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, Plan 9, LynxOS, VMS, OS/2,
14 QNX, AmigaOS, and Windows NT. Perl runs on Windows 95 as well, but it
15 cannot be built there, for lack of a reasonable command interpreter.
19 Most importantly, many bugs were fixed, including several security
20 problems. See the F<Changes> file in the distribution for details.
22 =head2 List assignment to %ENV works
24 C<%ENV = ()> and C<%ENV = @list> now work as expected (except on VMS
25 where it generates a fatal error).
27 =head2 "Can't locate Foo.pm in @INC" error now lists @INC
29 =head2 Compilation option: Binary compatibility with 5.003
31 There is a new Configure question that asks if you want to maintain
32 binary compatibility with Perl 5.003. If you choose binary
33 compatibility, you do not have to recompile your extensions, but you
34 might have symbol conflicts if you embed Perl in another application,
35 just as in the 5.003 release. By default, binary compatibility
36 is preserved at the expense of symbol table pollution.
38 =head2 $PERL5OPT environment variable
40 You may now put Perl options in the $PERL5OPT environment variable.
41 Unless Perl is running with taint checks, it will interpret this
42 variable as if its contents had appeared on a "#!perl" line at the
43 beginning of your script, except that hyphens are optional. PERL5OPT
44 may only be used to set the following switches: B<-[DIMUdmw]>.
46 =head2 Limitations on B<-M>, B<-m>, and B<-T> options
48 The C<-M> and C<-m> options are no longer allowed on the C<#!> line of
49 a script. If a script needs a module, it should invoke it with the
52 The B<-T> option is also forbidden on the C<#!> line of a script,
53 unless it was present on the Perl command line. Due to the way C<#!>
54 works, this usually means that B<-T> must be in the first argument.
59 will probably work for an executable script invoked as C<scriptname>,
64 will probably fail under the same conditions. (Non-Unix systems will
65 probably not follow this rule.) But C<perl scriptname> is guaranteed
66 to fail, since then there is no chance of B<-T> being found on the
67 command line before it is found on the C<#!> line.
69 =head2 More precise warnings
71 If you removed the B<-w> option from your Perl 5.003 scripts because it
72 made Perl too verbose, we recommend that you try putting it back when
73 you upgrade to Perl 5.004. Each new perl version tends to remove some
74 undesirable warnings, while adding new warnings that may catch bugs in
77 =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods
79 Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods
80 (using the C<@ISA> hierarchy), even when the function to be autoloaded
81 was called as a plain function (e.g. C<Foo::bar()>), not a method
82 (e.g. C<Foo-E<gt>bar()> or C<$obj-E<gt>bar()>).
84 Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s.
85 However, there is a significant base of existing code that may be using
86 the old behavior. So, as an interim step, Perl 5.004 issues an optional
87 warning when a non-method uses an inherited C<AUTOLOAD>.
89 The simple rule is: Inheritance will not work when autoloading
90 non-methods. The simple fix for old code is: In any module that used to
91 depend on inheriting C<AUTOLOAD> for non-methods from a base class named
92 C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup.
94 =head2 Previously deprecated %OVERLOAD is no longer usable
96 Using %OVERLOAD to define overloading was deprecated in 5.003.
97 Overloading is now defined using the overload pragma. %OVERLOAD is
98 still used internally but should not be used by Perl scripts. See
99 L<overload> for more details.
101 =head2 Subroutine arguments created only when they're modified
103 In Perl 5.004, nonexistent array and hash elements used as subroutine
104 parameters are brought into existence only if they are actually
105 assigned to (via C<@_>).
107 Earlier versions of Perl vary in their handling of such arguments.
108 Perl versions 5.002 and 5.003 always brought them into existence.
109 Perl versions 5.000 and 5.001 brought them into existence only if
110 they were not the first argument (which was almost certainly a bug).
111 Earlier versions of Perl never brought them into existence.
113 For example, given this code:
116 sub show { print $_[0] };
117 sub change { $_[0]++ };
121 After this code executes in Perl 5.004, $a{b} exists but $a[2] does
122 not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed
123 (but $a[2]'s value would have been undefined).
125 =head2 Group vector changeable with C<$)>
127 The C<$)> special variable has always (well, in Perl 5, at least)
128 reflected not only the current effective group, but also the group list
129 as returned by the C<getgroups()> C function (if there is one).
130 However, until this release, there has not been a way to call the
131 C<setgroups()> C function from Perl.
133 In Perl 5.004, assigning to C<$)> is exactly symmetrical with examining
134 it: The first number in its string value is used as the effective gid;
135 if there are any numbers after the first one, they are passed to the
136 C<setgroups()> C function (if there is one).
138 =head2 Fixed parsing of $$<digit>, &$<digit>, etc.
140 Perl versions before 5.004 misinterpreted any type marker followed by
141 "$" and a digit. For example, "$$0" was incorrectly taken to mean
142 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
144 However, the developers of Perl 5.004 could not fix this bug completely,
145 because at least two widely-used modules depend on the old meaning of
146 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
147 old (broken) way inside strings; but it generates this message as a
148 warning. And in Perl 5.005, this special treatment will cease.
150 =head2 Fixed localization of $<digit>, $&, etc.
152 Perl versions before 5.004 did not always properly localize the
153 regex-related special variables. Perl 5.004 does localize them, as
154 the documentation has always said it should. This may result in $1,
155 $2, etc. no longer being set where existing programs use them.
157 =head2 No resetting of $. on implicit close
159 The documentation for Perl 5.0 has always stated that C<$.> is I<not>
160 reset when an already-open file handle is reopened with no intervening
161 call to C<close>. Due to a bug, perl versions 5.000 through 5.003
162 I<did> reset C<$.> under that circumstance; Perl 5.004 does not.
164 =head2 C<wantarray> may return undef
166 The C<wantarray> operator returns true if a subroutine is expected to
167 return a list, and false otherwise. In Perl 5.004, C<wantarray> can
168 also return the undefined value if a subroutine's return value will
169 not be used at all, which allows subroutines to avoid a time-consuming
170 calculation of a return value if it isn't going to be used.
