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 Compilation option: Binary compatibility with 5.003
24 There is a new Configure question that asks if you want to maintain
25 binary compatibility with Perl 5.003. If you choose binary
26 compatibility, you do not have to recompile your extensions, but you
27 might have symbol conflicts if you embed Perl in another application,
28 just as in the 5.003 release. By default, binary compatibility
29 is preserved at the expense of symbol table pollution.
31 =head2 $PERL5OPT environment variable
33 You may now put Perl options in the $PERL5OPT environment variable.
34 Unless Perl is running with taint checks, it will interpret this
35 variable as if its contents had appeared on a "#!perl" line at the
36 beginning of your script, except that hyphens are optional. PERL5OPT
37 may only be used to set the following switches: B<-[DIMUdmw]>.
39 =head2 Limitations on B<-M>, B<-m>, and B<-T> options
41 The C<-M> and C<-m> options are no longer allowed on the C<#!> line of
42 a script. If a script needs a module, it should invoke it with the
45 The B<-T> option is also forbidden on the C<#!> line of a script,
46 unless it was present on the Perl command line. Due to the way C<#!>
47 works, this usually means that B<-T> must be in the first argument.
52 will probably work for an executable script invoked as C<scriptname>,
57 will probably fail under the same conditions. (Non-Unix systems will
58 probably not follow this rule.) But C<perl scriptname> is guaranteed
59 to fail, since then there is no chance of B<-T> being found on the
60 command line before it is found on the C<#!> line.
62 =head2 More precise warnings
64 If you removed the B<-w> option from your Perl 5.003 scripts because it
65 made Perl too verbose, we recommend that you try putting it back when
66 you upgrade to Perl 5.004. Each new perl version tends to remove some
67 undesirable warnings, while adding new warnings that may catch bugs in
70 =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods
72 Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods
73 (using the C<@ISA> hierarchy), even when the function to be autoloaded
74 was called as a plain function (e.g. C<Foo::bar()>), not a method
75 (e.g. C<Foo-E<gt>bar()> or C<$obj-E<gt>bar()>).
77 Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s.
78 However, there is a significant base of existing code that may be using
79 the old behavior. So, as an interim step, Perl 5.004 issues an optional
80 warning when a non-method uses an inherited C<AUTOLOAD>.
82 The simple rule is: Inheritance will not work when autoloading
83 non-methods. The simple fix for old code is: In any module that used to
84 depend on inheriting C<AUTOLOAD> for non-methods from a base class named
85 C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup.
87 =head2 Subroutine arguments created only when they're modified
89 In Perl 5.004, nonexistent array and hash elements used as subroutine
90 parameters are brought into existence only if they are actually
91 assigned to (via C<@_>).
93 Earlier versions of Perl vary in their handling of such arguments.
94 Perl versions 5.002 and 5.003 always brought them into existence.
95 Perl versions 5.000 and 5.001 brought them into existence only if
96 they were not the first argument (which was almost certainly a bug).
97 Earlier versions of Perl never brought them into existence.
99 For example, given this code:
102 sub show { print $_[0] };
103 sub change { $_[0]++ };
107 After this code executes in Perl 5.004, $a{b} exists but $a[2] does
108 not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed
109 (but $a[2]'s value would have been undefined).
111 =head2 Group vector changeable with C<$)>
113 The C<$)> special variable has always (well, in Perl 5, at least)
114 reflected not only the current effective group, but also the group list
115 as returned by the C<getgroups()> C function (if there is one).
116 However, until this release, there has not been a way to call the
117 C<setgroups()> C function from Perl.
119 In Perl 5.004, assigning to C<$)> is exactly symmetrical with examining
120 it: The first number in its string value is used as the effective gid;
121 if there are any numbers after the first one, they are passed to the
122 C<setgroups()> C function (if there is one).
124 =head2 Fixed parsing of $$<digit>, &$<digit>, etc.
126 Perl versions before 5.004 misinterpreted any type marker followed by
127 "$" and a digit. For example, "$$0" was incorrectly taken to mean
128 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
130 However, the developers of Perl 5.004 could not fix this bug completely,
131 because at least two widely-used modules depend on the old meaning of
132 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
133 old (broken) way inside strings; but it generates this message as a
134 warning. And in Perl 5.005, this special treatment will cease.
136 =head2 No resetting of $. on implicit close
138 The documentation for Perl 5.0 has always stated that C<$.> is I<not>
139 reset when an already-open file handle is reopened with no intervening
140 call to C<close>. Due to a bug, perl versions 5.000 through 5.003
141 I<did> reset C<$.> under that circumstance; Perl 5.004 does not.
143 =head2 C<wantarray> may return undef
145 The C<wantarray> operator returns true if a subroutine is expected to
146 return a list, and false otherwise. In Perl 5.004, C<wantarray> can
147 also return the undefined value if a subroutine's return value will
148 not be used at all, which allows subroutines to avoid a time-consuming
149 calculation of a return value if it isn't going to be used.
151 =head2 Changes to tainting checks
153 A bug in previous versions may have failed to detect some insecure
154 conditions when taint checks are turned on. (Taint checks are used
155 in setuid or setgid scripts, or when explicitly turned on with the
156 C<-T> invocation option.) Although it's unlikely, this may cause a
157 previously-working script to now fail -- which should be construed
158 as a blessing, since that indicates a potentially-serious security
159 hole was just plugged.
161 The new restrictions when tainting include:
165 =item No glob() or <*>
167 These operators may spawn the C shell (csh), which cannot be made
168 safe. This restriction will be lifted in a future version of Perl
169 when globbing is implemented without the use of an external program.
