1PERL561DELTA(1)        Perl Programmers Reference Guide        PERL561DELTA(1)
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NAME

6       perl561delta - what's new for perl v5.6.1
7

DESCRIPTION

9       This document describes differences between the 5.005 release and the
10       5.6.1 release.
11

Summary of changes between 5.6.0 and 5.6.1

13       This section contains a summary of the changes between the 5.6.0
14       release and the 5.6.1 release.  More details about the changes
15       mentioned here may be found in the Changes files that accompany the
16       Perl source distribution.  See perlhack for pointers to online
17       resources where you can inspect the individual patches described by
18       these changes.
19
20   Security Issues
21       suidperl will not run /bin/mail anymore, because some platforms have a
22       /bin/mail that is vulnerable to buffer overflow attacks.
23
24       Note that suidperl is neither built nor installed by default in any
25       recent version of perl.  Use of suidperl is highly discouraged.  If you
26       think you need it, try alternatives such as sudo first.  See
27       http://www.courtesan.com/sudo/ .
28
29   Core bug fixes
30       This is not an exhaustive list.  It is intended to cover only the
31       significant user-visible changes.
32
33       UNIVERSAL::isa()
34           A bug in the caching mechanism used by UNIVERSAL::isa() that
35           affected base.pm has been fixed.  The bug has existed since the
36           5.005 releases, but wasn't tickled by base.pm in those releases.
37
38       Memory leaks
39           Various cases of memory leaks and attempts to access uninitialized
40           memory have been cured.  See "Known Problems" below for further
41           issues.
42
43       Numeric conversions
44           Numeric conversions did not recognize changes in the string value
45           properly in certain circumstances.
46
47           In other situations, large unsigned numbers (those above 2**31)
48           could sometimes lose their unsignedness, causing bogus results in
49           arithmetic operations.
50
51           Integer modulus on large unsigned integers sometimes returned
52           incorrect values.
53
54           Perl 5.6.0 generated "not a number" warnings on certain conversions
55           where previous versions didn't.
56
57           These problems have all been rectified.
58
59           Infinity is now recognized as a number.
60
61       qw(a\\b)
62           In Perl 5.6.0, qw(a\\b) produced a string with two backslashes
63           instead of one, in a departure from the behavior in previous
64           versions.  The older behavior has been reinstated.
65
66       caller()
67           caller() could cause core dumps in certain situations.  Carp was
68           sometimes affected by this problem.
69
70       Bugs in regular expressions
71           Pattern matches on overloaded values are now handled correctly.
72
73           Perl 5.6.0 parsed m/\x{ab}/ incorrectly, leading to spurious
74           warnings.  This has been corrected.
75
76           The RE engine found in Perl 5.6.0 accidentally pessimised certain
77           kinds of simple pattern matches.  These are now handled better.
78
79           Regular expression debug output (whether through "use re 'debug'"
80           or via "-Dr") now looks better.
81
82           Multi-line matches like ""a\nxb\n" =~ /(?!\A)x/m" were flawed.  The
83           bug has been fixed.
84
85           Use of $& could trigger a core dump under some situations.  This is
86           now avoided.
87
88           Match variables $1 et al., weren't being unset when a pattern match
89           was backtracking, and the anomaly showed up inside "/...(?{ ...
90           }).../" etc.  These variables are now tracked correctly.
91
92           pos() did not return the correct value within s///ge in earlier
93           versions.  This is now handled correctly.
94
95       "slurp" mode
96           readline() on files opened in "slurp" mode could return an extra ""
97           at the end in certain situations.  This has been corrected.
98
99       Autovivification of symbolic references to special variables
100           Autovivification of symbolic references of special variables
101           described in perlvar (as in "${$num}") was accidentally disabled.
102           This works again now.
103
104       Lexical warnings
105           Lexical warnings now propagate correctly into "eval "..."".
106
107           "use warnings qw(FATAL all)" did not work as intended.  This has
108           been corrected.
109
110           Lexical warnings could leak into other scopes in some situations.
111           This is now fixed.
112
113           warnings::enabled() now reports the state of $^W correctly if the
114           caller isn't using lexical warnings.
115
116       Spurious warnings and errors
117           Perl 5.6.0 could emit spurious warnings about redefinition of
118           dl_error() when statically building extensions into perl.  This has
119           been corrected.
120
121           "our" variables could result in bogus "Variable will not stay
122           shared" warnings.  This is now fixed.
123
124           "our" variables of the same name declared in two sibling blocks
125           resulted in bogus warnings about "redeclaration" of the variables.
126           The problem has been corrected.
127
128       glob()
129           Compatibility of the builtin glob() with old csh-based glob has
130           been improved with the addition of GLOB_ALPHASORT option.  See
131           "File::Glob".
132
133           File::Glob::glob() has been renamed to File::Glob::bsd_glob()
134           because the name clashes with the builtin glob().  The older name
135           is still available for compatibility, but is deprecated.
136
137           Spurious syntax errors generated in certain situations, when glob()
138           caused File::Glob to be loaded for the first time, have been fixed.
139
140       Tainting
141           Some cases of inconsistent taint propagation (such as within hash
142           values) have been fixed.
143
144           The tainting behavior of sprintf() has been rationalized.  It does
145           not taint the result of floating point formats anymore, making the
146           behavior consistent with that of string interpolation.
147
148       sort()
149           Arguments to sort() weren't being provided the right wantarray()
150           context.  The comparison block is now run in scalar context, and
151           the arguments to be sorted are always provided list context.
152
153           sort() is also fully reentrant, in the sense that the sort function
154           can itself call sort().  This did not work reliably in previous
155           releases.
156
157       #line directives
158           #line directives now work correctly when they appear at the very
159           beginning of "eval "..."".
160
161       Subroutine prototypes
162           The (\&) prototype now works properly.
163
164       map()
165           map() could get pathologically slow when the result list it
166           generates is larger than the source list.  The performance has been
167           improved for common scenarios.
168
169       Debugger
170           Debugger exit code now reflects the script exit code.
171
172           Condition "0" in breakpoints is now treated correctly.
173
174           The "d" command now checks the line number.
175
176           $. is no longer corrupted by the debugger.
177
178           All debugger output now correctly goes to the socket if RemotePort
179           is set.
180
181       PERL5OPT
182           PERL5OPT can be set to more than one switch group.  Previously, it
183           used to be limited to one group of options only.
184
185       chop()
186           chop(@list) in list context returned the characters chopped in
187           reverse order.  This has been reversed to be in the right order.
188
189       Unicode support
190           Unicode support has seen a large number of incremental
191           improvements, but continues to be highly experimental.  It is not
192           expected to be fully supported in the 5.6.x maintenance releases.
193
194           substr(), join(), repeat(), reverse(), quotemeta() and string
195           concatenation were all handling Unicode strings incorrectly in Perl
196           5.6.0.  This has been corrected.
197
198           Support for "tr///CU" and "tr///UC" etc., have been removed since
199           we realized the interface is broken.  For similar functionality,
200           see "pack" in perlfunc.
201
202           The Unicode Character Database has been updated to version 3.0.1
203           with additions made available to the public as of August 30, 2000.
204
205           The Unicode character classes \p{Blank} and \p{SpacePerl} have been
206           added.  "Blank" is like C isblank(), that is, it contains only
207           "horizontal whitespace" (the space character is, the newline
208           isn't), and the "SpacePerl" is the Unicode equivalent of "\s"
209           (\p{Space} isn't, since that includes the vertical tabulator
210           character, whereas "\s" doesn't.)
211
212           If you are experimenting with Unicode support in perl, the
213           development versions of Perl may have more to offer.  In
214           particular, I/O layers are now available in the development track,
215           but not in the maintenance track, primarily to do backward
216           compatibility issues.  Unicode support is also evolving rapidly on
217           a daily basis in the development track--the maintenance track only
218           reflects the most conservative of these changes.
219
220       64-bit support
221           Support for 64-bit platforms has been improved, but continues to be
222           experimental.  The level of support varies greatly among platforms.
223
224       Compiler
225           The B Compiler and its various backends have had many incremental
226           improvements, but they continue to remain highly experimental.  Use
227           in production environments is discouraged.
228
229           The perlcc tool has been rewritten so that the user interface is
230           much more like that of a C compiler.
231
232           The perlbc tools has been removed.  Use "perlcc -B" instead.
233
234       Lvalue subroutines
235           There have been various bugfixes to support lvalue subroutines
236           better.  However, the feature still remains experimental.
237
238       IO::Socket
239           IO::Socket::INET failed to open the specified port if the service
240           name was not known.  It now correctly uses the supplied port number
241           as is.
242
243       File::Find
244           File::Find now chdir()s correctly when chasing symbolic links.
245
246       xsubpp
247           xsubpp now tolerates embedded POD sections.
248
249       "no Module;"
250           "no Module;" does not produce an error even if Module does not have
251           an unimport() method.  This parallels the behavior of "use" vis-a-
252           vis "import".
253
254       Tests
255           A large number of tests have been added.
256
257   Core features
258       untie() will now call an UNTIE() hook if it exists.  See perltie for
259       details.
260
261       The "-DT" command line switch outputs copious tokenizing information.
262       See perlrun.
263
264       Arrays are now always interpolated in double-quotish strings.
265       Previously, "foo@bar.com" used to be a fatal error at compile time, if
266       an array @bar was not used or declared.  This transitional behavior was
267       intended to help migrate perl4 code, and is deemed to be no longer
268       useful.  See "Arrays now always interpolate into double-quoted
269       strings".
270
271       keys(), each(), pop(), push(), shift(), splice() and unshift() can all
272       be overridden now.
273
274       "my __PACKAGE__ $obj" now does the expected thing.
275
276   Configuration issues
277       On some systems (IRIX and Solaris among them) the system malloc is
278       demonstrably better.  While the defaults haven't been changed in order
279       to retain binary compatibility with earlier releases, you may be better
280       off building perl with "Configure -Uusemymalloc ..." as discussed in
281       the INSTALL file.
282
283       "Configure" has been enhanced in various ways:
284
285       •   Minimizes use of temporary files.
286
287       •   By default, does not link perl with libraries not used by it, such
288           as the various dbm libraries.  SunOS 4.x hints preserve behavior on
289           that platform.
290
291       •   Support for pdp11-style memory models has been removed due to
292           obsolescence.
293
294       •   Building outside the source tree is supported on systems that have
295           symbolic links. This is done by running
296
297               sh /path/to/source/Configure -Dmksymlinks ...
298               make all test install
299
300           in a directory other than the perl source directory.  See INSTALL.
301
302       •   "Configure -S" can be run non-interactively.
303
304   Documentation
305       README.aix, README.solaris and README.macos have been added.
306       README.posix-bc has been renamed to README.bs2000.  These are installed
307       as perlaix, perlsolaris, perlmacos, and perlbs2000 respectively.
308
309       The following pod documents are brand new:
310
311           perlclib    Internal replacements for standard C library functions
312           perldebtut  Perl debugging tutorial
313           perlebcdic  Considerations for running Perl on EBCDIC platforms
314           perlnewmod  Perl modules: preparing a new module for distribution
315           perlrequick Perl regular expressions quick start
316           perlretut   Perl regular expressions tutorial
317           perlutil    utilities packaged with the Perl distribution
318
319       The INSTALL file has been expanded to cover various issues, such as
320       64-bit support.
321
322       A longer list of contributors has been added to the source
323       distribution.  See the file "AUTHORS".
324
325       Numerous other changes have been made to the included documentation and
326       FAQs.
327
328   Bundled modules
329       The following modules have been added.
330
331       B::Concise
332           Walks Perl syntax tree, printing concise info about ops.  See
333           B::Concise.
334
335       File::Temp
336           Returns name and handle of a temporary file safely.  See
337           File::Temp.
338
339       Pod::LaTeX
340           Converts Pod data to formatted LaTeX.  See Pod::LaTeX.
341
342       Pod::Text::Overstrike
343           Converts POD data to formatted overstrike text.  See
344           Pod::Text::Overstrike.
345
346       The following modules have been upgraded.
347
348       CGI CGI v2.752 is now included.
349
350       CPAN
351           CPAN v1.59_54 is now included.
352
353       Class::Struct
354           Various bugfixes have been added.
355
356       DB_File
357           DB_File v1.75 supports newer Berkeley DB versions, among other
358           improvements.
359
360       Devel::Peek
361           Devel::Peek has been enhanced to support dumping of memory
362           statistics, when perl is built with the included malloc().
363
364       File::Find
365           File::Find now supports pre and post-processing of the files in
366           order to sort() them, etc.
367
368       Getopt::Long
369           Getopt::Long v2.25 is included.
370
371       IO::Poll
372           Various bug fixes have been included.
373
374       IPC::Open3
375           IPC::Open3 allows use of numeric file descriptors.
376
377       Math::BigFloat
378           The fmod() function supports modulus operations.  Various bug fixes
379           have also been included.
380
381       Math::Complex
382           Math::Complex handles inf, NaN etc., better.
383
384       Net::Ping
385           ping() could fail on odd number of data bytes, and when the echo
386           service isn't running.  This has been corrected.
387
388       Opcode
389           A memory leak has been fixed.
390
391       Pod::Parser
392           Version 1.13 of the Pod::Parser suite is included.
393
394       Pod::Text
395           Pod::Text and related modules have been upgraded to the versions in
396           podlators suite v2.08.
397
398       SDBM_File
399           On dosish platforms, some keys went missing because of lack of
400           support for files with "holes".  A workaround for the problem has
401           been added.
402
403       Sys::Syslog
404           Various bug fixes have been included.
405
406       Tie::RefHash
407           Now supports Tie::RefHash::Nestable to automagically tie hashref
408           values.
409
410       Tie::SubstrHash
411           Various bug fixes have been included.
412
413   Platform-specific improvements
414       The following new ports are now available.
415
416       NCR MP-RAS
417       NonStop-UX
418
419       Perl now builds under Amdahl UTS.
420
421       Perl has also been verified to build under Amiga OS.
422
423       Support for EPOC has been much improved.  See README.epoc.
424
425       Building perl with -Duseithreads or -Duse5005threads now works under
426       HP-UX 10.20 (previously it only worked under 10.30 or later).  You will
427       need a thread library package installed.  See README.hpux.
428
429       Long doubles should now work under Linux.
430
431       Mac OS Classic is now supported in the mainstream source package.  See
432       README.macos.
433
434       Support for MPE/iX has been updated.  See README.mpeix.
435
436       Support for OS/2 has been improved.  See "os2/Changes" and README.os2.
437
438       Dynamic loading on z/OS (formerly OS/390) has been improved.  See
439       README.os390.
440
441       Support for VMS has seen many incremental improvements, including
442       better support for operators like backticks and system(), and better
443       %ENV handling.  See "README.vms" and perlvms.
444
445       Support for Stratus VOS has been improved.  See "vos/Changes" and
446       README.vos.
447
448       Support for Windows has been improved.
449
450fork() emulation has been improved in various ways, but still
451           continues to be experimental.  See perlfork for known bugs and
452           caveats.
453
454       •   %SIG has been enabled under USE_ITHREADS, but its use is completely
455           unsupported under all configurations.
456
457       •   Borland C++ v5.5 is now a supported compiler that can build Perl.
458           However, the generated binaries continue to be incompatible with
459           those generated by the other supported compilers (GCC and Visual
460           C++).
461
462       •   Non-blocking waits for child processes (or pseudo-processes) are
463           supported via "waitpid($pid, &POSIX::WNOHANG)".
464
465       •   A memory leak in accept() has been fixed.
466
467wait(), waitpid() and backticks now return the correct exit status
468           under Windows 9x.
469
470       •   Trailing new %ENV entries weren't propagated to child processes.
471           This is now fixed.
472
473       •   Current directory entries in %ENV are now correctly propagated to
474           child processes.
475
476       •   Duping socket handles with open(F, ">&MYSOCK") now works under
477           Windows 9x.
478
479       •   The makefiles now provide a single switch to bulk-enable all the
480           features enabled in ActiveState ActivePerl (a popular binary
481           distribution).
482
483Win32::GetCwd() correctly returns C:\ instead of C: when at the
484           drive root.  Other bugs in chdir() and Cwd::cwd() have also been
485           fixed.
486
487fork() correctly returns undef and sets EAGAIN when it runs out of
488           pseudo-process handles.
489
490       •   ExtUtils::MakeMaker now uses $ENV{LIB} to search for libraries.
491
492       •   UNC path handling is better when perl is built to support fork().
493
494       •   A handle leak in socket handling has been fixed.
495
496send() works from within a pseudo-process.
497
498       Unless specifically qualified otherwise, the remainder of this document
499       covers changes between the 5.005 and 5.6.0 releases.
500

