3 perldelta - what's new for perl5.004
7 This document describes differences between the 5.003 release (as
8 documented in I<Programming Perl>, second edition--the Camel Book) and
11 =head1 Supported Environments
13 Perl5.004 builds out of the box on Unix, Plan9, LynxOS, VMS, OS/2,
18 Most importantly, many bugs were fixed. See the F<Changes>
19 file in the distribution for details.
21 =head2 Compilation option: Binary compatibility with 5.003
23 There is a new Configure question that asks if you want to maintain
24 binary compatibility with Perl 5.003. If you choose binary
25 compatibility, you do not have to recompile your extensions, but you
26 might have symbol conflicts if you embed Perl in another application,
27 just as in the 5.003 release. By default, binary compatibility
28 is preserved at the expense of symbol table pollution.
30 =head2 $PERL5OPT environment variable
32 You may now put Perl options in the $PERL5OPT environment variable.
33 Unless Perl is running with taint checks, it will interpret this
34 variable as if its contents had appeared on a "#!perl" line at the
35 beginning of your script, except that hyphens are optional. PERL5OPT
36 may only be used to set the following switches: B<-[DIMUdmw]>.
38 =head2 Limitations on B<-M>, and C<-m>, and B<-T> options
40 The C<-M> and C<-m> options are no longer allowed on the C<#!> line of
41 a script. If a script needs a module, it should invoke it with the
44 The B<-T> option is also forbidden on the C<#!> line of a script,
45 unless it was present on the Perl command line. Due to the way C<#!>
46 works, this usually means that B<-T> must be in the first argument.
51 will probably work for an executable script invoked as C<scriptname>,
56 will probably fail under the same conditions. (Non-Unix systems will
57 probably not follow this rule.) But C<perl scriptname> is guaranteed
58 to fail, since then there is no chance of B<-T> being found on the
59 command line before it is found on the C<#!> line.
61 =head2 More precise warnings
63 If you removed the B<-w> option from your Perl 5.003 scripts because it
64 made Perl too verbose, we recommend that you try putting it back when
65 you upgrade to Perl 5.004. Each new perl version tends to remove some
66 undesirable warnings, while adding new warnings that may catch bugs in
69 =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods
71 Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods
72 (using the C<@ISA> hierarchy), even when the function to be autoloaded
73 was called as a plain function (e.g. C<Foo::bar()>), not a method
74 (e.g. C<Foo->bar()> or C<$obj->bar()>).
76 Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s.
77 However, there is a significant base of existing code that may be using
78 the old behavior. So, as an interim step, Perl 5.004 issues an optional
79 warning when a non-method uses an inherited C<AUTOLOAD>.
81 The simple rule is: Inheritance will not work when autoloading
82 non-methods. The simple fix for old code is: In any module that used to
83 depend on inheriting C<AUTOLOAD> for non-methods from a base class named
84 C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup.
86 =head2 Subroutine arguments created only when they're modified
88 In Perl 5.004, nonexistent array and hash elements used as subroutine
89 parameters are brought into existence only if they are actually
90 assigned to (via C<@_>).
92 Earlier versions of Perl vary in their handling of such arguments.
93 Perl versions 5.002 and 5.003 always brought them into existence.
94 Perl versions 5.000, 5.001, and 5.002 brought them into existence only
95 if they were not the first argument (which was almost certainly a
96 bug). Earlier versions of Perl never brought them into existence.
98 For example, given this code:
101 sub show { print $_[0] };
102 sub change { $_[0]++ };
106 After this code executes in Perl 5.004, $a{b} exists but $a[2] does
107 not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed
108 (but $a[2]'s value would have been undefined).
110 =head2 Group vector changeable with C<$)>
112 The C<$)> special variable has always (well, in Perl 5, at least)
113 reflected not only the current effective group, but also the group list
114 as returned by the C<getgroups()> C function (if there is one).
115 However, until this release, there has not been a way to call the
116 C<setgroups()> C function from Perl.
118 In Perl 5.004, assigning to C<$)> is exactly symmetrical with examining
119 it: The first number in its string value is used as the effective gid;
120 if there are any numbers after the first one, they are passed to the
121 C<setgroups()> C function (if there is one).
123 =head2 Fixed parsing of $$<digit>, &$<digit>, etc.
125 Perl versions before 5.004 misinterpreted any type marker followed by
126 "$" and a digit. For example, "$$0" was incorrectly taken to mean
127 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
129 However, the developers of Perl 5.004 could not fix this bug completely,
130 because at least two widely-used modules depend on the old meaning of
131 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
132 old (broken) way inside strings; but it generates this message as a
133 warning. And in Perl 5.005, this special treatment will cease.
135 =head2 No resetting of $. on implicit close
137 The documentation for Perl 5.0 has always stated that C<$.> is I<not>
138 reset when an already-open file handle is reopened with no intervening
139 call to C<close>. Due to a bug, perl versions 5.000 through 5.003
140 I<did> reset C<$.> under that circumstance; Perl 5.004 does not.
142 =head2 C<wantarray> may return undef
144 The C<wantarray> operator returns true if a subroutine is expected to
145 return a list, and false otherwise. In Perl 5.004, C<wantarray> can
146 also return the undefined value if a subroutine's return value will
147 not be used at all, which allows subroutines to avoid a time-consuming
148 calculation of a return value if it isn't going to be used.
