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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 | |
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21 | =head2 Compilation option: Binary compatibility with 5.003 |
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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 $PERL5OPT environment variable |
31 | |
32 | You may now put Perl options in the $PERL5OPT environment variable. |
33 | Unless Perl is running with taint checks, it will interpret this |
34 | variable as if its contents had appeared on a "#!perl" line at the |
35 | beginning of your script, except that hyphens are optional. PERL5OPT |
36 | may only be used to set the following switches: B<-[DIMUdmw]>. |
37 | |
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38 | =head2 Limitations on B<-M>, and C<-m>, and B<-T> options |
39 | |
40 | The C<-M> and C<-m> options are no longer allowed on the C<#!> line of |
41 | a script. If a script needs a module, it should invoke it with the |
42 | C<use> pragma. |
43 | |
44 | The B<-T> option is also forbidden on the C<#!> line of a script, |
45 | unless it was present on the Perl command line. Due to the way C<#!> |
46 | works, this usually means that B<-T> must be in the first argument. |
47 | Thus: |
48 | |
49 | #!/usr/bin/perl -T -w |
50 | |
51 | will probably work for an executable script invoked as C<scriptname>, |
52 | while: |
53 | |
54 | #!/usr/bin/perl -w -T |
55 | |
56 | will probably fail under the same conditions. (Non-Unix systems will |
57 | probably not follow this rule.) But C<perl scriptname> is guaranteed |
58 | to fail, since then there is no chance of B<-T> being found on the |
59 | command line before it is found on the C<#!> line. |
60 | |
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61 | =head2 More precise warnings |
62 | |
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63 | If you removed the B<-w> option from your Perl 5.003 scripts because it |
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64 | made Perl too verbose, we recommend that you try putting it back when |
65 | you upgrade to Perl 5.004. Each new perl version tends to remove some |
66 | undesirable warnings, while adding new warnings that may catch bugs in |
67 | your scripts. |
68 | |
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69 | =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods |
70 | |
71 | Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods |
72 | (using the C<@ISA> hierarchy), even when the function to be autoloaded |
73 | was called as a plain function (e.g. C<Foo::bar()>), not a method |
74 | (e.g. C<Foo->bar()> or C<$obj->bar()>). |
75 | |
76 | Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s. |
77 | However, there is a significant base of existing code that may be using |
78 | the old behavior. So, as an interim step, Perl 5.004 issues an optional |
79 | warning when a non-method uses an inherited C<AUTOLOAD>. |
80 | |
81 | The simple rule is: Inheritance will not work when autoloading |
82 | non-methods. The simple fix for old code is: In any module that used to |
83 | depend on inheriting C<AUTOLOAD> for non-methods from a base class named |
84 | C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup. |
85 | |
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86 | =head2 Subroutine arguments created only when they're modified |
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87 | |
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88 | In Perl 5.004, nonexistent array and hash elements used as subroutine |
89 | parameters are brought into existence only if they are actually |
90 | assigned to (via C<@_>). |
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91 | |
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92 | Earlier versions of Perl vary in their handling of such arguments. |
93 | Perl versions 5.002 and 5.003 always brought them into existence. |
94 | Perl versions 5.000, 5.001, and 5.002 brought them into existence only |
95 | if they were not the first argument (which was almost certainly a |
96 | bug). Earlier versions of Perl never brought them into existence. |
97 | |
98 | For example, given this code: |
99 | |
100 | undef @a; undef %a; |
101 | sub show { print $_[0] }; |
102 | sub change { $_[0]++ }; |
103 | show($a[2]); |
104 | change($a{b}); |
105 | |
106 | After this code executes in Perl 5.004, $a{b} exists but $a[2] does |
107 | not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed |
108 | (but $a[2]'s value would have been undefined). |
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109 | |
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110 | =head2 Group vector changeable with C<$)> |
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111 | |
112 | The C<$)> special variable has always (well, in Perl 5, at least) |
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113 | reflected not only the current effective group, but also the group list |
114 | as returned by the C<getgroups()> C function (if there is one). |
115 | However, until this release, there has not been a way to call the |
116 | C<setgroups()> C function from Perl. |
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117 | |
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118 | In Perl 5.004, assigning to C<$)> is exactly symmetrical with examining |
119 | it: The first number in its string value is used as the effective gid; |
120 | if there are any numbers after the first one, they are passed to the |
121 | C<setgroups()> C function (if there is one). |
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122 | |
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123 | =head2 Fixed parsing of $$<digit>, &$<digit>, etc. |
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124 | |
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125 | Perl versions before 5.004 misinterpreted any type marker followed by |
126 | "$" and a digit. For example, "$$0" was incorrectly taken to mean |
127 | "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004. |
128 | |
129 | However, the developers of Perl 5.004 could not fix this bug completely, |
130 | because at least two widely-used modules depend on the old meaning of |
131 | "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the |
132 | old (broken) way inside strings; but it generates this message as a |
133 | warning. And in Perl 5.005, this special treatment will cease. |
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134 | |
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135 | =head2 No resetting of $. on implicit close |
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136 | |
137 | The documentation for Perl 5.0 has always stated that C<$.> is I<not> |
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138 | reset when an already-open file handle is reopened with no intervening |
139 | call to C<close>. Due to a bug, perl versions 5.000 through 5.003 |
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140 | I<did> reset C<$.> under that circumstance; Perl 5.004 does not. |
141 | |
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142 | =head2 C<wantarray> may return undef |
143 | |
144 | The C<wantarray> operator returns true if a subroutine is expected to |
145 | return a list, and false otherwise. In Perl 5.004, C<wantarray> can |
146 | also return the undefined value if a subroutine's return value will |
147 | not be used at all, which allows subroutines to avoid a time-consuming |
148 | calculation of a return value if it isn't going to be used. |
149 | |
150 | =head2 Changes to tainting checks |
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151 | |
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152 | A bug in previous versions may have failed to detect some insecure |
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153 | conditions when taint checks are turned on. (Taint checks are used |
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154 | in setuid or setgid scripts, or when explicitly turned on with the |
