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a0d0e21e LW |
1 | =head1 NAME |
2 | ||
3 | perlmod - Perl modules (packages) | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | =head2 Packages | |
8 | ||
748a9306 | 9 | Perl provides a mechanism for alternative namespaces to protect packages |
d0c42abe | 10 | from stomping on each other's variables. In fact, apart from certain |
cb1a09d0 AD |
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 | |
a0d0e21e LW |
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<$Package::Variable>. If the package name is null, the C<main> package | |
d0c42abe | 25 | is assumed. That is, C<$::sail> is equivalent to C<$main::sail>. |
a0d0e21e LW |
26 | |
27 | (The old package delimiter was a single quote, but double colon | |
28 | is now the preferred delimiter, in part because it's more readable | |
29 | to humans, and in part because it's more readable to B<emacs> macros. | |
30 | It also makes C++ programmers feel like they know what's going on.) | |
31 | ||
32 | Packages may be nested inside other packages: C<$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 | |
cb1a09d0 AD |
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. | |
a0d0e21e LW |
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 | |
cb1a09d0 AD |
51 | to use leading underscore to indicate private variables and method names. |
52 | $_ is still global though.) | |
a0d0e21e LW |
53 | |
54 | Eval()ed strings are compiled in the package in which the eval() was | |
55 | compiled. (Assignments to C<$SIG{}>, however, assume the signal | |
748a9306 | 56 | handler specified is in the C<main> package. Qualify the signal handler |
a0d0e21e LW |
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 | ||
cb1a09d0 AD |
65 | See L<perlsub> for other scoping issues related to my() and local(), |
66 | or L<perlref> regarding closures. | |
67 | ||
a0d0e21e LW |
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 | |
d0c42abe | 72 | name is thus C<%main::>, or C<%::> for short. Likewise symbol table for |
73 | the nested package mentioned earlier is named C<%OUTER::INNER::>. | |
a0d0e21e | 74 | |
cb1a09d0 AD |
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: | |
a0d0e21e LW |
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 | ||
cb1a09d0 | 118 | Assignment to a typeglob performs an aliasing operation, i.e., |
a0d0e21e LW |
119 | |
120 | *dick = *richard; | |
121 | ||
748a9306 | 122 | causes variables, subroutines and file handles accessible via the |
d0c42abe | 123 | identifier C<richard> to also be accessible via the identifier C<dick>. If |
a0d0e21e LW |
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 | ||
cb1a09d0 AD |
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 | |
c36e9b62 | 148 | is a somewhat tricky way of passing around references cheaply |
cb1a09d0 AD |
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 $PI, which is probably a good thing all in all. | |
157 | ||
a0d0e21e LW |
158 | =head2 Package Constructors and Destructors |
159 | ||
160 | There are two special subroutine definitions that function as package | |
161 | constructors and destructors. These are the C<BEGIN> and C<END> | |
162 | routines. The C<sub> is optional for these routines. | |
163 | ||
164 | A C<BEGIN> subroutine is executed as soon as possible, that is, the | |
165 | moment it is completely defined, even before the rest of the containing | |
166 | file is parsed. You may have multiple C<BEGIN> blocks within a | |
167 | file--they will execute in order of definition. Because a C<BEGIN> | |
168 | block executes immediately, it can pull in definitions of subroutines | |
169 | and such from other files in time to be visible to the rest of the | |
170 | file. | |
171 | ||
172 | An C<END> subroutine is executed as late as possible, that is, when the | |
173 | interpreter is being exited, even if it is exiting as a result of a | |
174 | die() function. (But not if it's is being blown out of the water by a | |
175 | signal--you have to trap that yourself (if you can).) You may have | |
748a9306 | 176 | multiple C<END> blocks within a file--they will execute in reverse |
a0d0e21e LW |
177 | order of definition; that is: last in, first out (LIFO). |
178 | ||
c36e9b62 | 179 | Inside an C<END> subroutine C<$?> contains the value that the script is |
180 | going to pass to C<exit()>. You can modify C<$?> to change the exit | |
181 | value of the script. Beware of changing C<$?> by accident (eg, by | |
182 | running something via C<system>). | |
183 | ||
a0d0e21e LW |
184 | Note that when you use the B<-n> and B<-p> switches to Perl, C<BEGIN> |
185 | and C<END> work just as they do in B<awk>, as a degenerate case. | |
186 | ||
187 | =head2 Perl Classes | |
188 | ||
4633a7c4 | 189 | There is no special class syntax in Perl, but a package may function |
a0d0e21e LW |
190 | as a class if it provides subroutines that function as methods. Such a |
191 | package may also derive some of its methods from another class package | |
4633a7c4 LW |
192 | by listing the other package name in its @ISA array. |
193 | ||
194 | For more on this, see L<perlobj>. | |
a0d0e21e LW |
195 | |
196 | =head2 Perl Modules | |
197 | ||
