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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 | |
5f05dabc | 16 | will be in this namespace. A package statement affects only dynamic |
cb1a09d0 AD |
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 | |
5f05dabc | 20 | switch into a package in more than one place; it influences merely which |
a0d0e21e LW |
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 | |
5f05dabc | 42 | identifiers STDIN, STDOUT, STDERR, ARGV, ARGVOUT, ENV, INC, and SIG are |
cb1a09d0 AD |
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>, | |
5f05dabc | 45 | C<s>, or C<y>, then you can't use the qualified form of an identifier |
cb1a09d0 AD |
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 | ||
5f05dabc | 65 | See L<perlsub> for other scoping issues related to my() and local(), |
cb1a09d0 AD |
66 | or L<perlref> regarding closures. |
67 | ||
a0d0e21e LW |
68 | =head2 Symbol Tables |
69 | ||
aa689395 | 70 | The symbol table for a package happens to be stored in the hash of that |
71 | name with two colons appended. The main symbol table's name is thus | |
72 | C<%main::>, or C<%::> for short. Likewise symbol table for the nested | |
73 | package mentioned earlier is named C<%OUTER::INNER::>. | |
74 | ||
75 | The value in each entry of the hash is what you are referring to when you | |
76 | use the C<*name> typeglob notation. In fact, the following have the same | |
77 | effect, though the first is more efficient because it does the symbol | |
78 | 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 | ||
5f05dabc | 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 |
5f05dabc | 124 | you want to alias only a particular variable or subroutine, you can |
a0d0e21e LW |
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 | |
5f05dabc | 143 | return \%nhash; |
cb1a09d0 AD |
144 | } |
145 | ||
5f05dabc | 146 | On return, the reference will overwrite the hash slot in the |
cb1a09d0 | 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 | ||
55497cff | 158 | You can say C<*foo{PACKAGE}> and C<*foo{NAME}> to find out what name and |
159 | package the *foo symbol table entry comes from. This may be useful | |
160 | in a subroutine which is passed typeglobs as arguments | |
161 | ||
162 | sub identify_typeglob { | |
163 | my $glob = shift; | |
164 | print 'You gave me ', *{$glob}{PACKAGE}, '::', *{$glob}{NAME}, "\n"; | |
165 | } | |
166 | identify_typeglob *foo; | |
167 | identify_typeglob *bar::baz; | |
168 | ||
169 | This prints | |
170 | ||
171 | You gave me main::foo | |
172 | You gave me bar::baz | |
173 | ||
174 | The *foo{THING} notation can also be used to obtain references to the | |
175 | individual elements of *foo, see L<perlref>. | |
176 | ||
a0d0e21e LW |
177 | =head2 Package Constructors and Destructors |
178 | ||
179 | There are two special subroutine definitions that function as package | |
180 | constructors and destructors. These are the C<BEGIN> and C<END> | |
181 | routines. The C<sub> is optional for these routines. | |
182 | ||
183 | A C<BEGIN> subroutine is executed as soon as possible, that is, the | |
184 | moment it is completely defined, even before the rest of the containing | |
185 | file is parsed. You may have multiple C<BEGIN> blocks within a | |
186 | file--they will execute in order of definition. Because a C<BEGIN> | |
187 | block executes immediately, it can pull in definitions of subroutines | |
188 | and such from other files in time to be visible to the rest of the | |
189 | file. | |
190 | ||
191 | An C<END> subroutine is executed as late as possible, that is, when the | |
192 | interpreter is being exited, even if it is exiting as a result of a | |
193 | die() function. (But not if it's is being blown out of the water by a | |
194 | signal--you have to trap that yourself (if you can).) You may have | |
748a9306 | 195 | multiple C<END> blocks within a file--they will execute in reverse |
a0d0e21e LW |
196 | order of definition; that is: last in, first out (LIFO). |
197 | ||
c36e9b62 | 198 | Inside an C<END> subroutine C<$?> contains the value that the script is |
199 | going to pass to C<exit()>. You can modify C<$?> to change the exit | |
5f05dabc | 200 | value of the script. Beware of changing C<$?> by accident (e.g.,, by |
c36e9b62 | 201 | running something via C<system>). |
202 | ||
a0d0e21e LW |
203 | Note that when you use the B<-n> and B<-p> switches to Perl, C<BEGIN> |
204 | and C<END> work just as they do in B<awk>, as a degenerate case. | |
205 | ||
206 | =head2 Perl Classes | |
207 | ||
4633a7c4 | 208 | There is no special class syntax in Perl, but a package may function |
a0d0e21e LW |
209 | as a class if it provides subroutines that function as methods. Such a |
210 | package may also derive some of its methods from another class package | |
5f05dabc | 211 | by listing the other package name in its @ISA array. |
4633a7c4 LW |
212 | |
213 | For more on this, see L<perlobj>. | |
a0d0e21e LW |
214 | |
215 | =head2 Perl Modules | |
216 | ||
c07a80fd | 217 | A module is just a package that is defined in a library file of |
a0d0e21e LW |
218 | the same name, and is designed to be reusable. It may do this by |
219 | providing a mechanism for exporting some of its symbols into the symbol | |
220 | table of any package using it. Or it may function as a class | |
221 | definition and make its semantics available implicitly through method | |
222 | calls on the class and its objects, without explicit exportation of any | |
223 | symbols. Or it can do a little of both. | |
224 | ||
9607fc9c | 225 | For example, to start a normal module called Some::Module, create |
226 | a file called Some/Module.pm and start with this template: | |
227 | ||
228 | package Some::Module; # assumes Some/Module.pm | |
229 | ||
230 | use strict; | |
231 | ||
232 | BEGIN { | |
233 | use Exporter (); | |
234 | use vars qw($VERSION @ISA @EXPORT @EXPORT_OK %EXPORT_TAGS); | |
235 | ||
236 | # set the version for version checking | |
237 | $VERSION = 1.00; | |
238 | # if using RCS/CVS, this may be preferred | |
239 | $VERSION = do { my @r = (q$Revision: 2.21 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r }; # must be all one line, for MakeMaker | |
240 | ||
241 | @ISA = qw(Exporter); | |
242 | @EXPORT = qw(&func1 &func2 &func4); | |
243 | %EXPORT_TAGS = ( ); # eg: TAG => [ qw!name1 name2! ], | |
244 | ||
245 | # your exported package globals go here, | |
246 | # as well as any optionally exported functions | |
247 | @EXPORT_OK = qw($Var1 %Hashit &func3); | |
248 | } | |
249 | use vars @EXPORT_OK; | |
250 | ||
251 | # non-exported package globals go here | |
252 | use vars qw(@more $stuff); | |
253 | ||
254 | # initalize package globals, first exported ones | |
