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1 | =head1 NAME |
2 | |
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3 | perldelta - what's new for perl5.004 |
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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, Plan9, LynxOS, VMS, OS/2, |
14 | QNX, and AmigaOS. |
15 | |
16 | =head1 Core Changes |
17 | |
18 | Most importantly, many bugs were fixed. See the F<Changes> |
19 | file in the distribution for details. |
20 | |
21 | =head2 Compilation Option: Binary Compatibility With 5.003 |
22 | |
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 |
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26 | might have symbol conflicts if you embed Perl in another application, |
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27 | just as in the 5.003 release. By default, binary compatibility |
28 | is preserved at the expense of symbol table pollution. |
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29 | |
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30 | =head2 Subroutine arguments created only when they're modified |
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31 | |
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32 | In Perl 5.004, nonexistent array and hash elements used as subroutine |
33 | parameters are brought into existence only if they are actually |
34 | assigned to (via C<@_>). |
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35 | |
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36 | Earlier versions of Perl vary in their handling of such arguments. |
37 | Perl versions 5.002 and 5.003 always brought them into existence. |
38 | Perl versions 5.000, 5.001, and 5.002 brought them into existence only |
39 | if they were not the first argument (which was almost certainly a |
40 | bug). Earlier versions of Perl never brought them into existence. |
41 | |
42 | For example, given this code: |
43 | |
44 | undef @a; undef %a; |
45 | sub show { print $_[0] }; |
46 | sub change { $_[0]++ }; |
47 | show($a[2]); |
48 | change($a{b}); |
49 | |
50 | After this code executes in Perl 5.004, $a{b} exists but $a[2] does |
51 | not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed |
52 | (but $a[2]'s value would have been undefined). |
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53 | |
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54 | =head2 Fixed Parsing of $$<digit>, &$<digit>, etc. |
55 | |
56 | A bug in previous versions of Perl 5.0 prevented proper parsing of |
57 | numeric special variables as symbolic references. That bug has been |
58 | fixed. As a result, the string "$$0" is no longer equivalent to |
59 | C<$$."0">, but rather to C<${$0}>. To get the old behavior, change |
60 | "$$" followed by a digit to "${$}". |
61 | |
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62 | =head2 No Resetting of $. on Implicit Close |
63 | |
64 | The documentation for Perl 5.0 has always stated that C<$.> is I<not> |
65 | reset when an already-open file handle is re-opened with no intervening |
66 | call to C<close>. Due to a bug, perl versions 5.000 through 5.0003 |
67 | I<did> reset C<$.> under that circumstance; Perl 5.004 does not. |
68 | |
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69 | =head2 Changes to Tainting Checks |
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70 | |
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71 | A bug in previous versions may have failed to detect some insecure |
72 | conditions when taint checks are turned on. (Taint checks are used |
73 | in setuid or setgid scripts, or when explicitly turned on with the |
74 | C<-T> invocation option.) Although it's unlikely, this may cause a |
75 | previously-working script to now fail -- which should be construed |
76 | as a blessing, since that indicates a potentially-serious security |
77 | hole was just plugged. |
78 | |
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79 | =head2 New Opcode Module and Revised Safe Module |
80 | |
81 | A new Opcode module supports the creation, manipulation and |
82 | application of opcode masks. The revised Safe module has a new API |
83 | and is implemented using the new Opcode module. Please read the new |
84 | Opcode and Safe documentation. |
85 | |
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86 | =head2 Embedding Improvements |
87 | |
88 | In older versions of Perl it was not possible to create more than one |
89 | Perl interpreter instance inside a single process without leaking like a |
90 | sieve and/or crashing. The bugs that caused this behavior have all been |
91 | fixed. However, you still must take care when embedding Perl in a C |
92 | program. See the updated perlembed manpage for tips on how to manage |
93 | your interpreters. |
94 | |
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95 | =head2 Internal Change: FileHandle Class Based on IO::* Classes |
96 | |
97 | File handles are now stored internally as type IO::Handle. The |
98 | FileHandle module is still supported for backwards compatibility, but |
99 | it is now merely a front end to the IO::* modules -- specifically, |
100 | IO::Handle, IO::Seekable, and IO::File. We suggest, but do not |
101 | require, that you use the IO::* modules in new code. |
102 | |
103 | In harmony with this change, C<*GLOB{FILEHANDLE}> is now a |
104 | backward-compatible synonym for C<*STDOUT{IO}>. |
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105 | |
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106 | =head2 Internal Change: PerlIO internal IO abstraction interface |
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107 | |
108 | It is now possible to build Perl with AT&T's sfio IO package |
109 | instead of stdio. See L<perlapio> for more details, and |
110 | the F<INSTALL> file for how to use it. |
111 | |
112 | =head2 New and Changed Built-in Variables |
113 | |
114 | =over |
115 | |
116 | =item $^E |
117 | |
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118 | Extended error message on some platforms. (Also known as |
119 | $EXTENDED_OS_ERROR if you C<use English>). |
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120 | |
121 | =item $^H |
122 | |
123 | The current set of syntax checks enabled by C<use strict>. See the |
124 | documentation of C<strict> for more details. Not actually new, but |
125 | newly documented. |
126 | Because it is intended for internal use by Perl core components, |
127 | there is no C<use English> long name for this variable. |
128 | |
129 | =item $^M |
130 | |
