| =head1 NAME |
| |
| perlnewmod - preparing a new module for distribution |
| |
| =head1 DESCRIPTION |
| |
| This document gives you some suggestions about how to go about writing |
| Perl modules, preparing them for distribution, and making them available |
| via CPAN. |
| |
| One of the things that makes Perl really powerful is the fact that Perl |
| hackers tend to want to share the solutions to problems they've faced, |
| so you and I don't have to battle with the same problem again. |
| |
| The main way they do this is by abstracting the solution into a Perl |
| module. If you don't know what one of these is, the rest of this |
| document isn't going to be much use to you. You're also missing out on |
| an awful lot of useful code; consider having a look at L<perlmod>, |
| L<perlmodlib> and L<perlmodinstall> before coming back here. |
| |
| When you've found that there isn't a module available for what you're |
| trying to do, and you've had to write the code yourself, consider |
| packaging up the solution into a module and uploading it to CPAN so that |
| others can benefit. |
| |
| =head2 Warning |
| |
| We're going to primarily concentrate on Perl-only modules here, rather |
| than XS modules. XS modules serve a rather different purpose, and |
| you should consider different things before distributing them - the |
| popularity of the library you are gluing, the portability to other |
| operating systems, and so on. However, the notes on preparing the Perl |
| side of the module and packaging and distributing it will apply equally |
| well to an XS module as a pure-Perl one. |
| |
| =head2 What should I make into a module? |
| |
| You should make a module out of any code that you think is going to be |
| useful to others. Anything that's likely to fill a hole in the communal |
| library and which someone else can slot directly into their program. Any |
| part of your code which you can isolate and extract and plug into |
| something else is a likely candidate. |
| |
| Let's take an example. Suppose you're reading in data from a local |
| format into a hash-of-hashes in Perl, turning that into a tree, walking |
| the tree and then piping each node to an Acme Transmogrifier Server. |
| |
| Now, quite a few people have the Acme Transmogrifier, and you've had to |
| write something to talk the protocol from scratch - you'd almost |
| certainly want to make that into a module. The level at which you pitch |
| it is up to you: you might want protocol-level modules analogous to |
| L<Net::SMTP|Net::SMTP> which then talk to higher level modules analogous |
| to L<Mail::Send|Mail::Send>. The choice is yours, but you do want to get |
| a module out for that server protocol. |
| |
| Nobody else on the planet is going to talk your local data format, so we |
| can ignore that. But what about the thing in the middle? Building tree |
| structures from Perl variables and then traversing them is a nice, |
| general problem, and if nobody's already written a module that does |
| that, you might want to modularise that code too. |
| |
| So hopefully you've now got a few ideas about what's good to modularise. |
| Let's now see how it's done. |
| |
| =head2 Step-by-step: Preparing the ground |
| |
| Before we even start scraping out the code, there are a few things we'll |
| want to do in advance. |
| |
| =over 3 |
| |
| =item Look around |
| |
| Dig into a bunch of modules to see how they're written. I'd suggest |
| starting with L<Text::Tabs|Text::Tabs>, since it's in the standard |
| library and is nice and simple, and then looking at something a little |
| more complex like L<File::Copy|File::Copy>. For object oriented |
| code, C<WWW::Mechanize> or the C<Email::*> modules provide some good |
| examples. |
| |
| These should give you an overall feel for how modules are laid out and |
| written. |
| |
| =item Check it's new |
| |
| There are a lot of modules on CPAN, and it's easy to miss one that's |
| similar to what you're planning on contributing. Have a good plough |
| through the L<http://search.cpan.org> and make sure you're not the one |
| reinventing the wheel! |
| |
| =item Discuss the need |
| |
| You might love it. You might feel that everyone else needs it. But there |
| might not actually be any real demand for it out there. If you're unsure |
| about the demand your module will have, consider sending out feelers |
| on the C<comp.lang.perl.modules> newsgroup, or as a last resort, ask the |
| modules list at C<modules@perl.org>. Remember that this is a closed list |
| with a very long turn-around time - be prepared to wait a good while for |
| a response from them. |
| |
| =item Choose a name |
| |
| Perl modules included on CPAN have a naming hierarchy you should try to |
| fit in with. See L<perlmodlib> for more details on how this works, and |
| browse around CPAN and the modules list to get a feel of it. At the very |
| least, remember this: modules should be title capitalised, (This::Thing) |
| fit in with a category, and explain their purpose succinctly. |
| |
| =item Check again |
| |
| While you're doing that, make really sure you haven't missed a module |
| similar to the one you're about to write. |
| |
| When you've got your name sorted out and you're sure that your module is |
| wanted and not currently available, it's time to start coding. |
| |
| =back |
| |
| =head2 Step-by-step: Making the module |
| |
| =over 3 |
| |
| =item Start with F<module-starter> or F<h2xs> |
| |
| The F<module-starter> utility is distributed as part of the |
| L<Module::Starter|Module::Starter> CPAN package. It creates a directory |
| with stubs of all the necessary files to start a new module, according |
| to recent "best practice" for module development, and is invoked from |
| the command line, thus: |
| |
| module-starter --module=Foo::Bar \ |
| --author="Your Name" --email=yourname@cpan.org |
| |
| If you do not wish to install the L<Module::Starter|Module::Starter> |
| package from CPAN, F<h2xs> is an older tool, originally intended for the |
| development of XS modules, which comes packaged with the Perl |
