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. See the F<Changes>
20 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 $PERL5OPT environment variable.
34 Unless Perl is running with taint checks, it will interpret this
35 variable as if its contents had appeared on a "#!perl" line at the
36 beginning of your script, except that hyphens are optional. PERL5OPT
37 may only be used to set the following switches: B<-[DIMUdmw]>.
39 =head2 Limitations on B<-M>, and C<-m>, and B<-T> options
41 The C<-M> and C<-m> options are no longer allowed on the C<#!> line of
42 a script. If a script needs a module, it should invoke it with the
45 The B<-T> option is also forbidden on the C<#!> line of a script,
46 unless it was present on the Perl command line. Due to the way C<#!>
47 works, this usually means that B<-T> must be in the first argument.
52 will probably work for an executable script invoked as C<scriptname>,
57 will probably fail under the same conditions. (Non-Unix systems will
58 probably not follow this rule.) But C<perl scriptname> is guaranteed
59 to fail, since then there is no chance of B<-T> being found on the
60 command line before it is found on the C<#!> line.
62 =head2 More precise warnings
64 If you removed the B<-w> option from your Perl 5.003 scripts because it
65 made Perl too verbose, we recommend that you try putting it back when
66 you upgrade to Perl 5.004. Each new perl version tends to remove some
67 undesirable warnings, while adding new warnings that may catch bugs in
70 =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods
72 Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods
73 (using the C<@ISA> hierarchy), even when the function to be autoloaded
74 was called as a plain function (e.g. C<Foo::bar()>), not a method
75 (e.g. C<Foo-E<gt>bar()> or C<$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 =head2 New Opcode module and revised Safe module
163 A new Opcode module supports the creation, manipulation and
164 application of opcode masks. The revised Safe module has a new API
165 and is implemented using the new Opcode module. Please read the new
166 Opcode and Safe documentation.
168 =head2 Embedding improvements
170 In older versions of Perl it was not possible to create more than one
171 Perl interpreter instance inside a single process without leaking like a
172 sieve and/or crashing. The bugs that caused this behavior have all been
173 fixed. However, you still must take care when embedding Perl in a C
174 program. See the updated perlembed manpage for tips on how to manage
177 =head2 Internal change: FileHandle class based on IO::* classes
179 File handles are now stored internally as type IO::Handle. The
180 FileHandle module is still supported for backwards compatibility, but
181 it is now merely a front end to the IO::* modules -- specifically,
182 IO::Handle, IO::Seekable, and IO::File. We suggest, but do not
183 require, that you use the IO::* modules in new code.
185 In harmony with this change, C<*GLOB{FILEHANDLE}> is now a
186 backward-compatible synonym for C<*STDOUT{IO}>.
188 =head2 Internal change: PerlIO abstraction interface
190 It is now possible to build Perl with AT&T's sfio IO package
191 instead of stdio. See L<perlapio> for more details, and
192 the F<INSTALL> file for how to use it.
194 =head2 New and changed syntax
198 =item $coderef->(PARAMS)
200 A subroutine reference may now be suffixed with an arrow and a
201 (possibly empty) parameter list. This syntax denotes a call of the
202 referenced subroutine, with the given parameters (if any).
204 This new syntax follows the pattern of S<C<$hashref-E<gt>{FOO}>> and
205 S<C<$aryref-E<gt>[$foo]>>: You may now write S<C<&$subref($foo)>> as
206 S<C<$subref-E<gt>($foo)>>. All of these arrow terms may be chained;
207 thus, S<C<&{$table-E<gt>{FOO}}($bar)>> may now be written
208 S<C<$table-E<gt>{FOO}-E<gt>($bar)>>.
212 =head2 New and changed builtin constants
218 The current package name at compile time, or the undefined value if
219 there is no current package (due to a C<package;> directive). Like
220 C<__FILE__> and C<__LINE__>, C<__PACKAGE__> does I<not> interpolate
225 =head2 New and changed builtin variables
231 Extended error message on some platforms. (Also known as
232 $EXTENDED_OS_ERROR if you C<use English>).
236 The current set of syntax checks enabled by C<use strict>. See the
237 documentation of C<strict> for more details. Not actually new, but
239 Because it is intended for internal use by Perl core components,
240 there is no C<use English> long name for this variable.
244 By default, running out of memory it is not trappable. However, if
245 compiled for this, Perl may use the contents of C<$^M> as an emergency
246 pool after die()ing with this message. Suppose that your Perl were
247 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
251 would allocate a 64K buffer for use when in emergency.
252 See the F<INSTALL> file for information on how to enable this option.
253 As a disincentive to casual use of this advanced feature,
254 there is no C<use English> long name for this variable.
258 =head2 New and changed builtin functions
262 =item delete on slices
264 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
268 is now supported on more platforms, prefers fcntl to lockf when
269 emulating, and always flushes before (un)locking.
