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> and C<byte> pragmas are used to control this support
382 in the current lexical scope. See L<perlunicode>, L<utf8> and L<byte> for
385 =head2 Interpreter cloning, threads, and concurrency
387 WARNING: This is an experimental feature in a pre-alpha state. Use
390 Perl 5.005_63 introduces the beginnings of support for running multiple
391 interpreters concurrently in different threads. In conjunction with
392 the perl_clone() API call, which can be used to selectively duplicate
393 the state of any given interpreter, it is possible to compile a
394 piece of code once in an interpreter, clone that interpreter
395 one or more times, and run all the resulting interpreters in distinct
398 On Windows, this feature is used to emulate fork() at the interpreter
399 level. See L<perlfork>.
401 This feature is still in evolution. It is eventually meant to be used
402 to selectively clone a subroutine and data reachable from that
403 subroutine in a separate interpreter and run the cloned subroutine
404 in a separate thread. Since there is no shared data between the
405 interpreters, little or no locking will be needed (unless parts of
406 the symbol table are explicitly shared). This is obviously intended
407 to be an easy-to-use replacement for the existing threads support.
409 Support for cloning interpreters and interpreter concurrency can be
410 enabled using the -Dusethreads Configure option (see win32/Makefile for
411 how to enable it on Windows.) The resulting perl executable will be
412 functionally identical to one that was built with -Dmultiplicity, but
413 the perl_clone() API call will only be available in the former.
415 -Dusethreads enables, the cpp macros USE_ITHREADS by default, which enables
416 Perl source code changes that provide a clear separation between the op tree
417 and the data it operates with. The former is considered immutable, and can
418 therefore be shared between an interpreter and all of its clones, while the
419 latter is considered local to each interpreter, and is therefore copied for
422 Note that building Perl with the -Dusemultiplicity Configure option
423 is adequate if you wish to run multiple B<independent> interpreters
424 concurrently in different threads. -Dusethreads only provides the
425 additional functionality of the perl_clone() API call and other
426 support for running B<cloned> interpreters concurrently.
428 [XXX TODO - the Compiler backends may be broken when USE_ITHREADS is
431 =head2 Lexically scoped warning categories
433 You can now control the granularity of warnings emitted by perl at a finer
434 level using the C<use warnings> pragma. See L<warnings> and L<perllexwarn>
437 =head2 Lvalue subroutines
439 WARNING: This is an experimental feature.
442 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>,
443 Tuomas Lukka <lukka@fas.harvard.edu>)]
445 =head2 "our" declarations
447 An "our" declaration introduces a value that can be best understood
448 as a lexically scoped symbolic alias to a global variable in the
449 package that was current where the variable was declared. This is
450 mostly useful as an alternative to the C<vars> pragma, but also provides
451 the opportunity to introduce typing and other attributes for such
452 variables. See L<perlfunc/our>.
454 =head2 Support for version tuples
456 Literals of the form v1.2.3.4 are now parsed as the utf8 string
457 C<"\x{1}\x{2}\x{3}\x{4}">. This allows comparing version numbers using
458 regular string comparison operators C<eq>, C<ne>, C<lt>, C<gt> etc.
460 These "dotted tuples" are dual-valued. They are both strings of utf8
461 characters, and floating point numbers. Thus v1.2.3.4 has the string
462 value C<"\x{1}\x{2}\x{3}\x{4}"> and the numeric value 1.002_003_004.
463 As another example, v5.5.640 has the string value C<"\x{5}\x{5}\x{280}">
464 (remember 280 hexadecimal is 640 decimal) and the numeric value
467 In conjunction with the new C<$^V> magic variable (which contains
468 the perl version in this format), such literals can be used to
469 check if you're running a particular version of Perl.
471 if ($^V and $^V gt v5.5.640) {
472 # new style version numbers are supported
475 C<require> and C<use> also support such literals:
477 require v5.6.0; # croak if $^V lt v5.6.0
478 use v5.6.0; # same, but croaks at compile-time
480 =head2 Weak references
482 WARNING: This is an experimental feature.
484 change#3385, also need perlguts documentation
486 [TODO - Tuomas Lukka <lukka@fas.harvard.edu>]
488 =head2 File globbing implemented internally
490 WARNING: This is currently an experimental feature. Interfaces and
491 implementation are likely to change.
493 Perl now uses the File::Glob implementation of the glob() operator
494 automatically. This avoids using an external csh process and the
495 problems associated with it.
497 =head2 Binary numbers supported
499 Binary numbers are now supported as literals, in s?printf formats, and
503 printf "The answer is: %b\n", oct("0b101010");
505 =head2 Some arrows may be omitted in calls through references
507 Perl now allows the arrow to be omitted in many constructs
508 involving subroutine calls through references. For example,
509 C<$foo[10]->('foo')> may now be written C<$foo[10]('foo')>.
510 This is rather similar to how the arrow may be omitted from
511 C<$foo[10]->{'foo'}>. Note however, that the arrow is still
512 required for C<foo(10)->('bar')>.
514 =head2 exists() is supported on subroutine names
516 The exists() builtin now works on subroutine names. A subroutine
517 is considered to exist if it has been declared (even if implicitly).
518 See L<perlfunc/exists> for examples.
520 =head2 exists() and delete() are supported on array elements
522 The exists() and delete() builtins now work on simple arrays as well.
523 The behavior is similar to that on hash elements.
525 exists() can be used to check whether an array element has been
526 initialized without autovivifying it. If the array is tied, the
527 EXISTS() method in the corresponding tied package will be invoked.
529 delete() may be used to remove an element from the array and return
530 it. The array element at that position returns to its unintialized
531 state, so that testing for the same element with exists() will return
532 false. If the element happens to be the one at the end, the size of
533 the array also shrinks by one. If the array is tied, the DELETE() method
534 in the corresponding tied package will be invoked.
536 See L<perlfunc/exists> and L<perlfunc/delete> for examples.
538 =head2 syswrite() ease-of-use
540 The length argument of C<syswrite()> has become optional.
542 =head2 File and directory handles can be autovivified
544 Similar to how constructs such as C<$x->[0]> autovivify a reference,
545 handle constructors (open(), opendir(), pipe(), socketpair(), sysopen(),
546 socket(), and accept()) now autovivify a file or directory handle
547 if the handle passed to them is an uninitialized scalar variable. This
548 allows the constructs such as C<open(my $fh, ...)> and C<open(local $fh,...)>
549 to be used to create filehandles that will conveniently be closed
550 automatically when the scope ends, provided there are no other references
551 to them. This largely eliminates the need for typeglobs when opening
552 filehandles that must be passed around, as in the following example:
556 or die "Can't open '@_': $!";
561 my $f = myopen("</etc/motd");
563 # $f implicitly closed here
566 [TODO - this idiom needs more pod penetration]
568 =head2 64-bit support
570 All platforms that have 64-bit integers either (a) natively as longs
571 or ints (b) via special compiler flags (c) using long long are able to
572 use "quads" (64-integers) as follows:
578 constants (decimal, hexadecimal, octal, binary) in the code
582 arguments to oct() and hex()
586 arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)
594 pack() and unpack() "q" and "Q" formats
598 in basic arithmetics: + - * / %
602 vec() (but see the below note about bit arithmetics)
606 Note that unless you have the case (a) you will have to configure
607 and compile Perl using the -Duse64bits Configure flag.
