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 $PERL5OPT environment variable.
33 Unless Perl is running with taint checks, it will interpret this
34 variable as if its contents had appeared on a "#!perl" line at the
35 beginning of your script, except that hyphens are optional. PERL5OPT
36 may only be used to set the following switches: B<-[DIMUdmw]>.
38 =head2 Limitations on B<-M>, and C<-m>, and B<-T> options
40 The C<-M> and C<-m> options are no longer allowed on the C<#!> line of
41 a script. If a script needs a module, it should invoke it with the
44 The B<-T> option is also forbidden on the C<#!> line of a script,
45 unless it was present on the Perl command line. Due to the way C<#!>
46 works, this usually means that B<-T> must be in the first argument.
51 will probably work for an executable script invoked as C<scriptname>,
56 will probably fail under the same conditions. (Non-Unix systems will
57 probably not follow this rule.) But C<perl scriptname> is guaranteed
58 to fail, since then there is no chance of B<-T> being found on the
59 command line before it is found on the C<#!> line.
61 =head2 More precise warnings
63 If you removed the B<-w> option from your Perl 5.003 scripts because it
64 made Perl too verbose, we recommend that you try putting it back when
65 you upgrade to Perl 5.004. Each new perl version tends to remove some
66 undesirable warnings, while adding new warnings that may catch bugs in
69 =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods
71 Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods
72 (using the C<@ISA> hierarchy), even when the function to be autoloaded
73 was called as a plain function (e.g. C<Foo::bar()>), not a method
74 (e.g. C<Foo->bar()> or C<$obj->bar()>).
76 Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s.
77 However, there is a significant base of existing code that may be using
78 the old behavior. So, as an interim step, Perl 5.004 issues an optional
79 warning when a non-method uses an inherited C<AUTOLOAD>.
81 The simple rule is: Inheritance will not work when autoloading
82 non-methods. The simple fix for old code is: In any module that used to
83 depend on inheriting C<AUTOLOAD> for non-methods from a base class named
84 C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup.
86 =head2 Subroutine arguments created only when they're modified
88 In Perl 5.004, nonexistent array and hash elements used as subroutine
89 parameters are brought into existence only if they are actually
90 assigned to (via C<@_>).
92 Earlier versions of Perl vary in their handling of such arguments.
93 Perl versions 5.002 and 5.003 always brought them into existence.
94 Perl versions 5.000, 5.001, and 5.002 brought them into existence only
95 if they were not the first argument (which was almost certainly a
96 bug). Earlier versions of Perl never brought them into existence.
98 For example, given this code:
101 sub show { print $_[0] };
102 sub change { $_[0]++ };
106 After this code executes in Perl 5.004, $a{b} exists but $a[2] does
107 not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed
108 (but $a[2]'s value would have been undefined).
110 =head2 Group vector changeable with C<$)>
112 The C<$)> special variable has always (well, in Perl 5, at least)
113 reflected not only the current effective group, but also the group list
114 as returned by the C<getgroups()> C function (if there is one).
115 However, until this release, there has not been a way to call the
116 C<setgroups()> C function from Perl.
118 In Perl 5.004, assigning to C<$)> is exactly symmetrical with examining
119 it: The first number in its string value is used as the effective gid;
120 if there are any numbers after the first one, they are passed to the
121 C<setgroups()> C function (if there is one).
123 =head2 Fixed parsing of $$<digit>, &$<digit>, etc.
125 Perl versions before 5.004 misinterpreted any type marker followed by
126 "$" and a digit. For example, "$$0" was incorrectly taken to mean
127 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
129 However, the developers of Perl 5.004 could not fix this bug completely,
130 because at least two widely-used modules depend on the old meaning of
131 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
132 old (broken) way inside strings; but it generates this message as a
133 warning. And in Perl 5.005, this special treatment will cease.
135 =head2 No resetting of $. on implicit close
137 The documentation for Perl 5.0 has always stated that C<$.> is I<not>
138 reset when an already-open file handle is reopened with no intervening
139 call to C<close>. Due to a bug, perl versions 5.000 through 5.003
140 I<did> reset C<$.> under that circumstance; Perl 5.004 does not.
142 =head2 C<wantarray> may return undef
144 The C<wantarray> operator returns true if a subroutine is expected to
145 return a list, and false otherwise. In Perl 5.004, C<wantarray> can
146 also return the undefined value if a subroutine's return value will
147 not be used at all, which allows subroutines to avoid a time-consuming
148 calculation of a return value if it isn't going to be used.
150 =head2 Changes to tainting checks
152 A bug in previous versions may have failed to detect some insecure
153 conditions when taint checks are turned on. (Taint checks are used
154 in setuid or setgid scripts, or when explicitly turned on with the
155 C<-T> invocation option.) Although it's unlikely, this may cause a
156 previously-working script to now fail -- which should be construed
157 as a blessing, since that indicates a potentially-serious security
158 hole was just plugged.