Core Enhancements

502   Interpreter cloning, threads, and concurrency
503       Perl 5.6.0 introduces the beginnings of support for running multiple
504       interpreters concurrently in different threads.  In conjunction with
505       the perl_clone() API call, which can be used to selectively duplicate
506       the state of any given interpreter, it is possible to compile a piece
507       of code once in an interpreter, clone that interpreter one or more
508       times, and run all the resulting interpreters in distinct threads.
509
510       On the Windows platform, this feature is used to emulate fork() at the
511       interpreter level.  See perlfork for details about that.
512
513       This feature is still in evolution.  It is eventually meant to be used
514       to selectively clone a subroutine and data reachable from that
515       subroutine in a separate interpreter and run the cloned subroutine in a
516       separate thread.  Since there is no shared data between the
517       interpreters, little or no locking will be needed (unless parts of the
518       symbol table are explicitly shared).  This is obviously intended to be
519       an easy-to-use replacement for the existing threads support.
520
521       Support for cloning interpreters and interpreter concurrency can be
522       enabled using the -Dusethreads Configure option (see win32/Makefile for
523       how to enable it on Windows.)  The resulting perl executable will be
524       functionally identical to one that was built with -Dmultiplicity, but
525       the perl_clone() API call will only be available in the former.
526
527       -Dusethreads enables the cpp macro USE_ITHREADS by default, which in
528       turn enables Perl source code changes that provide a clear separation
529       between the op tree and the data it operates with.  The former is
530       immutable, and can therefore be shared between an interpreter and all
531       of its clones, while the latter is considered local to each
532       interpreter, and is therefore copied for each clone.
533
534       Note that building Perl with the -Dusemultiplicity Configure option is
535       adequate if you wish to run multiple independent interpreters
536       concurrently in different threads.  -Dusethreads only provides the
537       additional functionality of the perl_clone() API call and other support
538       for running cloned interpreters concurrently.
539
540           NOTE: This is an experimental feature.  Implementation details are
541           subject to change.
542
543   Lexically scoped warning categories
544       You can now control the granularity of warnings emitted by perl at a
545       finer level using the "use warnings" pragma.  warnings and perllexwarn
546       have copious documentation on this feature.
547
548   Unicode and UTF-8 support
549       Perl now uses UTF-8 as its internal representation for character
550       strings.  The "utf8" and "bytes" pragmas are used to control this
551       support in the current lexical scope.  See perlunicode, utf8 and bytes
552       for more information.
553
554       This feature is expected to evolve quickly to support some form of I/O
555       disciplines that can be used to specify the kind of input and output
556       data (bytes or characters).  Until that happens, additional modules
557       from CPAN will be needed to complete the toolkit for dealing with
558       Unicode.
559
560           NOTE: This should be considered an experimental feature.  Implementation
561           details are subject to change.
562
563   Support for interpolating named characters
564       The new "\N" escape interpolates named characters within strings.  For
565       example, "Hi! \N{WHITE SMILING FACE}" evaluates to a string with a
566       Unicode smiley face at the end.
567
568   "our" declarations
569       An "our" declaration introduces a value that can be best understood as
570       a lexically scoped symbolic alias to a global variable in the package
571       that was current where the variable was declared.  This is mostly
572       useful as an alternative to the "vars" pragma, but also provides the
573       opportunity to introduce typing and other attributes for such
574       variables.  See "our" in perlfunc.
575
576   Support for strings represented as a vector of ordinals
577       Literals of the form "v1.2.3.4" are now parsed as a string composed of
578       characters with the specified ordinals.  This is an alternative, more
579       readable way to construct (possibly Unicode) strings instead of
580       interpolating characters, as in "\x{1}\x{2}\x{3}\x{4}".  The leading
581       "v" may be omitted if there are more than two ordinals, so 1.2.3 is
582       parsed the same as "v1.2.3".
583
584       Strings written in this form are also useful to represent version
585       "numbers".  It is easy to compare such version "numbers" (which are
586       really just plain strings) using any of the usual string comparison
587       operators "eq", "ne", "lt", "gt", etc., or perform bitwise string
588       operations on them using "|", "&", etc.
589
590       In conjunction with the new $^V magic variable (which contains the perl
591       version as a string), such literals can be used as a readable way to
592       check if you're running a particular version of Perl:
593
594           # this will parse in older versions of Perl also
595           if ($^V and $^V gt v5.6.0) {
596               # new features supported
597           }
598
599       "require" and "use" also have some special magic to support such
600       literals.  They will be interpreted as a version rather than as a
601       module name:
602
603           require v5.6.0;             # croak if $^V lt v5.6.0
604           use v5.6.0;                 # same, but croaks at compile-time
605
606       Alternatively, the "v" may be omitted if there is more than one dot:
607
608           require 5.6.0;
609           use 5.6.0;
610
611       Also, "sprintf" and "printf" support the Perl-specific format flag %v
612       to print ordinals of characters in arbitrary strings:
613
614           printf "v%vd", $^V;         # prints current version, such as "v5.5.650"
615           printf "%*vX", ":", $addr;  # formats IPv6 address
616           printf "%*vb", " ", $bits;  # displays bitstring
617
618       See "Scalar value constructors" in perldata for additional information.
619
620   Improved Perl version numbering system
621       Beginning with Perl version 5.6.0, the version number convention has
622       been changed to a "dotted integer" scheme that is more commonly found
623       in open source projects.
624
625       Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc.
626       The next development series following v5.6.0 will be numbered v5.7.x,
627       beginning with v5.7.0, and the next major production release following
628       v5.6.0 will be v5.8.0.
629
630       The English module now sets $PERL_VERSION to $^V (a string value)
631       rather than $] (a numeric value).  (This is a potential
632       incompatibility.  Send us a report via perlbug if you are affected by
633       this.)
634
635       The v1.2.3 syntax is also now legal in Perl.  See "Support for strings
636       represented as a vector of ordinals" for more on that.
637
638       To cope with the new versioning system's use of at least three
639       significant digits for each version component, the method used for
640       incrementing the subversion number has also changed slightly.  We
641       assume that versions older than v5.6.0 have been incrementing the
642       subversion component in multiples of 10.  Versions after v5.6.0 will
643       increment them by 1.  Thus, using the new notation, 5.005_03 is the
644       "same" as v5.5.30, and the first maintenance version following v5.6.0
645       will be v5.6.1 (which should be read as being equivalent to a floating
646       point value of 5.006_001 in the older format, stored in $]).
647
648   New syntax for declaring subroutine attributes
649       Formerly, if you wanted to mark a subroutine as being a method call or
650       as requiring an automatic lock() when it is entered, you had to declare
651       that with a "use attrs" pragma in the body of the subroutine.  That can
652       now be accomplished with declaration syntax, like this:
653
654           sub mymethod : locked method;
655           ...
656           sub mymethod : locked method {
657               ...
658           }
659
660           sub othermethod :locked :method;
661           ...
662           sub othermethod :locked :method {
663               ...
664           }
665
666       (Note how only the first ":" is mandatory, and whitespace surrounding
667       the ":" is optional.)
668
669       AutoSplit.pm and SelfLoader.pm have been updated to keep the attributes
670       with the stubs they provide.  See attributes.
671
672   File and directory handles can be autovivified
673       Similar to how constructs such as "$x->[0]" autovivify a reference,
674       handle constructors (open(), opendir(), pipe(), socketpair(),
675       sysopen(), socket(), and accept()) now autovivify a file or directory
676       handle if the handle passed to them is an uninitialized scalar
677       variable.  This allows the constructs such as "open(my $fh, ...)" and
678       "open(local $fh,...)"  to be used to create filehandles that will
679       conveniently be closed automatically when the scope ends, provided
680       there are no other references to them.  This largely eliminates the
681       need for typeglobs when opening filehandles that must be passed around,
682       as in the following example:
683
684           sub myopen {
685               open my $fh, "@_"
686                    or die "Can't open '@_': $!";
687               return $fh;
688           }
689
690           {
691               my $f = myopen("</etc/motd");
692               print <$f>;
693               # $f implicitly closed here
694           }
695
696   open() with more than two arguments
697       If open() is passed three arguments instead of two, the second argument
698       is used as the mode and the third argument is taken to be the file
699       name.  This is primarily useful for protecting against unintended magic
700       behavior of the traditional two-argument form.  See "open" in perlfunc.
701
702   64-bit support
703       Any platform that has 64-bit integers either
704
705               (1) natively as longs or ints
706               (2) via special compiler flags
707               (3) using long long or int64_t
708
709       is able to use "quads" (64-bit integers) as follows:
710
711       •   constants (decimal, hexadecimal, octal, binary) in the code
712
713       •   arguments to oct() and hex()
714
715       •   arguments to print(), printf() and sprintf() (flag prefixes ll, L,
716           q)
717
718       •   printed as such
719
720pack() and unpack() "q" and "Q" formats
721
722       •   in basic arithmetics: + - * / % (NOTE: operating close to the
723           limits of the integer values may produce surprising results)
724
725       •   in bit arithmetics: & | ^ ~ << >> (NOTE: these used to be forced to
726           be 32 bits wide but now operate on the full native width.)
727
728vec()
729
730       Note that unless you have the case (a) you will have to configure and
731       compile Perl using the -Duse64bitint Configure flag.
732
733           NOTE: The Configure flags -Duselonglong and -Duse64bits have been
734           deprecated.  Use -Duse64bitint instead.
735
736       There are actually two modes of 64-bitness: the first one is achieved
737       using Configure -Duse64bitint and the second one using Configure
738       -Duse64bitall.  The difference is that the first one is minimal and the
739       second one maximal.  The first works in more places than the second.
740
741       The "use64bitint" does only as much as is required to get 64-bit
742       integers into Perl (this may mean, for example, using "long longs")
743       while your memory may still be limited to 2 gigabytes (because your
744       pointers could still be 32-bit).  Note that the name "64bitint" does
745       not imply that your C compiler will be using 64-bit "int"s (it might,
746       but it doesn't have to): the "use64bitint" means that you will be able
747       to have 64 bits wide scalar values.
748
749       The "use64bitall" goes all the way by attempting to switch also
750       integers (if it can), longs (and pointers) to being 64-bit.  This may
751       create an even more binary incompatible Perl than -Duse64bitint: the
752       resulting executable may not run at all in a 32-bit box, or you may
753       have to reboot/reconfigure/rebuild your operating system to be 64-bit
754       aware.
755
756       Natively 64-bit systems like Alpha and Cray need neither -Duse64bitint
757       nor -Duse64bitall.
758
759       Last but not least: note that due to Perl's habit of always using
760       floating point numbers, the quads are still not true integers.  When
761       quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
762       -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
763       are silently promoted to floating point numbers, after which they will
764       start losing precision (in their lower digits).
765
766           NOTE: 64-bit support is still experimental on most platforms.
767           Existing support only covers the LP64 data model.  In particular, the
768           LLP64 data model is not yet supported.  64-bit libraries and system
769           APIs on many platforms have not stabilized--your mileage may vary.
770
771   Large file support
772       If you have filesystems that support "large files" (files larger than 2
773       gigabytes), you may now also be able to create and access them from
774       Perl.
775
776           NOTE: The default action is to enable large file support, if
777           available on the platform.
778
779       If the large file support is on, and you have a Fcntl constant
780       O_LARGEFILE, the O_LARGEFILE is automatically added to the flags of
781       sysopen().
782
783       Beware that unless your filesystem also supports "sparse files" seeking
784       to umpteen petabytes may be inadvisable.
785
786       Note that in addition to requiring a proper file system to do large
787       files you may also need to adjust your per-process (or your per-system,
788       or per-process-group, or per-user-group) maximum filesize limits before
789       running Perl scripts that try to handle large files, especially if you
790       intend to write such files.
791
792       Finally, in addition to your process/process group maximum filesize
793       limits, you may have quota limits on your filesystems that stop you
794       (your user id or your user group id) from using large files.
795
796       Adjusting your process/user/group/file system/operating system limits
797       is outside the scope of Perl core language.  For process limits, you
798       may try increasing the limits using your shell's limits/limit/ulimit
799       command before running Perl.  The BSD::Resource extension (not included
800       with the standard Perl distribution) may also be of use, it offers the
801       getrlimit/setrlimit interface that can be used to adjust process
802       resource usage limits, including the maximum filesize limit.
803
804   Long doubles
805       In some systems you may be able to use long doubles to enhance the
806       range and precision of your double precision floating point numbers
807       (that is, Perl's numbers).  Use Configure -Duselongdouble to enable
808       this support (if it is available).
809
810   "more bits"
811       You can "Configure -Dusemorebits" to turn on both the 64-bit support
812       and the long double support.
813
814   Enhanced support for sort() subroutines
815       Perl subroutines with a prototype of "($$)", and XSUBs in general, can
816       now be used as sort subroutines.  In either case, the two elements to
817       be compared are passed as normal parameters in @_.  See "sort" in
818       perlfunc.
819
820       For unprototyped sort subroutines, the historical behavior of passing
821       the elements to be compared as the global variables $a and $b remains
822       unchanged.
823
824   "sort $coderef @foo" allowed
825       sort() did not accept a subroutine reference as the comparison function
826       in earlier versions.  This is now permitted.
827
828   File globbing implemented internally
829       Perl now uses the File::Glob implementation of the glob() operator
830       automatically.  This avoids using an external csh process and the
831       problems associated with it.
832
833           NOTE: This is currently an experimental feature.  Interfaces and
834           implementation are subject to change.
835
836   Support for CHECK blocks
837       In addition to "BEGIN", "INIT", "END", "DESTROY" and "AUTOLOAD",
838       subroutines named "CHECK" are now special.  These are queued up during
839       compilation and behave similar to END blocks, except they are called at
840       the end of compilation rather than at the end of execution.  They
841       cannot be called directly.
842
843   POSIX character class syntax [: :] supported
844       For example to match alphabetic characters use /[[:alpha:]]/.  See
845       perlre for details.
846
847   Better pseudo-random number generator
848       In 5.005_0x and earlier, perl's rand() function used the C library
849       rand(3) function.  As of 5.005_52, Configure tests for drand48(),
850       random(), and rand() (in that order) and picks the first one it finds.
851
852       These changes should result in better random numbers from rand().
853
854   Improved "qw//" operator
855       The "qw//" operator is now evaluated at compile time into a true list
856       instead of being replaced with a run time call to split().  This