c07a80fd | 198 | A module is just a package that is defined in a library file of |
a0d0e21e LW |
199 | the same name, and is designed to be reusable. It may do this by |
200 | providing a mechanism for exporting some of its symbols into the symbol | |
201 | table of any package using it. Or it may function as a class | |
202 | definition and make its semantics available implicitly through method | |
203 | calls on the class and its objects, without explicit exportation of any | |
204 | symbols. Or it can do a little of both. | |
205 | ||
4633a7c4 LW |
206 | For example, to start a normal module called Fred, create |
207 | a file called Fred.pm and put this at the start of it: | |
208 | ||
cf6f4e91 | 209 | package Fred; |
210 | use Exporter (); | |
4633a7c4 LW |
211 | @ISA = qw(Exporter); |
212 | @EXPORT = qw(func1 func2); | |
213 | @EXPORT_OK = qw($sally @listabob %harry func3); | |
214 | ||
215 | Then go on to declare and use your variables in functions | |
216 | without any qualifications. | |
217 | See L<Exporter> and the I<Perl Modules File> for details on | |
218 | mechanics and style issues in module creation. | |
219 | ||
220 | Perl modules are included into your program by saying | |
a0d0e21e LW |
221 | |
222 | use Module; | |
223 | ||
224 | or | |
225 | ||
226 | use Module LIST; | |
227 | ||
228 | This is exactly equivalent to | |
229 | ||
230 | BEGIN { require "Module.pm"; import Module; } | |
231 | ||
232 | or | |
233 | ||
234 | BEGIN { require "Module.pm"; import Module LIST; } | |
235 | ||
cb1a09d0 AD |
236 | As a special case |
237 | ||
238 | use Module (); | |
239 | ||
240 | is exactly equivalent to | |
241 | ||
242 | BEGIN { require "Module.pm"; } | |
243 | ||
a0d0e21e LW |
244 | All Perl module files have the extension F<.pm>. C<use> assumes this so |
245 | that you don't have to spell out "F<Module.pm>" in quotes. This also | |
246 | helps to differentiate new modules from old F<.pl> and F<.ph> files. | |
247 | Module names are also capitalized unless they're functioning as pragmas, | |
248 | "Pragmas" are in effect compiler directives, and are sometimes called | |
249 | "pragmatic modules" (or even "pragmata" if you're a classicist). | |
250 | ||
251 | Because the C<use> statement implies a C<BEGIN> block, the importation | |
252 | of semantics happens at the moment the C<use> statement is compiled, | |
253 | before the rest of the file is compiled. This is how it is able | |
254 | to function as a pragma mechanism, and also how modules are able to | |
255 | declare subroutines that are then visible as list operators for | |
256 | the rest of the current file. This will not work if you use C<require> | |
cb1a09d0 | 257 | instead of C<use>. With require you can get into this problem: |
a0d0e21e LW |
258 | |
259 | require Cwd; # make Cwd:: accessible | |
260 | $here = Cwd::getcwd(); | |
261 | ||
262 | use Cwd; # import names from Cwd:: | |
263 | $here = getcwd(); | |
264 | ||
265 | require Cwd; # make Cwd:: accessible | |
266 | $here = getcwd(); # oops! no main::getcwd() | |
267 | ||
cb1a09d0 AD |
268 | In general C<use Module ();> is recommended over C<require Module;>. |
269 | ||
a0d0e21e LW |
270 | Perl packages may be nested inside other package names, so we can have |
271 | package names containing C<::>. But if we used that package name | |
272 | directly as a filename it would makes for unwieldy or impossible | |
273 | filenames on some systems. Therefore, if a module's name is, say, | |
274 | C<Text::Soundex>, then its definition is actually found in the library | |
275 | file F<Text/Soundex.pm>. | |
276 | ||
277 | Perl modules always have a F<.pm> file, but there may also be dynamically | |
278 | linked executables or autoloaded subroutine definitions associated with | |
279 | the module. If so, these will be entirely transparent to the user of | |
280 | the module. It is the responsibility of the F<.pm> file to load (or | |
281 | arrange to autoload) any additional functionality. The POSIX module | |
282 | happens to do both dynamic loading and autoloading, but the user can | |
283 | just say C<use POSIX> to get it all. | |
284 | ||
8e07c86e | 285 | For more information on writing extension modules, see L<perlxs> |
a0d0e21e LW |
286 | and L<perlguts>. |
287 | ||
288 | =head1 NOTE | |
289 | ||
290 | Perl does not enforce private and public parts of its modules as you may | |
291 | have been used to in other languages like C++, Ada, or Modula-17. Perl | |
292 | doesn't have an infatuation with enforced privacy. It would prefer | |
293 | that you stayed out of its living room because you weren't invited, not | |
294 | because it has a shotgun. | |
295 | ||
296 | The module and its user have a contract, part of which is common law, | |
297 | and part of which is "written". Part of the common law contract is | |
298 | that a module doesn't pollute any namespace it wasn't asked to. The | |
299 | written contract for the module (AKA documentation) may make other | |
300 | provisions. But then you know when you C<use RedefineTheWorld> that | |
301 | you're redefining the world and willing to take the consequences. | |
302 | ||
303 | =head1 THE PERL MODULE LIBRARY | |
304 | ||
305 | A number of modules are included the the Perl distribution. These are | |
