1PERL58DELTA(1)         Perl Programmers Reference Guide         PERL58DELTA(1)
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3
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NAME

6       perl58delta - what is new for perl v5.8.0
7

DESCRIPTION

9       This document describes differences between the 5.6.0 release and the
10       5.8.0 release.
11
12       Many of the bug fixes in 5.8.0 were already seen in the 5.6.1
13       maintenance release since the two releases were kept closely
14       coordinated (while 5.8.0 was still called 5.7.something).
15
16       Changes that were integrated into the 5.6.1 release are marked "[561]".
17       Many of these changes have been further developed since 5.6.1 was
18       released, those are marked "[561+]".
19
20       You can see the list of changes in the 5.6.1 release (both from the
21       5.005_03 release and the 5.6.0 release) by reading perl561delta.
22

Highlights In 5.8.0

24       •   Better Unicode support
25
26       •   New IO Implementation
27
28       •   New Thread Implementation
29
30       •   Better Numeric Accuracy
31
32       •   Safe Signals
33
34       •   Many New Modules
35
36       •   More Extensive Regression Testing
37

Incompatible Changes

39   Binary Incompatibility
40       Perl 5.8 is not binary compatible with earlier releases of Perl.
41
42       You have to recompile your XS modules.
43
44       (Pure Perl modules should continue to work.)
45
46       The major reason for the discontinuity is the new IO architecture
47       called PerlIO.  PerlIO is the default configuration because without it
48       many new features of Perl 5.8 cannot be used.  In other words: you just
49       have to recompile your modules containing XS code, sorry about that.
50
51       In future releases of Perl, non-PerlIO aware XS modules may become
52       completely unsupported.  This shouldn't be too difficult for module
53       authors, however: PerlIO has been designed as a drop-in replacement (at
54       the source code level) for the stdio interface.
55
56       Depending on your platform, there are also other reasons why we decided
57       to break binary compatibility, please read on.
58
59   64-bit platforms and malloc
60       If your pointers are 64 bits wide, the Perl malloc is no longer being
61       used because it does not work well with 8-byte pointers.  Also, usually
62       the system mallocs on such platforms are much better optimized for such
63       large memory models than the Perl malloc.  Some memory-hungry Perl
64       applications like the PDL don't work well with Perl's malloc.  Finally,
65       other applications than Perl (such as mod_perl) tend to prefer the
66       system malloc.  Such platforms include Alpha and 64-bit HPPA, MIPS,
67       PPC, and Sparc.
68
69   AIX Dynaloading
70       The AIX dynaloading now uses in AIX releases 4.3 and newer the native
71       dlopen interface of AIX instead of the old emulated interface.  This
72       change will probably break backward compatibility with compiled
73       modules.  The change was made to make Perl more compliant with other
74       applications like mod_perl which are using the AIX native interface.
75
76   Attributes for "my" variables now handled at run-time
77       The "my EXPR : ATTRS" syntax now applies variable attributes at run-
78       time.  (Subroutine and "our" variables still get attributes applied at
79       compile-time.)  See attributes for additional details.  In particular,
80       however, this allows variable attributes to be useful for "tie"
81       interfaces, which was a deficiency of earlier releases.  Note that the
82       new semantics doesn't work with the Attribute::Handlers module (as of
83       version 0.76).
84
85   Socket Extension Dynamic in VMS
86       The Socket extension is now dynamically loaded instead of being
87       statically built in.  This may or may not be a problem with ancient
88       TCP/IP stacks of VMS: we do not know since we weren't able to test Perl
89       in such configurations.
90
91   IEEE-format Floating Point Default on OpenVMS Alpha
92       Perl now uses IEEE format (T_FLOAT) as the default internal floating
93       point format on OpenVMS Alpha, potentially breaking binary
94       compatibility with external libraries or existing data.  G_FLOAT is
95       still available as a configuration option.  The default on VAX
96       (D_FLOAT) has not changed.
97
98   New Unicode Semantics (no more "use utf8", almost)
99       Previously in Perl 5.6 to use Unicode one would say "use utf8" and then
100       the operations (like string concatenation) were Unicode-aware in that
101       lexical scope.
102
103       This was found to be an inconvenient interface, and in Perl 5.8 the
104       Unicode model has completely changed: now the "Unicodeness" is bound to
105       the data itself, and for most of the time "use utf8" is not needed at
106       all.  The only remaining use of "use utf8" is when the Perl script
107       itself has been written in the UTF-8 encoding of Unicode.  (UTF-8 has
108       not been made the default since there are many Perl scripts out there
109       that are using various national eight-bit character sets, which would
110       be illegal in UTF-8.)
111
112       See perluniintro for the explanation of the current model, and utf8 for
113       the current use of the utf8 pragma.
114
115   New Unicode Properties
116       Unicode scripts are now supported. Scripts are similar to (and superior
117       to) Unicode blocks. The difference between scripts and blocks is that
118       scripts are the glyphs used by a language or a group of languages,
119       while the blocks are more artificial groupings of (mostly) 256
120       characters based on the Unicode numbering.
121
122       In general, scripts are more inclusive, but not universally so. For
123       example, while the script "Latin" includes all the Latin characters and
124       their various diacritic-adorned versions, it does not include the
125       various punctuation or digits (since they are not solely "Latin").
126
127       A number of other properties are now supported, including "\p{L&}",
128       "\p{Any}" "\p{Assigned}", "\p{Unassigned}", "\p{Blank}" [561] and
129       "\p{SpacePerl}" [561] (along with their "\P{...}" versions, of course).
130       See perlunicode for details, and more additions.
131
132       The "In" or "Is" prefix to names used with the "\p{...}" and "\P{...}"
133       are now almost always optional. The only exception is that a "In"
134       prefix is required to signify a Unicode block when a block name
135       conflicts with a script name. For example, "\p{Tibetan}" refers to the
136       script, while "\p{InTibetan}" refers to the block. When there is no
137       name conflict, you can omit the "In" from the block name (e.g.
138       "\p{BraillePatterns}"), but to be safe, it's probably best to always
139       use the "In").
140
141   REF(...) Instead Of SCALAR(...)
142       A reference to a reference now stringifies as "REF(0x81485ec)" instead
143       of "SCALAR(0x81485ec)" in order to be more consistent with the return
144       value of ref().
145
146   pack/unpack D/F recycled
147       The undocumented pack/unpack template letters D/F have been recycled
148       for better use: now they stand for long double (if supported by the
149       platform) and NV (Perl internal floating point type).  (They used to be
150       aliases for d/f, but you never knew that.)
151
152   glob() now returns filenames in alphabetical order
153       The list of filenames from glob() (or <...>) is now by default sorted
154       alphabetically to be csh-compliant (which is what happened before in
155       most Unix platforms).  (bsd_glob() does still sort platform natively,
156       ASCII or EBCDIC, unless GLOB_ALPHASORT is specified.) [561]
157
158   Deprecations
159       •   The semantics of bless(REF, REF) were unclear and until someone
160           proves it to make some sense, it is forbidden.
161
162       •   The obsolete chat2 library that should never have been allowed to
163           escape the laboratory has been decommissioned.
164
165       •   Using chdir("") or chdir(undef) instead of explicit chdir() is
166           doubtful.  A failure (think chdir(some_function()) can lead into
167           unintended chdir() to the home directory, therefore this behaviour
168           is deprecated.
169
170       •   The builtin dump() function has probably outlived most of its
171           usefulness.  The core-dumping functionality will remain in future
172           available as an explicit call to "CORE::dump()", but in future
173           releases the behaviour of an unqualified "dump()" call may change.
174
175       •   The very dusty examples in the eg/ directory have been removed.
176           Suggestions for new shiny examples welcome but the main issue is
177           that the examples need to be documented, tested and (most
178           importantly) maintained.
179
180       •   The (bogus) escape sequences \8 and \9 now give an optional warning
181           ("Unrecognized escape passed through").  There is no need to
182           \-escape any "\w" character.
183
184       •   The *glob{FILEHANDLE} is deprecated, use *glob{IO} instead.
185
186       •   The "package;" syntax ("package" without an argument) has been
187           deprecated.  Its semantics were never that clear and its
188           implementation even less so.  If you have used that feature to
189           disallow all but fully qualified variables, "use strict;" instead.
190
191       •   The unimplemented POSIX regex features [[.cc.]] and [[=c=]] are
192           still recognised but now cause fatal errors.  The previous
193           behaviour of ignoring them by default and warning if requested was
194           unacceptable since it, in a way, falsely promised that the features
195           could be used.
196
197       •   In future releases, non-PerlIO aware XS modules may become
198           completely unsupported.  Since PerlIO is a drop-in replacement for
199           stdio at the source code level, this shouldn't be that drastic a
200           change.
201
202       •   Previous versions of perl and some readings of some sections of
203           Camel III implied that the ":raw" "discipline" was the inverse of
204           ":crlf".  Turning off "clrfness" is no longer enough to make a
205           stream truly binary. So the PerlIO ":raw" layer (or "discipline",
206           to use the Camel book's older terminology) is now formally defined
207           as being equivalent to binmode(FH) - which is in turn defined as
208           doing whatever is necessary to pass each byte as-is without any
209           translation.  In particular binmode(FH) - and hence ":raw" - will
210           now turn off both CRLF and UTF-8 translation and remove other
211           layers (e.g. :encoding()) which would modify byte stream.
212
213       •   The current user-visible implementation of pseudo-hashes (the weird
214           use of the first array element) is deprecated starting from Perl
215           5.8.0 and will be removed in Perl 5.10.0, and the feature will be
216           implemented differently.  Not only is the current interface rather
217           ugly, but the current implementation slows down normal array and
218           hash use quite noticeably. The "fields" pragma interface will
219           remain available.  The restricted hashes interface is expected to
220           be the replacement interface (see Hash::Util).  If your existing
221           programs depends on the underlying implementation, consider using
222           Class::PseudoHash from CPAN.
223
224       •   The syntaxes "@a->[...]" and  "%h->{...}" have now been deprecated.
225
226       •   After years of trying, suidperl is considered to be too complex to
227           ever be considered truly secure.  The suidperl functionality is
228           likely to be removed in a future release.
229
230       •   The 5.005 threads model (module "Thread") is deprecated and
231           expected to be removed in Perl 5.10.  Multithreaded code should be
232           migrated to the new ithreads model (see threads, threads::shared
233           and perlthrtut).
234
235       •   The long deprecated uppercase aliases for the string comparison
236           operators (EQ, NE, LT, LE, GE, GT) have now been removed.
237
238       •   The tr///C and tr///U features have been removed and will not
239           return; the interface was a mistake.  Sorry about that.  For
240           similar functionality, see pack('U0', ...) and pack('C0', ...).
241           [561]
242
243       •   Earlier Perls treated "sub foo (@bar)" as equivalent to "sub foo
244           (@)".  The prototypes are now checked better at compile-time for
245           invalid syntax.  An optional warning is generated ("Illegal
246           character in prototype...")  but this may be upgraded to a fatal
247           error in a future release.
248
249       •   The "exec LIST" and "system LIST" operations now produce warnings
250           on tainted data and in some future release they will produce fatal
251           errors.
252
253       •   The existing behaviour when localising tied arrays and hashes is
254           wrong, and will be changed in a future release, so do not rely on
255           the existing behaviour. See "Localising Tied Arrays and Hashes Is
256           Broken".
257