171 =item No spawning if tainted $CDPATH, $ENV, $BASH_ENV
173 These environment variables may alter the behavior of spawned programs
174 (especially shells) in ways that subvert security. So now they are
175 treated as dangerous, in the manner of $IFS and $PATH.
177 =item No spawning if tainted $TERM doesn't look like a terminal name
179 Some termcap libraries do unsafe things with $TERM. However, it would be
180 unnecessarily harsh to treat all $TERM values as unsafe, since only shell
181 metacharacters can cause trouble in $TERM. So a tainted $TERM is
182 considered to be safe if it contains only alphanumerics, underscores,
183 dashes, and colons, and unsafe if it contains other characters (including
188 =head2 New Opcode module and revised Safe module
190 A new Opcode module supports the creation, manipulation and
191 application of opcode masks. The revised Safe module has a new API
192 and is implemented using the new Opcode module. Please read the new
193 Opcode and Safe documentation.
195 =head2 Embedding improvements
197 In older versions of Perl it was not possible to create more than one
198 Perl interpreter instance inside a single process without leaking like a
199 sieve and/or crashing. The bugs that caused this behavior have all been
200 fixed. However, you still must take care when embedding Perl in a C
201 program. See the updated perlembed manpage for tips on how to manage
204 =head2 Internal change: FileHandle class based on IO::* classes
206 File handles are now stored internally as type IO::Handle. The
207 FileHandle module is still supported for backwards compatibility, but
208 it is now merely a front end to the IO::* modules -- specifically,
209 IO::Handle, IO::Seekable, and IO::File. We suggest, but do not
210 require, that you use the IO::* modules in new code.
212 In harmony with this change, C<*GLOB{FILEHANDLE}> is now just a
213 backward-compatible synonym for C<*GLOB{IO}>.
215 =head2 Internal change: PerlIO abstraction interface
217 It is now possible to build Perl with AT&T's sfio IO package
218 instead of stdio. See L<perlapio> for more details, and
219 the F<INSTALL> file for how to use it.
221 =head2 New and changed syntax
225 =item $coderef->(PARAMS)
227 A subroutine reference may now be suffixed with an arrow and a
228 (possibly empty) parameter list. This syntax denotes a call of the
229 referenced subroutine, with the given parameters (if any).
231 This new syntax follows the pattern of S<C<$hashref-E<gt>{FOO}>> and
232 S<C<$aryref-E<gt>[$foo]>>: You may now write S<C<&$subref($foo)>> as
233 S<C<$subref-E<gt>($foo)>>. All of these arrow terms may be chained;
234 thus, S<C<&{$table-E<gt>{FOO}}($bar)>> may now be written
235 S<C<$table-E<gt>{FOO}-E<gt>($bar)>>.
239 =head2 New and changed builtin constants
245 The current package name at compile time, or the undefined value if
246 there is no current package (due to a C<package;> directive). Like
247 C<__FILE__> and C<__LINE__>, C<__PACKAGE__> does I<not> interpolate
252 =head2 New and changed builtin variables
258 Extended error message on some platforms. (Also known as
259 $EXTENDED_OS_ERROR if you C<use English>).
263 The current set of syntax checks enabled by C<use strict>. See the
264 documentation of C<strict> for more details. Not actually new, but
266 Because it is intended for internal use by Perl core components,
267 there is no C<use English> long name for this variable.
271 By default, running out of memory it is not trappable. However, if
272 compiled for this, Perl may use the contents of C<$^M> as an emergency
273 pool after die()ing with this message. Suppose that your Perl were
274 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
278 would allocate a 64K buffer for use when in emergency.
279 See the F<INSTALL> file for information on how to enable this option.
280 As a disincentive to casual use of this advanced feature,
281 there is no C<use English> long name for this variable.
285 =head2 New and changed builtin functions
289 =item delete on slices
291 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
295 is now supported on more platforms, prefers fcntl to lockf when
296 emulating, and always flushes before (un)locking.
298 =item printf and sprintf
300 Perl now implements these functions itself; it doesn't use the C
301 library function sprintf() any more, except for floating-point
302 numbers, and even then only known flags are allowed. As a result, it
303 is now possible to know which conversions and flags will work, and
306 The new conversions in Perl's sprintf() are:
309 %p a pointer (the address of the Perl value, in hexadecimal)
310 %n special: *stores* the number of characters output so far
311 into the next variable in the parameter list
313 The new flags that go between the C<%> and the conversion are:
315 # prefix octal with "0", hex with "0x"
316 h interpret integer as C type "short" or "unsigned short"
317 V interpret integer as Perl's standard integer type
319 Also, where a number would appear in the flags, an asterisk ("*") may
320 be used instead, in which case Perl uses the next item in the
321 parameter list as the given number (that is, as the field width or
322 precision). If a field width obtained through "*" is negative, it has
323 the same effect as the '-' flag: left-justification.
325 See L<perlfunc/sprintf> for a complete list of conversion and flags.
327 =item keys as an lvalue
329 As an lvalue, C<keys> allows you to increase the number of hash buckets
330 allocated for the given hash. This can gain you a measure of efficiency if
331 you know the hash is going to get big. (This is similar to pre-extending
332 an array by assigning a larger number to $#array.) If you say
336 then C<%hash> will have at least 200 buckets allocated for it. These
337 buckets will be retained even if you do C<%hash = ()>; use C<undef
338 %hash> if you want to free the storage while C<%hash> is still in scope.
339 You can't shrink the number of buckets allocated for the hash using
340 C<keys> in this way (but you needn't worry about doing this by accident,
341 as trying has no effect).
