3 perldelta - what's new for perl v5.6 (as of v5.005_64)
7 This is an unsupported alpha release, meant for intrepid Perl developers
8 only. The included sources may not even build correctly on some platforms.
9 Subscribing to perl5-porters is the best way to monitor and contribute
10 to the progress of development releases (see www.perl.org for info).
12 This document describes differences between the 5.005 release and this one.
14 =head1 Incompatible Changes
16 =head2 Perl Source Incompatibilities
18 Beware that any new warnings that have been added or old ones
19 that have been enhanced are B<not> considered incompatible changes.
21 Since all new warnings must be explicitly requested via the C<-w>
22 switch or the C<warnings> pragma, it is ultimately the programmer's
23 responsibility to ensure that warnings are enabled judiciously.
27 =item CHECK is a new keyword
29 In addition to C<BEGIN>, C<INIT>, C<END>, C<DESTROY> and C<AUTOLOAD>,
30 subroutines named C<CHECK> are now special. These are queued up during
31 compilation and behave similar to END blocks, except they are called at
32 the end of compilation rather than at the end of execution. They cannot
35 =item Treatment of list slices of undef has changed
37 When taking a slice of a literal list (as opposed to a slice of
38 an array or hash), Perl used to return an empty list if the
39 result happened to be composed of all undef values.
41 The new behavior is to produce an empty list if (and only if)
42 the original list was empty. Consider the following example:
44 @a = (1,undef,undef,2)[2,1,2];
46 The old behavior would have resulted in @a having no elements.
47 The new behavior ensures it has three undefined elements.
49 Note in particular that the behavior of slices of the following
50 cases remains unchanged:
54 @a = (anything_returning_empty_list())[2,1,2];
60 =item Possibly changed pseudo-random number generator
62 In 5.005_0x and earlier, perl's rand() function used the C library
63 rand(3) function. As of 5.005_52, Configure tests for drand48(),
64 random(), and rand() (in that order) and picks the first one it finds.
65 Perl programs that depend on reproducing a specific set of pseudo-random
66 numbers will now likely produce different output. You can use
67 C<sh Configure -Drandfunc=rand> to obtain the old behavior.
69 =item Hashing function for hash keys has changed
71 Perl hashes are not order preserving. The apparently random order
72 encountered when iterating on the contents of a hash is determined
73 by the hashing algorithm used. To improve the distribution of lower
74 bits in the hashed value, the algorithm has changed slightly as of
75 5.005_52. When iterating over hashes, this may yield a random order
76 that is B<different> from that of previous versions.
78 =item C<undef> fails on read only values
80 Using the C<undef> operator on a readonly value (such as $1) has
81 the same effect as assigning C<undef> to the readonly value--it
84 =item Close-on-exec bit may be set on pipe() handles
86 On systems that support a close-on-exec flag on filehandles, the
87 flag will be set for any handles created by pipe(), if that is
88 warranted by the value of $^F that may be in effect. Earlier
89 versions neglected to set the flag for handles created with
90 pipe(). See L<perlfunc/pipe> and L<perlvar/$^F>.
92 =item Writing C<"$$1"> to mean C<"${$}1"> is unsupported
94 Perl 5.004 deprecated the interpretation of C<$$1> and
95 similar within interpolated strings to mean C<$$ . "1">,
98 In Perl 5.6 and later, C<"$$1"> always means C<"${$1}">.
100 =item delete(), values() and C<\(%h)> operate on aliases to values, not copies
102 delete(), each(), values() and hashes in a list context return the actual
103 values in the hash, instead of copies (as they used to in earlier
104 versions). Typical idioms for using these constructs copy the
105 returned values, but this can make a significant difference when
106 creating references to the returned values.
108 Keys in the hash are still returned as copies when iterating on
111 =item vec(EXPR,OFFSET,BITS) enforces powers-of-two BITS
113 vec() generates a run-time error if the BITS argument is not
114 a valid power-of-two integer.
116 =item Text of some diagnostic output has changed
118 Most references to internal Perl operations in diagnostics
119 have been changed to be more descriptive. This may be an
120 issue for programs that may incorrectly rely on the exact
121 text of diagnostics for proper functioning.
123 =item C<%@> has been removed
125 The undocumented special variable C<%@> that used to accumulate
126 "background" errors (such as those that happen in DESTROY())
127 has been removed, because it could potentially result in memory
130 =item Parenthesized not() behaves like a list operator
132 The C<not> operator now falls under the "if it looks like a function,
133 it behaves like a function" rule.
135 As a result, the parenthesized form can be used with C<grep> and C<map>.
136 The following construct used to be a syntax error before, but it works
139 grep not($_), @things;
141 On the other hand, using C<not> with a literal list slice may not
142 work. The following previously allowed construct:
144 print not (1,2,3)[0];
146 needs to be written with additional parentheses now:
148 print not((1,2,3)[0]);
150 The behavior remains unaffected when C<not> is not followed by parentheses.
152 =item Semantics of bareword prototype C<(*)> have changed
154 Arguments prototyped as C<*> will now be visible within the subroutine
155 as either a simple scalar or as a reference to a typeglob. Perl 5.005
156 always coerced simple scalar arguments to a typeglob, which wasn't useful
157 in situations where the subroutine must distinguish between a simple
158 scalar and a typeglob. See L<perlsub/Prototypes>.
162 =head2 C Source Incompatibilities
166 =item C<PERL_POLLUTE>
168 Release 5.005 grandfathered old global symbol names by providing preprocessor
169 macros for extension source compatibility. As of release 5.6, these
170 preprocessor definitions are not available by default. You need to explicitly
171 compile perl with C<-DPERL_POLLUTE> to get these definitions. For
172 extensions still using the old symbols, this option can be
173 specified via MakeMaker:
175 perl Makefile.PL POLLUTE=1
177 =item C<PERL_IMPLICIT_CONTEXT>
179 PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
180 with one of -Dusethreads, -Dusemultiplicity, or both. It is not
181 intended to be enabled by users at this time.
183 This new build option provides a set of macros for all API functions
184 such that an implicit interpreter/thread context argument is passed to
185 every API function. As a result of this, something like C<sv_setsv(foo,bar)>
186 amounts to a macro invocation that actually translates to something like
187 C<Perl_sv_setsv(my_perl,foo,bar)>. While this is generally expected
188 to not have any significant source compatibility issues, the difference
189 between a macro and a real function call will need to be considered.
191 This means that there B<is> a source compatibility issue as a result of
192 this if your extensions attempt to use pointers to any of the Perl API
195 Note that the above issue is not relevant to the default build of
196 Perl, whose interfaces continue to match those of prior versions
197 (but subject to the other options described here).
199 See L<perlguts/"The Perl API"> for detailed information on the
200 ramifications of building Perl using this option.
202 =item C<PERL_POLLUTE_MALLOC>
204 Enabling Perl's malloc in release 5.005 and earlier caused
205 the namespace of system versions of the malloc family of functions to
206 be usurped by the Perl versions, since by default they used the
209 Besides causing problems on platforms that do not allow these functions to
210 be cleanly replaced, this also meant that the system versions could not
211 be called in programs that used Perl's malloc. Previous versions of Perl
212 have allowed this behaviour to be suppressed with the HIDEMYMALLOC and
213 EMBEDMYMALLOC preprocessor definitions.
215 As of release 5.6, Perl's malloc family of functions have default names
216 distinct from the system versions. You need to explicitly compile perl with
217 C<-DPERL_POLLUTE_MALLOC> to get the older behaviour. HIDEMYMALLOC
218 and EMBEDMYMALLOC have no effect, since the behaviour they enabled is now
221 Note that these functions do B<not> constitute Perl's memory allocation API.
222 See L<perlguts/"Memory Allocation"> for further information about that.
226 =head2 Compatible C Source API Changes
230 =item C<PATCHLEVEL> is now C<PERL_VERSION>
232 The cpp macros C<PERL_REVISION>, C<PERL_VERSION>, and C<PERL_SUBVERSION>
233 are now available by default from perl.h, and reflect the base revision,
234 patchlevel, and subversion respectively. C<PERL_REVISION> had no
235 prior equivalent, while C<PERL_VERSION> and C<PERL_SUBVERSION> were
236 previously available as C<PATCHLEVEL> and C<SUBVERSION>.
238 The new names cause less pollution of the B<cpp> namespace and reflect what
239 the numbers have come to stand for in common practice. For compatibility,
240 the old names are still supported when F<patchlevel.h> is explicitly
241 included (as required before), so there is no source incompatibility
244 =item Support for C++ exceptions
246 change#3386, also needs perlguts documentation
247 [TODO - Chip Salzenberg <chip@perlsupport.com>]
251 =head2 Binary Incompatibilities
253 In general, the default build of this release is expected to be binary
254 compatible for extensions built with the 5.005 release or its maintenance
255 versions. However, specific platforms may have broken binary compatibility
256 due to changes in the defaults used in hints files. Therefore, please be
257 sure to always check the platform-specific README files for any notes to
260 The usethreads or usemultiplicity builds are B<not> binary compatible
261 with the corresponding builds in 5.005.
