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 $PERL5OPT environment variable
32 You may now put Perl options in the $PERL5OPT environment variable.
33 Unless Perl is running with taint checks, it will interpret this
34 variable as if its contents had appeared on a "#!perl" line at the
35 beginning of your script, except that hyphens are optional. PERL5OPT
36 may only be used to set the following switches: B<-[DIMUdmw]>.
38 =head2 More precise warnings
40 If you removed the B<-w> option from your Perl 5.003 scripts because it
41 made Perl too verbose, we recommend that you try putting it back when
42 you upgrade to Perl 5.004. Each new perl version tends to remove some
43 undesirable warnings, while adding new warnings that may catch bugs in
46 =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods
48 Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods
49 (using the C<@ISA> hierarchy), even when the function to be autoloaded
50 was called as a plain function (e.g. C<Foo::bar()>), not a method
51 (e.g. C<Foo->bar()> or C<$obj->bar()>).
53 Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s.
54 However, there is a significant base of existing code that may be using
55 the old behavior. So, as an interim step, Perl 5.004 issues an optional
56 warning when a non-method uses an inherited C<AUTOLOAD>.
58 The simple rule is: Inheritance will not work when autoloading
59 non-methods. The simple fix for old code is: In any module that used to
60 depend on inheriting C<AUTOLOAD> for non-methods from a base class named
61 C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup.
63 =head2 Subroutine arguments created only when they're modified
65 In Perl 5.004, nonexistent array and hash elements used as subroutine
66 parameters are brought into existence only if they are actually
67 assigned to (via C<@_>).
69 Earlier versions of Perl vary in their handling of such arguments.
70 Perl versions 5.002 and 5.003 always brought them into existence.
71 Perl versions 5.000, 5.001, and 5.002 brought them into existence only
72 if they were not the first argument (which was almost certainly a
73 bug). Earlier versions of Perl never brought them into existence.
75 For example, given this code:
78 sub show { print $_[0] };
79 sub change { $_[0]++ };
83 After this code executes in Perl 5.004, $a{b} exists but $a[2] does
84 not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed
85 (but $a[2]'s value would have been undefined).
87 =head2 Fixed parsing of $$<digit>, &$<digit>, etc.
89 A bug in previous versions of Perl 5.0 prevented proper parsing of
90 numeric special variables as symbolic references. That bug has been
91 fixed. As a result, the string "$$0" is no longer equivalent to
92 C<$$."0">, but rather to C<${$0}>. To get the old behavior, change
93 "$$" followed by a digit to "${$}".
95 =head2 No resetting of $. on implicit close
97 The documentation for Perl 5.0 has always stated that C<$.> is I<not>
98 reset when an already-open file handle is reopened with no intervening
99 call to C<close>. Due to a bug, perl versions 5.000 through 5.003
100 I<did> reset C<$.> under that circumstance; Perl 5.004 does not.
102 =head2 C<wantarray> may return undef
104 The C<wantarray> operator returns true if a subroutine is expected to
105 return a list, and false otherwise. In Perl 5.004, C<wantarray> can
106 also return the undefined value if a subroutine's return value will
107 not be used at all, which allows subroutines to avoid a time-consuming
108 calculation of a return value if it isn't going to be used.
110 =head2 Changes to tainting checks
112 A bug in previous versions may have failed to detect some insecure
113 conditions when taint checks are turned on. (Taint checks are used
114 in setuid or setgid scripts, or when explicitly turned on with the
115 C<-T> invocation option.) Although it's unlikely, this may cause a
116 previously-working script to now fail -- which should be construed
117 as a blessing, since that indicates a potentially-serious security
118 hole was just plugged.
120 =head2 New Opcode module and revised Safe module
122 A new Opcode module supports the creation, manipulation and
123 application of opcode masks. The revised Safe module has a new API
124 and is implemented using the new Opcode module. Please read the new
125 Opcode and Safe documentation.
127 =head2 Embedding improvements
129 In older versions of Perl it was not possible to create more than one
130 Perl interpreter instance inside a single process without leaking like a
131 sieve and/or crashing. The bugs that caused this behavior have all been
132 fixed. However, you still must take care when embedding Perl in a C
133 program. See the updated perlembed manpage for tips on how to manage
136 =head2 Internal change: FileHandle class based on IO::* classes
138 File handles are now stored internally as type IO::Handle. The
139 FileHandle module is still supported for backwards compatibility, but
140 it is now merely a front end to the IO::* modules -- specifically,
141 IO::Handle, IO::Seekable, and IO::File. We suggest, but do not
142 require, that you use the IO::* modules in new code.