609 Unfortunately bit arithmetics (&, |, ^, ~, <<, >>) for numbers are not
610 64-bit clean, they are explictly forced to be 32-bit. Bit arithmetics
611 for bit vectors (created by vec()) are not limited in their width.
613 Last but not least: note that due to Perl's habit of always using
614 floating point numbers the quads are still not true integers.
615 When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
616 -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
617 are silently promoted to floating point numbers, after which they will
618 start losing precision (their lower digits).
620 =head2 Large file support
622 If you have filesystems that support "large files" (files larger than
623 2 gigabytes), you may now also be able to create and access them from
624 Perl. You have to use Configure -Duselargefiles. Turning on the
625 large file support turns on also the 64-bit support on many platforms.
626 Beware that unless your filesystem also supports "sparse files" seeking
627 to umpteen petabytes may be unadvisable.
629 Note that in addition to requiring a proper file system to do large
630 files you may also need to adjust your per-process (or your
631 per-system, or per-process-group, or per-user-group) maximum filesize
632 limits before running Perl scripts that try to handle large files,
633 especially if you intend to write such files.
635 Finally, in addition to your process/process group maximum filesize
636 limits, you may have quota limits on your filesystems that stop you
637 (your user id or your user group id) from using large files.
639 Adjusting your process/user/group/file system/operating system limits
640 is outside the scope of Perl core language. For process limits, you
641 may try increasing the limits using your shell's limits/limit/ulimit
642 command before running Perl. The BSD::Resource extension (not
643 included with the standard Perl distribution) may also be of use, it
644 offers the getrlimit/setrlimit interface that can be used to adjust
645 process resource usage limits, including the maximum filesize limit.
649 In some systems you may be able to use long doubles to enhance the
650 range and precision of your double precision floating point numbers
651 (that is, Perl's numbers). Use Configure -Duselongdouble to enable
652 this support (if it is available).
656 You can "Configure -Dusemorebits" to turn on both the 64-bit support
657 and the long double support.
659 =head2 Enhanced support for sort() subroutines
661 Perl subroutines with a prototype of C<($$)> and XSUBs in general can
662 now be used as sort subroutines. In either case, the two elements to
663 be compared are passed as normal parameters in @_. See L<perlfunc/sort>.
665 For unprototyped sort subroutines, the historical behavior of passing
666 the elements to be compared as the global variables $a and $b remains
669 =head2 Better syntax checks on parenthesized unary operators
673 print defined(&foo,&bar,&baz);
674 print uc("foo","bar","baz");
677 used to be accidentally allowed in earlier versions, and produced
678 unpredictable behaviour. Some produced ancillary warnings
679 when used in this way; others silently did the wrong thing.
681 The parenthesized forms of most unary operators that expect a single
682 argument now ensure that they are not called with more than one
683 argument, making the cases shown above syntax errors. The usual
686 print defined &foo, &bar, &baz;
687 print uc "foo", "bar", "baz";
690 remains unchanged. See L<perlop>.
692 =head2 POSIX character class syntax [: :] supported
694 For example to match alphabetic characters use /[[:alpha:]]/.
695 See L<perlre> for details.
697 =head2 Improved C<qw//> operator
699 The C<qw//> operator is now evaluated at compile time into a true list
700 instead of being replaced with a run time call to C<split()>. This
701 removes the confusing misbehaviour of C<qw//> in scalar context, which
702 had inherited that behaviour from split().
706 $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
708 now correctly prints "3|a", instead of "2|a".
710 =head2 pack() format 'Z' supported
712 The new format type 'Z' is useful for packing and unpacking null-terminated
713 strings. See L<perlfunc/"pack">.
715 =head2 pack() format modifier '!' supported
717 The new format type modifier '!' is useful for packing and unpacking
718 native shorts, ints, and longs. See L<perlfunc/"pack">.
720 =head2 pack() and unpack() support counted strings
722 The template character '/' can be used to specify a counted string
723 type to be packed or unpacked. See L<perlfunc/"pack">.
725 =head2 Comments in pack() templates
727 The '#' character in a template introduces a comment up to
728 end of the line. This facilitates documentation of pack()
731 =head2 $^X variables may now have names longer than one character
733 Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
734 error. Now variable names that begin with a control character may be
735 arbitrarily long. However, for compatibility reasons, these variables
736 I<must> be written with explicit braces, as C<${^XY}> for example.
737 C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more
738 than one control character, such as C<${^XY^Z}>, are illegal.
740 The old syntax has not changed. As before, `^X' may be either a
741 literal control-X character or the two-character sequence `caret' plus
742 `X'. When braces are omitted, the variable name stops after the
743 control character. Thus C<"$^XYZ"> continues to be synonymous with
744 C<$^X . "YZ"> as before.
746 As before, lexical variables may not have names beginning with control
747 characters. As before, variables whose names begin with a control
748 character are always forced to be in package `main'. All such variables
749 are reserved for future extensions, except those that begin with
750 C<^_>, which may be used by user programs and are guaranteed not to
751 acquire special meaning in any future version of Perl.
753 =head2 C<use attrs> implicit in subroutine attributes
755 Formerly, if you wanted to mark a subroutine as being a method call or
756 as requiring an automatic lock() when it is entered, you had to declare
757 that with a C<use attrs> pragma in the body of the subroutine.
758 That can now be accomplished with declaration syntax, like this:
760 sub mymethod : locked method ;
762 sub mymethod : locked method {
766 sub othermethod :locked :method ;
768 sub othermethod :locked :method {
773 (Note how only the first C<:> is mandatory, and whitespace surrounding
774 the C<:> is optional.)
776 F<AutoSplit.pm> and F<SelfLoader.pm> have been updated to keep the attributes
777 with the stubs they provide. See L<attributes>.
779 =head2 Regular expression improvements
781 change#2827,2373,2372,2365,1813,1800,4112,4158,4215,4301
782 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
784 =head2 Overloading improvements
787 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
789 =head2 open() with more than two arguments
791 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
793 =head2 Support for interpolating named characters
796 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
798 =head2 Experimental support for user-hooks in @INC
800 [TODO - Ken Fox <kfox@ford.com>]
802 =head2 C<require> and C<do> may be overridden
804 C<require> and C<do 'file'> operations may be overridden locally
805 by importing subroutines of the same name into the current package
806 (or globally by importing them into the CORE::GLOBAL:: namespace).
807 Overriding C<require> will also affect C<use>, provided the override
808 is visible at compile-time.
809 See L<perlsub/"Overriding Built-in Functions">.
811 =head2 New variable $^C reflects C<-c> switch
813 C<$^C> has a boolean value that reflects whether perl is being run
814 in compile-only mode (i.e. via the C<-c> switch). Since
815 BEGIN blocks are executed under such conditions, this variable
816 enables perl code to determine whether actions that make sense
817 only during normal running are warranted. See L<perlvar>.
819 =head2 New variable $^V contains Perl version in v5.6.0 format
821 C<$^V> contains the Perl version number as a version tuple that
822 can be used in string or numeric comparisons. See
823 C<Support for version tuples> for an example.
825 =head2 Optional Y2K warnings
827 If Perl is built with the cpp macro C<PERL_Y2KWARN> defined,
828 it emits optional warnings when concatenating the number 19
831 This behavior must be specifically enabled when running Configure.
832 See L<INSTALL> and L<README.Y2K>.
834 =head1 Significant bug fixes
836 =head2 E<lt>HANDLEE<gt> on empty files
838 With C<$/> set to C<undef>, "slurping" an empty file returns a string of
839 zero length (instead of C<undef>, as it used to) the first time the
840 HANDLE is read after C<$/> is set to C<undef>. Further reads yield
843 This means that the following will append "foo" to an empty file (it used
846 perl -0777 -pi -e 's/^/foo/' empty_file
850 perl -pi -e 's/^/foo/' empty_file
852 is unchanged (it continues to leave the file empty).
