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1 | =head1 NAME |
2 | |
3 | perlmod - Perl modules (packages) |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | =head2 Packages |
8 | |
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9 | Perl provides a mechanism for alternative namespaces to protect packages |
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10 | from stomping on each others variables. In fact, apart from certain |
11 | magical variables, there's really no such thing as a global variable in |
12 | Perl. The package statement declares the compilation unit as being in the |
13 | given namespace. The scope of the package declaration is from the |
14 | declaration itself through the end of the enclosing block (the same scope |
15 | as the local() operator). All further unqualified dynamic identifiers |
16 | will be in this namespace. A package statement only affects dynamic |
17 | variables--including those you've used local() on--but I<not> lexical |
18 | variables created with my(). Typically it would be the first declaration |
19 | in a file to be included by the C<require> or C<use> operator. You can |
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20 | switch into a package in more than one place; it merely influences which |
21 | symbol table is used by the compiler for the rest of that block. You can |
22 | refer to variables and filehandles in other packages by prefixing the |
23 | identifier with the package name and a double colon: |
24 | C<$Package::Variable>. If the package name is null, the C<main> package |
25 | as assumed. That is, C<$::sail> is equivalent to C<$main::sail>. |
26 | |
27 | (The old package delimiter was a single quote, but double colon |
28 | is now the preferred delimiter, in part because it's more readable |
29 | to humans, and in part because it's more readable to B<emacs> macros. |
30 | It also makes C++ programmers feel like they know what's going on.) |
31 | |
32 | Packages may be nested inside other packages: C<$OUTER::INNER::var>. This |
33 | implies nothing about the order of name lookups, however. All symbols |
34 | are either local to the current package, or must be fully qualified |
35 | from the outer package name down. For instance, there is nowhere |
36 | within package C<OUTER> that C<$INNER::var> refers to C<$OUTER::INNER::var>. |
37 | It would treat package C<INNER> as a totally separate global package. |
38 | |
39 | Only identifiers starting with letters (or underscore) are stored in a |
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40 | package's symbol table. All other symbols are kept in package C<main>, |
41 | including all of the punctuation variables like $_. In addition, the |
42 | identifiers STDIN, STDOUT, STDERR, ARGV, ARGVOUT, ENV, INC and SIG are |
43 | forced to be in package C<main>, even when used for other purposes than |
44 | their built-in one. Note also that, if you have a package called C<m>, |
45 | C<s> or C<y>, then you can't use the qualified form of an identifier |
46 | because it will be interpreted instead as a pattern match, a substitution, |
47 | or a translation. |
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48 | |
49 | (Variables beginning with underscore used to be forced into package |
50 | main, but we decided it was more useful for package writers to be able |
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51 | to use leading underscore to indicate private variables and method names. |
52 | $_ is still global though.) |
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53 | |
54 | Eval()ed strings are compiled in the package in which the eval() was |
55 | compiled. (Assignments to C<$SIG{}>, however, assume the signal |
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56 | handler specified is in the C<main> package. Qualify the signal handler |
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57 | name if you wish to have a signal handler in a package.) For an |
58 | example, examine F<perldb.pl> in the Perl library. It initially switches |
59 | to the C<DB> package so that the debugger doesn't interfere with variables |
60 | in the script you are trying to debug. At various points, however, it |
61 | temporarily switches back to the C<main> package to evaluate various |
62 | expressions in the context of the C<main> package (or wherever you came |
63 | from). See L<perldebug>. |
64 | |
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65 | See L<perlsub> for other scoping issues related to my() and local(), |
66 | or L<perlref> regarding closures. |
67 | |
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68 | =head2 Symbol Tables |
69 | |
70 | The symbol table for a package happens to be stored in the associative |
71 | array of that name appended with two colons. The main symbol table's |
72 | name is thus C<%main::>, or C<%::> for short. Likewise the nested package |
73 | mentioned earlier is named C<%OUTER::INNER::>. |
74 | |
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75 | The value in each entry of the associative array is what you are referring |
76 | to when you use the C<*name> typeglob notation. In fact, the following |
77 | have the same effect, though the first is more efficient because it does |
78 | the symbol table lookups at compile time: |
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79 | |
80 | local(*main::foo) = *main::bar; local($main::{'foo'}) = |
81 | $main::{'bar'}; |
82 | |
83 | You can use this to print out all the variables in a package, for |
84 | instance. Here is F<dumpvar.pl> from the Perl library: |
85 | |
86 | package dumpvar; |
87 | sub main::dumpvar { |
88 | ($package) = @_; |
89 | local(*stab) = eval("*${package}::"); |
90 | while (($key,$val) = each(%stab)) { |
91 | local(*entry) = $val; |
92 | if (defined $entry) { |
93 | print "\$$key = '$entry'\n"; |
94 | } |
95 | |
96 | if (defined @entry) { |
97 | print "\@$key = (\n"; |
98 | foreach $num ($[ .. $#entry) { |
99 | print " $num\t'",$entry[$num],"'\n"; |
100 | } |
101 | print ")\n"; |
