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1 | =head1 NAME |
2 | |
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3 | perldelta - what's new for perl5.004 |
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4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | This document describes differences between the 5.003 release (as |
8 | documented in I<Programming Perl>, second edition--the Camel Book) and |
9 | this one. |
10 | |
11 | =head1 Supported Environments |
12 | |
13 | Perl5.004 builds out of the box on Unix, Plan9, LynxOS, VMS, OS/2, |
14 | QNX, and AmigaOS. |
15 | |
16 | =head1 Core Changes |
17 | |
18 | Most importantly, many bugs were fixed. See the F<Changes> |
19 | file in the distribution for details. |
20 | |
21 | =head2 Compilation Option: Binary Compatibility With 5.003 |
22 | |
23 | There is a new Configure question that asks if you want to maintain |
24 | binary compatibility with Perl 5.003. If you choose binary |
25 | compatibility, you do not have to recompile your extensions, but you |
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26 | might have symbol conflicts if you embed Perl in another application, |
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27 | just as in the 5.003 release. By default, binary compatibility |
28 | is preserved at the expense of symbol table pollution. |
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29 | |
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30 | =head2 New Opcode Module and Revised Safe Module |
31 | |
32 | A new Opcode module supports the creation, manipulation and |
33 | application of opcode masks. The revised Safe module has a new API |
34 | and is implemented using the new Opcode module. Please read the new |
35 | Opcode and Safe documentation. |
36 | |
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37 | =head2 Fixed Parsing of $$<digit>, &$<digit>, etc. |
38 | |
39 | A bug in previous versions of Perl 5.0 prevented proper parsing of |
40 | numeric special variables as symbolic references. That bug has been |
41 | fixed. As a result, the string "$$0" is no longer equivalent to |
42 | C<$$."0">, but rather to C<${$0}>. To get the old behavior, change |
43 | "$$" followed by a digit to "${$}". |
44 | |
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45 | =head2 Internal Change: FileHandle Deprecated |
46 | |
47 | Filehandles are now stored internally as type IO::Handle. |
48 | Although C<use FileHandle> and C<*STDOUT{FILEHANDLE}> |
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49 | are still supported for backwards compatibility, |
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50 | C<use IO::Handle> (or C<IO::Seekable> or C<IO::File>) and |
51 | C<*STDOUT{IO}> are the way of the future. |
52 | |
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53 | =head2 Internal Change: PerlIO internal IO abstraction interface |
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54 | |
55 | It is now possible to build Perl with AT&T's sfio IO package |
56 | instead of stdio. See L<perlapio> for more details, and |
57 | the F<INSTALL> file for how to use it. |
58 | |
59 | =head2 New and Changed Built-in Variables |
60 | |
61 | =over |
62 | |
63 | =item $^E |
64 | |
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65 | Extended error message on some platforms. (Also known as |
66 | $EXTENDED_OS_ERROR if you C<use English>). |
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67 | |
68 | =item $^H |
69 | |
70 | The current set of syntax checks enabled by C<use strict>. See the |
71 | documentation of C<strict> for more details. Not actually new, but |
72 | newly documented. |
73 | Because it is intended for internal use by Perl core components, |
74 | there is no C<use English> long name for this variable. |
75 | |
76 | =item $^M |
77 | |
78 | By default, running out of memory it is not trappable. However, if |
79 | compiled for this, Perl may use the contents of C<$^M> as an emergency |
80 | pool after die()ing with this message. Suppose that your Perl were |
81 | compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then |
82 | |
83 | $^M = 'a' x (1<<16); |
84 | |
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85 | would allocate a 64K buffer for use when in emergency. |
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86 | See the F<INSTALL> file for information on how to enable this option. |
87 | As a disincentive to casual use of this advanced feature, |
88 | there is no C<use English> long name for this variable. |
89 | |
90 | =back |
91 | |
92 | =head2 New and Changed Built-in Functions |
93 | |
94 | =over |
95 | |
96 | =item delete on slices |
97 | |
98 | This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>) |
99 | |
100 | =item flock |
101 | |
102 | is now supported on more platforms, and prefers fcntl |
103 | to lockf when emulating. |
104 | |
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105 | =item printf and sprintf |
106 | |
107 | now support "%i" as a synonym for "%d", and the "h" modifier. |
108 | So "%hi" means "short integer in decimal", and "%ho" means |
109 | "unsigned short integer as octal". |
110 | |
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111 | =item keys as an lvalue |
112 | |
113 | As an lvalue, C<keys> allows you to increase the number of hash buckets |
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114 | allocated for the given hash. This can gain you a measure of efficiency if |
115 | you know the hash is going to get big. (This is similar to pre-extending |
116 | an array by assigning a larger number to $#array.) If you say |
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117 | |
118 | keys %hash = 200; |
119 | |
120 | then C<%hash> will have at least 200 buckets allocated for it. These |
