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       perlnewmod - preparing a new module for distribution


       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.

       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

   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

       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
          <> 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 "". 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.

       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

       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"

          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 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/
              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

   Step-by-step: Distributing your module
       Get a CPAN user ID
          Every developer publishing modules on CPAN needs a CPAN ID.  Visit
          "", 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

       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...


       Simon Cozens, ""

       Updated by Kirrily "Skud" Robert, ""


       perlmod, perlmodlib, perlmodinstall, h2xs, strict, Carp, Exporter, perlpod, Test::Simple,
       Test::More ExtUtils::MakeMaker, Module::Build, Module::Starter , Ken
       Williams's tutorial on building your own module at