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 Internal Change: FileHandle Deprecated
47 Filehandles are now stored internally as type IO::Handle.
48 Although C<use FileHandle> and C<*STDOUT{FILEHANDLE}>
49 are still supported for backwards compatibility,
50 C<use IO::Handle> (or C<IO::Seekable> or C<IO::File>) and
51 C<*STDOUT{IO}> are the way of the future.
53 =head2 Internal Change: PerlIO internal IO abstraction interface
55 It is now possible to build Perl with AT&T's sfio IO package
56 instead of stdio. See L<perlapio> for more details, and
57 the F<INSTALL> file for how to use it.
59 =head2 New and Changed Built-in Variables
65 Extended error message on some platforms. (Also known as
66 $EXTENDED_OS_ERROR if you C<use English>).
70 The current set of syntax checks enabled by C<use strict>. See the
71 documentation of C<strict> for more details. Not actually new, but
73 Because it is intended for internal use by Perl core components,
74 there is no C<use English> long name for this variable.
78 By default, running out of memory it is not trappable. However, if
79 compiled for this, Perl may use the contents of C<$^M> as an emergency
80 pool after die()ing with this message. Suppose that your Perl were
81 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
85 would allocate a 64K buffer for use when in emergency.
86 See the F<INSTALL> file for information on how to enable this option.
87 As a disincentive to casual use of this advanced feature,
88 there is no C<use English> long name for this variable.
92 =head2 New and Changed Built-in Functions
96 =item delete on slices
98 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
102 is now supported on more platforms, and prefers fcntl
103 to lockf when emulating.
105 =item printf and sprintf
107 now support "%i" as a synonym for "%d", and the "h" modifier.
108 So "%hi" means "short integer in decimal", and "%ho" means
109 "unsigned short integer as octal".
111 =item keys as an lvalue
113 As an lvalue, C<keys> allows you to increase the number of hash buckets
114 allocated for the given hash. This can gain you a measure of efficiency if
115 you know the hash is going to get big. (This is similar to pre-extending
116 an array by assigning a larger number to $#array.) If you say
120 then C<%hash> will have at least 200 buckets allocated for it. These
121 buckets will be retained even if you do C<%hash = ()>; use C<undef
122 %hash> if you want to free the storage while C<%hash> is still in scope.
123 You can't shrink the number of buckets allocated for the hash using
124 C<keys> in this way (but you needn't worry about doing this by accident,
125 as trying has no effect).
127 =item my() in Control Structures
129 You can now use my() (with or without the parentheses) in the control
130 expressions of control structures such as:
132 while (defined(my $line = <>)) {
138 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
140 } elsif ($answer =~ /^n(o)?$/i) {
144 die "`$answer' is neither `yes' nor `no'";
147 Also, you can declare a foreach loop control variable as lexical by
148 preceding it with the word "my". For example, in:
150 foreach my $i (1, 2, 3) {
154 $i is a lexical variable, and the scope of $i extends to the end of
155 the loop, but not beyond it.
157 Note that you still cannot use my() on global punctuation variables
158 such as $_ and the like.
160 =item unpack() and pack()
162 A new format 'w' represents a BER compressed integer (as defined in
163 ASN.1). Its format is a sequence of one or more bytes, each of which
164 provides seven bits of the total value, with the most significant
165 first. Bit eight of each byte is set, except for the last byte, in
166 which bit eight is clear.
170 If the first argument to C<use> is a number, it is treated as a version
171 number instead of a module name. If the version of the Perl interpreter
172 is less than VERSION, then an error message is printed and Perl exits
173 immediately. Because C<use> occurs at compile time, this check happens
174 immediately during the compilation process, unlike C<require VERSION>,
175 which waits until run-time for the check. This is often useful if you
176 need to check the current Perl version before C<use>ing library modules
177 which have changed in incompatible ways from older versions of Perl.
178 (We try not to do this more than we have to.)