255 | $Var1 = ''; | |
256 | %Hashit = (); | |
257 | ||
258 | # then the others (which are still accessible as $Some::Module::stuff) | |
259 | $stuff = ''; | |
260 | @more = (); | |
261 | ||
262 | # all file-scoped lexicals must be created before | |
263 | # the functions below that use them. | |
264 | ||
265 | # file-private lexicals go here | |
266 | my $priv_var = ''; | |
267 | my %secret_hash = (); | |
268 | ||
269 | # here's a file-private function as a closure, | |
270 | # callable as &$priv_func; it cannot be prototyped. | |
271 | my $priv_func = sub { | |
272 | # stuff goes here. | |
273 | }; | |
274 | ||
275 | # make all your functions, whether exported or not; | |
276 | # remember to put something interesting in the {} stubs | |
277 | sub func1 {} # no prototype | |
278 | sub func2() {} # proto'd void | |
279 | sub func3($$) {} # proto'd to 2 scalars | |
280 | ||
281 | # this one isn't exported, but could be called! | |
282 | sub func4(\%) {} # proto'd to 1 hash ref | |
283 | ||
284 | END { } # module clean-up code here (global destructor) | |
4633a7c4 LW |
285 | |
286 | Then go on to declare and use your variables in functions | |
287 | without any qualifications. | |
5f05dabc | 288 | See L<Exporter> and the I<Perl Modules File> for details on |
4633a7c4 LW |
289 | mechanics and style issues in module creation. |
290 | ||
291 | Perl modules are included into your program by saying | |
a0d0e21e LW |
292 | |
293 | use Module; | |
294 | ||
295 | or | |
296 | ||
297 | use Module LIST; | |
298 | ||
299 | This is exactly equivalent to | |
300 | ||
301 | BEGIN { require "Module.pm"; import Module; } | |
302 | ||
303 | or | |
304 | ||
305 | BEGIN { require "Module.pm"; import Module LIST; } | |
306 | ||
cb1a09d0 AD |
307 | As a special case |
308 | ||
309 | use Module (); | |
310 | ||
311 | is exactly equivalent to | |
312 | ||
313 | BEGIN { require "Module.pm"; } | |
314 | ||
a0d0e21e LW |
315 | All Perl module files have the extension F<.pm>. C<use> assumes this so |
316 | that you don't have to spell out "F<Module.pm>" in quotes. This also | |
317 | helps to differentiate new modules from old F<.pl> and F<.ph> files. | |
318 | Module names are also capitalized unless they're functioning as pragmas, | |
319 | "Pragmas" are in effect compiler directives, and are sometimes called | |
320 | "pragmatic modules" (or even "pragmata" if you're a classicist). | |
321 | ||
322 | Because the C<use> statement implies a C<BEGIN> block, the importation | |
323 | of semantics happens at the moment the C<use> statement is compiled, | |
324 | before the rest of the file is compiled. This is how it is able | |
325 | to function as a pragma mechanism, and also how modules are able to | |
326 | declare subroutines that are then visible as list operators for | |
327 | the rest of the current file. This will not work if you use C<require> | |
cb1a09d0 | 328 | instead of C<use>. With require you can get into this problem: |
a0d0e21e LW |
329 | |
330 | require Cwd; # make Cwd:: accessible | |
331 | $here = Cwd::getcwd(); | |
332 | ||
5f05dabc | 333 | use Cwd; # import names from Cwd:: |
a0d0e21e LW |
334 | $here = getcwd(); |
335 | ||
336 | require Cwd; # make Cwd:: accessible | |
337 | $here = getcwd(); # oops! no main::getcwd() | |
338 | ||
cb1a09d0 AD |
339 | In general C<use Module ();> is recommended over C<require Module;>. |
340 | ||
a0d0e21e LW |
341 | Perl packages may be nested inside other package names, so we can have |
342 | package names containing C<::>. But if we used that package name | |
343 | directly as a filename it would makes for unwieldy or impossible | |
344 | filenames on some systems. Therefore, if a module's name is, say, | |
345 | C<Text::Soundex>, then its definition is actually found in the library | |
346 | file F<Text/Soundex.pm>. | |
347 | ||
348 | Perl modules always have a F<.pm> file, but there may also be dynamically | |
349 | linked executables or autoloaded subroutine definitions associated with | |
350 | the module. If so, these will be entirely transparent to the user of | |
351 | the module. It is the responsibility of the F<.pm> file to load (or | |
352 | arrange to autoload) any additional functionality. The POSIX module | |
353 | happens to do both dynamic loading and autoloading, but the user can | |
5f05dabc | 354 | say just C<use POSIX> to get it all. |
a0d0e21e | 355 | |
8e07c86e | 356 | For more information on writing extension modules, see L<perlxs> |
a0d0e21e LW |
357 | and L<perlguts>. |
358 | ||
359 | =head1 NOTE | |
360 | ||
361 | Perl does not enforce private and public parts of its modules as you may | |
362 | have been used to in other languages like C++, Ada, or Modula-17. Perl | |
363 | doesn't have an infatuation with enforced privacy. It would prefer | |
364 | that you stayed out of its living room because you weren't invited, not | |
365 | because it has a shotgun. | |
366 | ||
367 | The module and its user have a contract, part of which is common law, | |
368 | and part of which is "written". Part of the common law contract is | |
369 | that a module doesn't pollute any namespace it wasn't asked to. The | |
5f05dabc | 370 | written contract for the module (A.K.A. documentation) may make other |
a0d0e21e LW |
371 | provisions. But then you know when you C<use RedefineTheWorld> that |
372 | you're redefining the world and willing to take the consequences. | |
373 | ||
374 | =head1 THE PERL MODULE LIBRARY | |
375 | ||
5f05dabc | 376 | A number of modules are included the Perl distribution. These are |
377 | described below, and all end in F<.pm>. You may also discover files in | |
a0d0e21e | 378 | the library directory that end in either F<.pl> or F<.ph>. These are old |
748a9306 | 379 | libraries supplied so that old programs that use them still run. The |
a0d0e21e LW |
380 | F<.pl> files will all eventually be converted into standard modules, and |
381 | the F<.ph> files made by B<h2ph> will probably end up as extension modules | |
382 | made by B<h2xs>. (Some F<.ph> values may already be available through the | |
383 | POSIX module.) The B<pl2pm> file in the distribution may help in your | |
4fdae800 | 384 | conversion, but it's just a mechanical process and therefore far from |
385 | bulletproof. | |
a0d0e21e LW |
386 | |
387 | =head2 Pragmatic Modules | |
388 | ||
389 | They work somewhat like pragmas in that they tend to affect the compilation of | |
5f05dabc | 390 | your program, and thus will usually work well only when used within a |
55497cff | 391 | C<use>, or C<no>. Most of these are locally scoped, so an inner BLOCK |
392 | may countermand any of these by saying: | |
a0d0e21e LW |
393 | |
394 | no integer; | |