857       removes the confusing misbehaviour of "qw//" in scalar context, which
858       had inherited that behaviour from split().
859
860       Thus:
861
862           $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
863
864       now correctly prints "3|a", instead of "2|a".
865
866   Better worst-case behavior of hashes
867       Small changes in the hashing algorithm have been implemented in order
868       to improve the distribution of lower order bits in the hashed value.
869       This is expected to yield better performance on keys that are repeated
870       sequences.
871
872   pack() format 'Z' supported
873       The new format type 'Z' is useful for packing and unpacking null-
874       terminated strings.  See "pack" in perlfunc.
875
876   pack() format modifier '!' supported
877       The new format type modifier '!' is useful for packing and unpacking
878       native shorts, ints, and longs.  See "pack" in perlfunc.
879
880   pack() and unpack() support counted strings
881       The template character '/' can be used to specify a counted string type
882       to be packed or unpacked.  See "pack" in perlfunc.
883
884   Comments in pack() templates
885       The '#' character in a template introduces a comment up to end of the
886       line.  This facilitates documentation of pack() templates.
887
888   Weak references
889       In previous versions of Perl, you couldn't cache objects so as to allow
890       them to be deleted if the last reference from outside the cache is
891       deleted.  The reference in the cache would hold a reference count on
892       the object and the objects would never be destroyed.
893
894       Another familiar problem is with circular references.  When an object
895       references itself, its reference count would never go down to zero, and
896       it would not get destroyed until the program is about to exit.
897
898       Weak references solve this by allowing you to "weaken" any reference,
899       that is, make it not count towards the reference count.  When the last
900       non-weak reference to an object is deleted, the object is destroyed and
901       all the weak references to the object are automatically undef-ed.
902
903       To use this feature, you need the Devel::WeakRef package from CPAN,
904       which contains additional documentation.
905
906           NOTE: This is an experimental feature.  Details are subject to change.
907
908   Binary numbers supported
909       Binary numbers are now supported as literals, in s?printf formats, and
910       oct():
911
912           $answer = 0b101010;
913           printf "The answer is: %b\n", oct("0b101010");
914
915   Lvalue subroutines
916       Subroutines can now return modifiable lvalues.  See "Lvalue
917       subroutines" in perlsub.
918
919           NOTE: This is an experimental feature.  Details are subject to change.
920
921   Some arrows may be omitted in calls through references
922       Perl now allows the arrow to be omitted in many constructs involving
923       subroutine calls through references.  For example, "$foo[10]->('foo')"
924       may now be written "$foo[10]('foo')".  This is rather similar to how
925       the arrow may be omitted from "$foo[10]->{'foo'}".  Note however, that
926       the arrow is still required for "foo(10)->('bar')".
927
928   Boolean assignment operators are legal lvalues
929       Constructs such as "($a ||= 2) += 1" are now allowed.
930
931   exists() is supported on subroutine names
932       The exists() builtin now works on subroutine names.  A subroutine is
933       considered to exist if it has been declared (even if implicitly).  See
934       "exists" in perlfunc for examples.
935
936   exists() and delete() are supported on array elements
937       The exists() and delete() builtins now work on simple arrays as well.
938       The behavior is similar to that on hash elements.
939
940       exists() can be used to check whether an array element has been
941       initialized.  This avoids autovivifying array elements that don't
942       exist.  If the array is tied, the EXISTS() method in the corresponding
943       tied package will be invoked.
944
945       delete() may be used to remove an element from the array and return it.
946       The array element at that position returns to its uninitialized state,
947       so that testing for the same element with exists() will return false.
948       If the element happens to be the one at the end, the size of the array
949       also shrinks up to the highest element that tests true for exists(), or
950       0 if none such is found.  If the array is tied, the DELETE() method in
951       the corresponding tied package will be invoked.
952
953       See "exists" in perlfunc and "delete" in perlfunc for examples.
954
955   Pseudo-hashes work better
956       Dereferencing some types of reference values in a pseudo-hash, such as
957       "$ph->{foo}[1]", was accidentally disallowed.  This has been corrected.
958
959       When applied to a pseudo-hash element, exists() now reports whether the
960       specified value exists, not merely if the key is valid.
961
962       delete() now works on pseudo-hashes.  When given a pseudo-hash element
963       or slice it deletes the values corresponding to the keys (but not the
964       keys themselves).  See "Pseudo-hashes: Using an array as a hash" in
965       perlref.
966
967       Pseudo-hash slices with constant keys are now optimized to array
968       lookups at compile-time.
969
970       List assignments to pseudo-hash slices are now supported.
971
972       The "fields" pragma now provides ways to create pseudo-hashes, via
973       fields::new() and fields::phash().  See fields.
974
975           NOTE: The pseudo-hash data type continues to be experimental.
976           Limiting oneself to the interface elements provided by the
977           fields pragma will provide protection from any future changes.
978
979   Automatic flushing of output buffers
980       fork(), exec(), system(), qx//, and pipe open()s now flush buffers of
981       all files opened for output when the operation was attempted.  This
982       mostly eliminates confusing buffering mishaps suffered by users unaware
983       of how Perl internally handles I/O.
984
985       This is not supported on some platforms like Solaris where a suitably
986       correct implementation of fflush(NULL) isn't available.
987
988   Better diagnostics on meaningless filehandle operations
989       Constructs such as open(<FH>) and close(<FH>) are compile time errors.
990       Attempting to read from filehandles that were opened only for writing
991       will now produce warnings (just as writing to read-only filehandles
992       does).
993
994   Where possible, buffered data discarded from duped input filehandle
995       "open(NEW, "<&OLD")" now attempts to discard any data that was
996       previously read and buffered in "OLD" before duping the handle.  On
997       platforms where doing this is allowed, the next read operation on "NEW"
998       will return the same data as the corresponding operation on "OLD".
999       Formerly, it would have returned the data from the start of the
1000       following disk block instead.
1001
1002   eof() has the same old magic as <>
1003       eof() would return true if no attempt to read from "<>" had yet been
1004       made.  eof() has been changed to have a little magic of its own, it now
1005       opens the "<>" files.
1006
1007   binmode() can be used to set :crlf and :raw modes
1008       binmode() now accepts a second argument that specifies a discipline for
1009       the handle in question.  The two pseudo-disciplines ":raw" and ":crlf"
1010       are currently supported on DOS-derivative platforms.  See "binmode" in
1011       perlfunc and open.
1012
1013   "-T" filetest recognizes UTF-8 encoded files as "text"
1014       The algorithm used for the "-T" filetest has been enhanced to correctly
1015       identify UTF-8 content as "text".
1016
1017   system(), backticks and pipe open now reflect exec() failure
1018       On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
1019       etc., are implemented via fork() and exec().  When the underlying
1020       exec() fails, earlier versions did not report the error properly, since
1021       the exec() happened to be in a different process.
1022
1023       The child process now communicates with the parent about the error in
1024       launching the external command, which allows these constructs to return
1025       with their usual error value and set $!.
1026
1027   Improved diagnostics
1028       Line numbers are no longer suppressed (under most likely circumstances)
1029       during the global destruction phase.
1030
1031       Diagnostics emitted from code running in threads other than the main
1032       thread are now accompanied by the thread ID.
1033
1034       Embedded null characters in diagnostics now actually show up.  They
1035       used to truncate the message in prior versions.
1036
1037       $foo::a and $foo::b are now exempt from "possible typo" warnings only
1038       if sort() is encountered in package "foo".
1039
1040       Unrecognized alphabetic escapes encountered when parsing quote
1041       constructs now generate a warning, since they may take on new semantics
1042       in later versions of Perl.
1043
1044       Many diagnostics now report the internal operation in which the warning
1045       was provoked, like so:
1046
1047           Use of uninitialized value in concatenation (.) at (eval 1) line 1.
1048           Use of uninitialized value in print at (eval 1) line 1.
1049
1050       Diagnostics  that occur within eval may also report the file and line
1051       number where the eval is located, in addition to the eval sequence
1052       number and the line number within the evaluated text itself.  For
1053       example:
1054
1055           Not enough arguments for scalar at (eval 4)[newlib/perl5db.pl:1411] line 2, at EOF
1056
1057   Diagnostics follow STDERR
1058       Diagnostic output now goes to whichever file the "STDERR" handle is
1059       pointing at, instead of always going to the underlying C runtime
1060       library's "stderr".
1061
1062   More consistent close-on-exec behavior
1063       On systems that support a close-on-exec flag on filehandles, the flag
1064       is now set for any handles created by pipe(), socketpair(), socket(),
1065       and accept(), if that is warranted by the value of $^F that may be in
1066       effect.  Earlier versions neglected to set the flag for handles created
1067       with these operators.  See "pipe" in perlfunc, "socketpair" in
1068       perlfunc, "socket" in perlfunc, "accept" in perlfunc, and "$^F" in
1069       perlvar.
1070
1071   syswrite() ease-of-use
1072       The length argument of syswrite() has become optional.
1073
1074   Better syntax checks on parenthesized unary operators
1075       Expressions such as:
1076
1077           print defined(&foo,&bar,&baz);
1078           print uc("foo","bar","baz");
1079           undef($foo,&bar);
1080
1081       used to be accidentally allowed in earlier versions, and produced
1082       unpredictable behaviour.  Some produced ancillary warnings when used in
1083       this way; others silently did the wrong thing.
1084
1085       The parenthesized forms of most unary operators that expect a single
1086       argument now ensure that they are not called with more than one
1087       argument, making the cases shown above syntax errors.  The usual
1088       behaviour of:
1089
1090           print defined &foo, &bar, &baz;
1091           print uc "foo", "bar", "baz";
1092           undef $foo, &bar;
1093
1094       remains unchanged.  See perlop.
1095
1096   Bit operators support full native integer width
1097       The bit operators (& | ^ ~ << >>) now operate on the full native
1098       integral width (the exact size of which is available in
1099       $Config{ivsize}).  For example, if your platform is either natively
1100       64-bit or if Perl has been configured to use 64-bit integers, these
1101       operations apply to 8 bytes (as opposed to 4 bytes on 32-bit
1102       platforms).  For portability, be sure to mask off the excess bits in
1103       the result of unary "~", e.g., "~$x & 0xffffffff".
1104
1105   Improved security features
1106       More potentially unsafe operations taint their results for improved
1107       security.
1108
1109       The "passwd" and "shell" fields returned by the getpwent(), getpwnam(),
1110       and getpwuid() are now tainted, because the user can affect their own
1111       encrypted password and login shell.
1112
1113       The variable modified by shmread(), and messages returned by msgrcv()
1114       (and its object-oriented interface IPC::SysV::Msg::rcv) are also
1115       tainted, because other untrusted processes can modify messages and
1116       shared memory segments for their own nefarious purposes.
1117
1118   More functional bareword prototype (*)
1119       Bareword prototypes have been rationalized to enable them to be used to
1120       override builtins that accept barewords and interpret them in a special
1121       way, such as "require" or "do".
1122
1123       Arguments prototyped as "*" will now be visible within the subroutine
1124       as either a simple scalar or as a reference to a typeglob.  See
1125       "Prototypes" in perlsub.
1126
1127   "require" and "do" may be overridden
1128       "require" and "do 'file'" operations may be overridden locally by
1129       importing subroutines of the same name into the current package (or
1130       globally by importing them into the CORE::GLOBAL:: namespace).
1131       Overriding "require" will also affect "use", provided the override is
1132       visible at compile-time.  See "Overriding Built-in Functions" in
1133       perlsub.
1134
1135   $^X variables may now have names longer than one character
1136       Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
1137       error.  Now variable names that begin with a control character may be
1138       arbitrarily long.  However, for compatibility reasons, these variables
1139       must be written with explicit braces, as "${^XY}" for example.
1140       "${^XYZ}" is synonymous with ${"\cXYZ"}.  Variable names with more than
1141       one control character, such as "${^XY^Z}", are illegal.
1142
1143       The old syntax has not changed.  As before, `^X' may be either a
1144       literal control-X character or the two-character sequence `caret' plus
1145       `X'.  When braces are omitted, the variable name stops after the
1146       control character.  Thus "$^XYZ" continues to be synonymous with "$^X .
1147       "YZ"" as before.
1148
1149       As before, lexical variables may not have names beginning with control
1150       characters.  As before, variables whose names begin with a control
1151       character are always forced to be in package `main'.  All such
1152       variables are reserved for future extensions, except those that begin
1153       with "^_", which may be used by user programs and are guaranteed not to
1154       acquire special meaning in any future version of Perl.
1155
1156   New variable $^C reflects "-c" switch
1157       $^C has a boolean value that reflects whether perl is being run in
1158       compile-only mode (i.e. via the "-c" switch).  Since BEGIN blocks are
1159       executed under such conditions, this variable enables perl code to
1160       determine whether actions that make sense only during normal running
1161       are warranted.  See perlvar.
1162
1163   New variable $^V contains Perl version as a string
1164       $^V contains the Perl version number as a string composed of characters
1165       whose ordinals match the version numbers, i.e. v5.6.0.  This may be
1166       used in string comparisons.
1167
1168       See "Support for strings represented as a vector of ordinals" for an
1169       example.
1170
1171   Optional Y2K warnings
1172       If Perl is built with the cpp macro "PERL_Y2KWARN" defined, it emits
1173       optional warnings when concatenating the number 19 with another number.
1174
1175       This behavior must be specifically enabled when running Configure.  See
1176       INSTALL and README.Y2K.
1177
1178   Arrays now always interpolate into double-quoted strings
1179       In double-quoted strings, arrays now interpolate, no matter what.  The
1180       behavior in earlier versions of perl 5 was that arrays would
1181       interpolate into strings if the array had been mentioned before the
1182       string was compiled, and otherwise Perl would raise a fatal compile-
1183       time error.  In versions 5.000 through 5.003, the error was
1184
1185               Literal @example now requires backslash
1186
1187       In versions 5.004_01 through 5.6.0, the error was
1188
1189               In string, @example now must be written as \@example
1190
1191       The idea here was to get people into the habit of writing
1192       "fred\@example.com" when they wanted a literal "@" sign, just as they
1193       have always written "Give me back my \$5" when they wanted a literal
1194       "$" sign.
1195
1196       Starting with 5.6.1, when Perl now sees an "@" sign in a double-quoted
1197       string, it always attempts to interpolate an array, regardless of
1198       whether or not the array has been used or declared already.  The fatal
1199       error has been downgraded to an optional warning:
1200
1201               Possible unintended interpolation of @example in string
1202
1203       This warns you that "fred@example.com" is going to turn into "fred.com"
1204       if you don't backslash the "@".  See
1205       http://perl.plover.com/at-error.html for more details about the history
1206       here.
1207
1208   @- and @+ provide starting/ending offsets of regex submatches
1209       The new magic variables @- and @+ provide the starting and ending
1210       offsets, respectively, of $&, $1, $2, etc.  See perlvar for details.
1211