150 =head2 Changes to tainting checks
152 A bug in previous versions may have failed to detect some insecure
153 conditions when taint checks are turned on. (Taint checks are used
154 in setuid or setgid scripts, or when explicitly turned on with the
155 C<-T> invocation option.) Although it's unlikely, this may cause a
156 previously-working script to now fail -- which should be construed
157 as a blessing, since that indicates a potentially-serious security
158 hole was just plugged.
160 =head2 New Opcode module and revised Safe module
162 A new Opcode module supports the creation, manipulation and
163 application of opcode masks. The revised Safe module has a new API
164 and is implemented using the new Opcode module. Please read the new
165 Opcode and Safe documentation.
167 =head2 Embedding improvements
169 In older versions of Perl it was not possible to create more than one
170 Perl interpreter instance inside a single process without leaking like a
171 sieve and/or crashing. The bugs that caused this behavior have all been
172 fixed. However, you still must take care when embedding Perl in a C
173 program. See the updated perlembed manpage for tips on how to manage
176 =head2 Internal change: FileHandle class based on IO::* classes
178 File handles are now stored internally as type IO::Handle. The
179 FileHandle module is still supported for backwards compatibility, but
180 it is now merely a front end to the IO::* modules -- specifically,
181 IO::Handle, IO::Seekable, and IO::File. We suggest, but do not
182 require, that you use the IO::* modules in new code.
184 In harmony with this change, C<*GLOB{FILEHANDLE}> is now a
185 backward-compatible synonym for C<*STDOUT{IO}>.
187 =head2 Internal change: PerlIO abstraction interface
189 It is now possible to build Perl with AT&T's sfio IO package
190 instead of stdio. See L<perlapio> for more details, and
191 the F<INSTALL> file for how to use it.
193 =head2 New and changed builtin variables
199 Extended error message on some platforms. (Also known as
200 $EXTENDED_OS_ERROR if you C<use English>).
204 The current set of syntax checks enabled by C<use strict>. See the
205 documentation of C<strict> for more details. Not actually new, but
207 Because it is intended for internal use by Perl core components,
208 there is no C<use English> long name for this variable.
212 By default, running out of memory it is not trappable. However, if
213 compiled for this, Perl may use the contents of C<$^M> as an emergency
214 pool after die()ing with this message. Suppose that your Perl were
215 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
219 would allocate a 64K buffer for use when in emergency.
220 See the F<INSTALL> file for information on how to enable this option.
221 As a disincentive to casual use of this advanced feature,
222 there is no C<use English> long name for this variable.
226 =head2 New and changed builtin functions
230 =item delete on slices
232 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
236 is now supported on more platforms, prefers fcntl to lockf when
237 emulating, and always flushes before (un)locking.
239 =item printf and sprintf
241 Perl now implements these functions itself; it doesn't use the C
242 library function sprintf() any more, except for floating-point
243 numbers, and even then only known flags are allowed. As a result, it
244 is now possible to know which conversions and flags will work, and
247 The new conversions in Perl's sprintf() are:
250 %p a pointer (the address of the Perl value, in hexadecimal)
251 %n special: B<stores> into the next variable in the parameter
252 list the number of characters printed so far
254 The new flags that go between the C<%> and the conversion are:
256 # prefix octal with "0", hex with "0x"
257 h interpret integer as C type "short" or "unsigned short"
258 V interpret integer as Perl's standard integer type
260 Also, where a number would appear in the flags, an asterisk ("*") may
261 be used instead, in which case Perl uses the next item in the
262 parameter list as the given number (that is, as the field width or
263 precision). If a field width obtained through "*" is negative, it has
264 the same effect as the '-' flag: left-justification.
266 See L<perlfunc/sprintf> for a complete list of conversion and flags.
268 =item keys as an lvalue
270 As an lvalue, C<keys> allows you to increase the number of hash buckets
271 allocated for the given hash. This can gain you a measure of efficiency if
272 you know the hash is going to get big. (This is similar to pre-extending
273 an array by assigning a larger number to $#array.) If you say
277 then C<%hash> will have at least 200 buckets allocated for it. These
278 buckets will be retained even if you do C<%hash = ()>; use C<undef
279 %hash> if you want to free the storage while C<%hash> is still in scope.
280 You can't shrink the number of buckets allocated for the hash using
281 C<keys> in this way (but you needn't worry about doing this by accident,
282 as trying has no effect).
284 =item my() in Control Structures
286 You can now use my() (with or without the parentheses) in the control
287 expressions of control structures such as:
289 while (defined(my $line = <>)) {
295 if ((my $answer = <STDIN>) =~ /^y(es)?$/i) {
297 } elsif ($answer =~ /^n(o)?$/i) {
301 die "`$answer' is neither `yes' nor `no'";
304 Also, you can declare a foreach loop control variable as lexical by
305 preceding it with the word "my". For example, in:
307 foreach my $i (1, 2, 3) {
311 $i is a lexical variable, and the scope of $i extends to the end of
312 the loop, but not beyond it.
314 Note that you still cannot use my() on global punctuation variables
315 such as $_ and the like.
317 =item pack() and unpack()
319 A new format 'w' represents a BER compressed integer (as defined in
320 ASN.1). Its format is a sequence of one or more bytes, each of which
321 provides seven bits of the total value, with the most significant
322 first. Bit eight of each byte is set, except for the last byte, in
323 which bit eight is clear.