395 | no strict 'refs'; | |
396 | ||
397 | which lasts until the end of that BLOCK. | |
398 | ||
5f05dabc | 399 | Unlike the pragmas that effect the C<$^H> hints variable, the C<use |
55497cff | 400 | vars> and C<use subs> declarations are not BLOCK-scoped. They allow |
401 | you to pre-declare a variables or subroutines within a particular | |
4fdae800 | 402 | I<file> rather than just a block. Such declarations are effective |
55497cff | 403 | for the entire file for which they were declared. You cannot rescind |
404 | them with C<no vars> or C<no subs>. | |
405 | ||
406 | The following pragmas are defined (and have their own documentation). | |
a0d0e21e LW |
407 | |
408 | =over 12 | |
409 | ||
5f05dabc | 410 | =item blib |
411 | ||
412 | manipulate @INC at compile time to use MakeMaker's uninstalled version | |
413 | of a package | |
414 | ||
cb1a09d0 | 415 | =item diagnostics |
4633a7c4 | 416 | |
55497cff | 417 | force verbose warning diagnostics |
4633a7c4 | 418 | |
cb1a09d0 | 419 | =item integer |
a0d0e21e | 420 | |
55497cff | 421 | compute arithmetic in integer instead of double |
a0d0e21e | 422 | |
cb1a09d0 | 423 | =item less |
a0d0e21e | 424 | |
55497cff | 425 | request less of something from the compiler |
426 | ||
427 | =item lib | |
428 | ||
429 | manipulate @INC at compile time | |
a0d0e21e | 430 | |
5f05dabc | 431 | =item locale |
432 | ||
71be2cbc | 433 | use or ignore current locale for built-in operations (see L<perllocale>) |
5f05dabc | 434 | |
d0c42abe | 435 | =item ops |
436 | ||
5f05dabc | 437 | restrict named opcodes when compiling or running Perl code |
d0c42abe | 438 | |
cb1a09d0 AD |
439 | =item overload |
440 | ||
5f05dabc | 441 | overload basic Perl operations |
cb1a09d0 AD |
442 | |
443 | =item sigtrap | |
a0d0e21e | 444 | |
55497cff | 445 | enable simple signal handling |
a0d0e21e | 446 | |
cb1a09d0 | 447 | =item strict |
a0d0e21e | 448 | |
55497cff | 449 | restrict unsafe constructs |
a0d0e21e | 450 | |
cb1a09d0 | 451 | =item subs |
a0d0e21e | 452 | |
5f05dabc | 453 | pre-declare sub names |
a0d0e21e | 454 | |
ff0cee69 | 455 | =item vmsish |
456 | ||
457 | adopt certain VMS-specific behaviors | |
458 | ||
d0c42abe | 459 | =item vars |
460 | ||
5f05dabc | 461 | pre-declare global variable names |
d0c42abe | 462 | |
a0d0e21e LW |
463 | =back |
464 | ||
465 | =head2 Standard Modules | |
466 | ||
4633a7c4 | 467 | Standard, bundled modules are all expected to behave in a well-defined |
a0d0e21e | 468 | manner with respect to namespace pollution because they use the |
4633a7c4 | 469 | Exporter module. See their own documentation for details. |
a0d0e21e | 470 | |
cb1a09d0 AD |
471 | =over 12 |
472 | ||
473 | =item AnyDBM_File | |
474 | ||
475 | provide framework for multiple DBMs | |
476 | ||
477 | =item AutoLoader | |
478 | ||
479 | load functions only on demand | |
480 | ||
481 | =item AutoSplit | |
482 | ||
483 | split a package for autoloading | |
484 | ||
485 | =item Benchmark | |
486 | ||
487 | benchmark running times of code | |
488 | ||
71be2cbc | 489 | =item CPAN |
490 | ||
491 | interface to Comprehensive Perl Archive Network | |
492 | ||
493 | =item CPAN::FirstTime | |
494 | ||
495 | create a CPAN configuration file | |
496 | ||
497 | =item CPAN::Nox | |
498 | ||
499 | run CPAN while avoiding compiled extensions | |
500 | ||
cb1a09d0 AD |
501 | =item Carp |
502 | ||
503 | warn of errors (from perspective of caller) | |
504 | ||
5f05dabc | 505 | =item Class::Template |
506 | ||
507 | struct/member template builder | |
508 | ||
cb1a09d0 AD |
509 | =item Config |
510 | ||
55497cff | 511 | access Perl configuration information |
cb1a09d0 AD |
512 | |
513 | =item Cwd | |
514 | ||
515 | get pathname of current working directory | |
516 | ||
517 | =item DB_File | |
518 | ||
55497cff | 519 | access to Berkeley DB |
cb1a09d0 AD |
520 | |
521 | =item Devel::SelfStubber | |
522 | ||
523 | generate stubs for a SelfLoading module | |
524 | ||
55497cff | 525 | =item DirHandle |
526 | ||
527 | supply object methods for directory handles | |
528 | ||
cb1a09d0 AD |
529 | =item DynaLoader |
530 | ||
5f05dabc | 531 | dynamically load C libraries into Perl code |
cb1a09d0 AD |
532 | |
533 | =item English | |
534 | ||
55497cff | 535 | use nice English (or awk) names for ugly punctuation variables |
cb1a09d0 AD |
536 | |
537 | =item Env | |
538 | ||
55497cff | 539 | import environment variables |
cb1a09d0 AD |
540 | |
541 | =item Exporter | |
542 | ||
55497cff | 543 | implements default import method for modules |
544 | ||
545 | =item ExtUtils::Embed | |
546 | ||
5f05dabc | 547 | utilities for embedding Perl in C/C++ applications |
55497cff | 548 | |
549 | =item ExtUtils::Install | |
550 | ||
551 | install files from here to there | |
cb1a09d0 AD |
552 | |
553 | =item ExtUtils::Liblist | |
554 | ||
555 | determine libraries to use and how to use them | |
556 | ||
5f05dabc | 557 | =item ExtUtils::MM_OS2 |
558 | ||
559 | methods to override UN*X behaviour in ExtUtils::MakeMaker | |
560 | ||
561 | =item ExtUtils::MM_Unix | |
562 | ||
563 | methods used by ExtUtils::MakeMaker | |
564 | ||
565 | =item ExtUtils::MM_VMS | |
566 | ||
567 | methods to override UN*X behaviour in ExtUtils::MakeMaker | |
568 | ||
cb1a09d0 AD |
569 | =item ExtUtils::MakeMaker |
570 | ||
571 | create an extension Makefile | |
572 | ||
573 | =item ExtUtils::Manifest | |
574 | ||
575 | utilities to write and check a MANIFEST file | |
576 | ||
577 | =item ExtUtils::Mkbootstrap | |
578 | ||
579 | make a bootstrap file for use by DynaLoader | |
580 | ||
55497cff | 581 | =item ExtUtils::Mksymlists |
582 | ||
583 | write linker options files for dynamic extension | |
584 | ||
5f05dabc | 585 | =item ExtUtils::testlib |
55497cff | 586 | |
5f05dabc | 587 | add blib/* directories to @INC |
55497cff | 588 | |
cb1a09d0 AD |
589 | =item Fcntl |
590 | ||
591 | load the C Fcntl.h defines | |
592 | ||
593 | =item File::Basename | |
594 | ||
5f05dabc | 595 | split a pathname into pieces |
55497cff | 596 | |
cb1a09d0 AD |
597 | =item File::CheckTree |
598 | ||
599 | run many filetest checks on a tree | |
600 | ||
5f05dabc | 601 | =item File::Compare |
602 | ||
603 | compare files or filehandles | |
604 | ||
55497cff | 605 | =item File::Copy |
606 | ||
5f05dabc | 607 | copy files or filehandles |
55497cff | 608 | |
cb1a09d0 AD |
609 | =item File::Find |
610 | ||
611 | traverse a file tree | |
612 | ||
cb1a09d0 AD |
613 | =item File::Path |
614 | ||
615 | create or remove a series of directories | |
616 | ||
5f05dabc | 617 | =item File::stat |
618 | ||
619 | by-name interface to Perl's built-in stat() functions | |
620 | ||
621 | =item FileCache | |
622 | ||
623 | keep more files open than the system permits | |
624 | ||
625 | =item FileHandle | |
