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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 | |
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13 | Perl5.004 builds out of the box on Unix, Plan 9, LynxOS, VMS, OS/2, |
14 | QNX, AmigaOS, and Windows NT. Perl runs on Windows 95 as well, but it |
15 | cannot be built there, for lack of a reasonable command interpreter. |
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16 | |
17 | =head1 Core Changes |
18 | |
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19 | Most importantly, many bugs were fixed, including several security |
20 | problems. See the F<Changes> file in the distribution for details. |
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21 | |
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22 | =head2 List assignment to %ENV works |
23 | |
24 | C<%ENV = ()> and C<%ENV = @list> now work as expected (except on VMS |
25 | where it generates a fatal error). |
26 | |
27 | =head2 "Can't locate Foo.pm in @INC" error now lists @INC |
28 | |
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29 | =head2 Compilation option: Binary compatibility with 5.003 |
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30 | |
31 | There is a new Configure question that asks if you want to maintain |
32 | binary compatibility with Perl 5.003. If you choose binary |
33 | compatibility, you do not have to recompile your extensions, but you |
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34 | might have symbol conflicts if you embed Perl in another application, |
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35 | just as in the 5.003 release. By default, binary compatibility |
36 | is preserved at the expense of symbol table pollution. |
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37 | |
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38 | =head2 $PERL5OPT environment variable |
39 | |
40 | You may now put Perl options in the $PERL5OPT environment variable. |
41 | Unless Perl is running with taint checks, it will interpret this |
42 | variable as if its contents had appeared on a "#!perl" line at the |
43 | beginning of your script, except that hyphens are optional. PERL5OPT |
44 | may only be used to set the following switches: B<-[DIMUdmw]>. |
45 | |
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46 | =head2 Limitations on B<-M>, B<-m>, and B<-T> options |
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47 | |
48 | The C<-M> and C<-m> options are no longer allowed on the C<#!> line of |
49 | a script. If a script needs a module, it should invoke it with the |
50 | C<use> pragma. |
51 | |
52 | The B<-T> option is also forbidden on the C<#!> line of a script, |
53 | unless it was present on the Perl command line. Due to the way C<#!> |
54 | works, this usually means that B<-T> must be in the first argument. |
55 | Thus: |
56 | |
57 | #!/usr/bin/perl -T -w |
58 | |
59 | will probably work for an executable script invoked as C<scriptname>, |
60 | while: |
61 | |
62 | #!/usr/bin/perl -w -T |
63 | |
64 | will probably fail under the same conditions. (Non-Unix systems will |
65 | probably not follow this rule.) But C<perl scriptname> is guaranteed |
66 | to fail, since then there is no chance of B<-T> being found on the |
67 | command line before it is found on the C<#!> line. |
68 | |
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69 | =head2 More precise warnings |
70 | |
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71 | If you removed the B<-w> option from your Perl 5.003 scripts because it |
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72 | made Perl too verbose, we recommend that you try putting it back when |
73 | you upgrade to Perl 5.004. Each new perl version tends to remove some |
74 | undesirable warnings, while adding new warnings that may catch bugs in |
75 | your scripts. |
76 | |
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77 | =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods |
78 | |
79 | Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods |
80 | (using the C<@ISA> hierarchy), even when the function to be autoloaded |
81 | was called as a plain function (e.g. C<Foo::bar()>), not a method |
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82 | (e.g. C<Foo-E<gt>bar()> or C<$obj-E<gt>bar()>). |
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83 | |
84 | Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s. |
85 | However, there is a significant base of existing code that may be using |
86 | the old behavior. So, as an interim step, Perl 5.004 issues an optional |
87 | warning when a non-method uses an inherited C<AUTOLOAD>. |
88 | |
89 | The simple rule is: Inheritance will not work when autoloading |
90 | non-methods. The simple fix for old code is: In any module that used to |
91 | depend on inheriting C<AUTOLOAD> for non-methods from a base class named |
92 | C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup. |
93 | |
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94 | =head2 Previously deprecated %OVERLOAD is no longer usable |
95 | |
96 | Using %OVERLOAD to define overloading was deprecated in 5.003. |
97 | Overloading is now defined using the overload pragma. %OVERLOAD is |
98 | still used internally but should not be used by Perl scripts. See |
99 | L<overload> for more details. |
100 | |
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101 | =head2 Subroutine arguments created only when they're modified |
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102 | |
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103 | In Perl 5.004, nonexistent array and hash elements used as subroutine |
104 | parameters are brought into existence only if they are actually |
105 | assigned to (via C<@_>). |
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106 | |
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107 | Earlier versions of Perl vary in their handling of such arguments. |
108 | Perl versions 5.002 and 5.003 always brought them into existence. |
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109 | Perl versions 5.000 and 5.001 brought them into existence only if |
110 | they were not the first argument (which was almost certainly a bug). |
111 | Earlier versions of Perl never brought them into existence. |
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112 | |
113 | For example, given this code: |
114 | |
115 | undef @a; undef %a; |
116 | sub show { print $_[0] }; |
117 | sub change { $_[0]++ }; |
118 | show($a[2]); |
119 | change($a{b}); |
120 | |
121 | After this code executes in Perl 5.004, $a{b} exists but $a[2] does |
122 | not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed |
123 | (but $a[2]'s value would have been undefined). |
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124 | |
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125 | =head2 Group vector changeable with C<$)> |
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126 | |
127 | The C<$)> special variable has always (well, in Perl 5, at least) |
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128 | reflected not only the current effective group, but also the group list |
129 | as returned by the C<getgroups()> C function (if there is one). |
130 | However, until this release, there has not been a way to call the |
131 | C<setgroups()> C function from Perl. |
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132 | |
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133 | In Perl 5.004, assigning to C<$)> is exactly symmetrical with examining |
134 | it: The first number in its string value is used as the effective gid; |
135 | if there are any numbers after the first one, they are passed to the |
136 | C<setgroups()> C function (if there is one). |
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137 | |
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138 | =head2 Fixed parsing of $$<digit>, &$<digit>, etc. |
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139 | |
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140 | Perl versions before 5.004 misinterpreted any type marker followed by |
141 | "$" and a digit. For example, "$$0" was incorrectly taken to mean |
142 | "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004. |
143 | |
144 | However, the developers of Perl 5.004 could not fix this bug completely, |
145 | because at least two widely-used modules depend on the old meaning of |
146 | "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the |
147 | old (broken) way inside strings; but it generates this message as a |
148 | warning. And in Perl 5.005, this special treatment will cease. |
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149 | |
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150 | =head2 Fixed localization of $<digit>, $&, etc. |
151 | |
152 | Perl versions before 5.004 did not always properly localize the |
153 | regex-related special variables. Perl 5.004 does localize them, as |
154 | the documentation has always said it should. This may result in $1, |
155 | $2, etc. no longer being set where existing programs use them. |
156 | |
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157 | =head2 No resetting of $. on implicit close |
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158 | |
159 | The documentation for Perl 5.0 has always stated that C<$.> is I<not> |
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160 | reset when an already-open file handle is reopened with no intervening |