325 Both pack() and unpack() now fail when their templates contain invalid
326 types. (Invalid types used to be ignored.)
330 The new sysseek() operator is a variant of seek() that sets and gets the
331 file's system read/write position, using the lseek(2) system call. It is
332 the only reliable way to seek before using sysread() or syswrite(). Its
333 return value is the new position, or the undefined value on failure.
337 If the first argument to C<use> is a number, it is treated as a version
338 number instead of a module name. If the version of the Perl interpreter
339 is less than VERSION, then an error message is printed and Perl exits
340 immediately. Because C<use> occurs at compile time, this check happens
341 immediately during the compilation process, unlike C<require VERSION>,
342 which waits until runtime for the check. This is often useful if you
343 need to check the current Perl version before C<use>ing library modules
344 which have changed in incompatible ways from older versions of Perl.
345 (We try not to do this more than we have to.)
347 =item use Module VERSION LIST
349 If the VERSION argument is present between Module and LIST, then the
350 C<use> will call the VERSION method in class Module with the given
351 version as an argument. The default VERSION method, inherited from
352 the UNIVERSAL class, croaks if the given version is larger than the
353 value of the variable $Module::VERSION. (Note that there is not a
354 comma after VERSION!)
356 This version-checking mechanism is similar to the one currently used
357 in the Exporter module, but it is faster and can be used with modules
358 that don't use the Exporter. It is the recommended method for new
361 =item prototype(FUNCTION)
363 Returns the prototype of a function as a string (or C<undef> if the
364 function has no prototype). FUNCTION is a reference to or the name of the
365 function whose prototype you want to retrieve.
366 (Not actually new; just never documented before.)
370 The default seed for C<srand>, which used to be C<time>, has been changed.
371 Now it's a heady mix of difficult-to-predict system-dependent values,
372 which should be sufficient for most everyday purposes.
374 Previous to version 5.004, calling C<rand> without first calling C<srand>
375 would yield the same sequence of random numbers on most or all machines.
376 Now, when perl sees that you're calling C<rand> and haven't yet called
377 C<srand>, it calls C<srand> with the default seed. You should still call
378 C<srand> manually if your code might ever be run on a pre-5.004 system,
379 of course, or if you want a seed other than the default.
383 Functions documented in the Camel to default to $_ now in
384 fact do, and all those that do are so documented in L<perlfunc>.
386 =item C<m//g> does not reset search position on failure
388 The C<m//g> match iteration construct used to reset its target string's
389 search position (which is visible through the C<pos> operator) when a
390 match failed; as a result, the next C<m//g> match would start at the
391 beginning of the string). With Perl 5.004, the search position must be
392 reset explicitly, as with C<pos $str = 0;>, or by modifying the target
393 string. This change in Perl makes it possible to chain matches together
394 in conjunction with the C<\G> zero-width assertion. See L<perlop> and
397 Here is an illustration of what it takes to get the old behavior:
399 for ( qw(this and that are not what you think you got) ) {
400 while ( /(\w*t\w*)/g ) { print "t word is: $1\n" }
401 pos = 0; # REQUIRED FOR 5.004
402 while ( /(\w*a\w*)/g ) { print "a word is: $1\n" }
406 =item C<m//x> ignores whitespace before ?*+{}
408 The C<m//x> construct has always been intended to ignore all unescaped
409 whitespace. However, before Perl 5.004, whitespace had the effect of
410 escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was
411 (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004.
413 =item nested C<sub{}> closures work now
415 Prior to the 5.004 release, nested anonymous functions didn't work
418 =item formats work right on changing lexicals
420 Just like anonymous functions that contain lexical variables
421 that change (like a lexical index variable for a C<foreach> loop),
422 formats now work properly. For example, this silently failed
423 before, and is fine now:
426 foreach $i ( 1 .. 10 ) {
436 =head2 New builtin methods
438 The C<UNIVERSAL> package automatically contains the following methods that
439 are inherited by all other classes:
445 C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS>
447 C<isa> is also exportable and can be called as a sub with two arguments. This
448 allows the ability to check what a reference points to. Example:
450 use UNIVERSAL qw(isa);
452 if(isa($ref, 'ARRAY')) {
458 C<can> checks to see if its object has a method called C<METHOD>,
459 if it does then a reference to the sub is returned; if it does not then
460 I<undef> is returned.
462 =item VERSION( [NEED] )
464 C<VERSION> returns the version number of the class (package). If the
465 NEED argument is given then it will check that the current version (as
466 defined by the $VERSION variable in the given package) not less than
467 NEED; it will die if this is not the case. This method is normally
468 called as a class method. This method is called automatically by the
469 C<VERSION> form of C<use>.
471 use A 1.2 qw(some imported subs);
477 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
478 C<isa> uses a very similar method and caching strategy. This may cause
479 strange effects if the Perl code dynamically changes @ISA in any package.
481 You may add other methods to the UNIVERSAL class via Perl or XS code.
482 You do not need to C<use UNIVERSAL> in order to make these methods
483 available to your program. This is necessary only if you wish to
484 have C<isa> available as a plain subroutine in the current package.
486 =head2 TIEHANDLE now supported
488 See L<perltie> for other kinds of tie()s.
492 =item TIEHANDLE classname, LIST
494 This is the constructor for the class. That means it is expected to
495 return an object of some sort. The reference can be used to
496 hold some internal information.