131 | By default, running out of memory it is not trappable. However, if |
132 | compiled for this, Perl may use the contents of C<$^M> as an emergency |
133 | pool after die()ing with this message. Suppose that your Perl were |
134 | compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then |
135 | |
136 | $^M = 'a' x (1<<16); |
137 | |
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138 | would allocate a 64K buffer for use when in emergency. |
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139 | See the F<INSTALL> file for information on how to enable this option. |
140 | As a disincentive to casual use of this advanced feature, |
141 | there is no C<use English> long name for this variable. |
142 | |
143 | =back |
144 | |
145 | =head2 New and Changed Built-in Functions |
146 | |
147 | =over |
148 | |
149 | =item delete on slices |
150 | |
151 | This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>) |
152 | |
153 | =item flock |
154 | |
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155 | is now supported on more platforms, prefers fcntl to lockf when |
156 | emulating, and always flushes before (un)locking. |
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157 | |
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158 | =item printf and sprintf |
159 | |
160 | now support "%i" as a synonym for "%d", and the "h" modifier. |
161 | So "%hi" means "short integer in decimal", and "%ho" means |
162 | "unsigned short integer as octal". |
163 | |
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164 | =item keys as an lvalue |
165 | |
166 | As an lvalue, C<keys> allows you to increase the number of hash buckets |
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167 | allocated for the given hash. This can gain you a measure of efficiency if |
168 | you know the hash is going to get big. (This is similar to pre-extending |
169 | an array by assigning a larger number to $#array.) If you say |
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170 | |
171 | keys %hash = 200; |
172 | |
173 | then C<%hash> will have at least 200 buckets allocated for it. These |
174 | buckets will be retained even if you do C<%hash = ()>; use C<undef |
175 | %hash> if you want to free the storage while C<%hash> is still in scope. |
176 | You can't shrink the number of buckets allocated for the hash using |
177 | C<keys> in this way (but you needn't worry about doing this by accident, |
178 | as trying has no effect). |
179 | |
180 | =item my() in Control Structures |
181 | |
182 | You can now use my() (with or without the parentheses) in the control |
183 | expressions of control structures such as: |
184 | |
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185 | while (defined(my $line = <>)) { |
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186 | $line = lc $line; |
187 | } continue { |
188 | print $line; |
189 | } |
190 | |
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191 | if ((my $answer = <STDIN>) =~ /^y(es)?$/i) { |
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192 | user_agrees(); |
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193 | } elsif ($answer =~ /^n(o)?$/i) { |
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194 | user_disagrees(); |
195 | } else { |
196 | chomp $answer; |
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197 | die "`$answer' is neither `yes' nor `no'"; |
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198 | } |
199 | |
200 | Also, you can declare a foreach loop control variable as lexical by |
201 | preceding it with the word "my". For example, in: |
202 | |
203 | foreach my $i (1, 2, 3) { |
204 | some_function(); |
205 | } |
206 | |
207 | $i is a lexical variable, and the scope of $i extends to the end of |
208 | the loop, but not beyond it. |
209 | |
210 | Note that you still cannot use my() on global punctuation variables |
211 | such as $_ and the like. |
212 | |
213 | =item unpack() and pack() |
214 | |
215 | A new format 'w' represents a BER compressed integer (as defined in |
216 | ASN.1). Its format is a sequence of one or more bytes, each of which |
217 | provides seven bits of the total value, with the most significant |
218 | first. Bit eight of each byte is set, except for the last byte, in |
219 | which bit eight is clear. |
220 | |
221 | =item use VERSION |
222 | |
223 | If the first argument to C<use> is a number, it is treated as a version |
224 | number instead of a module name. If the version of the Perl interpreter |
225 | is less than VERSION, then an error message is printed and Perl exits |
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226 | immediately. Because C<use> occurs at compile time, this check happens |
227 | immediately during the compilation process, unlike C<require VERSION>, |
228 | which waits until run-time for the check. This is often useful if you |
229 | need to check the current Perl version before C<use>ing library modules |
230 | which have changed in incompatible ways from older versions of Perl. |
231 | (We try not to do this more than we have to.) |
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232 | |
233 | =item use Module VERSION LIST |
234 | |
235 | If the VERSION argument is present between Module and LIST, then the |
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236 | C<use> will call the VERSION method in class Module with the given |
237 | version as an argument. The default VERSION method, inherited from |
238 | the Universal class, croaks if the given version is larger than the |
239 | value of the variable $Module::VERSION. (Note that there is not a |
240 | comma after VERSION!) |
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241 | |
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242 | This version-checking mechanism is similar to the one currently used |
243 | in the Exporter module, but it is faster and can be used with modules |
244 | that don't use the Exporter. It is the recommended method for new |
245 | code. |
246 | |
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247 | =item prototype(FUNCTION) |
248 | |
249 | Returns the prototype of a function as a string (or C<undef> if the |
250 | function has no prototype). FUNCTION is a reference to or the name of the |
251 | function whose prototype you want to retrieve. |
252 | (Not actually new; just never documented before.) |
253 | |
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254 | =item srand |
255 | |
256 | The default seed for C<srand>, which used to be C<time>, has been changed. |
257 | Now it's a heady mix of difficult-to-predict system-dependent values, |