626 | ||
627 | supply object methods for filehandles | |
628 | ||
55497cff | 629 | =item FindBin |
630 | ||
631 | locate directory of original perl script | |
632 | ||
633 | =item GDBM_File | |
634 | ||
5f05dabc | 635 | access to the gdbm library |
55497cff | 636 | |
cb1a09d0 AD |
637 | =item Getopt::Long |
638 | ||
55497cff | 639 | extended processing of command line options |
cb1a09d0 AD |
640 | |
641 | =item Getopt::Std | |
642 | ||
55497cff | 643 | process single-character switches with switch clustering |
cb1a09d0 AD |
644 | |
645 | =item I18N::Collate | |
646 | ||
647 | compare 8-bit scalar data according to the current locale | |
648 | ||
55497cff | 649 | =item IO |
650 | ||
651 | load various IO modules | |
652 | ||
653 | =item IO::File | |
654 | ||
655 | supply object methods for filehandles | |
656 | ||
657 | =item IO::Handle | |
658 | ||
659 | supply object methods for I/O handles | |
660 | ||
661 | =item IO::Pipe | |
662 | ||
663 | supply object methods for pipes | |
664 | ||
665 | =item IO::Seekable | |
666 | ||
667 | supply seek based methods for I/O objects | |
668 | ||
669 | =item IO::Select | |
670 | ||
671 | OO interface to the select system call | |
672 | ||
673 | =item IO::Socket | |
674 | ||
675 | object interface to socket communications | |
676 | ||
cb1a09d0 AD |
677 | =item IPC::Open2 |
678 | ||
55497cff | 679 | open a process for both reading and writing |
cb1a09d0 AD |
680 | |
681 | =item IPC::Open3 | |
682 | ||
683 | open a process for reading, writing, and error handling | |
684 | ||
55497cff | 685 | =item Math::BigFloat |
686 | ||
687 | arbitrary length float math package | |
688 | ||
689 | =item Math::BigInt | |
690 | ||
691 | arbitrary size integer math package | |
692 | ||
693 | =item Math::Complex | |
694 | ||
695 | complex numbers and associated mathematical functions | |
696 | ||
697 | =item NDBM_File | |
698 | ||
699 | tied access to ndbm files | |
700 | ||
7e1af8bc | 701 | =item Net::Ping |
702 | ||
703 | Hello, anybody home? | |
704 | ||
5f05dabc | 705 | =item Net::hostent |
706 | ||
707 | by-name interface to Perl's built-in gethost*() functions | |
708 | ||
709 | =item Net::netent | |
710 | ||
711 | by-name interface to Perl's built-in getnet*() functions | |
712 | ||
713 | =item Net::protoent | |
714 | ||
715 | by-name interface to Perl's built-in getproto*() functions | |
716 | ||
717 | =item Net::servent | |
718 | ||
719 | by-name interface to Perl's built-in getserv*() functions | |
720 | ||
55497cff | 721 | =item Opcode |
722 | ||
5f05dabc | 723 | disable named opcodes when compiling or running perl code |
55497cff | 724 | |
725 | =item Pod::Text | |
726 | ||
727 | convert POD data to formatted ASCII text | |
728 | ||
cb1a09d0 AD |
729 | =item POSIX |
730 | ||
5f05dabc | 731 | interface to IEEE Standard 1003.1 |
55497cff | 732 | |
733 | =item SDBM_File | |
734 | ||
735 | tied access to sdbm files | |
736 | ||
5f05dabc | 737 | =item Safe |
738 | ||
739 | compile and execute code in restricted compartments | |
740 | ||
55497cff | 741 | =item Search::Dict |
742 | ||
743 | search for key in dictionary file | |
744 | ||
745 | =item SelectSaver | |
746 | ||
747 | save and restore selected file handle | |
cb1a09d0 AD |
748 | |
749 | =item SelfLoader | |
750 | ||
751 | load functions only on demand | |
752 | ||
55497cff | 753 | =item Shell |
a2927560 | 754 | |
55497cff | 755 | run shell commands transparently within perl |
a2927560 | 756 | |
cb1a09d0 AD |
757 | =item Socket |
758 | ||
759 | load the C socket.h defines and structure manipulators | |
760 | ||
55497cff | 761 | =item Symbol |
762 | ||
763 | manipulate Perl symbols and their names | |
764 | ||
765 | =item Sys::Hostname | |
766 | ||
767 | try every conceivable way to get hostname | |
768 | ||
769 | =item Sys::Syslog | |
770 | ||
771 | interface to the UNIX syslog(3) calls | |
772 | ||
773 | =item Term::Cap | |
774 | ||
5f05dabc | 775 | termcap interface |
55497cff | 776 | |
777 | =item Term::Complete | |
778 | ||
779 | word completion module | |
780 | ||
781 | =item Term::ReadLine | |
782 | ||
5f05dabc | 783 | interface to various C<readline> packages |
55497cff | 784 | |
cb1a09d0 AD |
785 | =item Test::Harness |
786 | ||
787 | run perl standard test scripts with statistics | |
788 | ||
789 | =item Text::Abbrev | |
790 | ||
c36e9b62 | 791 | create an abbreviation table from a list |
cb1a09d0 | 792 | |
55497cff | 793 | =item Text::ParseWords |
794 | ||
795 | parse text into an array of tokens | |
796 | ||
797 | =item Text::Soundex | |
798 | ||
5f05dabc | 799 | implementation of the Soundex Algorithm as described by Knuth |
55497cff | 800 | |
801 | =item Text::Tabs | |
802 | ||
803 | expand and unexpand tabs per the unix expand(1) and unexpand(1) | |
804 | ||
805 | =item Text::Wrap | |
806 | ||
807 | line wrapping to form simple paragraphs | |
808 | ||
809 | =item Tie::Hash | |
810 | ||
811 | base class definitions for tied hashes | |
812 | ||
5f05dabc | 813 | =item Tie::RefHash |
814 | ||
815 | base class definitions for tied hashes with references as keys | |
816 | ||
55497cff | 817 | =item Tie::Scalar |
818 | ||
819 | base class definitions for tied scalars | |
820 | ||
821 | =item Tie::SubstrHash | |
822 | ||
823 | fixed-table-size, fixed-key-length hashing | |
824 | ||
825 | =item Time::Local | |
826 | ||
827 | efficiently compute time from local and GMT time | |
828 | ||
5f05dabc | 829 | =item Time::gmtime |
830 | ||
831 | by-name interface to Perl's built-in gmtime() function | |
832 | ||
833 | =item Time::localtime | |
834 | ||
835 | by-name interface to Perl's built-in localtime() function | |
836 | ||
837 | =item Time::tm | |
838 | ||
839 | internal object used by Time::gmtime and Time::localtime | |
840 | ||
55497cff | 841 | =item UNIVERSAL |
842 | ||
843 | base class for ALL classes (blessed references) | |
844 | ||
5f05dabc | 845 | =item User::grent |
846 | ||
847 | by-name interface to Perl's built-in getgr*() functions | |
848 | ||
849 | =item User::pwent | |
850 | ||
851 | by-name interface to Perl's built-in getpw*() functions | |
852 | ||
cb1a09d0 AD |
853 | =back |
854 | ||
855 | To find out I<all> the modules installed on your system, including | |
856 | those without documentation or outside the standard release, do this: | |
a0d0e21e | 857 | |
4633a7c4 | 858 | find `perl -e 'print "@INC"'` -name '*.pm' -print |
a0d0e21e | 859 | |
4633a7c4 LW |
860 | They should all have their own documentation installed and accessible via |
861 | your system man(1) command. If that fails, try the I<perldoc> program. | |
a0d0e21e | 862 | |
4633a7c4 | 863 | =head2 Extension Modules |
a0d0e21e | 864 | |
4633a7c4 LW |
865 | Extension modules are written in C (or a mix of Perl and C) and get |