854 =head2 C<eval '...'> improvements
856 Line numbers (as reflected by caller() and most diagnostics) within
857 C<eval '...'> were often incorrect when here documents were involved.
858 This has been corrected.
860 Lexical lookups for variables appearing in C<eval '...'> within
861 functions that were themselves called within an C<eval '...'> were
862 searching the wrong place for lexicals. The lexical search now
863 correctly ends at the subroutine's block boundary.
865 Parsing of here documents used to be flawed when they appeared as
866 the replacement expression in C<eval 's/.../.../e'>. This has
869 =head2 All compilation errors are true errors
871 Some "errors" encountered at compile time were by neccessity
872 generated as warnings followed by eventual termination of the
873 program. This enabled more such errors to be reported in a
874 single run, rather than causing a hard stop at the first error
875 that was encountered.
877 The mechanism for reporting such errors has been reimplemented
878 to queue compile-time errors and report them at the end of the
879 compilation as true errors rather than as warnings. This fixes
880 cases where error messages leaked through in the form of warnings
881 when code was compiled at run time using C<eval STRING>, and
882 also allows such errors to be reliably trapped using __DIE__ hooks.
884 =head2 Automatic flushing of output buffers
886 fork(), exec(), system(), qx//, and pipe open()s now flush buffers
887 of all files opened for output when the operation
888 was attempted. This mostly eliminates confusing
889 buffering mishaps suffered by users unaware of how Perl internally
892 =head2 Better diagnostics on meaningless filehandle operations
894 Constructs such as C<open(E<lt>FHE<gt>)> and C<close(E<lt>FHE<gt>)>
895 are compile time errors. Attempting to read from filehandles that
896 were opened only for writing will now produce warnings (just as
897 writing to read-only filehandles does).
899 =head2 Where possible, buffered data discarded from duped input filehandle
901 C<open(NEW, "E<lt>&OLD")> now attempts to discard any data that
902 was previously read and buffered in C<OLD> before duping the handle.
903 On platforms where doing this is allowed, the next read operation
904 on C<NEW> will return the same data as the corresponding operation
905 on C<OLD>. Formerly, it would have returned the data from the start
906 of the following disk block instead.
908 =head2 eof() has the same old magic as <>
910 C<eof()> would return true if no attempt to read from C<E<lt>E<gt>> had
911 yet been made. C<eof()> has been changed to have a little magic of its
912 own, it now opens the C<E<lt>E<gt>> files.
914 =head2 system(), backticks and pipe open now reflect exec() failure
916 On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
917 etc., are implemented via fork() and exec(). When the underlying
918 exec() fails, earlier versions did not report the error properly,
919 since the exec() happened to be in a different process.
921 The child process now communicates with the parent about the
922 error in launching the external command, which allows these
923 constructs to return with their usual error value and set $!.
925 =head2 Implicitly closed filehandles are safer
927 Sometimes implicitly closed filehandles (as when they are localized,
928 and Perl automatically closes them on exiting the scope) could
929 inadvertently set $? or $!. This has been corrected.
931 =head2 C<(\$)> prototype and C<$foo{a}>
933 An scalar reference prototype now correctly allows a hash or
934 array element in that slot.
936 =head2 Pseudo-hashes work better
938 Dereferencing some types of reference values in a pseudo-hash,
939 such as C<$ph->{foo}[1]>, was accidentally disallowed. This has
942 When applied to a pseudo-hash element, exists() now reports whether
943 the specified value exists, not merely if the key is valid.
945 delete() now works on pseudo-hashes. When given a pseudo-hash element
946 or slice it deletes the values corresponding to the keys (but not the keys
947 themselves). See L<perlref/"Pseudo-hashes: Using an array as a hash">.
949 =head2 C<goto &sub> and AUTOLOAD
951 The C<goto &sub> construct works correctly when C<&sub> happens
954 =head2 C<-bareword> allowed under C<use integer>
956 The autoquoting of barewords preceded by C<-> did not work
957 in prior versions when the C<integer> pragma was enabled.
960 =head2 Boolean assignment operators are legal lvalues
962 Constructs such as C<($a ||= 2) += 1> are now allowed.
964 =head2 C<sort $coderef @foo> allowed
966 sort() did not accept a subroutine reference as the comparison
967 function in earlier versions. This is now permitted.
969 =head2 Failures in DESTROY()
971 When code in a destructor threw an exception, it went unnoticed
972 in earlier versions of Perl, unless someone happened to be
973 looking in $@ just after the point the destructor happened to
974 run. Such failures are now visible as warnings when warnings are
977 =head2 Locale bugs fixed
979 printf() and sprintf() previously reset the numeric locale
980 back to the default "C" locale. This has been fixed.
982 Numbers formatted according to the local numeric locale
983 (such as using a decimal comma instead of a decimal dot) caused
984 "isn't numeric" warnings, even while the operations accessing
985 those numbers produced correct results. The warnings are gone.
989 The C<eval 'return sub {...}'> construct could sometimes leak
990 memory. This has been fixed.
992 Operations that aren't filehandle constructors used to leak memory
993 when used on invalid filehandles. This has been fixed.
995 Constructs that modified C<@_> could fail to deallocate values
996 in C<@_> and thus leak memory. This has been corrected.
998 =head2 Spurious subroutine stubs after failed subroutine calls
1000 Perl could sometimes create empty subroutine stubs when a
1001 subroutine was not found in the package. Such cases stopped
1002 later method lookups from progressing into base packages.
1003 This has been corrected.
1005 =head2 Consistent numeric conversions
1008 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1010 =head2 Taint failures under C<-U>
1012 When running in unsafe mode, taint violations could sometimes
1013 cause silent failures. This has been fixed.
1015 =head2 END blocks and the C<-c> switch
1017 Prior versions used to run BEGIN B<and> END blocks when Perl was
1018 run in compile-only mode. Since this is typically not the expected
1019 behavior, END blocks are not executed anymore when the C<-c> switch
1022 See L<CHECK blocks> for how to run things when the compile phase ends.
1024 =head2 Potential to leak DATA filehandles
1026 Using the C<__DATA__> token creates an implicit filehandle to
1027 the file that contains the token. It is the program's
1028 responsibility to close it when it is done reading from it.
1030 This caveat is now better explained in the documentation.
1033 =head2 Diagnostics follow STDERR
1035 Diagnostic output now goes to whichever file the C<STDERR> handle
1036 is pointing at, instead of always going to the underlying C runtime
1037 library's C<stderr>.
1039 =head2 Other fixes for better diagnostics
1041 Line numbers are no longer suppressed (under most likely circumstances)
1042 during the global destruction phase.
1044 Diagnostics emitted from code running in threads other than the main
1045 thread are now accompanied by the thread ID.
1047 Embedded null characters in diagnostics now actually show up. They
1048 used to truncate the message in prior versions.
1050 $foo::a and $foo::b are now exempt from "possible typo" warnings only
1051 if sort() is encountered in package foo.