172 =head2 Changes to tainting checks
174 A bug in previous versions may have failed to detect some insecure
175 conditions when taint checks are turned on. (Taint checks are used
176 in setuid or setgid scripts, or when explicitly turned on with the
177 C<-T> invocation option.) Although it's unlikely, this may cause a
178 previously-working script to now fail -- which should be construed
179 as a blessing, since that indicates a potentially-serious security
180 hole was just plugged.
182 The new restrictions when tainting include:
186 =item No glob() or <*>
188 These operators may spawn the C shell (csh), which cannot be made
189 safe. This restriction will be lifted in a future version of Perl
190 when globbing is implemented without the use of an external program.
192 =item No spawning if tainted $CDPATH, $ENV, $BASH_ENV
194 These environment variables may alter the behavior of spawned programs
195 (especially shells) in ways that subvert security. So now they are
196 treated as dangerous, in the manner of $IFS and $PATH.
198 =item No spawning if tainted $TERM doesn't look like a terminal name
200 Some termcap libraries do unsafe things with $TERM. However, it would be
201 unnecessarily harsh to treat all $TERM values as unsafe, since only shell
202 metacharacters can cause trouble in $TERM. So a tainted $TERM is
203 considered to be safe if it contains only alphanumerics, underscores,
204 dashes, and colons, and unsafe if it contains other characters (including
209 =head2 New Opcode module and revised Safe module
211 A new Opcode module supports the creation, manipulation and
212 application of opcode masks. The revised Safe module has a new API
213 and is implemented using the new Opcode module. Please read the new
214 Opcode and Safe documentation.
216 =head2 Embedding improvements
218 In older versions of Perl it was not possible to create more than one
219 Perl interpreter instance inside a single process without leaking like a
220 sieve and/or crashing. The bugs that caused this behavior have all been
221 fixed. However, you still must take care when embedding Perl in a C
222 program. See the updated perlembed manpage for tips on how to manage
225 =head2 Internal change: FileHandle class based on IO::* classes
227 File handles are now stored internally as type IO::Handle. The
228 FileHandle module is still supported for backwards compatibility, but
229 it is now merely a front end to the IO::* modules -- specifically,
230 IO::Handle, IO::Seekable, and IO::File. We suggest, but do not
231 require, that you use the IO::* modules in new code.
233 In harmony with this change, C<*GLOB{FILEHANDLE}> is now just a
234 backward-compatible synonym for C<*GLOB{IO}>.
236 =head2 Internal change: PerlIO abstraction interface
238 It is now possible to build Perl with AT&T's sfio IO package
239 instead of stdio. See L<perlapio> for more details, and
240 the F<INSTALL> file for how to use it.
242 =head2 New and changed syntax
246 =item $coderef->(PARAMS)
248 A subroutine reference may now be suffixed with an arrow and a
249 (possibly empty) parameter list. This syntax denotes a call of the
250 referenced subroutine, with the given parameters (if any).
252 This new syntax follows the pattern of S<C<$hashref-E<gt>{FOO}>> and
253 S<C<$aryref-E<gt>[$foo]>>: You may now write S<C<&$subref($foo)>> as
254 S<C<$subref-E<gt>($foo)>>. All of these arrow terms may be chained;
255 thus, S<C<&{$table-E<gt>{FOO}}($bar)>> may now be written
256 S<C<$table-E<gt>{FOO}-E<gt>($bar)>>.
260 =head2 New and changed builtin constants
266 The current package name at compile time, or the undefined value if
267 there is no current package (due to a C<package;> directive). Like
268 C<__FILE__> and C<__LINE__>, C<__PACKAGE__> does I<not> interpolate
273 =head2 New and changed builtin variables
279 Extended error message on some platforms. (Also known as
280 $EXTENDED_OS_ERROR if you C<use English>).
284 The current set of syntax checks enabled by C<use strict>. See the
285 documentation of C<strict> for more details. Not actually new, but
287 Because it is intended for internal use by Perl core components,
288 there is no C<use English> long name for this variable.
292 By default, running out of memory it is not trappable. However, if
293 compiled for this, Perl may use the contents of C<$^M> as an emergency
294 pool after die()ing with this message. Suppose that your Perl were
295 compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc. Then
299 would allocate a 64K buffer for use when in emergency.
300 See the F<INSTALL> file for information on how to enable this option.
301 As a disincentive to casual use of this advanced feature,
302 there is no C<use English> long name for this variable.
306 =head2 New and changed builtin functions
310 =item delete on slices
312 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
316 is now supported on more platforms, prefers fcntl to lockf when
317 emulating, and always flushes before (un)locking.
319 =item printf and sprintf
321 Perl now implements these functions itself; it doesn't use the C
322 library function sprintf() any more, except for floating-point
323 numbers, and even then only known flags are allowed. As a result, it
324 is now possible to know which conversions and flags will work, and
327 The new conversions in Perl's sprintf() are:
330 %p a pointer (the address of the Perl value, in hexadecimal)
331 %n special: *stores* the number of characters output so far
332 into the next variable in the parameter list
334 The new flags that go between the C<%> and the conversion are:
336 # prefix octal with "0", hex with "0x"
337 h interpret integer as C type "short" or "unsigned short"
338 V interpret integer as Perl's standard integer type
340 Also, where a number would appear in the flags, an asterisk ("*") may
341 be used instead, in which case Perl uses the next item in the
342 parameter list as the given number (that is, as the field width or
343 precision). If a field width obtained through "*" is negative, it has
344 the same effect as the '-' flag: left-justification.
