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   1  =head1 NAME
   2  
   3  perlnewmod - preparing a new module for distribution
   4  
   5  =head1 DESCRIPTION
   6  
   7  This document gives you some suggestions about how to go about writing
   8  Perl modules, preparing them for distribution, and making them available
   9  via CPAN.
  10  
  11  One of the things that makes Perl really powerful is the fact that Perl
  12  hackers tend to want to share the solutions to problems they've faced,
  13  so you and I don't have to battle with the same problem again.
  14  
  15  The main way they do this is by abstracting the solution into a Perl
  16  module. If you don't know what one of these is, the rest of this
  17  document isn't going to be much use to you. You're also missing out on
  18  an awful lot of useful code; consider having a look at L<perlmod>,
  19  L<perlmodlib> and L<perlmodinstall> before coming back here.
  20  
  21  When you've found that there isn't a module available for what you're
  22  trying to do, and you've had to write the code yourself, consider
  23  packaging up the solution into a module and uploading it to CPAN so that
  24  others can benefit.
  25  
  26  =head2 Warning
  27  
  28  We're going to primarily concentrate on Perl-only modules here, rather
  29  than XS modules. XS modules serve a rather different purpose, and
  30  you should consider different things before distributing them - the
  31  popularity of the library you are gluing, the portability to other
  32  operating systems, and so on. However, the notes on preparing the Perl
  33  side of the module and packaging and distributing it will apply equally
  34  well to an XS module as a pure-Perl one.
  35  
  36  =head2 What should I make into a module?
  37  
  38  You should make a module out of any code that you think is going to be
  39  useful to others. Anything that's likely to fill a hole in the communal
  40  library and which someone else can slot directly into their program. Any
  41  part of your code which you can isolate and extract and plug into
  42  something else is a likely candidate.
  43  
  44  Let's take an example. Suppose you're reading in data from a local
  45  format into a hash-of-hashes in Perl, turning that into a tree, walking
  46  the tree and then piping each node to an Acme Transmogrifier Server.
  47  
  48  Now, quite a few people have the Acme Transmogrifier, and you've had to
  49  write something to talk the protocol from scratch - you'd almost
  50  certainly want to make that into a module. The level at which you pitch
  51  it is up to you: you might want protocol-level modules analogous to
  52  L<Net::SMTP|Net::SMTP> which then talk to higher level modules analogous
  53  to L<Mail::Send|Mail::Send>. The choice is yours, but you do want to get
  54  a module out for that server protocol.
  55  
  56  Nobody else on the planet is going to talk your local data format, so we
  57  can ignore that. But what about the thing in the middle? Building tree
  58  structures from Perl variables and then traversing them is a nice,
  59  general problem, and if nobody's already written a module that does
  60  that, you might want to modularise that code too.
  61  
  62  So hopefully you've now got a few ideas about what's good to modularise.
  63  Let's now see how it's done.
  64  
  65  =head2 Step-by-step: Preparing the ground
  66  
  67  Before we even start scraping out the code, there are a few things we'll
  68  want to do in advance.
  69  
  70  =over 3
  71  
  72  =item Look around
  73  
  74  Dig into a bunch of modules to see how they're written. I'd suggest
  75  starting with L<Text::Tabs|Text::Tabs>, since it's in the standard
  76  library and is nice and simple, and then looking at something a little
  77  more complex like L<File::Copy|File::Copy>.  For object oriented
  78  code, C<WWW::Mechanize> or the C<Email::*> modules provide some good
  79  examples.
  80  
  81  These should give you an overall feel for how modules are laid out and
  82  written.
  83  
  84  =item Check it's new
  85  
  86  There are a lot of modules on CPAN, and it's easy to miss one that's
  87  similar to what you're planning on contributing. Have a good plough
  88  through the L<http://search.cpan.org> and make sure you're not the one
  89  reinventing the wheel!
