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1=head1 NAME
2
3perlnewmod - preparing a new module for distribution
4
5=head1 DESCRIPTION
6
7This document gives you some suggestions about how to go about writing
8Perl modules, preparing them for distribution, and making them available
9via CPAN.
10
11One of the things that makes Perl really powerful is the fact that Perl
12hackers tend to want to share the solutions to problems they've faced,
13so you and I don't have to battle with the same problem again.
14
15The main way they do this is by abstracting the solution into a Perl
16module. If you don't know what one of these is, the rest of this
17document isn't going to be much use to you. You're also missing out on
18an awful lot of useful code; consider having a look at L<perlmod>,
19L<perlmodlib> and L<perlmodinstall> before coming back here.
20
21When you've found that there isn't a module available for what you're
22trying to do, and you've had to write the code yourself, consider
23packaging up the solution into a module and uploading it to CPAN so that
24others can benefit.
25
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26You should also take a look at L<perlmodstyle> for best practices in
27making a module.
28
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29=head2 Warning
30
31We're going to primarily concentrate on Perl-only modules here, rather
32than XS modules. XS modules serve a rather different purpose, and
33you should consider different things before distributing them - the
34popularity of the library you are gluing, the portability to other
35operating systems, and so on. However, the notes on preparing the Perl
36side of the module and packaging and distributing it will apply equally
37well to an XS module as a pure-Perl one.
38
39=head2 What should I make into a module?
40
41You should make a module out of any code that you think is going to be
42useful to others. Anything that's likely to fill a hole in the communal
43library and which someone else can slot directly into their program. Any
44part of your code which you can isolate and extract and plug into
45something else is a likely candidate.
46
47Let's take an example. Suppose you're reading in data from a local
48format into a hash-of-hashes in Perl, turning that into a tree, walking
49the tree and then piping each node to an Acme Transmogrifier Server.
50
51Now, quite a few people have the Acme Transmogrifier, and you've had to
52write something to talk the protocol from scratch - you'd almost
53certainly want to make that into a module. The level at which you pitch
54it is up to you: you might want protocol-level modules analogous to
55L<Net::SMTP|Net::SMTP> which then talk to higher level modules analogous
56to L<Mail::Send|Mail::Send>. The choice is yours, but you do want to get
57a module out for that server protocol.
58
59Nobody else on the planet is going to talk your local data format, so we
60can ignore that. But what about the thing in the middle? Building tree
61structures from Perl variables and then traversing them is a nice,
62general problem, and if nobody's already written a module that does
63that, you might want to modularise that code too.
64
65So hopefully you've now got a few ideas about what's good to modularise.
66Let's now see how it's done.
67
68=head2 Step-by-step: Preparing the ground
69
70Before we even start scraping out the code, there are a few things we'll
71want to do in advance.
72
73=over 3
74
75=item Look around
76
77Dig into a bunch of modules to see how they're written. I'd suggest
78starting with L<Text::Tabs|Text::Tabs>, since it's in the standard
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79library and is nice and simple, and then looking at something a little
80more complex like L<File::Copy|File::Copy>. For object oriented
12e02236 81code, L<WWW::Mechanize> or the C<Email::*> modules provide some good
4e9dada0 82examples.
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83
84These should give you an overall feel for how modules are laid out and
85written.
86
87=item Check it's new
88
89There are a lot of modules on CPAN, and it's easy to miss one that's
90similar to what you're planning on contributing. Have a good plough
12e02236 91through L<http://metacpan.org> and make sure you're not the one
4e9dada0 92reinventing the wheel!
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93
94=item Discuss the need
95
96You might love it. You might feel that everyone else needs it. But there
97might not actually be any real demand for it out there. If you're unsure
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98about the demand your module will have, consider asking the
99C<module-authors@perl.org> mailing list (send an email to
100C<module-authors-subscribe@perl.org> to subscribe; see
fdee78a1 101L<https://lists.perl.org/list/module-authors.html> for more information
32356571 102and a link to the archives).
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103
104=item Choose a name
105
106Perl modules included on CPAN have a naming hierarchy you should try to
107fit in with. See L<perlmodlib> for more details on how this works, and
108browse around CPAN and the modules list to get a feel of it. At the very
109least, remember this: modules should be title capitalised, (This::Thing)
110fit in with a category, and explain their purpose succinctly.
111
112=item Check again
113
114While you're doing that, make really sure you haven't missed a module
115similar to the one you're about to write.
116
117When you've got your name sorted out and you're sure that your module is
118wanted and not currently available, it's time to start coding.
119
120=back
121
122=head2 Step-by-step: Making the module
123
124=over 3
125
4e9dada0 126=item Start with F<module-starter> or F<h2xs>
2e1d04bc 127
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128The F<module-starter> utility is distributed as part of the
129L<Module::Starter|Module::Starter> CPAN package. It creates a directory
130with stubs of all the necessary files to start a new module, according
131to recent "best practice" for module development, and is invoked from
132the command line, thus:
2e1d04bc 133
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134 module-starter --module=Foo::Bar \
135 --author="Your Name" --email=yourname@cpan.org
2e1d04bc 136
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137If you do not wish to install the L<Module::Starter|Module::Starter>
138package from CPAN, F<h2xs> is an older tool, originally intended for the
139development of XS modules, which comes packaged with the Perl
140distribution.
141
142A typical invocation of L<h2xs|h2xs> for a pure Perl module is:
143
144 h2xs -AX --skip-exporter --use-new-tests -n Foo::Bar
145
146The C<-A> omits the Autoloader code, C<-X> omits XS elements,
147C<--skip-exporter> omits the Exporter code, C<--use-new-tests> sets up a
148modern testing environment, and C<-n> specifies the name of the module.