160 =head2 New Opcode module and revised Safe module
162 A new Opcode module supports the creation, manipulation and
163 application of opcode masks. The revised Safe module has a new API
164 and is implemented using the new Opcode module. Please read the new
165 Opcode and Safe documentation.
167 =head2 Embedding improvements
169 In older versions of Perl it was not possible to create more than one
170 Perl interpreter instance inside a single process without leaking like a
171 sieve and/or crashing. The bugs that caused this behavior have all been
172 fixed. However, you still must take care when embedding Perl in a C
173 program. See the updated perlembed manpage for tips on how to manage
176 =head2 Internal change: FileHandle class based on IO::* classes
178 File handles are now stored internally as type IO::Handle. The
179 FileHandle module is still supported for backwards compatibility, but
180 it is now merely a front end to the IO::* modules -- specifically,
181 IO::Handle, IO::Seekable, and IO::File. We suggest, but do not
182 require, that you use the IO::* modules in new code.
184 In harmony with this change, C<*GLOB{FILEHANDLE}> is now a
185 backward-compatible synonym for C<*STDOUT{IO}>.
187 =head2 Internal change: PerlIO abstraction interface
189 It is now possible to build Perl with AT&T's sfio IO package
190 instead of stdio. See L<perlapio> for more details, and
191 the F<INSTALL> file for how to use it.
193 =head2 New and changed builtin variables
199 Extended error message on some platforms. (Also known as
200 $EXTENDED_OS_ERROR if you C<use English>).
204 The current set of syntax checks enabled by C<use strict>. See the
205 documentation of C<strict> for more details. Not actually new, but
207 Because it is intended for internal use by Perl core components,
208 there is no C<use English> long name for this variable.
212 By default, running out of memory it is not trappable. However, if
213 compiled for this, Perl may use the contents of C<$^M> as an emergency
214 pool after die()ing with this message. Suppose that your Perl were
215 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
219 would allocate a 64K buffer for use when in emergency.
220 See the F<INSTALL> file for information on how to enable this option.
221 As a disincentive to casual use of this advanced feature,
222 there is no C<use English> long name for this variable.
226 =head2 New and changed builtin functions
230 =item delete on slices
232 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
236 is now supported on more platforms, prefers fcntl to lockf when
237 emulating, and always flushes before (un)locking.
239 =item printf and sprintf
241 now support "%i" as a synonym for "%d", and the "h" modifier.
242 So "%hi" means "short integer in decimal", and "%ho" means
243 "unsigned short integer as octal".
245 =item keys as an lvalue
247 As an lvalue, C<keys> allows you to increase the number of hash buckets
248 allocated for the given hash. This can gain you a measure of efficiency if
249 you know the hash is going to get big. (This is similar to pre-extending
250 an array by assigning a larger number to $#array.) If you say
254 then C<%hash> will have at least 200 buckets allocated for it. These
255 buckets will be retained even if you do C<%hash = ()>; use C<undef
256 %hash> if you want to free the storage while C<%hash> is still in scope.
257 You can't shrink the number of buckets allocated for the hash using
258 C<keys> in this way (but you needn't worry about doing this by accident,
259 as trying has no effect).
261 =item my() in Control Structures
263 You can now use my() (with or without the parentheses) in the control
264 expressions of control structures such as:
266 while (defined(my $line = <>)) {
272 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
274 } elsif ($answer =~ /^n(o)?$/i) {
278 die "`$answer' is neither `yes' nor `no'";
281 Also, you can declare a foreach loop control variable as lexical by
282 preceding it with the word "my". For example, in:
284 foreach my $i (1, 2, 3) {
288 $i is a lexical variable, and the scope of $i extends to the end of
289 the loop, but not beyond it.
291 Note that you still cannot use my() on global punctuation variables
292 such as $_ and the like.
294 =item pack() and unpack()
296 A new format 'w' represents a BER compressed integer (as defined in
297 ASN.1). Its format is a sequence of one or more bytes, each of which
298 provides seven bits of the total value, with the most significant
299 first. Bit eight of each byte is set, except for the last byte, in
300 which bit eight is clear.
304 This is a variant of seek() that works on the system file pointer.
305 It is the only reliable way to seek before sysread() or syswrite().
309 If the first argument to C<use> is a number, it is treated as a version
310 number instead of a module name. If the version of the Perl interpreter
311 is less than VERSION, then an error message is printed and Perl exits
312 immediately. Because C<use> occurs at compile time, this check happens
313 immediately during the compilation process, unlike C<require VERSION>,
314 which waits until runtime for the check. This is often useful if you
315 need to check the current Perl version before C<use>ing library modules
316 which have changed in incompatible ways from older versions of Perl.
317 (We try not to do this more than we have to.)