Core Enhancements

259   Unicode Overhaul
260       Unicode in general should be now much more usable than in Perl 5.6.0
261       (or even in 5.6.1).  Unicode can be used in hash keys, Unicode in
262       regular expressions should work now, Unicode in tr/// should work now,
263       Unicode in I/O should work now.  See perluniintro for introduction and
264       perlunicode for details.
265
266       •   The Unicode Character Database coming with Perl has been upgraded
267           to Unicode 3.2.0.  For more information, see
268           http://www.unicode.org/ .  [561+] (5.6.1 has UCD 3.0.1.)
269
270       •   For developers interested in enhancing Perl's Unicode capabilities:
271           almost all the UCD files are included with the Perl distribution in
272           the lib/unicore subdirectory.  The most notable omission, for space
273           considerations, is the Unihan database.
274
275       •   The properties \p{Blank} and \p{SpacePerl} have been added. "Blank"
276           is like C isblank(), that is, it contains only "horizontal
277           whitespace" (the space character is, the newline isn't), and the
278           "SpacePerl" is the Unicode equivalent of "\s" (\p{Space} isn't,
279           since that includes the vertical tabulator character, whereas "\s"
280           doesn't.)
281
282           See "New Unicode Properties" earlier in this document for
283           additional information on changes with Unicode properties.
284
285   PerlIO is Now The Default
286       •   IO is now by default done via PerlIO rather than system's "stdio".
287           PerlIO allows "layers" to be "pushed" onto a file handle to alter
288           the handle's behaviour.  Layers can be specified at open time via
289           3-arg form of open:
290
291              open($fh,'>:crlf :utf8', $path) || ...
292
293           or on already opened handles via extended "binmode":
294
295              binmode($fh,':encoding(iso-8859-7)');
296
297           The built-in layers are: unix (low level read/write), stdio (as in
298           previous Perls), perlio (re-implementation of stdio buffering in a
299           portable manner), crlf (does CRLF <=> "\n" translation as on Win32,
300           but available on any platform).  A mmap layer may be available if
301           platform supports it (mostly Unixes).
302
303           Layers to be applied by default may be specified via the 'open'
304           pragma.
305
306           See "Installation and Configuration Improvements" for the effects
307           of PerlIO on your architecture name.
308
309       •   If your platform supports fork(), you can use the list form of
310           "open" for pipes.  For example:
311
312               open KID_PS, "-|", "ps", "aux" or die $!;
313
314           forks the ps(1) command (without spawning a shell, as there are
315           more than three arguments to open()), and reads its standard output
316           via the "KID_PS" filehandle.  See perlipc.
317
318       •   File handles can be marked as accepting Perl's internal encoding of
319           Unicode (UTF-8 or UTF-EBCDIC depending on platform) by a pseudo
320           layer ":utf8" :
321
322              open($fh,">:utf8","Uni.txt");
323
324           Note for EBCDIC users: the pseudo layer ":utf8" is erroneously
325           named for you since it's not UTF-8 what you will be getting but
326           instead UTF-EBCDIC.  See perlunicode, utf8, and
327           http://www.unicode.org/reports/tr16/ for more information.  In
328           future releases this naming may change.  See perluniintro for more
329           information about UTF-8.
330
331       •   If your environment variables (LC_ALL, LC_CTYPE, LANG) look like
332           you want to use UTF-8 (any of the variables match "/utf-?8/i"),
333           your STDIN, STDOUT, STDERR handles and the default open layer (see
334           open) are marked as UTF-8.  (This feature, like other new features
335           that combine Unicode and I/O, work only if you are using PerlIO,
336           but that's the default.)
337
338           Note that after this Perl really does assume that everything is
339           UTF-8: for example if some input handle is not, Perl will probably
340           very soon complain about the input data like this "Malformed UTF-8
341           ..." since any old eight-bit data is not legal UTF-8.
342
343           Note for code authors: if you want to enable your users to use
344           UTF-8 as their default encoding  but in your code still have eight-
345           bit I/O streams (such as images or zip files), you need to
346           explicitly open() or binmode() with ":bytes" (see "open" in
347           perlfunc and "binmode" in perlfunc), or you can just use
348           "binmode(FH)" (nice for pre-5.8.0 backward compatibility).
349
350       •   File handles can translate character encodings from/to Perl's
351           internal Unicode form on read/write via the ":encoding()" layer.
352
353       •   File handles can be opened to "in memory" files held in Perl
354           scalars via:
355
356              open($fh,'>', \$variable) || ...
357
358       •   Anonymous temporary files are available without need to 'use
359           FileHandle' or other module via
360
361              open($fh,"+>", undef) || ...
362
363           That is a literal undef, not an undefined value.
364
365   ithreads
366       The new interpreter threads ("ithreads" for short) implementation of
367       multithreading, by Arthur Bergman, replaces the old "5.005 threads"
368       implementation.  In the ithreads model any data sharing between threads
369       must be explicit, as opposed to the model where data sharing was
370       implicit.  See threads and threads::shared, and perlthrtut.
371
372       As a part of the ithreads implementation Perl will also use any
373       necessary and detectable reentrant libc interfaces.
374
375   Restricted Hashes
376       A restricted hash is restricted to a certain set of keys, no keys
377       outside the set can be added.  Also individual keys can be restricted
378       so that the key cannot be deleted and the value cannot be changed.  No
379       new syntax is involved: the Hash::Util module is the interface.
380
381   Safe Signals
382       Perl used to be fragile in that signals arriving at inopportune moments
383       could corrupt Perl's internal state.  Now Perl postpones handling of
384       signals until it's safe (between opcodes).
385
386       This change may have surprising side effects because signals no longer
387       interrupt Perl instantly.  Perl will now first finish whatever it was
388       doing, like finishing an internal operation (like sort()) or an
389       external operation (like an I/O operation), and only then look at any
390       arrived signals (and before starting the next operation).  No more
391       corrupt internal state since the current operation is always finished
392       first, but the signal may take more time to get heard.  Note that
393       breaking out from potentially blocking operations should still work,
394       though.
395
396   Understanding of Numbers
397       In general a lot of fixing has happened in the area of Perl's
398       understanding of numbers, both integer and floating point.  Since in
399       many systems the standard number parsing functions like "strtoul()" and
400       "atof()" seem to have bugs, Perl tries to work around their
401       deficiencies.  This results hopefully in more accurate numbers.
402
403       Perl now tries internally to use integer values in numeric conversions
404       and basic arithmetics (+ - * /) if the arguments are integers, and
405       tries also to keep the results stored internally as integers.  This
406       change leads to often slightly faster and always less lossy
407       arithmetics. (Previously Perl always preferred floating point numbers
408       in its math.)
409
410   Arrays now always interpolate into double-quoted strings [561]
411       In double-quoted strings, arrays now interpolate, no matter what.  The
412       behavior in earlier versions of perl 5 was that arrays would
413       interpolate into strings if the array had been mentioned before the
414       string was compiled, and otherwise Perl would raise a fatal compile-
415       time error.  In versions 5.000 through 5.003, the error was
416
417               Literal @example now requires backslash
418
419       In versions 5.004_01 through 5.6.0, the error was
420
421               In string, @example now must be written as \@example
422
423       The idea here was to get people into the habit of writing
424       "fred\@example.com" when they wanted a literal "@" sign, just as they
425       have always written "Give me back my \$5" when they wanted a literal
426       "$" sign.
427
428       Starting with 5.6.1, when Perl now sees an "@" sign in a double-quoted
429       string, it always attempts to interpolate an array, regardless of
430       whether or not the array has been used or declared already.  The fatal
431       error has been downgraded to an optional warning:
432
433               Possible unintended interpolation of @example in string
434
435       This warns you that "fred@example.com" is going to turn into "fred.com"
436       if you don't backslash the "@".  See
437       http://perl.plover.com/at-error.html for more details about the history
438       here.
439
440   Miscellaneous Changes
441       •   AUTOLOAD is now lvaluable, meaning that you can add the :lvalue
442           attribute to AUTOLOAD subroutines and you can assign to the
443           AUTOLOAD return value.
444
445       •   The $Config{byteorder} (and corresponding BYTEORDER in config.h)
446           was previously wrong in platforms if sizeof(long) was 4, but
447           sizeof(IV) was 8.  The byteorder was only sizeof(long) bytes long
448           (1234 or 4321), but now it is correctly sizeof(IV) bytes long,
449           (12345678 or 87654321).  (This problem didn't affect Windows
450           platforms.)
451
452           Also, $Config{byteorder} is now computed dynamically--this is more
453           robust with "fat binaries" where an executable image contains
454           binaries for more than one binary platform, and when cross-
455           compiling.
456
457       •   "perl -d:Module=arg,arg,arg" now works (previously one couldn't
458           pass in multiple arguments.)
459
460       •   "do" followed by a bareword now ensures that this bareword isn't a
461           keyword (to avoid a bug where "do q(foo.pl)" tried to call a
462           subroutine called "q").  This means that for example instead of "do
463           format()" you must write "do &format()".
464
465       •   The builtin dump() now gives an optional warning "dump() better
466           written as CORE::dump()", meaning that by default "dump(...)" is
467           resolved as the builtin dump() which dumps core and aborts, not as
468           (possibly) user-defined "sub dump".  To call the latter, qualify
469           the call as "&dump(...)".  (The whole dump() feature is to
470           considered deprecated, and possibly removed/changed in future
471           releases.)
472
473chomp() and chop() are now overridable.  Note, however, that their
474           prototype (as given by "prototype("CORE::chomp")" is undefined,
475           because it cannot be expressed and therefore one cannot really
476           write replacements to override these builtins.
477
478       •   END blocks are now run even if you exit/die in a BEGIN block.
479           Internally, the execution of END blocks is now controlled by
480           PL_exit_flags & PERL_EXIT_DESTRUCT_END. This enables the new
481           behaviour for Perl embedders. This will default in 5.10. See
482           perlembed.
483
484       •   Formats now support zero-padded decimal fields.
485
486       •   Although "you shouldn't do that", it was possible to write code
487           that depends on Perl's hashed key order (Data::Dumper does this).
488           The new algorithm "One-at-a-Time" produces a different hashed key
489           order.  More details are in "Performance Enhancements".
490
491       •   lstat(FILEHANDLE) now gives a warning because the operation makes
492           no sense.  In future releases this may become a fatal error.
493
494       •   Spurious syntax errors generated in certain situations, when glob()
495           caused File::Glob to be loaded for the first time, have been fixed.
496           [561]
497
498       •   Lvalue subroutines can now return "undef" in list context.
499           However, the lvalue subroutine feature still remains experimental.
500           [561+]
501
502       •   A lost warning "Can't declare ... dereference in my" has been
503           restored (Perl had it earlier but it became lost in later
504           releases.)
505
506       •   A new special regular expression variable has been introduced: $^N,
507           which contains the most-recently closed group (submatch).
508
509       •   "no Module;" does not produce an error even if Module does not have
510           an unimport() method.  This parallels the behavior of "use" vis-a-
511           vis "import". [561]
512
513       •   The numerical comparison operators return "undef" if either operand
514           is a NaN.  Previously the behaviour was unspecified.
515
516       •   "our" can now have an experimental optional attribute "unique" that
517           affects how global variables are shared among multiple
518           interpreters, see "our" in perlfunc.
519
520       •   The following builtin functions are now overridable: each(),
521           keys(), pop(), push(), shift(), splice(), unshift(). [561]
522
523       •   "pack() / unpack()" can now group template letters with "()" and
524           then apply repetition/count modifiers on the groups.
525
526       •   "pack() / unpack()" can now process the Perl internal numeric
527           types: IVs, UVs, NVs-- and also long doubles, if supported by the
528           platform.  The template letters are "j", "J", "F", and "D".
529
530       •   "pack('U0a*', ...)" can now be used to force a string to UTF-8.
531
532       •   my __PACKAGE__ $obj now works. [561]
533
534POSIX::sleep() now returns the number of unslept seconds (as the
535           POSIX standard says), as opposed to CORE::sleep() which returns the
536           number of slept seconds.
537
538printf() and sprintf() now support parameter reordering using the
539           "%\d+\$" and "*\d+\$" syntaxes.  For example
540
541               printf "%2\$s %1\$s\n", "foo", "bar";
542
543           will print "bar foo\n".  This feature helps in writing
544           internationalised software, and in general when the order of the
545           parameters can vary.
546
547       •   The (\&) prototype now works properly. [561]
548
549       •   prototype(\[$@%&]) is now available to implicitly create references
550           (useful for example if you want to emulate the tie() interface).
551
552       •   A new command-line option, "-t" is available.  It is the little
553           brother of "-T": instead of dying on taint violations, lexical
554           warnings are given.  This is only meant as a temporary debugging
555           aid while securing the code of old legacy applications.  This is
556           not a substitute for -T.
557
558       •   In other taint news, the "exec LIST" and "system LIST" have now
559           been considered too risky (think "exec @ARGV": it can start any
560           program with any arguments), and now the said forms cause a warning
561           under lexical warnings.  You should carefully launder the arguments
562           to guarantee their validity.  In future releases of Perl the forms
563           will become fatal errors so consider starting laundering now.
564
565       •   Tied hash interfaces are now required to have the EXISTS and DELETE
566           methods (either own or inherited).
567
568       •   If tr/// is just counting characters, it doesn't attempt to modify
569           its target.
570
571untie() will now call an UNTIE() hook if it exists.  See perltie
572           for details. [561]
573
574       •   "utime" in perlfunc now supports "utime undef, undef, @files" to
575           change the file timestamps to the current time.
576
577       •   The rules for allowing underscores (underbars) in numeric constants
578           have been relaxed and simplified: now you can have an underscore
579           simply between digits.
580
581       •   Rather than relying on C's argv[0] (which may not contain a full
582           pathname) where possible $^X is now set by asking the operating
583           system.  (eg by reading /proc/self/exe on Linux, /proc/curproc/file
584           on FreeBSD)
585
586       •   A new variable, "${^TAINT}", indicates whether taint mode is
587           enabled.
588
589       •   You can now override the readline() builtin, and this overrides
590           also the <FILEHANDLE> angle bracket operator.
591
592       •   The command-line options -s and -F are now recognized on the
593           shebang (#!) line.
594
595       •   Use of the "/c" match modifier without an accompanying "/g"
596           modifier elicits a new warning: "Use of /c modifier is meaningless
597           without /g".
598
599           Use of "/c" in substitutions, even with "/g", elicits "Use of /c
600           modifier is meaningless in s///".
601
602           Use of "/g" with "split" elicits "Use of /g modifier is meaningless
603           in split".
604
605       •   Support for the "CLONE" special subroutine had been added.  With
606           ithreads, when a new thread is created, all Perl data is cloned,
607           however non-Perl data cannot be cloned automatically.  In "CLONE"
608           you can do whatever you need to do, like for example handle the
609           cloning of non-Perl data, if necessary.  "CLONE" will be executed
610           once for every package that has it defined or inherited.  It will
611           be called in the context of the new thread, so all modifications
612           are made in the new area.
613
614           See perlmod
615

