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 constants
199 The current package name at compile time, or the undefined value if
200 there is no current package (due to a C<package;> directive). Like
201 C<__FILE__> and C<__LINE__>, C<__PACKAGE__> does I<not> interpolate
206 =head2 New and changed builtin variables
212 Extended error message on some platforms. (Also known as
213 $EXTENDED_OS_ERROR if you C<use English>).
217 The current set of syntax checks enabled by C<use strict>. See the
218 documentation of C<strict> for more details. Not actually new, but
220 Because it is intended for internal use by Perl core components,
221 there is no C<use English> long name for this variable.
225 By default, running out of memory it is not trappable. However, if
226 compiled for this, Perl may use the contents of C<$^M> as an emergency
227 pool after die()ing with this message. Suppose that your Perl were
228 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
232 would allocate a 64K buffer for use when in emergency.
233 See the F<INSTALL> file for information on how to enable this option.
234 As a disincentive to casual use of this advanced feature,
235 there is no C<use English> long name for this variable.
239 =head2 New and changed builtin functions
243 =item delete on slices
245 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
249 is now supported on more platforms, prefers fcntl to lockf when
250 emulating, and always flushes before (un)locking.
252 =item printf and sprintf
254 Perl now implements these functions itself; it doesn't use the C
255 library function sprintf() any more, except for floating-point
256 numbers, and even then only known flags are allowed. As a result, it
257 is now possible to know which conversions and flags will work, and
260 The new conversions in Perl's sprintf() are:
263 %p a pointer (the address of the Perl value, in hexadecimal)
264 %n special: B<stores> into the next variable in the parameter
265 list the number of characters printed so far
267 The new flags that go between the C<%> and the conversion are:
269 # prefix octal with "0", hex with "0x"
270 h interpret integer as C type "short" or "unsigned short"
271 V interpret integer as Perl's standard integer type
273 Also, where a number would appear in the flags, an asterisk ("*") may
274 be used instead, in which case Perl uses the next item in the
275 parameter list as the given number (that is, as the field width or
276 precision). If a field width obtained through "*" is negative, it has
277 the same effect as the '-' flag: left-justification.
279 See L<perlfunc/sprintf> for a complete list of conversion and flags.
281 =item keys as an lvalue
283 As an lvalue, C<keys> allows you to increase the number of hash buckets
284 allocated for the given hash. This can gain you a measure of efficiency if
285 you know the hash is going to get big. (This is similar to pre-extending
286 an array by assigning a larger number to $#array.) If you say
290 then C<%hash> will have at least 200 buckets allocated for it. These
291 buckets will be retained even if you do C<%hash = ()>; use C<undef
292 %hash> if you want to free the storage while C<%hash> is still in scope.
293 You can't shrink the number of buckets allocated for the hash using
294 C<keys> in this way (but you needn't worry about doing this by accident,
295 as trying has no effect).
297 =item my() in Control Structures
299 You can now use my() (with or without the parentheses) in the control
300 expressions of control structures such as:
302 while (defined(my $line = <>)) {
308 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
310 } elsif ($answer =~ /^n(o)?$/i) {
314 die "`$answer' is neither `yes' nor `no'";
317 Also, you can declare a foreach loop control variable as lexical by
318 preceding it with the word "my". For example, in:
320 foreach my $i (1, 2, 3) {
324 $i is a lexical variable, and the scope of $i extends to the end of
325 the loop, but not beyond it.
327 Note that you still cannot use my() on global punctuation variables
328 such as $_ and the like.
330 =item pack() and unpack()
332 A new format 'w' represents a BER compressed integer (as defined in
333 ASN.1). Its format is a sequence of one or more bytes, each of which
334 provides seven bits of the total value, with the most significant
335 first. Bit eight of each byte is set, except for the last byte, in
336 which bit eight is clear.
338 Both pack() and unpack() now fail when their templates contain invalid
339 types. (Invalid types used to be ignored.)
343 The new sysseek() operator is a variant of seek() that sets and gets the
344 file's system read/write position, using the lseek(2) system call. It is
345 the only reliable way to seek before using sysread() or syswrite(). Its
346 return value is the new position, or the undefined value on failure.