180 =item use Module VERSION LIST
182 If the VERSION argument is present between Module and LIST, then the
183 C<use> will call the VERSION method in class Module with the given
184 version as an argument. The default VERSION method, inherited from
185 the Universal class, croaks if the given version is larger than the
186 value of the variable $Module::VERSION. (Note that there is not a
187 comma after VERSION!)
189 This version-checking mechanism is similar to the one currently used
190 in the Exporter module, but it is faster and can be used with modules
191 that don't use the Exporter. It is the recommended method for new
194 =item prototype(FUNCTION)
196 Returns the prototype of a function as a string (or C<undef> if the
197 function has no prototype). FUNCTION is a reference to or the name of the
198 function whose prototype you want to retrieve.
199 (Not actually new; just never documented before.)
203 Functions documented in the Camel to default to $_ now in
204 fact do, and all those that do are so documented in L<perlfunc>.
206 =item C<m//g> does not trigger a pos() reset on failure
208 The C<m//g> match iteration construct used to reset the iteration
209 when it failed to match (so that the next C<m//g> match would start at
210 the beginning of the string). You now have to explicitly do a
211 C<pos $str = 0;> to reset the "last match" position, or modify the
212 string in some way. This change makes it practical to chain C<m//g>
213 matches together in conjunction with ordinary matches using the C<\G>
214 zero-width assertion. See L<perlop> and L<perlre>.
216 =item nested C<sub{}> closures work now
218 Prior to the 5.004 release, nested anonymous functions
219 didn't work right. They do now.
221 =item formats work right on changing lexicals
223 Just like anonymous functions that contain lexical variables
224 that change (like a lexical index variable for a C<foreach> loop),
225 formats now work properly. For example, this silently failed
226 before, and is fine now:
229 foreach $i ( 1 .. 10 ) {
239 =head2 New Built-in Methods
241 The C<UNIVERSAL> package automatically contains the following methods that
242 are inherited by all other classes:
248 C<isa> returns I<true> if its object is blessed into a sub-class of C<CLASS>
250 C<isa> is also exportable and can be called as a sub with two arguments. This
251 allows the ability to check what a reference points to. Example:
253 use UNIVERSAL qw(isa);
255 if(isa($ref, 'ARRAY')) {
261 C<can> checks to see if its object has a method called C<METHOD>,
262 if it does then a reference to the sub is returned; if it does not then
263 I<undef> is returned.
265 =item VERSION( [NEED] )
267 C<VERSION> returns the version number of the class (package). If the
268 NEED argument is given then it will check that the current version (as
269 defined by the $VERSION variable in the given package) not less than
270 NEED; it will die if this is not the case. This method is normally
271 called as a class method. This method is called automatically by the
272 C<VERSION> form of C<use>.
274 use A 1.2 qw(some imported subs);
280 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
281 C<isa> uses a very similar method and caching strategy. This may cause
282 strange effects if the Perl code dynamically changes @ISA in any package.
284 You may add other methods to the UNIVERSAL class via Perl or XS code.
285 You do not need to C<use UNIVERSAL> in order to make these methods
286 available to your program. This is necessary only if you wish to
287 have C<isa> available as a plain subroutine in the current package.
289 =head2 TIEHANDLE Now Supported
291 See L<perltie> for other kinds of tie()s.
295 =item TIEHANDLE classname, LIST
297 This is the constructor for the class. That means it is expected to
298 return an object of some sort. The reference can be used to
299 hold some internal information.
304 return bless \$i, shift;
307 =item PRINT this, LIST
309 This method will be triggered every time the tied handle is printed to.
310 Beyond its self reference it also expects the list that was passed to
316 return print join( $, => map {uc} @_), $\;
321 This method will be called when the handle is read from. The method
322 should return undef when there is no more data.
326 return "PRINT called $$r times\n";
331 As with the other types of ties, this method will be called when the
332 tied handle is about to be destroyed. This is useful for debugging and
333 possibly for cleaning up.
