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