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 syswrite() ease-of-use
430 The length argument of C<syswrite()> has become optional.
432 =head2 Filehandles can be autovivified
434 Similar to how constructs such as C<$x->[0]> autovivify a reference,
435 open() now autovivifies a filehandle if the first argument is an
436 uninitialized variable. This allows the constructs C<open(my $fh, ...)> and
437 C<open(local $fh,...)> to be used to create filehandles that will
438 conveniently be closed automatically when the scope ends, provided there
439 are no other references to them. This largely eliminates the need for
440 typeglobs when opening filehandles that must be passed around, as in the
445 or die "Can't open '@_': $!";
450 my $f = myopen("</etc/motd");
452 # $f implicitly closed here
455 [TODO - this idiom needs more pod penetration]
457 =head2 64-bit support
459 All platforms that have 64-bit integers either (a) natively as longs
460 or ints (b) via special compiler flags (c) using long long are able to
461 use "quads" (64-integers) as follows:
467 constants (decimal, hexadecimal, octal, binary) in the code
471 arguments to oct() and hex()
475 arguments to print(), printf() and sprintf() (flag prefixes ll, L, q)
483 pack() and unpack() "q" and "Q" formats
487 in basic arithmetics: + - * / %
491 vec() (but see the below note about bit arithmetics)
495 Note that unless you have the case (a) you will have to configure
496 and compile Perl using the -Duse64bits Configure flag.
498 Unfortunately bit arithmetics (&, |, ^, ~, <<, >>) for numbers are not
499 64-bit clean, they are explictly forced to be 32-bit. Bit arithmetics
500 for bit vectors (created by vec()) are not limited in their width.
502 Last but not least: note that due to Perl's habit of always using
503 floating point numbers the quads are still not true integers.
504 When quads overflow their limits (0...18_446_744_073_709_551_615 unsigned,
505 -9_223_372_036_854_775_808...9_223_372_036_854_775_807 signed), they
506 are silently promoted to floating point numbers, after which they will
507 start losing precision (their lower digits).
509 =head2 Large file support
511 If you have filesystems that support "large files" (files larger than
512 2 gigabytes), you may now also be able to create and access them from
513 Perl. You have to use Configure -Duselargefiles. Turning on the
514 large file support turns on also the 64-bit support, for obvious reasons.
516 Note that in addition to requiring a proper file system to do large
517 files you may also need to adjust your per-process (or your
518 per-system, or per-process-group, or per-user-group) maximum filesize
519 limits before running Perl scripts that try to handle large files,
520 especially if you intend to write such files.
522 Finally, in addition to your process/process group maximum filesize
523 limits, you may have quota limits on your filesystems that stop you
524 (your user id or your user group id) from using large files.
526 Adjusting your process/user/group/file system/operating system limits
527 is outside the scope of Perl core language. For process limits, you
528 may try increasing the limits using your shell's limits/limit/ulimit
529 command before running Perl. The BSD::Resource extension (not
530 included with the standard Perl distribution) may also be of use, it
531 offers the getrlimit/setrlimit interface that can be used to adjust
532 process resource usage limits, including the maximum filesize limit.
536 In some systems you may be able to use long doubles to enhance the
537 range of precision of your double precision floating point numbers
538 (that is, Perl's numbers). Use Configure -Duselongdouble to enable
539 this support (if it is available).
543 You can Configure -Dusemorebits to turn on both the 64-bit support
544 and the long double support.
546 =head2 Enhanced support for sort() subroutines
548 Perl subroutines with a prototype of C<($$)> and XSUBs in general can
549 now be used as sort subroutines. In either case, the two elements to
550 be compared are passed as normal parameters in @_. See L<perlfunc/sort>.
552 For unprototyped sort subroutines, the historical behavior of passing
553 the elements to be compared as the global variables $a and $b remains
556 =head2 Better syntax checks on parenthesized unary operators
560 print defined(&foo,&bar,&baz);
561 print uc("foo","bar","baz");
564 used to be accidentally allowed in earlier versions, and produced
565 unpredictable behaviour. Some produced ancillary warnings
566 when used in this way; others silently did the wrong thing.
568 The parenthesized forms of most unary operators that expect a single
569 argument now ensure that they are not called with more than one
570 argument, making the cases shown above syntax errors. The usual
573 print defined &foo, &bar, &baz;
574 print uc "foo", "bar", "baz";
577 remains unchanged. See L<perlop>.
579 =head2 POSIX character class syntax [: :] supported
581 For example to match alphabetic characters use /[[:alpha:]]/.
582 See L<perlre> for details.
584 =head2 Improved C<qw//> operator
586 The C<qw//> operator is now evaluated at compile time into a true list
587 instead of being replaced with a run time call to C<split()>. This
588 removes the confusing misbehaviour of C<qw//> in scalar context, which
589 had inherited that behaviour from split().
593 $foo = ($bar) = qw(a b c); print "$foo|$bar\n";
595 now correctly prints "3|a", instead of "2|a".
597 =head2 pack() format 'Z' supported
599 The new format type 'Z' is useful for packing and unpacking null-terminated
600 strings. See L<perlfunc/"pack">.
602 =head2 pack() format modifier '!' supported
604 The new format type modifier '!' is useful for packing and unpacking
605 native shorts, ints, and longs. See L<perlfunc/"pack">.
607 =head2 pack() and unpack() support counted strings
609 The template character '/' can be used to specify a counted string
610 type to be packed or unpacked. See L<perlfunc/"pack">.
612 =head2 Comments in pack() templates
614 The '#' character in a template introduces a comment up to
615 end of the line. This facilitates documentation of pack()
618 =head2 $^X variables may now have names longer than one character
620 Formerly, $^X was synonymous with ${"\cX"}, but $^XY was a syntax
621 error. Now variable names that begin with a control character may be
622 arbitrarily long. However, for compatibility reasons, these variables
623 I<must> be written with explicit braces, as C<${^XY}> for example.
624 C<${^XYZ}> is synonymous with ${"\cXYZ"}. Variable names with more
625 than one control character, such as C<${^XY^Z}>, are illegal.