144 In harmony with this change, C<*GLOB{FILEHANDLE}> is now a
145 backward-compatible synonym for C<*STDOUT{IO}>.
147 =head2 Internal change: PerlIO abstraction interface
149 It is now possible to build Perl with AT&T's sfio IO package
150 instead of stdio. See L<perlapio> for more details, and
151 the F<INSTALL> file for how to use it.
153 =head2 New and changed builtin variables
159 Extended error message on some platforms. (Also known as
160 $EXTENDED_OS_ERROR if you C<use English>).
164 The current set of syntax checks enabled by C<use strict>. See the
165 documentation of C<strict> for more details. Not actually new, but
167 Because it is intended for internal use by Perl core components,
168 there is no C<use English> long name for this variable.
172 By default, running out of memory it is not trappable. However, if
173 compiled for this, Perl may use the contents of C<$^M> as an emergency
174 pool after die()ing with this message. Suppose that your Perl were
175 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
179 would allocate a 64K buffer for use when in emergency.
180 See the F<INSTALL> file for information on how to enable this option.
181 As a disincentive to casual use of this advanced feature,
182 there is no C<use English> long name for this variable.
186 =head2 New and changed builtin functions
190 =item delete on slices
192 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
196 is now supported on more platforms, prefers fcntl to lockf when
197 emulating, and always flushes before (un)locking.
199 =item printf and sprintf
201 now support "%i" as a synonym for "%d", and the "h" modifier.
202 So "%hi" means "short integer in decimal", and "%ho" means
203 "unsigned short integer as octal".
205 =item keys as an lvalue
207 As an lvalue, C<keys> allows you to increase the number of hash buckets
208 allocated for the given hash. This can gain you a measure of efficiency if
209 you know the hash is going to get big. (This is similar to pre-extending
210 an array by assigning a larger number to $#array.) If you say
214 then C<%hash> will have at least 200 buckets allocated for it. These
215 buckets will be retained even if you do C<%hash = ()>; use C<undef
216 %hash> if you want to free the storage while C<%hash> is still in scope.
217 You can't shrink the number of buckets allocated for the hash using
218 C<keys> in this way (but you needn't worry about doing this by accident,
219 as trying has no effect).
221 =item my() in Control Structures
223 You can now use my() (with or without the parentheses) in the control
224 expressions of control structures such as:
226 while (defined(my $line = <>)) {
232 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
234 } elsif ($answer =~ /^n(o)?$/i) {
238 die "`$answer' is neither `yes' nor `no'";
241 Also, you can declare a foreach loop control variable as lexical by
242 preceding it with the word "my". For example, in:
244 foreach my $i (1, 2, 3) {
248 $i is a lexical variable, and the scope of $i extends to the end of
249 the loop, but not beyond it.
251 Note that you still cannot use my() on global punctuation variables
252 such as $_ and the like.
254 =item unpack() and pack()
256 A new format 'w' represents a BER compressed integer (as defined in
257 ASN.1). Its format is a sequence of one or more bytes, each of which
258 provides seven bits of the total value, with the most significant
259 first. Bit eight of each byte is set, except for the last byte, in
260 which bit eight is clear.
264 If the first argument to C<use> is a number, it is treated as a version
265 number instead of a module name. If the version of the Perl interpreter
266 is less than VERSION, then an error message is printed and Perl exits
267 immediately. Because C<use> occurs at compile time, this check happens
268 immediately during the compilation process, unlike C<require VERSION>,
269 which waits until runtime for the check. This is often useful if you
270 need to check the current Perl version before C<use>ing library modules
271 which have changed in incompatible ways from older versions of Perl.
272 (We try not to do this more than we have to.)
274 =item use Module VERSION LIST
276 If the VERSION argument is present between Module and LIST, then the
277 C<use> will call the VERSION method in class Module with the given
278 version as an argument. The default VERSION method, inherited from
279 the UNIVERSAL class, croaks if the given version is larger than the
280 value of the variable $Module::VERSION. (Note that there is not a
281 comma after VERSION!)