258 | which should be sufficient for most everyday purposes. |
259 | |
260 | Previous to version 5.004, calling C<rand> without first calling C<srand> |
261 | would yield the same sequence of random numbers on most or all machines. |
262 | Now, when perl sees that you're calling C<rand> and haven't yet called |
263 | C<srand>, it calls C<srand> with the default seed. You should still call |
264 | C<srand> manually if your code might ever be run on a pre-5.004 system, |
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265 | of course, or if you want a seed other than the default. |
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266 | |
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267 | =item $_ as Default |
268 | |
269 | Functions documented in the Camel to default to $_ now in |
270 | fact do, and all those that do are so documented in L<perlfunc>. |
271 | |
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272 | =item C<m//g> does not trigger a pos() reset on failure |
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273 | |
274 | The C<m//g> match iteration construct used to reset the iteration |
275 | when it failed to match (so that the next C<m//g> match would start at |
276 | the beginning of the string). You now have to explicitly do a |
277 | C<pos $str = 0;> to reset the "last match" position, or modify the |
278 | string in some way. This change makes it practical to chain C<m//g> |
279 | matches together in conjunction with ordinary matches using the C<\G> |
280 | zero-width assertion. See L<perlop> and L<perlre>. |
281 | |
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282 | =item C<m//x> ignores whitespace before ?*+{} |
283 | |
284 | The C<m//x> construct has always been intended to ignore all unescaped |
285 | whitespace. However, before Perl 5.004, whitespace had the effect of |
286 | esacping repeat modifier like "*" or "?". For example, C</a *b/x> was |
287 | (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004. |
288 | |
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289 | =item nested C<sub{}> closures work now |
290 | |
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291 | Prior to the 5.004 release, nested anonymous functions didn't work |
292 | right. They do now. |
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293 | |
294 | =item formats work right on changing lexicals |
295 | |
296 | Just like anonymous functions that contain lexical variables |
297 | that change (like a lexical index variable for a C<foreach> loop), |
298 | formats now work properly. For example, this silently failed |
299 | before, and is fine now: |
300 | |
301 | my $i; |
302 | foreach $i ( 1 .. 10 ) { |
303 | format = |
304 | my i is @# |
305 | $i |
306 | . |
307 | write; |
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308 | } |
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309 | |
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310 | =back |
311 | |
312 | =head2 New Built-in Methods |
313 | |
314 | The C<UNIVERSAL> package automatically contains the following methods that |
315 | are inherited by all other classes: |
316 | |
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317 | =over |
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318 | |
319 | =item isa(CLASS) |
320 | |
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321 | C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS> |
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322 | |
323 | C<isa> is also exportable and can be called as a sub with two arguments. This |
324 | allows the ability to check what a reference points to. Example: |
325 | |
326 | use UNIVERSAL qw(isa); |
327 | |
328 | if(isa($ref, 'ARRAY')) { |
329 | ... |
330 | } |
331 | |
332 | =item can(METHOD) |
333 | |
334 | C<can> checks to see if its object has a method called C<METHOD>, |
335 | if it does then a reference to the sub is returned; if it does not then |
336 | I<undef> is returned. |
337 | |
338 | =item VERSION( [NEED] ) |
339 | |
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340 | C<VERSION> returns the version number of the class (package). If the |
341 | NEED argument is given then it will check that the current version (as |
342 | defined by the $VERSION variable in the given package) not less than |
343 | NEED; it will die if this is not the case. This method is normally |
344 | called as a class method. This method is called automatically by the |
345 | C<VERSION> form of C<use>. |
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346 | |
347 | use A 1.2 qw(some imported subs); |
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348 | # implies: |
349 | A->VERSION(1.2); |
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350 | |
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351 | =back |
352 | |
353 | B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and |
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354 | C<isa> uses a very similar method and caching strategy. This may cause |
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355 | strange effects if the Perl code dynamically changes @ISA in any package. |
356 | |
357 | You may add other methods to the UNIVERSAL class via Perl or XS code. |
358 | You do not need to C<use UNIVERSAL> in order to make these methods |
359 | available to your program. This is necessary only if you wish to |
360 | have C<isa> available as a plain subroutine in the current package. |
361 | |
362 | =head2 TIEHANDLE Now Supported |
363 | |
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364 | See L<perltie> for other kinds of tie()s. |
365 | |
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366 | =over |
367 | |
368 | =item TIEHANDLE classname, LIST |
369 | |
370 | This is the constructor for the class. That means it is expected to |
371 | return an object of some sort. The reference can be used to |
372 | hold some internal information. |
373 | |
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374 | sub TIEHANDLE { |
375 | print "<shout>\n"; |
376 | my $i; |
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377 | return bless \$i, shift; |
378 | } |
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379 | |
380 | =item PRINT this, LIST |
381 | |
382 | This method will be triggered every time the tied handle is printed to. |
383 | Beyond its self reference it also expects the list that was passed to |
384 | the print function. |
385 | |
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386 | sub PRINT { |
387 | $r = shift; |
388 | $$r++; |