121 | buckets will be retained even if you do C<%hash = ()>; use C<undef |
122 | %hash> if you want to free the storage while C<%hash> is still in scope. |
123 | You can't shrink the number of buckets allocated for the hash using |
124 | C<keys> in this way (but you needn't worry about doing this by accident, |
125 | as trying has no effect). |
126 | |
127 | =item my() in Control Structures |
128 | |
129 | You can now use my() (with or without the parentheses) in the control |
130 | expressions of control structures such as: |
131 | |
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132 | while (defined(my $line = <>)) { |
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133 | $line = lc $line; |
134 | } continue { |
135 | print $line; |
136 | } |
137 | |
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138 | if ((my $answer = <STDIN>) =~ /^y(es)?$/i) { |
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139 | user_agrees(); |
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140 | } elsif ($answer =~ /^n(o)?$/i) { |
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141 | user_disagrees(); |
142 | } else { |
143 | chomp $answer; |
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144 | die "`$answer' is neither `yes' nor `no'"; |
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145 | } |
146 | |
147 | Also, you can declare a foreach loop control variable as lexical by |
148 | preceding it with the word "my". For example, in: |
149 | |
150 | foreach my $i (1, 2, 3) { |
151 | some_function(); |
152 | } |
153 | |
154 | $i is a lexical variable, and the scope of $i extends to the end of |
155 | the loop, but not beyond it. |
156 | |
157 | Note that you still cannot use my() on global punctuation variables |
158 | such as $_ and the like. |
159 | |
160 | =item unpack() and pack() |
161 | |
162 | A new format 'w' represents a BER compressed integer (as defined in |
163 | ASN.1). Its format is a sequence of one or more bytes, each of which |
164 | provides seven bits of the total value, with the most significant |
165 | first. Bit eight of each byte is set, except for the last byte, in |
166 | which bit eight is clear. |
167 | |
168 | =item use VERSION |
169 | |
170 | If the first argument to C<use> is a number, it is treated as a version |
171 | number instead of a module name. If the version of the Perl interpreter |
172 | is less than VERSION, then an error message is printed and Perl exits |
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173 | immediately. Because C<use> occurs at compile time, this check happens |
174 | immediately during the compilation process, unlike C<require VERSION>, |
175 | which waits until run-time for the check. This is often useful if you |
176 | need to check the current Perl version before C<use>ing library modules |
177 | which have changed in incompatible ways from older versions of Perl. |
178 | (We try not to do this more than we have to.) |
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179 | |
180 | =item use Module VERSION LIST |
181 | |
182 | If the VERSION argument is present between Module and LIST, then the |
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183 | C<use> will call the VERSION method in class Module with the given |
184 | version as an argument. The default VERSION method, inherited from |
185 | the Universal class, croaks if the given version is larger than the |
186 | value of the variable $Module::VERSION. (Note that there is not a |
187 | comma after VERSION!) |
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188 | |
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189 | This version-checking mechanism is similar to the one currently used |
190 | in the Exporter module, but it is faster and can be used with modules |
191 | that don't use the Exporter. It is the recommended method for new |
192 | code. |
193 | |
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194 | =item prototype(FUNCTION) |
195 | |
196 | Returns the prototype of a function as a string (or C<undef> if the |
197 | function has no prototype). FUNCTION is a reference to or the name of the |
198 | function whose prototype you want to retrieve. |
199 | (Not actually new; just never documented before.) |
200 | |
201 | =item $_ as Default |
202 | |
203 | Functions documented in the Camel to default to $_ now in |
204 | fact do, and all those that do are so documented in L<perlfunc>. |
205 | |
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206 | =item C<m//g> does not trigger a pos() reset on failure |
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207 | |
208 | The C<m//g> match iteration construct used to reset the iteration |
209 | when it failed to match (so that the next C<m//g> match would start at |
210 | the beginning of the string). You now have to explicitly do a |
211 | C<pos $str = 0;> to reset the "last match" position, or modify the |
212 | string in some way. This change makes it practical to chain C<m//g> |
213 | matches together in conjunction with ordinary matches using the C<\G> |
214 | zero-width assertion. See L<perlop> and L<perlre>. |
215 | |
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216 | =item nested C<sub{}> closures work now |
217 | |
218 | Prior to the 5.004 release, nested anonymous functions |
219 | didn't work right. They do now. |
220 | |
221 | =item formats work right on changing lexicals |
222 | |
223 | Just like anonymous functions that contain lexical variables |
224 | that change (like a lexical index variable for a C<foreach> loop), |
225 | formats now work properly. For example, this silently failed |
226 | before, and is fine now: |
227 | |
228 | my $i; |
229 | foreach $i ( 1 .. 10 ) { |
230 | format = |
231 | my i is @# |
232 | $i |
233 | . |
234 | write; |
235 | } |
236 | |
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237 | =back |
