3 perldelta - what's new for perl5.004
7 This document describes differences between the 5.003 release (as
8 documented in I<Programming Perl>, second edition--the Camel Book) and
11 =head1 Supported Environments
13 Perl5.004 builds out of the box on Unix, Plan9, LynxOS, VMS, OS/2,
18 Most importantly, many bugs were fixed. See the F<Changes>
19 file in the distribution for details.
21 =head2 Compilation Option: Binary Compatibility With 5.003
23 There is a new Configure question that asks if you want to maintain
24 binary compatibility with Perl 5.003. If you choose binary
25 compatibility, you do not have to recompile your extensions, but you
26 might have symbol conflicts if you embed Perl in another application,
27 just as in the 5.003 release. By default, binary compatibility
28 is preserved at the expense of symbol table pollution.
30 =head2 New Opcode Module and Revised Safe Module
32 A new Opcode module supports the creation, manipulation and
33 application of opcode masks. The revised Safe module has a new API
34 and is implemented using the new Opcode module. Please read the new
35 Opcode and Safe documentation.
37 =head2 Fixed Parsing of $$<digit>, &$<digit>, etc.
39 A bug in previous versions of Perl 5.0 prevented proper parsing of
40 numeric special variables as symbolic references. That bug has been
41 fixed. As a result, the string "$$0" is no longer equivalent to
42 C<$$."0">, but rather to C<${$0}>. To get the old behavior, change
43 "$$" followed by a digit to "${$}".
45 =head2 Changes to Tainting Checks
47 A bug in previous versions may have failed to detect some insecure
48 conditions when taint checks are turned on. (Taint checks are used
49 in setuid or setgid scripts, or when explicitly turned on with the
50 C<-T> invocation option.) Although it's unlikely, this may cause a
51 previously-working script to now fail -- which should be construed
52 as a blessing, since that indicates a potentially-serious security
53 hole was just plugged.
55 =head2 Internal Change: FileHandle Deprecated
57 Filehandles are now stored internally as type IO::Handle.
58 Although C<use FileHandle> and C<*STDOUT{FILEHANDLE}>
59 are still supported for backwards compatibility,
60 C<use IO::Handle> (or C<IO::Seekable> or C<IO::File>) and
61 C<*STDOUT{IO}> are the way of the future.
63 =head2 Internal Change: PerlIO internal IO abstraction interface
65 It is now possible to build Perl with AT&T's sfio IO package
66 instead of stdio. See L<perlapio> for more details, and
67 the F<INSTALL> file for how to use it.
69 =head2 New and Changed Built-in Variables
75 Extended error message on some platforms. (Also known as
76 $EXTENDED_OS_ERROR if you C<use English>).
80 The current set of syntax checks enabled by C<use strict>. See the
81 documentation of C<strict> for more details. Not actually new, but
83 Because it is intended for internal use by Perl core components,
84 there is no C<use English> long name for this variable.
88 By default, running out of memory it is not trappable. However, if
89 compiled for this, Perl may use the contents of C<$^M> as an emergency
90 pool after die()ing with this message. Suppose that your Perl were
91 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
95 would allocate a 64K buffer for use when in emergency.
96 See the F<INSTALL> file for information on how to enable this option.
97 As a disincentive to casual use of this advanced feature,
98 there is no C<use English> long name for this variable.
102 =head2 New and Changed Built-in Functions
106 =item delete on slices
108 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
112 is now supported on more platforms, and prefers fcntl
113 to lockf when emulating.
115 =item printf and sprintf
117 now support "%i" as a synonym for "%d", and the "h" modifier.
118 So "%hi" means "short integer in decimal", and "%ho" means
119 "unsigned short integer as octal".
121 =item keys as an lvalue
123 As an lvalue, C<keys> allows you to increase the number of hash buckets
124 allocated for the given hash. This can gain you a measure of efficiency if
125 you know the hash is going to get big. (This is similar to pre-extending
126 an array by assigning a larger number to $#array.) If you say
130 then C<%hash> will have at least 200 buckets allocated for it. These
131 buckets will be retained even if you do C<%hash = ()>; use C<undef
132 %hash> if you want to free the storage while C<%hash> is still in scope.
133 You can't shrink the number of buckets allocated for the hash using
134 C<keys> in this way (but you needn't worry about doing this by accident,
135 as trying has no effect).
