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1 | =head1 NAME |
2 | |
3 | perlmod - Perl modules (packages) |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | =head2 Packages |
8 | |
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9 | Perl provides a mechanism for alternative namespaces to protect packages |
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10 | from stomping on each other's variables. In fact, apart from certain |
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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 |
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16 | will be in this namespace. A package statement affects only dynamic |
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17 | variables--including those you've used local() on--but I<not> lexical |
18 | variables created with my(). Typically it would be the first declaration |
19 | in a file to be included by the C<require> or C<use> operator. You can |
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20 | switch into a package in more than one place; it influences merely which |
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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<$Package::Variable>. If the package name is null, the C<main> package |
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25 | is assumed. That is, C<$::sail> is equivalent to C<$main::sail>. |
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26 | |
27 | (The old package delimiter was a single quote, but double colon |
28 | is now the preferred delimiter, in part because it's more readable |
29 | to humans, and in part because it's more readable to B<emacs> macros. |
30 | It also makes C++ programmers feel like they know what's going on.) |
31 | |
32 | Packages may be nested inside other packages: C<$OUTER::INNER::var>. This |
33 | implies nothing about the order of name lookups, however. All symbols |
34 | are either local to the current package, or must be fully qualified |
35 | from the outer package name down. For instance, there is nowhere |
36 | within package C<OUTER> that C<$INNER::var> refers to C<$OUTER::INNER::var>. |
37 | It would treat package C<INNER> as a totally separate global package. |
38 | |
39 | Only identifiers starting with letters (or underscore) are stored in a |
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40 | package's symbol table. All other symbols are kept in package C<main>, |
41 | including all of the punctuation variables like $_. In addition, the |
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42 | identifiers STDIN, STDOUT, STDERR, ARGV, ARGVOUT, ENV, INC, and SIG are |
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43 | forced to be in package C<main>, even when used for other purposes than |
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44 | their builtin one. Note also that, if you have a package called C<m>, |
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45 | C<s>, or C<y>, then you can't use the qualified form of an identifier |
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46 | because it will be interpreted instead as a pattern match, a substitution, |
47 | or a translation. |
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48 | |
49 | (Variables beginning with underscore used to be forced into package |
50 | main, but we decided it was more useful for package writers to be able |
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51 | to use leading underscore to indicate private variables and method names. |
52 | $_ is still global though.) |
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53 | |
54 | Eval()ed strings are compiled in the package in which the eval() was |
55 | compiled. (Assignments to C<$SIG{}>, however, assume the signal |
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56 | handler specified is in the C<main> package. Qualify the signal handler |
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57 | name if you wish to have a signal handler in a package.) For an |
58 | example, examine F<perldb.pl> in the Perl library. It initially switches |
59 | to the C<DB> package so that the debugger doesn't interfere with variables |
60 | in the script you are trying to debug. At various points, however, it |
61 | temporarily switches back to the C<main> package to evaluate various |
62 | expressions in the context of the C<main> package (or wherever you came |
63 | from). See L<perldebug>. |
64 | |
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65 | See L<perlsub> for other scoping issues related to my() and local(), |
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66 | or L<perlref> regarding closures. |
67 | |
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68 | =head2 Symbol Tables |
69 | |
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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: |
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79 | |
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80 | local(*main::foo) = *main::bar; |
81 | local($main::{'foo'}) = $main::{'bar'}; |
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82 | |
83 | You can use this to print out all the variables in a package, for |
84 | instance. Here is F<dumpvar.pl> from the Perl library: |
85 | |
86 | package dumpvar; |
87 | sub main::dumpvar { |
88 | ($package) = @_; |
89 | local(*stab) = eval("*${package}::"); |
90 | while (($key,$val) = each(%stab)) { |
91 | local(*entry) = $val; |
92 | if (defined $entry) { |
93 | print "\$$key = '$entry'\n"; |
94 | } |
95 | |
96 | if (defined @entry) { |
97 | print "\@$key = (\n"; |
98 | foreach $num ($[ .. $#entry) { |
99 | print " $num\t'",$entry[$num],"'\n"; |
100 | } |
101 | print ")\n"; |
102 | } |
103 | |
104 | if ($key ne "${package}::" && defined %entry) { |
105 | print "\%$key = (\n"; |
106 | foreach $key (sort keys(%entry)) { |
107 | print " $key\t'",$entry{$key},"'\n"; |
108 | } |
109 | print ")\n"; |
110 | } |
111 | } |
112 | } |
113 | |
114 | Note that even though the subroutine is compiled in package C<dumpvar>, |
115 | the name of the subroutine is qualified so that its name is inserted |
116 | into package C<main>. |
117 | |
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118 | Assignment to a typeglob performs an aliasing operation, i.e., |
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119 | |