501 return bless \$i, shift;
504 =item PRINT this, LIST
506 This method will be triggered every time the tied handle is printed to.
507 Beyond its self reference it also expects the list that was passed to
513 return print join( $, => map {uc} @_), $\;
516 =item PRINTF this, LIST
518 This method will be triggered every time the tied handle is printed to
519 with the C<printf()> function.
520 Beyond its self reference it also expects the format and list that was
521 passed to the printf function.
526 print sprintf($fmt, @_)."\n";
531 This method will be called when the handle is read from via the C<read>
532 or C<sysread> functions.
536 my($buf,$len,$offset) = @_;
537 print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
542 This method will be called when the handle is read from. The method
543 should return undef when there is no more data.
547 return "PRINT called $$r times\n"
552 This method will be called when the C<getc> function is called.
554 sub GETC { print "Don't GETC, Get Perl"; return "a"; }
558 As with the other types of ties, this method will be called when the
559 tied handle is about to be destroyed. This is useful for debugging and
560 possibly for cleaning up.
568 =head2 Malloc enhancements
570 Four new compilation flags are recognized by malloc.c. (They have no
571 effect if perl is compiled with system malloc().)
575 =item -DDEBUGGING_MSTATS
577 If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print
578 memory statistics at runtime by running Perl thusly:
580 env PERL_DEBUG_MSTATS=2 perl your_script_here
582 The value of 2 means to print statistics after compilation and on
583 exit; with a value of 1, the statistics ares printed only on exit.
584 (If you want the statistics at an arbitrary time, you'll need to
585 install the optional module Devel::Peek.)
587 =item -DEMERGENCY_SBRK
589 If this macro is defined, running out of memory need not be a fatal
590 error: a memory pool can allocated by assigning to the special
591 variable C<$^M>. See L<"$^M">.
595 Perl memory allocation is by bucket with sizes close to powers of two.
596 Because of these malloc overhead may be big, especially for data of
597 size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses
598 a slightly different algorithm for small allocations (up to 64 bytes
599 long), which makes it possible to have overhead down to 1 byte for
600 allocations which are powers of two (and appear quite often).
602 Expected memory savings (with 8-byte alignment in C<alignbytes>) is
603 about 20% for typical Perl usage. Expected slowdown due to additional
604 malloc overhead is in fractions of a percent (hard to measure, because
605 of the effect of saved memory on speed).
607 =item -DTWO_POT_OPTIMIZE
609 Similarly to C<PACK_MALLOC>, this macro improves allocations of data
610 with size close to a power of two; but this works for big allocations
611 (starting with 16K by default). Such allocations are typical for big
612 hashes and special-purpose scripts, especially image processing.
614 On recent systems, the fact that perl requires 2M from system for 1M
615 allocation will not affect speed of execution, since the tail of such
616 a chunk is not going to be touched (and thus will not require real
617 memory). However, it may result in a premature out-of-memory error.
618 So if you will be manipulating very large blocks with sizes close to
619 powers of two, it would be wise to define this macro.
621 Expected saving of memory is 0-100% (100% in applications which
622 require most memory in such 2**n chunks); expected slowdown is
627 =head2 Miscellaneous efficiency enhancements
629 Functions that have an empty prototype and that do nothing but return
630 a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>).
632 Each unique hash key is only allocated once, no matter how many hashes
633 have an entry with that key. So even if you have 100 copies of the
634 same hash, the hash keys never have to be reallocated.
638 Six new pragmatic modules exist:
642 =item use autouse MODULE => qw(sub1 sub2 sub3)
644 Defers C<require MODULE> until someone calls one of the specified
645 subroutines (which must be exported by MODULE). This pragma should be
646 used with caution, and only when necessary.
652 Looks for MakeMaker-like I<'blib'> directory structure starting in
653 I<dir> (or current directory) and working back up to five levels of
656 Intended for use on command line with B<-M> option as a way of testing
657 arbitrary scripts against an uninstalled version of a package.
659 =item use constant NAME => VALUE
661 Provides a convenient interface for creating compile-time constants,
662 See L<perlsub/"Constant Functions">.
666 Tells the compiler to enable (or disable) the use of POSIX locales for
669 When C<use locale> is in effect, the current LC_CTYPE locale is used
670 for regular expressions and case mapping; LC_COLLATE for string
671 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
672 (but B<not> in print). LC_NUMERIC is always used in write, since
673 lexical scoping of formats is problematic at best.
675 Each C<use locale> or C<no locale> affects statements to the end of
676 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
677 current file. Locales can be switched and queried with
680 See L<perllocale> for more information.
684 Disable unsafe opcodes, or any named opcodes, when compiling Perl code.
688 Enable VMS-specific language features. Currently, there are three
689 VMS-specific features available: 'status', which makes C<$?> and
690 C<system> return genuine VMS status values instead of emulating POSIX;
691 'exit', which makes C<exit> take a genuine VMS status value instead of
692 assuming that C<exit 1> is an error; and 'time', which makes all times
693 relative to the local time zone, in the VMS tradition.
699 =head2 Required Updates
701 Though Perl 5.004 is compatible with almost all modules that work
702 with Perl 5.003, there are a few exceptions:
704 Module Required Version for Perl 5.004
705 ------ -------------------------------
708 Tk Tk400.202 (-w makes noise)
710 Also, the majordomo mailing list program, version 1.94.1, doesn't work
711 with Perl 5.004 (nor with perl 4), because it executes an invalid
712 regular expression. This bug is fixed in majordomo version 1.94.2.