350 If the first argument to C<use> is a number, it is treated as a version
351 number instead of a module name. If the version of the Perl interpreter
352 is less than VERSION, then an error message is printed and Perl exits
353 immediately. Because C<use> occurs at compile time, this check happens
354 immediately during the compilation process, unlike C<require VERSION>,
355 which waits until runtime for the check. This is often useful if you
356 need to check the current Perl version before C<use>ing library modules
357 which have changed in incompatible ways from older versions of Perl.
358 (We try not to do this more than we have to.)
360 =item use Module VERSION LIST
362 If the VERSION argument is present between Module and LIST, then the
363 C<use> will call the VERSION method in class Module with the given
364 version as an argument. The default VERSION method, inherited from
365 the UNIVERSAL class, croaks if the given version is larger than the
366 value of the variable $Module::VERSION. (Note that there is not a
367 comma after VERSION!)
369 This version-checking mechanism is similar to the one currently used
370 in the Exporter module, but it is faster and can be used with modules
371 that don't use the Exporter. It is the recommended method for new
374 =item prototype(FUNCTION)
376 Returns the prototype of a function as a string (or C<undef> if the
377 function has no prototype). FUNCTION is a reference to or the name of the
378 function whose prototype you want to retrieve.
379 (Not actually new; just never documented before.)
383 The default seed for C<srand>, which used to be C<time>, has been changed.
384 Now it's a heady mix of difficult-to-predict system-dependent values,
385 which should be sufficient for most everyday purposes.
387 Previous to version 5.004, calling C<rand> without first calling C<srand>
388 would yield the same sequence of random numbers on most or all machines.
389 Now, when perl sees that you're calling C<rand> and haven't yet called
390 C<srand>, it calls C<srand> with the default seed. You should still call
391 C<srand> manually if your code might ever be run on a pre-5.004 system,
392 of course, or if you want a seed other than the default.
396 Functions documented in the Camel to default to $_ now in
397 fact do, and all those that do are so documented in L<perlfunc>.
399 =item C<m//g> does not reset search position on failure
401 The C<m//g> match iteration construct used to reset its target string's
402 search position (which is visible through the C<pos> operator) when a
403 match failed; as a result, the next C<m//g> match would start at the
404 beginning of the string). With Perl 5.004, the search position must be
405 reset explicitly, as with C<pos $str = 0;>, or by modifying the target
406 string. This change in Perl makes it possible to chain matches together
407 in conjunction with the C<\G> zero-width assertion. See L<perlop> and
410 Here is an illustration of what it takes to get the old behavior:
412 for ( qw(this and that are not what you think you got) ) {
413 while ( /(\w*t\w*)/g ) { print "t word is: $1\n" }
414 pos = 0; # REQUIRED FOR 5.004
415 while ( /(\w*a\w*)/g ) { print "a word is: $1\n" }
419 =item C<m//x> ignores whitespace before ?*+{}
421 The C<m//x> construct has always been intended to ignore all unescaped
422 whitespace. However, before Perl 5.004, whitespace had the effect of
423 escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was
424 (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004.
426 =item nested C<sub{}> closures work now
428 Prior to the 5.004 release, nested anonymous functions didn't work
431 =item formats work right on changing lexicals
433 Just like anonymous functions that contain lexical variables
434 that change (like a lexical index variable for a C<foreach> loop),
435 formats now work properly. For example, this silently failed
436 before, and is fine now:
439 foreach $i ( 1 .. 10 ) {
449 =head2 New builtin methods
451 The C<UNIVERSAL> package automatically contains the following methods that
452 are inherited by all other classes:
458 C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
460 C<isa> is also exportable and can be called as a sub with two arguments. This
461 allows the ability to check what a reference points to. Example:
463 use UNIVERSAL qw(isa);
465 if(isa($ref, 'ARRAY')) {
471 C<can> checks to see if its object has a method called C<METHOD>,
472 if it does then a reference to the sub is returned; if it does not then
473 I<undef> is returned.
475 =item VERSION( [NEED] )
477 C<VERSION> returns the version number of the class (package). If the
478 NEED argument is given then it will check that the current version (as
479 defined by the $VERSION variable in the given package) not less than
480 NEED; it will die if this is not the case. This method is normally
481 called as a class method. This method is called automatically by the
482 C<VERSION> form of C<use>.
484 use A 1.2 qw(some imported subs);
490 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
491 C<isa> uses a very similar method and caching strategy. This may cause
492 strange effects if the Perl code dynamically changes @ISA in any package.