271 =item printf and sprintf
273 Perl now implements these functions itself; it doesn't use the C
274 library function sprintf() any more, except for floating-point
275 numbers, and even then only known flags are allowed. As a result, it
276 is now possible to know which conversions and flags will work, and
279 The new conversions in Perl's sprintf() are:
282 %p a pointer (the address of the Perl value, in hexadecimal)
283 %n special: *stores* the number of characters output so far
284 into the next variable in the parameter list
286 The new flags that go between the C<%> and the conversion are:
288 # prefix octal with "0", hex with "0x"
289 h interpret integer as C type "short" or "unsigned short"
290 V interpret integer as Perl's standard integer type
292 Also, where a number would appear in the flags, an asterisk ("*") may
293 be used instead, in which case Perl uses the next item in the
294 parameter list as the given number (that is, as the field width or
295 precision). If a field width obtained through "*" is negative, it has
296 the same effect as the '-' flag: left-justification.
298 See L<perlfunc/sprintf> for a complete list of conversion and flags.
300 =item keys as an lvalue
302 As an lvalue, C<keys> allows you to increase the number of hash buckets
303 allocated for the given hash. This can gain you a measure of efficiency if
304 you know the hash is going to get big. (This is similar to pre-extending
305 an array by assigning a larger number to $#array.) If you say
309 then C<%hash> will have at least 200 buckets allocated for it. These
310 buckets will be retained even if you do C<%hash = ()>; use C<undef
311 %hash> if you want to free the storage while C<%hash> is still in scope.
312 You can't shrink the number of buckets allocated for the hash using
313 C<keys> in this way (but you needn't worry about doing this by accident,
314 as trying has no effect).
316 =item my() in Control Structures
318 You can now use my() (with or without the parentheses) in the control
319 expressions of control structures such as:
321 while (defined(my $line = <>)) {
327 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
329 } elsif ($answer =~ /^n(o)?$/i) {
333 die "`$answer' is neither `yes' nor `no'";
336 Also, you can declare a foreach loop control variable as lexical by
337 preceding it with the word "my". For example, in:
339 foreach my $i (1, 2, 3) {
343 $i is a lexical variable, and the scope of $i extends to the end of
344 the loop, but not beyond it.
346 Note that you still cannot use my() on global punctuation variables
347 such as $_ and the like.
349 =item pack() and unpack()
351 A new format 'w' represents a BER compressed integer (as defined in
352 ASN.1). Its format is a sequence of one or more bytes, each of which
353 provides seven bits of the total value, with the most significant
354 first. Bit eight of each byte is set, except for the last byte, in
355 which bit eight is clear.
357 Both pack() and unpack() now fail when their templates contain invalid
358 types. (Invalid types used to be ignored.)
362 The new sysseek() operator is a variant of seek() that sets and gets the
363 file's system read/write position, using the lseek(2) system call. It is
364 the only reliable way to seek before using sysread() or syswrite(). Its
365 return value is the new position, or the undefined value on failure.
369 If the first argument to C<use> is a number, it is treated as a version
370 number instead of a module name. If the version of the Perl interpreter
371 is less than VERSION, then an error message is printed and Perl exits
372 immediately. Because C<use> occurs at compile time, this check happens
373 immediately during the compilation process, unlike C<require VERSION>,
374 which waits until runtime for the check. This is often useful if you
375 need to check the current Perl version before C<use>ing library modules
376 which have changed in incompatible ways from older versions of Perl.
377 (We try not to do this more than we have to.)
379 =item use Module VERSION LIST
381 If the VERSION argument is present between Module and LIST, then the
382 C<use> will call the VERSION method in class Module with the given
383 version as an argument. The default VERSION method, inherited from
384 the UNIVERSAL class, croaks if the given version is larger than the
385 value of the variable $Module::VERSION. (Note that there is not a
386 comma after VERSION!)
388 This version-checking mechanism is similar to the one currently used
389 in the Exporter module, but it is faster and can be used with modules
390 that don't use the Exporter. It is the recommended method for new
393 =item prototype(FUNCTION)
395 Returns the prototype of a function as a string (or C<undef> if the
396 function has no prototype). FUNCTION is a reference to or the name of the
397 function whose prototype you want to retrieve.
398 (Not actually new; just never documented before.)
402 The default seed for C<srand>, which used to be C<time>, has been changed.
403 Now it's a heady mix of difficult-to-predict system-dependent values,
404 which should be sufficient for most everyday purposes.
406 Previous to version 5.004, calling C<rand> without first calling C<srand>
407 would yield the same sequence of random numbers on most or all machines.
408 Now, when perl sees that you're calling C<rand> and haven't yet called
409 C<srand>, it calls C<srand> with the default seed. You should still call
410 C<srand> manually if your code might ever be run on a pre-5.004 system,
411 of course, or if you want a seed other than the default.
415 Functions documented in the Camel to default to $_ now in
416 fact do, and all those that do are so documented in L<perlfunc>.