714 =head2 Installation directories
716 The I<installperl> script now places the Perl source files for
717 extensions in the architecture-specific library directory, which is
718 where the shared libraries for extensions have always been. This
719 change is intended to allow administrators to keep the Perl 5.004
720 library directory unchanged from a previous version, without running
721 the risk of binary incompatibility between extensions' Perl source and
724 =head2 Module information summary
726 Brand new modules, arranged by topic rather than strictly
729 CGI.pm Web server interface ("Common Gateway Interface")
730 CGI/Apache.pm Support for Apache's Perl module
731 CGI/Carp.pm Log server errors with helpful context
732 CGI/Fast.pm Support for FastCGI (persistent server process)
733 CGI/Push.pm Support for server push
734 CGI/Switch.pm Simple interface for multiple server types
736 CPAN Interface to Comprehensive Perl Archive Network
737 CPAN::FirstTime Utility for creating CPAN configuration file
738 CPAN::Nox Runs CPAN while avoiding compiled extensions
740 IO.pm Top-level interface to IO::* classes
741 IO/File.pm IO::File extension Perl module
742 IO/Handle.pm IO::Handle extension Perl module
743 IO/Pipe.pm IO::Pipe extension Perl module
744 IO/Seekable.pm IO::Seekable extension Perl module
745 IO/Select.pm IO::Select extension Perl module
746 IO/Socket.pm IO::Socket extension Perl module
748 Opcode.pm Disable named opcodes when compiling Perl code
750 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
751 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
753 FindBin.pm Find path of currently executing program
755 Class/Struct.pm Declare struct-like datatypes as Perl classes
756 File/stat.pm By-name interface to Perl's builtin stat
757 Net/hostent.pm By-name interface to Perl's builtin gethost*
758 Net/netent.pm By-name interface to Perl's builtin getnet*
759 Net/protoent.pm By-name interface to Perl's builtin getproto*
760 Net/servent.pm By-name interface to Perl's builtin getserv*
761 Time/gmtime.pm By-name interface to Perl's builtin gmtime
762 Time/localtime.pm By-name interface to Perl's builtin localtime
763 Time/tm.pm Internal object for Time::{gm,local}time
764 User/grent.pm By-name interface to Perl's builtin getgr*
765 User/pwent.pm By-name interface to Perl's builtin getpw*
767 Tie/RefHash.pm Base class for tied hashes with references as keys
769 UNIVERSAL.pm Base class for *ALL* classes
773 New constants in the existing Fcntl modules are now supported,
774 provided that your operating system happens to support them:
777 O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC
780 These constants are intended for use with the Perl operators sysopen()
781 and fcntl() and the basic database modules like SDBM_File. For the
782 exact meaning of these and other Fcntl constants please refer to your
783 operating system's documentation for fcntl() and open().
785 In addition, the Fcntl module now provides these constants for use
786 with the Perl operator flock():
788 LOCK_SH LOCK_EX LOCK_NB LOCK_UN
790 These constants are defined in all environments (because where there is
791 no flock() system call, Perl emulates it). However, for historical
792 reasons, these constants are not exported unless they are explicitly
793 requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>).
797 The IO module provides a simple mechanism to load all of the IO modules at one
798 go. Currently this includes:
806 For more information on any of these modules, please see its
807 respective documentation.
811 The Math::Complex module has been totally rewritten, and now supports
812 more operations. These are overloaded:
814 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
816 And these functions are now exported:
819 log10 logn ln cbrt root
832 This new module provides a simpler interface to parts of Math::Complex for
833 those who need trigonometric functions only for real numbers.
837 There have been quite a few changes made to DB_File. Here are a few of
844 Fixed a handful of bugs.
848 By public demand, added support for the standard hash function exists().
852 Made it compatible with Berkeley DB 1.86.
856 Made negative subscripts work with RECNO interface.
860 Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default
861 mode from 0640 to 0666.
865 Made DB_File automatically import the open() constants (O_RDWR,
866 O_CREAT etc.) from Fcntl, if available.
870 Updated documentation.
874 Refer to the HISTORY section in DB_File.pm for a complete list of
875 changes. Everything after DB_File 1.01 has been added since 5.003.
879 Major rewrite - support added for both udp echo and real icmp pings.
881 =head2 Object-oriented overrides for builtin operators
883 Many of the Perl builtins returning lists now have
884 object-oriented overrides. These are:
896 For example, you can now say
900 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
902 =head1 Utility Changes
908 =item C<void> XSUBs now default to returning nothing
910 Due to a documentation/implementation bug in previous versions of
911 Perl, XSUBs with a return type of C<void> have actually been
912 returning one value. Usually that value was the GV for the XSUB,
913 but sometimes it was some already freed or reused value, which would
914 sometimes lead to program failure.
916 In Perl 5.004, if an XSUB is declared as returning C<void>, it
917 actually returns no value, i.e. an empty list (though there is a
918 backward-compatibility exception; see below). If your XSUB really
919 does return an SV, you should give it a return type of C<SV *>.