120 | *dick = *richard; |
121 | |
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122 | causes variables, subroutines, and file handles accessible via the |
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123 | identifier C<richard> to also be accessible via the identifier C<dick>. If |
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124 | you want to alias only a particular variable or subroutine, you can |
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125 | assign a reference instead: |
126 | |
127 | *dick = \$richard; |
128 | |
129 | makes $richard and $dick the same variable, but leaves |
130 | @richard and @dick as separate arrays. Tricky, eh? |
131 | |
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132 | This mechanism may be used to pass and return cheap references |
133 | into or from subroutines if you won't want to copy the whole |
134 | thing. |
135 | |
136 | %some_hash = (); |
137 | *some_hash = fn( \%another_hash ); |
138 | sub fn { |
139 | local *hashsym = shift; |
140 | # now use %hashsym normally, and you |
141 | # will affect the caller's %another_hash |
142 | my %nhash = (); # do what you want |
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143 | return \%nhash; |
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144 | } |
145 | |
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146 | On return, the reference will overwrite the hash slot in the |
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147 | symbol table specified by the *some_hash typeglob. This |
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148 | is a somewhat tricky way of passing around references cheaply |
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149 | when you won't want to have to remember to dereference variables |
150 | explicitly. |
151 | |
152 | Another use of symbol tables is for making "constant" scalars. |
153 | |
154 | *PI = \3.14159265358979; |
155 | |
156 | Now you cannot alter $PI, which is probably a good thing all in all. |
157 | |
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158 | 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}, '::', *{$glob}{NAME}, "\n"; |
165 | } |
166 | identify_typeglob *foo; |
167 | identify_typeglob *bar::baz; |
168 | |
169 | This prints |
170 | |
171 | You gave me main::foo |
172 | You gave me bar::baz |
173 | |
174 | The *foo{THING} notation can also be used to obtain references to the |
175 | individual elements of *foo, see L<perlref>. |
176 | |
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177 | =head2 Package Constructors and Destructors |
178 | |
179 | There are two special subroutine definitions that function as package |
180 | constructors and destructors. These are the C<BEGIN> and C<END> |
181 | routines. The C<sub> is optional for these routines. |
182 | |
183 | A C<BEGIN> subroutine is executed as soon as possible, that is, the |
184 | moment it is completely defined, even before the rest of the containing |
185 | file is parsed. You may have multiple C<BEGIN> blocks within a |
186 | file--they will execute in order of definition. Because a C<BEGIN> |
187 | block executes immediately, it can pull in definitions of subroutines |
188 | and such from other files in time to be visible to the rest of the |
189 | file. |
190 | |
191 | An C<END> subroutine is executed as late as possible, that is, when the |
192 | interpreter is being exited, even if it is exiting as a result of a |
193 | die() function. (But not if it's is being blown out of the water by a |
194 | signal--you have to trap that yourself (if you can).) You may have |
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195 | multiple C<END> blocks within a file--they will execute in reverse |
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196 | order of definition; that is: last in, first out (LIFO). |
197 | |
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198 | Inside an C<END> subroutine C<$?> contains the value that the script is |
199 | going to pass to C<exit()>. You can modify C<$?> to change the exit |
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200 | value of the script. Beware of changing C<$?> by accident (e.g.,, by |
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201 | running something via C<system>). |
202 | |
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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 | |
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208 | There is no special class syntax in Perl, but a package may function |
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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 |
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211 | by listing the other package name in its @ISA array. |
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212 | |
213 | For more on this, see L<perlobj>. |
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214 | |
215 | =head2 Perl Modules |
216 | |
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217 | A module is just a package that is defined in a library file of |
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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 | |
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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) |
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285 | |
286 | Then go on to declare and use your variables in functions |
287 | without any qualifications. |
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288 | See L<Exporter> and the I<Perl Modules File> for details on |
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289 | mechanics and style issues in module creation. |
290 | |
291 | Perl modules are included into your program by saying |
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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 | |
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307 | As a special case |
308 | |
309 | use Module (); |
310 | |
311 | is exactly equivalent to |
312 | |
313 | BEGIN { require "Module.pm"; } |
314 | |
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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> |
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328 | instead of C<use>. With require you can get into this problem: |