283 This version-checking mechanism is similar to the one currently used
284 in the Exporter module, but it is faster and can be used with modules
285 that don't use the Exporter. It is the recommended method for new
288 =item prototype(FUNCTION)
290 Returns the prototype of a function as a string (or C<undef> if the
291 function has no prototype). FUNCTION is a reference to or the name of the
292 function whose prototype you want to retrieve.
293 (Not actually new; just never documented before.)
297 The default seed for C<srand>, which used to be C<time>, has been changed.
298 Now it's a heady mix of difficult-to-predict system-dependent values,
299 which should be sufficient for most everyday purposes.
301 Previous to version 5.004, calling C<rand> without first calling C<srand>
302 would yield the same sequence of random numbers on most or all machines.
303 Now, when perl sees that you're calling C<rand> and haven't yet called
304 C<srand>, it calls C<srand> with the default seed. You should still call
305 C<srand> manually if your code might ever be run on a pre-5.004 system,
306 of course, or if you want a seed other than the default.
310 Functions documented in the Camel to default to $_ now in
311 fact do, and all those that do are so documented in L<perlfunc>.
313 =item C<m//g> does not trigger a pos() reset on failure
315 The C<m//g> match iteration construct used to reset the iteration
316 when it failed to match (so that the next C<m//g> match would start at
317 the beginning of the string). You now have to explicitly do a
318 C<pos $str = 0;> to reset the "last match" position, or modify the
319 string in some way. This change makes it practical to chain C<m//g>
320 matches together in conjunction with ordinary matches using the C<\G>
321 zero-width assertion. See L<perlop> and L<perlre>.
323 =item C<m//x> ignores whitespace before ?*+{}
325 The C<m//x> construct has always been intended to ignore all unescaped
326 whitespace. However, before Perl 5.004, whitespace had the effect of
327 escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was
328 (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004.
330 =item nested C<sub{}> closures work now
332 Prior to the 5.004 release, nested anonymous functions didn't work
335 =item formats work right on changing lexicals
337 Just like anonymous functions that contain lexical variables
338 that change (like a lexical index variable for a C<foreach> loop),
339 formats now work properly. For example, this silently failed
340 before, and is fine now:
343 foreach $i ( 1 .. 10 ) {
353 =head2 New builtin methods
355 The C<UNIVERSAL> package automatically contains the following methods that
356 are inherited by all other classes:
362 C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
364 C<isa> is also exportable and can be called as a sub with two arguments. This
365 allows the ability to check what a reference points to. Example:
367 use UNIVERSAL qw(isa);
369 if(isa($ref, 'ARRAY')) {
375 C<can> checks to see if its object has a method called C<METHOD>,
376 if it does then a reference to the sub is returned; if it does not then
377 I<undef> is returned.
379 =item VERSION( [NEED] )
381 C<VERSION> returns the version number of the class (package). If the
382 NEED argument is given then it will check that the current version (as
383 defined by the $VERSION variable in the given package) not less than
384 NEED; it will die if this is not the case. This method is normally
385 called as a class method. This method is called automatically by the
386 C<VERSION> form of C<use>.
388 use A 1.2 qw(some imported subs);
394 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
395 C<isa> uses a very similar method and caching strategy. This may cause
396 strange effects if the Perl code dynamically changes @ISA in any package.
398 You may add other methods to the UNIVERSAL class via Perl or XS code.
399 You do not need to C<use UNIVERSAL> in order to make these methods
400 available to your program. This is necessary only if you wish to
401 have C<isa> available as a plain subroutine in the current package.
403 =head2 TIEHANDLE now supported
405 See L<perltie> for other kinds of tie()s.
409 =item TIEHANDLE classname, LIST
411 This is the constructor for the class. That means it is expected to
412 return an object of some sort. The reference can be used to
413 hold some internal information.
418 return bless \$i, shift;
421 =item PRINT this, LIST
423 This method will be triggered every time the tied handle is printed to.
424 Beyond its self reference it also expects the list that was passed to
430 return print join( $, => map {uc} @_), $\;
435 This method will be called when the handle is read from via the C<read>
436 or C<sysread> functions.
440 my($buf,$len,$offset) = @_;
441 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
446 This method will be called when the handle is read from. The method
447 should return undef when there is no more data.
451 return "PRINT called $$r times\n"
456 This method will be called when the C<getc> function is called.
458 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
462 As with the other types of ties, this method will be called when the
463 tied handle is about to be destroyed. This is useful for debugging and
464 possibly for cleaning up.
