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1 | =head1 NAME |
2 | ||
3 | perldelta - what's new for perl5.004 | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | This document describes differences between the 5.003 release (as | |
8 | documented in I<Programming Perl>, second edition--the Camel Book) and | |
9 | this one. | |
10 | ||
11 | =head1 Supported Environments | |
12 | ||
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. | |
16 | ||
17 | =head1 Core Changes | |
18 | ||
19 | Most importantly, many bugs were fixed, including several security | |
20 | problems. See the F<Changes> file in the distribution for details. | |
21 | ||
22 | =head2 List assignment to %ENV works | |
23 | ||
24 | C<%ENV = ()> and C<%ENV = @list> now work as expected (except on VMS | |
25 | where it generates a fatal error). | |
26 | ||
27 | =head2 "Can't locate Foo.pm in @INC" error now lists @INC | |
28 | ||
29 | =head2 Compilation option: Binary compatibility with 5.003 | |
30 | ||
31 | There is a new Configure question that asks if you want to maintain | |
32 | binary compatibility with Perl 5.003. If you choose binary | |
33 | compatibility, you do not have to recompile your extensions, but you | |
34 | might have symbol conflicts if you embed Perl in another application, | |
35 | just as in the 5.003 release. By default, binary compatibility | |
36 | is preserved at the expense of symbol table pollution. | |
37 | ||
38 | =head2 $PERL5OPT environment variable | |
39 | ||
40 | You may now put Perl options in the $PERL5OPT environment variable. | |
41 | Unless Perl is running with taint checks, it will interpret this | |
42 | variable as if its contents had appeared on a "#!perl" line at the | |
43 | beginning of your script, except that hyphens are optional. PERL5OPT | |
44 | may only be used to set the following switches: B<-[DIMUdmw]>. | |
45 | ||
46 | =head2 Limitations on B<-M>, B<-m>, and B<-T> options | |
47 | ||
48 | The C<-M> and C<-m> options are no longer allowed on the C<#!> line of | |
49 | a script. If a script needs a module, it should invoke it with the | |
50 | C<use> pragma. | |
51 | ||
52 | The B<-T> option is also forbidden on the C<#!> line of a script, | |
53 | unless it was present on the Perl command line. Due to the way C<#!> | |
54 | works, this usually means that B<-T> must be in the first argument. | |
55 | Thus: | |
56 | ||
57 | #!/usr/bin/perl -T -w | |
58 | ||
59 | will probably work for an executable script invoked as C<scriptname>, | |
60 | while: | |
61 | ||
62 | #!/usr/bin/perl -w -T | |
63 | ||
64 | will probably fail under the same conditions. (Non-Unix systems will | |
65 | probably not follow this rule.) But C<perl scriptname> is guaranteed | |
66 | to fail, since then there is no chance of B<-T> being found on the | |
67 | command line before it is found on the C<#!> line. | |
68 | ||
69 | =head2 More precise warnings | |
70 | ||
71 | If you removed the B<-w> option from your Perl 5.003 scripts because it | |
72 | made Perl too verbose, we recommend that you try putting it back when | |
73 | you upgrade to Perl 5.004. Each new perl version tends to remove some | |
74 | undesirable warnings, while adding new warnings that may catch bugs in | |
75 | your scripts. | |
76 | ||
77 | =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods | |
78 | ||
79 | Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods | |
80 | (using the C<@ISA> hierarchy), even when the function to be autoloaded | |
81 | was called as a plain function (e.g. C<Foo::bar()>), not a method | |
c47ff5f1 | 82 | (e.g. C<< Foo->bar() >> or C<< $obj->bar() >>). |
6ee623d5 GS |
83 | |
84 | Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s. | |
85 | However, there is a significant base of existing code that may be using | |
86 | the old behavior. So, as an interim step, Perl 5.004 issues an optional | |
87 | warning when a non-method uses an inherited C<AUTOLOAD>. | |
88 | ||
89 | The simple rule is: Inheritance will not work when autoloading | |
90 | non-methods. The simple fix for old code is: In any module that used to | |
91 | depend on inheriting C<AUTOLOAD> for non-methods from a base class named | |
92 | C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup. | |
93 | ||
94 | =head2 Previously deprecated %OVERLOAD is no longer usable | |
95 | ||
96 | Using %OVERLOAD to define overloading was deprecated in 5.003. | |
97 | Overloading is now defined using the overload pragma. %OVERLOAD is | |
98 | still used internally but should not be used by Perl scripts. See | |
99 | L<overload> for more details. | |
100 | ||
101 | =head2 Subroutine arguments created only when they're modified | |
102 | ||
103 | In Perl 5.004, nonexistent array and hash elements used as subroutine | |
104 | parameters are brought into existence only if they are actually | |
105 | assigned to (via C<@_>). | |
106 | ||
107 | Earlier versions of Perl vary in their handling of such arguments. | |
108 | Perl versions 5.002 and 5.003 always brought them into existence. | |
109 | Perl versions 5.000 and 5.001 brought them into existence only if | |
110 | they were not the first argument (which was almost certainly a bug). | |
111 | Earlier versions of Perl never brought them into existence. | |
112 | ||
113 | For example, given this code: | |
114 | ||
115 | undef @a; undef %a; | |
116 | sub show { print $_[0] }; | |
117 | sub change { $_[0]++ }; | |
118 | show($a[2]); | |
119 | change($a{b}); | |
120 | ||
121 | After this code executes in Perl 5.004, $a{b} exists but $a[2] does | |
122 | not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed | |
123 | (but $a[2]'s value would have been undefined). | |
124 | ||
125 | =head2 Group vector changeable with C<$)> | |
126 | ||
127 | The C<$)> special variable has always (well, in Perl 5, at least) | |
128 | reflected not only the current effective group, but also the group list | |
129 | as returned by the C<getgroups()> C function (if there is one). | |
130 | However, until this release, there has not been a way to call the | |
131 | C<setgroups()> C function from Perl. | |
132 | ||
133 | In Perl 5.004, assigning to C<$)> is exactly symmetrical with examining | |
134 | it: The first number in its string value is used as the effective gid; | |
135 | if there are any numbers after the first one, they are passed to the | |
136 | C<setgroups()> C function (if there is one). | |
137 | ||
138 | =head2 Fixed parsing of $$<digit>, &$<digit>, etc. | |
139 | ||
140 | Perl versions before 5.004 misinterpreted any type marker followed by | |
141 | "$" and a digit. For example, "$$0" was incorrectly taken to mean | |
142 | "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004. | |
143 | ||
144 | However, the developers of Perl 5.004 could not fix this bug completely, | |
145 | because at least two widely-used modules depend on the old meaning of | |
146 | "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the | |
147 | old (broken) way inside strings; but it generates this message as a | |
148 | warning. And in Perl 5.005, this special treatment will cease. | |
149 | ||
150 | =head2 Fixed localization of $<digit>, $&, etc. | |
151 | ||
152 | Perl versions before 5.004 did not always properly localize the | |
153 | regex-related special variables. Perl 5.004 does localize them, as | |
154 | the documentation has always said it should. This may result in $1, | |
155 | $2, etc. no longer being set where existing programs use them. | |
156 | ||
157 | =head2 No resetting of $. on implicit close | |
158 | ||
159 | The documentation for Perl 5.0 has always stated that C<$.> is I<not> | |
160 | reset when an already-open file handle is reopened with no intervening | |
161 | call to C<close>. Due to a bug, perl versions 5.000 through 5.003 | |
162 | I<did> reset C<$.> under that circumstance; Perl 5.004 does not. | |
163 | ||
164 | =head2 C<wantarray> may return undef | |
165 | ||
166 | The C<wantarray> operator returns true if a subroutine is expected to | |
167 | return a list, and false otherwise. In Perl 5.004, C<wantarray> can | |
168 | also return the undefined value if a subroutine's return value will | |
169 | not be used at all, which allows subroutines to avoid a time-consuming | |
170 | calculation of a return value if it isn't going to be used. | |
171 | ||
172 | =head2 C<eval EXPR> determines value of EXPR in scalar context | |
173 | ||
174 | Perl (version 5) used to determine the value of EXPR inconsistently, | |
175 | sometimes incorrectly using the surrounding context for the determination. | |
176 | Now, the value of EXPR (before being parsed by eval) is always determined in | |
177 | a scalar context. Once parsed, it is executed as before, by providing | |
178 | the context that the scope surrounding the eval provided. This change | |