102 | } |
103 | |
104 | if ($key ne "${package}::" && defined %entry) { |
105 | print "\%$key = (\n"; |
106 | foreach $key (sort keys(%entry)) { |
107 | print " $key\t'",$entry{$key},"'\n"; |
108 | } |
109 | print ")\n"; |
110 | } |
111 | } |
112 | } |
113 | |
114 | Note that even though the subroutine is compiled in package C<dumpvar>, |
115 | the name of the subroutine is qualified so that its name is inserted |
116 | into package C<main>. |
117 | |
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118 | Assignment to a typeglob performs an aliasing operation, i.e., |
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119 | |
120 | *dick = *richard; |
121 | |
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122 | causes variables, subroutines and file handles accessible via the |
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123 | identifier C<richard> to also be accessible via the symbol C<dick>. If |
124 | you only want to alias a particular variable or subroutine, you can |
125 | assign a reference instead: |
126 | |
127 | *dick = \$richard; |
128 | |
129 | makes $richard and $dick the same variable, but leaves |
130 | @richard and @dick as separate arrays. Tricky, eh? |
131 | |
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132 | This mechanism may be used to pass and return cheap references |
133 | into or from subroutines if you won't want to copy the whole |
134 | thing. |
135 | |
136 | %some_hash = (); |
137 | *some_hash = fn( \%another_hash ); |
138 | sub fn { |
139 | local *hashsym = shift; |
140 | # now use %hashsym normally, and you |
141 | # will affect the caller's %another_hash |
142 | my %nhash = (); # do what you want |
143 | return \%nhash; |
144 | } |
145 | |
146 | On return, the reference wil overwrite the hash slot in the |
147 | symbol table specified by the *some_hash typeglob. This |
148 | is a somewhat tricky way of passing around refernces cheaply |
149 | when you won't want to have to remember to dereference variables |
150 | explicitly. |
151 | |
152 | Another use of symbol tables is for making "constant" scalars. |
153 | |
154 | *PI = \3.14159265358979; |
155 | |
156 | Now you cannot alter $PI, which is probably a good thing all in all. |
157 | |
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158 | =head2 Package Constructors and Destructors |
159 | |
160 | There are two special subroutine definitions that function as package |
161 | constructors and destructors. These are the C<BEGIN> and C<END> |
162 | routines. The C<sub> is optional for these routines. |
163 | |
164 | A C<BEGIN> subroutine is executed as soon as possible, that is, the |
165 | moment it is completely defined, even before the rest of the containing |
166 | file is parsed. You may have multiple C<BEGIN> blocks within a |
167 | file--they will execute in order of definition. Because a C<BEGIN> |
168 | block executes immediately, it can pull in definitions of subroutines |
169 | and such from other files in time to be visible to the rest of the |
170 | file. |
171 | |
172 | An C<END> subroutine is executed as late as possible, that is, when the |
173 | interpreter is being exited, even if it is exiting as a result of a |
174 | die() function. (But not if it's is being blown out of the water by a |
175 | signal--you have to trap that yourself (if you can).) You may have |
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176 | multiple C<END> blocks within a file--they will execute in reverse |
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177 | order of definition; that is: last in, first out (LIFO). |
178 | |
179 | Note that when you use the B<-n> and B<-p> switches to Perl, C<BEGIN> |
180 | and C<END> work just as they do in B<awk>, as a degenerate case. |
181 | |
182 | =head2 Perl Classes |
183 | |
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184 | There is no special class syntax in Perl, but a package may function |
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185 | as a class if it provides subroutines that function as methods. Such a |
186 | package may also derive some of its methods from another class package |
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187 | by listing the other package name in its @ISA array. |
188 | |
189 | For more on this, see L<perlobj>. |
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190 | |
191 | =head2 Perl Modules |
192 | |
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193 | A module is just a package that is defined in a library file of |
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194 | the same name, and is designed to be reusable. It may do this by |
195 | providing a mechanism for exporting some of its symbols into the symbol |
196 | table of any package using it. Or it may function as a class |
197 | definition and make its semantics available implicitly through method |
198 | calls on the class and its objects, without explicit exportation of any |
199 | symbols. Or it can do a little of both. |
200 | |
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201 | For example, to start a normal module called Fred, create |
202 | a file called Fred.pm and put this at the start of it: |
203 | |
204 | package Fred; |
205 | require Exporter; |
206 | @ISA = qw(Exporter); |
207 | @EXPORT = qw(func1 func2); |
208 | @EXPORT_OK = qw($sally @listabob %harry func3); |
209 | |
210 | Then go on to declare and use your variables in functions |
211 | without any qualifications. |
212 | See L<Exporter> and the I<Perl Modules File> for details on |
213 | mechanics and style issues in module creation. |
214 | |
215 | Perl modules are included into your program by saying |
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216 | |
217 | use Module; |
218 | |
219 | or |
220 | |
221 | use Module LIST; |
222 | |
223 | This is exactly equivalent to |
224 | |
225 | BEGIN { require "Module.pm"; import Module; } |
226 | |
227 | or |
228 | |
229 | BEGIN { require "Module.pm"; import Module LIST; } |
230 | |
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231 | As a special case |
