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.
302 Both pack() and unpack() now fail when their templates contain invalid
303 types. (Invalid types used to be ignored.)
307 The new sysseek() operator is a variant of seek() that sets and gets the
308 file's system read/write position, using the lseek(2) system call. It is
309 the only reliable way to seek before using sysread() or syswrite(). Its
310 return value is the new position, or the undefined value on failure.
314 If the first argument to C<use> is a number, it is treated as a version
315 number instead of a module name. If the version of the Perl interpreter
316 is less than VERSION, then an error message is printed and Perl exits
317 immediately. Because C<use> occurs at compile time, this check happens
318 immediately during the compilation process, unlike C<require VERSION>,
319 which waits until runtime for the check. This is often useful if you
320 need to check the current Perl version before C<use>ing library modules
321 which have changed in incompatible ways from older versions of Perl.
322 (We try not to do this more than we have to.)
324 =item use Module VERSION LIST
326 If the VERSION argument is present between Module and LIST, then the
327 C<use> will call the VERSION method in class Module with the given
328 version as an argument. The default VERSION method, inherited from
329 the UNIVERSAL class, croaks if the given version is larger than the
330 value of the variable $Module::VERSION. (Note that there is not a
331 comma after VERSION!)
333 This version-checking mechanism is similar to the one currently used
334 in the Exporter module, but it is faster and can be used with modules
335 that don't use the Exporter. It is the recommended method for new
338 =item prototype(FUNCTION)
340 Returns the prototype of a function as a string (or C<undef> if the
341 function has no prototype). FUNCTION is a reference to or the name of the
342 function whose prototype you want to retrieve.
343 (Not actually new; just never documented before.)
347 The default seed for C<srand>, which used to be C<time>, has been changed.
348 Now it's a heady mix of difficult-to-predict system-dependent values,
349 which should be sufficient for most everyday purposes.
351 Previous to version 5.004, calling C<rand> without first calling C<srand>
352 would yield the same sequence of random numbers on most or all machines.
353 Now, when perl sees that you're calling C<rand> and haven't yet called
354 C<srand>, it calls C<srand> with the default seed. You should still call
355 C<srand> manually if your code might ever be run on a pre-5.004 system,
356 of course, or if you want a seed other than the default.
360 Functions documented in the Camel to default to $_ now in
361 fact do, and all those that do are so documented in L<perlfunc>.
363 =item C<m//g> does not reset search position on failure
365 The C<m//g> match iteration construct used to reset its target string's
366 search position (which is visible through the C<pos> operator) when a
367 match failed; as a result, the next C<m//g> match would start at the
368 beginning of the string). With Perl 5.004, the search position must be
369 reset explicitly, as with C<pos $str = 0;>, or by modifying the target
370 string. This change in Perl makes it possible to chain matches together
371 in conjunction with the C<\G> zero-width assertion. See L<perlop> and
374 Here is an illustration of what it takes to get the old behavior:
376 for ( qw(this and that are not what you think you got) ) {
377 while ( /(\w*t\w*)/g ) { print "t word is: $1\n" }
378 pos = 0; # REQUIRED FOR 5.004
379 while ( /(\w*a\w*)/g ) { print "a word is: $1\n" }
383 =item C<m//x> ignores whitespace before ?*+{}
385 The C<m//x> construct has always been intended to ignore all unescaped
386 whitespace. However, before Perl 5.004, whitespace had the effect of
387 escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was
388 (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004.
