1PERLNEWMOD(1)          Perl Programmers Reference Guide          PERLNEWMOD(1)
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NAME

6       perlnewmod - preparing a new module for distribution
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DESCRIPTION

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

242       Simon Cozens, "simon@cpan.org"
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244       Updated by Kirrily "Skud" Robert, "skud@cpan.org"
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SEE ALSO

247       perlmod, perlmodlib, perlmodinstall, h2xs, strict, Carp, Exporter,
248       perlpod, Test::Simple, Test::More ExtUtils::MakeMaker, Module::Build,
249       Module::Starter http://www.cpan.org/ , Ken Williams' tutorial on
250       building your own module at http://mathforum.org/~ken/perl_modules.html
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254perl v5.10.1                      2009-02-12                     PERLNEWMOD(1)
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