418 =item C<m//g> does not reset search position on failure
420 The C<m//g> match iteration construct used to reset its target string's
421 search position (which is visible through the C<pos> operator) when a
422 match failed; as a result, the next C<m//g> match would start at the
423 beginning of the string). With Perl 5.004, the search position must be
424 reset explicitly, as with C<pos $str = 0;>, or by modifying the target
425 string. This change in Perl makes it possible to chain matches together
426 in conjunction with the C<\G> zero-width assertion. See L<perlop> and
429 Here is an illustration of what it takes to get the old behavior:
431 for ( qw(this and that are not what you think you got) ) {
432 while ( /(\w*t\w*)/g ) { print "t word is: $1\n" }
433 pos = 0; # REQUIRED FOR 5.004
434 while ( /(\w*a\w*)/g ) { print "a word is: $1\n" }
438 =item C<m//x> ignores whitespace before ?*+{}
440 The C<m//x> construct has always been intended to ignore all unescaped
441 whitespace. However, before Perl 5.004, whitespace had the effect of
442 escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was
443 (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004.
445 =item nested C<sub{}> closures work now
447 Prior to the 5.004 release, nested anonymous functions didn't work
450 =item formats work right on changing lexicals
452 Just like anonymous functions that contain lexical variables
453 that change (like a lexical index variable for a C<foreach> loop),
454 formats now work properly. For example, this silently failed
455 before, and is fine now:
458 foreach $i ( 1 .. 10 ) {
468 =head2 New builtin methods
470 The C<UNIVERSAL> package automatically contains the following methods that
471 are inherited by all other classes:
477 C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
479 C<isa> is also exportable and can be called as a sub with two arguments. This
480 allows the ability to check what a reference points to. Example:
482 use UNIVERSAL qw(isa);
484 if(isa($ref, 'ARRAY')) {
490 C<can> checks to see if its object has a method called C<METHOD>,
491 if it does then a reference to the sub is returned; if it does not then
492 I<undef> is returned.
494 =item VERSION( [NEED] )
496 C<VERSION> returns the version number of the class (package). If the
497 NEED argument is given then it will check that the current version (as
498 defined by the $VERSION variable in the given package) not less than
499 NEED; it will die if this is not the case. This method is normally
500 called as a class method. This method is called automatically by the
501 C<VERSION> form of C<use>.
503 use A 1.2 qw(some imported subs);
509 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
510 C<isa> uses a very similar method and caching strategy. This may cause
511 strange effects if the Perl code dynamically changes @ISA in any package.
513 You may add other methods to the UNIVERSAL class via Perl or XS code.
514 You do not need to C<use UNIVERSAL> in order to make these methods
515 available to your program. This is necessary only if you wish to
516 have C<isa> available as a plain subroutine in the current package.
518 =head2 TIEHANDLE now supported
520 See L<perltie> for other kinds of tie()s.
524 =item TIEHANDLE classname, LIST
526 This is the constructor for the class. That means it is expected to
527 return an object of some sort. The reference can be used to
528 hold some internal information.
533 return bless \$i, shift;
536 =item PRINT this, LIST
538 This method will be triggered every time the tied handle is printed to.
539 Beyond its self reference it also expects the list that was passed to
545 return print join( $, => map {uc} @_), $\;
548 =item PRINTF this, LIST
550 This method will be triggered every time the tied handle is printed to
551 with the C<printf()> function.
552 Beyond its self reference it also expects the format and list that was
553 passed to the printf function.
558 print sprintf($fmt, @_)."\n";
563 This method will be called when the handle is read from via the C<read>
564 or C<sysread> functions.
568 my($buf,$len,$offset) = @_;
569 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
574 This method will be called when the handle is read from. The method
575 should return undef when there is no more data.
579 return "PRINT called $$r times\n"
584 This method will be called when the C<getc> function is called.
586 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
590 As with the other types of ties, this method will be called when the
591 tied handle is about to be destroyed. This is useful for debugging and
592 possibly for cleaning up.
600 =head2 Malloc enhancements
602 Four new compilation flags are recognized by malloc.c. (They have no
603 effect if perl is compiled with system malloc().)
607 =item -DDEBUGGING_MSTATS
609 If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print
610 memory statistics at runtime by running Perl thusly:
612 env PERL_DEBUG_MSTATS=2 perl your_script_here
614 The value of 2 means to print statistics after compilation and on
615 exit; with a value of 1, the statistics ares printed only on exit.
616 (If you want the statistics at an arbitrary time, you'll need to
617 install the optional module Devel::Peek.)
619 =item -DEMERGENCY_SBRK
621 If this macro is defined, running out of memory need not be a fatal
622 error: a memory pool can allocated by assigning to the special
623 variable C<$^M>. See L<"$^M">.
627 Perl memory allocation is by bucket with sizes close to powers of two.
628 Because of these malloc overhead may be big, especially for data of
629 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
630 a slightly different algorithm for small allocations (up to 64 bytes
631 long), which makes it possible to have overhead down to 1 byte for
632 allocations which are powers of two (and appear quite often).
634 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
635 about 20% for typical Perl usage. Expected slowdown due to additional
636 malloc overhead is in fractions of a percent (hard to measure, because
637 of the effect of saved memory on speed).
639 =item -DTWO_POT_OPTIMIZE
641 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
642 with size close to a power of two; but this works for big allocations
643 (starting with 16K by default). Such allocations are typical for big
644 hashes and special-purpose scripts, especially image processing.