| distribution. |
| |
| A typical invocation of L<h2xs|h2xs> for a pure Perl module is: |
| |
| h2xs -AX --skip-exporter --use-new-tests -n Foo::Bar |
| |
| The C<-A> omits the Autoloader code, C<-X> omits XS elements, |
| C<--skip-exporter> omits the Exporter code, C<--use-new-tests> sets up a |
| modern testing environment, and C<-n> specifies the name of the module. |
| |
| =item Use L<strict|strict> and L<warnings|warnings> |
| |
| A module's code has to be warning and strict-clean, since you can't |
| guarantee the conditions that it'll be used under. Besides, you wouldn't |
| want to distribute code that wasn't warning or strict-clean anyway, |
| right? |
| |
| =item Use L<Carp|Carp> |
| |
| The L<Carp|Carp> module allows you to present your error messages from |
| the caller's perspective; this gives you a way to signal a problem with |
| the caller and not your module. For instance, if you say this: |
| |
| warn "No hostname given"; |
| |
| the user will see something like this: |
| |
| No hostname given at /usr/local/lib/perl5/site_perl/5.6.0/Net/Acme.pm |
| line 123. |
| |
| which looks like your module is doing something wrong. Instead, you want |
| to put the blame on the user, and say this: |
| |
| No hostname given at bad_code, line 10. |
| |
| You do this by using L<Carp|Carp> and replacing your C<warn>s with |
| C<carp>s. If you need to C<die>, say C<croak> instead. However, keep |
| C<warn> and C<die> in place for your sanity checks - where it really is |
| your module at fault. |
| |
| =item Use L<Exporter|Exporter> - wisely! |
| |
| L<Exporter|Exporter> gives you a standard way of exporting symbols and |
| subroutines from your module into the caller's namespace. For instance, |
| saying C<use Net::Acme qw(&frob)> would import the C<frob> subroutine. |
| |
| The package variable C<@EXPORT> will determine which symbols will get |
| exported when the caller simply says C<use Net::Acme> - you will hardly |
| ever want to put anything in there. C<@EXPORT_OK>, on the other hand, |
| specifies which symbols you're willing to export. If you do want to |
| export a bunch of symbols, use the C<%EXPORT_TAGS> and define a standard |
| export set - look at L<Exporter> for more details. |
| |
| =item Use L<plain old documentation|perlpod> |
| |
| The work isn't over until the paperwork is done, and you're going to |
| need to put in some time writing some documentation for your module. |
| C<module-starter> or C<h2xs> will provide a stub for you to fill in; if |
| you're not sure about the format, look at L<perlpod> for an |
| introduction. Provide a good synopsis of how your module is used in |
| code, a description, and then notes on the syntax and function of the |
| individual subroutines or methods. Use Perl comments for developer notes |
| and POD for end-user notes. |
| |
| =item Write tests |
| |
| You're encouraged to create self-tests for your module to ensure it's |
| working as intended on the myriad platforms Perl supports; if you upload |
| your module to CPAN, a host of testers will build your module and send |
| you the results of the tests. Again, C<module-starter> and C<h2xs> |
| provide a test framework which you can extend - you should do something |
| more than just checking your module will compile. |
| L<Test::Simple|Test::Simple> and L<Test::More|Test::More> are good |
| places to start when writing a test suite. |
| |
| =item Write the README |
| |
| If you're uploading to CPAN, the automated gremlins will extract the |
| README file and place that in your CPAN directory. It'll also appear in |
| the main F<by-module> and F<by-category> directories if you make it onto |
| the modules list. It's a good idea to put here what the module actually |
| does in detail, and the user-visible changes since the last release. |
| |
| =back |
| |
| =head2 Step-by-step: Distributing your module |
| |
| =over 3 |
| |
| =item Get a CPAN user ID |
| |
| Every developer publishing modules on CPAN needs a CPAN ID. Visit |
| C<http://pause.perl.org/>, select "Request PAUSE Account", and wait for |
| your request to be approved by the PAUSE administrators. |
| |
| =item C<perl Makefile.PL; make test; make dist> |
| |
| Once again, C<module-starter> or C<h2xs> has done all the work for you. |
| They produce the standard C<Makefile.PL> you see when you download and |
| install modules, and this produces a Makefile with a C<dist> target. |
| |
| Once you've ensured that your module passes its own tests - always a |
| good thing to make sure - you can C<make dist>, and the Makefile will |
| hopefully produce you a nice tarball of your module, ready for upload. |
| |
| =item Upload the tarball |
| |
| The email you got when you received your CPAN ID will tell you how to |
| log in to PAUSE, the Perl Authors Upload SErver. From the menus there, |
| you can upload your module to CPAN. |
| |
| =item Announce to the modules list |
| |
| Once uploaded, it'll sit unnoticed in your author directory. If you want |
| it connected to the rest of the CPAN, you'll need to go to "Register |
| Namespace" on PAUSE. Once registered, your module will appear in the |
| by-module and by-category listings on CPAN. |
| |
| =item Announce to clpa |
| |
| If you have a burning desire to tell the world about your release, post |
| an announcement to the moderated C<comp.lang.perl.announce> newsgroup. |
| |
| =item Fix bugs! |
| |
| Once you start accumulating users, they'll send you bug reports. If |
| you're lucky, they'll even send you patches. Welcome to the joys of |
| maintaining a software project... |
| |
| =back |
| |
| =head1 AUTHOR |
| |
| Simon Cozens, C<simon@cpan.org> |
| |
| Updated by Kirrily "Skud" Robert, C<skud@cpan.org> |
| |
| =head1 SEE ALSO |
| |
| L<perlmod>, L<perlmodlib>, L<perlmodinstall>, L<h2xs>, L<strict>, |
| L<Carp>, L<Exporter>, L<perlpod>, L<Test::Simple>, L<Test::More> |
| L<ExtUtils::MakeMaker>, L<Module::Build>, L<Module::Starter> |
| http://www.cpan.org/ , Ken Williams's tutorial on building your own |
| module at http://mathforum.org/~ken/perl_modules.html |