232 | |
233 | use Module (); |
234 | |
235 | is exactly equivalent to |
236 | |
237 | BEGIN { require "Module.pm"; } |
238 | |
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239 | All Perl module files have the extension F<.pm>. C<use> assumes this so |
240 | that you don't have to spell out "F<Module.pm>" in quotes. This also |
241 | helps to differentiate new modules from old F<.pl> and F<.ph> files. |
242 | Module names are also capitalized unless they're functioning as pragmas, |
243 | "Pragmas" are in effect compiler directives, and are sometimes called |
244 | "pragmatic modules" (or even "pragmata" if you're a classicist). |
245 | |
246 | Because the C<use> statement implies a C<BEGIN> block, the importation |
247 | of semantics happens at the moment the C<use> statement is compiled, |
248 | before the rest of the file is compiled. This is how it is able |
249 | to function as a pragma mechanism, and also how modules are able to |
250 | declare subroutines that are then visible as list operators for |
251 | the rest of the current file. This will not work if you use C<require> |
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252 | instead of C<use>. With require you can get into this problem: |
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253 | |
254 | require Cwd; # make Cwd:: accessible |
255 | $here = Cwd::getcwd(); |
256 | |
257 | use Cwd; # import names from Cwd:: |
258 | $here = getcwd(); |
259 | |
260 | require Cwd; # make Cwd:: accessible |
261 | $here = getcwd(); # oops! no main::getcwd() |
262 | |
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263 | In general C<use Module ();> is recommended over C<require Module;>. |
264 | |
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265 | Perl packages may be nested inside other package names, so we can have |
266 | package names containing C<::>. But if we used that package name |
267 | directly as a filename it would makes for unwieldy or impossible |
268 | filenames on some systems. Therefore, if a module's name is, say, |
269 | C<Text::Soundex>, then its definition is actually found in the library |
270 | file F<Text/Soundex.pm>. |
271 | |
272 | Perl modules always have a F<.pm> file, but there may also be dynamically |
273 | linked executables or autoloaded subroutine definitions associated with |
274 | the module. If so, these will be entirely transparent to the user of |
275 | the module. It is the responsibility of the F<.pm> file to load (or |
276 | arrange to autoload) any additional functionality. The POSIX module |
277 | happens to do both dynamic loading and autoloading, but the user can |
278 | just say C<use POSIX> to get it all. |
279 | |
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280 | For more information on writing extension modules, see L<perlxs> |
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281 | and L<perlguts>. |
282 | |
283 | =head1 NOTE |
284 | |
285 | Perl does not enforce private and public parts of its modules as you may |
286 | have been used to in other languages like C++, Ada, or Modula-17. Perl |
287 | doesn't have an infatuation with enforced privacy. It would prefer |
288 | that you stayed out of its living room because you weren't invited, not |
289 | because it has a shotgun. |
290 | |
291 | The module and its user have a contract, part of which is common law, |
292 | and part of which is "written". Part of the common law contract is |
293 | that a module doesn't pollute any namespace it wasn't asked to. The |
294 | written contract for the module (AKA documentation) may make other |
295 | provisions. But then you know when you C<use RedefineTheWorld> that |
296 | you're redefining the world and willing to take the consequences. |
297 | |
298 | =head1 THE PERL MODULE LIBRARY |
299 | |
300 | A number of modules are included the the Perl distribution. These are |
301 | described below, and all end in F<.pm>. You may also discover files in |
302 | the library directory that end in either F<.pl> or F<.ph>. These are old |
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303 | libraries supplied so that old programs that use them still run. The |
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304 | F<.pl> files will all eventually be converted into standard modules, and |
305 | the F<.ph> files made by B<h2ph> will probably end up as extension modules |
306 | made by B<h2xs>. (Some F<.ph> values may already be available through the |
307 | POSIX module.) The B<pl2pm> file in the distribution may help in your |
308 | conversion, but it's just a mechanical process, so is far from bullet proof. |
309 | |
310 | =head2 Pragmatic Modules |
311 | |
312 | They work somewhat like pragmas in that they tend to affect the compilation of |
313 | your program, and thus will usually only work well when used within a |
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314 | C<use>, or C<no>. These are locally scoped, so an inner BLOCK |
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315 | may countermand any of these by saying |
316 | |
317 | no integer; |
318 | no strict 'refs'; |
319 | |
320 | which lasts until the end of that BLOCK. |
321 | |
322 | The following programs are defined (and have their own documentation). |
323 | |
324 | =over 12 |
325 | |
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326 | =item diagnostics |
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327 | |
328 | Pragma to produce enhanced diagnostics |
329 | |
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330 | =item integer |
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331 | |
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332 | Pragma to compute arithmetic in integer instead of double |
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333 | |
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334 | =item less |
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335 | |
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336 | Pragma to request less of something from the compiler |