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329 | |
330 | require Cwd; # make Cwd:: accessible |
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331 | $here = Cwd::getcwd(); |
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332 | |
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333 | use Cwd; # import names from Cwd:: |
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334 | $here = getcwd(); |
335 | |
336 | require Cwd; # make Cwd:: accessible |
337 | $here = getcwd(); # oops! no main::getcwd() |
338 | |
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339 | In general C<use Module ();> is recommended over C<require Module;>. |
340 | |
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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 |
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354 | say just C<use POSIX> to get it all. |
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355 | |
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356 | For more information on writing extension modules, see L<perlxs> |
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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 |
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370 | written contract for the module (A.K.A. documentation) may make other |
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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 | |
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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 |
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378 | the library directory that end in either F<.pl> or F<.ph>. These are old |
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379 | libraries supplied so that old programs that use them still run. The |
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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 |
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384 | conversion, but it's just a mechanical process and therefore far from |
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385 | bulletproof. |
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386 | |
387 | =head2 Pragmatic Modules |
388 | |
389 | They work somewhat like pragmas in that they tend to affect the compilation of |
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390 | your program, and thus will usually work well only when used within a |
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391 | C<use>, or C<no>. Most of these are locally scoped, so an inner BLOCK |
392 | may countermand any of these by saying: |
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393 | |
394 | no integer; |
395 | no strict 'refs'; |
396 | |
397 | which lasts until the end of that BLOCK. |
398 | |
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399 | Unlike the pragmas that effect the C<$^H> hints variable, the C<use |
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400 | vars> and C<use subs> declarations are not BLOCK-scoped. They allow |
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401 | you to predeclare a variables or subroutines within a particular |
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402 | I<file> rather than just a block. Such declarations are effective |
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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). |
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407 | |
408 | =over 12 |
409 | |
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410 | =item blib |
411 | |
412 | manipulate @INC at compile time to use MakeMaker's uninstalled version |
413 | of a package |
414 | |
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415 | =item diagnostics |
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416 | |
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417 | force verbose warning diagnostics |
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418 | |
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419 | =item integer |
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420 | |
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421 | compute arithmetic in integer instead of double |
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422 | |
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423 | =item less |
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424 | |
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425 | request less of something from the compiler |
426 | |
427 | =item lib |
428 | |
429 | manipulate @INC at compile time |
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430 | |
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431 | =item locale |
432 | |
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433 | use or ignore current locale for builtin operations (see L<perllocale>) |
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434 | |
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435 | =item ops |
436 | |
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437 | restrict named opcodes when compiling or running Perl code |
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438 | |
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439 | =item overload |
440 | |
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441 | overload basic Perl operations |
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442 | |
443 | =item sigtrap |
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444 | |
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445 | enable simple signal handling |
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446 | |
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447 | =item strict |
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448 | |
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449 | restrict unsafe constructs |
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450 | |
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451 | =item subs |
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452 | |
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453 | predeclare sub names |
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454 | |
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455 | =item vmsish |
456 | |
457 | adopt certain VMS-specific behaviors |
458 | |
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459 | =item vars |
