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 STOP is a new keyword
29 In addition to C<BEGIN>, C<INIT>, C<END>, C<DESTROY> and C<AUTOLOAD>,
30 subroutines named C<STOP> 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.
154 =head2 C Source Incompatibilities
158 =item C<PERL_POLLUTE>
160 Release 5.005 grandfathered old global symbol names by providing preprocessor
161 macros for extension source compatibility. As of release 5.6, these
162 preprocessor definitions are not available by default. You need to explicitly
163 compile perl with C<-DPERL_POLLUTE> to get these definitions. For
164 extensions still using the old symbols, this option can be
165 specified via MakeMaker:
167 perl Makefile.PL POLLUTE=1
169 =item C<PERL_IMPLICIT_CONTEXT>
171 PERL_IMPLICIT_CONTEXT is automatically enabled whenever Perl is built
172 with one of -Dusethreads, -Dusemultiplicity, or both. It is not
173 intended to be enabled by users at this time.
175 This new build option provides a set of macros for all API functions
176 such that an implicit interpreter/thread context argument is passed to
177 every API function. As a result of this, something like C<sv_setsv(foo,bar)>
178 amounts to a macro invocation that actually translates to something like
179 C<Perl_sv_setsv(my_perl,foo,bar)>. While this is generally expected
180 to not have any significant source compatibility issues, the difference
181 between a macro and a real function call will need to be considered.
183 This means that there B<is> a source compatibility issue as a result of
184 this if your extensions attempt to use pointers to any of the Perl API
187 Note that the above issue is not relevant to the default build of
188 Perl, whose interfaces continue to match those of prior versions
189 (but subject to the other options described here).
191 See L<perlguts/"The Perl API"> for detailed information on the
192 ramifications of building Perl using this option.
194 =item C<PERL_POLLUTE_MALLOC>
196 Enabling Perl's malloc in release 5.005 and earlier caused
197 the namespace of system versions of the malloc family of functions to
198 be usurped by the Perl versions, since by default they used the
201 Besides causing problems on platforms that do not allow these functions to
202 be cleanly replaced, this also meant that the system versions could not
203 be called in programs that used Perl's malloc. Previous versions of Perl
204 have allowed this behaviour to be suppressed with the HIDEMYMALLOC and
205 EMBEDMYMALLOC preprocessor definitions.
207 As of release 5.6, Perl's malloc family of functions have default names
208 distinct from the system versions. You need to explicitly compile perl with
209 C<-DPERL_POLLUTE_MALLOC> to get the older behaviour. HIDEMYMALLOC
210 and EMBEDMYMALLOC have no effect, since the behaviour they enabled is now
213 Note that these functions do B<not> constitute Perl's memory allocation API.
214 See L<perlguts/"Memory Allocation"> for further information about that.
218 =head2 Compatible C Source API Changes
222 =item C<PATCHLEVEL> is now C<PERL_VERSION>
224 The cpp macros C<PERL_REVISION>, C<PERL_VERSION>, and C<PERL_SUBVERSION>
225 are now available by default from perl.h, and reflect the base revision,
226 patchlevel, and subversion respectively. C<PERL_REVISION> had no
227 prior equivalent, while C<PERL_VERSION> and C<PERL_SUBVERSION> were
228 previously available as C<PATCHLEVEL> and C<SUBVERSION>.
230 The new names cause less pollution of the B<cpp> namespace and reflect what
231 the numbers have come to stand for in common practice. For compatibility,
232 the old names are still supported when F<patchlevel.h> is explicitly
233 included (as required before), so there is no source incompatibility
236 =item Support for C++ exceptions
238 change#3386, also needs perlguts documentation
239 [TODO - Chip Salzenberg <chip@perlsupport.com>]
243 =head2 Binary Incompatibilities
245 The default build of this release is binary compatible with the 5.005
246 release or its maintenance versions.
248 The usethreads or usemultiplicity builds are B<not> binary compatible
249 with the corresponding builds in 5.005.
251 =head1 Installation and Configuration Improvements
253 =head2 New Configure flags
255 The following new flags may be enabled on the Configure command line
256 by running Configure with C<-Dflag>.
264 =head2 -Dusethreads and -Duse64bits now more daring
266 The Configure options enabling the use of threads and the use of
267 64-bitness are now more daring in the sense that they no more have
268 an explicit list of operating systems of known threads/64-bit
269 capabilities. In other words: if your operating system has the
270 necessary APIs, you should be able just to go ahead and use them.
271 See also L<"64-bit support">.
275 Some platforms have "long doubles", floating point numbers of even
276 larger range than ordinary "doubles". To enable using long doubles for
277 Perl's scalars, use -Duselongdouble.
281 You can enable both -Duse64bits and -Dlongdouble by -Dusemorebits.
282 See also L<"64-bit support">.
284 =head2 -Duselargefiles
286 Some platforms support large files, files larger than two gigabytes.
287 See L<"Large file support"> for more information.
289 =head2 installusrbinperl
291 You can use "Configure -Uinstallusrbinperl" which causes installperl
292 to skip installing perl also as /usr/bin/perl. This is useful if you
293 prefer not to modify /usr/bin for some reason or another but harmful
294 because many scripts assume to find Perl in /usr/bin/perl.
298 You can use "Configure -Dusesocks" which causes Perl to probe
299 for the SOCKS (v5, not v4) proxy protocol library,
300 http://www.socks.nec.com/
304 You can "post-edit" the Configure variables using the Configure C<-A>
305 flag. The editing happens immediately after the platform specific
306 hints files have been processed but before the actual configuration
307 process starts. Run C<Configure -h> to find out the full C<-A> syntax.
309 =head2 Enhanced Installation Directories
311 The installation structure has been enriched to improve the support for
312 maintaining multiple versions of perl, to provide locations for
313 vendor-supplied modules and scripts, and to ease maintenance of
314 locally-added modules and scripts. See the section on Installation
315 Directories in the INSTALL file for complete details. For most users
316 building and installing from source, the defaults should be fine.
320 =head2 Unicode and UTF-8 support
322 Perl can optionally use UTF-8 as its internal representation for character
323 strings. The C<utf8> pragma enables this support in the current lexical
324 scope. See L<utf8> for more information.
326 =head2 Interpreter threads
328 WARNING: This is an experimental feature in a pre-alpha state. Use
331 Perl 5.005_63 introduces the beginnings of support for running multiple
332 interpreters concurrently in different threads. In conjunction with
333 the perl_clone() API call, which can be used to selectively duplicate
334 the state of any given interpreter, it is possible to compile a
335 piece of code once in an interpreter, clone that interpreter
336 one or more times, and run all the resulting interpreters in distinct
339 On Windows, this feature is used to emulate fork() at the interpreter
340 level. See L<perlfork>.
342 This feature is still in evolution. It is eventually meant to be used
343 to selectively clone a subroutine and data reachable from that
344 subroutine in a separate interpreter and run the cloned subroutine
345 in a separate thread. Since there is no shared data between the
346 interpreters, little or no locking will be needed (unless parts of
347 the symbol table are explicitly shared). This is obviously intended
348 to be an easy-to-use replacement for the existing threads support.
350 Support for cloning interpreters must currently be manually enabled
351 by defining the cpp macro USE_ITHREADS on non-Windows platforms.
352 (See win32/Makefile for how to enable it on Windows.) The resulting
353 perl executable will be functionally identical to one that was built
354 without USE_ITHREADS, but the perl_clone() API call will only be
355 available in the former.
