3 perlnews - 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.
28 =head2 Internal Change: FileHandle Deprecated
30 Filehandles are now stored internally as type IO::Handle.
31 Although C<use FileHandle> and C<*STDOUT{FILEHANDLE}>
32 are still supported for backwards compatibility
33 C<use IO::Handle> (or C<IO::Seekable> or C<IO::File>) and
34 C<*STDOUT{IO}> are the way of the future.
36 =head2 Internal Change: Safe Module Absorbed into Opcode
38 A new Opcode module subsumes 5.003's Safe module. The Safe
39 interface is still available, so existing scripts should still
40 work, but users are encouraged to read the new Opcode documentation.
42 =head2 Internal Change: PerlIO internal IO abstraction interface.
44 It is now possible to build Perl with AT&T's sfio IO package
45 instead of stdio. See L<perlapio> for more details, and
46 the F<INSTALL> file for how to use it.
48 =head2 New and Changed Built-in Variables
54 Extended error message under some platforms ($EXTENDED_OS_ERROR
55 if you C<use English>).
59 The current set of syntax checks enabled by C<use strict>. See the
60 documentation of C<strict> for more details. Not actually new, but
62 Because it is intended for internal use by Perl core components,
63 there is no C<use English> long name for this variable.
67 By default, running out of memory it is not trappable. However, if
68 compiled for this, Perl may use the contents of C<$^M> as an emergency
69 pool after die()ing with this message. Suppose that your Perl were
70 compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then
74 would allocate 64K buffer for use when in emergency.
75 See the F<INSTALL> file for information on how to enable this option.
76 As a disincentive to casual use of this advanced feature,
77 there is no C<use English> long name for this variable.
81 =head2 New and Changed Built-in Functions
85 =item delete on slices
87 This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>)
91 is now supported on more platforms, and prefers fcntl
92 to lockf when emulating.
94 =item keys as an lvalue
96 As an lvalue, C<keys> allows you to increase the number of hash buckets
97 allocated for the given associative array. This can gain you a measure
98 of efficiency if you know the hash is going to get big. (This is
99 similar to pre-extending an array by assigning a larger number to
104 then C<%hash> will have at least 200 buckets allocated for it. These
105 buckets will be retained even if you do C<%hash = ()>; use C<undef
106 %hash> if you want to free the storage while C<%hash> is still in scope.
107 You can't shrink the number of buckets allocated for the hash using
108 C<keys> in this way (but you needn't worry about doing this by accident,
109 as trying has no effect).
111 =item my() in Control Structures
113 You can now use my() (with or without the parentheses) in the control
114 expressions of control structures such as:
116 while (my $line = <>) {
122 if ((my $answer = <STDIN>) =~ /^yes$/i) {
124 } elsif ($answer =~ /^no$/i) {
128 die "'$answer' is neither 'yes' nor 'no'";
131 Also, you can declare a foreach loop control variable as lexical by
132 preceding it with the word "my". For example, in:
134 foreach my $i (1, 2, 3) {
138 $i is a lexical variable, and the scope of $i extends to the end of
139 the loop, but not beyond it.
141 Note that you still cannot use my() on global punctuation variables
142 such as $_ and the like.
144 =item unpack() and pack()
146 A new format 'w' represents a BER compressed integer (as defined in
147 ASN.1). Its format is a sequence of one or more bytes, each of which
148 provides seven bits of the total value, with the most significant
149 first. Bit eight of each byte is set, except for the last byte, in
150 which bit eight is clear.
154 If the first argument to C<use> is a number, it is treated as a version
155 number instead of a module name. If the version of the Perl interpreter
156 is less than VERSION, then an error message is printed and Perl exits
157 immediately. This is often useful if you need to check the current
158 Perl version before C<use>ing library modules which have changed in
159 incompatible ways from older versions of Perl. (We try not to do
160 this more than we have to.)
162 =item use Module VERSION LIST
164 If the VERSION argument is present between Module and LIST, then the
165 C<use> will call the VERSION method in class Module with the given
166 version as an argument. The default VERSION method, inherited from
167 the Universal class, croaks if the given version is larger than the
168 value of the variable $Module::VERSION. (Note that there is not a
169 comma after VERSION!)