1053 Unrecognized alphabetic escapes encountered when parsing quote
1054 constructs now generate a warning, since they may take on new
1055 semantics in later versions of Perl.
1057 =head1 Performance enhancements
1059 =head2 Simple sort() using { $a <=> $b } and the like are optimized
1061 Many common sort() operations using a simple inlined block are now
1062 optimized for faster performance.
1064 =head2 Optimized assignments to lexical variables
1066 Certain operations in the RHS of assignment statements have been
1067 optimized to directly set the lexical variable on the LHS,
1068 eliminating redundant copying overheads.
1070 =head2 Method lookups optimized
1072 [TODO - Chip Salzenberg <chip@perlsupport.com>]
1074 =head2 Faster mechanism to invoke XSUBs
1077 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1079 =head2 Perl_malloc() improvements
1082 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1084 =head2 Faster subroutine calls
1086 Minor changes in how subroutine calls are handled internally
1087 provide marginal improvements in performance.
1089 =head1 Platform specific changes
1091 =head2 Additional supported platforms
1097 VM/ESA is now supported.
1101 Siemens BS2000 is now supported under the POSIX Shell.
1105 The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
1110 GNU/Hurd is now supported.
1114 Rhapsody is now supported.
1118 EPOC is is now supported (on Psion 5).
1128 Perl now works with djgpp 2.02 (and 2.03 alpha).
1132 Environment variable names are not converted to uppercase any more.
1136 Wrong exit code from backticks now fixed.
1140 This port is still using its own builtin globbing.
1146 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1150 [TODO - Charles Bailey <bailey@newman.upenn.edu>]
1154 Site library searches failed to look for ".../site/5.XXX/lib"
1155 if ".../site/5.XXXYY/lib" wasn't found. This has been corrected.
1157 When given a pathname that consists only of a drivename, such
1158 as C<A:>, opendir() and stat() now use the current working
1159 directory for the drive rather than the drive root.
1161 The builtin XSUB functions in the Win32:: namespace are
1162 documented. See L<Win32>.
1164 $^X now contains the full path name of the running executable.
1166 A Win32::GetLongPathName() function is provided to complement
1167 Win32::GetFullPathName() and Win32::GetShortPathName(). See L<Win32>.
1169 POSIX::uname() is supported.
1171 system(1,...) now returns true process IDs rather than process
1172 handles. kill() accepts any real process id, rather than strictly
1173 return values from system(1,...).
1175 The C<Shell> module is supported.
1177 Rudimentary support for building under command.com in Windows 95
1180 Scripts are read in binary mode by default to allow ByteLoader (and
1181 the filter mechanism in general) to work properly. For compatibility,
1182 the DATA filehandle will be set to text mode if a carriage return is
1183 detected at the end of the line containing the __END__ or __DATA__
1184 token; if not, the DATA filehandle will be left open in binary mode.
1185 Earlier versions always opened the DATA filehandle in text mode.
1187 The glob() operator is implemented via the L<File::Glob> extension,
1188 which supports glob syntax of the C shell. This increases the flexibility
1189 of the glob() operator, but there may be compatibility issues for
1190 programs that relied on the older globbing syntax. If you want to
1191 preserve compatibility with the older syntax, you might want to put
1192 a C<use File::DosGlob;> in your program. For details and compatibility
1193 information, see L<File::Glob>.
1203 Compatibility tests for C<sub : attrs> vs the older C<use attrs>.
1207 IO constants (SEEK_*, _IO*).
1211 Directory-related IO methods (new, read, close, rewind, tied delete).
1213 =item lib/io_multihomed
1215 INET sockets with multi-homed hosts.
1227 Regression tests for C<my ($x,@y,%z) : attrs> and <sub : attrs>.
1231 File test operators.
1235 Verify operations that access pad objects (lexicals and temporaries).
1239 Verify C<exists &sub> operations.
1243 =head1 Modules and Pragmata
1251 While used internally by Perl as a pragma, this module also
1252 provides a way to fetch subroutine and variable attributes.
1257 The Perl Compiler suite has been extensively reworked for this
1260 [TODO - Vishal Bhatia <vishal@gol.com>,
1261 Nick Ing-Simmons <nick@ni-s.u-net.com>]
1265 The ByteLoader is a dedicated extension to generate and run
1266 Perl bytecode. See L<ByteLoader>.
1270 References can now be used.
1272 The new version also allows a leading underscore in constant names, but
1273 disallows a double leading underscore (as in "__LINE__"). Some other names
1274 are disallowed or warned against, including BEGIN, END, etc. Some names
1275 which were forced into main:: used to fail silently in some cases; now they're
1276 fatal (outside of main::) and an optional warning (inside of main::).
1277 The ability to detect whether a constant had been set with a given name has
1285 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1289 A C<Maxdepth> setting can be specified to avoid venturing
1290 too deeply into deep data structures. See L<Data::Dumper>.
1292 Dumping C<qr//> objects works correctly.
1296 C<DB> is an experimental module that exposes a clean abstraction
1297 to Perl's debugging API.
1301 DB_File can now be built with Berkeley DB versions 1, 2 or 3.
1302 See C<ext/DB_File/Changes>.
1306 Devel::DProf, a Perl source code profiler has been added. See
1307 L<Devel::DProf> and L<dprofpp>.
1311 The Dumpvalue module provides screen dumps of Perl data.
1315 Overall, Benchmark results exhibit lower average error and better timing
1318 You can now run tests for I<n> seconds instead of guessing the right
1319 number of tests to run: e.g. timethese(-5, ...) will run each
1320 code for at least 5 CPU seconds. Zero as the "number of repetitions"
1321 means "for at least 3 CPU seconds". The output format has also
1322 changed. For example:
1324 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
1326 will now output something like this:
1328 Benchmark: running a, b, each for at least 5 CPU seconds...
1329 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
1330 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
1332 New features: "each for at least N CPU seconds...", "wallclock secs",
1333 and the "@ operations/CPU second (n=operations)".
1335 timethese() now returns a reference to a hash of Benchmark objects containing
1336 the test results, keyed on the names of the tests.
1338 timethis() now returns the iterations field in the Benchmark result object
1341 timethese(), timethis(), and the new cmpthese() (see below) can also take
1342 a format specifier of 'none' to suppress output.
1344 A new function countit() is just like timeit() except that it takes a
1345 TIME instead of a COUNT.
1347 A new function cmpthese() prints a chart comparing the results of each test
1348 returned from a timethese() call. For each possible pair of tests, the
1349 percentage speed difference (iters/sec or seconds/iter) is shown.
1351 For other details, see L<Benchmark>.
1355 The Devel::Peek module provides access to the internal representation
1356 of Perl variables and data. It is a data debugging tool for the XS programmer.
1358 =item ExtUtils::MakeMaker
1360 change#4135, also needs docs in module pod
1361 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1365 More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
1366 large file (more than 4GB) access Note that the O_LARGEFILE is
1367 automatically/transparently added to sysopen() flags if large file
1368 support has been configured), Free/Net/OpenBSD locking behaviour flags
1369 F_FLOCK, F_POSIX, Linux F_SHLCK, and O_ACCMODE: the combined mask of
1370 O_RDONLY, O_WRONLY, and O_RDWR. Also SEEK_SET, SEEK_CUR, and SEEK_END
1371 added for one-stop shopping of the seek/sysseek constants.