357 USE_ITHREADS enables Perl source code changes that provide a clear
358 separation between the op tree and the data it operates with. The
359 former is considered immutable, and can therefore be shared between
360 an interpreter and all of its clones, while the latter is considered
361 local to each interpreter, and is therefore copied for each clone.
363 Note that building Perl with the -Dusemultiplicity Configure option
364 is adequate if you wish to run multiple B<independent> interpreters
365 concurrently in different threads. USE_ITHREADS only needs to be
366 enabled if you wish to obtain access to perl_clone() and cloned
369 [XXX TODO - the Compiler backends may be broken when USE_ITHREADS is
372 =head2 Lexically scoped warning categories
374 You can now control the granularity of warnings emitted by perl at a finer
375 level using the C<use warnings> pragma. See L<warnings> and L<perllexwarn>
378 =head2 Lvalue subroutines
380 WARNING: This is an experimental feature.
383 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>,
384 Tuomas Lukka <lukka@fas.harvard.edu>)]
386 =head2 "our" declarations
388 An "our" declaration introduces a value that can be best understood
389 as a lexically scoped symbolic alias to a global variable in the
390 current package. This is mostly useful as an alternative to the
391 C<vars> pragma, but also provides the opportunity to introduce
392 typing and other attributes for such variables. See L<perlfunc/our>.
394 =head2 Weak references
396 WARNING: This is an experimental feature.
398 change#3385, also need perlguts documentation
400 [TODO - Tuomas Lukka <lukka@fas.harvard.edu>]
402 =head2 File globbing implemented internally
404 WARNING: This is currently an experimental feature. Interfaces and
405 implementation are likely to change.
407 Perl now uses the File::Glob implementation of the glob() operator
408 automatically. This avoids using an external csh process and the
409 problems associated with it.
411 =head2 Binary numbers supported
413 Binary numbers are now supported as literals, in s?printf formats, and
417 printf "The answer is: %b\n", oct("0b101010");
419 =head2 Some arrows may be omitted in calls through references
421 Perl now allows the arrow to be omitted in many constructs
422 involving subroutine calls through references. For example,
423 C<$foo[10]->('foo')> may now be written C<$foo[10]('foo')>.
424 This is rather similar to how the arrow may be omitted from
425 C<$foo[10]->{'foo'}>. Note however, that the arrow is still
426 required for C<foo(10)->('bar')>.
428 =head2 exists() and delete() are supported on array elements
430 The exists() and delete() builtins now work on simple arrays as well.
431 The behavior is similar to that on hash elements.
433 exists() can be used to check whether an array element has been
434 initialized without autovivifying it. If the array is tied, the
435 EXISTS() method in the corresponding tied package will be invoked.
437 delete() may be used to remove an element from the array and return
438 it. The array element at that position returns to its unintialized
439 state, so that testing for the same element with exists() will return
440 false. If the element happens to be the one at the end, the size of
441 the array also shrinks by one. If the array is tied, the DELETE() method
442 in the corresponding tied package will be invoked.
444 See L<perlfunc/exists> and L<perlfunc/delete> for examples.
446 =head2 syswrite() ease-of-use
448 The length argument of C<syswrite()> has become optional.
450 =head2 Filehandles can be autovivified
452 Similar to how constructs such as C<$x->[0]> autovivify a reference,
453 open() now autovivifies a filehandle if the first argument is an
454 uninitialized variable. This allows the constructs C<open(my $fh, ...)> and
455 C<open(local $fh,...)> to be used to create filehandles that will
456 conveniently be closed automatically when the scope ends, provided there
457 are no other references to them. This largely eliminates the need for
458 typeglobs when opening filehandles that must be passed around, as in the
463 or die "Can't open '@_': $!";
468 my $f = myopen("</etc/motd");
470 # $f implicitly closed here
473 [TODO - this idiom needs more pod penetration]
475 =head2 64-bit support
477 All platforms that have 64-bit integers either (a) natively as longs
478 or ints (b) via special compiler flags (c) using long long are able to
479 use "quads" (64-integers) as follows:
485 constants (decimal, hexadecimal, octal, binary) in the code
489 arguments to oct() and hex()
493 arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)
501 pack() and unpack() "q" and "Q" formats
505 in basic arithmetics: + - * / %
509 vec() (but see the below note about bit arithmetics)
513 Note that unless you have the case (a) you will have to configure
514 and compile Perl using the -Duse64bits Configure flag.
516 Unfortunately bit arithmetics (&, |, ^, ~, <<, >>) for numbers are not
517 64-bit clean, they are explictly forced to be 32-bit. Bit arithmetics
518 for bit vectors (created by vec()) are not limited in their width.
520 Last but not least: note that due to Perl's habit of always using
521 floating point numbers the quads are still not true integers.
522 When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
523 -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
524 are silently promoted to floating point numbers, after which they will
525 start losing precision (their lower digits).
527 =head2 Large file support
529 If you have filesystems that support "large files" (files larger than
530 2 gigabytes), you may now also be able to create and access them from
531 Perl. You have to use Configure -Duselargefiles. Turning on the
532 large file support turns on also the 64-bit support, for obvious reasons.
534 Note that in addition to requiring a proper file system to do large
535 files you may also need to adjust your per-process (or your
536 per-system, or per-process-group, or per-user-group) maximum filesize
537 limits before running Perl scripts that try to handle large files,
538 especially if you intend to write such files.
540 Finally, in addition to your process/process group maximum filesize
541 limits, you may have quota limits on your filesystems that stop you
542 (your user id or your user group id) from using large files.
544 Adjusting your process/user/group/file system/operating system limits
545 is outside the scope of Perl core language. For process limits, you
546 may try increasing the limits using your shell's limits/limit/ulimit
547 command before running Perl. The BSD::Resource extension (not
548 included with the standard Perl distribution) may also be of use, it
549 offers the getrlimit/setrlimit interface that can be used to adjust
550 process resource usage limits, including the maximum filesize limit.
554 In some systems you may be able to use long doubles to enhance the
555 range of precision of your double precision floating point numbers
556 (that is, Perl's numbers). Use Configure -Duselongdouble to enable
557 this support (if it is available).
561 You can Configure -Dusemorebits to turn on both the 64-bit support
562 and the long double support.
564 =head2 Enhanced support for sort() subroutines
566 Perl subroutines with a prototype of C<($$)> and XSUBs in general can
567 now be used as sort subroutines. In either case, the two elements to
568 be compared are passed as normal parameters in @_. See L<perlfunc/sort>.
570 For unprototyped sort subroutines, the historical behavior of passing
571 the elements to be compared as the global variables $a and $b remains
574 =head2 Better syntax checks on parenthesized unary operators
578 print defined(&foo,&bar,&baz);
579 print uc("foo","bar","baz");
582 used to be accidentally allowed in earlier versions, and produced
583 unpredictable behaviour. Some produced ancillary warnings
584 when used in this way; others silently did the wrong thing.
586 The parenthesized forms of most unary operators that expect a single
587 argument now ensure that they are not called with more than one
588 argument, making the cases shown above syntax errors. The usual
591 print defined &foo, &bar, &baz;
592 print uc "foo", "bar", "baz";
595 remains unchanged. See L<perlop>.
