Страницы справочника OS X

Эта страница руководства для  версии 10.9 Mac OS X

Читать страницы руководства

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



NAME
       perlnewmod - preparing a new module for distribution

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 perlmod, perlmodlib and 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.

   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 themthe
       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.

   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 Net::SMTP which then
       talk to higher level modules analogous to 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.

   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.

       Look around
          Dig into a bunch of modules to see how they're written. I'd suggest starting with Text::Tabs,
          since it's in the standard library and is nice and simple, and then looking at something a little
          more complex like File::Copy.  For object oriented code, "WWW::Mechanize" or the "Email::*"
          modules provide some good examples.

          These should give you an overall feel for how modules are laid out and written.

       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 <http://search.cpan.org> and make sure
          you're not the one reinventing the wheel!

       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 "comp.lang.perl.modules" newsgroup, or as a last resort, ask the
          modules list at "modules@perl.org". Remember that this is a closed list with a very long turn-around turnaround
          around time - be prepared to wait a good while for a response from them.

       Choose a name
          Perl modules included on CPAN have a naming hierarchy you should try to fit in with. See
          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.

       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.

   Step-by-step: Making the module
       Start with module-starter or h2xs
          The module-starter utility is distributed as part of the 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 Module::Starter package from CPAN, h2xs is an older tool,
          originally intended for the development of XS modules, which comes packaged with the Perl
          distribution.

          A typical invocation of h2xs for a pure Perl module is:

              h2xs -AX --skip-exporter --use-new-tests -n Foo::Bar

          The "-A" omits the Autoloader code, "-X" omits XS elements, "--skip-exporter" omits the Exporter
          code, "--use-new-tests" sets up a modern testing environment, and "-n" specifies the name of the
          module.

       Use strict and 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 strictclean
          clean anyway, right?

       Use Carp
          The 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 Carp and replacing your "warn"s with "carp"s. If you need to "die", say
          "croak" instead. However, keep "warn" and "die" in place for your sanity checks - where it really
          is your module at fault.

       Use Exporter - wisely!
          Exporter gives you a standard way of exporting symbols and subroutines from your module into the
          caller's namespace. For instance, saying "use Net::Acme qw(&frob)" would import the "frob"
          subroutine.

          The package variable @EXPORT will determine which symbols will get exported when the caller simply
          says "use Net::Acme" - you will hardly ever want to put anything in there. @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 %EXPORT_TAGS and define a standard export set - look at Exporter for more
          details.

       Use plain old documentation
          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.  "module-starter" or "h2xs" will provide a stub for
          you to fill in; if you're not sure about the format, look at 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.

       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, "module-starter" and "h2xs" provide a
          test framework which you can extend - you should do something more than just checking your module
          will compile.  Test::Simple and Test::More are good places to start when writing a test suite.

       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 by-module and 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.

   Step-by-step: Distributing your module
       Get a CPAN user ID
          Every developer publishing modules on CPAN needs a CPAN ID.  Visit "http://pause.perl.org/",
          select "Request PAUSE Account", and wait for your request to be approved by the PAUSE
          administrators.

       "perl Makefile.PL; make test; make dist"
          Once again, "module-starter" or "h2xs" has done all the work for you.  They produce the standard
          "Makefile.PL" you see when you download and install modules, and this produces a Makefile with a
          "dist" target.

          Once you've ensured that your module passes its own tests - always a good thing to make sure - you
          can "make dist", and the Makefile will hopefully produce you a nice tarball of your module, ready
          for upload.

       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.

       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.

       Announce to clpa
          If you have a burning desire to tell the world about your release, post an announcement to the
          moderated "comp.lang.perl.announce" newsgroup.

       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...

AUTHOR
       Simon Cozens, "simon@cpan.org"

       Updated by Kirrily "Skud" Robert, "skud@cpan.org"

SEE ALSO
       perlmod, perlmodlib, perlmodinstall, h2xs, strict, Carp, Exporter, perlpod, Test::Simple, Test::More
       ExtUtils::MakeMaker, Module::Build, Module::Starter http://www.cpan.org/ , Ken Williams's tutorial on
       building your own module at http://mathforum.org/~ken/perl_modules.html



perl v5.16.2                                     2012-08-26                                    PERLNEWMOD(1)