263 On platforms that require an explicit list of exports (AIX, OS/2 and Windows,
264 among others), purely internal symbols such as parser functions and the
265 run time opcodes are not exported by default. Perl 5.005 used to export
266 all functions irrespective of whether they were considered part of the
269 For the full list of public API functions, see L<perlapi>.
271 =head1 Installation and Configuration Improvements
273 =head2 -Dusethreads means something different
275 WARNING: Support for threads continues to be an experimental feature.
276 Interfaces and implementation are subject to sudden and drastic changes.
278 The -Dusethreads flag now enables the experimental interpreter-based thread
279 support by default. To get the flavor of experimental threads that was in
280 5.005 instead, you need to ask for -Duse5005threads.
282 As of v5.5.640, interpreter-threads support is still lacking a way to
283 create new threads from Perl (i.e., C<use Thread;> will not work with
284 interpreter threads). C<use Thread;> continues to be available when you
285 ask for -Duse5005threads, bugs and all.
287 =head2 Perl's version numbering has changed
289 Beginning with Perl version 5.6, the version number convention has been
290 changed to a "dotted tuple" scheme that is more commonly found in open
293 Maintenance versions of v5.6.0 will be released as v5.6.1, v5.6.2 etc.
294 The next development series following v5.6 will be numbered v5.7.x,
295 beginning with v5.7.0, and the next major production release following
298 The v1.2.3 syntax is also now legal in Perl. See L<Support for version tuples>
301 To cope with the new versioning system's use of at least three significant
302 digits for each version component, the method used for incrementing the
303 subversion number has also changed slightly. We assume that versions older
304 than v5.6 have been incrementing the subversion component in multiples of
305 10. Versions after v5.6 will increment them by 1. Thus, using the new
306 notation, 5.005_03 is the same as v5.5.30, and the first maintenance
307 version following v5.6 will be v5.6.1, which amounts to a floating point
310 =head2 New Configure flags
312 The following new flags may be enabled on the Configure command line
313 by running Configure with C<-Dflag>.
322 =head2 -Dusethreads and -Duse64bits now more daring
324 The Configure options enabling the use of threads and the use of
325 64-bitness are now more daring in the sense that they no more have
326 an explicit list of operating systems of known threads/64-bit
327 capabilities. In other words: if your operating system has the
328 necessary APIs, you should be able just to go ahead and use them.
329 See also L<"64-bit support">.
333 Some platforms have "long doubles", floating point numbers of even
334 larger range than ordinary "doubles". To enable using long doubles for
335 Perl's scalars, use -Duselongdouble.
339 You can enable both -Duse64bits and -Dlongdouble by -Dusemorebits.
340 See also L<"64-bit support">.
342 =head2 -Duselargefiles
344 Some platforms support large files, files larger than two gigabytes.
345 See L<"Large file support"> for more information.
347 =head2 installusrbinperl
349 You can use "Configure -Uinstallusrbinperl" which causes installperl
350 to skip installing perl also as /usr/bin/perl. This is useful if you
351 prefer not to modify /usr/bin for some reason or another but harmful
352 because many scripts assume to find Perl in /usr/bin/perl.
356 You can use "Configure -Dusesocks" which causes Perl to probe
357 for the SOCKS (v5, not v4) proxy protocol library,
358 http://www.socks.nec.com/
362 You can "post-edit" the Configure variables using the Configure C<-A>
363 flag. The editing happens immediately after the platform specific
364 hints files have been processed but before the actual configuration
365 process starts. Run C<Configure -h> to find out the full C<-A> syntax.
367 =head2 Enhanced Installation Directories
369 The installation structure has been enriched to improve the support for
370 maintaining multiple versions of perl, to provide locations for
371 vendor-supplied modules and scripts, and to ease maintenance of
372 locally-added modules and scripts. See the section on Installation
373 Directories in the INSTALL file for complete details. For most users
374 building and installing from source, the defaults should be fine.
378 =head2 Unicode and UTF-8 support
380 Perl can optionally use UTF-8 as its internal representation for character
381 strings. The C<utf8> pragma enables this support in the current lexical
382 scope. See L<utf8> for more information.
384 =head2 Interpreter cloning, threads, and concurrency
386 WARNING: This is an experimental feature in a pre-alpha state. Use
389 Perl 5.005_63 introduces the beginnings of support for running multiple
390 interpreters concurrently in different threads. In conjunction with
391 the perl_clone() API call, which can be used to selectively duplicate
392 the state of any given interpreter, it is possible to compile a
393 piece of code once in an interpreter, clone that interpreter
394 one or more times, and run all the resulting interpreters in distinct
397 On Windows, this feature is used to emulate fork() at the interpreter
398 level. See L<perlfork>.
400 This feature is still in evolution. It is eventually meant to be used
401 to selectively clone a subroutine and data reachable from that
402 subroutine in a separate interpreter and run the cloned subroutine
403 in a separate thread. Since there is no shared data between the
404 interpreters, little or no locking will be needed (unless parts of
405 the symbol table are explicitly shared). This is obviously intended
406 to be an easy-to-use replacement for the existing threads support.
408 Support for cloning interpreters and interpreter concurrency can be
409 enabled using the -Dusethreads Configure option (see win32/Makefile for
410 how to enable it on Windows.) The resulting perl executable will be
411 functionally identical to one that was built with -Dmultiplicity, but
412 the perl_clone() API call will only be available in the former.
414 -Dusethreads enables, the cpp macros USE_ITHREADS by default, which enables
415 Perl source code changes that provide a clear separation between the op tree
416 and the data it operates with. The former is considered immutable, and can
417 therefore be shared between an interpreter and all of its clones, while the
418 latter is considered local to each interpreter, and is therefore copied for
421 Note that building Perl with the -Dusemultiplicity Configure option
422 is adequate if you wish to run multiple B<independent> interpreters
423 concurrently in different threads. -Dusethreads only provides the
424 additional functionality of the perl_clone() API call and other
425 support for running B<cloned> interpreters concurrently.
427 [XXX TODO - the Compiler backends may be broken when USE_ITHREADS is
430 =head2 Lexically scoped warning categories
432 You can now control the granularity of warnings emitted by perl at a finer
433 level using the C<use warnings> pragma. See L<warnings> and L<perllexwarn>
436 =head2 Lvalue subroutines
438 WARNING: This is an experimental feature.
441 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>,
442 Tuomas Lukka <lukka@fas.harvard.edu>)]
444 =head2 "our" declarations
446 An "our" declaration introduces a value that can be best understood
447 as a lexically scoped symbolic alias to a global variable in the
448 package that was current where the variable was declared. This is
449 mostly useful as an alternative to the C<vars> pragma, but also provides
450 the opportunity to introduce typing and other attributes for such
451 variables. See L<perlfunc/our>.
453 =head2 Support for version tuples
455 Literals of the form v1.2.3.4 are now parsed as the utf8 string
456 C<"\x{1}\x{2}\x{3}\x{4}">. This allows comparing version numbers using
457 regular string comparison operators C<eq>, C<ne>, C<lt>, C<gt> etc.
459 These "dotted tuples" are dual-valued. They are both strings of utf8
460 characters, and floating point numbers. Thus v1.2.3.4 has the string
461 value C<"\x{1}\x{2}\x{3}\x{4}"> and the numeric value 1.002_003_004.
462 As another example, v5.5.640 has the string value C<"\x{5}\x{5}\x{280}">
463 (remember 280 hexadecimal is 640 decimal) and the numeric value
466 In conjunction with the new C<$^V> magic variable (which contains
467 the perl version in this format), such literals can be used to
468 check if you're running a particular version of Perl.
470 if ($^V and $^V gt v5.5.640) {
471 # new style version numbers are supported
474 C<require> and C<use> also support such literals:
476 require v5.6.0; # croak if $^V lt v5.6.0
477 use v5.6.0; # same, but croaks at compile-time
479 =head2 Weak references
481 WARNING: This is an experimental feature.
483 change#3385, also need perlguts documentation
485 [TODO - Tuomas Lukka <lukka@fas.harvard.edu>]
487 =head2 File globbing implemented internally
489 WARNING: This is currently an experimental feature. Interfaces and
490 implementation are likely to change.
492 Perl now uses the File::Glob implementation of the glob() operator
493 automatically. This avoids using an external csh process and the
494 problems associated with it.
496 =head2 Binary numbers supported
498 Binary numbers are now supported as literals, in s?printf formats, and
502 printf "The answer is: %b\n", oct("0b101010");
504 =head2 Some arrows may be omitted in calls through references
506 Perl now allows the arrow to be omitted in many constructs
507 involving subroutine calls through references. For example,
508 C<$foo[10]->('foo')> may now be written C<$foo[10]('foo')>.
509 This is rather similar to how the arrow may be omitted from
510 C<$foo[10]->{'foo'}>. Note however, that the arrow is still
511 required for C<foo(10)->('bar')>.