627 The old syntax has not changed. As before, `^X' may be either a
628 literal control-X character or the two-character sequence `caret' plus
629 `X'. When braces are omitted, the variable name stops after the
630 control character. Thus C<"$^XYZ"> continues to be synonymous with
631 C<$^X . "YZ"> as before.
633 As before, lexical variables may not have names beginning with control
634 characters. As before, variables whose names begin with a control
635 character are always forced to be in package `main'. All such variables
636 are reserved for future extensions, except those that begin with
637 C<^_>, which may be used by user programs and are guaranteed not to
638 acquire special meaning in any future version of Perl.
640 =head2 C<use attrs> implicit in subroutine attributes
642 Formerly, if you wanted to mark a subroutine as being a method call or
643 as requiring an automatic lock() when it is entered, you had to declare
644 that with a C<use attrs> pragma in the body of the subroutine.
645 That can now be accomplished with a declaration syntax, like this:
647 sub mymethod : locked, method ;
649 sub mymethod : locked, method {
653 F<AutoSplit.pm> and F<SelfLoader.pm> have been updated to keep the attributes
654 with the stubs they provide. See L<attributes>.
656 =head2 Regular expression improvements
658 change#2827,2373,2372,2365,1813,1800,4112,4158,4215,4301
659 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
661 =head2 Overloading improvements
664 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
666 =head2 open() with more than two arguments
668 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
670 =head2 Support for interpolating named characters
673 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
675 =head2 Experimental support for user-hooks in @INC
677 [TODO - Ken Fox <kfox@ford.com>]
679 =head2 C<require> and C<do> may be overridden
681 C<require> and C<do 'file'> operations may be overridden locally
682 by importing subroutines of the same name into the current package
683 (or globally by importing them into the CORE::GLOBAL:: namespace).
684 Overriding C<require> will also affect C<use>, provided the override
685 is visible at compile-time.
686 See L<perlsub/"Overriding Built-in Functions">.
688 =head2 New variable $^C reflects C<-c> switch
690 C<$^C> has a boolean value that reflects whether perl is being run
691 in compile-only mode (i.e. via the C<-c> switch). Since
692 BEGIN blocks are executed under such conditions, this variable
693 enables perl code to determine whether actions that make sense
694 only during normal running are warranted. See L<perlvar>.
696 =head2 Optional Y2K warnings
698 If Perl is built with the cpp macro C<PERL_Y2KWARN> defined,
699 it emits optional warnings when concatenating the number 19
702 This behavior must be specifically enabled when running Configure.
703 See L<INSTALL> and L<README.Y2K>.
705 =head1 Significant bug fixes
707 =head2 E<lt>HANDLEE<gt> on empty files
709 With C<$/> set to C<undef>, slurping an empty file returns a string of
710 zero length (instead of C<undef>, as it used to) the first time the
711 HANDLE is read. Further reads yield C<undef>.
713 This means that the following will append "foo" to an empty file (it used
716 perl -0777 -pi -e 's/^/foo/' empty_file
720 perl -pi -e 's/^/foo/' empty_file
722 is unchanged (it continues to leave the file empty).
724 =head2 C<eval '...'> improvements
726 Line numbers (as reflected by caller() and most diagnostics) within
727 C<eval '...'> were often incorrect when here documents were involved.
728 This has been corrected.
730 Lexical lookups for variables appearing in C<eval '...'> within
731 functions that were themselves called within an C<eval '...'> were
732 searching the wrong place for lexicals. The lexical search now
733 correctly ends at the subroutine's block boundary.
735 Parsing of here documents used to be flawed when they appeared as
736 the replacement expression in C<eval 's/.../.../e'>. This has
739 =head2 All compilation errors are true errors
741 Some "errors" encountered at compile time were by neccessity
742 generated as warnings followed by eventual termination of the
743 program. This enabled more such errors to be reported in a
744 single run, rather than causing a hard stop at the first error
745 that was encountered.
747 The mechanism for reporting such errors has been reimplemented
748 to queue compile-time errors and report them at the end of the
749 compilation as true errors rather than as warnings. This fixes
750 cases where error messages leaked through in the form of warnings
751 when code was compiled at run time using C<eval STRING>, and
752 also allows such errors to be reliably trapped using __DIE__ hooks.
754 =head2 Automatic flushing of output buffers
756 fork(), exec(), system(), qx//, and pipe open()s now flush buffers
757 of all files opened for output when the operation
758 was attempted. This mostly eliminates confusing
759 buffering mishaps suffered by users unaware of how Perl internally
762 =head2 Better diagnostics on meaningless filehandle operations
764 Constructs such as C<open(E<lt>FHE<gt>)> and C<close(E<lt>FHE<gt>)>
765 are compile time errors. Attempting to read from filehandles that
766 were opened only for writing will now produce warnings (just as
767 writing to read-only filehandles does).
769 =head2 Where possible, buffered data discarded from duped input filehandle
771 C<open(NEW, "E<lt>&OLD")> now attempts to discard any data that
772 was previously read and buffered in C<OLD> before duping the handle.
773 On platforms where doing this is allowed, the next read operation
774 on C<NEW> will return the same data as the corresponding operation
775 on C<OLD>. Formerly, it would have returned the data from the start
776 of the following disk block instead.
778 =head2 eof() has the same old magic as <>
780 C<eof()> would return true if no attempt to read from C<E<lt>E<gt>> had
781 yet been made. C<eof()> has been changed to have a little magic of its
782 own, it now opens the C<E<lt>E<gt>> files.
784 =head2 system(), backticks and pipe open now reflect exec() failure
786 On Unix and similar platforms, system(), qx() and open(FOO, "cmd |")
787 etc., are implemented via fork() and exec(). When the underlying
788 exec() fails, earlier versions did not report the error properly,
789 since the exec() happened to be in a different process.
791 The child process now communicates with the parent about the
792 error in launching the external command, which allows these
793 constructs to return with their usual error value and set $!.
795 =head2 Implicitly closed filehandles are safer
797 Sometimes implicitly closed filehandles (as when they are localized,
798 and Perl automatically closes them on exiting the scope) could
799 inadvertently set $? or $!. This has been corrected.
801 =head2 C<(\$)> prototype and C<$foo{a}>
803 An scalar reference prototype now correctly allows a hash or
804 array element in that slot.