319 =item use Module VERSION LIST
321 If the VERSION argument is present between Module and LIST, then the
322 C<use> will call the VERSION method in class Module with the given
323 version as an argument. The default VERSION method, inherited from
324 the UNIVERSAL class, croaks if the given version is larger than the
325 value of the variable $Module::VERSION. (Note that there is not a
326 comma after VERSION!)
328 This version-checking mechanism is similar to the one currently used
329 in the Exporter module, but it is faster and can be used with modules
330 that don't use the Exporter. It is the recommended method for new
333 =item prototype(FUNCTION)
335 Returns the prototype of a function as a string (or C<undef> if the
336 function has no prototype). FUNCTION is a reference to or the name of the
337 function whose prototype you want to retrieve.
338 (Not actually new; just never documented before.)
342 The default seed for C<srand>, which used to be C<time>, has been changed.
343 Now it's a heady mix of difficult-to-predict system-dependent values,
344 which should be sufficient for most everyday purposes.
346 Previous to version 5.004, calling C<rand> without first calling C<srand>
347 would yield the same sequence of random numbers on most or all machines.
348 Now, when perl sees that you're calling C<rand> and haven't yet called
349 C<srand>, it calls C<srand> with the default seed. You should still call
350 C<srand> manually if your code might ever be run on a pre-5.004 system,
351 of course, or if you want a seed other than the default.
355 Functions documented in the Camel to default to $_ now in
356 fact do, and all those that do are so documented in L<perlfunc>.
358 =item C<m//g> does not reset search position on failure
360 The C<m//g> match iteration construct used to reset its target string's
361 search position (which is visible through the C<pos> operator) when a
362 match failed; as a result, the next C<m//g> match would start at the
363 beginning of the string). With Perl 5.004, the search position must be
364 reset explicitly, as with C<pos $str = 0;>, or by modifying the target
365 string. This change in Perl makes it possible to chain matches together
366 in conjunction with the C<\G> zero-width assertion. See L<perlop> and
369 Here is an illustration of what it takes to get the old behavior:
371 for ( qw(this and that are not what you think you got) ) {
372 while ( /(\w*t\w*)/g ) { print "t word is: $1\n" }
373 pos = 0; # REQUIRED FOR 5.004
374 while ( /(\w*a\w*)/g ) { print "a word is: $1\n" }
378 =item C<m//x> ignores whitespace before ?*+{}
380 The C<m//x> construct has always been intended to ignore all unescaped
381 whitespace. However, before Perl 5.004, whitespace had the effect of
382 escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was
383 (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004.
385 =item nested C<sub{}> closures work now
387 Prior to the 5.004 release, nested anonymous functions didn't work
390 =item formats work right on changing lexicals
392 Just like anonymous functions that contain lexical variables
393 that change (like a lexical index variable for a C<foreach> loop),
394 formats now work properly. For example, this silently failed
395 before, and is fine now:
398 foreach $i ( 1 .. 10 ) {
408 =head2 New builtin methods
410 The C<UNIVERSAL> package automatically contains the following methods that
411 are inherited by all other classes:
417 C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
419 C<isa> is also exportable and can be called as a sub with two arguments. This
420 allows the ability to check what a reference points to. Example:
422 use UNIVERSAL qw(isa);
424 if(isa($ref, 'ARRAY')) {
430 C<can> checks to see if its object has a method called C<METHOD>,
431 if it does then a reference to the sub is returned; if it does not then
432 I<undef> is returned.
434 =item VERSION( [NEED] )
436 C<VERSION> returns the version number of the class (package). If the
437 NEED argument is given then it will check that the current version (as
438 defined by the $VERSION variable in the given package) not less than
439 NEED; it will die if this is not the case. This method is normally
440 called as a class method. This method is called automatically by the
441 C<VERSION> form of C<use>.
443 use A 1.2 qw(some imported subs);
449 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
450 C<isa> uses a very similar method and caching strategy. This may cause
451 strange effects if the Perl code dynamically changes @ISA in any package.
453 You may add other methods to the UNIVERSAL class via Perl or XS code.
454 You do not need to C<use UNIVERSAL> in order to make these methods
455 available to your program. This is necessary only if you wish to
456 have C<isa> available as a plain subroutine in the current package.
458 =head2 TIEHANDLE now supported
460 See L<perltie> for other kinds of tie()s.
464 =item TIEHANDLE classname, LIST
466 This is the constructor for the class. That means it is expected to
467 return an object of some sort. The reference can be used to
468 hold some internal information.
473 return bless \$i, shift;
476 =item PRINT this, LIST
478 This method will be triggered every time the tied handle is printed to.
479 Beyond its self reference it also expects the list that was passed to
485 return print join( $, => map {uc} @_), $\;
490 This method will be called when the handle is read from via the C<read>
491 or C<sysread> functions.
495 my($buf,$len,$offset) = @_;
496 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
501 This method will be called when the handle is read from. The method
502 should return undef when there is no more data.