513 =head2 exists() is supported on subroutine names
515 The exists() builtin now works on subroutine names. A subroutine
516 is considered to exist if it has been declared (even if implicitly).
517 See L<perlfunc/exists> for examples.
519 =head2 exists() and delete() are supported on array elements
521 The exists() and delete() builtins now work on simple arrays as well.
522 The behavior is similar to that on hash elements.
524 exists() can be used to check whether an array element has been
525 initialized without autovivifying it. If the array is tied, the
526 EXISTS() method in the corresponding tied package will be invoked.
528 delete() may be used to remove an element from the array and return
529 it. The array element at that position returns to its unintialized
530 state, so that testing for the same element with exists() will return
531 false. If the element happens to be the one at the end, the size of
532 the array also shrinks by one. If the array is tied, the DELETE() method
533 in the corresponding tied package will be invoked.
535 See L<perlfunc/exists> and L<perlfunc/delete> for examples.
537 =head2 syswrite() ease-of-use
539 The length argument of C<syswrite()> has become optional.
541 =head2 File and directory handles can be autovivified
543 Similar to how constructs such as C<$x->[0]> autovivify a reference,
544 handle constructors (open(), opendir(), pipe(), socketpair(), sysopen(),
545 socket(), and accept()) now autovivify a file or directory handle
546 if the handle passed to them is an uninitialized scalar variable. This
547 allows the constructs such as C<open(my $fh, ...)> and C<open(local $fh,...)>
548 to be used to create filehandles that will conveniently be closed
549 automatically when the scope ends, provided there are no other references
550 to them. This largely eliminates the need for typeglobs when opening
551 filehandles that must be passed around, as in the following example:
555 or die "Can't open '@_': $!";
560 my $f = myopen("</etc/motd");
562 # $f implicitly closed here
565 [TODO - this idiom needs more pod penetration]
567 =head2 64-bit support
569 All platforms that have 64-bit integers either (a) natively as longs
570 or ints (b) via special compiler flags (c) using long long are able to
571 use "quads" (64-integers) as follows:
577 constants (decimal, hexadecimal, octal, binary) in the code
581 arguments to oct() and hex()
585 arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)
593 pack() and unpack() "q" and "Q" formats
597 in basic arithmetics: + - * / %
601 vec() (but see the below note about bit arithmetics)
605 Note that unless you have the case (a) you will have to configure
606 and compile Perl using the -Duse64bits Configure flag.
608 Unfortunately bit arithmetics (&, |, ^, ~, <<, >>) for numbers are not
609 64-bit clean, they are explictly forced to be 32-bit. Bit arithmetics
610 for bit vectors (created by vec()) are not limited in their width.
612 Last but not least: note that due to Perl's habit of always using
613 floating point numbers the quads are still not true integers.
614 When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
615 -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
616 are silently promoted to floating point numbers, after which they will
617 start losing precision (their lower digits).
619 =head2 Large file support
621 If you have filesystems that support "large files" (files larger than
622 2 gigabytes), you may now also be able to create and access them from
623 Perl. You have to use Configure -Duselargefiles. Turning on the
624 large file support turns on also the 64-bit support on many platforms.
625 Beware that unless your filesystem also supports "sparse files" seeking
626 to umpteen petabytes may be unadvisable.
628 Note that in addition to requiring a proper file system to do large
629 files you may also need to adjust your per-process (or your
630 per-system, or per-process-group, or per-user-group) maximum filesize
631 limits before running Perl scripts that try to handle large files,
632 especially if you intend to write such files.
634 Finally, in addition to your process/process group maximum filesize
635 limits, you may have quota limits on your filesystems that stop you
636 (your user id or your user group id) from using large files.
638 Adjusting your process/user/group/file system/operating system limits
639 is outside the scope of Perl core language. For process limits, you
640 may try increasing the limits using your shell's limits/limit/ulimit
641 command before running Perl. The BSD::Resource extension (not
642 included with the standard Perl distribution) may also be of use, it
643 offers the getrlimit/setrlimit interface that can be used to adjust
644 process resource usage limits, including the maximum filesize limit.
648 In some systems you may be able to use long doubles to enhance the
649 range and precision of your double precision floating point numbers
650 (that is, Perl's numbers). Use Configure -Duselongdouble to enable
651 this support (if it is available).
655 You can "Configure -Dusemorebits" to turn on both the 64-bit support
656 and the long double support.
658 =head2 Enhanced support for sort() subroutines
660 Perl subroutines with a prototype of C<($$)> and XSUBs in general can
661 now be used as sort subroutines. In either case, the two elements to
662 be compared are passed as normal parameters in @_. See L<perlfunc/sort>.
664 For unprototyped sort subroutines, the historical behavior of passing
665 the elements to be compared as the global variables $a and $b remains
668 =head2 Better syntax checks on parenthesized unary operators
672 print defined(&foo,&bar,&baz);
673 print uc("foo","bar","baz");
676 used to be accidentally allowed in earlier versions, and produced
677 unpredictable behaviour. Some produced ancillary warnings
678 when used in this way; others silently did the wrong thing.
680 The parenthesized forms of most unary operators that expect a single
681 argument now ensure that they are not called with more than one
682 argument, making the cases shown above syntax errors. The usual
685 print defined &foo, &bar, &baz;
686 print uc "foo", "bar", "baz";
689 remains unchanged. See L<perlop>.
691 =head2 POSIX character class syntax [: :] supported
693 For example to match alphabetic characters use /[[:alpha:]]/.
694 See L<perlre> for details.
696 =head2 Improved C<qw//> operator
698 The C<qw//> operator is now evaluated at compile time into a true list
699 instead of being replaced with a run time call to C<split()>. This
700 removes the confusing misbehaviour of C<qw//> in scalar context, which
701 had inherited that behaviour from split().
705 $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
707 now correctly prints "3|a", instead of "2|a".
709 =head2 pack() format 'Z' supported
711 The new format type 'Z' is useful for packing and unpacking null-terminated
712 strings. See L<perlfunc/"pack">.
714 =head2 pack() format modifier '!' supported
716 The new format type modifier '!' is useful for packing and unpacking
717 native shorts, ints, and longs. See L<perlfunc/"pack">.
719 =head2 pack() and unpack() support counted strings
721 The template character '/' can be used to specify a counted string
722 type to be packed or unpacked. See L<perlfunc/"pack">.
724 =head2 Comments in pack() templates
726 The '#' character in a template introduces a comment up to
727 end of the line. This facilitates documentation of pack()
730 =head2 $^X variables may now have names longer than one character
732 Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
733 error. Now variable names that begin with a control character may be
734 arbitrarily long. However, for compatibility reasons, these variables
735 I<must> be written with explicit braces, as C<${^XY}> for example.
736 C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more
737 than one control character, such as C<${^XY^Z}>, are illegal.
739 The old syntax has not changed. As before, `^X' may be either a
740 literal control-X character or the two-character sequence `caret' plus
741 `X'. When braces are omitted, the variable name stops after the
742 control character. Thus C<"$^XYZ"> continues to be synonymous with
743 C<$^X . "YZ"> as before.
745 As before, lexical variables may not have names beginning with control
746 characters. As before, variables whose names begin with a control
747 character are always forced to be in package `main'. All such variables
748 are reserved for future extensions, except those that begin with
749 C<^_>, which may be used by user programs and are guaranteed not to
750 acquire special meaning in any future version of Perl.
752 =head2 C<use attrs> implicit in subroutine attributes
754 Formerly, if you wanted to mark a subroutine as being a method call or
755 as requiring an automatic lock() when it is entered, you had to declare
756 that with a C<use attrs> pragma in the body of the subroutine.
757 That can now be accomplished with declaration syntax, like this:
759 sub mymethod : locked method ;
761 sub mymethod : locked method {
765 sub othermethod :locked :method ;
767 sub othermethod :locked :method {
772 (Note how only the first C<:> is mandatory, and whitespace surrounding
773 the C<:> is optional.)
775 F<AutoSplit.pm> and F<SelfLoader.pm> have been updated to keep the attributes
776 with the stubs they provide. See L<attributes>.
778 =head2 Regular expression improvements
780 change#2827,2373,2372,2365,1813,1800,4112,4158,4215,4301
781 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
783 =head2 Overloading improvements
786 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
788 =head2 open() with more than two arguments
790 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
792 =head2 Support for interpolating named characters
795 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
797 =head2 Experimental support for user-hooks in @INC
799 [TODO - Ken Fox <kfox@ford.com>]
801 =head2 C<require> and C<do> may be overridden
803 C<require> and C<do 'file'> operations may be overridden locally
804 by importing subroutines of the same name into the current package
805 (or globally by importing them into the CORE::GLOBAL:: namespace).
806 Overriding C<require> will also affect C<use>, provided the override
807 is visible at compile-time.