1375 A compare_text() function has been added, which allows custom
1376 comparison functions. See L<File::Compare>.
1380 File::Find now works correctly when the wanted() function is either
1381 autoloaded or is a symbolic reference.
1383 A bug that caused File::Find to lose track of the working directory
1384 when pruning top-level directories has been fixed.
1386 File::Find now also supports several other options to control its
1387 behavior. It can follow symbolic links if the C<follow> option is
1388 specified. Enabling the C<no_chdir> option will make File::Find skip
1389 changing the current directory when walking directories. The C<untaint>
1390 flag can be useful when running with taint checks enabled.
1396 This extension implements BSD-style file globbing. By default,
1397 it will also be used for the internal implementation of the glob()
1398 operator. See L<File::Glob>.
1402 New methods have been added to the File::Spec module: devnull() returns
1403 the name of the null device (/dev/null on Unix) and tmpdir() the name of
1404 the temp directory (normally /tmp on Unix). There are now also methods
1405 to convert between absolute and relative filenames: abs2rel() and
1406 rel2abs(). For compatibility with operating systems that specify volume
1407 names in file paths, the splitpath(), splitdir(), and catdir() methods
1410 =item File::Spec::Functions
1412 The new File::Spec::Functions modules provides a function interface
1413 to the File::Spec module. Allows shorthand
1415 $fullname = catfile($dir1, $dir2, $file);
1419 $fullname = File::Spec->catfile($dir1, $dir2, $file);
1423 Getopt::Long licensing has changed to allow the Perl Artistic License
1424 as well as the GPL. It used to be GPL only, which got in the way of
1425 non-GPL applications that wanted to use Getopt::Long.
1427 Getopt::Long encourages the use of Pod::Usage to produce help
1428 messages. For example:
1434 GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
1435 pod2usage(1) if $help;
1436 pod2usage(-exitstatus => 0, -verbose => 2) if $man;
1442 sample - Using GetOpt::Long and Pod::Usage
1446 sample [options] [file ...]
1449 -help brief help message
1450 -man full documentation
1458 Print a brief help message and exits.
1462 Prints the manual page and exits.
1468 B<This program> will read the given input file(s) and do someting
1469 useful with the contents thereof.
1473 See L<Pod::Usage> for details.
1475 A bug that prevented the non-option call-back E<lt>E<gt> from being
1476 specified as the first argument has been fixed.
1478 To specify the characters E<lt> and E<gt> as option starters, use
1479 E<gt>E<lt>. Note, however, that changing option starters is strongly
1484 write() and syswrite() will now accept a single-argument
1485 form of the call, for consistency with Perl's syswrite().
1487 You can now create a TCP-based IO::Socket::INET without forcing
1488 a connect attempt. This allows you to configure its options
1489 (like making it non-blocking) and then call connect() manually.
1491 A bug that prevented the IO::Socket::protocol() accessor
1492 from ever returning the correct value has been corrected.
1496 Java Perl Lingo is now distributed with Perl. See jpl/README
1497 for more information.
1501 C<use lib> now weeds out any trailing duplicate entries.
1502 C<no lib> removes all named entries.
1506 The bitwise operations C<E<lt>E<lt>>, C<E<gt>E<gt>>, C<&>, C<|>,
1507 and C<~> are now supported on bigints.
1511 The accessor methods Re, Im, arg, abs, rho, and theta can now also
1512 act as mutators (accessor $z->Re(), mutator $z->Re(3)).
1516 A little bit of radial trigonometry (cylindrical and spherical),
1517 radial coordinate conversions, and the great circle distance were added.
1521 [TODO - Brad Appleton <bradapp@enteract.com>]
1523 =item Pod::Text and Pod::Man
1525 [TODO - Russ Allbery <rra@stanford.edu>]
1529 An EXISTS method has been added to this module (and sdbm_exists() has
1530 been added to the underlying sdbm library), so one can now call exists
1531 on an SDBM_File tied hash and get the correct result, rather than a
1534 A bug that may have caused data loss when more than one disk block
1535 happens to be read from the database in a single FETCH() has been
1540 The timelocal() and timegm() functions used to silently return bogus
1541 results when the date fell outside the machine's integer range. They
1542 now consistently croak() if the date falls in an unsupported range.
1546 The error return value in list context has been changed for all functions
1547 that return a list of values. Previously these functions returned a list
1548 with a single element C<undef> if an error occurred. Now these functions
1549 return the empty list in these situations. This applies to the following
1555 The remaining functions are unchanged and continue to return C<undef> on
1556 error even in list context.
1558 The Win32::SetLastError(ERROR) function has been added as a complement
1559 to the Win32::GetLastError() function.
1561 The new Win32::GetFullPathName(FILENAME) returns the full absolute
1562 pathname for FILENAME in scalar context. In list context it returns
1563 a two-element list containing the fully qualified directory name and
1564 the filename. See L<Win32>.
1568 A new feature called "DBM Filters" has been added to all the
1569 DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
1570 DBM Filters add four new methods to each DBM module:
1577 These can be used to filter key-value pairs before the pairs are
1578 written to the database or just after they are read from the database.
1579 See L<perldbmfilter> for further information.
1585 C<use attrs> is now obsolete, and is only provided for
1586 backward-compatibility. It's been replaced by the C<sub : attributes>
1587 syntax. See L<perlsub/"Subroutine Attributes"> and L<attributes>.
1589 C<use utf8> to enable UTF-8 and Unicode support.
1591 Lexical warnings pragma, C<use warnings;>, to control optional warnings.
1594 C<use filetest> to control the behaviour of filetests (C<-r> C<-w>
1595 ...). Currently only one subpragma implemented, "use filetest
1596 'access';", that uses access(2) or equivalent to check permissions
1597 instead of using stat(2) as usual. This matters in filesystems
1598 where there are ACLs (access control lists): the stat(2) might lie,
1599 but access(2) knows better.
1601 =head1 Utility Changes
1605 [TODO - Kurt Starsinic <kstar@chapin.edu>]
1609 C<perlcc> now supports the C and Bytecode backends. By default,
1610 it generates output from the simple C backend rather than the
1611 optimized C backend.
1613 Support for non-Unix platforms has been improved.
1618 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1620 =head1 Documentation Changes
1626 The official list of public Perl API functions.
1628 =item perlcompile.pod
1630 An introduction to using the Perl Compiler suite.
1632 =item perlfilter.pod
1634 An introduction to writing Perl source filters.
1638 Some guidelines for hacking the Perl source code.
1640 =item perlintern.pod
1642 A list of internal functions in the Perl source code.
1643 (List is currently empty.)
1645 =item perlopentut.pod
1647 A tutorial on using open() effectively.
1649 =item perlreftut.pod
1651 A tutorial that introduces the essentials of references.
1655 A tutorial on managing class data for object modules.
1657 =item perlunicode.pod
1659 An introduction to Unicode support features in Perl.
1663 =head1 New or Changed Diagnostics
1667 =item "%s" variable %s masks earlier declaration in same %s
1669 (W) A "my" or "our" variable has been redeclared in the current scope or statement,
1670 effectively eliminating all access to the previous instance. This is almost
1671 always a typographical error. Note that the earlier variable will still exist
1672 until the end of the scope or until all closure referents to it are
1675 =item "my sub" not yet implemented
1677 (F) Lexically scoped subroutines are not yet implemented. Don't try that
1680 =item "our" variable %s redeclared
1682 (W) You seem to have already declared the same global once before in the
1683 current lexical scope.