137 =item my() in Control Structures
139 You can now use my() (with or without the parentheses) in the control
140 expressions of control structures such as:
142 while (defined(my $line = <>)) {
148 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
150 } elsif ($answer =~ /^n(o)?$/i) {
154 die "`$answer' is neither `yes' nor `no'";
157 Also, you can declare a foreach loop control variable as lexical by
158 preceding it with the word "my". For example, in:
160 foreach my $i (1, 2, 3) {
164 $i is a lexical variable, and the scope of $i extends to the end of
165 the loop, but not beyond it.
167 Note that you still cannot use my() on global punctuation variables
168 such as $_ and the like.
170 =item unpack() and pack()
172 A new format 'w' represents a BER compressed integer (as defined in
173 ASN.1). Its format is a sequence of one or more bytes, each of which
174 provides seven bits of the total value, with the most significant
175 first. Bit eight of each byte is set, except for the last byte, in
176 which bit eight is clear.
180 If the first argument to C<use> is a number, it is treated as a version
181 number instead of a module name. If the version of the Perl interpreter
182 is less than VERSION, then an error message is printed and Perl exits
183 immediately. Because C<use> occurs at compile time, this check happens
184 immediately during the compilation process, unlike C<require VERSION>,
185 which waits until run-time for the check. This is often useful if you
186 need to check the current Perl version before C<use>ing library modules
187 which have changed in incompatible ways from older versions of Perl.
188 (We try not to do this more than we have to.)
190 =item use Module VERSION LIST
192 If the VERSION argument is present between Module and LIST, then the
193 C<use> will call the VERSION method in class Module with the given
194 version as an argument. The default VERSION method, inherited from
195 the Universal class, croaks if the given version is larger than the
196 value of the variable $Module::VERSION. (Note that there is not a
197 comma after VERSION!)
199 This version-checking mechanism is similar to the one currently used
200 in the Exporter module, but it is faster and can be used with modules
201 that don't use the Exporter. It is the recommended method for new
204 =item prototype(FUNCTION)
206 Returns the prototype of a function as a string (or C<undef> if the
207 function has no prototype). FUNCTION is a reference to or the name of the
208 function whose prototype you want to retrieve.
209 (Not actually new; just never documented before.)
213 The default seed for C<srand>, which used to be C<time>, has been changed.
214 Now it's a heady mix of difficult-to-predict system-dependent values,
215 which should be sufficient for most everyday purposes.
217 Previous to version 5.004, calling C<rand> without first calling C<srand>
218 would yield the same sequence of random numbers on most or all machines.
219 Now, when perl sees that you're calling C<rand> and haven't yet called
220 C<srand>, it calls C<srand> with the default seed. You should still call
221 C<srand> manually if your code might ever be run on a pre-5.004 system,
222 of course, or if you want a seed other than the default.
226 Functions documented in the Camel to default to $_ now in
227 fact do, and all those that do are so documented in L<perlfunc>.
229 =item C<m//g> does not trigger a pos() reset on failure
231 The C<m//g> match iteration construct used to reset the iteration
232 when it failed to match (so that the next C<m//g> match would start at
233 the beginning of the string). You now have to explicitly do a
234 C<pos $str = 0;> to reset the "last match" position, or modify the
235 string in some way. This change makes it practical to chain C<m//g>
236 matches together in conjunction with ordinary matches using the C<\G>
237 zero-width assertion. See L<perlop> and L<perlre>.
239 =item nested C<sub{}> closures work now
241 Prior to the 5.004 release, nested anonymous functions
242 didn't work right. They do now.
244 =item formats work right on changing lexicals
246 Just like anonymous functions that contain lexical variables
247 that change (like a lexical index variable for a C<foreach> loop),
248 formats now work properly. For example, this silently failed
249 before, and is fine now:
252 foreach $i ( 1 .. 10 ) {
262 =head2 New Built-in Methods
264 The C<UNIVERSAL> package automatically contains the following methods that
265 are inherited by all other classes:
271 C<isa> returns I<true> if its object is blessed into a sub-class of C<CLASS>
273 C<isa> is also exportable and can be called as a sub with two arguments. This
274 allows the ability to check what a reference points to. Example:
276 use UNIVERSAL qw(isa);