390 =item nested C<sub{}> closures work now
392 Prior to the 5.004 release, nested anonymous functions didn't work
395 =item formats work right on changing lexicals
397 Just like anonymous functions that contain lexical variables
398 that change (like a lexical index variable for a C<foreach> loop),
399 formats now work properly. For example, this silently failed
400 before, and is fine now:
403 foreach $i ( 1 .. 10 ) {
413 =head2 New builtin methods
415 The C<UNIVERSAL> package automatically contains the following methods that
416 are inherited by all other classes:
422 C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
424 C<isa> is also exportable and can be called as a sub with two arguments. This
425 allows the ability to check what a reference points to. Example:
427 use UNIVERSAL qw(isa);
429 if(isa($ref, 'ARRAY')) {
435 C<can> checks to see if its object has a method called C<METHOD>,
436 if it does then a reference to the sub is returned; if it does not then
437 I<undef> is returned.
439 =item VERSION( [NEED] )
441 C<VERSION> returns the version number of the class (package). If the
442 NEED argument is given then it will check that the current version (as
443 defined by the $VERSION variable in the given package) not less than
444 NEED; it will die if this is not the case. This method is normally
445 called as a class method. This method is called automatically by the
446 C<VERSION> form of C<use>.
448 use A 1.2 qw(some imported subs);
454 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
455 C<isa> uses a very similar method and caching strategy. This may cause
456 strange effects if the Perl code dynamically changes @ISA in any package.
458 You may add other methods to the UNIVERSAL class via Perl or XS code.
459 You do not need to C<use UNIVERSAL> in order to make these methods
460 available to your program. This is necessary only if you wish to
461 have C<isa> available as a plain subroutine in the current package.
463 =head2 TIEHANDLE now supported
465 See L<perltie> for other kinds of tie()s.
469 =item TIEHANDLE classname, LIST
471 This is the constructor for the class. That means it is expected to
472 return an object of some sort. The reference can be used to
473 hold some internal information.
478 return bless \$i, shift;
481 =item PRINT this, LIST
483 This method will be triggered every time the tied handle is printed to.
484 Beyond its self reference it also expects the list that was passed to
490 return print join( $, => map {uc} @_), $\;
493 =item PRINTF this, LIST
495 This method will be triggered every time the tied handle is printed to
496 with the C<printf()> function.
497 Beyond its self reference it also expects the format and list that was
498 passed to the printf function.
503 print sprintf($fmt, @_)."\n";
508 This method will be called when the handle is read from via the C<read>
509 or C<sysread> functions.
513 my($buf,$len,$offset) = @_;
514 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
519 This method will be called when the handle is read from. The method
520 should return undef when there is no more data.
524 return "PRINT called $$r times\n"
529 This method will be called when the C<getc> function is called.
531 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
535 As with the other types of ties, this method will be called when the
536 tied handle is about to be destroyed. This is useful for debugging and
537 possibly for cleaning up.
545 =head2 Malloc enhancements
547 Four new compilation flags are recognized by malloc.c. (They have no
548 effect if perl is compiled with system malloc().)
552 =item -DDEBUGGING_MSTATS
554 If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print
555 memory statistics at runtime by running Perl thusly:
557 env PERL_DEBUG_MSTATS=2 perl your_script_here
559 The value of 2 means to print statistics after compilation and on
560 exit; with a value of 1, the statistics ares printed only on exit.
561 (If you want the statistics at an arbitrary time, you'll need to
562 install the optional module Devel::Peek.)
564 =item -DEMERGENCY_SBRK
566 If this macro is defined, running out of memory need not be a fatal
567 error: a memory pool can allocated by assigning to the special
568 variable C<$^M>. See L<"$^M">.
572 Perl memory allocation is by bucket with sizes close to powers of two.
573 Because of these malloc overhead may be big, especially for data of
574 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
575 a slightly different algorithm for small allocations (up to 64 bytes
576 long), which makes it possible to have overhead down to 1 byte for
577 allocations which are powers of two (and appear quite often).
579 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
580 about 20% for typical Perl usage. Expected slowdown due to additional
581 malloc overhead is in fractions of a percent (hard to measure, because
582 of the effect of saved memory on speed).
584 =item -DTWO_POT_OPTIMIZE
586 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
587 with size close to a power of two; but this works for big allocations
588 (starting with 16K by default). Such allocations are typical for big
589 hashes and special-purpose scripts, especially image processing.