306 | described below, and all end in F<.pm>. You may also discover files in | |
307 | the library directory that end in either F<.pl> or F<.ph>. These are old | |
748a9306 | 308 | libraries supplied so that old programs that use them still run. The |
a0d0e21e LW |
309 | F<.pl> files will all eventually be converted into standard modules, and |
310 | the F<.ph> files made by B<h2ph> will probably end up as extension modules | |
311 | made by B<h2xs>. (Some F<.ph> values may already be available through the | |
312 | POSIX module.) The B<pl2pm> file in the distribution may help in your | |
d0c42abe | 313 | conversion, but it's just a mechanical process, so is far from bulletproof. |
a0d0e21e LW |
314 | |
315 | =head2 Pragmatic Modules | |
316 | ||
317 | They work somewhat like pragmas in that they tend to affect the compilation of | |
318 | your program, and thus will usually only work well when used within a | |
748a9306 | 319 | C<use>, or C<no>. These are locally scoped, so an inner BLOCK |
a0d0e21e LW |
320 | may countermand any of these by saying |
321 | ||
322 | no integer; | |
323 | no strict 'refs'; | |
324 | ||
325 | which lasts until the end of that BLOCK. | |
326 | ||
327 | The following programs are defined (and have their own documentation). | |
328 | ||
329 | =over 12 | |
330 | ||
cb1a09d0 | 331 | =item diagnostics |
4633a7c4 LW |
332 | |
333 | Pragma to produce enhanced diagnostics | |
334 | ||
cb1a09d0 | 335 | =item integer |
a0d0e21e | 336 | |
4633a7c4 | 337 | Pragma to compute arithmetic in integer instead of double |
a0d0e21e | 338 | |
cb1a09d0 | 339 | =item less |
a0d0e21e | 340 | |
4633a7c4 | 341 | Pragma to request less of something from the compiler |
a0d0e21e | 342 | |
d0c42abe | 343 | =item ops |
344 | ||
345 | Pragma to restrict use of unsafe opcodes | |
346 | ||
cb1a09d0 AD |
347 | =item overload |
348 | ||
349 | Pragma for overloading operators | |
350 | ||
351 | =item sigtrap | |
a0d0e21e | 352 | |
4633a7c4 | 353 | Pragma to enable stack backtrace on unexpected signals |
a0d0e21e | 354 | |
cb1a09d0 | 355 | =item strict |
a0d0e21e | 356 | |
4633a7c4 | 357 | Pragma to restrict unsafe constructs |
a0d0e21e | 358 | |
cb1a09d0 | 359 | =item subs |
a0d0e21e | 360 | |
4633a7c4 | 361 | Pragma to predeclare sub names |
a0d0e21e | 362 | |
d0c42abe | 363 | =item vars |
364 | ||
365 | Pragma to predeclare global symbols | |
366 | ||
a0d0e21e LW |
367 | =back |
368 | ||
369 | =head2 Standard Modules | |
370 | ||
4633a7c4 | 371 | Standard, bundled modules are all expected to behave in a well-defined |
a0d0e21e | 372 | manner with respect to namespace pollution because they use the |
4633a7c4 | 373 | Exporter module. See their own documentation for details. |
a0d0e21e | 374 | |
cb1a09d0 AD |
375 | =over 12 |
376 | ||
377 | =item AnyDBM_File | |
378 | ||
379 | provide framework for multiple DBMs | |
380 | ||
381 | =item AutoLoader | |
382 | ||
383 | load functions only on demand | |
384 | ||
385 | =item AutoSplit | |
386 | ||
387 | split a package for autoloading | |
388 | ||
389 | =item Benchmark | |
390 | ||
391 | benchmark running times of code | |
392 | ||
393 | =item Carp | |
394 | ||
395 | warn of errors (from perspective of caller) | |
396 | ||
397 | =item Config | |
398 | ||
399 | access Perl configuration option | |
400 | ||
401 | =item Cwd | |
402 | ||
403 | get pathname of current working directory | |
404 | ||
405 | =item DB_File | |
406 | ||
407 | Perl access to Berkeley DB | |
408 | ||
409 | =item Devel::SelfStubber | |
410 | ||
411 | generate stubs for a SelfLoading module | |
412 | ||
413 | =item DynaLoader | |
414 | ||
415 | Dynamically load C libraries into Perl code | |
416 | ||
417 | =item English | |
418 | ||
c36e9b62 | 419 | use nice English (or B<awk>) names for ugly punctuation variables |
cb1a09d0 AD |
420 | |
421 | =item Env | |
422 | ||
423 | perl module that imports environment variables | |
424 | ||
425 | =item Exporter | |
426 | ||
c36e9b62 | 427 | provide import/export controls for Perl modules |
cb1a09d0 AD |
428 | |
429 | =item ExtUtils::Liblist | |
430 | ||
431 | determine libraries to use and how to use them | |
432 | ||
433 | =item ExtUtils::MakeMaker | |
434 | ||
435 | create an extension Makefile | |
436 | ||
437 | =item ExtUtils::Manifest | |
438 | ||
439 | utilities to write and check a MANIFEST file | |
440 | ||
441 | =item ExtUtils::Mkbootstrap | |
442 | ||
443 | make a bootstrap file for use by DynaLoader | |
444 | ||
445 | =item ExtUtils::Miniperl | |
446 | ||
447 | !!!GOOD QUESTION!!! | |
448 | ||
449 | =item Fcntl | |
450 | ||
451 | load the C Fcntl.h defines | |
452 | ||
453 | =item File::Basename | |
454 | ||
455 | parse file specifications | |
456 | ||
457 | =item File::CheckTree | |
458 | ||
459 | run many filetest checks on a tree | |
460 | ||
461 | =item File::Find | |
462 | ||
463 | traverse a file tree | |
464 | ||
465 | =item FileHandle | |
466 | ||
467 | supply object methods for filehandles | |
468 | ||
469 | =item File::Path | |
470 | ||
471 | create or remove a series of directories | |
472 | ||
473 | =item Getopt::Long | |
474 | ||
475 | extended getopt processing | |
476 | ||
477 | =item Getopt::Std | |
478 | ||
479 | Process single-character switches with switch clustering | |