Modules and Pragmata

1213   Modules
1214       attributes
1215           While used internally by Perl as a pragma, this module also
1216           provides a way to fetch subroutine and variable attributes.  See
1217           attributes.
1218
1219       B   The Perl Compiler suite has been extensively reworked for this
1220           release.  More of the standard Perl test suite passes when run
1221           under the Compiler, but there is still a significant way to go to
1222           achieve production quality compiled executables.
1223
1224               NOTE: The Compiler suite remains highly experimental.  The
1225               generated code may not be correct, even when it manages to execute
1226               without errors.
1227
1228       Benchmark
1229           Overall, Benchmark results exhibit lower average error and better
1230           timing accuracy.
1231
1232           You can now run tests for n seconds instead of guessing the right
1233           number of tests to run: e.g., timethese(-5, ...) will run each code
1234           for at least 5 CPU seconds.  Zero as the "number of repetitions"
1235           means "for at least 3 CPU seconds".  The output format has also
1236           changed.  For example:
1237
1238              use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
1239
1240           will now output something like this:
1241
1242              Benchmark: running a, b, each for at least 5 CPU seconds...
1243                       a:  5 wallclock secs ( 5.77 usr +  0.00 sys =  5.77 CPU) @ 200551.91/s (n=1156516)
1244                       b:  4 wallclock secs ( 5.00 usr +  0.02 sys =  5.02 CPU) @ 159605.18/s (n=800686)
1245
1246           New features: "each for at least N CPU seconds...", "wallclock
1247           secs", and the "@ operations/CPU second (n=operations)".
1248
1249           timethese() now returns a reference to a hash of Benchmark objects
1250           containing the test results, keyed on the names of the tests.
1251
1252           timethis() now returns the iterations field in the Benchmark result
1253           object instead of 0.
1254
1255           timethese(), timethis(), and the new cmpthese() (see below) can
1256           also take a format specifier of 'none' to suppress output.
1257
1258           A new function countit() is just like timeit() except that it takes
1259           a TIME instead of a COUNT.
1260
1261           A new function cmpthese() prints a chart comparing the results of
1262           each test returned from a timethese() call.  For each possible pair
1263           of tests, the percentage speed difference (iters/sec or
1264           seconds/iter) is shown.
1265
1266           For other details, see Benchmark.
1267
1268       ByteLoader
1269           The ByteLoader is a dedicated extension to generate and run Perl
1270           bytecode.  See ByteLoader.
1271
1272       constant
1273           References can now be used.
1274
1275           The new version also allows a leading underscore in constant names,
1276           but disallows a double leading underscore (as in "__LINE__").  Some
1277           other names are disallowed or warned against, including BEGIN, END,
1278           etc.  Some names which were forced into main:: used to fail
1279           silently in some cases; now they're fatal (outside of main::) and
1280           an optional warning (inside of main::).  The ability to detect
1281           whether a constant had been set with a given name has been added.
1282
1283           See constant.
1284
1285       charnames
1286           This pragma implements the "\N" string escape.  See charnames.
1287
1288       Data::Dumper
1289           A "Maxdepth" setting can be specified to avoid venturing too deeply
1290           into deep data structures.  See Data::Dumper.
1291
1292           The XSUB implementation of Dump() is now automatically called if
1293           the "Useqq" setting is not in use.
1294
1295           Dumping "qr//" objects works correctly.
1296
1297       DB  "DB" is an experimental module that exposes a clean abstraction to
1298           Perl's debugging API.
1299
1300       DB_File
1301           DB_File can now be built with Berkeley DB versions 1, 2 or 3.  See
1302           "ext/DB_File/Changes".
1303
1304       Devel::DProf
1305           Devel::DProf, a Perl source code profiler has been added.  See
1306           Devel::DProf and dprofpp.
1307
1308       Devel::Peek
1309           The Devel::Peek module provides access to the internal
1310           representation of Perl variables and data.  It is a data debugging
1311           tool for the XS programmer.
1312
1313       Dumpvalue
1314           The Dumpvalue module provides screen dumps of Perl data.
1315
1316       DynaLoader
1317           DynaLoader now supports a dl_unload_file() function on platforms
1318           that support unloading shared objects using dlclose().
1319
1320           Perl can also optionally arrange to unload all extension shared
1321           objects loaded by Perl.  To enable this, build Perl with the
1322           Configure option "-Accflags=-DDL_UNLOAD_ALL_AT_EXIT".  (This maybe
1323           useful if you are using Apache with mod_perl.)
1324
1325       English
1326           $PERL_VERSION now stands for $^V (a string value) rather than for
1327           $] (a numeric value).
1328
1329       Env Env now supports accessing environment variables like PATH as array
1330           variables.
1331
1332       Fcntl
1333           More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
1334           large file (more than 4GB) access (NOTE: the O_LARGEFILE is
1335           automatically added to sysopen() flags if large file support has
1336           been configured, as is the default), Free/Net/OpenBSD locking
1337           behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the
1338           combined mask of O_RDONLY, O_WRONLY, and O_RDWR.  The
1339           seek()/sysseek() constants SEEK_SET, SEEK_CUR, and SEEK_END are
1340           available via the ":seek" tag.  The chmod()/stat() S_IF* constants
1341           and S_IS* functions are available via the ":mode" tag.
1342
1343       File::Compare
1344           A compare_text() function has been added, which allows custom
1345           comparison functions.  See File::Compare.
1346
1347       File::Find
1348           File::Find now works correctly when the wanted() function is either
1349           autoloaded or is a symbolic reference.
1350
1351           A bug that caused File::Find to lose track of the working directory
1352           when pruning top-level directories has been fixed.
1353
1354           File::Find now also supports several other options to control its
1355           behavior.  It can follow symbolic links if the "follow" option is
1356           specified.  Enabling the "no_chdir" option will make File::Find
1357           skip changing the current directory when walking directories.  The
1358           "untaint" flag can be useful when running with taint checks
1359           enabled.
1360
1361           See File::Find.
1362
1363       File::Glob
1364           This extension implements BSD-style file globbing.  By default, it
1365           will also be used for the internal implementation of the glob()
1366           operator.  See File::Glob.
1367
1368       File::Spec
1369           New methods have been added to the File::Spec module: devnull()
1370           returns the name of the null device (/dev/null on Unix) and
1371           tmpdir() the name of the temp directory (normally /tmp on Unix).
1372           There are now also methods to convert between absolute and relative
1373           filenames: abs2rel() and rel2abs().  For compatibility with
1374           operating systems that specify volume names in file paths, the
1375           splitpath(), splitdir(), and catdir() methods have been added.
1376
1377       File::Spec::Functions
1378           The new File::Spec::Functions modules provides a function interface
1379           to the File::Spec module.  Allows shorthand
1380
1381               $fullname = catfile($dir1, $dir2, $file);
1382
1383           instead of
1384
1385               $fullname = File::Spec->catfile($dir1, $dir2, $file);
1386
1387       Getopt::Long
1388           Getopt::Long licensing has changed to allow the Perl Artistic
1389           License as well as the GPL. It used to be GPL only, which got in
1390           the way of non-GPL applications that wanted to use Getopt::Long.
1391
1392           Getopt::Long encourages the use of Pod::Usage to produce help
1393           messages. For example:
1394
1395               use Getopt::Long;
1396               use Pod::Usage;
1397               my $man = 0;
1398               my $help = 0;
1399               GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
1400               pod2usage(1) if $help;
1401               pod2usage(-exitstatus => 0, -verbose => 2) if $man;
1402
1403               __END__
1404
1405               =head1 NAME
1406
1407               sample - Using Getopt::Long and Pod::Usage
1408
1409               =head1 SYNOPSIS
1410
1411               sample [options] [file ...]
1412
1413                Options:
1414                  -help            brief help message
1415                  -man             full documentation
1416
1417               =head1 OPTIONS
1418
1419               =over 8
1420
1421               =item B<-help>
1422
1423               Print a brief help message and exits.
1424
1425               =item B<-man>
1426
1427               Prints the manual page and exits.
1428
1429               =back
1430
1431               =head1 DESCRIPTION
1432
1433               B<This program> will read the given input file(s) and do something
1434               useful with the contents thereof.
1435
1436               =cut
1437
1438           See Pod::Usage for details.
1439
1440           A bug that prevented the non-option call-back <> from being
1441           specified as the first argument has been fixed.
1442
1443           To specify the characters < and > as option starters, use ><. Note,
1444           however, that changing option starters is strongly deprecated.
1445
1446       IO  write() and syswrite() will now accept a single-argument form of
1447           the call, for consistency with Perl's syswrite().
1448
1449           You can now create a TCP-based IO::Socket::INET without forcing a
1450           connect attempt.  This allows you to configure its options (like
1451           making it non-blocking) and then call connect() manually.
1452
1453           A bug that prevented the IO::Socket::protocol() accessor from ever
1454           returning the correct value has been corrected.
1455
1456           IO::Socket::connect now uses non-blocking IO instead of alarm() to
1457           do connect timeouts.
1458
1459           IO::Socket::accept now uses select() instead of alarm() for doing
1460           timeouts.
1461
1462           IO::Socket::INET->new now sets $! correctly on failure. $@ is still
1463           set for backwards compatibility.
1464
1465       JPL Java Perl Lingo is now distributed with Perl.  See jpl/README for
1466           more information.
1467
1468       lib "use lib" now weeds out any trailing duplicate entries.  "no lib"
1469           removes all named entries.
1470
1471       Math::BigInt
1472           The bitwise operations "<<", ">>", "&", "|", and "~" are now
1473           supported on bigints.
1474
1475       Math::Complex
1476           The accessor methods Re, Im, arg, abs, rho, and theta can now also
1477           act as mutators (accessor $z->Re(), mutator $z->Re(3)).
1478
1479           The class method "display_format" and the corresponding object
1480           method "display_format", in addition to accepting just one
1481           argument, now can also accept a parameter hash.  Recognized keys of
1482           a parameter hash are "style", which corresponds to the old one
1483           parameter case, and two new parameters: "format", which is a
1484           printf()-style format string (defaults usually to "%.15g", you can
1485           revert to the default by setting the format string to "undef") used
1486           for both parts of a complex number, and "polar_pretty_print"
1487           (defaults to true), which controls whether an attempt is made to
1488           try to recognize small multiples and rationals of pi (2pi, pi/2) at
1489           the argument (angle) of a polar complex number.
1490
1491           The potentially disruptive change is that in list context both
1492           methods now return the parameter hash, instead of only the value of
1493           the "style" parameter.
1494
1495       Math::Trig
1496           A little bit of radial trigonometry (cylindrical and spherical),
1497           radial coordinate conversions, and the great circle distance were
1498           added.
1499
1500       Pod::Parser, Pod::InputObjects
1501           Pod::Parser is a base class for parsing and selecting sections of
1502           pod documentation from an input stream.  This module takes care of
1503           identifying pod paragraphs and commands in the input and hands off
1504           the parsed paragraphs and commands to user-defined methods which
1505           are free to interpret or translate them as they see fit.
1506
1507           Pod::InputObjects defines some input objects needed by Pod::Parser,
1508           and for advanced users of Pod::Parser that need more about a
1509           command besides its name and text.
1510
1511           As of release 5.6.0 of Perl, Pod::Parser is now the officially
1512           sanctioned "base parser code" recommended for use by all pod2xxx
1513           translators.  Pod::Text (pod2text) and Pod::Man (pod2man) have
1514           already been converted to use Pod::Parser and efforts to convert
1515           Pod::HTML (pod2html) are already underway.  For any questions or
1516           comments about pod parsing and translating issues and utilities,
1517           please use the pod-people@perl.org mailing list.
1518
1519           For further information, please see Pod::Parser and
1520           Pod::InputObjects.
1521
1522       Pod::Checker, podchecker
1523           This utility checks pod files for correct syntax, according to
1524           perlpod.  Obvious errors are flagged as such, while warnings are
1525           printed for mistakes that can be handled gracefully.  The checklist
1526           is not complete yet.  See Pod::Checker.
1527
1528       Pod::ParseUtils, Pod::Find
1529           These modules provide a set of gizmos that are useful mainly for
1530           pod translators.  Pod::Find traverses directory structures and
1531           returns found pod files, along with their canonical names (like
1532           "File::Spec::Unix").  Pod::ParseUtils contains Pod::List (useful
1533           for storing pod list information), Pod::Hyperlink (for parsing the
1534           contents of "L<>" sequences) and Pod::Cache (for caching
1535           information about pod files, e.g., link nodes).
1536
1537       Pod::Select, podselect
1538           Pod::Select is a subclass of Pod::Parser which provides a function
1539           named "podselect()" to filter out user-specified sections of raw
1540           pod documentation from an input stream. podselect is a script that
1541           provides access to Pod::Select from other scripts to be used as a
1542           filter.  See Pod::Select.
1543
1544       Pod::Usage, pod2usage
1545           Pod::Usage provides the function "pod2usage()" to print usage
1546           messages for a Perl script based on its embedded pod documentation.
1547           The pod2usage() function is generally useful to all script authors
1548           since it lets them write and maintain a single source (the pods)
1549           for documentation, thus removing the need to create and maintain
1550           redundant usage message text consisting of information already in
1551           the pods.
1552
1553           There is also a pod2usage script which can be used from other kinds
1554           of scripts to print usage messages from pods (even for non-Perl
1555           scripts with pods embedded in comments).
1556
1557           For details and examples, please see Pod::Usage.
1558
1559       Pod::Text and Pod::Man
1560           Pod::Text has been rewritten to use Pod::Parser.  While pod2text()
1561           is still available for backwards compatibility, the module now has
1562           a new preferred interface.  See Pod::Text for the details.  The new
1563           Pod::Text module is easily subclassed for tweaks to the output, and
1564           two such subclasses (Pod::Text::Termcap for man-page-style bold and
1565           underlining using termcap information, and Pod::Text::Color for
1566           markup with ANSI color sequences) are now standard.
1567
1568           pod2man has been turned into a module, Pod::Man, which also uses
1569           Pod::Parser.  In the process, several outstanding bugs related to
1570           quotes in section headers, quoting of code escapes, and nested
1571           lists have been fixed.  pod2man is now a wrapper script around this
1572           module.
1573
1574       SDBM_File
1575           An EXISTS method has been added to this module (and sdbm_exists()
1576           has been added to the underlying sdbm library), so one can now call
1577           exists on an SDBM_File tied hash and get the correct result, rather
1578           than a runtime error.
1579
1580           A bug that may have caused data loss when more than one disk block
1581           happens to be read from the database in a single FETCH() has been
1582           fixed.
1583
1584       Sys::Syslog
1585           Sys::Syslog now uses XSUBs to access facilities from syslog.h so it
1586           no longer requires syslog.ph to exist.
1587
1588       Sys::Hostname
1589           Sys::Hostname now uses XSUBs to call the C library's gethostname()
1590           or uname() if they exist.
1591
1592       Term::ANSIColor
1593           Term::ANSIColor is a very simple module to provide easy and
1594           readable access to the ANSI color and highlighting escape
1595           sequences, supported by most ANSI terminal emulators.  It is now
1596           included standard.
1597
1598       Time::Local
1599           The timelocal() and timegm() functions used to silently return
1600           bogus results when the date fell outside the machine's integer
1601           range.  They now consistently croak() if the date falls in an
1602           unsupported range.
1603
1604       Win32
1605           The error return value in list context has been changed for all
1606           functions that return a list of values.  Previously these functions
1607           returned a list with a single element "undef" if an error occurred.
1608           Now these functions return the empty list in these situations.
1609           This applies to the following functions:
1610
1611               Win32::FsType
1612               Win32::GetOSVersion
1613
1614           The remaining functions are unchanged and continue to return
1615           "undef" on error even in list context.
1616
1617           The Win32::SetLastError(ERROR) function has been added as a
1618           complement to the Win32::GetLastError() function.
1619
1620           The new Win32::GetFullPathName(FILENAME) returns the full absolute
1621           pathname for FILENAME in scalar context.  In list context it
1622           returns a two-element list containing the fully qualified directory
1623           name and the filename.  See Win32.
1624
1625       XSLoader
1626           The XSLoader extension is a simpler alternative to DynaLoader.  See
1627           XSLoader.
1628
1629       DBM Filters
1630           A new feature called "DBM Filters" has been added to all the DBM
1631           modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
1632           DBM Filters add four new methods to each DBM module:
1633
1634               filter_store_key
1635               filter_store_value
1636               filter_fetch_key
1637               filter_fetch_value
1638
1639           These can be used to filter key-value pairs before the pairs are
1640           written to the database or just after they are read from the
1641           database.  See perldbmfilter for further information.
1642
1643   Pragmata
1644       "use attrs" is now obsolete, and is only provided for backward-
1645       compatibility.  It's been replaced by the "sub : attributes" syntax.
1646       See "Subroutine Attributes" in perlsub and attributes.
1647
1648       Lexical warnings pragma, "use warnings;", to control optional warnings.
1649       See perllexwarn.
1650
1651       "use filetest" to control the behaviour of filetests ("-r" "-w" ...).
1652       Currently only one subpragma implemented, "use filetest 'access';",
1653       that uses access(2) or equivalent to check permissions instead of using
1654       stat(2) as usual.  This matters in filesystems where there are ACLs
1655       (access control lists): the stat(2) might lie, but access(2) knows
1656       better.
1657
1658       The "open" pragma can be used to specify default disciplines for handle
1659       constructors (e.g. open()) and for qx//.  The two pseudo-disciplines
1660       ":raw" and ":crlf" are currently supported on DOS-derivative platforms
1661       (i.e. where binmode is not a no-op).  See also "binmode() can be used
1662       to set :crlf and :raw modes".
1663