161 | call to C<close>. Due to a bug, perl versions 5.000 through 5.003 |
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162 | I<did> reset C<$.> under that circumstance; Perl 5.004 does not. |
163 | |
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164 | =head2 C<wantarray> may return undef |
165 | |
166 | The C<wantarray> operator returns true if a subroutine is expected to |
167 | return a list, and false otherwise. In Perl 5.004, C<wantarray> can |
168 | also return the undefined value if a subroutine's return value will |
169 | not be used at all, which allows subroutines to avoid a time-consuming |
170 | calculation of a return value if it isn't going to be used. |
171 | |
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172 | =head2 C<eval EXPR> determines value of EXPR in scalar context |
173 | |
174 | Perl (version 5) used to determine the value of EXPR inconsistently, |
175 | sometimes incorrectly using the surrounding context for the determination. |
176 | Now, the value of EXPR (before being parsed by eval) is always determined in |
177 | a scalar context. Once parsed, it is executed as before, by providing |
178 | the context that the scope surrounding the eval provided. This change |
179 | makes the behavior Perl4 compatible, besides fixing bugs resulting from |
180 | the inconsistent behavior. This program: |
181 | |
182 | @a = qw(time now is time); |
183 | print eval @a; |
184 | print '|', scalar eval @a; |
185 | |
186 | used to print something like "timenowis881399109|4", but now (and in perl4) |
187 | prints "4|4". |
188 | |
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189 | =head2 Changes to tainting checks |
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190 | |
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191 | A bug in previous versions may have failed to detect some insecure |
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192 | conditions when taint checks are turned on. (Taint checks are used |
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193 | in setuid or setgid scripts, or when explicitly turned on with the |
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194 | C<-T> invocation option.) Although it's unlikely, this may cause a |
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195 | previously-working script to now fail -- which should be construed |
196 | as a blessing, since that indicates a potentially-serious security |
197 | hole was just plugged. |
198 | |
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199 | The new restrictions when tainting include: |
200 | |
201 | =over |
202 | |
203 | =item No glob() or <*> |
204 | |
205 | These operators may spawn the C shell (csh), which cannot be made |
206 | safe. This restriction will be lifted in a future version of Perl |
207 | when globbing is implemented without the use of an external program. |
208 | |
209 | =item No spawning if tainted $CDPATH, $ENV, $BASH_ENV |
210 | |
211 | These environment variables may alter the behavior of spawned programs |
212 | (especially shells) in ways that subvert security. So now they are |
213 | treated as dangerous, in the manner of $IFS and $PATH. |
214 | |
215 | =item No spawning if tainted $TERM doesn't look like a terminal name |
216 | |
217 | Some termcap libraries do unsafe things with $TERM. However, it would be |
218 | unnecessarily harsh to treat all $TERM values as unsafe, since only shell |
219 | metacharacters can cause trouble in $TERM. So a tainted $TERM is |
220 | considered to be safe if it contains only alphanumerics, underscores, |
221 | dashes, and colons, and unsafe if it contains other characters (including |
222 | whitespace). |
223 | |
224 | =back |
225 | |
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226 | =head2 New Opcode module and revised Safe module |
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227 | |
228 | A new Opcode module supports the creation, manipulation and |
229 | application of opcode masks. The revised Safe module has a new API |
230 | and is implemented using the new Opcode module. Please read the new |
231 | Opcode and Safe documentation. |
232 | |
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233 | =head2 Embedding improvements |
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234 | |
235 | In older versions of Perl it was not possible to create more than one |
236 | Perl interpreter instance inside a single process without leaking like a |
237 | sieve and/or crashing. The bugs that caused this behavior have all been |
238 | fixed. However, you still must take care when embedding Perl in a C |
239 | program. See the updated perlembed manpage for tips on how to manage |
240 | your interpreters. |
241 | |
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242 | =head2 Internal change: FileHandle class based on IO::* classes |
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243 | |
244 | File handles are now stored internally as type IO::Handle. The |
245 | FileHandle module is still supported for backwards compatibility, but |
246 | it is now merely a front end to the IO::* modules -- specifically, |
247 | IO::Handle, IO::Seekable, and IO::File. We suggest, but do not |
248 | require, that you use the IO::* modules in new code. |
249 | |
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250 | In harmony with this change, C<*GLOB{FILEHANDLE}> is now just a |
251 | backward-compatible synonym for C<*GLOB{IO}>. |
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252 | |
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253 | =head2 Internal change: PerlIO abstraction interface |
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254 | |
255 | It is now possible to build Perl with AT&T's sfio IO package |
256 | instead of stdio. See L<perlapio> for more details, and |
257 | the F<INSTALL> file for how to use it. |
258 | |
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259 | =head2 New and changed syntax |
260 | |
261 | =over |
262 | |
263 | =item $coderef->(PARAMS) |
264 | |
265 | A subroutine reference may now be suffixed with an arrow and a |
266 | (possibly empty) parameter list. This syntax denotes a call of the |
267 | referenced subroutine, with the given parameters (if any). |
268 | |
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269 | This new syntax follows the pattern of S<C<$hashref-E<gt>{FOO}>> and |
270 | S<C<$aryref-E<gt>[$foo]>>: You may now write S<C<&$subref($foo)>> as |
271 | S<C<$subref-E<gt>($foo)>>. All of these arrow terms may be chained; |
272 | thus, S<C<&{$table-E<gt>{FOO}}($bar)>> may now be written |
273 | S<C<$table-E<gt>{FOO}-E<gt>($bar)>>. |
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274 | |
275 | =back |
276 | |
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277 | =head2 New and changed builtin constants |
278 | |
279 | =over |
280 | |
281 | =item __PACKAGE__ |
282 | |
283 | The current package name at compile time, or the undefined value if |
284 | there is no current package (due to a C<package;> directive). Like |
285 | C<__FILE__> and C<__LINE__>, C<__PACKAGE__> does I<not> interpolate |
286 | into strings. |
287 | |
288 | =back |
289 | |
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290 | =head2 New and changed builtin variables |
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291 | |
292 | =over |
293 | |
294 | =item $^E |
295 | |
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296 | Extended error message on some platforms. (Also known as |
297 | $EXTENDED_OS_ERROR if you C<use English>). |
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298 | |
299 | =item $^H |
300 | |
301 | The current set of syntax checks enabled by C<use strict>. See the |
302 | documentation of C<strict> for more details. Not actually new, but |
303 | newly documented. |
304 | Because it is intended for internal use by Perl core components, |
305 | there is no C<use English> long name for this variable. |
306 | |
307 | =item $^M |
308 | |
309 | By default, running out of memory it is not trappable. However, if |
310 | compiled for this, Perl may use the contents of C<$^M> as an emergency |
311 | pool after die()ing with this message. Suppose that your Perl were |
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312 | compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc. Then |
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313 | |
314 | $^M = 'a' x (1<<16); |
315 | |
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316 | would allocate a 64K buffer for use when in emergency. |
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317 | See the F<INSTALL> file for information on how to enable this option. |
318 | As a disincentive to casual use of this advanced feature, |
319 | there is no C<use English> long name for this variable. |
320 | |
321 | =back |
322 | |
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323 | =head2 New and changed builtin functions |
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324 | |
325 | =over |
326 | |
327 | =item delete on slices |
328 | |
329 | This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>) |
330 | |
331 | =item flock |
332 | |
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333 | is now supported on more platforms, prefers fcntl to lockf when |
334 | emulating, and always flushes before (un)locking. |
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335 | |