460 | |
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461 | predeclare global variable names |
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462 | |
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463 | =back |
464 | |
465 | =head2 Standard Modules |
466 | |
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467 | Standard, bundled modules are all expected to behave in a well-defined |
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468 | manner with respect to namespace pollution because they use the |
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469 | Exporter module. See their own documentation for details. |
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470 | |
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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 | |
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501 | =item Carp |
502 | |
503 | warn of errors (from perspective of caller) |
504 | |
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505 | =item Class::Struct |
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506 | |
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507 | declare struct-like datatypes |
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508 | |
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509 | =item Config |
510 | |
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511 | access Perl configuration information |
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512 | |
513 | =item Cwd |
514 | |
515 | get pathname of current working directory |
516 | |
517 | =item DB_File |
518 | |
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519 | access to Berkeley DB |
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520 | |
521 | =item Devel::SelfStubber |
522 | |
523 | generate stubs for a SelfLoading module |
524 | |
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525 | =item DirHandle |
526 | |
527 | supply object methods for directory handles |
528 | |
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529 | =item DynaLoader |
530 | |
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531 | dynamically load C libraries into Perl code |
cb1a09d0 |
532 | |
533 | =item English |
534 | |
55497cff |
535 | use nice English (or awk) names for ugly punctuation variables |
cb1a09d0 |
536 | |
537 | =item Env |
538 | |
55497cff |
539 | import environment variables |
cb1a09d0 |
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 |
552 | |
553 | =item ExtUtils::Liblist |
554 | |
555 | determine libraries to use and how to use them |
556 | |
5f05dabc |
557 | =item ExtUtils::MM_OS2 |
558 | |
54310121 |
559 | methods to override Unix behaviour in ExtUtils::MakeMaker |
5f05dabc |
560 | |
561 | =item ExtUtils::MM_Unix |
562 | |
563 | methods used by ExtUtils::MakeMaker |
564 | |
565 | =item ExtUtils::MM_VMS |
566 | |
54310121 |
567 | methods to override Unix behaviour in ExtUtils::MakeMaker |
5f05dabc |
568 | |
cb1a09d0 |
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 |
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 |
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 |
609 | =item File::Find |
610 | |
611 | traverse a file tree |
612 | |
cb1a09d0 |
613 | =item File::Path |
614 | |
615 | create or remove a series of directories |
616 | |
5f05dabc |
617 | =item File::stat |
618 | |
54310121 |
619 | by-name interface to Perl's builtin stat() functions |
5f05dabc |
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 |
637 | =item Getopt::Long |
638 | |
55497cff |
639 | extended processing of command line options |
cb1a09d0 |
640 | |
641 | =item Getopt::Std |
642 | |
55497cff |
643 | process single-character switches with switch clustering |
cb1a09d0 |
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 |
677 | =item IPC::Open2 |
678 | |
55497cff |
679 | open a process for both reading and writing |
cb1a09d0 |
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 | |
54310121 |
707 | by-name interface to Perl's builtin gethost*() functions |
5f05dabc |
708 | |
709 | =item Net::netent |
710 | |
54310121 |
711 | by-name interface to Perl's builtin getnet*() functions |
5f05dabc |
712 | |
713 | =item Net::protoent |
714 | |
54310121 |
715 | by-name interface to Perl's builtin getproto*() functions |
5f05dabc |
716 | |
717 | =item Net::servent |
718 | |
54310121 |
719 | by-name interface to Perl's builtin getserv*() functions |
5f05dabc |
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 |
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 |
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 |
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 | |
54310121 |
771 | interface to the Unix syslog(3) calls |
55497cff |
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 |
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 | |
54310121 |
803 | expand and unexpand tabs per the Unix expand(1) and unexpand(1) |
55497cff |
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 | |
54310121 |
831 | by-name interface to Perl's builtin gmtime() function |
5f05dabc |
832 | |
833 | =item Time::localtime |
834 | |
54310121 |
835 | by-name interface to Perl's builtin localtime() function |
5f05dabc |
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 | |
54310121 |
847 | by-name interface to Perl's builtin getgr*() functions |
5f05dabc |
848 | |
849 | =item User::pwent |
850 | |
54310121 |
851 | by-name interface to Perl's builtin getpw*() functions |
5f05dabc |
852 | |
cb1a09d0 |
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 |
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 | |
54310121 |
865 | Extension modules are written in C (or a mix of Perl and C) and may be |
866 | statically linked or in general are |
4633a7c4 |
867 | dynamically loaded into Perl if and when you need them. Supported |
868 | extension modules include the Socket, Fcntl, and POSIX modules. |
a0d0e21e |
869 | |
cb1a09d0 |
870 | Many popular C extension modules do not come bundled (at least, not |
5f05dabc |
871 | completely) due to their sizes, volatility, or simply lack of time for |
cb1a09d0 |
872 | adequate testing and configuration across the multitude of platforms on |
873 | which Perl was beta-tested. You are encouraged to look for them in |
874 | archie(1L), the Perl FAQ or Meta-FAQ, the WWW page, and even with their |