238 | |
239 | =head2 New Built-in Methods |
240 | |
241 | The C<UNIVERSAL> package automatically contains the following methods that |
242 | are inherited by all other classes: |
243 | |
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244 | =over |
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245 | |
246 | =item isa(CLASS) |
247 | |
248 | C<isa> returns I<true> if its object is blessed into a sub-class of C<CLASS> |
249 | |
250 | C<isa> is also exportable and can be called as a sub with two arguments. This |
251 | allows the ability to check what a reference points to. Example: |
252 | |
253 | use UNIVERSAL qw(isa); |
254 | |
255 | if(isa($ref, 'ARRAY')) { |
256 | ... |
257 | } |
258 | |
259 | =item can(METHOD) |
260 | |
261 | C<can> checks to see if its object has a method called C<METHOD>, |
262 | if it does then a reference to the sub is returned; if it does not then |
263 | I<undef> is returned. |
264 | |
265 | =item VERSION( [NEED] ) |
266 | |
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267 | C<VERSION> returns the version number of the class (package). If the |
268 | NEED argument is given then it will check that the current version (as |
269 | defined by the $VERSION variable in the given package) not less than |
270 | NEED; it will die if this is not the case. This method is normally |
271 | called as a class method. This method is called automatically by the |
272 | C<VERSION> form of C<use>. |
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273 | |
274 | use A 1.2 qw(some imported subs); |
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275 | # implies: |
276 | A->VERSION(1.2); |
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277 | |
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278 | =back |
279 | |
280 | B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and |
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281 | C<isa> uses a very similar method and caching strategy. This may cause |
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282 | strange effects if the Perl code dynamically changes @ISA in any package. |
283 | |
284 | You may add other methods to the UNIVERSAL class via Perl or XS code. |
285 | You do not need to C<use UNIVERSAL> in order to make these methods |
286 | available to your program. This is necessary only if you wish to |
287 | have C<isa> available as a plain subroutine in the current package. |
288 | |
289 | =head2 TIEHANDLE Now Supported |
290 | |
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291 | See L<perltie> for other kinds of tie()s. |
292 | |
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293 | =over |
294 | |
295 | =item TIEHANDLE classname, LIST |
296 | |
297 | This is the constructor for the class. That means it is expected to |
298 | return an object of some sort. The reference can be used to |
299 | hold some internal information. |
300 | |
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301 | sub TIEHANDLE { |
302 | print "<shout>\n"; |
303 | my $i; |
304 | return bless \$i, shift; |
305 | } |
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306 | |
307 | =item PRINT this, LIST |
308 | |
309 | This method will be triggered every time the tied handle is printed to. |
310 | Beyond its self reference it also expects the list that was passed to |
311 | the print function. |
312 | |
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313 | sub PRINT { |
314 | $r = shift; |
315 | $$r++; |
316 | return print join( $, => map {uc} @_), $\; |
317 | } |
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318 | |
319 | =item READLINE this |
320 | |
321 | This method will be called when the handle is read from. The method |
322 | should return undef when there is no more data. |
323 | |
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324 | sub READLINE { |
325 | $r = shift; |
326 | return "PRINT called $$r times\n"; |
327 | } |
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328 | |
329 | =item DESTROY this |
330 | |
331 | As with the other types of ties, this method will be called when the |
332 | tied handle is about to be destroyed. This is useful for debugging and |
333 | possibly for cleaning up. |
334 | |
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335 | sub DESTROY { |
336 | print "</shout>\n"; |
337 | } |
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338 | |
339 | =back |
340 | |
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341 | =head2 Malloc Enhancements |
342 | |
343 | If perl's malloc() is used, you can print memory statistics at runtime |
344 | by running Perl thusly: |
345 | |
346 | env PERL_DEBUG_MSTATS=2 perl your_script_here |
347 | |
348 | The value of 2 means to print statistics after compilation and on |
349 | exit; with a value of 1, the statistics ares printed only on exit. |
350 | (If you want the statistics at an arbitrary time, you'll need to |
351 | install the optional module Devel::Peek.) |
352 | |
353 | In addition, three new compilation flags are recognized by malloc.c. |
354 | (They have no effect if perl is compiled with system malloc().) |
355 | |
356 | =over |
357 | |
358 | =item -DEMERGENCY_SBRK |
359 | |
360 | If this macro is defined, running out of memory need not be a fatal |
361 | error: a memory pool can allocated by assigning to the special |
362 | variable C<$^M>. See L<"$^M">. |
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363 | |
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364 | =item -DPACK_MALLOC |
365 | |
366 | Perl memory allocation is by bucket with sizes close to powers of two. |
367 | Because of these malloc overhead may be big, especially for data of |
368 | size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses |
369 | a slightly different algorithm for small allocations (up to 64 bytes |