346 See L<perlfunc/sprintf> for a complete list of conversion and flags.
348 =item keys as an lvalue
350 As an lvalue, C<keys> allows you to increase the number of hash buckets
351 allocated for the given hash. This can gain you a measure of efficiency if
352 you know the hash is going to get big. (This is similar to pre-extending
353 an array by assigning a larger number to $#array.) If you say
357 then C<%hash> will have at least 200 buckets allocated for it. These
358 buckets will be retained even if you do C<%hash = ()>; use C<undef
359 %hash> if you want to free the storage while C<%hash> is still in scope.
360 You can't shrink the number of buckets allocated for the hash using
361 C<keys> in this way (but you needn't worry about doing this by accident,
362 as trying has no effect).
364 =item my() in Control Structures
366 You can now use my() (with or without the parentheses) in the control
367 expressions of control structures such as:
369 while (defined(my $line = <>)) {
375 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
377 } elsif ($answer =~ /^n(o)?$/i) {
381 die "`$answer' is neither `yes' nor `no'";
384 Also, you can declare a foreach loop control variable as lexical by
385 preceding it with the word "my". For example, in:
387 foreach my $i (1, 2, 3) {
391 $i is a lexical variable, and the scope of $i extends to the end of
392 the loop, but not beyond it.
394 Note that you still cannot use my() on global punctuation variables
395 such as $_ and the like.
397 =item pack() and unpack()
399 A new format 'w' represents a BER compressed integer (as defined in
400 ASN.1). Its format is a sequence of one or more bytes, each of which
401 provides seven bits of the total value, with the most significant
402 first. Bit eight of each byte is set, except for the last byte, in
403 which bit eight is clear.
405 If 'p' or 'P' are given undef as values, they now generate a NULL
408 Both pack() and unpack() now fail when their templates contain invalid
409 types. (Invalid types used to be ignored.)
413 The new sysseek() operator is a variant of seek() that sets and gets the
414 file's system read/write position, using the lseek(2) system call. It is
415 the only reliable way to seek before using sysread() or syswrite(). Its
416 return value is the new position, or the undefined value on failure.
420 If the first argument to C<use> is a number, it is treated as a version
421 number instead of a module name. If the version of the Perl interpreter
422 is less than VERSION, then an error message is printed and Perl exits
423 immediately. Because C<use> occurs at compile time, this check happens
424 immediately during the compilation process, unlike C<require VERSION>,
425 which waits until runtime for the check. This is often useful if you
426 need to check the current Perl version before C<use>ing library modules
427 which have changed in incompatible ways from older versions of Perl.
428 (We try not to do this more than we have to.)
430 =item use Module VERSION LIST
432 If the VERSION argument is present between Module and LIST, then the
433 C<use> will call the VERSION method in class Module with the given
434 version as an argument. The default VERSION method, inherited from
435 the UNIVERSAL class, croaks if the given version is larger than the
436 value of the variable $Module::VERSION. (Note that there is not a
437 comma after VERSION!)
439 This version-checking mechanism is similar to the one currently used
440 in the Exporter module, but it is faster and can be used with modules
441 that don't use the Exporter. It is the recommended method for new
444 =item prototype(FUNCTION)
446 Returns the prototype of a function as a string (or C<undef> if the
447 function has no prototype). FUNCTION is a reference to or the name of the
448 function whose prototype you want to retrieve.
449 (Not actually new; just never documented before.)
453 The default seed for C<srand>, which used to be C<time>, has been changed.
454 Now it's a heady mix of difficult-to-predict system-dependent values,
455 which should be sufficient for most everyday purposes.
457 Previous to version 5.004, calling C<rand> without first calling C<srand>
458 would yield the same sequence of random numbers on most or all machines.
459 Now, when perl sees that you're calling C<rand> and haven't yet called
460 C<srand>, it calls C<srand> with the default seed. You should still call
461 C<srand> manually if your code might ever be run on a pre-5.004 system,
462 of course, or if you want a seed other than the default.
466 Functions documented in the Camel to default to $_ now in
467 fact do, and all those that do are so documented in L<perlfunc>.
469 =item C<m//gc> does not reset search position on failure
471 The C<m//g> match iteration construct has always reset its target
472 string's search position (which is visible through the C<pos> operator)
473 when a match fails; as a result, the next C<m//g> match after a failure
474 starts again at the beginning of the string. With Perl 5.004, this
475 reset may be disabled by adding the "c" (for "continue") modifier,
476 i.e. C<m//gc>. This feature, in conjunction with the C<\G> zero-width
477 assertion, makes it possible to chain matches together. See L<perlop>
480 =item C<m//x> ignores whitespace before ?*+{}
482 The C<m//x> construct has always been intended to ignore all unescaped
483 whitespace. However, before Perl 5.004, whitespace had the effect of
484 escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was
485 (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004.
487 =item nested C<sub{}> closures work now
489 Prior to the 5.004 release, nested anonymous functions didn't work
492 =item formats work right on changing lexicals
494 Just like anonymous functions that contain lexical variables
495 that change (like a lexical index variable for a C<foreach> loop),
496 formats now work properly. For example, this silently failed
497 before (printed only zeros), but is fine now:
500 foreach $i ( 1 .. 10 ) {
508 However, it still fails (without a warning) if the foreach is within a
513 foreach $i ( 1 .. 10 ) {
525 =head2 New builtin methods
527 The C<UNIVERSAL> package automatically contains the following methods that
528 are inherited by all other classes:
534 C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
536 C<isa> is also exportable and can be called as a sub with two arguments. This
537 allows the ability to check what a reference points to. Example:
539 use UNIVERSAL qw(isa);
541 if(isa($ref, 'ARRAY')) {
547 C<can> checks to see if its object has a method called C<METHOD>,
548 if it does then a reference to the sub is returned; if it does not then
549 I<undef> is returned.
551 =item VERSION( [NEED] )
553 C<VERSION> returns the version number of the class (package). If the
554 NEED argument is given then it will check that the current version (as
555 defined by the $VERSION variable in the given package) not less than
556 NEED; it will die if this is not the case. This method is normally
557 called as a class method. This method is called automatically by the
558 C<VERSION> form of C<use>.
560 use A 1.2 qw(some imported subs);
566 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
567 C<isa> uses a very similar method and caching strategy. This may cause
568 strange effects if the Perl code dynamically changes @ISA in any package.