Modules and Pragmata

617   New Modules and Pragmata
618       •   "Attribute::Handlers", originally by Damian Conway and now
619           maintained by Arthur Bergman, allows a class to define attribute
620           handlers.
621
622               package MyPack;
623               use Attribute::Handlers;
624               sub Wolf :ATTR(SCALAR) { print "howl!\n" }
625
626               # later, in some package using or inheriting from MyPack...
627
628               my MyPack $Fluffy : Wolf; # the attribute handler Wolf will be called
629
630           Both variables and routines can have attribute handlers.  Handlers
631           can be specific to type (SCALAR, ARRAY, HASH, or CODE), or specific
632           to the exact compilation phase (BEGIN, CHECK, INIT, or END).  See
633           Attribute::Handlers.
634
635       •   "B::Concise", by Stephen McCamant, is a new compiler backend for
636           walking the Perl syntax tree, printing concise info about ops.  The
637           output is highly customisable.  See B::Concise. [561+]
638
639       •   The new bignum, bigint, and bigrat pragmas, by Tels, implement
640           transparent bignum support (using the Math::BigInt, Math::BigFloat,
641           and Math::BigRat backends).
642
643       •   "Class::ISA", by Sean Burke, is a module for reporting the search
644           path for a class's ISA tree.  See Class::ISA.
645
646       •   "Cwd" now has a split personality: if possible, an XS extension is
647           used, (this will hopefully be faster, more secure, and more robust)
648           but if not possible, the familiar Perl implementation is used.
649
650       •   "Devel::PPPort", originally by Kenneth Albanowski and now
651           maintained by Paul Marquess, has been added.  It is primarily used
652           by "h2xs" to enhance portability of XS modules between different
653           versions of Perl.  See Devel::PPPort.
654
655       •   "Digest", frontend module for calculating digests (checksums), from
656           Gisle Aas, has been added.  See Digest.
657
658       •   "Digest::MD5" for calculating MD5 digests (checksums) as defined in
659           RFC 1321, from Gisle Aas, has been added.  See Digest::MD5.
660
661               use Digest::MD5 'md5_hex';
662
663               $digest = md5_hex("Thirsty Camel");
664
665               print $digest, "\n"; # 01d19d9d2045e005c3f1b80e8b164de1
666
667           NOTE: the "MD5" backward compatibility module is deliberately not
668           included since its further use is discouraged.
669
670           See also PerlIO::via::QuotedPrint.
671
672       •   "Encode", originally by Nick Ing-Simmons and now maintained by Dan
673           Kogai, provides a mechanism to translate between different
674           character encodings.  Support for Unicode, ISO-8859-1, and ASCII
675           are compiled in to the module.  Several other encodings (like the
676           rest of the ISO-8859, CP*/Win*, Mac, KOI8-R, three variants EBCDIC,
677           Chinese, Japanese, and Korean encodings) are included and can be
678           loaded at runtime.  (For space considerations, the largest Chinese
679           encodings have been separated into their own CPAN module,
680           Encode::HanExtra, which Encode will use if available).  See Encode.
681
682           Any encoding supported by Encode module is also available to the
683           ":encoding()" layer if PerlIO is used.
684
685       •   "Hash::Util" is the interface to the new restricted hashes feature.
686           (Implemented by Jeffrey Friedl, Nick Ing-Simmons, and Michael
687           Schwern.)  See Hash::Util.
688
689       •   "I18N::Langinfo" can be used to query locale information.  See
690           I18N::Langinfo.
691
692       •   "I18N::LangTags", by Sean Burke, has functions for dealing with
693           RFC3066-style language tags.  See I18N::LangTags.
694
695       •   "ExtUtils::Constant", by Nicholas Clark, is a new tool for
696           extension writers for generating XS code to import C header
697           constants.  See ExtUtils::Constant.
698
699       •   "Filter::Simple", by Damian Conway, is an easy-to-use frontend to
700           Filter::Util::Call.  See Filter::Simple.
701
702               # in MyFilter.pm:
703
704               package MyFilter;
705
706               use Filter::Simple sub {
707                   while (my ($from, $to) = splice @_, 0, 2) {
708                           s/$from/$to/g;
709                   }
710               };
711
712               1;
713
714               # in user's code:
715
716               use MyFilter qr/red/ => 'green';
717
718               print "red\n";   # this code is filtered, will print "green\n"
719               print "bored\n"; # this code is filtered, will print "bogreen\n"
720
721               no MyFilter;
722
723               print "red\n";   # this code is not filtered, will print "red\n"
724
725       •   "File::Temp", by Tim Jenness, allows one to create temporary files
726           and directories in an easy, portable, and secure way.  See
727           File::Temp.  [561+]
728
729       •   "Filter::Util::Call", by Paul Marquess, provides you with the
730           framework to write source filters in Perl.  For most uses, the
731           frontend Filter::Simple is to be preferred.  See
732           Filter::Util::Call.
733
734       •   "if", by Ilya Zakharevich, is a new pragma for conditional
735           inclusion of modules.
736
737       •   libnet, by Graham Barr, is a collection of perl5 modules related to
738           network programming.  See Net::FTP, Net::NNTP, Net::Ping (not part
739           of libnet, but related), Net::POP3, Net::SMTP, and Net::Time.
740
741           Perl installation leaves libnet unconfigured; use libnetcfg to
742           configure it.
743
744       •   "List::Util", by Graham Barr, is a selection of general-utility
745           list subroutines, such as sum(), min(), first(), and shuffle().
746           See List::Util.
747
748       •   "Locale::Constants", "Locale::Country", "Locale::Currency"
749           "Locale::Language", and Locale::Script, by Neil Bowers, have been
750           added.  They provide the codes for various locale standards, such
751           as "fr" for France, "usd" for US Dollar, and "ja" for Japanese.
752
753               use Locale::Country;
754
755               $country = code2country('jp');               # $country gets 'Japan'
756               $code    = country2code('Norway');           # $code gets 'no'
757
758           See Locale::Constants, Locale::Country, Locale::Currency, and
759           Locale::Language.
760
761       •   "Locale::Maketext", by Sean Burke, is a localization framework.
762           See Locale::Maketext, and Locale::Maketext::TPJ13.  The latter is
763           an article about software localization, originally published in The
764           Perl Journal #13, and republished here with kind permission.
765
766       •   "Math::BigRat" for big rational numbers, to accompany Math::BigInt
767           and Math::BigFloat, from Tels.  See Math::BigRat.
768
769       •   "Memoize" can make your functions faster by trading space for time,
770           from Mark-Jason Dominus.  See Memoize.
771
772       •   "MIME::Base64", by Gisle Aas, allows you to encode data in base64,
773           as defined in RFC 2045 - MIME (Multipurpose Internet Mail
774           Extensions).
775
776               use MIME::Base64;
777
778               $encoded = encode_base64('Aladdin:open sesame');
779               $decoded = decode_base64($encoded);
780
781               print $encoded, "\n"; # "QWxhZGRpbjpvcGVuIHNlc2FtZQ=="
782
783           See MIME::Base64.
784
785       •   "MIME::QuotedPrint", by Gisle Aas, allows you to encode data in
786           quoted-printable encoding, as defined in RFC 2045 - MIME
787           (Multipurpose Internet Mail Extensions).
788
789               use MIME::QuotedPrint;
790
791               $encoded = encode_qp("\xDE\xAD\xBE\xEF");
792               $decoded = decode_qp($encoded);
793
794               print $encoded, "\n"; # "=DE=AD=BE=EF\n"
795               print $decoded, "\n"; # "\xDE\xAD\xBE\xEF\n"
796
797           See also PerlIO::via::QuotedPrint.
798
799       •   "NEXT", by Damian Conway, is a pseudo-class for method redispatch.
800           See NEXT.
801
802       •   "open" is a new pragma for setting the default I/O layers for
803           open().
804
805       •   "PerlIO::scalar", by Nick Ing-Simmons, provides the implementation
806           of IO to "in memory" Perl scalars as discussed above.  It also
807           serves as an example of a loadable PerlIO layer.  Other future
808           possibilities include PerlIO::Array and PerlIO::Code.  See
809           PerlIO::scalar.
810
811       •   "PerlIO::via", by Nick Ing-Simmons, acts as a PerlIO layer and
812           wraps PerlIO layer functionality provided by a class (typically
813           implemented in Perl code).
814
815       •   "PerlIO::via::QuotedPrint", by Elizabeth Mattijsen, is an example
816           of a "PerlIO::via" class:
817
818               use PerlIO::via::QuotedPrint;
819               open($fh,">:via(QuotedPrint)",$path);
820
821           This will automatically convert everything output to $fh to Quoted-
822           Printable.  See PerlIO::via and PerlIO::via::QuotedPrint.
823
824       •   "Pod::ParseLink", by Russ Allbery, has been added, to parse L<>
825           links in pods as described in the new perlpodspec.
826
827       •   "Pod::Text::Overstrike", by Joe Smith, has been added.  It converts
828           POD data to formatted overstrike text.  See Pod::Text::Overstrike.
829           [561+]
830
831       •   "Scalar::Util" is a selection of general-utility scalar
832           subroutines, such as blessed(), reftype(), and tainted().  See
833           Scalar::Util.
834
835       •   "sort" is a new pragma for controlling the behaviour of sort().
836
837       •   "Storable" gives persistence to Perl data structures by allowing
838           the storage and retrieval of Perl data to and from files in a fast
839           and compact binary format.  Because in effect Storable does
840           serialisation of Perl data structures, with it you can also clone
841           deep, hierarchical datastructures.  Storable was originally created
842           by Raphael Manfredi, but it is now maintained by Abhijit Menon-Sen.
843           Storable has been enhanced to understand the two new hash features,
844           Unicode keys and restricted hashes.  See Storable.
845
846       •   "Switch", by Damian Conway, has been added.  Just by saying
847
848               use Switch;
849
850           you have "switch" and "case" available in Perl.
851
852               use Switch;
853
854               switch ($val) {
855
856                           case 1          { print "number 1" }
857                           case "a"        { print "string a" }
858                           case [1..10,42] { print "number in list" }
859                           case (@array)   { print "number in list" }
860                           case /\w+/      { print "pattern" }
861                           case qr/\w+/    { print "pattern" }
862                           case (%hash)    { print "entry in hash" }
863                           case (\%hash)   { print "entry in hash" }
864                           case (\&sub)    { print "arg to subroutine" }
865                           else            { print "previous case not true" }
866               }
867
868           See Switch.
869
870       •   "Test::More", by Michael Schwern, is yet another framework for
871           writing test scripts, more extensive than Test::Simple.  See
872           Test::More.
873
874       •   "Test::Simple", by Michael Schwern, has basic utilities for writing
875           tests.   See Test::Simple.
876
877       •   "Text::Balanced", by Damian Conway, has been added, for extracting
878           delimited text sequences from strings.
879
880               use Text::Balanced 'extract_delimited';
881
882               ($a, $b) = extract_delimited("'never say never', he never said", "'", '');
883
884           $a will be "'never say never'", $b will be ', he never said'.
885
886           In addition to extract_delimited(), there are also
887           extract_bracketed(), extract_quotelike(), extract_codeblock(),
888           extract_variable(), extract_tagged(), extract_multiple(),
889           gen_delimited_pat(), and gen_extract_tagged().  With these, you can
890           implement rather advanced parsing algorithms.  See Text::Balanced.
891
892       •   "threads", by Arthur Bergman, is an interface to interpreter
893           threads.  Interpreter threads (ithreads) is the new thread model
894           introduced in Perl 5.6 but only available as an internal interface
895           for extension writers (and for Win32 Perl for "fork()" emulation).
896           See threads, threads::shared, and perlthrtut.
897
898       •   "threads::shared", by Arthur Bergman, allows data sharing for
899           interpreter threads.  See threads::shared.
900
901       •   "Tie::File", by Mark-Jason Dominus, associates a Perl array with
902           the lines of a file.  See Tie::File.
903
904       •   "Tie::Memoize", by Ilya Zakharevich, provides on-demand loaded
905           hashes.  See Tie::Memoize.
906
907       •   "Tie::RefHash::Nestable", by Edward Avis, allows storing hash
908           references (unlike the standard Tie::RefHash)  The module is
909           contained within Tie::RefHash.  See Tie::RefHash.
910
911       •   "Time::HiRes", by Douglas E. Wegscheid, provides high resolution
912           timing (ualarm, usleep, and gettimeofday).  See Time::HiRes.
913
914       •   "Unicode::UCD" offers a querying interface to the Unicode Character
915           Database.  See Unicode::UCD.
916
917       •   "Unicode::Collate", by SADAHIRO Tomoyuki, implements the UCA
918           (Unicode Collation Algorithm) for sorting Unicode strings.  See
919           Unicode::Collate.
920
921       •   "Unicode::Normalize", by SADAHIRO Tomoyuki, implements the various
922           Unicode normalization forms.  See Unicode::Normalize.
923
924       •   "XS::APItest", by Tim Jenness, is a test extension that exercises
925           XS APIs.  Currently only "printf()" is tested: how to output
926           various basic data types from XS.
927
928       •   "XS::Typemap", by Tim Jenness, is a test extension that exercises
929           XS typemaps.  Nothing gets installed, but the code is worth
930           studying for extension writers.
931
932   Updated And Improved Modules and Pragmata
933       •   The following independently supported modules have been updated to
934           the newest versions from CPAN: CGI, CPAN, DB_File, File::Spec,
935           File::Temp, Getopt::Long, Math::BigFloat, Math::BigInt, the
936           podlators bundle (Pod::Man, Pod::Text), Pod::LaTeX [561+],
937           Pod::Parser, Storable, Term::ANSIColor, Test, Text-Tabs+Wrap.
938
939attributes::reftype() now works on tied arguments.
940
941       •   AutoLoader can now be disabled with "no AutoLoader;".
942
943       •   B::Deparse has been significantly enhanced by Robin Houston.  It
944           can now deparse almost all of the standard test suite (so that the
945           tests still succeed).  There is a make target "test.deparse" for
946           trying this out.
947
948       •   Carp now has better interface documentation, and the @CARP_NOT
949           interface has been added to get optional control over where errors
950           are reported independently of @ISA, by Ben Tilly.
951
952       •   Class::Struct can now define the classes in compile time.
953
954       •   Class::Struct now assigns the array/hash element if the accessor is
955           called with an array/hash element as the sole argument.
956
957       •   The return value of Cwd::fastcwd() is now tainted.
958
959       •   Data::Dumper now has an option to sort hashes.
960
961       •   Data::Dumper now has an option to dump code references using
962           B::Deparse.
963
964       •   DB_File now supports newer Berkeley DB versions, among other
965           improvements.
966
967       •   Devel::Peek now has an interface for the Perl memory statistics
968           (this works only if you are using perl's malloc, and if you have
969           compiled with debugging).
970
971       •   The English module can now be used without the infamous performance
972           hit by saying
973
974                   use English '-no_match_vars';
975
976           (Assuming, of course, that you don't need the troublesome variables
977           "$`", $&, or "$'".)  Also, introduced @LAST_MATCH_START and
978           @LAST_MATCH_END English aliases for "@-" and "@+".
979
980       •   ExtUtils::MakeMaker has been significantly cleaned up and fixed.
981           The enhanced version has also been backported to earlier releases
982           of Perl and submitted to CPAN so that the earlier releases can
983           enjoy the fixes.
984
985       •   The arguments of WriteMakefile() in Makefile.PL are now checked for
986           sanity much more carefully than before.  This may cause new
987           warnings when modules are being installed.  See ExtUtils::MakeMaker
988           for more details.
989
990       •   ExtUtils::MakeMaker now uses File::Spec internally, which hopefully
991           leads to better portability.
992
993       •   Fcntl, Socket, and Sys::Syslog have been rewritten by Nicholas
994           Clark to use the new-style constant dispatch section (see
995           ExtUtils::Constant).  This means that they will be more robust and
996           hopefully faster.
997
998       •   File::Find now chdir()s correctly when chasing symbolic links.
999           [561]
1000
1001       •   File::Find now has pre- and post-processing callbacks.  It also
1002           correctly changes directories when chasing symbolic links.
1003           Callbacks (naughtily) exiting with "next;" instead of "return;" now
1004           work.
1005
1006       •   File::Find is now (again) reentrant.  It also has been made more
1007           portable.
1008
1009       •   The warnings issued by File::Find now belong to their own category.
1010           You can enable/disable them with "use/no warnings 'File::Find';".
1011
1012File::Glob::glob() has been renamed to File::Glob::bsd_glob()
1013           because the name clashes with the builtin glob().  The older name
1014           is still available for compatibility, but is deprecated. [561]
1015
1016       •   File::Glob now supports "GLOB_LIMIT" constant to limit the size of
1017           the returned list of filenames.
1018
1019       •   IPC::Open3 now allows the use of numeric file descriptors.
1020
1021       •   IO::Socket now has an atmark() method, which returns true if the
1022           socket is positioned at the out-of-band mark.  The method is also
1023           exportable as a sockatmark() function.
1024
1025       •   IO::Socket::INET failed to open the specified port if the service
1026           name was not known.  It now correctly uses the supplied port number
1027           as is. [561]
1028
1029       •   IO::Socket::INET has support for the ReusePort option (if your
1030           platform supports it).  The Reuse option now has an alias,
1031           ReuseAddr.  For clarity, you may want to prefer ReuseAddr.
1032
1033       •   IO::Socket::INET now supports a value of zero for "LocalPort"
1034           (usually meaning that the operating system will make one up.)
1035
1036       •   'use lib' now works identically to @INC.  Removing directories with
1037           'no lib' now works.
1038
1039       •   Math::BigFloat and Math::BigInt have undergone a full rewrite by
1040           Tels.  They are now magnitudes faster, and they support various
1041           bignum libraries such as GMP and PARI as their backends.
1042
1043       •   Math::Complex handles inf, NaN etc., better.
1044
1045       •   Net::Ping has been considerably enhanced by Rob Brown: multihoming
1046           is now supported, Win32 functionality is better, there is now time
1047           measuring functionality (optionally high-resolution using
1048           Time::HiRes), and there is now "external" protocol which uses
1049           Net::Ping::External module which runs your external ping utility
1050           and parses the output.  A version of Net::Ping::External is
1051           available in CPAN.
1052
1053           Note that some of the Net::Ping tests are disabled when running
1054           under the Perl distribution since one cannot assume one or more of
1055           the following: enabled echo port at localhost, full Internet
1056           connectivity, or sympathetic firewalls.  You can set the
1057           environment variable PERL_TEST_Net_Ping to "1" (one) before running
1058           the Perl test suite to enable all the Net::Ping tests.
1059
1060POSIX::sigaction() is now much more flexible and robust.  You can
1061           now install coderef handlers, 'DEFAULT', and 'IGNORE' handlers,
1062           installing new handlers was not atomic.
1063
1064       •   In Safe, %INC is now localised in a Safe compartment so that
1065           use/require work.
1066
1067       •   In SDBM_File on DOSish platforms, some keys went missing because of
1068           lack of support for files with "holes".  A workaround for the
1069           problem has been added.
1070
1071       •   In Search::Dict one can now have a pre-processing hook for the
1072           lines being searched.
1073
1074       •   The Shell module now has an OO interface.
1075
1076       •   In Sys::Syslog there is now a failover mechanism that will go
1077           through alternative connection mechanisms until the message is
1078           successfully logged.
1079
1080       •   The Test module has been significantly enhanced.
1081
1082Time::Local::timelocal() does not handle fractional seconds
1083           anymore.  The rationale is that neither does localtime(), and
1084           timelocal() and localtime() are supposed to be inverses of each
1085           other.
1086
1087       •   The vars pragma now supports declaring fully qualified variables.
1088           (Something that "our()" does not and will not support.)
1089
1090       •   The "utf8::" name space (as in the pragma) provides various Perl-
1091           callable functions to provide low level access to Perl's internal
1092           Unicode representation.  At the moment only length() has been
1093           implemented.
1094