866 | dynamically loaded into Perl if and when you need them. Supported | |
867 | extension modules include the Socket, Fcntl, and POSIX modules. | |
a0d0e21e | 868 | |
cb1a09d0 | 869 | Many popular C extension modules do not come bundled (at least, not |
5f05dabc | 870 | completely) due to their sizes, volatility, or simply lack of time for |
cb1a09d0 AD |
871 | adequate testing and configuration across the multitude of platforms on |
872 | which Perl was beta-tested. You are encouraged to look for them in | |
873 | archie(1L), the Perl FAQ or Meta-FAQ, the WWW page, and even with their | |
874 | authors before randomly posting asking for their present condition and | |
875 | disposition. | |
a0d0e21e | 876 | |
cb1a09d0 | 877 | =head1 CPAN |
a0d0e21e | 878 | |
4633a7c4 | 879 | CPAN stands for the Comprehensive Perl Archive Network. This is a globally |
5f05dabc | 880 | replicated collection of all known Perl materials, including hundreds |
c36e9b62 | 881 | of unbundled modules. Here are the major categories of modules: |
a0d0e21e | 882 | |
4633a7c4 | 883 | =over |
a0d0e21e | 884 | |
4633a7c4 | 885 | =item * |
5f05dabc | 886 | Language Extensions and Documentation Tools |
a0d0e21e | 887 | |
4633a7c4 LW |
888 | =item * |
889 | Development Support | |
a0d0e21e | 890 | |
4633a7c4 LW |
891 | =item * |
892 | Operating System Interfaces | |
a0d0e21e | 893 | |
4633a7c4 LW |
894 | =item * |
895 | Networking, Device Control (modems) and InterProcess Communication | |
a0d0e21e | 896 | |
4633a7c4 LW |
897 | =item * |
898 | Data Types and Data Type Utilities | |
a0d0e21e | 899 | |
4633a7c4 LW |
900 | =item * |
901 | Database Interfaces | |
a0d0e21e | 902 | |
4633a7c4 LW |
903 | =item * |
904 | User Interfaces | |
a0d0e21e | 905 | |
4633a7c4 LW |
906 | =item * |
907 | Interfaces to / Emulations of Other Programming Languages | |
a0d0e21e | 908 | |
4633a7c4 LW |
909 | =item * |
910 | File Names, File Systems and File Locking (see also File Handles) | |
a0d0e21e | 911 | |
4633a7c4 | 912 | =item * |
5f05dabc | 913 | String Processing, Language Text Processing, Parsing, and Searching |
a0d0e21e | 914 | |
4633a7c4 | 915 | =item * |
5f05dabc | 916 | Option, Argument, Parameter, and Configuration File Processing |
a0d0e21e | 917 | |
4633a7c4 LW |
918 | =item * |
919 | Internationalization and Locale | |
a0d0e21e | 920 | |
4633a7c4 | 921 | =item * |
5f05dabc | 922 | Authentication, Security, and Encryption |
a0d0e21e | 923 | |
4633a7c4 LW |
924 | =item * |
925 | World Wide Web, HTML, HTTP, CGI, MIME | |
a0d0e21e | 926 | |
4633a7c4 LW |
927 | =item * |
928 | Server and Daemon Utilities | |
a0d0e21e | 929 | |
4633a7c4 LW |
930 | =item * |
931 | Archiving and Compression | |
a0d0e21e | 932 | |
4633a7c4 | 933 | =item * |
5f05dabc | 934 | Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing |
a0d0e21e | 935 | |
4633a7c4 LW |
936 | =item * |
937 | Mail and Usenet News | |
a0d0e21e | 938 | |
4633a7c4 LW |
939 | =item * |
940 | Control Flow Utilities (callbacks and exceptions etc) | |
a0d0e21e | 941 | |
4633a7c4 LW |
942 | =item * |
943 | File Handle and Input/Output Stream Utilities | |
a0d0e21e | 944 | |
4633a7c4 LW |
945 | =item * |
946 | Miscellaneous Modules | |
a0d0e21e | 947 | |
4633a7c4 | 948 | =back |
a0d0e21e | 949 | |
d0c42abe | 950 | The registered CPAN sites as of this writing include the following. |
4633a7c4 | 951 | You should try to choose one close to you: |
a0d0e21e | 952 | |
4633a7c4 | 953 | =over |
a0d0e21e | 954 | |
4633a7c4 | 955 | =item * |
9607fc9c | 956 | Africa |
a0d0e21e | 957 | |
9607fc9c | 958 | South Africa ftp://ftp.is.co.za/programming/perl/CPAN/ |
a0d0e21e | 959 | |
4633a7c4 | 960 | =item * |
9607fc9c | 961 | Asia |
a0d0e21e | 962 | |
9607fc9c | 963 | Hong Kong ftp://ftp.hkstar.com/pub/CPAN/ |
964 | Japan ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/ | |
965 | ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/ | |
966 | South Korea ftp://ftp.nuri.net/pub/CPAN/ | |
967 | Taiwan ftp://dongpo.math.ncu.edu.tw/perl/CPAN/ | |
968 | ftp://ftp.wownet.net/pub2/PERL/ | |
a0d0e21e | 969 | |
4633a7c4 | 970 | =item * |
9607fc9c | 971 | Australasia |
a0d0e21e | 972 | |
9607fc9c | 973 | Australia ftp://ftp.netinfo.com.au/pub/perl/CPAN/ |
974 | New Zealand ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/ | |
a0d0e21e | 975 | |
4633a7c4 | 976 | =item * |
9607fc9c | 977 | Europe |
978 | ||
979 | Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/ | |
980 | Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/ | |
981 | Czech Republic ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/ | |
982 | Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/ | |
983 | Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/ | |
984 | France ftp://ftp.ibp.fr/pub/perl/CPAN/ | |
985 | ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/ | |
986 | Germany ftp://ftp.gmd.de/packages/CPAN/ | |
987 | ftp://ftp.leo.org/pub/comp/programming/languages/perl/CPAN/ | |
988 | ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/ | |
989 | ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/ | |
990 | ftp://ftp.uni-erlangen.de/pub/source/Perl/CPAN/ | |
991 | ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/ | |
992 | Greece ftp://ftp.ntua.gr/pub/lang/perl/ | |
993 | Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/ | |
994 | Italy ftp://cis.utovrm.it/CPAN/ | |
995 | the Netherlands ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/ | |
996 | ftp://ftp.EU.net/packages/cpan/ | |
997 | Norway ftp://ftp.uit.no/pub/languages/perl/cpan/ | |
998 | Poland ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/ | |
999 | ftp://sunsite.icm.edu.pl/pub/CPAN/ | |
1000 | Portugal ftp://ftp.ci.uminho.pt/pub/lang/perl/ | |
1001 | ftp://ftp.telepac.pt/pub/CPAN/ | |
1002 | Russia ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/ | |
1003 | Slovenia ftp://ftp.arnes.si/software/perl/CPAN/ | |
1004 | Spain ftp://ftp.etse.urv.es/pub/mirror/perl/ | |
1005 | ftp://ftp.rediris.es/mirror/CPAN/ | |
1006 | Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/ | |
9607fc9c | 1007 | UK ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/ |
1008 | ftp://sunsite.doc.ic.ac.uk/packages/CPAN/ | |
1009 | ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/ | |
a0d0e21e | 1010 | |
4633a7c4 | 1011 | =item * |
9607fc9c | 1012 | North America |
1013 | ||
1014 | Ontario ftp://ftp.utilis.com/public/CPAN/ | |
1015 | ftp://enterprise.ic.gc.ca/pub/perl/CPAN/ | |
1016 | Manitoba ftp://theory.uwinnipeg.ca/pub/CPAN/ | |
1017 | California ftp://ftp.digital.com/pub/plan/perl/CPAN/ | |
30f5542a | 1018 | ftp://ftp.cdrom.com/pub/perl/CPAN/ |
9607fc9c | 1019 | Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/ |
1020 | Florida ftp://ftp.cis.ufl.edu/pub/perl/CPAN/ | |