806 =head2 Pseudo-hashes work better
808 Dereferencing some types of reference values in a pseudo-hash,
809 such as C<$ph->{foo}[1]>, was accidentally disallowed. This has
812 When applied to a pseudo-hash element, exists() now reports whether
813 the specified value exists, not merely if the key is valid.
815 =head2 C<goto &sub> and AUTOLOAD
817 The C<goto &sub> construct works correctly when C<&sub> happens
820 =head2 C<-bareword> allowed under C<use integer>
822 The autoquoting of barewords preceded by C<-> did not work
823 in prior versions when the C<integer> pragma was enabled.
826 =head2 Boolean assignment operators are legal lvalues
828 Constructs such as C<($a ||= 2) += 1> are now allowed.
830 =head2 C<sort $coderef @foo> allowed
832 sort() did not accept a subroutine reference as the comparison
833 function in earlier versions. This is now permitted.
835 =head2 Failures in DESTROY()
837 When code in a destructor threw an exception, it went unnoticed
838 in earlier versions of Perl, unless someone happened to be
839 looking in $@ just after the point the destructor happened to
840 run. Such failures are now visible as warnings when warnings are
843 =head2 Locale bugs fixed
845 printf() and sprintf() previously reset the numeric locale
846 back to the default "C" locale. This has been fixed.
848 Numbers formatted according to the local numeric locale
849 (such as using a decimal comma instead of a decimal dot) caused
850 "isn't numeric" warnings, even while the operations accessing
851 those numbers produced correct results. The warnings are gone.
855 The C<eval 'return sub {...}'> construct could sometimes leak
856 memory. This has been fixed.
858 Operations that aren't filehandle constructors used to leak memory
859 when used on invalid filehandles. This has been fixed.
861 Constructs that modified C<@_> could fail to deallocate values
862 in C<@_> and thus leak memory. This has been corrected.
864 =head2 Spurious subroutine stubs after failed subroutine calls
866 Perl could sometimes create empty subroutine stubs when a
867 subroutine was not found in the package. Such cases stopped
868 later method lookups from progressing into base packages.
869 This has been corrected.
871 =head2 Consistent numeric conversions
874 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
876 =head2 Taint failures under C<-U>
878 When running in unsafe mode, taint violations could sometimes
879 cause silent failures. This has been fixed.
881 =head2 END blocks and the C<-c> switch
883 Prior versions used to run BEGIN B<and> END blocks when Perl was
884 run in compile-only mode. Since this is typically not the expected
885 behavior, END blocks are not executed anymore when the C<-c> switch
888 See L<STOP blocks> for how to run things when the compile phase ends.
890 =head2 Potential to leak DATA filehandles
892 Using the C<__DATA__> token creates an implicit filehandle to
893 the file that contains the token. It is the program's
894 responsibility to close it when it is done reading from it.
896 This caveat is now better explained in the documentation.
899 =head2 Diagnostics follow STDERR
901 Diagnostic output now goes to whichever file the C<STDERR> handle
902 is pointing at, instead of always going to the underlying C runtime
905 =head2 Other fixes for better diagnostics
907 Line numbers are no longer suppressed (under most likely circumstances)
908 during the global destruction phase.
910 Diagnostics emitted from code running in threads other than the main
911 thread are now accompanied by the thread ID.
913 Embedded null characters in diagnostics now actually show up. They
914 used to truncate the message in prior versions.
916 $foo::a and $foo::b are now exempt from "possible typo" warnings only
917 if sort() is encountered in package foo.
919 Unrecognized alphabetic escapes encountered when parsing quote
920 constructs now generate a warning, since they may take on new
921 semantics in later versions of Perl.
923 =head1 Performance enhancements
925 =head2 Simple sort() using { $a <=> $b } and the like are optimized
927 Many common sort() operations using a simple inlined block are now
928 optimized for faster performance.
930 =head2 Optimized assignments to lexical variables
932 Certain operations in the RHS of assignment statements have been
933 optimized to directly set the lexical variable on the LHS,
934 eliminating redundant copying overheads.
936 =head2 Method lookups optimized
938 [TODO - Chip Salzenberg <chip@perlsupport.com>]
940 =head2 Faster mechanism to invoke XSUBs
943 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
945 =head2 Perl_malloc() improvements
948 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
950 =head2 Faster subroutine calls
952 Minor changes in how subroutine calls are handled internally
953 provide marginal improvements in performance.
955 =head1 Platform specific changes
957 =head2 Additional supported platforms
963 VM/ESA is now supported.
967 Siemens BS2000 is now supported under the POSIX Shell.
971 The Mach CThreads (NEXTSTEP, OPENSTEP) are now supported by the Thread
976 GNU/Hurd is now supported.
980 Rhapsody is now supported.
984 EPOC is is now supported (on Psion 5).
994 Perl now works with djgpp 2.02 (and 2.03 alpha).
998 Environment variable names are not converted to uppercase any more.
1002 Wrong exit code from backticks now fixed.
1006 This port is still using its own builtin globbing.
1012 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1016 [TODO - Charles Bailey <bailey@newman.upenn.edu>]
1020 Site library searches failed to look for ".../site/5.XXX/lib"
1021 if ".../site/5.XXXYY/lib" wasn't found. This has been corrected.
1023 When given a pathname that consists only of a drivename, such
1024 as C<A:>, opendir() and stat() now use the current working
1025 directory for the drive rather than the drive root.
1027 The builtin XSUB functions in the Win32:: namespace are
1028 documented. See L<Win32>.
1030 $^X now contains the full path name of the running executable.
1032 A Win32::GetLongPathName() function is provided to complement
1033 Win32::GetFullPathName() and Win32::GetShortPathName(). See L<Win32>.
1035 POSIX::uname() is supported.
1037 system(1,...) now returns true process IDs rather than process
1038 handles. kill() accepts any real process id, rather than strictly
1039 return values from system(1,...).
1041 The C<Shell> module is supported.
1043 Rudimentary support for building under command.com in Windows 95
1046 Scripts are read in binary mode by default to allow ByteLoader (and
1047 the filter mechanism in general) to work properly. For compatibility,
1048 the DATA filehandle continues to be set to text mode.