494 You may add other methods to the UNIVERSAL class via Perl or XS code.
495 You do not need to C<use UNIVERSAL> in order to make these methods
496 available to your program. This is necessary only if you wish to
497 have C<isa> available as a plain subroutine in the current package.
499 =head2 TIEHANDLE now supported
501 See L<perltie> for other kinds of tie()s.
505 =item TIEHANDLE classname, LIST
507 This is the constructor for the class. That means it is expected to
508 return an object of some sort. The reference can be used to
509 hold some internal information.
514 return bless \$i, shift;
517 =item PRINT this, LIST
519 This method will be triggered every time the tied handle is printed to.
520 Beyond its self reference it also expects the list that was passed to
526 return print join( $, => map {uc} @_), $\;
529 =item PRINTF this, LIST
531 This method will be triggered every time the tied handle is printed to
532 with the C<printf()> function.
533 Beyond its self reference it also expects the format and list that was
534 passed to the printf function.
539 print sprintf($fmt, @_)."\n";
544 This method will be called when the handle is read from via the C<read>
545 or C<sysread> functions.
549 my($buf,$len,$offset) = @_;
550 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
555 This method will be called when the handle is read from. The method
556 should return undef when there is no more data.
560 return "PRINT called $$r times\n"
565 This method will be called when the C<getc> function is called.
567 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
571 As with the other types of ties, this method will be called when the
572 tied handle is about to be destroyed. This is useful for debugging and
573 possibly for cleaning up.
581 =head2 Malloc enhancements
583 Four new compilation flags are recognized by malloc.c. (They have no
584 effect if perl is compiled with system malloc().)
588 =item -DDEBUGGING_MSTATS
590 If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print
591 memory statistics at runtime by running Perl thusly:
593 env PERL_DEBUG_MSTATS=2 perl your_script_here
595 The value of 2 means to print statistics after compilation and on
596 exit; with a value of 1, the statistics ares printed only on exit.
597 (If you want the statistics at an arbitrary time, you'll need to
598 install the optional module Devel::Peek.)
600 =item -DEMERGENCY_SBRK
602 If this macro is defined, running out of memory need not be a fatal
603 error: a memory pool can allocated by assigning to the special
604 variable C<$^M>. See L<"$^M">.
608 Perl memory allocation is by bucket with sizes close to powers of two.
609 Because of these malloc overhead may be big, especially for data of
610 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
611 a slightly different algorithm for small allocations (up to 64 bytes
612 long), which makes it possible to have overhead down to 1 byte for
613 allocations which are powers of two (and appear quite often).
615 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
616 about 20% for typical Perl usage. Expected slowdown due to additional
617 malloc overhead is in fractions of a percent (hard to measure, because
618 of the effect of saved memory on speed).
620 =item -DTWO_POT_OPTIMIZE
622 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
623 with size close to a power of two; but this works for big allocations
624 (starting with 16K by default). Such allocations are typical for big
625 hashes and special-purpose scripts, especially image processing.
627 On recent systems, the fact that perl requires 2M from system for 1M
628 allocation will not affect speed of execution, since the tail of such
629 a chunk is not going to be touched (and thus will not require real
630 memory). However, it may result in a premature out-of-memory error.
631 So if you will be manipulating very large blocks with sizes close to
632 powers of two, it would be wise to define this macro.
634 Expected saving of memory is 0-100% (100% in applications which
635 require most memory in such 2**n chunks); expected slowdown is
640 =head2 Miscellaneous efficiency enhancements
642 Functions that have an empty prototype and that do nothing but return
643 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
645 Each unique hash key is only allocated once, no matter how many hashes
646 have an entry with that key. So even if you have 100 copies of the
647 same hash, the hash keys never have to be reallocated.
651 Six new pragmatic modules exist:
655 =item use autouse MODULE => qw(sub1 sub2 sub3)
657 Defers C<require MODULE> until someone calls one of the specified
658 subroutines (which must be exported by MODULE). This pragma should be
659 used with caution, and only when necessary.
665 Looks for MakeMaker-like I<'blib'> directory structure starting in
666 I<dir> (or current directory) and working back up to five levels of
669 Intended for use on command line with B<-M> option as a way of testing
670 arbitrary scripts against an uninstalled version of a package.