341 =head2 Malloc Enhancements
343 If perl's malloc() is used, you can print memory statistics at runtime
344 by running Perl thusly:
346 env PERL_DEBUG_MSTATS=2 perl your_script_here
348 The value of 2 means to print statistics after compilation and on
349 exit; with a value of 1, the statistics ares printed only on exit.
350 (If you want the statistics at an arbitrary time, you'll need to
351 install the optional module Devel::Peek.)
353 In addition, three new compilation flags are recognized by malloc.c.
354 (They have no effect if perl is compiled with system malloc().)
358 =item -DEMERGENCY_SBRK
360 If this macro is defined, running out of memory need not be a fatal
361 error: a memory pool can allocated by assigning to the special
362 variable C<$^M>. See L<"$^M">.
366 Perl memory allocation is by bucket with sizes close to powers of two.
367 Because of these malloc overhead may be big, especially for data of
368 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
369 a slightly different algorithm for small allocations (up to 64 bytes
370 long), which makes it possible to have overhead down to 1 byte for
371 allocations which are powers of two (and appear quite often).
373 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
374 about 20% for typical Perl usage. Expected slowdown due to additional
375 malloc overhead is in fractions of a percent (hard to measure, because
376 of the effect of saved memory on speed).
378 =item -DTWO_POT_OPTIMIZE
380 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
381 with size close to a power of two; but this works for big allocations
382 (starting with 16K by default). Such allocations are typical for big
383 hashes and special-purpose scripts, especially image processing.
385 On recent systems, the fact that perl requires 2M from system for 1M
386 allocation will not affect speed of execution, since the tail of such
387 a chunk is not going to be touched (and thus will not require real
388 memory). However, it may result in a premature out-of-memory error.
389 So if you will be manipulating very large blocks with sizes close to
390 powers of two, it would be wise to define this macro.
392 Expected saving of memory is 0-100% (100% in applications which
393 require most memory in such 2**n chunks); expected slowdown is
398 =head2 Miscellaneous Efficiency Enhancements
400 Functions that have an empty prototype and that do nothing but return
401 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
403 Each unique hash key is only allocated once, no matter how many hashes
404 have an entry with that key. So even if you have 100 copies of the
405 same hash, the hash keys never have to be re-allocated.
409 Four new pragmatic modules exist:
417 Looks for MakeMaker-like I<'blib'> directory structure starting in
418 I<dir> (or current directory) and working back up to five levels of
421 Intended for use on command line with B<-M> option as a way of testing
422 arbitrary scripts against an uninstalled version of a package.
426 Tells the compiler to enable (or disable) the use of POSIX locales for
429 When C<use locale> is in effect, the current LC_CTYPE locale is used
430 for regular expressions and case mapping; LC_COLLATE for string
431 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
432 (but B<not> in print). LC_NUMERIC is always used in write, since
433 lexical scoping of formats is problematic at best.
435 Each C<use locale> or C<no locale> affects statements to the end of
436 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
437 current file. Locales can be switched and queried with
440 See L<perllocale> for more information.
444 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
448 Enable VMS-specific language features. Currently, there are three
449 VMS-specific features available: 'status', which makes C<$?> and
450 C<system> return genuine VMS status values instead of emulating POSIX;
451 'exit', which makes C<exit> take a genuine VMS status value instead of
452 assuming that C<exit 1> is an error; and 'time', which makes all times
453 relative to the local time zone, in the VMS tradition.
459 =head2 Installation Directories
461 The I<installperl> script now places the Perl source files for
462 extensions in the architecture-specific library directory, which is
463 where the shared libraries for extensions have always been. This
464 change is intended to allow administrators to keep the Perl 5.004
465 library directory unchanged from a previous version, without running
466 the risk of binary incompatibility between extensions' Perl source and
471 New constants in the existing Fcntl modules are now supported,
472 provided that your operating system happens to support them:
475 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
478 These constants are intended for use with the Perl operators sysopen()
479 and fcntl() and the basic database modules like SDBM_File. For the
480 exact meaning of these and other Fcntl constants please refer to your
481 operating system's documentation for fcntl() and open().