179 | makes the behavior Perl4 compatible, besides fixing bugs resulting from | |
180 | the inconsistent behavior. This program: | |
181 | ||
182 | @a = qw(time now is time); | |
183 | print eval @a; | |
184 | print '|', scalar eval @a; | |
185 | ||
186 | used to print something like "timenowis881399109|4", but now (and in perl4) | |
187 | prints "4|4". | |
188 | ||
189 | =head2 Changes to tainting checks | |
190 | ||
191 | A bug in previous versions may have failed to detect some insecure | |
192 | conditions when taint checks are turned on. (Taint checks are used | |
193 | in setuid or setgid scripts, or when explicitly turned on with the | |
194 | C<-T> invocation option.) Although it's unlikely, this may cause a | |
195 | previously-working script to now fail -- which should be construed | |
196 | as a blessing, since that indicates a potentially-serious security | |
197 | hole was just plugged. | |
198 | ||
199 | The new restrictions when tainting include: | |
200 | ||
201 | =over | |
202 | ||
203 | =item No glob() or <*> | |
204 | ||
205 | These operators may spawn the C shell (csh), which cannot be made | |
206 | safe. This restriction will be lifted in a future version of Perl | |
207 | when globbing is implemented without the use of an external program. | |
208 | ||
209 | =item No spawning if tainted $CDPATH, $ENV, $BASH_ENV | |
210 | ||
211 | These environment variables may alter the behavior of spawned programs | |
212 | (especially shells) in ways that subvert security. So now they are | |
213 | treated as dangerous, in the manner of $IFS and $PATH. | |
214 | ||
215 | =item No spawning if tainted $TERM doesn't look like a terminal name | |
216 | ||
217 | Some termcap libraries do unsafe things with $TERM. However, it would be | |
218 | unnecessarily harsh to treat all $TERM values as unsafe, since only shell | |
219 | metacharacters can cause trouble in $TERM. So a tainted $TERM is | |
220 | considered to be safe if it contains only alphanumerics, underscores, | |
221 | dashes, and colons, and unsafe if it contains other characters (including | |
222 | whitespace). | |
223 | ||
224 | =back | |
225 | ||
226 | =head2 New Opcode module and revised Safe module | |
227 | ||
228 | A new Opcode module supports the creation, manipulation and | |
229 | application of opcode masks. The revised Safe module has a new API | |
230 | and is implemented using the new Opcode module. Please read the new | |
231 | Opcode and Safe documentation. | |
232 | ||
233 | =head2 Embedding improvements | |
234 | ||
235 | In older versions of Perl it was not possible to create more than one | |
236 | Perl interpreter instance inside a single process without leaking like a | |
237 | sieve and/or crashing. The bugs that caused this behavior have all been | |
238 | fixed. However, you still must take care when embedding Perl in a C | |
239 | program. See the updated perlembed manpage for tips on how to manage | |
240 | your interpreters. | |
241 | ||
242 | =head2 Internal change: FileHandle class based on IO::* classes | |
243 | ||
244 | File handles are now stored internally as type IO::Handle. The | |
245 | FileHandle module is still supported for backwards compatibility, but | |
246 | it is now merely a front end to the IO::* modules -- specifically, | |
247 | IO::Handle, IO::Seekable, and IO::File. We suggest, but do not | |
248 | require, that you use the IO::* modules in new code. | |
249 | ||
250 | In harmony with this change, C<*GLOB{FILEHANDLE}> is now just a | |
251 | backward-compatible synonym for C<*GLOB{IO}>. | |
252 | ||
253 | =head2 Internal change: PerlIO abstraction interface | |
254 | ||
255 | It is now possible to build Perl with AT&T's sfio IO package | |
256 | instead of stdio. See L<perlapio> for more details, and | |
257 | the F<INSTALL> file for how to use it. | |
258 | ||
259 | =head2 New and changed syntax | |
260 | ||
261 | =over | |
262 | ||
263 | =item $coderef->(PARAMS) | |
264 | ||
265 | A subroutine reference may now be suffixed with an arrow and a | |
266 | (possibly empty) parameter list. This syntax denotes a call of the | |
267 | referenced subroutine, with the given parameters (if any). | |
268 | ||
c47ff5f1 GS |
269 | This new syntax follows the pattern of S<C<< $hashref->{FOO} >>> and |
270 | S<C<< $aryref->[$foo] >>>: You may now write S<C<&$subref($foo)>> as | |
271 | S<C<< $subref->($foo) >>>. All these arrow terms may be chained; | |
272 | thus, S<C<< &{$table->{FOO}}($bar) >>> may now be written | |
273 | S<C<< $table->{FOO}->($bar) >>>. | |
6ee623d5 GS |
274 | |
275 | =back | |
276 | ||
277 | =head2 New and changed builtin constants | |
278 | ||
279 | =over | |
280 | ||
281 | =item __PACKAGE__ | |
282 | ||
283 | The current package name at compile time, or the undefined value if | |
284 | there is no current package (due to a C<package;> directive). Like | |
285 | C<__FILE__> and C<__LINE__>, C<__PACKAGE__> does I<not> interpolate | |
286 | into strings. | |
287 | ||
288 | =back | |
289 | ||
290 | =head2 New and changed builtin variables | |
291 | ||
292 | =over | |
293 | ||
294 | =item $^E | |
295 | ||
296 | Extended error message on some platforms. (Also known as | |
297 | $EXTENDED_OS_ERROR if you C<use English>). | |
298 | ||
299 | =item $^H | |
300 | ||
301 | The current set of syntax checks enabled by C<use strict>. See the | |
302 | documentation of C<strict> for more details. Not actually new, but | |
303 | newly documented. | |
304 | Because it is intended for internal use by Perl core components, | |
305 | there is no C<use English> long name for this variable. | |
306 | ||
307 | =item $^M | |
308 | ||
309 | By default, running out of memory it is not trappable. However, if | |
310 | compiled for this, Perl may use the contents of C<$^M> as an emergency | |
311 | pool after die()ing with this message. Suppose that your Perl were | |
312 | compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc. Then | |
313 | ||
314 | $^M = 'a' x (1<<16); | |
315 | ||
316 | would allocate a 64K buffer for use when in emergency. | |
317 | See the F<INSTALL> file for information on how to enable this option. | |
318 | As a disincentive to casual use of this advanced feature, | |
319 | there is no C<use English> long name for this variable. | |
320 | ||
321 | =back | |
322 | ||
323 | =head2 New and changed builtin functions | |
324 | ||
325 | =over | |
326 | ||
327 | =item delete on slices | |
328 | ||
329 | This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>) | |
330 | ||
331 | =item flock | |
332 | ||
333 | is now supported on more platforms, prefers fcntl to lockf when | |
334 | emulating, and always flushes before (un)locking. | |
335 | ||
336 | =item printf and sprintf | |
337 | ||
338 | Perl now implements these functions itself; it doesn't use the C | |
339 | library function sprintf() any more, except for floating-point | |
340 | numbers, and even then only known flags are allowed. As a result, it | |
341 | is now possible to know which conversions and flags will work, and | |
342 | what they will do. | |
343 | ||
344 | The new conversions in Perl's sprintf() are: | |
345 | ||
346 | %i a synonym for %d | |
347 | %p a pointer (the address of the Perl value, in hexadecimal) | |
348 | %n special: *stores* the number of characters output so far | |
349 | into the next variable in the parameter list | |
350 | ||
351 | The new flags that go between the C<%> and the conversion are: | |
352 | ||
353 | # prefix octal with "0", hex with "0x" | |
354 | h interpret integer as C type "short" or "unsigned short" | |
355 | V interpret integer as Perl's standard integer type | |
356 | ||
357 | Also, where a number would appear in the flags, an asterisk ("*") may | |
358 | be used instead, in which case Perl uses the next item in the | |
359 | parameter list as the given number (that is, as the field width or | |
360 | precision). If a field width obtained through "*" is negative, it has | |
361 | the same effect as the '-' flag: left-justification. | |
362 | ||
363 | See L<perlfunc/sprintf> for a complete list of conversion and flags. | |
364 | ||
365 | =item keys as an lvalue | |
366 | ||
367 | As an lvalue, C<keys> allows you to increase the number of hash buckets | |
368 | allocated for the given hash. This can gain you a measure of efficiency if | |
369 | you know the hash is going to get big. (This is similar to pre-extending | |
370 | an array by assigning a larger number to $#array.) If you say | |
371 | ||
372 | keys %hash = 200; | |
373 | ||
374 | then C<%hash> will have at least 200 buckets allocated for it. These | |
375 | buckets will be retained even if you do C<%hash = ()>; use C<undef | |
376 | %hash> if you want to free the storage while C<%hash> is still in scope. | |