875 | authors before randomly posting asking for their present condition and |
876 | disposition. |
a0d0e21e |
877 | |
cb1a09d0 |
878 | =head1 CPAN |
a0d0e21e |
879 | |
4633a7c4 |
880 | CPAN stands for the Comprehensive Perl Archive Network. This is a globally |
5f05dabc |
881 | replicated collection of all known Perl materials, including hundreds |
c36e9b62 |
882 | of unbundled modules. Here are the major categories of modules: |
a0d0e21e |
883 | |
4633a7c4 |
884 | =over |
a0d0e21e |
885 | |
4633a7c4 |
886 | =item * |
5f05dabc |
887 | Language Extensions and Documentation Tools |
a0d0e21e |
888 | |
4633a7c4 |
889 | =item * |
890 | Development Support |
a0d0e21e |
891 | |
4633a7c4 |
892 | =item * |
893 | Operating System Interfaces |
a0d0e21e |
894 | |
4633a7c4 |
895 | =item * |
896 | Networking, Device Control (modems) and InterProcess Communication |
a0d0e21e |
897 | |
4633a7c4 |
898 | =item * |
899 | Data Types and Data Type Utilities |
a0d0e21e |
900 | |
4633a7c4 |
901 | =item * |
902 | Database Interfaces |
a0d0e21e |
903 | |
4633a7c4 |
904 | =item * |
905 | User Interfaces |
a0d0e21e |
906 | |
4633a7c4 |
907 | =item * |
908 | Interfaces to / Emulations of Other Programming Languages |
a0d0e21e |
909 | |
4633a7c4 |
910 | =item * |
911 | File Names, File Systems and File Locking (see also File Handles) |
a0d0e21e |
912 | |
4633a7c4 |
913 | =item * |
5f05dabc |
914 | String Processing, Language Text Processing, Parsing, and Searching |
a0d0e21e |
915 | |
4633a7c4 |
916 | =item * |
5f05dabc |
917 | Option, Argument, Parameter, and Configuration File Processing |
a0d0e21e |
918 | |
4633a7c4 |
919 | =item * |
920 | Internationalization and Locale |
a0d0e21e |
921 | |
4633a7c4 |
922 | =item * |
5f05dabc |
923 | Authentication, Security, and Encryption |
a0d0e21e |
924 | |
4633a7c4 |
925 | =item * |
926 | World Wide Web, HTML, HTTP, CGI, MIME |
a0d0e21e |
927 | |
4633a7c4 |
928 | =item * |
929 | Server and Daemon Utilities |
a0d0e21e |
930 | |
4633a7c4 |
931 | =item * |
932 | Archiving and Compression |
a0d0e21e |
933 | |
4633a7c4 |
934 | =item * |
5f05dabc |
935 | Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing |
a0d0e21e |
936 | |
4633a7c4 |
937 | =item * |
938 | Mail and Usenet News |
a0d0e21e |
939 | |
4633a7c4 |
940 | =item * |
941 | Control Flow Utilities (callbacks and exceptions etc) |
a0d0e21e |
942 | |
4633a7c4 |
943 | =item * |
944 | File Handle and Input/Output Stream Utilities |
a0d0e21e |
945 | |
4633a7c4 |
946 | =item * |
947 | Miscellaneous Modules |
a0d0e21e |
948 | |
4633a7c4 |
949 | =back |
a0d0e21e |
950 | |
d0c42abe |
951 | The registered CPAN sites as of this writing include the following. |
4633a7c4 |
952 | You should try to choose one close to you: |
a0d0e21e |
953 | |
4633a7c4 |
954 | =over |
a0d0e21e |
955 | |
4633a7c4 |
956 | =item * |
9607fc9c |
957 | Africa |
a0d0e21e |
958 | |
9607fc9c |
959 | South Africa ftp://ftp.is.co.za/programming/perl/CPAN/ |
a0d0e21e |
960 | |
4633a7c4 |
961 | =item * |
9607fc9c |
962 | Asia |
a0d0e21e |
963 | |
9607fc9c |
964 | Hong Kong ftp://ftp.hkstar.com/pub/CPAN/ |
965 | Japan ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/ |
966 | ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/ |
967 | South Korea ftp://ftp.nuri.net/pub/CPAN/ |
968 | Taiwan ftp://dongpo.math.ncu.edu.tw/perl/CPAN/ |
969 | ftp://ftp.wownet.net/pub2/PERL/ |
a0d0e21e |
970 | |
4633a7c4 |
971 | =item * |
9607fc9c |
972 | Australasia |
a0d0e21e |
973 | |
9607fc9c |
974 | Australia ftp://ftp.netinfo.com.au/pub/perl/CPAN/ |
975 | New Zealand ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/ |
a0d0e21e |
976 | |
4633a7c4 |
977 | =item * |
9607fc9c |
978 | Europe |
979 | |
980 | Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/ |
981 | Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/ |
982 | Czech Republic ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/ |
983 | Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/ |
984 | Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/ |
985 | France ftp://ftp.ibp.fr/pub/perl/CPAN/ |
986 | ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/ |
987 | Germany ftp://ftp.gmd.de/packages/CPAN/ |
988 | ftp://ftp.leo.org/pub/comp/programming/languages/perl/CPAN/ |
989 | ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/ |
990 | ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/ |
991 | ftp://ftp.uni-erlangen.de/pub/source/Perl/CPAN/ |
992 | ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/ |
993 | Greece ftp://ftp.ntua.gr/pub/lang/perl/ |
994 | Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/ |
995 | Italy ftp://cis.utovrm.it/CPAN/ |
996 | the Netherlands ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/ |
997 | ftp://ftp.EU.net/packages/cpan/ |
998 | Norway ftp://ftp.uit.no/pub/languages/perl/cpan/ |
999 | Poland ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/ |
1000 | ftp://sunsite.icm.edu.pl/pub/CPAN/ |
1001 | Portugal ftp://ftp.ci.uminho.pt/pub/lang/perl/ |
1002 | ftp://ftp.telepac.pt/pub/CPAN/ |
1003 | Russia ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/ |
1004 | Slovenia ftp://ftp.arnes.si/software/perl/CPAN/ |
1005 | Spain ftp://ftp.etse.urv.es/pub/mirror/perl/ |
1006 | ftp://ftp.rediris.es/mirror/CPAN/ |
1007 | Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/ |
9607fc9c |
1008 | UK ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/ |
1009 | ftp://sunsite.doc.ic.ac.uk/packages/CPAN/ |
1010 | ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/ |
a0d0e21e |
1011 | |
4633a7c4 |
1012 | =item * |
9607fc9c |
1013 | North America |
1014 | |
1015 | Ontario ftp://ftp.utilis.com/public/CPAN/ |
1016 | ftp://enterprise.ic.gc.ca/pub/perl/CPAN/ |
1017 | Manitoba ftp://theory.uwinnipeg.ca/pub/CPAN/ |
1018 | California ftp://ftp.digital.com/pub/plan/perl/CPAN/ |
30f5542a |
1019 | ftp://ftp.cdrom.com/pub/perl/CPAN/ |
9607fc9c |
1020 | Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/ |
1021 | Florida ftp://ftp.cis.ufl.edu/pub/perl/CPAN/ |
1022 | Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/ |
1023 | Massachusetts ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/ |
1024 | New York ftp://ftp.rge.com/pub/languages/perl/ |
1025 | North Carolina ftp://ftp.duke.edu/pub/perl/ |
1026 | Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/ |
30f5542a |
1027 | Oregon http://www.perl.org/CPAN/ |
1028 | ftp://ftp.orst.edu/pub/packages/CPAN/ |