370 | long), which makes it possible to have overhead down to 1 byte for |
371 | allocations which are powers of two (and appear quite often). |
372 | |
373 | Expected memory savings (with 8-byte alignment in C<alignbytes>) is |
374 | about 20% for typical Perl usage. Expected slowdown due to additional |
375 | malloc overhead is in fractions of a percent (hard to measure, because |
376 | of the effect of saved memory on speed). |
377 | |
378 | =item -DTWO_POT_OPTIMIZE |
379 | |
380 | Similarly to C<PACK_MALLOC>, this macro improves allocations of data |
381 | with size close to a power of two; but this works for big allocations |
382 | (starting with 16K by default). Such allocations are typical for big |
383 | hashes and special-purpose scripts, especially image processing. |
384 | |
385 | On recent systems, the fact that perl requires 2M from system for 1M |
386 | allocation will not affect speed of execution, since the tail of such |
387 | a chunk is not going to be touched (and thus will not require real |
388 | memory). However, it may result in a premature out-of-memory error. |
389 | So if you will be manipulating very large blocks with sizes close to |
390 | powers of two, it would be wise to define this macro. |
391 | |
392 | Expected saving of memory is 0-100% (100% in applications which |
393 | require most memory in such 2**n chunks); expected slowdown is |
394 | negligible. |
395 | |
396 | =back |
397 | |
398 | =head2 Miscellaneous Efficiency Enhancements |
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399 | |
400 | Functions that have an empty prototype and that do nothing but return |
401 | a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>). |
402 | |
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403 | Each unique hash key is only allocated once, no matter how many hashes |
404 | have an entry with that key. So even if you have 100 copies of the |
405 | same hash, the hash keys never have to be re-allocated. |
406 | |
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407 | =head1 Pragmata |
408 | |
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409 | Four new pragmatic modules exist: |
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410 | |
411 | =over |
412 | |
413 | =item use blib |
414 | |
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415 | =item use blib 'dir' |
416 | |
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417 | Looks for MakeMaker-like I<'blib'> directory structure starting in |
418 | I<dir> (or current directory) and working back up to five levels of |
419 | parent directories. |
420 | |
421 | Intended for use on command line with B<-M> option as a way of testing |
422 | arbitrary scripts against an uninstalled version of a package. |
423 | |
424 | =item use locale |
425 | |
426 | Tells the compiler to enable (or disable) the use of POSIX locales for |
427 | built-in operations. |
428 | |
429 | When C<use locale> is in effect, the current LC_CTYPE locale is used |
430 | for regular expressions and case mapping; LC_COLLATE for string |
431 | ordering; and LC_NUMERIC for numeric formating in printf and sprintf |
432 | (but B<not> in print). LC_NUMERIC is always used in write, since |
433 | lexical scoping of formats is problematic at best. |
434 | |
435 | Each C<use locale> or C<no locale> affects statements to the end of |
436 | the enclosing BLOCK or, if not inside a BLOCK, to the end of the |
437 | current file. Locales can be switched and queried with |
438 | POSIX::setlocale(). |
439 | |
440 | See L<perllocale> for more information. |
441 | |
442 | =item use ops |
443 | |
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444 | Disable unsafe opcodes, or any named opcodes, when compiling Perl code. |
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445 | |
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446 | =item use vmsish |
447 | |
448 | Enable VMS-specific language features. Currently, there are three |
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449 | VMS-specific features available: 'status', which makes C<$?> and |
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450 | C<system> return genuine VMS status values instead of emulating POSIX; |
451 | 'exit', which makes C<exit> take a genuine VMS status value instead of |
452 | assuming that C<exit 1> is an error; and 'time', which makes all times |
453 | relative to the local time zone, in the VMS tradition. |
454 | |
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455 | =back |
456 | |
457 | =head1 Modules |
458 | |
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459 | =head2 Installation Directories |
460 | |
461 | The I<installperl> script now places the Perl source files for |
462 | extensions in the architecture-specific library directory, which is |
463 | where the shared libraries for extensions have always been. This |
464 | change is intended to allow administrators to keep the Perl 5.004 |
465 | library directory unchanged from a previous version, without running |
466 | the risk of binary incompatibility between extensions' Perl source and |
467 | shared libraries. |
468 | |
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469 | =head2 Fcntl |
470 | |
471 | New constants in the existing Fcntl modules are now supported, |
472 | provided that your operating system happens to support them: |
473 | |
474 | F_GETOWN F_SETOWN |
475 | O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC |
476 | O_EXLOCK O_SHLOCK |
477 | |
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478 | These constants are intended for use with the Perl operators sysopen() |
479 | and fcntl() and the basic database modules like SDBM_File. For the |
480 | exact meaning of these and other Fcntl constants please refer to your |
481 | operating system's documentation for fcntl() and open(). |