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337 | |
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338 | =item overload |
339 | |
340 | Pragma for overloading operators |
341 | |
342 | =item sigtrap |
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343 | |
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344 | Pragma to enable stack backtrace on unexpected signals |
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345 | |
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346 | =item strict |
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347 | |
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348 | Pragma to restrict unsafe constructs |
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349 | |
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350 | =item subs |
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351 | |
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352 | Pragma to predeclare sub names |
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353 | |
354 | =back |
355 | |
356 | =head2 Standard Modules |
357 | |
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358 | Standard, bundled modules are all expected to behave in a well-defined |
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359 | manner with respect to namespace pollution because they use the |
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360 | Exporter module. See their own documentation for details. |
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361 | |
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362 | =over 12 |
363 | |
364 | =item AnyDBM_File |
365 | |
366 | provide framework for multiple DBMs |
367 | |
368 | =item AutoLoader |
369 | |
370 | load functions only on demand |
371 | |
372 | =item AutoSplit |
373 | |
374 | split a package for autoloading |
375 | |
376 | =item Benchmark |
377 | |
378 | benchmark running times of code |
379 | |
380 | =item Carp |
381 | |
382 | warn of errors (from perspective of caller) |
383 | |
384 | =item Config |
385 | |
386 | access Perl configuration option |
387 | |
388 | =item Cwd |
389 | |
390 | get pathname of current working directory |
391 | |
392 | =item DB_File |
393 | |
394 | Perl access to Berkeley DB |
395 | |
396 | =item Devel::SelfStubber |
397 | |
398 | generate stubs for a SelfLoading module |
399 | |
400 | =item DynaLoader |
401 | |
402 | Dynamically load C libraries into Perl code |
403 | |
404 | =item English |
405 | |
406 | use nice English (or awk) names for ugly punctuation variables |
407 | |
408 | =item Env |
409 | |
410 | perl module that imports environment variables |
411 | |
412 | =item Exporter |
413 | |
414 | provide inport/export controls for Perl modules |
415 | |
416 | =item ExtUtils::Liblist |
417 | |
418 | determine libraries to use and how to use them |
419 | |
420 | =item ExtUtils::MakeMaker |
421 | |
422 | create an extension Makefile |
423 | |
424 | =item ExtUtils::Manifest |
425 | |
426 | utilities to write and check a MANIFEST file |
427 | |
428 | =item ExtUtils::Mkbootstrap |
429 | |
430 | make a bootstrap file for use by DynaLoader |
431 | |
432 | =item ExtUtils::Miniperl |
433 | |
434 | !!!GOOD QUESTION!!! |
435 | |
436 | =item Fcntl |
437 | |
438 | load the C Fcntl.h defines |
439 | |
440 | =item File::Basename |
441 | |
442 | parse file specifications |
443 | |
444 | =item File::CheckTree |
445 | |
446 | run many filetest checks on a tree |
447 | |
448 | =item File::Find |
449 | |
450 | traverse a file tree |
451 | |
452 | =item FileHandle |
453 | |
454 | supply object methods for filehandles |
455 | |
456 | =item File::Path |
457 | |
458 | create or remove a series of directories |
459 | |
460 | =item Getopt::Long |
461 | |
462 | extended getopt processing |
463 | |
464 | =item Getopt::Std |
465 | |
466 | Process single-character switches with switch clustering |
467 | |
468 | =item I18N::Collate |
469 | |
470 | compare 8-bit scalar data according to the current locale |
471 | |
472 | =item IPC::Open2 |
473 | |
474 | a process for both reading and writing |
475 | |
476 | =item IPC::Open3 |
477 | |
478 | open a process for reading, writing, and error handling |
479 | |
480 | =item Net::Ping |
481 | |
482 | check a host for upness |
483 | |
484 | =item POSIX |
485 | |
486 | Perl interface to IEEE Std 1003.1 |
487 | |
488 | =item SelfLoader |
489 | |
490 | load functions only on demand |
491 | |
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492 | =item Safe |
493 | |
494 | Creation controlled compartments in which perl code can be evaluated. |
495 | |
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496 | =item Socket |
497 | |
498 | load the C socket.h defines and structure manipulators |
499 | |
500 | =item Test::Harness |
501 | |
502 | run perl standard test scripts with statistics |
503 | |
504 | =item Text::Abbrev |
505 | |
506 | rceate an abbreviation table from a list |
507 | |
508 | =back |
509 | |
510 | To find out I<all> the modules installed on your system, including |
511 | those without documentation or outside the standard release, do this: |
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512 | |
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513 | find `perl -e 'print "@INC"'` -name '*.pm' -print |
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514 | |
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515 | They should all have their own documentation installed and accessible via |
516 | your system man(1) command. If that fails, try the I<perldoc> program. |
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517 | |
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518 | =head2 Extension Modules |
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519 | |
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520 | Extension modules are written in C (or a mix of Perl and C) and get |
521 | dynamically loaded into Perl if and when you need them. Supported |
522 | extension modules include the Socket, Fcntl, and POSIX modules. |
