several logical names used internally by Perl.
2238
2239Miscellaneous bugfixing and porting of new core code to VMS.
2240
2241Thanks are gladly extended to the many people who have contributed VMS
2242patches, testing, and ideas.
2243
2244=head2 Win32
2245
2246Perl can now emulate fork() internally, using multiple interpreters running
2247in different concurrent threads. This support must be enabled at build
2248time. See L<perlfork> for detailed information.
2249
2250When given a pathname that consists only of a drivename, such as C<A:>,
2251opendir() and stat() now use the current working directory for the drive
2252rather than the drive root.
2253
2254The builtin XSUB functions in the Win32:: namespace are documented. See
2255L<Win32>.
2256
2257$^X now contains the full path name of the running executable.
2258
2259A Win32::GetLongPathName() function is provided to complement
2260Win32::GetFullPathName() and Win32::GetShortPathName(). See L<Win32>.
2261
2262POSIX::uname() is supported.
2263
2264system(1,...) now returns true process IDs rather than process
2265handles. kill() accepts any real process id, rather than strictly
2266return values from system(1,...).
2267
2268For better compatibility with Unix, C<kill(0, $pid)> can now be used to
2269test whether a process exists.
2270
2271The C<Shell> module is supported.
2272
2273Better support for building Perl under command.com in Windows 95
2274has been added.
2275
2276Scripts are read in binary mode by default to allow ByteLoader (and
2277the filter mechanism in general) to work properly. For compatibility,
2278the DATA filehandle will be set to text mode if a carriage return is
2279detected at the end of the line containing the __END__ or __DATA__
2280token; if not, the DATA filehandle will be left open in binary mode.
2281Earlier versions always opened the DATA filehandle in text mode.
2282
2283The glob() operator is implemented via the C<File::Glob> extension,
2284which supports glob syntax of the C shell. This increases the flexibility
2285of the glob() operator, but there may be compatibility issues for
2286programs that relied on the older globbing syntax. If you want to
2287preserve compatibility with the older syntax, you might want to run
2288perl with C<-MFile::DosGlob>. For details and compatibility information,
2289see L<File::Glob>.
2290
2291=head1 Significant bug fixes
2292
2293=head2 <HANDLE> on empty files
2294
2295With C<$/> set to C<undef>, "slurping" an empty file returns a string of
2296zero length (instead of C<undef>, as it used to) the first time the
2297HANDLE is read after C<$/> is set to C<undef>. Further reads yield
2298C<undef>.
2299
2300This means that the following will append "foo" to an empty file (it used
2301to do nothing):
2302
2303 perl -0777 -pi -e 's/^/foo/' empty_file
2304
2305The behaviour of:
2306
2307 perl -pi -e 's/^/foo/' empty_file
2308
2309is unchanged (it continues to leave the file empty).
2310
2311=head2 C<eval '...'> improvements
2312
2313Line numbers (as reflected by caller() and most diagnostics) within
2314C<eval '...'> were often incorrect where here documents were involved.
2315This has been corrected.
2316
2317Lexical lookups for variables appearing in C<eval '...'> within
2318functions that were themselves called within an C<eval '...'> were
2319searching the wrong place for lexicals. The lexical search now
2320correctly ends at the subroutine's block boundary.
2321
2322The use of C<return> within C<eval {...}> caused $@ not to be reset
2323correctly when no exception occurred within the eval. This has
2324been fixed.
2325
2326Parsing of here documents used to be flawed when they appeared as
2327the replacement expression in C<eval 's/.../.../e'>. This has
2328been fixed.
2329
2330=head2 All compilation errors are true errors
2331
2332Some "errors" encountered at compile time were by necessity
2333generated as warnings followed by eventual termination of the
2334program. This enabled more such errors to be reported in a
2335single run, rather than causing a hard stop at the first error
2336that was encountered.
2337
2338The mechanism for reporting such errors has been reimplemented
2339to queue compile-time errors and report them at the end of the
2340compilation as true errors rather than as warnings. This fixes
2341cases where error messages leaked through in the form of warnings
2342when code was compiled at run time using C<eval STRING>, and
2343also allows such errors to be reliably trapped using C<eval "...">.
2344
2345=head2 Implicitly closed filehandles are safer
2346
2347Sometimes implicitly closed filehandles (as when they are localized,
2348and Perl automatically closes them on exiting the scope) could
2349inadvertently set $? or $!. This has been corrected.
2350
2351
2352=head2 Behavior of list slices is more consistent
2353
2354When taking a slice of a literal list (as opposed to a slice of
2355an array or hash), Perl used to return an empty list if the
2356result happened to be composed of all undef values.
2357
2358The new behavior is to produce an empty list if (and only if)
2359the original list was empty. Consider the following example:
2360
2361 @a = (1,undef,undef,2)[2,1,2];
2362
2363The old behavior would have resulted in @a having no elements.
2364The new behavior ensures it has three undefined elements.
2365
2366Note in particular that the behavior of slices of the following
2367cases remains unchanged:
2368
2369 @a = ()[1,2];
2370 @a = (getpwent)[7,0];
2371 @a = (anything_returning_empty_list())[2,1,2];
2372 @a = @b[2,1,2];
2373 @a = @c{'a','b','c'};
2374
2375See L<perldata>.
2376
2377=head2 C<(\$)> prototype and C<$foo{a}>
2378
2379A scalar reference prototype now correctly allows a hash or
2380array element in that slot.
2381
2382=head2 C<goto &sub> and AUTOLOAD
2383
2384The C<goto &sub> construct works correctly when C<&sub> happens
2385to be autoloaded.
2386
2387=head2 C<-bareword> allowed under C<use integer>
2388
2389The autoquoting of barewords preceded by C<-> did not work
2390in prior versions when the C<integer> pragma was enabled.
2391This has been fixed.
2392
2393=head2 Failures in DESTROY()
2394
2395When code in a destructor threw an exception, it went unnoticed
2396in earlier versions of Perl, unless someone happened to be
2397looking in $@ just after the point the destructor happened to
2398run. Such failures are now visible as warnings when warnings are
2399enabled.
2400
2401=head2 Locale bugs fixed
2402
2403printf() and sprintf() previously reset the numeric locale
2404back to the default "C" locale. This has been fixed.
2405
2406Numbers formatted according to the local numeric locale
2407(such as using a decimal comma instead of a decimal dot) caused
2408"isn't numeric" warnings, even while the operations accessing
2409those numbers produced correct results. These warnings have been
2410discontinued.
