PERLNEWMOD(1) Perl Programmers Reference Guide PERLNEWMOD(1) #
PERLNEWMOD(1) Perl Programmers Reference Guide PERLNEWMOD(1)
NNAAMMEE #
perlnewmod - preparing a new module for distribution
DDEESSCCRRIIPPTTIIOONN #
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.
You should also take a look at perlmodstyle for best practices in making
a module.
WWaarrnniinngg 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.
WWhhaatt sshhoouulldd II mmaakkee iinnttoo aa mmoodduullee?? 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.
SStteepp--bbyy--sstteepp:: PPrreeppaarriinngg tthhee ggrroouunndd 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 <http://metacpan.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 asking
the "module-authors@perl.org" mailing list (send an email to
"module-authors-subscribe@perl.org" to subscribe; see
<https://lists.perl.org/list/module-authors.html> for more information
and a link to the archives).
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.
SStteepp--bbyy--sstteepp:: MMaakkiinngg tthhee mmoodduullee Start with _m_o_d_u_l_e_-_s_t_a_r_t_e_r or _h_2_x_s The _m_o_d_u_l_e_-_s_t_a_r_t_e_r 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,
_h_2_x_s 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/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 _R_E_A_D_M_E
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 _b_y_-_m_o_d_u_l_e and _b_y_-_c_a_t_e_g_o_r_y directories if you make it onto
the modules list. It's a good idea to put here what the module
actually does in detail.
Write _C_h_a_n_g_e_s
Add any user-visible changes since the last release to your _C_h_a_n_g_e_s
file.
SStteepp--bbyy--sstteepp:: DDiissttrriibbuuttiinngg yyoouurr mmoodduullee 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.
Make the tarball
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.
perl Makefile.PL && make test && make distcheck && make dist
Once you've ensured that your module passes its own tests - always a
good thing to make sure - you can "make distcheck" to make sure
everything looks OK, followed by "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.
Alternatively you can use the _c_p_a_n_-_u_p_l_o_a_d script, part of the
CPAN::Uploader distribution on CPAN.
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...
AAUUTTHHOORR #
Simon Cozens, "simon@cpan.org"
Updated by Kirrily "Skud" Robert, "skud@cpan.org"
SSEEEE AALLSSOO #
perlmod, perlmodlib, perlmodinstall, h2xs, strict, Carp, Exporter,
perlpod, Test::Simple, Test::More ExtUtils::MakeMaker, Module::Build,
Module::Starter <http://www.cpan.org/>
perl v5.36.3 2023-02-15 PERLNEWMOD(1)