808 See L<perlsub/"Overriding Built-in Functions">.
810 =head2 New variable $^C reflects C<-c> switch
812 C<$^C> has a boolean value that reflects whether perl is being run
813 in compile-only mode (i.e. via the C<-c> switch). Since
814 BEGIN blocks are executed under such conditions, this variable
815 enables perl code to determine whether actions that make sense
816 only during normal running are warranted. See L<perlvar>.
818 =head2 New variable $^V contains Perl version in v5.6.0 format
820 C<$^V> contains the Perl version number as a version tuple that
821 can be used in string or numeric comparisons. See
822 C<Support for version tuples> for an example.
824 =head2 Optional Y2K warnings
826 If Perl is built with the cpp macro C<PERL_Y2KWARN> defined,
827 it emits optional warnings when concatenating the number 19
830 This behavior must be specifically enabled when running Configure.
831 See L<INSTALL> and L<README.Y2K>.
833 =head1 Significant bug fixes
835 =head2 E<lt>HANDLEE<gt> on empty files
837 With C<$/> set to C<undef>, "slurping" an empty file returns a string of
838 zero length (instead of C<undef>, as it used to) the first time the
839 HANDLE is read after C<$/> is set to C<undef>. Further reads yield
842 This means that the following will append "foo" to an empty file (it used
845 perl -0777 -pi -e 's/^/foo/' empty_file
849 perl -pi -e 's/^/foo/' empty_file
851 is unchanged (it continues to leave the file empty).
853 =head2 C<eval '...'> improvements
855 Line numbers (as reflected by caller() and most diagnostics) within
856 C<eval '...'> were often incorrect when here documents were involved.
857 This has been corrected.
859 Lexical lookups for variables appearing in C<eval '...'> within
860 functions that were themselves called within an C<eval '...'> were
861 searching the wrong place for lexicals. The lexical search now
862 correctly ends at the subroutine's block boundary.
864 Parsing of here documents used to be flawed when they appeared as
865 the replacement expression in C<eval 's/.../.../e'>. This has
868 =head2 All compilation errors are true errors
870 Some "errors" encountered at compile time were by neccessity
871 generated as warnings followed by eventual termination of the
872 program. This enabled more such errors to be reported in a
873 single run, rather than causing a hard stop at the first error
874 that was encountered.
876 The mechanism for reporting such errors has been reimplemented
877 to queue compile-time errors and report them at the end of the
878 compilation as true errors rather than as warnings. This fixes
879 cases where error messages leaked through in the form of warnings
880 when code was compiled at run time using C<eval STRING>, and
881 also allows such errors to be reliably trapped using __DIE__ hooks.
883 =head2 Automatic flushing of output buffers
885 fork(), exec(), system(), qx//, and pipe open()s now flush buffers
886 of all files opened for output when the operation
887 was attempted. This mostly eliminates confusing
888 buffering mishaps suffered by users unaware of how Perl internally
891 =head2 Better diagnostics on meaningless filehandle operations
893 Constructs such as C<open(E<lt>FHE<gt>)> and C<close(E<lt>FHE<gt>)>
894 are compile time errors. Attempting to read from filehandles that
895 were opened only for writing will now produce warnings (just as
896 writing to read-only filehandles does).
898 =head2 Where possible, buffered data discarded from duped input filehandle
900 C<open(NEW, "E<lt>&OLD")> now attempts to discard any data that
901 was previously read and buffered in C<OLD> before duping the handle.
902 On platforms where doing this is allowed, the next read operation
903 on C<NEW> will return the same data as the corresponding operation
904 on C<OLD>. Formerly, it would have returned the data from the start
905 of the following disk block instead.
907 =head2 eof() has the same old magic as <>
909 C<eof()> would return true if no attempt to read from C<E<lt>E<gt>> had
910 yet been made. C<eof()> has been changed to have a little magic of its
911 own, it now opens the C<E<lt>E<gt>> files.
913 =head2 system(), backticks and pipe open now reflect exec() failure
915 On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
916 etc., are implemented via fork() and exec(). When the underlying
917 exec() fails, earlier versions did not report the error properly,
918 since the exec() happened to be in a different process.
920 The child process now communicates with the parent about the
921 error in launching the external command, which allows these
922 constructs to return with their usual error value and set $!.
924 =head2 Implicitly closed filehandles are safer
926 Sometimes implicitly closed filehandles (as when they are localized,
927 and Perl automatically closes them on exiting the scope) could
928 inadvertently set $? or $!. This has been corrected.
930 =head2 C<(\$)> prototype and C<$foo{a}>
932 An scalar reference prototype now correctly allows a hash or
933 array element in that slot.
935 =head2 Pseudo-hashes work better
937 Dereferencing some types of reference values in a pseudo-hash,
938 such as C<$ph->{foo}[1]>, was accidentally disallowed. This has
941 When applied to a pseudo-hash element, exists() now reports whether
942 the specified value exists, not merely if the key is valid.
944 delete() now works on pseudo-hashes. When given a pseudo-hash element
945 or slice it deletes the values corresponding to the keys (but not the keys
946 themselves). See L<perlref/"Pseudo-hashes: Using an array as a hash">.
948 =head2 C<goto &sub> and AUTOLOAD
950 The C<goto &sub> construct works correctly when C<&sub> happens
953 =head2 C<-bareword> allowed under C<use integer>
955 The autoquoting of barewords preceded by C<-> did not work
956 in prior versions when the C<integer> pragma was enabled.
959 =head2 Boolean assignment operators are legal lvalues
961 Constructs such as C<($a ||= 2) += 1> are now allowed.
963 =head2 C<sort $coderef @foo> allowed
965 sort() did not accept a subroutine reference as the comparison
966 function in earlier versions. This is now permitted.
968 =head2 Failures in DESTROY()
970 When code in a destructor threw an exception, it went unnoticed
971 in earlier versions of Perl, unless someone happened to be
972 looking in $@ just after the point the destructor happened to
973 run. Such failures are now visible as warnings when warnings are
976 =head2 Locale bugs fixed
978 printf() and sprintf() previously reset the numeric locale
979 back to the default "C" locale. This has been fixed.
981 Numbers formatted according to the local numeric locale
982 (such as using a decimal comma instead of a decimal dot) caused
983 "isn't numeric" warnings, even while the operations accessing
984 those numbers produced correct results. The warnings are gone.
988 The C<eval 'return sub {...}'> construct could sometimes leak
989 memory. This has been fixed.
991 Operations that aren't filehandle constructors used to leak memory
992 when used on invalid filehandles. This has been fixed.
994 Constructs that modified C<@_> could fail to deallocate values
995 in C<@_> and thus leak memory. This has been corrected.
997 =head2 Spurious subroutine stubs after failed subroutine calls
999 Perl could sometimes create empty subroutine stubs when a
1000 subroutine was not found in the package. Such cases stopped
1001 later method lookups from progressing into base packages.
1002 This has been corrected.
1004 =head2 Consistent numeric conversions
1007 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1009 =head2 Taint failures under C<-U>
1011 When running in unsafe mode, taint violations could sometimes
1012 cause silent failures. This has been fixed.
1014 =head2 END blocks and the C<-c> switch
1016 Prior versions used to run BEGIN B<and> END blocks when Perl was
1017 run in compile-only mode. Since this is typically not the expected
1018 behavior, END blocks are not executed anymore when the C<-c> switch
1021 See L<CHECK blocks> for how to run things when the compile phase ends.
1023 =head2 Potential to leak DATA filehandles
1025 Using the C<__DATA__> token creates an implicit filehandle to
1026 the file that contains the token. It is the program's
1027 responsibility to close it when it is done reading from it.
1029 This caveat is now better explained in the documentation.
1032 =head2 Diagnostics follow STDERR
1034 Diagnostic output now goes to whichever file the C<STDERR> handle
1035 is pointing at, instead of always going to the underlying C runtime
1036 library's C<stderr>.
1038 =head2 Other fixes for better diagnostics
1040 Line numbers are no longer suppressed (under most likely circumstances)
1041 during the global destruction phase.
1043 Diagnostics emitted from code running in threads other than the main
1044 thread are now accompanied by the thread ID.
1046 Embedded null characters in diagnostics now actually show up. They
1047 used to truncate the message in prior versions.
1049 $foo::a and $foo::b are now exempt from "possible typo" warnings only
1050 if sort() is encountered in package foo.
1052 Unrecognized alphabetic escapes encountered when parsing quote
1053 constructs now generate a warning, since they may take on new
1054 semantics in later versions of Perl.
1056 =head1 Performance enhancements
1058 =head2 Simple sort() using { $a <=> $b } and the like are optimized
1060 Many common sort() operations using a simple inlined block are now
1061 optimized for faster performance.
1063 =head2 Optimized assignments to lexical variables
1065 Certain operations in the RHS of assignment statements have been
1066 optimized to directly set the lexical variable on the LHS,
1067 eliminating redundant copying overheads.