2411
2412=head2 Memory leaks
2413
2414The C<eval 'return sub {...}'> construct could sometimes leak
2415memory. This has been fixed.
2416
2417Operations that aren't filehandle constructors used to leak memory
2418when used on invalid filehandles. This has been fixed.
2419
2420Constructs that modified C<@_> could fail to deallocate values
2421in C<@_> and thus leak memory. This has been corrected.
2422
2423=head2 Spurious subroutine stubs after failed subroutine calls
2424
2425Perl could sometimes create empty subroutine stubs when a
2426subroutine was not found in the package. Such cases stopped
2427later method lookups from progressing into base packages.
2428This has been corrected.
2429
2430=head2 Taint failures under C<-U>
2431
2432When running in unsafe mode, taint violations could sometimes
2433cause silent failures. This has been fixed.
2434
2435=head2 END blocks and the C<-c> switch
2436
2437Prior versions used to run BEGIN B<and> END blocks when Perl was
2438run in compile-only mode. Since this is typically not the expected
2439behavior, END blocks are not executed anymore when the C<-c> switch
2440is used, or if compilation fails.
2441
2442See L</"Support for CHECK blocks"> for how to run things when the compile
2443phase ends.
2444
2445=head2 Potential to leak DATA filehandles
2446
2447Using the C<__DATA__> token creates an implicit filehandle to
2448the file that contains the token. It is the program's
2449responsibility to close it when it is done reading from it.
2450
2451This caveat is now better explained in the documentation.
2452See L<perldata>.
2453
2454=head1 New or Changed Diagnostics
2455
2456=over 4
2457
2458=item "%s" variable %s masks earlier declaration in same %s
2459
2460(W misc) A "my" or "our" variable has been redeclared in the current scope or statement,
2461effectively eliminating all access to the previous instance. This is almost
2462always a typographical error. Note that the earlier variable will still exist
2463until the end of the scope or until all closure referents to it are
2464destroyed.
2465
2466=item "my sub" not yet implemented
2467
2468(F) Lexically scoped subroutines are not yet implemented. Don't try that
2469yet.
2470
2471=item "our" variable %s redeclared
2472
2473(W misc) You seem to have already declared the same global once before in the
2474current lexical scope.
2475
2476=item '!' allowed only after types %s
2477
2478(F) The '!' is allowed in pack() and unpack() only after certain types.
2479See L<perlfunc/pack>.
2480
2481=item / cannot take a count
2482
2483(F) You had an unpack template indicating a counted-length string,
2484but you have also specified an explicit size for the string.
2485See L<perlfunc/pack>.
2486
2487=item / must be followed by a, A or Z
2488
2489(F) You had an unpack template indicating a counted-length string,
2490which must be followed by one of the letters a, A or Z
2491to indicate what sort of string is to be unpacked.
2492See L<perlfunc/pack>.
2493
2494=item / must be followed by a*, A* or Z*
2495
2496(F) You had a pack template indicating a counted-length string,
2497Currently the only things that can have their length counted are a*, A* or Z*.
2498See L<perlfunc/pack>.
2499
2500=item / must follow a numeric type
2501
2502(F) You had an unpack template that contained a '#',
2503but this did not follow some numeric unpack specification.
2504See L<perlfunc/pack>.
2505
2506=item /%s/: Unrecognized escape \\%c passed through
2507
2508(W regexp) You used a backslash-character combination which is not recognized
2509by Perl. This combination appears in an interpolated variable or a
2510C<'>-delimited regular expression. The character was understood literally.
2511
2512=item /%s/: Unrecognized escape \\%c in character class passed through
2513
2514(W regexp) You used a backslash-character combination which is not recognized
2515by Perl inside character classes. The character was understood literally.
2516
2517=item /%s/ should probably be written as "%s"
2518
2519(W syntax) You have used a pattern where Perl expected to find a string,
2520as in the first argument to C<join>. Perl will treat the true
2521or false result of matching the pattern against $_ as the string,
2522which is probably not what you had in mind.
2523
2524=item %s() called too early to check prototype
2525
2526(W prototype) You've called a function that has a prototype before the parser saw a
2527definition or declaration for it, and Perl could not check that the call
2528conforms to the prototype. You need to either add an early prototype
2529declaration for the subroutine in question, or move the subroutine
2530definition ahead of the call to get proper prototype checking. Alternatively,
2531if you are certain that you're calling the function correctly, you may put
2532an ampersand before the name to avoid the warning. See L<perlsub>.
2533
2534=item %s argument is not a HASH or ARRAY element
2535
2536(F) The argument to exists() must be a hash or array element, such as:
2537
2538 $foo{$bar}
2539 $ref->{"susie"}[12]
2540
2541=item %s argument is not a HASH or ARRAY element or slice
2542
2543(F) The argument to delete() must be either a hash or array element, such as:
2544
2545 $foo{$bar}
2546 $ref->{"susie"}[12]
2547
2548or a hash or array slice, such as:
2549
2550 @foo[$bar, $baz, $xyzzy]
2551 @{$ref->[12]}{"susie", "queue"}
2552
2553=item %s argument is not a subroutine name
2554
2555(F) The argument to exists() for C<exists &sub> must be a subroutine
2556name, and not a subroutine call. C<exists &sub()> will generate this error.
2557
2558=item %s package attribute may clash with future reserved word: %s
2559
2560(W reserved) A lowercase attribute name was used that had a package-specific handler.
2561That name might have a meaning to Perl itself some day, even though it
2562doesn't yet. Perhaps you should use a mixed-case attribute name, instead.
2563See L<attributes>.
2564
2565=item (in cleanup) %s
2566
2567(W misc) This prefix usually indicates that a DESTROY() method raised
2568the indicated exception. Since destructors are usually called by
2569the system at arbitrary points during execution, and often a vast
2570number of times, the warning is issued only once for any number
2571of failures that would otherwise result in the same message being
2572repeated.
2573
2574Failure of user callbacks dispatched using the C<G_KEEPERR> flag
2575could also result in this warning. See L<perlcall/G_KEEPERR>.
2576
2577=item <> should be quotes
2578
2579(F) You wrote C<< require <file> >> when you should have written
2580C<require 'file'>.
2581
2582=item Attempt to join self
2583
2584(F) You tried to join a thread from within itself, which is an
2585impossible task. You may be joining the wrong thread, or you may
2586need to move the join() to some other thread.