343 =item my() in Control Structures
345 You can now use my() (with or without the parentheses) in the control
346 expressions of control structures such as:
348 while (defined(my $line = <>)) {
354 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
356 } elsif ($answer =~ /^n(o)?$/i) {
360 die "`$answer' is neither `yes' nor `no'";
363 Also, you can declare a foreach loop control variable as lexical by
364 preceding it with the word "my". For example, in:
366 foreach my $i (1, 2, 3) {
370 $i is a lexical variable, and the scope of $i extends to the end of
371 the loop, but not beyond it.
373 Note that you still cannot use my() on global punctuation variables
374 such as $_ and the like.
376 =item pack() and unpack()
378 A new format 'w' represents a BER compressed integer (as defined in
379 ASN.1). Its format is a sequence of one or more bytes, each of which
380 provides seven bits of the total value, with the most significant
381 first. Bit eight of each byte is set, except for the last byte, in
382 which bit eight is clear.
384 Both pack() and unpack() now fail when their templates contain invalid
385 types. (Invalid types used to be ignored.)
389 The new sysseek() operator is a variant of seek() that sets and gets the
390 file's system read/write position, using the lseek(2) system call. It is
391 the only reliable way to seek before using sysread() or syswrite(). Its
392 return value is the new position, or the undefined value on failure.
396 If the first argument to C<use> is a number, it is treated as a version
397 number instead of a module name. If the version of the Perl interpreter
398 is less than VERSION, then an error message is printed and Perl exits
399 immediately. Because C<use> occurs at compile time, this check happens
400 immediately during the compilation process, unlike C<require VERSION>,
401 which waits until runtime for the check. This is often useful if you
402 need to check the current Perl version before C<use>ing library modules
403 which have changed in incompatible ways from older versions of Perl.
404 (We try not to do this more than we have to.)
406 =item use Module VERSION LIST
408 If the VERSION argument is present between Module and LIST, then the
409 C<use> will call the VERSION method in class Module with the given
410 version as an argument. The default VERSION method, inherited from
411 the UNIVERSAL class, croaks if the given version is larger than the
412 value of the variable $Module::VERSION. (Note that there is not a
413 comma after VERSION!)
415 This version-checking mechanism is similar to the one currently used
416 in the Exporter module, but it is faster and can be used with modules
417 that don't use the Exporter. It is the recommended method for new
420 =item prototype(FUNCTION)
422 Returns the prototype of a function as a string (or C<undef> if the
423 function has no prototype). FUNCTION is a reference to or the name of the
424 function whose prototype you want to retrieve.
425 (Not actually new; just never documented before.)
429 The default seed for C<srand>, which used to be C<time>, has been changed.
430 Now it's a heady mix of difficult-to-predict system-dependent values,
431 which should be sufficient for most everyday purposes.
433 Previous to version 5.004, calling C<rand> without first calling C<srand>
434 would yield the same sequence of random numbers on most or all machines.
435 Now, when perl sees that you're calling C<rand> and haven't yet called
436 C<srand>, it calls C<srand> with the default seed. You should still call
437 C<srand> manually if your code might ever be run on a pre-5.004 system,
438 of course, or if you want a seed other than the default.
442 Functions documented in the Camel to default to $_ now in
443 fact do, and all those that do are so documented in L<perlfunc>.
445 =item C<m//gc> does not reset search position on failure
447 The C<m//g> match iteration construct has always reset its target
448 string's search position (which is visible through the C<pos> operator)
449 when a match fails; as a result, the next C<m//g> match after a failure
450 starts again at the beginning of the string. With Perl 5.004, this
451 reset may be disabled by adding the "c" (for "continue") modifier,
452 i.e. C<m//gc>. This feature, in conjunction with the C<\G> zero-width
453 assertion, makes it possible to chain matches together. See L<perlop>
456 =item C<m//x> ignores whitespace before ?*+{}
458 The C<m//x> construct has always been intended to ignore all unescaped
459 whitespace. However, before Perl 5.004, whitespace had the effect of
460 escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was
461 (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004.
463 =item nested C<sub{}> closures work now
465 Prior to the 5.004 release, nested anonymous functions didn't work
468 =item formats work right on changing lexicals
470 Just like anonymous functions that contain lexical variables
471 that change (like a lexical index variable for a C<foreach> loop),
472 formats now work properly. For example, this silently failed
473 before (printed only zeros), but is fine now:
476 foreach $i ( 1 .. 10 ) {
486 =head2 New builtin methods
488 The C<UNIVERSAL> package automatically contains the following methods that
489 are inherited by all other classes:
495 C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
497 C<isa> is also exportable and can be called as a sub with two arguments. This
498 allows the ability to check what a reference points to. Example:
500 use UNIVERSAL qw(isa);
502 if(isa($ref, 'ARRAY')) {
508 C<can> checks to see if its object has a method called C<METHOD>,
509 if it does then a reference to the sub is returned; if it does not then
510 I<undef> is returned.
512 =item VERSION( [NEED] )
514 C<VERSION> returns the version number of the class (package). If the
515 NEED argument is given then it will check that the current version (as
516 defined by the $VERSION variable in the given package) not less than
517 NEED; it will die if this is not the case. This method is normally
518 called as a class method. This method is called automatically by the
519 C<VERSION> form of C<use>.
521 use A 1.2 qw(some imported subs);
527 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
528 C<isa> uses a very similar method and caching strategy. This may cause
529 strange effects if the Perl code dynamically changes @ISA in any package.
531 You may add other methods to the UNIVERSAL class via Perl or XS code.
532 You do not need to C<use UNIVERSAL> in order to make these methods
533 available to your program. This is necessary only if you wish to
534 have C<isa> available as a plain subroutine in the current package.