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389 | return print join( $, => map {uc} @_), $\; |
390 | } |
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391 | |
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392 | =item READ this LIST |
393 | |
394 | This method will be called when the handle is read from via the C<read> |
395 | or C<sysread> functions. |
396 | |
397 | sub READ { |
398 | $r = shift; |
399 | my($buf,$len,$offset) = @_; |
400 | print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset"; |
401 | } |
402 | |
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403 | =item READLINE this |
404 | |
405 | This method will be called when the handle is read from. The method |
406 | should return undef when there is no more data. |
407 | |
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408 | sub READLINE { |
409 | $r = shift; |
410 | return "PRINT called $$r times\n" |
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411 | } |
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412 | |
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413 | =item GETC this |
414 | |
415 | This method will be called when the C<getc> function is called. |
416 | |
417 | sub GETC { print "Don't GETC, Get Perl"; return "a"; } |
418 | |
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419 | =item DESTROY this |
420 | |
421 | As with the other types of ties, this method will be called when the |
422 | tied handle is about to be destroyed. This is useful for debugging and |
423 | possibly for cleaning up. |
424 | |
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425 | sub DESTROY { |
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426 | print "</shout>\n"; |
427 | } |
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428 | |
429 | =back |
430 | |
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431 | =head2 Malloc Enhancements |
432 | |
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433 | Four new compilation flags are recognized by malloc.c. (They have no |
434 | effect if perl is compiled with system malloc().) |
435 | |
436 | =over |
437 | |
438 | =item -DDEBUGGING_MSTATS |
439 | |
440 | If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print |
441 | memory statistics at runtime by running Perl thusly: |
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442 | |
443 | env PERL_DEBUG_MSTATS=2 perl your_script_here |
444 | |
445 | The value of 2 means to print statistics after compilation and on |
446 | exit; with a value of 1, the statistics ares printed only on exit. |
447 | (If you want the statistics at an arbitrary time, you'll need to |
448 | install the optional module Devel::Peek.) |
449 | |
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450 | =item -DEMERGENCY_SBRK |
451 | |
452 | If this macro is defined, running out of memory need not be a fatal |
453 | error: a memory pool can allocated by assigning to the special |
454 | variable C<$^M>. See L<"$^M">. |
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455 | |
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456 | =item -DPACK_MALLOC |
457 | |
458 | Perl memory allocation is by bucket with sizes close to powers of two. |
459 | Because of these malloc overhead may be big, especially for data of |
460 | size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses |
461 | a slightly different algorithm for small allocations (up to 64 bytes |
462 | long), which makes it possible to have overhead down to 1 byte for |
463 | allocations which are powers of two (and appear quite often). |
464 | |
465 | Expected memory savings (with 8-byte alignment in C<alignbytes>) is |
466 | about 20% for typical Perl usage. Expected slowdown due to additional |
467 | malloc overhead is in fractions of a percent (hard to measure, because |
468 | of the effect of saved memory on speed). |
469 | |
470 | =item -DTWO_POT_OPTIMIZE |
471 | |
472 | Similarly to C<PACK_MALLOC>, this macro improves allocations of data |
473 | with size close to a power of two; but this works for big allocations |
474 | (starting with 16K by default). Such allocations are typical for big |
475 | hashes and special-purpose scripts, especially image processing. |
476 | |
477 | On recent systems, the fact that perl requires 2M from system for 1M |
478 | allocation will not affect speed of execution, since the tail of such |
479 | a chunk is not going to be touched (and thus will not require real |
480 | memory). However, it may result in a premature out-of-memory error. |
481 | So if you will be manipulating very large blocks with sizes close to |
482 | powers of two, it would be wise to define this macro. |
483 | |
484 | Expected saving of memory is 0-100% (100% in applications which |
485 | require most memory in such 2**n chunks); expected slowdown is |
486 | negligible. |
487 | |
488 | =back |
489 | |
490 | =head2 Miscellaneous Efficiency Enhancements |
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491 | |
492 | Functions that have an empty prototype and that do nothing but return |
493 | a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>). |
494 | |
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495 | Each unique hash key is only allocated once, no matter how many hashes |
496 | have an entry with that key. So even if you have 100 copies of the |
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497 | same hash, the hash keys never have to be reallocated. |
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498 | |
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499 | =head1 Pragmata |
500 | |
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501 | Four new pragmatic modules exist: |
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502 | |
503 | =over |
504 | |
505 | =item use blib |
506 | |
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507 | =item use blib 'dir' |
508 | |
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509 | Looks for MakeMaker-like I<'blib'> directory structure starting in |
510 | I<dir> (or current directory) and working back up to five levels of |
511 | parent directories. |
512 | |
513 | Intended for use on command line with B<-M> option as a way of testing |
514 | arbitrary scripts against an uninstalled version of a package. |
515 | |
516 | =item use locale |
517 | |
518 | Tells the compiler to enable (or disable) the use of POSIX locales for |
519 | built-in operations. |
520 | |
521 | When C<use locale> is in effect, the current LC_CTYPE locale is used |
522 | for regular expressions and case mapping; LC_COLLATE for string |