2587
2588=item Bad evalled substitution pattern
2589
2590(F) You've used the /e switch to evaluate the replacement for a
2591substitution, but perl found a syntax error in the code to evaluate,
2592most likely an unexpected right brace '}'.
2593
2594=item Bad realloc() ignored
2595
2596(S) An internal routine called realloc() on something that had never been
2597malloc()ed in the first place. Mandatory, but can be disabled by
2598setting environment variable C<PERL_BADFREE> to 1.
2599
2600=item Bareword found in conditional
2601
2602(W bareword) The compiler found a bareword where it expected a conditional,
2603which often indicates that an || or && was parsed as part of the
2604last argument of the previous construct, for example:
2605
2606 open FOO || die;
2607
2608It may also indicate a misspelled constant that has been interpreted
2609as a bareword:
2610
2611 use constant TYPO => 1;
2612 if (TYOP) { print "foo" }
2613
2614The C<strict> pragma is useful in avoiding such errors.
2615
2616=item Binary number > 0b11111111111111111111111111111111 non-portable
2617
2618(W portable) The binary number you specified is larger than 2**32-1
2619(4294967295) and therefore non-portable between systems. See
2620L<perlport> for more on portability concerns.
2621
2622=item Bit vector size > 32 non-portable
2623
2624(W portable) Using bit vector sizes larger than 32 is non-portable.
2625
2626=item Buffer overflow in prime_env_iter: %s
2627
2628(W internal) A warning peculiar to VMS. While Perl was preparing to iterate over
2629%ENV, it encountered a logical name or symbol definition which was too long,
2630so it was truncated to the string shown.
2631
2632=item Can't check filesystem of script "%s"
2633
2634(P) For some reason you can't check the filesystem of the script for nosuid.
2635
2636=item Can't declare class for non-scalar %s in "%s"
2637
2638(S) Currently, only scalar variables can declared with a specific class
2639qualifier in a "my" or "our" declaration. The semantics may be extended
2640for other types of variables in future.
2641
2642=item Can't declare %s in "%s"
2643
2644(F) Only scalar, array, and hash variables may be declared as "my" or
2645"our" variables. They must have ordinary identifiers as names.
2646
2647=item Can't ignore signal CHLD, forcing to default
2648
2649(W signal) Perl has detected that it is being run with the SIGCHLD signal
2650(sometimes known as SIGCLD) disabled. Since disabling this signal
2651will interfere with proper determination of exit status of child
2652processes, Perl has reset the signal to its default value.
2653This situation typically indicates that the parent program under
2654which Perl may be running (e.g., cron) is being very careless.
2655
2656=item Can't modify non-lvalue subroutine call
2657
2658(F) Subroutines meant to be used in lvalue context should be declared as
2659such, see L<perlsub/"Lvalue subroutines">.
2660
2661=item Can't read CRTL environ
2662
2663(S) A warning peculiar to VMS. Perl tried to read an element of %ENV
2664from the CRTL's internal environment array and discovered the array was
2665missing. You need to figure out where your CRTL misplaced its environ
2666or define F<PERL_ENV_TABLES> (see L<perlvms>) so that environ is not searched.
2667
2668=item Can't remove %s: %s, skipping file
2669
2670(S) You requested an inplace edit without creating a backup file. Perl
2671was unable to remove the original file to replace it with the modified
2672file. The file was left unmodified.
2673
2674=item Can't return %s from lvalue subroutine
2675
2676(F) Perl detected an attempt to return illegal lvalues (such
2677as temporary or readonly values) from a subroutine used as an lvalue.
2678This is not allowed.
2679
2680=item Can't weaken a nonreference
2681
2682(F) You attempted to weaken something that was not a reference. Only
2683references can be weakened.
2684
2685=item Character class [:%s:] unknown
2686
2687(F) The class in the character class [: :] syntax is unknown.
2688See L<perlre>.
2689
2690=item Character class syntax [%s] belongs inside character classes
2691
2692(W unsafe) The character class constructs [: :], [= =], and [. .] go
2693I<inside> character classes, the [] are part of the construct,
2694for example: /[012[:alpha:]345]/. Note that [= =] and [. .]
2695are not currently implemented; they are simply placeholders for
2696future extensions.
2697
2698=item Constant is not %s reference
2699
2700(F) A constant value (perhaps declared using the C<use constant> pragma)
2701is being dereferenced, but it amounts to the wrong type of reference. The
2702message indicates the type of reference that was expected. This usually
2703indicates a syntax error in dereferencing the constant value.
2704See L<perlsub/"Constant Functions"> and L<constant>.
2705
2706=item constant(%s): %s
2707
2708(F) The parser found inconsistencies either while attempting to define an
2709overloaded constant, or when trying to find the character name specified
2710in the C<\N{...}> escape. Perhaps you forgot to load the corresponding
2711C<overload> or C<charnames> pragma? See L<charnames> and L<overload>.
2712
2713=item CORE::%s is not a keyword
2714
2715(F) The CORE:: namespace is reserved for Perl keywords.
2716
2717=item defined(@array) is deprecated
2718
2719(D) defined() is not usually useful on arrays because it checks for an
2720undefined I<scalar> value. If you want to see if the array is empty,
2721just use C<if (@array) { # not empty }> for example.
2722
2723=item defined(%hash) is deprecated
2724
2725(D) defined() is not usually useful on hashes because it checks for an
2726undefined I<scalar> value. If you want to see if the hash is empty,
2727just use C<if (%hash) { # not empty }> for example.
2728
2729=item Did not produce a valid header
2730
2731See Server error.
2732
2733=item (Did you mean "local" instead of "our"?)
2734
2735(W misc) Remember that "our" does not localize the declared global variable.
2736You have declared it again in the same lexical scope, which seems superfluous.
2737
2738=item Document contains no data
2739
2740See Server error.
2741
2742=item entering effective %s failed
2743
2744(F) While under the C<use filetest> pragma, switching the real and
2745effective uids or gids failed.
2746
2747=item false [] range "%s" in regexp
2748
2749(W regexp) A character class range must start and end at a literal character, not
2750another character class like C<\d> or C<[:alpha:]>. The "-" in your false
2751range is interpreted as a literal "-". Consider quoting the "-", "\-".
2752See L<perlre>.