921 For backward compatibility, I<xsubpp> tries to guess whether a
922 C<void> XSUB is really C<void> or if it wants to return an C<SV *>.
923 It does so by examining the text of the XSUB: if I<xsubpp> finds
924 what looks like an assignment to C<ST(0)>, it assumes that the
925 XSUB's return type is really C<SV *>.
929 =head1 C Language API Changes
933 =item C<gv_fetchmethod> and C<perl_call_sv>
935 The C<gv_fetchmethod> function finds a method for an object, just like
936 in Perl 5.003. The GV it returns may be a method cache entry.
937 However, in Perl 5.004, method cache entries are not visible to users;
938 therefore, they can no longer be passed directly to C<perl_call_sv>.
939 Instead, you should use the C<GvCV> macro on the GV to extract its CV,
940 and pass the CV to C<perl_call_sv>.
942 The most likely symptom of passing the result of C<gv_fetchmethod> to
943 C<perl_call_sv> is Perl's producing an "Undefined subroutine called"
944 error on the I<second> call to a given method (since there is no cache
947 =item C<perl_eval_pv>
949 A new function handy for eval'ing strings of Perl code inside C code.
950 This function returns the value from the eval statement, which can
951 be used instead of fetching globals from the symbol table. See
952 L<perlguts>, L<perlembed> and L<perlcall> for details and examples.
954 =item Extended API for manipulating hashes
956 Internal handling of hash keys has changed. The old hashtable API is
957 still fully supported, and will likely remain so. The additions to the
958 API allow passing keys as C<SV*>s, so that C<tied> hashes can be given
959 real scalars as keys rather than plain strings (nontied hashes still
960 can only use strings as keys). New extensions must use the new hash
961 access functions and macros if they wish to use C<SV*> keys. These
962 additions also make it feasible to manipulate C<HE*>s (hash entries),
963 which can be more efficient. See L<perlguts> for details.
967 =head1 Documentation Changes
969 Many of the base and library pods were updated. These
970 new pods are included in section 1:
980 Locale support (internationalization and localization).
984 Tutorial on Perl OO programming.
988 Perl internal IO abstraction interface.
992 Although not new, this has been massively updated.
996 Although not new, this has been massively updated.
1000 =head1 New Diagnostics
1002 Several new conditions will trigger warnings that were
1003 silent before. Some only affect certain platforms.
1004 The following new warnings and errors outline these.
1005 These messages are classified as follows (listed in
1006 increasing order of desperation):
1008 (W) A warning (optional).
1009 (D) A deprecation (optional).
1010 (S) A severe warning (mandatory).
1011 (F) A fatal error (trappable).
1012 (P) An internal error you should never see (trappable).
1013 (X) A very fatal error (nontrappable).
1014 (A) An alien error message (not generated by Perl).
1018 =item "my" variable %s masks earlier declaration in same scope
1020 (S) A lexical variable has been redeclared in the same scope, effectively
1021 eliminating all access to the previous instance. This is almost always
1022 a typographical error. Note that the earlier variable will still exist
1023 until the end of the scope or until all closure referents to it are
1026 =item %s argument is not a HASH element or slice
1028 (F) The argument to delete() must be either a hash element, such as
1031 $ref->[12]->{"susie"}
1033 or a hash slice, such as
1035 @foo{$bar, $baz, $xyzzy}
1036 @{$ref->[12]}{"susie", "queue"}
1038 =item Allocation too large: %lx
1040 (X) You can't allocate more than 64K on an MS-DOS machine.
1042 =item Allocation too large
1044 (F) You can't allocate more than 2^31+"small amount" bytes.
1046 =item Applying %s to %s will act on scalar(%s)
1048 (W) The pattern match (//), substitution (s///), and translation (tr///)
1049 operators work on scalar values. If you apply one of them to an array
1050 or a hash, it will convert the array or hash to a scalar value -- the
1051 length of an array, or the population info of a hash -- and then work on
1052 that scalar value. This is probably not what you meant to do. See
1053 L<perlfunc/grep> and L<perlfunc/map> for alternatives.
1055 =item Attempt to free nonexistent shared string
1057 (P) Perl maintains a reference counted internal table of strings to
1058 optimize the storage and access of hash keys and other strings. This
1059 indicates someone tried to decrement the reference count of a string
1060 that can no longer be found in the table.
1062 =item Attempt to use reference as lvalue in substr
1064 (W) You supplied a reference as the first argument to substr() used
1065 as an lvalue, which is pretty strange. Perhaps you forgot to
1066 dereference it first. See L<perlfunc/substr>.
1068 =item Can't use bareword ("%s") as %s ref while "strict refs" in use
1070 (F) Only hard references are allowed by "strict refs". Symbolic references
1071 are disallowed. See L<perlref>.
1073 =item Cannot resolve method `%s' overloading `%s' in package `%s'
1075 (P) Internal error trying to resolve overloading specified by a method
1076 name (as opposed to a subroutine reference).
1078 =item Constant subroutine %s redefined
1080 (S) You redefined a subroutine which had previously been eligible for
1081 inlining. See L<perlsub/"Constant Functions"> for commentary and
1084 =item Constant subroutine %s undefined
1086 (S) You undefined a subroutine which had previously been eligible for
1087 inlining. See L<perlsub/"Constant Functions"> for commentary and
1090 =item Copy method did not return a reference
1092 (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>.
1096 (F) You passed die() an empty string (the equivalent of C<die "">) or
1097 you called it with no args and both C<$@> and C<$_> were empty.
1099 =item Exiting pseudo-block via %s
1101 (W) You are exiting a rather special block construct (like a sort block or
1102 subroutine) by unconventional means, such as a goto, or a loop control
1103 statement. See L<perlfunc/sort>.