278 if(isa($ref, 'ARRAY')) {
284 C<can> checks to see if its object has a method called C<METHOD>,
285 if it does then a reference to the sub is returned; if it does not then
286 I<undef> is returned.
288 =item VERSION( [NEED] )
290 C<VERSION> returns the version number of the class (package). If the
291 NEED argument is given then it will check that the current version (as
292 defined by the $VERSION variable in the given package) not less than
293 NEED; it will die if this is not the case. This method is normally
294 called as a class method. This method is called automatically by the
295 C<VERSION> form of C<use>.
297 use A 1.2 qw(some imported subs);
303 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
304 C<isa> uses a very similar method and caching strategy. This may cause
305 strange effects if the Perl code dynamically changes @ISA in any package.
307 You may add other methods to the UNIVERSAL class via Perl or XS code.
308 You do not need to C<use UNIVERSAL> in order to make these methods
309 available to your program. This is necessary only if you wish to
310 have C<isa> available as a plain subroutine in the current package.
312 =head2 TIEHANDLE Now Supported
314 See L<perltie> for other kinds of tie()s.
318 =item TIEHANDLE classname, LIST
320 This is the constructor for the class. That means it is expected to
321 return an object of some sort. The reference can be used to
322 hold some internal information.
327 return bless \$i, shift;
330 =item PRINT this, LIST
332 This method will be triggered every time the tied handle is printed to.
333 Beyond its self reference it also expects the list that was passed to
339 return print join( $, => map {uc} @_), $\;
344 This method will be called when the handle is read from. The method
345 should return undef when there is no more data.
349 return "PRINT called $$r times\n";
354 As with the other types of ties, this method will be called when the
355 tied handle is about to be destroyed. This is useful for debugging and
356 possibly for cleaning up.
364 =head2 Malloc Enhancements
366 If perl's malloc() is used, you can print memory statistics at runtime
367 by running Perl thusly:
369 env PERL_DEBUG_MSTATS=2 perl your_script_here
371 The value of 2 means to print statistics after compilation and on
372 exit; with a value of 1, the statistics ares printed only on exit.
373 (If you want the statistics at an arbitrary time, you'll need to
374 install the optional module Devel::Peek.)
376 In addition, three new compilation flags are recognized by malloc.c.
377 (They have no effect if perl is compiled with system malloc().)
381 =item -DEMERGENCY_SBRK
383 If this macro is defined, running out of memory need not be a fatal
384 error: a memory pool can allocated by assigning to the special
385 variable C<$^M>. See L<"$^M">.
389 Perl memory allocation is by bucket with sizes close to powers of two.
390 Because of these malloc overhead may be big, especially for data of
391 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
392 a slightly different algorithm for small allocations (up to 64 bytes
393 long), which makes it possible to have overhead down to 1 byte for
394 allocations which are powers of two (and appear quite often).
396 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
397 about 20% for typical Perl usage. Expected slowdown due to additional
398 malloc overhead is in fractions of a percent (hard to measure, because
399 of the effect of saved memory on speed).
401 =item -DTWO_POT_OPTIMIZE
403 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
404 with size close to a power of two; but this works for big allocations
405 (starting with 16K by default). Such allocations are typical for big
406 hashes and special-purpose scripts, especially image processing.
408 On recent systems, the fact that perl requires 2M from system for 1M
409 allocation will not affect speed of execution, since the tail of such
410 a chunk is not going to be touched (and thus will not require real
411 memory). However, it may result in a premature out-of-memory error.
412 So if you will be manipulating very large blocks with sizes close to
413 powers of two, it would be wise to define this macro.
415 Expected saving of memory is 0-100% (100% in applications which
416 require most memory in such 2**n chunks); expected slowdown is
421 =head2 Miscellaneous Efficiency Enhancements
423 Functions that have an empty prototype and that do nothing but return
424 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
426 Each unique hash key is only allocated once, no matter how many hashes
427 have an entry with that key. So even if you have 100 copies of the
428 same hash, the hash keys never have to be re-allocated.
432 Four new pragmatic modules exist:
440 Looks for MakeMaker-like I<'blib'> directory structure starting in
441 I<dir> (or current directory) and working back up to five levels of
444 Intended for use on command line with B<-M> option as a way of testing
445 arbitrary scripts against an uninstalled version of a package.