9607fc9c |
1029 | Pennsylvania ftp://ftp.epix.net/pub/languages/perl/ |
1030 | Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/ |
1031 | ftp://ftp.metronet.com/pub/perl/ |
a0d0e21e |
1032 | |
4633a7c4 |
1033 | =item * |
9607fc9c |
1034 | South America |
a0d0e21e |
1035 | |
9607fc9c |
1036 | Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/perl/CPAN/ |
a0d0e21e |
1037 | |
1038 | =back |
4633a7c4 |
1039 | |
5f05dabc |
1040 | For an up-to-date listing of CPAN sites, |
d0c42abe |
1041 | see F<http://www.perl.com/perl/CPAN> or F<ftp://ftp.perl.com/perl/>. |
cb1a09d0 |
1042 | |
5f05dabc |
1043 | =head1 Modules: Creation, Use, and Abuse |
cb1a09d0 |
1044 | |
1045 | (The following section is borrowed directly from Tim Bunce's modules |
1046 | file, available at your nearest CPAN site.) |
1047 | |
5f05dabc |
1048 | Perl implements a class using a package, but the presence of a |
cb1a09d0 |
1049 | package doesn't imply the presence of a class. A package is just a |
1050 | namespace. A class is a package that provides subroutines that can be |
1051 | used as methods. A method is just a subroutine that expects, as its |
1052 | first argument, either the name of a package (for "static" methods), |
1053 | or a reference to something (for "virtual" methods). |
1054 | |
1055 | A module is a file that (by convention) provides a class of the same |
1056 | name (sans the .pm), plus an import method in that class that can be |
1057 | called to fetch exported symbols. This module may implement some of |
1058 | its methods by loading dynamic C or C++ objects, but that should be |
1059 | totally transparent to the user of the module. Likewise, the module |
1060 | might set up an AUTOLOAD function to slurp in subroutine definitions on |
1061 | demand, but this is also transparent. Only the .pm file is required to |
1062 | exist. |
1063 | |
1064 | =head2 Guidelines for Module Creation |
1065 | |
1066 | =over 4 |
1067 | |
1068 | =item Do similar modules already exist in some form? |
1069 | |
1070 | If so, please try to reuse the existing modules either in whole or |
1071 | by inheriting useful features into a new class. If this is not |
1072 | practical try to get together with the module authors to work on |
1073 | extending or enhancing the functionality of the existing modules. |
1074 | A perfect example is the plethora of packages in perl4 for dealing |
1075 | with command line options. |
1076 | |
1077 | If you are writing a module to expand an already existing set of |
1078 | modules, please coordinate with the author of the package. It |
1079 | helps if you follow the same naming scheme and module interaction |
1080 | scheme as the original author. |
1081 | |
1082 | =item Try to design the new module to be easy to extend and reuse. |
1083 | |
1084 | Use blessed references. Use the two argument form of bless to bless |
1085 | into the class name given as the first parameter of the constructor, |
5f05dabc |
1086 | e.g.,: |
cb1a09d0 |
1087 | |
5f05dabc |
1088 | sub new { |
cb1a09d0 |
1089 | my $class = shift; |
1090 | return bless {}, $class; |
1091 | } |
1092 | |
1093 | or even this if you'd like it to be used as either a static |
1094 | or a virtual method. |
1095 | |
5f05dabc |
1096 | sub new { |
cb1a09d0 |
1097 | my $self = shift; |
1098 | my $class = ref($self) || $self; |
1099 | return bless {}, $class; |
1100 | } |
1101 | |
1102 | Pass arrays as references so more parameters can be added later |
1103 | (it's also faster). Convert functions into methods where |
1104 | appropriate. Split large methods into smaller more flexible ones. |
1105 | Inherit methods from other modules if appropriate. |
1106 | |
c36e9b62 |
1107 | Avoid class name tests like: C<die "Invalid" unless ref $ref eq 'FOO'>. |
1108 | Generally you can delete the "C<eq 'FOO'>" part with no harm at all. |
4a6725af |
1109 | Let the objects look after themselves! Generally, avoid hard-wired |
cb1a09d0 |
1110 | class names as far as possible. |
1111 | |
c36e9b62 |
1112 | Avoid C<$r-E<gt>Class::func()> where using C<@ISA=qw(... Class ...)> and |
1113 | C<$r-E<gt>func()> would work (see L<perlbot> for more details). |
cb1a09d0 |
1114 | |
1115 | Use autosplit so little used or newly added functions won't be a |
1116 | burden to programs which don't use them. Add test functions to |
1117 | the module after __END__ either using AutoSplit or by saying: |
1118 | |
1119 | eval join('',<main::DATA>) || die $@ unless caller(); |
1120 | |
30f5542a |
1121 | Does your module pass the 'empty subclass' test? If you say |
c36e9b62 |
1122 | "C<@SUBCLASS::ISA = qw(YOURCLASS);>" your applications should be able |
cb1a09d0 |
1123 | to use SUBCLASS in exactly the same way as YOURCLASS. For example, |
c36e9b62 |
1124 | does your application still work if you change: C<$obj = new YOURCLASS;> |
1125 | into: C<$obj = new SUBCLASS;> ? |
cb1a09d0 |
1126 | |
1127 | Avoid keeping any state information in your packages. It makes it |
1128 | difficult for multiple other packages to use yours. Keep state |
1129 | information in objects. |
1130 | |
c36e9b62 |
1131 | Always use B<-w>. Try to C<use strict;> (or C<use strict qw(...);>). |
cb1a09d0 |
1132 | Remember that you can add C<no strict qw(...);> to individual blocks |
c36e9b62 |
1133 | of code which need less strictness. Always use B<-w>. Always use B<-w>! |
cb1a09d0 |
1134 | Follow the guidelines in the perlstyle(1) manual. |
1135 | |
1136 | =item Some simple style guidelines |
1137 | |
1138 | The perlstyle manual supplied with perl has many helpful points. |
1139 | |
1140 | Coding style is a matter of personal taste. Many people evolve their |
1141 | style over several years as they learn what helps them write and |
1142 | maintain good code. Here's one set of assorted suggestions that |
1143 | seem to be widely used by experienced developers: |
1144 | |
1145 | Use underscores to separate words. It is generally easier to read |
1146 | $var_names_like_this than $VarNamesLikeThis, especially for |
1147 | non-native speakers of English. It's also a simple rule that works |
1148 | consistently with VAR_NAMES_LIKE_THIS. |
1149 | |
1150 | Package/Module names are an exception to this rule. Perl informally |
1151 | reserves lowercase module names for 'pragma' modules like integer |
1152 | and strict. Other modules normally begin with a capital letter and |
1153 | use mixed case with no underscores (need to be short and portable). |