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155 | C<-T> invocation option.) Although it's unlikely, this may cause a |
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156 | previously-working script to now fail -- which should be construed |
157 | as a blessing, since that indicates a potentially-serious security |
158 | hole was just plugged. |
159 | |
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160 | =head2 New Opcode module and revised Safe module |
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161 | |
162 | A new Opcode module supports the creation, manipulation and |
163 | application of opcode masks. The revised Safe module has a new API |
164 | and is implemented using the new Opcode module. Please read the new |
165 | Opcode and Safe documentation. |
166 | |
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167 | =head2 Embedding improvements |
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168 | |
169 | In older versions of Perl it was not possible to create more than one |
170 | Perl interpreter instance inside a single process without leaking like a |
171 | sieve and/or crashing. The bugs that caused this behavior have all been |
172 | fixed. However, you still must take care when embedding Perl in a C |
173 | program. See the updated perlembed manpage for tips on how to manage |
174 | your interpreters. |
175 | |
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176 | =head2 Internal change: FileHandle class based on IO::* classes |
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177 | |
178 | File handles are now stored internally as type IO::Handle. The |
179 | FileHandle module is still supported for backwards compatibility, but |
180 | it is now merely a front end to the IO::* modules -- specifically, |
181 | IO::Handle, IO::Seekable, and IO::File. We suggest, but do not |
182 | require, that you use the IO::* modules in new code. |
183 | |
184 | In harmony with this change, C<*GLOB{FILEHANDLE}> is now a |
185 | backward-compatible synonym for C<*STDOUT{IO}>. |
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186 | |
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187 | =head2 Internal change: PerlIO abstraction interface |
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188 | |
189 | It is now possible to build Perl with AT&T's sfio IO package |
190 | instead of stdio. See L<perlapio> for more details, and |
191 | the F<INSTALL> file for how to use it. |
192 | |
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193 | =head2 New and changed builtin variables |
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194 | |
195 | =over |
196 | |
197 | =item $^E |
198 | |
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199 | Extended error message on some platforms. (Also known as |
200 | $EXTENDED_OS_ERROR if you C<use English>). |
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201 | |
202 | =item $^H |
203 | |
204 | The current set of syntax checks enabled by C<use strict>. See the |
205 | documentation of C<strict> for more details. Not actually new, but |
206 | newly documented. |
207 | Because it is intended for internal use by Perl core components, |
208 | there is no C<use English> long name for this variable. |
209 | |
210 | =item $^M |
211 | |
212 | By default, running out of memory it is not trappable. However, if |
213 | compiled for this, Perl may use the contents of C<$^M> as an emergency |
214 | pool after die()ing with this message. Suppose that your Perl were |
215 | compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then |
216 | |
217 | $^M = 'a' x (1<<16); |
218 | |
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219 | would allocate a 64K buffer for use when in emergency. |
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220 | See the F<INSTALL> file for information on how to enable this option. |
221 | As a disincentive to casual use of this advanced feature, |
222 | there is no C<use English> long name for this variable. |
223 | |
224 | =back |
225 | |
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226 | =head2 New and changed builtin functions |
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227 | |
228 | =over |
229 | |
230 | =item delete on slices |
231 | |
232 | This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>) |
233 | |
234 | =item flock |
235 | |
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236 | is now supported on more platforms, prefers fcntl to lockf when |
237 | emulating, and always flushes before (un)locking. |
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238 | |
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239 | =item printf and sprintf |
240 | |
241 | now support "%i" as a synonym for "%d", and the "h" modifier. |
242 | So "%hi" means "short integer in decimal", and "%ho" means |
243 | "unsigned short integer as octal". |
244 | |
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245 | =item keys as an lvalue |
246 | |
247 | As an lvalue, C<keys> allows you to increase the number of hash buckets |
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248 | allocated for the given hash. This can gain you a measure of efficiency if |
249 | you know the hash is going to get big. (This is similar to pre-extending |
250 | an array by assigning a larger number to $#array.) If you say |
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251 | |
252 | keys %hash = 200; |
253 | |
254 | then C<%hash> will have at least 200 buckets allocated for it. These |
255 | buckets will be retained even if you do C<%hash = ()>; use C<undef |
256 | %hash> if you want to free the storage while C<%hash> is still in scope. |
257 | You can't shrink the number of buckets allocated for the hash using |
258 | C<keys> in this way (but you needn't worry about doing this by accident, |
259 | as trying has no effect). |
260 | |
261 | =item my() in Control Structures |
262 | |
263 | You can now use my() (with or without the parentheses) in the control |
264 | expressions of control structures such as: |
265 | |
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266 | while (defined(my $line = <>)) { |
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267 | $line = lc $line; |
268 | } continue { |
269 | print $line; |
270 | } |
271 | |
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272 | if ((my $answer = <STDIN>) =~ /^y(es)?$/i) { |
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273 | user_agrees(); |
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274 | } elsif ($answer =~ /^n(o)?$/i) { |
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275 | user_disagrees(); |
276 | } else { |
277 | chomp $answer; |
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278 | die "`$answer' is neither `yes' nor `no'"; |
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279 | } |
280 | |
281 | Also, you can declare a foreach loop control variable as lexical by |
282 | preceding it with the word "my". For example, in: |
283 | |
284 | foreach my $i (1, 2, 3) { |
285 | some_function(); |
286 | } |
287 | |
288 | $i is a lexical variable, and the scope of $i extends to the end of |
289 | the loop, but not beyond it. |
290 | |
291 | Note that you still cannot use my() on global punctuation variables |
292 | such as $_ and the like. |
293 | |
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294 | =item pack() and unpack() |
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295 | |
296 | A new format 'w' represents a BER compressed integer (as defined in |
297 | ASN.1). Its format is a sequence of one or more bytes, each of which |
298 | provides seven bits of the total value, with the most significant |
299 | first. Bit eight of each byte is set, except for the last byte, in |
300 | which bit eight is clear. |
301 | |
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302 | =item sysseek() and systell() |
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303 | |
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304 | These are new. The sysseek() operator is a variant of seek() that works |