2753
2754=item Filehandle %s opened only for output
2755
2756(W io) You tried to read from a filehandle opened only for writing. If you
2757intended it to be a read/write filehandle, you needed to open it with
2758"+<" or "+>" or "+>>" instead of with "<" or nothing. If
2759you intended only to read from the file, use "<". See
2760L<perlfunc/open>.
2761
2762=item flock() on closed filehandle %s
2763
2764(W closed) The filehandle you're attempting to flock() got itself closed some
2765time before now. Check your logic flow. flock() operates on filehandles.
2766Are you attempting to call flock() on a dirhandle by the same name?
2767
2768=item Global symbol "%s" requires explicit package name
2769
2770(F) You've said "use strict vars", which indicates that all variables
2771must either be lexically scoped (using "my"), declared beforehand using
2772"our", or explicitly qualified to say which package the global variable
2773is in (using "::").
2774
2775=item Hexadecimal number > 0xffffffff non-portable
2776
2777(W portable) The hexadecimal number you specified is larger than 2**32-1
2778(4294967295) and therefore non-portable between systems. See
2779L<perlport> for more on portability concerns.
2780
2781=item Ill-formed CRTL environ value "%s"
2782
2783(W internal) A warning peculiar to VMS. Perl tried to read the CRTL's internal
2784environ array, and encountered an element without the C<=> delimiter
2785used to separate keys from values. The element is ignored.
2786
2787=item Ill-formed message in prime_env_iter: |%s|
2788
2789(W internal) A warning peculiar to VMS. Perl tried to read a logical name
2790or CLI symbol definition when preparing to iterate over %ENV, and
2791didn't see the expected delimiter between key and value, so the
2792line was ignored.
2793
2794=item Illegal binary digit %s
2795
2796(F) You used a digit other than 0 or 1 in a binary number.
2797
2798=item Illegal binary digit %s ignored
2799
2800(W digit) You may have tried to use a digit other than 0 or 1 in a binary number.
2801Interpretation of the binary number stopped before the offending digit.
2802
2803=item Illegal number of bits in vec
2804
2805(F) The number of bits in vec() (the third argument) must be a power of
2806two from 1 to 32 (or 64, if your platform supports that).
2807
2808=item Integer overflow in %s number
2809
2810(W overflow) The hexadecimal, octal or binary number you have specified either
2811as a literal or as an argument to hex() or oct() is too big for your
2812architecture, and has been converted to a floating point number. On a
281332-bit architecture the largest hexadecimal, octal or binary number
2814representable without overflow is 0xFFFFFFFF, 037777777777, or
28150b11111111111111111111111111111111 respectively. Note that Perl
2816transparently promotes all numbers to a floating point representation
2817internally--subject to loss of precision errors in subsequent
2818operations.
2819
2820=item Invalid %s attribute: %s
2821
2822The indicated attribute for a subroutine or variable was not recognized
2823by Perl or by a user-supplied handler. See L<attributes>.
2824
2825=item Invalid %s attributes: %s
2826
2827The indicated attributes for a subroutine or variable were not recognized
2828by Perl or by a user-supplied handler. See L<attributes>.
2829
2830=item invalid [] range "%s" in regexp
2831
2832The offending range is now explicitly displayed.
2833
2834=item Invalid separator character %s in attribute list
2835
2836(F) Something other than a colon or whitespace was seen between the
2837elements of an attribute list. If the previous attribute
2838had a parenthesised parameter list, perhaps that list was terminated
2839too soon. See L<attributes>.
2840
2841=item Invalid separator character %s in subroutine attribute list
2842
2843(F) Something other than a colon or whitespace was seen between the
2844elements of a subroutine attribute list. If the previous attribute
2845had a parenthesised parameter list, perhaps that list was terminated
2846too soon.
2847
2848=item leaving effective %s failed
2849
2850(F) While under the C<use filetest> pragma, switching the real and
2851effective uids or gids failed.
2852
2853=item Lvalue subs returning %s not implemented yet
2854
2855(F) Due to limitations in the current implementation, array and hash
2856values cannot be returned in subroutines used in lvalue context.
2857See L<perlsub/"Lvalue subroutines">.
2858
2859=item Method %s not permitted
2860
2861See Server error.
2862
2863=item Missing %sbrace%s on \N{}
2864
2865(F) Wrong syntax of character name literal C<\N{charname}> within
2866double-quotish context.
2867
2868=item Missing command in piped open
2869
2870(W pipe) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
2871construction, but the command was missing or blank.
2872
2873=item Missing name in "my sub"
2874
2875(F) The reserved syntax for lexically scoped subroutines requires that they
2876have a name with which they can be found.
2877
2878=item No %s specified for -%c
2879
2880(F) The indicated command line switch needs a mandatory argument, but
2881you haven't specified one.
2882
2883=item No package name allowed for variable %s in "our"
2884
2885(F) Fully qualified variable names are not allowed in "our" declarations,
2886because that doesn't make much sense under existing semantics. Such
2887syntax is reserved for future extensions.
2888
2889=item No space allowed after -%c
2890
2891(F) The argument to the indicated command line switch must follow immediately
2892after the switch, without intervening spaces.
2893
2894=item no UTC offset information; assuming local time is UTC
2895
2896(S) A warning peculiar to VMS. Perl was unable to find the local
2897timezone offset, so it's assuming that local system time is equivalent
2898to UTC. If it's not, define the logical name F<SYS$TIMEZONE_DIFFERENTIAL>
2899to translate to the number of seconds which need to be added to UTC to
2900get local time.
2901
2902=item Octal number > 037777777777 non-portable
2903
2904(W portable) The octal number you specified is larger than 2**32-1 (4294967295)
2905and therefore non-portable between systems. See L<perlport> for more
2906on portability concerns.
2907
2908See also L<perlport> for writing portable code.
2909
2910=item panic: del_backref
2911
2912(P) Failed an internal consistency check while trying to reset a weak
2913reference.
2914
2915=item panic: kid popen errno read
2916
2917(F) forked child returned an incomprehensible message about its errno.
2918
2919=item panic: magic_killbackrefs
2920
2921(P) Failed an internal consistency check while trying to reset all weak
2922references to an object.
2923
2924=item Parentheses missing around "%s" list
2925
2926(W parenthesis) You said something like
2927
2928 my $foo, $bar = @_;
2929
2930when you meant
2931
2932 my ($foo, $bar) = @_;
2933
2934Remember that "my", "our", and "local" bind tighter than comma.