646 On recent systems, the fact that perl requires 2M from system for 1M
647 allocation will not affect speed of execution, since the tail of such
648 a chunk is not going to be touched (and thus will not require real
649 memory). However, it may result in a premature out-of-memory error.
650 So if you will be manipulating very large blocks with sizes close to
651 powers of two, it would be wise to define this macro.
653 Expected saving of memory is 0-100% (100% in applications which
654 require most memory in such 2**n chunks); expected slowdown is
659 =head2 Miscellaneous efficiency enhancements
661 Functions that have an empty prototype and that do nothing but return
662 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
664 Each unique hash key is only allocated once, no matter how many hashes
665 have an entry with that key. So even if you have 100 copies of the
666 same hash, the hash keys never have to be reallocated.
668 =head1 Support for More Operating Systems
670 Support for the following operating systems is new in Perl 5.004.
674 Perl 5.004 now includes support for building a "native" perl under
675 Windows NT, using the Microsoft Visual C++ compiler (versions 2.0
676 and above). The resulting perl can be used under Windows 95 (if it
677 is installed in the same directory locations as it got installed
678 in Windows NT). This port includes support for perl extension
679 building tools like L<MakeMaker> and L<h2xs>, so that many extensions
680 available on the Comprehensive Perl Archive Network (CPAN) can now be
681 readily built under Windows NT. See http://www.perl.com/ for more
682 information on CPAN, and L<README.win32> for more details on how to
683 get started with building this port.
685 There is also support for building perl under the Cygwin32 environment.
686 Cygwin32 is a set of GNU tools that make it possible to compile and run
687 many UNIX programs under Windows NT by providing a mostly UNIX-like
688 interface for compilation and execution. See L<README.cygwin32> for
689 more details on this port, and how to obtain the Cygwin32 toolkit.
690 This port has not been as well tested as the "native" port described
691 above (which is not as well tested as we'd like either :)
703 See L<README.amigaos>.
707 Six new pragmatic modules exist:
711 =item use autouse MODULE => qw(sub1 sub2 sub3)
713 Defers C<require MODULE> until someone calls one of the specified
714 subroutines (which must be exported by MODULE). This pragma should be
715 used with caution, and only when necessary.
721 Looks for MakeMaker-like I<'blib'> directory structure starting in
722 I<dir> (or current directory) and working back up to five levels of
725 Intended for use on command line with B<-M> option as a way of testing
726 arbitrary scripts against an uninstalled version of a package.
728 =item use constant NAME => VALUE
730 Provides a convenient interface for creating compile-time constants,
731 See L<perlsub/"Constant Functions">.
735 Tells the compiler to enable (or disable) the use of POSIX locales for
738 When C<use locale> is in effect, the current LC_CTYPE locale is used
739 for regular expressions and case mapping; LC_COLLATE for string
740 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
741 (but B<not> in print). LC_NUMERIC is always used in write, since
742 lexical scoping of formats is problematic at best.
744 Each C<use locale> or C<no locale> affects statements to the end of
745 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
746 current file. Locales can be switched and queried with
749 See L<perllocale> for more information.
753 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
757 Enable VMS-specific language features. Currently, there are three
758 VMS-specific features available: 'status', which makes C<$?> and
759 C<system> return genuine VMS status values instead of emulating POSIX;
760 'exit', which makes C<exit> take a genuine VMS status value instead of
761 assuming that C<exit 1> is an error; and 'time', which makes all times
762 relative to the local time zone, in the VMS tradition.
768 =head2 Required Updates
770 Though Perl 5.004 is compatible with almost all modules that work
771 with Perl 5.003, there are a few exceptions:
773 Module Required Version for Perl 5.004
774 ------ -------------------------------
777 Tk Tk400.202 (-w makes noise)
779 Also, the majordomo mailing list program, version 1.94.1, doesn't work
780 with Perl 5.004 (nor with perl 4), because it executes an invalid
781 regular expression. This bug is fixed in majordomo version 1.94.2.