523 | ordering; and LC_NUMERIC for numeric formating in printf and sprintf |
524 | (but B<not> in print). LC_NUMERIC is always used in write, since |
525 | lexical scoping of formats is problematic at best. |
526 | |
527 | Each C<use locale> or C<no locale> affects statements to the end of |
528 | the enclosing BLOCK or, if not inside a BLOCK, to the end of the |
529 | current file. Locales can be switched and queried with |
530 | POSIX::setlocale(). |
531 | |
532 | See L<perllocale> for more information. |
533 | |
534 | =item use ops |
535 | |
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536 | Disable unsafe opcodes, or any named opcodes, when compiling Perl code. |
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537 | |
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538 | =item use vmsish |
539 | |
540 | Enable VMS-specific language features. Currently, there are three |
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541 | VMS-specific features available: 'status', which makes C<$?> and |
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542 | C<system> return genuine VMS status values instead of emulating POSIX; |
543 | 'exit', which makes C<exit> take a genuine VMS status value instead of |
544 | assuming that C<exit 1> is an error; and 'time', which makes all times |
545 | relative to the local time zone, in the VMS tradition. |
546 | |
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547 | =back |
548 | |
549 | =head1 Modules |
550 | |
f86702cc |
551 | =head2 Installation Directories |
552 | |
553 | The I<installperl> script now places the Perl source files for |
554 | extensions in the architecture-specific library directory, which is |
555 | where the shared libraries for extensions have always been. This |
556 | change is intended to allow administrators to keep the Perl 5.004 |
557 | library directory unchanged from a previous version, without running |
558 | the risk of binary incompatibility between extensions' Perl source and |
559 | shared libraries. |
560 | |
774d564b |
561 | =head2 Fcntl |
562 | |
563 | New constants in the existing Fcntl modules are now supported, |
564 | provided that your operating system happens to support them: |
565 | |
566 | F_GETOWN F_SETOWN |
2ae324a7 |
567 | O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC |
774d564b |
568 | O_EXLOCK O_SHLOCK |
569 | |
0a753a76 |
570 | These constants are intended for use with the Perl operators sysopen() |
571 | and fcntl() and the basic database modules like SDBM_File. For the |
572 | exact meaning of these and other Fcntl constants please refer to your |
573 | operating system's documentation for fcntl() and open(). |
574 | |
575 | In addition, the Fcntl module now provides these constants for use |
576 | with the Perl operator flock(): |
577 | |
578 | LOCK_SH LOCK_EX LOCK_NB LOCK_UN |
579 | |
580 | These constants are defined in all environments (because where there is |
581 | no flock() system call, Perl emulates it). However, for historical |
582 | reasons, these constants are not exported unless they are explicitly |
583 | requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>). |
584 | |
5f05dabc |
585 | =head2 Module Information Summary |
586 | |
774d564b |
587 | Brand new modules, arranged by topic rather than strictly |
588 | alphabetically: |
589 | |
590 | CPAN interface to Comprehensive Perl Archive Network |
591 | CPAN::FirstTime create a CPAN configuration file |
592 | CPAN::Nox run CPAN while avoiding compiled extensions |
5f05dabc |
593 | |
594 | IO.pm Top-level interface to IO::* classes |
595 | IO/File.pm IO::File extension Perl module |
596 | IO/Handle.pm IO::Handle extension Perl module |
597 | IO/Pipe.pm IO::Pipe extension Perl module |
598 | IO/Seekable.pm IO::Seekable extension Perl module |
599 | IO/Select.pm IO::Select extension Perl module |
600 | IO/Socket.pm IO::Socket extension Perl module |
601 | |
602 | Opcode.pm Disable named opcodes when compiling Perl code |
603 | |
604 | ExtUtils/Embed.pm Utilities for embedding Perl in C programs |
605 | ExtUtils/testlib.pm Fixes up @INC to use just-built extension |
606 | |
5f05dabc |
607 | FindBin.pm Find path of currently executing program |
608 | |
609 | Class/Template.pm Structure/member template builder |
610 | File/stat.pm Object-oriented wrapper around CORE::stat |
611 | Net/hostent.pm Object-oriented wrapper around CORE::gethost* |
612 | Net/netent.pm Object-oriented wrapper around CORE::getnet* |
613 | Net/protoent.pm Object-oriented wrapper around CORE::getproto* |
614 | Net/servent.pm Object-oriented wrapper around CORE::getserv* |
615 | Time/gmtime.pm Object-oriented wrapper around CORE::gmtime |
616 | Time/localtime.pm Object-oriented wrapper around CORE::localtime |
617 | Time/tm.pm Perl implementation of "struct tm" for {gm,local}time |
618 | User/grent.pm Object-oriented wrapper around CORE::getgr* |
619 | User/pwent.pm Object-oriented wrapper around CORE::getpw* |
620 | |
774d564b |
621 | Tie/RefHash.pm Base class for tied hashes with references as keys |
7a4c00b4 |
622 | |
5f05dabc |
623 | UNIVERSAL.pm Base class for *ALL* classes |
624 | |
625 | =head2 IO |
626 | |
627 | The IO module provides a simple mechanism to load all of the IO modules at one |
628 | go. Currently this includes: |
629 | |
630 | IO::Handle |
631 | IO::Seekable |
632 | IO::File |
633 | IO::Pipe |
634 | IO::Socket |
635 | |
636 | For more information on any of these modules, please see its |
637 | respective documentation. |
638 | |
639 | =head2 Math::Complex |
640 | |
641 | The Math::Complex module has been totally rewritten, and now supports |
642 | more operations. These are overloaded: |
643 | |
644 | + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify) |
645 | |
646 | And these functions are now exported: |
647 | |
648 | pi i Re Im arg |
649 | log10 logn cbrt root |
650 | tan cotan asin acos atan acotan |
651 | sinh cosh tanh cotanh asinh acosh atanh acotanh |
652 | cplx cplxe |
653 | |
0a753a76 |
654 | =head2 DB_File |
655 | |
656 | There have been quite a few changes made to DB_File. Here are a few of |
657 | the highlights: |
658 | |
659 | =over |
660 | |
661 | =item * |
662 | |
663 | Fixed a handful of bugs. |
664 | |
665 | =item * |
666 | |
667 | By public demand, added support for the standard hash function exists(). |
668 | |
669 | =item * |
670 | |
671 | Made it compatible with Berkeley DB 1.86. |
672 | |
673 | =item * |
674 | |
675 | Made negative subscripts work with RECNO interface. |
676 | |
677 | =item * |
678 | |
679 | Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default |
680 | mode from 0640 to 0666. |