171 =item prototype(FUNCTION)
173 Returns the prototype of a function as a string (or C<undef> if the
174 function has no prototype). FUNCTION is a reference to or the name of the
175 function whose prototype you want to retrieve.
176 (Not actually new; just never documented before.)
180 Functions documented in the Camel to default to $_ now in
181 fact do, and all those that do are so documented in L<perlfunc>.
185 =head2 New Built-in Methods
187 The C<UNIVERSAL> package automatically contains the following methods that
188 are inherited by all other classes:
194 C<isa> returns I<true> if its object is blessed into a sub-class of C<CLASS>
196 C<isa> is also exportable and can be called as a sub with two arguments. This
197 allows the ability to check what a reference points to. Example:
199 use UNIVERSAL qw(isa);
201 if(isa($ref, 'ARRAY')) {
207 C<can> checks to see if its object has a method called C<METHOD>,
208 if it does then a reference to the sub is returned; if it does not then
209 I<undef> is returned.
211 =item VERSION( [NEED] )
213 C<VERSION> returns the version number of the class (package). If the
214 NEED argument is given then it will check that the current version (as
215 defined by the $VERSION variable in the given package) not less than
216 NEED; it will die if this is not the case. This method is normally
217 called as a class method. This method is called automatically by the
218 C<VERSION> form of C<use>.
220 use A 1.2 qw(some imported subs);
226 C<class> returns the class name of its object.
230 C<is_instance> returns true if its object is an instance of some
231 class, false if its object is the class (package) itself. Example
233 A->is_instance(); # False
236 $var->is_instance(); # False
238 $ref = bless [], 'A';
239 $ref->is_instance(); # True
243 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
244 C<isa> uses a very similar method and cache-ing strategy. This may cause
245 strange effects if the Perl code dynamically changes @ISA in any package.
247 You may add other methods to the UNIVERSAL class via Perl or XS code.
248 You do not need to C<use UNIVERSAL> in order to make these methods
249 available to your program. This is necessary only if you wish to
250 have C<isa> available as a plain subroutine in the current package.
252 =head2 TIEHANDLE Now Supported
256 =item TIEHANDLE classname, LIST
258 This is the constructor for the class. That means it is expected to
259 return an object of some sort. The reference can be used to
260 hold some internal information.
262 sub TIEHANDLE { print "<shout>\n"; my $i; bless \$i, shift }
264 =item PRINT this, LIST
266 This method will be triggered every time the tied handle is printed to.
267 Beyond its self reference it also expects the list that was passed to
270 sub PRINT { $r = shift; $$r++; print join($,,map(uc($_),@_)),$\ }
274 This method will be called when the handle is read from. The method
275 should return undef when there is no more data.
277 sub READLINE { $r = shift; "PRINT called $$r times\n"; }
281 As with the other types of ties, this method will be called when the
282 tied handle is about to be destroyed. This is useful for debugging and
283 possibly for cleaning up.
285 sub DESTROY { print "</shout>\n" }
291 Three new pragmatic modules exist:
297 Looks for MakeMaker-like I<'blib'> directory structure starting in
298 I<dir> (or current directory) and working back up to five levels of
301 Intended for use on command line with B<-M> option as a way of testing
302 arbitrary scripts against an uninstalled version of a package.
306 Tells the compiler to enable (or disable) the use of POSIX locales for
309 When C<use locale> is in effect, the current LC_CTYPE locale is used
310 for regular expressions and case mapping; LC_COLLATE for string
311 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
312 (but B<not> in print). LC_NUMERIC is always used in write, since
313 lexical scoping of formats is problematic at best.