449 Tells the compiler to enable (or disable) the use of POSIX locales for
452 When C<use locale> is in effect, the current LC_CTYPE locale is used
453 for regular expressions and case mapping; LC_COLLATE for string
454 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
455 (but B<not> in print). LC_NUMERIC is always used in write, since
456 lexical scoping of formats is problematic at best.
458 Each C<use locale> or C<no locale> affects statements to the end of
459 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
460 current file. Locales can be switched and queried with
463 See L<perllocale> for more information.
467 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
471 Enable VMS-specific language features. Currently, there are three
472 VMS-specific features available: 'status', which makes C<$?> and
473 C<system> return genuine VMS status values instead of emulating POSIX;
474 'exit', which makes C<exit> take a genuine VMS status value instead of
475 assuming that C<exit 1> is an error; and 'time', which makes all times
476 relative to the local time zone, in the VMS tradition.
482 =head2 Installation Directories
484 The I<installperl> script now places the Perl source files for
485 extensions in the architecture-specific library directory, which is
486 where the shared libraries for extensions have always been. This
487 change is intended to allow administrators to keep the Perl 5.004
488 library directory unchanged from a previous version, without running
489 the risk of binary incompatibility between extensions' Perl source and
494 New constants in the existing Fcntl modules are now supported,
495 provided that your operating system happens to support them:
498 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
501 These constants are intended for use with the Perl operators sysopen()
502 and fcntl() and the basic database modules like SDBM_File. For the
503 exact meaning of these and other Fcntl constants please refer to your
504 operating system's documentation for fcntl() and open().
506 In addition, the Fcntl module now provides these constants for use
507 with the Perl operator flock():
509 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
511 These constants are defined in all environments (because where there is
512 no flock() system call, Perl emulates it). However, for historical
513 reasons, these constants are not exported unless they are explicitly
514 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
516 =head2 Module Information Summary
518 Brand new modules, arranged by topic rather than strictly
521 CPAN interface to Comprehensive Perl Archive Network
522 CPAN::FirstTime create a CPAN configuration file
523 CPAN::Nox run CPAN while avoiding compiled extensions
525 IO.pm Top-level interface to IO::* classes
526 IO/File.pm IO::File extension Perl module
527 IO/Handle.pm IO::Handle extension Perl module
528 IO/Pipe.pm IO::Pipe extension Perl module
529 IO/Seekable.pm IO::Seekable extension Perl module
530 IO/Select.pm IO::Select extension Perl module
531 IO/Socket.pm IO::Socket extension Perl module
533 Opcode.pm Disable named opcodes when compiling Perl code
535 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
536 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
538 FindBin.pm Find path of currently executing program
540 Class/Template.pm Structure/member template builder
541 File/stat.pm Object-oriented wrapper around CORE::stat
542 Net/hostent.pm Object-oriented wrapper around CORE::gethost*
543 Net/netent.pm Object-oriented wrapper around CORE::getnet*
544 Net/protoent.pm Object-oriented wrapper around CORE::getproto*
545 Net/servent.pm Object-oriented wrapper around CORE::getserv*
546 Time/gmtime.pm Object-oriented wrapper around CORE::gmtime
547 Time/localtime.pm Object-oriented wrapper around CORE::localtime
548 Time/tm.pm Perl implementation of "struct tm" for {gm,local}time
549 User/grent.pm Object-oriented wrapper around CORE::getgr*
550 User/pwent.pm Object-oriented wrapper around CORE::getpw*
552 Tie/RefHash.pm Base class for tied hashes with references as keys
554 UNIVERSAL.pm Base class for *ALL* classes
558 The IO module provides a simple mechanism to load all of the IO modules at one
559 go. Currently this includes:
567 For more information on any of these modules, please see its
568 respective documentation.
572 The Math::Complex module has been totally rewritten, and now supports
573 more operations. These are overloaded:
575 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
577 And these functions are now exported:
581 tan cotan asin acos atan acotan
582 sinh cosh tanh cotanh asinh acosh atanh acotanh
587 There have been quite a few changes made to DB_File. Here are a few of
594 Fixed a handful of bugs.
598 By public demand, added support for the standard hash function exists().
602 Made it compatible with Berkeley DB 1.86.
606 Made negative subscripts work with RECNO interface.
610 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
611 mode from 0640 to 0666.