1021 | Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/ | |
1022 | Massachusetts ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/ | |
1023 | New York ftp://ftp.rge.com/pub/languages/perl/ | |
1024 | North Carolina ftp://ftp.duke.edu/pub/perl/ | |
1025 | Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/ | |
30f5542a LV |
1026 | Oregon http://www.perl.org/CPAN/ |
1027 | ftp://ftp.orst.edu/pub/packages/CPAN/ | |
9607fc9c | 1028 | Pennsylvania ftp://ftp.epix.net/pub/languages/perl/ |
1029 | Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/ | |
1030 | ftp://ftp.metronet.com/pub/perl/ | |
a0d0e21e | 1031 | |
4633a7c4 | 1032 | =item * |
9607fc9c | 1033 | South America |
a0d0e21e | 1034 | |
9607fc9c | 1035 | Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/perl/CPAN/ |
a0d0e21e LW |
1036 | |
1037 | =back | |
4633a7c4 | 1038 | |
5f05dabc | 1039 | For an up-to-date listing of CPAN sites, |
d0c42abe | 1040 | see F<http://www.perl.com/perl/CPAN> or F<ftp://ftp.perl.com/perl/>. |
cb1a09d0 | 1041 | |
5f05dabc | 1042 | =head1 Modules: Creation, Use, and Abuse |
cb1a09d0 AD |
1043 | |
1044 | (The following section is borrowed directly from Tim Bunce's modules | |
1045 | file, available at your nearest CPAN site.) | |
1046 | ||
5f05dabc | 1047 | Perl implements a class using a package, but the presence of a |
cb1a09d0 AD |
1048 | package doesn't imply the presence of a class. A package is just a |
1049 | namespace. A class is a package that provides subroutines that can be | |
1050 | used as methods. A method is just a subroutine that expects, as its | |
1051 | first argument, either the name of a package (for "static" methods), | |
1052 | or a reference to something (for "virtual" methods). | |
1053 | ||
1054 | A module is a file that (by convention) provides a class of the same | |
1055 | name (sans the .pm), plus an import method in that class that can be | |
1056 | called to fetch exported symbols. This module may implement some of | |
1057 | its methods by loading dynamic C or C++ objects, but that should be | |
1058 | totally transparent to the user of the module. Likewise, the module | |
1059 | might set up an AUTOLOAD function to slurp in subroutine definitions on | |
1060 | demand, but this is also transparent. Only the .pm file is required to | |
1061 | exist. | |
1062 | ||
1063 | =head2 Guidelines for Module Creation | |
1064 | ||
1065 | =over 4 | |
1066 | ||
1067 | =item Do similar modules already exist in some form? | |
1068 | ||
1069 | If so, please try to reuse the existing modules either in whole or | |
1070 | by inheriting useful features into a new class. If this is not | |
1071 | practical try to get together with the module authors to work on | |
1072 | extending or enhancing the functionality of the existing modules. | |
1073 | A perfect example is the plethora of packages in perl4 for dealing | |
1074 | with command line options. | |
1075 | ||
1076 | If you are writing a module to expand an already existing set of | |
1077 | modules, please coordinate with the author of the package. It | |
1078 | helps if you follow the same naming scheme and module interaction | |
1079 | scheme as the original author. | |
1080 | ||
1081 | =item Try to design the new module to be easy to extend and reuse. | |
1082 | ||
1083 | Use blessed references. Use the two argument form of bless to bless | |
1084 | into the class name given as the first parameter of the constructor, | |
5f05dabc | 1085 | e.g.,: |
cb1a09d0 | 1086 | |
5f05dabc | 1087 | sub new { |
cb1a09d0 AD |
1088 | my $class = shift; |
1089 | return bless {}, $class; | |
1090 | } | |
1091 | ||
1092 | or even this if you'd like it to be used as either a static | |
1093 | or a virtual method. | |
1094 | ||
5f05dabc | 1095 | sub new { |
cb1a09d0 AD |
1096 | my $self = shift; |
1097 | my $class = ref($self) || $self; | |
1098 | return bless {}, $class; | |
1099 | } | |
1100 | ||
1101 | Pass arrays as references so more parameters can be added later | |
1102 | (it's also faster). Convert functions into methods where | |
1103 | appropriate. Split large methods into smaller more flexible ones. | |
1104 | Inherit methods from other modules if appropriate. | |
1105 | ||
c36e9b62 | 1106 | Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>. |
1107 | Generally you can delete the "C<eq 'FOO'>" part with no harm at all. | |
cb1a09d0 AD |
1108 | Let the objects look after themselves! Generally, avoid hardwired |
1109 | class names as far as possible. | |
1110 | ||
c36e9b62 | 1111 | Avoid C<$r-E<gt>Class::func()> where using C<@ISA=qw(... Class ...)> and |
1112 | C<$r-E<gt>func()> would work (see L<perlbot> for more details). | |
cb1a09d0 AD |
1113 | |
1114 | Use autosplit so little used or newly added functions won't be a | |
1115 | burden to programs which don't use them. Add test functions to | |
1116 | the module after __END__ either using AutoSplit or by saying: | |
1117 | ||
1118 | eval join('',<main::DATA>) || die $@ unless caller(); | |
1119 | ||
30f5542a | 1120 | Does your module pass the 'empty subclass' test? If you say |
c36e9b62 | 1121 | "C<@SUBCLASS::ISA = qw(YOURCLASS);>" your applications should be able |
cb1a09d0 | 1122 | to use SUBCLASS in exactly the same way as YOURCLASS. For example, |
c36e9b62 | 1123 | does your application still work if you change: C<$obj = new YOURCLASS;> |
1124 | into: C<$obj = new SUBCLASS;> ? | |
cb1a09d0 AD |
1125 | |
1126 | Avoid keeping any state information in your packages. It makes it | |
1127 | difficult for multiple other packages to use yours. Keep state | |
1128 | information in objects. | |
1129 | ||
c36e9b62 | 1130 | Always use B<-w>. Try to C<use strict;> (or C<use strict qw(...);>). |
cb1a09d0 | 1131 | Remember that you can add C<no strict qw(...);> to individual blocks |
c36e9b62 | 1132 | of code which need less strictness. Always use B<-w>. Always use B<-w>! |
cb1a09d0 AD |
1133 | Follow the guidelines in the perlstyle(1) manual. |
1134 | ||
1135 | =item Some simple style guidelines | |
1136 | ||
1137 | The perlstyle manual supplied with perl has many helpful points. | |
1138 | ||
1139 | Coding style is a matter of personal taste. Many people evolve their | |
1140 | style over several years as they learn what helps them write and | |
1141 | maintain good code. Here's one set of assorted suggestions that | |
1142 | seem to be widely used by experienced developers: | |
1143 | ||
1144 | Use underscores to separate words. It is generally easier to read | |
1145 | $var_names_like_this than $VarNamesLikeThis, especially for | |
1146 | non-native speakers of English. It's also a simple rule that works | |
1147 | consistently with VAR_NAMES_LIKE_THIS. | |
1148 | ||