681 | |
682 | =item * |
683 | |
684 | Made DB_File automatically import the open() constants (O_RDWR, |
685 | O_CREAT etc.) from Fcntl, if available. |
686 | |
687 | =item * |
688 | |
689 | Updated documentation. |
690 | |
691 | =back |
692 | |
693 | Refer to the HISTORY section in DB_File.pm for a complete list of |
694 | changes. Everything after DB_File 1.01 has been added since 5.003. |
695 | |
696 | =head2 Net::Ping |
697 | |
698 | Major rewrite - support added for both udp echo and real icmp pings. |
699 | |
5f05dabc |
700 | =head2 Overridden Built-ins |
701 | |
702 | Many of the Perl built-ins returning lists now have |
703 | object-oriented overrides. These are: |
704 | |
705 | File::stat |
706 | Net::hostent |
707 | Net::netent |
708 | Net::protoent |
709 | Net::servent |
710 | Time::gmtime |
711 | Time::localtime |
712 | User::grent |
713 | User::pwent |
714 | |
715 | For example, you can now say |
716 | |
717 | use File::stat; |
718 | use User::pwent; |
719 | $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid); |
720 | |
774d564b |
721 | =head1 Utility Changes |
5f05dabc |
722 | |
774d564b |
723 | =head2 xsubpp |
5f05dabc |
724 | |
0a753a76 |
725 | =over |
726 | |
774d564b |
727 | =item C<void> XSUBs now default to returning nothing |
728 | |
729 | Due to a documentation/implementation bug in previous versions of |
730 | Perl, XSUBs with a return type of C<void> have actually been |
731 | returning one value. Usually that value was the GV for the XSUB, |
732 | but sometimes it was some already freed or reused value, which would |
733 | sometimes lead to program failure. |
734 | |
735 | In Perl 5.004, if an XSUB is declared as returning C<void>, it |
736 | actually returns no value, i.e. an empty list (though there is a |
737 | backward-compatibility exception; see below). If your XSUB really |
738 | does return an SV, you should give it a return type of C<SV *>. |
739 | |
740 | For backward compatibility, I<xsubpp> tries to guess whether a |
741 | C<void> XSUB is really C<void> or if it wants to return an C<SV *>. |
742 | It does so by examining the text of the XSUB: if I<xsubpp> finds |
743 | what looks like an assignment to C<ST(0)>, it assumes that the |
744 | XSUB's return type is really C<SV *>. |
5f05dabc |
745 | |
0a753a76 |
746 | =back |
747 | |
748 | =head1 C Language API Changes |
749 | |
750 | =over |
751 | |
752 | =item C<gv_fetchmethod> and C<perl_call_sv> |
753 | |
754 | The C<gv_fetchmethod> function finds a method for an object, just like |
755 | in Perl 5.003. The GV it returns may be a method cache entry. |
756 | However, in Perl 5.004, method cache entries are not visible to users; |
757 | therefore, they can no longer be passed directly to C<perl_call_sv>. |
758 | Instead, you should use the C<GvCV> macro on the GV to extract its CV, |
759 | and pass the CV to C<perl_call_sv>. |
760 | |
761 | The most likely symptom of passing the result of C<gv_fetchmethod> to |
762 | C<perl_call_sv> is Perl's producing an "Undefined subroutine called" |
763 | error on the I<second> call to a given method (since there is no cache |
764 | on the first call). |
765 | |
1e422769 |
766 | =item Extended API for manipulating hashes |
767 | |
768 | Internal handling of hash keys has changed. The old hashtable API is |
769 | still fully supported, and will likely remain so. The additions to the |
770 | API allow passing keys as C<SV*>s, so that C<tied> hashes can be given |
771 | real scalars as keys rather than plain strings (non-tied hashes still |
772 | can only use strings as keys). New extensions must use the new hash |
773 | access functions and macros if they wish to use C<SV*> keys. These |
774 | additions also make it feasible to manipulate C<HE*>s (hash entries), |
775 | which can be more efficient. See L<perlguts> for details. |
776 | |
0a753a76 |
777 | =back |
778 | |
5f05dabc |
779 | =head1 Documentation Changes |
780 | |
781 | Many of the base and library pods were updated. These |
782 | new pods are included in section 1: |
783 | |
0a753a76 |
784 | =over |
5f05dabc |
785 | |
774d564b |
786 | =item L<perldelta> |
5f05dabc |
787 | |
71be2cbc |
788 | This document. |
5f05dabc |
789 | |
71be2cbc |
790 | =item L<perllocale> |
5f05dabc |
791 | |
71be2cbc |
792 | Locale support (internationalization and localization). |
5f05dabc |
793 | |
794 | =item L<perltoot> |
795 | |
796 | Tutorial on Perl OO programming. |
797 | |
71be2cbc |
798 | =item L<perlapio> |
799 | |
800 | Perl internal IO abstraction interface. |
801 | |
5f05dabc |
802 | =item L<perldebug> |
803 | |
804 | Although not new, this has been massively updated. |
805 | |
806 | =item L<perlsec> |
807 | |
808 | Although not new, this has been massively updated. |
809 | |
810 | =back |
811 | |
812 | =head1 New Diagnostics |
813 | |
814 | Several new conditions will trigger warnings that were |
815 | silent before. Some only affect certain platforms. |
2ae324a7 |
816 | The following new warnings and errors outline these. |
774d564b |
817 | These messages are classified as follows (listed in |
818 | increasing order of desperation): |
819 | |
820 | (W) A warning (optional). |
821 | (D) A deprecation (optional). |
822 | (S) A severe warning (mandatory). |
823 | (F) A fatal error (trappable). |
824 | (P) An internal error you should never see (trappable). |
825 | (X) A very fatal error (non-trappable). |
826 | (A) An alien error message (not generated by Perl). |
5f05dabc |
827 | |
0a753a76 |
828 | =over |
5f05dabc |
829 | |
830 | =item "my" variable %s masks earlier declaration in same scope |
831 | |
832 | (S) A lexical variable has been redeclared in the same scope, effectively |
833 | eliminating all access to the previous instance. This is almost always |
834 | a typographical error. Note that the earlier variable will still exist |
835 | until the end of the scope or until all closure referents to it are |
836 | destroyed. |
837 | |
774d564b |
838 | =item %s argument is not a HASH element or slice |
839 | |
840 | (F) The argument to delete() must be either a hash element, such as |
841 | |
842 | $foo{$bar} |
843 | $ref->[12]->{"susie"} |
844 | |
845 | or a hash slice, such as |
846 | |
847 | @foo{$bar, $baz, $xyzzy} |
848 | @{$ref->[12]}{"susie", "queue"} |
849 | |
5f05dabc |
850 | =item Allocation too large: %lx |
851 | |
852 | (X) You can't allocate more than 64K on an MSDOS machine. |
853 | |
854 | =item Allocation too large |
855 | |
856 | (F) You can't allocate more than 2^31+"small amount" bytes. |
857 | |
858 | =item Attempt to free non-existent shared string |
859 | |