Utility Changes

1096       •   Emacs perl mode (emacs/cperl-mode.el) has been updated to version
1097           4.31.
1098
1099emacs/e2ctags.pl is now much faster.
1100
1101       •   "enc2xs" is a tool for people adding their own encodings to the
1102           Encode module.
1103
1104       •   "h2ph" now supports C trigraphs.
1105
1106       •   "h2xs" now produces a template README.
1107
1108       •   "h2xs" now uses "Devel::PPPort" for better portability between
1109           different versions of Perl.
1110
1111       •   "h2xs" uses the new ExtUtils::Constant module which will affect
1112           newly created extensions that define constants.  Since the new code
1113           is more correct (if you have two constants where the first one is a
1114           prefix of the second one, the first constant never got defined),
1115           less lossy (it uses integers for integer constant, as opposed to
1116           the old code that used floating point numbers even for integer
1117           constants), and slightly faster, you might want to consider
1118           regenerating your extension code (the new scheme makes regenerating
1119           easy).  h2xs now also supports C trigraphs.
1120
1121       •   "libnetcfg" has been added to configure libnet.
1122
1123       •   "perlbug" is now much more robust.  It also sends the bug report to
1124           perl.org, not perl.com.
1125
1126       •   "perlcc" has been rewritten and its user interface (that is,
1127           command line) is much more like that of the Unix C compiler, cc.
1128           (The perlbc tools has been removed.  Use "perlcc -B" instead.)
1129           Note that perlcc is still considered very experimental and
1130           unsupported. [561]
1131
1132       •   "perlivp" is a new Installation Verification Procedure utility for
1133           running any time after installing Perl.
1134
1135       •   "piconv" is an implementation of the character conversion utility
1136           "iconv", demonstrating the new Encode module.
1137
1138       •   "pod2html" now allows specifying a cache directory.
1139
1140       •   "pod2html" now produces XHTML 1.0.
1141
1142       •   "pod2html" now understands POD written using different line endings
1143           (PC-like CRLF versus Unix-like LF versus MacClassic-like CR).
1144
1145       •   "s2p" has been completely rewritten in Perl.  (It is in fact a full
1146           implementation of sed in Perl: you can use the sed functionality by
1147           using the "psed" utility.)
1148
1149       •   "xsubpp" now understands POD documentation embedded in the *.xs
1150           files. [561]
1151
1152       •   "xsubpp" now supports the OUT keyword.
1153

New Documentation

1155       •   perl56delta details the changes between the 5.005 release and the
1156           5.6.0 release.
1157
1158       •   perlclib documents the internal replacements for standard C library
1159           functions.  (Interesting only for extension writers and Perl core
1160           hackers.) [561+]
1161
1162       •   perldebtut is a Perl debugging tutorial. [561+]
1163
1164       •   perlebcdic contains considerations for running Perl on EBCDIC
1165           platforms. [561+]
1166
1167       •   perlintro is a gentle introduction to Perl.
1168
1169       •   perliol documents the internals of PerlIO with layers.
1170
1171       •   perlmodstyle is a style guide for writing modules.
1172
1173       •   perlnewmod tells about writing and submitting a new module. [561+]
1174
1175       •   perlpacktut is a pack() tutorial.
1176
1177       •   perlpod has been rewritten to be clearer and to record the best
1178           practices gathered over the years.
1179
1180       •   perlpodspec is a more formal specification of the pod format,
1181           mainly of interest for writers of pod applications, not to people
1182           writing in pod.
1183
1184       •   perlretut is a regular expression tutorial. [561+]
1185
1186       •   perlrequick is a regular expressions quick-start guide.  Yes, much
1187           quicker than perlretut. [561]
1188
1189       •   perltodo has been updated.
1190
1191       •   perltootc has been renamed as perltooc (to not to conflict with
1192           perltoot in filesystems restricted to "8.3" names).
1193
1194       •   perluniintro is an introduction to using Unicode in Perl.
1195           (perlunicode is more of a detailed reference and background
1196           information)
1197
1198       •   perlutil explains the command line utilities packaged with the Perl
1199           distribution. [561+]
1200
1201       The following platform-specific documents are available before the
1202       installation as README.platform, and after the installation as
1203       perlplatform:
1204
1205           perlaix perlamiga perlapollo perlbeos perlbs2000
1206           perlce perlcygwin perldgux perldos perlepoc perlfreebsd perlhpux
1207           perlhurd perlirix perlmachten perlmacos perlmint perlmpeix
1208           perlnetware perlos2 perlos390 perlplan9 perlqnx perlsolaris
1209           perltru64 perluts perlvmesa perlvms perlvos perlwin32
1210
1211       These documents usually detail one or more of the following subjects:
1212       configuring, building, testing, installing, and sometimes also using
1213       Perl on the said platform.
1214
1215       Eastern Asian Perl users are now welcomed in their own languages:
1216       README.jp (Japanese), README.ko (Korean), README.cn (simplified
1217       Chinese) and README.tw (traditional Chinese), which are written in
1218       normal pod but encoded in EUC-JP, EUC-KR, EUC-CN and Big5.  These will
1219       get installed as
1220
1221          perljp perlko perlcn perltw
1222
1223       •   The documentation for the POSIX-BC platform is called "BS2000", to
1224           avoid confusion with the Perl POSIX module.
1225
1226       •   The documentation for the WinCE platform is called perlce
1227           (README.ce in the source code kit), to avoid confusion with the
1228           perlwin32 documentation on 8.3-restricted filesystems.
1229

Performance Enhancements

1231map() could get pathologically slow when the result list it
1232           generates is larger than the source list.  The performance has been
1233           improved for common scenarios. [561]
1234
1235sort() is also fully reentrant, in the sense that the sort function
1236           can itself call sort().  This did not work reliably in previous
1237           releases. [561]
1238
1239sort() has been changed to use primarily mergesort internally as
1240           opposed to the earlier quicksort.  For very small lists this may
1241           result in slightly slower sorting times, but in general the speedup
1242           should be at least 20%.  Additional bonuses are that the worst case
1243           behaviour of sort() is now better (in computer science terms it now
1244           runs in time O(N log N), as opposed to quicksort's Theta(N**2)
1245           worst-case run time behaviour), and that sort() is now stable
1246           (meaning that elements with identical keys will stay ordered as
1247           they were before the sort).  See the "sort" pragma for information.
1248
1249           The story in more detail: suppose you want to serve yourself a
1250           little slice of Pi.
1251
1252               @digits = ( 3,1,4,1,5,9 );
1253
1254           A numerical sort of the digits will yield (1,1,3,4,5,9), as
1255           expected.  Which 1 comes first is hard to know, since one 1 looks
1256           pretty much like any other.  You can regard this as totally
1257           trivial, or somewhat profound.  However, if you just want to sort
1258           the even digits ahead of the odd ones, then what will
1259
1260               sort { ($a % 2) <=> ($b % 2) } @digits;
1261
1262           yield?  The only even digit, 4, will come first.  But how about the
1263           odd numbers, which all compare equal?  With the quicksort algorithm
1264           used to implement Perl 5.6 and earlier, the order of ties is left
1265           up to the sort.  So, as you add more and more digits of Pi, the
1266           order in which the sorted even and odd digits appear will change.
1267           and, for sufficiently large slices of Pi, the quicksort algorithm
1268           in Perl 5.8 won't return the same results even if reinvoked with
1269           the same input.  The justification for this rests with quicksort's
1270           worst case behavior.  If you run
1271
1272              sort { $a <=> $b } ( 1 .. $N , 1 .. $N );
1273
1274           (something you might approximate if you wanted to merge two sorted
1275           arrays using sort), doubling $N doesn't just double the quicksort
1276           time, it quadruples it.  Quicksort has a worst case run time that
1277           can grow like N**2, so-called quadratic behaviour, and it can
1278           happen on patterns that may well arise in normal use.  You won't
1279           notice this for small arrays, but you will notice it with larger
1280           arrays, and you may not live long enough for the sort to complete
1281           on arrays of a million elements.  So the 5.8 quicksort scrambles
1282           large arrays before sorting them, as a statistical defence against
1283           quadratic behaviour.  But that means if you sort the same large
1284           array twice, ties may be broken in different ways.
1285
1286           Because of the unpredictability of tie-breaking order, and the
1287           quadratic worst-case behaviour, quicksort was almost replaced
1288           completely with a stable mergesort.  Stable means that ties are
1289           broken to preserve the original order of appearance in the input
1290           array.  So
1291
1292               sort { ($a % 2) <=> ($b % 2) } (3,1,4,1,5,9);
1293
1294           will yield (4,3,1,1,5,9), guaranteed.  The even and odd numbers
1295           appear in the output in the same order they appeared in the input.
1296           Mergesort has worst case O(N log N) behaviour, the best value
1297           attainable.  And, ironically, this mergesort does particularly well
1298           where quicksort goes quadratic:  mergesort sorts (1..$N, 1..$N) in
1299           O(N) time.  But quicksort was rescued at the last moment because it
1300           is faster than mergesort on certain inputs and platforms.  For
1301           example, if you really don't care about the order of even and odd
1302           digits, quicksort will run in O(N) time; it's very good at sorting
1303           many repetitions of a small number of distinct elements.  The
1304           quicksort divide and conquer strategy works well on platforms with
1305           relatively small, very fast, caches.  Eventually, the problem gets
1306           whittled down to one that fits in the cache, from which point it
1307           benefits from the increased memory speed.
1308
1309           Quicksort was rescued by implementing a sort pragma to control
1310           aspects of the sort.  The stable subpragma forces stable behaviour,
1311           regardless of algorithm.  The _quicksort and _mergesort subpragmas
1312           are heavy-handed ways to select the underlying implementation.  The
1313           leading "_" is a reminder that these subpragmas may not survive
1314           beyond 5.8.  More appropriate mechanisms for selecting the
1315           implementation exist, but they wouldn't have arrived in time to
1316           save quicksort.
1317
1318       •   Hashes now use Bob Jenkins "One-at-a-Time" hashing key algorithm (
1319           http://burtleburtle.net/bob/hash/doobs.html ).  This algorithm is
1320           reasonably fast while producing a much better spread of values than
1321           the old hashing algorithm (originally by Chris Torek, later tweaked
1322           by Ilya Zakharevich).  Hash values output from the algorithm on a
1323           hash of all 3-char printable ASCII keys comes much closer to
1324           passing the DIEHARD random number generation tests.  According to
1325           perlbench, this change has not affected the overall speed of Perl.
1326
1327unshift() should now be noticeably faster.
1328