570 You may add other methods to the UNIVERSAL class via Perl or XS code.
571 You do not need to C<use UNIVERSAL> in order to make these methods
572 available to your program. This is necessary only if you wish to
573 have C<isa> available as a plain subroutine in the current package.
575 =head2 TIEHANDLE now supported
577 See L<perltie> for other kinds of tie()s.
581 =item TIEHANDLE classname, LIST
583 This is the constructor for the class. That means it is expected to
584 return an object of some sort. The reference can be used to
585 hold some internal information.
590 return bless \$i, shift;
593 =item PRINT this, LIST
595 This method will be triggered every time the tied handle is printed to.
596 Beyond its self reference it also expects the list that was passed to
602 return print join( $, => map {uc} @_), $\;
605 =item PRINTF this, LIST
607 This method will be triggered every time the tied handle is printed to
608 with the C<printf()> function.
609 Beyond its self reference it also expects the format and list that was
610 passed to the printf function.
615 print sprintf($fmt, @_)."\n";
620 This method will be called when the handle is read from via the C<read>
621 or C<sysread> functions.
625 my($buf,$len,$offset) = @_;
626 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
631 This method will be called when the handle is read from. The method
632 should return undef when there is no more data.
636 return "PRINT called $$r times\n"
641 This method will be called when the C<getc> function is called.
643 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
647 As with the other types of ties, this method will be called when the
648 tied handle is about to be destroyed. This is useful for debugging and
649 possibly for cleaning up.
657 =head2 Malloc enhancements
659 If perl is compiled with the malloc included with the perl distribution
660 (that is, if C<perl -V:d_mymalloc> is 'define') then you can print
661 memory statistics at runtime by running Perl thusly:
663 env PERL_DEBUG_MSTATS=2 perl your_script_here
665 The value of 2 means to print statistics after compilation and on
666 exit; with a value of 1, the statistics are printed only on exit.
667 (If you want the statistics at an arbitrary time, you'll need to
668 install the optional module Devel::Peek.)
670 Three new compilation flags are recognized by malloc.c. (They have no
671 effect if perl is compiled with system malloc().)
675 =item -DPERL_EMERGENCY_SBRK
677 If this macro is defined, running out of memory need not be a fatal
678 error: a memory pool can allocated by assigning to the special
679 variable C<$^M>. See L<"$^M">.
683 Perl memory allocation is by bucket with sizes close to powers of two.
684 Because of these malloc overhead may be big, especially for data of
685 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
686 a slightly different algorithm for small allocations (up to 64 bytes
687 long), which makes it possible to have overhead down to 1 byte for
688 allocations which are powers of two (and appear quite often).
690 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
691 about 20% for typical Perl usage. Expected slowdown due to additional
692 malloc overhead is in fractions of a percent (hard to measure, because
693 of the effect of saved memory on speed).
695 =item -DTWO_POT_OPTIMIZE
697 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
698 with size close to a power of two; but this works for big allocations
699 (starting with 16K by default). Such allocations are typical for big
700 hashes and special-purpose scripts, especially image processing.
702 On recent systems, the fact that perl requires 2M from system for 1M
703 allocation will not affect speed of execution, since the tail of such
704 a chunk is not going to be touched (and thus will not require real
705 memory). However, it may result in a premature out-of-memory error.
706 So if you will be manipulating very large blocks with sizes close to
707 powers of two, it would be wise to define this macro.
709 Expected saving of memory is 0-100% (100% in applications which
710 require most memory in such 2**n chunks); expected slowdown is
715 =head2 Miscellaneous efficiency enhancements
717 Functions that have an empty prototype and that do nothing but return
718 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
720 Each unique hash key is only allocated once, no matter how many hashes
721 have an entry with that key. So even if you have 100 copies of the
722 same hash, the hash keys never have to be reallocated.
724 =head1 Support for More Operating Systems
726 Support for the following operating systems is new in Perl 5.004.
730 Perl 5.004 now includes support for building a "native" perl under
731 Windows NT, using the Microsoft Visual C++ compiler (versions 2.0
732 and above) or the Borland C++ compiler (versions 5.02 and above).
733 The resulting perl can be used under Windows 95 (if it
734 is installed in the same directory locations as it got installed
735 in Windows NT). This port includes support for perl extension
736 building tools like L<MakeMaker> and L<h2xs>, so that many extensions
737 available on the Comprehensive Perl Archive Network (CPAN) can now be
738 readily built under Windows NT. See http://www.perl.com/ for more
739 information on CPAN, and L<README.win32> for more details on how to
740 get started with building this port.
742 There is also support for building perl under the Cygwin32 environment.
743 Cygwin32 is a set of GNU tools that make it possible to compile and run
744 many UNIX programs under Windows NT by providing a mostly UNIX-like
745 interface for compilation and execution. See L<README.cygwin32> for
746 more details on this port, and how to obtain the Cygwin32 toolkit.
758 See L<README.amigaos>.
762 Six new pragmatic modules exist:
766 =item use autouse MODULE => qw(sub1 sub2 sub3)
768 Defers C<require MODULE> until someone calls one of the specified
769 subroutines (which must be exported by MODULE). This pragma should be
770 used with caution, and only when necessary.