377 | You can't shrink the number of buckets allocated for the hash using | |
378 | C<keys> in this way (but you needn't worry about doing this by accident, | |
379 | as trying has no effect). | |
380 | ||
381 | =item my() in Control Structures | |
382 | ||
383 | You can now use my() (with or without the parentheses) in the control | |
384 | expressions of control structures such as: | |
385 | ||
386 | while (defined(my $line = <>)) { | |
387 | $line = lc $line; | |
388 | } continue { | |
389 | print $line; | |
390 | } | |
391 | ||
392 | if ((my $answer = <STDIN>) =~ /^y(es)?$/i) { | |
393 | user_agrees(); | |
394 | } elsif ($answer =~ /^n(o)?$/i) { | |
395 | user_disagrees(); | |
396 | } else { | |
397 | chomp $answer; | |
398 | die "`$answer' is neither `yes' nor `no'"; | |
399 | } | |
400 | ||
401 | Also, you can declare a foreach loop control variable as lexical by | |
402 | preceding it with the word "my". For example, in: | |
403 | ||
404 | foreach my $i (1, 2, 3) { | |
405 | some_function(); | |
406 | } | |
407 | ||
408 | $i is a lexical variable, and the scope of $i extends to the end of | |
409 | the loop, but not beyond it. | |
410 | ||
411 | Note that you still cannot use my() on global punctuation variables | |
412 | such as $_ and the like. | |
413 | ||
414 | =item pack() and unpack() | |
415 | ||
416 | A new format 'w' represents a BER compressed integer (as defined in | |
417 | ASN.1). Its format is a sequence of one or more bytes, each of which | |
418 | provides seven bits of the total value, with the most significant | |
419 | first. Bit eight of each byte is set, except for the last byte, in | |
420 | which bit eight is clear. | |
421 | ||
422 | If 'p' or 'P' are given undef as values, they now generate a NULL | |
423 | pointer. | |
424 | ||
425 | Both pack() and unpack() now fail when their templates contain invalid | |
426 | types. (Invalid types used to be ignored.) | |
427 | ||
428 | =item sysseek() | |
429 | ||
430 | The new sysseek() operator is a variant of seek() that sets and gets the | |
431 | file's system read/write position, using the lseek(2) system call. It is | |
432 | the only reliable way to seek before using sysread() or syswrite(). Its | |
433 | return value is the new position, or the undefined value on failure. | |
434 | ||
435 | =item use VERSION | |
436 | ||
437 | If the first argument to C<use> is a number, it is treated as a version | |
438 | number instead of a module name. If the version of the Perl interpreter | |
439 | is less than VERSION, then an error message is printed and Perl exits | |
440 | immediately. Because C<use> occurs at compile time, this check happens | |
441 | immediately during the compilation process, unlike C<require VERSION>, | |
442 | which waits until runtime for the check. This is often useful if you | |
443 | need to check the current Perl version before C<use>ing library modules | |
444 | which have changed in incompatible ways from older versions of Perl. | |
445 | (We try not to do this more than we have to.) | |
446 | ||
447 | =item use Module VERSION LIST | |
448 | ||
449 | If the VERSION argument is present between Module and LIST, then the | |
450 | C<use> will call the VERSION method in class Module with the given | |
451 | version as an argument. The default VERSION method, inherited from | |
452 | the UNIVERSAL class, croaks if the given version is larger than the | |
453 | value of the variable $Module::VERSION. (Note that there is not a | |
454 | comma after VERSION!) | |
455 | ||
456 | This version-checking mechanism is similar to the one currently used | |
457 | in the Exporter module, but it is faster and can be used with modules | |
458 | that don't use the Exporter. It is the recommended method for new | |
459 | code. | |
460 | ||
461 | =item prototype(FUNCTION) | |
462 | ||
463 | Returns the prototype of a function as a string (or C<undef> if the | |
464 | function has no prototype). FUNCTION is a reference to or the name of the | |
465 | function whose prototype you want to retrieve. | |
466 | (Not actually new; just never documented before.) | |
467 | ||
468 | =item srand | |
469 | ||
470 | The default seed for C<srand>, which used to be C<time>, has been changed. | |
471 | Now it's a heady mix of difficult-to-predict system-dependent values, | |
472 | which should be sufficient for most everyday purposes. | |
473 | ||
474 | Previous to version 5.004, calling C<rand> without first calling C<srand> | |
475 | would yield the same sequence of random numbers on most or all machines. | |
476 | Now, when perl sees that you're calling C<rand> and haven't yet called | |
477 | C<srand>, it calls C<srand> with the default seed. You should still call | |
478 | C<srand> manually if your code might ever be run on a pre-5.004 system, | |
479 | of course, or if you want a seed other than the default. | |
480 | ||
481 | =item $_ as Default | |
482 | ||
483 | Functions documented in the Camel to default to $_ now in | |
484 | fact do, and all those that do are so documented in L<perlfunc>. | |
485 | ||
486 | =item C<m//gc> does not reset search position on failure | |
487 | ||
488 | The C<m//g> match iteration construct has always reset its target | |
489 | string's search position (which is visible through the C<pos> operator) | |
490 | when a match fails; as a result, the next C<m//g> match after a failure | |
491 | starts again at the beginning of the string. With Perl 5.004, this | |
492 | reset may be disabled by adding the "c" (for "continue") modifier, | |
493 | i.e. C<m//gc>. This feature, in conjunction with the C<\G> zero-width | |
494 | assertion, makes it possible to chain matches together. See L<perlop> | |
495 | and L<perlre>. | |
496 | ||
497 | =item C<m//x> ignores whitespace before ?*+{} | |
498 | ||
499 | The C<m//x> construct has always been intended to ignore all unescaped | |
500 | whitespace. However, before Perl 5.004, whitespace had the effect of | |
501 | escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was | |
502 | (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004. | |
503 | ||
504 | =item nested C<sub{}> closures work now | |
505 | ||
506 | Prior to the 5.004 release, nested anonymous functions didn't work | |
507 | right. They do now. | |
508 | ||
509 | =item formats work right on changing lexicals | |
510 | ||
511 | Just like anonymous functions that contain lexical variables | |
512 | that change (like a lexical index variable for a C<foreach> loop), | |
513 | formats now work properly. For example, this silently failed | |
514 | before (printed only zeros), but is fine now: | |
515 | ||
516 | my $i; | |
517 | foreach $i ( 1 .. 10 ) { | |
518 | write; | |
519 | } | |
520 | format = | |
521 | my i is @# | |
522 | $i | |
523 | . | |
524 | ||
525 | However, it still fails (without a warning) if the foreach is within a | |
526 | subroutine: | |
527 | ||
528 | my $i; | |
529 | sub foo { | |
530 | foreach $i ( 1 .. 10 ) { | |
531 | write; | |
532 | } | |
533 | } | |
534 | foo; | |
535 | format = | |
536 | my i is @# | |
537 | $i | |
538 | . | |
539 | ||
540 | =back | |
541 | ||
542 | =head2 New builtin methods | |
543 | ||
544 | The C<UNIVERSAL> package automatically contains the following methods that | |
545 | are inherited by all other classes: | |
546 | ||
547 | =over | |
548 | ||
549 | =item isa(CLASS) | |
550 | ||
551 | C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS> | |
552 | ||
553 | C<isa> is also exportable and can be called as a sub with two arguments. This | |
554 | allows the ability to check what a reference points to. Example: | |
555 | ||
556 | use UNIVERSAL qw(isa); | |
557 | ||
558 | if(isa($ref, 'ARRAY')) { | |
559 | ... | |
560 | } | |
561 | ||
562 | =item can(METHOD) | |
563 | ||
564 | C<can> checks to see if its object has a method called C<METHOD>, | |
565 | if it does then a reference to the sub is returned; if it does not then | |
566 | I<undef> is returned. | |
567 | ||
568 | =item VERSION( [NEED] ) | |
569 | ||
570 | C<VERSION> returns the version number of the class (package). If the | |
571 | NEED argument is given then it will check that the current version (as | |
572 | defined by the $VERSION variable in the given package) not less than | |
573 | NEED; it will die if this is not the case. This method is normally | |
574 | called as a class method. This method is called automatically by the | |
575 | C<VERSION> form of C<use>. | |
576 | ||
577 | use A 1.2 qw(some imported subs); | |
578 | # implies: | |
579 | A->VERSION(1.2); | |
580 | ||
581 | =back | |
582 | ||
583 | B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and | |
584 | C<isa> uses a very similar method and caching strategy. This may cause | |
585 | strange effects if the Perl code dynamically changes @ISA in any package. | |