483 In addition, the Fcntl module now provides these constants for use
484 with the Perl operator flock():
486 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
488 These constants are defined in all environments (because where there is
489 no flock() system call, Perl emulates it). However, for historical
490 reasons, these constants are not exported unless they are explicitly
491 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
493 =head2 Module Information Summary
495 Brand new modules, arranged by topic rather than strictly
498 CPAN interface to Comprehensive Perl Archive Network
499 CPAN::FirstTime create a CPAN configuration file
500 CPAN::Nox run CPAN while avoiding compiled extensions
502 IO.pm Top-level interface to IO::* classes
503 IO/File.pm IO::File extension Perl module
504 IO/Handle.pm IO::Handle extension Perl module
505 IO/Pipe.pm IO::Pipe extension Perl module
506 IO/Seekable.pm IO::Seekable extension Perl module
507 IO/Select.pm IO::Select extension Perl module
508 IO/Socket.pm IO::Socket extension Perl module
510 Opcode.pm Disable named opcodes when compiling Perl code
512 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
513 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
515 FindBin.pm Find path of currently executing program
517 Class/Template.pm Structure/member template builder
518 File/stat.pm Object-oriented wrapper around CORE::stat
519 Net/hostent.pm Object-oriented wrapper around CORE::gethost*
520 Net/netent.pm Object-oriented wrapper around CORE::getnet*
521 Net/protoent.pm Object-oriented wrapper around CORE::getproto*
522 Net/servent.pm Object-oriented wrapper around CORE::getserv*
523 Time/gmtime.pm Object-oriented wrapper around CORE::gmtime
524 Time/localtime.pm Object-oriented wrapper around CORE::localtime
525 Time/tm.pm Perl implementation of "struct tm" for {gm,local}time
526 User/grent.pm Object-oriented wrapper around CORE::getgr*
527 User/pwent.pm Object-oriented wrapper around CORE::getpw*
529 Tie/RefHash.pm Base class for tied hashes with references as keys
531 UNIVERSAL.pm Base class for *ALL* classes
535 The IO module provides a simple mechanism to load all of the IO modules at one
536 go. Currently this includes:
544 For more information on any of these modules, please see its
545 respective documentation.
549 The Math::Complex module has been totally rewritten, and now supports
550 more operations. These are overloaded:
552 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
554 And these functions are now exported:
558 tan cotan asin acos atan acotan
559 sinh cosh tanh cotanh asinh acosh atanh acotanh
564 There have been quite a few changes made to DB_File. Here are a few of
571 Fixed a handful of bugs.
575 By public demand, added support for the standard hash function exists().
579 Made it compatible with Berkeley DB 1.86.
583 Made negative subscripts work with RECNO interface.
587 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
588 mode from 0640 to 0666.
592 Made DB_File automatically import the open() constants (O_RDWR,
593 O_CREAT etc.) from Fcntl, if available.
597 Updated documentation.
601 Refer to the HISTORY section in DB_File.pm for a complete list of
602 changes. Everything after DB_File 1.01 has been added since 5.003.
606 Major rewrite - support added for both udp echo and real icmp pings.
608 =head2 Overridden Built-ins
610 Many of the Perl built-ins returning lists now have
611 object-oriented overrides. These are:
623 For example, you can now say
627 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
629 =head1 Utility Changes
635 =item C<void> XSUBs now default to returning nothing
637 Due to a documentation/implementation bug in previous versions of
638 Perl, XSUBs with a return type of C<void> have actually been
639 returning one value. Usually that value was the GV for the XSUB,
640 but sometimes it was some already freed or reused value, which would
641 sometimes lead to program failure.
643 In Perl 5.004, if an XSUB is declared as returning C<void>, it
644 actually returns no value, i.e. an empty list (though there is a
645 backward-compatibility exception; see below). If your XSUB really
646 does return an SV, you should give it a return type of C<SV *>.