1058 Compatibility tests for C<sub : attrs> vs the older C<use attrs>.
1062 IO constants (SEEK_*, _IO*).
1066 Directory-related IO methods (new, read, close, rewind, tied delete).
1068 =item lib/io_multihomed
1070 INET sockets with multi-homed hosts.
1082 Regression tests for C<my ($x,@y,%z) : attrs> and <sub : attrs>.
1086 File test operators.
1090 Verify operations that access pad objects (lexicals and temporaries).
1094 =head1 Modules and Pragmata
1102 While used internally by Perl as a pragma, this module also
1103 provides a way to fetch subroutine and variable attributes.
1108 The Perl Compiler suite has been extensively reworked for this
1111 [TODO - Vishal Bhatia <vishal@gol.com>,
1112 Nick Ing-Simmons <nick@ni-s.u-net.com>]
1116 The ByteLoader is a dedicated extension to generate and run
1117 Perl bytecode. See L<ByteLoader>.
1121 References can now be used.
1123 The new version also allows a leading underscore in constant names, but
1124 disallows a double leading underscore (as in "__LINE__"). Some other names
1125 are disallowed or warned against, including BEGIN, END, etc. Some names
1126 which were forced into main:: used to fail silently in some cases; now they're
1127 fatal (outside of main::) and an optional warning (inside of main::).
1128 The ability to detect whether a constant had been set with a given name has
1136 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1140 A C<Maxdepth> setting can be specified to avoid venturing
1141 too deeply into deep data structures. See L<Data::Dumper>.
1143 Dumping C<qr//> objects works correctly.
1147 C<DB> is an experimental module that exposes a clean abstraction
1148 to Perl's debugging API.
1152 DB_File can now be built with Berkeley DB versions 1, 2 or 3.
1153 See C<ext/DB_File/Changes>.
1157 Devel::DProf, a Perl source code profiler has been added. See
1158 L<Devel::DProf> and L<dprofpp>.
1162 The Dumpvalue module provides screen dumps of Perl data.
1166 Overall, Benchmark results exhibit lower average error and better timing
1169 You can now run tests for I<n> seconds instead of guessing the right
1170 number of tests to run: e.g. timethese(-5, ...) will run each
1171 code for at least 5 CPU seconds. Zero as the "number of repetitions"
1172 means "for at least 3 CPU seconds". The output format has also
1173 changed. For example:
1175 use Benchmark;$x=3;timethese(-5,{a=>sub{$x*$x},b=>sub{$x**2}})
1177 will now output something like this:
1179 Benchmark: running a, b, each for at least 5 CPU seconds...
1180 a: 5 wallclock secs ( 5.77 usr + 0.00 sys = 5.77 CPU) @ 200551.91/s (n=1156516)
1181 b: 4 wallclock secs ( 5.00 usr + 0.02 sys = 5.02 CPU) @ 159605.18/s (n=800686)
1183 New features: "each for at least N CPU seconds...", "wallclock secs",
1184 and the "@ operations/CPU second (n=operations)".
1186 timethese() now returns a reference to a hash of Benchmark objects containing
1187 the test results, keyed on the names of the tests.
1189 timethis() now returns the iterations field in the Benchmark result object
1192 timethese(), timethis(), and the new cmpthese() (see below) can also take
1193 a format specifier of 'none' to suppress output.
1195 A new function countit() is just like timeit() except that it takes a
1196 TIME instead of a COUNT.
1198 A new function cmpthese() prints a chart comparing the results of each test
1199 returned from a timethese() call. For each possible pair of tests, the
1200 percentage speed difference (iters/sec or seconds/iter) is shown.
1202 For other details, see L<Benchmark>.
1206 The Devel::Peek module provides access to the internal representation
1207 of Perl variables and data. It is a data debugging tool for the XS programmer.
1209 =item ExtUtils::MakeMaker
1211 change#4135, also needs docs in module pod
1212 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1216 More Fcntl constants added: F_SETLK64, F_SETLKW64, O_LARGEFILE for
1217 large (more than 4G) file access (64-bit support is not yet
1218 working, though, so no need to get overly excited), Free/Net/OpenBSD
1219 locking behaviour flags F_FLOCK, F_POSIX, Linux F_SHLCK, and
1220 O_ACCMODE: the mask of O_RDONLY, O_WRONLY, and O_RDWR.
1224 A compare_text() function has been added, which allows custom
1225 comparison functions. See L<File::Compare>.
1229 File::Find now works correctly when the wanted() function is either
1230 autoloaded or is a symbolic reference.
1232 A bug that caused File::Find to lose track of the working directory
1233 when pruning top-level directories has been fixed.
1235 File::Find now also supports several other options to control its
1236 behavior. It can follow symbolic links if the C<follow> option is
1237 specified. Enabling the C<no_chdir> option will make File::Find skip
1238 changing the current directory when walking directories. The C<untaint>
1239 flag can be useful when running with taint checks enabled.
1245 This extension implements BSD-style file globbing. By default,
1246 it will also be used for the internal implementation of the glob()
1247 operator. See L<File::Glob>.
1251 New methods have been added to the File::Spec module: devnull() returns
1252 the name of the null device (/dev/null on Unix) and tmpdir() the name of
1253 the temp directory (normally /tmp on Unix). There are now also methods
1254 to convert between absolute and relative filenames: abs2rel() and
1255 rel2abs(). For compatibility with operating systems that specify volume
1256 names in file paths, the splitpath(), splitdir(), and catdir() methods
1259 =item File::Spec::Functions
1261 The new File::Spec::Functions modules provides a function interface
1262 to the File::Spec module. Allows shorthand
1264 $fullname = catfile($dir1, $dir2, $file);
1268 $fullname = File::Spec->catfile($dir1, $dir2, $file);
1272 Getopt::Long licensing has changed to allow the Perl Artistic License
1273 as well as the GPL. It used to be GPL only, which got in the way of
1274 non-GPL applications that wanted to use Getopt::Long.
1276 Getopt::Long encourages the use of Pod::Usage to produce help
1277 messages. For example:
1283 GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
1284 pod2usage(1) if $help;
1285 pod2usage(-exitstatus => 0, -verbose => 2) if $man;
1291 sample - Using GetOpt::Long and Pod::Usage
1295 sample [options] [file ...]