536 =head2 TIEHANDLE now supported
538 See L<perltie> for other kinds of tie()s.
542 =item TIEHANDLE classname, LIST
544 This is the constructor for the class. That means it is expected to
545 return an object of some sort. The reference can be used to
546 hold some internal information.
551 return bless \$i, shift;
554 =item PRINT this, LIST
556 This method will be triggered every time the tied handle is printed to.
557 Beyond its self reference it also expects the list that was passed to
563 return print join( $, => map {uc} @_), $\;
566 =item PRINTF this, LIST
568 This method will be triggered every time the tied handle is printed to
569 with the C<printf()> function.
570 Beyond its self reference it also expects the format and list that was
571 passed to the printf function.
576 print sprintf($fmt, @_)."\n";
581 This method will be called when the handle is read from via the C<read>
582 or C<sysread> functions.
586 my($buf,$len,$offset) = @_;
587 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
592 This method will be called when the handle is read from. The method
593 should return undef when there is no more data.
597 return "PRINT called $$r times\n"
602 This method will be called when the C<getc> function is called.
604 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
608 As with the other types of ties, this method will be called when the
609 tied handle is about to be destroyed. This is useful for debugging and
610 possibly for cleaning up.
618 =head2 Malloc enhancements
620 Four new compilation flags are recognized by malloc.c. (They have no
621 effect if perl is compiled with system malloc().)
625 =item -DDEBUGGING_MSTATS
627 If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print
628 memory statistics at runtime by running Perl thusly:
630 env PERL_DEBUG_MSTATS=2 perl your_script_here
632 The value of 2 means to print statistics after compilation and on
633 exit; with a value of 1, the statistics ares printed only on exit.
634 (If you want the statistics at an arbitrary time, you'll need to
635 install the optional module Devel::Peek.)
637 =item -DEMERGENCY_SBRK
639 If this macro is defined, running out of memory need not be a fatal
640 error: a memory pool can allocated by assigning to the special
641 variable C<$^M>. See L<"$^M">.
645 Perl memory allocation is by bucket with sizes close to powers of two.
646 Because of these malloc overhead may be big, especially for data of
647 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
648 a slightly different algorithm for small allocations (up to 64 bytes
649 long), which makes it possible to have overhead down to 1 byte for
650 allocations which are powers of two (and appear quite often).
652 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
653 about 20% for typical Perl usage. Expected slowdown due to additional
654 malloc overhead is in fractions of a percent (hard to measure, because
655 of the effect of saved memory on speed).
657 =item -DTWO_POT_OPTIMIZE
659 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
660 with size close to a power of two; but this works for big allocations
661 (starting with 16K by default). Such allocations are typical for big
662 hashes and special-purpose scripts, especially image processing.
664 On recent systems, the fact that perl requires 2M from system for 1M
665 allocation will not affect speed of execution, since the tail of such
666 a chunk is not going to be touched (and thus will not require real
667 memory). However, it may result in a premature out-of-memory error.
668 So if you will be manipulating very large blocks with sizes close to
669 powers of two, it would be wise to define this macro.
671 Expected saving of memory is 0-100% (100% in applications which
672 require most memory in such 2**n chunks); expected slowdown is
677 =head2 Miscellaneous efficiency enhancements
679 Functions that have an empty prototype and that do nothing but return
680 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
682 Each unique hash key is only allocated once, no matter how many hashes
683 have an entry with that key. So even if you have 100 copies of the
684 same hash, the hash keys never have to be reallocated.
686 =head1 Support for More Operating Systems
688 Support for the following operating systems is new in Perl 5.004.
692 Perl 5.004 now includes support for building a "native" perl under
693 Windows NT, using the Microsoft Visual C++ compiler (versions 2.0
694 and above). The resulting perl can be used under Windows 95 (if it
695 is installed in the same directory locations as it got installed
696 in Windows NT). This port includes support for perl extension
697 building tools like L<MakeMaker> and L<h2xs>, so that many extensions
698 available on the Comprehensive Perl Archive Network (CPAN) can now be
699 readily built under Windows NT. See http://www.perl.com/ for more
700 information on CPAN, and L<README.win32> for more details on how to
701 get started with building this port.
703 There is also support for building perl under the Cygwin32 environment.
704 Cygwin32 is a set of GNU tools that make it possible to compile and run
705 many UNIX programs under Windows NT by providing a mostly UNIX-like
706 interface for compilation and execution. See L<README.cygwin32> for
707 more details on this port, and how to obtain the Cygwin32 toolkit.
708 This port has not been as well tested as the "native" port described
709 above (which is not as well tested as we'd like either :)
721 See L<README.amigaos>.
725 Six new pragmatic modules exist:
729 =item use autouse MODULE => qw(sub1 sub2 sub3)
731 Defers C<require MODULE> until someone calls one of the specified
732 subroutines (which must be exported by MODULE). This pragma should be
733 used with caution, and only when necessary.
739 Looks for MakeMaker-like I<'blib'> directory structure starting in
740 I<dir> (or current directory) and working back up to five levels of
743 Intended for use on command line with B<-M> option as a way of testing
744 arbitrary scripts against an uninstalled version of a package.
746 =item use constant NAME => VALUE
748 Provides a convenient interface for creating compile-time constants,
749 See L<perlsub/"Constant Functions">.
753 Tells the compiler to enable (or disable) the use of POSIX locales for
756 When C<use locale> is in effect, the current LC_CTYPE locale is used
757 for regular expressions and case mapping; LC_COLLATE for string
758 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
759 (but B<not> in print). LC_NUMERIC is always used in write, since
760 lexical scoping of formats is problematic at best.