305 | on the system file pointer. It is the only reliable way to seek before |
306 | using sysread() or syswrite(). Its companion operator systell() reports |
307 | the current position of the system file pointer. |
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308 | |
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309 | =item use VERSION |
310 | |
311 | If the first argument to C<use> is a number, it is treated as a version |
312 | number instead of a module name. If the version of the Perl interpreter |
313 | is less than VERSION, then an error message is printed and Perl exits |
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314 | immediately. Because C<use> occurs at compile time, this check happens |
315 | immediately during the compilation process, unlike C<require VERSION>, |
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316 | which waits until runtime for the check. This is often useful if you |
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317 | need to check the current Perl version before C<use>ing library modules |
318 | which have changed in incompatible ways from older versions of Perl. |
319 | (We try not to do this more than we have to.) |
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320 | |
321 | =item use Module VERSION LIST |
322 | |
323 | If the VERSION argument is present between Module and LIST, then the |
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324 | C<use> will call the VERSION method in class Module with the given |
325 | version as an argument. The default VERSION method, inherited from |
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326 | the UNIVERSAL class, croaks if the given version is larger than the |
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327 | value of the variable $Module::VERSION. (Note that there is not a |
328 | comma after VERSION!) |
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329 | |
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330 | This version-checking mechanism is similar to the one currently used |
331 | in the Exporter module, but it is faster and can be used with modules |
332 | that don't use the Exporter. It is the recommended method for new |
333 | code. |
334 | |
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335 | =item prototype(FUNCTION) |
336 | |
337 | Returns the prototype of a function as a string (or C<undef> if the |
338 | function has no prototype). FUNCTION is a reference to or the name of the |
339 | function whose prototype you want to retrieve. |
340 | (Not actually new; just never documented before.) |
341 | |
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342 | =item srand |
343 | |
344 | The default seed for C<srand>, which used to be C<time>, has been changed. |
345 | Now it's a heady mix of difficult-to-predict system-dependent values, |
346 | which should be sufficient for most everyday purposes. |
347 | |
348 | Previous to version 5.004, calling C<rand> without first calling C<srand> |
349 | would yield the same sequence of random numbers on most or all machines. |
350 | Now, when perl sees that you're calling C<rand> and haven't yet called |
351 | C<srand>, it calls C<srand> with the default seed. You should still call |
352 | C<srand> manually if your code might ever be run on a pre-5.004 system, |
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353 | of course, or if you want a seed other than the default. |
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354 | |
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355 | =item $_ as Default |
356 | |
357 | Functions documented in the Camel to default to $_ now in |
358 | fact do, and all those that do are so documented in L<perlfunc>. |
359 | |
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360 | =item C<m//g> does not reset search position on failure |
361 | |
362 | The C<m//g> match iteration construct used to reset its target string's |
363 | search position (which is visible through the C<pos> operator) when a |
364 | match failed; as a result, the next C<m//g> match would start at the |
365 | beginning of the string). With Perl 5.004, the search position must be |
366 | reset explicitly, as with C<pos $str = 0;>, or by modifying the target |
367 | string. This change in Perl makes it possible to chain matches together |
368 | in conjunction with the C<\G> zero-width assertion. See L<perlop> and |
369 | L<perlre>. |
370 | |
371 | Here is an illustration of what it takes to get the old behavior: |
372 | |
373 | for ( qw(this and that are not what you think you got) ) { |
374 | while ( /(\w*t\w*)/g ) { print "t word is: $1\n" } |
375 | pos = 0; # REQUIRED FOR 5.004 |
376 | while ( /(\w*a\w*)/g ) { print "a word is: $1\n" } |
377 | print "\n"; |
378 | } |
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379 | |
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380 | =item C<m//x> ignores whitespace before ?*+{} |
381 | |
382 | The C<m//x> construct has always been intended to ignore all unescaped |
383 | whitespace. However, before Perl 5.004, whitespace had the effect of |
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384 | escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was |
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385 | (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004. |
386 | |
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387 | =item nested C<sub{}> closures work now |
388 | |
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389 | Prior to the 5.004 release, nested anonymous functions didn't work |
390 | right. They do now. |
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391 | |
392 | =item formats work right on changing lexicals |
393 | |
394 | Just like anonymous functions that contain lexical variables |
395 | that change (like a lexical index variable for a C<foreach> loop), |
396 | formats now work properly. For example, this silently failed |
397 | before, and is fine now: |
398 | |
399 | my $i; |
400 | foreach $i ( 1 .. 10 ) { |
401 | format = |
402 | my i is @# |
403 | $i |
404 | . |
405 | write; |
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406 | } |
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407 | |
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408 | =back |
409 | |
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410 | =head2 New builtin methods |
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411 | |
412 | The C<UNIVERSAL> package automatically contains the following methods that |
413 | are inherited by all other classes: |
414 | |
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415 | =over |
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416 | |
417 | =item isa(CLASS) |
418 | |
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419 | C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS> |
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420 | |
421 | C<isa> is also exportable and can be called as a sub with two arguments. This |
422 | allows the ability to check what a reference points to. Example: |
423 | |
424 | use UNIVERSAL qw(isa); |
425 | |
426 | if(isa($ref, 'ARRAY')) { |
427 | ... |
428 | } |
429 | |
430 | =item can(METHOD) |
431 | |
432 | C<can> checks to see if its object has a method called C<METHOD>, |
433 | if it does then a reference to the sub is returned; if it does not then |
434 | I<undef> is returned. |
435 | |
436 | =item VERSION( [NEED] ) |
437 | |
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438 | C<VERSION> returns the version number of the class (package). If the |
439 | NEED argument is given then it will check that the current version (as |
440 | defined by the $VERSION variable in the given package) not less than |
441 | NEED; it will die if this is not the case. This method is normally |
442 | called as a class method. This method is called automatically by the |
443 | C<VERSION> form of C<use>. |
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444 | |
445 | use A 1.2 qw(some imported subs); |
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446 | # implies: |