482 | |
483 | In addition, the Fcntl module now provides these constants for use |
484 | with the Perl operator flock(): |
485 | |
486 | LOCK_SH LOCK_EX LOCK_NB LOCK_UN |
487 | |
488 | These constants are defined in all environments (because where there is |
489 | no flock() system call, Perl emulates it). However, for historical |
490 | reasons, these constants are not exported unless they are explicitly |
491 | requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>). |
492 | |
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493 | =head2 Module Information Summary |
494 | |
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495 | Brand new modules, arranged by topic rather than strictly |
496 | alphabetically: |
497 | |
498 | CPAN interface to Comprehensive Perl Archive Network |
499 | CPAN::FirstTime create a CPAN configuration file |
500 | CPAN::Nox run CPAN while avoiding compiled extensions |
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501 | |
502 | IO.pm Top-level interface to IO::* classes |
503 | IO/File.pm IO::File extension Perl module |
504 | IO/Handle.pm IO::Handle extension Perl module |
505 | IO/Pipe.pm IO::Pipe extension Perl module |
506 | IO/Seekable.pm IO::Seekable extension Perl module |
507 | IO/Select.pm IO::Select extension Perl module |
508 | IO/Socket.pm IO::Socket extension Perl module |
509 | |
510 | Opcode.pm Disable named opcodes when compiling Perl code |
511 | |
512 | ExtUtils/Embed.pm Utilities for embedding Perl in C programs |
513 | ExtUtils/testlib.pm Fixes up @INC to use just-built extension |
514 | |
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515 | FindBin.pm Find path of currently executing program |
516 | |
517 | Class/Template.pm Structure/member template builder |
518 | File/stat.pm Object-oriented wrapper around CORE::stat |
519 | Net/hostent.pm Object-oriented wrapper around CORE::gethost* |
520 | Net/netent.pm Object-oriented wrapper around CORE::getnet* |
521 | Net/protoent.pm Object-oriented wrapper around CORE::getproto* |
522 | Net/servent.pm Object-oriented wrapper around CORE::getserv* |
523 | Time/gmtime.pm Object-oriented wrapper around CORE::gmtime |
524 | Time/localtime.pm Object-oriented wrapper around CORE::localtime |
525 | Time/tm.pm Perl implementation of "struct tm" for {gm,local}time |
526 | User/grent.pm Object-oriented wrapper around CORE::getgr* |
527 | User/pwent.pm Object-oriented wrapper around CORE::getpw* |
528 | |
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529 | Tie/RefHash.pm Base class for tied hashes with references as keys |
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530 | |
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531 | UNIVERSAL.pm Base class for *ALL* classes |
532 | |
533 | =head2 IO |
534 | |
535 | The IO module provides a simple mechanism to load all of the IO modules at one |
536 | go. Currently this includes: |
537 | |
538 | IO::Handle |
539 | IO::Seekable |
540 | IO::File |
541 | IO::Pipe |
542 | IO::Socket |
543 | |
544 | For more information on any of these modules, please see its |
545 | respective documentation. |
546 | |
547 | =head2 Math::Complex |
548 | |
549 | The Math::Complex module has been totally rewritten, and now supports |
550 | more operations. These are overloaded: |
551 | |
552 | + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify) |
553 | |
554 | And these functions are now exported: |
555 | |
556 | pi i Re Im arg |
557 | log10 logn cbrt root |
558 | tan cotan asin acos atan acotan |
559 | sinh cosh tanh cotanh asinh acosh atanh acotanh |
560 | cplx cplxe |
561 | |
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562 | =head2 DB_File |
563 | |
564 | There have been quite a few changes made to DB_File. Here are a few of |
565 | the highlights: |
566 | |
567 | =over |
568 | |
569 | =item * |
570 | |
571 | Fixed a handful of bugs. |
572 | |
573 | =item * |
574 | |
575 | By public demand, added support for the standard hash function exists(). |
576 | |
577 | =item * |
578 | |
579 | Made it compatible with Berkeley DB 1.86. |
580 | |
581 | =item * |
582 | |
583 | Made negative subscripts work with RECNO interface. |
584 | |
585 | =item * |
586 | |
587 | Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default |
588 | mode from 0640 to 0666. |
589 | |
590 | =item * |
591 | |
592 | Made DB_File automatically import the open() constants (O_RDWR, |
593 | O_CREAT etc.) from Fcntl, if available. |
594 | |
595 | =item * |
596 | |
597 | Updated documentation. |
598 | |
599 | =back |
600 | |
601 | Refer to the HISTORY section in DB_File.pm for a complete list of |
602 | changes. Everything after DB_File 1.01 has been added since 5.003. |
603 | |
604 | =head2 Net::Ping |
605 | |
606 | Major rewrite - support added for both udp echo and real icmp pings. |
607 | |
5f05dabc |
608 | =head2 Overridden Built-ins |
609 | |
610 | Many of the Perl built-ins returning lists now have |
611 | object-oriented overrides. These are: |
612 | |
613 | File::stat |
614 | Net::hostent |
615 | Net::netent |
616 | Net::protoent |
617 | Net::servent |
618 | Time::gmtime |
619 | Time::localtime |
620 | User::grent |
621 | User::pwent |
622 | |
623 | For example, you can now say |
624 | |
625 | use File::stat; |
626 | use User::pwent; |
627 | $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid); |
628 | |
774d564b |
629 | =head1 Utility Changes |
5f05dabc |
630 | |
774d564b |
631 | =head2 xsubpp |
5f05dabc |
632 | |
0a753a76 |
633 | =over |
634 | |
774d564b |
635 | =item C<void> XSUBs now default to returning nothing |
636 | |
637 | Due to a documentation/implementation bug in previous versions of |
638 | Perl, XSUBs with a return type of C<void> have actually been |
639 | returning one value. Usually that value was the GV for the XSUB, |