586 | ||
587 | You may add other methods to the UNIVERSAL class via Perl or XS code. | |
588 | You do not need to C<use UNIVERSAL> in order to make these methods | |
589 | available to your program. This is necessary only if you wish to | |
590 | have C<isa> available as a plain subroutine in the current package. | |
591 | ||
592 | =head2 TIEHANDLE now supported | |
593 | ||
594 | See L<perltie> for other kinds of tie()s. | |
595 | ||
596 | =over | |
597 | ||
598 | =item TIEHANDLE classname, LIST | |
599 | ||
600 | This is the constructor for the class. That means it is expected to | |
601 | return an object of some sort. The reference can be used to | |
602 | hold some internal information. | |
603 | ||
604 | sub TIEHANDLE { | |
605 | print "<shout>\n"; | |
606 | my $i; | |
607 | return bless \$i, shift; | |
608 | } | |
609 | ||
610 | =item PRINT this, LIST | |
611 | ||
612 | This method will be triggered every time the tied handle is printed to. | |
613 | Beyond its self reference it also expects the list that was passed to | |
614 | the print function. | |
615 | ||
616 | sub PRINT { | |
617 | $r = shift; | |
618 | $$r++; | |
619 | return print join( $, => map {uc} @_), $\; | |
620 | } | |
621 | ||
622 | =item PRINTF this, LIST | |
623 | ||
624 | This method will be triggered every time the tied handle is printed to | |
625 | with the C<printf()> function. | |
626 | Beyond its self reference it also expects the format and list that was | |
627 | passed to the printf function. | |
628 | ||
629 | sub PRINTF { | |
630 | shift; | |
631 | my $fmt = shift; | |
632 | print sprintf($fmt, @_)."\n"; | |
633 | } | |
634 | ||
635 | =item READ this LIST | |
636 | ||
637 | This method will be called when the handle is read from via the C<read> | |
638 | or C<sysread> functions. | |
639 | ||
640 | sub READ { | |
641 | $r = shift; | |
642 | my($buf,$len,$offset) = @_; | |
643 | print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset"; | |
644 | } | |
645 | ||
646 | =item READLINE this | |
647 | ||
648 | This method will be called when the handle is read from. The method | |
649 | should return undef when there is no more data. | |
650 | ||
651 | sub READLINE { | |
652 | $r = shift; | |
653 | return "PRINT called $$r times\n" | |
654 | } | |
655 | ||
656 | =item GETC this | |
657 | ||
658 | This method will be called when the C<getc> function is called. | |
659 | ||
660 | sub GETC { print "Don't GETC, Get Perl"; return "a"; } | |
661 | ||
662 | =item DESTROY this | |
663 | ||
664 | As with the other types of ties, this method will be called when the | |
665 | tied handle is about to be destroyed. This is useful for debugging and | |
666 | possibly for cleaning up. | |
667 | ||
668 | sub DESTROY { | |
669 | print "</shout>\n"; | |
670 | } | |
671 | ||
672 | =back | |
673 | ||
674 | =head2 Malloc enhancements | |
675 | ||
676 | If perl is compiled with the malloc included with the perl distribution | |
677 | (that is, if C<perl -V:d_mymalloc> is 'define') then you can print | |
678 | memory statistics at runtime by running Perl thusly: | |
679 | ||
680 | env PERL_DEBUG_MSTATS=2 perl your_script_here | |
681 | ||
682 | The value of 2 means to print statistics after compilation and on | |
683 | exit; with a value of 1, the statistics are printed only on exit. | |
684 | (If you want the statistics at an arbitrary time, you'll need to | |
685 | install the optional module Devel::Peek.) | |
686 | ||
687 | Three new compilation flags are recognized by malloc.c. (They have no | |
688 | effect if perl is compiled with system malloc().) | |
689 | ||
690 | =over | |
691 | ||
692 | =item -DPERL_EMERGENCY_SBRK | |
693 | ||
694 | If this macro is defined, running out of memory need not be a fatal | |
695 | error: a memory pool can allocated by assigning to the special | |
696 | variable C<$^M>. See L<"$^M">. | |
697 | ||
698 | =item -DPACK_MALLOC | |
699 | ||
700 | Perl memory allocation is by bucket with sizes close to powers of two. | |
701 | Because of these malloc overhead may be big, especially for data of | |
702 | size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses | |
703 | a slightly different algorithm for small allocations (up to 64 bytes | |
704 | long), which makes it possible to have overhead down to 1 byte for | |
705 | allocations which are powers of two (and appear quite often). | |
706 | ||
707 | Expected memory savings (with 8-byte alignment in C<alignbytes>) is | |
708 | about 20% for typical Perl usage. Expected slowdown due to additional | |
709 | malloc overhead is in fractions of a percent (hard to measure, because | |
710 | of the effect of saved memory on speed). | |
711 | ||
712 | =item -DTWO_POT_OPTIMIZE | |
713 | ||
714 | Similarly to C<PACK_MALLOC>, this macro improves allocations of data | |
715 | with size close to a power of two; but this works for big allocations | |
716 | (starting with 16K by default). Such allocations are typical for big | |
717 | hashes and special-purpose scripts, especially image processing. | |
718 | ||
719 | On recent systems, the fact that perl requires 2M from system for 1M | |
720 | allocation will not affect speed of execution, since the tail of such | |
721 | a chunk is not going to be touched (and thus will not require real | |
722 | memory). However, it may result in a premature out-of-memory error. | |
723 | So if you will be manipulating very large blocks with sizes close to | |
724 | powers of two, it would be wise to define this macro. | |
725 | ||
726 | Expected saving of memory is 0-100% (100% in applications which | |
727 | require most memory in such 2**n chunks); expected slowdown is | |
728 | negligible. | |
729 | ||
730 | =back | |
731 | ||
732 | =head2 Miscellaneous efficiency enhancements | |
733 | ||
734 | Functions that have an empty prototype and that do nothing but return | |
735 | a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>). | |
736 | ||
737 | Each unique hash key is only allocated once, no matter how many hashes | |
738 | have an entry with that key. So even if you have 100 copies of the | |
739 | same hash, the hash keys never have to be reallocated. | |
740 | ||
741 | =head1 Support for More Operating Systems | |
742 | ||
743 | Support for the following operating systems is new in Perl 5.004. | |
744 | ||
745 | =head2 Win32 | |
746 | ||
747 | Perl 5.004 now includes support for building a "native" perl under | |
748 | Windows NT, using the Microsoft Visual C++ compiler (versions 2.0 | |
749 | and above) or the Borland C++ compiler (versions 5.02 and above). | |
750 | The resulting perl can be used under Windows 95 (if it | |
751 | is installed in the same directory locations as it got installed | |
752 | in Windows NT). This port includes support for perl extension | |
753 | building tools like L<MakeMaker> and L<h2xs>, so that many extensions | |
754 | available on the Comprehensive Perl Archive Network (CPAN) can now be | |
755 | readily built under Windows NT. See http://www.perl.com/ for more | |
7b8d334a GS |
756 | information on CPAN and F<README.win32> in the perl distribution for more |
757 | details on how to get started with building this port. | |
6ee623d5 GS |
758 | |
759 | There is also support for building perl under the Cygwin32 environment. | |
760 | Cygwin32 is a set of GNU tools that make it possible to compile and run | |
19799a22 | 761 | many Unix programs under Windows NT by providing a mostly Unix-like |
7b8d334a GS |
762 | interface for compilation and execution. See F<README.cygwin32> in the |
763 | perl distribution for more details on this port and how to obtain the | |
764 | Cygwin32 toolkit. | |
6ee623d5 GS |
765 | |
766 | =head2 Plan 9 | |
767 | ||
7b8d334a | 768 | See F<README.plan9> in the perl distribution. |
6ee623d5 GS |
769 | |
770 | =head2 QNX | |
771 | ||
7b8d334a | 772 | See F<README.qnx> in the perl distribution. |
6ee623d5 GS |
773 | |
774 | =head2 AmigaOS | |
775 | ||
7b8d334a | 776 | See F<README.amigaos> in the perl distribution. |
6ee623d5 GS |
777 | |
778 | =head1 Pragmata | |
779 | ||
780 | Six new pragmatic modules exist: | |
781 | ||
782 | =over | |
783 | ||
784 | =item use autouse MODULE => qw(sub1 sub2 sub3) | |
785 | ||
786 | Defers C<require MODULE> until someone calls one of the specified | |
787 | subroutines (which must be exported by MODULE). This pragma should be | |
788 | used with caution, and only when necessary. | |
789 | ||
790 | =item use blib | |
791 | ||
792 | =item use blib 'dir' | |
793 | ||
794 | Looks for MakeMaker-like I<'blib'> directory structure starting in | |
795 | I<dir> (or current directory) and working back up to five levels of | |
796 | parent directories. | |
797 | ||
798 | Intended for use on command line with B<-M> option as a way of testing | |