648 For backward compatibility, I<xsubpp> tries to guess whether a
649 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
650 It does so by examining the text of the XSUB: if I<xsubpp> finds
651 what looks like an assignment to C<ST(0)>, it assumes that the
652 XSUB's return type is really C<SV *>.
656 =head1 C Language API Changes
660 =item C<gv_fetchmethod> and C<perl_call_sv>
662 The C<gv_fetchmethod> function finds a method for an object, just like
663 in Perl 5.003. The GV it returns may be a method cache entry.
664 However, in Perl 5.004, method cache entries are not visible to users;
665 therefore, they can no longer be passed directly to C<perl_call_sv>.
666 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
667 and pass the CV to C<perl_call_sv>.
669 The most likely symptom of passing the result of C<gv_fetchmethod> to
670 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
671 error on the I<second> call to a given method (since there is no cache
674 =item Extended API for manipulating hashes
676 Internal handling of hash keys has changed. The old hashtable API
677 is still fully supported, and will likely remain that way. The additions
678 to the API allow passing keys as C<SV*>s, so that C<tied> hashes can be
679 given real scalars as keys rather than plain strings (non-tied hashes still
680 can only use strings as keys). All new extensions must use the new
681 hash access functions and macros if they wish to use C<SV*> keys. These
682 additions also make it feasible to manipulate whole C<HE*>s (hash entries),
683 allowing for more efficient handling of hash data. See L<perlguts> for
688 =head1 Documentation Changes
690 Many of the base and library pods were updated. These
691 new pods are included in section 1:
697 A "howto" on reporting perl bugs.
705 Locale support (internationalization and localization).
709 Tutorial on Perl OO programming.
713 Perl internal IO abstraction interface.
717 Although not new, this has been massively updated.
721 Although not new, this has been massively updated.
725 =head1 New Diagnostics
727 Several new conditions will trigger warnings that were
728 silent before. Some only affect certain platforms.
729 The following new warnings and errors outline these.
730 These messages are classified as follows (listed in
731 increasing order of desperation):
733 (W) A warning (optional).
734 (D) A deprecation (optional).
735 (S) A severe warning (mandatory).
736 (F) A fatal error (trappable).
737 (P) An internal error you should never see (trappable).
738 (X) A very fatal error (non-trappable).
739 (A) An alien error message (not generated by Perl).
743 =item "my" variable %s masks earlier declaration in same scope
745 (S) A lexical variable has been redeclared in the same scope, effectively
746 eliminating all access to the previous instance. This is almost always
747 a typographical error. Note that the earlier variable will still exist
748 until the end of the scope or until all closure referents to it are
751 =item %s argument is not a HASH element or slice
753 (F) The argument to delete() must be either a hash element, such as
756 $ref->[12]->{"susie"}
758 or a hash slice, such as
760 @foo{$bar, $baz, $xyzzy}
761 @{$ref->[12]}{"susie", "queue"}
763 =item Allocation too large: %lx
765 (X) You can't allocate more than 64K on an MSDOS machine.
767 =item Allocation too large
769 (F) You can't allocate more than 2^31+"small amount" bytes.
771 =item Attempt to free non-existent shared string
773 (P) Perl maintains a reference counted internal table of strings to
774 optimize the storage and access of hash keys and other strings. This
775 indicates someone tried to decrement the reference count of a string
776 that can no longer be found in the table.
778 =item Attempt to use reference as lvalue in substr
780 (W) You supplied a reference as the first argument to substr() used
781 as an lvalue, which is pretty strange. Perhaps you forgot to
782 dereference it first. See L<perlfunc/substr>.
784 =item Unsupported function fork
786 (F) Your version of executable does not support forking.
788 Note that under some systems, like OS/2, there may be different flavors of
789 Perl executables, some of which may support fork, some not. Try changing
790 the name you call Perl by to C<perl_>, C<perl__>, and so on.