480 | ||
481 | =item I18N::Collate | |
482 | ||
483 | compare 8-bit scalar data according to the current locale | |
484 | ||
485 | =item IPC::Open2 | |
486 | ||
487 | a process for both reading and writing | |
488 | ||
489 | =item IPC::Open3 | |
490 | ||
491 | open a process for reading, writing, and error handling | |
492 | ||
493 | =item Net::Ping | |
494 | ||
495 | check a host for upness | |
496 | ||
497 | =item POSIX | |
498 | ||
499 | Perl interface to IEEE Std 1003.1 | |
500 | ||
501 | =item SelfLoader | |
502 | ||
503 | load functions only on demand | |
504 | ||
a2927560 | 505 | =item Safe |
506 | ||
507 | Creation controlled compartments in which perl code can be evaluated. | |
508 | ||
cb1a09d0 AD |
509 | =item Socket |
510 | ||
511 | load the C socket.h defines and structure manipulators | |
512 | ||
513 | =item Test::Harness | |
514 | ||
515 | run perl standard test scripts with statistics | |
516 | ||
517 | =item Text::Abbrev | |
518 | ||
c36e9b62 | 519 | create an abbreviation table from a list |
cb1a09d0 AD |
520 | |
521 | =back | |
522 | ||
523 | To find out I<all> the modules installed on your system, including | |
524 | those without documentation or outside the standard release, do this: | |
a0d0e21e | 525 | |
4633a7c4 | 526 | find `perl -e 'print "@INC"'` -name '*.pm' -print |
a0d0e21e | 527 | |
4633a7c4 LW |
528 | They should all have their own documentation installed and accessible via |
529 | your system man(1) command. If that fails, try the I<perldoc> program. | |
a0d0e21e | 530 | |
4633a7c4 | 531 | =head2 Extension Modules |
a0d0e21e | 532 | |
4633a7c4 LW |
533 | Extension modules are written in C (or a mix of Perl and C) and get |
534 | dynamically loaded into Perl if and when you need them. Supported | |
535 | extension modules include the Socket, Fcntl, and POSIX modules. | |
a0d0e21e | 536 | |
cb1a09d0 AD |
537 | Many popular C extension modules do not come bundled (at least, not |
538 | completely) due to their size, volatility, or simply lack of time for | |
539 | adequate testing and configuration across the multitude of platforms on | |
540 | which Perl was beta-tested. You are encouraged to look for them in | |
541 | archie(1L), the Perl FAQ or Meta-FAQ, the WWW page, and even with their | |
542 | authors before randomly posting asking for their present condition and | |
543 | disposition. | |
a0d0e21e | 544 | |
cb1a09d0 | 545 | =head1 CPAN |
a0d0e21e | 546 | |
4633a7c4 LW |
547 | CPAN stands for the Comprehensive Perl Archive Network. This is a globally |
548 | replicated collection of all known Perl materials, including hundreds | |
c36e9b62 | 549 | of unbundled modules. Here are the major categories of modules: |
a0d0e21e | 550 | |
4633a7c4 | 551 | =over |
a0d0e21e | 552 | |
4633a7c4 LW |
553 | =item * |
554 | Language Extensions and Documentation Tools | |
a0d0e21e | 555 | |
4633a7c4 LW |
556 | =item * |
557 | Development Support | |
a0d0e21e | 558 | |
4633a7c4 LW |
559 | =item * |
560 | Operating System Interfaces | |
a0d0e21e | 561 | |
4633a7c4 LW |
562 | =item * |
563 | Networking, Device Control (modems) and InterProcess Communication | |
a0d0e21e | 564 | |
4633a7c4 LW |
565 | =item * |
566 | Data Types and Data Type Utilities | |
a0d0e21e | 567 | |
4633a7c4 LW |
568 | =item * |
569 | Database Interfaces | |
a0d0e21e | 570 | |
4633a7c4 LW |
571 | =item * |
572 | User Interfaces | |
a0d0e21e | 573 | |
4633a7c4 LW |
574 | =item * |
575 | Interfaces to / Emulations of Other Programming Languages | |
a0d0e21e | 576 | |
4633a7c4 LW |
577 | =item * |
578 | File Names, File Systems and File Locking (see also File Handles) | |
a0d0e21e | 579 | |
4633a7c4 LW |
580 | =item * |
581 | String Processing, Language Text Processing, Parsing and Searching | |
a0d0e21e | 582 | |
4633a7c4 LW |
583 | =item * |
584 | Option, Argument, Parameter and Configuration File Processing | |
a0d0e21e | 585 | |
4633a7c4 LW |
586 | =item * |
587 | Internationalization and Locale | |
a0d0e21e | 588 | |
4633a7c4 LW |
589 | =item * |
590 | Authentication, Security and Encryption | |
a0d0e21e | 591 | |
4633a7c4 LW |
592 | =item * |
593 | World Wide Web, HTML, HTTP, CGI, MIME | |
a0d0e21e | 594 | |
4633a7c4 LW |
595 | =item * |
596 | Server and Daemon Utilities | |
a0d0e21e | 597 | |
4633a7c4 LW |
598 | =item * |
599 | Archiving and Compression | |
a0d0e21e | 600 | |
4633a7c4 LW |
601 | =item * |
602 | Images, Pixmap and Bitmap Manipulation, Drawing and Graphing | |
a0d0e21e | 603 | |
4633a7c4 LW |
604 | =item * |
605 | Mail and Usenet News | |
a0d0e21e | 606 | |
4633a7c4 LW |
607 | =item * |
608 | Control Flow Utilities (callbacks and exceptions etc) | |
a0d0e21e | 609 | |
4633a7c4 LW |
610 | =item * |
611 | File Handle and Input/Output Stream Utilities | |
a0d0e21e | 612 | |
4633a7c4 LW |
613 | =item * |
614 | Miscellaneous Modules | |
a0d0e21e | 615 | |
4633a7c4 | 616 | =back |
a0d0e21e | 617 | |
d0c42abe | 618 | The registered CPAN sites as of this writing include the following. |
4633a7c4 | 619 | You should try to choose one close to you: |
a0d0e21e | 620 | |
4633a7c4 | 621 | =over |
a0d0e21e | 622 | |
4633a7c4 LW |
623 | =item * |
624 | ftp://ftp.sterling.com/programming/languages/perl/ | |