2935
2936=item Possible unintended interpolation of %s in string
2937
2938(W ambiguous) It used to be that Perl would try to guess whether you
2939wanted an array interpolated or a literal @. It no longer does this;
2940arrays are now I<always> interpolated into strings. This means that
2941if you try something like:
2942
2943 print "fred@example.com";
2944
2945and the array C<@example> doesn't exist, Perl is going to print
2946C<fred.com>, which is probably not what you wanted. To get a literal
2947C<@> sign in a string, put a backslash before it, just as you would
2948to get a literal C<$> sign.
2949
2950=item Possible Y2K bug: %s
2951
2952(W y2k) You are concatenating the number 19 with another number, which
2953could be a potential Year 2000 problem.
2954
2955=item pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead
2956
2957(W deprecated) You have written something like this:
2958
2959 sub doit
2960 {
2961 use attrs qw(locked);
2962 }
2963
2964You should use the new declaration syntax instead.
2965
2966 sub doit : locked
2967 {
2968 ...
2969
2970The C<use attrs> pragma is now obsolete, and is only provided for
2971backward-compatibility. See L<perlsub/"Subroutine Attributes">.
2972
2973
2974=item Premature end of script headers
2975
2976See Server error.
2977
2978=item Repeat count in pack overflows
2979
2980(F) You can't specify a repeat count so large that it overflows
2981your signed integers. See L<perlfunc/pack>.
2982
2983=item Repeat count in unpack overflows
2984
2985(F) You can't specify a repeat count so large that it overflows
2986your signed integers. See L<perlfunc/unpack>.
2987
2988=item realloc() of freed memory ignored
2989
2990(S) An internal routine called realloc() on something that had already
2991been freed.
2992
2993=item Reference is already weak
2994
2995(W misc) You have attempted to weaken a reference that is already weak.
2996Doing so has no effect.
2997
2998=item setpgrp can't take arguments
2999
3000(F) Your system has the setpgrp() from BSD 4.2, which takes no arguments,
3001unlike POSIX setpgid(), which takes a process ID and process group ID.
3002
3003=item Strange *+?{} on zero-length expression
3004
3005(W regexp) You applied a regular expression quantifier in a place where it
3006makes no sense, such as on a zero-width assertion.
3007Try putting the quantifier inside the assertion instead. For example,
3008the way to match "abc" provided that it is followed by three
3009repetitions of "xyz" is C</abc(?=(?:xyz){3})/>, not C</abc(?=xyz){3}/>.
3010
3011=item switching effective %s is not implemented
3012
3013(F) While under the C<use filetest> pragma, we cannot switch the
3014real and effective uids or gids.
3015
3016=item This Perl can't reset CRTL environ elements (%s)
3017
3018=item This Perl can't set CRTL environ elements (%s=%s)
3019
3020(W internal) Warnings peculiar to VMS. You tried to change or delete an element
3021of the CRTL's internal environ array, but your copy of Perl wasn't
3022built with a CRTL that contained the setenv() function. You'll need to
3023rebuild Perl with a CRTL that does, or redefine F<PERL_ENV_TABLES> (see
3024L<perlvms>) so that the environ array isn't the target of the change to
3025%ENV which produced the warning.
3026
3027=item Too late to run %s block
3028
3029(W void) A CHECK or INIT block is being defined during run time proper,
3030when the opportunity to run them has already passed. Perhaps you are
3031loading a file with C<require> or C<do> when you should be using
3032C<use> instead. Or perhaps you should put the C<require> or C<do>
3033inside a BEGIN block.
3034
3035=item Unknown open() mode '%s'
3036
3037(F) The second argument of 3-argument open() is not among the list
3038of valid modes: C<< < >>, C<< > >>, C<<< >> >>>, C<< +< >>,
3039C<< +> >>, C<<< +>> >>>, C<-|>, C<|->.
3040
3041=item Unknown process %x sent message to prime_env_iter: %s
3042
3043(P) An error peculiar to VMS. Perl was reading values for %ENV before
3044iterating over it, and someone else stuck a message in the stream of
3045data Perl expected. Someone's very confused, or perhaps trying to
3046subvert Perl's population of %ENV for nefarious purposes.
3047
3048=item Unrecognized escape \\%c passed through
3049
3050(W misc) You used a backslash-character combination which is not recognized
3051by Perl. The character was understood literally.
3052
3053=item Unterminated attribute parameter in attribute list
3054
3055(F) The lexer saw an opening (left) parenthesis character while parsing an
3056attribute list, but the matching closing (right) parenthesis
3057character was not found. You may need to add (or remove) a backslash
3058character to get your parentheses to balance. See L<attributes>.
3059
3060=item Unterminated attribute list
3061
3062(F) The lexer found something other than a simple identifier at the start
3063of an attribute, and it wasn't a semicolon or the start of a
3064block. Perhaps you terminated the parameter list of the previous attribute
3065too soon. See L<attributes>.
3066
3067=item Unterminated attribute parameter in subroutine attribute list
3068
3069(F) The lexer saw an opening (left) parenthesis character while parsing a
3070subroutine attribute list, but the matching closing (right) parenthesis
3071character was not found. You may need to add (or remove) a backslash
3072character to get your parentheses to balance.
3073
3074=item Unterminated subroutine attribute list
3075
3076(F) The lexer found something other than a simple identifier at the start
3077of a subroutine attribute, and it wasn't a semicolon or the start of a
3078block. Perhaps you terminated the parameter list of the previous attribute
3079too soon.
3080
3081=item Value of CLI symbol "%s" too long
3082
3083(W misc) A warning peculiar to VMS. Perl tried to read the value of an %ENV
3084element from a CLI symbol table, and found a resultant string longer
3085than 1024 characters. The return value has been truncated to 1024
3086characters.
3087
3088=item Version number must be a constant number
3089
3090(P) The attempt to translate a C<use Module n.n LIST> statement into
3091its equivalent C<BEGIN> block found an internal inconsistency with
3092the version number.
3093
3094=back
3095
3096=head1 New tests
3097
3098=over 4
3099
3100=item lib/attrs
3101
3102Compatibility tests for C<sub : attrs> vs the older C<use attrs>.
3103
3104=item lib/env
3105
3106Tests for new environment scalar capability (e.g., C<use Env qw($BAR);>).
3107
3108=item lib/env-array
3109
3110Tests for new environment array capability (e.g., C<use Env qw(@PATH);>).
3111
3112=item lib/io_const
3113
3114IO constants (SEEK_*, _IO*).