472 =head2 Malloc enhancements
474 Four new compilation flags are recognized by malloc.c. (They have no
475 effect if perl is compiled with system malloc().)
479 =item -DDEBUGGING_MSTATS
481 If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print
482 memory statistics at runtime by running Perl thusly:
484 env PERL_DEBUG_MSTATS=2 perl your_script_here
486 The value of 2 means to print statistics after compilation and on
487 exit; with a value of 1, the statistics ares printed only on exit.
488 (If you want the statistics at an arbitrary time, you'll need to
489 install the optional module Devel::Peek.)
491 =item -DEMERGENCY_SBRK
493 If this macro is defined, running out of memory need not be a fatal
494 error: a memory pool can allocated by assigning to the special
495 variable C<$^M>. See L<"$^M">.
499 Perl memory allocation is by bucket with sizes close to powers of two.
500 Because of these malloc overhead may be big, especially for data of
501 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
502 a slightly different algorithm for small allocations (up to 64 bytes
503 long), which makes it possible to have overhead down to 1 byte for
504 allocations which are powers of two (and appear quite often).
506 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
507 about 20% for typical Perl usage. Expected slowdown due to additional
508 malloc overhead is in fractions of a percent (hard to measure, because
509 of the effect of saved memory on speed).
511 =item -DTWO_POT_OPTIMIZE
513 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
514 with size close to a power of two; but this works for big allocations
515 (starting with 16K by default). Such allocations are typical for big
516 hashes and special-purpose scripts, especially image processing.
518 On recent systems, the fact that perl requires 2M from system for 1M
519 allocation will not affect speed of execution, since the tail of such
520 a chunk is not going to be touched (and thus will not require real
521 memory). However, it may result in a premature out-of-memory error.
522 So if you will be manipulating very large blocks with sizes close to
523 powers of two, it would be wise to define this macro.
525 Expected saving of memory is 0-100% (100% in applications which
526 require most memory in such 2**n chunks); expected slowdown is
531 =head2 Miscellaneous efficiency enhancements
533 Functions that have an empty prototype and that do nothing but return
534 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
536 Each unique hash key is only allocated once, no matter how many hashes
537 have an entry with that key. So even if you have 100 copies of the
538 same hash, the hash keys never have to be reallocated.
542 Six new pragmatic modules exist:
546 =item use autouse MODULE => qw(sub1 sub2 sub3)
548 Defers C<require MODULE> until someone calls one of the specified
549 subroutines (which must be exported by MODULE). This pragma should be
550 used with caution, and only when necessary.
556 Looks for MakeMaker-like I<'blib'> directory structure starting in
557 I<dir> (or current directory) and working back up to five levels of
560 Intended for use on command line with B<-M> option as a way of testing
561 arbitrary scripts against an uninstalled version of a package.
563 =item use constant NAME => VALUE
565 Provides a convenient interface for creating compile-time constants,
566 See L<perlsub/"Constant Functions">.
570 Tells the compiler to enable (or disable) the use of POSIX locales for
573 When C<use locale> is in effect, the current LC_CTYPE locale is used
574 for regular expressions and case mapping; LC_COLLATE for string
575 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
576 (but B<not> in print). LC_NUMERIC is always used in write, since
577 lexical scoping of formats is problematic at best.
579 Each C<use locale> or C<no locale> affects statements to the end of
580 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
581 current file. Locales can be switched and queried with
584 See L<perllocale> for more information.
588 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
592 Enable VMS-specific language features. Currently, there are three
593 VMS-specific features available: 'status', which makes C<$?> and
594 C<system> return genuine VMS status values instead of emulating POSIX;
595 'exit', which makes C<exit> take a genuine VMS status value instead of
596 assuming that C<exit 1> is an error; and 'time', which makes all times
597 relative to the local time zone, in the VMS tradition.