762 Each C<use locale> or C<no locale> affects statements to the end of
763 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
764 current file. Locales can be switched and queried with
767 See L<perllocale> for more information.
771 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
775 Enable VMS-specific language features. Currently, there are three
776 VMS-specific features available: 'status', which makes C<$?> and
777 C<system> return genuine VMS status values instead of emulating POSIX;
778 'exit', which makes C<exit> take a genuine VMS status value instead of
779 assuming that C<exit 1> is an error; and 'time', which makes all times
780 relative to the local time zone, in the VMS tradition.
786 =head2 Required Updates
788 Though Perl 5.004 is compatible with almost all modules that work
789 with Perl 5.003, there are a few exceptions:
791 Module Required Version for Perl 5.004
792 ------ -------------------------------
795 Tk Tk400.202 (-w makes noise)
797 Also, the majordomo mailing list program, version 1.94.1, doesn't work
798 with Perl 5.004 (nor with perl 4), because it executes an invalid
799 regular expression. This bug is fixed in majordomo version 1.94.2.
801 =head2 Installation directories
803 The I<installperl> script now places the Perl source files for
804 extensions in the architecture-specific library directory, which is
805 where the shared libraries for extensions have always been. This
806 change is intended to allow administrators to keep the Perl 5.004
807 library directory unchanged from a previous version, without running
808 the risk of binary incompatibility between extensions' Perl source and
811 =head2 Module information summary
813 Brand new modules, arranged by topic rather than strictly
816 CGI.pm Web server interface ("Common Gateway Interface")
817 CGI/Apache.pm Support for Apache's Perl module
818 CGI/Carp.pm Log server errors with helpful context
819 CGI/Fast.pm Support for FastCGI (persistent server process)
820 CGI/Push.pm Support for server push
821 CGI/Switch.pm Simple interface for multiple server types
823 CPAN Interface to Comprehensive Perl Archive Network
824 CPAN::FirstTime Utility for creating CPAN configuration file
825 CPAN::Nox Runs CPAN while avoiding compiled extensions
827 IO.pm Top-level interface to IO::* classes
828 IO/File.pm IO::File extension Perl module
829 IO/Handle.pm IO::Handle extension Perl module
830 IO/Pipe.pm IO::Pipe extension Perl module
831 IO/Seekable.pm IO::Seekable extension Perl module
832 IO/Select.pm IO::Select extension Perl module
833 IO/Socket.pm IO::Socket extension Perl module
835 Opcode.pm Disable named opcodes when compiling Perl code
837 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
838 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
840 FindBin.pm Find path of currently executing program
842 Class/Struct.pm Declare struct-like datatypes as Perl classes
843 File/stat.pm By-name interface to Perl's builtin stat
844 Net/hostent.pm By-name interface to Perl's builtin gethost*
845 Net/netent.pm By-name interface to Perl's builtin getnet*
846 Net/protoent.pm By-name interface to Perl's builtin getproto*
847 Net/servent.pm By-name interface to Perl's builtin getserv*
848 Time/gmtime.pm By-name interface to Perl's builtin gmtime
849 Time/localtime.pm By-name interface to Perl's builtin localtime
850 Time/tm.pm Internal object for Time::{gm,local}time
851 User/grent.pm By-name interface to Perl's builtin getgr*
852 User/pwent.pm By-name interface to Perl's builtin getpw*
854 Tie/RefHash.pm Base class for tied hashes with references as keys
856 UNIVERSAL.pm Base class for *ALL* classes
860 New constants in the existing Fcntl modules are now supported,
861 provided that your operating system happens to support them:
864 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
867 These constants are intended for use with the Perl operators sysopen()
868 and fcntl() and the basic database modules like SDBM_File. For the
869 exact meaning of these and other Fcntl constants please refer to your
870 operating system's documentation for fcntl() and open().
872 In addition, the Fcntl module now provides these constants for use
873 with the Perl operator flock():
875 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
877 These constants are defined in all environments (because where there is
878 no flock() system call, Perl emulates it). However, for historical
879 reasons, these constants are not exported unless they are explicitly
880 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
884 The IO module provides a simple mechanism to load all of the IO modules at one
885 go. Currently this includes:
893 For more information on any of these modules, please see its
894 respective documentation.
898 The Math::Complex module has been totally rewritten, and now supports
899 more operations. These are overloaded:
901 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
903 And these functions are now exported:
906 log10 logn ln cbrt root
919 This new module provides a simpler interface to parts of Math::Complex for
920 those who need trigonometric functions only for real numbers.
924 There have been quite a few changes made to DB_File. Here are a few of
931 Fixed a handful of bugs.
935 By public demand, added support for the standard hash function exists().
939 Made it compatible with Berkeley DB 1.86.
943 Made negative subscripts work with RECNO interface.
947 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
948 mode from 0640 to 0666.
952 Made DB_File automatically import the open() constants (O_RDWR,
953 O_CREAT etc.) from Fcntl, if available.
957 Updated documentation.
961 Refer to the HISTORY section in DB_File.pm for a complete list of
962 changes. Everything after DB_File 1.01 has been added since 5.003.
966 Major rewrite - support added for both udp echo and real icmp pings.
968 =head2 Object-oriented overrides for builtin operators
970 Many of the Perl builtins returning lists now have
971 object-oriented overrides. These are:
983 For example, you can now say
987 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
989 =head1 Utility Changes
995 =item Sends converted HTML to standard output
997 The I<pod2html> utility included with Perl 5.004 is entirely new.
998 By default, it sends the converted HTML to its standard output,
999 instead of writing it to a file like Perl 5.003's I<pod2html> did.