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336 | =item printf and sprintf |
337 | |
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338 | Perl now implements these functions itself; it doesn't use the C |
339 | library function sprintf() any more, except for floating-point |
340 | numbers, and even then only known flags are allowed. As a result, it |
341 | is now possible to know which conversions and flags will work, and |
342 | what they will do. |
343 | |
344 | The new conversions in Perl's sprintf() are: |
345 | |
346 | %i a synonym for %d |
347 | %p a pointer (the address of the Perl value, in hexadecimal) |
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348 | %n special: *stores* the number of characters output so far |
349 | into the next variable in the parameter list |
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350 | |
351 | The new flags that go between the C<%> and the conversion are: |
352 | |
353 | # prefix octal with "0", hex with "0x" |
354 | h interpret integer as C type "short" or "unsigned short" |
355 | V interpret integer as Perl's standard integer type |
356 | |
357 | Also, where a number would appear in the flags, an asterisk ("*") may |
358 | be used instead, in which case Perl uses the next item in the |
359 | parameter list as the given number (that is, as the field width or |
360 | precision). If a field width obtained through "*" is negative, it has |
361 | the same effect as the '-' flag: left-justification. |
362 | |
363 | See L<perlfunc/sprintf> for a complete list of conversion and flags. |
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364 | |
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365 | =item keys as an lvalue |
366 | |
367 | As an lvalue, C<keys> allows you to increase the number of hash buckets |
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368 | allocated for the given hash. This can gain you a measure of efficiency if |
369 | you know the hash is going to get big. (This is similar to pre-extending |
370 | an array by assigning a larger number to $#array.) If you say |
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371 | |
372 | keys %hash = 200; |
373 | |
374 | then C<%hash> will have at least 200 buckets allocated for it. These |
375 | buckets will be retained even if you do C<%hash = ()>; use C<undef |
376 | %hash> if you want to free the storage while C<%hash> is still in scope. |
377 | You can't shrink the number of buckets allocated for the hash using |
378 | C<keys> in this way (but you needn't worry about doing this by accident, |
379 | as trying has no effect). |
380 | |
381 | =item my() in Control Structures |
382 | |
383 | You can now use my() (with or without the parentheses) in the control |
384 | expressions of control structures such as: |
385 | |
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386 | while (defined(my $line = <>)) { |
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387 | $line = lc $line; |
388 | } continue { |
389 | print $line; |
390 | } |
391 | |
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392 | if ((my $answer = <STDIN>) =~ /^y(es)?$/i) { |
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393 | user_agrees(); |
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394 | } elsif ($answer =~ /^n(o)?$/i) { |
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395 | user_disagrees(); |
396 | } else { |
397 | chomp $answer; |
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398 | die "`$answer' is neither `yes' nor `no'"; |
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399 | } |
400 | |
401 | Also, you can declare a foreach loop control variable as lexical by |
402 | preceding it with the word "my". For example, in: |
403 | |
404 | foreach my $i (1, 2, 3) { |
405 | some_function(); |
406 | } |
407 | |
408 | $i is a lexical variable, and the scope of $i extends to the end of |
409 | the loop, but not beyond it. |
410 | |
411 | Note that you still cannot use my() on global punctuation variables |
412 | such as $_ and the like. |
413 | |
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414 | =item pack() and unpack() |
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415 | |
416 | A new format 'w' represents a BER compressed integer (as defined in |
417 | ASN.1). Its format is a sequence of one or more bytes, each of which |
418 | provides seven bits of the total value, with the most significant |
419 | first. Bit eight of each byte is set, except for the last byte, in |
420 | which bit eight is clear. |
421 | |
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422 | If 'p' or 'P' are given undef as values, they now generate a NULL |
423 | pointer. |
424 | |
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425 | Both pack() and unpack() now fail when their templates contain invalid |
426 | types. (Invalid types used to be ignored.) |
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427 | |
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428 | =item sysseek() |
429 | |
430 | The new sysseek() operator is a variant of seek() that sets and gets the |
431 | file's system read/write position, using the lseek(2) system call. It is |
432 | the only reliable way to seek before using sysread() or syswrite(). Its |
433 | return value is the new position, or the undefined value on failure. |
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434 | |
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435 | =item use VERSION |
436 | |
437 | If the first argument to C<use> is a number, it is treated as a version |
438 | number instead of a module name. If the version of the Perl interpreter |
439 | is less than VERSION, then an error message is printed and Perl exits |
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440 | immediately. Because C<use> occurs at compile time, this check happens |
441 | immediately during the compilation process, unlike C<require VERSION>, |
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442 | which waits until runtime for the check. This is often useful if you |
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443 | need to check the current Perl version before C<use>ing library modules |
444 | which have changed in incompatible ways from older versions of Perl. |
445 | (We try not to do this more than we have to.) |
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446 | |
447 | =item use Module VERSION LIST |
448 | |
449 | If the VERSION argument is present between Module and LIST, then the |
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450 | C<use> will call the VERSION method in class Module with the given |
451 | version as an argument. The default VERSION method, inherited from |
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452 | the UNIVERSAL class, croaks if the given version is larger than the |
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453 | value of the variable $Module::VERSION. (Note that there is not a |
454 | comma after VERSION!) |
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455 | |
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456 | This version-checking mechanism is similar to the one currently used |
457 | in the Exporter module, but it is faster and can be used with modules |
458 | that don't use the Exporter. It is the recommended method for new |
459 | code. |
460 | |
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461 | =item prototype(FUNCTION) |
462 | |
463 | Returns the prototype of a function as a string (or C<undef> if the |
464 | function has no prototype). FUNCTION is a reference to or the name of the |
465 | function whose prototype you want to retrieve. |
466 | (Not actually new; just never documented before.) |
467 | |
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468 | =item srand |
469 | |
470 | The default seed for C<srand>, which used to be C<time>, has been changed. |
471 | Now it's a heady mix of difficult-to-predict system-dependent values, |
472 | which should be sufficient for most everyday purposes. |
473 | |
474 | Previous to version 5.004, calling C<rand> without first calling C<srand> |
475 | would yield the same sequence of random numbers on most or all machines. |
476 | Now, when perl sees that you're calling C<rand> and haven't yet called |
477 | C<srand>, it calls C<srand> with the default seed. You should still call |
478 | C<srand> manually if your code might ever be run on a pre-5.004 system, |
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479 | of course, or if you want a seed other than the default. |
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480 | |
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481 | =item $_ as Default |
482 | |
483 | Functions documented in the Camel to default to $_ now in |
484 | fact do, and all those that do are so documented in L<perlfunc>. |
485 | |
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486 | =item C<m//gc> does not reset search position on failure |
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487 | |
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488 | The C<m//g> match iteration construct has always reset its target |
489 | string's search position (which is visible through the C<pos> operator) |
490 | when a match fails; as a result, the next C<m//g> match after a failure |
491 | starts again at the beginning of the string. With Perl 5.004, this |
492 | reset may be disabled by adding the "c" (for "continue") modifier, |