615 Made DB_File automatically import the open() constants (O_RDWR,
616 O_CREAT etc.) from Fcntl, if available.
620 Updated documentation.
624 Refer to the HISTORY section in DB_File.pm for a complete list of
625 changes. Everything after DB_File 1.01 has been added since 5.003.
629 Major rewrite - support added for both udp echo and real icmp pings.
631 =head2 Overridden Built-ins
633 Many of the Perl built-ins returning lists now have
634 object-oriented overrides. These are:
646 For example, you can now say
650 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
652 =head1 Utility Changes
658 =item C<void> XSUBs now default to returning nothing
660 Due to a documentation/implementation bug in previous versions of
661 Perl, XSUBs with a return type of C<void> have actually been
662 returning one value. Usually that value was the GV for the XSUB,
663 but sometimes it was some already freed or reused value, which would
664 sometimes lead to program failure.
666 In Perl 5.004, if an XSUB is declared as returning C<void>, it
667 actually returns no value, i.e. an empty list (though there is a
668 backward-compatibility exception; see below). If your XSUB really
669 does return an SV, you should give it a return type of C<SV *>.
671 For backward compatibility, I<xsubpp> tries to guess whether a
672 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
673 It does so by examining the text of the XSUB: if I<xsubpp> finds
674 what looks like an assignment to C<ST(0)>, it assumes that the
675 XSUB's return type is really C<SV *>.
679 =head1 C Language API Changes
683 =item C<gv_fetchmethod> and C<perl_call_sv>
685 The C<gv_fetchmethod> function finds a method for an object, just like
686 in Perl 5.003. The GV it returns may be a method cache entry.
687 However, in Perl 5.004, method cache entries are not visible to users;
688 therefore, they can no longer be passed directly to C<perl_call_sv>.
689 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
690 and pass the CV to C<perl_call_sv>.
692 The most likely symptom of passing the result of C<gv_fetchmethod> to
693 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
694 error on the I<second> call to a given method (since there is no cache
697 =item Extended API for manipulating hashes
699 Internal handling of hash keys has changed. The old hashtable API is
700 still fully supported, and will likely remain so. The additions to the
701 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
702 real scalars as keys rather than plain strings (non-tied hashes still
703 can only use strings as keys). New extensions must use the new hash
704 access functions and macros if they wish to use C<SV*> keys. These
705 additions also make it feasible to manipulate C<HE*>s (hash entries),
706 which can be more efficient. See L<perlguts> for details.
710 =head1 Documentation Changes
712 Many of the base and library pods were updated. These
713 new pods are included in section 1:
723 Locale support (internationalization and localization).
727 Tutorial on Perl OO programming.
731 Perl internal IO abstraction interface.
735 Although not new, this has been massively updated.
739 Although not new, this has been massively updated.
743 =head1 New Diagnostics
745 Several new conditions will trigger warnings that were
746 silent before. Some only affect certain platforms.
747 The following new warnings and errors outline these.
748 These messages are classified as follows (listed in
749 increasing order of desperation):
751 (W) A warning (optional).
752 (D) A deprecation (optional).
753 (S) A severe warning (mandatory).
754 (F) A fatal error (trappable).
755 (P) An internal error you should never see (trappable).
756 (X) A very fatal error (non-trappable).
757 (A) An alien error message (not generated by Perl).
761 =item "my" variable %s masks earlier declaration in same scope
763 (S) A lexical variable has been redeclared in the same scope, effectively
764 eliminating all access to the previous instance. This is almost always
765 a typographical error. Note that the earlier variable will still exist
766 until the end of the scope or until all closure referents to it are
769 =item %s argument is not a HASH element or slice
771 (F) The argument to delete() must be either a hash element, such as
774 $ref->[12]->{"susie"}
776 or a hash slice, such as
778 @foo{$bar, $baz, $xyzzy}
779 @{$ref->[12]}{"susie", "queue"}
781 =item Allocation too large: %lx
783 (X) You can't allocate more than 64K on an MSDOS machine.
785 =item Allocation too large
787 (F) You can't allocate more than 2^31+"small amount" bytes.
789 =item Attempt to free non-existent shared string
791 (P) Perl maintains a reference counted internal table of strings to
792 optimize the storage and access of hash keys and other strings. This
793 indicates someone tried to decrement the reference count of a string
794 that can no longer be found in the table.