591 On recent systems, the fact that perl requires 2M from system for 1M
592 allocation will not affect speed of execution, since the tail of such
593 a chunk is not going to be touched (and thus will not require real
594 memory). However, it may result in a premature out-of-memory error.
595 So if you will be manipulating very large blocks with sizes close to
596 powers of two, it would be wise to define this macro.
598 Expected saving of memory is 0-100% (100% in applications which
599 require most memory in such 2**n chunks); expected slowdown is
604 =head2 Miscellaneous efficiency enhancements
606 Functions that have an empty prototype and that do nothing but return
607 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
609 Each unique hash key is only allocated once, no matter how many hashes
610 have an entry with that key. So even if you have 100 copies of the
611 same hash, the hash keys never have to be reallocated.
615 Six new pragmatic modules exist:
619 =item use autouse MODULE => qw(sub1 sub2 sub3)
621 Defers C<require MODULE> until someone calls one of the specified
622 subroutines (which must be exported by MODULE). This pragma should be
623 used with caution, and only when necessary.
629 Looks for MakeMaker-like I<'blib'> directory structure starting in
630 I<dir> (or current directory) and working back up to five levels of
633 Intended for use on command line with B<-M> option as a way of testing
634 arbitrary scripts against an uninstalled version of a package.
636 =item use constant NAME => VALUE
638 Provides a convenient interface for creating compile-time constants,
639 See L<perlsub/"Constant Functions">.
643 Tells the compiler to enable (or disable) the use of POSIX locales for
646 When C<use locale> is in effect, the current LC_CTYPE locale is used
647 for regular expressions and case mapping; LC_COLLATE for string
648 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
649 (but B<not> in print). LC_NUMERIC is always used in write, since
650 lexical scoping of formats is problematic at best.
652 Each C<use locale> or C<no locale> affects statements to the end of
653 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
654 current file. Locales can be switched and queried with
657 See L<perllocale> for more information.
661 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
665 Enable VMS-specific language features. Currently, there are three
666 VMS-specific features available: 'status', which makes C<$?> and
667 C<system> return genuine VMS status values instead of emulating POSIX;
668 'exit', which makes C<exit> take a genuine VMS status value instead of
669 assuming that C<exit 1> is an error; and 'time', which makes all times
670 relative to the local time zone, in the VMS tradition.
676 =head2 Required Updates
678 Though Perl 5.004 is compatible with almost all modules that work
679 with Perl 5.003, there are a few exceptions:
681 Module Required Version for Perl 5.004
682 ------ -------------------------------
685 Tk Tk400.202 (-w makes noise)
687 Also, the majordomo mailing list program, version 1.94.1, doesn't work
688 with Perl 5.004 (nor with perl 4), because it executes an invalid
689 regular expression. This bug is fixed in majordomo version 1.94.2.