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149
150=item Use L<strict|strict> and L<warnings|warnings>
151
152A module's code has to be warning and strict-clean, since you can't
153guarantee the conditions that it'll be used under. Besides, you wouldn't
154want to distribute code that wasn't warning or strict-clean anyway,
155right?
156
157=item Use L<Carp|Carp>
158
159The L<Carp|Carp> module allows you to present your error messages from
160the caller's perspective; this gives you a way to signal a problem with
161the caller and not your module. For instance, if you say this:
162
163 warn "No hostname given";
164
165the user will see something like this:
166
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167 No hostname given at
168 /usr/local/lib/perl5/site_perl/5.6.0/Net/Acme.pm line 123.
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169
170which looks like your module is doing something wrong. Instead, you want
171to put the blame on the user, and say this:
172
173 No hostname given at bad_code, line 10.
174
175You do this by using L<Carp|Carp> and replacing your C<warn>s with
176C<carp>s. If you need to C<die>, say C<croak> instead. However, keep
177C<warn> and C<die> in place for your sanity checks - where it really is
178your module at fault.
179
180=item Use L<Exporter|Exporter> - wisely!
181
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182L<Exporter|Exporter> gives you a standard way of exporting symbols and
183subroutines from your module into the caller's namespace. For instance,
184saying C<use Net::Acme qw(&frob)> would import the C<frob> subroutine.
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185
186The package variable C<@EXPORT> will determine which symbols will get
187exported when the caller simply says C<use Net::Acme> - you will hardly
188ever want to put anything in there. C<@EXPORT_OK>, on the other hand,
189specifies which symbols you're willing to export. If you do want to
190export a bunch of symbols, use the C<%EXPORT_TAGS> and define a standard
191export set - look at L<Exporter> for more details.
192
193=item Use L<plain old documentation|perlpod>
194
195The work isn't over until the paperwork is done, and you're going to
196need to put in some time writing some documentation for your module.
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197C<module-starter> or C<h2xs> will provide a stub for you to fill in; if
198you're not sure about the format, look at L<perlpod> for an
199introduction. Provide a good synopsis of how your module is used in
200code, a description, and then notes on the syntax and function of the
201individual subroutines or methods. Use Perl comments for developer notes
202and POD for end-user notes.
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203
204=item Write tests
205
206You're encouraged to create self-tests for your module to ensure it's
207working as intended on the myriad platforms Perl supports; if you upload
208your module to CPAN, a host of testers will build your module and send
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209you the results of the tests. Again, C<module-starter> and C<h2xs>
210provide a test framework which you can extend - you should do something
211more than just checking your module will compile.
212L<Test::Simple|Test::Simple> and L<Test::More|Test::More> are good
213places to start when writing a test suite.
2e1d04bc 214
12e02236 215=item Write the F<README>
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216
217If you're uploading to CPAN, the automated gremlins will extract the
218README file and place that in your CPAN directory. It'll also appear in
219the main F<by-module> and F<by-category> directories if you make it onto
220the modules list. It's a good idea to put here what the module actually
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221does in detail.
222
223=item Write F<Changes>
224
225Add any user-visible changes since the last release to your F<Changes>
226file.
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227
228=back
229
230=head2 Step-by-step: Distributing your module
231
232=over 3
233
234=item Get a CPAN user ID
235
4e9dada0 236Every developer publishing modules on CPAN needs a CPAN ID. Visit
4b05bc8e 237C<L<http://pause.perl.org/>>, select "Request PAUSE Account", and wait for
4e9dada0 238your request to be approved by the PAUSE administrators.
2e1d04bc 239
12e02236 240=item C<perl Makefile.PL; make test; make distcheck; make dist>
2e1d04bc 241
4e9dada0 242Once again, C<module-starter> or C<h2xs> has done all the work for you.
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243They produce the standard C<Makefile.PL> you see when you download and
244install modules, and this produces a Makefile with a C<dist> target.
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245
246Once you've ensured that your module passes its own tests - always a
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247good thing to make sure - you can C<make distcheck> to make sure
248everything looks OK, followed by C<make dist>, and the Makefile will
b1866b2d 249hopefully produce you a nice tarball of your module, ready for upload.
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250
251=item Upload the tarball
252
253The email you got when you received your CPAN ID will tell you how to
254log in to PAUSE, the Perl Authors Upload SErver. From the menus there,
255you can upload your module to CPAN.
256
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257Alternatively you can use the F<cpan-upload> script, part of the
258L<CPAN::Uploader> distribution on CPAN.
2e1d04bc 259
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260=item Fix bugs!
261
262Once you start accumulating users, they'll send you bug reports. If
263you're lucky, they'll even send you patches. Welcome to the joys of
264maintaining a software project...
265
266=back
267
268=head1 AUTHOR
269
270Simon Cozens, C<simon@cpan.org>
271
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272Updated by Kirrily "Skud" Robert, C<skud@cpan.org>
273
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274=head1 SEE ALSO
275
276L<perlmod>, L<perlmodlib>, L<perlmodinstall>, L<h2xs>, L<strict>,
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277L<Carp>, L<Exporter>, L<perlpod>, L<Test::Simple>, L<Test::More>
278L<ExtUtils::MakeMaker>, L<Module::Build>, L<Module::Starter>
4b05bc8e 279L<http://www.cpan.org/>, Ken Williams' tutorial on building your own
12e02236 280module at L<http://mathforum.org/~ken/perl_modules.html>