  90  
  91  =item Discuss the need
  92  
  93  You might love it. You might feel that everyone else needs it. But there
  94  might not actually be any real demand for it out there. If you're unsure
  95  about the demand your module will have, consider sending out feelers
  96  on the C<comp.lang.perl.modules> newsgroup, or as a last resort, ask the
  97  modules list at C<modules@perl.org>. Remember that this is a closed list
  98  with a very long turn-around time - be prepared to wait a good while for
  99  a response from them.
 100  
 101  =item Choose a name
 102  
 103  Perl modules included on CPAN have a naming hierarchy you should try to
 104  fit in with. See L<perlmodlib> for more details on how this works, and
 105  browse around CPAN and the modules list to get a feel of it. At the very
 106  least, remember this: modules should be title capitalised, (This::Thing)
 107  fit in with a category, and explain their purpose succinctly.
 108  
 109  =item Check again
 110  
 111  While you're doing that, make really sure you haven't missed a module
 112  similar to the one you're about to write.
 113  
 114  When you've got your name sorted out and you're sure that your module is
 115  wanted and not currently available, it's time to start coding.
 116  
 117  =back
 118  
 119  =head2 Step-by-step: Making the module
 120  
 121  =over 3
 122  
 123  =item Start with F<module-starter> or F<h2xs>
 124  
 125  The F<module-starter> utility is distributed as part of the
 126  L<Module::Starter|Module::Starter> CPAN package.  It creates a directory
 127  with stubs of all the necessary files to start a new module, according
 128  to recent "best practice" for module development, and is invoked from
 129  the command line, thus:
 130  
 131      module-starter --module=Foo::Bar \
 132         --author="Your Name" --email=yourname@cpan.org
 133  
 134  If you do not wish to install the L<Module::Starter|Module::Starter>
 135  package from CPAN, F<h2xs> is an older tool, originally intended for the
 136  development of XS modules, which comes packaged with the Perl
 137  distribution. 
 138  
 139  A typical invocation of L<h2xs|h2xs> for a pure Perl module is:
 140  
 141      h2xs -AX --skip-exporter --use-new-tests -n Foo::Bar 
 142  
 143  The C<-A> omits the Autoloader code, C<-X> omits XS elements,
 144  C<--skip-exporter> omits the Exporter code, C<--use-new-tests> sets up a
 145  modern testing environment, and C<-n> specifies the name of the module.
 146  
 147  =item Use L<strict|strict> and L<warnings|warnings>
 148  
 149  A module's code has to be warning and strict-clean, since you can't
 150  guarantee the conditions that it'll be used under. Besides, you wouldn't
 151  want to distribute code that wasn't warning or strict-clean anyway,
 152  right?
 153  
 154  =item Use L<Carp|Carp>
 155  
 156  The L<Carp|Carp> module allows you to present your error messages from
 157  the caller's perspective; this gives you a way to signal a problem with
 158  the caller and not your module. For instance, if you say this:
 159  
 160      warn "No hostname given";
 161  
 162  the user will see something like this:
 163  
 164      No hostname given at /usr/local/lib/perl5/site_perl/5.6.0/Net/Acme.pm
 165      line 123.
 166  
 167  which looks like your module is doing something wrong. Instead, you want
 168  to put the blame on the user, and say this:
 169  
 170      No hostname given at bad_code, line 10.
 171  
 172  You do this by using L<Carp|Carp> and replacing your C<warn>s with
 173  C<carp>s. If you need to C<die>, say C<croak> instead. However, keep
 174  C<warn> and C<die> in place for your sanity checks - where it really is
 175  your module at fault.
 176  
 177  =item Use L<Exporter|Exporter> - wisely!
 178  
 179  L<Exporter|Exporter> gives you a standard way of exporting symbols and
 180  subroutines from your module into the caller's namespace. For instance,
 181  saying C<use Net::Acme qw(&frob)> would import the C<frob> subroutine.
 182  
 183  The package variable C<@EXPORT> will determine which symbols will get
 184  exported when the caller simply says C<use Net::Acme> - you will hardly
 185  ever want to put anything in there. C<@EXPORT_OK>, on the other hand,
 186  specifies which symbols you're willing to export. If you do want to
 187  export a bunch of symbols, use the C<%EXPORT_TAGS> and define a standard
 188  export set - look at L<Exporter> for more details.
