perlnewmod(1)

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

241       Simon Cozens, "simon@cpan.org"
242
243       Updated by Kirrily "Skud" Robert, "skud@cpan.org"
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NAME

DESCRIPTION

AUTHOR

SEE ALSO