672 =item use constant NAME => VALUE
674 Provides a convenient interface for creating compile-time constants,
675 See L<perlsub/"Constant Functions">.
679 Tells the compiler to enable (or disable) the use of POSIX locales for
682 When C<use locale> is in effect, the current LC_CTYPE locale is used
683 for regular expressions and case mapping; LC_COLLATE for string
684 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
685 (but B<not> in print). LC_NUMERIC is always used in write, since
686 lexical scoping of formats is problematic at best.
688 Each C<use locale> or C<no locale> affects statements to the end of
689 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
690 current file. Locales can be switched and queried with
693 See L<perllocale> for more information.
697 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
701 Enable VMS-specific language features. Currently, there are three
702 VMS-specific features available: 'status', which makes C<$?> and
703 C<system> return genuine VMS status values instead of emulating POSIX;
704 'exit', which makes C<exit> take a genuine VMS status value instead of
705 assuming that C<exit 1> is an error; and 'time', which makes all times
706 relative to the local time zone, in the VMS tradition.
712 =head2 Required Updates
714 Though Perl 5.004 is compatible with almost all modules that work
715 with Perl 5.003, there are a few exceptions:
717 Module Required Version for Perl 5.004
718 ------ -------------------------------
721 Tk Tk400.202 (-w makes noise)
723 Also, the majordomo mailing list program, version 1.94.1, doesn't work
724 with Perl 5.004 (nor with perl 4), because it executes an invalid
725 regular expression. This bug is fixed in majordomo version 1.94.2.
727 =head2 Installation directories
729 The I<installperl> script now places the Perl source files for
730 extensions in the architecture-specific library directory, which is
731 where the shared libraries for extensions have always been. This
732 change is intended to allow administrators to keep the Perl 5.004
733 library directory unchanged from a previous version, without running
734 the risk of binary incompatibility between extensions' Perl source and
737 =head2 Module information summary
739 Brand new modules, arranged by topic rather than strictly
742 CGI.pm Web server interface ("Common Gateway Interface")
743 CGI/Apache.pm Support for Apache's Perl module
744 CGI/Carp.pm Log server errors with helpful context
745 CGI/Fast.pm Support for FastCGI (persistent server process)
746 CGI/Push.pm Support for server push
747 CGI/Switch.pm Simple interface for multiple server types
749 CPAN Interface to Comprehensive Perl Archive Network
750 CPAN::FirstTime Utility for creating CPAN configuration file
751 CPAN::Nox Runs CPAN while avoiding compiled extensions
753 IO.pm Top-level interface to IO::* classes
754 IO/File.pm IO::File extension Perl module
755 IO/Handle.pm IO::Handle extension Perl module
756 IO/Pipe.pm IO::Pipe extension Perl module
757 IO/Seekable.pm IO::Seekable extension Perl module
758 IO/Select.pm IO::Select extension Perl module
759 IO/Socket.pm IO::Socket extension Perl module
761 Opcode.pm Disable named opcodes when compiling Perl code
763 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
764 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
766 FindBin.pm Find path of currently executing program
768 Class/Struct.pm Declare struct-like datatypes as Perl classes
769 File/stat.pm By-name interface to Perl's builtin stat
770 Net/hostent.pm By-name interface to Perl's builtin gethost*
771 Net/netent.pm By-name interface to Perl's builtin getnet*
772 Net/protoent.pm By-name interface to Perl's builtin getproto*
773 Net/servent.pm By-name interface to Perl's builtin getserv*
774 Time/gmtime.pm By-name interface to Perl's builtin gmtime
775 Time/localtime.pm By-name interface to Perl's builtin localtime
776 Time/tm.pm Internal object for Time::{gm,local}time
777 User/grent.pm By-name interface to Perl's builtin getgr*
778 User/pwent.pm By-name interface to Perl's builtin getpw*
780 Tie/RefHash.pm Base class for tied hashes with references as keys
782 UNIVERSAL.pm Base class for *ALL* classes
786 New constants in the existing Fcntl modules are now supported,
787 provided that your operating system happens to support them:
790 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
793 These constants are intended for use with the Perl operators sysopen()
794 and fcntl() and the basic database modules like SDBM_File. For the
795 exact meaning of these and other Fcntl constants please refer to your
796 operating system's documentation for fcntl() and open().