493 | i.e. C<m//gc>. This feature, in conjunction with the C<\G> zero-width |
494 | assertion, makes it possible to chain matches together. See L<perlop> |
495 | and L<perlre>. |
44a8e56a |
496 | |
3fe9a6f1 |
497 | =item C<m//x> ignores whitespace before ?*+{} |
498 | |
499 | The C<m//x> construct has always been intended to ignore all unescaped |
500 | whitespace. However, before Perl 5.004, whitespace had the effect of |
54310121 |
501 | escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was |
3fe9a6f1 |
502 | (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004. |
503 | |
774d564b |
504 | =item nested C<sub{}> closures work now |
505 | |
2ae324a7 |
506 | Prior to the 5.004 release, nested anonymous functions didn't work |
507 | right. They do now. |
774d564b |
508 | |
509 | =item formats work right on changing lexicals |
510 | |
511 | Just like anonymous functions that contain lexical variables |
512 | that change (like a lexical index variable for a C<foreach> loop), |
513 | formats now work properly. For example, this silently failed |
c90c0ff4 |
514 | before (printed only zeros), but is fine now: |
774d564b |
515 | |
516 | my $i; |
517 | foreach $i ( 1 .. 10 ) { |
c90c0ff4 |
518 | write; |
519 | } |
520 | format = |
774d564b |
521 | my i is @# |
522 | $i |
523 | . |
774d564b |
524 | |
84902520 |
525 | However, it still fails (without a warning) if the foreach is within a |
526 | subroutine: |
527 | |
528 | my $i; |
529 | sub foo { |
530 | foreach $i ( 1 .. 10 ) { |
531 | write; |
532 | } |
533 | } |
534 | foo; |
535 | format = |
536 | my i is @# |
537 | $i |
538 | . |
539 | |
5f05dabc |
540 | =back |
541 | |
54310121 |
542 | =head2 New builtin methods |
5f05dabc |
543 | |
544 | The C<UNIVERSAL> package automatically contains the following methods that |
545 | are inherited by all other classes: |
546 | |
0a753a76 |
547 | =over |
5f05dabc |
548 | |
549 | =item isa(CLASS) |
550 | |
68dc0745 |
551 | C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS> |
5f05dabc |
552 | |
553 | C<isa> is also exportable and can be called as a sub with two arguments. This |
554 | allows the ability to check what a reference points to. Example: |
555 | |
556 | use UNIVERSAL qw(isa); |
557 | |
558 | if(isa($ref, 'ARRAY')) { |
559 | ... |
560 | } |
561 | |
562 | =item can(METHOD) |
563 | |
564 | C<can> checks to see if its object has a method called C<METHOD>, |
565 | if it does then a reference to the sub is returned; if it does not then |
566 | I<undef> is returned. |
567 | |
568 | =item VERSION( [NEED] ) |
569 | |
71be2cbc |
570 | C<VERSION> returns the version number of the class (package). If the |
571 | NEED argument is given then it will check that the current version (as |
572 | defined by the $VERSION variable in the given package) not less than |
573 | NEED; it will die if this is not the case. This method is normally |
574 | called as a class method. This method is called automatically by the |
575 | C<VERSION> form of C<use>. |
5f05dabc |
576 | |
577 | use A 1.2 qw(some imported subs); |
71be2cbc |
578 | # implies: |
579 | A->VERSION(1.2); |
5f05dabc |
580 | |
5f05dabc |
581 | =back |
582 | |
583 | B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and |
774d564b |
584 | C<isa> uses a very similar method and caching strategy. This may cause |
5f05dabc |
585 | strange effects if the Perl code dynamically changes @ISA in any package. |
586 | |
587 | You may add other methods to the UNIVERSAL class via Perl or XS code. |
588 | You do not need to C<use UNIVERSAL> in order to make these methods |
589 | available to your program. This is necessary only if you wish to |
590 | have C<isa> available as a plain subroutine in the current package. |
591 | |
54310121 |
592 | =head2 TIEHANDLE now supported |
5f05dabc |
593 | |
774d564b |
594 | See L<perltie> for other kinds of tie()s. |
595 | |
5f05dabc |
596 | =over |
597 | |
598 | =item TIEHANDLE classname, LIST |
599 | |
600 | This is the constructor for the class. That means it is expected to |
601 | return an object of some sort. The reference can be used to |
602 | hold some internal information. |
603 | |
2ae324a7 |
604 | sub TIEHANDLE { |
605 | print "<shout>\n"; |
606 | my $i; |
774d564b |
607 | return bless \$i, shift; |
608 | } |
5f05dabc |
609 | |
610 | =item PRINT this, LIST |
611 | |
612 | This method will be triggered every time the tied handle is printed to. |
613 | Beyond its self reference it also expects the list that was passed to |
614 | the print function. |
615 | |
2ae324a7 |
616 | sub PRINT { |
617 | $r = shift; |
618 | $$r++; |
774d564b |
619 | return print join( $, => map {uc} @_), $\; |
620 | } |
5f05dabc |
621 | |
46fc3d4c |
622 | =item PRINTF this, LIST |
623 | |
624 | This method will be triggered every time the tied handle is printed to |
625 | with the C<printf()> function. |
626 | Beyond its self reference it also expects the format and list that was |
627 | passed to the printf function. |
628 | |
629 | sub PRINTF { |
630 | shift; |
631 | my $fmt = shift; |
632 | print sprintf($fmt, @_)."\n"; |
633 | } |
634 | |
2ae324a7 |
635 | =item READ this LIST |
636 | |
637 | This method will be called when the handle is read from via the C<read> |
638 | or C<sysread> functions. |
639 | |
640 | sub READ { |
641 | $r = shift; |
642 | my($buf,$len,$offset) = @_; |
643 | print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset"; |
644 | } |
645 | |
5f05dabc |
646 | =item READLINE this |
647 | |
648 | This method will be called when the handle is read from. The method |
649 | should return undef when there is no more data. |
650 | |
2ae324a7 |
651 | sub READLINE { |
652 | $r = shift; |
653 | return "PRINT called $$r times\n" |
774d564b |
654 | } |
5f05dabc |
655 | |
2ae324a7 |
656 | =item GETC this |
657 | |
658 | This method will be called when the C<getc> function is called. |
659 | |
660 | sub GETC { print "Don't GETC, Get Perl"; return "a"; } |
661 | |
5f05dabc |
662 | =item DESTROY this |
663 | |
664 | As with the other types of ties, this method will be called when the |
665 | tied handle is about to be destroyed. This is useful for debugging and |
666 | possibly for cleaning up. |
667 | |
2ae324a7 |
668 | sub DESTROY { |
774d564b |
669 | print "</shout>\n"; |
670 | } |
5f05dabc |
671 | |
672 | =back |
673 | |
54310121 |
674 | =head2 Malloc enhancements |
aa689395 |
675 | |
84902520 |
676 | If perl is compiled with the malloc included with the perl distribution |
677 | (that is, if C<perl -V:d_mymalloc> is 'define') then you can print |
2ae324a7 |
678 | memory statistics at runtime by running Perl thusly: |
aa689395 |
679 | |
680 | env PERL_DEBUG_MSTATS=2 perl your_script_here |
681 | |
682 | The value of 2 means to print statistics after compilation and on |
84902520 |
683 | exit; with a value of 1, the statistics are printed only on exit. |
aa689395 |
684 | (If you want the statistics at an arbitrary time, you'll need to |
685 | install the optional module Devel::Peek.) |
686 | |
84902520 |
687 | Three new compilation flags are recognized by malloc.c. (They have no |
688 | effect if perl is compiled with system malloc().) |
689 | |
690 | =over |
691 | |
692 | =item -DPERL_EMERGENCY_SBRK |
aa689395 |
693 | |
694 | If this macro is defined, running out of memory need not be a fatal |
695 | error: a memory pool can allocated by assigning to the special |
696 | variable C<$^M>. See L<"$^M">. |
774d564b |
697 | |
aa689395 |
698 | =item -DPACK_MALLOC |
699 | |
700 | Perl memory allocation is by bucket with sizes close to powers of two. |
701 | Because of these malloc overhead may be big, especially for data of |
702 | size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses |
703 | a slightly different algorithm for small allocations (up to 64 bytes |
704 | long), which makes it possible to have overhead down to 1 byte for |
705 | allocations which are powers of two (and appear quite often). |
706 | |
707 | Expected memory savings (with 8-byte alignment in C<alignbytes>) is |
708 | about 20% for typical Perl usage. Expected slowdown due to additional |
709 | malloc overhead is in fractions of a percent (hard to measure, because |
710 | of the effect of saved memory on speed). |
711 | |
712 | =item -DTWO_POT_OPTIMIZE |
713 | |
714 | Similarly to C<PACK_MALLOC>, this macro improves allocations of data |
715 | with size close to a power of two; but this works for big allocations |
716 | (starting with 16K by default). Such allocations are typical for big |
717 | hashes and special-purpose scripts, especially image processing. |
718 | |
719 | On recent systems, the fact that perl requires 2M from system for 1M |
720 | allocation will not affect speed of execution, since the tail of such |
721 | a chunk is not going to be touched (and thus will not require real |
722 | memory). However, it may result in a premature out-of-memory error. |
723 | So if you will be manipulating very large blocks with sizes close to |
724 | powers of two, it would be wise to define this macro. |
725 | |
726 | Expected saving of memory is 0-100% (100% in applications which |
727 | require most memory in such 2**n chunks); expected slowdown is |
728 | negligible. |
729 | |
730 | =back |
731 | |
54310121 |
732 | =head2 Miscellaneous efficiency enhancements |
774d564b |
733 | |
734 | Functions that have an empty prototype and that do nothing but return |
735 | a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>). |
736 | |
aa689395 |
737 | Each unique hash key is only allocated once, no matter how many hashes |