799 | arbitrary scripts against an uninstalled version of a package. | |
800 | ||
801 | =item use constant NAME => VALUE | |
802 | ||
803 | Provides a convenient interface for creating compile-time constants, | |
804 | See L<perlsub/"Constant Functions">. | |
805 | ||
806 | =item use locale | |
807 | ||
808 | Tells the compiler to enable (or disable) the use of POSIX locales for | |
809 | builtin operations. | |
810 | ||
811 | When C<use locale> is in effect, the current LC_CTYPE locale is used | |
812 | for regular expressions and case mapping; LC_COLLATE for string | |
813 | ordering; and LC_NUMERIC for numeric formating in printf and sprintf | |
814 | (but B<not> in print). LC_NUMERIC is always used in write, since | |
815 | lexical scoping of formats is problematic at best. | |
816 | ||
817 | Each C<use locale> or C<no locale> affects statements to the end of | |
818 | the enclosing BLOCK or, if not inside a BLOCK, to the end of the | |
819 | current file. Locales can be switched and queried with | |
820 | POSIX::setlocale(). | |
821 | ||
822 | See L<perllocale> for more information. | |
823 | ||
824 | =item use ops | |
825 | ||
826 | Disable unsafe opcodes, or any named opcodes, when compiling Perl code. | |
827 | ||
828 | =item use vmsish | |
829 | ||
830 | Enable VMS-specific language features. Currently, there are three | |
831 | VMS-specific features available: 'status', which makes C<$?> and | |
832 | C<system> return genuine VMS status values instead of emulating POSIX; | |
833 | 'exit', which makes C<exit> take a genuine VMS status value instead of | |
834 | assuming that C<exit 1> is an error; and 'time', which makes all times | |
835 | relative to the local time zone, in the VMS tradition. | |
836 | ||
837 | =back | |
838 | ||
839 | =head1 Modules | |
840 | ||
841 | =head2 Required Updates | |
842 | ||
843 | Though Perl 5.004 is compatible with almost all modules that work | |
844 | with Perl 5.003, there are a few exceptions: | |
845 | ||
846 | Module Required Version for Perl 5.004 | |
847 | ------ ------------------------------- | |
848 | Filter Filter-1.12 | |
849 | LWP libwww-perl-5.08 | |
850 | Tk Tk400.202 (-w makes noise) | |
851 | ||
852 | Also, the majordomo mailing list program, version 1.94.1, doesn't work | |
853 | with Perl 5.004 (nor with perl 4), because it executes an invalid | |
854 | regular expression. This bug is fixed in majordomo version 1.94.2. | |
855 | ||
856 | =head2 Installation directories | |
857 | ||
858 | The I<installperl> script now places the Perl source files for | |
859 | extensions in the architecture-specific library directory, which is | |
860 | where the shared libraries for extensions have always been. This | |
861 | change is intended to allow administrators to keep the Perl 5.004 | |
862 | library directory unchanged from a previous version, without running | |
863 | the risk of binary incompatibility between extensions' Perl source and | |
864 | shared libraries. | |
865 | ||
866 | =head2 Module information summary | |
867 | ||
868 | Brand new modules, arranged by topic rather than strictly | |
869 | alphabetically: | |
870 | ||
871 | CGI.pm Web server interface ("Common Gateway Interface") | |
872 | CGI/Apache.pm Support for Apache's Perl module | |
873 | CGI/Carp.pm Log server errors with helpful context | |
874 | CGI/Fast.pm Support for FastCGI (persistent server process) | |
875 | CGI/Push.pm Support for server push | |
876 | CGI/Switch.pm Simple interface for multiple server types | |
877 | ||
878 | CPAN Interface to Comprehensive Perl Archive Network | |
879 | CPAN::FirstTime Utility for creating CPAN configuration file | |
880 | CPAN::Nox Runs CPAN while avoiding compiled extensions | |
881 | ||
882 | IO.pm Top-level interface to IO::* classes | |
883 | IO/File.pm IO::File extension Perl module | |
884 | IO/Handle.pm IO::Handle extension Perl module | |
885 | IO/Pipe.pm IO::Pipe extension Perl module | |
886 | IO/Seekable.pm IO::Seekable extension Perl module | |
887 | IO/Select.pm IO::Select extension Perl module | |
888 | IO/Socket.pm IO::Socket extension Perl module | |
889 | ||
890 | Opcode.pm Disable named opcodes when compiling Perl code | |
891 | ||
892 | ExtUtils/Embed.pm Utilities for embedding Perl in C programs | |
893 | ExtUtils/testlib.pm Fixes up @INC to use just-built extension | |
894 | ||
895 | FindBin.pm Find path of currently executing program | |
896 | ||
897 | Class/Struct.pm Declare struct-like datatypes as Perl classes | |
898 | File/stat.pm By-name interface to Perl's builtin stat | |
899 | Net/hostent.pm By-name interface to Perl's builtin gethost* | |
900 | Net/netent.pm By-name interface to Perl's builtin getnet* | |
901 | Net/protoent.pm By-name interface to Perl's builtin getproto* | |
902 | Net/servent.pm By-name interface to Perl's builtin getserv* | |
903 | Time/gmtime.pm By-name interface to Perl's builtin gmtime | |
904 | Time/localtime.pm By-name interface to Perl's builtin localtime | |
905 | Time/tm.pm Internal object for Time::{gm,local}time | |
906 | User/grent.pm By-name interface to Perl's builtin getgr* | |
907 | User/pwent.pm By-name interface to Perl's builtin getpw* | |
908 | ||
909 | Tie/RefHash.pm Base class for tied hashes with references as keys | |
910 | ||
911 | UNIVERSAL.pm Base class for *ALL* classes | |
912 | ||
913 | =head2 Fcntl | |
914 | ||
915 | New constants in the existing Fcntl modules are now supported, | |
916 | provided that your operating system happens to support them: | |
917 | ||
918 | F_GETOWN F_SETOWN | |
919 | O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC | |
920 | O_EXLOCK O_SHLOCK | |
921 | ||
922 | These constants are intended for use with the Perl operators sysopen() | |
923 | and fcntl() and the basic database modules like SDBM_File. For the | |
924 | exact meaning of these and other Fcntl constants please refer to your | |
925 | operating system's documentation for fcntl() and open(). | |
926 | ||
927 | In addition, the Fcntl module now provides these constants for use | |
928 | with the Perl operator flock(): | |
929 | ||
930 | LOCK_SH LOCK_EX LOCK_NB LOCK_UN | |
931 | ||
932 | These constants are defined in all environments (because where there is | |
933 | no flock() system call, Perl emulates it). However, for historical | |
934 | reasons, these constants are not exported unless they are explicitly | |
935 | requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>). | |
936 | ||
937 | =head2 IO | |
938 | ||
19799a22 | 939 | The IO module provides a simple mechanism to load all the IO modules at one |
6ee623d5 GS |
940 | go. Currently this includes: |
941 | ||
942 | IO::Handle | |
943 | IO::Seekable | |
944 | IO::File | |
945 | IO::Pipe | |
946 | IO::Socket | |
947 | ||
948 | For more information on any of these modules, please see its | |
949 | respective documentation. | |
950 | ||
951 | =head2 Math::Complex | |
952 | ||
953 | The Math::Complex module has been totally rewritten, and now supports | |
954 | more operations. These are overloaded: | |
955 | ||
956 | + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify) | |
957 | ||
958 | And these functions are now exported: | |
959 | ||
960 | pi i Re Im arg | |
961 | log10 logn ln cbrt root | |
962 | tan | |
963 | csc sec cot | |
964 | asin acos atan | |
965 | acsc asec acot | |
966 | sinh cosh tanh | |
967 | csch sech coth | |
968 | asinh acosh atanh | |
969 | acsch asech acoth | |
970 | cplx cplxe | |
971 | ||
972 | =head2 Math::Trig | |
973 | ||
974 | This new module provides a simpler interface to parts of Math::Complex for | |
975 | those who need trigonometric functions only for real numbers. | |
976 | ||
977 | =head2 DB_File | |
978 | ||
979 | There have been quite a few changes made to DB_File. Here are a few of | |
980 | the highlights: | |
981 | ||
982 | =over | |
983 | ||
984 | =item * | |
985 | ||
986 | Fixed a handful of bugs. | |
987 | ||
988 | =item * | |
989 | ||
990 | By public demand, added support for the standard hash function exists(). | |
991 | ||
992 | =item * | |
993 | ||
994 | Made it compatible with Berkeley DB 1.86. | |
995 | ||
996 | =item * | |
997 | ||
998 | Made negative subscripts work with RECNO interface. | |
999 | ||
1000 | =item * | |
1001 | ||
1002 | Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default | |
1003 | mode from 0640 to 0666. | |
1004 | ||
1005 | =item * | |
1006 | ||
1007 | Made DB_File automatically import the open() constants (O_RDWR, | |
1008 | O_CREAT etc.) from Fcntl, if available. | |
1009 | ||
1010 | =item * | |
1011 | ||
1012 | Updated documentation. | |
1013 | ||
1014 | =back | |
1015 | ||
1016 | Refer to the HISTORY section in DB_File.pm for a complete list of | |
1017 | changes. Everything after DB_File 1.01 has been added since 5.003. | |
1018 | ||
1019 | =head2 Net::Ping | |
