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 fail if the $VERSION variable in package Module is
168 Note that there is not a comma after the version!
170 =item prototype(FUNCTION)
172 Returns the prototype of a function as a string (or C<undef> if the
173 function has no prototype). FUNCTION is a reference to or the name of the
174 function whose prototype you want to retrieve.
175 (Not actually new; just never documented before.)
179 Functions documented in the Camel to default to $_ now in
180 fact do, and all those that do are so documented in L<perlfunc>.
184 =head2 New Built-in Methods
186 The C<UNIVERSAL> package automatically contains the following methods that
187 are inherited by all other classes:
193 C<isa> returns I<true> if its object is blessed into a sub-class of C<CLASS>
195 C<isa> is also exportable and can be called as a sub with two arguments. This
196 allows the ability to check what a reference points to. Example:
198 use UNIVERSAL qw(isa);
200 if(isa($ref, 'ARRAY')) {
206 C<can> checks to see if its object has a method called C<METHOD>,
207 if it does then a reference to the sub is returned; if it does not then
208 I<undef> is returned.
210 =item VERSION( [NEED] )
212 C<VERSION> returns the version number of the class (package). If the
213 NEED argument is given then it will check that the current version is
214 not less than NEED and die if this is not the case. This method is
215 normally called as a class method. This method is also called when the
216 C<VERSION> form of C<use> is used.
218 use A 1.2 qw(some imported subs);
221 $ref->is_instance(); # True
225 C<class> returns the class name of its object.
229 C<is_instance> returns true if its object is an instance of some
230 class, false if its object is the class (package) itself. Example
232 A->is_instance(); # False
235 $var->is_instance(); # False
237 $ref = bless [], 'A';
238 $ref->is_instance(); # True
242 B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and
243 C<isa> uses a very similar method and cache-ing strategy. This may cause
244 strange effects if the Perl code dynamically changes @ISA in any package.
246 You may add other methods to the UNIVERSAL class via Perl or XS code.
247 You do not need to C<use UNIVERSAL> in order to make these methods
248 available to your program. This is necessary only if you wish to
249 have C<isa> available as a plain subroutine in the current package.
251 =head2 TIEHANDLE Now Supported
255 =item TIEHANDLE classname, LIST
257 This is the constructor for the class. That means it is expected to
258 return an object of some sort. The reference can be used to
259 hold some internal information.
261 sub TIEHANDLE { print "<shout>\n"; my $i; bless \$i, shift }
263 =item PRINT this, LIST
265 This method will be triggered every time the tied handle is printed to.
266 Beyond its self reference it also expects the list that was passed to
269 sub PRINT { $r = shift; $$r++; print join($,,map(uc($_),@_)),$\ }
273 This method will be called when the handle is read from. The method
274 should return undef when there is no more data.
276 sub READLINE { $r = shift; "PRINT called $$r times\n"; }
280 As with the other types of ties, this method will be called when the
281 tied handle is about to be destroyed. This is useful for debugging and
282 possibly for cleaning up.
284 sub DESTROY { print "</shout>\n" }
290 Three new pragmatic modules exist:
296 Looks for MakeMaker-like I<'blib'> directory structure starting in
297 I<dir> (or current directory) and working back up to five levels of
300 Intended for use on command line with B<-M> option as a way of testing
301 arbitrary scripts against an uninstalled version of a package.
305 Tells the compiler to enable (or disable) the use of POSIX locales for
308 When C<use locale> is in effect, the current LC_CTYPE locale is used
309 for regular expressions and case mapping; LC_COLLATE for string
310 ordering; and LC_NUMERIC for numeric formating in printf and sprintf
311 (but B<not> in print). LC_NUMERIC is always used in write, since
312 lexical scoping of formats is problematic at best.