1000 Use the B<--outfile=FILENAME> option to write to a file.
1008 =item C<void> XSUBs now default to returning nothing
1010 Due to a documentation/implementation bug in previous versions of
1011 Perl, XSUBs with a return type of C<void> have actually been
1012 returning one value. Usually that value was the GV for the XSUB,
1013 but sometimes it was some already freed or reused value, which would
1014 sometimes lead to program failure.
1016 In Perl 5.004, if an XSUB is declared as returning C<void>, it
1017 actually returns no value, i.e. an empty list (though there is a
1018 backward-compatibility exception; see below). If your XSUB really
1019 does return an SV, you should give it a return type of C<SV *>.
1021 For backward compatibility, I<xsubpp> tries to guess whether a
1022 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
1023 It does so by examining the text of the XSUB: if I<xsubpp> finds
1024 what looks like an assignment to C<ST(0)>, it assumes that the
1025 XSUB's return type is really C<SV *>.
1029 =head1 C Language API Changes
1033 =item C<gv_fetchmethod> and C<perl_call_sv>
1035 The C<gv_fetchmethod> function finds a method for an object, just like
1036 in Perl 5.003. The GV it returns may be a method cache entry.
1037 However, in Perl 5.004, method cache entries are not visible to users;
1038 therefore, they can no longer be passed directly to C<perl_call_sv>.
1039 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
1040 and pass the CV to C<perl_call_sv>.
1042 The most likely symptom of passing the result of C<gv_fetchmethod> to
1043 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
1044 error on the I<second> call to a given method (since there is no cache
1047 =item C<perl_eval_pv>
1049 A new function handy for eval'ing strings of Perl code inside C code.
1050 This function returns the value from the eval statement, which can
1051 be used instead of fetching globals from the symbol table. See
1052 L<perlguts>, L<perlembed> and L<perlcall> for details and examples.
1054 =item Extended API for manipulating hashes
1056 Internal handling of hash keys has changed. The old hashtable API is
1057 still fully supported, and will likely remain so. The additions to the
1058 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
1059 real scalars as keys rather than plain strings (nontied hashes still
1060 can only use strings as keys). New extensions must use the new hash
1061 access functions and macros if they wish to use C<SV*> keys. These
1062 additions also make it feasible to manipulate C<HE*>s (hash entries),
1063 which can be more efficient. See L<perlguts> for details.
1067 =head1 Documentation Changes
1069 Many of the base and library pods were updated. These
1070 new pods are included in section 1:
1080 Frequently asked questions.
1084 Locale support (internationalization and localization).
1088 Tutorial on Perl OO programming.
1092 Perl internal IO abstraction interface.
1096 Perl module library and recommended practice for module creation.
1097 Extracted from L<perlmod> (which is much smaller as a result).
1101 Although not new, this has been massively updated.
1105 Although not new, this has been massively updated.
1109 =head1 New Diagnostics
1111 Several new conditions will trigger warnings that were
1112 silent before. Some only affect certain platforms.
1113 The following new warnings and errors outline these.
1114 These messages are classified as follows (listed in
1115 increasing order of desperation):
1117 (W) A warning (optional).
1118 (D) A deprecation (optional).
1119 (S) A severe warning (mandatory).
1120 (F) A fatal error (trappable).
1121 (P) An internal error you should never see (trappable).
1122 (X) A very fatal error (nontrappable).
1123 (A) An alien error message (not generated by Perl).
1127 =item "my" variable %s masks earlier declaration in same scope
1129 (S) A lexical variable has been redeclared in the same scope, effectively
1130 eliminating all access to the previous instance. This is almost always
1131 a typographical error. Note that the earlier variable will still exist
1132 until the end of the scope or until all closure referents to it are
1135 =item %s argument is not a HASH element or slice
1137 (F) The argument to delete() must be either a hash element, such as
1140 $ref->[12]->{"susie"}
1142 or a hash slice, such as
1144 @foo{$bar, $baz, $xyzzy}
1145 @{$ref->[12]}{"susie", "queue"}
1147 =item Allocation too large: %lx
1149 (X) You can't allocate more than 64K on an MS-DOS machine.
1151 =item Allocation too large
1153 (F) You can't allocate more than 2^31+"small amount" bytes.
1155 =item Applying %s to %s will act on scalar(%s)
1157 (W) The pattern match (//), substitution (s///), and translation (tr///)
1158 operators work on scalar values. If you apply one of them to an array
1159 or a hash, it will convert the array or hash to a scalar value -- the
1160 length of an array, or the population info of a hash -- and then work on
1161 that scalar value. This is probably not what you meant to do. See
1162 L<perlfunc/grep> and L<perlfunc/map> for alternatives.
1164 =item Attempt to free nonexistent shared string
1166 (P) Perl maintains a reference counted internal table of strings to
1167 optimize the storage and access of hash keys and other strings. This
1168 indicates someone tried to decrement the reference count of a string
1169 that can no longer be found in the table.
1171 =item Attempt to use reference as lvalue in substr
1173 (W) You supplied a reference as the first argument to substr() used
1174 as an lvalue, which is pretty strange. Perhaps you forgot to
1175 dereference it first. See L<perlfunc/substr>.
1177 =item Can't redefine active sort subroutine %s
1179 (F) Perl optimizes the internal handling of sort subroutines and keeps
1180 pointers into them. You tried to redefine one such sort subroutine when it
1181 was currently active, which is not allowed. If you really want to do
1182 this, you should write C<sort { &func } @x> instead of C<sort func @x>.
1184 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
1186 (F) Only hard references are allowed by "strict refs". Symbolic references
1187 are disallowed. See L<perlref>.