1105 =item Identifier too long
1107 (F) Perl limits identifiers (names for variables, functions, etc.) to
1108 252 characters for simple names, somewhat more for compound names (like
1109 C<$A::B>). You've exceeded Perl's limits. Future versions of Perl are
1110 likely to eliminate these arbitrary limitations.
1112 =item Illegal character %s (carriage return)
1114 (F) A carriage return character was found in the input. This is an
1115 error, and not a warning, because carriage return characters can break
1116 multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>).
1118 =item Illegal switch in PERL5OPT: %s
1120 (X) The PERL5OPT environment variable may only be used to set the
1121 following switches: B<-[DIMUdmw]>.
1123 =item Integer overflow in hex number
1125 (S) The literal hex number you have specified is too big for your
1126 architecture. On a 32-bit architecture the largest hex literal is
1129 =item Integer overflow in octal number
1131 (S) The literal octal number you have specified is too big for your
1132 architecture. On a 32-bit architecture the largest octal literal is
1135 =item internal error: glob failed
1137 (P) Something went wrong with the external program(s) used for C<glob>
1138 and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is
1139 broken. If so, you should change all of the csh-related variables in
1140 config.sh: If you have tcsh, make the variables refer to it as if it
1141 were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all
1142 empty (except that C<d_csh> should be C<'undef'>) so that Perl will
1143 think csh is missing. In either case, after editing config.sh, run
1144 C<./Configure -S> and rebuild Perl.
1146 =item Invalid type in pack: '%s'
1148 (F) The given character is not a valid pack type. See L<perlfunc/pack>.
1150 =item Invalid type in unpack: '%s'
1152 (F) The given character is not a valid unpack type. See L<perlfunc/unpack>.
1154 =item Name "%s::%s" used only once: possible typo
1156 (W) Typographical errors often show up as unique variable names.
1157 If you had a good reason for having a unique name, then just mention
1158 it again somehow to suppress the message (the C<use vars> pragma is
1159 provided for just this purpose).
1161 =item Null picture in formline
1163 (F) The first argument to formline must be a valid format picture
1164 specification. It was found to be empty, which probably means you
1165 supplied it an uninitialized value. See L<perlform>.
1167 =item Offset outside string
1169 (F) You tried to do a read/write/send/recv operation with an offset
1170 pointing outside the buffer. This is difficult to imagine.
1171 The sole exception to this is that C<sysread()>ing past the buffer
1172 will extend the buffer and zero pad the new area.
1174 =item Out of memory!
1176 (X|F) The malloc() function returned 0, indicating there was insufficient
1177 remaining memory (or virtual memory) to satisfy the request.
1179 The request was judged to be small, so the possibility to trap it
1180 depends on the way Perl was compiled. By default it is not trappable.
1181 However, if compiled for this, Perl may use the contents of C<$^M> as
1182 an emergency pool after die()ing with this message. In this case the
1183 error is trappable I<once>.
1185 =item Out of memory during request for %s
1187 (F) The malloc() function returned 0, indicating there was insufficient
1188 remaining memory (or virtual memory) to satisfy the request. However,
1189 the request was judged large enough (compile-time default is 64K), so
1190 a possibility to shut down by trapping this error is granted.
1192 =item Possible attempt to put comments in qw() list
1194 (W) qw() lists contain items separated by whitespace; as with literal
1195 strings, comment characters are not ignored, but are instead treated
1196 as literal data. (You may have used different delimiters than the
1197 exclamation marks parentheses shown here; braces are also frequently
1200 You probably wrote something like this:
1207 when you should have written this:
1214 If you really want comments, build your list the
1215 old-fashioned way, with quotes and commas:
1219 'b', # another comment
1222 =item Possible attempt to separate words with commas
1224 (W) qw() lists contain items separated by whitespace; therefore commas
1225 aren't needed to separate the items. (You may have used different
1226 delimiters than the parentheses shown here; braces are also frequently
1229 You probably wrote something like this:
1233 which puts literal commas into some of the list items. Write it without
1234 commas if you don't want them to appear in your data:
1238 =item Scalar value @%s{%s} better written as $%s{%s}
1240 (W) You've used a hash slice (indicated by @) to select a single element of
1241 a hash. Generally it's better to ask for a scalar value (indicated by $).
1242 The difference is that C<$foo{&bar}> always behaves like a scalar, both when
1243 assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves
1244 like a list when you assign to it, and provides a list context to its
1245 subscript, which can do weird things if you're expecting only one subscript.
1247 =item Stub found while resolving method `%s' overloading `%s' in package `%s'
1249 (P) Overloading resolution over @ISA tree may be broken by importing stubs.
1250 Stubs should never be implicitely created, but explicit calls to C<can>
1253 =item Too late for "B<-T>" option
1255 (X) The #! line (or local equivalent) in a Perl script contains the
1256 B<-T> option, but Perl was not invoked with B<-T> in its argument
1257 list. This is an error because, by the time Perl discovers a B<-T> in
1258 a script, it's too late to properly taint everything from the
1259 environment. So Perl gives up.
1261 =item untie attempted while %d inner references still exist
1263 (W) A copy of the object returned from C<tie> (or C<tied>) was still
1264 valid when C<untie> was called.