1154 | |
1155 | You may find it helpful to use letter case to indicate the scope |
1156 | or nature of a variable. For example: |
1157 | |
1158 | $ALL_CAPS_HERE constants only (beware clashes with perl vars) |
1159 | $Some_Caps_Here package-wide global/static |
1160 | $no_caps_here function scope my() or local() variables |
1161 | |
1162 | Function and method names seem to work best as all lowercase. |
5f05dabc |
1163 | e.g.,, C<$obj-E<gt>as_string()>. |
cb1a09d0 |
1164 | |
1165 | You can use a leading underscore to indicate that a variable or |
1166 | function should not be used outside the package that defined it. |
1167 | |
1168 | =item Select what to export. |
1169 | |
1170 | Do NOT export method names! |
1171 | |
1172 | Do NOT export anything else by default without a good reason! |
1173 | |
1174 | Exports pollute the namespace of the module user. If you must |
1175 | export try to use @EXPORT_OK in preference to @EXPORT and avoid |
1176 | short or common names to reduce the risk of name clashes. |
1177 | |
1178 | Generally anything not exported is still accessible from outside the |
c36e9b62 |
1179 | module using the ModuleName::item_name (or C<$blessed_ref-E<gt>method>) |
cb1a09d0 |
1180 | syntax. By convention you can use a leading underscore on names to |
5f05dabc |
1181 | indicate informally that they are 'internal' and not for public use. |
cb1a09d0 |
1182 | |
1183 | (It is actually possible to get private functions by saying: |
c36e9b62 |
1184 | C<my $subref = sub { ... }; &$subref;>. But there's no way to call that |
5f05dabc |
1185 | directly as a method, because a method must have a name in the symbol |
cb1a09d0 |
1186 | table.) |
1187 | |
1188 | As a general rule, if the module is trying to be object oriented |
1189 | then export nothing. If it's just a collection of functions then |
1190 | @EXPORT_OK anything but use @EXPORT with caution. |
1191 | |
1192 | =item Select a name for the module. |
1193 | |
5f05dabc |
1194 | This name should be as descriptive, accurate, and complete as |
cb1a09d0 |
1195 | possible. Avoid any risk of ambiguity. Always try to use two or |
1196 | more whole words. Generally the name should reflect what is special |
1197 | about what the module does rather than how it does it. Please use |
5f05dabc |
1198 | nested module names to group informally or categorize a module. |
1199 | There should be a very good reason for a module not to have a nested name. |
cb1a09d0 |
1200 | Module names should begin with a capital letter. |
1201 | |
1202 | Having 57 modules all called Sort will not make life easy for anyone |
1203 | (though having 23 called Sort::Quick is only marginally better :-). |
1204 | Imagine someone trying to install your module alongside many others. |
1205 | If in any doubt ask for suggestions in comp.lang.perl.misc. |
1206 | |
1207 | If you are developing a suite of related modules/classes it's good |
1208 | practice to use nested classes with a common prefix as this will |
1209 | avoid namespace clashes. For example: Xyz::Control, Xyz::View, |
1210 | Xyz::Model etc. Use the modules in this list as a naming guide. |
1211 | |
1212 | If adding a new module to a set, follow the original author's |
1213 | standards for naming modules and the interface to methods in |
1214 | those modules. |
1215 | |
1216 | To be portable each component of a module name should be limited to |
54310121 |
1217 | 11 characters. If it might be used on MS-DOS then try to ensure each is |
cb1a09d0 |
1218 | unique in the first 8 characters. Nested modules make this easier. |
1219 | |
1220 | =item Have you got it right? |
1221 | |
1222 | How do you know that you've made the right decisions? Have you |
1223 | picked an interface design that will cause problems later? Have |
1224 | you picked the most appropriate name? Do you have any questions? |
1225 | |
1226 | The best way to know for sure, and pick up many helpful suggestions, |
1227 | is to ask someone who knows. Comp.lang.perl.misc is read by just about |
1228 | all the people who develop modules and it's the best place to ask. |
1229 | |
1230 | All you need to do is post a short summary of the module, its |
1231 | purpose and interfaces. A few lines on each of the main methods is |
1232 | probably enough. (If you post the whole module it might be ignored |
1233 | by busy people - generally the very people you want to read it!) |
1234 | |
1235 | Don't worry about posting if you can't say when the module will be |
1236 | ready - just say so in the message. It might be worth inviting |
1237 | others to help you, they may be able to complete it for you! |
1238 | |
1239 | =item README and other Additional Files. |
1240 | |
1241 | It's well known that software developers usually fully document the |
1242 | software they write. If, however, the world is in urgent need of |
1243 | your software and there is not enough time to write the full |
1244 | documentation please at least provide a README file containing: |
1245 | |
1246 | =over 10 |
1247 | |
1248 | =item * |
1249 | A description of the module/package/extension etc. |
1250 | |
1251 | =item * |
1252 | A copyright notice - see below. |
1253 | |
1254 | =item * |
1255 | Prerequisites - what else you may need to have. |
1256 | |
1257 | =item * |
1258 | How to build it - possible changes to Makefile.PL etc. |
1259 | |
1260 | =item * |
1261 | How to install it. |
1262 | |
1263 | =item * |
1264 | Recent changes in this release, especially incompatibilities |
1265 | |
1266 | =item * |
1267 | Changes / enhancements you plan to make in the future. |
1268 | |
1269 | =back |
1270 | |
1271 | If the README file seems to be getting too large you may wish to |
1272 | split out some of the sections into separate files: INSTALL, |
1273 | Copying, ToDo etc. |
1274 | |
d0c42abe |
1275 | =over 4 |
1276 | |
cb1a09d0 |
1277 | =item Adding a Copyright Notice. |
1278 | |
5f05dabc |
1279 | How you choose to license your work is a personal decision. |
cb1a09d0 |
1280 | The general mechanism is to assert your Copyright and then make |
1281 | a declaration of how others may copy/use/modify your work. |
1282 | |
54310121 |
1283 | Perl, for example, is supplied with two types of licence: The GNU |
1284 | GPL and The Artistic Licence (see the files README, Copying, and |
cb1a09d0 |
1285 | Artistic). Larry has good reasons for NOT just using the GNU GPL. |