a0d0e21e | 625 | |
4633a7c4 LW |
626 | =item * |
627 | ftp://ftp.sedl.org/pub/mirrors/CPAN/ | |
a0d0e21e | 628 | |
4633a7c4 LW |
629 | =item * |
630 | ftp://ftp.uoknor.edu/mirrors/CPAN/ | |
a0d0e21e | 631 | |
4633a7c4 LW |
632 | =item * |
633 | ftp://ftp.delphi.com/pub/mirrors/packages/perl/CPAN/ | |
a0d0e21e | 634 | |
4633a7c4 LW |
635 | =item * |
636 | ftp://uiarchive.cso.uiuc.edu/pub/lang/perl/CPAN/ | |
a0d0e21e | 637 | |
4633a7c4 LW |
638 | =item * |
639 | ftp://ftp.cis.ufl.edu/pub/perl/CPAN/ | |
a0d0e21e | 640 | |
4633a7c4 LW |
641 | =item * |
642 | ftp://ftp.switch.ch/mirror/CPAN/ | |
a0d0e21e | 643 | |
4633a7c4 LW |
644 | =item * |
645 | ftp://ftp.sunet.se/pub/lang/perl/CPAN/ | |
a0d0e21e | 646 | |
4633a7c4 LW |
647 | =item * |
648 | ftp://ftp.ci.uminho.pt/pub/lang/perl/ | |
a0d0e21e | 649 | |
4633a7c4 LW |
650 | =item * |
651 | ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/ | |
a0d0e21e | 652 | |
4633a7c4 LW |
653 | =item * |
654 | ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/ | |
a0d0e21e | 655 | |
4633a7c4 LW |
656 | =item * |
657 | ftp://ftp.rz.ruhr-uni-bochum.de/pub/programming/languages/perl/CPAN/ | |
a0d0e21e | 658 | |
4633a7c4 LW |
659 | =item * |
660 | ftp://ftp.leo.org/pub/comp/programming/languages/perl/CPAN/ | |
a0d0e21e | 661 | |
4633a7c4 LW |
662 | =item * |
663 | ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/ | |
a0d0e21e | 664 | |
4633a7c4 LW |
665 | =item * |
666 | ftp://ftp.ibp.fr/pub/perl/CPAN/ | |
a0d0e21e | 667 | |
4633a7c4 LW |
668 | =item * |
669 | ftp://ftp.funet.fi/pub/languages/perl/CPAN/ | |
a0d0e21e | 670 | |
4633a7c4 LW |
671 | =item * |
672 | ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/ | |
a0d0e21e | 673 | |
4633a7c4 LW |
674 | =item * |
675 | ftp://ftp.mame.mu.oz.au/pub/perl/CPAN/ | |
a0d0e21e | 676 | |
4633a7c4 LW |
677 | =item * |
678 | ftp://coombs.anu.edu.au/pub/perl/ | |
a0d0e21e | 679 | |
4633a7c4 LW |
680 | =item * |
681 | ftp://dongpo.math.ncu.edu.tw/perl/CPAN/ | |
a0d0e21e | 682 | |
4633a7c4 LW |
683 | =item * |
684 | ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/ | |
a0d0e21e | 685 | |
4633a7c4 LW |
686 | =item * |
687 | ftp://ftp.is.co.za/programming/perl/CPAN/ | |
a0d0e21e LW |
688 | |
689 | =back | |
4633a7c4 LW |
690 | |
691 | For an up-to-date listing of CPAN sites, | |
d0c42abe | 692 | see F<http://www.perl.com/perl/CPAN> or F<ftp://ftp.perl.com/perl/>. |
cb1a09d0 AD |
693 | |
694 | =head1 Modules: Creation, Use and Abuse | |
695 | ||
696 | (The following section is borrowed directly from Tim Bunce's modules | |
697 | file, available at your nearest CPAN site.) | |
698 | ||
699 | Perl 5 implements a class using a package, but the presence of a | |
700 | package doesn't imply the presence of a class. A package is just a | |
701 | namespace. A class is a package that provides subroutines that can be | |
702 | used as methods. A method is just a subroutine that expects, as its | |
703 | first argument, either the name of a package (for "static" methods), | |
704 | or a reference to something (for "virtual" methods). | |
705 | ||
706 | A module is a file that (by convention) provides a class of the same | |
707 | name (sans the .pm), plus an import method in that class that can be | |
708 | called to fetch exported symbols. This module may implement some of | |
709 | its methods by loading dynamic C or C++ objects, but that should be | |
710 | totally transparent to the user of the module. Likewise, the module | |
711 | might set up an AUTOLOAD function to slurp in subroutine definitions on | |
712 | demand, but this is also transparent. Only the .pm file is required to | |
713 | exist. | |
714 | ||
715 | =head2 Guidelines for Module Creation | |
716 | ||
717 | =over 4 | |
718 | ||
719 | =item Do similar modules already exist in some form? | |
720 | ||
721 | If so, please try to reuse the existing modules either in whole or | |
722 | by inheriting useful features into a new class. If this is not | |
723 | practical try to get together with the module authors to work on | |
724 | extending or enhancing the functionality of the existing modules. | |
725 | A perfect example is the plethora of packages in perl4 for dealing | |
726 | with command line options. | |
727 | ||
728 | If you are writing a module to expand an already existing set of | |
729 | modules, please coordinate with the author of the package. It | |
730 | helps if you follow the same naming scheme and module interaction | |
731 | scheme as the original author. | |
732 | ||
733 | =item Try to design the new module to be easy to extend and reuse. | |
734 | ||
735 | Use blessed references. Use the two argument form of bless to bless | |
736 | into the class name given as the first parameter of the constructor, | |
737 | e.g.: | |
738 | ||
739 | sub new { | |
740 | my $class = shift; | |
741 | return bless {}, $class; | |
742 | } | |
743 | ||
744 | or even this if you'd like it to be used as either a static | |
745 | or a virtual method. | |
746 | ||
747 | sub new { | |
748 | my $self = shift; | |
749 | my $class = ref($self) || $self; | |
750 | return bless {}, $class; | |
751 | } | |
752 | ||
753 | Pass arrays as references so more parameters can be added later | |