603 =head2 Installation directories
605 The I<installperl> script now places the Perl source files for
606 extensions in the architecture-specific library directory, which is
607 where the shared libraries for extensions have always been. This
608 change is intended to allow administrators to keep the Perl 5.004
609 library directory unchanged from a previous version, without running
610 the risk of binary incompatibility between extensions' Perl source and
613 =head2 Module information summary
615 Brand new modules, arranged by topic rather than strictly
618 CPAN interface to Comprehensive Perl Archive Network
619 CPAN::FirstTime create a CPAN configuration file
620 CPAN::Nox run CPAN while avoiding compiled extensions
622 IO.pm Top-level interface to IO::* classes
623 IO/File.pm IO::File extension Perl module
624 IO/Handle.pm IO::Handle extension Perl module
625 IO/Pipe.pm IO::Pipe extension Perl module
626 IO/Seekable.pm IO::Seekable extension Perl module
627 IO/Select.pm IO::Select extension Perl module
628 IO/Socket.pm IO::Socket extension Perl module
630 Opcode.pm Disable named opcodes when compiling Perl code
632 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
633 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
635 FindBin.pm Find path of currently executing program
637 Class/Template.pm Structure/member template builder
638 File/stat.pm Object-oriented wrapper around CORE::stat
639 Net/hostent.pm Object-oriented wrapper around CORE::gethost*
640 Net/netent.pm Object-oriented wrapper around CORE::getnet*
641 Net/protoent.pm Object-oriented wrapper around CORE::getproto*
642 Net/servent.pm Object-oriented wrapper around CORE::getserv*
643 Time/gmtime.pm Object-oriented wrapper around CORE::gmtime
644 Time/localtime.pm Object-oriented wrapper around CORE::localtime
645 Time/tm.pm Perl implementation of "struct tm" for {gm,local}time
646 User/grent.pm Object-oriented wrapper around CORE::getgr*
647 User/pwent.pm Object-oriented wrapper around CORE::getpw*
649 Tie/RefHash.pm Base class for tied hashes with references as keys
651 UNIVERSAL.pm Base class for *ALL* classes
655 New constants in the existing Fcntl modules are now supported,
656 provided that your operating system happens to support them:
659 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
662 These constants are intended for use with the Perl operators sysopen()
663 and fcntl() and the basic database modules like SDBM_File. For the
664 exact meaning of these and other Fcntl constants please refer to your
665 operating system's documentation for fcntl() and open().
667 In addition, the Fcntl module now provides these constants for use
668 with the Perl operator flock():
670 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
672 These constants are defined in all environments (because where there is
673 no flock() system call, Perl emulates it). However, for historical
674 reasons, these constants are not exported unless they are explicitly
675 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
679 The IO module provides a simple mechanism to load all of the IO modules at one
680 go. Currently this includes:
688 For more information on any of these modules, please see its
689 respective documentation.
693 The Math::Complex module has been totally rewritten, and now supports
694 more operations. These are overloaded:
696 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
698 And these functions are now exported:
702 tan cotan asin acos atan acotan
703 sinh cosh tanh cotanh asinh acosh atanh acotanh
708 This module provides a simpler interface to parts of Math::Complex for
709 those who need trigonometric functions only for real numbers.
713 There have been quite a few changes made to DB_File. Here are a few of
720 Fixed a handful of bugs.
724 By public demand, added support for the standard hash function exists().
728 Made it compatible with Berkeley DB 1.86.
732 Made negative subscripts work with RECNO interface.
736 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
737 mode from 0640 to 0666.
741 Made DB_File automatically import the open() constants (O_RDWR,
742 O_CREAT etc.) from Fcntl, if available.
746 Updated documentation.
750 Refer to the HISTORY section in DB_File.pm for a complete list of
751 changes. Everything after DB_File 1.01 has been added since 5.003.
755 Major rewrite - support added for both udp echo and real icmp pings.
757 =head2 Object-oriented overrides for builtin operators
759 Many of the Perl builtins returning lists now have
760 object-oriented overrides. These are:
772 For example, you can now say
776 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
778 =head1 Utility Changes
784 =item C<void> XSUBs now default to returning nothing
786 Due to a documentation/implementation bug in previous versions of
787 Perl, XSUBs with a return type of C<void> have actually been
788 returning one value. Usually that value was the GV for the XSUB,
789 but sometimes it was some already freed or reused value, which would
790 sometimes lead to program failure.
792 In Perl 5.004, if an XSUB is declared as returning C<void>, it
793 actually returns no value, i.e. an empty list (though there is a
794 backward-compatibility exception; see below). If your XSUB really
795 does return an SV, you should give it a return type of C<SV *>.
797 For backward compatibility, I<xsubpp> tries to guess whether a
798 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
799 It does so by examining the text of the XSUB: if I<xsubpp> finds
800 what looks like an assignment to C<ST(0)>, it assumes that the
801 XSUB's return type is really C<SV *>.
805 =head1 C Language API Changes
809 =item C<gv_fetchmethod> and C<perl_call_sv>
811 The C<gv_fetchmethod> function finds a method for an object, just like
812 in Perl 5.003. The GV it returns may be a method cache entry.