798 In addition, the Fcntl module now provides these constants for use
799 with the Perl operator flock():
801 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
803 These constants are defined in all environments (because where there is
804 no flock() system call, Perl emulates it). However, for historical
805 reasons, these constants are not exported unless they are explicitly
806 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
810 The IO module provides a simple mechanism to load all of the IO modules at one
811 go. Currently this includes:
819 For more information on any of these modules, please see its
820 respective documentation.
824 The Math::Complex module has been totally rewritten, and now supports
825 more operations. These are overloaded:
827 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
829 And these functions are now exported:
832 log10 logn ln cbrt root
845 This new module provides a simpler interface to parts of Math::Complex for
846 those who need trigonometric functions only for real numbers.
850 There have been quite a few changes made to DB_File. Here are a few of
857 Fixed a handful of bugs.
861 By public demand, added support for the standard hash function exists().
865 Made it compatible with Berkeley DB 1.86.
869 Made negative subscripts work with RECNO interface.
873 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
874 mode from 0640 to 0666.
878 Made DB_File automatically import the open() constants (O_RDWR,
879 O_CREAT etc.) from Fcntl, if available.
883 Updated documentation.
887 Refer to the HISTORY section in DB_File.pm for a complete list of
888 changes. Everything after DB_File 1.01 has been added since 5.003.
892 Major rewrite - support added for both udp echo and real icmp pings.
894 =head2 Object-oriented overrides for builtin operators
896 Many of the Perl builtins returning lists now have
897 object-oriented overrides. These are:
909 For example, you can now say
913 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
915 =head1 Utility Changes
921 =item C<void> XSUBs now default to returning nothing
923 Due to a documentation/implementation bug in previous versions of
924 Perl, XSUBs with a return type of C<void> have actually been
925 returning one value. Usually that value was the GV for the XSUB,
926 but sometimes it was some already freed or reused value, which would
927 sometimes lead to program failure.
929 In Perl 5.004, if an XSUB is declared as returning C<void>, it
930 actually returns no value, i.e. an empty list (though there is a
931 backward-compatibility exception; see below). If your XSUB really
932 does return an SV, you should give it a return type of C<SV *>.
934 For backward compatibility, I<xsubpp> tries to guess whether a
935 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
936 It does so by examining the text of the XSUB: if I<xsubpp> finds
937 what looks like an assignment to C<ST(0)>, it assumes that the
938 XSUB's return type is really C<SV *>.
942 =head1 C Language API Changes
946 =item C<gv_fetchmethod> and C<perl_call_sv>
948 The C<gv_fetchmethod> function finds a method for an object, just like
949 in Perl 5.003. The GV it returns may be a method cache entry.
950 However, in Perl 5.004, method cache entries are not visible to users;
951 therefore, they can no longer be passed directly to C<perl_call_sv>.
952 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
953 and pass the CV to C<perl_call_sv>.
955 The most likely symptom of passing the result of C<gv_fetchmethod> to
956 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
957 error on the I<second> call to a given method (since there is no cache
960 =item C<perl_eval_pv>
962 A new function handy for eval'ing strings of Perl code inside C code.
963 This function returns the value from the eval statement, which can
964 be used instead of fetching globals from the symbol table. See
965 L<perlguts>, L<perlembed> and L<perlcall> for details and examples.
967 =item Extended API for manipulating hashes
969 Internal handling of hash keys has changed. The old hashtable API is
970 still fully supported, and will likely remain so. The additions to the
971 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
972 real scalars as keys rather than plain strings (nontied hashes still
973 can only use strings as keys). New extensions must use the new hash
974 access functions and macros if they wish to use C<SV*> keys. These
975 additions also make it feasible to manipulate C<HE*>s (hash entries),
976 which can be more efficient. See L<perlguts> for details.
980 =head1 Documentation Changes
982 Many of the base and library pods were updated. These
983 new pods are included in section 1:
993 Locale support (internationalization and localization).
997 Tutorial on Perl OO programming.
1001 Perl internal IO abstraction interface.
1005 Although not new, this has been massively updated.
1009 Although not new, this has been massively updated.
1013 =head1 New Diagnostics
1015 Several new conditions will trigger warnings that were
1016 silent before. Some only affect certain platforms.
1017 The following new warnings and errors outline these.
1018 These messages are classified as follows (listed in
1019 increasing order of desperation):
1021 (W) A warning (optional).
1022 (D) A deprecation (optional).
1023 (S) A severe warning (mandatory).
1024 (F) A fatal error (trappable).
1025 (P) An internal error you should never see (trappable).