754 | (it's also faster). Convert functions into methods where | |
755 | appropriate. Split large methods into smaller more flexible ones. | |
756 | Inherit methods from other modules if appropriate. | |
757 | ||
c36e9b62 | 758 | Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>. |
759 | Generally you can delete the "C<eq 'FOO'>" part with no harm at all. | |
cb1a09d0 AD |
760 | Let the objects look after themselves! Generally, avoid hardwired |
761 | class names as far as possible. | |
762 | ||
c36e9b62 | 763 | Avoid C<$r-E<gt>Class::func()> where using C<@ISA=qw(... Class ...)> and |
764 | C<$r-E<gt>func()> would work (see L<perlbot> for more details). | |
cb1a09d0 AD |
765 | |
766 | Use autosplit so little used or newly added functions won't be a | |
767 | burden to programs which don't use them. Add test functions to | |
768 | the module after __END__ either using AutoSplit or by saying: | |
769 | ||
770 | eval join('',<main::DATA>) || die $@ unless caller(); | |
771 | ||
772 | Does your module pass the 'empty sub-class' test? If you say | |
c36e9b62 | 773 | "C<@SUBCLASS::ISA = qw(YOURCLASS);>" your applications should be able |
cb1a09d0 | 774 | to use SUBCLASS in exactly the same way as YOURCLASS. For example, |
c36e9b62 | 775 | does your application still work if you change: C<$obj = new YOURCLASS;> |
776 | into: C<$obj = new SUBCLASS;> ? | |
cb1a09d0 AD |
777 | |
778 | Avoid keeping any state information in your packages. It makes it | |
779 | difficult for multiple other packages to use yours. Keep state | |
780 | information in objects. | |
781 | ||
c36e9b62 | 782 | Always use B<-w>. Try to C<use strict;> (or C<use strict qw(...);>). |
cb1a09d0 | 783 | Remember that you can add C<no strict qw(...);> to individual blocks |
c36e9b62 | 784 | of code which need less strictness. Always use B<-w>. Always use B<-w>! |
cb1a09d0 AD |
785 | Follow the guidelines in the perlstyle(1) manual. |
786 | ||
787 | =item Some simple style guidelines | |
788 | ||
789 | The perlstyle manual supplied with perl has many helpful points. | |
790 | ||
791 | Coding style is a matter of personal taste. Many people evolve their | |
792 | style over several years as they learn what helps them write and | |
793 | maintain good code. Here's one set of assorted suggestions that | |
794 | seem to be widely used by experienced developers: | |
795 | ||
796 | Use underscores to separate words. It is generally easier to read | |
797 | $var_names_like_this than $VarNamesLikeThis, especially for | |
798 | non-native speakers of English. It's also a simple rule that works | |
799 | consistently with VAR_NAMES_LIKE_THIS. | |
800 | ||
801 | Package/Module names are an exception to this rule. Perl informally | |
802 | reserves lowercase module names for 'pragma' modules like integer | |
803 | and strict. Other modules normally begin with a capital letter and | |
804 | use mixed case with no underscores (need to be short and portable). | |
805 | ||
806 | You may find it helpful to use letter case to indicate the scope | |
807 | or nature of a variable. For example: | |
808 | ||
809 | $ALL_CAPS_HERE constants only (beware clashes with perl vars) | |
810 | $Some_Caps_Here package-wide global/static | |
811 | $no_caps_here function scope my() or local() variables | |
812 | ||
813 | Function and method names seem to work best as all lowercase. | |
c36e9b62 | 814 | E.g., C<$obj-E<gt>as_string()>. |
cb1a09d0 AD |
815 | |
816 | You can use a leading underscore to indicate that a variable or | |
817 | function should not be used outside the package that defined it. | |
818 | ||
819 | =item Select what to export. | |
820 | ||
821 | Do NOT export method names! | |
822 | ||
823 | Do NOT export anything else by default without a good reason! | |
824 | ||
825 | Exports pollute the namespace of the module user. If you must | |
826 | export try to use @EXPORT_OK in preference to @EXPORT and avoid | |
827 | short or common names to reduce the risk of name clashes. | |
828 | ||
829 | Generally anything not exported is still accessible from outside the | |
c36e9b62 | 830 | module using the ModuleName::item_name (or C<$blessed_ref-E<gt>method>) |
cb1a09d0 AD |
831 | syntax. By convention you can use a leading underscore on names to |
832 | informally indicate that they are 'internal' and not for public use. | |
833 | ||
834 | (It is actually possible to get private functions by saying: | |
c36e9b62 | 835 | C<my $subref = sub { ... }; &$subref;>. But there's no way to call that |
cb1a09d0 AD |
836 | directly as a method, since a method must have a name in the symbol |
837 | table.) | |
838 | ||
839 | As a general rule, if the module is trying to be object oriented | |
840 | then export nothing. If it's just a collection of functions then | |
841 | @EXPORT_OK anything but use @EXPORT with caution. | |
842 | ||
843 | =item Select a name for the module. | |
844 | ||
845 | This name should be as descriptive, accurate and complete as | |
846 | possible. Avoid any risk of ambiguity. Always try to use two or | |
847 | more whole words. Generally the name should reflect what is special | |
848 | about what the module does rather than how it does it. Please use | |
849 | nested module names to informally group or categorise a module. | |