597 =head2 POSIX character class syntax [: :] supported
599 For example to match alphabetic characters use /[[:alpha:]]/.
600 See L<perlre> for details.
602 =head2 Improved C<qw//> operator
604 The C<qw//> operator is now evaluated at compile time into a true list
605 instead of being replaced with a run time call to C<split()>. This
606 removes the confusing misbehaviour of C<qw//> in scalar context, which
607 had inherited that behaviour from split().
611 $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
613 now correctly prints "3|a", instead of "2|a".
615 =head2 pack() format 'Z' supported
617 The new format type 'Z' is useful for packing and unpacking null-terminated
618 strings. See L<perlfunc/"pack">.
620 =head2 pack() format modifier '!' supported
622 The new format type modifier '!' is useful for packing and unpacking
623 native shorts, ints, and longs. See L<perlfunc/"pack">.
625 =head2 pack() and unpack() support counted strings
627 The template character '/' can be used to specify a counted string
628 type to be packed or unpacked. See L<perlfunc/"pack">.
630 =head2 Comments in pack() templates
632 The '#' character in a template introduces a comment up to
633 end of the line. This facilitates documentation of pack()
636 =head2 $^X variables may now have names longer than one character
638 Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
639 error. Now variable names that begin with a control character may be
640 arbitrarily long. However, for compatibility reasons, these variables
641 I<must> be written with explicit braces, as C<${^XY}> for example.
642 C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more
643 than one control character, such as C<${^XY^Z}>, are illegal.
645 The old syntax has not changed. As before, `^X' may be either a
646 literal control-X character or the two-character sequence `caret' plus
647 `X'. When braces are omitted, the variable name stops after the
648 control character. Thus C<"$^XYZ"> continues to be synonymous with
649 C<$^X . "YZ"> as before.
651 As before, lexical variables may not have names beginning with control
652 characters. As before, variables whose names begin with a control
653 character are always forced to be in package `main'. All such variables
654 are reserved for future extensions, except those that begin with
655 C<^_>, which may be used by user programs and are guaranteed not to
656 acquire special meaning in any future version of Perl.
658 =head2 C<use attrs> implicit in subroutine attributes
660 Formerly, if you wanted to mark a subroutine as being a method call or
661 as requiring an automatic lock() when it is entered, you had to declare
662 that with a C<use attrs> pragma in the body of the subroutine.
663 That can now be accomplished with a declaration syntax, like this:
665 sub mymethod : locked, method ;
667 sub mymethod : locked, method {
671 F<AutoSplit.pm> and F<SelfLoader.pm> have been updated to keep the attributes
672 with the stubs they provide. See L<attributes>.
674 =head2 Regular expression improvements
676 change#2827,2373,2372,2365,1813,1800,4112,4158,4215,4301
677 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
679 =head2 Overloading improvements
682 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
684 =head2 open() with more than two arguments
686 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
688 =head2 Support for interpolating named characters
691 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
693 =head2 Experimental support for user-hooks in @INC
695 [TODO - Ken Fox <kfox@ford.com>]
697 =head2 C<require> and C<do> may be overridden
699 C<require> and C<do 'file'> operations may be overridden locally
700 by importing subroutines of the same name into the current package
701 (or globally by importing them into the CORE::GLOBAL:: namespace).
702 Overriding C<require> will also affect C<use>, provided the override
703 is visible at compile-time.
704 See L<perlsub/"Overriding Built-in Functions">.
706 =head2 New variable $^C reflects C<-c> switch
708 C<$^C> has a boolean value that reflects whether perl is being run
709 in compile-only mode (i.e. via the C<-c> switch). Since
710 BEGIN blocks are executed under such conditions, this variable
711 enables perl code to determine whether actions that make sense
712 only during normal running are warranted. See L<perlvar>.
714 =head2 Optional Y2K warnings
716 If Perl is built with the cpp macro C<PERL_Y2KWARN> defined,
717 it emits optional warnings when concatenating the number 19
720 This behavior must be specifically enabled when running Configure.
721 See L<INSTALL> and L<README.Y2K>.
723 =head1 Significant bug fixes
725 =head2 E<lt>HANDLEE<gt> on empty files
727 With C<$/> set to C<undef>, slurping an empty file returns a string of
728 zero length (instead of C<undef>, as it used to) the first time the
729 HANDLE is read. Further reads yield C<undef>.
731 This means that the following will append "foo" to an empty file (it used
734 perl -0777 -pi -e 's/^/foo/' empty_file
738 perl -pi -e 's/^/foo/' empty_file
740 is unchanged (it continues to leave the file empty).
742 =head2 C<eval '...'> improvements
744 Line numbers (as reflected by caller() and most diagnostics) within
745 C<eval '...'> were often incorrect when here documents were involved.
746 This has been corrected.
748 Lexical lookups for variables appearing in C<eval '...'> within
749 functions that were themselves called within an C<eval '...'> were
750 searching the wrong place for lexicals. The lexical search now
751 correctly ends at the subroutine's block boundary.
753 Parsing of here documents used to be flawed when they appeared as
754 the replacement expression in C<eval 's/.../.../e'>. This has
757 =head2 All compilation errors are true errors
759 Some "errors" encountered at compile time were by neccessity
760 generated as warnings followed by eventual termination of the
761 program. This enabled more such errors to be reported in a
762 single run, rather than causing a hard stop at the first error
763 that was encountered.
765 The mechanism for reporting such errors has been reimplemented
766 to queue compile-time errors and report them at the end of the
767 compilation as true errors rather than as warnings. This fixes
768 cases where error messages leaked through in the form of warnings
769 when code was compiled at run time using C<eval STRING>, and
770 also allows such errors to be reliably trapped using __DIE__ hooks.
772 =head2 Automatic flushing of output buffers
774 fork(), exec(), system(), qx//, and pipe open()s now flush buffers
775 of all files opened for output when the operation
776 was attempted. This mostly eliminates confusing
777 buffering mishaps suffered by users unaware of how Perl internally
780 =head2 Better diagnostics on meaningless filehandle operations
782 Constructs such as C<open(E<lt>FHE<gt>)> and C<close(E<lt>FHE<gt>)>
783 are compile time errors. Attempting to read from filehandles that
784 were opened only for writing will now produce warnings (just as
785 writing to read-only filehandles does).
787 =head2 Where possible, buffered data discarded from duped input filehandle
789 C<open(NEW, "E<lt>&OLD")> now attempts to discard any data that
790 was previously read and buffered in C<OLD> before duping the handle.
791 On platforms where doing this is allowed, the next read operation
792 on C<NEW> will return the same data as the corresponding operation
793 on C<OLD>. Formerly, it would have returned the data from the start
794 of the following disk block instead.
796 =head2 eof() has the same old magic as <>
798 C<eof()> would return true if no attempt to read from C<E<lt>E<gt>> had
799 yet been made. C<eof()> has been changed to have a little magic of its
800 own, it now opens the C<E<lt>E<gt>> files.
802 =head2 system(), backticks and pipe open now reflect exec() failure
804 On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
805 etc., are implemented via fork() and exec(). When the underlying
806 exec() fails, earlier versions did not report the error properly,
807 since the exec() happened to be in a different process.
809 The child process now communicates with the parent about the
810 error in launching the external command, which allows these
811 constructs to return with their usual error value and set $!.
813 =head2 Implicitly closed filehandles are safer
815 Sometimes implicitly closed filehandles (as when they are localized,
816 and Perl automatically closes them on exiting the scope) could
817 inadvertently set $? or $!. This has been corrected.