Installation and Configuration Improvements

1330   Generic Improvements
1331       •   INSTALL now explains how you can configure Perl to use 64-bit
1332           integers even on non-64-bit platforms.
1333
1334       •   Policy.sh policy change: if you are reusing a Policy.sh file (see
1335           INSTALL) and you use Configure -Dprefix=/foo/bar and in the old
1336           Policy $prefix eq $siteprefix and $prefix eq $vendorprefix, all of
1337           them will now be changed to the new prefix, /foo/bar.  (Previously
1338           only $prefix changed.)  If you do not like this new behaviour,
1339           specify prefix, siteprefix, and vendorprefix explicitly.
1340
1341       •   A new optional location for Perl libraries, otherlibdirs, is
1342           available.  It can be used for example for vendor add-ons without
1343           disturbing Perl's own library directories.
1344
1345       •   In many platforms, the vendor-supplied 'cc' is too stripped-down to
1346           build Perl (basically, 'cc' doesn't do ANSI C).  If this seems to
1347           be the case and 'cc' does not seem to be the GNU C compiler 'gcc',
1348           an automatic attempt is made to find and use 'gcc' instead.
1349
1350       •   gcc needs to closely track the operating system release to avoid
1351           build problems. If Configure finds that gcc was built for a
1352           different operating system release than is running, it now gives a
1353           clearly visible warning that there may be trouble ahead.
1354
1355       •   Since Perl 5.8 is not binary-compatible with previous releases of
1356           Perl, Configure no longer suggests including the 5.005 modules in
1357           @INC.
1358
1359       •   Configure "-S" can now run non-interactively. [561]
1360
1361       •   Configure support for pdp11-style memory models has been removed
1362           due to obsolescence. [561]
1363
1364       •   configure.gnu now works with options with whitespace in them.
1365
1366       •   installperl now outputs everything to STDERR.
1367
1368       •   Because PerlIO is now the default on most platforms, "-perlio"
1369           doesn't get appended to the $Config{archname} (also known as $^O)
1370           anymore.  Instead, if you explicitly choose not to use perlio
1371           (Configure command line option -Uuseperlio), you will get "-stdio"
1372           appended.
1373
1374       •   Another change related to the architecture name is that "-64all"
1375           (-Duse64bitall, or "maximally 64-bit") is appended only if your
1376           pointers are 64 bits wide.  (To be exact, the use64bitall is
1377           ignored.)
1378
1379       •   In AFS installations, one can configure the root of the AFS to be
1380           somewhere else than the default /afs by using the Configure
1381           parameter "-Dafsroot=/some/where/else".
1382
1383       •   APPLLIB_EXP, a lesser-known configuration-time definition, has been
1384           documented.  It can be used to prepend site-specific directories to
1385           Perl's default search path (@INC); see INSTALL for information.
1386
1387       •   The version of Berkeley DB used when the Perl (and, presumably, the
1388           DB_File extension) was built is now available as
1389           @Config{qw(db_version_major db_version_minor db_version_patch)}
1390           from Perl and as "DB_VERSION_MAJOR_CFG DB_VERSION_MINOR_CFG
1391           DB_VERSION_PATCH_CFG" from C.
1392
1393       •   Building Berkeley DB3 for compatibility modes for DB, NDBM, and
1394           ODBM has been documented in INSTALL.
1395
1396       •   If you have CPAN access (either network or a local copy such as a
1397           CD-ROM) you can during specify extra modules to Configure to build
1398           and install with Perl using the -Dextras=...  option.  See INSTALL
1399           for more details.
1400
1401       •   In addition to config.over, a new override file, config.arch, is
1402           available.  This file is supposed to be used by hints file writers
1403           for architecture-wide changes (as opposed to config.over which is
1404           for site-wide changes).
1405
1406       •   If your file system supports symbolic links, you can build Perl
1407           outside of the source directory by
1408
1409                   mkdir perl/build/directory
1410                   cd perl/build/directory
1411                   sh /path/to/perl/source/Configure -Dmksymlinks ...
1412
1413           This will create in perl/build/directory a tree of symbolic links
1414           pointing to files in /path/to/perl/source.  The original files are
1415           left unaffected.  After Configure has finished, you can just say
1416
1417                   make all test
1418
1419           and Perl will be built and tested, all in perl/build/directory.
1420           [561]
1421
1422       •   For Perl developers, several new make targets for profiling and
1423           debugging have been added; see perlhack.
1424
1425           •       Use of the gprof tool to profile Perl has been documented
1426                   in perlhack.  There is a make target called "perl.gprof"
1427                   for generating a gprofiled Perl executable.
1428
1429           •       If you have GCC 3, there is a make target called
1430                   "perl.gcov" for creating a gcoved Perl executable for
1431                   coverage analysis.  See perlhack.
1432
1433           •       If you are on IRIX or Tru64 platforms, new
1434                   profiling/debugging options have been added; see perlhack
1435                   for more information about pixie and Third Degree.
1436
1437       •   Guidelines of how to construct minimal Perl installations have been
1438           added to INSTALL.
1439
1440       •   The Thread extension is now not built at all under ithreads
1441           ("Configure -Duseithreads") because it wouldn't work anyway (the
1442           Thread extension requires being Configured with
1443           "-Duse5005threads").
1444
1445           Note that the 5.005 threads are unsupported and deprecated: if you
1446           have code written for the old threads you should migrate it to the
1447           new ithreads model.
1448
1449       •   The Gconvert macro ($Config{d_Gconvert}) used by perl for
1450           stringifying floating-point numbers is now more picky about using
1451           sprintf %.*g rules for the conversion.  Some platforms that used to
1452           use gcvt may now resort to the slower sprintf.
1453
1454       •   The obsolete method of making a special (e.g., debugging) flavor of
1455           perl by saying
1456
1457                   make LIBPERL=libperld.a
1458
1459           has been removed. Use -DDEBUGGING instead.
1460
1461   New Or Improved Platforms
1462       For the list of platforms known to support Perl, see "Supported
1463       Platforms" in perlport.
1464
1465       •   AIX dynamic loading should be now better supported.
1466
1467       •   AIX should now work better with gcc, threads, and 64-bitness.  Also
1468           the long doubles support in AIX should be better now.  See perlaix.
1469
1470       •   AtheOS ( http://www.atheos.cx/ ) is a new platform.
1471
1472       •   BeOS has been reclaimed.
1473
1474       •   The DG/UX platform now supports 5.005-style threads.  See perldgux.
1475
1476       •   The DYNIX/ptx platform (also known as dynixptx) is supported at or
1477           near osvers 4.5.2.
1478
1479       •   EBCDIC platforms (z/OS (also known as OS/390), POSIX-BC, and
1480           VM/ESA) have been regained.  Many test suite tests still fail and
1481           the co-existence of Unicode and EBCDIC isn't quite settled, but the
1482           situation is much better than with Perl 5.6.  See perlos390,
1483           perlbs2000 (for POSIX-BC), and perlvmesa for more information.
1484           (Note: support for VM/ESA was removed in Perl v5.18.0. The relevant
1485           information was in README.vmesa)
1486
1487       •   Building perl with -Duseithreads or -Duse5005threads now works
1488           under HP-UX 10.20 (previously it only worked under 10.30 or later).
1489           You will need a thread library package installed. See README.hpux.
1490           [561]
1491
1492       •   Mac OS Classic is now supported in the mainstream source package
1493           (MacPerl has of course been available since perl 5.004 but now the
1494           source code bases of standard Perl and MacPerl have been
1495           synchronised) [561]
1496
1497       •   Mac OS X (or Darwin) should now be able to build Perl even on HFS+
1498           filesystems.  (The case-insensitivity used to confuse the Perl
1499           build process.)
1500
1501       •   NCR MP-RAS is now supported. [561]
1502
1503       •   All the NetBSD specific patches (except for the installation
1504           specific ones) have been merged back to the main distribution.
1505
1506       •   NetWare from Novell is now supported.  See perlnetware.
1507
1508       •   NonStop-UX is now supported. [561]
1509
1510       •   NEC SUPER-UX is now supported.
1511
1512       •   All the OpenBSD specific patches (except for the installation
1513           specific ones) have been merged back to the main distribution.
1514
1515       •   Perl has been tested with the GNU pth userlevel thread package (
1516           http://www.gnu.org/software/pth/pth.html ).  All thread tests of
1517           Perl now work, but not without adding some yield()s to the tests,
1518           so while pth (and other userlevel thread implementations) can be
1519           considered to be "working" with Perl ithreads, keep in mind the
1520           possible non-preemptability of the underlying thread
1521           implementation.
1522
1523       •   Stratus VOS is now supported using Perl's native build method
1524           (Configure).  This is the recommended method to build Perl on VOS.
1525           The older methods, which build miniperl, are still available.  See
1526           perlvos. [561+]
1527
1528       •   The Amdahl UTS Unix mainframe platform is now supported. [561]
1529
1530       •   WinCE is now supported.  See perlce.
1531
1532       •   z/OS (formerly known as OS/390, formerly known as MVS OE) now has
1533           support for dynamic loading.  This is not selected by default,
1534           however, you must specify -Dusedl in the arguments of Configure.
1535           [561]
1536