1026 (X) A very fatal error (nontrappable).
1027 (A) An alien error message (not generated by Perl).
1031 =item "my" variable %s masks earlier declaration in same scope
1033 (S) A lexical variable has been redeclared in the same scope, effectively
1034 eliminating all access to the previous instance. This is almost always
1035 a typographical error. Note that the earlier variable will still exist
1036 until the end of the scope or until all closure referents to it are
1039 =item %s argument is not a HASH element or slice
1041 (F) The argument to delete() must be either a hash element, such as
1044 $ref->[12]->{"susie"}
1046 or a hash slice, such as
1048 @foo{$bar, $baz, $xyzzy}
1049 @{$ref->[12]}{"susie", "queue"}
1051 =item Allocation too large: %lx
1053 (X) You can't allocate more than 64K on an MS-DOS machine.
1055 =item Allocation too large
1057 (F) You can't allocate more than 2^31+"small amount" bytes.
1059 =item Applying %s to %s will act on scalar(%s)
1061 (W) The pattern match (//), substitution (s///), and translation (tr///)
1062 operators work on scalar values. If you apply one of them to an array
1063 or a hash, it will convert the array or hash to a scalar value -- the
1064 length of an array, or the population info of a hash -- and then work on
1065 that scalar value. This is probably not what you meant to do. See
1066 L<perlfunc/grep> and L<perlfunc/map> for alternatives.
1068 =item Attempt to free nonexistent shared string
1070 (P) Perl maintains a reference counted internal table of strings to
1071 optimize the storage and access of hash keys and other strings. This
1072 indicates someone tried to decrement the reference count of a string
1073 that can no longer be found in the table.
1075 =item Attempt to use reference as lvalue in substr
1077 (W) You supplied a reference as the first argument to substr() used
1078 as an lvalue, which is pretty strange. Perhaps you forgot to
1079 dereference it first. See L<perlfunc/substr>.
1081 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
1083 (F) Only hard references are allowed by "strict refs". Symbolic references
1084 are disallowed. See L<perlref>.
1086 =item Cannot resolve method `%s' overloading `%s' in package `%s'
1088 (P) Internal error trying to resolve overloading specified by a method
1089 name (as opposed to a subroutine reference).
1091 =item Constant subroutine %s redefined
1093 (S) You redefined a subroutine which had previously been eligible for
1094 inlining. See L<perlsub/"Constant Functions"> for commentary and
1097 =item Constant subroutine %s undefined
1099 (S) You undefined a subroutine which had previously been eligible for
1100 inlining. See L<perlsub/"Constant Functions"> for commentary and
1103 =item Copy method did not return a reference
1105 (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>.
1109 (F) You passed die() an empty string (the equivalent of C<die "">) or
1110 you called it with no args and both C<$@> and C<$_> were empty.
1112 =item Exiting pseudo-block via %s
1114 (W) You are exiting a rather special block construct (like a sort block or
1115 subroutine) by unconventional means, such as a goto, or a loop control
1116 statement. See L<perlfunc/sort>.
1118 =item Identifier too long
1120 (F) Perl limits identifiers (names for variables, functions, etc.) to
1121 252 characters for simple names, somewhat more for compound names (like
1122 C<$A::B>). You've exceeded Perl's limits. Future versions of Perl are
1123 likely to eliminate these arbitrary limitations.
1125 =item Illegal character %s (carriage return)
1127 (F) A carriage return character was found in the input. This is an
1128 error, and not a warning, because carriage return characters can break
1129 multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>).
1131 =item Illegal switch in PERL5OPT: %s
1133 (X) The PERL5OPT environment variable may only be used to set the
1134 following switches: B<-[DIMUdmw]>.
1136 =item Integer overflow in hex number
1138 (S) The literal hex number you have specified is too big for your
1139 architecture. On a 32-bit architecture the largest hex literal is
1142 =item Integer overflow in octal number
1144 (S) The literal octal number you have specified is too big for your
1145 architecture. On a 32-bit architecture the largest octal literal is
1148 =item internal error: glob failed
1150 (P) Something went wrong with the external program(s) used for C<glob>
1151 and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is
1152 broken. If so, you should change all of the csh-related variables in
1153 config.sh: If you have tcsh, make the variables refer to it as if it
1154 were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all
1155 empty (except that C<d_csh> should be C<'undef'>) so that Perl will
1156 think csh is missing. In either case, after editing config.sh, run
1157 C<./Configure -S> and rebuild Perl.
1159 =item Invalid type in pack: '%s'
1161 (F) The given character is not a valid pack type. See L<perlfunc/pack>.