1069 =head2 Method lookups optimized
1071 [TODO - Chip Salzenberg <chip@perlsupport.com>]
1073 =head2 Faster mechanism to invoke XSUBs
1076 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1078 =head2 Perl_malloc() improvements
1081 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1083 =head2 Faster subroutine calls
1085 Minor changes in how subroutine calls are handled internally
1086 provide marginal improvements in performance.
1088 =head1 Platform specific changes
1090 =head2 Additional supported platforms
1096 VM/ESA is now supported.
1100 Siemens BS2000 is now supported under the POSIX Shell.
1104 The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
1109 GNU/Hurd is now supported.
1113 Rhapsody is now supported.
1117 EPOC is is now supported (on Psion 5).
1127 Perl now works with djgpp 2.02 (and 2.03 alpha).
1131 Environment variable names are not converted to uppercase any more.
1135 Wrong exit code from backticks now fixed.
1139 This port is still using its own builtin globbing.
1145 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1149 [TODO - Charles Bailey <bailey@newman.upenn.edu>]
1153 Site library searches failed to look for ".../site/5.XXX/lib"
1154 if ".../site/5.XXXYY/lib" wasn't found. This has been corrected.
1156 When given a pathname that consists only of a drivename, such
1157 as C<A:>, opendir() and stat() now use the current working
1158 directory for the drive rather than the drive root.
1160 The builtin XSUB functions in the Win32:: namespace are
1161 documented. See L<Win32>.
1163 $^X now contains the full path name of the running executable.
1165 A Win32::GetLongPathName() function is provided to complement
1166 Win32::GetFullPathName() and Win32::GetShortPathName(). See L<Win32>.
1168 POSIX::uname() is supported.
1170 system(1,...) now returns true process IDs rather than process
1171 handles. kill() accepts any real process id, rather than strictly
1172 return values from system(1,...).
1174 The C<Shell> module is supported.
1176 Rudimentary support for building under command.com in Windows 95
1179 Scripts are read in binary mode by default to allow ByteLoader (and
1180 the filter mechanism in general) to work properly. For compatibility,
1181 the DATA filehandle will be set to text mode if a carriage return is
1182 detected at the end of the line containing the __END__ or __DATA__
1183 token; if not, the DATA filehandle will be left open in binary mode.
1184 Earlier versions always opened the DATA filehandle in text mode.
1186 The glob() operator is implemented via the L<File::Glob> extension,
1187 which supports glob syntax of the C shell. This increases the flexibility
1188 of the glob() operator, but there may be compatibility issues for
1189 programs that relied on the older globbing syntax. If you want to
1190 preserve compatibility with the older syntax, you might want to put
1191 a C<use File::DosGlob;> in your program. For details and compatibility
1192 information, see L<File::Glob>.
1202 Compatibility tests for C<sub : attrs> vs the older C<use attrs>.
1206 IO constants (SEEK_*, _IO*).
1210 Directory-related IO methods (new, read, close, rewind, tied delete).
1212 =item lib/io_multihomed
1214 INET sockets with multi-homed hosts.
1226 Regression tests for C<my ($x,@y,%z) : attrs> and <sub : attrs>.
1230 File test operators.
1234 Verify operations that access pad objects (lexicals and temporaries).
1238 Verify C<exists &sub> operations.
1242 =head1 Modules and Pragmata
1250 While used internally by Perl as a pragma, this module also
1251 provides a way to fetch subroutine and variable attributes.
1256 The Perl Compiler suite has been extensively reworked for this
1259 [TODO - Vishal Bhatia <vishal@gol.com>,
1260 Nick Ing-Simmons <nick@ni-s.u-net.com>]
1264 The ByteLoader is a dedicated extension to generate and run
1265 Perl bytecode. See L<ByteLoader>.
1269 References can now be used.
1271 The new version also allows a leading underscore in constant names, but
1272 disallows a double leading underscore (as in "__LINE__"). Some other names
1273 are disallowed or warned against, including BEGIN, END, etc. Some names
1274 which were forced into main:: used to fail silently in some cases; now they're
1275 fatal (outside of main::) and an optional warning (inside of main::).
1276 The ability to detect whether a constant had been set with a given name has
1284 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1288 A C<Maxdepth> setting can be specified to avoid venturing
1289 too deeply into deep data structures. See L<Data::Dumper>.
1291 Dumping C<qr//> objects works correctly.
1295 C<DB> is an experimental module that exposes a clean abstraction
1296 to Perl's debugging API.
1300 DB_File can now be built with Berkeley DB versions 1, 2 or 3.
1301 See C<ext/DB_File/Changes>.
1305 Devel::DProf, a Perl source code profiler has been added. See
1306 L<Devel::DProf> and L<dprofpp>.
1310 The Dumpvalue module provides screen dumps of Perl data.
1314 Overall, Benchmark results exhibit lower average error and better timing
1317 You can now run tests for I<n> seconds instead of guessing the right
1318 number of tests to run: e.g. timethese(-5, ...) will run each
1319 code for at least 5 CPU seconds. Zero as the "number of repetitions"
1320 means "for at least 3 CPU seconds". The output format has also
1321 changed. For example:
1323 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
1325 will now output something like this:
1327 Benchmark: running a, b, each for at least 5 CPU seconds...
1328 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
1329 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
1331 New features: "each for at least N CPU seconds...", "wallclock secs",
1332 and the "@ operations/CPU second (n=operations)".
1334 timethese() now returns a reference to a hash of Benchmark objects containing
1335 the test results, keyed on the names of the tests.
1337 timethis() now returns the iterations field in the Benchmark result object
1340 timethese(), timethis(), and the new cmpthese() (see below) can also take
1341 a format specifier of 'none' to suppress output.
1343 A new function countit() is just like timeit() except that it takes a
1344 TIME instead of a COUNT.
1346 A new function cmpthese() prints a chart comparing the results of each test
1347 returned from a timethese() call. For each possible pair of tests, the
1348 percentage speed difference (iters/sec or seconds/iter) is shown.
1350 For other details, see L<Benchmark>.
1354 The Devel::Peek module provides access to the internal representation
1355 of Perl variables and data. It is a data debugging tool for the XS programmer.
1357 =item ExtUtils::MakeMaker
1359 change#4135, also needs docs in module pod
1360 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1364 More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
1365 large file (more than 4GB) access Note that the O_LARGEFILE is
1366 automatically/transparently added to sysopen() flags if large file
1367 support has been configured), Free/Net/OpenBSD locking behaviour flags
1368 F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the combined mask of
1369 O_RDONLY, O_WRONLY, and O_RDWR. Also SEEK_SET, SEEK_CUR, and SEEK_END
1370 added for one-stop shopping of the seek/sysseek constants.
1374 A compare_text() function has been added, which allows custom
1375 comparison functions. See L<File::Compare>.
1379 File::Find now works correctly when the wanted() function is either
1380 autoloaded or is a symbolic reference.
1382 A bug that caused File::Find to lose track of the working directory
1383 when pruning top-level directories has been fixed.
1385 File::Find now also supports several other options to control its
1386 behavior. It can follow symbolic links if the C<follow> option is
1387 specified. Enabling the C<no_chdir> option will make File::Find skip
1388 changing the current directory when walking directories. The C<untaint>
1389 flag can be useful when running with taint checks enabled.
1395 This extension implements BSD-style file globbing. By default,
1396 it will also be used for the internal implementation of the glob()
1397 operator. See L<File::Glob>.
1401 New methods have been added to the File::Spec module: devnull() returns
1402 the name of the null device (/dev/null on Unix) and tmpdir() the name of
1403 the temp directory (normally /tmp on Unix). There are now also methods
1404 to convert between absolute and relative filenames: abs2rel() and
1405 rel2abs(). For compatibility with operating systems that specify volume
1406 names in file paths, the splitpath(), splitdir(), and catdir() methods
1409 =item File::Spec::Functions
1411 The new File::Spec::Functions modules provides a function interface
1412 to the File::Spec module. Allows shorthand
1414 $fullname = catfile($dir1, $dir2, $file);
1418 $fullname = File::Spec->catfile($dir1, $dir2, $file);
1422 Getopt::Long licensing has changed to allow the Perl Artistic License
1423 as well as the GPL. It used to be GPL only, which got in the way of
1424 non-GPL applications that wanted to use Getopt::Long.
1426 Getopt::Long encourages the use of Pod::Usage to produce help
1427 messages. For example:
1433 GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
1434 pod2usage(1) if $help;
1435 pod2usage(-exitstatus => 0, -verbose => 2) if $man;
1441 sample - Using GetOpt::Long and Pod::Usage
1445 sample [options] [file ...]
1448 -help brief help message
1449 -man full documentation
1457 Print a brief help message and exits.
1461 Prints the manual page and exits.
1467 B<This program> will read the given input file(s) and do someting
1468 useful with the contents thereof.
1472 See L<Pod::Usage> for details.
1474 A bug that prevented the non-option call-back E<lt>E<gt> from being
1475 specified as the first argument has been fixed.
1477 To specify the characters E<lt> and E<gt> as option starters, use
1478 E<gt>E<lt>. Note, however, that changing option starters is strongly
1483 write() and syswrite() will now accept a single-argument
1484 form of the call, for consistency with Perl's syswrite().