Selected Bug Fixes

1538       Numerous memory leaks and uninitialized memory accesses have been
1539       hunted down.  Most importantly, anonymous subs used to leak quite a
1540       bit. [561]
1541
1542       •   The autouse pragma didn't work for Multi::Part::Function::Names.
1543
1544caller() could cause core dumps in certain situations.  Carp was
1545           sometimes affected by this problem.  In particular, caller() now
1546           returns a subroutine name of "(unknown)" for subroutines that have
1547           been removed from the symbol table.
1548
1549       •   chop(@list) in list context returned the characters chopped in
1550           reverse order.  This has been reversed to be in the right order.
1551           [561]
1552
1553       •   Configure no longer includes the DBM libraries (dbm, gdbm, db,
1554           ndbm) when building the Perl binary.  The only exception to this is
1555           SunOS 4.x, which needs them. [561]
1556
1557       •   The behaviour of non-decimal but numeric string constants such as
1558           "0x23" was platform-dependent: in some platforms that was seen as
1559           35, in some as 0, in some as a floating point number (don't ask).
1560           This was caused by Perl's using the operating system libraries in a
1561           situation where the result of the string to number conversion is
1562           undefined: now Perl consistently handles such strings as zero in
1563           numeric contexts.
1564
1565       •   Several debugger fixes: exit code now reflects the script exit
1566           code, condition "0" now treated correctly, the "d" command now
1567           checks line number, $. no longer gets corrupted, and all debugger
1568           output now goes correctly to the socket if RemotePort is set. [561]
1569
1570       •   The debugger (perl5db.pl) has been modified to present a more
1571           consistent commands interface, via (CommandSet=580).  perl5db.t was
1572           also added to test the changes, and as a placeholder for further
1573           tests.
1574
1575           See perldebug.
1576
1577       •   The debugger has a new "dumpDepth" option to control the maximum
1578           depth to which nested structures are dumped.  The "x" command has
1579           been extended so that "x N EXPR" dumps out the value of EXPR to a
1580           depth of at most N levels.
1581
1582       •   The debugger can now show lexical variables if you have the CPAN
1583           module PadWalker installed.
1584
1585       •   The order of DESTROYs has been made more predictable.
1586
1587       •   Perl 5.6.0 could emit spurious warnings about redefinition of
1588           dl_error() when statically building extensions into perl.  This has
1589           been corrected. [561]
1590
1591       •   dprofpp -R didn't work.
1592
1593       •   *foo{FORMAT} now works.
1594
1595       •   Infinity is now recognized as a number.
1596
1597       •   UNIVERSAL::isa no longer caches methods incorrectly.  (This broke
1598           the Tk extension with 5.6.0.) [561]
1599
1600       •   Lexicals I: lexicals outside an eval "" weren't resolved correctly
1601           inside a subroutine definition inside the eval "" if they were not
1602           already referenced in the top level of the eval""ed code.
1603
1604       •   Lexicals II: lexicals leaked at file scope into subroutines that
1605           were declared before the lexicals.
1606
1607       •   Lexical warnings now propagating correctly between scopes and into
1608           "eval "..."".
1609
1610       •   "use warnings qw(FATAL all)" did not work as intended.  This has
1611           been corrected. [561]
1612
1613warnings::enabled() now reports the state of $^W correctly if the
1614           caller isn't using lexical warnings. [561]
1615
1616       •   Line renumbering with eval and "#line" now works. [561]
1617
1618       •   Fixed numerous memory leaks, especially in eval "".
1619
1620       •   Localised tied variables no longer leak memory
1621
1622               use Tie::Hash;
1623               tie my %tied_hash => 'Tie::StdHash';
1624
1625               ...
1626
1627               # Used to leak memory every time local() was called;
1628               # in a loop, this added up.
1629               local($tied_hash{Foo}) = 1;
1630
1631       •   Localised hash elements (and %ENV) are correctly unlocalised to not
1632           exist, if they didn't before they were localised.
1633
1634               use Tie::Hash;
1635               tie my %tied_hash => 'Tie::StdHash';
1636
1637               ...
1638
1639               # Nothing has set the FOO element so far
1640
1641               { local $tied_hash{FOO} = 'Bar' }
1642
1643               # This used to print, but not now.
1644               print "exists!\n" if exists $tied_hash{FOO};
1645
1646           As a side effect of this fix, tied hash interfaces must define the
1647           EXISTS and DELETE methods.
1648
1649mkdir() now ignores trailing slashes in the directory name, as
1650           mandated by POSIX.
1651
1652       •   Some versions of glibc have a broken modfl().  This affects builds
1653           with "-Duselongdouble".  This version of Perl detects this
1654           brokenness and has a workaround for it.  The glibc release 2.2.2 is
1655           known to have fixed the modfl() bug.
1656
1657       •   Modulus of unsigned numbers now works (4063328477 % 65535 used to
1658           return 27406, instead of 27047). [561]
1659
1660       •   Some "not a number" warnings introduced in 5.6.0 eliminated to be
1661           more compatible with 5.005.  Infinity is now recognised as a
1662           number. [561]
1663
1664       •   Numeric conversions did not recognize changes in the string value
1665           properly in certain circumstances. [561]
1666
1667       •   Attributes (such as :shared) didn't work with our().
1668
1669our() variables will not cause bogus "Variable will not stay
1670           shared" warnings. [561]
1671
1672       •   "our" variables of the same name declared in two sibling blocks
1673           resulted in bogus warnings about "redeclaration" of the variables.
1674           The problem has been corrected. [561]
1675
1676       •   pack "Z" now correctly terminates the string with "\0".
1677
1678       •   Fix password routines which in some shadow password platforms (e.g.
1679           HP-UX) caused getpwent() to return every other entry.
1680
1681       •   The PERL5OPT environment variable (for passing command line
1682           arguments to Perl) didn't work for more than a single group of
1683           options. [561]
1684
1685       •   PERL5OPT with embedded spaces didn't work.
1686
1687printf() no longer resets the numeric locale to "C".
1688
1689       •   "qw(a\\b)" now parses correctly as 'a\\b': that is, as three
1690           characters, not four. [561]
1691
1692pos() did not return the correct value within s///ge in earlier
1693           versions.  This is now handled correctly. [561]
1694
1695       •   Printing quads (64-bit integers) with printf/sprintf now works
1696           without the q L ll prefixes (assuming you are on a quad-capable
1697           platform).
1698
1699       •   Regular expressions on references and overloaded scalars now work.
1700           [561+]
1701
1702       •   Right-hand side magic (GMAGIC) could in many cases such as string
1703           concatenation be invoked too many times.
1704
1705scalar() now forces scalar context even when used in void context.
1706
1707       •   SOCKS support is now much more robust.
1708
1709sort() arguments are now compiled in the right wantarray context
1710           (they were accidentally using the context of the sort() itself).
1711           The comparison block is now run in scalar context, and the
1712           arguments to be sorted are always provided list context. [561]
1713
1714       •   Changed the POSIX character class "[[:space:]]" to include the
1715           (very rarely used) vertical tab character.  Added a new POSIX-ish
1716           character class "[[:blank:]]" which stands for horizontal
1717           whitespace (currently, the space and the tab).
1718
1719       •   The tainting behaviour of sprintf() has been rationalized.  It does
1720           not taint the result of floating point formats anymore, making the
1721           behaviour consistent with that of string interpolation. [561]
1722
1723       •   Some cases of inconsistent taint propagation (such as within hash
1724           values) have been fixed.
1725
1726       •   The RE engine found in Perl 5.6.0 accidentally pessimised certain
1727           kinds of simple pattern matches.  These are now handled better.
1728           [561]
1729
1730       •   Regular expression debug output (whether through "use re 'debug'"
1731           or via "-Dr") now looks better. [561]
1732
1733       •   Multi-line matches like ""a\nxb\n" =~ /(?!\A)x/m" were flawed.  The
1734           bug has been fixed. [561]
1735
1736       •   Use of $& could trigger a core dump under some situations.  This is
1737           now avoided. [561]
1738
1739       •   The regular expression captured submatches ($1, $2, ...) are now
1740           more consistently unset if the match fails, instead of leaving
1741           false data lying around in them. [561]
1742
1743readline() on files opened in "slurp" mode could return an extra ""
1744           (blank line) at the end in certain situations.  This has been
1745           corrected. [561]
1746
1747       •   Autovivification of symbolic references of special variables
1748           described in perlvar (as in "${$num}") was accidentally disabled.
1749           This works again now. [561]
1750
1751       •   Sys::Syslog ignored the "LOG_AUTH" constant.
1752
1753       •   $AUTOLOAD, sort(), lock(), and spawning subprocesses in multiple
1754           threads simultaneously are now thread-safe.
1755
1756       •   Tie::Array's SPLICE method was broken.
1757
1758       •   Allow a read-only string on the left-hand side of a non-modifying
1759           tr///.
1760
1761       •   If "STDERR" is tied, warnings caused by "warn" and "die" now
1762           correctly pass to it.
1763
1764       •   Several Unicode fixes.
1765
1766           •       BOMs (byte order marks) at the beginning of Perl files
1767                   (scripts, modules) should now be transparently skipped.
1768                   UTF-16 and UCS-2 encoded Perl files should now be read
1769                   correctly.
1770
1771           •       The character tables have been updated to Unicode 3.2.0.
1772
1773           •       Comparing with utf8 data does not magically upgrade
1774                   non-utf8 data into utf8.  (This was a problem for example
1775                   if you were mixing data from I/O and Unicode data: your
1776                   output might have got magically encoded as UTF-8.)
1777
1778           •       Generating illegal Unicode code points such as U+FFFE, or
1779                   the UTF-16 surrogates, now also generates an optional
1780                   warning.
1781
1782           •       "IsAlnum", "IsAlpha", and "IsWord" now match titlecase.
1783
1784           •       Concatenation with the "." operator or via variable
1785                   interpolation, "eq", "substr", "reverse", "quotemeta", the
1786                   "x" operator, substitution with "s///", single-quoted
1787                   UTF-8, should now work.
1788
1789           •       The "tr///" operator now works.  Note that the "tr///CU"
1790                   functionality has been removed (but see pack('U0', ...)).
1791
1792           •       "eval "v200"" now works.
1793
1794           •       Perl 5.6.0 parsed m/\x{ab}/ incorrectly, leading to
1795                   spurious warnings.  This has been corrected. [561]
1796
1797           •       Zero entries were missing from the Unicode classes such as
1798                   "IsDigit".
1799
1800       •   Large unsigned numbers (those above 2**31) could sometimes lose
1801           their unsignedness, causing bogus results in arithmetic operations.
1802           [561]
1803
1804       •   The Perl parser has been stress tested using both random input and
1805           Markov chain input and the few found crashes and lockups have been
1806           fixed.
1807
1808   Platform Specific Changes and Fixes
1809       •   BSDI 4.*
1810
1811           Perl now works on post-4.0 BSD/OSes.
1812
1813       •   All BSDs
1814
1815           Setting $0 now works (as much as possible; see perlvar for
1816           details).
1817
1818       •   Cygwin
1819
1820           Numerous updates; currently synchronised with Cygwin 1.3.10.
1821
1822       •   Previously DYNIX/ptx had problems in its Configure probe for non-
1823           blocking I/O.
1824
1825       •   EPOC
1826
1827           EPOC now better supported.  See README.epoc. [561]
1828
1829       •   FreeBSD 3.*
1830
1831           Perl now works on post-3.0 FreeBSDs.
1832
1833       •   HP-UX
1834
1835           README.hpux updated; "Configure -Duse64bitall" now works; now uses
1836           HP-UX malloc instead of Perl malloc.
1837
1838       •   IRIX
1839
1840           Numerous compilation flag and hint enhancements; accidental mixing
1841           of 32-bit and 64-bit libraries (a doomed attempt) made much harder.
1842
1843       •   Linux
1844
1845           •       Long doubles should now work (see INSTALL). [561]
1846
1847           •       Linux previously had problems related to sockaddrlen when
1848                   using accept(), recvfrom() (in Perl: recv()),
1849                   getpeername(), and getsockname().
1850
1851       •   Mac OS Classic
1852
1853           Compilation of the standard Perl distribution in Mac OS Classic
1854           should now work if you have the Metrowerks development environment
1855           and the missing Mac-specific toolkit bits.  Contact the macperl
1856           mailing list for details.
1857
1858       •   MPE/iX
1859
1860           MPE/iX update after Perl 5.6.0.  See README.mpeix. [561]
1861
1862       •   NetBSD/threads: try installing the GNU pth (should be in the
1863           packages collection, or http://www.gnu.org/software/pth/), and
1864           Configure with -Duseithreads.
1865
1866       •   NetBSD/sparc
1867
1868           Perl now works on NetBSD/sparc.
1869
1870       •   OS/2
1871
1872           Now works with usethreads (see INSTALL). [561]
1873
1874       •   Solaris
1875
1876           64-bitness using the Sun Workshop compiler now works.
1877
1878       •   Stratus VOS
1879
1880           The native build method requires at least VOS Release 14.5.0 and
1881           GNU C++/GNU Tools 2.0.1 or later.  The Perl pack function now maps
1882           overflowed values to +infinity and underflowed values to -infinity.
1883
1884       •   Tru64 (aka Digital UNIX, aka DEC OSF/1)
1885
1886           The operating system version letter now recorded in
1887           $Config{osvers}.  Allow compiling with gcc (previously explicitly
1888           forbidden).  Compiling with gcc still not recommended because buggy
1889           code results, even with gcc 2.95.2.
1890
1891       •   Unicos
1892
1893           Fixed various alignment problems that lead into core dumps either
1894           during build or later; no longer dies on math errors at runtime;
1895           now using full quad integers (64 bits), previously was using only
1896           46 bit integers for speed.
1897
1898       •   VMS
1899
1900           See "Socket Extension Dynamic in VMS" and "IEEE-format Floating
1901           Point Default on OpenVMS Alpha" for important changes not otherwise
1902           listed here.
1903
1904           chdir() now works better despite a CRT bug; now works with
1905           MULTIPLICITY (see INSTALL); now works with Perl's malloc.
1906
1907           The tainting of %ENV elements via "keys" or "values" was previously
1908           unimplemented.  It now works as documented.
1909
1910           The "waitpid" emulation has been improved.  The worst bug (now
1911           fixed) was that a pid of -1 would cause a wildcard search of all
1912           processes on the system.
1913
1914           POSIX-style signals are now emulated much better on VMS versions
1915           prior to 7.0.
1916
1917           The "system" function and backticks operator have improved
1918           functionality and better error handling. [561]
1919
1920           File access tests now use current process privileges rather than
1921           the user's default privileges, which could sometimes result in a
1922           mismatch between reported access and actual access.  This
1923           improvement is only available on VMS v6.0 and later.
1924
1925           There is a new "kill" implementation based on "sys$sigprc" that
1926           allows older VMS systems (pre-7.0) to use "kill" to send signals
1927           rather than simply force exit.  This implementation also allows
1928           later systems to call "kill" from within a signal handler.
1929
1930           Iterative logical name translations are now limited to 10
1931           iterations in imitation of SHOW LOGICAL and other OpenVMS
1932           facilities.
1933
1934       •   Windows
1935
1936           •       Signal handling now works better than it used to.  It is
1937                   now implemented using a Windows message loop, and is
1938                   therefore less prone to random crashes.
1939
1940fork() emulation is now more robust, but still continues to
1941                   have a few esoteric bugs and caveats.  See perlfork for
1942                   details. [561+]
1943
1944           •       A failed (pseudo)fork now returns undef and sets errno to
1945                   EAGAIN. [561]
1946
1947           •       The following modules now work on Windows:
1948
1949                       ExtUtils::Embed         [561]
1950                       IO::Pipe
1951                       IO::Poll
1952                       Net::Ping
1953
1954IO::File::new_tmpfile() is no longer limited to 32767
1955                   invocations per-process.
1956
1957           •       Better chdir() return value for a non-existent directory.
1958
1959           •       Compiling perl using the 64-bit Platform SDK tools is now
1960                   supported.
1961
1962           •       The Win32::SetChildShowWindow() builtin can be used to
1963                   control the visibility of windows created by child
1964                   processes.  See Win32 for details.
1965
1966           •       Non-blocking waits for child processes (or pseudo-
1967                   processes) are supported via "waitpid($pid,
1968                   &POSIX::WNOHANG)".
1969
1970           •       The behavior of system() with multiple arguments has been
1971                   rationalized.  Each unquoted argument will be automatically
1972                   quoted to protect whitespace, and any existing whitespace
1973                   in the arguments will be preserved.  This improves the
1974                   portability of system(@args) by avoiding the need for
1975                   Windows "cmd" shell specific quoting in perl programs.
1976
1977                   Note that this means that some scripts that may have relied
1978                   on earlier buggy behavior may no longer work correctly.
1979                   For example, "system("nmake /nologo", @args)" will now
1980                   attempt to run the file "nmake /nologo" and will fail when
1981                   such a file isn't found.  On the other hand, perl will now
1982                   execute code such as "system("c:/Program
1983                   Files/MyApp/foo.exe", @args)" correctly.
1984
1985           •       The perl header files no longer suppress common warnings
1986                   from the Microsoft Visual C++ compiler.  This means that
1987                   additional warnings may now show up when compiling XS code.
1988
1989           •       Borland C++ v5.5 is now a supported compiler that can build
1990                   Perl.  However, the generated binaries continue to be
1991                   incompatible with those generated by the other supported
1992                   compilers (GCC and Visual C++). [561]
1993
1994           •       Duping socket handles with open(F, ">&MYSOCK") now works
1995                   under Windows 9x.  [561]
1996
1997           •       Current directory entries in %ENV are now correctly
1998                   propagated to child processes. [561]
1999
2000           •       New %ENV entries now propagate to subprocesses. [561]
2001
2002Win32::GetCwd() correctly returns C:\ instead of C: when at
2003                   the drive root.  Other bugs in chdir() and Cwd::cwd() have
2004                   also been fixed. [561]
2005
2006           •       The makefiles now default to the features enabled in
2007                   ActiveState ActivePerl (a popular Win32 binary
2008                   distribution). [561]
2009
2010           •       HTML files will now be installed in c:\perl\html instead of
2011                   c:\perl\lib\pod\html
2012
2013           •       REG_EXPAND_SZ keys are now allowed in registry settings
2014                   used by perl. [561]
2015
2016           •       Can now send() from all threads, not just the first one.
2017                   [561]
2018
2019           •       ExtUtils::MakeMaker now uses $ENV{LIB} to search for
2020                   libraries. [561]
2021
2022           •       Less stack reserved per thread so that more threads can run
2023                   concurrently. (Still 16M per thread.) [561]
2024
2025           •       "File::Spec->tmpdir()" now prefers C:/temp over /tmp (works
2026                   better when perl is running as service).
2027
2028           •       Better UNC path handling under ithreads. [561]
2029
2030wait(), waitpid(), and backticks now return the correct
2031                   exit status under Windows 9x. [561]
2032
2033           •       A socket handle leak in accept() has been fixed. [561]
2034

New or Changed Diagnostics

2036       Please see perldiag for more details.
2037
2038       •   Ambiguous range in the transliteration operator (like a-z-9) now
2039           gives a warning.
2040
2041       •   chdir("") and chdir(undef) now give a deprecation warning because
2042           they cause a possible unintentional chdir to the home directory.
2043           Say chdir() if you really mean that.
2044
2045       •   Two new debugging options have been added: if you have compiled
2046           your Perl with debugging, you can use the -DT [561] and -DR options
2047           to trace tokenising and to add reference counts to displaying
2048           variables, respectively.
2049
2050       •   The lexical warnings category "deprecated" is no longer a sub-
2051           category of the "syntax" category. It is now a top-level category
2052           in its own right.
2053
2054       •   Unadorned dump() will now give a warning suggesting to use explicit
2055           CORE::dump() if that's what really is meant.
2056
2057       •   The "Unrecognized escape" warning has been extended to include
2058           "\8", "\9", and "\_".  There is no need to escape any of the "\w"
2059           characters.
2060
2061       •   All regular expression compilation error messages are now hopefully
2062           easier to understand both because the error message now comes
2063           before the failed regex and because the point of failure is now
2064           clearly marked by a "<-- HERE" marker.
2065
2066       •   Various I/O (and socket) functions like binmode(), close(), and so
2067           forth now more consistently warn if they are used illogically
2068           either on a yet unopened or on an already closed filehandle (or
2069           socket).
2070
2071       •   Using lstat() on a filehandle now gives a warning.  (It's a non-
2072           sensical thing to do.)
2073
2074       •   The "-M" and "-m" options now warn if you didn't supply the module
2075           name.
2076
2077       •   If you in "use" specify a required minimum version, modules
2078           matching the name and but not defining a $VERSION will cause a
2079           fatal failure.
2080
2081       •   Using negative offset for vec() in lvalue context is now a warnable
2082           offense.
2083
2084       •   Odd number of arguments to overload::constant now elicits a
2085           warning.
2086
2087       •   Odd number of elements in anonymous hash now elicits a warning.
2088
2089       •   The various "opened only for", "on closed", "never opened" warnings
2090           drop the "main::" prefix for filehandles in the "main" package, for
2091           example "STDIN" instead of "main::STDIN".
2092
2093       •   Subroutine prototypes are now checked more carefully, you may get
2094           warnings for example if you have used non-prototype characters.
2095
2096       •   If an attempt to use a (non-blessed) reference as an array index is
2097           made, a warning is given.
2098
2099       •   "push @a;" and "unshift @a;" (with no values to push or unshift)
2100           now give a warning.  This may be a problem for generated and
2101           eval'ed code.
2102
2103       •   If you try to "pack" in perlfunc a number less than 0 or larger
2104           than 255 using the "C" format you will get an optional warning.
2105           Similarly for the "c" format and a number less than -128 or more
2106           than 127.
2107
2108       •   pack "P" format now demands an explicit size.
2109
2110       •   unpack "w" now warns of unterminated compressed integers.
2111
2112       •   Warnings relating to the use of PerlIO have been added.
2113
2114       •   Certain regex modifiers such as "(?o)" make sense only if applied
2115           to the entire regex.  You will get an optional warning if you try
2116           to do otherwise.
2117
2118       •   Variable length lookbehind has not yet been implemented, trying to
2119           use it will tell that.
2120
2121       •   Using arrays or hashes as references (e.g. "%foo->{bar}" has been
2122           deprecated for a while.  Now you will get an optional warning.
2123
2124       •   Warnings relating to the use of the new restricted hashes feature
2125           have been added.
2126
2127       •   Self-ties of arrays and hashes are not supported and fatal errors
2128           will happen even at an attempt to do so.
2129
2130       •   Using "sort" in scalar context now issues an optional warning.
2131           This didn't do anything useful, as the sort was not performed.
2132
2133       •   Using the /g modifier in split() is meaningless and will cause a
2134           warning.
2135
2136       •   Using splice() past the end of an array now causes a warning.
2137
2138       •   Malformed Unicode encodings (UTF-8 and UTF-16) cause a lot of
2139           warnings, as does trying to use UTF-16 surrogates (which are
2140           unimplemented).
2141
2142       •   Trying to use Unicode characters on an I/O stream without marking
2143           the stream's encoding (using open() or binmode()) will cause "Wide
2144           character" warnings.
2145
2146       •   Use of v-strings in use/require causes a (backward) portability
2147           warning.
2148
2149       •   Warnings relating to the use interpreter threads and their shared
2150           data have been added.
2151

Changed Internals

2153       •   PerlIO is now the default.
2154
2155       •   perlapi.pod (a companion to perlguts) now attempts to document the
2156           internal API.
2157
2158       •   You can now build a really minimal perl called microperl.  Building
2159           microperl does not require even running Configure; "make -f
2160           Makefile.micro" should be enough.  Beware: microperl makes many
2161           assumptions, some of which may be too bold; the resulting
2162           executable may crash or otherwise misbehave in wondrous ways.  For
2163           careful hackers only.
2164
2165       •   Added rsignal(), whichsig(), do_join(), op_clear, op_null,
2166           ptr_table_clear(), ptr_table_free(), sv_setref_uv(), and several
2167           UTF-8 interfaces to the publicised API.  For the full list of the
2168           available APIs see perlapi.
2169
2170       •   Made possible to propagate customised exceptions via croak()ing.
2171
2172       •   Now xsubs can have attributes just like subs.  (Well, at least the
2173           built-in attributes.)
2174
2175       •   dTHR and djSP have been obsoleted; the former removed (because it's
2176           a no-op) and the latter replaced with dSP.
2177
2178       •   PERL_OBJECT has been completely removed.
2179
2180       •   The MAGIC constants (e.g. 'P') have been macrofied (e.g.
2181           "PERL_MAGIC_TIED") for better source code readability and
2182           maintainability.
2183
2184       •   The regex compiler now maintains a structure that identifies nodes
2185           in the compiled bytecode with the corresponding syntactic features
2186           of the original regex expression.  The information is attached to
2187           the new "offsets" member of the "struct regexp". See perldebguts
2188           for more complete information.
2189
2190       •   The C code has been made much more "gcc -Wall" clean.  Some warning
2191           messages still remain in some platforms, so if you are compiling
2192           with gcc you may see some warnings about dubious practices.  The
2193           warnings are being worked on.
2194
2195perly.c, sv.c, and sv.h have now been extensively commented.
2196
2197       •   Documentation on how to use the Perl source repository has been
2198           added to Porting/repository.pod.
2199
2200       •   There are now several profiling make targets.
2201