819 =head2 C<(\$)> prototype and C<$foo{a}>
821 An scalar reference prototype now correctly allows a hash or
822 array element in that slot.
824 =head2 Pseudo-hashes work better
826 Dereferencing some types of reference values in a pseudo-hash,
827 such as C<$ph->{foo}[1]>, was accidentally disallowed. This has
830 When applied to a pseudo-hash element, exists() now reports whether
831 the specified value exists, not merely if the key is valid.
833 delete() now works on pseudo-hashes. When given a pseudo-hash element
834 or slice it deletes the values corresponding to the keys (but not the keys
835 themselves). See L<perlref/"Pseudo-hashes: Using an array as a hash">.
837 =head2 C<goto &sub> and AUTOLOAD
839 The C<goto &sub> construct works correctly when C<&sub> happens
842 =head2 C<-bareword> allowed under C<use integer>
844 The autoquoting of barewords preceded by C<-> did not work
845 in prior versions when the C<integer> pragma was enabled.
848 =head2 Boolean assignment operators are legal lvalues
850 Constructs such as C<($a ||= 2) += 1> are now allowed.
852 =head2 C<sort $coderef @foo> allowed
854 sort() did not accept a subroutine reference as the comparison
855 function in earlier versions. This is now permitted.
857 =head2 Failures in DESTROY()
859 When code in a destructor threw an exception, it went unnoticed
860 in earlier versions of Perl, unless someone happened to be
861 looking in $@ just after the point the destructor happened to
862 run. Such failures are now visible as warnings when warnings are
865 =head2 Locale bugs fixed
867 printf() and sprintf() previously reset the numeric locale
868 back to the default "C" locale. This has been fixed.
870 Numbers formatted according to the local numeric locale
871 (such as using a decimal comma instead of a decimal dot) caused
872 "isn't numeric" warnings, even while the operations accessing
873 those numbers produced correct results. The warnings are gone.
877 The C<eval 'return sub {...}'> construct could sometimes leak
878 memory. This has been fixed.
880 Operations that aren't filehandle constructors used to leak memory
881 when used on invalid filehandles. This has been fixed.
883 Constructs that modified C<@_> could fail to deallocate values
884 in C<@_> and thus leak memory. This has been corrected.
886 =head2 Spurious subroutine stubs after failed subroutine calls
888 Perl could sometimes create empty subroutine stubs when a
889 subroutine was not found in the package. Such cases stopped
890 later method lookups from progressing into base packages.
891 This has been corrected.
893 =head2 Consistent numeric conversions
896 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
898 =head2 Taint failures under C<-U>
900 When running in unsafe mode, taint violations could sometimes
901 cause silent failures. This has been fixed.
903 =head2 END blocks and the C<-c> switch
905 Prior versions used to run BEGIN B<and> END blocks when Perl was
906 run in compile-only mode. Since this is typically not the expected
907 behavior, END blocks are not executed anymore when the C<-c> switch
910 See L<STOP blocks> for how to run things when the compile phase ends.
912 =head2 Potential to leak DATA filehandles
914 Using the C<__DATA__> token creates an implicit filehandle to
915 the file that contains the token. It is the program's
916 responsibility to close it when it is done reading from it.
918 This caveat is now better explained in the documentation.
921 =head2 Diagnostics follow STDERR
923 Diagnostic output now goes to whichever file the C<STDERR> handle
924 is pointing at, instead of always going to the underlying C runtime
927 =head2 Other fixes for better diagnostics
929 Line numbers are no longer suppressed (under most likely circumstances)
930 during the global destruction phase.
932 Diagnostics emitted from code running in threads other than the main
933 thread are now accompanied by the thread ID.
935 Embedded null characters in diagnostics now actually show up. They
936 used to truncate the message in prior versions.
938 $foo::a and $foo::b are now exempt from "possible typo" warnings only
939 if sort() is encountered in package foo.
941 Unrecognized alphabetic escapes encountered when parsing quote
942 constructs now generate a warning, since they may take on new
943 semantics in later versions of Perl.
945 =head1 Performance enhancements
947 =head2 Simple sort() using { $a <=> $b } and the like are optimized
949 Many common sort() operations using a simple inlined block are now
950 optimized for faster performance.
952 =head2 Optimized assignments to lexical variables
954 Certain operations in the RHS of assignment statements have been
955 optimized to directly set the lexical variable on the LHS,
956 eliminating redundant copying overheads.
958 =head2 Method lookups optimized
960 [TODO - Chip Salzenberg <chip@perlsupport.com>]
962 =head2 Faster mechanism to invoke XSUBs
965 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
967 =head2 Perl_malloc() improvements
970 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
972 =head2 Faster subroutine calls
974 Minor changes in how subroutine calls are handled internally
975 provide marginal improvements in performance.
977 =head1 Platform specific changes
979 =head2 Additional supported platforms
985 VM/ESA is now supported.
989 Siemens BS2000 is now supported under the POSIX Shell.
993 The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
998 GNU/Hurd is now supported.
1002 Rhapsody is now supported.
1006 EPOC is is now supported (on Psion 5).
1016 Perl now works with djgpp 2.02 (and 2.03 alpha).
1020 Environment variable names are not converted to uppercase any more.
1024 Wrong exit code from backticks now fixed.
1028 This port is still using its own builtin globbing.
1034 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1038 [TODO - Charles Bailey <bailey@newman.upenn.edu>]
1042 Site library searches failed to look for ".../site/5.XXX/lib"
1043 if ".../site/5.XXXYY/lib" wasn't found. This has been corrected.
1045 When given a pathname that consists only of a drivename, such
1046 as C<A:>, opendir() and stat() now use the current working
1047 directory for the drive rather than the drive root.
1049 The builtin XSUB functions in the Win32:: namespace are
1050 documented. See L<Win32>.
1052 $^X now contains the full path name of the running executable.
1054 A Win32::GetLongPathName() function is provided to complement
1055 Win32::GetFullPathName() and Win32::GetShortPathName(). See L<Win32>.
1057 POSIX::uname() is supported.
1059 system(1,...) now returns true process IDs rather than process
1060 handles. kill() accepts any real process id, rather than strictly
1061 return values from system(1,...).
1063 The C<Shell> module is supported.
1065 Rudimentary support for building under command.com in Windows 95
1068 Scripts are read in binary mode by default to allow ByteLoader (and
1069 the filter mechanism in general) to work properly. For compatibility,
1070 the DATA filehandle will be set to text mode if a carriage return is
1071 detected at the end of the line containing the __END__ or __DATA__
1072 token; if not, the DATA filehandle will be left open in binary mode.
1073 Earlier versions always opened the DATA filehandle in text mode.
1083 Compatibility tests for C<sub : attrs> vs the older C<use attrs>.
1087 IO constants (SEEK_*, _IO*).
1091 Directory-related IO methods (new, read, close, rewind, tied delete).
1093 =item lib/io_multihomed
1095 INET sockets with multi-homed hosts.
1107 Regression tests for C<my ($x,@y,%z) : attrs> and <sub : attrs>.
1111 File test operators.
1115 Verify operations that access pad objects (lexicals and temporaries).
1119 =head1 Modules and Pragmata
1127 While used internally by Perl as a pragma, this module also
1128 provides a way to fetch subroutine and variable attributes.