640 | but sometimes it was some already freed or reused value, which would |
641 | sometimes lead to program failure. |
642 | |
643 | In Perl 5.004, if an XSUB is declared as returning C<void>, it |
644 | actually returns no value, i.e. an empty list (though there is a |
645 | backward-compatibility exception; see below). If your XSUB really |
646 | does return an SV, you should give it a return type of C<SV *>. |
647 | |
648 | For backward compatibility, I<xsubpp> tries to guess whether a |
649 | C<void> XSUB is really C<void> or if it wants to return an C<SV *>. |
650 | It does so by examining the text of the XSUB: if I<xsubpp> finds |
651 | what looks like an assignment to C<ST(0)>, it assumes that the |
652 | XSUB's return type is really C<SV *>. |
5f05dabc |
653 | |
0a753a76 |
654 | =back |
655 | |
656 | =head1 C Language API Changes |
657 | |
658 | =over |
659 | |
660 | =item C<gv_fetchmethod> and C<perl_call_sv> |
661 | |
662 | The C<gv_fetchmethod> function finds a method for an object, just like |
663 | in Perl 5.003. The GV it returns may be a method cache entry. |
664 | However, in Perl 5.004, method cache entries are not visible to users; |
665 | therefore, they can no longer be passed directly to C<perl_call_sv>. |
666 | Instead, you should use the C<GvCV> macro on the GV to extract its CV, |
667 | and pass the CV to C<perl_call_sv>. |
668 | |
669 | The most likely symptom of passing the result of C<gv_fetchmethod> to |
670 | C<perl_call_sv> is Perl's producing an "Undefined subroutine called" |
671 | error on the I<second> call to a given method (since there is no cache |
672 | on the first call). |
673 | |
674 | =back |
675 | |
5f05dabc |
676 | =head1 Documentation Changes |
677 | |
678 | Many of the base and library pods were updated. These |
679 | new pods are included in section 1: |
680 | |
0a753a76 |
681 | =over |
5f05dabc |
682 | |
d121ca8c |
683 | =item L<perlbug> |
684 | |
685 | A "howto" on reporting perl bugs. |
686 | |
774d564b |
687 | =item L<perldelta> |
5f05dabc |
688 | |
71be2cbc |
689 | This document. |
5f05dabc |
690 | |
71be2cbc |
691 | =item L<perllocale> |
5f05dabc |
692 | |
71be2cbc |
693 | Locale support (internationalization and localization). |
5f05dabc |
694 | |
695 | =item L<perltoot> |
696 | |
697 | Tutorial on Perl OO programming. |
698 | |
71be2cbc |
699 | =item L<perlapio> |
700 | |
701 | Perl internal IO abstraction interface. |
702 | |
5f05dabc |
703 | =item L<perldebug> |
704 | |
705 | Although not new, this has been massively updated. |
706 | |
707 | =item L<perlsec> |
708 | |
709 | Although not new, this has been massively updated. |
710 | |
711 | =back |
712 | |
713 | =head1 New Diagnostics |
714 | |
715 | Several new conditions will trigger warnings that were |
716 | silent before. Some only affect certain platforms. |
774d564b |
717 | The following new warnings and errors outline these. |
718 | These messages are classified as follows (listed in |
719 | increasing order of desperation): |
720 | |
721 | (W) A warning (optional). |
722 | (D) A deprecation (optional). |
723 | (S) A severe warning (mandatory). |
724 | (F) A fatal error (trappable). |
725 | (P) An internal error you should never see (trappable). |
726 | (X) A very fatal error (non-trappable). |
727 | (A) An alien error message (not generated by Perl). |
5f05dabc |
728 | |
0a753a76 |
729 | =over |
5f05dabc |
730 | |
731 | =item "my" variable %s masks earlier declaration in same scope |
732 | |
733 | (S) A lexical variable has been redeclared in the same scope, effectively |
734 | eliminating all access to the previous instance. This is almost always |
735 | a typographical error. Note that the earlier variable will still exist |
736 | until the end of the scope or until all closure referents to it are |
737 | destroyed. |
738 | |
774d564b |
739 | =item %s argument is not a HASH element or slice |
740 | |
741 | (F) The argument to delete() must be either a hash element, such as |
742 | |
743 | $foo{$bar} |
744 | $ref->[12]->{"susie"} |
745 | |
746 | or a hash slice, such as |
747 | |
748 | @foo{$bar, $baz, $xyzzy} |
749 | @{$ref->[12]}{"susie", "queue"} |
750 | |
5f05dabc |
751 | =item Allocation too large: %lx |
752 | |
753 | (X) You can't allocate more than 64K on an MSDOS machine. |
754 | |
755 | =item Allocation too large |
756 | |
757 | (F) You can't allocate more than 2^31+"small amount" bytes. |
758 | |
759 | =item Attempt to free non-existent shared string |
760 | |
761 | (P) Perl maintains a reference counted internal table of strings to |
762 | optimize the storage and access of hash keys and other strings. This |
763 | indicates someone tried to decrement the reference count of a string |
764 | that can no longer be found in the table. |
765 | |
766 | =item Attempt to use reference as lvalue in substr |
767 | |
768 | (W) You supplied a reference as the first argument to substr() used |
769 | as an lvalue, which is pretty strange. Perhaps you forgot to |
770 | dereference it first. See L<perlfunc/substr>. |
771 | |
772 | =item Unsupported function fork |
773 | |
774 | (F) Your version of executable does not support forking. |
775 | |
776 | Note that under some systems, like OS/2, there may be different flavors of |
777 | Perl executables, some of which may support fork, some not. Try changing |
778 | the name you call Perl by to C<perl_>, C<perl__>, and so on. |
779 | |
780 | =item Ill-formed logical name |%s| in prime_env_iter |
781 | |
782 | (W) A warning peculiar to VMS. A logical name was encountered when preparing |
783 | to iterate over %ENV which violates the syntactic rules governing logical |
784 | names. Since it cannot be translated normally, it is skipped, and will not |
785 | appear in %ENV. This may be a benign occurrence, as some software packages |
786 | might directly modify logical name tables and introduce non-standard names, |