783 =head2 Installation directories
785 The I<installperl> script now places the Perl source files for
786 extensions in the architecture-specific library directory, which is
787 where the shared libraries for extensions have always been. This
788 change is intended to allow administrators to keep the Perl 5.004
789 library directory unchanged from a previous version, without running
790 the risk of binary incompatibility between extensions' Perl source and
793 =head2 Module information summary
795 Brand new modules, arranged by topic rather than strictly
798 CGI.pm Web server interface ("Common Gateway Interface")
799 CGI/Apache.pm Support for Apache's Perl module
800 CGI/Carp.pm Log server errors with helpful context
801 CGI/Fast.pm Support for FastCGI (persistent server process)
802 CGI/Push.pm Support for server push
803 CGI/Switch.pm Simple interface for multiple server types
805 CPAN Interface to Comprehensive Perl Archive Network
806 CPAN::FirstTime Utility for creating CPAN configuration file
807 CPAN::Nox Runs CPAN while avoiding compiled extensions
809 IO.pm Top-level interface to IO::* classes
810 IO/File.pm IO::File extension Perl module
811 IO/Handle.pm IO::Handle extension Perl module
812 IO/Pipe.pm IO::Pipe extension Perl module
813 IO/Seekable.pm IO::Seekable extension Perl module
814 IO/Select.pm IO::Select extension Perl module
815 IO/Socket.pm IO::Socket extension Perl module
817 Opcode.pm Disable named opcodes when compiling Perl code
819 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
820 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
822 FindBin.pm Find path of currently executing program
824 Class/Struct.pm Declare struct-like datatypes as Perl classes
825 File/stat.pm By-name interface to Perl's builtin stat
826 Net/hostent.pm By-name interface to Perl's builtin gethost*
827 Net/netent.pm By-name interface to Perl's builtin getnet*
828 Net/protoent.pm By-name interface to Perl's builtin getproto*
829 Net/servent.pm By-name interface to Perl's builtin getserv*
830 Time/gmtime.pm By-name interface to Perl's builtin gmtime
831 Time/localtime.pm By-name interface to Perl's builtin localtime
832 Time/tm.pm Internal object for Time::{gm,local}time
833 User/grent.pm By-name interface to Perl's builtin getgr*
834 User/pwent.pm By-name interface to Perl's builtin getpw*
836 Tie/RefHash.pm Base class for tied hashes with references as keys
838 UNIVERSAL.pm Base class for *ALL* classes
842 New constants in the existing Fcntl modules are now supported,
843 provided that your operating system happens to support them:
846 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
849 These constants are intended for use with the Perl operators sysopen()
850 and fcntl() and the basic database modules like SDBM_File. For the
851 exact meaning of these and other Fcntl constants please refer to your
852 operating system's documentation for fcntl() and open().
854 In addition, the Fcntl module now provides these constants for use
855 with the Perl operator flock():
857 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
859 These constants are defined in all environments (because where there is
860 no flock() system call, Perl emulates it). However, for historical
861 reasons, these constants are not exported unless they are explicitly
862 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
866 The IO module provides a simple mechanism to load all of the IO modules at one
867 go. Currently this includes:
875 For more information on any of these modules, please see its
876 respective documentation.
880 The Math::Complex module has been totally rewritten, and now supports
881 more operations. These are overloaded:
883 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
885 And these functions are now exported:
888 log10 logn ln cbrt root
901 This new module provides a simpler interface to parts of Math::Complex for
902 those who need trigonometric functions only for real numbers.
906 There have been quite a few changes made to DB_File. Here are a few of
913 Fixed a handful of bugs.
917 By public demand, added support for the standard hash function exists().
921 Made it compatible with Berkeley DB 1.86.
925 Made negative subscripts work with RECNO interface.
929 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
930 mode from 0640 to 0666.
934 Made DB_File automatically import the open() constants (O_RDWR,
935 O_CREAT etc.) from Fcntl, if available.
939 Updated documentation.
943 Refer to the HISTORY section in DB_File.pm for a complete list of
944 changes. Everything after DB_File 1.01 has been added since 5.003.
948 Major rewrite - support added for both udp echo and real icmp pings.
950 =head2 Object-oriented overrides for builtin operators
952 Many of the Perl builtins returning lists now have
953 object-oriented overrides. These are:
965 For example, you can now say
969 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
971 =head1 Utility Changes
977 =item Sends converted HTML to standard output
979 The I<pod2html> utility included with Perl 5.004 is entirely new.
980 By default, it sends the converted HTML to its standard output,
981 instead of writing it to a file like Perl 5.003's I<pod2html> did.
982 Use the B<--outfile=FILENAME> option to write to a file.
990 =item C<void> XSUBs now default to returning nothing
992 Due to a documentation/implementation bug in previous versions of
993 Perl, XSUBs with a return type of C<void> have actually been
994 returning one value. Usually that value was the GV for the XSUB,
995 but sometimes it was some already freed or reused value, which would
996 sometimes lead to program failure.
998 In Perl 5.004, if an XSUB is declared as returning C<void>, it
999 actually returns no value, i.e. an empty list (though there is a
1000 backward-compatibility exception; see below). If your XSUB really
1001 does return an SV, you should give it a return type of C<SV *>.
1003 For backward compatibility, I<xsubpp> tries to guess whether a
1004 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
1005 It does so by examining the text of the XSUB: if I<xsubpp> finds
1006 what looks like an assignment to C<ST(0)>, it assumes that the
1007 XSUB's return type is really C<SV *>.
1011 =head1 C Language API Changes
1015 =item C<gv_fetchmethod> and C<perl_call_sv>
1017 The C<gv_fetchmethod> function finds a method for an object, just like
1018 in Perl 5.003. The GV it returns may be a method cache entry.
1019 However, in Perl 5.004, method cache entries are not visible to users;
1020 therefore, they can no longer be passed directly to C<perl_call_sv>.
1021 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
1022 and pass the CV to C<perl_call_sv>.