Utility Changes

1665   dprofpp
1666       "dprofpp" is used to display profile data generated using
1667       "Devel::DProf".  See dprofpp.
1668
1669   find2perl
1670       The "find2perl" utility now uses the enhanced features of the
1671       File::Find module.  The -depth and -follow options are supported.  Pod
1672       documentation is also included in the script.
1673
1674   h2xs
1675       The "h2xs" tool can now work in conjunction with "C::Scan" (available
1676       from CPAN) to automatically parse real-life header files.  The "-M",
1677       "-a", "-k", and "-o" options are new.
1678
1679   perlcc
1680       "perlcc" now supports the C and Bytecode backends.  By default, it
1681       generates output from the simple C backend rather than the optimized C
1682       backend.
1683
1684       Support for non-Unix platforms has been improved.
1685
1686   perldoc
1687       "perldoc" has been reworked to avoid possible security holes.  It will
1688       not by default let itself be run as the superuser, but you may still
1689       use the -U switch to try to make it drop privileges first.
1690
1691   The Perl Debugger
1692       Many bug fixes and enhancements were added to perl5db.pl, the Perl
1693       debugger.  The help documentation was rearranged.  New commands include
1694       "< ?", "> ?", and "{ ?" to list out current actions, "man docpage" to
1695       run your doc viewer on some perl docset, and support for quoted
1696       options.  The help information was rearranged, and should be viewable
1697       once again if you're using less as your pager.  A serious security hole
1698       was plugged--you should immediately remove all older versions of the
1699       Perl debugger as installed in previous releases, all the way back to
1700       perl3, from your system to avoid being bitten by this.
1701

Improved Documentation

1703       Many of the platform-specific README files are now part of the perl
1704       installation.  See perl for the complete list.
1705
1706       perlapi.pod
1707           The official list of public Perl API functions.
1708
1709       perlboot.pod
1710           A tutorial for beginners on object-oriented Perl.
1711
1712       perlcompile.pod
1713           An introduction to using the Perl Compiler suite.
1714
1715       perldbmfilter.pod
1716           A howto document on using the DBM filter facility.
1717
1718       perldebug.pod
1719           All material unrelated to running the Perl debugger, plus all low-
1720           level guts-like details that risked crushing the casual user of the
1721           debugger, have been relocated from the old manpage to the next
1722           entry below.
1723
1724       perldebguts.pod
1725           This new manpage contains excessively low-level material not
1726           related to the Perl debugger, but slightly related to debugging
1727           Perl itself.  It also contains some arcane internal details of how
1728           the debugging process works that may only be of interest to
1729           developers of Perl debuggers.
1730
1731       perlfork.pod
1732           Notes on the fork() emulation currently available for the Windows
1733           platform.
1734
1735       perlfilter.pod
1736           An introduction to writing Perl source filters.
1737
1738       perlhack.pod
1739           Some guidelines for hacking the Perl source code.
1740
1741       perlintern.pod
1742           A list of internal functions in the Perl source code.  (List is
1743           currently empty.)
1744
1745       perllexwarn.pod
1746           Introduction and reference information about lexically scoped
1747           warning categories.
1748
1749       perlnumber.pod
1750           Detailed information about numbers as they are represented in Perl.
1751
1752       perlopentut.pod
1753           A tutorial on using open() effectively.
1754
1755       perlreftut.pod
1756           A tutorial that introduces the essentials of references.
1757
1758       perltootc.pod
1759           A tutorial on managing class data for object modules.
1760
1761       perltodo.pod
1762           Discussion of the most often wanted features that may someday be
1763           supported in Perl.
1764
1765       perlunicode.pod
1766           An introduction to Unicode support features in Perl.
1767

Performance enhancements

1769   Simple sort() using { $a <=> $b } and the like are optimized
1770       Many common sort() operations using a simple inlined block are now
1771       optimized for faster performance.
1772
1773   Optimized assignments to lexical variables
1774       Certain operations in the RHS of assignment statements have been
1775       optimized to directly set the lexical variable on the LHS, eliminating
1776       redundant copying overheads.
1777
1778   Faster subroutine calls
1779       Minor changes in how subroutine calls are handled internally provide
1780       marginal improvements in performance.
1781
1782   delete(), each(), values() and hash iteration are faster
1783       The hash values returned by delete(), each(), values() and hashes in a
1784       list context are the actual values in the hash, instead of copies.
1785       This results in significantly better performance, because it eliminates
1786       needless copying in most situations.
1787

Installation and Configuration Improvements

1789   -Dusethreads means something different
1790       The -Dusethreads flag now enables the experimental interpreter-based
1791       thread support by default.  To get the flavor of experimental threads
1792       that was in 5.005 instead, you need to run Configure with "-Dusethreads
1793       -Duse5005threads".
1794
1795       As of v5.6.0, interpreter-threads support is still lacking a way to
1796       create new threads from Perl (i.e., "use Thread;" will not work with
1797       interpreter threads).  "use Thread;" continues to be available when you
1798       specify the -Duse5005threads option to Configure, bugs and all.
1799
1800           NOTE: Support for threads continues to be an experimental feature.
1801           Interfaces and implementation are subject to sudden and drastic changes.
1802
1803   New Configure flags
1804       The following new flags may be enabled on the Configure command line by
1805       running Configure with "-Dflag".
1806
1807           usemultiplicity
1808           usethreads useithreads      (new interpreter threads: no Perl API yet)
1809           usethreads use5005threads   (threads as they were in 5.005)
1810
1811           use64bitint                 (equal to now deprecated 'use64bits')
1812           use64bitall
1813
1814           uselongdouble
1815           usemorebits
1816           uselargefiles
1817           usesocks                    (only SOCKS v5 supported)
1818
1819   Threadedness and 64-bitness now more daring
1820       The Configure options enabling the use of threads and the use of
1821       64-bitness are now more daring in the sense that they no more have an
1822       explicit list of operating systems of known threads/64-bit
1823       capabilities.  In other words: if your operating system has the
1824       necessary APIs and datatypes, you should be able just to go ahead and
1825       use them, for threads by Configure -Dusethreads, and for 64 bits either
1826       explicitly by Configure -Duse64bitint or implicitly if your system has
1827       64-bit wide datatypes.  See also "64-bit support".
1828
1829   Long Doubles
1830       Some platforms have "long doubles", floating point numbers of even
1831       larger range than ordinary "doubles".  To enable using long doubles for
1832       Perl's scalars, use -Duselongdouble.
1833
1834   -Dusemorebits
1835       You can enable both -Duse64bitint and -Duselongdouble with
1836       -Dusemorebits.  See also "64-bit support".
1837
1838   -Duselargefiles
1839       Some platforms support system APIs that are capable of handling large
1840       files (typically, files larger than two gigabytes).  Perl will try to
1841       use these APIs if you ask for -Duselargefiles.
1842
1843       See "Large file support" for more information.
1844
1845   installusrbinperl
1846       You can use "Configure -Uinstallusrbinperl" which causes installperl to
1847       skip installing perl also as /usr/bin/perl.  This is useful if you
1848       prefer not to modify /usr/bin for some reason or another but harmful
1849       because many scripts assume to find Perl in /usr/bin/perl.
1850
1851   SOCKS support
1852       You can use "Configure -Dusesocks" which causes Perl to probe for the
1853       SOCKS proxy protocol library (v5, not v4).  For more information on
1854       SOCKS, see:
1855
1856           http://www.socks.nec.com/
1857
1858   "-A" flag
1859       You can "post-edit" the Configure variables using the Configure "-A"
1860       switch.  The editing happens immediately after the platform specific
1861       hints files have been processed but before the actual configuration
1862       process starts.  Run "Configure -h" to find out the full "-A" syntax.
1863
1864   Enhanced Installation Directories
1865       The installation structure has been enriched to improve the support for
1866       maintaining multiple versions of perl, to provide locations for vendor-
1867       supplied modules, scripts, and manpages, and to ease maintenance of
1868       locally-added modules, scripts, and manpages.  See the section on
1869       Installation Directories in the INSTALL file for complete details.  For
1870       most users building and installing from source, the defaults should be
1871       fine.
1872
1873       If you previously used "Configure -Dsitelib" or "-Dsitearch" to set
1874       special values for library directories, you might wish to consider
1875       using the new "-Dsiteprefix" setting instead.  Also, if you wish to re-
1876       use a config.sh file from an earlier version of perl, you should be
1877       sure to check that Configure makes sensible choices for the new
1878       directories.  See INSTALL for complete details.
1879
1880   gcc automatically tried if 'cc' does not seem to be working
1881       In many platforms the vendor-supplied 'cc' is too stripped-down to
1882       build Perl (basically, the 'cc' doesn't do ANSI C).  If this seems to
1883       be the case and the 'cc' does not seem to be the GNU C compiler 'gcc',
1884       an automatic attempt is made to find and use 'gcc' instead.
1885

Platform specific changes

1887   Supported platforms
1888       •   The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the
1889           Thread extension.
1890
1891       •   GNU/Hurd is now supported.
1892
1893       •   Rhapsody/Darwin is now supported.
1894
1895       •   EPOC is now supported (on Psion 5).
1896
1897       •   The cygwin port (formerly cygwin32) has been greatly improved.
1898
1899   DOS
1900       •   Perl now works with djgpp 2.02 (and 2.03 alpha).
1901
1902       •   Environment variable names are not converted to uppercase any more.
1903
1904       •   Incorrect exit codes from backticks have been fixed.
1905
1906       •   This port continues to use its own builtin globbing (not
1907           File::Glob).
1908
1909   OS390 (OpenEdition MVS)
1910       Support for this EBCDIC platform has not been renewed in this release.
1911       There are difficulties in reconciling Perl's standardization on UTF-8
1912       as its internal representation for characters with the EBCDIC character
1913       set, because the two are incompatible.
1914
1915       It is unclear whether future versions will renew support for this
1916       platform, but the possibility exists.
1917
1918   VMS
1919       Numerous revisions and extensions to configuration, build, testing, and
1920       installation process to accommodate core changes and VMS-specific
1921       options.
1922
1923       Expand %ENV-handling code to allow runtime mapping to logical names,
1924       CLI symbols, and CRTL environ array.
1925
1926       Extension of subprocess invocation code to accept filespecs as command
1927       "verbs".
1928
1929       Add to Perl command line processing the ability to use default file
1930       types and to recognize Unix-style "2>&1".
1931
1932       Expansion of File::Spec::VMS routines, and integration into
1933       ExtUtils::MM_VMS.
1934
1935       Extension of ExtUtils::MM_VMS to handle complex extensions more
1936       flexibly.
1937
1938       Barewords at start of Unix-syntax paths may be treated as text rather
1939       than only as logical names.
1940
1941       Optional secure translation of several logical names used internally by
1942       Perl.
1943
1944       Miscellaneous bugfixing and porting of new core code to VMS.
1945
1946       Thanks are gladly extended to the many people who have contributed VMS
1947       patches, testing, and ideas.
1948
1949   Win32
1950       Perl can now emulate fork() internally, using multiple interpreters
1951       running in different concurrent threads.  This support must be enabled
1952       at build time.  See perlfork for detailed information.
1953
1954       When given a pathname that consists only of a drivename, such as "A:",
1955       opendir() and stat() now use the current working directory for the
1956       drive rather than the drive root.
1957
1958       The builtin XSUB functions in the Win32:: namespace are documented.
1959       See Win32.
1960
1961       $^X now contains the full path name of the running executable.
1962
1963       A Win32::GetLongPathName() function is provided to complement
1964       Win32::GetFullPathName() and Win32::GetShortPathName().  See Win32.
1965
1966       POSIX::uname() is supported.
1967
1968       system(1,...) now returns true process IDs rather than process handles.
1969       kill() accepts any real process id, rather than strictly return values
1970       from system(1,...).
1971
1972       For better compatibility with Unix, "kill(0, $pid)" can now be used to
1973       test whether a process exists.
1974
1975       The "Shell" module is supported.
1976
1977       Better support for building Perl under command.com in Windows 95 has
1978       been added.
1979
1980       Scripts are read in binary mode by default to allow ByteLoader (and the
1981       filter mechanism in general) to work properly.  For compatibility, the
1982       DATA filehandle will be set to text mode if a carriage return is
1983       detected at the end of the line containing the __END__ or __DATA__
1984       token; if not, the DATA filehandle will be left open in binary mode.
1985       Earlier versions always opened the DATA filehandle in text mode.
1986
1987       The glob() operator is implemented via the "File::Glob" extension,
1988       which supports glob syntax of the C shell.  This increases the
1989       flexibility of the glob() operator, but there may be compatibility
1990       issues for programs that relied on the older globbing syntax.  If you
1991       want to preserve compatibility with the older syntax, you might want to
1992       run perl with "-MFile::DosGlob".  For details and compatibility
1993       information, see File::Glob.
1994