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523 | |
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524 | Many popular C extension modules do not come bundled (at least, not |
525 | completely) due to their size, volatility, or simply lack of time for |
526 | adequate testing and configuration across the multitude of platforms on |
527 | which Perl was beta-tested. You are encouraged to look for them in |
528 | archie(1L), the Perl FAQ or Meta-FAQ, the WWW page, and even with their |
529 | authors before randomly posting asking for their present condition and |
530 | disposition. |
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531 | |
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532 | =head1 CPAN |
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533 | |
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534 | CPAN stands for the Comprehensive Perl Archive Network. This is a globally |
535 | replicated collection of all known Perl materials, including hundreds |
536 | of unbunded modules. Here are the major categories of modules: |
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537 | |
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538 | =over |
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539 | |
4633a7c4 |
540 | =item * |
541 | Language Extensions and Documentation Tools |
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542 | |
4633a7c4 |
543 | =item * |
544 | Development Support |
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545 | |
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546 | =item * |
547 | Operating System Interfaces |
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548 | |
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549 | =item * |
550 | Networking, Device Control (modems) and InterProcess Communication |
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551 | |
4633a7c4 |
552 | =item * |
553 | Data Types and Data Type Utilities |
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554 | |
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555 | =item * |
556 | Database Interfaces |
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557 | |
4633a7c4 |
558 | =item * |
559 | User Interfaces |
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560 | |
4633a7c4 |
561 | =item * |
562 | Interfaces to / Emulations of Other Programming Languages |
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563 | |
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564 | =item * |
565 | File Names, File Systems and File Locking (see also File Handles) |
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566 | |
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567 | =item * |
568 | String Processing, Language Text Processing, Parsing and Searching |
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569 | |
4633a7c4 |
570 | =item * |
571 | Option, Argument, Parameter and Configuration File Processing |
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572 | |
4633a7c4 |
573 | =item * |
574 | Internationalization and Locale |
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575 | |
4633a7c4 |
576 | =item * |
577 | Authentication, Security and Encryption |
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578 | |
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579 | =item * |
580 | World Wide Web, HTML, HTTP, CGI, MIME |
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581 | |
4633a7c4 |
582 | =item * |
583 | Server and Daemon Utilities |
a0d0e21e |
584 | |
4633a7c4 |
585 | =item * |
586 | Archiving and Compression |
a0d0e21e |
587 | |
4633a7c4 |
588 | =item * |
589 | Images, Pixmap and Bitmap Manipulation, Drawing and Graphing |
a0d0e21e |
590 | |
4633a7c4 |
591 | =item * |
592 | Mail and Usenet News |
a0d0e21e |
593 | |
4633a7c4 |
594 | =item * |
595 | Control Flow Utilities (callbacks and exceptions etc) |
a0d0e21e |
596 | |
4633a7c4 |
597 | =item * |
598 | File Handle and Input/Output Stream Utilities |
a0d0e21e |
599 | |
4633a7c4 |
600 | =item * |
601 | Miscellaneous Modules |
a0d0e21e |
602 | |
4633a7c4 |
603 | =back |
a0d0e21e |
604 | |
4633a7c4 |
605 | Some of the reguster CPAN sites as of this writing include the following. |
606 | You should try to choose one close to you: |
a0d0e21e |
607 | |
4633a7c4 |
608 | =over |
a0d0e21e |
609 | |
4633a7c4 |
610 | =item * |
611 | ftp://ftp.sterling.com/programming/languages/perl/ |
a0d0e21e |
612 | |
4633a7c4 |
613 | =item * |
614 | ftp://ftp.sedl.org/pub/mirrors/CPAN/ |
a0d0e21e |
615 | |
4633a7c4 |
616 | =item * |
617 | ftp://ftp.uoknor.edu/mirrors/CPAN/ |
a0d0e21e |
618 | |
4633a7c4 |
619 | =item * |
620 | ftp://ftp.delphi.com/pub/mirrors/packages/perl/CPAN/ |
a0d0e21e |
621 | |
4633a7c4 |
622 | =item * |
623 | ftp://uiarchive.cso.uiuc.edu/pub/lang/perl/CPAN/ |
a0d0e21e |
624 | |
4633a7c4 |
625 | =item * |
626 | ftp://ftp.cis.ufl.edu/pub/perl/CPAN/ |
a0d0e21e |
627 | |
4633a7c4 |
628 | =item * |
629 | ftp://ftp.switch.ch/mirror/CPAN/ |
a0d0e21e |
630 | |
4633a7c4 |
631 | =item * |
632 | ftp://ftp.sunet.se/pub/lang/perl/CPAN/ |
a0d0e21e |
633 | |
4633a7c4 |
634 | =item * |
635 | ftp://ftp.ci.uminho.pt/pub/lang/perl/ |
a0d0e21e |
636 | |
4633a7c4 |
637 | =item * |
638 | ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/ |
a0d0e21e |
639 | |
4633a7c4 |
640 | =item * |
641 | ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/ |
a0d0e21e |
642 | |
4633a7c4 |
643 | =item * |
644 | ftp://ftp.rz.ruhr-uni-bochum.de/pub/programming/languages/perl/CPAN/ |
a0d0e21e |
645 | |
4633a7c4 |
646 | =item * |
647 | ftp://ftp.leo.org/pub/comp/programming/languages/perl/CPAN/ |
a0d0e21e |
648 | |
4633a7c4 |
649 | =item * |
650 | ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/ |
a0d0e21e |
651 | |
4633a7c4 |
652 | =item * |
653 | ftp://ftp.ibp.fr/pub/perl/CPAN/ |
a0d0e21e |
654 | |
4633a7c4 |
655 | =item * |
656 | ftp://ftp.funet.fi/pub/languages/perl/CPAN/ |
a0d0e21e |
657 | |
4633a7c4 |
658 | =item * |
659 | ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/ |
a0d0e21e |