447 | A->VERSION(1.2); |
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448 | |
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449 | =back |
450 | |
451 | B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and |
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452 | C<isa> uses a very similar method and caching strategy. This may cause |
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453 | strange effects if the Perl code dynamically changes @ISA in any package. |
454 | |
455 | You may add other methods to the UNIVERSAL class via Perl or XS code. |
456 | You do not need to C<use UNIVERSAL> in order to make these methods |
457 | available to your program. This is necessary only if you wish to |
458 | have C<isa> available as a plain subroutine in the current package. |
459 | |
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460 | =head2 TIEHANDLE now supported |
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461 | |
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462 | See L<perltie> for other kinds of tie()s. |
463 | |
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464 | =over |
465 | |
466 | =item TIEHANDLE classname, LIST |
467 | |
468 | This is the constructor for the class. That means it is expected to |
469 | return an object of some sort. The reference can be used to |
470 | hold some internal information. |
471 | |
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472 | sub TIEHANDLE { |
473 | print "<shout>\n"; |
474 | my $i; |
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475 | return bless \$i, shift; |
476 | } |
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477 | |
478 | =item PRINT this, LIST |
479 | |
480 | This method will be triggered every time the tied handle is printed to. |
481 | Beyond its self reference it also expects the list that was passed to |
482 | the print function. |
483 | |
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484 | sub PRINT { |
485 | $r = shift; |
486 | $$r++; |
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487 | return print join( $, => map {uc} @_), $\; |
488 | } |
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489 | |
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490 | =item READ this LIST |
491 | |
492 | This method will be called when the handle is read from via the C<read> |
493 | or C<sysread> functions. |
494 | |
495 | sub READ { |
496 | $r = shift; |
497 | my($buf,$len,$offset) = @_; |
498 | print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset"; |
499 | } |
500 | |
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501 | =item READLINE this |
502 | |
503 | This method will be called when the handle is read from. The method |
504 | should return undef when there is no more data. |
505 | |
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506 | sub READLINE { |
507 | $r = shift; |
508 | return "PRINT called $$r times\n" |
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509 | } |
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510 | |
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511 | =item GETC this |
512 | |
513 | This method will be called when the C<getc> function is called. |
514 | |
515 | sub GETC { print "Don't GETC, Get Perl"; return "a"; } |
516 | |
5f05dabc |
517 | =item DESTROY this |
518 | |
519 | As with the other types of ties, this method will be called when the |
520 | tied handle is about to be destroyed. This is useful for debugging and |
521 | possibly for cleaning up. |
522 | |
2ae324a7 |
523 | sub DESTROY { |
774d564b |
524 | print "</shout>\n"; |
525 | } |
5f05dabc |
526 | |
527 | =back |
528 | |
54310121 |
529 | =head2 Malloc enhancements |
aa689395 |
530 | |
2ae324a7 |
531 | Four new compilation flags are recognized by malloc.c. (They have no |
532 | effect if perl is compiled with system malloc().) |
533 | |
534 | =over |
535 | |
536 | =item -DDEBUGGING_MSTATS |
537 | |
538 | If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print |
539 | memory statistics at runtime by running Perl thusly: |
aa689395 |
540 | |
541 | env PERL_DEBUG_MSTATS=2 perl your_script_here |
542 | |
543 | The value of 2 means to print statistics after compilation and on |
544 | exit; with a value of 1, the statistics ares printed only on exit. |
545 | (If you want the statistics at an arbitrary time, you'll need to |
546 | install the optional module Devel::Peek.) |
547 | |
aa689395 |
548 | =item -DEMERGENCY_SBRK |
549 | |
550 | If this macro is defined, running out of memory need not be a fatal |
551 | error: a memory pool can allocated by assigning to the special |
552 | variable C<$^M>. See L<"$^M">. |
774d564b |
553 | |
aa689395 |
554 | =item -DPACK_MALLOC |
555 | |
556 | Perl memory allocation is by bucket with sizes close to powers of two. |
557 | Because of these malloc overhead may be big, especially for data of |
558 | size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses |
559 | a slightly different algorithm for small allocations (up to 64 bytes |
560 | long), which makes it possible to have overhead down to 1 byte for |
561 | allocations which are powers of two (and appear quite often). |
562 | |
563 | Expected memory savings (with 8-byte alignment in C<alignbytes>) is |
564 | about 20% for typical Perl usage. Expected slowdown due to additional |
565 | malloc overhead is in fractions of a percent (hard to measure, because |
566 | of the effect of saved memory on speed). |
567 | |
568 | =item -DTWO_POT_OPTIMIZE |
569 | |
570 | Similarly to C<PACK_MALLOC>, this macro improves allocations of data |
571 | with size close to a power of two; but this works for big allocations |
572 | (starting with 16K by default). Such allocations are typical for big |
573 | hashes and special-purpose scripts, especially image processing. |
574 | |
575 | On recent systems, the fact that perl requires 2M from system for 1M |
576 | allocation will not affect speed of execution, since the tail of such |
577 | a chunk is not going to be touched (and thus will not require real |
578 | memory). However, it may result in a premature out-of-memory error. |
579 | So if you will be manipulating very large blocks with sizes close to |
580 | powers of two, it would be wise to define this macro. |
581 | |
582 | Expected saving of memory is 0-100% (100% in applications which |
583 | require most memory in such 2**n chunks); expected slowdown is |
584 | negligible. |
585 | |
586 | =back |
587 | |
54310121 |
588 | =head2 Miscellaneous efficiency enhancements |
774d564b |
589 | |
590 | Functions that have an empty prototype and that do nothing but return |
591 | a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>). |
592 | |
aa689395 |
593 | Each unique hash key is only allocated once, no matter how many hashes |
594 | have an entry with that key. So even if you have 100 copies of the |
68dc0745 |
595 | same hash, the hash keys never have to be reallocated. |
aa689395 |
596 | |
5f05dabc |
597 | =head1 Pragmata |
598 | |
54310121 |
599 | Six new pragmatic modules exist: |
5f05dabc |
600 | |
601 | =over |
602 | |
54310121 |
603 | =item use autouse MODULE => qw(sub1 sub2 sub3) |
604 | |
605 | Defers C<require MODULE> until someone calls one of the specified |
606 | subroutines (which must be exported by MODULE). This pragma should be |
607 | used with caution, and only when necessary. |
608 | |
5f05dabc |
609 | =item use blib |
610 | |
774d564b |
611 | =item use blib 'dir' |
612 | |
5f05dabc |
613 | Looks for MakeMaker-like I<'blib'> directory structure starting in |
614 | I<dir> (or current directory) and working back up to five levels of |
615 | parent directories. |
616 | |
617 | Intended for use on command line with B<-M> option as a way of testing |
618 | arbitrary scripts against an uninstalled version of a package. |
619 | |
54310121 |
620 | =item use constant NAME => VALUE |
621 | |
622 | Provides a convenient interface for creating compile-time constants, |
623 | See L<perlsub/"Constant Functions">. |
624 | |
5f05dabc |
625 | =item use locale |
626 | |