1149 | Package/Module names are an exception to this rule. Perl informally | |
1150 | reserves lowercase module names for 'pragma' modules like integer | |
1151 | and strict. Other modules normally begin with a capital letter and | |
1152 | use mixed case with no underscores (need to be short and portable). | |
1153 | ||
1154 | You may find it helpful to use letter case to indicate the scope | |
1155 | or nature of a variable. For example: | |
1156 | ||
1157 | $ALL_CAPS_HERE constants only (beware clashes with perl vars) | |
1158 | $Some_Caps_Here package-wide global/static | |
1159 | $no_caps_here function scope my() or local() variables | |
1160 | ||
1161 | Function and method names seem to work best as all lowercase. | |
5f05dabc | 1162 | e.g.,, C<$obj-E<gt>as_string()>. |
cb1a09d0 AD |
1163 | |
1164 | You can use a leading underscore to indicate that a variable or | |
1165 | function should not be used outside the package that defined it. | |
1166 | ||
1167 | =item Select what to export. | |
1168 | ||
1169 | Do NOT export method names! | |
1170 | ||
1171 | Do NOT export anything else by default without a good reason! | |
1172 | ||
1173 | Exports pollute the namespace of the module user. If you must | |
1174 | export try to use @EXPORT_OK in preference to @EXPORT and avoid | |
1175 | short or common names to reduce the risk of name clashes. | |
1176 | ||
1177 | Generally anything not exported is still accessible from outside the | |
c36e9b62 | 1178 | module using the ModuleName::item_name (or C<$blessed_ref-E<gt>method>) |
cb1a09d0 | 1179 | syntax. By convention you can use a leading underscore on names to |
5f05dabc | 1180 | indicate informally that they are 'internal' and not for public use. |
cb1a09d0 AD |
1181 | |
1182 | (It is actually possible to get private functions by saying: | |
c36e9b62 | 1183 | C<my $subref = sub { ... }; &$subref;>. But there's no way to call that |
5f05dabc | 1184 | directly as a method, because a method must have a name in the symbol |
cb1a09d0 AD |
1185 | table.) |
1186 | ||
1187 | As a general rule, if the module is trying to be object oriented | |
1188 | then export nothing. If it's just a collection of functions then | |
1189 | @EXPORT_OK anything but use @EXPORT with caution. | |
1190 | ||
1191 | =item Select a name for the module. | |
1192 | ||
5f05dabc | 1193 | This name should be as descriptive, accurate, and complete as |
cb1a09d0 AD |
1194 | possible. Avoid any risk of ambiguity. Always try to use two or |
1195 | more whole words. Generally the name should reflect what is special | |
1196 | about what the module does rather than how it does it. Please use | |
5f05dabc | 1197 | nested module names to group informally or categorize a module. |
1198 | There should be a very good reason for a module not to have a nested name. | |
cb1a09d0 AD |
1199 | Module names should begin with a capital letter. |
1200 | ||
1201 | Having 57 modules all called Sort will not make life easy for anyone | |
1202 | (though having 23 called Sort::Quick is only marginally better :-). | |
1203 | Imagine someone trying to install your module alongside many others. | |
1204 | If in any doubt ask for suggestions in comp.lang.perl.misc. | |
1205 | ||
1206 | If you are developing a suite of related modules/classes it's good | |
1207 | practice to use nested classes with a common prefix as this will | |
1208 | avoid namespace clashes. For example: Xyz::Control, Xyz::View, | |
1209 | Xyz::Model etc. Use the modules in this list as a naming guide. | |
1210 | ||
1211 | If adding a new module to a set, follow the original author's | |
1212 | standards for naming modules and the interface to methods in | |
1213 | those modules. | |
1214 | ||
1215 | To be portable each component of a module name should be limited to | |
1216 | 11 characters. If it might be used on DOS then try to ensure each is | |
1217 | unique in the first 8 characters. Nested modules make this easier. | |
1218 | ||
1219 | =item Have you got it right? | |
1220 | ||
1221 | How do you know that you've made the right decisions? Have you | |
1222 | picked an interface design that will cause problems later? Have | |
1223 | you picked the most appropriate name? Do you have any questions? | |
1224 | ||
1225 | The best way to know for sure, and pick up many helpful suggestions, | |
1226 | is to ask someone who knows. Comp.lang.perl.misc is read by just about | |
1227 | all the people who develop modules and it's the best place to ask. | |
1228 | ||
1229 | All you need to do is post a short summary of the module, its | |
1230 | purpose and interfaces. A few lines on each of the main methods is | |
1231 | probably enough. (If you post the whole module it might be ignored | |
1232 | by busy people - generally the very people you want to read it!) | |
1233 | ||
1234 | Don't worry about posting if you can't say when the module will be | |
1235 | ready - just say so in the message. It might be worth inviting | |
1236 | others to help you, they may be able to complete it for you! | |
1237 | ||
1238 | =item README and other Additional Files. | |
1239 | ||
1240 | It's well known that software developers usually fully document the | |
1241 | software they write. If, however, the world is in urgent need of | |
1242 | your software and there is not enough time to write the full | |
1243 | documentation please at least provide a README file containing: | |
1244 | ||
1245 | =over 10 | |
1246 | ||
1247 | =item * | |
1248 | A description of the module/package/extension etc. | |
1249 | ||
1250 | =item * | |
1251 | A copyright notice - see below. | |
1252 | ||
1253 | =item * | |
1254 | Prerequisites - what else you may need to have. | |
1255 | ||
1256 | =item * | |
1257 | How to build it - possible changes to Makefile.PL etc. | |
1258 | ||
1259 | =item * | |
1260 | How to install it. | |
1261 | ||
1262 | =item * | |
1263 | Recent changes in this release, especially incompatibilities | |
1264 | ||
1265 | =item * | |
1266 | Changes / enhancements you plan to make in the future. | |
1267 | ||
1268 | =back | |
1269 | ||
1270 | If the README file seems to be getting too large you may wish to | |
1271 | split out some of the sections into separate files: INSTALL, | |
1272 | Copying, ToDo etc. | |
1273 | ||
d0c42abe | 1274 | =over 4 |
1275 | ||
cb1a09d0 AD |
1276 | =item Adding a Copyright Notice. |
1277 | ||
5f05dabc | 1278 | How you choose to license your work is a personal decision. |
cb1a09d0 AD |
1279 | The general mechanism is to assert your Copyright and then make |
1280 | a declaration of how others may copy/use/modify your work. | |
1281 | ||
c36e9b62 | 1282 | Perl, for example, is supplied with two types of license: The GNU |
5f05dabc | 1283 | GPL and The Artistic License (see the files README, Copying, and |