787 | or it may indicate that a logical name table has been corrupted. |
788 | |
774d564b |
789 | =item Can't use bareword ("%s") as %s ref while "strict refs" in use |
790 | |
791 | (F) Only hard references are allowed by "strict refs". Symbolic references |
792 | are disallowed. See L<perlref>. |
793 | |
794 | =item Constant subroutine %s redefined |
795 | |
796 | (S) You redefined a subroutine which had previously been eligible for |
797 | inlining. See L<perlsub/"Constant Functions"> for commentary and |
798 | workarounds. |
799 | |
800 | =item Died |
801 | |
802 | (F) You passed die() an empty string (the equivalent of C<die "">) or |
803 | you called it with no args and both C<$@> and C<$_> were empty. |
804 | |
5f05dabc |
805 | =item Integer overflow in hex number |
806 | |
807 | (S) The literal hex number you have specified is too big for your |
808 | architecture. On a 32-bit architecture the largest hex literal is |
809 | 0xFFFFFFFF. |
810 | |
811 | =item Integer overflow in octal number |
812 | |
813 | (S) The literal octal number you have specified is too big for your |
814 | architecture. On a 32-bit architecture the largest octal literal is |
815 | 037777777777. |
816 | |
774d564b |
817 | =item Name "%s::%s" used only once: possible typo |
818 | |
819 | (W) Typographical errors often show up as unique variable names. |
820 | If you had a good reason for having a unique name, then just mention |
821 | it again somehow to suppress the message (the C<use vars> pragma is |
822 | provided for just this purpose). |
823 | |
5f05dabc |
824 | =item Null picture in formline |
825 | |
826 | (F) The first argument to formline must be a valid format picture |
827 | specification. It was found to be empty, which probably means you |
828 | supplied it an uninitialized value. See L<perlform>. |
829 | |
830 | =item Offset outside string |
831 | |
832 | (F) You tried to do a read/write/send/recv operation with an offset |
833 | pointing outside the buffer. This is difficult to imagine. |
834 | The sole exception to this is that C<sysread()>ing past the buffer |
835 | will extend the buffer and zero pad the new area. |
836 | |
774d564b |
837 | =item Stub found while resolving method `%s' overloading `%s' in package `%s' |
838 | |
839 | (P) Overloading resolution over @ISA tree may be broken by importing stubs. |
840 | Stubs should never be implicitely created, but explicit calls to C<can> |
841 | may break this. |
842 | |
843 | =item Cannot resolve method `%s' overloading `%s' in package `s' |
844 | |
845 | (P) Internal error trying to resolve overloading specified by a method |
846 | name (as opposed to a subroutine reference). |
847 | |
5f05dabc |
848 | =item Out of memory! |
849 | |
850 | (X|F) The malloc() function returned 0, indicating there was insufficient |
851 | remaining memory (or virtual memory) to satisfy the request. |
852 | |
853 | The request was judged to be small, so the possibility to trap it |
854 | depends on the way Perl was compiled. By default it is not trappable. |
855 | However, if compiled for this, Perl may use the contents of C<$^M> as |
856 | an emergency pool after die()ing with this message. In this case the |
857 | error is trappable I<once>. |
858 | |
859 | =item Out of memory during request for %s |
860 | |
861 | (F) The malloc() function returned 0, indicating there was insufficient |
862 | remaining memory (or virtual memory) to satisfy the request. However, |
863 | the request was judged large enough (compile-time default is 64K), so |
864 | a possibility to shut down by trapping this error is granted. |
865 | |
866 | =item Possible attempt to put comments in qw() list |
867 | |
774d564b |
868 | (W) qw() lists contain items separated by whitespace; as with literal |
869 | strings, comment characters are not ignored, but are instead treated |
870 | as literal data. (You may have used different delimiters than the |
871 | exclamation marks parentheses shown here; braces are also frequently |
872 | used.) |
873 | |
874 | You probably wrote something like this: |
5f05dabc |
875 | |
774d564b |
876 | @list = qw( |
877 | a # a comment |
5f05dabc |
878 | b # another comment |
774d564b |
879 | ); |
5f05dabc |
880 | |
881 | when you should have written this: |
882 | |
774d564b |
883 | @list = qw( |
884 | a |
5f05dabc |
885 | b |
774d564b |
886 | ); |
887 | |
888 | If you really want comments, build your list the |
889 | old-fashioned way, with quotes and commas: |
890 | |
891 | @list = ( |
892 | 'a', # a comment |
893 | 'b', # another comment |
894 | ); |
5f05dabc |
895 | |
896 | =item Possible attempt to separate words with commas |
897 | |
774d564b |
898 | (W) qw() lists contain items separated by whitespace; therefore commas |
899 | aren't needed to separate the items. (You may have used different |
900 | delimiters than the parentheses shown here; braces are also frequently |
901 | used.) |
5f05dabc |
902 | |
774d564b |
903 | You probably wrote something like this: |
5f05dabc |
904 | |
774d564b |
905 | qw! a, b, c !; |
906 | |
907 | which puts literal commas into some of the list items. Write it without |
908 | commas if you don't want them to appear in your data: |
909 | |
910 | qw! a b c !; |
5f05dabc |
911 | |
774d564b |
912 | =item Scalar value @%s{%s} better written as $%s{%s} |
913 | |
914 | (W) You've used a hash slice (indicated by @) to select a single element of |
915 | a hash. Generally it's better to ask for a scalar value (indicated by $). |
916 | The difference is that C<$foo{&bar}> always behaves like a scalar, both when |
917 | assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves |
918 | like a list when you assign to it, and provides a list context to its |
919 | subscript, which can do weird things if you're expecting only one subscript. |
5f05dabc |
920 | |