1486 You can now create a TCP-based IO::Socket::INET without forcing
1487 a connect attempt. This allows you to configure its options
1488 (like making it non-blocking) and then call connect() manually.
1490 A bug that prevented the IO::Socket::protocol() accessor
1491 from ever returning the correct value has been corrected.
1495 Java Perl Lingo is now distributed with Perl. See jpl/README
1496 for more information.
1500 C<use lib> now weeds out any trailing duplicate entries.
1501 C<no lib> removes all named entries.
1505 The bitwise operations C<E<lt>E<lt>>, C<E<gt>E<gt>>, C<&>, C<|>,
1506 and C<~> are now supported on bigints.
1510 The accessor methods Re, Im, arg, abs, rho, and theta can now also
1511 act as mutators (accessor $z->Re(), mutator $z->Re(3)).
1515 A little bit of radial trigonometry (cylindrical and spherical),
1516 radial coordinate conversions, and the great circle distance were added.
1520 [TODO - Brad Appleton <bradapp@enteract.com>]
1522 =item Pod::Text and Pod::Man
1524 [TODO - Russ Allbery <rra@stanford.edu>]
1528 An EXISTS method has been added to this module (and sdbm_exists() has
1529 been added to the underlying sdbm library), so one can now call exists
1530 on an SDBM_File tied hash and get the correct result, rather than a
1533 A bug that may have caused data loss when more than one disk block
1534 happens to be read from the database in a single FETCH() has been
1539 The timelocal() and timegm() functions used to silently return bogus
1540 results when the date fell outside the machine's integer range. They
1541 now consistently croak() if the date falls in an unsupported range.
1545 The error return value in list context has been changed for all functions
1546 that return a list of values. Previously these functions returned a list
1547 with a single element C<undef> if an error occurred. Now these functions
1548 return the empty list in these situations. This applies to the following
1554 The remaining functions are unchanged and continue to return C<undef> on
1555 error even in list context.
1557 The Win32::SetLastError(ERROR) function has been added as a complement
1558 to the Win32::GetLastError() function.
1560 The new Win32::GetFullPathName(FILENAME) returns the full absolute
1561 pathname for FILENAME in scalar context. In list context it returns
1562 a two-element list containing the fully qualified directory name and
1563 the filename. See L<Win32>.
1567 A new feature called "DBM Filters" has been added to all the
1568 DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
1569 DBM Filters add four new methods to each DBM module:
1576 These can be used to filter key-value pairs before the pairs are
1577 written to the database or just after they are read from the database.
1578 See L<perldbmfilter> for further information.
1584 C<use attrs> is now obsolete, and is only provided for
1585 backward-compatibility. It's been replaced by the C<sub : attributes>
1586 syntax. See L<perlsub/"Subroutine Attributes"> and L<attributes>.
1588 C<use utf8> to enable UTF-8 and Unicode support.
1590 Lexical warnings pragma, C<use warnings;>, to control optional warnings.
1593 C<use filetest> to control the behaviour of filetests (C<-r> C<-w>
1594 ...). Currently only one subpragma implemented, "use filetest
1595 'access';", that uses access(2) or equivalent to check permissions
1596 instead of using stat(2) as usual. This matters in filesystems
1597 where there are ACLs (access control lists): the stat(2) might lie,
1598 but access(2) knows better.
1600 =head1 Utility Changes
1604 [TODO - Kurt Starsinic <kstar@chapin.edu>]
1608 C<perlcc> now supports the C and Bytecode backends. By default,
1609 it generates output from the simple C backend rather than the
1610 optimized C backend.
1612 Support for non-Unix platforms has been improved.
1617 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1619 =head1 Documentation Changes
1625 The official list of public Perl API functions.
1627 =item perlcompile.pod
1629 An introduction to using the Perl Compiler suite.
1631 =item perlfilter.pod
1633 An introduction to writing Perl source filters.
1637 Some guidelines for hacking the Perl source code.
1639 =item perlintern.pod
1641 A list of internal functions in the Perl source code.
1642 (List is currently empty.)
1644 =item perlopentut.pod
1646 A tutorial on using open() effectively.
1648 =item perlreftut.pod
1650 A tutorial that introduces the essentials of references.
1654 A tutorial on managing class data for object modules.
1658 =head1 New or Changed Diagnostics
1662 =item "%s" variable %s masks earlier declaration in same %s
1664 (W) A "my" or "our" variable has been redeclared in the current scope or statement,
1665 effectively eliminating all access to the previous instance. This is almost
1666 always a typographical error. Note that the earlier variable will still exist
1667 until the end of the scope or until all closure referents to it are
1670 =item "my sub" not yet implemented
1672 (F) Lexically scoped subroutines are not yet implemented. Don't try that
1675 =item "our" variable %s redeclared
1677 (W) You seem to have already declared the same global once before in the
1678 current lexical scope.
1680 =item '!' allowed only after types %s
1682 (F) The '!' is allowed in pack() and unpack() only after certain types.
1683 See L<perlfunc/pack>.
1685 =item / cannot take a count
1687 (F) You had an unpack template indicating a counted-length string,
1688 but you have also specified an explicit size for the string.
1689 See L<perlfunc/pack>.
1691 =item / must be followed by a, A or Z
1693 (F) You had an unpack template indicating a counted-length string,
1694 which must be followed by one of the letters a, A or Z
1695 to indicate what sort of string is to be unpacked.
1696 See L<perlfunc/pack>.
1698 =item / must be followed by a*, A* or Z*
1700 (F) You had a pack template indicating a counted-length string,
1701 Currently the only things that can have their length counted are a*, A* or Z*.
1702 See L<perlfunc/pack>.
1704 =item / must follow a numeric type
1706 (F) You had an unpack template that contained a '#',
1707 but this did not follow some numeric unpack specification.
1708 See L<perlfunc/pack>.
1710 =item /%s/: Unrecognized escape \\%c passed through
1712 (W) You used a backslash-character combination which is not recognized
1713 by Perl. This combination appears in an interpolated variable or a
1714 C<'>-delimited regular expression. The character was understood literally.
1716 =item /%s/: Unrecognized escape \\%c in character class passed through
1718 (W) You used a backslash-character combination which is not recognized
1719 by Perl inside character classes. The character was understood literally.
1721 =item /%s/ should probably be written as "%s"
1723 (W) You have used a pattern where Perl expected to find a string,
1724 as in the first argument to C<join>. Perl will treat the true
1725 or false result of matching the pattern against $_ as the string,
1726 which is probably not what you had in mind.
1728 =item %s() called too early to check prototype
1730 (W) You've called a function that has a prototype before the parser saw a
1731 definition or declaration for it, and Perl could not check that the call
1732 conforms to the prototype. You need to either add an early prototype
1733 declaration for the subroutine in question, or move the subroutine
1734 definition ahead of the call to get proper prototype checking. Alternatively,
1735 if you are certain that you're calling the function correctly, you may put
1736 an ampersand before the name to avoid the warning. See L<perlsub>.
1738 =item %s argument is not a HASH or ARRAY element
1740 (F) The argument to exists() must be a hash or array element, such as:
1743 $ref->[12]->["susie"]
1745 =item %s argument is not a HASH or ARRAY element or slice
1747 (F) The argument to delete() must be either a hash or array element, such as:
1750 $ref->[12]->["susie"]
1752 or a hash or array slice, such as:
1754 @foo[$bar, $baz, $xyzzy]
1755 @{$ref->[12]}{"susie", "queue"}
1757 =item %s argument is not a subroutine name
1759 (F) The argument to exists() for C<exists &sub> must be a subroutine
1760 name, and not a subroutine call. C<exists &sub()> will generate this error.
1762 =item %s package attribute may clash with future reserved word: %s
1764 (W) A lowercase attribute name was used that had a package-specific handler.
1765 That name might have a meaning to Perl itself some day, even though it
1766 doesn't yet. Perhaps you should use a mixed-case attribute name, instead.
1769 =item (in cleanup) %s
1771 (W) This prefix usually indicates that a DESTROY() method raised
1772 the indicated exception. Since destructors are usually called by
1773 the system at arbitrary points during execution, and often a vast
1774 number of times, the warning is issued only once for any number
1775 of failures that would otherwise result in the same message being
1778 Failure of user callbacks dispatched using the C<G_KEEPERR> flag
1779 could also result in this warning. See L<perlcall/G_KEEPERR>.
1781 =item <> should be quotes
1783 (F) You wrote C<require E<lt>fileE<gt>> when you should have written
1786 =item Attempt to join self
1788 (F) You tried to join a thread from within itself, which is an
1789 impossible task. You may be joining the wrong thread, or you may
1790 need to move the join() to some other thread.
1792 =item Bad evalled substitution pattern
1794 (F) You've used the /e switch to evaluate the replacement for a
1795 substitution, but perl found a syntax error in the code to evaluate,
1796 most likely an unexpected right brace '}'.