776 Looks for MakeMaker-like I<'blib'> directory structure starting in
777 I<dir> (or current directory) and working back up to five levels of
780 Intended for use on command line with B<-M> option as a way of testing
781 arbitrary scripts against an uninstalled version of a package.
783 =item use constant NAME => VALUE
785 Provides a convenient interface for creating compile-time constants,
786 See L<perlsub/"Constant Functions">.
790 Tells the compiler to enable (or disable) the use of POSIX locales for
793 When C<use locale> is in effect, the current LC_CTYPE locale is used
794 for regular expressions and case mapping; LC_COLLATE for string
795 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
796 (but B<not> in print). LC_NUMERIC is always used in write, since
797 lexical scoping of formats is problematic at best.
799 Each C<use locale> or C<no locale> affects statements to the end of
800 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
801 current file. Locales can be switched and queried with
804 See L<perllocale> for more information.
808 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
812 Enable VMS-specific language features. Currently, there are three
813 VMS-specific features available: 'status', which makes C<$?> and
814 C<system> return genuine VMS status values instead of emulating POSIX;
815 'exit', which makes C<exit> take a genuine VMS status value instead of
816 assuming that C<exit 1> is an error; and 'time', which makes all times
817 relative to the local time zone, in the VMS tradition.
823 =head2 Required Updates
825 Though Perl 5.004 is compatible with almost all modules that work
826 with Perl 5.003, there are a few exceptions:
828 Module Required Version for Perl 5.004
829 ------ -------------------------------
832 Tk Tk400.202 (-w makes noise)
834 Also, the majordomo mailing list program, version 1.94.1, doesn't work
835 with Perl 5.004 (nor with perl 4), because it executes an invalid
836 regular expression. This bug is fixed in majordomo version 1.94.2.
838 =head2 Installation directories
840 The I<installperl> script now places the Perl source files for
841 extensions in the architecture-specific library directory, which is
842 where the shared libraries for extensions have always been. This
843 change is intended to allow administrators to keep the Perl 5.004
844 library directory unchanged from a previous version, without running
845 the risk of binary incompatibility between extensions' Perl source and
848 =head2 Module information summary
850 Brand new modules, arranged by topic rather than strictly
853 CGI.pm Web server interface ("Common Gateway Interface")
854 CGI/Apache.pm Support for Apache's Perl module
855 CGI/Carp.pm Log server errors with helpful context
856 CGI/Fast.pm Support for FastCGI (persistent server process)
857 CGI/Push.pm Support for server push
858 CGI/Switch.pm Simple interface for multiple server types
860 CPAN Interface to Comprehensive Perl Archive Network
861 CPAN::FirstTime Utility for creating CPAN configuration file
862 CPAN::Nox Runs CPAN while avoiding compiled extensions
864 IO.pm Top-level interface to IO::* classes
865 IO/File.pm IO::File extension Perl module
866 IO/Handle.pm IO::Handle extension Perl module
867 IO/Pipe.pm IO::Pipe extension Perl module
868 IO/Seekable.pm IO::Seekable extension Perl module
869 IO/Select.pm IO::Select extension Perl module
870 IO/Socket.pm IO::Socket extension Perl module
872 Opcode.pm Disable named opcodes when compiling Perl code
874 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
875 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
877 FindBin.pm Find path of currently executing program
879 Class/Struct.pm Declare struct-like datatypes as Perl classes
880 File/stat.pm By-name interface to Perl's builtin stat
881 Net/hostent.pm By-name interface to Perl's builtin gethost*
882 Net/netent.pm By-name interface to Perl's builtin getnet*
883 Net/protoent.pm By-name interface to Perl's builtin getproto*
884 Net/servent.pm By-name interface to Perl's builtin getserv*
885 Time/gmtime.pm By-name interface to Perl's builtin gmtime
886 Time/localtime.pm By-name interface to Perl's builtin localtime
887 Time/tm.pm Internal object for Time::{gm,local}time
888 User/grent.pm By-name interface to Perl's builtin getgr*
889 User/pwent.pm By-name interface to Perl's builtin getpw*
891 Tie/RefHash.pm Base class for tied hashes with references as keys
893 UNIVERSAL.pm Base class for *ALL* classes
897 New constants in the existing Fcntl modules are now supported,
898 provided that your operating system happens to support them:
901 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
904 These constants are intended for use with the Perl operators sysopen()
905 and fcntl() and the basic database modules like SDBM_File. For the
906 exact meaning of these and other Fcntl constants please refer to your
907 operating system's documentation for fcntl() and open().
909 In addition, the Fcntl module now provides these constants for use
910 with the Perl operator flock():
912 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
914 These constants are defined in all environments (because where there is
915 no flock() system call, Perl emulates it). However, for historical
916 reasons, these constants are not exported unless they are explicitly
917 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
921 The IO module provides a simple mechanism to load all of the IO modules at one
922 go. Currently this includes:
930 For more information on any of these modules, please see its
931 respective documentation.
935 The Math::Complex module has been totally rewritten, and now supports
936 more operations. These are overloaded:
938 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
940 And these functions are now exported:
943 log10 logn ln cbrt root
956 This new module provides a simpler interface to parts of Math::Complex for
957 those who need trigonometric functions only for real numbers.
961 There have been quite a few changes made to DB_File. Here are a few of
968 Fixed a handful of bugs.
972 By public demand, added support for the standard hash function exists().
976 Made it compatible with Berkeley DB 1.86.
980 Made negative subscripts work with RECNO interface.
984 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
985 mode from 0640 to 0666.
989 Made DB_File automatically import the open() constants (O_RDWR,
990 O_CREAT etc.) from Fcntl, if available.
994 Updated documentation.
998 Refer to the HISTORY section in DB_File.pm for a complete list of
999 changes. Everything after DB_File 1.01 has been added since 5.003.