691 =head2 Installation directories
693 The I<installperl> script now places the Perl source files for
694 extensions in the architecture-specific library directory, which is
695 where the shared libraries for extensions have always been. This
696 change is intended to allow administrators to keep the Perl 5.004
697 library directory unchanged from a previous version, without running
698 the risk of binary incompatibility between extensions' Perl source and
701 =head2 Module information summary
703 Brand new modules, arranged by topic rather than strictly
706 CGI.pm Web server interface ("Common Gateway Interface")
707 CGI/Apache.pm Support for Apache's Perl module
708 CGI/Carp.pm Log server errors with helpful context
709 CGI/Fast.pm Support for FastCGI (persistent server process)
710 CGI/Push.pm Support for server push
711 CGI/Switch.pm Simple interface for multiple server types
713 CPAN Interface to Comprehensive Perl Archive Network
714 CPAN::FirstTime Utility for creating CPAN configuration file
715 CPAN::Nox Runs CPAN while avoiding compiled extensions
717 IO.pm Top-level interface to IO::* classes
718 IO/File.pm IO::File extension Perl module
719 IO/Handle.pm IO::Handle extension Perl module
720 IO/Pipe.pm IO::Pipe extension Perl module
721 IO/Seekable.pm IO::Seekable extension Perl module
722 IO/Select.pm IO::Select extension Perl module
723 IO/Socket.pm IO::Socket extension Perl module
725 Opcode.pm Disable named opcodes when compiling Perl code
727 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
728 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
730 FindBin.pm Find path of currently executing program
732 Class/Struct.pm Declare struct-like datatypes as Perl classes
733 File/stat.pm By-name interface to Perl's built-in stat
734 Net/hostent.pm By-name interface to Perl's built-in gethost*
735 Net/netent.pm By-name interface to Perl's built-in getnet*
736 Net/protoent.pm By-name interface to Perl's built-in getproto*
737 Net/servent.pm By-name interface to Perl's built-in getserv*
738 Time/gmtime.pm By-name interface to Perl's built-in gmtime
739 Time/localtime.pm By-name interface to Perl's built-in localtime
740 Time/tm.pm Internal object for Time::{gm,local}time
741 User/grent.pm By-name interface to Perl's built-in getgr*
742 User/pwent.pm By-name interface to Perl's built-in getpw*
744 Tie/RefHash.pm Base class for tied hashes with references as keys
746 UNIVERSAL.pm Base class for *ALL* classes
750 New constants in the existing Fcntl modules are now supported,
751 provided that your operating system happens to support them:
754 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
757 These constants are intended for use with the Perl operators sysopen()
758 and fcntl() and the basic database modules like SDBM_File. For the
759 exact meaning of these and other Fcntl constants please refer to your
760 operating system's documentation for fcntl() and open().
762 In addition, the Fcntl module now provides these constants for use
763 with the Perl operator flock():
765 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
767 These constants are defined in all environments (because where there is
768 no flock() system call, Perl emulates it). However, for historical
769 reasons, these constants are not exported unless they are explicitly
770 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
774 The IO module provides a simple mechanism to load all of the IO modules at one
775 go. Currently this includes:
783 For more information on any of these modules, please see its
784 respective documentation.
788 The Math::Complex module has been totally rewritten, and now supports
789 more operations. These are overloaded:
791 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
793 And these functions are now exported:
796 log10 logn ln cbrt root
809 This new module provides a simpler interface to parts of Math::Complex for
810 those who need trigonometric functions only for real numbers.
814 There have been quite a few changes made to DB_File. Here are a few of
821 Fixed a handful of bugs.
825 By public demand, added support for the standard hash function exists().
829 Made it compatible with Berkeley DB 1.86.
833 Made negative subscripts work with RECNO interface.
837 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
838 mode from 0640 to 0666.
842 Made DB_File automatically import the open() constants (O_RDWR,
843 O_CREAT etc.) from Fcntl, if available.
847 Updated documentation.
851 Refer to the HISTORY section in DB_File.pm for a complete list of
852 changes. Everything after DB_File 1.01 has been added since 5.003.
856 Major rewrite - support added for both udp echo and real icmp pings.
858 =head2 Object-oriented overrides for builtin operators
860 Many of the Perl builtins returning lists now have
861 object-oriented overrides. These are:
873 For example, you can now say
877 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
879 =head1 Utility Changes
885 =item C<void> XSUBs now default to returning nothing
887 Due to a documentation/implementation bug in previous versions of
888 Perl, XSUBs with a return type of C<void> have actually been
889 returning one value. Usually that value was the GV for the XSUB,
890 but sometimes it was some already freed or reused value, which would
891 sometimes lead to program failure.
893 In Perl 5.004, if an XSUB is declared as returning C<void>, it
894 actually returns no value, i.e. an empty list (though there is a
895 backward-compatibility exception; see below). If your XSUB really
896 does return an SV, you should give it a return type of C<SV *>.