Significant bug fixes

1996   <HANDLE> on empty files
1997       With $/ set to "undef", "slurping" an empty file returns a string of
1998       zero length (instead of "undef", as it used to) the first time the
1999       HANDLE is read after $/ is set to "undef".  Further reads yield
2000       "undef".
2001
2002       This means that the following will append "foo" to an empty file (it
2003       used to do nothing):
2004
2005           perl -0777 -pi -e 's/^/foo/' empty_file
2006
2007       The behaviour of:
2008
2009           perl -pi -e 's/^/foo/' empty_file
2010
2011       is unchanged (it continues to leave the file empty).
2012
2013   "eval '...'" improvements
2014       Line numbers (as reflected by caller() and most diagnostics) within
2015       "eval '...'" were often incorrect where here documents were involved.
2016       This has been corrected.
2017
2018       Lexical lookups for variables appearing in "eval '...'" within
2019       functions that were themselves called within an "eval '...'" were
2020       searching the wrong place for lexicals.  The lexical search now
2021       correctly ends at the subroutine's block boundary.
2022
2023       The use of "return" within "eval {...}" caused $@ not to be reset
2024       correctly when no exception occurred within the eval.  This has been
2025       fixed.
2026
2027       Parsing of here documents used to be flawed when they appeared as the
2028       replacement expression in "eval 's/.../.../e'".  This has been fixed.
2029
2030   All compilation errors are true errors
2031       Some "errors" encountered at compile time were by necessity generated
2032       as warnings followed by eventual termination of the program.  This
2033       enabled more such errors to be reported in a single run, rather than
2034       causing a hard stop at the first error that was encountered.
2035
2036       The mechanism for reporting such errors has been reimplemented to queue
2037       compile-time errors and report them at the end of the compilation as
2038       true errors rather than as warnings.  This fixes cases where error
2039       messages leaked through in the form of warnings when code was compiled
2040       at run time using "eval STRING", and also allows such errors to be
2041       reliably trapped using "eval "..."".
2042
2043   Implicitly closed filehandles are safer
2044       Sometimes implicitly closed filehandles (as when they are localized,
2045       and Perl automatically closes them on exiting the scope) could
2046       inadvertently set $? or $!.  This has been corrected.
2047
2048   Behavior of list slices is more consistent
2049       When taking a slice of a literal list (as opposed to a slice of an
2050       array or hash), Perl used to return an empty list if the result
2051       happened to be composed of all undef values.
2052
2053       The new behavior is to produce an empty list if (and only if) the
2054       original list was empty.  Consider the following example:
2055
2056           @a = (1,undef,undef,2)[2,1,2];
2057
2058       The old behavior would have resulted in @a having no elements.  The new
2059       behavior ensures it has three undefined elements.
2060
2061       Note in particular that the behavior of slices of the following cases
2062       remains unchanged:
2063
2064           @a = ()[1,2];
2065           @a = (getpwent)[7,0];
2066           @a = (anything_returning_empty_list())[2,1,2];
2067           @a = @b[2,1,2];
2068           @a = @c{'a','b','c'};
2069
2070       See perldata.
2071
2072   "(\$)" prototype and $foo{a}
2073       A scalar reference prototype now correctly allows a hash or array
2074       element in that slot.
2075
2076   "goto &sub" and AUTOLOAD
2077       The "goto &sub" construct works correctly when &sub happens to be
2078       autoloaded.
2079
2080   "-bareword" allowed under "use integer"
2081       The autoquoting of barewords preceded by "-" did not work in prior
2082       versions when the "integer" pragma was enabled.  This has been fixed.
2083
2084   Failures in DESTROY()
2085       When code in a destructor threw an exception, it went unnoticed in
2086       earlier versions of Perl, unless someone happened to be looking in $@
2087       just after the point the destructor happened to run.  Such failures are
2088       now visible as warnings when warnings are enabled.
2089
2090   Locale bugs fixed
2091       printf() and sprintf() previously reset the numeric locale back to the
2092       default "C" locale.  This has been fixed.
2093
2094       Numbers formatted according to the local numeric locale (such as using
2095       a decimal comma instead of a decimal dot) caused "isn't numeric"
2096       warnings, even while the operations accessing those numbers produced
2097       correct results.  These warnings have been discontinued.
2098
2099   Memory leaks
2100       The "eval 'return sub {...}'" construct could sometimes leak memory.
2101       This has been fixed.
2102
2103       Operations that aren't filehandle constructors used to leak memory when
2104       used on invalid filehandles.  This has been fixed.
2105
2106       Constructs that modified @_ could fail to deallocate values in @_ and
2107       thus leak memory.  This has been corrected.
2108
2109   Spurious subroutine stubs after failed subroutine calls
2110       Perl could sometimes create empty subroutine stubs when a subroutine
2111       was not found in the package.  Such cases stopped later method lookups
2112       from progressing into base packages.  This has been corrected.
2113
2114   Taint failures under "-U"
2115       When running in unsafe mode, taint violations could sometimes cause
2116       silent failures.  This has been fixed.
2117
2118   END blocks and the "-c" switch
2119       Prior versions used to run BEGIN and END blocks when Perl was run in
2120       compile-only mode.  Since this is typically not the expected behavior,
2121       END blocks are not executed anymore when the "-c" switch is used, or if
2122       compilation fails.
2123
2124       See "Support for CHECK blocks" for how to run things when the compile
2125       phase ends.
2126
2127   Potential to leak DATA filehandles
2128       Using the "__DATA__" token creates an implicit filehandle to the file
2129       that contains the token.  It is the program's responsibility to close
2130       it when it is done reading from it.
2131
2132       This caveat is now better explained in the documentation.  See
2133       perldata.
2134