1133 The Perl Compiler suite has been extensively reworked for this
1136 [TODO - Vishal Bhatia <vishal@gol.com>,
1137 Nick Ing-Simmons <nick@ni-s.u-net.com>]
1141 The ByteLoader is a dedicated extension to generate and run
1142 Perl bytecode. See L<ByteLoader>.
1146 References can now be used.
1148 The new version also allows a leading underscore in constant names, but
1149 disallows a double leading underscore (as in "__LINE__"). Some other names
1150 are disallowed or warned against, including BEGIN, END, etc. Some names
1151 which were forced into main:: used to fail silently in some cases; now they're
1152 fatal (outside of main::) and an optional warning (inside of main::).
1153 The ability to detect whether a constant had been set with a given name has
1161 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1165 A C<Maxdepth> setting can be specified to avoid venturing
1166 too deeply into deep data structures. See L<Data::Dumper>.
1168 Dumping C<qr//> objects works correctly.
1172 C<DB> is an experimental module that exposes a clean abstraction
1173 to Perl's debugging API.
1177 DB_File can now be built with Berkeley DB versions 1, 2 or 3.
1178 See C<ext/DB_File/Changes>.
1182 Devel::DProf, a Perl source code profiler has been added. See
1183 L<Devel::DProf> and L<dprofpp>.
1187 The Dumpvalue module provides screen dumps of Perl data.
1191 Overall, Benchmark results exhibit lower average error and better timing
1194 You can now run tests for I<n> seconds instead of guessing the right
1195 number of tests to run: e.g. timethese(-5, ...) will run each
1196 code for at least 5 CPU seconds. Zero as the "number of repetitions"
1197 means "for at least 3 CPU seconds". The output format has also
1198 changed. For example:
1200 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
1202 will now output something like this:
1204 Benchmark: running a, b, each for at least 5 CPU seconds...
1205 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
1206 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
1208 New features: "each for at least N CPU seconds...", "wallclock secs",
1209 and the "@ operations/CPU second (n=operations)".
1211 timethese() now returns a reference to a hash of Benchmark objects containing
1212 the test results, keyed on the names of the tests.
1214 timethis() now returns the iterations field in the Benchmark result object
1217 timethese(), timethis(), and the new cmpthese() (see below) can also take
1218 a format specifier of 'none' to suppress output.
1220 A new function countit() is just like timeit() except that it takes a
1221 TIME instead of a COUNT.
1223 A new function cmpthese() prints a chart comparing the results of each test
1224 returned from a timethese() call. For each possible pair of tests, the
1225 percentage speed difference (iters/sec or seconds/iter) is shown.
1227 For other details, see L<Benchmark>.
1231 The Devel::Peek module provides access to the internal representation
1232 of Perl variables and data. It is a data debugging tool for the XS programmer.
1234 =item ExtUtils::MakeMaker
1236 change#4135, also needs docs in module pod
1237 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1241 More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
1242 large (more than 4G) file access (64-bit support is not yet
1243 working, though, so no need to get overly excited), Free/Net/OpenBSD
1244 locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and
1245 O_ACCMODE: the mask of O_RDONLY, O_WRONLY, and O_RDWR.
1249 A compare_text() function has been added, which allows custom
1250 comparison functions. See L<File::Compare>.
1254 File::Find now works correctly when the wanted() function is either
1255 autoloaded or is a symbolic reference.
1257 A bug that caused File::Find to lose track of the working directory
1258 when pruning top-level directories has been fixed.
1260 File::Find now also supports several other options to control its
1261 behavior. It can follow symbolic links if the C<follow> option is
1262 specified. Enabling the C<no_chdir> option will make File::Find skip
1263 changing the current directory when walking directories. The C<untaint>
1264 flag can be useful when running with taint checks enabled.
1270 This extension implements BSD-style file globbing. By default,
1271 it will also be used for the internal implementation of the glob()
1272 operator. See L<File::Glob>.
1276 New methods have been added to the File::Spec module: devnull() returns
1277 the name of the null device (/dev/null on Unix) and tmpdir() the name of
1278 the temp directory (normally /tmp on Unix). There are now also methods
1279 to convert between absolute and relative filenames: abs2rel() and
1280 rel2abs(). For compatibility with operating systems that specify volume
1281 names in file paths, the splitpath(), splitdir(), and catdir() methods
1284 =item File::Spec::Functions
1286 The new File::Spec::Functions modules provides a function interface
1287 to the File::Spec module. Allows shorthand
1289 $fullname = catfile($dir1, $dir2, $file);
1293 $fullname = File::Spec->catfile($dir1, $dir2, $file);
1297 Getopt::Long licensing has changed to allow the Perl Artistic License
1298 as well as the GPL. It used to be GPL only, which got in the way of
1299 non-GPL applications that wanted to use Getopt::Long.
1301 Getopt::Long encourages the use of Pod::Usage to produce help
1302 messages. For example:
1308 GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
1309 pod2usage(1) if $help;
1310 pod2usage(-exitstatus => 0, -verbose => 2) if $man;
1316 sample - Using GetOpt::Long and Pod::Usage
1320 sample [options] [file ...]
1323 -help brief help message
1324 -man full documentation
1332 Print a brief help message and exits.
1336 Prints the manual page and exits.
1342 B<This program> will read the given input file(s) and do someting
1343 useful with the contents thereof.
1347 See L<Pod::Usage> for details.
1349 A bug that prevented the non-option call-back E<lt>E<gt> from being
1350 specified as the first argument has been fixed.
1352 To specify the characters E<lt> and E<gt> as option starters, use
1353 E<gt>E<lt>. Note, however, that changing option starters is strongly
1358 write() and syswrite() will now accept a single-argument
1359 form of the call, for consistency with Perl's syswrite().
1361 You can now create a TCP-based IO::Socket::INET without forcing
1362 a connect attempt. This allows you to configure its options
1363 (like making it non-blocking) and then call connect() manually.
1365 A bug that prevented the IO::Socket::protocol() accessor
1366 from ever returning the correct value has been corrected.
1370 Java Perl Lingo is now distributed with Perl. See jpl/README
1371 for more information.
1375 C<use lib> now weeds out any trailing duplicate entries.
1376 C<no lib> removes all named entries.
1380 The bitwise operations C<E<lt>E<lt>>, C<E<gt>E<gt>>, C<&>, C<|>,
1381 and C<~> are now supported on bigints.
1385 The accessor methods Re, Im, arg, abs, rho, and theta can now also
1386 act as mutators (accessor $z->Re(), mutator $z->Re(3)).
1390 A little bit of radial trigonometry (cylindrical and spherical),
1391 radial coordinate conversions, and the great circle distance were added.
1395 [TODO - Brad Appleton <bradapp@enteract.com>]
1397 =item Pod::Text and Pod::Man
1399 [TODO - Russ Allbery <rra@stanford.edu>]
1403 An EXISTS method has been added to this module (and sdbm_exists() has
1404 been added to the underlying sdbm library), so one can now call exists
1405 on an SDBM_File tied hash and get the correct result, rather than a
1408 A bug that may have caused data loss when more than one disk block
1409 happens to be read from the database in a single FETCH() has been
1414 The timelocal() and timegm() functions used to silently return bogus
1415 results when the date fell outside the machine's integer range. They
1416 now consistently croak() if the date falls in an unsupported range.
1420 The error return value in list context has been changed for all functions
1421 that return a list of values. Previously these functions returned a list
1422 with a single element C<undef> if an error occurred. Now these functions
1423 return the empty list in these situations. This applies to the following
1429 The remaining functions are unchanged and continue to return C<undef> on
1430 error even in list context.