1798 =item Bad realloc() ignored
1800 (S) An internal routine called realloc() on something that had never been
1801 malloc()ed in the first place. Mandatory, but can be disabled by
1802 setting environment variable C<PERL_BADFREE> to 1.
1804 =item Binary number > 0b11111111111111111111111111111111 non-portable
1806 (W) The binary number you specified is larger than 2**32-1
1807 (4294967295) and therefore non-portable between systems. See
1808 L<perlport> for more on portability concerns.
1810 =item Bit vector size > 32 non-portable
1812 (W) Using bit vector sizes larger than 32 is non-portable.
1814 =item Buffer overflow in prime_env_iter: %s
1816 (W) A warning peculiar to VMS. While Perl was preparing to iterate over
1817 %ENV, it encountered a logical name or symbol definition which was too long,
1818 so it was truncated to the string shown.
1820 =item Can't check filesystem of script "%s"
1822 (P) For some reason you can't check the filesystem of the script for nosuid.
1824 =item Can't declare class for non-scalar %s in "%s"
1826 (S) Currently, only scalar variables can declared with a specific class
1827 qualifier in a "my" or "our" declaration. The semantics may be extended
1828 for other types of variables in future.
1830 =item Can't declare %s in "%s"
1832 (F) Only scalar, array, and hash variables may be declared as "my" or
1833 "our" variables. They must have ordinary identifiers as names.
1835 =item Can't ignore signal CHLD, forcing to default
1837 (W) Perl has detected that it is being run with the SIGCHLD signal
1838 (sometimes known as SIGCLD) disabled. Since disabling this signal
1839 will interfere with proper determination of exit status of child
1840 processes, Perl has reset the signal to its default value.
1841 This situation typically indicates that the parent program under
1842 which Perl may be running (e.g. cron) is being very careless.
1844 =item Can't modify non-lvalue subroutine call
1846 (F) Subroutines meant to be used in lvalue context should be declared as
1847 such, see L<perlsub/"Lvalue subroutines">.
1849 =item Can't read CRTL environ
1851 (S) A warning peculiar to VMS. Perl tried to read an element of %ENV
1852 from the CRTL's internal environment array and discovered the array was
1853 missing. You need to figure out where your CRTL misplaced its environ
1854 or define F<PERL_ENV_TABLES> (see L<perlvms>) so that environ is not searched.
1856 =item Can't remove %s: %s, skipping file
1858 (S) You requested an inplace edit without creating a backup file. Perl
1859 was unable to remove the original file to replace it with the modified
1860 file. The file was left unmodified.
1862 =item Can't return %s from lvalue subroutine
1864 (F) Perl detected an attempt to return illegal lvalues (such
1865 as temporary or readonly values) from a subroutine used as an lvalue.
1866 This is not allowed.
1868 =item Can't weaken a nonreference
1870 (F) You attempted to weaken something that was not a reference. Only
1871 references can be weakened.
1873 =item Character class [:%s:] unknown
1875 (F) The class in the character class [: :] syntax is unknown.
1878 =item Character class syntax [%s] belongs inside character classes
1880 (W) The character class constructs [: :], [= =], and [. .] go
1881 I<inside> character classes, the [] are part of the construct,
1882 for example: /[012[:alpha:]345]/. Note that [= =] and [. .]
1883 are not currently implemented; they are simply placeholders for
1886 =item Constant is not %s reference
1888 (F) A constant value (perhaps declared using the C<use constant> pragma)
1889 is being dereferenced, but it amounts to the wrong type of reference. The
1890 message indicates the type of reference that was expected. This usually
1891 indicates a syntax error in dereferencing the constant value.
1892 See L<perlsub/"Constant Functions"> and L<constant>.
1894 =item constant(%s): %%^H is not localized
1896 (F) When setting compile-time-lexicalized hash %^H one should set the
1897 corresponding bit of $^H as well.
1899 =item constant(%s): %s
1901 (F) Compile-time-substitutions (such as overloaded constants and
1902 character names) were not correctly set up.
1904 =item defined(@array) is deprecated
1906 (D) defined() is not usually useful on arrays because it checks for an
1907 undefined I<scalar> value. If you want to see if the array is empty,
1908 just use C<if (@array) { # not empty }> for example.
1910 =item defined(%hash) is deprecated
1912 (D) defined() is not usually useful on hashes because it checks for an
1913 undefined I<scalar> value. If you want to see if the hash is empty,
1914 just use C<if (%hash) { # not empty }> for example.
1916 =item Did not produce a valid header
1920 =item Did you mean "local" instead of "our"?
1922 (W) Remember that "our" does not localize the declared global variable.
1923 You have declared it again in the same lexical scope, which seems superfluous.
1925 =item Document contains no data
1929 =item entering effective %s failed
1931 (F) While under the C<use filetest> pragma, switching the real and
1932 effective uids or gids failed.
1934 =item false [] range "%s" in regexp
1936 (W) A character class range must start and end at a literal character, not
1937 another character class like C<\d> or C<[:alpha:]>. The "-" in your false
1938 range is interpreted as a literal "-". Consider quoting the "-", "\-".
1941 =item Filehandle %s opened only for output
1943 (W) You tried to read from a filehandle opened only for writing. If you
1944 intended it to be a read/write filehandle, you needed to open it with
1945 "+E<lt>" or "+E<gt>" or "+E<gt>E<gt>" instead of with "E<lt>" or nothing. If
1946 you intended only to read from the file, use "E<lt>". See
1949 =item flock() on closed filehandle %s
1951 (W) The filehandle you're attempting to flock() got itself closed some
1952 time before now. Check your logic flow. flock() operates on filehandles.
1953 Are you attempting to call flock() on a dirhandle by the same name?
1955 =item Global symbol "%s" requires explicit package name
1957 (F) You've said "use strict vars", which indicates that all variables
1958 must either be lexically scoped (using "my"), declared beforehand using
1959 "our", or explicitly qualified to say which package the global variable
1962 =item Hexadecimal number > 0xffffffff non-portable
1964 (W) The hexadecimal number you specified is larger than 2**32-1
1965 (4294967295) and therefore non-portable between systems. See
1966 L<perlport> for more on portability concerns.
1968 =item Ill-formed CRTL environ value "%s"
1970 (W) A warning peculiar to VMS. Perl tried to read the CRTL's internal
1971 environ array, and encountered an element without the C<=> delimiter
1972 used to spearate keys from values. The element is ignored.
1974 =item Ill-formed message in prime_env_iter: |%s|
1976 (W) A warning peculiar to VMS. Perl tried to read a logical name
1977 or CLI symbol definition when preparing to iterate over %ENV, and
1978 didn't see the expected delimiter between key and value, so the
1981 =item Illegal binary digit %s
1983 (F) You used a digit other than 0 or 1 in a binary number.
1985 =item Illegal binary digit %s ignored
1987 (W) You may have tried to use a digit other than 0 or 1 in a binary number.
1988 Interpretation of the binary number stopped before the offending digit.
1990 =item Illegal number of bits in vec
1992 (F) The number of bits in vec() (the third argument) must be a power of
1993 two from 1 to 32 (or 64, if your platform supports that).
1995 =item Integer overflow in %s number
1997 (W) The hexadecimal, octal or binary number you have specified either
1998 as a literal or as an argument to hex() or oct() is too big for your
1999 architecture, and has been converted to a floating point number. On a
2000 32-bit architecture the largest hexadecimal, octal or binary number
2001 representable without overflow is 0xFFFFFFFF, 037777777777, or
2002 0b11111111111111111111111111111111 respectively. Note that Perl
2003 transparently promotes all numbers to a floating point representation
2004 internally--subject to loss of precision errors in subsequent
2007 =item Invalid %s attribute: %s
2009 The indicated attribute for a subroutine or variable was not recognized
2010 by Perl or by a user-supplied handler. See L<attributes>.
2012 =item Invalid %s attributes: %s
2014 The indicated attributes for a subroutine or variable were not recognized
2015 by Perl or by a user-supplied handler. See L<attributes>.
2017 =item invalid [] range "%s" in regexp
2019 The offending range is now explicitly displayed.
2021 =item Invalid separator character %s in attribute list
2023 (F) Something other than a colon or whitespace was seen between the
2024 elements of an attribute list. If the previous attribute
2025 had a parenthesised parameter list, perhaps that list was terminated
2026 too soon. See L<attributes>.
2028 =item Invalid separator character %s in subroutine attribute list
2030 (F) Something other than a colon or whitespace was seen between the
2031 elements of a subroutine attribute list. If the previous attribute
2032 had a parenthesised parameter list, perhaps that list was terminated
2035 =item leaving effective %s failed
2037 (F) While under the C<use filetest> pragma, switching the real and
2038 effective uids or gids failed.
2040 =item Lvalue subs returning %s not implemented yet
2042 (F) Due to limitations in the current implementation, array and hash
2043 values cannot be returned in subroutines used in lvalue context.