1020 | ||
1021 | Major rewrite - support added for both udp echo and real icmp pings. | |
1022 | ||
1023 | =head2 Object-oriented overrides for builtin operators | |
1024 | ||
1025 | Many of the Perl builtins returning lists now have | |
1026 | object-oriented overrides. These are: | |
1027 | ||
1028 | File::stat | |
1029 | Net::hostent | |
1030 | Net::netent | |
1031 | Net::protoent | |
1032 | Net::servent | |
1033 | Time::gmtime | |
1034 | Time::localtime | |
1035 | User::grent | |
1036 | User::pwent | |
1037 | ||
1038 | For example, you can now say | |
1039 | ||
1040 | use File::stat; | |
1041 | use User::pwent; | |
1042 | $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid); | |
1043 | ||
1044 | =head1 Utility Changes | |
1045 | ||
1046 | =head2 pod2html | |
1047 | ||
1048 | =over | |
1049 | ||
1050 | =item Sends converted HTML to standard output | |
1051 | ||
1052 | The I<pod2html> utility included with Perl 5.004 is entirely new. | |
1053 | By default, it sends the converted HTML to its standard output, | |
1054 | instead of writing it to a file like Perl 5.003's I<pod2html> did. | |
1055 | Use the B<--outfile=FILENAME> option to write to a file. | |
1056 | ||
1057 | =back | |
1058 | ||
1059 | =head2 xsubpp | |
1060 | ||
1061 | =over | |
1062 | ||
1063 | =item C<void> XSUBs now default to returning nothing | |
1064 | ||
1065 | Due to a documentation/implementation bug in previous versions of | |
1066 | Perl, XSUBs with a return type of C<void> have actually been | |
1067 | returning one value. Usually that value was the GV for the XSUB, | |
1068 | but sometimes it was some already freed or reused value, which would | |
1069 | sometimes lead to program failure. | |
1070 | ||
1071 | In Perl 5.004, if an XSUB is declared as returning C<void>, it | |
1072 | actually returns no value, i.e. an empty list (though there is a | |
1073 | backward-compatibility exception; see below). If your XSUB really | |
1074 | does return an SV, you should give it a return type of C<SV *>. | |
1075 | ||
1076 | For backward compatibility, I<xsubpp> tries to guess whether a | |
1077 | C<void> XSUB is really C<void> or if it wants to return an C<SV *>. | |
1078 | It does so by examining the text of the XSUB: if I<xsubpp> finds | |
1079 | what looks like an assignment to C<ST(0)>, it assumes that the | |
1080 | XSUB's return type is really C<SV *>. | |
1081 | ||
1082 | =back | |
1083 | ||
1084 | =head1 C Language API Changes | |
1085 | ||
1086 | =over | |
1087 | ||
1088 | =item C<gv_fetchmethod> and C<perl_call_sv> | |
1089 | ||
1090 | The C<gv_fetchmethod> function finds a method for an object, just like | |
1091 | in Perl 5.003. The GV it returns may be a method cache entry. | |
1092 | However, in Perl 5.004, method cache entries are not visible to users; | |
1093 | therefore, they can no longer be passed directly to C<perl_call_sv>. | |
1094 | Instead, you should use the C<GvCV> macro on the GV to extract its CV, | |
1095 | and pass the CV to C<perl_call_sv>. | |
1096 | ||
1097 | The most likely symptom of passing the result of C<gv_fetchmethod> to | |
1098 | C<perl_call_sv> is Perl's producing an "Undefined subroutine called" | |
1099 | error on the I<second> call to a given method (since there is no cache | |
1100 | on the first call). | |
1101 | ||
1102 | =item C<perl_eval_pv> | |
1103 | ||
1104 | A new function handy for eval'ing strings of Perl code inside C code. | |
1105 | This function returns the value from the eval statement, which can | |
1106 | be used instead of fetching globals from the symbol table. See | |
1107 | L<perlguts>, L<perlembed> and L<perlcall> for details and examples. | |
1108 | ||
1109 | =item Extended API for manipulating hashes | |
1110 | ||
1111 | Internal handling of hash keys has changed. The old hashtable API is | |
1112 | still fully supported, and will likely remain so. The additions to the | |
1113 | API allow passing keys as C<SV*>s, so that C<tied> hashes can be given | |
1114 | real scalars as keys rather than plain strings (nontied hashes still | |
1115 | can only use strings as keys). New extensions must use the new hash | |
1116 | access functions and macros if they wish to use C<SV*> keys. These | |
1117 | additions also make it feasible to manipulate C<HE*>s (hash entries), | |
1118 | which can be more efficient. See L<perlguts> for details. | |
1119 | ||
1120 | =back | |
1121 | ||
1122 | =head1 Documentation Changes | |
1123 | ||
1124 | Many of the base and library pods were updated. These | |
1125 | new pods are included in section 1: | |
1126 | ||
1127 | =over | |
1128 | ||
1129 | =item L<perldelta> | |
1130 | ||
1131 | This document. | |
1132 | ||
1133 | =item L<perlfaq> | |
1134 | ||
1135 | Frequently asked questions. | |
1136 | ||
1137 | =item L<perllocale> | |
1138 | ||
1139 | Locale support (internationalization and localization). | |
1140 | ||
1141 | =item L<perltoot> | |
1142 | ||
1143 | Tutorial on Perl OO programming. | |
1144 | ||
1145 | =item L<perlapio> | |
1146 | ||
1147 | Perl internal IO abstraction interface. | |
1148 | ||
1149 | =item L<perlmodlib> | |
1150 | ||
1151 | Perl module library and recommended practice for module creation. | |
1152 | Extracted from L<perlmod> (which is much smaller as a result). | |
1153 | ||
1154 | =item L<perldebug> | |
1155 | ||
1156 | Although not new, this has been massively updated. | |
1157 | ||
1158 | =item L<perlsec> | |
1159 | ||
1160 | Although not new, this has been massively updated. | |
1161 | ||
1162 | =back | |
1163 | ||
1164 | =head1 New Diagnostics | |
1165 | ||
1166 | Several new conditions will trigger warnings that were | |
1167 | silent before. Some only affect certain platforms. | |
1168 | The following new warnings and errors outline these. | |
1169 | These messages are classified as follows (listed in | |
1170 | increasing order of desperation): | |
1171 | ||
1172 | (W) A warning (optional). | |
1173 | (D) A deprecation (optional). | |
1174 | (S) A severe warning (mandatory). | |
1175 | (F) A fatal error (trappable). | |
1176 | (P) An internal error you should never see (trappable). | |
1177 | (X) A very fatal error (nontrappable). | |
1178 | (A) An alien error message (not generated by Perl). | |
1179 | ||
1180 | =over | |
1181 | ||
1182 | =item "my" variable %s masks earlier declaration in same scope | |
1183 | ||
1184 | (W) A lexical variable has been redeclared in the same scope, effectively | |
1185 | eliminating all access to the previous instance. This is almost always | |
1186 | a typographical error. Note that the earlier variable will still exist | |
1187 | until the end of the scope or until all closure referents to it are | |
1188 | destroyed. | |
1189 | ||
1190 | =item %s argument is not a HASH element or slice | |
1191 | ||
1192 | (F) The argument to delete() must be either a hash element, such as | |
1193 | ||
1194 | $foo{$bar} | |
1195 | $ref->[12]->{"susie"} | |
1196 | ||
1197 | or a hash slice, such as | |
1198 | ||
1199 | @foo{$bar, $baz, $xyzzy} | |
1200 | @{$ref->[12]}{"susie", "queue"} | |
1201 | ||
1202 | =item Allocation too large: %lx | |
1203 | ||
1204 | (X) You can't allocate more than 64K on an MS-DOS machine. | |
1205 | ||
1206 | =item Allocation too large | |
1207 | ||
1208 | (F) You can't allocate more than 2^31+"small amount" bytes. | |
1209 | ||
1210 | =item Applying %s to %s will act on scalar(%s) | |
1211 | ||
1212 | (W) The pattern match (//), substitution (s///), and transliteration (tr///) | |
1213 | operators work on scalar values. If you apply one of them to an array | |
1214 | or a hash, it will convert the array or hash to a scalar value -- the | |
1215 | length of an array, or the population info of a hash -- and then work on | |
1216 | that scalar value. This is probably not what you meant to do. See | |
1217 | L<perlfunc/grep> and L<perlfunc/map> for alternatives. | |
1218 | ||
1219 | =item Attempt to free nonexistent shared string | |
1220 | ||
1221 | (P) Perl maintains a reference counted internal table of strings to | |
1222 | optimize the storage and access of hash keys and other strings. This | |
1223 | indicates someone tried to decrement the reference count of a string | |
1224 | that can no longer be found in the table. | |
1225 | ||
1226 | =item Attempt to use reference as lvalue in substr | |
1227 | ||
1228 | (W) You supplied a reference as the first argument to substr() used | |
1229 | as an lvalue, which is pretty strange. Perhaps you forgot to | |
1230 | dereference it first. See L<perlfunc/substr>. | |
1231 | ||
1232 | =item Bareword "%s" refers to nonexistent package | |
1233 | ||
1234 | (W) You used a qualified bareword of the form C<Foo::>, but | |
1235 | the compiler saw no other uses of that namespace before that point. | |
1236 | Perhaps you need to predeclare a package? | |