1685 =item '!' allowed only after types %s
1687 (F) The '!' is allowed in pack() and unpack() only after certain types.
1688 See L<perlfunc/pack>.
1690 =item / cannot take a count
1692 (F) You had an unpack template indicating a counted-length string,
1693 but you have also specified an explicit size for the string.
1694 See L<perlfunc/pack>.
1696 =item / must be followed by a, A or Z
1698 (F) You had an unpack template indicating a counted-length string,
1699 which must be followed by one of the letters a, A or Z
1700 to indicate what sort of string is to be unpacked.
1701 See L<perlfunc/pack>.
1703 =item / must be followed by a*, A* or Z*
1705 (F) You had a pack template indicating a counted-length string,
1706 Currently the only things that can have their length counted are a*, A* or Z*.
1707 See L<perlfunc/pack>.
1709 =item / must follow a numeric type
1711 (F) You had an unpack template that contained a '#',
1712 but this did not follow some numeric unpack specification.
1713 See L<perlfunc/pack>.
1715 =item /%s/: Unrecognized escape \\%c passed through
1717 (W) You used a backslash-character combination which is not recognized
1718 by Perl. This combination appears in an interpolated variable or a
1719 C<'>-delimited regular expression. The character was understood literally.
1721 =item /%s/: Unrecognized escape \\%c in character class passed through
1723 (W) You used a backslash-character combination which is not recognized
1724 by Perl inside character classes. The character was understood literally.
1726 =item /%s/ should probably be written as "%s"
1728 (W) You have used a pattern where Perl expected to find a string,
1729 as in the first argument to C<join>. Perl will treat the true
1730 or false result of matching the pattern against $_ as the string,
1731 which is probably not what you had in mind.
1733 =item %s() called too early to check prototype
1735 (W) You've called a function that has a prototype before the parser saw a
1736 definition or declaration for it, and Perl could not check that the call
1737 conforms to the prototype. You need to either add an early prototype
1738 declaration for the subroutine in question, or move the subroutine
1739 definition ahead of the call to get proper prototype checking. Alternatively,
1740 if you are certain that you're calling the function correctly, you may put
1741 an ampersand before the name to avoid the warning. See L<perlsub>.
1743 =item %s argument is not a HASH or ARRAY element
1745 (F) The argument to exists() must be a hash or array element, such as:
1748 $ref->[12]->["susie"]
1750 =item %s argument is not a HASH or ARRAY element or slice
1752 (F) The argument to delete() must be either a hash or array element, such as:
1755 $ref->[12]->["susie"]
1757 or a hash or array slice, such as:
1759 @foo[$bar, $baz, $xyzzy]
1760 @{$ref->[12]}{"susie", "queue"}
1762 =item %s argument is not a subroutine name
1764 (F) The argument to exists() for C<exists &sub> must be a subroutine
1765 name, and not a subroutine call. C<exists &sub()> will generate this error.
1767 =item %s package attribute may clash with future reserved word: %s
1769 (W) A lowercase attribute name was used that had a package-specific handler.
1770 That name might have a meaning to Perl itself some day, even though it
1771 doesn't yet. Perhaps you should use a mixed-case attribute name, instead.
1774 =item (in cleanup) %s
1776 (W) This prefix usually indicates that a DESTROY() method raised
1777 the indicated exception. Since destructors are usually called by
1778 the system at arbitrary points during execution, and often a vast
1779 number of times, the warning is issued only once for any number
1780 of failures that would otherwise result in the same message being
1783 Failure of user callbacks dispatched using the C<G_KEEPERR> flag
1784 could also result in this warning. See L<perlcall/G_KEEPERR>.
1786 =item <> should be quotes
1788 (F) You wrote C<require E<lt>fileE<gt>> when you should have written
1791 =item Attempt to join self
1793 (F) You tried to join a thread from within itself, which is an
1794 impossible task. You may be joining the wrong thread, or you may
1795 need to move the join() to some other thread.
1797 =item Bad evalled substitution pattern
1799 (F) You've used the /e switch to evaluate the replacement for a
1800 substitution, but perl found a syntax error in the code to evaluate,
1801 most likely an unexpected right brace '}'.
1803 =item Bad realloc() ignored
1805 (S) An internal routine called realloc() on something that had never been
1806 malloc()ed in the first place. Mandatory, but can be disabled by
1807 setting environment variable C<PERL_BADFREE> to 1.
1809 =item Binary number > 0b11111111111111111111111111111111 non-portable
1811 (W) The binary number you specified is larger than 2**32-1
1812 (4294967295) and therefore non-portable between systems. See
1813 L<perlport> for more on portability concerns.
1815 =item Bit vector size > 32 non-portable
1817 (W) Using bit vector sizes larger than 32 is non-portable.
1819 =item Buffer overflow in prime_env_iter: %s
1821 (W) A warning peculiar to VMS. While Perl was preparing to iterate over
1822 %ENV, it encountered a logical name or symbol definition which was too long,
1823 so it was truncated to the string shown.
1825 =item Can't check filesystem of script "%s"
1827 (P) For some reason you can't check the filesystem of the script for nosuid.
1829 =item Can't declare class for non-scalar %s in "%s"
1831 (S) Currently, only scalar variables can declared with a specific class
1832 qualifier in a "my" or "our" declaration. The semantics may be extended
1833 for other types of variables in future.
1835 =item Can't declare %s in "%s"
1837 (F) Only scalar, array, and hash variables may be declared as "my" or
1838 "our" variables. They must have ordinary identifiers as names.
1840 =item Can't ignore signal CHLD, forcing to default
1842 (W) Perl has detected that it is being run with the SIGCHLD signal
1843 (sometimes known as SIGCLD) disabled. Since disabling this signal
1844 will interfere with proper determination of exit status of child
1845 processes, Perl has reset the signal to its default value.
1846 This situation typically indicates that the parent program under
1847 which Perl may be running (e.g. cron) is being very careless.
1849 =item Can't modify non-lvalue subroutine call
1851 (F) Subroutines meant to be used in lvalue context should be declared as
1852 such, see L<perlsub/"Lvalue subroutines">.
1854 =item Can't read CRTL environ
1856 (S) A warning peculiar to VMS. Perl tried to read an element of %ENV
1857 from the CRTL's internal environment array and discovered the array was
1858 missing. You need to figure out where your CRTL misplaced its environ
1859 or define F<PERL_ENV_TABLES> (see L<perlvms>) so that environ is not searched.
1861 =item Can't remove %s: %s, skipping file
1863 (S) You requested an inplace edit without creating a backup file. Perl
1864 was unable to remove the original file to replace it with the modified
1865 file. The file was left unmodified.
1867 =item Can't return %s from lvalue subroutine
1869 (F) Perl detected an attempt to return illegal lvalues (such
1870 as temporary or readonly values) from a subroutine used as an lvalue.
1871 This is not allowed.
1873 =item Can't weaken a nonreference
1875 (F) You attempted to weaken something that was not a reference. Only
1876 references can be weakened.
1878 =item Character class [:%s:] unknown
1880 (F) The class in the character class [: :] syntax is unknown.
1883 =item Character class syntax [%s] belongs inside character classes
1885 (W) The character class constructs [: :], [= =], and [. .] go
1886 I<inside> character classes, the [] are part of the construct,
1887 for example: /[012[:alpha:]345]/. Note that [= =] and [. .]