1286 | |
5f05dabc |
1287 | My personal recommendation, out of respect for Larry, Perl, and the |
1288 | perl community at large is to state something simply like: |
cb1a09d0 |
1289 | |
1290 | Copyright (c) 1995 Your Name. All rights reserved. |
1291 | This program is free software; you can redistribute it and/or |
1292 | modify it under the same terms as Perl itself. |
1293 | |
1294 | This statement should at least appear in the README file. You may |
1295 | also wish to include it in a Copying file and your source files. |
1296 | Remember to include the other words in addition to the Copyright. |
1297 | |
1298 | =item Give the module a version/issue/release number. |
1299 | |
1300 | To be fully compatible with the Exporter and MakeMaker modules you |
1301 | should store your module's version number in a non-my package |
5f05dabc |
1302 | variable called $VERSION. This should be a floating point |
1303 | number with at least two digits after the decimal (i.e., hundredths, |
c36e9b62 |
1304 | e.g, C<$VERSION = "0.01">). Don't use a "1.3.2" style version. |
cb1a09d0 |
1305 | See Exporter.pm in Perl5.001m or later for details. |
1306 | |
1307 | It may be handy to add a function or method to retrieve the number. |
1308 | Use the number in announcements and archive file names when |
1309 | releasing the module (ModuleName-1.02.tar.Z). |
1310 | See perldoc ExtUtils::MakeMaker.pm for details. |
1311 | |
1312 | =item How to release and distribute a module. |
1313 | |
1314 | It's good idea to post an announcement of the availability of your |
1315 | module (or the module itself if small) to the comp.lang.perl.announce |
1316 | Usenet newsgroup. This will at least ensure very wide once-off |
1317 | distribution. |
1318 | |
1319 | If possible you should place the module into a major ftp archive and |
5f05dabc |
1320 | include details of its location in your announcement. |
cb1a09d0 |
1321 | |
1322 | Some notes about ftp archives: Please use a long descriptive file |
1323 | name which includes the version number. Most incoming directories |
1324 | will not be readable/listable, i.e., you won't be able to see your |
1325 | file after uploading it. Remember to send your email notification |
1326 | message as soon as possible after uploading else your file may get |
1327 | deleted automatically. Allow time for the file to be processed |
1328 | and/or check the file has been processed before announcing its |
1329 | location. |
1330 | |
1331 | FTP Archives for Perl Modules: |
1332 | |
1333 | Follow the instructions and links on |
1334 | |
1335 | http://franz.ww.tu-berlin.de/modulelist |
1336 | |
5f05dabc |
1337 | or upload to one of these sites: |
cb1a09d0 |
1338 | |
1339 | ftp://franz.ww.tu-berlin.de/incoming |
5f05dabc |
1340 | ftp://ftp.cis.ufl.edu/incoming |
cb1a09d0 |
1341 | |
9607fc9c |
1342 | and notify <F<upload@franz.ww.tu-berlin.de>>. |
cb1a09d0 |
1343 | |
1344 | By using the WWW interface you can ask the Upload Server to mirror |
1345 | your modules from your ftp or WWW site into your own directory on |
1346 | CPAN! |
1347 | |
1348 | Please remember to send me an updated entry for the Module list! |
1349 | |
1350 | =item Take care when changing a released module. |
1351 | |
1352 | Always strive to remain compatible with previous released versions |
1353 | (see 2.2 above) Otherwise try to add a mechanism to revert to the |
1354 | old behaviour if people rely on it. Document incompatible changes. |
1355 | |
1356 | =back |
1357 | |
d0c42abe |
1358 | =back |
1359 | |
cb1a09d0 |
1360 | =head2 Guidelines for Converting Perl 4 Library Scripts into Modules |
1361 | |
1362 | =over 4 |
1363 | |
1364 | =item There is no requirement to convert anything. |
1365 | |
1366 | If it ain't broke, don't fix it! Perl 4 library scripts should |
1367 | continue to work with no problems. You may need to make some minor |
1368 | changes (like escaping non-array @'s in double quoted strings) but |
1369 | there is no need to convert a .pl file into a Module for just that. |
1370 | |
1371 | =item Consider the implications. |
1372 | |
1373 | All the perl applications which make use of the script will need to |
1374 | be changed (slightly) if the script is converted into a module. Is |
1375 | it worth it unless you plan to make other changes at the same time? |
1376 | |
1377 | =item Make the most of the opportunity. |
1378 | |
1379 | If you are going to convert the script to a module you can use the |
1380 | opportunity to redesign the interface. The 'Guidelines for Module |
1381 | Creation' above include many of the issues you should consider. |
1382 | |
1383 | =item The pl2pm utility will get you started. |
1384 | |
1385 | This utility will read *.pl files (given as parameters) and write |
1386 | corresponding *.pm files. The pl2pm utilities does the following: |
1387 | |
1388 | =over 10 |
1389 | |
1390 | =item * |
1391 | Adds the standard Module prologue lines |
1392 | |
1393 | =item * |
1394 | Converts package specifiers from ' to :: |
1395 | |
1396 | =item * |
1397 | Converts die(...) to croak(...) |
1398 | |
1399 | =item * |
1400 | Several other minor changes |
1401 | |
1402 | =back |
1403 | |
1404 | Being a mechanical process pl2pm is not bullet proof. The converted |
1405 | code will need careful checking, especially any package statements. |
1406 | Don't delete the original .pl file till the new .pm one works! |
1407 | |
1408 | =back |
1409 | |
1410 | =head2 Guidelines for Reusing Application Code |
1411 | |
1412 | =over 4 |
1413 | |
1414 | =item Complete applications rarely belong in the Perl Module Library. |
1415 | |
1416 | =item Many applications contain some perl code which could be reused. |
1417 | |
1418 | Help save the world! Share your code in a form that makes it easy |
1419 | to reuse. |
1420 | |
1421 | =item Break-out the reusable code into one or more separate module files. |
1422 | |
1423 | =item Take the opportunity to reconsider and redesign the interfaces. |
1424 | |
1425 | =item In some cases the 'application' can then be reduced to a small |
1426 | |
1427 | fragment of code built on top of the reusable modules. In these cases |
1428 | the application could invoked as: |
1429 | |
1430 | perl -e 'use Module::Name; method(@ARGV)' ... |
5f05dabc |
1431 | or |
3fe9a6f1 |
1432 | perl -mModule::Name ... (in perl5.002 or higher) |
cb1a09d0 |
1433 | |
1434 | =back |