506 return "PRINT called $$r times\n"
511 This method will be called when the C<getc> function is called.
513 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
517 As with the other types of ties, this method will be called when the
518 tied handle is about to be destroyed. This is useful for debugging and
519 possibly for cleaning up.
527 =head2 Malloc enhancements
529 Four new compilation flags are recognized by malloc.c. (They have no
530 effect if perl is compiled with system malloc().)
534 =item -DDEBUGGING_MSTATS
536 If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print
537 memory statistics at runtime by running Perl thusly:
539 env PERL_DEBUG_MSTATS=2 perl your_script_here
541 The value of 2 means to print statistics after compilation and on
542 exit; with a value of 1, the statistics ares printed only on exit.
543 (If you want the statistics at an arbitrary time, you'll need to
544 install the optional module Devel::Peek.)
546 =item -DEMERGENCY_SBRK
548 If this macro is defined, running out of memory need not be a fatal
549 error: a memory pool can allocated by assigning to the special
550 variable C<$^M>. See L<"$^M">.
554 Perl memory allocation is by bucket with sizes close to powers of two.
555 Because of these malloc overhead may be big, especially for data of
556 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
557 a slightly different algorithm for small allocations (up to 64 bytes
558 long), which makes it possible to have overhead down to 1 byte for
559 allocations which are powers of two (and appear quite often).
561 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
562 about 20% for typical Perl usage. Expected slowdown due to additional
563 malloc overhead is in fractions of a percent (hard to measure, because
564 of the effect of saved memory on speed).
566 =item -DTWO_POT_OPTIMIZE
568 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
569 with size close to a power of two; but this works for big allocations
570 (starting with 16K by default). Such allocations are typical for big
571 hashes and special-purpose scripts, especially image processing.
573 On recent systems, the fact that perl requires 2M from system for 1M
574 allocation will not affect speed of execution, since the tail of such
575 a chunk is not going to be touched (and thus will not require real
576 memory). However, it may result in a premature out-of-memory error.
577 So if you will be manipulating very large blocks with sizes close to
578 powers of two, it would be wise to define this macro.
580 Expected saving of memory is 0-100% (100% in applications which
581 require most memory in such 2**n chunks); expected slowdown is
586 =head2 Miscellaneous efficiency enhancements
588 Functions that have an empty prototype and that do nothing but return
589 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
591 Each unique hash key is only allocated once, no matter how many hashes
592 have an entry with that key. So even if you have 100 copies of the
593 same hash, the hash keys never have to be reallocated.
597 Six new pragmatic modules exist:
601 =item use autouse MODULE => qw(sub1 sub2 sub3)
603 Defers C<require MODULE> until someone calls one of the specified
604 subroutines (which must be exported by MODULE). This pragma should be
605 used with caution, and only when necessary.
611 Looks for MakeMaker-like I<'blib'> directory structure starting in
612 I<dir> (or current directory) and working back up to five levels of
615 Intended for use on command line with B<-M> option as a way of testing
616 arbitrary scripts against an uninstalled version of a package.
618 =item use constant NAME => VALUE
620 Provides a convenient interface for creating compile-time constants,
621 See L<perlsub/"Constant Functions">.
625 Tells the compiler to enable (or disable) the use of POSIX locales for
628 When C<use locale> is in effect, the current LC_CTYPE locale is used
629 for regular expressions and case mapping; LC_COLLATE for string
630 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
631 (but B<not> in print). LC_NUMERIC is always used in write, since
632 lexical scoping of formats is problematic at best.
634 Each C<use locale> or C<no locale> affects statements to the end of
635 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
636 current file. Locales can be switched and queried with
639 See L<perllocale> for more information.
643 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
647 Enable VMS-specific language features. Currently, there are three
648 VMS-specific features available: 'status', which makes C<$?> and
649 C<system> return genuine VMS status values instead of emulating POSIX;
650 'exit', which makes C<exit> take a genuine VMS status value instead of
651 assuming that C<exit 1> is an error; and 'time', which makes all times
652 relative to the local time zone, in the VMS tradition.
658 =head2 Required Updates
660 Though Perl 5.004 is compatible with almost all modules that work
661 with Perl 5.003, there are a few exceptions:
663 Module Required Version for Perl 5.004
664 ------ -------------------------------
667 Tk Tk400.202 (-w makes noise)
669 Also, the majordomo mailing list program, version 1.94.1, doesn't work
670 with Perl 5.004 (nor with perl 4), because it executes an invalid
671 regular expression. This bug is fixed in majordomo version 1.94.2.