1888 are not currently implemented; they are simply placeholders for
1891 =item Constant is not %s reference
1893 (F) A constant value (perhaps declared using the C<use constant> pragma)
1894 is being dereferenced, but it amounts to the wrong type of reference. The
1895 message indicates the type of reference that was expected. This usually
1896 indicates a syntax error in dereferencing the constant value.
1897 See L<perlsub/"Constant Functions"> and L<constant>.
1899 =item constant(%s): %%^H is not localized
1901 (F) When setting compile-time-lexicalized hash %^H one should set the
1902 corresponding bit of $^H as well.
1904 =item constant(%s): %s
1906 (F) Compile-time-substitutions (such as overloaded constants and
1907 character names) were not correctly set up.
1909 =item defined(@array) is deprecated
1911 (D) defined() is not usually useful on arrays because it checks for an
1912 undefined I<scalar> value. If you want to see if the array is empty,
1913 just use C<if (@array) { # not empty }> for example.
1915 =item defined(%hash) is deprecated
1917 (D) defined() is not usually useful on hashes because it checks for an
1918 undefined I<scalar> value. If you want to see if the hash is empty,
1919 just use C<if (%hash) { # not empty }> for example.
1921 =item Did not produce a valid header
1925 =item Did you mean "local" instead of "our"?
1927 (W) Remember that "our" does not localize the declared global variable.
1928 You have declared it again in the same lexical scope, which seems superfluous.
1930 =item Document contains no data
1934 =item entering effective %s failed
1936 (F) While under the C<use filetest> pragma, switching the real and
1937 effective uids or gids failed.
1939 =item false [] range "%s" in regexp
1941 (W) A character class range must start and end at a literal character, not
1942 another character class like C<\d> or C<[:alpha:]>. The "-" in your false
1943 range is interpreted as a literal "-". Consider quoting the "-", "\-".
1946 =item Filehandle %s opened only for output
1948 (W) You tried to read from a filehandle opened only for writing. If you
1949 intended it to be a read/write filehandle, you needed to open it with
1950 "+E<lt>" or "+E<gt>" or "+E<gt>E<gt>" instead of with "E<lt>" or nothing. If
1951 you intended only to read from the file, use "E<lt>". See
1954 =item flock() on closed filehandle %s
1956 (W) The filehandle you're attempting to flock() got itself closed some
1957 time before now. Check your logic flow. flock() operates on filehandles.
1958 Are you attempting to call flock() on a dirhandle by the same name?
1960 =item Global symbol "%s" requires explicit package name
1962 (F) You've said "use strict vars", which indicates that all variables
1963 must either be lexically scoped (using "my"), declared beforehand using
1964 "our", or explicitly qualified to say which package the global variable
1967 =item Hexadecimal number > 0xffffffff non-portable
1969 (W) The hexadecimal number you specified is larger than 2**32-1
1970 (4294967295) and therefore non-portable between systems. See
1971 L<perlport> for more on portability concerns.
1973 =item Ill-formed CRTL environ value "%s"
1975 (W) A warning peculiar to VMS. Perl tried to read the CRTL's internal
1976 environ array, and encountered an element without the C<=> delimiter
1977 used to spearate keys from values. The element is ignored.
1979 =item Ill-formed message in prime_env_iter: |%s|
1981 (W) A warning peculiar to VMS. Perl tried to read a logical name
1982 or CLI symbol definition when preparing to iterate over %ENV, and
1983 didn't see the expected delimiter between key and value, so the
1986 =item Illegal binary digit %s
1988 (F) You used a digit other than 0 or 1 in a binary number.
1990 =item Illegal binary digit %s ignored
1992 (W) You may have tried to use a digit other than 0 or 1 in a binary number.
1993 Interpretation of the binary number stopped before the offending digit.
1995 =item Illegal number of bits in vec
1997 (F) The number of bits in vec() (the third argument) must be a power of
1998 two from 1 to 32 (or 64, if your platform supports that).
2000 =item Integer overflow in %s number
2002 (W) The hexadecimal, octal or binary number you have specified either
2003 as a literal or as an argument to hex() or oct() is too big for your
2004 architecture, and has been converted to a floating point number. On a
2005 32-bit architecture the largest hexadecimal, octal or binary number
2006 representable without overflow is 0xFFFFFFFF, 037777777777, or
2007 0b11111111111111111111111111111111 respectively. Note that Perl
2008 transparently promotes all numbers to a floating point representation
2009 internally--subject to loss of precision errors in subsequent
2012 =item Invalid %s attribute: %s
2014 The indicated attribute for a subroutine or variable was not recognized
2015 by Perl or by a user-supplied handler. See L<attributes>.
2017 =item Invalid %s attributes: %s
2019 The indicated attributes for a subroutine or variable were not recognized
2020 by Perl or by a user-supplied handler. See L<attributes>.
2022 =item invalid [] range "%s" in regexp
2024 The offending range is now explicitly displayed.
2026 =item Invalid separator character %s in attribute list
2028 (F) Something other than a colon or whitespace was seen between the
2029 elements of an attribute list. If the previous attribute
2030 had a parenthesised parameter list, perhaps that list was terminated
2031 too soon. See L<attributes>.
2033 =item Invalid separator character %s in subroutine attribute list
2035 (F) Something other than a colon or whitespace was seen between the
2036 elements of a subroutine attribute list. If the previous attribute
2037 had a parenthesised parameter list, perhaps that list was terminated
2040 =item leaving effective %s failed
2042 (F) While under the C<use filetest> pragma, switching the real and
2043 effective uids or gids failed.
2045 =item Lvalue subs returning %s not implemented yet
2047 (F) Due to limitations in the current implementation, array and hash
2048 values cannot be returned in subroutines used in lvalue context.
2049 See L<perlsub/"Lvalue subroutines">.
2051 =item Method %s not permitted
2055 =item Missing %sbrace%s on \N{}
2057 (F) Wrong syntax of character name literal C<\N{charname}> within
2058 double-quotish context.
2060 =item Missing command in piped open
2062 (W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
2063 construction, but the command was missing or blank.
2065 =item Missing name in "my sub"
2067 (F) The reserved syntax for lexically scoped subroutines requires that they
2068 have a name with which they can be found.
2070 =item No %s specified for -%c
2072 (F) The indicated command line switch needs a mandatory argument, but
2073 you haven't specified one.
2075 =item No package name allowed for variable %s in "our"
2077 (F) Fully qualified variable names are not allowed in "our" declarations,
2078 because that doesn't make much sense under existing semantics. Such
2079 syntax is reserved for future extensions.
2081 =item No space allowed after -%c
2083 (F) The argument to the indicated command line switch must follow immediately
2084 after the switch, without intervening spaces.
2086 =item no UTC offset information; assuming local time is UTC
2088 (S) A warning peculiar to VMS. Perl was unable to find the local
2089 timezone offset, so it's assuming that local system time is equivalent
2090 to UTC. If it's not, define the logical name F<SYS$TIMEZONE_DIFFERENTIAL>
2091 to translate to the number of seconds which need to be added to UTC to
2094 =item Octal number > 037777777777 non-portable
2096 (W) The octal number you specified is larger than 2**32-1 (4294967295)
2097 and therefore non-portable between systems. See L<perlport> for more
2098 on portability concerns.