738 | have an entry with that key. So even if you have 100 copies of the |
68dc0745 |
739 | same hash, the hash keys never have to be reallocated. |
aa689395 |
740 | |
7bac28a0 |
741 | =head1 Support for More Operating Systems |
742 | |
743 | Support for the following operating systems is new in Perl 5.004. |
744 | |
745 | =head2 Win32 |
746 | |
747 | Perl 5.004 now includes support for building a "native" perl under |
748 | Windows NT, using the Microsoft Visual C++ compiler (versions 2.0 |
f7c603cb |
749 | and above) or the Borland C++ compiler (versions 5.02 and above). |
750 | The resulting perl can be used under Windows 95 (if it |
7bac28a0 |
751 | is installed in the same directory locations as it got installed |
752 | in Windows NT). This port includes support for perl extension |
753 | building tools like L<MakeMaker> and L<h2xs>, so that many extensions |
754 | available on the Comprehensive Perl Archive Network (CPAN) can now be |
755 | readily built under Windows NT. See http://www.perl.com/ for more |
756 | information on CPAN, and L<README.win32> for more details on how to |
757 | get started with building this port. |
758 | |
759 | There is also support for building perl under the Cygwin32 environment. |
760 | Cygwin32 is a set of GNU tools that make it possible to compile and run |
761 | many UNIX programs under Windows NT by providing a mostly UNIX-like |
762 | interface for compilation and execution. See L<README.cygwin32> for |
763 | more details on this port, and how to obtain the Cygwin32 toolkit. |
7bac28a0 |
764 | |
765 | =head2 Plan 9 |
766 | |
767 | See L<README.plan9>. |
768 | |
769 | =head2 QNX |
770 | |
771 | See L<README.qnx>. |
772 | |
773 | =head2 AmigaOS |
774 | |
775 | See L<README.amigaos>. |
776 | |
5f05dabc |
777 | =head1 Pragmata |
778 | |
54310121 |
779 | Six new pragmatic modules exist: |
5f05dabc |
780 | |
781 | =over |
782 | |
54310121 |
783 | =item use autouse MODULE => qw(sub1 sub2 sub3) |
784 | |
785 | Defers C<require MODULE> until someone calls one of the specified |
786 | subroutines (which must be exported by MODULE). This pragma should be |
787 | used with caution, and only when necessary. |
788 | |
5f05dabc |
789 | =item use blib |
790 | |
774d564b |
791 | =item use blib 'dir' |
792 | |
5f05dabc |
793 | Looks for MakeMaker-like I<'blib'> directory structure starting in |
794 | I<dir> (or current directory) and working back up to five levels of |
795 | parent directories. |
796 | |
797 | Intended for use on command line with B<-M> option as a way of testing |
798 | arbitrary scripts against an uninstalled version of a package. |
799 | |
54310121 |
800 | =item use constant NAME => VALUE |
801 | |
802 | Provides a convenient interface for creating compile-time constants, |
803 | See L<perlsub/"Constant Functions">. |
804 | |
5f05dabc |
805 | =item use locale |
806 | |
807 | Tells the compiler to enable (or disable) the use of POSIX locales for |
54310121 |
808 | builtin operations. |
5f05dabc |
809 | |
810 | When C<use locale> is in effect, the current LC_CTYPE locale is used |
811 | for regular expressions and case mapping; LC_COLLATE for string |
812 | ordering; and LC_NUMERIC for numeric formating in printf and sprintf |
813 | (but B<not> in print). LC_NUMERIC is always used in write, since |
814 | lexical scoping of formats is problematic at best. |
815 | |
816 | Each C<use locale> or C<no locale> affects statements to the end of |
817 | the enclosing BLOCK or, if not inside a BLOCK, to the end of the |
818 | current file. Locales can be switched and queried with |
819 | POSIX::setlocale(). |
820 | |
821 | See L<perllocale> for more information. |
822 | |
823 | =item use ops |
824 | |
7cfe7857 |
825 | Disable unsafe opcodes, or any named opcodes, when compiling Perl code. |
5f05dabc |
826 | |
ff0cee69 |
827 | =item use vmsish |
828 | |
829 | Enable VMS-specific language features. Currently, there are three |
aa689395 |
830 | VMS-specific features available: 'status', which makes C<$?> and |
ff0cee69 |
831 | C<system> return genuine VMS status values instead of emulating POSIX; |
832 | 'exit', which makes C<exit> take a genuine VMS status value instead of |
833 | assuming that C<exit 1> is an error; and 'time', which makes all times |
834 | relative to the local time zone, in the VMS tradition. |
835 | |
5f05dabc |
836 | =back |
837 | |
838 | =head1 Modules |
839 | |
5cd24f17 |
840 | =head2 Required Updates |
841 | |
842 | Though Perl 5.004 is compatible with almost all modules that work |
843 | with Perl 5.003, there are a few exceptions: |
844 | |
845 | Module Required Version for Perl 5.004 |
846 | ------ ------------------------------- |
137443ea |
847 | Filter Filter-1.12 |
848 | LWP libwww-perl-5.08 |
5cd24f17 |
849 | Tk Tk400.202 (-w makes noise) |
850 | |
137443ea |
851 | Also, the majordomo mailing list program, version 1.94.1, doesn't work |
852 | with Perl 5.004 (nor with perl 4), because it executes an invalid |
853 | regular expression. This bug is fixed in majordomo version 1.94.2. |
854 | |
54310121 |
855 | =head2 Installation directories |
f86702cc |
856 | |
857 | The I<installperl> script now places the Perl source files for |
858 | extensions in the architecture-specific library directory, which is |
859 | where the shared libraries for extensions have always been. This |
860 | change is intended to allow administrators to keep the Perl 5.004 |
861 | library directory unchanged from a previous version, without running |
862 | the risk of binary incompatibility between extensions' Perl source and |
863 | shared libraries. |
864 | |
54310121 |
865 | =head2 Module information summary |
5f05dabc |
866 | |
774d564b |
867 | Brand new modules, arranged by topic rather than strictly |
868 | alphabetically: |
869 | |
137443ea |
870 | CGI.pm Web server interface ("Common Gateway Interface") |
871 | CGI/Apache.pm Support for Apache's Perl module |
872 | CGI/Carp.pm Log server errors with helpful context |
873 | CGI/Fast.pm Support for FastCGI (persistent server process) |
874 | CGI/Push.pm Support for server push |
875 | CGI/Switch.pm Simple interface for multiple server types |
876 | |
877 | CPAN Interface to Comprehensive Perl Archive Network |
878 | CPAN::FirstTime Utility for creating CPAN configuration file |
879 | CPAN::Nox Runs CPAN while avoiding compiled extensions |
5f05dabc |
880 | |
881 | IO.pm Top-level interface to IO::* classes |
882 | IO/File.pm IO::File extension Perl module |
883 | IO/Handle.pm IO::Handle extension Perl module |
884 | IO/Pipe.pm IO::Pipe extension Perl module |
885 | IO/Seekable.pm IO::Seekable extension Perl module |
886 | IO/Select.pm IO::Select extension Perl module |
887 | IO/Socket.pm IO::Socket extension Perl module |
888 | |
889 | Opcode.pm Disable named opcodes when compiling Perl code |
890 | |
891 | ExtUtils/Embed.pm Utilities for embedding Perl in C programs |
892 | ExtUtils/testlib.pm Fixes up @INC to use just-built extension |
893 | |
5f05dabc |
894 | FindBin.pm Find path of currently executing program |
895 | |
8cc95fdb |
896 | Class/Struct.pm Declare struct-like datatypes as Perl classes |
46fc3d4c |
897 | File/stat.pm By-name interface to Perl's builtin stat |
898 | Net/hostent.pm By-name interface to Perl's builtin gethost* |
899 | Net/netent.pm By-name interface to Perl's builtin getnet* |
900 | Net/protoent.pm By-name interface to Perl's builtin getproto* |
901 | Net/servent.pm By-name interface to Perl's builtin getserv* |
902 | Time/gmtime.pm By-name interface to Perl's builtin gmtime |
903 | Time/localtime.pm By-name interface to Perl's builtin localtime |
8cc95fdb |
904 | Time/tm.pm Internal object for Time::{gm,local}time |
46fc3d4c |
905 | User/grent.pm By-name interface to Perl's builtin getgr* |
906 | User/pwent.pm By-name interface to Perl's builtin getpw* |
5f05dabc |
907 | |
774d564b |
908 | Tie/RefHash.pm Base class for tied hashes with references as keys |
7a4c00b4 |
909 | |
5f05dabc |
910 | UNIVERSAL.pm Base class for *ALL* classes |
911 | |
54310121 |
912 | =head2 Fcntl |
913 | |
914 | New constants in the existing Fcntl modules are now supported, |
915 | provided that your operating system happens to support them: |
916 | |
917 | F_GETOWN F_SETOWN |
918 | O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC |
919 | O_EXLOCK O_SHLOCK |
920 | |
921 | These constants are intended for use with the Perl operators sysopen() |
922 | and fcntl() and the basic database modules like SDBM_File. For the |
923 | exact meaning of these and other Fcntl constants please refer to your |
924 | operating system's documentation for fcntl() and open(). |
925 | |
926 | In addition, the Fcntl module now provides these constants for use |
927 | with the Perl operator flock(): |
928 | |
929 | LOCK_SH LOCK_EX LOCK_NB LOCK_UN |
930 | |
931 | These constants are defined in all environments (because where there is |
932 | no flock() system call, Perl emulates it). However, for historical |
933 | reasons, these constants are not exported unless they are explicitly |
934 | requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>). |
935 | |
5f05dabc |
936 | =head2 IO |
937 | |
938 | The IO module provides a simple mechanism to load all of the IO modules at one |
939 | go. Currently this includes: |
940 | |
941 | IO::Handle |
942 | IO::Seekable |
943 | IO::File |
944 | IO::Pipe |
945 | IO::Socket |
946 | |
947 | For more information on any of these modules, please see its |
948 | respective documentation. |
949 | |
950 | =head2 Math::Complex |