673 =head2 Installation directories
675 The I<installperl> script now places the Perl source files for
676 extensions in the architecture-specific library directory, which is
677 where the shared libraries for extensions have always been. This
678 change is intended to allow administrators to keep the Perl 5.004
679 library directory unchanged from a previous version, without running
680 the risk of binary incompatibility between extensions' Perl source and
683 =head2 Module information summary
685 Brand new modules, arranged by topic rather than strictly
688 CGI.pm Web server interface ("Common Gateway Interface")
689 CGI/Apache.pm Support for Apache's Perl module
690 CGI/Carp.pm Log server errors with helpful context
691 CGI/Fast.pm Support for FastCGI (persistent server process)
692 CGI/Push.pm Support for server push
693 CGI/Switch.pm Simple interface for multiple server types
695 CPAN Interface to Comprehensive Perl Archive Network
696 CPAN::FirstTime Utility for creating CPAN configuration file
697 CPAN::Nox Runs CPAN while avoiding compiled extensions
699 IO.pm Top-level interface to IO::* classes
700 IO/File.pm IO::File extension Perl module
701 IO/Handle.pm IO::Handle extension Perl module
702 IO/Pipe.pm IO::Pipe extension Perl module
703 IO/Seekable.pm IO::Seekable extension Perl module
704 IO/Select.pm IO::Select extension Perl module
705 IO/Socket.pm IO::Socket extension Perl module
707 Opcode.pm Disable named opcodes when compiling Perl code
709 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
710 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
712 FindBin.pm Find path of currently executing program
714 Class/Struct.pm Declare struct-like datatypes as Perl classes
715 File/stat.pm By-name interface to Perl's built-in stat
716 Net/hostent.pm By-name interface to Perl's built-in gethost*
717 Net/netent.pm By-name interface to Perl's built-in getnet*
718 Net/protoent.pm By-name interface to Perl's built-in getproto*
719 Net/servent.pm By-name interface to Perl's built-in getserv*
720 Time/gmtime.pm By-name interface to Perl's built-in gmtime
721 Time/localtime.pm By-name interface to Perl's built-in localtime
722 Time/tm.pm Internal object for Time::{gm,local}time
723 User/grent.pm By-name interface to Perl's built-in getgr*
724 User/pwent.pm By-name interface to Perl's built-in getpw*
726 Tie/RefHash.pm Base class for tied hashes with references as keys
728 UNIVERSAL.pm Base class for *ALL* classes
732 New constants in the existing Fcntl modules are now supported,
733 provided that your operating system happens to support them:
736 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
739 These constants are intended for use with the Perl operators sysopen()
740 and fcntl() and the basic database modules like SDBM_File. For the
741 exact meaning of these and other Fcntl constants please refer to your
742 operating system's documentation for fcntl() and open().
744 In addition, the Fcntl module now provides these constants for use
745 with the Perl operator flock():
747 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
749 These constants are defined in all environments (because where there is
750 no flock() system call, Perl emulates it). However, for historical
751 reasons, these constants are not exported unless they are explicitly
752 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
756 The IO module provides a simple mechanism to load all of the IO modules at one
757 go. Currently this includes:
765 For more information on any of these modules, please see its
766 respective documentation.
770 The Math::Complex module has been totally rewritten, and now supports
771 more operations. These are overloaded:
773 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
775 And these functions are now exported:
778 log10 logn ln cbrt root
791 This new module provides a simpler interface to parts of Math::Complex for
792 those who need trigonometric functions only for real numbers.
796 There have been quite a few changes made to DB_File. Here are a few of
803 Fixed a handful of bugs.
807 By public demand, added support for the standard hash function exists().
811 Made it compatible with Berkeley DB 1.86.
815 Made negative subscripts work with RECNO interface.
819 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
820 mode from 0640 to 0666.
824 Made DB_File automatically import the open() constants (O_RDWR,
825 O_CREAT etc.) from Fcntl, if available.
829 Updated documentation.
833 Refer to the HISTORY section in DB_File.pm for a complete list of
834 changes. Everything after DB_File 1.01 has been added since 5.003.
838 Major rewrite - support added for both udp echo and real icmp pings.
840 =head2 Object-oriented overrides for builtin operators
842 Many of the Perl builtins returning lists now have
843 object-oriented overrides. These are:
855 For example, you can now say
859 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
861 =head1 Utility Changes
867 =item C<void> XSUBs now default to returning nothing
869 Due to a documentation/implementation bug in previous versions of
870 Perl, XSUBs with a return type of C<void> have actually been
871 returning one value. Usually that value was the GV for the XSUB,
872 but sometimes it was some already freed or reused value, which would
873 sometimes lead to program failure.
875 In Perl 5.004, if an XSUB is declared as returning C<void>, it
876 actually returns no value, i.e. an empty list (though there is a
877 backward-compatibility exception; see below). If your XSUB really
878 does return an SV, you should give it a return type of C<SV *>.