2100 See also L<perlport> for writing portable code.
2102 =item panic: del_backref
2104 (P) Failed an internal consistency check while trying to reset a weak
2107 =item panic: kid popen errno read
2109 (F) forked child returned an incomprehensible message about its errno.
2111 =item panic: magic_killbackrefs
2113 (P) Failed an internal consistency check while trying to reset all weak
2114 references to an object.
2116 =item Parentheses missing around "%s" list
2118 (W) You said something like
2124 my ($foo, $bar) = @_;
2126 Remember that "my", "our" and "local" bind closer than comma.
2128 =item Possible Y2K bug: %s
2130 (W) You are concatenating the number 19 with another number, which
2131 could be a potential Year 2000 problem.
2133 =item Premature end of script headers
2137 =item Repeat count in pack overflows
2139 (F) You can't specify a repeat count so large that it overflows
2140 your signed integers. See L<perlfunc/pack>.
2142 =item Repeat count in unpack overflows
2144 (F) You can't specify a repeat count so large that it overflows
2145 your signed integers. See L<perlfunc/unpack>.
2147 =item realloc() of freed memory ignored
2149 (S) An internal routine called realloc() on something that had already
2152 =item Reference is already weak
2154 (W) You have attempted to weaken a reference that is already weak.
2155 Doing so has no effect.
2157 =item setpgrp can't take arguments
2159 (F) Your system has the setpgrp() from BSD 4.2, which takes no arguments,
2160 unlike POSIX setpgid(), which takes a process ID and process group ID.
2162 =item Strange *+?{} on zero-length expression
2164 (W) You applied a regular expression quantifier in a place where it
2165 makes no sense, such as on a zero-width assertion.
2166 Try putting the quantifier inside the assertion instead. For example,
2167 the way to match "abc" provided that it is followed by three
2168 repetitions of "xyz" is C</abc(?=(?:xyz){3})/>, not C</abc(?=xyz){3}/>.
2170 =item switching effective %s is not implemented
2172 (F) While under the C<use filetest> pragma, we cannot switch the
2173 real and effective uids or gids.
2175 =item This Perl can't reset CRTL environ elements (%s)
2177 =item This Perl can't set CRTL environ elements (%s=%s)
2179 (W) Warnings peculiar to VMS. You tried to change or delete an element
2180 of the CRTL's internal environ array, but your copy of Perl wasn't
2181 built with a CRTL that contained the setenv() function. You'll need to
2182 rebuild Perl with a CRTL that does, or redefine F<PERL_ENV_TABLES> (see
2183 L<perlvms>) so that the environ array isn't the target of the change to
2184 %ENV which produced the warning.
2186 =item Unknown open() mode '%s'
2188 (F) The second argument of 3-argument open() is not among the list
2189 of valid modes: C<L<lt>>, C<L<gt>>, C<E<gt>E<gt>>, C<+L<lt>>,
2190 C<+L<gt>>, C<+E<gt>E<gt>>, C<-|>, C<|->.
2192 =item Unknown process %x sent message to prime_env_iter: %s
2194 (P) An error peculiar to VMS. Perl was reading values for %ENV before
2195 iterating over it, and someone else stuck a message in the stream of
2196 data Perl expected. Someone's very confused, or perhaps trying to
2197 subvert Perl's population of %ENV for nefarious purposes.
2199 =item Unrecognized escape \\%c passed through
2201 (W) You used a backslash-character combination which is not recognized
2202 by Perl. The character was understood literally.
2204 =item Unterminated attribute parameter in attribute list
2206 (F) The lexer saw an opening (left) parenthesis character while parsing an
2207 attribute list, but the matching closing (right) parenthesis
2208 character was not found. You may need to add (or remove) a backslash
2209 character to get your parentheses to balance. See L<attributes>.
2211 =item Unterminated attribute list
2213 (F) The lexer found something other than a simple identifier at the start
2214 of an attribute, and it wasn't a semicolon or the start of a
2215 block. Perhaps you terminated the parameter list of the previous attribute
2216 too soon. See L<attributes>.
2218 =item Unterminated attribute parameter in subroutine attribute list
2220 (F) The lexer saw an opening (left) parenthesis character while parsing a
2221 subroutine attribute list, but the matching closing (right) parenthesis
2222 character was not found. You may need to add (or remove) a backslash
2223 character to get your parentheses to balance.
2225 =item Unterminated subroutine attribute list
2227 (F) The lexer found something other than a simple identifier at the start
2228 of a subroutine attribute, and it wasn't a semicolon or the start of a
2229 block. Perhaps you terminated the parameter list of the previous attribute
2232 =item Value of CLI symbol "%s" too long
2234 (W) A warning peculiar to VMS. Perl tried to read the value of an %ENV
2235 element from a CLI symbol table, and found a resultant string longer
2236 than 1024 characters. The return value has been truncated to 1024
2239 =item Version number must be a constant number
2241 (P) The attempt to translate a C<use Module n.n LIST> statement into
2242 its equivalent C<BEGIN> block found an internal inconsistency with
2247 =head1 Obsolete Diagnostics
2251 =item Character class syntax [: :] is reserved for future extensions
2253 (W) Within regular expression character classes ([]) the syntax beginning
2254 with "[:" and ending with ":]" is reserved for future extensions.
2255 If you need to represent those character sequences inside a regular
2256 expression character class, just quote the square brackets with the
2257 backslash: "\[:" and ":\]".
2259 =item Ill-formed logical name |%s| in prime_env_iter
2261 (W) A warning peculiar to VMS. A logical name was encountered when preparing
2262 to iterate over %ENV which violates the syntactic rules governing logical
2263 names. Because it cannot be translated normally, it is skipped, and will not
2264 appear in %ENV. This may be a benign occurrence, as some software packages
2265 might directly modify logical name tables and introduce nonstandard names,
2266 or it may indicate that a logical name table has been corrupted.
2268 =item regexp too big
2270 (F) The current implementation of regular expressions uses shorts as
2271 address offsets within a string. Unfortunately this means that if
2272 the regular expression compiles to longer than 32767, it'll blow up.
2273 Usually when you want a regular expression this big, there is a better
2274 way to do it with multiple statements. See L<perlre>.
2276 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
2278 (D) Perl versions before 5.004 misinterpreted any type marker followed
2279 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
2280 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
2282 However, the developers of Perl 5.004 could not fix this bug completely,
2283 because at least two widely-used modules depend on the old meaning of
2284 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
2285 old (broken) way inside strings; but it generates this message as a
2286 warning. And in Perl 5.005, this special treatment will cease.
2292 If you find what you think is a bug, you might check the
2293 articles recently posted to the comp.lang.perl.misc newsgroup.
2294 There may also be information at http://www.perl.com/perl/, the Perl
2297 If you believe you have an unreported bug, please run the B<perlbug>
2298 program included with your release. Make sure to trim your bug down
2299 to a tiny but sufficient test case. Your bug report, along with the
2300 output of C<perl -V>, will be sent off to perlbug@perl.com to be
2301 analysed by the Perl porting team.
2305 The F<Changes> file for exhaustive details on what changed.
2307 The F<INSTALL> file for how to build Perl.
2309 The F<README> file for general stuff.
2311 The F<Artistic> and F<Copying> files for copyright information.
2315 Written by Gurusamy Sarathy <F<gsar@activestate.com>>, with many
2316 contributions from The Perl Porters.
2318 Send omissions or corrections to <F<perlbug@perl.com>>.