627 | Tells the compiler to enable (or disable) the use of POSIX locales for |
54310121 |
628 | builtin operations. |
5f05dabc |
629 | |
630 | When C<use locale> is in effect, the current LC_CTYPE locale is used |
631 | for regular expressions and case mapping; LC_COLLATE for string |
632 | ordering; and LC_NUMERIC for numeric formating in printf and sprintf |
633 | (but B<not> in print). LC_NUMERIC is always used in write, since |
634 | lexical scoping of formats is problematic at best. |
635 | |
636 | Each C<use locale> or C<no locale> affects statements to the end of |
637 | the enclosing BLOCK or, if not inside a BLOCK, to the end of the |
638 | current file. Locales can be switched and queried with |
639 | POSIX::setlocale(). |
640 | |
641 | See L<perllocale> for more information. |
642 | |
643 | =item use ops |
644 | |
7cfe7857 |
645 | Disable unsafe opcodes, or any named opcodes, when compiling Perl code. |
5f05dabc |
646 | |
ff0cee69 |
647 | =item use vmsish |
648 | |
649 | Enable VMS-specific language features. Currently, there are three |
aa689395 |
650 | VMS-specific features available: 'status', which makes C<$?> and |
ff0cee69 |
651 | C<system> return genuine VMS status values instead of emulating POSIX; |
652 | 'exit', which makes C<exit> take a genuine VMS status value instead of |
653 | assuming that C<exit 1> is an error; and 'time', which makes all times |
654 | relative to the local time zone, in the VMS tradition. |
655 | |
5f05dabc |
656 | =back |
657 | |
658 | =head1 Modules |
659 | |
5cd24f17 |
660 | =head2 Required Updates |
661 | |
662 | Though Perl 5.004 is compatible with almost all modules that work |
663 | with Perl 5.003, there are a few exceptions: |
664 | |
665 | Module Required Version for Perl 5.004 |
666 | ------ ------------------------------- |
137443ea |
667 | Filter Filter-1.12 |
668 | LWP libwww-perl-5.08 |
5cd24f17 |
669 | Tk Tk400.202 (-w makes noise) |
670 | |
137443ea |
671 | Also, the majordomo mailing list program, version 1.94.1, doesn't work |
672 | with Perl 5.004 (nor with perl 4), because it executes an invalid |
673 | regular expression. This bug is fixed in majordomo version 1.94.2. |
674 | |
54310121 |
675 | =head2 Installation directories |
f86702cc |
676 | |
677 | The I<installperl> script now places the Perl source files for |
678 | extensions in the architecture-specific library directory, which is |
679 | where the shared libraries for extensions have always been. This |
680 | change is intended to allow administrators to keep the Perl 5.004 |
681 | library directory unchanged from a previous version, without running |
682 | the risk of binary incompatibility between extensions' Perl source and |
683 | shared libraries. |
684 | |
54310121 |
685 | =head2 Module information summary |
5f05dabc |
686 | |
774d564b |
687 | Brand new modules, arranged by topic rather than strictly |
688 | alphabetically: |
689 | |
137443ea |
690 | CGI.pm Web server interface ("Common Gateway Interface") |
691 | CGI/Apache.pm Support for Apache's Perl module |
692 | CGI/Carp.pm Log server errors with helpful context |
693 | CGI/Fast.pm Support for FastCGI (persistent server process) |
694 | CGI/Push.pm Support for server push |
695 | CGI/Switch.pm Simple interface for multiple server types |
696 | |
697 | CPAN Interface to Comprehensive Perl Archive Network |
698 | CPAN::FirstTime Utility for creating CPAN configuration file |
699 | CPAN::Nox Runs CPAN while avoiding compiled extensions |
5f05dabc |
700 | |
701 | IO.pm Top-level interface to IO::* classes |
702 | IO/File.pm IO::File extension Perl module |
703 | IO/Handle.pm IO::Handle extension Perl module |
704 | IO/Pipe.pm IO::Pipe extension Perl module |
705 | IO/Seekable.pm IO::Seekable extension Perl module |
706 | IO/Select.pm IO::Select extension Perl module |
707 | IO/Socket.pm IO::Socket extension Perl module |
708 | |
709 | Opcode.pm Disable named opcodes when compiling Perl code |
710 | |
711 | ExtUtils/Embed.pm Utilities for embedding Perl in C programs |
712 | ExtUtils/testlib.pm Fixes up @INC to use just-built extension |
713 | |
5f05dabc |
714 | FindBin.pm Find path of currently executing program |
715 | |
8cc95fdb |
716 | Class/Struct.pm Declare struct-like datatypes as Perl classes |
717 | File/stat.pm By-name interface to Perl's built-in stat |
718 | Net/hostent.pm By-name interface to Perl's built-in gethost* |
719 | Net/netent.pm By-name interface to Perl's built-in getnet* |
720 | Net/protoent.pm By-name interface to Perl's built-in getproto* |
721 | Net/servent.pm By-name interface to Perl's built-in getserv* |
722 | Time/gmtime.pm By-name interface to Perl's built-in gmtime |
723 | Time/localtime.pm By-name interface to Perl's built-in localtime |
724 | Time/tm.pm Internal object for Time::{gm,local}time |
725 | User/grent.pm By-name interface to Perl's built-in getgr* |
726 | User/pwent.pm By-name interface to Perl's built-in getpw* |
5f05dabc |
727 | |
774d564b |
728 | Tie/RefHash.pm Base class for tied hashes with references as keys |
7a4c00b4 |
729 | |
5f05dabc |
730 | UNIVERSAL.pm Base class for *ALL* classes |
731 | |
54310121 |
732 | =head2 Fcntl |
733 | |
734 | New constants in the existing Fcntl modules are now supported, |
735 | provided that your operating system happens to support them: |
736 | |
737 | F_GETOWN F_SETOWN |
738 | O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC |
739 | O_EXLOCK O_SHLOCK |
740 | |
741 | These constants are intended for use with the Perl operators sysopen() |
742 | and fcntl() and the basic database modules like SDBM_File. For the |
743 | exact meaning of these and other Fcntl constants please refer to your |
744 | operating system's documentation for fcntl() and open(). |
745 | |
746 | In addition, the Fcntl module now provides these constants for use |
747 | with the Perl operator flock(): |
748 | |
749 | LOCK_SH LOCK_EX LOCK_NB LOCK_UN |
750 | |
751 | These constants are defined in all environments (because where there is |
752 | no flock() system call, Perl emulates it). However, for historical |
753 | reasons, these constants are not exported unless they are explicitly |
754 | requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>). |
755 | |
5f05dabc |
756 | =head2 IO |
757 | |
758 | The IO module provides a simple mechanism to load all of the IO modules at one |
759 | go. Currently this includes: |
760 | |
761 | IO::Handle |
762 | IO::Seekable |
763 | IO::File |
764 | IO::Pipe |
765 | IO::Socket |
766 | |
767 | For more information on any of these modules, please see its |
768 | respective documentation. |
769 | |
770 | =head2 Math::Complex |
771 | |
772 | The Math::Complex module has been totally rewritten, and now supports |
773 | more operations. These are overloaded: |
774 | |
775 | + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify) |
776 | |
777 | And these functions are now exported: |
778 | |
779 | pi i Re Im arg |
5cd24f17 |
780 | log10 logn ln cbrt root |
781 | tan |
782 | csc sec cot |
783 | asin acos atan |
784 | acsc asec acot |
785 | sinh cosh tanh |
786 | csch sech coth |
787 | asinh acosh atanh |
788 | acsch asech acoth |
5f05dabc |
789 | cplx cplxe |
790 | |
5aabfad6 |
791 | =head2 Math::Trig |
792 | |
5cd24f17 |
793 | This new module provides a simpler interface to parts of Math::Complex for |
5aabfad6 |
794 | those who need trigonometric functions only for real numbers. |
795 | |
0a753a76 |
796 | =head2 DB_File |
797 | |
798 | There have been quite a few changes made to DB_File. Here are a few of |
799 | the highlights: |
800 | |
801 | =over |
802 | |
803 | =item * |
804 | |
805 | Fixed a handful of bugs. |
806 | |
807 | =item * |
808 | |
809 | By public demand, added support for the standard hash function exists(). |
810 | |
811 | =item * |
812 | |
813 | Made it compatible with Berkeley DB 1.86. |
814 | |
815 | =item * |
816 | |
817 | Made negative subscripts work with RECNO interface. |
818 | |
819 | =item * |
820 | |
821 | Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default |
822 | mode from 0640 to 0666. |
823 | |
824 | =item * |
825 | |
826 | Made DB_File automatically import the open() constants (O_RDWR, |