New or Changed Diagnostics

2136       "%s" variable %s masks earlier declaration in same %s
2137           (W misc) A "my" or "our" variable has been redeclared in the
2138           current scope or statement, effectively eliminating all access to
2139           the previous instance.  This is almost always a typographical
2140           error.  Note that the earlier variable will still exist until the
2141           end of the scope or until all closure referents to it are
2142           destroyed.
2143
2144       "my sub" not yet implemented
2145           (F) Lexically scoped subroutines are not yet implemented.  Don't
2146           try that yet.
2147
2148       "our" variable %s redeclared
2149           (W misc) You seem to have already declared the same global once
2150           before in the current lexical scope.
2151
2152       '!' allowed only after types %s
2153           (F) The '!' is allowed in pack() and unpack() only after certain
2154           types.  See "pack" in perlfunc.
2155
2156       / cannot take a count
2157           (F) You had an unpack template indicating a counted-length string,
2158           but you have also specified an explicit size for the string.  See
2159           "pack" in perlfunc.
2160
2161       / must be followed by a, A or Z
2162           (F) You had an unpack template indicating a counted-length string,
2163           which must be followed by one of the letters a, A or Z to indicate
2164           what sort of string is to be unpacked.  See "pack" in perlfunc.
2165
2166       / must be followed by a*, A* or Z*
2167           (F) You had a pack template indicating a counted-length string,
2168           Currently the only things that can have their length counted are
2169           a*, A* or Z*.  See "pack" in perlfunc.
2170
2171       / must follow a numeric type
2172           (F) You had an unpack template that contained a '#', but this did
2173           not follow some numeric unpack specification.  See "pack" in
2174           perlfunc.
2175
2176       /%s/: Unrecognized escape \\%c passed through
2177           (W regexp) You used a backslash-character combination which is not
2178           recognized by Perl.  This combination appears in an interpolated
2179           variable or a "'"-delimited regular expression.  The character was
2180           understood literally.
2181
2182       /%s/: Unrecognized escape \\%c in character class passed through
2183           (W regexp) You used a backslash-character combination which is not
2184           recognized by Perl inside character classes.  The character was
2185           understood literally.
2186
2187       /%s/ should probably be written as "%s"
2188           (W syntax) You have used a pattern where Perl expected to find a
2189           string, as in the first argument to "join".  Perl will treat the
2190           true or false result of matching the pattern against $_ as the
2191           string, which is probably not what you had in mind.
2192
2193       %s() called too early to check prototype
2194           (W prototype) You've called a function that has a prototype before
2195           the parser saw a definition or declaration for it, and Perl could
2196           not check that the call conforms to the prototype.  You need to
2197           either add an early prototype declaration for the subroutine in
2198           question, or move the subroutine definition ahead of the call to
2199           get proper prototype checking.  Alternatively, if you are certain
2200           that you're calling the function correctly, you may put an
2201           ampersand before the name to avoid the warning.  See perlsub.
2202
2203       %s argument is not a HASH or ARRAY element
2204           (F) The argument to exists() must be a hash or array element, such
2205           as:
2206
2207               $foo{$bar}
2208               $ref->{"susie"}[12]
2209
2210       %s argument is not a HASH or ARRAY element or slice
2211           (F) The argument to delete() must be either a hash or array
2212           element, such as:
2213
2214               $foo{$bar}
2215               $ref->{"susie"}[12]
2216
2217           or a hash or array slice, such as:
2218
2219               @foo[$bar, $baz, $xyzzy]
2220               @{$ref->[12]}{"susie", "queue"}
2221
2222       %s argument is not a subroutine name
2223           (F) The argument to exists() for "exists &sub" must be a subroutine
2224           name, and not a subroutine call.  "exists &sub()" will generate
2225           this error.
2226
2227       %s package attribute may clash with future reserved word: %s
2228           (W reserved) A lowercase attribute name was used that had a
2229           package-specific handler.  That name might have a meaning to Perl
2230           itself some day, even though it doesn't yet.  Perhaps you should
2231           use a mixed-case attribute name, instead.  See attributes.
2232
2233       (in cleanup) %s
2234           (W misc) This prefix usually indicates that a DESTROY() method
2235           raised the indicated exception.  Since destructors are usually
2236           called by the system at arbitrary points during execution, and
2237           often a vast number of times, the warning is issued only once for
2238           any number of failures that would otherwise result in the same
2239           message being repeated.
2240
2241           Failure of user callbacks dispatched using the "G_KEEPERR" flag
2242           could also result in this warning.  See "G_KEEPERR" in perlcall.
2243
2244       <> should be quotes
2245           (F) You wrote "require <file>" when you should have written
2246           "require 'file'".
2247
2248       Attempt to join self
2249           (F) You tried to join a thread from within itself, which is an
2250           impossible task.  You may be joining the wrong thread, or you may
2251           need to move the join() to some other thread.
2252
2253       Bad evalled substitution pattern
2254           (F) You've used the /e switch to evaluate the replacement for a
2255           substitution, but perl found a syntax error in the code to
2256           evaluate, most likely an unexpected right brace '}'.
2257
2258       Bad realloc() ignored
2259           (S) An internal routine called realloc() on something that had
2260           never been malloc()ed in the first place. Mandatory, but can be
2261           disabled by setting environment variable "PERL_BADFREE" to 1.
2262
2263       Bareword found in conditional
2264           (W bareword) The compiler found a bareword where it expected a
2265           conditional, which often indicates that an || or && was parsed as
2266           part of the last argument of the previous construct, for example:
2267
2268               open FOO || die;
2269
2270           It may also indicate a misspelled constant that has been
2271           interpreted as a bareword:
2272
2273               use constant TYPO => 1;
2274               if (TYOP) { print "foo" }
2275
2276           The "strict" pragma is useful in avoiding such errors.
2277
2278       Binary number > 0b11111111111111111111111111111111 non-portable
2279           (W portable) The binary number you specified is larger than 2**32-1
2280           (4294967295) and therefore non-portable between systems.  See
2281           perlport for more on portability concerns.
2282
2283       Bit vector size > 32 non-portable
2284           (W portable) Using bit vector sizes larger than 32 is non-portable.
2285
2286       Buffer overflow in prime_env_iter: %s
2287           (W internal) A warning peculiar to VMS.  While Perl was preparing
2288           to iterate over %ENV, it encountered a logical name or symbol
2289           definition which was too long, so it was truncated to the string
2290           shown.
2291
2292       Can't check filesystem of script "%s"
2293           (P) For some reason you can't check the filesystem of the script
2294           for nosuid.
2295
2296       Can't declare class for non-scalar %s in "%s"
2297           (S) Currently, only scalar variables can declared with a specific
2298           class qualifier in a "my" or "our" declaration.  The semantics may
2299           be extended for other types of variables in future.
2300
2301       Can't declare %s in "%s"
2302           (F) Only scalar, array, and hash variables may be declared as "my"
2303           or "our" variables.  They must have ordinary identifiers as names.
2304
2305       Can't ignore signal CHLD, forcing to default
2306           (W signal) Perl has detected that it is being run with the SIGCHLD
2307           signal (sometimes known as SIGCLD) disabled.  Since disabling this
2308           signal will interfere with proper determination of exit status of
2309           child processes, Perl has reset the signal to its default value.
2310           This situation typically indicates that the parent program under
2311           which Perl may be running (e.g., cron) is being very careless.
2312
2313       Can't modify non-lvalue subroutine call
2314           (F) Subroutines meant to be used in lvalue context should be
2315           declared as such, see "Lvalue subroutines" in perlsub.
2316
2317       Can't read CRTL environ
2318           (S) A warning peculiar to VMS.  Perl tried to read an element of
2319           %ENV from the CRTL's internal environment array and discovered the
2320           array was missing.  You need to figure out where your CRTL
2321           misplaced its environ or define PERL_ENV_TABLES (see perlvms) so
2322           that environ is not searched.
2323
2324       Can't remove %s: %s, skipping file
2325           (S) You requested an inplace edit without creating a backup file.
2326           Perl was unable to remove the original file to replace it with the
2327           modified file.  The file was left unmodified.
2328
2329       Can't return %s from lvalue subroutine
2330           (F) Perl detected an attempt to return illegal lvalues (such as
2331           temporary or readonly values) from a subroutine used as an lvalue.
2332           This is not allowed.
2333
2334       Can't weaken a nonreference
2335           (F) You attempted to weaken something that was not a reference.
2336           Only references can be weakened.
2337
2338       Character class [:%s:] unknown
2339           (F) The class in the character class [: :] syntax is unknown.  See
2340           perlre.
2341
2342       Character class syntax [%s] belongs inside character classes
2343           (W unsafe) The character class constructs [: :], [= =], and [. .]
2344           go inside character classes, the [] are part of the construct, for
2345           example: /[012[:alpha:]345]/.  Note that [= =] and [. .]  are not
2346           currently implemented; they are simply placeholders for future
2347           extensions.
2348
2349       Constant is not %s reference
2350           (F) A constant value (perhaps declared using the "use constant"
2351           pragma) is being dereferenced, but it amounts to the wrong type of
2352           reference.  The message indicates the type of reference that was
2353           expected. This usually indicates a syntax error in dereferencing
2354           the constant value.  See "Constant Functions" in perlsub and
2355           constant.
2356
2357       constant(%s): %s
2358           (F) The parser found inconsistencies either while attempting to
2359           define an overloaded constant, or when trying to find the character
2360           name specified in the "\N{...}" escape.  Perhaps you forgot to load
2361           the corresponding "overload" or "charnames" pragma?  See charnames
2362           and overload.
2363
2364       CORE::%s is not a keyword
2365           (F) The CORE:: namespace is reserved for Perl keywords.
2366
2367       defined(@array) is deprecated
2368           (D) defined() is not usually useful on arrays because it checks for
2369           an undefined scalar value.  If you want to see if the array is
2370           empty, just use "if (@array) { # not empty }" for example.
2371
2372       defined(%hash) is deprecated
2373           (D) defined() is not usually useful on hashes because it checks for
2374           an undefined scalar value.  If you want to see if the hash is
2375           empty, just use "if (%hash) { # not empty }" for example.
2376
2377       Did not produce a valid header
2378           See Server error.
2379
2380       (Did you mean "local" instead of "our"?)
2381           (W misc) Remember that "our" does not localize the declared global
2382           variable.  You have declared it again in the same lexical scope,
2383           which seems superfluous.
2384
2385       Document contains no data
2386           See Server error.
2387
2388       entering effective %s failed
2389           (F) While under the "use filetest" pragma, switching the real and
2390           effective uids or gids failed.
2391
2392       false [] range "%s" in regexp
2393           (W regexp) A character class range must start and end at a literal
2394           character, not another character class like "\d" or "[:alpha:]".
2395           The "-" in your false range is interpreted as a literal "-".
2396           Consider quoting the "-",  "\-".  See perlre.
2397
2398       Filehandle %s opened only for output
2399           (W io) You tried to read from a filehandle opened only for writing.
2400           If you intended it to be a read/write filehandle, you needed to
2401           open it with "+<" or "+>" or "+>>" instead of with "<" or nothing.
2402           If you intended only to read from the file, use "<".  See "open" in
2403           perlfunc.
2404
2405       flock() on closed filehandle %s
2406           (W closed) The filehandle you're attempting to flock() got itself
2407           closed some time before now.  Check your logic flow.  flock()
2408           operates on filehandles.  Are you attempting to call flock() on a
2409           dirhandle by the same name?
2410
2411       Global symbol "%s" requires explicit package name
2412           (F) You've said "use strict vars", which indicates that all
2413           variables must either be lexically scoped (using "my"), declared
2414           beforehand using "our", or explicitly qualified to say which
2415           package the global variable is in (using "::").
2416
2417       Hexadecimal number > 0xffffffff non-portable
2418           (W portable) The hexadecimal number you specified is larger than
2419           2**32-1 (4294967295) and therefore non-portable between systems.
2420           See perlport for more on portability concerns.
2421
2422       Ill-formed CRTL environ value "%s"
2423           (W internal) A warning peculiar to VMS.  Perl tried to read the
2424           CRTL's internal environ array, and encountered an element without
2425           the "=" delimiter used to separate keys from values.  The element
2426           is ignored.
2427
2428       Ill-formed message in prime_env_iter: |%s|
2429           (W internal) A warning peculiar to VMS.  Perl tried to read a
2430           logical name or CLI symbol definition when preparing to iterate
2431           over %ENV, and didn't see the expected delimiter between key and
2432           value, so the line was ignored.
2433
2434       Illegal binary digit %s
2435           (F) You used a digit other than 0 or 1 in a binary number.
2436
2437       Illegal binary digit %s ignored
2438           (W digit) You may have tried to use a digit other than 0 or 1 in a
2439           binary number.  Interpretation of the binary number stopped before
2440           the offending digit.
2441
2442       Illegal number of bits in vec
2443           (F) The number of bits in vec() (the third argument) must be a
2444           power of two from 1 to 32 (or 64, if your platform supports that).
2445
2446       Integer overflow in %s number
2447           (W overflow) The hexadecimal, octal or binary number you have
2448           specified either as a literal or as an argument to hex() or oct()
2449           is too big for your architecture, and has been converted to a
2450           floating point number.  On a 32-bit architecture the largest
2451           hexadecimal, octal or binary number representable without overflow
2452           is 0xFFFFFFFF, 037777777777, or 0b11111111111111111111111111111111
2453           respectively.  Note that Perl transparently promotes all numbers to
2454           a floating point representation internally--subject to loss of
2455           precision errors in subsequent operations.
2456
2457       Invalid %s attribute: %s
2458           The indicated attribute for a subroutine or variable was not
2459           recognized by Perl or by a user-supplied handler.  See attributes.
2460
2461       Invalid %s attributes: %s
2462           The indicated attributes for a subroutine or variable were not
2463           recognized by Perl or by a user-supplied handler.  See attributes.
2464
2465       invalid [] range "%s" in regexp
2466           The offending range is now explicitly displayed.
2467
2468       Invalid separator character %s in attribute list
2469           (F) Something other than a colon or whitespace was seen between the
2470           elements of an attribute list.  If the previous attribute had a
2471           parenthesised parameter list, perhaps that list was terminated too
2472           soon.  See attributes.
2473
2474       Invalid separator character %s in subroutine attribute list
2475           (F) Something other than a colon or whitespace was seen between the
2476           elements of a subroutine attribute list.  If the previous attribute
2477           had a parenthesised parameter list, perhaps that list was
2478           terminated too soon.
2479
2480       leaving effective %s failed
2481           (F) While under the "use filetest" pragma, switching the real and
2482           effective uids or gids failed.
2483
2484       Lvalue subs returning %s not implemented yet
2485           (F) Due to limitations in the current implementation, array and
2486           hash values cannot be returned in subroutines used in lvalue
2487           context.  See "Lvalue subroutines" in perlsub.
2488
2489       Method %s not permitted
2490           See Server error.
2491
2492       Missing %sbrace%s on \N{}
2493           (F) Wrong syntax of character name literal "\N{charname}" within
2494           double-quotish context.
2495
2496       Missing command in piped open
2497           (W pipe) You used the "open(FH, "| command")" or "open(FH, "command
2498           |")" construction, but the command was missing or blank.
2499
2500       Missing name in "my sub"
2501           (F) The reserved syntax for lexically scoped subroutines requires
2502           that they have a name with which they can be found.
2503
2504       No %s specified for -%c
2505           (F) The indicated command line switch needs a mandatory argument,
2506           but you haven't specified one.
2507
2508       No package name allowed for variable %s in "our"
2509           (F) Fully qualified variable names are not allowed in "our"
2510           declarations, because that doesn't make much sense under existing
2511           semantics.  Such syntax is reserved for future extensions.
2512
2513       No space allowed after -%c
2514           (F) The argument to the indicated command line switch must follow
2515           immediately after the switch, without intervening spaces.
2516
2517       no UTC offset information; assuming local time is UTC
2518           (S) A warning peculiar to VMS.  Perl was unable to find the local
2519           timezone offset, so it's assuming that local system time is
2520           equivalent to UTC.  If it's not, define the logical name
2521           SYS$TIMEZONE_DIFFERENTIAL to translate to the number of seconds
2522           which need to be added to UTC to get local time.
2523
2524       Octal number > 037777777777 non-portable
2525           (W portable) The octal number you specified is larger than 2**32-1
2526           (4294967295) and therefore non-portable between systems.  See
2527           perlport for more on portability concerns.
2528
2529           See also perlport for writing portable code.
2530
2531       panic: del_backref
2532           (P) Failed an internal consistency check while trying to reset a
2533           weak reference.
2534
2535       panic: kid popen errno read
2536           (F) forked child returned an incomprehensible message about its
2537           errno.
2538
2539       panic: magic_killbackrefs
2540           (P) Failed an internal consistency check while trying to reset all
2541           weak references to an object.
2542
2543       Parentheses missing around "%s" list
2544           (W parenthesis) You said something like
2545
2546               my $foo, $bar = @_;
2547
2548           when you meant
2549
2550               my ($foo, $bar) = @_;
2551
2552           Remember that "my", "our", and "local" bind tighter than comma.
2553
2554       Possible unintended interpolation of %s in string
2555           (W ambiguous) It used to be that Perl would try to guess whether
2556           you wanted an array interpolated or a literal @.  It no longer does
2557           this; arrays are now always interpolated into strings.  This means
2558           that if you try something like:
2559
2560                   print "fred@example.com";
2561
2562           and the array @example doesn't exist, Perl is going to print
2563           "fred.com", which is probably not what you wanted.  To get a
2564           literal "@" sign in a string, put a backslash before it, just as
2565           you would to get a literal "$" sign.
2566
2567       Possible Y2K bug: %s
2568           (W y2k) You are concatenating the number 19 with another number,
2569           which could be a potential Year 2000 problem.
2570
2571       pragma "attrs" is deprecated, use "sub NAME : ATTRS" instead
2572           (W deprecated) You have written something like this:
2573
2574               sub doit
2575               {
2576                   use attrs qw(locked);
2577               }
2578
2579           You should use the new declaration syntax instead.
2580
2581               sub doit : locked
2582               {
2583                   ...
2584
2585           The "use attrs" pragma is now obsolete, and is only provided for
2586           backward-compatibility. See "Subroutine Attributes" in perlsub.
2587
2588       Premature end of script headers
2589           See Server error.
2590
2591       Repeat count in pack overflows
2592           (F) You can't specify a repeat count so large that it overflows
2593           your signed integers.  See "pack" in perlfunc.
2594
2595       Repeat count in unpack overflows
2596           (F) You can't specify a repeat count so large that it overflows
2597           your signed integers.  See "unpack" in perlfunc.
2598
2599       realloc() of freed memory ignored
2600           (S) An internal routine called realloc() on something that had
2601           already been freed.
2602
2603       Reference is already weak
2604           (W misc) You have attempted to weaken a reference that is already
2605           weak.  Doing so has no effect.
2606
2607       setpgrp can't take arguments
2608           (F) Your system has the setpgrp() from BSD 4.2, which takes no
2609           arguments, unlike POSIX setpgid(), which takes a process ID and
2610           process group ID.
2611
2612       Strange *+?{} on zero-length expression
2613           (W regexp) You applied a regular expression quantifier in a place
2614           where it makes no sense, such as on a zero-width assertion.  Try
2615           putting the quantifier inside the assertion instead.  For example,
2616           the way to match "abc" provided that it is followed by three
2617           repetitions of "xyz" is "/abc(?=(?:xyz){3})/", not
2618           "/abc(?=xyz){3}/".
2619
2620       switching effective %s is not implemented
2621           (F) While under the "use filetest" pragma, we cannot switch the
2622           real and effective uids or gids.
2623
2624       This Perl can't reset CRTL environ elements (%s)
2625       This Perl can't set CRTL environ elements (%s=%s)
2626           (W internal) Warnings peculiar to VMS.  You tried to change or
2627           delete an element of the CRTL's internal environ array, but your
2628           copy of Perl wasn't built with a CRTL that contained the setenv()
2629           function.  You'll need to rebuild Perl with a CRTL that does, or
2630           redefine PERL_ENV_TABLES (see perlvms) so that the environ array
2631           isn't the target of the change to %ENV which produced the warning.
2632
2633       Too late to run %s block
2634           (W void) A CHECK or INIT block is being defined during run time
2635           proper, when the opportunity to run them has already passed.
2636           Perhaps you are loading a file with "require" or "do" when you
2637           should be using "use" instead.  Or perhaps you should put the
2638           "require" or "do" inside a BEGIN block.
2639
2640       Unknown open() mode '%s'
2641           (F) The second argument of 3-argument open() is not among the list
2642           of valid modes: "<", ">", ">>", "+<", "+>", "+>>", "-|", "|-".
2643
2644       Unknown process %x sent message to prime_env_iter: %s
2645           (P) An error peculiar to VMS.  Perl was reading values for %ENV
2646           before iterating over it, and someone else stuck a message in the
2647           stream of data Perl expected.  Someone's very confused, or perhaps
2648           trying to subvert Perl's population of %ENV for nefarious purposes.
2649
2650       Unrecognized escape \\%c passed through
2651           (W misc) You used a backslash-character combination which is not
2652           recognized by Perl.  The character was understood literally.
2653
2654       Unterminated attribute parameter in attribute list
2655           (F) The lexer saw an opening (left) parenthesis character while
2656           parsing an attribute list, but the matching closing (right)
2657           parenthesis character was not found.  You may need to add (or
2658           remove) a backslash character to get your parentheses to balance.
2659           See attributes.
2660
2661       Unterminated attribute list
2662           (F) The lexer found something other than a simple identifier at the
2663           start of an attribute, and it wasn't a semicolon or the start of a
2664           block.  Perhaps you terminated the parameter list of the previous
2665           attribute too soon.  See attributes.
2666
2667       Unterminated attribute parameter in subroutine attribute list
2668           (F) The lexer saw an opening (left) parenthesis character while
2669           parsing a subroutine attribute list, but the matching closing
2670           (right) parenthesis character was not found.  You may need to add
2671           (or remove) a backslash character to get your parentheses to
2672           balance.
2673
2674       Unterminated subroutine attribute list
2675           (F) The lexer found something other than a simple identifier at the
2676           start of a subroutine attribute, and it wasn't a semicolon or the
2677           start of a block.  Perhaps you terminated the parameter list of the
2678           previous attribute too soon.
2679
2680       Value of CLI symbol "%s" too long
2681           (W misc) A warning peculiar to VMS.  Perl tried to read the value
2682           of an %ENV element from a CLI symbol table, and found a resultant
2683           string longer than 1024 characters.  The return value has been
2684           truncated to 1024 characters.
2685
2686       Version number must be a constant number
2687           (P) The attempt to translate a "use Module n.n LIST" statement into
2688           its equivalent "BEGIN" block found an internal inconsistency with
2689           the version number.
2690

New tests

2692       lib/attrs
2693           Compatibility tests for "sub : attrs" vs the older "use attrs".
2694
2695       lib/env
2696           Tests for new environment scalar capability (e.g., "use Env
2697           qw($BAR);").
2698
2699       lib/env-array
2700           Tests for new environment array capability (e.g., "use Env
2701           qw(@PATH);").
2702
2703       lib/io_const
2704           IO constants (SEEK_*, _IO*).
2705
2706       lib/io_dir
2707           Directory-related IO methods (new, read, close, rewind, tied
2708           delete).
2709
2710       lib/io_multihomed
2711           INET sockets with multi-homed hosts.
2712
2713       lib/io_poll
2714           IO poll().
2715
2716       lib/io_unix
2717           UNIX sockets.
2718
2719       op/attrs
2720           Regression tests for "my ($x,@y,%z) : attrs" and <sub : attrs>.
2721
2722       op/filetest
2723           File test operators.
2724
2725       op/lex_assign
2726           Verify operations that access pad objects (lexicals and
2727           temporaries).
2728
2729       op/exists_sub
2730           Verify "exists &sub" operations.
2731