860 | (P) Perl maintains a reference counted internal table of strings to |
861 | optimize the storage and access of hash keys and other strings. This |
862 | indicates someone tried to decrement the reference count of a string |
863 | that can no longer be found in the table. |
864 | |
865 | =item Attempt to use reference as lvalue in substr |
866 | |
867 | (W) You supplied a reference as the first argument to substr() used |
868 | as an lvalue, which is pretty strange. Perhaps you forgot to |
869 | dereference it first. See L<perlfunc/substr>. |
870 | |
871 | =item Unsupported function fork |
872 | |
873 | (F) Your version of executable does not support forking. |
874 | |
875 | Note that under some systems, like OS/2, there may be different flavors of |
876 | Perl executables, some of which may support fork, some not. Try changing |
877 | the name you call Perl by to C<perl_>, C<perl__>, and so on. |
878 | |
879 | =item Ill-formed logical name |%s| in prime_env_iter |
880 | |
881 | (W) A warning peculiar to VMS. A logical name was encountered when preparing |
882 | to iterate over %ENV which violates the syntactic rules governing logical |
883 | names. Since it cannot be translated normally, it is skipped, and will not |
884 | appear in %ENV. This may be a benign occurrence, as some software packages |
885 | might directly modify logical name tables and introduce non-standard names, |
886 | or it may indicate that a logical name table has been corrupted. |
887 | |
774d564b |
888 | =item Can't use bareword ("%s") as %s ref while "strict refs" in use |
889 | |
890 | (F) Only hard references are allowed by "strict refs". Symbolic references |
891 | are disallowed. See L<perlref>. |
892 | |
893 | =item Constant subroutine %s redefined |
894 | |
895 | (S) You redefined a subroutine which had previously been eligible for |
896 | inlining. See L<perlsub/"Constant Functions"> for commentary and |
897 | workarounds. |
898 | |
899 | =item Died |
900 | |
901 | (F) You passed die() an empty string (the equivalent of C<die "">) or |
902 | you called it with no args and both C<$@> and C<$_> were empty. |
903 | |
5f05dabc |
904 | =item Integer overflow in hex number |
905 | |
906 | (S) The literal hex number you have specified is too big for your |
907 | architecture. On a 32-bit architecture the largest hex literal is |
908 | 0xFFFFFFFF. |
909 | |
910 | =item Integer overflow in octal number |
911 | |
912 | (S) The literal octal number you have specified is too big for your |
913 | architecture. On a 32-bit architecture the largest octal literal is |
914 | 037777777777. |
915 | |
774d564b |
916 | =item Name "%s::%s" used only once: possible typo |
917 | |
918 | (W) Typographical errors often show up as unique variable names. |
919 | If you had a good reason for having a unique name, then just mention |
920 | it again somehow to suppress the message (the C<use vars> pragma is |
921 | provided for just this purpose). |
922 | |
5f05dabc |
923 | =item Null picture in formline |
924 | |
925 | (F) The first argument to formline must be a valid format picture |
926 | specification. It was found to be empty, which probably means you |
927 | supplied it an uninitialized value. See L<perlform>. |
928 | |
929 | =item Offset outside string |
930 | |
931 | (F) You tried to do a read/write/send/recv operation with an offset |
932 | pointing outside the buffer. This is difficult to imagine. |
933 | The sole exception to this is that C<sysread()>ing past the buffer |
934 | will extend the buffer and zero pad the new area. |
935 | |
774d564b |
936 | =item Stub found while resolving method `%s' overloading `%s' in package `%s' |
937 | |
938 | (P) Overloading resolution over @ISA tree may be broken by importing stubs. |
939 | Stubs should never be implicitely created, but explicit calls to C<can> |
940 | may break this. |
941 | |
942 | =item Cannot resolve method `%s' overloading `%s' in package `s' |
943 | |
944 | (P) Internal error trying to resolve overloading specified by a method |
945 | name (as opposed to a subroutine reference). |
946 | |
5f05dabc |
947 | =item Out of memory! |
948 | |
949 | (X|F) The malloc() function returned 0, indicating there was insufficient |
950 | remaining memory (or virtual memory) to satisfy the request. |
951 | |
952 | The request was judged to be small, so the possibility to trap it |
953 | depends on the way Perl was compiled. By default it is not trappable. |
954 | However, if compiled for this, Perl may use the contents of C<$^M> as |
955 | an emergency pool after die()ing with this message. In this case the |
956 | error is trappable I<once>. |
957 | |
958 | =item Out of memory during request for %s |
959 | |
960 | (F) The malloc() function returned 0, indicating there was insufficient |
961 | remaining memory (or virtual memory) to satisfy the request. However, |
962 | the request was judged large enough (compile-time default is 64K), so |
963 | a possibility to shut down by trapping this error is granted. |
964 | |
965 | =item Possible attempt to put comments in qw() list |
966 | |
774d564b |
967 | (W) qw() lists contain items separated by whitespace; as with literal |
968 | strings, comment characters are not ignored, but are instead treated |
969 | as literal data. (You may have used different delimiters than the |
970 | exclamation marks parentheses shown here; braces are also frequently |
971 | used.) |
972 | |
973 | You probably wrote something like this: |
5f05dabc |
974 | |
2ae324a7 |
975 | @list = qw( |
774d564b |
976 | a # a comment |
5f05dabc |
977 | b # another comment |
774d564b |
978 | ); |
5f05dabc |
979 | |
980 | when you should have written this: |
981 | |
774d564b |
982 | @list = qw( |
2ae324a7 |
983 | a |
5f05dabc |
984 | b |
774d564b |
985 | ); |
986 | |
987 | If you really want comments, build your list the |
988 | old-fashioned way, with quotes and commas: |
989 | |
990 | @list = ( |
991 | 'a', # a comment |
992 | 'b', # another comment |
993 | ); |
5f05dabc |
994 | |
995 | =item Possible attempt to separate words with commas |
996 | |
774d564b |
997 | (W) qw() lists contain items separated by whitespace; therefore commas |
998 | aren't needed to separate the items. (You may have used different |
999 | delimiters than the parentheses shown here; braces are also frequently |
1000 | used.) |
5f05dabc |
1001 | |
2ae324a7 |
1002 | You probably wrote something like this: |
5f05dabc |
1003 | |
774d564b |
1004 | qw! a, b, c !; |
1005 | |
1006 | which puts literal commas into some of the list items. Write it without |
1007 | commas if you don't want them to appear in your data: |