792 =item Ill-formed logical name |%s| in prime_env_iter
794 (W) A warning peculiar to VMS. A logical name was encountered when preparing
795 to iterate over %ENV which violates the syntactic rules governing logical
796 names. Since it cannot be translated normally, it is skipped, and will not
797 appear in %ENV. This may be a benign occurrence, as some software packages
798 might directly modify logical name tables and introduce non-standard names,
799 or it may indicate that a logical name table has been corrupted.
801 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
803 (F) Only hard references are allowed by "strict refs". Symbolic references
804 are disallowed. See L<perlref>.
806 =item Constant subroutine %s redefined
808 (S) You redefined a subroutine which had previously been eligible for
809 inlining. See L<perlsub/"Constant Functions"> for commentary and
814 (F) You passed die() an empty string (the equivalent of C<die "">) or
815 you called it with no args and both C<$@> and C<$_> were empty.
817 =item Integer overflow in hex number
819 (S) The literal hex number you have specified is too big for your
820 architecture. On a 32-bit architecture the largest hex literal is
823 =item Integer overflow in octal number
825 (S) The literal octal number you have specified is too big for your
826 architecture. On a 32-bit architecture the largest octal literal is
829 =item Name "%s::%s" used only once: possible typo
831 (W) Typographical errors often show up as unique variable names.
832 If you had a good reason for having a unique name, then just mention
833 it again somehow to suppress the message (the C<use vars> pragma is
834 provided for just this purpose).
836 =item Null picture in formline
838 (F) The first argument to formline must be a valid format picture
839 specification. It was found to be empty, which probably means you
840 supplied it an uninitialized value. See L<perlform>.
842 =item Offset outside string
844 (F) You tried to do a read/write/send/recv operation with an offset
845 pointing outside the buffer. This is difficult to imagine.
846 The sole exception to this is that C<sysread()>ing past the buffer
847 will extend the buffer and zero pad the new area.
849 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
851 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
852 Stubs should never be implicitely created, but explicit calls to C<can>
855 =item Cannot resolve method `%s' overloading `%s' in package `s'
857 (P) Internal error trying to resolve overloading specified by a method
858 name (as opposed to a subroutine reference).
862 (X|F) The malloc() function returned 0, indicating there was insufficient
863 remaining memory (or virtual memory) to satisfy the request.
865 The request was judged to be small, so the possibility to trap it
866 depends on the way Perl was compiled. By default it is not trappable.
867 However, if compiled for this, Perl may use the contents of C<$^M> as
868 an emergency pool after die()ing with this message. In this case the
869 error is trappable I<once>.
871 =item Out of memory during request for %s
873 (F) The malloc() function returned 0, indicating there was insufficient
874 remaining memory (or virtual memory) to satisfy the request. However,
875 the request was judged large enough (compile-time default is 64K), so
876 a possibility to shut down by trapping this error is granted.
878 =item Possible attempt to put comments in qw() list
880 (W) qw() lists contain items separated by whitespace; as with literal
881 strings, comment characters are not ignored, but are instead treated
882 as literal data. (You may have used different delimiters than the
883 exclamation marks parentheses shown here; braces are also frequently
886 You probably wrote something like this:
893 when you should have written this:
900 If you really want comments, build your list the
901 old-fashioned way, with quotes and commas:
905 'b', # another comment
908 =item Possible attempt to separate words with commas
910 (W) qw() lists contain items separated by whitespace; therefore commas
911 aren't needed to separate the items. (You may have used different
912 delimiters than the parentheses shown here; braces are also frequently
915 You probably wrote something like this:
919 which puts literal commas into some of the list items. Write it without
920 commas if you don't want them to appear in your data:
924 =item Scalar value @%s{%s} better written as $%s{%s}
926 (W) You've used a hash slice (indicated by @) to select a single element of
927 a hash. Generally it's better to ask for a scalar value (indicated by $).
928 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
929 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
930 like a list when you assign to it, and provides a list context to its
931 subscript, which can do weird things if you're expecting only one subscript.
933 =item untie attempted while %d inner references still exist
935 (W) A copy of the object returned from C<tie> (or C<tied>) was still
936 valid when C<untie> was called.