1189 =item Cannot resolve method `%s' overloading `%s' in package `%s'
1191 (P) Internal error trying to resolve overloading specified by a method
1192 name (as opposed to a subroutine reference).
1194 =item Constant subroutine %s redefined
1196 (S) You redefined a subroutine which had previously been eligible for
1197 inlining. See L<perlsub/"Constant Functions"> for commentary and
1200 =item Constant subroutine %s undefined
1202 (S) You undefined a subroutine which had previously been eligible for
1203 inlining. See L<perlsub/"Constant Functions"> for commentary and
1206 =item Copy method did not return a reference
1208 (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>.
1212 (F) You passed die() an empty string (the equivalent of C<die "">) or
1213 you called it with no args and both C<$@> and C<$_> were empty.
1215 =item Exiting pseudo-block via %s
1217 (W) You are exiting a rather special block construct (like a sort block or
1218 subroutine) by unconventional means, such as a goto, or a loop control
1219 statement. See L<perlfunc/sort>.
1221 =item Identifier too long
1223 (F) Perl limits identifiers (names for variables, functions, etc.) to
1224 252 characters for simple names, somewhat more for compound names (like
1225 C<$A::B>). You've exceeded Perl's limits. Future versions of Perl are
1226 likely to eliminate these arbitrary limitations.
1228 =item Illegal character %s (carriage return)
1230 (F) A carriage return character was found in the input. This is an
1231 error, and not a warning, because carriage return characters can break
1232 multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>).
1234 =item Illegal switch in PERL5OPT: %s
1236 (X) The PERL5OPT environment variable may only be used to set the
1237 following switches: B<-[DIMUdmw]>.
1239 =item Integer overflow in hex number
1241 (S) The literal hex number you have specified is too big for your
1242 architecture. On a 32-bit architecture the largest hex literal is
1245 =item Integer overflow in octal number
1247 (S) The literal octal number you have specified is too big for your
1248 architecture. On a 32-bit architecture the largest octal literal is
1251 =item internal error: glob failed
1253 (P) Something went wrong with the external program(s) used for C<glob>
1254 and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is
1255 broken. If so, you should change all of the csh-related variables in
1256 config.sh: If you have tcsh, make the variables refer to it as if it
1257 were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all
1258 empty (except that C<d_csh> should be C<'undef'>) so that Perl will
1259 think csh is missing. In either case, after editing config.sh, run
1260 C<./Configure -S> and rebuild Perl.
1262 =item Invalid conversion in %s: "%s"
1264 (W) Perl does not understand the given format conversion.
1265 See L<perlfunc/sprintf>.
1267 =item Invalid type in pack: '%s'
1269 (F) The given character is not a valid pack type. See L<perlfunc/pack>.
1271 =item Invalid type in unpack: '%s'
1273 (F) The given character is not a valid unpack type. See L<perlfunc/unpack>.
1275 =item Name "%s::%s" used only once: possible typo
1277 (W) Typographical errors often show up as unique variable names.
1278 If you had a good reason for having a unique name, then just mention
1279 it again somehow to suppress the message (the C<use vars> pragma is
1280 provided for just this purpose).
1282 =item Null picture in formline
1284 (F) The first argument to formline must be a valid format picture
1285 specification. It was found to be empty, which probably means you
1286 supplied it an uninitialized value. See L<perlform>.
1288 =item Offset outside string
1290 (F) You tried to do a read/write/send/recv operation with an offset
1291 pointing outside the buffer. This is difficult to imagine.
1292 The sole exception to this is that C<sysread()>ing past the buffer
1293 will extend the buffer and zero pad the new area.
1295 =item Out of memory!
1297 (X|F) The malloc() function returned 0, indicating there was insufficient
1298 remaining memory (or virtual memory) to satisfy the request.
1300 The request was judged to be small, so the possibility to trap it
1301 depends on the way Perl was compiled. By default it is not trappable.
1302 However, if compiled for this, Perl may use the contents of C<$^M> as
1303 an emergency pool after die()ing with this message. In this case the
1304 error is trappable I<once>.
1306 =item Out of memory during request for %s
1308 (F) The malloc() function returned 0, indicating there was insufficient
1309 remaining memory (or virtual memory) to satisfy the request. However,
1310 the request was judged large enough (compile-time default is 64K), so
1311 a possibility to shut down by trapping this error is granted.
1315 (P) The library function frexp() failed, making printf("%f") impossible.
1317 =item Possible attempt to put comments in qw() list
1319 (W) qw() lists contain items separated by whitespace; as with literal
1320 strings, comment characters are not ignored, but are instead treated
1321 as literal data. (You may have used different delimiters than the
1322 exclamation marks parentheses shown here; braces are also frequently
1325 You probably wrote something like this:
1332 when you should have written this:
1339 If you really want comments, build your list the
1340 old-fashioned way, with quotes and commas:
1344 'b', # another comment
1347 =item Possible attempt to separate words with commas
1349 (W) qw() lists contain items separated by whitespace; therefore commas
1350 aren't needed to separate the items. (You may have used different
1351 delimiters than the parentheses shown here; braces are also frequently
1354 You probably wrote something like this:
1358 which puts literal commas into some of the list items. Write it without
1359 commas if you don't want them to appear in your data:
1363 =item Scalar value @%s{%s} better written as $%s{%s}
1365 (W) You've used a hash slice (indicated by @) to select a single element of
1366 a hash. Generally it's better to ask for a scalar value (indicated by $).
1367 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
1368 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
1369 like a list when you assign to it, and provides a list context to its
1370 subscript, which can do weird things if you're expecting only one subscript.