898 For backward compatibility, I<xsubpp> tries to guess whether a
899 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
900 It does so by examining the text of the XSUB: if I<xsubpp> finds
901 what looks like an assignment to C<ST(0)>, it assumes that the
902 XSUB's return type is really C<SV *>.
906 =head1 C Language API Changes
910 =item C<gv_fetchmethod> and C<perl_call_sv>
912 The C<gv_fetchmethod> function finds a method for an object, just like
913 in Perl 5.003. The GV it returns may be a method cache entry.
914 However, in Perl 5.004, method cache entries are not visible to users;
915 therefore, they can no longer be passed directly to C<perl_call_sv>.
916 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
917 and pass the CV to C<perl_call_sv>.
919 The most likely symptom of passing the result of C<gv_fetchmethod> to
920 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
921 error on the I<second> call to a given method (since there is no cache
924 =item C<perl_eval_pv>
926 A new function handy for eval'ing strings of Perl code inside C code.
927 This function returns the value from the eval statement, which can
928 be used instead of fetching globals from the symbol table. See
929 L<perlguts>, L<perlembed> and L<perlcall> for details and examples.
931 =item Extended API for manipulating hashes
933 Internal handling of hash keys has changed. The old hashtable API is
934 still fully supported, and will likely remain so. The additions to the
935 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
936 real scalars as keys rather than plain strings (nontied hashes still
937 can only use strings as keys). New extensions must use the new hash
938 access functions and macros if they wish to use C<SV*> keys. These
939 additions also make it feasible to manipulate C<HE*>s (hash entries),
940 which can be more efficient. See L<perlguts> for details.
944 =head1 Documentation Changes
946 Many of the base and library pods were updated. These
947 new pods are included in section 1:
957 Locale support (internationalization and localization).
961 Tutorial on Perl OO programming.
965 Perl internal IO abstraction interface.
969 Although not new, this has been massively updated.
973 Although not new, this has been massively updated.
977 =head1 New Diagnostics
979 Several new conditions will trigger warnings that were
980 silent before. Some only affect certain platforms.
981 The following new warnings and errors outline these.
982 These messages are classified as follows (listed in
983 increasing order of desperation):
985 (W) A warning (optional).
986 (D) A deprecation (optional).
987 (S) A severe warning (mandatory).
988 (F) A fatal error (trappable).
989 (P) An internal error you should never see (trappable).
990 (X) A very fatal error (nontrappable).
991 (A) An alien error message (not generated by Perl).
995 =item "my" variable %s masks earlier declaration in same scope
997 (S) A lexical variable has been redeclared in the same scope, effectively
998 eliminating all access to the previous instance. This is almost always
999 a typographical error. Note that the earlier variable will still exist
1000 until the end of the scope or until all closure referents to it are
1003 =item %s argument is not a HASH element or slice
1005 (F) The argument to delete() must be either a hash element, such as
1008 $ref->[12]->{"susie"}
1010 or a hash slice, such as
1012 @foo{$bar, $baz, $xyzzy}
1013 @{$ref->[12]}{"susie", "queue"}
1015 =item Allocation too large: %lx
1017 (X) You can't allocate more than 64K on an MS-DOS machine.
1019 =item Allocation too large
1021 (F) You can't allocate more than 2^31+"small amount" bytes.
1023 =item Applying %s to %s will act on scalar(%s)
1025 (W) The pattern match (//), substitution (s///), and translation (tr///)
1026 operators work on scalar values. If you apply one of them to an array
1027 or a hash, it will convert the array or hash to a scalar value -- the
1028 length of an array, or the population info of a hash -- and then work on
1029 that scalar value. This is probably not what you meant to do. See
1030 L<perlfunc/grep> and L<perlfunc/map> for alternatives.
1032 =item Attempt to free nonexistent shared string
1034 (P) Perl maintains a reference counted internal table of strings to
1035 optimize the storage and access of hash keys and other strings. This
1036 indicates someone tried to decrement the reference count of a string
1037 that can no longer be found in the table.