1237 | ||
1238 | =item Can't redefine active sort subroutine %s | |
1239 | ||
1240 | (F) Perl optimizes the internal handling of sort subroutines and keeps | |
1241 | pointers into them. You tried to redefine one such sort subroutine when it | |
1242 | was currently active, which is not allowed. If you really want to do | |
1243 | this, you should write C<sort { &func } @x> instead of C<sort func @x>. | |
1244 | ||
1245 | =item Can't use bareword ("%s") as %s ref while "strict refs" in use | |
1246 | ||
1247 | (F) Only hard references are allowed by "strict refs". Symbolic references | |
1248 | are disallowed. See L<perlref>. | |
1249 | ||
1250 | =item Cannot resolve method `%s' overloading `%s' in package `%s' | |
1251 | ||
1252 | (P) Internal error trying to resolve overloading specified by a method | |
1253 | name (as opposed to a subroutine reference). | |
1254 | ||
1255 | =item Constant subroutine %s redefined | |
1256 | ||
1257 | (S) You redefined a subroutine which had previously been eligible for | |
1258 | inlining. See L<perlsub/"Constant Functions"> for commentary and | |
1259 | workarounds. | |
1260 | ||
1261 | =item Constant subroutine %s undefined | |
1262 | ||
1263 | (S) You undefined a subroutine which had previously been eligible for | |
1264 | inlining. See L<perlsub/"Constant Functions"> for commentary and | |
1265 | workarounds. | |
1266 | ||
1267 | =item Copy method did not return a reference | |
1268 | ||
1269 | (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>. | |
1270 | ||
1271 | =item Died | |
1272 | ||
1273 | (F) You passed die() an empty string (the equivalent of C<die "">) or | |
1274 | you called it with no args and both C<$@> and C<$_> were empty. | |
1275 | ||
1276 | =item Exiting pseudo-block via %s | |
1277 | ||
1278 | (W) You are exiting a rather special block construct (like a sort block or | |
1279 | subroutine) by unconventional means, such as a goto, or a loop control | |
1280 | statement. See L<perlfunc/sort>. | |
1281 | ||
1282 | =item Identifier too long | |
1283 | ||
1284 | (F) Perl limits identifiers (names for variables, functions, etc.) to | |
1285 | 252 characters for simple names, somewhat more for compound names (like | |
1286 | C<$A::B>). You've exceeded Perl's limits. Future versions of Perl are | |
1287 | likely to eliminate these arbitrary limitations. | |
1288 | ||
1289 | =item Illegal character %s (carriage return) | |
1290 | ||
1291 | (F) A carriage return character was found in the input. This is an | |
1292 | error, and not a warning, because carriage return characters can break | |
c47ff5f1 | 1293 | multi-line strings, including here documents (e.g., C<print <<EOF;>). |
6ee623d5 GS |
1294 | |
1295 | =item Illegal switch in PERL5OPT: %s | |
1296 | ||
1297 | (X) The PERL5OPT environment variable may only be used to set the | |
1298 | following switches: B<-[DIMUdmw]>. | |
1299 | ||
1300 | =item Integer overflow in hex number | |
1301 | ||
1302 | (S) The literal hex number you have specified is too big for your | |
1303 | architecture. On a 32-bit architecture the largest hex literal is | |
1304 | 0xFFFFFFFF. | |
1305 | ||
1306 | =item Integer overflow in octal number | |
1307 | ||
1308 | (S) The literal octal number you have specified is too big for your | |
1309 | architecture. On a 32-bit architecture the largest octal literal is | |
1310 | 037777777777. | |
1311 | ||
1312 | =item internal error: glob failed | |
1313 | ||
1314 | (P) Something went wrong with the external program(s) used for C<glob> | |
c47ff5f1 | 1315 | and C<< <*.c> >>. This may mean that your csh (C shell) is |
6ee623d5 GS |
1316 | broken. If so, you should change all of the csh-related variables in |
1317 | config.sh: If you have tcsh, make the variables refer to it as if it | |
1318 | were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all | |
1319 | empty (except that C<d_csh> should be C<'undef'>) so that Perl will | |
1320 | think csh is missing. In either case, after editing config.sh, run | |
1321 | C<./Configure -S> and rebuild Perl. | |
1322 | ||
1323 | =item Invalid conversion in %s: "%s" | |
1324 | ||
1325 | (W) Perl does not understand the given format conversion. | |
1326 | See L<perlfunc/sprintf>. | |
1327 | ||
1328 | =item Invalid type in pack: '%s' | |
1329 | ||
1330 | (F) The given character is not a valid pack type. See L<perlfunc/pack>. | |
1331 | ||
1332 | =item Invalid type in unpack: '%s' | |
1333 | ||
1334 | (F) The given character is not a valid unpack type. See L<perlfunc/unpack>. | |
1335 | ||
1336 | =item Name "%s::%s" used only once: possible typo | |
1337 | ||
1338 | (W) Typographical errors often show up as unique variable names. | |
1339 | If you had a good reason for having a unique name, then just mention | |
1340 | it again somehow to suppress the message (the C<use vars> pragma is | |
1341 | provided for just this purpose). | |
1342 | ||
1343 | =item Null picture in formline | |
1344 | ||
1345 | (F) The first argument to formline must be a valid format picture | |
1346 | specification. It was found to be empty, which probably means you | |
1347 | supplied it an uninitialized value. See L<perlform>. | |
1348 | ||
1349 | =item Offset outside string | |
1350 | ||
1351 | (F) You tried to do a read/write/send/recv operation with an offset | |
1352 | pointing outside the buffer. This is difficult to imagine. | |
1353 | The sole exception to this is that C<sysread()>ing past the buffer | |
1354 | will extend the buffer and zero pad the new area. | |
1355 | ||
1356 | =item Out of memory! | |
1357 | ||
1358 | (X|F) The malloc() function returned 0, indicating there was insufficient | |
1359 | remaining memory (or virtual memory) to satisfy the request. | |
1360 | ||
1361 | The request was judged to be small, so the possibility to trap it | |
1362 | depends on the way Perl was compiled. By default it is not trappable. | |
1363 | However, if compiled for this, Perl may use the contents of C<$^M> as | |
1364 | an emergency pool after die()ing with this message. In this case the | |
1365 | error is trappable I<once>. | |
1366 | ||
1367 | =item Out of memory during request for %s | |
1368 | ||
1369 | (F) The malloc() function returned 0, indicating there was insufficient | |
1370 | remaining memory (or virtual memory) to satisfy the request. However, | |
1371 | the request was judged large enough (compile-time default is 64K), so | |
1372 | a possibility to shut down by trapping this error is granted. | |
1373 | ||
1374 | =item panic: frexp | |
1375 | ||
1376 | (P) The library function frexp() failed, making printf("%f") impossible. | |
1377 | ||
1378 | =item Possible attempt to put comments in qw() list | |
1379 | ||
1380 | (W) qw() lists contain items separated by whitespace; as with literal | |
1381 | strings, comment characters are not ignored, but are instead treated | |
1382 | as literal data. (You may have used different delimiters than the | |
7b8d334a | 1383 | parentheses shown here; braces are also frequently used.) |
6ee623d5 GS |
1384 | |
1385 | You probably wrote something like this: | |
1386 | ||
1387 | @list = qw( | |
1388 | a # a comment | |
1389 | b # another comment | |
1390 | ); | |
1391 | ||
1392 | when you should have written this: | |
1393 | ||
1394 | @list = qw( | |
1395 | a | |
1396 | b | |
1397 | ); | |
1398 | ||
1399 | If you really want comments, build your list the | |
1400 | old-fashioned way, with quotes and commas: | |
1401 | ||
1402 | @list = ( | |
1403 | 'a', # a comment | |
1404 | 'b', # another comment | |
1405 | ); | |
1406 | ||
1407 | =item Possible attempt to separate words with commas | |
1408 | ||
1409 | (W) qw() lists contain items separated by whitespace; therefore commas | |
1410 | aren't needed to separate the items. (You may have used different | |
1411 | delimiters than the parentheses shown here; braces are also frequently | |
1412 | used.) | |
1413 | ||
1414 | You probably wrote something like this: | |
1415 | ||
1416 | qw! a, b, c !; | |
1417 | ||
1418 | which puts literal commas into some of the list items. Write it without | |
1419 | commas if you don't want them to appear in your data: | |
1420 | ||
1421 | qw! a b c !; | |
1422 | ||
1423 | =item Scalar value @%s{%s} better written as $%s{%s} | |
1424 | ||
1425 | (W) You've used a hash slice (indicated by @) to select a single element of | |
1426 | a hash. Generally it's better to ask for a scalar value (indicated by $). | |
1427 | The difference is that C<$foo{&bar}> always behaves like a scalar, both when | |
1428 | assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves | |
1429 | like a list when you assign to it, and provides a list context to its | |
1430 | subscript, which can do weird things if you're expecting only one subscript. | |
1431 | ||