1298 -help brief help message
1299 -man full documentation
1307 Print a brief help message and exits.
1311 Prints the manual page and exits.
1317 B<This program> will read the given input file(s) and do someting
1318 useful with the contents thereof.
1322 See L<Pod::Usage> for details.
1324 A bug that prevented the non-option call-back E<lt>E<gt> from being
1325 specified as the first argument has been fixed.
1327 To specify the characters E<lt> and E<gt> as option starters, use
1328 E<gt>E<lt>. Note, however, that changing option starters is strongly
1333 write() and syswrite() will now accept a single-argument
1334 form of the call, for consistency with Perl's syswrite().
1336 You can now create a TCP-based IO::Socket::INET without forcing
1337 a connect attempt. This allows you to configure its options
1338 (like making it non-blocking) and then call connect() manually.
1340 A bug that prevented the IO::Socket::protocol() accessor
1341 from ever returning the correct value has been corrected.
1345 Java Perl Lingo is now distributed with Perl. See jpl/README
1346 for more information.
1350 C<use lib> now weeds out any trailing duplicate entries.
1351 C<no lib> removes all named entries.
1355 The bitwise operations C<E<lt>E<lt>>, C<E<gt>E<gt>>, C<&>, C<|>,
1356 and C<~> are now supported on bigints.
1360 The accessor methods Re, Im, arg, abs, rho, and theta can now also
1361 act as mutators (accessor $z->Re(), mutator $z->Re(3)).
1365 A little bit of radial trigonometry (cylindrical and spherical),
1366 radial coordinate conversions, and the great circle distance were added.
1370 [TODO - Brad Appleton <bradapp@enteract.com>]
1372 =item Pod::Text and Pod::Man
1374 [TODO - Russ Allbery <rra@stanford.edu>]
1378 An EXISTS method has been added to this module (and sdbm_exists() has
1379 been added to the underlying sdbm library), so one can now call exists
1380 on an SDBM_File tied hash and get the correct result, rather than a
1383 A bug that may have caused data loss when more than one disk block
1384 happens to be read from the database in a single FETCH() has been
1389 The timelocal() and timegm() functions used to silently return bogus
1390 results when the date fell outside the machine's integer range. They
1391 now consistently croak() if the date falls in an unsupported range.
1395 The error return value in list context has been changed for all functions
1396 that return a list of values. Previously these functions returned a list
1397 with a single element C<undef> if an error occurred. Now these functions
1398 return the empty list in these situations. This applies to the following
1404 The remaining functions are unchanged and continue to return C<undef> on
1405 error even in list context.
1407 The Win32::SetLastError(ERROR) function has been added as a complement
1408 to the Win32::GetLastError() function.
1410 The new Win32::GetFullPathName(FILENAME) returns the full absolute
1411 pathname for FILENAME in scalar context. In list context it returns
1412 a two-element list containing the fully qualified directory name and
1413 the filename. See L<Win32>.
1417 A new feature called "DBM Filters" has been added to all the
1418 DBM modules--DB_File, GDBM_File, NDBM_File, ODBM_File, and SDBM_File.
1419 DBM Filters add four new methods to each DBM module:
1426 These can be used to filter key-value pairs before the pairs are
1427 written to the database or just after they are read from the database.
1428 See L<perldbmfilter> for further information.
1434 C<use attrs> is now obsolete, and is only provided for
1435 backward-compatibility. It's been replaced by the C<sub : attributes>
1436 syntax. See L<perlsub/"Subroutine Attributes"> and L<attributes>.
1438 C<use utf8> to enable UTF-8 and Unicode support.
1440 C<use caller 'encoding'> allows modules to inherit pragmatic attributes
1441 from the caller's context. C<encoding> is currently the only supported
1444 Lexical warnings pragma, C<use warnings;>, to control optional warnings.
1447 C<use filetest> to control the behaviour of filetests (C<-r> C<-w>
1448 ...). Currently only one subpragma implemented, "use filetest
1449 'access';", that uses access(2) or equivalent to check permissions
1450 instead of using stat(2) as usual. This matters in filesystems
1451 where there are ACLs (access control lists): the stat(2) might lie,
1452 but access(2) knows better.
1454 =head1 Utility Changes
1458 [TODO - Kurt Starsinic <kstar@chapin.edu>]
1462 C<perlcc> now supports the C and Bytecode backends. By default,
1463 it generates output from the simple C backend rather than the
1464 optimized C backend.
1466 Support for non-Unix platforms has been improved.
1471 [TODO - Ilya Zakharevich <ilya@math.ohio-state.edu>]
1473 =head1 Documentation Changes
1477 =item perlcompile.pod
1479 An introduction to using the Perl Compiler suite.
1481 =item perlfilter.pod
1483 An introduction to writing Perl source filters.
1487 Some guidelines for hacking the Perl source code.
1489 =item perlopentut.pod
1491 A tutorial on using open() effectively.
1493 =item perlreftut.pod
1495 A tutorial that introduces the essentials of references.
1499 A tutorial on managing class data for object modules.
1503 =head1 New or Changed Diagnostics
1507 =item "my sub" not yet implemented
1509 (F) Lexically scoped subroutines are not yet implemented. Don't try that
1512 =item '!' allowed only after types %s
1514 (F) The '!' is allowed in pack() and unpack() only after certain types.
1515 See L<perlfunc/pack>.
1517 =item / cannot take a count
1519 (F) You had an unpack template indicating a counted-length string,
1520 but you have also specified an explicit size for the string.
1521 See L<perlfunc/pack>.
1523 =item / must be followed by a, A or Z
1525 (F) You had an unpack template indicating a counted-length string,
1526 which must be followed by one of the letters a, A or Z
1527 to indicate what sort of string is to be unpacked.
1528 See L<perlfunc/pack>.
1530 =item / must be followed by a*, A* or Z*
1532 (F) You had a pack template indicating a counted-length string,
1533 Currently the only things that can have their length counted are a*, A* or Z*.
1534 See L<perlfunc/pack>.
1536 =item / must follow a numeric type
1538 (F) You had an unpack template that contained a '#',
1539 but this did not follow some numeric unpack specification.