813 However, in Perl 5.004, method cache entries are not visible to users;
814 therefore, they can no longer be passed directly to C<perl_call_sv>.
815 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
816 and pass the CV to C<perl_call_sv>.
818 The most likely symptom of passing the result of C<gv_fetchmethod> to
819 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
820 error on the I<second> call to a given method (since there is no cache
823 =item Extended API for manipulating hashes
825 Internal handling of hash keys has changed. The old hashtable API is
826 still fully supported, and will likely remain so. The additions to the
827 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
828 real scalars as keys rather than plain strings (nontied hashes still
829 can only use strings as keys). New extensions must use the new hash
830 access functions and macros if they wish to use C<SV*> keys. These
831 additions also make it feasible to manipulate C<HE*>s (hash entries),
832 which can be more efficient. See L<perlguts> for details.
836 =head1 Documentation Changes
838 Many of the base and library pods were updated. These
839 new pods are included in section 1:
849 Locale support (internationalization and localization).
853 Tutorial on Perl OO programming.
857 Perl internal IO abstraction interface.
861 Although not new, this has been massively updated.
865 Although not new, this has been massively updated.
869 =head1 New Diagnostics
871 Several new conditions will trigger warnings that were
872 silent before. Some only affect certain platforms.
873 The following new warnings and errors outline these.
874 These messages are classified as follows (listed in
875 increasing order of desperation):
877 (W) A warning (optional).
878 (D) A deprecation (optional).
879 (S) A severe warning (mandatory).
880 (F) A fatal error (trappable).
881 (P) An internal error you should never see (trappable).
882 (X) A very fatal error (nontrappable).
883 (A) An alien error message (not generated by Perl).
887 =item "my" variable %s masks earlier declaration in same scope
889 (S) A lexical variable has been redeclared in the same scope, effectively
890 eliminating all access to the previous instance. This is almost always
891 a typographical error. Note that the earlier variable will still exist
892 until the end of the scope or until all closure referents to it are
895 =item %s argument is not a HASH element or slice
897 (F) The argument to delete() must be either a hash element, such as
900 $ref->[12]->{"susie"}
902 or a hash slice, such as
904 @foo{$bar, $baz, $xyzzy}
905 @{$ref->[12]}{"susie", "queue"}
907 =item Allocation too large: %lx
909 (X) You can't allocate more than 64K on an MS-DOS machine.
911 =item Allocation too large
913 (F) You can't allocate more than 2^31+"small amount" bytes.
915 =item Applying %s to %s will act on scalar(%s)
917 (W) The pattern match (//), substitution (s///), and translation (tr///)
918 operators work on scalar values. If you apply one of them to an array
919 or a hash, it will convert the array or hash to a scalar value -- the
920 length of an array, or the population info of a hash -- and then work on
921 that scalar value. This is probably not what you meant to do. See
922 L<perlfunc/grep> and L<perlfunc/map> for alternatives.
924 =item Attempt to free nonexistent shared string
926 (P) Perl maintains a reference counted internal table of strings to
927 optimize the storage and access of hash keys and other strings. This
928 indicates someone tried to decrement the reference count of a string
929 that can no longer be found in the table.
931 =item Attempt to use reference as lvalue in substr
933 (W) You supplied a reference as the first argument to substr() used
934 as an lvalue, which is pretty strange. Perhaps you forgot to
935 dereference it first. See L<perlfunc/substr>.
937 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
939 (F) Only hard references are allowed by "strict refs". Symbolic references
940 are disallowed. See L<perlref>.
942 =item Cannot resolve method `%s' overloading `%s' in package `%s'
944 (P) Internal error trying to resolve overloading specified by a method
945 name (as opposed to a subroutine reference).
947 =item Constant subroutine %s redefined
949 (S) You redefined a subroutine which had previously been eligible for
950 inlining. See L<perlsub/"Constant Functions"> for commentary and
953 =item Constant subroutine %s undefined
955 (S) You undefined a subroutine which had previously been eligible for
956 inlining. See L<perlsub/"Constant Functions"> for commentary and
959 =item Copy method did not return a reference
961 (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>.
965 (F) You passed die() an empty string (the equivalent of C<die "">) or
966 you called it with no args and both C<$@> and C<$_> were empty.