314 Each C<use locale> or C<no locale> affects statements to the end of
315 the enclosing BLOCK or, if not inside a BLOCK, to the end of the
316 current file. Locales can be switched and queried with
319 See L<perllocale> for more information.
323 Restricts unsafe operations when compiling.
329 =head2 Module Information Summary
333 IO.pm Top-level interface to IO::* classes
334 IO/File.pm IO::File extension Perl module
335 IO/Handle.pm IO::Handle extension Perl module
336 IO/Pipe.pm IO::Pipe extension Perl module
337 IO/Seekable.pm IO::Seekable extension Perl module
338 IO/Select.pm IO::Select extension Perl module
339 IO/Socket.pm IO::Socket extension Perl module
341 Opcode.pm Disable named opcodes when compiling Perl code
343 ExtUtils/Embed.pm Utilities for embedding Perl in C programs
344 ExtUtils/testlib.pm Fixes up @INC to use just-built extension
346 Fatal.pm Make do-or-die equivalents of functions
347 FindBin.pm Find path of currently executing program
349 Class/Template.pm Structure/member template builder
350 File/stat.pm Object-oriented wrapper around CORE::stat
351 Net/hostent.pm Object-oriented wrapper around CORE::gethost*
352 Net/netent.pm Object-oriented wrapper around CORE::getnet*
353 Net/protoent.pm Object-oriented wrapper around CORE::getproto*
354 Net/servent.pm Object-oriented wrapper around CORE::getserv*
355 Time/gmtime.pm Object-oriented wrapper around CORE::gmtime
356 Time/localtime.pm Object-oriented wrapper around CORE::localtime
357 Time/tm.pm Perl implementation of "struct tm" for {gm,local}time
358 User/grent.pm Object-oriented wrapper around CORE::getgr*
359 User/pwent.pm Object-oriented wrapper around CORE::getpw*
361 UNIVERSAL.pm Base class for *ALL* classes
365 The IO module provides a simple mechanism to load all of the IO modules at one
366 go. Currently this includes:
374 For more information on any of these modules, please see its
375 respective documentation.
379 The Math::Complex module has been totally rewritten, and now supports
380 more operations. These are overloaded:
382 + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify)
384 And these functions are now exported:
388 tan cotan asin acos atan acotan
389 sinh cosh tanh cotanh asinh acosh atanh acotanh
392 =head2 Overridden Built-ins
394 Many of the Perl built-ins returning lists now have
395 object-oriented overrides. These are:
407 For example, you can now say
411 $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid);
413 =head1 Efficiency Enhancements
415 All hash keys with the same string are only allocated once, so
416 even if you have 100 copies of the same hash, the immutable keys
417 never have to be re-allocated.
419 Functions that do nothing but return a fixed value are now inlined.
421 =head1 Documentation Changes
423 Many of the base and library pods were updated. These
424 new pods are included in section 1:
430 Internationalization.
434 Perl internal IO abstraction interface.
438 Tutorial on Perl OO programming.
442 Although not new, this has been massively updated.
446 Although not new, this has been massively updated.
450 =head1 New Diagnostics
452 Several new conditions will trigger warnings that were
453 silent before. Some only affect certain platforms.
454 The following new warnings and errors
459 =item "my" variable %s masks earlier declaration in same scope
461 (S) A lexical variable has been redeclared in the same scope, effectively
462 eliminating all access to the previous instance. This is almost always
463 a typographical error. Note that the earlier variable will still exist
464 until the end of the scope or until all closure referents to it are
467 =item Allocation too large: %lx
469 (X) You can't allocate more than 64K on an MSDOS machine.
471 =item Allocation too large
473 (F) You can't allocate more than 2^31+"small amount" bytes.
475 =item Attempt to free non-existent shared string
477 (P) Perl maintains a reference counted internal table of strings to
478 optimize the storage and access of hash keys and other strings. This
479 indicates someone tried to decrement the reference count of a string
480 that can no longer be found in the table.
482 =item Attempt to use reference as lvalue in substr
484 (W) You supplied a reference as the first argument to substr() used
485 as an lvalue, which is pretty strange. Perhaps you forgot to
486 dereference it first. See L<perlfunc/substr>.
488 =item Unsupported function fork
490 (F) Your version of executable does not support forking.
492 Note that under some systems, like OS/2, there may be different flavors of
493 Perl executables, some of which may support fork, some not. Try changing
494 the name you call Perl by to C<perl_>, C<perl__>, and so on.