1372 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
1374 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
1375 Stubs should never be implicitely created, but explicit calls to C<can>
1378 =item Too late for "B<-T>" option
1380 (X) The #! line (or local equivalent) in a Perl script contains the
1381 B<-T> option, but Perl was not invoked with B<-T> in its argument
1382 list. This is an error because, by the time Perl discovers a B<-T> in
1383 a script, it's too late to properly taint everything from the
1384 environment. So Perl gives up.
1386 =item untie attempted while %d inner references still exist
1388 (W) A copy of the object returned from C<tie> (or C<tied>) was still
1389 valid when C<untie> was called.
1391 =item Unrecognized character %s
1393 (F) The Perl parser has no idea what to do with the specified character
1394 in your Perl script (or eval). Perhaps you tried to run a compressed
1395 script, a binary program, or a directory as a Perl program.
1397 =item Unsupported function fork
1399 (F) Your version of executable does not support forking.
1401 Note that under some systems, like OS/2, there may be different flavors of
1402 Perl executables, some of which may support fork, some not. Try changing
1403 the name you call Perl by to C<perl_>, C<perl__>, and so on.
1405 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
1407 (D) Perl versions before 5.004 misinterpreted any type marker followed
1408 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
1409 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
1411 However, the developers of Perl 5.004 could not fix this bug completely,
1412 because at least two widely-used modules depend on the old meaning of
1413 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
1414 old (broken) way inside strings; but it generates this message as a
1415 warning. And in Perl 5.005, this special treatment will cease.
1417 =item Value of %s can be "0"; test with defined()
1419 (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>,
1420 or C<readdir()> as a boolean value. Each of these constructs can return a
1421 value of "0"; that would make the conditional expression false, which is
1422 probably not what you intended. When using these constructs in conditional
1423 expressions, test their values with the C<defined> operator.
1425 =item Variable "%s" may be unavailable
1427 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1428 subroutine, and outside that is another subroutine; and the anonymous
1429 (innermost) subroutine is referencing a lexical variable defined in
1430 the outermost subroutine. For example:
1432 sub outermost { my $a; sub middle { sub { $a } } }
1434 If the anonymous subroutine is called or referenced (directly or
1435 indirectly) from the outermost subroutine, it will share the variable
1436 as you would expect. But if the anonymous subroutine is called or
1437 referenced when the outermost subroutine is not active, it will see
1438 the value of the shared variable as it was before and during the
1439 *first* call to the outermost subroutine, which is probably not what
1442 In these circumstances, it is usually best to make the middle
1443 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1444 support for shared variables in nested anonymous subroutines; a named
1445 subroutine in between interferes with this feature.
1447 =item Variable "%s" will not stay shared
1449 (W) An inner (nested) I<named> subroutine is referencing a lexical
1450 variable defined in an outer subroutine.
1452 When the inner subroutine is called, it will probably see the value of
1453 the outer subroutine's variable as it was before and during the
1454 *first* call to the outer subroutine; in this case, after the first
1455 call to the outer subroutine is complete, the inner and outer
1456 subroutines will no longer share a common value for the variable. In
1457 other words, the variable will no longer be shared.
1459 Furthermore, if the outer subroutine is anonymous and references a
1460 lexical variable outside itself, then the outer and inner subroutines
1461 will I<never> share the given variable.
1463 This problem can usually be solved by making the inner subroutine
1464 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1465 reference variables in outer subroutines are called or referenced,
1466 they are automatically rebound to the current values of such
1469 =item Warning: something's wrong
1471 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1472 you called it with no args and C<$_> was empty.
1474 =item Ill-formed logical name |%s| in prime_env_iter
1476 (W) A warning peculiar to VMS. A logical name was encountered when preparing
1477 to iterate over %ENV which violates the syntactic rules governing logical
1478 names. Since it cannot be translated normally, it is skipped, and will not
1479 appear in %ENV. This may be a benign occurrence, as some software packages
1480 might directly modify logical name tables and introduce nonstandard names,
1481 or it may indicate that a logical name table has been corrupted.
1483 =item Got an error from DosAllocMem
1485 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1486 version of Perl, and this should not happen anyway.
1488 =item Malformed PERLLIB_PREFIX
1490 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1498 with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix
1499 of a builtin library search path, prefix2 is substituted. The error
1500 may appear if components are not found, or are too long. See
1501 "PERLLIB_PREFIX" in F<README.os2>.
1503 =item PERL_SH_DIR too long
1505 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1506 C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>.
1508 =item Process terminated by SIG%s
1510 (W) This is a standard message issued by OS/2 applications, while *nix
1511 applications die in silence. It is considered a feature of the OS/2
1512 port. One can easily disable this by appropriate sighandlers, see
1513 L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT"
1520 If you find what you think is a bug, you might check the headers of
1521 recently posted articles in the comp.lang.perl.misc newsgroup.
1522 There may also be information at http://www.perl.com/perl/, the Perl
1525 If you believe you have an unreported bug, please run the B<perlbug>
1526 program included with your release. Make sure you trim your bug down
1527 to a tiny but sufficient test case. Your bug report, along with the
1528 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1529 analysed by the Perl porting team.
1533 The F<Changes> file for exhaustive details on what changed.
1535 The F<INSTALL> file for how to build Perl. This file has been
1536 significantly updated for 5.004, so even veteran users should
1539 The F<README> file for general stuff.
1541 The F<Copying> file for copyright information.
1545 Constructed by Tom Christiansen, grabbing material with permission
1546 from innumerable contributors, with kibitzing by more than a few Perl
1549 Last update: Wed May 14 11:14:09 EDT 1997