968 =item Exiting pseudo-block via %s
970 (W) You are exiting a rather special block construct (like a sort block or
971 subroutine) by unconventional means, such as a goto, or a loop control
972 statement. See L<perlfunc/sort>.
974 =item Illegal character %s (carriage return)
976 (F) A carriage return character was found in the input. This is an
977 error, and not a warning, because carriage return characters can break
978 multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>).
980 =item Illegal switch in PERL5OPT: %s
982 (X) The PERL5OPT environment variable may only be used to set the
983 following switches: B<-[DIMUdmw]>.
985 =item Integer overflow in hex number
987 (S) The literal hex number you have specified is too big for your
988 architecture. On a 32-bit architecture the largest hex literal is
991 =item Integer overflow in octal number
993 (S) The literal octal number you have specified is too big for your
994 architecture. On a 32-bit architecture the largest octal literal is
997 =item Name "%s::%s" used only once: possible typo
999 (W) Typographical errors often show up as unique variable names.
1000 If you had a good reason for having a unique name, then just mention
1001 it again somehow to suppress the message (the C<use vars> pragma is
1002 provided for just this purpose).
1004 =item Null picture in formline
1006 (F) The first argument to formline must be a valid format picture
1007 specification. It was found to be empty, which probably means you
1008 supplied it an uninitialized value. See L<perlform>.
1010 =item Offset outside string
1012 (F) You tried to do a read/write/send/recv operation with an offset
1013 pointing outside the buffer. This is difficult to imagine.
1014 The sole exception to this is that C<sysread()>ing past the buffer
1015 will extend the buffer and zero pad the new area.
1017 =item Out of memory!
1019 (X|F) The malloc() function returned 0, indicating there was insufficient
1020 remaining memory (or virtual memory) to satisfy the request.
1022 The request was judged to be small, so the possibility to trap it
1023 depends on the way Perl was compiled. By default it is not trappable.
1024 However, if compiled for this, Perl may use the contents of C<$^M> as
1025 an emergency pool after die()ing with this message. In this case the
1026 error is trappable I<once>.
1028 =item Out of memory during request for %s
1030 (F) The malloc() function returned 0, indicating there was insufficient
1031 remaining memory (or virtual memory) to satisfy the request. However,
1032 the request was judged large enough (compile-time default is 64K), so
1033 a possibility to shut down by trapping this error is granted.
1035 =item Possible attempt to put comments in qw() list
1037 (W) qw() lists contain items separated by whitespace; as with literal
1038 strings, comment characters are not ignored, but are instead treated
1039 as literal data. (You may have used different delimiters than the
1040 exclamation marks parentheses shown here; braces are also frequently
1043 You probably wrote something like this:
1050 when you should have written this:
1057 If you really want comments, build your list the
1058 old-fashioned way, with quotes and commas:
1062 'b', # another comment
1065 =item Possible attempt to separate words with commas
1067 (W) qw() lists contain items separated by whitespace; therefore commas
1068 aren't needed to separate the items. (You may have used different
1069 delimiters than the parentheses shown here; braces are also frequently
1072 You probably wrote something like this:
1076 which puts literal commas into some of the list items. Write it without
1077 commas if you don't want them to appear in your data:
1081 =item Scalar value @%s{%s} better written as $%s{%s}
1083 (W) You've used a hash slice (indicated by @) to select a single element of
1084 a hash. Generally it's better to ask for a scalar value (indicated by $).
1085 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
1086 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
1087 like a list when you assign to it, and provides a list context to its
1088 subscript, which can do weird things if you're expecting only one subscript.
1090 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
1092 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
1093 Stubs should never be implicitely created, but explicit calls to C<can>
1096 =item Too late for "B<-T>" option
1098 (X) The #! line (or local equivalent) in a Perl script contains the
1099 B<-T> option, but Perl was not invoked with B<-T> in its argument
1100 list. This is an error because, by the time Perl discovers a B<-T> in
1101 a script, it's too late to properly taint everything from the
1102 environment. So Perl gives up.
1104 =item untie attempted while %d inner references still exist
1106 (W) A copy of the object returned from C<tie> (or C<tied>) was still
1107 valid when C<untie> was called.
1109 =item Unrecognized character %s
1111 (F) The Perl parser has no idea what to do with the specified character
1112 in your Perl script (or eval). Perhaps you tried to run a compressed
1113 script, a binary program, or a directory as a Perl program.