880 For backward compatibility, I<xsubpp> tries to guess whether a
881 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
882 It does so by examining the text of the XSUB: if I<xsubpp> finds
883 what looks like an assignment to C<ST(0)>, it assumes that the
884 XSUB's return type is really C<SV *>.
888 =head1 C Language API Changes
892 =item C<gv_fetchmethod> and C<perl_call_sv>
894 The C<gv_fetchmethod> function finds a method for an object, just like
895 in Perl 5.003. The GV it returns may be a method cache entry.
896 However, in Perl 5.004, method cache entries are not visible to users;
897 therefore, they can no longer be passed directly to C<perl_call_sv>.
898 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
899 and pass the CV to C<perl_call_sv>.
901 The most likely symptom of passing the result of C<gv_fetchmethod> to
902 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
903 error on the I<second> call to a given method (since there is no cache
906 =item C<perl_eval_pv>
908 A new function handy for eval'ing strings of Perl code inside C code.
909 This function returns the value from the eval statement, which can
910 be used instead of fetching globals from the symbol table. See
911 L<perlguts>, L<perlembed> and L<perlcall> for details and examples.
913 =item Extended API for manipulating hashes
915 Internal handling of hash keys has changed. The old hashtable API is
916 still fully supported, and will likely remain so. The additions to the
917 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
918 real scalars as keys rather than plain strings (nontied hashes still
919 can only use strings as keys). New extensions must use the new hash
920 access functions and macros if they wish to use C<SV*> keys. These
921 additions also make it feasible to manipulate C<HE*>s (hash entries),
922 which can be more efficient. See L<perlguts> for details.
926 =head1 Documentation Changes
928 Many of the base and library pods were updated. These
929 new pods are included in section 1:
939 Locale support (internationalization and localization).
943 Tutorial on Perl OO programming.
947 Perl internal IO abstraction interface.
951 Although not new, this has been massively updated.
955 Although not new, this has been massively updated.
959 =head1 New Diagnostics
961 Several new conditions will trigger warnings that were
962 silent before. Some only affect certain platforms.
963 The following new warnings and errors outline these.
964 These messages are classified as follows (listed in
965 increasing order of desperation):
967 (W) A warning (optional).
968 (D) A deprecation (optional).
969 (S) A severe warning (mandatory).
970 (F) A fatal error (trappable).
971 (P) An internal error you should never see (trappable).
972 (X) A very fatal error (nontrappable).
973 (A) An alien error message (not generated by Perl).
977 =item "my" variable %s masks earlier declaration in same scope
979 (S) A lexical variable has been redeclared in the same scope, effectively
980 eliminating all access to the previous instance. This is almost always
981 a typographical error. Note that the earlier variable will still exist
982 until the end of the scope or until all closure referents to it are
985 =item %s argument is not a HASH element or slice
987 (F) The argument to delete() must be either a hash element, such as
990 $ref->[12]->{"susie"}
992 or a hash slice, such as
994 @foo{$bar, $baz, $xyzzy}
995 @{$ref->[12]}{"susie", "queue"}
997 =item Allocation too large: %lx
999 (X) You can't allocate more than 64K on an MS-DOS machine.
1001 =item Allocation too large
1003 (F) You can't allocate more than 2^31+"small amount" bytes.
1005 =item Applying %s to %s will act on scalar(%s)
1007 (W) The pattern match (//), substitution (s///), and translation (tr///)
1008 operators work on scalar values. If you apply one of them to an array
1009 or a hash, it will convert the array or hash to a scalar value -- the
1010 length of an array, or the population info of a hash -- and then work on
1011 that scalar value. This is probably not what you meant to do. See
1012 L<perlfunc/grep> and L<perlfunc/map> for alternatives.
1014 =item Attempt to free nonexistent shared string
1016 (P) Perl maintains a reference counted internal table of strings to
1017 optimize the storage and access of hash keys and other strings. This
1018 indicates someone tried to decrement the reference count of a string
1019 that can no longer be found in the table.
1021 =item Attempt to use reference as lvalue in substr
1023 (W) You supplied a reference as the first argument to substr() used
1024 as an lvalue, which is pretty strange. Perhaps you forgot to
1025 dereference it first. See L<perlfunc/substr>.
1027 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
1029 (F) Only hard references are allowed by "strict refs". Symbolic references
1030 are disallowed. See L<perlref>.
1032 =item Cannot resolve method `%s' overloading `%s' in package `%s'
1034 (P) Internal error trying to resolve overloading specified by a method
1035 name (as opposed to a subroutine reference).
1037 =item Constant subroutine %s redefined
1039 (S) You redefined a subroutine which had previously been eligible for
1040 inlining. See L<perlsub/"Constant Functions"> for commentary and
1043 =item Constant subroutine %s undefined
1045 (S) You undefined a subroutine which had previously been eligible for
1046 inlining. See L<perlsub/"Constant Functions"> for commentary and
1049 =item Copy method did not return a reference
1051 (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>.
1055 (F) You passed die() an empty string (the equivalent of C<die "">) or
1056 you called it with no args and both C<$@> and C<$_> were empty.