1039 =item Attempt to use reference as lvalue in substr
1041 (W) You supplied a reference as the first argument to substr() used
1042 as an lvalue, which is pretty strange. Perhaps you forgot to
1043 dereference it first. See L<perlfunc/substr>.
1045 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
1047 (F) Only hard references are allowed by "strict refs". Symbolic references
1048 are disallowed. See L<perlref>.
1050 =item Cannot resolve method `%s' overloading `%s' in package `%s'
1052 (P) Internal error trying to resolve overloading specified by a method
1053 name (as opposed to a subroutine reference).
1055 =item Constant subroutine %s redefined
1057 (S) You redefined a subroutine which had previously been eligible for
1058 inlining. See L<perlsub/"Constant Functions"> for commentary and
1061 =item Constant subroutine %s undefined
1063 (S) You undefined a subroutine which had previously been eligible for
1064 inlining. See L<perlsub/"Constant Functions"> for commentary and
1067 =item Copy method did not return a reference
1069 (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>.
1073 (F) You passed die() an empty string (the equivalent of C<die "">) or
1074 you called it with no args and both C<$@> and C<$_> were empty.
1076 =item Exiting pseudo-block via %s
1078 (W) You are exiting a rather special block construct (like a sort block or
1079 subroutine) by unconventional means, such as a goto, or a loop control
1080 statement. See L<perlfunc/sort>.
1082 =item Identifier too long
1084 (F) Perl limits identifiers (names for variables, functions, etc.) to
1085 252 characters for simple names, somewhat more for compound names (like
1086 C<$A::B>). You've exceeded Perl's limits. Future versions of Perl are
1087 likely to eliminate these arbitrary limitations.
1089 =item Illegal character %s (carriage return)
1091 (F) A carriage return character was found in the input. This is an
1092 error, and not a warning, because carriage return characters can break
1093 multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>).
1095 =item Illegal switch in PERL5OPT: %s
1097 (X) The PERL5OPT environment variable may only be used to set the
1098 following switches: B<-[DIMUdmw]>.
1100 =item Integer overflow in hex number
1102 (S) The literal hex number you have specified is too big for your
1103 architecture. On a 32-bit architecture the largest hex literal is
1106 =item Integer overflow in octal number
1108 (S) The literal octal number you have specified is too big for your
1109 architecture. On a 32-bit architecture the largest octal literal is
1112 =item internal error: glob failed
1114 (P) Something went wrong with the external program(s) used for C<glob>
1115 and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is
1116 broken. If so, you should change all of the csh-related variables in
1117 config.sh: If you have tcsh, make the variables refer to it as if it
1118 were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all
1119 empty (except that C<d_csh> should be C<'undef'>) so that Perl will
1120 think csh is missing. In either case, after editing config.sh, run
1121 C<./Configure -S> and rebuild Perl.
1123 =item Invalid type in pack: '%s'
1125 (F) The given character is not a valid pack type. See L<perlfunc/pack>.
1127 =item Invalid type in unpack: '%s'
1129 (F) The given character is not a valid unpack type. See L<perlfunc/unpack>.
1131 =item Name "%s::%s" used only once: possible typo
1133 (W) Typographical errors often show up as unique variable names.
1134 If you had a good reason for having a unique name, then just mention
1135 it again somehow to suppress the message (the C<use vars> pragma is
1136 provided for just this purpose).
1138 =item Null picture in formline
1140 (F) The first argument to formline must be a valid format picture
1141 specification. It was found to be empty, which probably means you
1142 supplied it an uninitialized value. See L<perlform>.
1144 =item Offset outside string
1146 (F) You tried to do a read/write/send/recv operation with an offset
1147 pointing outside the buffer. This is difficult to imagine.
