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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 avail
       able 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 theyve faced,
       so you and I dont 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 dont know what one of these is, the rest of this docu
       ment isnt going to be much use to you. Youre also missing out on an
       awful lot of useful code; consider having a look at perlmod, perlmodlib
       and perlmodinstall before coming back here.

       When youve found that there isnt a module available for what youre
       trying to do, and youve had to write the code yourself, consider pack
       aging up the solution into a module and uploading it to CPAN so that
       others can benefit.


       Were 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 popu
       larity of the library you are gluing, the portability to other operat
       ing 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 thats 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.

       Lets take an example. Suppose youre reading in data from a local for
       mat 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 youve had to
       write something to talk the protocol from scratch - youd almost cer
       tainly 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 nobodys already written a module that does
       that, you might want to modularise that code too.

       So hopefully youve now got a few ideas about whats good to modu
       larise.	Lets now see how its done.

       Step-by-step: Preparing the ground

       Before we even start scraping out the code, there are a few things
       well want to do in advance.

       Look around
	  Dig into a bunch of modules to see how theyre written. Id suggest
	  starting with Text::Tabs, since its 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 its new
	  There are a lot of modules on CPAN, and its easy to miss one thats
	  similar to what youre planning on contributing. Have a good plough
	  through the  and make sure youre 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
	  youre unsure about the demand your module will have, consider send
	  ing 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 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 suc

       Check again
	  While youre doing that, make really sure you havent missed a mod
	  ule similar to the one youre about to write.

	  When youve got your name sorted out and youre sure that your mod
	  ule is wanted and not currently available, its time to start cod

       Step-by-step: Making the module

       Start with module-starter or h2xs
	  The module-starter utility is distributed as part of the Mod
	  ule::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

       Use strict and warnings
	  A modules code has to be warning and strict-clean, since you cant
	  guarantee the conditions that itll be used under. Besides, you
	  wouldnt want to distribute code that wasnt warning or strict-clean
	  anyway, right?

       Use Carp
	  The Carp module allows you to present your error messages from the
	  callers 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 mod
	  ule at fault.

       Use Exporter - wisely!
	  Exporter gives you a standard way of exporting symbols and subrou
	  tines from your module into the callers 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 youre 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 isnt over until the paperwork is done, and youre 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 youre not sure about the format, look at perlpod for an intro
	  duction. 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
	  Youre encouraged to create self-tests for your module to ensure
	  its 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, "mod
	  ule-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 youre uploading to CPAN, the automated gremlins will extract the
	  README file and place that in your CPAN directory. Itll also appear
	  in the main by-module and by-category directories if you make it
	  onto the modules list. Its 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
	  "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 down
	  load and install modules, and this produces a Makefile with a "dist"

	  Once youve 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, itll sit unnoticed in your author directory. If you
	  want it connected to the rest of the CPAN, youll 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, theyll send you bug reports. If
	  youre lucky, theyll even send you patches. Welcome to the joys of
	  maintaining a software project...

       Simon Cozens, "simon@cpan.org"

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

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

perl v5.8.8			  2008-04-25			 PERLNEWMOD(1)

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