1058 =item Exiting pseudo-block via %s
1060 (W) You are exiting a rather special block construct (like a sort block or
1061 subroutine) by unconventional means, such as a goto, or a loop control
1062 statement. See L<perlfunc/sort>.
1064 =item Illegal character %s (carriage return)
1066 (F) A carriage return character was found in the input. This is an
1067 error, and not a warning, because carriage return characters can break
1068 multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>).
1070 =item Illegal switch in PERL5OPT: %s
1072 (X) The PERL5OPT environment variable may only be used to set the
1073 following switches: B<-[DIMUdmw]>.
1075 =item Integer overflow in hex number
1077 (S) The literal hex number you have specified is too big for your
1078 architecture. On a 32-bit architecture the largest hex literal is
1081 =item Integer overflow in octal number
1083 (S) The literal octal number you have specified is too big for your
1084 architecture. On a 32-bit architecture the largest octal literal is
1087 =item internal error: glob failed
1089 (P) Something went wrong with the external program(s) used for C<glob>
1090 and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is
1091 broken. If so, you should change all of the csh-related variables in
1092 config.sh: If you have tcsh, make the variables refer to it as if it
1093 were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all
1094 empty (except that C<d_csh> should be C<'undef'>) so that Perl will
1095 think csh is missing. In either case, after editing config.sh, run
1096 C<./Configure -S> and rebuild Perl.
1098 =item Name "%s::%s" used only once: possible typo
1100 (W) Typographical errors often show up as unique variable names.
1101 If you had a good reason for having a unique name, then just mention
1102 it again somehow to suppress the message (the C<use vars> pragma is
1103 provided for just this purpose).
1105 =item Null picture in formline
1107 (F) The first argument to formline must be a valid format picture
1108 specification. It was found to be empty, which probably means you
1109 supplied it an uninitialized value. See L<perlform>.
1111 =item Offset outside string
1113 (F) You tried to do a read/write/send/recv operation with an offset
1114 pointing outside the buffer. This is difficult to imagine.
1115 The sole exception to this is that C<sysread()>ing past the buffer
1116 will extend the buffer and zero pad the new area.
1118 =item Out of memory!
1120 (X|F) The malloc() function returned 0, indicating there was insufficient
1121 remaining memory (or virtual memory) to satisfy the request.
1123 The request was judged to be small, so the possibility to trap it
1124 depends on the way Perl was compiled. By default it is not trappable.
1125 However, if compiled for this, Perl may use the contents of C<$^M> as
1126 an emergency pool after die()ing with this message. In this case the
1127 error is trappable I<once>.
1129 =item Out of memory during request for %s
1131 (F) The malloc() function returned 0, indicating there was insufficient
1132 remaining memory (or virtual memory) to satisfy the request. However,
1133 the request was judged large enough (compile-time default is 64K), so
1134 a possibility to shut down by trapping this error is granted.
1136 =item Possible attempt to put comments in qw() list
1138 (W) qw() lists contain items separated by whitespace; as with literal
1139 strings, comment characters are not ignored, but are instead treated
1140 as literal data. (You may have used different delimiters than the
1141 exclamation marks parentheses shown here; braces are also frequently
1144 You probably wrote something like this:
1151 when you should have written this:
1158 If you really want comments, build your list the
1159 old-fashioned way, with quotes and commas:
1163 'b', # another comment
1166 =item Possible attempt to separate words with commas
1168 (W) qw() lists contain items separated by whitespace; therefore commas
1169 aren't needed to separate the items. (You may have used different
1170 delimiters than the parentheses shown here; braces are also frequently
1173 You probably wrote something like this:
1177 which puts literal commas into some of the list items. Write it without
1178 commas if you don't want them to appear in your data:
1182 =item Scalar value @%s{%s} better written as $%s{%s}
1184 (W) You've used a hash slice (indicated by @) to select a single element of
1185 a hash. Generally it's better to ask for a scalar value (indicated by $).
1186 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
1187 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
1188 like a list when you assign to it, and provides a list context to its
1189 subscript, which can do weird things if you're expecting only one subscript.
1191 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
1193 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
1194 Stubs should never be implicitely created, but explicit calls to C<can>
1197 =item Too late for "B<-T>" option
1199 (X) The #! line (or local equivalent) in a Perl script contains the
1200 B<-T> option, but Perl was not invoked with B<-T> in its argument
1201 list. This is an error because, by the time Perl discovers a B<-T> in
1202 a script, it's too late to properly taint everything from the
1203 environment. So Perl gives up.
1205 =item untie attempted while %d inner references still exist
1207 (W) A copy of the object returned from C<tie> (or C<tied>) was still
1208 valid when C<untie> was called.
1210 =item Unrecognized character %s
1212 (F) The Perl parser has no idea what to do with the specified character
1213 in your Perl script (or eval). Perhaps you tried to run a compressed
1214 script, a binary program, or a directory as a Perl program.