Security Vulnerability Closed [561]

2203       (This change was already made in 5.7.0 but bears repeating here.)
2204       (5.7.0 came out before 5.6.1: the development branch 5.7 released
2205       earlier than the maintenance branch 5.6)
2206
2207       A potential security vulnerability in the optional suidperl component
2208       of Perl was identified in August 2000.  suidperl is neither built nor
2209       installed by default.  As of November 2001 the only known vulnerable
2210       platform is Linux, most likely all Linux distributions.  CERT and
2211       various vendors and distributors have been alerted about the
2212       vulnerability.  See
2213       http://www.cpan.org/src/5.0/sperl-2000-08-05/sperl-2000-08-05.txt for
2214       more information.
2215
2216       The problem was caused by Perl trying to report a suspected security
2217       exploit attempt using an external program, /bin/mail.  On Linux
2218       platforms the /bin/mail program had an undocumented feature which when
2219       combined with suidperl gave access to a root shell, resulting in a
2220       serious compromise instead of reporting the exploit attempt.  If you
2221       don't have /bin/mail, or if you have 'safe setuid scripts', or if
2222       suidperl is not installed, you are safe.
2223
2224       The exploit attempt reporting feature has been completely removed from
2225       Perl 5.8.0 (and the maintenance release 5.6.1, and it was removed also
2226       from all the Perl 5.7 releases), so that particular vulnerability isn't
2227       there anymore.  However, further security vulnerabilities are,
2228       unfortunately, always possible.  The suidperl functionality is most
2229       probably going to be removed in Perl 5.10.  In any case, suidperl
2230       should only be used by security experts who know exactly what they are
2231       doing and why they are using suidperl instead of some other solution
2232       such as sudo ( see http://www.courtesan.com/sudo/ ).
2233

New Tests

2235       Several new tests have been added, especially for the lib and ext
2236       subsections.  There are now about 69 000 individual tests (spread over
2237       about 700 test scripts), in the regression suite (5.6.1 has about 11
2238       700 tests, in 258 test scripts)  The exact numbers depend on the
2239       platform and Perl configuration used.  Many of the new tests are of
2240       course introduced by the new modules, but still in general Perl is now
2241       more thoroughly tested.
2242
2243       Because of the large number of tests, running the regression suite will
2244       take considerably longer time than it used to: expect the suite to take
2245       up to 4-5 times longer to run than in perl 5.6.  On a really fast
2246       machine you can hope to finish the suite in about 6-8 minutes
2247       (wallclock time).
2248
2249       The tests are now reported in a different order than in earlier Perls.
2250       (This happens because the test scripts from under t/lib have been moved
2251       to be closer to the library/extension they are testing.)
2252

Known Problems

2254   The Compiler Suite Is Still Very Experimental
2255       The compiler suite is slowly getting better but it continues to be
2256       highly experimental.  Use in production environments is discouraged.
2257
2258   Localising Tied Arrays and Hashes Is Broken
2259           local %tied_array;
2260
2261       doesn't work as one would expect: the old value is restored
2262       incorrectly.  This will be changed in a future release, but we don't
2263       know yet what the new semantics will exactly be.  In any case, the
2264       change will break existing code that relies on the current (ill-
2265       defined) semantics, so just avoid doing this in general.
2266
2267   Building Extensions Can Fail Because Of Largefiles
2268       Some extensions like mod_perl are known to have issues with
2269       `largefiles', a change brought by Perl 5.6.0 in which file offsets
2270       default to 64 bits wide, where supported.  Modules may fail to compile
2271       at all, or they may compile and work incorrectly.  Currently, there is
2272       no good solution for the problem, but Configure now provides
2273       appropriate non-largefile ccflags, ldflags, libswanted, and libs in the
2274       %Config hash (e.g., $Config{ccflags_nolargefiles}) so the extensions
2275       that are having problems can try configuring themselves without the
2276       largefileness.  This is admittedly not a clean solution, and the
2277       solution may not even work at all.  One potential failure is whether
2278       one can (or, if one can, whether it's a good idea to) link together at
2279       all binaries with different ideas about file offsets; all this is
2280       platform-dependent.
2281
2282   Modifying $_ Inside for(..)
2283          for (1..5) { $_++ }
2284
2285       works without complaint.  It shouldn't.  (You should be able to modify
2286       only lvalue elements inside the loops.)  You can see the correct
2287       behaviour by replacing the 1..5 with 1, 2, 3, 4, 5.
2288
2289   mod_perl 1.26 Doesn't Build With Threaded Perl
2290       Use mod_perl 1.27 or higher.
2291
2292   lib/ftmp-security tests warn 'system possibly insecure'
2293       Don't panic.  Read the 'make test' section of INSTALL instead.
2294
2295   libwww-perl (LWP) fails base/date #51
2296       Use libwww-perl 5.65 or later.
2297
2298   PDL failing some tests
2299       Use PDL 2.3.4 or later.
2300
2301   Perl_get_sv
2302       You may get errors like 'Undefined symbol "Perl_get_sv"' or "can't
2303       resolve symbol 'Perl_get_sv'", or the symbol may be "Perl_sv_2pv".
2304       This probably means that you are trying to use an older shared Perl
2305       library (or extensions linked with such) with Perl 5.8.0 executable.
2306       Perl used to have such a subroutine, but that is no more the case.
2307       Check your shared library path, and any shared Perl libraries in those
2308       directories.
2309
2310       Sometimes this problem may also indicate a partial Perl 5.8.0
2311       installation, see "Mac OS X dyld undefined symbols" for an example and
2312       how to deal with it.
2313
2314   Self-tying Problems
2315       Self-tying of arrays and hashes is broken in rather deep and hard-to-
2316       fix ways.  As a stop-gap measure to avoid people from getting
2317       frustrated at the mysterious results (core dumps, most often), it is
2318       forbidden for now (you will get a fatal error even from an attempt).
2319
2320       A change to self-tying of globs has caused them to be recursively
2321       referenced (see: "Two-Phased Garbage Collection" in perlobj).  You will
2322       now need an explicit untie to destroy a self-tied glob.  This behaviour
2323       may be fixed at a later date.
2324
2325       Self-tying of scalars and IO thingies works.
2326
2327   ext/threads/t/libc
2328       If this test fails, it indicates that your libc (C library) is not
2329       threadsafe.  This particular test stress tests the localtime() call to
2330       find out whether it is threadsafe.  See perlthrtut for more
2331       information.
2332
2333   Failure of Thread (5.005-style) tests
2334       Note that support for 5.005-style threading is deprecated, experimental
2335       and practically unsupported.  In 5.10, it is expected to be removed.
2336       You should migrate your code to ithreads.
2337
2338       The following tests are known to fail due to fundamental problems in
2339       the 5.005 threading implementation. These are not new failures--Perl
2340       5.005_0x has the same bugs, but didn't have these tests.
2341
2342        ../ext/B/t/xref.t                    255 65280    14   12  85.71%  3-14
2343        ../ext/List/Util/t/first.t           255 65280     7    4  57.14%  2 5-7
2344        ../lib/English.t                       2   512    54    2   3.70%  2-3
2345        ../lib/FileCache.t                                 5    1  20.00%  5
2346        ../lib/Filter/Simple/t/data.t                      6    3  50.00%  1-3
2347        ../lib/Filter/Simple/t/filter_only.                9    3  33.33%  1-2 5
2348        ../lib/Math/BigInt/t/bare_mbf.t                 1627    4   0.25%  8 11 1626-1627
2349        ../lib/Math/BigInt/t/bigfltpm.t                 1629    4   0.25%  10 13 1628-
2350                                                                           1629
2351        ../lib/Math/BigInt/t/sub_mbf.t                  1633    4   0.24%  8 11 1632-1633
2352        ../lib/Math/BigInt/t/with_sub.t                 1628    4   0.25%  9 12 1627-1628
2353        ../lib/Tie/File/t/31_autodefer.t     255 65280    65   32  49.23%  34-65
2354        ../lib/autouse.t                                  10    1  10.00%  4
2355        op/flip.t                                         15    1   6.67%  15
2356
2357       These failures are unlikely to get fixed as 5.005-style threads are
2358       considered fundamentally broken.  (Basically what happens is that
2359       competing threads can corrupt shared global state, one good example
2360       being regular expression engine's state.)
2361
2362   Timing problems
2363       The following tests may fail intermittently because of timing problems,
2364       for example if the system is heavily loaded.
2365
2366           t/op/alarm.t
2367           ext/Time/HiRes/HiRes.t
2368           lib/Benchmark.t
2369           lib/Memoize/t/expmod_t.t
2370           lib/Memoize/t/speed.t
2371
2372       In case of failure please try running them manually, for example
2373
2374           ./perl -Ilib ext/Time/HiRes/HiRes.t
2375
2376   Tied/Magical Array/Hash Elements Do Not Autovivify
2377       For normal arrays "$foo = \$bar[1]" will assign "undef" to $bar[1]
2378       (assuming that it didn't exist before), but for tied/magical arrays and
2379       hashes such autovivification does not happen because there is currently
2380       no way to catch the reference creation.  The same problem affects
2381       slicing over non-existent indices/keys of a tied/magical array/hash.
2382
2383   Unicode in package/class and subroutine names does not work
2384       One can have Unicode in identifier names, but not in package/class or
2385       subroutine names.  While some limited functionality towards this does
2386       exist as of Perl 5.8.0, that is more accidental than designed; use of
2387       Unicode for the said purposes is unsupported.
2388
2389       One reason of this unfinishedness is its (currently) inherent
2390       unportability: since both package names and subroutine names may need
2391       to be mapped to file and directory names, the Unicode capability of the
2392       filesystem becomes important-- and there unfortunately aren't portable
2393       answers.
2394