827 | O_CREAT etc.) from Fcntl, if available. |
828 | |
829 | =item * |
830 | |
831 | Updated documentation. |
832 | |
833 | =back |
834 | |
835 | Refer to the HISTORY section in DB_File.pm for a complete list of |
836 | changes. Everything after DB_File 1.01 has been added since 5.003. |
837 | |
838 | =head2 Net::Ping |
839 | |
840 | Major rewrite - support added for both udp echo and real icmp pings. |
841 | |
54310121 |
842 | =head2 Object-oriented overrides for builtin operators |
5f05dabc |
843 | |
54310121 |
844 | Many of the Perl builtins returning lists now have |
5f05dabc |
845 | object-oriented overrides. These are: |
846 | |
847 | File::stat |
848 | Net::hostent |
849 | Net::netent |
850 | Net::protoent |
851 | Net::servent |
852 | Time::gmtime |
853 | Time::localtime |
854 | User::grent |
855 | User::pwent |
856 | |
857 | For example, you can now say |
858 | |
859 | use File::stat; |
860 | use User::pwent; |
861 | $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid); |
862 | |
774d564b |
863 | =head1 Utility Changes |
5f05dabc |
864 | |
774d564b |
865 | =head2 xsubpp |
5f05dabc |
866 | |
0a753a76 |
867 | =over |
868 | |
774d564b |
869 | =item C<void> XSUBs now default to returning nothing |
870 | |
871 | Due to a documentation/implementation bug in previous versions of |
872 | Perl, XSUBs with a return type of C<void> have actually been |
873 | returning one value. Usually that value was the GV for the XSUB, |
874 | but sometimes it was some already freed or reused value, which would |
875 | sometimes lead to program failure. |
876 | |
877 | In Perl 5.004, if an XSUB is declared as returning C<void>, it |
878 | actually returns no value, i.e. an empty list (though there is a |
879 | backward-compatibility exception; see below). If your XSUB really |
880 | does return an SV, you should give it a return type of C<SV *>. |
881 | |
882 | For backward compatibility, I<xsubpp> tries to guess whether a |
883 | C<void> XSUB is really C<void> or if it wants to return an C<SV *>. |
884 | It does so by examining the text of the XSUB: if I<xsubpp> finds |
885 | what looks like an assignment to C<ST(0)>, it assumes that the |
886 | XSUB's return type is really C<SV *>. |
5f05dabc |
887 | |
0a753a76 |
888 | =back |
889 | |
890 | =head1 C Language API Changes |
891 | |
892 | =over |
893 | |
894 | =item C<gv_fetchmethod> and C<perl_call_sv> |
895 | |
896 | The C<gv_fetchmethod> function finds a method for an object, just like |
897 | in Perl 5.003. The GV it returns may be a method cache entry. |
898 | However, in Perl 5.004, method cache entries are not visible to users; |
899 | therefore, they can no longer be passed directly to C<perl_call_sv>. |
900 | Instead, you should use the C<GvCV> macro on the GV to extract its CV, |
901 | and pass the CV to C<perl_call_sv>. |
902 | |
903 | The most likely symptom of passing the result of C<gv_fetchmethod> to |
904 | C<perl_call_sv> is Perl's producing an "Undefined subroutine called" |
905 | error on the I<second> call to a given method (since there is no cache |
906 | on the first call). |
907 | |
137443ea |
908 | =item C<perl_eval_pv> |
909 | |
910 | A new function handy for eval'ing strings of Perl code inside C code. |
911 | This function returns the value from the eval statement, which can |
912 | be used instead of fetching globals from the symbol table. See |
913 | L<perlguts>, L<perlembed> and L<perlcall> for details and examples. |
914 | |
1e422769 |
915 | =item Extended API for manipulating hashes |
916 | |
917 | Internal handling of hash keys has changed. The old hashtable API is |
918 | still fully supported, and will likely remain so. The additions to the |
919 | API allow passing keys as C<SV*>s, so that C<tied> hashes can be given |
54310121 |
920 | real scalars as keys rather than plain strings (nontied hashes still |
1e422769 |
921 | can only use strings as keys). New extensions must use the new hash |
922 | access functions and macros if they wish to use C<SV*> keys. These |
923 | additions also make it feasible to manipulate C<HE*>s (hash entries), |
924 | which can be more efficient. See L<perlguts> for details. |
925 | |
0a753a76 |
926 | =back |
927 | |
5f05dabc |
928 | =head1 Documentation Changes |
929 | |
930 | Many of the base and library pods were updated. These |
931 | new pods are included in section 1: |
932 | |
0a753a76 |
933 | =over |
5f05dabc |
934 | |
774d564b |
935 | =item L<perldelta> |
5f05dabc |
936 | |
71be2cbc |
937 | This document. |
5f05dabc |
938 | |
71be2cbc |
939 | =item L<perllocale> |
5f05dabc |
940 | |
71be2cbc |
941 | Locale support (internationalization and localization). |
5f05dabc |
942 | |
943 | =item L<perltoot> |
944 | |
945 | Tutorial on Perl OO programming. |
946 | |
71be2cbc |
947 | =item L<perlapio> |
948 | |
949 | Perl internal IO abstraction interface. |
950 | |
5f05dabc |
951 | =item L<perldebug> |
952 | |
953 | Although not new, this has been massively updated. |
954 | |
955 | =item L<perlsec> |
956 | |
957 | Although not new, this has been massively updated. |
958 | |
959 | =back |
960 | |
961 | =head1 New Diagnostics |
962 | |
963 | Several new conditions will trigger warnings that were |
964 | silent before. Some only affect certain platforms. |
2ae324a7 |
965 | The following new warnings and errors outline these. |
774d564b |
966 | These messages are classified as follows (listed in |
967 | increasing order of desperation): |
968 | |
969 | (W) A warning (optional). |
970 | (D) A deprecation (optional). |
971 | (S) A severe warning (mandatory). |
972 | (F) A fatal error (trappable). |
973 | (P) An internal error you should never see (trappable). |
54310121 |
974 | (X) A very fatal error (nontrappable). |
774d564b |
975 | (A) An alien error message (not generated by Perl). |
5f05dabc |
976 | |
0a753a76 |
977 | =over |
5f05dabc |
978 | |
979 | =item "my" variable %s masks earlier declaration in same scope |
980 | |
981 | (S) A lexical variable has been redeclared in the same scope, effectively |
982 | eliminating all access to the previous instance. This is almost always |
983 | a typographical error. Note that the earlier variable will still exist |
984 | until the end of the scope or until all closure referents to it are |
985 | destroyed. |
986 | |
774d564b |
987 | =item %s argument is not a HASH element or slice |
988 | |
989 | (F) The argument to delete() must be either a hash element, such as |
990 | |
991 | $foo{$bar} |
992 | $ref->[12]->{"susie"} |
993 | |
994 | or a hash slice, such as |
995 | |
996 | @foo{$bar, $baz, $xyzzy} |
997 | @{$ref->[12]}{"susie", "queue"} |
998 | |
5f05dabc |
999 | =item Allocation too large: %lx |
1000 | |
54310121 |
1001 | (X) You can't allocate more than 64K on an MS-DOS machine. |
5f05dabc |
1002 | |
1003 | =item Allocation too large |
1004 | |
1005 | (F) You can't allocate more than 2^31+"small amount" bytes. |
1006 | |
54310121 |
1007 | =item Applying %s to %s will act on scalar(%s) |
1008 | |
1009 | (W) The pattern match (//), substitution (s///), and translation (tr///) |
1010 | operators work on scalar values. If you apply one of them to an array |
1011 | or a hash, it will convert the array or hash to a scalar value -- the |
1012 | length of an array, or the population info of a hash -- and then work on |
1013 | that scalar value. This is probably not what you meant to do. See |
1014 | L<perlfunc/grep> and L<perlfunc/map> for alternatives. |
1015 | |
1016 | =item Attempt to free nonexistent shared string |
5f05dabc |
1017 | |
1018 | (P) Perl maintains a reference counted internal table of strings to |
1019 | optimize the storage and access of hash keys and other strings. This |
1020 | indicates someone tried to decrement the reference count of a string |
1021 | that can no longer be found in the table. |
1022 | |
1023 | =item Attempt to use reference as lvalue in substr |
1024 | |
1025 | (W) You supplied a reference as the first argument to substr() used |
1026 | as an lvalue, which is pretty strange. Perhaps you forgot to |
1027 | dereference it first. See L<perlfunc/substr>. |