1432 The Win32::SetLastError(ERROR) function has been added as a complement
1433 to the Win32::GetLastError() function.
1435 The new Win32::GetFullPathName(FILENAME) returns the full absolute
1436 pathname for FILENAME in scalar context. In list context it returns
1437 a two-element list containing the fully qualified directory name and
1438 the filename. See L<Win32>.
1442 A new feature called "DBM Filters" has been added to all the
1443 DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
1444 DBM Filters add four new methods to each DBM module:
1451 These can be used to filter key-value pairs before the pairs are
1452 written to the database or just after they are read from the database.
1453 See L<perldbmfilter> for further information.
1459 C<use attrs> is now obsolete, and is only provided for
1460 backward-compatibility. It's been replaced by the C<sub : attributes>
1461 syntax. See L<perlsub/"Subroutine Attributes"> and L<attributes>.
1463 C<use utf8> to enable UTF-8 and Unicode support.
1465 C<use caller 'encoding'> allows modules to inherit pragmatic attributes
1466 from the caller's context. C<encoding> is currently the only supported
1469 Lexical warnings pragma, C<use warnings;>, to control optional warnings.
1472 C<use filetest> to control the behaviour of filetests (C<-r> C<-w>
1473 ...). Currently only one subpragma implemented, "use filetest
1474 'access';", that uses access(2) or equivalent to check permissions
1475 instead of using stat(2) as usual. This matters in filesystems
1476 where there are ACLs (access control lists): the stat(2) might lie,
1477 but access(2) knows better.
1479 =head1 Utility Changes
1483 [TODO - Kurt Starsinic <kstar@chapin.edu>]
1487 C<perlcc> now supports the C and Bytecode backends. By default,
1488 it generates output from the simple C backend rather than the
1489 optimized C backend.
1491 Support for non-Unix platforms has been improved.
1496 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1498 =head1 Documentation Changes
1502 =item perlcompile.pod
1504 An introduction to using the Perl Compiler suite.
1506 =item perlfilter.pod
1508 An introduction to writing Perl source filters.
1512 Some guidelines for hacking the Perl source code.
1514 =item perlopentut.pod
1516 A tutorial on using open() effectively.
1518 =item perlreftut.pod
1520 A tutorial that introduces the essentials of references.
1524 A tutorial on managing class data for object modules.
1528 =head1 New or Changed Diagnostics
1532 =item "my sub" not yet implemented
1534 (F) Lexically scoped subroutines are not yet implemented. Don't try that
1537 =item '!' allowed only after types %s
1539 (F) The '!' is allowed in pack() and unpack() only after certain types.
1540 See L<perlfunc/pack>.
1542 =item / cannot take a count
1544 (F) You had an unpack template indicating a counted-length string,
1545 but you have also specified an explicit size for the string.
1546 See L<perlfunc/pack>.
1548 =item / must be followed by a, A or Z
1550 (F) You had an unpack template indicating a counted-length string,
1551 which must be followed by one of the letters a, A or Z
1552 to indicate what sort of string is to be unpacked.
1553 See L<perlfunc/pack>.
1555 =item / must be followed by a*, A* or Z*
1557 (F) You had a pack template indicating a counted-length string,
1558 Currently the only things that can have their length counted are a*, A* or Z*.
1559 See L<perlfunc/pack>.
1561 =item / must follow a numeric type
1563 (F) You had an unpack template that contained a '#',
1564 but this did not follow some numeric unpack specification.
1565 See L<perlfunc/pack>.
1567 =item /%s/: Unrecognized escape \\%c passed through
1569 (W) You used a backslash-character combination which is not recognized
1570 by Perl. This combination appears in an interpolated variable or a
1571 C<'>-delimited regular expression. The character was understood literally.
1573 =item /%s/: Unrecognized escape \\%c in character class passed through
1575 (W) You used a backslash-character combination which is not recognized
1576 by Perl inside character classes. The character was understood literally.
1578 =item /%s/ should probably be written as "%s"
1580 (W) You have used a pattern where Perl expected to find a string,
1581 as in the first argument to C<join>. Perl will treat the true
1582 or false result of matching the pattern against $_ as the string,
1583 which is probably not what you had in mind.
1585 =item %s() called too early to check prototype
1587 (W) You've called a function that has a prototype before the parser saw a
1588 definition or declaration for it, and Perl could not check that the call
1589 conforms to the prototype. You need to either add an early prototype
1590 declaration for the subroutine in question, or move the subroutine
1591 definition ahead of the call to get proper prototype checking. Alternatively,
1592 if you are certain that you're calling the function correctly, you may put
1593 an ampersand before the name to avoid the warning. See L<perlsub>.
1595 =item %s package attribute may clash with future reserved word: %s
1597 (W) A lowercase attribute name was used that had a package-specific handler.
1598 That name might have a meaning to Perl itself some day, even though it
1599 doesn't yet. Perhaps you should use a mixed-case attribute name, instead.
1602 =item (in cleanup) %s
1604 (W) This prefix usually indicates that a DESTROY() method raised
1605 the indicated exception. Since destructors are usually called by
1606 the system at arbitrary points during execution, and often a vast
1607 number of times, the warning is issued only once for any number
1608 of failures that would otherwise result in the same message being
1611 Failure of user callbacks dispatched using the C<G_KEEPERR> flag
1612 could also result in this warning. See L<perlcall/G_KEEPERR>.
1614 =item <> should be quotes
1616 (F) You wrote C<require E<lt>fileE<gt>> when you should have written
1619 =item Attempt to join self
1621 (F) You tried to join a thread from within itself, which is an
1622 impossible task. You may be joining the wrong thread, or you may
1623 need to move the join() to some other thread.
1625 =item Bad evalled substitution pattern
1627 (F) You've used the /e switch to evaluate the replacement for a
1628 substitution, but perl found a syntax error in the code to evaluate,
1629 most likely an unexpected right brace '}'.
1631 =item Bad realloc() ignored
1633 (S) An internal routine called realloc() on something that had never been
1634 malloc()ed in the first place. Mandatory, but can be disabled by
1635 setting environment variable C<PERL_BADFREE> to 1.
1637 =item Binary number > 0b11111111111111111111111111111111 non-portable
1639 (W) The binary number you specified is larger than 2**32-1
1640 (4294967295) and therefore non-portable between systems. See
1641 L<perlport> for more on portability concerns.
1643 =item Bit vector size > 32 non-portable
1645 (W) Using bit vector sizes larger than 32 is non-portable.
1647 =item Buffer overflow in prime_env_iter: %s
1649 (W) A warning peculiar to VMS. While Perl was preparing to iterate over
1650 %ENV, it encountered a logical name or symbol definition which was too long,
1651 so it was truncated to the string shown.
1653 =item Can't check filesystem of script "%s"
1655 (P) For some reason you can't check the filesystem of the script for nosuid.
1657 =item Can't ignore signal CHLD, forcing to default
1659 (W) Perl has detected that it is being run with the SIGCHLD signal
1660 (sometimes known as SIGCLD) disabled. Since disabling this signal
1661 will interfere with proper determination of exit status of child
1662 processes, Perl has reset the signal to its default value.
1663 This situation typically indicates that the parent program under
1664 which Perl may be running (e.g. cron) is being very careless.