3115
3116=item lib/io_dir
3117
3118Directory-related IO methods (new, read, close, rewind, tied delete).
3119
3120=item lib/io_multihomed
3121
3122INET sockets with multi-homed hosts.
3123
3124=item lib/io_poll
3125
3126IO poll().
3127
3128=item lib/io_unix
3129
3130UNIX sockets.
3131
3132=item op/attrs
3133
3134Regression tests for C<my ($x,@y,%z) : attrs> and <sub : attrs>.
3135
3136=item op/filetest
3137
3138File test operators.
3139
3140=item op/lex_assign
3141
3142Verify operations that access pad objects (lexicals and temporaries).
3143
3144=item op/exists_sub
3145
3146Verify C<exists &sub> operations.
3147
3148=back
3149
3150=head1 Incompatible Changes
3151
3152=head2 Perl Source Incompatibilities
3153
3154Beware that any new warnings that have been added or old ones
3155that have been enhanced are B<not> considered incompatible changes.
3156
3157Since all new warnings must be explicitly requested via the C<-w>
3158switch or the C<warnings> pragma, it is ultimately the programmer's
3159responsibility to ensure that warnings are enabled judiciously.
3160
3161=over 4
3162
3163=item CHECK is a new keyword
3164
3165All subroutine definitions named CHECK are now special. See
3166C</"Support for CHECK blocks"> for more information.
3167
3168=item Treatment of list slices of undef has changed
3169
3170There is a potential incompatibility in the behavior of list slices
3171that are comprised entirely of undefined values.
3172See L</"Behavior of list slices is more consistent">.
3173
3174=item Format of $English::PERL_VERSION is different
3175
3176The English module now sets $PERL_VERSION to $^V (a string value) rather
3177than C<$]> (a numeric value). This is a potential incompatibility.
3178Send us a report via perlbug if you are affected by this.
3179
3180See L</"Improved Perl version numbering system"> for the reasons for
3181this change.
3182
3183=item Literals of the form C<1.2.3> parse differently
3184
3185Previously, numeric literals with more than one dot in them were
3186interpreted as a floating point number concatenated with one or more
3187numbers. Such "numbers" are now parsed as strings composed of the
3188specified ordinals.
3189
3190For example, C<print 97.98.99> used to output C<97.9899> in earlier
3191versions, but now prints C<abc>.
3192
3193See L</"Support for strings represented as a vector of ordinals">.
3194
3195=item Possibly changed pseudo-random number generator
3196
3197Perl programs that depend on reproducing a specific set of pseudo-random
3198numbers may now produce different output due to improvements made to the
3199rand() builtin. You can use C<sh Configure -Drandfunc=rand> to obtain
3200the old behavior.
3201
3202See L</"Better pseudo-random number generator">.
3203
3204=item Hashing function for hash keys has changed
3205
3206Even though Perl hashes are not order preserving, the apparently
3207random order encountered when iterating on the contents of a hash
3208is actually determined by the hashing algorithm used. Improvements
3209in the algorithm may yield a random order that is B<different> from
3210that of previous versions, especially when iterating on hashes.
3211
3212See L</"Better worst-case behavior of hashes"> for additional
3213information.
3214
3215=item C<undef> fails on read only values
3216
3217Using the C<undef> operator on a readonly value (such as $1) has
3218the same effect as assigning C<undef> to the readonly value--it
3219throws an exception.
3220
3221=item Close-on-exec bit may be set on pipe and socket handles
3222
3223Pipe and socket handles are also now subject to the close-on-exec
3224behavior determined by the special variable $^F.
3225
3226See L</"More consistent close-on-exec behavior">.
3227
3228=item Writing C<"$$1"> to mean C<"${$}1"> is unsupported
3229
3230Perl 5.004 deprecated the interpretation of C<$$1> and
3231similar within interpolated strings to mean C<$$ . "1">,
3232but still allowed it.
3233
3234In Perl 5.6.0 and later, C<"$$1"> always means C<"${$1}">.
3235
3236=item delete(), each(), values() and C<\(%h)>
3237
3238operate on aliases to values, not copies
3239
3240delete(), each(), values() and hashes (e.g. C<\(%h)>)
3241in a list context return the actual
3242values in the hash, instead of copies (as they used to in earlier
3243versions). Typical idioms for using these constructs copy the
3244returned values, but this can make a significant difference when
3245creating references to the returned values. Keys in the hash are still
3246returned as copies when iterating on a hash.
3247
3248See also L</"delete(), each(), values() and hash iteration are faster">.
3249
3250=item vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS
3251
3252vec() generates a run-time error if the BITS argument is not
3253a valid power-of-two integer.
3254
3255=item Text of some diagnostic output has changed
3256
3257Most references to internal Perl operations in diagnostics
3258have been changed to be more descriptive. This may be an
3259issue for programs that may incorrectly rely on the exact
3260text of diagnostics for proper functioning.
3261
3262=item C<%@> has been removed
3263
3264The undocumented special variable C<%@> that used to accumulate
3265"background" errors (such as those that happen in DESTROY())
3266has been removed, because it could potentially result in memory
3267leaks.
3268
3269=item Parenthesized not() behaves like a list operator
3270
3271The C<not> operator now falls under the "if it looks like a function,
3272it behaves like a function" rule.
3273
3274As a result, the parenthesized form can be used with C<grep> and C<map>.
3275The following construct used to be a syntax error before, but it works
3276as expected now:
3277
3278 grep not($_), @things;
3279
3280On the other hand, using C<not> with a literal list slice may not
3281work. The following previously allowed construct:
3282
3283 print not (1,2,3)[0];
3284
3285needs to be written with additional parentheses now:
3286
3287 print not((1,2,3)[0]);
3288
3289The behavior remains unaffected when C<not> is not followed by parentheses.
3290
3291=item Semantics of bareword prototype C<(*)> have changed
3292
3293The semantics of the bareword prototype C<*> have changed. Perl 5.005
3294always coerced simple scalar arguments to a typeglob, which wasn't useful
3295in situations where the subroutine must distinguish between a simple
3296scalar and a typeglob. The new behavior is to not coerce bareword
3297arguments to a typeglob. The value will always be visible as either
3298a simple scalar or as a reference to a typeglob.
3299
3300See L</"More functional bareword prototype (*)">.