1540 See L<perlfunc/pack>.
1542 =item /%s/: Unrecognized escape \\%c passed through
1544 (W) You used a backslash-character combination which is not recognized
1545 by Perl. This combination appears in an interpolated variable or a
1546 C<'>-delimited regular expression. The character was understood literally.
1548 =item /%s/: Unrecognized escape \\%c in character class passed through
1550 (W) You used a backslash-character combination which is not recognized
1551 by Perl inside character classes. The character was understood literally.
1553 =item /%s/ should probably be written as "%s"
1555 (W) You have used a pattern where Perl expected to find a string,
1556 as in the first argument to C<join>. Perl will treat the true
1557 or false result of matching the pattern against $_ as the string,
1558 which is probably not what you had in mind.
1560 =item %s() called too early to check prototype
1562 (W) You've called a function that has a prototype before the parser saw a
1563 definition or declaration for it, and Perl could not check that the call
1564 conforms to the prototype. You need to either add an early prototype
1565 declaration for the subroutine in question, or move the subroutine
1566 definition ahead of the call to get proper prototype checking. Alternatively,
1567 if you are certain that you're calling the function correctly, you may put
1568 an ampersand before the name to avoid the warning. See L<perlsub>.
1570 =item %s package attribute may clash with future reserved word: %s
1572 (W) A lowercase attribute name was used that had a package-specific handler.
1573 That name might have a meaning to Perl itself some day, even though it
1574 doesn't yet. Perhaps you should use a mixed-case attribute name, instead.
1577 =item (in cleanup) %s
1579 (W) This prefix usually indicates that a DESTROY() method raised
1580 the indicated exception. Since destructors are usually called by
1581 the system at arbitrary points during execution, and often a vast
1582 number of times, the warning is issued only once for any number
1583 of failures that would otherwise result in the same message being
1586 Failure of user callbacks dispatched using the C<G_KEEPERR> flag
1587 could also result in this warning. See L<perlcall/G_KEEPERR>.
1589 =item <> should be quotes
1591 (F) You wrote C<require E<lt>fileE<gt>> when you should have written
1594 =item Attempt to join self
1596 (F) You tried to join a thread from within itself, which is an
1597 impossible task. You may be joining the wrong thread, or you may
1598 need to move the join() to some other thread.
1600 =item Bad evalled substitution pattern
1602 (F) You've used the /e switch to evaluate the replacement for a
1603 substitution, but perl found a syntax error in the code to evaluate,
1604 most likely an unexpected right brace '}'.
1606 =item Bad realloc() ignored
1608 (S) An internal routine called realloc() on something that had never been
1609 malloc()ed in the first place. Mandatory, but can be disabled by
1610 setting environment variable C<PERL_BADFREE> to 1.
1612 =item Binary number > 0b11111111111111111111111111111111 non-portable
1614 (W) The binary number you specified is larger than 2**32-1
1615 (4294967295) and therefore non-portable between systems. See
1616 L<perlport> for more on portability concerns.
1618 =item Bit vector size > 32 non-portable
1620 (W) Using bit vector sizes larger than 32 is non-portable.
1622 =item Buffer overflow in prime_env_iter: %s
1624 (W) A warning peculiar to VMS. While Perl was preparing to iterate over
1625 %ENV, it encountered a logical name or symbol definition which was too long,
1626 so it was truncated to the string shown.
1628 =item Can't check filesystem of script "%s"
1630 (P) For some reason you can't check the filesystem of the script for nosuid.
1632 =item Can't ignore signal CHLD, forcing to default
1634 (W) Perl has detected that it is being run with the SIGCHLD signal
1635 (sometimes known as SIGCLD) disabled. Since disabling this signal
1636 will interfere with proper determination of exit status of child
1637 processes, Perl has reset the signal to its default value.
1638 This situation typically indicates that the parent program under
1639 which Perl may be running (e.g. cron) is being very careless.
1641 =item Can't modify non-lvalue subroutine call
1643 (F) Subroutines meant to be used in lvalue context should be declared as
1644 such, see L<perlsub/"Lvalue subroutines">.
1646 =item Can't read CRTL environ
1648 (S) A warning peculiar to VMS. Perl tried to read an element of %ENV
1649 from the CRTL's internal environment array and discovered the array was
1650 missing. You need to figure out where your CRTL misplaced its environ
1651 or define F<PERL_ENV_TABLES> (see L<perlvms>) so that environ is not searched.
1653 =item Can't remove %s: %s, skipping file
1655 (S) You requested an inplace edit without creating a backup file. Perl
1656 was unable to remove the original file to replace it with the modified
1657 file. The file was left unmodified.
1659 =item Can't return %s from lvalue subroutine
1661 (F) Perl detected an attempt to return illegal lvalues (such
1662 as temporary or readonly values) from a subroutine used as an lvalue.
1663 This is not allowed.
1665 =item Can't weaken a nonreference
1667 (F) You attempted to weaken something that was not a reference. Only
1668 references can be weakened.
1670 =item Character class [:%s:] unknown
1672 (F) The class in the character class [: :] syntax is unknown.
1675 =item Character class syntax [%s] belongs inside character classes
1677 (W) The character class constructs [: :], [= =], and [. .] go
1678 I<inside> character classes, the [] are part of the construct,
1679 for example: /[012[:alpha:]345]/. Note that [= =] and [. .]
1680 are not currently implemented; they are simply placeholders for
1683 =item Constant is not %s reference
1685 (F) A constant value (perhaps declared using the C<use constant> pragma)
1686 is being dereferenced, but it amounts to the wrong type of reference. The
1687 message indicates the type of reference that was expected. This usually
1688 indicates a syntax error in dereferencing the constant value.
1689 See L<perlsub/"Constant Functions"> and L<constant>.
1691 =item constant(%s): %%^H is not localized
1693 (F) When setting compile-time-lexicalized hash %^H one should set the
1694 corresponding bit of $^H as well.
1696 =item constant(%s): %s
1698 (F) Compile-time-substitutions (such as overloaded constants and
1699 character names) were not correctly set up.
1701 =item defined(@array) is deprecated
1703 (D) defined() is not usually useful on arrays because it checks for an
1704 undefined I<scalar> value. If you want to see if the array is empty,
1705 just use C<if (@array) { # not empty }> for example.