1666 =item Can't modify non-lvalue subroutine call
1668 (F) Subroutines meant to be used in lvalue context should be declared as
1669 such, see L<perlsub/"Lvalue subroutines">.
1671 =item Can't read CRTL environ
1673 (S) A warning peculiar to VMS. Perl tried to read an element of %ENV
1674 from the CRTL's internal environment array and discovered the array was
1675 missing. You need to figure out where your CRTL misplaced its environ
1676 or define F<PERL_ENV_TABLES> (see L<perlvms>) so that environ is not searched.
1678 =item Can't remove %s: %s, skipping file
1680 (S) You requested an inplace edit without creating a backup file. Perl
1681 was unable to remove the original file to replace it with the modified
1682 file. The file was left unmodified.
1684 =item Can't return %s from lvalue subroutine
1686 (F) Perl detected an attempt to return illegal lvalues (such
1687 as temporary or readonly values) from a subroutine used as an lvalue.
1688 This is not allowed.
1690 =item Can't weaken a nonreference
1692 (F) You attempted to weaken something that was not a reference. Only
1693 references can be weakened.
1695 =item Character class [:%s:] unknown
1697 (F) The class in the character class [: :] syntax is unknown.
1700 =item Character class syntax [%s] belongs inside character classes
1702 (W) The character class constructs [: :], [= =], and [. .] go
1703 I<inside> character classes, the [] are part of the construct,
1704 for example: /[012[:alpha:]345]/. Note that [= =] and [. .]
1705 are not currently implemented; they are simply placeholders for
1708 =item Constant is not %s reference
1710 (F) A constant value (perhaps declared using the C<use constant> pragma)
1711 is being dereferenced, but it amounts to the wrong type of reference. The
1712 message indicates the type of reference that was expected. This usually
1713 indicates a syntax error in dereferencing the constant value.
1714 See L<perlsub/"Constant Functions"> and L<constant>.
1716 =item constant(%s): %%^H is not localized
1718 (F) When setting compile-time-lexicalized hash %^H one should set the
1719 corresponding bit of $^H as well.
1721 =item constant(%s): %s
1723 (F) Compile-time-substitutions (such as overloaded constants and
1724 character names) were not correctly set up.
1726 =item defined(@array) is deprecated
1728 (D) defined() is not usually useful on arrays because it checks for an
1729 undefined I<scalar> value. If you want to see if the array is empty,
1730 just use C<if (@array) { # not empty }> for example.
1732 =item defined(%hash) is deprecated
1734 (D) defined() is not usually useful on hashes because it checks for an
1735 undefined I<scalar> value. If you want to see if the hash is empty,
1736 just use C<if (%hash) { # not empty }> for example.
1738 =item Did not produce a valid header
1742 =item Document contains no data
1746 =item entering effective %s failed
1748 (F) While under the C<use filetest> pragma, switching the real and
1749 effective uids or gids failed.
1751 =item false [] range "%s" in regexp
1753 (W) A character class range must start and end at a literal character, not
1754 another character class like C<\d> or C<[:alpha:]>. The "-" in your false
1755 range is interpreted as a literal "-". Consider quoting the "-", "\-".
1758 =item Filehandle %s opened only for output
1760 (W) You tried to read from a filehandle opened only for writing. If you
1761 intended it to be a read/write filehandle, you needed to open it with
1762 "+E<lt>" or "+E<gt>" or "+E<gt>E<gt>" instead of with "E<lt>" or nothing. If
1763 you intended only to read from the file, use "E<lt>". See
1766 =item Hexadecimal number > 0xffffffff non-portable
1768 (W) The hexadecimal number you specified is larger than 2**32-1
1769 (4294967295) and therefore non-portable between systems. See
1770 L<perlport> for more on portability concerns.
1772 =item Ill-formed CRTL environ value "%s"
1774 (W) A warning peculiar to VMS. Perl tried to read the CRTL's internal
1775 environ array, and encountered an element without the C<=> delimiter
1776 used to spearate keys from values. The element is ignored.
1778 =item Ill-formed message in prime_env_iter: |%s|
1780 (W) A warning peculiar to VMS. Perl tried to read a logical name
1781 or CLI symbol definition when preparing to iterate over %ENV, and
1782 didn't see the expected delimiter between key and value, so the
1785 =item Illegal binary digit %s
1787 (F) You used a digit other than 0 or 1 in a binary number.
1789 =item Illegal binary digit %s ignored
1791 (W) You may have tried to use a digit other than 0 or 1 in a binary number.
1792 Interpretation of the binary number stopped before the offending digit.
1794 =item Illegal number of bits in vec
1796 (F) The number of bits in vec() (the third argument) must be a power of
1797 two from 1 to 32 (or 64, if your platform supports that).
1799 =item Integer overflow in %s number
1801 (W) The hexadecimal, octal or binary number you have specified either
1802 as a literal or as an argument to hex() or oct() is too big for your
1803 architecture, and has been converted to a floating point number. On a
1804 32-bit architecture the largest hexadecimal, octal or binary number
1805 representable without overflow is 0xFFFFFFFF, 037777777777, or
1806 0b11111111111111111111111111111111 respectively. Note that Perl
1807 transparently promotes all numbers to a floating point representation
1808 internally--subject to loss of precision errors in subsequent
1811 =item Invalid %s attribute: %s
1813 The indicated attribute for a subroutine or variable was not recognized
1814 by Perl or by a user-supplied handler. See L<attributes>.
1816 =item Invalid %s attributes: %s
1818 The indicated attributes for a subroutine or variable were not recognized
1819 by Perl or by a user-supplied handler. See L<attributes>.
1821 =item invalid [] range "%s" in regexp
1823 The offending range is now explicitly displayed.
1825 =item Invalid separator character %s in attribute list
1827 (F) Something other than a comma or whitespace was seen between the
1828 elements of an attribute list. If the previous attribute
1829 had a parenthesised parameter list, perhaps that list was terminated
1830 too soon. See L<attributes>.
1832 =item Invalid separator character %s in subroutine attribute list
1834 (F) Something other than a comma or whitespace was seen between the
1835 elements of a subroutine attribute list. If the previous attribute
1836 had a parenthesised parameter list, perhaps that list was terminated
1839 =item leaving effective %s failed
1841 (F) While under the C<use filetest> pragma, switching the real and
1842 effective uids or gids failed.
1844 =item Lvalue subs returning %s not implemented yet
1846 (F) Due to limitations in the current implementation, array and hash
1847 values cannot be returned in subroutines used in lvalue context.
1848 See L<perlsub/"Lvalue subroutines">.
1850 =item Method %s not permitted
1854 =item Missing %sbrace%s on \N{}
1856 (F) Wrong syntax of character name literal C<\N{charname}> within
1857 double-quotish context.
1859 =item Missing command in piped open
1861 (W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
1862 construction, but the command was missing or blank.
1864 =item Missing name in "my sub"
1866 (F) The reserved syntax for lexically scoped subroutines requires that they
1867 have a name with which they can be found.
1869 =item no UTC offset information; assuming local time is UTC
1871 (S) A warning peculiar to VMS. Perl was unable to find the local
1872 timezone offset, so it's assuming that local system time is equivalent
1873 to UTC. If it's not, define the logical name F<SYS$TIMEZONE_DIFFERENTIAL>
1874 to translate to the number of seconds which need to be added to UTC to
1877 =item Octal number > 037777777777 non-portable
1879 (W) The octal number you specified is larger than 2**32-1 (4294967295)
1880 and therefore non-portable between systems. See L<perlport> for more
1881 on portability concerns.
