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

       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 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 <> 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

   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

       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"

	  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 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"

       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

perl v5.12.2			  2010-09-05			 PERLNEWMOD(1)
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