1148 The sole exception to this is that C<sysread()>ing past the buffer
1149 will extend the buffer and zero pad the new area.
1151 =item Out of memory!
1153 (X|F) The malloc() function returned 0, indicating there was insufficient
1154 remaining memory (or virtual memory) to satisfy the request.
1156 The request was judged to be small, so the possibility to trap it
1157 depends on the way Perl was compiled. By default it is not trappable.
1158 However, if compiled for this, Perl may use the contents of C<$^M> as
1159 an emergency pool after die()ing with this message. In this case the
1160 error is trappable I<once>.
1162 =item Out of memory during request for %s
1164 (F) The malloc() function returned 0, indicating there was insufficient
1165 remaining memory (or virtual memory) to satisfy the request. However,
1166 the request was judged large enough (compile-time default is 64K), so
1167 a possibility to shut down by trapping this error is granted.
1169 =item Possible attempt to put comments in qw() list
1171 (W) qw() lists contain items separated by whitespace; as with literal
1172 strings, comment characters are not ignored, but are instead treated
1173 as literal data. (You may have used different delimiters than the
1174 exclamation marks parentheses shown here; braces are also frequently
1177 You probably wrote something like this:
1184 when you should have written this:
1191 If you really want comments, build your list the
1192 old-fashioned way, with quotes and commas:
1196 'b', # another comment
1199 =item Possible attempt to separate words with commas
1201 (W) qw() lists contain items separated by whitespace; therefore commas
1202 aren't needed to separate the items. (You may have used different
1203 delimiters than the parentheses shown here; braces are also frequently
1206 You probably wrote something like this:
1210 which puts literal commas into some of the list items. Write it without
1211 commas if you don't want them to appear in your data:
1215 =item Scalar value @%s{%s} better written as $%s{%s}
1217 (W) You've used a hash slice (indicated by @) to select a single element of
1218 a hash. Generally it's better to ask for a scalar value (indicated by $).
1219 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
1220 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
1221 like a list when you assign to it, and provides a list context to its
1222 subscript, which can do weird things if you're expecting only one subscript.
1224 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
1226 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
1227 Stubs should never be implicitely created, but explicit calls to C<can>
1230 =item Too late for "B<-T>" option
1232 (X) The #! line (or local equivalent) in a Perl script contains the
1233 B<-T> option, but Perl was not invoked with B<-T> in its argument
1234 list. This is an error because, by the time Perl discovers a B<-T> in
1235 a script, it's too late to properly taint everything from the
1236 environment. So Perl gives up.
1238 =item untie attempted while %d inner references still exist
1240 (W) A copy of the object returned from C<tie> (or C<tied>) was still
1241 valid when C<untie> was called.
1243 =item Unrecognized character %s
1245 (F) The Perl parser has no idea what to do with the specified character
1246 in your Perl script (or eval). Perhaps you tried to run a compressed
1247 script, a binary program, or a directory as a Perl program.
1249 =item Unsupported function fork
1251 (F) Your version of executable does not support forking.
1253 Note that under some systems, like OS/2, there may be different flavors of
1254 Perl executables, some of which may support fork, some not. Try changing
1255 the name you call Perl by to C<perl_>, C<perl__>, and so on.
1257 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
1259 (D) Perl versions before 5.004 misinterpreted any type marker followed
1260 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
1261 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
1263 However, the developers of Perl 5.004 could not fix this bug completely,
1264 because at least two widely-used modules depend on the old meaning of
1265 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
1266 old (broken) way inside strings; but it generates this message as a
1267 warning. And in Perl 5.005, this special treatment will cease.
1269 =item Value of %s can be "0"; test with defined()
1271 (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>,
1272 or C<readdir()> as a boolean value. Each of these constructs can return a
1273 value of "0"; that would make the conditional expression false, which is
1274 probably not what you intended. When using these constructs in conditional
1275 expressions, test their values with the C<defined> operator.