315 Each C<use locale> or C<no locale> affects statements to the end of
316 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
317 current file. Locales can be switched and queried with
320 See L<perllocale> for more information.
324 Restricts unsafe operations when compiling.
330 =head2 Module Information Summary
334 IO.pm Top-level interface to IO::* classes
335 IO/File.pm IO::File extension Perl module
336 IO/Handle.pm IO::Handle extension Perl module
337 IO/Pipe.pm IO::Pipe extension Perl module
338 IO/Seekable.pm IO::Seekable extension Perl module
339 IO/Select.pm IO::Select extension Perl module
340 IO/Socket.pm IO::Socket extension Perl module
342 Opcode.pm Disable named opcodes when compiling Perl code
344 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
345 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
347 Fatal.pm Make do-or-die equivalents of functions
348 FindBin.pm Find path of currently executing program
350 Class/Template.pm Structure/member template builder
351 File/stat.pm Object-oriented wrapper around CORE::stat
352 Net/hostent.pm Object-oriented wrapper around CORE::gethost*
353 Net/netent.pm Object-oriented wrapper around CORE::getnet*
354 Net/protoent.pm Object-oriented wrapper around CORE::getproto*
355 Net/servent.pm Object-oriented wrapper around CORE::getserv*
356 Time/gmtime.pm Object-oriented wrapper around CORE::gmtime
357 Time/localtime.pm Object-oriented wrapper around CORE::localtime
358 Time/tm.pm Perl implementation of "struct tm" for {gm,local}time
359 User/grent.pm Object-oriented wrapper around CORE::getgr*
360 User/pwent.pm Object-oriented wrapper around CORE::getpw*
362 lib/Tie/RefHash.pm Base class for tied hashes with references as keys
364 UNIVERSAL.pm Base class for *ALL* classes
368 The IO module provides a simple mechanism to load all of the IO modules at one
369 go. Currently this includes:
377 For more information on any of these modules, please see its
378 respective documentation.
382 The Math::Complex module has been totally rewritten, and now supports
383 more operations. These are overloaded:
385 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
387 And these functions are now exported:
391 tan cotan asin acos atan acotan
392 sinh cosh tanh cotanh asinh acosh atanh acotanh
395 =head2 Overridden Built-ins
397 Many of the Perl built-ins returning lists now have
398 object-oriented overrides. These are:
410 For example, you can now say
414 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
416 =head1 Efficiency Enhancements
418 All hash keys with the same string are only allocated once, so
419 even if you have 100 copies of the same hash, the immutable keys
420 never have to be re-allocated.
422 Functions that do nothing but return a fixed value are now inlined.
424 =head1 Documentation Changes
426 Many of the base and library pods were updated. These
427 new pods are included in section 1:
437 Locale support (internationalization and localization).
441 Tutorial on Perl OO programming.
445 Perl internal IO abstraction interface.
449 Although not new, this has been massively updated.
453 Although not new, this has been massively updated.
457 =head1 New Diagnostics
459 Several new conditions will trigger warnings that were
460 silent before. Some only affect certain platforms.
461 The following new warnings and errors
466 =item "my" variable %s masks earlier declaration in same scope
468 (S) A lexical variable has been redeclared in the same scope, effectively
469 eliminating all access to the previous instance. This is almost always
470 a typographical error. Note that the earlier variable will still exist
471 until the end of the scope or until all closure referents to it are
474 =item Allocation too large: %lx
476 (X) You can't allocate more than 64K on an MSDOS machine.
478 =item Allocation too large
480 (F) You can't allocate more than 2^31+"small amount" bytes.
482 =item Attempt to free non-existent shared string
484 (P) Perl maintains a reference counted internal table of strings to
485 optimize the storage and access of hash keys and other strings. This
486 indicates someone tried to decrement the reference count of a string
487 that can no longer be found in the table.
489 =item Attempt to use reference as lvalue in substr
491 (W) You supplied a reference as the first argument to substr() used
492 as an lvalue, which is pretty strange. Perhaps you forgot to
493 dereference it first. See L<perlfunc/substr>.
495 =item Unsupported function fork
497 (F) Your version of executable does not support forking.
499 Note that under some systems, like OS/2, there may be different flavors of
500 Perl executables, some of which may support fork, some not. Try changing
501 the name you call Perl by to C<perl_>, C<perl__>, and so on.