796 =item Attempt to use reference as lvalue in substr
798 (W) You supplied a reference as the first argument to substr() used
799 as an lvalue, which is pretty strange. Perhaps you forgot to
800 dereference it first. See L<perlfunc/substr>.
802 =item Unsupported function fork
804 (F) Your version of executable does not support forking.
806 Note that under some systems, like OS/2, there may be different flavors of
807 Perl executables, some of which may support fork, some not. Try changing
808 the name you call Perl by to C<perl_>, C<perl__>, and so on.
810 =item Ill-formed logical name |%s| in prime_env_iter
812 (W) A warning peculiar to VMS. A logical name was encountered when preparing
813 to iterate over %ENV which violates the syntactic rules governing logical
814 names. Since it cannot be translated normally, it is skipped, and will not
815 appear in %ENV. This may be a benign occurrence, as some software packages
816 might directly modify logical name tables and introduce non-standard names,
817 or it may indicate that a logical name table has been corrupted.
819 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
821 (F) Only hard references are allowed by "strict refs". Symbolic references
822 are disallowed. See L<perlref>.
824 =item Constant subroutine %s redefined
826 (S) You redefined a subroutine which had previously been eligible for
827 inlining. See L<perlsub/"Constant Functions"> for commentary and
832 (F) You passed die() an empty string (the equivalent of C<die "">) or
833 you called it with no args and both C<$@> and C<$_> were empty.
835 =item Integer overflow in hex number
837 (S) The literal hex number you have specified is too big for your
838 architecture. On a 32-bit architecture the largest hex literal is
841 =item Integer overflow in octal number
843 (S) The literal octal number you have specified is too big for your
844 architecture. On a 32-bit architecture the largest octal literal is
847 =item Name "%s::%s" used only once: possible typo
849 (W) Typographical errors often show up as unique variable names.
850 If you had a good reason for having a unique name, then just mention
851 it again somehow to suppress the message (the C<use vars> pragma is
852 provided for just this purpose).
854 =item Null picture in formline
856 (F) The first argument to formline must be a valid format picture
857 specification. It was found to be empty, which probably means you
858 supplied it an uninitialized value. See L<perlform>.
860 =item Offset outside string
862 (F) You tried to do a read/write/send/recv operation with an offset
863 pointing outside the buffer. This is difficult to imagine.
864 The sole exception to this is that C<sysread()>ing past the buffer
865 will extend the buffer and zero pad the new area.
867 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
869 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
870 Stubs should never be implicitely created, but explicit calls to C<can>
873 =item Cannot resolve method `%s' overloading `%s' in package `s'
875 (P) Internal error trying to resolve overloading specified by a method
876 name (as opposed to a subroutine reference).
880 (X|F) The malloc() function returned 0, indicating there was insufficient
881 remaining memory (or virtual memory) to satisfy the request.
883 The request was judged to be small, so the possibility to trap it
884 depends on the way Perl was compiled. By default it is not trappable.
885 However, if compiled for this, Perl may use the contents of C<$^M> as
886 an emergency pool after die()ing with this message. In this case the
887 error is trappable I<once>.
889 =item Out of memory during request for %s
891 (F) The malloc() function returned 0, indicating there was insufficient
892 remaining memory (or virtual memory) to satisfy the request. However,
893 the request was judged large enough (compile-time default is 64K), so
894 a possibility to shut down by trapping this error is granted.
896 =item Possible attempt to put comments in qw() list
898 (W) qw() lists contain items separated by whitespace; as with literal
899 strings, comment characters are not ignored, but are instead treated
900 as literal data. (You may have used different delimiters than the
901 exclamation marks parentheses shown here; braces are also frequently
904 You probably wrote something like this:
911 when you should have written this:
918 If you really want comments, build your list the
919 old-fashioned way, with quotes and commas:
923 'b', # another comment
926 =item Possible attempt to separate words with commas
928 (W) qw() lists contain items separated by whitespace; therefore commas
929 aren't needed to separate the items. (You may have used different
930 delimiters than the parentheses shown here; braces are also frequently
933 You probably wrote something like this:
937 which puts literal commas into some of the list items. Write it without
938 commas if you don't want them to appear in your data:
942 =item Scalar value @%s{%s} better written as $%s{%s}
944 (W) You've used a hash slice (indicated by @) to select a single element of
945 a hash. Generally it's better to ask for a scalar value (indicated by $).