921 | =item untie attempted while %d inner references still exist |
922 | |
923 | (W) A copy of the object returned from C<tie> (or C<tied>) was still |
924 | valid when C<untie> was called. |
925 | |
774d564b |
926 | =item Value of %s construct can be "0"; test with defined() |
927 | |
928 | (W) In a conditional expression, you used <HANDLE>, <*> (glob), or |
929 | C<readdir> as a boolean value. Each of these constructs can return a |
930 | value of "0"; that would make the conditional expression false, which |
931 | is probably not what you intended. When using these constructs in |
932 | conditional expressions, test their values with the C<defined> operator. |
933 | |
934 | =item Variable "%s" may be unavailable |
935 | |
936 | (W) An inner (nested) I<anonymous> subroutine is inside a I<named> |
937 | subroutine, and outside that is another subroutine; and the anonymous |
938 | (innermost) subroutine is referencing a lexical variable defined in |
939 | the outermost subroutine. For example: |
940 | |
941 | sub outermost { my $a; sub middle { sub { $a } } } |
942 | |
943 | If the anonymous subroutine is called or referenced (directly or |
944 | indirectly) from the outermost subroutine, it will share the variable |
945 | as you would expect. But if the anonymous subroutine is called or |
946 | referenced when the outermost subroutine is not active, it will see |
947 | the value of the shared variable as it was before and during the |
948 | *first* call to the outermost subroutine, which is probably not what |
949 | you want. |
950 | |
951 | In these circumstances, it is usually best to make the middle |
952 | subroutine anonymous, using the C<sub {}> syntax. Perl has specific |
953 | support for shared variables in nested anonymous subroutines; a named |
954 | subroutine in between interferes with this feature. |
955 | |
956 | =item Variable "%s" will not stay shared |
957 | |
958 | (W) An inner (nested) I<named> subroutine is referencing a lexical |
959 | variable defined in an outer subroutine. |
960 | |
961 | When the inner subroutine is called, it will probably see the value of |
962 | the outer subroutine's variable as it was before and during the |
963 | *first* call to the outer subroutine; in this case, after the first |
964 | call to the outer subroutine is complete, the inner and outer |
965 | subroutines will no longer share a common value for the variable. In |
966 | other words, the variable will no longer be shared. |
967 | |
968 | Furthermore, if the outer subroutine is anonymous and references a |
969 | lexical variable outside itself, then the outer and inner subroutines |
970 | will I<never> share the given variable. |
971 | |
972 | This problem can usually be solved by making the inner subroutine |
973 | anonymous, using the C<sub {}> syntax. When inner anonymous subs that |
974 | reference variables in outer subroutines are called or referenced, |
975 | they are automatically re-bound to the current values of such |
976 | variables. |
977 | |
978 | =item Warning: something's wrong |
979 | |
980 | (W) You passed warn() an empty string (the equivalent of C<warn "">) or |
981 | you called it with no args and C<$_> was empty. |
982 | |
983 | =item Got an error from DosAllocMem |
5f05dabc |
984 | |
774d564b |
985 | (P) An error peculiar to OS/2. Most probably you're using an obsolete |
986 | version of Perl, and this should not happen anyway. |
5f05dabc |
987 | |
988 | =item Malformed PERLLIB_PREFIX |
989 | |
990 | (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form |
991 | |
992 | prefix1;prefix2 |
993 | |
994 | or |
995 | |
996 | prefix1 prefix2 |
997 | |
998 | with non-empty prefix1 and prefix2. If C<prefix1> is indeed a prefix of |
999 | a builtin library search path, prefix2 is substituted. The error may appear |
1000 | if components are not found, or are too long. See L<perlos2/"PERLLIB_PREFIX">. |
1001 | |
1002 | =item PERL_SH_DIR too long |
1003 | |
1004 | (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the |
1005 | C<sh>-shell in. See L<perlos2/"PERL_SH_DIR">. |
1006 | |
1007 | =item Process terminated by SIG%s |
1008 | |
1009 | (W) This is a standard message issued by OS/2 applications, while *nix |
1010 | applications die in silence. It is considered a feature of the OS/2 |
1011 | port. One can easily disable this by appropriate sighandlers, see |
1012 | L<perlipc/"Signals">. See L<perlos2/"Process terminated by SIGTERM/SIGINT">. |
1013 | |
1014 | =back |
1015 | |
1016 | =head1 BUGS |
1017 | |
774d564b |
1018 | If you find what you think is a bug, you might check the headers of |
1019 | recently posted articles in the comp.lang.perl.misc newsgroup. |
1020 | There may also be information at http://www.perl.com/perl/, the Perl |
1021 | Home Page. |
5f05dabc |
1022 | |
1023 | If you believe you have an unreported bug, please run the B<perlbug> |
1024 | program included with your release. Make sure you trim your bug |
1025 | down to a tiny but sufficient test case. Your bug report, along |
1026 | with the output of C<perl -V>, will be sent off to perlbug@perl.com |
1027 | to be analysed by the Perl porting team. |
1028 | |
1029 | =head1 SEE ALSO |
1030 | |
1031 | The F<Changes> file for exhaustive details on what changed. |
1032 | |
1033 | The F<INSTALL> file for how to build Perl. This file has been |
1034 | significantly updated for 5.004, so even veteran users should |
1035 | look through it. |
1036 | |
1037 | The F<README> file for general stuff. |
1038 | |
1039 | The F<Copying> file for copyright information. |
1040 | |
1041 | =head1 HISTORY |
1042 | |
1043 | Constructed by Tom Christiansen, grabbing material with permission |
1044 | from innumerable contributors, with kibitzing by more than a few Perl |
1045 | porters. |
1046 | |
44a8e56a |
1047 | Last update: Tue Jan 14 14:03:02 EST 1997 |