1003 Major rewrite - support added for both udp echo and real icmp pings.
1005 =head2 Object-oriented overrides for builtin operators
1007 Many of the Perl builtins returning lists now have
1008 object-oriented overrides. These are:
1020 For example, you can now say
1024 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
1026 =head1 Utility Changes
1032 =item Sends converted HTML to standard output
1034 The I<pod2html> utility included with Perl 5.004 is entirely new.
1035 By default, it sends the converted HTML to its standard output,
1036 instead of writing it to a file like Perl 5.003's I<pod2html> did.
1037 Use the B<--outfile=FILENAME> option to write to a file.
1045 =item C<void> XSUBs now default to returning nothing
1047 Due to a documentation/implementation bug in previous versions of
1048 Perl, XSUBs with a return type of C<void> have actually been
1049 returning one value. Usually that value was the GV for the XSUB,
1050 but sometimes it was some already freed or reused value, which would
1051 sometimes lead to program failure.
1053 In Perl 5.004, if an XSUB is declared as returning C<void>, it
1054 actually returns no value, i.e. an empty list (though there is a
1055 backward-compatibility exception; see below). If your XSUB really
1056 does return an SV, you should give it a return type of C<SV *>.
1058 For backward compatibility, I<xsubpp> tries to guess whether a
1059 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
1060 It does so by examining the text of the XSUB: if I<xsubpp> finds
1061 what looks like an assignment to C<ST(0)>, it assumes that the
1062 XSUB's return type is really C<SV *>.
1066 =head1 C Language API Changes
1070 =item C<gv_fetchmethod> and C<perl_call_sv>
1072 The C<gv_fetchmethod> function finds a method for an object, just like
1073 in Perl 5.003. The GV it returns may be a method cache entry.
1074 However, in Perl 5.004, method cache entries are not visible to users;
1075 therefore, they can no longer be passed directly to C<perl_call_sv>.
1076 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
1077 and pass the CV to C<perl_call_sv>.
1079 The most likely symptom of passing the result of C<gv_fetchmethod> to
1080 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
1081 error on the I<second> call to a given method (since there is no cache
1084 =item C<perl_eval_pv>
1086 A new function handy for eval'ing strings of Perl code inside C code.
1087 This function returns the value from the eval statement, which can
1088 be used instead of fetching globals from the symbol table. See
1089 L<perlguts>, L<perlembed> and L<perlcall> for details and examples.
1091 =item Extended API for manipulating hashes
1093 Internal handling of hash keys has changed. The old hashtable API is
1094 still fully supported, and will likely remain so. The additions to the
1095 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
1096 real scalars as keys rather than plain strings (nontied hashes still
1097 can only use strings as keys). New extensions must use the new hash
1098 access functions and macros if they wish to use C<SV*> keys. These
1099 additions also make it feasible to manipulate C<HE*>s (hash entries),
1100 which can be more efficient. See L<perlguts> for details.
1104 =head1 Documentation Changes
1106 Many of the base and library pods were updated. These
1107 new pods are included in section 1:
1117 Frequently asked questions.
1121 Locale support (internationalization and localization).
1125 Tutorial on Perl OO programming.
1129 Perl internal IO abstraction interface.
1133 Perl module library and recommended practice for module creation.
1134 Extracted from L<perlmod> (which is much smaller as a result).
1138 Although not new, this has been massively updated.
1142 Although not new, this has been massively updated.
1146 =head1 New Diagnostics
1148 Several new conditions will trigger warnings that were
1149 silent before. Some only affect certain platforms.
1150 The following new warnings and errors outline these.
1151 These messages are classified as follows (listed in
1152 increasing order of desperation):
1154 (W) A warning (optional).
1155 (D) A deprecation (optional).
1156 (S) A severe warning (mandatory).
1157 (F) A fatal error (trappable).
1158 (P) An internal error you should never see (trappable).
1159 (X) A very fatal error (nontrappable).
1160 (A) An alien error message (not generated by Perl).
1164 =item "my" variable %s masks earlier declaration in same scope
1166 (W) A lexical variable has been redeclared in the same scope, effectively
1167 eliminating all access to the previous instance. This is almost always
1168 a typographical error. Note that the earlier variable will still exist
1169 until the end of the scope or until all closure referents to it are
1172 =item %s argument is not a HASH element or slice
1174 (F) The argument to delete() must be either a hash element, such as
1177 $ref->[12]->{"susie"}
1179 or a hash slice, such as
1181 @foo{$bar, $baz, $xyzzy}
1182 @{$ref->[12]}{"susie", "queue"}
1184 =item Allocation too large: %lx
1186 (X) You can't allocate more than 64K on an MS-DOS machine.
1188 =item Allocation too large
1190 (F) You can't allocate more than 2^31+"small amount" bytes.
1192 =item Applying %s to %s will act on scalar(%s)
1194 (W) The pattern match (//), substitution (s///), and translation (tr///)
1195 operators work on scalar values. If you apply one of them to an array
1196 or a hash, it will convert the array or hash to a scalar value -- the
1197 length of an array, or the population info of a hash -- and then work on
1198 that scalar value. This is probably not what you meant to do. See
1199 L<perlfunc/grep> and L<perlfunc/map> for alternatives.
1201 =item Attempt to free nonexistent shared string
1203 (P) Perl maintains a reference counted internal table of strings to
1204 optimize the storage and access of hash keys and other strings. This
1205 indicates someone tried to decrement the reference count of a string
1206 that can no longer be found in the table.
1208 =item Attempt to use reference as lvalue in substr
1210 (W) You supplied a reference as the first argument to substr() used
1211 as an lvalue, which is pretty strange. Perhaps you forgot to
1212 dereference it first. See L<perlfunc/substr>.