Platform Specific Problems

2396   AIX
2397       •   If using the AIX native make command, instead of just "make" issue
2398           "make all".  In some setups the former has been known to spuriously
2399           also try to run "make install".  Alternatively, you may want to use
2400           GNU make.
2401
2402       •   In AIX 4.2, Perl extensions that use C++ functions that use statics
2403           may have problems in that the statics are not getting initialized.
2404           In newer AIX releases, this has been solved by linking Perl with
2405           the libC_r library, but unfortunately in AIX 4.2 the said library
2406           has an obscure bug where the various functions related to time
2407           (such as time() and gettimeofday()) return broken values, and
2408           therefore in AIX 4.2 Perl is not linked against libC_r.
2409
2410       •   vac 5.0.0.0 May Produce Buggy Code For Perl
2411
2412           The AIX C compiler vac version 5.0.0.0 may produce buggy code,
2413           resulting in a few random tests failing when run as part of "make
2414           test", but when the failing tests are run by hand, they succeed.
2415           We suggest upgrading to at least vac version 5.0.1.0, that has been
2416           known to compile Perl correctly.  "lslpp -L|grep vac.C" will tell
2417           you the vac version.  See README.aix.
2418
2419       •   If building threaded Perl, you may get compilation warning from
2420           pp_sys.c:
2421
2422             "pp_sys.c", line 4651.39: 1506-280 (W) Function argument assignment between types "unsigned char*" and "const void*" is not allowed.
2423
2424           This is harmless; it is caused by the getnetbyaddr() and
2425           getnetbyaddr_r() having slightly different types for their first
2426           argument.
2427
2428   Alpha systems with old gccs fail several tests
2429       If you see op/pack, op/pat, op/regexp, or ext/Storable tests failing in
2430       a Linux/alpha or *BSD/Alpha, it's probably time to upgrade your gcc.
2431       gccs prior to 2.95.3 are definitely not good enough, and gcc 3.1 may be
2432       even better.  (RedHat Linux/alpha with gcc 3.1 reported no problems, as
2433       did Linux 2.4.18 with gcc 2.95.4.)  (In Tru64, it is preferable to use
2434       the bundled C compiler.)
2435
2436   AmigaOS
2437       Perl 5.8.0 doesn't build in AmigaOS.  It broke at some point during the
2438       ithreads work and we could not find Amiga experts to unbreak the
2439       problems.  Perl 5.6.1 still works for AmigaOS (as does the 5.7.2
2440       development release).
2441
2442   BeOS
2443       The following tests fail on 5.8.0 Perl in BeOS Personal 5.03:
2444
2445        t/op/lfs............................FAILED at test 17
2446        t/op/magic..........................FAILED at test 24
2447        ext/Fcntl/t/syslfs..................FAILED at test 17
2448        ext/File/Glob/t/basic...............FAILED at test 3
2449        ext/POSIX/t/sigaction...............FAILED at test 13
2450        ext/POSIX/t/waitpid.................FAILED at test 1
2451
2452       (Note: more information was available in README.beos until support for
2453       BeOS was removed in Perl v5.18.0)
2454
2455   Cygwin "unable to remap"
2456       For example when building the Tk extension for Cygwin, you may get an
2457       error message saying "unable to remap".  This is known problem with
2458       Cygwin, and a workaround is detailed in here:
2459       http://sources.redhat.com/ml/cygwin/2001-12/msg00894.html
2460
2461   Cygwin ndbm tests fail on FAT
2462       One can build but not install (or test the build of) the NDBM_File on
2463       FAT filesystems.  Installation (or build) on NTFS works fine.  If one
2464       attempts the test on a FAT install (or build) the following failures
2465       are expected:
2466
2467        ../ext/NDBM_File/ndbm.t       13  3328    71   59  83.10%  1-2 4 16-71
2468        ../ext/ODBM_File/odbm.t      255 65280    ??   ??       %  ??
2469        ../lib/AnyDBM_File.t           2   512    12    2  16.67%  1 4
2470        ../lib/Memoize/t/errors.t      0   139    11    5  45.45%  7-11
2471        ../lib/Memoize/t/tie_ndbm.t   13  3328     4    4 100.00%  1-4
2472        run/fresh_perl.t                          97    1   1.03%  91
2473
2474       NDBM_File fails and ODBM_File just coredumps.
2475
2476       If you intend to run only on FAT (or if using AnyDBM_File on FAT), run
2477       Configure with the -Ui_ndbm and -Ui_dbm options to prevent NDBM_File
2478       and ODBM_File being built.
2479
2480   DJGPP Failures
2481        t/op/stat............................FAILED at test 29
2482        lib/File/Find/t/find.................FAILED at test 1
2483        lib/File/Find/t/taint................FAILED at test 1
2484        lib/h2xs.............................FAILED at test 15
2485        lib/Pod/t/eol........................FAILED at test 1
2486        lib/Test/Harness/t/strap-analyze.....FAILED at test 8
2487        lib/Test/Harness/t/test-harness......FAILED at test 23
2488        lib/Test/Simple/t/exit...............FAILED at test 1
2489
2490       The above failures are known as of 5.8.0 with native builds with long
2491       filenames, but there are a few more if running under dosemu because of
2492       limitations (and maybe bugs) of dosemu:
2493
2494        t/comp/cpp...........................FAILED at test 3
2495        t/op/inccode.........................(crash)
2496
2497       and a few lib/ExtUtils tests, and several hundred Encode/t/Aliases.t
2498       failures that work fine with long filenames.  So you really might
2499       prefer native builds and long filenames.
2500
2501   FreeBSD built with ithreads coredumps reading large directories
2502       This is a known bug in FreeBSD 4.5's readdir_r(), it has been fixed in
2503       FreeBSD 4.6 (see perlfreebsd (README.freebsd)).
2504
2505   FreeBSD Failing locale Test 117 For ISO 8859-15 Locales
2506       The ISO 8859-15 locales may fail the locale test 117 in FreeBSD.  This
2507       is caused by the characters \xFF (y with diaeresis) and \xBE (Y with
2508       diaeresis) not behaving correctly when being matched case-
2509       insensitively.  Apparently this problem has been fixed in the latest
2510       FreeBSD releases.  ( http://www.freebsd.org/cgi/query-pr.cgi?pr=34308 )
2511
2512   IRIX fails ext/List/Util/t/shuffle.t or Digest::MD5
2513       IRIX with MIPSpro 7.3.1.2m or 7.3.1.3m compiler may fail the List::Util
2514       test ext/List/Util/t/shuffle.t by dumping core.  This seems to be a
2515       compiler error since if compiled with gcc no core dump ensues, and no
2516       failures have been seen on the said test on any other platform.
2517
2518       Similarly, building the Digest::MD5 extension has been known to fail
2519       with "*** Termination code 139 (bu21)".
2520
2521       The cure is to drop optimization level (Configure -Doptimize=-O2).
2522
2523   HP-UX lib/posix Subtest 9 Fails When LP64-Configured
2524       If perl is configured with -Duse64bitall, the successful result of the
2525       subtest 10 of lib/posix may arrive before the successful result of the
2526       subtest 9, which confuses the test harness so much that it thinks the
2527       subtest 9 failed.
2528
2529   Linux with glibc 2.2.5 fails t/op/int subtest #6 with -Duse64bitint
2530       This is a known bug in the glibc 2.2.5 with long long integers.  (
2531       http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=65612 )
2532
2533   Linux With Sfio Fails op/misc Test 48
2534       No known fix.
2535
2536   Mac OS X
2537       Please remember to set your environment variable LC_ALL to "C" (setenv
2538       LC_ALL C) before running "make test" to avoid a lot of warnings about
2539       the broken locales of Mac OS X.
2540
2541       The following tests are known to fail in Mac OS X 10.1.5 because of
2542       buggy (old) implementations of Berkeley DB included in Mac OS X:
2543
2544        Failed Test                 Stat Wstat Total Fail  Failed  List of Failed
2545        -------------------------------------------------------------------------
2546        ../ext/DB_File/t/db-btree.t    0    11    ??   ??       %  ??
2547        ../ext/DB_File/t/db-recno.t              149    3   2.01%  61 63 65
2548
2549       If you are building on a UFS partition, you will also probably see
2550       t/op/stat.t subtest #9 fail.  This is caused by Darwin's UFS not
2551       supporting inode change time.
2552
2553       Also the ext/POSIX/t/posix.t subtest #10 fails but it is skipped for
2554       now because the failure is Apple's fault, not Perl's (blocked signals
2555       are lost).
2556
2557       If you Configure with ithreads, ext/threads/t/libc.t will fail. Again,
2558       this is not Perl's fault-- the libc of Mac OS X is not threadsafe (in
2559       this particular test, the localtime() call is found to be
2560       threadunsafe.)
2561
2562   Mac OS X dyld undefined symbols
2563       If after installing Perl 5.8.0 you are getting warnings about missing
2564       symbols, for example
2565
2566           dyld: perl Undefined symbols
2567           _perl_sv_2pv
2568           _perl_get_sv
2569
2570       you probably have an old pre-Perl-5.8.0 installation (or parts of one)
2571       in /Library/Perl (the undefined symbols used to exist in pre-5.8.0
2572       Perls).  It seems that for some reason "make install" doesn't always
2573       completely overwrite the files in /Library/Perl.  You can move the old
2574       Perl shared library out of the way like this:
2575
2576           cd /Library/Perl/darwin/CORE
2577           mv libperl.dylib libperlold.dylib
2578
2579       and then reissue "make install".  Note that the above of course is
2580       extremely disruptive for anything using the /usr/local/bin/perl.  If
2581       that doesn't help, you may have to try removing all the .bundle files
2582       from beneath /Library/Perl, and again "make install"-ing.
2583
2584   OS/2 Test Failures
2585       The following tests are known to fail on OS/2 (for clarity only the
2586       failures are shown, not the full error messages):
2587
2588        ../lib/ExtUtils/t/Mkbootstrap.t    1   256    18    1   5.56%  8
2589        ../lib/ExtUtils/t/Packlist.t       1   256    34    1   2.94%  17
2590        ../lib/ExtUtils/t/basic.t          1   256    17    1   5.88%  14
2591        lib/os2_process.t                  2   512   227    2   0.88%  174 209
2592        lib/os2_process_kid.t                        227    2   0.88%  174 209
2593        lib/rx_cmprt.t                   255 65280    18    3  16.67%  16-18
2594
2595   op/sprintf tests 91, 129, and 130
2596       The op/sprintf tests 91, 129, and 130 are known to fail on some
2597       platforms.  Examples include any platform using sfio, and
2598       Compaq/Tandem's NonStop-UX.
2599
2600       Test 91 is known to fail on QNX6 (nto), because "sprintf '%e',0"
2601       incorrectly produces 0.000000e+0 instead of 0.000000e+00.
2602
2603       For tests 129 and 130, the failing platforms do not comply with the
2604       ANSI C Standard: lines 19ff on page 134 of ANSI X3.159 1989, to be
2605       exact.  (They produce something other than "1" and "-1" when formatting
2606       0.6 and -0.6 using the printf format "%.0f"; most often, they produce
2607       "0" and "-0".)
2608
2609   SCO
2610       The socketpair tests are known to be unhappy in SCO 3.2v5.0.4:
2611
2612        ext/Socket/socketpair.t...............FAILED tests 15-45
2613
2614   Solaris 2.5
2615       In case you are still using Solaris 2.5 (aka SunOS 5.5), you may
2616       experience failures (the test core dumping) in lib/locale.t.  The
2617       suggested cure is to upgrade your Solaris.
2618
2619   Solaris x86 Fails Tests With -Duse64bitint
2620       The following tests are known to fail in Solaris x86 with Perl
2621       configured to use 64 bit integers:
2622
2623        ext/Data/Dumper/t/dumper.............FAILED at test 268
2624        ext/Devel/Peek/Peek..................FAILED at test 7
2625
2626   SUPER-UX (NEC SX)
2627       The following tests are known to fail on SUPER-UX:
2628
2629        op/64bitint...........................FAILED tests 29-30, 32-33, 35-36
2630        op/arith..............................FAILED tests 128-130
2631        op/pack...............................FAILED tests 25-5625
2632        op/pow................................
2633        op/taint..............................# msgsnd failed
2634        ../ext/IO/lib/IO/t/io_poll............FAILED tests 3-4
2635        ../ext/IPC/SysV/ipcsysv...............FAILED tests 2, 5-6
2636        ../ext/IPC/SysV/t/msg.................FAILED tests 2, 4-6
2637        ../ext/Socket/socketpair..............FAILED tests 12
2638        ../lib/IPC/SysV.......................FAILED tests 2, 5-6
2639        ../lib/warnings.......................FAILED tests 115-116, 118-119
2640
2641       The op/pack failure ("Cannot compress negative numbers at op/pack.t
2642       line 126") is serious but as of yet unsolved.  It points at some
2643       problems with the signedness handling of the C compiler, as do the
2644       64bitint, arith, and pow failures.  Most of the rest point at problems
2645       with SysV IPC.
2646
2647   Term::ReadKey not working on Win32
2648       Use Term::ReadKey 2.20 or later.
2649
2650   UNICOS/mk
2651       •   During Configure, the test
2652
2653               Guessing which symbols your C compiler and preprocessor define...
2654
2655           will probably fail with error messages like
2656
2657               CC-20 cc: ERROR File = try.c, Line = 3
2658                 The identifier "bad" is undefined.
2659
2660                 bad switch yylook 79bad switch yylook 79bad switch yylook 79bad switch yylook 79#ifdef A29K
2661                 ^
2662
2663               CC-65 cc: ERROR File = try.c, Line = 3
2664                 A semicolon is expected at this point.
2665
2666           This is caused by a bug in the awk utility of UNICOS/mk.  You can
2667           ignore the error, but it does cause a slight problem: you cannot
2668           fully benefit from the h2ph utility (see h2ph) that can be used to
2669           convert C headers to Perl libraries, mainly used to be able to
2670           access from Perl the constants defined using C preprocessor, cpp.
2671           Because of the above error, parts of the converted headers will be
2672           invisible.  Luckily, these days the need for h2ph is rare.
2673
2674       •   If building Perl with interpreter threads (ithreads), the
2675           getgrent(), getgrnam(), and getgrgid() functions cannot return the
2676           list of the group members due to a bug in the multithreaded support
2677           of UNICOS/mk.  What this means is that in list context the
2678           functions will return only three values, not four.
2679
2680   UTS
2681       There are a few known test failures.  (Note: the relevant information
2682       was available in README.uts until support for UTS was removed in Perl
2683       v5.18.0)
2684
2685   VOS (Stratus)
2686       When Perl is built using the native build process on VOS Release 14.5.0
2687       and GNU C++/GNU Tools 2.0.1, all attempted tests either pass or result
2688       in TODO (ignored) failures.
2689
2690   VMS
2691       There should be no reported test failures with a default configuration,
2692       though there are a number of tests marked TODO that point to areas
2693       needing further debugging and/or porting work.
2694
2695   Win32
2696       In multi-CPU boxes, there are some problems with the I/O buffering:
2697       some output may appear twice.
2698
2699   XML::Parser not working
2700       Use XML::Parser 2.31 or later.
2701
2702   z/OS (OS/390)
2703       z/OS has rather many test failures but the situation is actually much
2704       better than it was in 5.6.0; it's just that so many new modules and
2705       tests have been added.
2706
2707        Failed Test                   Stat Wstat Total Fail  Failed  List of Failed
2708        ---------------------------------------------------------------------------
2709        ../ext/Data/Dumper/t/dumper.t              357    8   2.24%  311 314 325 327
2710                                                                     331 333 337 339
2711        ../ext/IO/lib/IO/t/io_unix.t                 5    4  80.00%  2-5
2712        ../ext/Storable/t/downgrade.t   12  3072   169   12   7.10%  14-15 46-47 78-79
2713                                                                     110-111 150 161
2714        ../lib/ExtUtils/t/Constant.t   121 30976    48   48 100.00%  1-48
2715        ../lib/ExtUtils/t/Embed.t                    9    9 100.00%  1-9
2716        op/pat.t                                   922    7   0.76%  665 776 785 832-
2717                                                                     834 845
2718        op/sprintf.t                               224    3   1.34%  98 100 136
2719        op/tr.t                                     97    5   5.15%  63 71-74
2720        uni/fold.t                                 780    6   0.77%  61 169 196 661
2721                                                                     710-711
2722
2723       The failures in dumper.t and downgrade.t are problems in the tests,
2724       those in io_unix and sprintf are problems in the USS (UDP sockets and
2725       printf formats).  The pat, tr, and fold failures are genuine Perl
2726       problems caused by EBCDIC (and in the pat and fold cases, combining
2727       that with Unicode).  The Constant and Embed are probably problems in
2728       the tests (since they test Perl's ability to build extensions, and that
2729       seems to be working reasonably well.)
2730
2731   Unicode Support on EBCDIC Still Spotty
2732       Though mostly working, Unicode support still has problem spots on
2733       EBCDIC platforms.  One such known spot are the "\p{}" and "\P{}"
2734       regular expression constructs for code points less than 256: the "pP"
2735       are testing for Unicode code points, not knowing about EBCDIC.
2736
2737   Seen In Perl 5.7 But Gone Now
2738       "Time::Piece" (previously known as "Time::Object") was removed because
2739       it was felt that it didn't have enough value in it to be a core module.
2740       It is still a useful module, though, and is available from the CPAN.
2741
2742       Perl 5.8 unfortunately does not build anymore on AmigaOS; this broke
2743       accidentally at some point.  Since there are not that many Amiga
2744       developers available, we could not get this fixed and tested in time
2745       for 5.8.0.  Perl 5.6.1 still works for AmigaOS (as does the 5.7.2
2746       development release).
2747
2748       The "PerlIO::Scalar" and "PerlIO::Via" (capitalised) were renamed as
2749       "PerlIO::scalar" and "PerlIO::via" (all lowercase) just before 5.8.0.
2750       The main rationale was to have all core PerlIO layers to have all
2751       lowercase names.  The "plugins" are named as usual, for example
2752       "PerlIO::via::QuotedPrint".
2753
2754       The "threads::shared::queue" and "threads::shared::semaphore" were
2755       renamed as "Thread::Queue" and "Thread::Semaphore" just before 5.8.0.
2756       The main rationale was to have thread modules to obey normal naming,
2757       "Thread::" (the "threads" and "threads::shared" themselves are more
2758       pragma-like, they affect compile-time, so they stay lowercase).
2759

Reporting Bugs

2761       If you find what you think is a bug, you might check the articles
2762       recently posted to the comp.lang.perl.misc newsgroup and the perl bug
2763       database at http://bugs.perl.org/ .  There may also be information at
2764       http://www.perl.com/ , the Perl Home Page.
2765
2766       If you believe you have an unreported bug, please run the perlbug
2767       program included with your release.  Be sure to trim your bug down to a
2768       tiny but sufficient test case.  Your bug report, along with the output
2769       of "perl -V", will be sent off to perlbug@perl.org to be analysed by
2770       the Perl porting team.
2771

SEE ALSO

2773       The Changes file for exhaustive details on what changed.
2774
2775       The INSTALL file for how to build Perl.
2776
2777       The README file for general stuff.
2778
2779       The Artistic and Copying files for copyright information.
2780

HISTORY

2782       Written by Jarkko Hietaniemi <jhi@iki.fi>.
2783
2784
2785
2786perl v5.36.3                      2023-11-30                    PERL58DELTA(1)
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