496 =item Ill-formed logical name |%s| in prime_env_iter
498 (W) A warning peculiar to VMS. A logical name was encountered when preparing
499 to iterate over %ENV which violates the syntactic rules governing logical
500 names. Since it cannot be translated normally, it is skipped, and will not
501 appear in %ENV. This may be a benign occurrence, as some software packages
502 might directly modify logical name tables and introduce non-standard names,
503 or it may indicate that a logical name table has been corrupted.
505 =item Integer overflow in hex number
507 (S) The literal hex number you have specified is too big for your
508 architecture. On a 32-bit architecture the largest hex literal is
511 =item Integer overflow in octal number
513 (S) The literal octal number you have specified is too big for your
514 architecture. On a 32-bit architecture the largest octal literal is
517 =item Null picture in formline
519 (F) The first argument to formline must be a valid format picture
520 specification. It was found to be empty, which probably means you
521 supplied it an uninitialized value. See L<perlform>.
523 =item Offset outside string
525 (F) You tried to do a read/write/send/recv operation with an offset
526 pointing outside the buffer. This is difficult to imagine.
527 The sole exception to this is that C<sysread()>ing past the buffer
528 will extend the buffer and zero pad the new area.
532 (X|F) The malloc() function returned 0, indicating there was insufficient
533 remaining memory (or virtual memory) to satisfy the request.
535 The request was judged to be small, so the possibility to trap it
536 depends on the way Perl was compiled. By default it is not trappable.
537 However, if compiled for this, Perl may use the contents of C<$^M> as
538 an emergency pool after die()ing with this message. In this case the
539 error is trappable I<once>.
541 =item Out of memory during request for %s
543 (F) The malloc() function returned 0, indicating there was insufficient
544 remaining memory (or virtual memory) to satisfy the request. However,
545 the request was judged large enough (compile-time default is 64K), so
546 a possibility to shut down by trapping this error is granted.
548 =item Possible attempt to put comments in qw() list
550 (W) You probably wrote something like this:
556 when you should have written this:
562 =item Possible attempt to separate words with commas
564 (W) You probably wrote something like this:
568 when you should have written this:
572 =item untie attempted while %d inner references still exist
574 (W) A copy of the object returned from C<tie> (or C<tied>) was still
575 valid when C<untie> was called.
577 =item Got an error from DosAllocMem:
579 (P) An error peculiar to OS/2. Most probably you use an obsolete version
580 of Perl, and should not happen anyway.
582 =item Malformed PERLLIB_PREFIX
584 (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form
592 with non-empty prefix1 and prefix2. If C<prefix1> is indeed a prefix of
593 a builtin library search path, prefix2 is substituted. The error may appear
594 if components are not found, or are too long. See L<perlos2/"PERLLIB_PREFIX">.
596 =item PERL_SH_DIR too long
598 (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the
599 C<sh>-shell in. See L<perlos2/"PERL_SH_DIR">.
601 =item Process terminated by SIG%s
603 (W) This is a standard message issued by OS/2 applications, while *nix
604 applications die in silence. It is considered a feature of the OS/2
605 port. One can easily disable this by appropriate sighandlers, see
606 L<perlipc/"Signals">. See L<perlos2/"Process terminated by SIGTERM/SIGINT">.
612 If you find what you think is a bug, you might check the headers
613 of recently posted articles
614 in the comp.lang.perl.misc newsgroup. There may also be
615 information at http://www.perl.com/perl/, the Perl Home Page.
617 If you believe you have an unreported bug, please run the B<perlbug>
618 program included with your release. Make sure you trim your bug
619 down to a tiny but sufficient test case. Your bug report, along
620 with the output of C<perl -V>, will be sent off to perlbug@perl.com
621 to be analysed by the Perl porting team.
625 The F<Changes> file for exhaustive details on what changed.
627 The F<INSTALL> file for how to build Perl. This file has been
628 significantly updated for 5.004, so even veteran users should
631 The F<README> file for general stuff.
633 The F<Copying> file for copyright information.
637 Constructed by Tom Christiansen, grabbing material with permission
638 from innumerable contributors, with kibitzing by more than a few Perl
642 Wed Dec 18 16:18:27 EST 1996