1214 =item Can't redefine active sort subroutine %s
1216 (F) Perl optimizes the internal handling of sort subroutines and keeps
1217 pointers into them. You tried to redefine one such sort subroutine when it
1218 was currently active, which is not allowed. If you really want to do
1219 this, you should write C<sort { &func } @x> instead of C<sort func @x>.
1221 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
1223 (F) Only hard references are allowed by "strict refs". Symbolic references
1224 are disallowed. See L<perlref>.
1226 =item Cannot resolve method `%s' overloading `%s' in package `%s'
1228 (P) Internal error trying to resolve overloading specified by a method
1229 name (as opposed to a subroutine reference).
1231 =item Constant subroutine %s redefined
1233 (S) You redefined a subroutine which had previously been eligible for
1234 inlining. See L<perlsub/"Constant Functions"> for commentary and
1237 =item Constant subroutine %s undefined
1239 (S) You undefined a subroutine which had previously been eligible for
1240 inlining. See L<perlsub/"Constant Functions"> for commentary and
1243 =item Copy method did not return a reference
1245 (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>.
1249 (F) You passed die() an empty string (the equivalent of C<die "">) or
1250 you called it with no args and both C<$@> and C<$_> were empty.
1252 =item Exiting pseudo-block via %s
1254 (W) You are exiting a rather special block construct (like a sort block or
1255 subroutine) by unconventional means, such as a goto, or a loop control
1256 statement. See L<perlfunc/sort>.
1258 =item Identifier too long
1260 (F) Perl limits identifiers (names for variables, functions, etc.) to
1261 252 characters for simple names, somewhat more for compound names (like
1262 C<$A::B>). You've exceeded Perl's limits. Future versions of Perl are
1263 likely to eliminate these arbitrary limitations.
1265 =item Illegal character %s (carriage return)
1267 (F) A carriage return character was found in the input. This is an
1268 error, and not a warning, because carriage return characters can break
1269 multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>).
1271 =item Illegal switch in PERL5OPT: %s
1273 (X) The PERL5OPT environment variable may only be used to set the
1274 following switches: B<-[DIMUdmw]>.
1276 =item Integer overflow in hex number
1278 (S) The literal hex number you have specified is too big for your
1279 architecture. On a 32-bit architecture the largest hex literal is
1282 =item Integer overflow in octal number
1284 (S) The literal octal number you have specified is too big for your
1285 architecture. On a 32-bit architecture the largest octal literal is
1288 =item internal error: glob failed
1290 (P) Something went wrong with the external program(s) used for C<glob>
1291 and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is
1292 broken. If so, you should change all of the csh-related variables in
1293 config.sh: If you have tcsh, make the variables refer to it as if it
1294 were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all
1295 empty (except that C<d_csh> should be C<'undef'>) so that Perl will
1296 think csh is missing. In either case, after editing config.sh, run
1297 C<./Configure -S> and rebuild Perl.
1299 =item Invalid conversion in %s: "%s"
1301 (W) Perl does not understand the given format conversion.
1302 See L<perlfunc/sprintf>.
1304 =item Invalid type in pack: '%s'
1306 (F) The given character is not a valid pack type. See L<perlfunc/pack>.
1308 =item Invalid type in unpack: '%s'
1310 (F) The given character is not a valid unpack type. See L<perlfunc/unpack>.
1312 =item Name "%s::%s" used only once: possible typo
1314 (W) Typographical errors often show up as unique variable names.
1315 If you had a good reason for having a unique name, then just mention
1316 it again somehow to suppress the message (the C<use vars> pragma is
1317 provided for just this purpose).
1319 =item Null picture in formline
1321 (F) The first argument to formline must be a valid format picture
1322 specification. It was found to be empty, which probably means you
1323 supplied it an uninitialized value. See L<perlform>.
1325 =item Offset outside string
1327 (F) You tried to do a read/write/send/recv operation with an offset
1328 pointing outside the buffer. This is difficult to imagine.
1329 The sole exception to this is that C<sysread()>ing past the buffer
1330 will extend the buffer and zero pad the new area.
1332 =item Out of memory!
1334 (X|F) The malloc() function returned 0, indicating there was insufficient
1335 remaining memory (or virtual memory) to satisfy the request.
1337 The request was judged to be small, so the possibility to trap it
1338 depends on the way Perl was compiled. By default it is not trappable.
1339 However, if compiled for this, Perl may use the contents of C<$^M> as
1340 an emergency pool after die()ing with this message. In this case the
1341 error is trappable I<once>.
1343 =item Out of memory during request for %s
1345 (F) The malloc() function returned 0, indicating there was insufficient
1346 remaining memory (or virtual memory) to satisfy the request. However,
1347 the request was judged large enough (compile-time default is 64K), so
1348 a possibility to shut down by trapping this error is granted.
1352 (P) The library function frexp() failed, making printf("%f") impossible.
1354 =item Possible attempt to put comments in qw() list
1356 (W) qw() lists contain items separated by whitespace; as with literal
1357 strings, comment characters are not ignored, but are instead treated
1358 as literal data. (You may have used different delimiters than the
1359 exclamation marks parentheses shown here; braces are also frequently
1362 You probably wrote something like this:
1369 when you should have written this:
1376 If you really want comments, build your list the
1377 old-fashioned way, with quotes and commas:
1381 'b', # another comment
1384 =item Possible attempt to separate words with commas
1386 (W) qw() lists contain items separated by whitespace; therefore commas
1387 aren't needed to separate the items. (You may have used different
1388 delimiters than the parentheses shown here; braces are also frequently
1391 You probably wrote something like this:
1395 which puts literal commas into some of the list items. Write it without
1396 commas if you don't want them to appear in your data:
1400 =item Scalar value @%s{%s} better written as $%s{%s}
1402 (W) You've used a hash slice (indicated by @) to select a single element of
1403 a hash. Generally it's better to ask for a scalar value (indicated by $).