946 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
947 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
948 like a list when you assign to it, and provides a list context to its
949 subscript, which can do weird things if you're expecting only one subscript.
951 =item untie attempted while %d inner references still exist
953 (W) A copy of the object returned from C<tie> (or C<tied>) was still
954 valid when C<untie> was called.
956 =item Value of %s construct can be "0"; test with defined()
958 (W) In a conditional expression, you used <HANDLE>, <*> (glob), or
959 C<readdir> as a boolean value. Each of these constructs can return a
960 value of "0"; that would make the conditional expression false, which
961 is probably not what you intended. When using these constructs in
962 conditional expressions, test their values with the C<defined> operator.
964 =item Variable "%s" may be unavailable
966 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
967 subroutine, and outside that is another subroutine; and the anonymous
968 (innermost) subroutine is referencing a lexical variable defined in
969 the outermost subroutine. For example:
971 sub outermost { my $a; sub middle { sub { $a } } }
973 If the anonymous subroutine is called or referenced (directly or
974 indirectly) from the outermost subroutine, it will share the variable
975 as you would expect. But if the anonymous subroutine is called or
976 referenced when the outermost subroutine is not active, it will see
977 the value of the shared variable as it was before and during the
978 *first* call to the outermost subroutine, which is probably not what
981 In these circumstances, it is usually best to make the middle
982 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
983 support for shared variables in nested anonymous subroutines; a named
984 subroutine in between interferes with this feature.
986 =item Variable "%s" will not stay shared
988 (W) An inner (nested) I<named> subroutine is referencing a lexical
989 variable defined in an outer subroutine.
991 When the inner subroutine is called, it will probably see the value of
992 the outer subroutine's variable as it was before and during the
993 *first* call to the outer subroutine; in this case, after the first
994 call to the outer subroutine is complete, the inner and outer
995 subroutines will no longer share a common value for the variable. In
996 other words, the variable will no longer be shared.
998 Furthermore, if the outer subroutine is anonymous and references a
999 lexical variable outside itself, then the outer and inner subroutines
1000 will I<never> share the given variable.
1002 This problem can usually be solved by making the inner subroutine
1003 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1004 reference variables in outer subroutines are called or referenced,
1005 they are automatically re-bound to the current values of such
1008 =item Warning: something's wrong
1010 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1011 you called it with no args and C<$_> was empty.
1013 =item Got an error from DosAllocMem
1015 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1016 version of Perl, and this should not happen anyway.
1018 =item Malformed PERLLIB_PREFIX
1020 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1028 with non-empty prefix1 and prefix2. If C<prefix1> is indeed a prefix of
1029 a builtin library search path, prefix2 is substituted. The error may appear
1030 if components are not found, or are too long. See L<perlos2/"PERLLIB_PREFIX">.
1032 =item PERL_SH_DIR too long
1034 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1035 C<sh>-shell in. See L<perlos2/"PERL_SH_DIR">.
1037 =item Process terminated by SIG%s
1039 (W) This is a standard message issued by OS/2 applications, while *nix
1040 applications die in silence. It is considered a feature of the OS/2
1041 port. One can easily disable this by appropriate sighandlers, see
1042 L<perlipc/"Signals">. See L<perlos2/"Process terminated by SIGTERM/SIGINT">.
1048 If you find what you think is a bug, you might check the headers of
1049 recently posted articles in the comp.lang.perl.misc newsgroup.
1050 There may also be information at http://www.perl.com/perl/, the Perl
1053 If you believe you have an unreported bug, please run the B<perlbug>
1054 program included with your release. Make sure you trim your bug
1055 down to a tiny but sufficient test case. Your bug report, along
1056 with the output of C<perl -V>, will be sent off to F<perlbug@perl.com>
1057 to be analysed by the Perl porting team.
1061 The F<Changes> file for exhaustive details on what changed.
1063 The F<INSTALL> file for how to build Perl. This file has been
1064 significantly updated for 5.004, so even veteran users should
1067 The F<README> file for general stuff.
1069 The F<Copying> file for copyright information.
1073 Constructed by Tom Christiansen, grabbing material with permission
1074 from innumerable contributors, with kibitzing by more than a few Perl
1077 Last update: Tue Jan 14 14:03:02 EST 1997