951 | |
952 | The Math::Complex module has been totally rewritten, and now supports |
953 | more operations. These are overloaded: |
954 | |
955 | + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify) |
956 | |
957 | And these functions are now exported: |
958 | |
959 | pi i Re Im arg |
5cd24f17 |
960 | log10 logn ln cbrt root |
961 | tan |
962 | csc sec cot |
963 | asin acos atan |
964 | acsc asec acot |
965 | sinh cosh tanh |
966 | csch sech coth |
967 | asinh acosh atanh |
968 | acsch asech acoth |
5f05dabc |
969 | cplx cplxe |
970 | |
5aabfad6 |
971 | =head2 Math::Trig |
972 | |
5cd24f17 |
973 | This new module provides a simpler interface to parts of Math::Complex for |
5aabfad6 |
974 | those who need trigonometric functions only for real numbers. |
975 | |
0a753a76 |
976 | =head2 DB_File |
977 | |
978 | There have been quite a few changes made to DB_File. Here are a few of |
979 | the highlights: |
980 | |
981 | =over |
982 | |
983 | =item * |
984 | |
985 | Fixed a handful of bugs. |
986 | |
987 | =item * |
988 | |
989 | By public demand, added support for the standard hash function exists(). |
990 | |
991 | =item * |
992 | |
993 | Made it compatible with Berkeley DB 1.86. |
994 | |
995 | =item * |
996 | |
997 | Made negative subscripts work with RECNO interface. |
998 | |
999 | =item * |
1000 | |
1001 | Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default |
1002 | mode from 0640 to 0666. |
1003 | |
1004 | =item * |
1005 | |
1006 | Made DB_File automatically import the open() constants (O_RDWR, |
1007 | O_CREAT etc.) from Fcntl, if available. |
1008 | |
1009 | =item * |
1010 | |
1011 | Updated documentation. |
1012 | |
1013 | =back |
1014 | |
1015 | Refer to the HISTORY section in DB_File.pm for a complete list of |
1016 | changes. Everything after DB_File 1.01 has been added since 5.003. |
1017 | |
1018 | =head2 Net::Ping |
1019 | |
1020 | Major rewrite - support added for both udp echo and real icmp pings. |
1021 | |
54310121 |
1022 | =head2 Object-oriented overrides for builtin operators |
5f05dabc |
1023 | |
54310121 |
1024 | Many of the Perl builtins returning lists now have |
5f05dabc |
1025 | object-oriented overrides. These are: |
1026 | |
1027 | File::stat |
1028 | Net::hostent |
1029 | Net::netent |
1030 | Net::protoent |
1031 | Net::servent |
1032 | Time::gmtime |
1033 | Time::localtime |
1034 | User::grent |
1035 | User::pwent |
1036 | |
1037 | For example, you can now say |
1038 | |
1039 | use File::stat; |
1040 | use User::pwent; |
1041 | $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid); |
1042 | |
774d564b |
1043 | =head1 Utility Changes |
5f05dabc |
1044 | |
7bac28a0 |
1045 | =head2 pod2html |
1046 | |
1047 | =over |
1048 | |
1049 | =item Sends converted HTML to standard output |
1050 | |
1051 | The I<pod2html> utility included with Perl 5.004 is entirely new. |
1052 | By default, it sends the converted HTML to its standard output, |
1053 | instead of writing it to a file like Perl 5.003's I<pod2html> did. |
1054 | Use the B<--outfile=FILENAME> option to write to a file. |
1055 | |
1056 | =back |
1057 | |
774d564b |
1058 | =head2 xsubpp |
5f05dabc |
1059 | |
0a753a76 |
1060 | =over |
1061 | |
774d564b |
1062 | =item C<void> XSUBs now default to returning nothing |
1063 | |
1064 | Due to a documentation/implementation bug in previous versions of |
1065 | Perl, XSUBs with a return type of C<void> have actually been |
1066 | returning one value. Usually that value was the GV for the XSUB, |
1067 | but sometimes it was some already freed or reused value, which would |
1068 | sometimes lead to program failure. |
1069 | |
1070 | In Perl 5.004, if an XSUB is declared as returning C<void>, it |
1071 | actually returns no value, i.e. an empty list (though there is a |
1072 | backward-compatibility exception; see below). If your XSUB really |
1073 | does return an SV, you should give it a return type of C<SV *>. |
1074 | |
1075 | For backward compatibility, I<xsubpp> tries to guess whether a |
1076 | C<void> XSUB is really C<void> or if it wants to return an C<SV *>. |
1077 | It does so by examining the text of the XSUB: if I<xsubpp> finds |
1078 | what looks like an assignment to C<ST(0)>, it assumes that the |
1079 | XSUB's return type is really C<SV *>. |
5f05dabc |
1080 | |
0a753a76 |
1081 | =back |
1082 | |
1083 | =head1 C Language API Changes |
1084 | |
1085 | =over |
1086 | |
1087 | =item C<gv_fetchmethod> and C<perl_call_sv> |
1088 | |
1089 | The C<gv_fetchmethod> function finds a method for an object, just like |
1090 | in Perl 5.003. The GV it returns may be a method cache entry. |
1091 | However, in Perl 5.004, method cache entries are not visible to users; |
1092 | therefore, they can no longer be passed directly to C<perl_call_sv>. |
1093 | Instead, you should use the C<GvCV> macro on the GV to extract its CV, |
1094 | and pass the CV to C<perl_call_sv>. |
1095 | |
1096 | The most likely symptom of passing the result of C<gv_fetchmethod> to |
1097 | C<perl_call_sv> is Perl's producing an "Undefined subroutine called" |
1098 | error on the I<second> call to a given method (since there is no cache |
1099 | on the first call). |
1100 | |
137443ea |
1101 | =item C<perl_eval_pv> |
1102 | |
8903cb82 |
1103 | A new function handy for eval'ing strings of Perl code inside C code. |
137443ea |
1104 | This function returns the value from the eval statement, which can |
1105 | be used instead of fetching globals from the symbol table. See |
1106 | L<perlguts>, L<perlembed> and L<perlcall> for details and examples. |
1107 | |
1e422769 |
1108 | =item Extended API for manipulating hashes |
1109 | |
1110 | Internal handling of hash keys has changed. The old hashtable API is |
1111 | still fully supported, and will likely remain so. The additions to the |
1112 | API allow passing keys as C<SV*>s, so that C<tied> hashes can be given |
54310121 |
1113 | real scalars as keys rather than plain strings (nontied hashes still |
1e422769 |
1114 | can only use strings as keys). New extensions must use the new hash |
1115 | access functions and macros if they wish to use C<SV*> keys. These |
1116 | additions also make it feasible to manipulate C<HE*>s (hash entries), |
1117 | which can be more efficient. See L<perlguts> for details. |
1118 | |
0a753a76 |
1119 | =back |
1120 | |
5f05dabc |
1121 | =head1 Documentation Changes |
1122 | |
1123 | Many of the base and library pods were updated. These |
1124 | new pods are included in section 1: |
1125 | |
0a753a76 |
1126 | =over |
5f05dabc |
1127 | |
774d564b |
1128 | =item L<perldelta> |
5f05dabc |
1129 | |
71be2cbc |
1130 | This document. |
5f05dabc |
1131 | |
c90c0ff4 |
1132 | =item L<perlfaq> |
1133 | |
1134 | Frequently asked questions. |
1135 | |
71be2cbc |
1136 | =item L<perllocale> |
5f05dabc |
1137 | |
71be2cbc |
1138 | Locale support (internationalization and localization). |
5f05dabc |
1139 | |
1140 | =item L<perltoot> |
1141 | |
1142 | Tutorial on Perl OO programming. |
1143 | |
71be2cbc |
1144 | =item L<perlapio> |
1145 | |
1146 | Perl internal IO abstraction interface. |
1147 | |
c90c0ff4 |
1148 | =item L<perlmodlib> |
1149 | |
1150 | Perl module library and recommended practice for module creation. |
1151 | Extracted from L<perlmod> (which is much smaller as a result). |
1152 | |
5f05dabc |
1153 | =item L<perldebug> |
1154 | |
1155 | Although not new, this has been massively updated. |
1156 | |
1157 | =item L<perlsec> |
1158 | |
1159 | Although not new, this has been massively updated. |
1160 | |
1161 | =back |
1162 | |
1163 | =head1 New Diagnostics |
1164 | |
1165 | Several new conditions will trigger warnings that were |
1166 | silent before. Some only affect certain platforms. |
2ae324a7 |
1167 | The following new warnings and errors outline these. |
774d564b |
1168 | These messages are classified as follows (listed in |
1169 | increasing order of desperation): |
1170 | |
1171 | (W) A warning (optional). |
1172 | (D) A deprecation (optional). |
1173 | (S) A severe warning (mandatory). |
1174 | (F) A fatal error (trappable). |
1175 | (P) An internal error you should never see (trappable). |
54310121 |
1176 | (X) A very fatal error (nontrappable). |
774d564b |
1177 | (A) An alien error message (not generated by Perl). |
5f05dabc |
1178 | |
0a753a76 |
1179 | =over |
5f05dabc |
1180 | |
1181 | =item "my" variable %s masks earlier declaration in same scope |
1182 | |
fb73857a |
1183 | (W) A lexical variable has been redeclared in the same scope, effectively |
5f05dabc |
1184 | eliminating all access to the previous instance. This is almost always |
1185 | a typographical error. Note that the earlier variable will still exist |
1186 | until the end of the scope or until all closure referents to it are |
1187 | destroyed. |
1188 | |
774d564b |
1189 | =item %s argument is not a HASH element or slice |
1190 | |
1191 | (F) The argument to delete() must be either a hash element, such as |
1192 | |
1193 | $foo{$bar} |
1194 | $ref->[12]->{"susie"} |
1195 | |
1196 | or a hash slice, such as |
1197 | |
1198 | @foo{$bar, $baz, $xyzzy} |
1199 | @{$ref->[12]}{"susie", "queue"} |
1200 | |
5f05dabc |
1201 | =item Allocation too large: %lx |
1202 | |
54310121 |
1203 | (X) You can't allocate more than 64K on an MS-DOS machine. |
5f05dabc |
1204 | |
1205 | =item Allocation too large |
1206 | |
1207 | (F) You can't allocate more than 2^31+"small amount" bytes. |
1208 | |
54310121 |
1209 | =item Applying %s to %s will act on scalar(%s) |
1210 | |
2c268ad5 |
