man > perlnewmod(1)

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

NAME
       perlnewmod - preparing a new module for distribution

DESCRIPTION
       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.

   Warning
       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 <https://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 AT perl.org"  mailing  list  (send  an
          email       to       "module-authors-subscribe AT 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.

   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" --email=yourname AT 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 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 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.

       Write Changes
          Add any user-visible changes since the last release to your Changes file.

   Step-by-step: Distributing your module
       Get a CPAN user ID
          Every   developer   publishing   modules   on   CPAN   needs    a    CPAN    ID.     Visit
          "<https://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 cpan-upload 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...

AUTHOR
       Simon Cozens, "simon AT cpan.org"

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

SEE ALSO
       perlmod, perlmodlib, perlmodinstall, h2xs, strict,  Carp,  Exporter,  perlpod,  Test::Simple,
       Test::More ExtUtils::MakeMaker, Module::Build, Module::Starter <https://www.cpan.org/>

perl v5.38.2                                 2026-06-12                                PERLNEWMOD(1)