1163 =item Invalid type in unpack: '%s'
1165 (F) The given character is not a valid unpack type. See L<perlfunc/unpack>.
1167 =item Name "%s::%s" used only once: possible typo
1169 (W) Typographical errors often show up as unique variable names.
1170 If you had a good reason for having a unique name, then just mention
1171 it again somehow to suppress the message (the C<use vars> pragma is
1172 provided for just this purpose).
1174 =item Null picture in formline
1176 (F) The first argument to formline must be a valid format picture
1177 specification. It was found to be empty, which probably means you
1178 supplied it an uninitialized value. See L<perlform>.
1180 =item Offset outside string
1182 (F) You tried to do a read/write/send/recv operation with an offset
1183 pointing outside the buffer. This is difficult to imagine.
1184 The sole exception to this is that C<sysread()>ing past the buffer
1185 will extend the buffer and zero pad the new area.
1187 =item Out of memory!
1189 (X|F) The malloc() function returned 0, indicating there was insufficient
1190 remaining memory (or virtual memory) to satisfy the request.
1192 The request was judged to be small, so the possibility to trap it
1193 depends on the way Perl was compiled. By default it is not trappable.
1194 However, if compiled for this, Perl may use the contents of C<$^M> as
1195 an emergency pool after die()ing with this message. In this case the
1196 error is trappable I<once>.
1198 =item Out of memory during request for %s
1200 (F) The malloc() function returned 0, indicating there was insufficient
1201 remaining memory (or virtual memory) to satisfy the request. However,
1202 the request was judged large enough (compile-time default is 64K), so
1203 a possibility to shut down by trapping this error is granted.
1205 =item Possible attempt to put comments in qw() list
1207 (W) qw() lists contain items separated by whitespace; as with literal
1208 strings, comment characters are not ignored, but are instead treated
1209 as literal data. (You may have used different delimiters than the
1210 exclamation marks parentheses shown here; braces are also frequently
1213 You probably wrote something like this:
1220 when you should have written this:
1227 If you really want comments, build your list the
1228 old-fashioned way, with quotes and commas:
1232 'b', # another comment
1235 =item Possible attempt to separate words with commas
1237 (W) qw() lists contain items separated by whitespace; therefore commas
1238 aren't needed to separate the items. (You may have used different
1239 delimiters than the parentheses shown here; braces are also frequently
1242 You probably wrote something like this:
1246 which puts literal commas into some of the list items. Write it without
1247 commas if you don't want them to appear in your data:
1251 =item Scalar value @%s{%s} better written as $%s{%s}
1253 (W) You've used a hash slice (indicated by @) to select a single element of
1254 a hash. Generally it's better to ask for a scalar value (indicated by $).
1255 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
1256 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
1257 like a list when you assign to it, and provides a list context to its
1258 subscript, which can do weird things if you're expecting only one subscript.
1260 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
1262 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
1263 Stubs should never be implicitely created, but explicit calls to C<can>
1266 =item Too late for "B<-T>" option
1268 (X) The #! line (or local equivalent) in a Perl script contains the
1269 B<-T> option, but Perl was not invoked with B<-T> in its argument
1270 list. This is an error because, by the time Perl discovers a B<-T> in
1271 a script, it's too late to properly taint everything from the
1272 environment. So Perl gives up.
1274 =item untie attempted while %d inner references still exist
1276 (W) A copy of the object returned from C<tie> (or C<tied>) was still
1277 valid when C<untie> was called.
1279 =item Unrecognized character %s
1281 (F) The Perl parser has no idea what to do with the specified character
1282 in your Perl script (or eval). Perhaps you tried to run a compressed
1283 script, a binary program, or a directory as a Perl program.
1285 =item Unsupported function fork
1287 (F) Your version of executable does not support forking.
1289 Note that under some systems, like OS/2, there may be different flavors of
1290 Perl executables, some of which may support fork, some not. Try changing
1291 the name you call Perl by to C<perl_>, C<perl__>, and so on.