1266 =item Unrecognized character %s
1268 (F) The Perl parser has no idea what to do with the specified character
1269 in your Perl script (or eval). Perhaps you tried to run a compressed
1270 script, a binary program, or a directory as a Perl program.
1272 =item Unsupported function fork
1274 (F) Your version of executable does not support forking.
1276 Note that under some systems, like OS/2, there may be different flavors of
1277 Perl executables, some of which may support fork, some not. Try changing
1278 the name you call Perl by to C<perl_>, C<perl__>, and so on.
1280 =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated
1282 (D) Perl versions before 5.004 misinterpreted any type marker followed
1283 by "$" and a digit. For example, "$$0" was incorrectly taken to mean
1284 "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004.
1286 However, the developers of Perl 5.004 could not fix this bug completely,
1287 because at least two widely-used modules depend on the old meaning of
1288 "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the
1289 old (broken) way inside strings; but it generates this message as a
1290 warning. And in Perl 5.005, this special treatment will cease.
1292 =item Value of %s can be "0"; test with defined()
1294 (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>,
1295 or C<readdir()> as a boolean value. Each of these constructs can return a
1296 value of "0"; that would make the conditional expression false, which is
1297 probably not what you intended. When using these constructs in conditional
1298 expressions, test their values with the C<defined> operator.
1300 =item Variable "%s" may be unavailable
1302 (W) An inner (nested) I<anonymous> subroutine is inside a I<named>
1303 subroutine, and outside that is another subroutine; and the anonymous
1304 (innermost) subroutine is referencing a lexical variable defined in
1305 the outermost subroutine. For example:
1307 sub outermost { my $a; sub middle { sub { $a } } }
1309 If the anonymous subroutine is called or referenced (directly or
1310 indirectly) from the outermost subroutine, it will share the variable
1311 as you would expect. But if the anonymous subroutine is called or
1312 referenced when the outermost subroutine is not active, it will see
1313 the value of the shared variable as it was before and during the
1314 *first* call to the outermost subroutine, which is probably not what
1317 In these circumstances, it is usually best to make the middle
1318 subroutine anonymous, using the C<sub {}> syntax. Perl has specific
1319 support for shared variables in nested anonymous subroutines; a named
1320 subroutine in between interferes with this feature.
1322 =item Variable "%s" will not stay shared
1324 (W) An inner (nested) I<named> subroutine is referencing a lexical
1325 variable defined in an outer subroutine.
1327 When the inner subroutine is called, it will probably see the value of
1328 the outer subroutine's variable as it was before and during the
1329 *first* call to the outer subroutine; in this case, after the first
1330 call to the outer subroutine is complete, the inner and outer
1331 subroutines will no longer share a common value for the variable. In
1332 other words, the variable will no longer be shared.
1334 Furthermore, if the outer subroutine is anonymous and references a
1335 lexical variable outside itself, then the outer and inner subroutines
1336 will I<never> share the given variable.
1338 This problem can usually be solved by making the inner subroutine
1339 anonymous, using the C<sub {}> syntax. When inner anonymous subs that
1340 reference variables in outer subroutines are called or referenced,
1341 they are automatically rebound to the current values of such
1344 =item Warning: something's wrong
1346 (W) You passed warn() an empty string (the equivalent of C<warn "">) or
1347 you called it with no args and C<$_> was empty.
1349 =item Ill-formed logical name |%s| in prime_env_iter
1351 (W) A warning peculiar to VMS. A logical name was encountered when preparing
1352 to iterate over %ENV which violates the syntactic rules governing logical
1353 names. Since it cannot be translated normally, it is skipped, and will not
1354 appear in %ENV. This may be a benign occurrence, as some software packages
1355 might directly modify logical name tables and introduce nonstandard names,
1356 or it may indicate that a logical name table has been corrupted.
1358 =item Got an error from DosAllocMem
1360 (P) An error peculiar to OS/2. Most probably you're using an obsolete
1361 version of Perl, and this should not happen anyway.
1363 =item Malformed PERLLIB_PREFIX
1365 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
1373 with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix
1374 of a builtin library search path, prefix2 is substituted. The error
1375 may appear if components are not found, or are too long. See
1376 "PERLLIB_PREFIX" in F<README.os2>.
1378 =item PERL_SH_DIR too long
1380 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
1381 C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>.
1383 =item Process terminated by SIG%s
1385 (W) This is a standard message issued by OS/2 applications, while *nix
1386 applications die in silence. It is considered a feature of the OS/2
1387 port. One can easily disable this by appropriate sighandlers, see
1388 L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT"
1395 If you find what you think is a bug, you might check the headers of
1396 recently posted articles in the comp.lang.perl.misc newsgroup.
1397 There may also be information at http://www.perl.com/perl/, the Perl
1400 If you believe you have an unreported bug, please run the B<perlbug>
1401 program included with your release. Make sure you trim your bug down
1402 to a tiny but sufficient test case. Your bug report, along with the
1403 output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be
1404 analysed by the Perl porting team.
1408 The F<Changes> file for exhaustive details on what changed.
1410 The F<INSTALL> file for how to build Perl. This file has been
1411 significantly updated for 5.004, so even veteran users should
1414 The F<README> file for general stuff.
1416 The F<Copying> file for copyright information.
1420 Constructed by Tom Christiansen, grabbing material with permission
1421 from innumerable contributors, with kibitzing by more than a few Perl
1424 Last update: Sat Mar 8 19:51:26 EST 1997