 189  
 190  =item Use L<plain old documentation|perlpod>
 191  
 192  The work isn't over until the paperwork is done, and you're going to
 193  need to put in some time writing some documentation for your module.
 194  C<module-starter> or C<h2xs> will provide a stub for you to fill in; if
 195  you're not sure about the format, look at L<perlpod> for an
 196  introduction. Provide a good synopsis of how your module is used in
 197  code, a description, and then notes on the syntax and function of the
 198  individual subroutines or methods. Use Perl comments for developer notes
 199  and POD for end-user notes.
 200  
 201  =item Write tests
 202  
 203  You're encouraged to create self-tests for your module to ensure it's
 204  working as intended on the myriad platforms Perl supports; if you upload
 205  your module to CPAN, a host of testers will build your module and send
 206  you the results of the tests. Again, C<module-starter> and C<h2xs>
 207  provide a test framework which you can extend - you should do something
 208  more than just checking your module will compile.
 209  L<Test::Simple|Test::Simple> and L<Test::More|Test::More> are good
 210  places to start when writing a test suite.
 211  
 212  =item Write the README
 213  
 214  If you're uploading to CPAN, the automated gremlins will extract the
 215  README file and place that in your CPAN directory. It'll also appear in
 216  the main F<by-module> and F<by-category> directories if you make it onto
 217  the modules list. It's a good idea to put here what the module actually
 218  does in detail, and the user-visible changes since the last release.
 219  
 220  =back
 221  
 222  =head2 Step-by-step: Distributing your module
 223  
 224  =over 3
 225  
 226  =item Get a CPAN user ID
 227  
 228  Every developer publishing modules on CPAN needs a CPAN ID.  Visit
 229  C<http://pause.perl.org/>, select "Request PAUSE Account", and wait for
 230  your request to be approved by the PAUSE administrators.
 231  
 232  =item C<perl Makefile.PL; make test; make dist>
 233  
 234  Once again, C<module-starter> or C<h2xs> has done all the work for you.
 235  They produce the standard C<Makefile.PL> you see when you download and
 236  install modules, and this produces a Makefile with a C<dist> target.
 237  
 238  Once you've ensured that your module passes its own tests - always a
 239  good thing to make sure - you can C<make dist>, and the Makefile will
 240  hopefully produce you a nice tarball of your module, ready for upload.
 241  
 242  =item Upload the tarball
 243  
 244  The email you got when you received your CPAN ID will tell you how to
 245  log in to PAUSE, the Perl Authors Upload SErver. From the menus there,
 246  you can upload your module to CPAN.
 247  
 248  =item Announce to the modules list
 249  
 250  Once uploaded, it'll sit unnoticed in your author directory. If you want
 251  it connected to the rest of the CPAN, you'll need to go to "Register
 252  Namespace" on PAUSE.  Once registered, your module will appear in the
 253  by-module and by-category listings on CPAN.
 254  
 255  =item Announce to clpa
 256  
 257  If you have a burning desire to tell the world about your release, post
 258  an announcement to the moderated C<comp.lang.perl.announce> newsgroup.
 259  
 260  =item Fix bugs!
 261  
 262  Once you start accumulating users, they'll send you bug reports. If
 263  you're lucky, they'll even send you patches. Welcome to the joys of
 264  maintaining a software project...
 265  
 266  =back
 267  
 268  =head1 AUTHOR
 269  
 270  Simon Cozens, C<simon@cpan.org>
 271  
 272  Updated by Kirrily "Skud" Robert, C<skud@cpan.org>
 273  
 274  =head1 SEE ALSO
 275  
 276  L<perlmod>, L<perlmodlib>, L<perlmodinstall>, L<h2xs>, L<strict>,
 277  L<Carp>, L<Exporter>, L<perlpod>, L<Test::Simple>, L<Test::More>
 278  L<ExtUtils::MakeMaker>, L<Module::Build>, L<Module::Starter>
 279  http://www.cpan.org/ , Ken Williams' tutorial on building your own
 280  module at http://mathforum.org/~ken/perl_modules.html