1115 =item Unsupported function fork
1117 (F) Your version of executable does not support forking.
1119 Note that under some systems, like OS/2, there may be different flavors of
1120 Perl executables, some of which may support fork, some not. Try changing
1121 the name you call Perl by to C<perl_>, C<perl__>, and so on.
1123 =item Value of %s can be "0"; test with defined()
1125 (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>,
1126 or C<readdir()> as a boolean value. Each of these constructs can return a
1127 value of "0"; that would make the conditional expression false, which is
1128 probably not what you intended. When using these constructs in conditional
1129 expressions, test their values with the C<defined> operator.
1131 =item Variable "%s" may be unavailable
1133 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1134 subroutine, and outside that is another subroutine; and the anonymous
1135 (innermost) subroutine is referencing a lexical variable defined in
1136 the outermost subroutine. For example:
1138 sub outermost { my $a; sub middle { sub { $a } } }
1140 If the anonymous subroutine is called or referenced (directly or
1141 indirectly) from the outermost subroutine, it will share the variable
1142 as you would expect. But if the anonymous subroutine is called or
1143 referenced when the outermost subroutine is not active, it will see
1144 the value of the shared variable as it was before and during the
1145 *first* call to the outermost subroutine, which is probably not what
1148 In these circumstances, it is usually best to make the middle
1149 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1150 support for shared variables in nested anonymous subroutines; a named
1151 subroutine in between interferes with this feature.
1153 =item Variable "%s" will not stay shared
1155 (W) An inner (nested) I<named> subroutine is referencing a lexical
1156 variable defined in an outer subroutine.
1158 When the inner subroutine is called, it will probably see the value of
1159 the outer subroutine's variable as it was before and during the
1160 *first* call to the outer subroutine; in this case, after the first
1161 call to the outer subroutine is complete, the inner and outer
1162 subroutines will no longer share a common value for the variable. In
1163 other words, the variable will no longer be shared.
1165 Furthermore, if the outer subroutine is anonymous and references a
1166 lexical variable outside itself, then the outer and inner subroutines
1167 will I<never> share the given variable.
1169 This problem can usually be solved by making the inner subroutine
1170 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1171 reference variables in outer subroutines are called or referenced,
1172 they are automatically rebound to the current values of such
1175 =item Warning: something's wrong
1177 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1178 you called it with no args and C<$_> was empty.
1180 =item Ill-formed logical name |%s| in prime_env_iter
1182 (W) A warning peculiar to VMS. A logical name was encountered when preparing
1183 to iterate over %ENV which violates the syntactic rules governing logical
1184 names. Since it cannot be translated normally, it is skipped, and will not
1185 appear in %ENV. This may be a benign occurrence, as some software packages
1186 might directly modify logical name tables and introduce nonstandard names,
1187 or it may indicate that a logical name table has been corrupted.
1189 =item Got an error from DosAllocMem
1191 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1192 version of Perl, and this should not happen anyway.
1194 =item Malformed PERLLIB_PREFIX
1196 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1204 with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix
1205 of a builtin library search path, prefix2 is substituted. The error
1206 may appear if components are not found, or are too long. See
1207 "PERLLIB_PREFIX" in F<README.os2>.
1209 =item PERL_SH_DIR too long
1211 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1212 C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>.
1214 =item Process terminated by SIG%s
1216 (W) This is a standard message issued by OS/2 applications, while *nix
1217 applications die in silence. It is considered a feature of the OS/2
1218 port. One can easily disable this by appropriate sighandlers, see
1219 L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT"
1226 If you find what you think is a bug, you might check the headers of
1227 recently posted articles in the comp.lang.perl.misc newsgroup.
1228 There may also be information at http://www.perl.com/perl/, the Perl
1231 If you believe you have an unreported bug, please run the B<perlbug>
1232 program included with your release. Make sure you trim your bug down
1233 to a tiny but sufficient test case. Your bug report, along with the
1234 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1235 analysed by the Perl porting team.
1239 The F<Changes> file for exhaustive details on what changed.
1241 The F<INSTALL> file for how to build Perl. This file has been
1242 significantly updated for 5.004, so even veteran users should
1245 The F<README> file for general stuff.
1247 The F<Copying> file for copyright information.
1251 Constructed by Tom Christiansen, grabbing material with permission
1252 from innumerable contributors, with kibitzing by more than a few Perl
1255 Last update: Sat Mar 8 19:51:26 EST 1997