1211 | (W) The pattern match (//), substitution (s///), and transliteration (tr///) |
54310121 |
1212 | operators work on scalar values. If you apply one of them to an array |
1213 | or a hash, it will convert the array or hash to a scalar value -- the |
1214 | length of an array, or the population info of a hash -- and then work on |
1215 | that scalar value. This is probably not what you meant to do. See |
1216 | L<perlfunc/grep> and L<perlfunc/map> for alternatives. |
1217 | |
1218 | =item Attempt to free nonexistent shared string |
5f05dabc |
1219 | |
1220 | (P) Perl maintains a reference counted internal table of strings to |
1221 | optimize the storage and access of hash keys and other strings. This |
1222 | indicates someone tried to decrement the reference count of a string |
1223 | that can no longer be found in the table. |
1224 | |
1225 | =item Attempt to use reference as lvalue in substr |
1226 | |
1227 | (W) You supplied a reference as the first argument to substr() used |
1228 | as an lvalue, which is pretty strange. Perhaps you forgot to |
1229 | dereference it first. See L<perlfunc/substr>. |
1230 | |
c3e0f903 |
1231 | =item Bareword "%s" refers to nonexistent package |
1232 | |
1233 | (W) You used a qualified bareword of the form C<Foo::>, but |
1234 | the compiler saw no other uses of that namespace before that point. |
1235 | Perhaps you need to predeclare a package? |
1236 | |
7bac28a0 |
1237 | =item Can't redefine active sort subroutine %s |
1238 | |
1239 | (F) Perl optimizes the internal handling of sort subroutines and keeps |
1240 | pointers into them. You tried to redefine one such sort subroutine when it |
1241 | was currently active, which is not allowed. If you really want to do |
1242 | this, you should write C<sort { &func } @x> instead of C<sort func @x>. |
1243 | |
774d564b |
1244 | =item Can't use bareword ("%s") as %s ref while "strict refs" in use |
1245 | |
1246 | (F) Only hard references are allowed by "strict refs". Symbolic references |
1247 | are disallowed. See L<perlref>. |
1248 | |
54310121 |
1249 | =item Cannot resolve method `%s' overloading `%s' in package `%s' |
1250 | |
1251 | (P) Internal error trying to resolve overloading specified by a method |
1252 | name (as opposed to a subroutine reference). |
1253 | |
774d564b |
1254 | =item Constant subroutine %s redefined |
1255 | |
1256 | (S) You redefined a subroutine which had previously been eligible for |
dc848c6f |
1257 | inlining. See L<perlsub/"Constant Functions"> for commentary and |
54310121 |
1258 | workarounds. |
1259 | |
1260 | =item Constant subroutine %s undefined |
1261 | |
1262 | (S) You undefined a subroutine which had previously been eligible for |
774d564b |
1263 | inlining. See L<perlsub/"Constant Functions"> for commentary and |
1264 | workarounds. |
1265 | |
54310121 |
1266 | =item Copy method did not return a reference |
1267 | |
1268 | (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>. |
1269 | |
774d564b |
1270 | =item Died |
1271 | |
1272 | (F) You passed die() an empty string (the equivalent of C<die "">) or |
1273 | you called it with no args and both C<$@> and C<$_> were empty. |
1274 | |
54310121 |
1275 | =item Exiting pseudo-block via %s |
1276 | |
1277 | (W) You are exiting a rather special block construct (like a sort block or |
1278 | subroutine) by unconventional means, such as a goto, or a loop control |
1279 | statement. See L<perlfunc/sort>. |
1280 | |
8903cb82 |
1281 | =item Identifier too long |
1282 | |
1283 | (F) Perl limits identifiers (names for variables, functions, etc.) to |
1284 | 252 characters for simple names, somewhat more for compound names (like |
1285 | C<$A::B>). You've exceeded Perl's limits. Future versions of Perl are |
1286 | likely to eliminate these arbitrary limitations. |
1287 | |
54310121 |
1288 | =item Illegal character %s (carriage return) |
1289 | |
1290 | (F) A carriage return character was found in the input. This is an |
1291 | error, and not a warning, because carriage return characters can break |
1292 | multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>). |
1293 | |
1294 | =item Illegal switch in PERL5OPT: %s |
1295 | |
1296 | (X) The PERL5OPT environment variable may only be used to set the |
1297 | following switches: B<-[DIMUdmw]>. |
1298 | |
5f05dabc |
1299 | =item Integer overflow in hex number |
1300 | |
1301 | (S) The literal hex number you have specified is too big for your |
1302 | architecture. On a 32-bit architecture the largest hex literal is |
1303 | 0xFFFFFFFF. |
1304 | |
1305 | =item Integer overflow in octal number |
1306 | |
1307 | (S) The literal octal number you have specified is too big for your |
1308 | architecture. On a 32-bit architecture the largest octal literal is |
1309 | 037777777777. |
1310 | |
5cd24f17 |
1311 | =item internal error: glob failed |
1312 | |
1313 | (P) Something went wrong with the external program(s) used for C<glob> |
1314 | and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is |
1315 | broken. If so, you should change all of the csh-related variables in |
1316 | config.sh: If you have tcsh, make the variables refer to it as if it |
1317 | were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all |
1318 | empty (except that C<d_csh> should be C<'undef'>) so that Perl will |
1319 | think csh is missing. In either case, after editing config.sh, run |
1320 | C<./Configure -S> and rebuild Perl. |
1321 | |
878e08df |
1322 | =item Invalid conversion in %s: "%s" |
1323 | |
1324 | (W) Perl does not understand the given format conversion. |
1325 | See L<perlfunc/sprintf>. |
1326 | |
8903cb82 |
1327 | =item Invalid type in pack: '%s' |
1328 | |
1329 | (F) The given character is not a valid pack type. See L<perlfunc/pack>. |
1330 | |
1331 | =item Invalid type in unpack: '%s' |
1332 | |
1333 | (F) The given character is not a valid unpack type. See L<perlfunc/unpack>. |
1334 | |
774d564b |
1335 | =item Name "%s::%s" used only once: possible typo |
1336 | |
1337 | (W) Typographical errors often show up as unique variable names. |
1338 | If you had a good reason for having a unique name, then just mention |
1339 | it again somehow to suppress the message (the C<use vars> pragma is |
1340 | provided for just this purpose). |
1341 | |
5f05dabc |
1342 | =item Null picture in formline |
1343 | |
1344 | (F) The first argument to formline must be a valid format picture |
1345 | specification. It was found to be empty, which probably means you |
1346 | supplied it an uninitialized value. See L<perlform>. |
1347 | |
1348 | =item Offset outside string |
1349 | |
1350 | (F) You tried to do a read/write/send/recv operation with an offset |
1351 | pointing outside the buffer. This is difficult to imagine. |
1352 | The sole exception to this is that C<sysread()>ing past the buffer |
1353 | will extend the buffer and zero pad the new area. |
1354 | |
1355 | =item Out of memory! |
1356 | |
1357 | (X|F) The malloc() function returned 0, indicating there was insufficient |
1358 | remaining memory (or virtual memory) to satisfy the request. |
1359 | |
1360 | The request was judged to be small, so the possibility to trap it |
1361 | depends on the way Perl was compiled. By default it is not trappable. |
1362 | However, if compiled for this, Perl may use the contents of C<$^M> as |
1363 | an emergency pool after die()ing with this message. In this case the |
1364 | error is trappable I<once>. |
1365 | |
1366 | =item Out of memory during request for %s |
1367 | |
1368 | (F) The malloc() function returned 0, indicating there was insufficient |
1369 | remaining memory (or virtual memory) to satisfy the request. However, |
1370 | the request was judged large enough (compile-time default is 64K), so |
1371 | a possibility to shut down by trapping this error is granted. |
1372 | |
878e08df |
1373 | =item panic: frexp |
1374 | |
1375 | (P) The library function frexp() failed, making printf("%f") impossible. |
1376 | |
5f05dabc |
1377 | =item Possible attempt to put comments in qw() list |
1378 | |
774d564b |
1379 | (W) qw() lists contain items separated by whitespace; as with literal |
1380 | strings, comment characters are not ignored, but are instead treated |
1381 | as literal data. (You may have used different delimiters than the |
1382 | exclamation marks parentheses shown here; braces are also frequently |
1383 | used.) |
1384 | |
1385 | You probably wrote something like this: |
5f05dabc |
1386 | |
2ae324a7 |
1387 | @list = qw( |
774d564b |
1388 | a # a comment |
5f05dabc |
1389 | b # another comment |
774d564b |
1390 | ); |
5f05dabc |
1391 | |
1392 | when you should have written this: |
1393 | |
774d564b |
1394 | @list = qw( |
2ae324a7 |
1395 | a |
5f05dabc |
1396 | b |
774d564b |
1397 | ); |
1398 | |
1399 | If you really want comments, build your list the |
1400 | old-fashioned way, with quotes and commas: |
1401 | |
1402 | @list = ( |
1403 | 'a', # a comment |
1404 | 'b', # another comment |
1405 | ); |
5f05dabc |
1406 | |
1407 | =item Possible attempt to separate words with commas |
1408 | |
774d564b |
1409 | (W) qw() lists contain items separated by whitespace; therefore commas |
1410 | aren't needed to separate the items. (You may have used different |
1411 | delimiters than the parentheses shown here; braces are also frequently |
1412 | used.) |
5f05dabc |
1413 | |
2ae324a7 |
1414 | You probably wrote something like this: |
5f05dabc |
1415 | |
774d564b |
1416 | qw! a, b, c !; |
1417 | |
1418 | which puts literal commas into some of the list items. Write it without |