1707 =item defined(%hash) is deprecated
1709 (D) defined() is not usually useful on hashes because it checks for an
1710 undefined I<scalar> value. If you want to see if the hash is empty,
1711 just use C<if (%hash) { # not empty }> for example.
1713 =item Did not produce a valid header
1717 =item Document contains no data
1721 =item entering effective %s failed
1723 (F) While under the C<use filetest> pragma, switching the real and
1724 effective uids or gids failed.
1726 =item false [] range "%s" in regexp
1728 (W) A character class range must start and end at a literal character, not
1729 another character class like C<\d> or C<[:alpha:]>. The "-" in your false
1730 range is interpreted as a literal "-". Consider quoting the "-", "\-".
1733 =item Filehandle %s opened only for output
1735 (W) You tried to read from a filehandle opened only for writing. If you
1736 intended it to be a read/write filehandle, you needed to open it with
1737 "+E<lt>" or "+E<gt>" or "+E<gt>E<gt>" instead of with "E<lt>" or nothing. If
1738 you intended only to read from the file, use "E<lt>". See
1741 =item Hexadecimal number > 0xffffffff non-portable
1743 (W) The hexadecimal number you specified is larger than 2**32-1
1744 (4294967295) and therefore non-portable between systems. See
1745 L<perlport> for more on portability concerns.
1747 =item Ill-formed CRTL environ value "%s"
1749 (W) A warning peculiar to VMS. Perl tried to read the CRTL's internal
1750 environ array, and encountered an element without the C<=> delimiter
1751 used to spearate keys from values. The element is ignored.
1753 =item Ill-formed message in prime_env_iter: |%s|
1755 (W) A warning peculiar to VMS. Perl tried to read a logical name
1756 or CLI symbol definition when preparing to iterate over %ENV, and
1757 didn't see the expected delimiter between key and value, so the
1760 =item Illegal binary digit %s
1762 (F) You used a digit other than 0 or 1 in a binary number.
1764 =item Illegal binary digit %s ignored
1766 (W) You may have tried to use a digit other than 0 or 1 in a binary number.
1767 Interpretation of the binary number stopped before the offending digit.
1769 =item Illegal number of bits in vec
1771 (F) The number of bits in vec() (the third argument) must be a power of
1772 two from 1 to 32 (or 64, if your platform supports that).
1774 =item Integer overflow in %s number
1776 (W) The hexadecimal, octal or binary number you have specified either
1777 as a literal or as an argument to hex() or oct() is too big for your
1778 architecture, and has been converted to a floating point number. On a
1779 32-bit architecture the largest hexadecimal, octal or binary number
1780 representable without overflow is 0xFFFFFFFF, 037777777777, or
1781 0b11111111111111111111111111111111 respectively. Note that Perl
1782 transparently promotes all numbers to a floating point representation
1783 internally--subject to loss of precision errors in subsequent
1786 =item Invalid %s attribute: %s
1788 The indicated attribute for a subroutine or variable was not recognized
1789 by Perl or by a user-supplied handler. See L<attributes>.
1791 =item Invalid %s attributes: %s
1793 The indicated attributes for a subroutine or variable were not recognized
1794 by Perl or by a user-supplied handler. See L<attributes>.
1796 =item invalid [] range "%s" in regexp
1798 The offending range is now explicitly displayed.
1800 =item Invalid separator character %s in attribute list
1802 (F) Something other than a comma or whitespace was seen between the
1803 elements of an attribute list. If the previous attribute
1804 had a parenthesised parameter list, perhaps that list was terminated
1805 too soon. See L<attributes>.
1807 =item Invalid separator character %s in subroutine attribute list
1809 (F) Something other than a comma or whitespace was seen between the
1810 elements of a subroutine attribute list. If the previous attribute
1811 had a parenthesised parameter list, perhaps that list was terminated
1814 =item leaving effective %s failed
1816 (F) While under the C<use filetest> pragma, switching the real and
1817 effective uids or gids failed.
1819 =item Lvalue subs returning %s not implemented yet
1821 (F) Due to limitations in the current implementation, array and hash
1822 values cannot be returned in subroutines used in lvalue context.
1823 See L<perlsub/"Lvalue subroutines">.
1825 =item Method %s not permitted
1829 =item Missing %sbrace%s on \N{}
1831 (F) Wrong syntax of character name literal C<\N{charname}> within
1832 double-quotish context.
1834 =item Missing command in piped open
1836 (W) You used the C<open(FH, "| command")> or C<open(FH, "command |")>
1837 construction, but the command was missing or blank.
1839 =item Missing name in "my sub"
1841 (F) The reserved syntax for lexically scoped subroutines requires that they
1842 have a name with which they can be found.
1844 =item no UTC offset information; assuming local time is UTC
1846 (S) A warning peculiar to VMS. Perl was unable to find the local
1847 timezone offset, so it's assuming that local system time is equivalent
1848 to UTC. If it's not, define the logical name F<SYS$TIMEZONE_DIFFERENTIAL>
1849 to translate to the number of seconds which need to be added to UTC to
1852 =item Octal number > 037777777777 non-portable
1854 (W) The octal number you specified is larger than 2**32-1 (4294967295)
1855 and therefore non-portable between systems. See L<perlport> for more
1856 on portability concerns.
1858 See also L<perlport> for writing portable code.
1860 =item panic: del_backref
1862 (P) Failed an internal consistency check while trying to reset a weak
1865 =item panic: kid popen errno read
1867 (F) forked child returned an incomprehensible message about its errno.
1869 =item panic: magic_killbackrefs
1871 (P) Failed an internal consistency check while trying to reset all weak
1872 references to an object.
1874 =item Possible Y2K bug: %s
1876 (W) You are concatenating the number 19 with another number, which
1877 could be a potential Year 2000 problem.
1879 =item Premature end of script headers
1883 =item Repeat count in pack overflows
1885 (F) You can't specify a repeat count so large that it overflows
1886 your signed integers. See L<perlfunc/pack>.
1888 =item Repeat count in unpack overflows
1890 (F) You can't specify a repeat count so large that it overflows
1891 your signed integers. See L<perlfunc/unpack>.
1893 =item realloc() of freed memory ignored
1895 (S) An internal routine called realloc() on something that had already
1898 =item Reference is already weak
1900 (W) You have attempted to weaken a reference that is already weak.