1028 | |
774d564b |
1029 | =item Can't use bareword ("%s") as %s ref while "strict refs" in use |
1030 | |
1031 | (F) Only hard references are allowed by "strict refs". Symbolic references |
1032 | are disallowed. See L<perlref>. |
1033 | |
54310121 |
1034 | =item Cannot resolve method `%s' overloading `%s' in package `%s' |
1035 | |
1036 | (P) Internal error trying to resolve overloading specified by a method |
1037 | name (as opposed to a subroutine reference). |
1038 | |
774d564b |
1039 | =item Constant subroutine %s redefined |
1040 | |
1041 | (S) You redefined a subroutine which had previously been eligible for |
dc848c6f |
1042 | inlining. See L<perlsub/"Constant Functions"> for commentary and |
54310121 |
1043 | workarounds. |
1044 | |
1045 | =item Constant subroutine %s undefined |
1046 | |
1047 | (S) You undefined a subroutine which had previously been eligible for |
774d564b |
1048 | inlining. See L<perlsub/"Constant Functions"> for commentary and |
1049 | workarounds. |
1050 | |
54310121 |
1051 | =item Copy method did not return a reference |
1052 | |
1053 | (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>. |
1054 | |
774d564b |
1055 | =item Died |
1056 | |
1057 | (F) You passed die() an empty string (the equivalent of C<die "">) or |
1058 | you called it with no args and both C<$@> and C<$_> were empty. |
1059 | |
54310121 |
1060 | =item Exiting pseudo-block via %s |
1061 | |
1062 | (W) You are exiting a rather special block construct (like a sort block or |
1063 | subroutine) by unconventional means, such as a goto, or a loop control |
1064 | statement. See L<perlfunc/sort>. |
1065 | |
1066 | =item Illegal character %s (carriage return) |
1067 | |
1068 | (F) A carriage return character was found in the input. This is an |
1069 | error, and not a warning, because carriage return characters can break |
1070 | multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>). |
1071 | |
1072 | =item Illegal switch in PERL5OPT: %s |
1073 | |
1074 | (X) The PERL5OPT environment variable may only be used to set the |
1075 | following switches: B<-[DIMUdmw]>. |
1076 | |
5f05dabc |
1077 | =item Integer overflow in hex number |
1078 | |
1079 | (S) The literal hex number you have specified is too big for your |
1080 | architecture. On a 32-bit architecture the largest hex literal is |
1081 | 0xFFFFFFFF. |
1082 | |
1083 | =item Integer overflow in octal number |
1084 | |
1085 | (S) The literal octal number you have specified is too big for your |
1086 | architecture. On a 32-bit architecture the largest octal literal is |
1087 | 037777777777. |
1088 | |
5cd24f17 |
1089 | =item internal error: glob failed |
1090 | |
1091 | (P) Something went wrong with the external program(s) used for C<glob> |
1092 | and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is |
1093 | broken. If so, you should change all of the csh-related variables in |
1094 | config.sh: If you have tcsh, make the variables refer to it as if it |
1095 | were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all |
1096 | empty (except that C<d_csh> should be C<'undef'>) so that Perl will |
1097 | think csh is missing. In either case, after editing config.sh, run |
1098 | C<./Configure -S> and rebuild Perl. |
1099 | |
774d564b |
1100 | =item Name "%s::%s" used only once: possible typo |
1101 | |
1102 | (W) Typographical errors often show up as unique variable names. |
1103 | If you had a good reason for having a unique name, then just mention |
1104 | it again somehow to suppress the message (the C<use vars> pragma is |
1105 | provided for just this purpose). |
1106 | |
5f05dabc |
1107 | =item Null picture in formline |
1108 | |
1109 | (F) The first argument to formline must be a valid format picture |
1110 | specification. It was found to be empty, which probably means you |
1111 | supplied it an uninitialized value. See L<perlform>. |
1112 | |
1113 | =item Offset outside string |
1114 | |
1115 | (F) You tried to do a read/write/send/recv operation with an offset |
1116 | pointing outside the buffer. This is difficult to imagine. |
1117 | The sole exception to this is that C<sysread()>ing past the buffer |
1118 | will extend the buffer and zero pad the new area. |
1119 | |
1120 | =item Out of memory! |
1121 | |
1122 | (X|F) The malloc() function returned 0, indicating there was insufficient |
1123 | remaining memory (or virtual memory) to satisfy the request. |
1124 | |
1125 | The request was judged to be small, so the possibility to trap it |
1126 | depends on the way Perl was compiled. By default it is not trappable. |
1127 | However, if compiled for this, Perl may use the contents of C<$^M> as |
1128 | an emergency pool after die()ing with this message. In this case the |
1129 | error is trappable I<once>. |
1130 | |
1131 | =item Out of memory during request for %s |
1132 | |
1133 | (F) The malloc() function returned 0, indicating there was insufficient |
1134 | remaining memory (or virtual memory) to satisfy the request. However, |
1135 | the request was judged large enough (compile-time default is 64K), so |
1136 | a possibility to shut down by trapping this error is granted. |
1137 | |
1138 | =item Possible attempt to put comments in qw() list |
1139 | |
774d564b |
1140 | (W) qw() lists contain items separated by whitespace; as with literal |
1141 | strings, comment characters are not ignored, but are instead treated |
1142 | as literal data. (You may have used different delimiters than the |
1143 | exclamation marks parentheses shown here; braces are also frequently |
1144 | used.) |
1145 | |
1146 | You probably wrote something like this: |
5f05dabc |
1147 | |
2ae324a7 |
1148 | @list = qw( |
774d564b |
1149 | a # a comment |
5f05dabc |
1150 | b # another comment |
774d564b |
1151 | ); |
5f05dabc |
1152 | |
1153 | when you should have written this: |
1154 | |
774d564b |
1155 | @list = qw( |
2ae324a7 |
1156 | a |
5f05dabc |
1157 | b |
774d564b |
1158 | ); |
1159 | |
1160 | If you really want comments, build your list the |
1161 | old-fashioned way, with quotes and commas: |
1162 | |
1163 | @list = ( |
1164 | 'a', # a comment |
1165 | 'b', # another comment |
1166 | ); |
5f05dabc |
1167 | |
1168 | =item Possible attempt to separate words with commas |
1169 | |
774d564b |
1170 | (W) qw() lists contain items separated by whitespace; therefore commas |
1171 | aren't needed to separate the items. (You may have used different |
1172 | delimiters than the parentheses shown here; braces are also frequently |
1173 | used.) |
5f05dabc |
1174 | |
2ae324a7 |
1175 | You probably wrote something like this: |
5f05dabc |
1176 | |
774d564b |
1177 | qw! a, b, c !; |
1178 | |
1179 | which puts literal commas into some of the list items. Write it without |
1180 | commas if you don't want them to appear in your data: |
1181 | |
1182 | qw! a b c !; |
5f05dabc |
1183 | |
774d564b |
1184 | =item Scalar value @%s{%s} better written as $%s{%s} |
1185 | |
1186 | (W) You've used a hash slice (indicated by @) to select a single element of |
1187 | a hash. Generally it's better to ask for a scalar value (indicated by $). |
1188 | The difference is that C<$foo{&bar}> always behaves like a scalar, both when |
1189 | assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves |
1190 | like a list when you assign to it, and provides a list context to its |
1191 | subscript, which can do weird things if you're expecting only one subscript. |
5f05dabc |
1192 | |
54310121 |
1193 | =item Stub found while resolving method `%s' overloading `%s' in package `%s' |
1194 | |
1195 | (P) Overloading resolution over @ISA tree may be broken by importing stubs. |
1196 | Stubs should never be implicitely created, but explicit calls to C<can> |
1197 | may break this. |
1198 | |
1199 | =item Too late for "B<-T>" option |
1200 | |
1201 | (X) The #! line (or local equivalent) in a Perl script contains the |
1202 | B<-T> option, but Perl was not invoked with B<-T> in its argument |
1203 | list. This is an error because, by the time Perl discovers a B<-T> in |
1204 | a script, it's too late to properly taint everything from the |