1024 The most likely symptom of passing the result of C<gv_fetchmethod> to
1025 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
1026 error on the I<second> call to a given method (since there is no cache
1029 =item C<perl_eval_pv>
1031 A new function handy for eval'ing strings of Perl code inside C code.
1032 This function returns the value from the eval statement, which can
1033 be used instead of fetching globals from the symbol table. See
1034 L<perlguts>, L<perlembed> and L<perlcall> for details and examples.
1036 =item Extended API for manipulating hashes
1038 Internal handling of hash keys has changed. The old hashtable API is
1039 still fully supported, and will likely remain so. The additions to the
1040 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
1041 real scalars as keys rather than plain strings (nontied hashes still
1042 can only use strings as keys). New extensions must use the new hash
1043 access functions and macros if they wish to use C<SV*> keys. These
1044 additions also make it feasible to manipulate C<HE*>s (hash entries),
1045 which can be more efficient. See L<perlguts> for details.
1049 =head1 Documentation Changes
1051 Many of the base and library pods were updated. These
1052 new pods are included in section 1:
1062 Locale support (internationalization and localization).
1066 Tutorial on Perl OO programming.
1070 Perl internal IO abstraction interface.
1074 Although not new, this has been massively updated.
1078 Although not new, this has been massively updated.
1082 =head1 New Diagnostics
1084 Several new conditions will trigger warnings that were
1085 silent before. Some only affect certain platforms.
1086 The following new warnings and errors outline these.
1087 These messages are classified as follows (listed in
1088 increasing order of desperation):
1090 (W) A warning (optional).
1091 (D) A deprecation (optional).
1092 (S) A severe warning (mandatory).
1093 (F) A fatal error (trappable).
1094 (P) An internal error you should never see (trappable).
1095 (X) A very fatal error (nontrappable).
1096 (A) An alien error message (not generated by Perl).
1100 =item "my" variable %s masks earlier declaration in same scope
1102 (S) A lexical variable has been redeclared in the same scope, effectively
1103 eliminating all access to the previous instance. This is almost always
1104 a typographical error. Note that the earlier variable will still exist
1105 until the end of the scope or until all closure referents to it are
1108 =item %s argument is not a HASH element or slice
1110 (F) The argument to delete() must be either a hash element, such as
1113 $ref->[12]->{"susie"}
1115 or a hash slice, such as
1117 @foo{$bar, $baz, $xyzzy}
1118 @{$ref->[12]}{"susie", "queue"}
1120 =item Allocation too large: %lx
1122 (X) You can't allocate more than 64K on an MS-DOS machine.
1124 =item Allocation too large
1126 (F) You can't allocate more than 2^31+"small amount" bytes.
1128 =item Applying %s to %s will act on scalar(%s)
1130 (W) The pattern match (//), substitution (s///), and translation (tr///)
1131 operators work on scalar values. If you apply one of them to an array
1132 or a hash, it will convert the array or hash to a scalar value -- the
1133 length of an array, or the population info of a hash -- and then work on
1134 that scalar value. This is probably not what you meant to do. See
1135 L<perlfunc/grep> and L<perlfunc/map> for alternatives.
1137 =item Attempt to free nonexistent shared string
1139 (P) Perl maintains a reference counted internal table of strings to
1140 optimize the storage and access of hash keys and other strings. This
1141 indicates someone tried to decrement the reference count of a string
1142 that can no longer be found in the table.
1144 =item Attempt to use reference as lvalue in substr
1146 (W) You supplied a reference as the first argument to substr() used
1147 as an lvalue, which is pretty strange. Perhaps you forgot to
1148 dereference it first. See L<perlfunc/substr>.
1150 =item Can't redefine active sort subroutine %s
1152 (F) Perl optimizes the internal handling of sort subroutines and keeps
1153 pointers into them. You tried to redefine one such sort subroutine when it
1154 was currently active, which is not allowed. If you really want to do
1155 this, you should write C<sort { &func } @x> instead of C<sort func @x>.
1157 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
1159 (F) Only hard references are allowed by "strict refs". Symbolic references
1160 are disallowed. See L<perlref>.
1162 =item Cannot resolve method `%s' overloading `%s' in package `%s'
1164 (P) Internal error trying to resolve overloading specified by a method
1165 name (as opposed to a subroutine reference).
1167 =item Constant subroutine %s redefined
1169 (S) You redefined a subroutine which had previously been eligible for
1170 inlining. See L<perlsub/"Constant Functions"> for commentary and
1173 =item Constant subroutine %s undefined
1175 (S) You undefined a subroutine which had previously been eligible for
1176 inlining. See L<perlsub/"Constant Functions"> for commentary and
1179 =item Copy method did not return a reference
1181 (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>.
1185 (F) You passed die() an empty string (the equivalent of C<die "">) or
1186 you called it with no args and both C<$@> and C<$_> were empty.
1188 =item Exiting pseudo-block via %s
1190 (W) You are exiting a rather special block construct (like a sort block or
1191 subroutine) by unconventional means, such as a goto, or a loop control
1192 statement. See L<perlfunc/sort>.