938 =item Value of %s construct can be "0"; test with defined()
940 (W) In a conditional expression, you used <HANDLE>, <*> (glob), or
941 C<readdir> as a boolean value. Each of these constructs can return a
942 value of "0"; that would make the conditional expression false, which
943 is probably not what you intended. When using these constructs in
944 conditional expressions, test their values with the C<defined> operator.
946 =item Variable "%s" may be unavailable
948 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
949 subroutine, and outside that is another subroutine; and the anonymous
950 (innermost) subroutine is referencing a lexical variable defined in
951 the outermost subroutine. For example:
953 sub outermost { my $a; sub middle { sub { $a } } }
955 If the anonymous subroutine is called or referenced (directly or
956 indirectly) from the outermost subroutine, it will share the variable
957 as you would expect. But if the anonymous subroutine is called or
958 referenced when the outermost subroutine is not active, it will see
959 the value of the shared variable as it was before and during the
960 *first* call to the outermost subroutine, which is probably not what
963 In these circumstances, it is usually best to make the middle
964 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
965 support for shared variables in nested anonymous subroutines; a named
966 subroutine in between interferes with this feature.
968 =item Variable "%s" will not stay shared
970 (W) An inner (nested) I<named> subroutine is referencing a lexical
971 variable defined in an outer subroutine.
973 When the inner subroutine is called, it will probably see the value of
974 the outer subroutine's variable as it was before and during the
975 *first* call to the outer subroutine; in this case, after the first
976 call to the outer subroutine is complete, the inner and outer
977 subroutines will no longer share a common value for the variable. In
978 other words, the variable will no longer be shared.
980 Furthermore, if the outer subroutine is anonymous and references a
981 lexical variable outside itself, then the outer and inner subroutines
982 will I<never> share the given variable.
984 This problem can usually be solved by making the inner subroutine
985 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
986 reference variables in outer subroutines are called or referenced,
987 they are automatically re-bound to the current values of such
990 =item Warning: something's wrong
992 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
993 you called it with no args and C<$_> was empty.
995 =item Got an error from DosAllocMem
997 (P) An error peculiar to OS/2. Most probably you're using an obsolete
998 version of Perl, and this should not happen anyway.
1000 =item Malformed PERLLIB_PREFIX
1002 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1010 with non-empty prefix1 and prefix2. If C<prefix1> is indeed a prefix of
1011 a builtin library search path, prefix2 is substituted. The error may appear
1012 if components are not found, or are too long. See L<perlos2/"PERLLIB_PREFIX">.
1014 =item PERL_SH_DIR too long
1016 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1017 C<sh>-shell in. See L<perlos2/"PERL_SH_DIR">.
1019 =item Process terminated by SIG%s
1021 (W) This is a standard message issued by OS/2 applications, while *nix
1022 applications die in silence. It is considered a feature of the OS/2
1023 port. One can easily disable this by appropriate sighandlers, see
1024 L<perlipc/"Signals">. See L<perlos2/"Process terminated by SIGTERM/SIGINT">.
1030 If you find what you think is a bug, you might check the headers of
1031 recently posted articles in the comp.lang.perl.misc newsgroup.
1032 There may also be information at http://www.perl.com/perl/, the Perl
1035 If you believe you have an unreported bug, please run the B<perlbug>
1036 program included with your release. Make sure you trim your bug
1037 down to a tiny but sufficient test case. Your bug report, along
1038 with the output of C<perl -V>, will be sent off to perlbug@perl.com
1039 to be analysed by the Perl porting team.
1043 The F<Changes> file for exhaustive details on what changed.
1045 The F<INSTALL> file for how to build Perl. This file has been
1046 significantly updated for 5.004, so even veteran users should
1049 The F<README> file for general stuff.
1051 The F<Copying> file for copyright information.
1055 Constructed by Tom Christiansen, grabbing material with permission
1056 from innumerable contributors, with kibitzing by more than a few Perl
1059 Last update: Tue Jan 14 14:03:02 EST 1997