1432 | =item Stub found while resolving method `%s' overloading `%s' in package `%s' | |
1433 | ||
1434 | (P) Overloading resolution over @ISA tree may be broken by importing stubs. | |
c2611fb3 | 1435 | Stubs should never be implicitly created, but explicit calls to C<can> |
6ee623d5 GS |
1436 | may break this. |
1437 | ||
1438 | =item Too late for "B<-T>" option | |
1439 | ||
1440 | (X) The #! line (or local equivalent) in a Perl script contains the | |
1441 | B<-T> option, but Perl was not invoked with B<-T> in its argument | |
1442 | list. This is an error because, by the time Perl discovers a B<-T> in | |
1443 | a script, it's too late to properly taint everything from the | |
1444 | environment. So Perl gives up. | |
1445 | ||
1446 | =item untie attempted while %d inner references still exist | |
1447 | ||
1448 | (W) A copy of the object returned from C<tie> (or C<tied>) was still | |
1449 | valid when C<untie> was called. | |
1450 | ||
1451 | =item Unrecognized character %s | |
1452 | ||
1453 | (F) The Perl parser has no idea what to do with the specified character | |
1454 | in your Perl script (or eval). Perhaps you tried to run a compressed | |
1455 | script, a binary program, or a directory as a Perl program. | |
1456 | ||
1457 | =item Unsupported function fork | |
1458 | ||
1459 | (F) Your version of executable does not support forking. | |
1460 | ||
1461 | Note that under some systems, like OS/2, there may be different flavors of | |
1462 | Perl executables, some of which may support fork, some not. Try changing | |
1463 | the name you call Perl by to C<perl_>, C<perl__>, and so on. | |
1464 | ||
1465 | =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated | |
1466 | ||
1467 | (D) Perl versions before 5.004 misinterpreted any type marker followed | |
1468 | by "$" and a digit. For example, "$$0" was incorrectly taken to mean | |
1469 | "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004. | |
1470 | ||
1471 | However, the developers of Perl 5.004 could not fix this bug completely, | |
1472 | because at least two widely-used modules depend on the old meaning of | |
1473 | "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the | |
1474 | old (broken) way inside strings; but it generates this message as a | |
1475 | warning. And in Perl 5.005, this special treatment will cease. | |
1476 | ||
1477 | =item Value of %s can be "0"; test with defined() | |
1478 | ||
1479 | (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>, | |
1480 | or C<readdir()> as a boolean value. Each of these constructs can return a | |
1481 | value of "0"; that would make the conditional expression false, which is | |
1482 | probably not what you intended. When using these constructs in conditional | |
1483 | expressions, test their values with the C<defined> operator. | |
1484 | ||
1485 | =item Variable "%s" may be unavailable | |
1486 | ||
1487 | (W) An inner (nested) I<anonymous> subroutine is inside a I<named> | |
1488 | subroutine, and outside that is another subroutine; and the anonymous | |
1489 | (innermost) subroutine is referencing a lexical variable defined in | |
1490 | the outermost subroutine. For example: | |
1491 | ||
1492 | sub outermost { my $a; sub middle { sub { $a } } } | |
1493 | ||
1494 | If the anonymous subroutine is called or referenced (directly or | |
1495 | indirectly) from the outermost subroutine, it will share the variable | |
1496 | as you would expect. But if the anonymous subroutine is called or | |
1497 | referenced when the outermost subroutine is not active, it will see | |
1498 | the value of the shared variable as it was before and during the | |
1499 | *first* call to the outermost subroutine, which is probably not what | |
1500 | you want. | |
1501 | ||
1502 | In these circumstances, it is usually best to make the middle | |
1503 | subroutine anonymous, using the C<sub {}> syntax. Perl has specific | |
1504 | support for shared variables in nested anonymous subroutines; a named | |
1505 | subroutine in between interferes with this feature. | |
1506 | ||
1507 | =item Variable "%s" will not stay shared | |
1508 | ||
1509 | (W) An inner (nested) I<named> subroutine is referencing a lexical | |
1510 | variable defined in an outer subroutine. | |
1511 | ||
1512 | When the inner subroutine is called, it will probably see the value of | |
1513 | the outer subroutine's variable as it was before and during the | |
1514 | *first* call to the outer subroutine; in this case, after the first | |
1515 | call to the outer subroutine is complete, the inner and outer | |
1516 | subroutines will no longer share a common value for the variable. In | |
1517 | other words, the variable will no longer be shared. | |
1518 | ||
1519 | Furthermore, if the outer subroutine is anonymous and references a | |
1520 | lexical variable outside itself, then the outer and inner subroutines | |
1521 | will I<never> share the given variable. | |
1522 | ||
1523 | This problem can usually be solved by making the inner subroutine | |
1524 | anonymous, using the C<sub {}> syntax. When inner anonymous subs that | |
1525 | reference variables in outer subroutines are called or referenced, | |
1526 | they are automatically rebound to the current values of such | |
1527 | variables. | |
1528 | ||
1529 | =item Warning: something's wrong | |
1530 | ||
1531 | (W) You passed warn() an empty string (the equivalent of C<warn "">) or | |
1532 | you called it with no args and C<$_> was empty. | |
1533 | ||
1534 | =item Ill-formed logical name |%s| in prime_env_iter | |
1535 | ||
1536 | (W) A warning peculiar to VMS. A logical name was encountered when preparing | |
1537 | to iterate over %ENV which violates the syntactic rules governing logical | |
1538 | names. Since it cannot be translated normally, it is skipped, and will not | |
1539 | appear in %ENV. This may be a benign occurrence, as some software packages | |
1540 | might directly modify logical name tables and introduce nonstandard names, | |
1541 | or it may indicate that a logical name table has been corrupted. | |
1542 | ||
1543 | =item Got an error from DosAllocMem | |
1544 | ||
1545 | (P) An error peculiar to OS/2. Most probably you're using an obsolete | |
1546 | version of Perl, and this should not happen anyway. | |
1547 | ||
1548 | =item Malformed PERLLIB_PREFIX | |
1549 | ||
1550 | (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form | |
1551 | ||
1552 | prefix1;prefix2 | |
1553 | ||
1554 | or | |
1555 | ||
1556 | prefix1 prefix2 | |
1557 | ||
1558 | with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix | |
1559 | of a builtin library search path, prefix2 is substituted. The error | |
1560 | may appear if components are not found, or are too long. See | |
1561 | "PERLLIB_PREFIX" in F<README.os2>. | |
1562 | ||
1563 | =item PERL_SH_DIR too long | |
1564 | ||
1565 | (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the | |
1566 | C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>. | |
1567 | ||
1568 | =item Process terminated by SIG%s | |
1569 | ||
1570 | (W) This is a standard message issued by OS/2 applications, while *nix | |
1571 | applications die in silence. It is considered a feature of the OS/2 | |
1572 | port. One can easily disable this by appropriate sighandlers, see | |
1573 | L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT" | |
1574 | in F<README.os2>. | |
1575 | ||
1576 | =back | |
1577 | ||
1578 | =head1 BUGS | |
1579 | ||
1580 | If you find what you think is a bug, you might check the headers of | |
1581 | recently posted articles in the comp.lang.perl.misc newsgroup. | |
1582 | There may also be information at http://www.perl.com/perl/, the Perl | |
1583 | Home Page. | |
1584 | ||
1585 | If you believe you have an unreported bug, please run the B<perlbug> | |
1586 | program included with your release. Make sure you trim your bug down | |
1587 | to a tiny but sufficient test case. Your bug report, along with the | |
1588 | output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be | |
1589 | analysed by the Perl porting team. | |
1590 | ||
1591 | =head1 SEE ALSO | |
1592 | ||
1593 | The F<Changes> file for exhaustive details on what changed. | |
1594 | ||
1595 | The F<INSTALL> file for how to build Perl. This file has been | |
1596 | significantly updated for 5.004, so even veteran users should | |
1597 | look through it. | |
1598 | ||
1599 | The F<README> file for general stuff. | |
1600 | ||
1601 | The F<Copying> file for copyright information. | |
1602 | ||
1603 | =head1 HISTORY | |
1604 | ||
1605 | Constructed by Tom Christiansen, grabbing material with permission | |
1606 | from innumerable contributors, with kibitzing by more than a few Perl | |
1607 | porters. | |
1608 | ||
1609 | Last update: Wed May 14 11:14:09 EDT 1997 |