1901 Doing so has no effect.
1903 =item setpgrp can't take arguments
1905 (F) Your system has the setpgrp() from BSD 4.2, which takes no arguments,
1906 unlike POSIX setpgid(), which takes a process ID and process group ID.
1908 =item Strange *+?{} on zero-length expression
1910 (W) You applied a regular expression quantifier in a place where it
1911 makes no sense, such as on a zero-width assertion.
1912 Try putting the quantifier inside the assertion instead. For example,
1913 the way to match "abc" provided that it is followed by three
1914 repetitions of "xyz" is C</abc(?=(?:xyz){3})/>, not C</abc(?=xyz){3}/>.
1916 =item switching effective %s is not implemented
1918 (F) While under the C<use filetest> pragma, we cannot switch the
1919 real and effective uids or gids.
1921 =item This Perl can't reset CRTL environ elements (%s)
1923 =item This Perl can't set CRTL environ elements (%s=%s)
1925 (W) Warnings peculiar to VMS. You tried to change or delete an element
1926 of the CRTL's internal environ array, but your copy of Perl wasn't
1927 built with a CRTL that contained the setenv() function. You'll need to
1928 rebuild Perl with a CRTL that does, or redefine F<PERL_ENV_TABLES> (see
1929 L<perlvms>) so that the environ array isn't the target of the change to
1930 %ENV which produced the warning.
1932 =item Unknown open() mode '%s'
1934 (F) The second argument of 3-argument open() is not among the list
1935 of valid modes: C<L<lt>>, C<L<gt>>, C<E<gt>E<gt>>, C<+L<lt>>,
1936 C<+L<gt>>, C<+E<gt>E<gt>>, C<-|>, C<|->.
1938 =item Unknown process %x sent message to prime_env_iter: %s
1940 (P) An error peculiar to VMS. Perl was reading values for %ENV before
1941 iterating over it, and someone else stuck a message in the stream of
1942 data Perl expected. Someone's very confused, or perhaps trying to
1943 subvert Perl's population of %ENV for nefarious purposes.
1945 =item Unrecognized escape \\%c passed through
1947 (W) You used a backslash-character combination which is not recognized
1948 by Perl. The character was understood literally.
1950 =item Unterminated attribute parameter in attribute list
1952 (F) The lexer saw an opening (left) parenthesis character while parsing an
1953 attribute list, but the matching closing (right) parenthesis
1954 character was not found. You may need to add (or remove) a backslash
1955 character to get your parentheses to balance. See L<attributes>.
1957 =item Unterminated attribute list
1959 (F) The lexer found something other than a simple identifier at the start
1960 of an attribute, and it wasn't a semicolon or the start of a
1961 block. Perhaps you terminated the parameter list of the previous attribute
1962 too soon. See L<attributes>.
1964 =item Unterminated attribute parameter in subroutine attribute list
1966 (F) The lexer saw an opening (left) parenthesis character while parsing a
1967 subroutine attribute list, but the matching closing (right) parenthesis
1968 character was not found. You may need to add (or remove) a backslash
1969 character to get your parentheses to balance.
1971 =item Unterminated subroutine attribute list
1973 (F) The lexer found something other than a simple identifier at the start
1974 of a subroutine attribute, and it wasn't a semicolon or the start of a
1975 block. Perhaps you terminated the parameter list of the previous attribute
1978 =item Value of CLI symbol "%s" too long
1980 (W) A warning peculiar to VMS. Perl tried to read the value of an %ENV
1981 element from a CLI symbol table, and found a resultant string longer
1982 than 1024 characters. The return value has been truncated to 1024
1985 =item Version number must be a constant number
1987 (P) The attempt to translate a C<use Module n.n LIST> statement into
1988 its equivalent C<BEGIN> block found an internal inconsistency with
1993 =head1 Obsolete Diagnostics
1997 =item Character class syntax [: :] is reserved for future extensions
1999 (W) Within regular expression character classes ([]) the syntax beginning
2000 with "[:" and ending with ":]" is reserved for future extensions.
2001 If you need to represent those character sequences inside a regular
2002 expression character class, just quote the square brackets with the
2003 backslash: "\[:" and ":\]".
2005 =item Ill-formed logical name |%s| in prime_env_iter
2007 (W) A warning peculiar to VMS. A logical name was encountered when preparing
2008 to iterate over %ENV which violates the syntactic rules governing logical
2009 names. Because it cannot be translated normally, it is skipped, and will not
2010 appear in %ENV. This may be a benign occurrence, as some software packages
2011 might directly modify logical name tables and introduce nonstandard names,
2012 or it may indicate that a logical name table has been corrupted.
2014 =item regexp too big
2016 (F) The current implementation of regular expressions uses shorts as
2017 address offsets within a string. Unfortunately this means that if
2018 the regular expression compiles to longer than 32767, it'll blow up.
2019 Usually when you want a regular expression this big, there is a better
2020 way to do it with multiple statements. See L<perlre>.
2022 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
2024 (D) Perl versions before 5.004 misinterpreted any type marker followed
2025 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
2026 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
2028 However, the developers of Perl 5.004 could not fix this bug completely,
2029 because at least two widely-used modules depend on the old meaning of
2030 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
2031 old (broken) way inside strings; but it generates this message as a
2032 warning. And in Perl 5.005, this special treatment will cease.
2038 If you find what you think is a bug, you might check the
2039 articles recently posted to the comp.lang.perl.misc newsgroup.
2040 There may also be information at http://www.perl.com/perl/, the Perl
2043 If you believe you have an unreported bug, please run the B<perlbug>
2044 program included with your release. Make sure to trim your bug down
2045 to a tiny but sufficient test case. Your bug report, along with the
2046 output of C<perl -V>, will be sent off to perlbug@perl.com to be
2047 analysed by the Perl porting team.
2051 The F<Changes> file for exhaustive details on what changed.
2053 The F<INSTALL> file for how to build Perl.
2055 The F<README> file for general stuff.
2057 The F<Artistic> and F<Copying> files for copyright information.
2061 Written by Gurusamy Sarathy <F<gsar@activestate.com>>, with many
2062 contributions from The Perl Porters.
2064 Send omissions or corrections to <F<perlbug@perl.com>>.