1883 See also L<perlport> for writing portable code.
1885 =item panic: del_backref
1887 (P) Failed an internal consistency check while trying to reset a weak
1890 =item panic: kid popen errno read
1892 (F) forked child returned an incomprehensible message about its errno.
1894 =item panic: magic_killbackrefs
1896 (P) Failed an internal consistency check while trying to reset all weak
1897 references to an object.
1899 =item Possible Y2K bug: %s
1901 (W) You are concatenating the number 19 with another number, which
1902 could be a potential Year 2000 problem.
1904 =item Premature end of script headers
1908 =item Repeat count in pack overflows
1910 (F) You can't specify a repeat count so large that it overflows
1911 your signed integers. See L<perlfunc/pack>.
1913 =item Repeat count in unpack overflows
1915 (F) You can't specify a repeat count so large that it overflows
1916 your signed integers. See L<perlfunc/unpack>.
1918 =item realloc() of freed memory ignored
1920 (S) An internal routine called realloc() on something that had already
1923 =item Reference is already weak
1925 (W) You have attempted to weaken a reference that is already weak.
1926 Doing so has no effect.
1928 =item setpgrp can't take arguments
1930 (F) Your system has the setpgrp() from BSD 4.2, which takes no arguments,
1931 unlike POSIX setpgid(), which takes a process ID and process group ID.
1933 =item Strange *+?{} on zero-length expression
1935 (W) You applied a regular expression quantifier in a place where it
1936 makes no sense, such as on a zero-width assertion.
1937 Try putting the quantifier inside the assertion instead. For example,
1938 the way to match "abc" provided that it is followed by three
1939 repetitions of "xyz" is C</abc(?=(?:xyz){3})/>, not C</abc(?=xyz){3}/>.
1941 =item switching effective %s is not implemented
1943 (F) While under the C<use filetest> pragma, we cannot switch the
1944 real and effective uids or gids.
1946 =item This Perl can't reset CRTL environ elements (%s)
1948 =item This Perl can't set CRTL environ elements (%s=%s)
1950 (W) Warnings peculiar to VMS. You tried to change or delete an element
1951 of the CRTL's internal environ array, but your copy of Perl wasn't
1952 built with a CRTL that contained the setenv() function. You'll need to
1953 rebuild Perl with a CRTL that does, or redefine F<PERL_ENV_TABLES> (see
1954 L<perlvms>) so that the environ array isn't the target of the change to
1955 %ENV which produced the warning.
1957 =item Unknown open() mode '%s'
1959 (F) The second argument of 3-argument open() is not among the list
1960 of valid modes: C<L<lt>>, C<L<gt>>, C<E<gt>E<gt>>, C<+L<lt>>,
1961 C<+L<gt>>, C<+E<gt>E<gt>>, C<-|>, C<|->.
1963 =item Unknown process %x sent message to prime_env_iter: %s
1965 (P) An error peculiar to VMS. Perl was reading values for %ENV before
1966 iterating over it, and someone else stuck a message in the stream of
1967 data Perl expected. Someone's very confused, or perhaps trying to
1968 subvert Perl's population of %ENV for nefarious purposes.
1970 =item Unrecognized escape \\%c passed through
1972 (W) You used a backslash-character combination which is not recognized
1973 by Perl. The character was understood literally.
1975 =item Unterminated attribute parameter in attribute list
1977 (F) The lexer saw an opening (left) parenthesis character while parsing an
1978 attribute list, but the matching closing (right) parenthesis
1979 character was not found. You may need to add (or remove) a backslash
1980 character to get your parentheses to balance. See L<attributes>.
1982 =item Unterminated attribute list
1984 (F) The lexer found something other than a simple identifier at the start
1985 of an attribute, and it wasn't a semicolon or the start of a
1986 block. Perhaps you terminated the parameter list of the previous attribute
1987 too soon. See L<attributes>.
1989 =item Unterminated attribute parameter in subroutine attribute list
1991 (F) The lexer saw an opening (left) parenthesis character while parsing a
1992 subroutine attribute list, but the matching closing (right) parenthesis
1993 character was not found. You may need to add (or remove) a backslash
1994 character to get your parentheses to balance.
1996 =item Unterminated subroutine attribute list
1998 (F) The lexer found something other than a simple identifier at the start
1999 of a subroutine attribute, and it wasn't a semicolon or the start of a
2000 block. Perhaps you terminated the parameter list of the previous attribute
2003 =item Value of CLI symbol "%s" too long
2005 (W) A warning peculiar to VMS. Perl tried to read the value of an %ENV
2006 element from a CLI symbol table, and found a resultant string longer
2007 than 1024 characters. The return value has been truncated to 1024
2010 =item Version number must be a constant number
2012 (P) The attempt to translate a C<use Module n.n LIST> statement into
2013 its equivalent C<BEGIN> block found an internal inconsistency with
2018 =head1 Obsolete Diagnostics
2022 =item Character class syntax [: :] is reserved for future extensions
2024 (W) Within regular expression character classes ([]) the syntax beginning
2025 with "[:" and ending with ":]" is reserved for future extensions.
2026 If you need to represent those character sequences inside a regular
2027 expression character class, just quote the square brackets with the
2028 backslash: "\[:" and ":\]".
2030 =item Ill-formed logical name |%s| in prime_env_iter
2032 (W) A warning peculiar to VMS. A logical name was encountered when preparing
2033 to iterate over %ENV which violates the syntactic rules governing logical
2034 names. Because it cannot be translated normally, it is skipped, and will not
2035 appear in %ENV. This may be a benign occurrence, as some software packages
2036 might directly modify logical name tables and introduce nonstandard names,
2037 or it may indicate that a logical name table has been corrupted.
2039 =item regexp too big
2041 (F) The current implementation of regular expressions uses shorts as
2042 address offsets within a string. Unfortunately this means that if
2043 the regular expression compiles to longer than 32767, it'll blow up.
2044 Usually when you want a regular expression this big, there is a better
2045 way to do it with multiple statements. See L<perlre>.
2047 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
2049 (D) Perl versions before 5.004 misinterpreted any type marker followed
2050 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
2051 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
2053 However, the developers of Perl 5.004 could not fix this bug completely,
2054 because at least two widely-used modules depend on the old meaning of
2055 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
2056 old (broken) way inside strings; but it generates this message as a
2057 warning. And in Perl 5.005, this special treatment will cease.
2063 If you find what you think is a bug, you might check the
2064 articles recently posted to the comp.lang.perl.misc newsgroup.
2065 There may also be information at http://www.perl.com/perl/, the Perl
2068 If you believe you have an unreported bug, please run the B<perlbug>
2069 program included with your release. Make sure to trim your bug down
2070 to a tiny but sufficient test case. Your bug report, along with the
2071 output of C<perl -V>, will be sent off to perlbug@perl.com to be
2072 analysed by the Perl porting team.
2076 The F<Changes> file for exhaustive details on what changed.
2078 The F<INSTALL> file for how to build Perl.
2080 The F<README> file for general stuff.
2082 The F<Artistic> and F<Copying> files for copyright information.
2086 Written by Gurusamy Sarathy <F<gsar@activestate.com>>, with many
2087 contributions from The Perl Porters.
2089 Send omissions or corrections to <F<perlbug@perl.com>>.