3301
3302=item Semantics of bit operators may have changed on 64-bit platforms
3303
3304If your platform is either natively 64-bit or if Perl has been
3305configured to used 64-bit integers, i.e., $Config{ivsize} is 8,
3306there may be a potential incompatibility in the behavior of bitwise
3307numeric operators (& | ^ ~ << >>). These operators used to strictly
3308operate on the lower 32 bits of integers in previous versions, but now
3309operate over the entire native integral width. In particular, note
3310that unary C<~> will produce different results on platforms that have
3311different $Config{ivsize}. For portability, be sure to mask off
3312the excess bits in the result of unary C<~>, e.g., C<~$x & 0xffffffff>.
3313
3314See L</"Bit operators support full native integer width">.
3315
3316=item More builtins taint their results
3317
3318As described in L</"Improved security features">, there may be more
3319sources of taint in a Perl program.
3320
3321To avoid these new tainting behaviors, you can build Perl with the
3322Configure option C<-Accflags=-DINCOMPLETE_TAINTS>. Beware that the
3323ensuing perl binary may be insecure.
3324
3325=back
3326
3327=head2 C Source Incompatibilities
3328
3329=over 4
3330
3331=item C<PERL_POLLUTE>
3332
3333Release 5.005 grandfathered old global symbol names by providing preprocessor
3334macros for extension source compatibility. As of release 5.6.0, these
3335preprocessor definitions are not available by default. You need to explicitly
3336compile perl with C<-DPERL_POLLUTE> to get these definitions. For
3337extensions still using the old symbols, this option can be
3338specified via MakeMaker:
3339
3340 perl Makefile.PL POLLUTE=1
3341
3342=item C<PERL_IMPLICIT_CONTEXT>
3343
3344This new build option provides a set of macros for all API functions
3345such that an implicit interpreter/thread context argument is passed to
3346every API function. As a result of this, something like C<sv_setsv(foo,bar)>
3347amounts to a macro invocation that actually translates to something like
3348C<Perl_sv_setsv(my_perl,foo,bar)>. While this is generally expected
3349to not have any significant source compatibility issues, the difference
3350between a macro and a real function call will need to be considered.
3351
3352This means that there B<is> a source compatibility issue as a result of
3353this if your extensions attempt to use pointers to any of the Perl API
3354functions.
3355
3356Note that the above issue is not relevant to the default build of
3357Perl, whose interfaces continue to match those of prior versions
3358(but subject to the other options described here).
3359
3360See L<perlguts/"The Perl API"> for detailed information on the
3361ramifications of building Perl with this option.
3362
3363 NOTE: PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
3364 with one of -Dusethreads, -Dusemultiplicity, or both. It is not
3365 intended to be enabled by users at this time.
3366
3367=item C<PERL_POLLUTE_MALLOC>
3368
3369Enabling Perl's malloc in release 5.005 and earlier caused the namespace of
3370the system's malloc family of functions to be usurped by the Perl versions,
3371since by default they used the same names. Besides causing problems on
3372platforms that do not allow these functions to be cleanly replaced, this
3373also meant that the system versions could not be called in programs that
3374used Perl's malloc. Previous versions of Perl have allowed this behaviour
3375to be suppressed with the HIDEMYMALLOC and EMBEDMYMALLOC preprocessor
3376definitions.
3377
3378As of release 5.6.0, Perl's malloc family of functions have default names
3379distinct from the system versions. You need to explicitly compile perl with
3380C<-DPERL_POLLUTE_MALLOC> to get the older behaviour. HIDEMYMALLOC
3381and EMBEDMYMALLOC have no effect, since the behaviour they enabled is now
3382the default.
3383
3384Note that these functions do B<not> constitute Perl's memory allocation API.
3385See L<perlguts/"Memory Allocation"> for further information about that.
3386
3387=back
3388
3389=head2 Compatible C Source API Changes
3390
3391=over 4
3392
3393=item C<PATCHLEVEL> is now C<PERL_VERSION>
3394
3395The cpp macros C<PERL_REVISION>, C<PERL_VERSION>, and C<PERL_SUBVERSION>
3396are now available by default from perl.h, and reflect the base revision,
3397patchlevel, and subversion respectively. C<PERL_REVISION> had no
3398prior equivalent, while C<PERL_VERSION> and C<PERL_SUBVERSION> were
3399previously available as C<PATCHLEVEL> and C<SUBVERSION>.
3400
3401The new names cause less pollution of the B<cpp> namespace and reflect what
3402the numbers have come to stand for in common practice. For compatibility,
3403the old names are still supported when F<patchlevel.h> is explicitly
3404included (as required before), so there is no source incompatibility
3405from the change.
3406
3407=back
3408
3409=head2 Binary Incompatibilities
3410
3411In general, the default build of this release is expected to be binary
3412compatible for extensions built with the 5.005 release or its maintenance
3413versions. However, specific platforms may have broken binary compatibility
3414due to changes in the defaults used in hints files. Therefore, please be
3415sure to always check the platform-specific README files for any notes to
3416the contrary.
3417
3418The usethreads or usemultiplicity builds are B<not> binary compatible
3419with the corresponding builds in 5.005.
3420
3421On platforms that require an explicit list of exports (AIX, OS/2 and Windows,
3422among others), purely internal symbols such as parser functions and the
3423run time opcodes are not exported by default. Perl 5.005 used to export
3424all functions irrespective of whether they were considered part of the
3425public API or not.
3426
3427For the full list of public API functions, see L<perlapi>.
3428
3429=head1 Known Problems
3430
3431=head2 Localizing a tied hash element may leak memory
3432
3433As of the 5.6.1 release, there is a known leak when code such as this
3434is executed:
3435
3436 use Tie::Hash;
3437 tie my %tie_hash => 'Tie::StdHash';
3438
3439 ...
3440
3441 local($tie_hash{Foo}) = 1; # leaks
3442
3443=head2 Known test failures
3444
3445=over
3446
3447=item 64-bit builds
3448
3449Subtest #15 of lib/b.t may fail under 64-bit builds on platforms such
3450as HP-UX PA64 and Linux IA64. The issue is still being investigated.
3451
3452The lib/io_multihomed test may hang in HP-UX if Perl has been
3453configured to be 64-bit. Because other 64-bit platforms do not
3454hang in this test, HP-UX is suspect. All other tests pass
3455in 64-bit HP-UX. The test attempts to create and connect to
3456"multihomed" sockets (sockets which have multiple IP addresses).
3457
3458Note that 64-bit support is still experimental.