1194 =item Identifier too long
1196 (F) Perl limits identifiers (names for variables, functions, etc.) to
1197 252 characters for simple names, somewhat more for compound names (like
1198 C<$A::B>). You've exceeded Perl's limits. Future versions of Perl are
1199 likely to eliminate these arbitrary limitations.
1201 =item Illegal character %s (carriage return)
1203 (F) A carriage return character was found in the input. This is an
1204 error, and not a warning, because carriage return characters can break
1205 multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>).
1207 =item Illegal switch in PERL5OPT: %s
1209 (X) The PERL5OPT environment variable may only be used to set the
1210 following switches: B<-[DIMUdmw]>.
1212 =item Integer overflow in hex number
1214 (S) The literal hex number you have specified is too big for your
1215 architecture. On a 32-bit architecture the largest hex literal is
1218 =item Integer overflow in octal number
1220 (S) The literal octal number you have specified is too big for your
1221 architecture. On a 32-bit architecture the largest octal literal is
1224 =item internal error: glob failed
1226 (P) Something went wrong with the external program(s) used for C<glob>
1227 and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is
1228 broken. If so, you should change all of the csh-related variables in
1229 config.sh: If you have tcsh, make the variables refer to it as if it
1230 were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all
1231 empty (except that C<d_csh> should be C<'undef'>) so that Perl will
1232 think csh is missing. In either case, after editing config.sh, run
1233 C<./Configure -S> and rebuild Perl.
1235 =item Invalid conversion in %s: "%s"
1237 (W) Perl does not understand the given format conversion.
1238 See L<perlfunc/sprintf>.
1240 =item Invalid type in pack: '%s'
1242 (F) The given character is not a valid pack type. See L<perlfunc/pack>.
1244 =item Invalid type in unpack: '%s'
1246 (F) The given character is not a valid unpack type. See L<perlfunc/unpack>.
1248 =item Name "%s::%s" used only once: possible typo
1250 (W) Typographical errors often show up as unique variable names.
1251 If you had a good reason for having a unique name, then just mention
1252 it again somehow to suppress the message (the C<use vars> pragma is
1253 provided for just this purpose).
1255 =item Null picture in formline
1257 (F) The first argument to formline must be a valid format picture
1258 specification. It was found to be empty, which probably means you
1259 supplied it an uninitialized value. See L<perlform>.
1261 =item Offset outside string
1263 (F) You tried to do a read/write/send/recv operation with an offset
1264 pointing outside the buffer. This is difficult to imagine.
1265 The sole exception to this is that C<sysread()>ing past the buffer
1266 will extend the buffer and zero pad the new area.
1268 =item Out of memory!
1270 (X|F) The malloc() function returned 0, indicating there was insufficient
1271 remaining memory (or virtual memory) to satisfy the request.
1273 The request was judged to be small, so the possibility to trap it
1274 depends on the way Perl was compiled. By default it is not trappable.
1275 However, if compiled for this, Perl may use the contents of C<$^M> as
1276 an emergency pool after die()ing with this message. In this case the
1277 error is trappable I<once>.
1279 =item Out of memory during request for %s
1281 (F) The malloc() function returned 0, indicating there was insufficient
1282 remaining memory (or virtual memory) to satisfy the request. However,
1283 the request was judged large enough (compile-time default is 64K), so
1284 a possibility to shut down by trapping this error is granted.
1288 (P) The library function frexp() failed, making printf("%f") impossible.
1290 =item Possible attempt to put comments in qw() list
1292 (W) qw() lists contain items separated by whitespace; as with literal
1293 strings, comment characters are not ignored, but are instead treated
1294 as literal data. (You may have used different delimiters than the
1295 exclamation marks parentheses shown here; braces are also frequently
1298 You probably wrote something like this:
1305 when you should have written this:
1312 If you really want comments, build your list the
1313 old-fashioned way, with quotes and commas:
1317 'b', # another comment
1320 =item Possible attempt to separate words with commas
1322 (W) qw() lists contain items separated by whitespace; therefore commas
1323 aren't needed to separate the items. (You may have used different
1324 delimiters than the parentheses shown here; braces are also frequently
1327 You probably wrote something like this:
1331 which puts literal commas into some of the list items. Write it without
1332 commas if you don't want them to appear in your data:
1336 =item Scalar value @%s{%s} better written as $%s{%s}
1338 (W) You've used a hash slice (indicated by @) to select a single element of
1339 a hash. Generally it's better to ask for a scalar value (indicated by $).
1340 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
1341 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
1342 like a list when you assign to it, and provides a list context to its
1343 subscript, which can do weird things if you're expecting only one subscript.
1345 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
1347 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
1348 Stubs should never be implicitely created, but explicit calls to C<can>
1351 =item Too late for "B<-T>" option
1353 (X) The #! line (or local equivalent) in a Perl script contains the
1354 B<-T> option, but Perl was not invoked with B<-T> in its argument
1355 list. This is an error because, by the time Perl discovers a B<-T> in
1356 a script, it's too late to properly taint everything from the
1357 environment. So Perl gives up.
1359 =item untie attempted while %d inner references still exist
1361 (W) A copy of the object returned from C<tie> (or C<tied>) was still
1362 valid when C<untie> was called.