1277 =item Variable "%s" may be unavailable
1279 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1280 subroutine, and outside that is another subroutine; and the anonymous
1281 (innermost) subroutine is referencing a lexical variable defined in
1282 the outermost subroutine. For example:
1284 sub outermost { my $a; sub middle { sub { $a } } }
1286 If the anonymous subroutine is called or referenced (directly or
1287 indirectly) from the outermost subroutine, it will share the variable
1288 as you would expect. But if the anonymous subroutine is called or
1289 referenced when the outermost subroutine is not active, it will see
1290 the value of the shared variable as it was before and during the
1291 *first* call to the outermost subroutine, which is probably not what
1294 In these circumstances, it is usually best to make the middle
1295 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1296 support for shared variables in nested anonymous subroutines; a named
1297 subroutine in between interferes with this feature.
1299 =item Variable "%s" will not stay shared
1301 (W) An inner (nested) I<named> subroutine is referencing a lexical
1302 variable defined in an outer subroutine.
1304 When the inner subroutine is called, it will probably see the value of
1305 the outer subroutine's variable as it was before and during the
1306 *first* call to the outer subroutine; in this case, after the first
1307 call to the outer subroutine is complete, the inner and outer
1308 subroutines will no longer share a common value for the variable. In
1309 other words, the variable will no longer be shared.
1311 Furthermore, if the outer subroutine is anonymous and references a
1312 lexical variable outside itself, then the outer and inner subroutines
1313 will I<never> share the given variable.
1315 This problem can usually be solved by making the inner subroutine
1316 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1317 reference variables in outer subroutines are called or referenced,
1318 they are automatically rebound to the current values of such
1321 =item Warning: something's wrong
1323 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1324 you called it with no args and C<$_> was empty.
1326 =item Ill-formed logical name |%s| in prime_env_iter
1328 (W) A warning peculiar to VMS. A logical name was encountered when preparing
1329 to iterate over %ENV which violates the syntactic rules governing logical
1330 names. Since it cannot be translated normally, it is skipped, and will not
1331 appear in %ENV. This may be a benign occurrence, as some software packages
1332 might directly modify logical name tables and introduce nonstandard names,
1333 or it may indicate that a logical name table has been corrupted.
1335 =item Got an error from DosAllocMem
1337 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1338 version of Perl, and this should not happen anyway.
1340 =item Malformed PERLLIB_PREFIX
1342 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1350 with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix
1351 of a builtin library search path, prefix2 is substituted. The error
1352 may appear if components are not found, or are too long. See
1353 "PERLLIB_PREFIX" in F<README.os2>.
1355 =item PERL_SH_DIR too long
1357 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1358 C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>.
1360 =item Process terminated by SIG%s
1362 (W) This is a standard message issued by OS/2 applications, while *nix
1363 applications die in silence. It is considered a feature of the OS/2
1364 port. One can easily disable this by appropriate sighandlers, see
1365 L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT"
1372 If you find what you think is a bug, you might check the headers of
1373 recently posted articles in the comp.lang.perl.misc newsgroup.
1374 There may also be information at http://www.perl.com/perl/, the Perl
1377 If you believe you have an unreported bug, please run the B<perlbug>
1378 program included with your release. Make sure you trim your bug down
1379 to a tiny but sufficient test case. Your bug report, along with the
1380 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1381 analysed by the Perl porting team.
1385 The F<Changes> file for exhaustive details on what changed.
1387 The F<INSTALL> file for how to build Perl. This file has been
1388 significantly updated for 5.004, so even veteran users should
1391 The F<README> file for general stuff.
1393 The F<Copying> file for copyright information.
1397 Constructed by Tom Christiansen, grabbing material with permission
1398 from innumerable contributors, with kibitzing by more than a few Perl
1401 Last update: Sat Mar 8 19:51:26 EST 1997