1293 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
1295 (D) Perl versions before 5.004 misinterpreted any type marker followed
1296 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
1297 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
1299 However, the developers of Perl 5.004 could not fix this bug completely,
1300 because at least two widely-used modules depend on the old meaning of
1301 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
1302 old (broken) way inside strings; but it generates this message as a
1303 warning. And in Perl 5.005, this special treatment will cease.
1305 =item Value of %s can be "0"; test with defined()
1307 (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>,
1308 or C<readdir()> as a boolean value. Each of these constructs can return a
1309 value of "0"; that would make the conditional expression false, which is
1310 probably not what you intended. When using these constructs in conditional
1311 expressions, test their values with the C<defined> operator.
1313 =item Variable "%s" may be unavailable
1315 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1316 subroutine, and outside that is another subroutine; and the anonymous
1317 (innermost) subroutine is referencing a lexical variable defined in
1318 the outermost subroutine. For example:
1320 sub outermost { my $a; sub middle { sub { $a } } }
1322 If the anonymous subroutine is called or referenced (directly or
1323 indirectly) from the outermost subroutine, it will share the variable
1324 as you would expect. But if the anonymous subroutine is called or
1325 referenced when the outermost subroutine is not active, it will see
1326 the value of the shared variable as it was before and during the
1327 *first* call to the outermost subroutine, which is probably not what
1330 In these circumstances, it is usually best to make the middle
1331 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1332 support for shared variables in nested anonymous subroutines; a named
1333 subroutine in between interferes with this feature.
1335 =item Variable "%s" will not stay shared
1337 (W) An inner (nested) I<named> subroutine is referencing a lexical
1338 variable defined in an outer subroutine.
1340 When the inner subroutine is called, it will probably see the value of
1341 the outer subroutine's variable as it was before and during the
1342 *first* call to the outer subroutine; in this case, after the first
1343 call to the outer subroutine is complete, the inner and outer
1344 subroutines will no longer share a common value for the variable. In
1345 other words, the variable will no longer be shared.
1347 Furthermore, if the outer subroutine is anonymous and references a
1348 lexical variable outside itself, then the outer and inner subroutines
1349 will I<never> share the given variable.
1351 This problem can usually be solved by making the inner subroutine
1352 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1353 reference variables in outer subroutines are called or referenced,
1354 they are automatically rebound to the current values of such
1357 =item Warning: something's wrong
1359 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1360 you called it with no args and C<$_> was empty.
1362 =item Ill-formed logical name |%s| in prime_env_iter
1364 (W) A warning peculiar to VMS. A logical name was encountered when preparing
1365 to iterate over %ENV which violates the syntactic rules governing logical
1366 names. Since it cannot be translated normally, it is skipped, and will not
1367 appear in %ENV. This may be a benign occurrence, as some software packages
1368 might directly modify logical name tables and introduce nonstandard names,
1369 or it may indicate that a logical name table has been corrupted.
1371 =item Got an error from DosAllocMem
1373 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1374 version of Perl, and this should not happen anyway.
1376 =item Malformed PERLLIB_PREFIX
1378 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1386 with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix
1387 of a builtin library search path, prefix2 is substituted. The error
1388 may appear if components are not found, or are too long. See
1389 "PERLLIB_PREFIX" in F<README.os2>.
1391 =item PERL_SH_DIR too long
1393 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1394 C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>.
1396 =item Process terminated by SIG%s
1398 (W) This is a standard message issued by OS/2 applications, while *nix
1399 applications die in silence. It is considered a feature of the OS/2
1400 port. One can easily disable this by appropriate sighandlers, see
1401 L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT"
1408 If you find what you think is a bug, you might check the headers of
1409 recently posted articles in the comp.lang.perl.misc newsgroup.
1410 There may also be information at http://www.perl.com/perl/, the Perl
1413 If you believe you have an unreported bug, please run the B<perlbug>
1414 program included with your release. Make sure you trim your bug down
1415 to a tiny but sufficient test case. Your bug report, along with the
1416 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1417 analysed by the Perl porting team.
1421 The F<Changes> file for exhaustive details on what changed.
1423 The F<INSTALL> file for how to build Perl. This file has been
1424 significantly updated for 5.004, so even veteran users should
1427 The F<README> file for general stuff.
1429 The F<Copying> file for copyright information.
1433 Constructed by Tom Christiansen, grabbing material with permission
1434 from innumerable contributors, with kibitzing by more than a few Perl
1437 Last update: Sat Mar 8 19:51:26 EST 1997