1205 | environment. So Perl gives up. |
1206 | |
5f05dabc |
1207 | =item untie attempted while %d inner references still exist |
1208 | |
1209 | (W) A copy of the object returned from C<tie> (or C<tied>) was still |
1210 | valid when C<untie> was called. |
1211 | |
54310121 |
1212 | =item Unrecognized character %s |
1213 | |
1214 | (F) The Perl parser has no idea what to do with the specified character |
1215 | in your Perl script (or eval). Perhaps you tried to run a compressed |
1216 | script, a binary program, or a directory as a Perl program. |
1217 | |
1218 | =item Unsupported function fork |
1219 | |
1220 | (F) Your version of executable does not support forking. |
1221 | |
1222 | Note that under some systems, like OS/2, there may be different flavors of |
1223 | Perl executables, some of which may support fork, some not. Try changing |
1224 | the name you call Perl by to C<perl_>, C<perl__>, and so on. |
1225 | |
5cd24f17 |
1226 | =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated |
1227 | |
1228 | (D) Perl versions before 5.004 misinterpreted any type marker followed |
1229 | by "$" and a digit. For example, "$$0" was incorrectly taken to mean |
1230 | "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004. |
1231 | |
1232 | However, the developers of Perl 5.004 could not fix this bug completely, |
1233 | because at least two widely-used modules depend on the old meaning of |
1234 | "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the |
1235 | old (broken) way inside strings; but it generates this message as a |
1236 | warning. And in Perl 5.005, this special treatment will cease. |
1237 | |
54310121 |
1238 | =item Value of %s can be "0"; test with defined() |
774d564b |
1239 | |
54310121 |
1240 | (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>, |
1241 | or C<readdir()> as a boolean value. Each of these constructs can return a |
1242 | value of "0"; that would make the conditional expression false, which is |
1243 | probably not what you intended. When using these constructs in conditional |
1244 | expressions, test their values with the C<defined> operator. |
774d564b |
1245 | |
1246 | =item Variable "%s" may be unavailable |
1247 | |
1248 | (W) An inner (nested) I<anonymous> subroutine is inside a I<named> |
1249 | subroutine, and outside that is another subroutine; and the anonymous |
1250 | (innermost) subroutine is referencing a lexical variable defined in |
1251 | the outermost subroutine. For example: |
1252 | |
1253 | sub outermost { my $a; sub middle { sub { $a } } } |
1254 | |
1255 | If the anonymous subroutine is called or referenced (directly or |
1256 | indirectly) from the outermost subroutine, it will share the variable |
1257 | as you would expect. But if the anonymous subroutine is called or |
1258 | referenced when the outermost subroutine is not active, it will see |
1259 | the value of the shared variable as it was before and during the |
1260 | *first* call to the outermost subroutine, which is probably not what |
1261 | you want. |
1262 | |
1263 | In these circumstances, it is usually best to make the middle |
1264 | subroutine anonymous, using the C<sub {}> syntax. Perl has specific |
1265 | support for shared variables in nested anonymous subroutines; a named |
1266 | subroutine in between interferes with this feature. |
1267 | |
1268 | =item Variable "%s" will not stay shared |
1269 | |
1270 | (W) An inner (nested) I<named> subroutine is referencing a lexical |
1271 | variable defined in an outer subroutine. |
1272 | |
1273 | When the inner subroutine is called, it will probably see the value of |
1274 | the outer subroutine's variable as it was before and during the |
1275 | *first* call to the outer subroutine; in this case, after the first |
1276 | call to the outer subroutine is complete, the inner and outer |
1277 | subroutines will no longer share a common value for the variable. In |
1278 | other words, the variable will no longer be shared. |
1279 | |
1280 | Furthermore, if the outer subroutine is anonymous and references a |
1281 | lexical variable outside itself, then the outer and inner subroutines |
1282 | will I<never> share the given variable. |
1283 | |
1284 | This problem can usually be solved by making the inner subroutine |
1285 | anonymous, using the C<sub {}> syntax. When inner anonymous subs that |
1286 | reference variables in outer subroutines are called or referenced, |
54310121 |
1287 | they are automatically rebound to the current values of such |
774d564b |
1288 | variables. |
1289 | |
1290 | =item Warning: something's wrong |
1291 | |
1292 | (W) You passed warn() an empty string (the equivalent of C<warn "">) or |
1293 | you called it with no args and C<$_> was empty. |
1294 | |
54310121 |
1295 | =item Ill-formed logical name |%s| in prime_env_iter |
1296 | |
1297 | (W) A warning peculiar to VMS. A logical name was encountered when preparing |
1298 | to iterate over %ENV which violates the syntactic rules governing logical |
1299 | names. Since it cannot be translated normally, it is skipped, and will not |
1300 | appear in %ENV. This may be a benign occurrence, as some software packages |
1301 | might directly modify logical name tables and introduce nonstandard names, |
1302 | or it may indicate that a logical name table has been corrupted. |
1303 | |
774d564b |
1304 | =item Got an error from DosAllocMem |
5f05dabc |
1305 | |
774d564b |
1306 | (P) An error peculiar to OS/2. Most probably you're using an obsolete |
1307 | version of Perl, and this should not happen anyway. |
5f05dabc |
1308 | |
1309 | =item Malformed PERLLIB_PREFIX |
1310 | |
dc848c6f |
1311 | (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form |
5f05dabc |
1312 | |
1313 | prefix1;prefix2 |
1314 | |
1315 | or |
1316 | |
1317 | prefix1 prefix2 |
1318 | |
dc848c6f |
1319 | with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix |
1320 | of a builtin library search path, prefix2 is substituted. The error |
1321 | may appear if components are not found, or are too long. See |
1322 | "PERLLIB_PREFIX" in F<README.os2>. |
5f05dabc |
1323 | |
1324 | =item PERL_SH_DIR too long |
1325 | |
1326 | (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the |
dc848c6f |
1327 | C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>. |
5f05dabc |
1328 | |
1329 | =item Process terminated by SIG%s |
1330 | |
1331 | (W) This is a standard message issued by OS/2 applications, while *nix |
dc848c6f |
1332 | applications die in silence. It is considered a feature of the OS/2 |
1333 | port. One can easily disable this by appropriate sighandlers, see |
1334 | L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT" |
1335 | in F<README.os2>. |
5f05dabc |
1336 | |
1337 | =back |
1338 | |
1339 | =head1 BUGS |
1340 | |
774d564b |
1341 | If you find what you think is a bug, you might check the headers of |
1342 | recently posted articles in the comp.lang.perl.misc newsgroup. |
1343 | There may also be information at http://www.perl.com/perl/, the Perl |
1344 | Home Page. |
5f05dabc |
1345 | |
1346 | If you believe you have an unreported bug, please run the B<perlbug> |
9607fc9c |
1347 | program included with your release. Make sure you trim your bug down |
1348 | to a tiny but sufficient test case. Your bug report, along with the |
1349 | output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be |
1350 | analysed by the Perl porting team. |
5f05dabc |
1351 | |
1352 | =head1 SEE ALSO |
1353 | |
1354 | The F<Changes> file for exhaustive details on what changed. |
1355 | |
1356 | The F<INSTALL> file for how to build Perl. This file has been |
1357 | significantly updated for 5.004, so even veteran users should |
1358 | look through it. |
1359 | |
1360 | The F<README> file for general stuff. |
1361 | |
1362 | The F<Copying> file for copyright information. |
1363 | |
1364 | =head1 HISTORY |
1365 | |
1366 | Constructed by Tom Christiansen, grabbing material with permission |
1367 | from innumerable contributors, with kibitzing by more than a few Perl |
1368 | porters. |
1369 | |
2ae324a7 |
1370 | Last update: Sat Mar 8 19:51:26 EST 1997 |