660 | |
4633a7c4 |
661 | =item * |
662 | ftp://ftp.mame.mu.oz.au/pub/perl/CPAN/ |
a0d0e21e |
663 | |
4633a7c4 |
664 | =item * |
665 | ftp://coombs.anu.edu.au/pub/perl/ |
a0d0e21e |
666 | |
4633a7c4 |
667 | =item * |
668 | ftp://dongpo.math.ncu.edu.tw/perl/CPAN/ |
a0d0e21e |
669 | |
4633a7c4 |
670 | =item * |
671 | ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/ |
a0d0e21e |
672 | |
4633a7c4 |
673 | =item * |
674 | ftp://ftp.is.co.za/programming/perl/CPAN/ |
a0d0e21e |
675 | |
676 | =back |
4633a7c4 |
677 | |
678 | For an up-to-date listing of CPAN sites, |
cb1a09d0 |
679 | see http://www.perl.com/perl/ or ftp://ftp.perl.com/perl/ . |
680 | |
681 | =head1 Modules: Creation, Use and Abuse |
682 | |
683 | (The following section is borrowed directly from Tim Bunce's modules |
684 | file, available at your nearest CPAN site.) |
685 | |
686 | Perl 5 implements a class using a package, but the presence of a |
687 | package doesn't imply the presence of a class. A package is just a |
688 | namespace. A class is a package that provides subroutines that can be |
689 | used as methods. A method is just a subroutine that expects, as its |
690 | first argument, either the name of a package (for "static" methods), |
691 | or a reference to something (for "virtual" methods). |
692 | |
693 | A module is a file that (by convention) provides a class of the same |
694 | name (sans the .pm), plus an import method in that class that can be |
695 | called to fetch exported symbols. This module may implement some of |
696 | its methods by loading dynamic C or C++ objects, but that should be |
697 | totally transparent to the user of the module. Likewise, the module |
698 | might set up an AUTOLOAD function to slurp in subroutine definitions on |
699 | demand, but this is also transparent. Only the .pm file is required to |
700 | exist. |
701 | |
702 | =head2 Guidelines for Module Creation |
703 | |
704 | =over 4 |
705 | |
706 | =item Do similar modules already exist in some form? |
707 | |
708 | If so, please try to reuse the existing modules either in whole or |
709 | by inheriting useful features into a new class. If this is not |
710 | practical try to get together with the module authors to work on |
711 | extending or enhancing the functionality of the existing modules. |
712 | A perfect example is the plethora of packages in perl4 for dealing |
713 | with command line options. |
714 | |
715 | If you are writing a module to expand an already existing set of |
716 | modules, please coordinate with the author of the package. It |
717 | helps if you follow the same naming scheme and module interaction |
718 | scheme as the original author. |
719 | |
720 | =item Try to design the new module to be easy to extend and reuse. |
721 | |
722 | Use blessed references. Use the two argument form of bless to bless |
723 | into the class name given as the first parameter of the constructor, |
724 | e.g.: |
725 | |
726 | sub new { |
727 | my $class = shift; |
728 | return bless {}, $class; |
729 | } |
730 | |
731 | or even this if you'd like it to be used as either a static |
732 | or a virtual method. |
733 | |
734 | sub new { |
735 | my $self = shift; |
736 | my $class = ref($self) || $self; |
737 | return bless {}, $class; |
738 | } |
739 | |
740 | Pass arrays as references so more parameters can be added later |
741 | (it's also faster). Convert functions into methods where |
742 | appropriate. Split large methods into smaller more flexible ones. |
743 | Inherit methods from other modules if appropriate. |
744 | |
745 | Avoid class name tests like: die "Invalid" unless ref $ref eq 'FOO'. |
746 | Generally you can delete the "eq 'FOO'" part with no harm at all. |
747 | Let the objects look after themselves! Generally, avoid hardwired |
748 | class names as far as possible. |
749 | |
d28ebecd |
750 | Avoid $r-E<gt>Class::func() where using @ISA=qw(... Class ...) and |
751 | $r-E<gt>func() would work (see perlbot man page for more details). |
cb1a09d0 |
752 | |
753 | Use autosplit so little used or newly added functions won't be a |
754 | burden to programs which don't use them. Add test functions to |
755 | the module after __END__ either using AutoSplit or by saying: |
756 | |
757 | eval join('',<main::DATA>) || die $@ unless caller(); |
758 | |
759 | Does your module pass the 'empty sub-class' test? If you say |
760 | "@SUBCLASS::ISA = qw(YOURCLASS);" your applications should be able |
761 | to use SUBCLASS in exactly the same way as YOURCLASS. For example, |
762 | does your application still work if you change: $obj = new YOURCLASS; |
763 | into: $obj = new SUBCLASS; ? |
764 | |
765 | Avoid keeping any state information in your packages. It makes it |
766 | difficult for multiple other packages to use yours. Keep state |
767 | information in objects. |
768 | |
769 | Always use C<-w>. Try to C<use strict;> (or C<use strict qw(...);>). |
770 | Remember that you can add C<no strict qw(...);> to individual blocks |
771 | of code which need less strictness. Always use C<-w>. Always use C<-w>! |
772 | Follow the guidelines in the perlstyle(1) manual. |
773 | |
774 | =item Some simple style guidelines |
775 | |
776 | The perlstyle manual supplied with perl has many helpful points. |
777 | |
778 | Coding style is a matter of personal taste. Many people evolve their |
779 | style over several years as they learn what helps them write and |
780 | maintain good code. Here's one set of assorted suggestions that |
781 | seem to be widely used by experienced developers: |
782 | |
783 | Use underscores to separate words. It is generally easier to read |
784 | $var_names_like_this than $VarNamesLikeThis, especially for |
785 | non-native speakers of English. It's also a simple rule that works |
786 | consistently with VAR_NAMES_LIKE_THIS. |
787 | |
788 | Package/Module names are an exception to this rule. Perl informally |
789 | reserves lowercase module names for 'pragma' modules like integer |
790 | and strict. Other modules normally begin with a capital letter and |