3459
3460=item Failure of Thread tests
3461
3462The subtests 19 and 20 of lib/thr5005.t test are known to fail due to
3463fundamental problems in the 5.005 threading implementation. These are
3464not new failures--Perl 5.005_0x has the same bugs, but didn't have these
3465tests. (Note that support for 5.005-style threading remains experimental.)
3466
3467=item NEXTSTEP 3.3 POSIX test failure
3468
3469In NEXTSTEP 3.3p2 the implementation of the strftime(3) in the
3470operating system libraries is buggy: the %j format numbers the days of
3471a month starting from zero, which, while being logical to programmers,
3472will cause the subtests 19 to 27 of the lib/posix test may fail.
3473
3474=item Tru64 (aka Digital UNIX, aka DEC OSF/1) lib/sdbm test failure with gcc
3475
3476If compiled with gcc 2.95 the lib/sdbm test will fail (dump core).
3477The cure is to use the vendor cc, it comes with the operating system
3478and produces good code.
3479
3480=back
3481
3482=head2 EBCDIC platforms not fully supported
3483
3484In earlier releases of Perl, EBCDIC environments like OS390 (also
3485known as Open Edition MVS) and VM-ESA were supported. Due to changes
3486required by the UTF-8 (Unicode) support, the EBCDIC platforms are not
3487supported in Perl 5.6.0.
3488
3489The 5.6.1 release improves support for EBCDIC platforms, but they
3490are not fully supported yet.
3491
3492=head2 UNICOS/mk CC failures during Configure run
3493
3494In UNICOS/mk the following errors may appear during the Configure run:
3495
3496 Guessing which symbols your C compiler and preprocessor define...
3497 CC-20 cc: ERROR File = try.c, Line = 3
3498 ...
3499 bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K
3500 ...
3501 4 errors detected in the compilation of "try.c".
3502
3503The culprit is the broken awk of UNICOS/mk. The effect is fortunately
3504rather mild: Perl itself is not adversely affected by the error, only
3505the h2ph utility coming with Perl, and that is rather rarely needed
3506these days.
3507
3508=head2 Arrow operator and arrays
3509
3510When the left argument to the arrow operator C<< -> >> is an array, or
3511the C<scalar> operator operating on an array, the result of the
3512operation must be considered erroneous. For example:
3513
3514 @x->[2]
3515 scalar(@x)->[2]
3516
3517These expressions will get run-time errors in some future release of
3518Perl.
3519
3520=head2 Experimental features
3521
3522As discussed above, many features are still experimental. Interfaces and
3523implementation of these features are subject to change, and in extreme cases,
3524even subject to removal in some future release of Perl. These features
3525include the following:
3526
3527=over 4
3528
3529=item Threads
3530
3531=item Unicode
3532
3533=item 64-bit support
3534
3535=item Lvalue subroutines
3536
3537=item Weak references
3538
3539=item The pseudo-hash data type
3540
3541=item The Compiler suite
3542
3543=item Internal implementation of file globbing
3544
3545=item The DB module
3546
3547=item The regular expression code constructs:
3548
3549C<(?{ code })> and C<(??{ code })>
3550
3551=back
3552
3553=head1 Obsolete Diagnostics
3554
3555=over 4
3556
3557=item Character class syntax [: :] is reserved for future extensions
3558
3559(W) Within regular expression character classes ([]) the syntax beginning
3560with "[:" and ending with ":]" is reserved for future extensions.
3561If you need to represent those character sequences inside a regular
3562expression character class, just quote the square brackets with the
3563backslash: "\[:" and ":\]".
3564
3565=item Ill-formed logical name |%s| in prime_env_iter
3566
3567(W) A warning peculiar to VMS. A logical name was encountered when preparing
3568to iterate over %ENV which violates the syntactic rules governing logical
3569names. Because it cannot be translated normally, it is skipped, and will not
3570appear in %ENV. This may be a benign occurrence, as some software packages
3571might directly modify logical name tables and introduce nonstandard names,
3572or it may indicate that a logical name table has been corrupted.
3573
3574=item In string, @%s now must be written as \@%s
3575
3576The description of this error used to say:
3577
3578 (Someday it will simply assume that an unbackslashed @
3579 interpolates an array.)
3580
3581That day has come, and this fatal error has been removed. It has been
3582replaced by a non-fatal warning instead.
3583See L</Arrays now always interpolate into double-quoted strings> for
3584details.
3585
3586=item Probable precedence problem on %s
3587
3588(W) The compiler found a bareword where it expected a conditional,
3589which often indicates that an || or && was parsed as part of the
3590last argument of the previous construct, for example:
3591
3592 open FOO || die;
3593
3594=item regexp too big
3595
3596(F) The current implementation of regular expressions uses shorts as
3597address offsets within a string. Unfortunately this means that if
3598the regular expression compiles to longer than 32767, it'll blow up.
3599Usually when you want a regular expression this big, there is a better
3600way to do it with multiple statements. See L<perlre>.
3601
3602=item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
3603
3604(D) Perl versions before 5.004 misinterpreted any type marker followed
3605by "$" and a digit. For example, "$$0" was incorrectly taken to mean
3606"${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
3607
3608However, the developers of Perl 5.004 could not fix this bug completely,
3609because at least two widely-used modules depend on the old meaning of
3610"$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
3611old (broken) way inside strings; but it generates this message as a
3612warning. And in Perl 5.005, this special treatment will cease.
3613
3614=back
3615
3616=head1 Reporting Bugs
3617
3618If you find what you think is a bug, you might check the
3619articles recently posted to the comp.lang.perl.misc newsgroup.
3620There may also be information at http://www.perl.com/, the Perl
3621Home Page.
3622
3623If you believe you have an unreported bug, please run the B<perlbug>
3624program included with your release. Be sure to trim your bug down
3625to a tiny but sufficient test case. Your bug report, along with the
3626output of C<perl -V>, will be sent off to perlbug@perl.org to be
3627analysed by the Perl porting team.
3628
3629=head1 SEE ALSO
3630
3631The F<Changes> file for exhaustive details on what changed.
3632
3633The F<INSTALL> file for how to build Perl.
3634
3635The F<README> file for general stuff.
3636
3637The F<Artistic> and F<Copying> files for copyright information.
3638
3639=head1 HISTORY
3640
3641Written by Gurusamy Sarathy <F<gsar@ActiveState.com>>, with many
3642contributions from The Perl Porters.
3643
3644Send omissions or corrections to <F<perlbug@perl.org>>.
3645
3646=cut