850 | A module should have a very good reason not to have a nested name. | |
851 | Module names should begin with a capital letter. | |
852 | ||
853 | Having 57 modules all called Sort will not make life easy for anyone | |
854 | (though having 23 called Sort::Quick is only marginally better :-). | |
855 | Imagine someone trying to install your module alongside many others. | |
856 | If in any doubt ask for suggestions in comp.lang.perl.misc. | |
857 | ||
858 | If you are developing a suite of related modules/classes it's good | |
859 | practice to use nested classes with a common prefix as this will | |
860 | avoid namespace clashes. For example: Xyz::Control, Xyz::View, | |
861 | Xyz::Model etc. Use the modules in this list as a naming guide. | |
862 | ||
863 | If adding a new module to a set, follow the original author's | |
864 | standards for naming modules and the interface to methods in | |
865 | those modules. | |
866 | ||
867 | To be portable each component of a module name should be limited to | |
868 | 11 characters. If it might be used on DOS then try to ensure each is | |
869 | unique in the first 8 characters. Nested modules make this easier. | |
870 | ||
871 | =item Have you got it right? | |
872 | ||
873 | How do you know that you've made the right decisions? Have you | |
874 | picked an interface design that will cause problems later? Have | |
875 | you picked the most appropriate name? Do you have any questions? | |
876 | ||
877 | The best way to know for sure, and pick up many helpful suggestions, | |
878 | is to ask someone who knows. Comp.lang.perl.misc is read by just about | |
879 | all the people who develop modules and it's the best place to ask. | |
880 | ||
881 | All you need to do is post a short summary of the module, its | |
882 | purpose and interfaces. A few lines on each of the main methods is | |
883 | probably enough. (If you post the whole module it might be ignored | |
884 | by busy people - generally the very people you want to read it!) | |
885 | ||
886 | Don't worry about posting if you can't say when the module will be | |
887 | ready - just say so in the message. It might be worth inviting | |
888 | others to help you, they may be able to complete it for you! | |
889 | ||
890 | =item README and other Additional Files. | |
891 | ||
892 | It's well known that software developers usually fully document the | |
893 | software they write. If, however, the world is in urgent need of | |
894 | your software and there is not enough time to write the full | |
895 | documentation please at least provide a README file containing: | |
896 | ||
897 | =over 10 | |
898 | ||
899 | =item * | |
900 | A description of the module/package/extension etc. | |
901 | ||
902 | =item * | |
903 | A copyright notice - see below. | |
904 | ||
905 | =item * | |
906 | Prerequisites - what else you may need to have. | |
907 | ||
908 | =item * | |
909 | How to build it - possible changes to Makefile.PL etc. | |
910 | ||
911 | =item * | |
912 | How to install it. | |
913 | ||
914 | =item * | |
915 | Recent changes in this release, especially incompatibilities | |
916 | ||
917 | =item * | |
918 | Changes / enhancements you plan to make in the future. | |
919 | ||
920 | =back | |
921 | ||
922 | If the README file seems to be getting too large you may wish to | |
923 | split out some of the sections into separate files: INSTALL, | |
924 | Copying, ToDo etc. | |
925 | ||
d0c42abe | 926 | =over 4 |
927 | ||
cb1a09d0 AD |
928 | =item Adding a Copyright Notice. |
929 | ||
c36e9b62 | 930 | How you choose to license your work is a personal decision. |
cb1a09d0 AD |
931 | The general mechanism is to assert your Copyright and then make |
932 | a declaration of how others may copy/use/modify your work. | |
933 | ||
c36e9b62 | 934 | Perl, for example, is supplied with two types of license: The GNU |
cb1a09d0 AD |
935 | GPL and The Artistic License (see the files README, Copying and |
936 | Artistic). Larry has good reasons for NOT just using the GNU GPL. | |
937 | ||
938 | My personal recommendation, out of respect for Larry, Perl and the | |
939 | perl community at large is to simply state something like: | |
940 | ||
941 | Copyright (c) 1995 Your Name. All rights reserved. | |
942 | This program is free software; you can redistribute it and/or | |
943 | modify it under the same terms as Perl itself. | |
944 | ||
945 | This statement should at least appear in the README file. You may | |
946 | also wish to include it in a Copying file and your source files. | |
947 | Remember to include the other words in addition to the Copyright. | |
948 | ||
949 | =item Give the module a version/issue/release number. | |
950 | ||
951 | To be fully compatible with the Exporter and MakeMaker modules you | |
952 | should store your module's version number in a non-my package | |
953 | variable called $VERSION. This should be a valid floating point | |
954 | number with at least two digits after the decimal (ie hundredths, | |
c36e9b62 | 955 | e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version. |
cb1a09d0 AD |
956 | See Exporter.pm in Perl5.001m or later for details. |
957 | ||
958 | It may be handy to add a function or method to retrieve the number. | |