791 | use mixed case with no underscores (need to be short and portable). |
792 | |
793 | You may find it helpful to use letter case to indicate the scope |
794 | or nature of a variable. For example: |
795 | |
796 | $ALL_CAPS_HERE constants only (beware clashes with perl vars) |
797 | $Some_Caps_Here package-wide global/static |
798 | $no_caps_here function scope my() or local() variables |
799 | |
800 | Function and method names seem to work best as all lowercase. |
d28ebecd |
801 | E.g., $obj-E<gt>as_string(). |
cb1a09d0 |
802 | |
803 | You can use a leading underscore to indicate that a variable or |
804 | function should not be used outside the package that defined it. |
805 | |
806 | =item Select what to export. |
807 | |
808 | Do NOT export method names! |
809 | |
810 | Do NOT export anything else by default without a good reason! |
811 | |
812 | Exports pollute the namespace of the module user. If you must |
813 | export try to use @EXPORT_OK in preference to @EXPORT and avoid |
814 | short or common names to reduce the risk of name clashes. |
815 | |
816 | Generally anything not exported is still accessible from outside the |
d28ebecd |
817 | module using the ModuleName::item_name (or $blessed_ref-E<gt>method) |
cb1a09d0 |
818 | syntax. By convention you can use a leading underscore on names to |
819 | informally indicate that they are 'internal' and not for public use. |
820 | |
821 | (It is actually possible to get private functions by saying: |
822 | my $subref = sub { ... }; &$subref; But there's no way to call that |
823 | directly as a method, since a method must have a name in the symbol |
824 | table.) |
825 | |
826 | As a general rule, if the module is trying to be object oriented |
827 | then export nothing. If it's just a collection of functions then |
828 | @EXPORT_OK anything but use @EXPORT with caution. |
829 | |
830 | =item Select a name for the module. |
831 | |
832 | This name should be as descriptive, accurate and complete as |
833 | possible. Avoid any risk of ambiguity. Always try to use two or |
834 | more whole words. Generally the name should reflect what is special |
835 | about what the module does rather than how it does it. Please use |
836 | nested module names to informally group or categorise a module. |
837 | A module should have a very good reason not to have a nested name. |
838 | Module names should begin with a capital letter. |
839 | |
840 | Having 57 modules all called Sort will not make life easy for anyone |
841 | (though having 23 called Sort::Quick is only marginally better :-). |
842 | Imagine someone trying to install your module alongside many others. |
843 | If in any doubt ask for suggestions in comp.lang.perl.misc. |
844 | |
845 | If you are developing a suite of related modules/classes it's good |
846 | practice to use nested classes with a common prefix as this will |
847 | avoid namespace clashes. For example: Xyz::Control, Xyz::View, |
848 | Xyz::Model etc. Use the modules in this list as a naming guide. |
849 | |
850 | If adding a new module to a set, follow the original author's |
851 | standards for naming modules and the interface to methods in |
852 | those modules. |
853 | |
854 | To be portable each component of a module name should be limited to |
855 | 11 characters. If it might be used on DOS then try to ensure each is |
856 | unique in the first 8 characters. Nested modules make this easier. |
857 | |
858 | =item Have you got it right? |
859 | |
860 | How do you know that you've made the right decisions? Have you |
861 | picked an interface design that will cause problems later? Have |
862 | you picked the most appropriate name? Do you have any questions? |
863 | |
864 | The best way to know for sure, and pick up many helpful suggestions, |
865 | is to ask someone who knows. Comp.lang.perl.misc is read by just about |
866 | all the people who develop modules and it's the best place to ask. |
867 | |
868 | All you need to do is post a short summary of the module, its |
869 | purpose and interfaces. A few lines on each of the main methods is |
870 | probably enough. (If you post the whole module it might be ignored |
871 | by busy people - generally the very people you want to read it!) |
872 | |
873 | Don't worry about posting if you can't say when the module will be |
874 | ready - just say so in the message. It might be worth inviting |
875 | others to help you, they may be able to complete it for you! |
876 | |
877 | =item README and other Additional Files. |
878 | |
879 | It's well known that software developers usually fully document the |
880 | software they write. If, however, the world is in urgent need of |
881 | your software and there is not enough time to write the full |
882 | documentation please at least provide a README file containing: |
883 | |
884 | =over 10 |
885 | |
886 | =item * |
887 | A description of the module/package/extension etc. |
888 | |
889 | =item * |
890 | A copyright notice - see below. |
891 | |
892 | =item * |
893 | Prerequisites - what else you may need to have. |
894 | |
895 | =item * |
896 | How to build it - possible changes to Makefile.PL etc. |
897 | |
898 | =item * |
899 | How to install it. |
900 | |
901 | =item * |
902 | Recent changes in this release, especially incompatibilities |
903 | |
904 | =item * |
905 | Changes / enhancements you plan to make in the future. |
906 | |
907 | =back |
908 | |
909 | If the README file seems to be getting too large you may wish to |
910 | split out some of the sections into separate files: INSTALL, |
911 | Copying, ToDo etc. |
912 | |
913 | =item Adding a Copyright Notice. |
914 | |
915 | How you choose to licence your work is a personal decision. |
916 | The general mechanism is to assert your Copyright and then make |
917 | a declaration of how others may copy/use/modify your work. |
918 | |
919 | Perl, for example, is supplied with two types of licence: The GNU |
920 | GPL and The Artistic License (see the files README, Copying and |
921 | Artistic). Larry has good reasons for NOT just using the GNU GPL. |