cb1a09d0 AD |
1284 | Artistic). Larry has good reasons for NOT just using the GNU GPL. |
1285 | ||
5f05dabc | 1286 | My personal recommendation, out of respect for Larry, Perl, and the |
1287 | perl community at large is to state something simply like: | |
cb1a09d0 AD |
1288 | |
1289 | Copyright (c) 1995 Your Name. All rights reserved. | |
1290 | This program is free software; you can redistribute it and/or | |
1291 | modify it under the same terms as Perl itself. | |
1292 | ||
1293 | This statement should at least appear in the README file. You may | |
1294 | also wish to include it in a Copying file and your source files. | |
1295 | Remember to include the other words in addition to the Copyright. | |
1296 | ||
1297 | =item Give the module a version/issue/release number. | |
1298 | ||
1299 | To be fully compatible with the Exporter and MakeMaker modules you | |
1300 | should store your module's version number in a non-my package | |
5f05dabc | 1301 | variable called $VERSION. This should be a floating point |
1302 | number with at least two digits after the decimal (i.e., hundredths, | |
c36e9b62 | 1303 | e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version. |
cb1a09d0 AD |
1304 | See Exporter.pm in Perl5.001m or later for details. |
1305 | ||
1306 | It may be handy to add a function or method to retrieve the number. | |
1307 | Use the number in announcements and archive file names when | |
1308 | releasing the module (ModuleName-1.02.tar.Z). | |
1309 | See perldoc ExtUtils::MakeMaker.pm for details. | |
1310 | ||
1311 | =item How to release and distribute a module. | |
1312 | ||
1313 | It's good idea to post an announcement of the availability of your | |
1314 | module (or the module itself if small) to the comp.lang.perl.announce | |
1315 | Usenet newsgroup. This will at least ensure very wide once-off | |
1316 | distribution. | |
1317 | ||
1318 | If possible you should place the module into a major ftp archive and | |
5f05dabc | 1319 | include details of its location in your announcement. |
cb1a09d0 AD |
1320 | |
1321 | Some notes about ftp archives: Please use a long descriptive file | |
1322 | name which includes the version number. Most incoming directories | |
1323 | will not be readable/listable, i.e., you won't be able to see your | |
1324 | file after uploading it. Remember to send your email notification | |
1325 | message as soon as possible after uploading else your file may get | |
1326 | deleted automatically. Allow time for the file to be processed | |
1327 | and/or check the file has been processed before announcing its | |
1328 | location. | |
1329 | ||
1330 | FTP Archives for Perl Modules: | |
1331 | ||
1332 | Follow the instructions and links on | |
1333 | ||
1334 | http://franz.ww.tu-berlin.de/modulelist | |
1335 | ||
5f05dabc | 1336 | or upload to one of these sites: |
cb1a09d0 AD |
1337 | |
1338 | ftp://franz.ww.tu-berlin.de/incoming | |
5f05dabc | 1339 | ftp://ftp.cis.ufl.edu/incoming |
cb1a09d0 | 1340 | |
9607fc9c | 1341 | and notify <F<upload@franz.ww.tu-berlin.de>>. |
cb1a09d0 AD |
1342 | |
1343 | By using the WWW interface you can ask the Upload Server to mirror | |
1344 | your modules from your ftp or WWW site into your own directory on | |
1345 | CPAN! | |
1346 | ||
1347 | Please remember to send me an updated entry for the Module list! | |
1348 | ||
1349 | =item Take care when changing a released module. | |
1350 | ||
1351 | Always strive to remain compatible with previous released versions | |
1352 | (see 2.2 above) Otherwise try to add a mechanism to revert to the | |
1353 | old behaviour if people rely on it. Document incompatible changes. | |
1354 | ||
1355 | =back | |
1356 | ||
d0c42abe | 1357 | =back |
1358 | ||
cb1a09d0 AD |
1359 | =head2 Guidelines for Converting Perl 4 Library Scripts into Modules |
1360 | ||
1361 | =over 4 | |
1362 | ||
1363 | =item There is no requirement to convert anything. | |
1364 | ||
1365 | If it ain't broke, don't fix it! Perl 4 library scripts should | |
1366 | continue to work with no problems. You may need to make some minor | |
1367 | changes (like escaping non-array @'s in double quoted strings) but | |
1368 | there is no need to convert a .pl file into a Module for just that. | |
1369 | ||
1370 | =item Consider the implications. | |
1371 | ||
1372 | All the perl applications which make use of the script will need to | |
1373 | be changed (slightly) if the script is converted into a module. Is | |
1374 | it worth it unless you plan to make other changes at the same time? | |
1375 | ||
1376 | =item Make the most of the opportunity. | |
1377 | ||
1378 | If you are going to convert the script to a module you can use the | |
1379 | opportunity to redesign the interface. The 'Guidelines for Module | |
1380 | Creation' above include many of the issues you should consider. | |
1381 | ||
1382 | =item The pl2pm utility will get you started. | |
1383 | ||
1384 | This utility will read *.pl files (given as parameters) and write | |
1385 | corresponding *.pm files. The pl2pm utilities does the following: | |
1386 | ||
1387 | =over 10 | |
1388 | ||
1389 | =item * | |
1390 | Adds the standard Module prologue lines | |
1391 | ||
1392 | =item * | |
1393 | Converts package specifiers from ' to :: | |
1394 | ||
1395 | =item * | |
1396 | Converts die(...) to croak(...) | |
1397 | ||
1398 | =item * | |
1399 | Several other minor changes | |
1400 | ||
1401 | =back | |
1402 | ||
1403 | Being a mechanical process pl2pm is not bullet proof. The converted | |
1404 | code will need careful checking, especially any package statements. | |
1405 | Don't delete the original .pl file till the new .pm one works! | |
1406 | ||
1407 | =back | |
1408 | ||
1409 | =head2 Guidelines for Reusing Application Code | |
1410 | ||
1411 | =over 4 | |
1412 | ||
1413 | =item Complete applications rarely belong in the Perl Module Library. | |
1414 | ||
1415 | =item Many applications contain some perl code which could be reused. | |
1416 | ||
1417 | Help save the world! Share your code in a form that makes it easy | |
1418 | to reuse. | |
1419 | ||
1420 | =item Break-out the reusable code into one or more separate module files. | |
1421 | ||
1422 | =item Take the opportunity to reconsider and redesign the interfaces. | |
1423 | ||
1424 | =item In some cases the 'application' can then be reduced to a small | |
1425 | ||
1426 | fragment of code built on top of the reusable modules. In these cases | |
1427 | the application could invoked as: | |
1428 | ||
1429 | perl -e 'use Module::Name; method(@ARGV)' ... | |
5f05dabc | 1430 | or |
3fe9a6f1 | 1431 | perl -mModule::Name ... (in perl5.002 or higher) |
cb1a09d0 AD |
1432 | |
1433 | =back |