1404 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
1405 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
1406 like a list when you assign to it, and provides a list context to its
1407 subscript, which can do weird things if you're expecting only one subscript.
1409 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
1411 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
1412 Stubs should never be implicitely created, but explicit calls to C<can>
1415 =item Too late for "B<-T>" option
1417 (X) The #! line (or local equivalent) in a Perl script contains the
1418 B<-T> option, but Perl was not invoked with B<-T> in its argument
1419 list. This is an error because, by the time Perl discovers a B<-T> in
1420 a script, it's too late to properly taint everything from the
1421 environment. So Perl gives up.
1423 =item untie attempted while %d inner references still exist
1425 (W) A copy of the object returned from C<tie> (or C<tied>) was still
1426 valid when C<untie> was called.
1428 =item Unrecognized character %s
1430 (F) The Perl parser has no idea what to do with the specified character
1431 in your Perl script (or eval). Perhaps you tried to run a compressed
1432 script, a binary program, or a directory as a Perl program.
1434 =item Unsupported function fork
1436 (F) Your version of executable does not support forking.
1438 Note that under some systems, like OS/2, there may be different flavors of
1439 Perl executables, some of which may support fork, some not. Try changing
1440 the name you call Perl by to C<perl_>, C<perl__>, and so on.
1442 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
1444 (D) Perl versions before 5.004 misinterpreted any type marker followed
1445 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
1446 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
1448 However, the developers of Perl 5.004 could not fix this bug completely,
1449 because at least two widely-used modules depend on the old meaning of
1450 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
1451 old (broken) way inside strings; but it generates this message as a
1452 warning. And in Perl 5.005, this special treatment will cease.
1454 =item Value of %s can be "0"; test with defined()
1456 (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>,
1457 or C<readdir()> as a boolean value. Each of these constructs can return a
1458 value of "0"; that would make the conditional expression false, which is
1459 probably not what you intended. When using these constructs in conditional
1460 expressions, test their values with the C<defined> operator.
1462 =item Variable "%s" may be unavailable
1464 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1465 subroutine, and outside that is another subroutine; and the anonymous
1466 (innermost) subroutine is referencing a lexical variable defined in
1467 the outermost subroutine. For example:
1469 sub outermost { my $a; sub middle { sub { $a } } }
1471 If the anonymous subroutine is called or referenced (directly or
1472 indirectly) from the outermost subroutine, it will share the variable
1473 as you would expect. But if the anonymous subroutine is called or
1474 referenced when the outermost subroutine is not active, it will see
1475 the value of the shared variable as it was before and during the
1476 *first* call to the outermost subroutine, which is probably not what
1479 In these circumstances, it is usually best to make the middle
1480 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1481 support for shared variables in nested anonymous subroutines; a named
1482 subroutine in between interferes with this feature.
1484 =item Variable "%s" will not stay shared
1486 (W) An inner (nested) I<named> subroutine is referencing a lexical
1487 variable defined in an outer subroutine.
1489 When the inner subroutine is called, it will probably see the value of
1490 the outer subroutine's variable as it was before and during the
1491 *first* call to the outer subroutine; in this case, after the first
1492 call to the outer subroutine is complete, the inner and outer
1493 subroutines will no longer share a common value for the variable. In
1494 other words, the variable will no longer be shared.
1496 Furthermore, if the outer subroutine is anonymous and references a
1497 lexical variable outside itself, then the outer and inner subroutines
1498 will I<never> share the given variable.
1500 This problem can usually be solved by making the inner subroutine
1501 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1502 reference variables in outer subroutines are called or referenced,
1503 they are automatically rebound to the current values of such
1506 =item Warning: something's wrong
1508 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1509 you called it with no args and C<$_> was empty.
1511 =item Ill-formed logical name |%s| in prime_env_iter
1513 (W) A warning peculiar to VMS. A logical name was encountered when preparing
1514 to iterate over %ENV which violates the syntactic rules governing logical
1515 names. Since it cannot be translated normally, it is skipped, and will not
1516 appear in %ENV. This may be a benign occurrence, as some software packages
1517 might directly modify logical name tables and introduce nonstandard names,
1518 or it may indicate that a logical name table has been corrupted.
1520 =item Got an error from DosAllocMem
1522 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1523 version of Perl, and this should not happen anyway.
1525 =item Malformed PERLLIB_PREFIX
1527 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1535 with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix
1536 of a builtin library search path, prefix2 is substituted. The error
1537 may appear if components are not found, or are too long. See
1538 "PERLLIB_PREFIX" in F<README.os2>.
1540 =item PERL_SH_DIR too long
1542 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1543 C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>.
1545 =item Process terminated by SIG%s
1547 (W) This is a standard message issued by OS/2 applications, while *nix
1548 applications die in silence. It is considered a feature of the OS/2
1549 port. One can easily disable this by appropriate sighandlers, see
1550 L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT"
1557 If you find what you think is a bug, you might check the headers of
1558 recently posted articles in the comp.lang.perl.misc newsgroup.
1559 There may also be information at http://www.perl.com/perl/, the Perl
1562 If you believe you have an unreported bug, please run the B<perlbug>
1563 program included with your release. Make sure you trim your bug down
1564 to a tiny but sufficient test case. Your bug report, along with the
1565 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1566 analysed by the Perl porting team.
1570 The F<Changes> file for exhaustive details on what changed.
1572 The F<INSTALL> file for how to build Perl. This file has been
1573 significantly updated for 5.004, so even veteran users should
1576 The F<README> file for general stuff.
1578 The F<Copying> file for copyright information.
1582 Constructed by Tom Christiansen, grabbing material with permission
1583 from innumerable contributors, with kibitzing by more than a few Perl
1586 Last update: Wed May 14 11:14:09 EDT 1997