922 | |
923 | My personal recommendation, out of respect for Larry, Perl and the |
924 | perl community at large is to simply state something like: |
925 | |
926 | Copyright (c) 1995 Your Name. All rights reserved. |
927 | This program is free software; you can redistribute it and/or |
928 | modify it under the same terms as Perl itself. |
929 | |
930 | This statement should at least appear in the README file. You may |
931 | also wish to include it in a Copying file and your source files. |
932 | Remember to include the other words in addition to the Copyright. |
933 | |
934 | =item Give the module a version/issue/release number. |
935 | |
936 | To be fully compatible with the Exporter and MakeMaker modules you |
937 | should store your module's version number in a non-my package |
938 | variable called $VERSION. This should be a valid floating point |
939 | number with at least two digits after the decimal (ie hundredths, |
940 | e.g, $VERSION = "0.01"). Don't use a "1.3.2" style version. |
941 | See Exporter.pm in Perl5.001m or later for details. |
942 | |
943 | It may be handy to add a function or method to retrieve the number. |
944 | Use the number in announcements and archive file names when |
945 | releasing the module (ModuleName-1.02.tar.Z). |
946 | See perldoc ExtUtils::MakeMaker.pm for details. |
947 | |
948 | =item How to release and distribute a module. |
949 | |
950 | It's good idea to post an announcement of the availability of your |
951 | module (or the module itself if small) to the comp.lang.perl.announce |
952 | Usenet newsgroup. This will at least ensure very wide once-off |
953 | distribution. |
954 | |
955 | If possible you should place the module into a major ftp archive and |
956 | include details of it's location in your announcement. |
957 | |
958 | Some notes about ftp archives: Please use a long descriptive file |
959 | name which includes the version number. Most incoming directories |
960 | will not be readable/listable, i.e., you won't be able to see your |
961 | file after uploading it. Remember to send your email notification |
962 | message as soon as possible after uploading else your file may get |
963 | deleted automatically. Allow time for the file to be processed |
964 | and/or check the file has been processed before announcing its |
965 | location. |
966 | |
967 | FTP Archives for Perl Modules: |
968 | |
969 | Follow the instructions and links on |
970 | |
971 | http://franz.ww.tu-berlin.de/modulelist |
972 | |
973 | or upload to one of these sites: |
974 | |
975 | ftp://franz.ww.tu-berlin.de/incoming |
976 | ftp://ftp.cis.ufl.edu/incoming |
977 | |
978 | and notify upload@franz.ww.tu-berlin.de. |
979 | |
980 | By using the WWW interface you can ask the Upload Server to mirror |
981 | your modules from your ftp or WWW site into your own directory on |
982 | CPAN! |
983 | |
984 | Please remember to send me an updated entry for the Module list! |
985 | |
986 | =item Take care when changing a released module. |
987 | |
988 | Always strive to remain compatible with previous released versions |
989 | (see 2.2 above) Otherwise try to add a mechanism to revert to the |
990 | old behaviour if people rely on it. Document incompatible changes. |
991 | |
992 | =back |
993 | |
994 | =head2 Guidelines for Converting Perl 4 Library Scripts into Modules |
995 | |
996 | =over 4 |
997 | |
998 | =item There is no requirement to convert anything. |
999 | |
1000 | If it ain't broke, don't fix it! Perl 4 library scripts should |
1001 | continue to work with no problems. You may need to make some minor |
1002 | changes (like escaping non-array @'s in double quoted strings) but |
1003 | there is no need to convert a .pl file into a Module for just that. |
1004 | |
1005 | =item Consider the implications. |
1006 | |
1007 | All the perl applications which make use of the script will need to |
1008 | be changed (slightly) if the script is converted into a module. Is |
1009 | it worth it unless you plan to make other changes at the same time? |
1010 | |
1011 | =item Make the most of the opportunity. |
1012 | |
1013 | If you are going to convert the script to a module you can use the |
1014 | opportunity to redesign the interface. The 'Guidelines for Module |
1015 | Creation' above include many of the issues you should consider. |
1016 | |
1017 | =item The pl2pm utility will get you started. |
1018 | |
1019 | This utility will read *.pl files (given as parameters) and write |
1020 | corresponding *.pm files. The pl2pm utilities does the following: |
1021 | |
1022 | =over 10 |
1023 | |
1024 | =item * |
1025 | Adds the standard Module prologue lines |
1026 | |
1027 | =item * |
1028 | Converts package specifiers from ' to :: |
1029 | |
1030 | =item * |
1031 | Converts die(...) to croak(...) |
1032 | |
1033 | =item * |
1034 | Several other minor changes |
1035 | |
1036 | =back |
1037 | |
1038 | Being a mechanical process pl2pm is not bullet proof. The converted |
1039 | code will need careful checking, especially any package statements. |
1040 | Don't delete the original .pl file till the new .pm one works! |
1041 | |
1042 | =back |
1043 | |
1044 | =head2 Guidelines for Reusing Application Code |
1045 | |
1046 | =over 4 |
1047 | |
1048 | =item Complete applications rarely belong in the Perl Module Library. |
1049 | |
1050 | =item Many applications contain some perl code which could be reused. |
1051 | |
1052 | Help save the world! Share your code in a form that makes it easy |
1053 | to reuse. |
1054 | |
1055 | =item Break-out the reusable code into one or more separate module files. |
1056 | |
1057 | =item Take the opportunity to reconsider and redesign the interfaces. |
1058 | |
1059 | =item In some cases the 'application' can then be reduced to a small |
1060 | |
1061 | fragment of code built on top of the reusable modules. In these cases |
1062 | the application could invoked as: |
1063 | |
1064 | perl -e 'use Module::Name; method(@ARGV)' ... |
1065 | or |
1066 | perl -mModule::Name ... (in perl5.002?) |
1067 | |
1068 | =back |
1069 | |