1216 =item Unsupported function fork
1218 (F) Your version of executable does not support forking.
1220 Note that under some systems, like OS/2, there may be different flavors of
1221 Perl executables, some of which may support fork, some not. Try changing
1222 the name you call Perl by to C<perl_>, C<perl__>, and so on.
1224 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
1226 (D) Perl versions before 5.004 misinterpreted any type marker followed
1227 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
1228 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
1230 However, the developers of Perl 5.004 could not fix this bug completely,
1231 because at least two widely-used modules depend on the old meaning of
1232 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
1233 old (broken) way inside strings; but it generates this message as a
1234 warning. And in Perl 5.005, this special treatment will cease.
1236 =item Value of %s can be "0"; test with defined()
1238 (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>,
1239 or C<readdir()> as a boolean value. Each of these constructs can return a
1240 value of "0"; that would make the conditional expression false, which is
1241 probably not what you intended. When using these constructs in conditional
1242 expressions, test their values with the C<defined> operator.
1244 =item Variable "%s" may be unavailable
1246 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1247 subroutine, and outside that is another subroutine; and the anonymous
1248 (innermost) subroutine is referencing a lexical variable defined in
1249 the outermost subroutine. For example:
1251 sub outermost { my $a; sub middle { sub { $a } } }
1253 If the anonymous subroutine is called or referenced (directly or
1254 indirectly) from the outermost subroutine, it will share the variable
1255 as you would expect. But if the anonymous subroutine is called or
1256 referenced when the outermost subroutine is not active, it will see
1257 the value of the shared variable as it was before and during the
1258 *first* call to the outermost subroutine, which is probably not what
1261 In these circumstances, it is usually best to make the middle
1262 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1263 support for shared variables in nested anonymous subroutines; a named
1264 subroutine in between interferes with this feature.
1266 =item Variable "%s" will not stay shared
1268 (W) An inner (nested) I<named> subroutine is referencing a lexical
1269 variable defined in an outer subroutine.
1271 When the inner subroutine is called, it will probably see the value of
1272 the outer subroutine's variable as it was before and during the
1273 *first* call to the outer subroutine; in this case, after the first
1274 call to the outer subroutine is complete, the inner and outer
1275 subroutines will no longer share a common value for the variable. In
1276 other words, the variable will no longer be shared.
1278 Furthermore, if the outer subroutine is anonymous and references a
1279 lexical variable outside itself, then the outer and inner subroutines
1280 will I<never> share the given variable.
1282 This problem can usually be solved by making the inner subroutine
1283 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1284 reference variables in outer subroutines are called or referenced,
1285 they are automatically rebound to the current values of such
1288 =item Warning: something's wrong
1290 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1291 you called it with no args and C<$_> was empty.
1293 =item Ill-formed logical name |%s| in prime_env_iter
1295 (W) A warning peculiar to VMS. A logical name was encountered when preparing
1296 to iterate over %ENV which violates the syntactic rules governing logical
1297 names. Since it cannot be translated normally, it is skipped, and will not
1298 appear in %ENV. This may be a benign occurrence, as some software packages
1299 might directly modify logical name tables and introduce nonstandard names,
1300 or it may indicate that a logical name table has been corrupted.
1302 =item Got an error from DosAllocMem
1304 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1305 version of Perl, and this should not happen anyway.
1307 =item Malformed PERLLIB_PREFIX
1309 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1317 with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix
1318 of a builtin library search path, prefix2 is substituted. The error
1319 may appear if components are not found, or are too long. See
1320 "PERLLIB_PREFIX" in F<README.os2>.
1322 =item PERL_SH_DIR too long
1324 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1325 C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>.
1327 =item Process terminated by SIG%s
1329 (W) This is a standard message issued by OS/2 applications, while *nix
1330 applications die in silence. It is considered a feature of the OS/2
1331 port. One can easily disable this by appropriate sighandlers, see
1332 L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT"
1339 If you find what you think is a bug, you might check the headers of
1340 recently posted articles in the comp.lang.perl.misc newsgroup.
1341 There may also be information at http://www.perl.com/perl/, the Perl
1344 If you believe you have an unreported bug, please run the B<perlbug>
1345 program included with your release. Make sure you trim your bug down
1346 to a tiny but sufficient test case. Your bug report, along with the
1347 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1348 analysed by the Perl porting team.
1352 The F<Changes> file for exhaustive details on what changed.
1354 The F<INSTALL> file for how to build Perl. This file has been
1355 significantly updated for 5.004, so even veteran users should
1358 The F<README> file for general stuff.
1360 The F<Copying> file for copyright information.
1364 Constructed by Tom Christiansen, grabbing material with permission
1365 from innumerable contributors, with kibitzing by more than a few Perl
1368 Last update: Sat Mar 8 19:51:26 EST 1997