503 =item Ill-formed logical name |%s| in prime_env_iter
505 (W) A warning peculiar to VMS. A logical name was encountered when preparing
506 to iterate over %ENV which violates the syntactic rules governing logical
507 names. Since it cannot be translated normally, it is skipped, and will not
508 appear in %ENV. This may be a benign occurrence, as some software packages
509 might directly modify logical name tables and introduce non-standard names,
510 or it may indicate that a logical name table has been corrupted.
512 =item Integer overflow in hex number
514 (S) The literal hex number you have specified is too big for your
515 architecture. On a 32-bit architecture the largest hex literal is
518 =item Integer overflow in octal number
520 (S) The literal octal number you have specified is too big for your
521 architecture. On a 32-bit architecture the largest octal literal is
524 =item Null picture in formline
526 (F) The first argument to formline must be a valid format picture
527 specification. It was found to be empty, which probably means you
528 supplied it an uninitialized value. See L<perlform>.
530 =item Offset outside string
532 (F) You tried to do a read/write/send/recv operation with an offset
533 pointing outside the buffer. This is difficult to imagine.
534 The sole exception to this is that C<sysread()>ing past the buffer
535 will extend the buffer and zero pad the new area.
539 (X|F) The malloc() function returned 0, indicating there was insufficient
540 remaining memory (or virtual memory) to satisfy the request.
542 The request was judged to be small, so the possibility to trap it
543 depends on the way Perl was compiled. By default it is not trappable.
544 However, if compiled for this, Perl may use the contents of C<$^M> as
545 an emergency pool after die()ing with this message. In this case the
546 error is trappable I<once>.
548 =item Out of memory during request for %s
550 (F) The malloc() function returned 0, indicating there was insufficient
551 remaining memory (or virtual memory) to satisfy the request. However,
552 the request was judged large enough (compile-time default is 64K), so
553 a possibility to shut down by trapping this error is granted.
555 =item Possible attempt to put comments in qw() list
557 (W) You probably wrote something like this:
563 when you should have written this:
569 =item Possible attempt to separate words with commas
571 (W) You probably wrote something like this:
575 when you should have written this:
579 =item untie attempted while %d inner references still exist
581 (W) A copy of the object returned from C<tie> (or C<tied>) was still
582 valid when C<untie> was called.
584 =item Got an error from DosAllocMem:
586 (P) An error peculiar to OS/2. Most probably you use an obsolete version
587 of Perl, and should not happen anyway.
589 =item Malformed PERLLIB_PREFIX
591 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
599 with non-empty prefix1 and prefix2. If C<prefix1> is indeed a prefix of
600 a builtin library search path, prefix2 is substituted. The error may appear
601 if components are not found, or are too long. See L<perlos2/"PERLLIB_PREFIX">.
603 =item PERL_SH_DIR too long
605 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
606 C<sh>-shell in. See L<perlos2/"PERL_SH_DIR">.
608 =item Process terminated by SIG%s
610 (W) This is a standard message issued by OS/2 applications, while *nix
611 applications die in silence. It is considered a feature of the OS/2
612 port. One can easily disable this by appropriate sighandlers, see
613 L<perlipc/"Signals">. See L<perlos2/"Process terminated by SIGTERM/SIGINT">.
619 If you find what you think is a bug, you might check the headers
620 of recently posted articles
621 in the comp.lang.perl.misc newsgroup. There may also be
622 information at http://www.perl.com/perl/, the Perl Home Page.
624 If you believe you have an unreported bug, please run the B<perlbug>
625 program included with your release. Make sure you trim your bug
626 down to a tiny but sufficient test case. Your bug report, along
627 with the output of C<perl -V>, will be sent off to perlbug@perl.com
628 to be analysed by the Perl porting team.
632 The F<Changes> file for exhaustive details on what changed.
634 The F<INSTALL> file for how to build Perl. This file has been
635 significantly updated for 5.004, so even veteran users should
638 The F<README> file for general stuff.
640 The F<Copying> file for copyright information.
644 Constructed by Tom Christiansen, grabbing material with permission
645 from innumerable contributors, with kibitzing by more than a few Perl
648 Last update: Tue Dec 24 16:45:14 EST 1996