1008 | |
1009 | qw! a b c !; |
5f05dabc |
1010 | |
774d564b |
1011 | =item Scalar value @%s{%s} better written as $%s{%s} |
1012 | |
1013 | (W) You've used a hash slice (indicated by @) to select a single element of |
1014 | a hash. Generally it's better to ask for a scalar value (indicated by $). |
1015 | The difference is that C<$foo{&bar}> always behaves like a scalar, both when |
1016 | assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves |
1017 | like a list when you assign to it, and provides a list context to its |
1018 | subscript, which can do weird things if you're expecting only one subscript. |
5f05dabc |
1019 | |
1020 | =item untie attempted while %d inner references still exist |
1021 | |
1022 | (W) A copy of the object returned from C<tie> (or C<tied>) was still |
1023 | valid when C<untie> was called. |
1024 | |
774d564b |
1025 | =item Value of %s construct can be "0"; test with defined() |
1026 | |
1027 | (W) In a conditional expression, you used <HANDLE>, <*> (glob), or |
1028 | C<readdir> as a boolean value. Each of these constructs can return a |
1029 | value of "0"; that would make the conditional expression false, which |
1030 | is probably not what you intended. When using these constructs in |
1031 | conditional expressions, test their values with the C<defined> operator. |
1032 | |
1033 | =item Variable "%s" may be unavailable |
1034 | |
1035 | (W) An inner (nested) I<anonymous> subroutine is inside a I<named> |
1036 | subroutine, and outside that is another subroutine; and the anonymous |
1037 | (innermost) subroutine is referencing a lexical variable defined in |
1038 | the outermost subroutine. For example: |
1039 | |
1040 | sub outermost { my $a; sub middle { sub { $a } } } |
1041 | |
1042 | If the anonymous subroutine is called or referenced (directly or |
1043 | indirectly) from the outermost subroutine, it will share the variable |
1044 | as you would expect. But if the anonymous subroutine is called or |
1045 | referenced when the outermost subroutine is not active, it will see |
1046 | the value of the shared variable as it was before and during the |
1047 | *first* call to the outermost subroutine, which is probably not what |
1048 | you want. |
1049 | |
1050 | In these circumstances, it is usually best to make the middle |
1051 | subroutine anonymous, using the C<sub {}> syntax. Perl has specific |
1052 | support for shared variables in nested anonymous subroutines; a named |
1053 | subroutine in between interferes with this feature. |
1054 | |
1055 | =item Variable "%s" will not stay shared |
1056 | |
1057 | (W) An inner (nested) I<named> subroutine is referencing a lexical |
1058 | variable defined in an outer subroutine. |
1059 | |
1060 | When the inner subroutine is called, it will probably see the value of |
1061 | the outer subroutine's variable as it was before and during the |
1062 | *first* call to the outer subroutine; in this case, after the first |
1063 | call to the outer subroutine is complete, the inner and outer |
1064 | subroutines will no longer share a common value for the variable. In |
1065 | other words, the variable will no longer be shared. |
1066 | |
1067 | Furthermore, if the outer subroutine is anonymous and references a |
1068 | lexical variable outside itself, then the outer and inner subroutines |
1069 | will I<never> share the given variable. |
1070 | |
1071 | This problem can usually be solved by making the inner subroutine |
1072 | anonymous, using the C<sub {}> syntax. When inner anonymous subs that |
1073 | reference variables in outer subroutines are called or referenced, |
1074 | they are automatically re-bound to the current values of such |
1075 | variables. |
1076 | |
1077 | =item Warning: something's wrong |
1078 | |
1079 | (W) You passed warn() an empty string (the equivalent of C<warn "">) or |
1080 | you called it with no args and C<$_> was empty. |
1081 | |
1082 | =item Got an error from DosAllocMem |
5f05dabc |
1083 | |
774d564b |
1084 | (P) An error peculiar to OS/2. Most probably you're using an obsolete |
1085 | version of Perl, and this should not happen anyway. |
5f05dabc |
1086 | |
1087 | =item Malformed PERLLIB_PREFIX |
1088 | |
1089 | (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form |
1090 | |
1091 | prefix1;prefix2 |
1092 | |
1093 | or |
1094 | |
1095 | prefix1 prefix2 |
1096 | |
1097 | with non-empty prefix1 and prefix2. If C<prefix1> is indeed a prefix of |
1098 | a builtin library search path, prefix2 is substituted. The error may appear |
1099 | if components are not found, or are too long. See L<perlos2/"PERLLIB_PREFIX">. |
1100 | |
1101 | =item PERL_SH_DIR too long |
1102 | |
1103 | (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the |
1104 | C<sh>-shell in. See L<perlos2/"PERL_SH_DIR">. |
1105 | |
1106 | =item Process terminated by SIG%s |
1107 | |
1108 | (W) This is a standard message issued by OS/2 applications, while *nix |
1109 | applications die in silence. It is considered a feature of the OS/2 |
1110 | port. One can easily disable this by appropriate sighandlers, see |
1111 | L<perlipc/"Signals">. See L<perlos2/"Process terminated by SIGTERM/SIGINT">. |
1112 | |
1113 | =back |
1114 | |
1115 | =head1 BUGS |
1116 | |
774d564b |
1117 | If you find what you think is a bug, you might check the headers of |
1118 | recently posted articles in the comp.lang.perl.misc newsgroup. |
1119 | There may also be information at http://www.perl.com/perl/, the Perl |
1120 | Home Page. |
5f05dabc |
1121 | |
1122 | If you believe you have an unreported bug, please run the B<perlbug> |
9607fc9c |
1123 | program included with your release. Make sure you trim your bug down |
1124 | to a tiny but sufficient test case. Your bug report, along with the |
1125 | output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be |
1126 | analysed by the Perl porting team. |
5f05dabc |
1127 | |
1128 | =head1 SEE ALSO |
1129 | |
1130 | The F<Changes> file for exhaustive details on what changed. |
1131 | |
1132 | The F<INSTALL> file for how to build Perl. This file has been |
1133 | significantly updated for 5.004, so even veteran users should |
1134 | look through it. |
1135 | |
1136 | The F<README> file for general stuff. |
1137 | |
1138 | The F<Copying> file for copyright information. |
1139 | |
1140 | =head1 HISTORY |
1141 | |
1142 | Constructed by Tom Christiansen, grabbing material with permission |
1143 | from innumerable contributors, with kibitzing by more than a few Perl |
1144 | porters. |
1145 | |
2ae324a7 |
1146 | Last update: Sat Mar 8 19:51:26 EST 1997 |