Incompatible Changes

2733   Perl Source Incompatibilities
2734       Beware that any new warnings that have been added or old ones that have
2735       been enhanced are not considered incompatible changes.
2736
2737       Since all new warnings must be explicitly requested via the "-w" switch
2738       or the "warnings" pragma, it is ultimately the programmer's
2739       responsibility to ensure that warnings are enabled judiciously.
2740
2741       CHECK is a new keyword
2742           All subroutine definitions named CHECK are now special.  See
2743           "/"Support for CHECK blocks"" for more information.
2744
2745       Treatment of list slices of undef has changed
2746           There is a potential incompatibility in the behavior of list slices
2747           that are comprised entirely of undefined values.  See "Behavior of
2748           list slices is more consistent".
2749
2750       Format of $English::PERL_VERSION is different
2751           The English module now sets $PERL_VERSION to $^V (a string value)
2752           rather than $] (a numeric value).  This is a potential
2753           incompatibility.  Send us a report via perlbug if you are affected
2754           by this.
2755
2756           See "Improved Perl version numbering system" for the reasons for
2757           this change.
2758
2759       Literals of the form 1.2.3 parse differently
2760           Previously, numeric literals with more than one dot in them were
2761           interpreted as a floating point number concatenated with one or
2762           more numbers.  Such "numbers" are now parsed as strings composed of
2763           the specified ordinals.
2764
2765           For example, "print 97.98.99" used to output 97.9899 in earlier
2766           versions, but now prints "abc".
2767
2768           See "Support for strings represented as a vector of ordinals".
2769
2770       Possibly changed pseudo-random number generator
2771           Perl programs that depend on reproducing a specific set of pseudo-
2772           random numbers may now produce different output due to improvements
2773           made to the rand() builtin.  You can use "sh Configure
2774           -Drandfunc=rand" to obtain the old behavior.
2775
2776           See "Better pseudo-random number generator".
2777
2778       Hashing function for hash keys has changed
2779           Even though Perl hashes are not order preserving, the apparently
2780           random order encountered when iterating on the contents of a hash
2781           is actually determined by the hashing algorithm used.  Improvements
2782           in the algorithm may yield a random order that is different from
2783           that of previous versions, especially when iterating on hashes.
2784
2785           See "Better worst-case behavior of hashes" for additional
2786           information.
2787
2788       "undef" fails on read only values
2789           Using the "undef" operator on a readonly value (such as $1) has the
2790           same effect as assigning "undef" to the readonly value--it throws
2791           an exception.
2792
2793       Close-on-exec bit may be set on pipe and socket handles
2794           Pipe and socket handles are also now subject to the close-on-exec
2795           behavior determined by the special variable $^F.
2796
2797           See "More consistent close-on-exec behavior".
2798
2799       Writing "$$1" to mean "${$}1" is unsupported
2800           Perl 5.004 deprecated the interpretation of $$1 and similar within
2801           interpolated strings to mean "$$ . "1"", but still allowed it.
2802
2803           In Perl 5.6.0 and later, "$$1" always means "${$1}".
2804
2805       delete(), each(), values() and "\(%h)"
2806           operate on aliases to values, not copies
2807
2808           delete(), each(), values() and hashes (e.g. "\(%h)") in a list
2809           context return the actual values in the hash, instead of copies (as
2810           they used to in earlier versions).  Typical idioms for using these
2811           constructs copy the returned values, but this can make a
2812           significant difference when creating references to the returned
2813           values.  Keys in the hash are still returned as copies when
2814           iterating on a hash.
2815
2816           See also "delete(), each(), values() and hash iteration are
2817           faster".
2818
2819       vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS
2820           vec() generates a run-time error if the BITS argument is not a
2821           valid power-of-two integer.
2822
2823       Text of some diagnostic output has changed
2824           Most references to internal Perl operations in diagnostics have
2825           been changed to be more descriptive.  This may be an issue for
2826           programs that may incorrectly rely on the exact text of diagnostics
2827           for proper functioning.
2828
2829       "%@" has been removed
2830           The undocumented special variable "%@" that used to accumulate
2831           "background" errors (such as those that happen in DESTROY()) has
2832           been removed, because it could potentially result in memory leaks.
2833
2834       Parenthesized not() behaves like a list operator
2835           The "not" operator now falls under the "if it looks like a
2836           function, it behaves like a function" rule.
2837
2838           As a result, the parenthesized form can be used with "grep" and
2839           "map".  The following construct used to be a syntax error before,
2840           but it works as expected now:
2841
2842               grep not($_), @things;
2843
2844           On the other hand, using "not" with a literal list slice may not
2845           work.  The following previously allowed construct:
2846
2847               print not (1,2,3)[0];
2848
2849           needs to be written with additional parentheses now:
2850
2851               print not((1,2,3)[0]);
2852
2853           The behavior remains unaffected when "not" is not followed by
2854           parentheses.
2855
2856       Semantics of bareword prototype "(*)" have changed
2857           The semantics of the bareword prototype "*" have changed.  Perl
2858           5.005 always coerced simple scalar arguments to a typeglob, which
2859           wasn't useful in situations where the subroutine must distinguish
2860           between a simple scalar and a typeglob.  The new behavior is to not
2861           coerce bareword arguments to a typeglob.  The value will always be
2862           visible as either a simple scalar or as a reference to a typeglob.
2863
2864           See "More functional bareword prototype (*)".
2865
2866       Semantics of bit operators may have changed on 64-bit platforms
2867           If your platform is either natively 64-bit or if Perl has been
2868           configured to used 64-bit integers, i.e., $Config{ivsize} is 8,
2869           there may be a potential incompatibility in the behavior of bitwise
2870           numeric operators (& | ^ ~ << >>).  These operators used to
2871           strictly operate on the lower 32 bits of integers in previous
2872           versions, but now operate over the entire native integral width.
2873           In particular, note that unary "~" will produce different results
2874           on platforms that have different $Config{ivsize}.  For portability,
2875           be sure to mask off the excess bits in the result of unary "~",
2876           e.g., "~$x & 0xffffffff".
2877
2878           See "Bit operators support full native integer width".
2879
2880       More builtins taint their results
2881           As described in "Improved security features", there may be more
2882           sources of taint in a Perl program.
2883
2884           To avoid these new tainting behaviors, you can build Perl with the
2885           Configure option "-Accflags=-DINCOMPLETE_TAINTS".  Beware that the
2886           ensuing perl binary may be insecure.
2887
2888   C Source Incompatibilities
2889       "PERL_POLLUTE"
2890           Release 5.005 grandfathered old global symbol names by providing
2891           preprocessor macros for extension source compatibility.  As of
2892           release 5.6.0, these preprocessor definitions are not available by
2893           default.  You need to explicitly compile perl with "-DPERL_POLLUTE"
2894           to get these definitions.  For extensions still using the old
2895           symbols, this option can be specified via MakeMaker:
2896
2897               perl Makefile.PL POLLUTE=1
2898
2899       "PERL_IMPLICIT_CONTEXT"
2900           This new build option provides a set of macros for all API
2901           functions such that an implicit interpreter/thread context argument
2902           is passed to every API function.  As a result of this, something
2903           like "sv_setsv(foo,bar)" amounts to a macro invocation that
2904           actually translates to something like
2905           "Perl_sv_setsv(my_perl,foo,bar)".  While this is generally expected
2906           to not have any significant source compatibility issues, the
2907           difference between a macro and a real function call will need to be
2908           considered.
2909
2910           This means that there is a source compatibility issue as a result
2911           of this if your extensions attempt to use pointers to any of the
2912           Perl API functions.
2913
2914           Note that the above issue is not relevant to the default build of
2915           Perl, whose interfaces continue to match those of prior versions
2916           (but subject to the other options described here).
2917
2918           See "Background and PERL_IMPLICIT_CONTEXT" in perlguts for detailed
2919           information on the ramifications of building Perl with this option.
2920
2921               NOTE: PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
2922               with one of -Dusethreads, -Dusemultiplicity, or both.  It is not
2923               intended to be enabled by users at this time.
2924
2925       "PERL_POLLUTE_MALLOC"
2926           Enabling Perl's malloc in release 5.005 and earlier caused the
2927           namespace of the system's malloc family of functions to be usurped
2928           by the Perl versions, since by default they used the same names.
2929           Besides causing problems on platforms that do not allow these
2930           functions to be cleanly replaced, this also meant that the system
2931           versions could not be called in programs that used Perl's malloc.
2932           Previous versions of Perl have allowed this behaviour to be
2933           suppressed with the HIDEMYMALLOC and EMBEDMYMALLOC preprocessor
2934           definitions.
2935
2936           As of release 5.6.0, Perl's malloc family of functions have default
2937           names distinct from the system versions.  You need to explicitly
2938           compile perl with "-DPERL_POLLUTE_MALLOC" to get the older
2939           behaviour.  HIDEMYMALLOC and EMBEDMYMALLOC have no effect, since
2940           the behaviour they enabled is now the default.
2941
2942           Note that these functions do not constitute Perl's memory
2943           allocation API.  See "Memory Allocation" in perlguts for further
2944           information about that.
2945
2946   Compatible C Source API Changes
2947       "PATCHLEVEL" is now "PERL_VERSION"
2948           The cpp macros "PERL_REVISION", "PERL_VERSION", and
2949           "PERL_SUBVERSION" are now available by default from perl.h, and
2950           reflect the base revision, patchlevel, and subversion respectively.
2951           "PERL_REVISION" had no prior equivalent, while "PERL_VERSION" and
2952           "PERL_SUBVERSION" were previously available as "PATCHLEVEL" and
2953           "SUBVERSION".
2954
2955           The new names cause less pollution of the cpp namespace and reflect
2956           what the numbers have come to stand for in common practice.  For
2957           compatibility, the old names are still supported when patchlevel.h
2958           is explicitly included (as required before), so there is no source
2959           incompatibility from the change.
2960
2961   Binary Incompatibilities
2962       In general, the default build of this release is expected to be binary
2963       compatible for extensions built with the 5.005 release or its
2964       maintenance versions.  However, specific platforms may have broken
2965       binary compatibility due to changes in the defaults used in hints
2966       files.  Therefore, please be sure to always check the platform-specific
2967       README files for any notes to the contrary.
2968
2969       The usethreads or usemultiplicity builds are not binary compatible with
2970       the corresponding builds in 5.005.
2971
2972       On platforms that require an explicit list of exports (AIX, OS/2 and
2973       Windows, among others), purely internal symbols such as parser
2974       functions and the run time opcodes are not exported by default.  Perl
2975       5.005 used to export all functions irrespective of whether they were
2976       considered part of the public API or not.
2977
2978       For the full list of public API functions, see perlapi.
2979

Known Problems

2981   Localizing a tied hash element may leak memory
2982       As of the 5.6.1 release, there is a known leak when code such as this
2983       is executed:
2984
2985           use Tie::Hash;
2986           tie my %tie_hash => 'Tie::StdHash';
2987
2988           ...
2989
2990           local($tie_hash{Foo}) = 1; # leaks
2991
2992   Known test failures
2993       •   64-bit builds
2994
2995           Subtest #15 of lib/b.t may fail under 64-bit builds on platforms
2996           such as HP-UX PA64 and Linux IA64.  The issue is still being
2997           investigated.
2998
2999           The lib/io_multihomed test may hang in HP-UX if Perl has been
3000           configured to be 64-bit.  Because other 64-bit platforms do not
3001           hang in this test, HP-UX is suspect.  All other tests pass in
3002           64-bit HP-UX.  The test attempts to create and connect to
3003           "multihomed" sockets (sockets which have multiple IP addresses).
3004
3005           Note that 64-bit support is still experimental.
3006
3007       •   Failure of Thread tests
3008
3009           The subtests 19 and 20 of lib/thr5005.t test are known to fail due
3010           to fundamental problems in the 5.005 threading implementation.
3011           These are not new failures--Perl 5.005_0x has the same bugs, but
3012           didn't have these tests.  (Note that support for 5.005-style
3013           threading remains experimental.)
3014
3015       •   NEXTSTEP 3.3 POSIX test failure
3016
3017           In NEXTSTEP 3.3p2 the implementation of the strftime(3) in the
3018           operating system libraries is buggy: the %j format numbers the days
3019           of a month starting from zero, which, while being logical to
3020           programmers, will cause the subtests 19 to 27 of the lib/posix test
3021           may fail.
3022
3023       •   Tru64 (aka Digital UNIX, aka DEC OSF/1) lib/sdbm test failure with
3024           gcc
3025
3026           If compiled with gcc 2.95 the lib/sdbm test will fail (dump core).
3027           The cure is to use the vendor cc, it comes with the operating
3028           system and produces good code.
3029
3030   EBCDIC platforms not fully supported
3031       In earlier releases of Perl, EBCDIC environments like OS390 (also known
3032       as Open Edition MVS) and VM-ESA were supported.  Due to changes
3033       required by the UTF-8 (Unicode) support, the EBCDIC platforms are not
3034       supported in Perl 5.6.0.
3035
3036       The 5.6.1 release improves support for EBCDIC platforms, but they are
3037       not fully supported yet.
3038
3039   UNICOS/mk CC failures during Configure run
3040       In UNICOS/mk the following errors may appear during the Configure run:
3041
3042               Guessing which symbols your C compiler and preprocessor define...
3043               CC-20 cc: ERROR File = try.c, Line = 3
3044               ...
3045                 bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K
3046               ...
3047               4 errors detected in the compilation of "try.c".
3048
3049       The culprit is the broken awk of UNICOS/mk.  The effect is fortunately
3050       rather mild: Perl itself is not adversely affected by the error, only
3051       the h2ph utility coming with Perl, and that is rather rarely needed
3052       these days.
3053
3054   Arrow operator and arrays
3055       When the left argument to the arrow operator "->" is an array, or the
3056       "scalar" operator operating on an array, the result of the operation
3057       must be considered erroneous. For example:
3058
3059           @x->[2]
3060           scalar(@x)->[2]
3061
3062       These expressions will get run-time errors in some future release of
3063       Perl.
3064
3065   Experimental features
3066       As discussed above, many features are still experimental.  Interfaces
3067       and implementation of these features are subject to change, and in
3068       extreme cases, even subject to removal in some future release of Perl.
3069       These features include the following:
3070
3071       Threads
3072       Unicode
3073       64-bit support
3074       Lvalue subroutines
3075       Weak references
3076       The pseudo-hash data type
3077       The Compiler suite
3078       Internal implementation of file globbing
3079       The DB module
3080       The regular expression code constructs:
3081           "(?{ code })" and "(??{ code })"
3082

Obsolete Diagnostics

3084       Character class syntax [: :] is reserved for future extensions
3085           (W) Within regular expression character classes ([]) the syntax
3086           beginning with "[:" and ending with ":]" is reserved for future
3087           extensions.  If you need to represent those character sequences
3088           inside a regular expression character class, just quote the square
3089           brackets with the backslash: "\[:" and ":\]".
3090
3091       Ill-formed logical name |%s| in prime_env_iter
3092           (W) A warning peculiar to VMS.  A logical name was encountered when
3093           preparing to iterate over %ENV which violates the syntactic rules
3094           governing logical names.  Because it cannot be translated normally,
3095           it is skipped, and will not appear in %ENV.  This may be a benign
3096           occurrence, as some software packages might directly modify logical
3097           name tables and introduce nonstandard names, or it may indicate
3098           that a logical name table has been corrupted.
3099
3100       In string, @%s now must be written as \@%s
3101           The description of this error used to say:
3102
3103                   (Someday it will simply assume that an unbackslashed @
3104                    interpolates an array.)
3105
3106           That day has come, and this fatal error has been removed.  It has
3107           been replaced by a non-fatal warning instead.  See "Arrays now
3108           always interpolate into double-quoted strings" for details.
3109
3110       Probable precedence problem on %s
3111           (W) The compiler found a bareword where it expected a conditional,
3112           which often indicates that an || or && was parsed as part of the
3113           last argument of the previous construct, for example:
3114
3115               open FOO || die;
3116
3117       regexp too big
3118           (F) The current implementation of regular expressions uses shorts
3119           as address offsets within a string.  Unfortunately this means that
3120           if the regular expression compiles to longer than 32767, it'll blow
3121           up.  Usually when you want a regular expression this big, there is
3122           a better way to do it with multiple statements.  See perlre.
3123
3124       Use of "$$<digit>" to mean "${$}<digit>" is deprecated
3125           (D) Perl versions before 5.004 misinterpreted any type marker
3126           followed by "$" and a digit.  For example, "$$0" was incorrectly
3127           taken to mean "${$}0" instead of "${$0}".  This bug is (mostly)
3128           fixed in Perl 5.004.
3129
3130           However, the developers of Perl 5.004 could not fix this bug
3131           completely, because at least two widely-used modules depend on the
3132           old meaning of "$$0" in a string.  So Perl 5.004 still interprets
3133           "$$<digit>" in the old (broken) way inside strings; but it
3134           generates this message as a warning.  And in Perl 5.005, this
3135           special treatment will cease.
3136

Reporting Bugs

3138       If you find what you think is a bug, you might check the articles
3139       recently posted to the comp.lang.perl.misc newsgroup.  There may also
3140       be information at http://www.perl.com/ , the Perl Home Page.
3141
3142       If you believe you have an unreported bug, please run the perlbug
3143       program included with your release.  Be sure to trim your bug down to a
3144       tiny but sufficient test case.  Your bug report, along with the output
3145       of "perl -V", will be sent off to perlbug@perl.org to be analysed by
3146       the Perl porting team.
3147

SEE ALSO

3149       The Changes file for exhaustive details on what changed.
3150
3151       The INSTALL file for how to build Perl.
3152
3153       The README file for general stuff.
3154
3155       The Artistic and Copying files for copyright information.
3156

HISTORY

3158       Written by Gurusamy Sarathy <gsar@ActiveState.com>, with many
3159       contributions from The Perl Porters.
3160
3161       Send omissions or corrections to <perlbug@perl.org>.
3162
3163
3164
3165perl v5.38.2                      2023-11-30                   PERL561DELTA(1)
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