959 | Use the number in announcements and archive file names when | |
960 | releasing the module (ModuleName-1.02.tar.Z). | |
961 | See perldoc ExtUtils::MakeMaker.pm for details. | |
962 | ||
963 | =item How to release and distribute a module. | |
964 | ||
965 | It's good idea to post an announcement of the availability of your | |
966 | module (or the module itself if small) to the comp.lang.perl.announce | |
967 | Usenet newsgroup. This will at least ensure very wide once-off | |
968 | distribution. | |
969 | ||
970 | If possible you should place the module into a major ftp archive and | |
971 | include details of it's location in your announcement. | |
972 | ||
973 | Some notes about ftp archives: Please use a long descriptive file | |
974 | name which includes the version number. Most incoming directories | |
975 | will not be readable/listable, i.e., you won't be able to see your | |
976 | file after uploading it. Remember to send your email notification | |
977 | message as soon as possible after uploading else your file may get | |
978 | deleted automatically. Allow time for the file to be processed | |
979 | and/or check the file has been processed before announcing its | |
980 | location. | |
981 | ||
982 | FTP Archives for Perl Modules: | |
983 | ||
984 | Follow the instructions and links on | |
985 | ||
986 | http://franz.ww.tu-berlin.de/modulelist | |
987 | ||
988 | or upload to one of these sites: | |
989 | ||
990 | ftp://franz.ww.tu-berlin.de/incoming | |
991 | ftp://ftp.cis.ufl.edu/incoming | |
992 | ||
993 | and notify upload@franz.ww.tu-berlin.de. | |
994 | ||
995 | By using the WWW interface you can ask the Upload Server to mirror | |
996 | your modules from your ftp or WWW site into your own directory on | |
997 | CPAN! | |
998 | ||
999 | Please remember to send me an updated entry for the Module list! | |
1000 | ||
1001 | =item Take care when changing a released module. | |
1002 | ||
1003 | Always strive to remain compatible with previous released versions | |
1004 | (see 2.2 above) Otherwise try to add a mechanism to revert to the | |
1005 | old behaviour if people rely on it. Document incompatible changes. | |
1006 | ||
1007 | =back | |
1008 | ||
d0c42abe | 1009 | =back |
1010 | ||
cb1a09d0 AD |
1011 | =head2 Guidelines for Converting Perl 4 Library Scripts into Modules |
1012 | ||
1013 | =over 4 | |
1014 | ||
1015 | =item There is no requirement to convert anything. | |
1016 | ||
1017 | If it ain't broke, don't fix it! Perl 4 library scripts should | |
1018 | continue to work with no problems. You may need to make some minor | |
1019 | changes (like escaping non-array @'s in double quoted strings) but | |
1020 | there is no need to convert a .pl file into a Module for just that. | |
1021 | ||
1022 | =item Consider the implications. | |
1023 | ||
1024 | All the perl applications which make use of the script will need to | |
1025 | be changed (slightly) if the script is converted into a module. Is | |
1026 | it worth it unless you plan to make other changes at the same time? | |
1027 | ||
1028 | =item Make the most of the opportunity. | |
1029 | ||
1030 | If you are going to convert the script to a module you can use the | |
1031 | opportunity to redesign the interface. The 'Guidelines for Module | |
1032 | Creation' above include many of the issues you should consider. | |
1033 | ||
1034 | =item The pl2pm utility will get you started. | |
1035 | ||
1036 | This utility will read *.pl files (given as parameters) and write | |
1037 | corresponding *.pm files. The pl2pm utilities does the following: | |
1038 | ||
1039 | =over 10 | |
1040 | ||
1041 | =item * | |
1042 | Adds the standard Module prologue lines | |
1043 | ||
1044 | =item * | |
1045 | Converts package specifiers from ' to :: | |
1046 | ||
1047 | =item * | |
1048 | Converts die(...) to croak(...) | |
1049 | ||
1050 | =item * | |
1051 | Several other minor changes | |
1052 | ||
1053 | =back | |
1054 | ||
1055 | Being a mechanical process pl2pm is not bullet proof. The converted | |
1056 | code will need careful checking, especially any package statements. | |
1057 | Don't delete the original .pl file till the new .pm one works! | |
1058 | ||
1059 | =back | |
1060 | ||
1061 | =head2 Guidelines for Reusing Application Code | |
1062 | ||
1063 | =over 4 | |
1064 | ||
1065 | =item Complete applications rarely belong in the Perl Module Library. | |
1066 | ||
1067 | =item Many applications contain some perl code which could be reused. | |
1068 | ||
1069 | Help save the world! Share your code in a form that makes it easy | |
1070 | to reuse. | |
1071 | ||
1072 | =item Break-out the reusable code into one or more separate module files. | |
1073 | ||
1074 | =item Take the opportunity to reconsider and redesign the interfaces. | |
1075 | ||
1076 | =item In some cases the 'application' can then be reduced to a small | |
1077 | ||
1078 | fragment of code built on top of the reusable modules. In these cases | |
1079 | the application could invoked as: | |
1080 | ||
1081 | perl -e 'use Module::Name; method(@ARGV)' ... | |
1082 | or | |
d0c42abe | 1083 | perl -mModule::Name ... (in perl5.002) |
cb1a09d0 AD |
1084 | |
1085 | =back | |
1086 |