2044 See L<perlsub/"Lvalue subroutines">.
2046 =item Method %s not permitted
2050 =item Missing %sbrace%s on \N{}
2052 (F) Wrong syntax of character name literal C<\N{charname}> within
2053 double-quotish context.
2055 =item Missing command in piped open
2057 (W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
2058 construction, but the command was missing or blank.
2060 =item Missing name in "my sub"
2062 (F) The reserved syntax for lexically scoped subroutines requires that they
2063 have a name with which they can be found.
2065 =item No %s specified for -%c
2067 (F) The indicated command line switch needs a mandatory argument, but
2068 you haven't specified one.
2070 =item No package name allowed for variable %s in "our"
2072 (F) Fully qualified variable names are not allowed in "our" declarations,
2073 because that doesn't make much sense under existing semantics. Such
2074 syntax is reserved for future extensions.
2076 =item No space allowed after -%c
2078 (F) The argument to the indicated command line switch must follow immediately
2079 after the switch, without intervening spaces.
2081 =item no UTC offset information; assuming local time is UTC
2083 (S) A warning peculiar to VMS. Perl was unable to find the local
2084 timezone offset, so it's assuming that local system time is equivalent
2085 to UTC. If it's not, define the logical name F<SYS$TIMEZONE_DIFFERENTIAL>
2086 to translate to the number of seconds which need to be added to UTC to
2089 =item Octal number > 037777777777 non-portable
2091 (W) The octal number you specified is larger than 2**32-1 (4294967295)
2092 and therefore non-portable between systems. See L<perlport> for more
2093 on portability concerns.
2095 See also L<perlport> for writing portable code.
2097 =item panic: del_backref
2099 (P) Failed an internal consistency check while trying to reset a weak
2102 =item panic: kid popen errno read
2104 (F) forked child returned an incomprehensible message about its errno.
2106 =item panic: magic_killbackrefs
2108 (P) Failed an internal consistency check while trying to reset all weak
2109 references to an object.
2111 =item Parentheses missing around "%s" list
2113 (W) You said something like
2119 my ($foo, $bar) = @_;
2121 Remember that "my", "our" and "local" bind closer than comma.
2123 =item Possible Y2K bug: %s
2125 (W) You are concatenating the number 19 with another number, which
2126 could be a potential Year 2000 problem.
2128 =item Premature end of script headers
2132 =item Repeat count in pack overflows
2134 (F) You can't specify a repeat count so large that it overflows
2135 your signed integers. See L<perlfunc/pack>.
2137 =item Repeat count in unpack overflows
2139 (F) You can't specify a repeat count so large that it overflows
2140 your signed integers. See L<perlfunc/unpack>.
2142 =item realloc() of freed memory ignored
2144 (S) An internal routine called realloc() on something that had already
2147 =item Reference is already weak
2149 (W) You have attempted to weaken a reference that is already weak.
2150 Doing so has no effect.
2152 =item setpgrp can't take arguments
2154 (F) Your system has the setpgrp() from BSD 4.2, which takes no arguments,
2155 unlike POSIX setpgid(), which takes a process ID and process group ID.
2157 =item Strange *+?{} on zero-length expression
2159 (W) You applied a regular expression quantifier in a place where it
2160 makes no sense, such as on a zero-width assertion.
2161 Try putting the quantifier inside the assertion instead. For example,
2162 the way to match "abc" provided that it is followed by three
2163 repetitions of "xyz" is C</abc(?=(?:xyz){3})/>, not C</abc(?=xyz){3}/>.
2165 =item switching effective %s is not implemented
2167 (F) While under the C<use filetest> pragma, we cannot switch the
2168 real and effective uids or gids.
2170 =item This Perl can't reset CRTL environ elements (%s)
2172 =item This Perl can't set CRTL environ elements (%s=%s)
2174 (W) Warnings peculiar to VMS. You tried to change or delete an element
2175 of the CRTL's internal environ array, but your copy of Perl wasn't
2176 built with a CRTL that contained the setenv() function. You'll need to
2177 rebuild Perl with a CRTL that does, or redefine F<PERL_ENV_TABLES> (see
2178 L<perlvms>) so that the environ array isn't the target of the change to
2179 %ENV which produced the warning.
2181 =item Unknown open() mode '%s'
2183 (F) The second argument of 3-argument open() is not among the list
2184 of valid modes: C<L<lt>>, C<L<gt>>, C<E<gt>E<gt>>, C<+L<lt>>,
2185 C<+L<gt>>, C<+E<gt>E<gt>>, C<-|>, C<|->.
2187 =item Unknown process %x sent message to prime_env_iter: %s
2189 (P) An error peculiar to VMS. Perl was reading values for %ENV before
2190 iterating over it, and someone else stuck a message in the stream of
2191 data Perl expected. Someone's very confused, or perhaps trying to
2192 subvert Perl's population of %ENV for nefarious purposes.
2194 =item Unrecognized escape \\%c passed through
2196 (W) You used a backslash-character combination which is not recognized
2197 by Perl. The character was understood literally.
2199 =item Unterminated attribute parameter in attribute list
2201 (F) The lexer saw an opening (left) parenthesis character while parsing an
2202 attribute list, but the matching closing (right) parenthesis
2203 character was not found. You may need to add (or remove) a backslash
2204 character to get your parentheses to balance. See L<attributes>.
2206 =item Unterminated attribute list
2208 (F) The lexer found something other than a simple identifier at the start
2209 of an attribute, and it wasn't a semicolon or the start of a
2210 block. Perhaps you terminated the parameter list of the previous attribute
2211 too soon. See L<attributes>.
2213 =item Unterminated attribute parameter in subroutine attribute list
2215 (F) The lexer saw an opening (left) parenthesis character while parsing a
2216 subroutine attribute list, but the matching closing (right) parenthesis
2217 character was not found. You may need to add (or remove) a backslash
2218 character to get your parentheses to balance.
2220 =item Unterminated subroutine attribute list
2222 (F) The lexer found something other than a simple identifier at the start
2223 of a subroutine attribute, and it wasn't a semicolon or the start of a
2224 block. Perhaps you terminated the parameter list of the previous attribute
2227 =item Value of CLI symbol "%s" too long
2229 (W) A warning peculiar to VMS. Perl tried to read the value of an %ENV
2230 element from a CLI symbol table, and found a resultant string longer
2231 than 1024 characters. The return value has been truncated to 1024
2234 =item Version number must be a constant number
2236 (P) The attempt to translate a C<use Module n.n LIST> statement into
2237 its equivalent C<BEGIN> block found an internal inconsistency with
2242 =head1 Obsolete Diagnostics
2246 =item Character class syntax [: :] is reserved for future extensions
2248 (W) Within regular expression character classes ([]) the syntax beginning
2249 with "[:" and ending with ":]" is reserved for future extensions.
2250 If you need to represent those character sequences inside a regular
2251 expression character class, just quote the square brackets with the
2252 backslash: "\[:" and ":\]".
2254 =item Ill-formed logical name |%s| in prime_env_iter
2256 (W) A warning peculiar to VMS. A logical name was encountered when preparing
2257 to iterate over %ENV which violates the syntactic rules governing logical
2258 names. Because it cannot be translated normally, it is skipped, and will not
2259 appear in %ENV. This may be a benign occurrence, as some software packages
2260 might directly modify logical name tables and introduce nonstandard names,
2261 or it may indicate that a logical name table has been corrupted.
2263 =item regexp too big
2265 (F) The current implementation of regular expressions uses shorts as
2266 address offsets within a string. Unfortunately this means that if
2267 the regular expression compiles to longer than 32767, it'll blow up.
2268 Usually when you want a regular expression this big, there is a better
2269 way to do it with multiple statements. See L<perlre>.
2271 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
2273 (D) Perl versions before 5.004 misinterpreted any type marker followed
2274 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
2275 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
2277 However, the developers of Perl 5.004 could not fix this bug completely,
2278 because at least two widely-used modules depend on the old meaning of
2279 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
2280 old (broken) way inside strings; but it generates this message as a
2281 warning. And in Perl 5.005, this special treatment will cease.
2287 If you find what you think is a bug, you might check the
2288 articles recently posted to the comp.lang.perl.misc newsgroup.
2289 There may also be information at http://www.perl.com/perl/, the Perl
2292 If you believe you have an unreported bug, please run the B<perlbug>
2293 program included with your release. Make sure to trim your bug down
2294 to a tiny but sufficient test case. Your bug report, along with the
2295 output of C<perl -V>, will be sent off to perlbug@perl.com to be
2296 analysed by the Perl porting team.
2300 The F<Changes> file for exhaustive details on what changed.
2302 The F<INSTALL> file for how to build Perl.
2304 The F<README> file for general stuff.
2306 The F<Artistic> and F<Copying> files for copyright information.
2310 Written by Gurusamy Sarathy <F<gsar@activestate.com>>, with many
2311 contributions from The Perl Porters.
2313 Send omissions or corrections to <F<perlbug@perl.com>>.