1419 | commas if you don't want them to appear in your data: |
1420 | |
1421 | qw! a b c !; |
5f05dabc |
1422 | |
774d564b |
1423 | =item Scalar value @%s{%s} better written as $%s{%s} |
1424 | |
1425 | (W) You've used a hash slice (indicated by @) to select a single element of |
1426 | a hash. Generally it's better to ask for a scalar value (indicated by $). |
1427 | The difference is that C<$foo{&bar}> always behaves like a scalar, both when |
1428 | assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves |
1429 | like a list when you assign to it, and provides a list context to its |
1430 | subscript, which can do weird things if you're expecting only one subscript. |
5f05dabc |
1431 | |
54310121 |
1432 | =item Stub found while resolving method `%s' overloading `%s' in package `%s' |
1433 | |
1434 | (P) Overloading resolution over @ISA tree may be broken by importing stubs. |
1435 | Stubs should never be implicitely created, but explicit calls to C<can> |
1436 | may break this. |
1437 | |
1438 | =item Too late for "B<-T>" option |
1439 | |
1440 | (X) The #! line (or local equivalent) in a Perl script contains the |
1441 | B<-T> option, but Perl was not invoked with B<-T> in its argument |
1442 | list. This is an error because, by the time Perl discovers a B<-T> in |
1443 | a script, it's too late to properly taint everything from the |
1444 | environment. So Perl gives up. |
1445 | |
5f05dabc |
1446 | =item untie attempted while %d inner references still exist |
1447 | |
1448 | (W) A copy of the object returned from C<tie> (or C<tied>) was still |
1449 | valid when C<untie> was called. |
1450 | |
54310121 |
1451 | =item Unrecognized character %s |
1452 | |
1453 | (F) The Perl parser has no idea what to do with the specified character |
1454 | in your Perl script (or eval). Perhaps you tried to run a compressed |
1455 | script, a binary program, or a directory as a Perl program. |
1456 | |
1457 | =item Unsupported function fork |
1458 | |
1459 | (F) Your version of executable does not support forking. |
1460 | |
1461 | Note that under some systems, like OS/2, there may be different flavors of |
1462 | Perl executables, some of which may support fork, some not. Try changing |
1463 | the name you call Perl by to C<perl_>, C<perl__>, and so on. |
1464 | |
5cd24f17 |
1465 | =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated |
1466 | |
1467 | (D) Perl versions before 5.004 misinterpreted any type marker followed |
1468 | by "$" and a digit. For example, "$$0" was incorrectly taken to mean |
1469 | "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004. |
1470 | |
1471 | However, the developers of Perl 5.004 could not fix this bug completely, |
1472 | because at least two widely-used modules depend on the old meaning of |
1473 | "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the |
1474 | old (broken) way inside strings; but it generates this message as a |
1475 | warning. And in Perl 5.005, this special treatment will cease. |
1476 | |
54310121 |
1477 | =item Value of %s can be "0"; test with defined() |
774d564b |
1478 | |
54310121 |
1479 | (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>, |
1480 | or C<readdir()> as a boolean value. Each of these constructs can return a |
1481 | value of "0"; that would make the conditional expression false, which is |
1482 | probably not what you intended. When using these constructs in conditional |
1483 | expressions, test their values with the C<defined> operator. |
774d564b |
1484 | |
1485 | =item Variable "%s" may be unavailable |
1486 | |
1487 | (W) An inner (nested) I<anonymous> subroutine is inside a I<named> |
1488 | subroutine, and outside that is another subroutine; and the anonymous |
1489 | (innermost) subroutine is referencing a lexical variable defined in |
1490 | the outermost subroutine. For example: |
1491 | |
1492 | sub outermost { my $a; sub middle { sub { $a } } } |
1493 | |
1494 | If the anonymous subroutine is called or referenced (directly or |
1495 | indirectly) from the outermost subroutine, it will share the variable |
1496 | as you would expect. But if the anonymous subroutine is called or |
1497 | referenced when the outermost subroutine is not active, it will see |
1498 | the value of the shared variable as it was before and during the |
1499 | *first* call to the outermost subroutine, which is probably not what |
1500 | you want. |
1501 | |
1502 | In these circumstances, it is usually best to make the middle |
1503 | subroutine anonymous, using the C<sub {}> syntax. Perl has specific |
1504 | support for shared variables in nested anonymous subroutines; a named |
1505 | subroutine in between interferes with this feature. |
1506 | |
1507 | =item Variable "%s" will not stay shared |
1508 | |
1509 | (W) An inner (nested) I<named> subroutine is referencing a lexical |
1510 | variable defined in an outer subroutine. |
1511 | |
1512 | When the inner subroutine is called, it will probably see the value of |
1513 | the outer subroutine's variable as it was before and during the |
1514 | *first* call to the outer subroutine; in this case, after the first |
1515 | call to the outer subroutine is complete, the inner and outer |
1516 | subroutines will no longer share a common value for the variable. In |
1517 | other words, the variable will no longer be shared. |
1518 | |
1519 | Furthermore, if the outer subroutine is anonymous and references a |
1520 | lexical variable outside itself, then the outer and inner subroutines |
1521 | will I<never> share the given variable. |
1522 | |
1523 | This problem can usually be solved by making the inner subroutine |
1524 | anonymous, using the C<sub {}> syntax. When inner anonymous subs that |
1525 | reference variables in outer subroutines are called or referenced, |
54310121 |
1526 | they are automatically rebound to the current values of such |
774d564b |
1527 | variables. |
1528 | |
1529 | =item Warning: something's wrong |
1530 | |
1531 | (W) You passed warn() an empty string (the equivalent of C<warn "">) or |
1532 | you called it with no args and C<$_> was empty. |
1533 | |
54310121 |
1534 | =item Ill-formed logical name |%s| in prime_env_iter |
1535 | |
1536 | (W) A warning peculiar to VMS. A logical name was encountered when preparing |
1537 | to iterate over %ENV which violates the syntactic rules governing logical |
1538 | names. Since it cannot be translated normally, it is skipped, and will not |
1539 | appear in %ENV. This may be a benign occurrence, as some software packages |
1540 | might directly modify logical name tables and introduce nonstandard names, |
1541 | or it may indicate that a logical name table has been corrupted. |
1542 | |
774d564b |
1543 | =item Got an error from DosAllocMem |
5f05dabc |
1544 | |
774d564b |
1545 | (P) An error peculiar to OS/2. Most probably you're using an obsolete |
1546 | version of Perl, and this should not happen anyway. |
5f05dabc |
1547 | |
1548 | =item Malformed PERLLIB_PREFIX |
1549 | |
dc848c6f |
1550 | (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form |
5f05dabc |
1551 | |
1552 | prefix1;prefix2 |
1553 | |
1554 | or |
1555 | |
1556 | prefix1 prefix2 |
1557 | |
dc848c6f |
1558 | with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix |
1559 | of a builtin library search path, prefix2 is substituted. The error |
1560 | may appear if components are not found, or are too long. See |
1561 | "PERLLIB_PREFIX" in F<README.os2>. |
5f05dabc |
1562 | |
1563 | =item PERL_SH_DIR too long |
1564 | |
1565 | (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the |
dc848c6f |
1566 | C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>. |
5f05dabc |
1567 | |
1568 | =item Process terminated by SIG%s |
1569 | |
1570 | (W) This is a standard message issued by OS/2 applications, while *nix |
dc848c6f |
1571 | applications die in silence. It is considered a feature of the OS/2 |
1572 | port. One can easily disable this by appropriate sighandlers, see |
1573 | L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT" |
1574 | in F<README.os2>. |
5f05dabc |
1575 | |
1576 | =back |
1577 | |
1578 | =head1 BUGS |
1579 | |
774d564b |
1580 | If you find what you think is a bug, you might check the headers of |
1581 | recently posted articles in the comp.lang.perl.misc newsgroup. |
1582 | There may also be information at http://www.perl.com/perl/, the Perl |
1583 | Home Page. |
5f05dabc |
1584 | |
1585 | If you believe you have an unreported bug, please run the B<perlbug> |
9607fc9c |
1586 | program included with your release. Make sure you trim your bug down |
1587 | to a tiny but sufficient test case. Your bug report, along with the |
1588 | output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be |
1589 | analysed by the Perl porting team. |
5f05dabc |
1590 | |
1591 | =head1 SEE ALSO |
1592 | |
1593 | The F<Changes> file for exhaustive details on what changed. |
1594 | |
1595 | The F<INSTALL> file for how to build Perl. This file has been |
1596 | significantly updated for 5.004, so even veteran users should |
1597 | look through it. |
1598 | |
1599 | The F<README> file for general stuff. |
1600 | |
1601 | The F<Copying> file for copyright information. |
1602 | |
1603 | =head1 HISTORY |
1604 | |
1605 | Constructed by Tom Christiansen, grabbing material with permission |
1606 | from innumerable contributors, with kibitzing by more than a few Perl |
1607 | porters. |
1608 | |
c90c0ff4 |
1609 | Last update: Wed May 14 11:14:09 EDT 1997 |