1364 =item Unrecognized character %s
1366 (F) The Perl parser has no idea what to do with the specified character
1367 in your Perl script (or eval). Perhaps you tried to run a compressed
1368 script, a binary program, or a directory as a Perl program.
1370 =item Unsupported function fork
1372 (F) Your version of executable does not support forking.
1374 Note that under some systems, like OS/2, there may be different flavors of
1375 Perl executables, some of which may support fork, some not. Try changing
1376 the name you call Perl by to C<perl_>, C<perl__>, and so on.
1378 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
1380 (D) Perl versions before 5.004 misinterpreted any type marker followed
1381 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
1382 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
1384 However, the developers of Perl 5.004 could not fix this bug completely,
1385 because at least two widely-used modules depend on the old meaning of
1386 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
1387 old (broken) way inside strings; but it generates this message as a
1388 warning. And in Perl 5.005, this special treatment will cease.
1390 =item Value of %s can be "0"; test with defined()
1392 (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>,
1393 or C<readdir()> as a boolean value. Each of these constructs can return a
1394 value of "0"; that would make the conditional expression false, which is
1395 probably not what you intended. When using these constructs in conditional
1396 expressions, test their values with the C<defined> operator.
1398 =item Variable "%s" may be unavailable
1400 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1401 subroutine, and outside that is another subroutine; and the anonymous
1402 (innermost) subroutine is referencing a lexical variable defined in
1403 the outermost subroutine. For example:
1405 sub outermost { my $a; sub middle { sub { $a } } }
1407 If the anonymous subroutine is called or referenced (directly or
1408 indirectly) from the outermost subroutine, it will share the variable
1409 as you would expect. But if the anonymous subroutine is called or
1410 referenced when the outermost subroutine is not active, it will see
1411 the value of the shared variable as it was before and during the
1412 *first* call to the outermost subroutine, which is probably not what
1415 In these circumstances, it is usually best to make the middle
1416 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1417 support for shared variables in nested anonymous subroutines; a named
1418 subroutine in between interferes with this feature.
1420 =item Variable "%s" will not stay shared
1422 (W) An inner (nested) I<named> subroutine is referencing a lexical
1423 variable defined in an outer subroutine.
1425 When the inner subroutine is called, it will probably see the value of
1426 the outer subroutine's variable as it was before and during the
1427 *first* call to the outer subroutine; in this case, after the first
1428 call to the outer subroutine is complete, the inner and outer
1429 subroutines will no longer share a common value for the variable. In
1430 other words, the variable will no longer be shared.
1432 Furthermore, if the outer subroutine is anonymous and references a
1433 lexical variable outside itself, then the outer and inner subroutines
1434 will I<never> share the given variable.
1436 This problem can usually be solved by making the inner subroutine
1437 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1438 reference variables in outer subroutines are called or referenced,
1439 they are automatically rebound to the current values of such
1442 =item Warning: something's wrong
1444 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1445 you called it with no args and C<$_> was empty.
1447 =item Ill-formed logical name |%s| in prime_env_iter
1449 (W) A warning peculiar to VMS. A logical name was encountered when preparing
1450 to iterate over %ENV which violates the syntactic rules governing logical
1451 names. Since it cannot be translated normally, it is skipped, and will not
1452 appear in %ENV. This may be a benign occurrence, as some software packages
1453 might directly modify logical name tables and introduce nonstandard names,
1454 or it may indicate that a logical name table has been corrupted.
1456 =item Got an error from DosAllocMem
1458 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1459 version of Perl, and this should not happen anyway.
1461 =item Malformed PERLLIB_PREFIX
1463 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1471 with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix
1472 of a builtin library search path, prefix2 is substituted. The error
1473 may appear if components are not found, or are too long. See
1474 "PERLLIB_PREFIX" in F<README.os2>.
1476 =item PERL_SH_DIR too long
1478 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1479 C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>.
1481 =item Process terminated by SIG%s
1483 (W) This is a standard message issued by OS/2 applications, while *nix
1484 applications die in silence. It is considered a feature of the OS/2
1485 port. One can easily disable this by appropriate sighandlers, see
1486 L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT"
1493 If you find what you think is a bug, you might check the headers of
1494 recently posted articles in the comp.lang.perl.misc newsgroup.
1495 There may also be information at http://www.perl.com/perl/, the Perl
1498 If you believe you have an unreported bug, please run the B<perlbug>
1499 program included with your release. Make sure you trim your bug down
1500 to a tiny but sufficient test case. Your bug report, along with the
1501 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1502 analysed by the Perl porting team.
1506 The F<Changes> file for exhaustive details on what changed.
1508 The F<INSTALL> file for how to build Perl. This file has been
1509 significantly updated for 5.004, so even veteran users should
1512 The F<README> file for general stuff.
1514 The F<Copying> file for copyright information.
1518 Constructed by Tom Christiansen, grabbing material with permission
1519 from innumerable contributors, with kibitzing by more than a few Perl
1522 Last update: Sat Mar 8 19:51:26 EST 1997