Writing Perl Modules

Kevin Eye

Buffalo Perl Mongers

Why write modules?

• reusable
• namespaces
• modular
• testable

Installing modules

• search.cpan.org
• cpan install Some::Module
• compiling
• perl Makefile.PL
• man perlmodinstall
• etc.

Using modules

• include path
  • @INC
  • perl -V
  • use lib '/some/directory'
  • PERL5LIB
• perl -MSome::Module -le 'print $Some::Module::VERSION'

Packages and the symbol table

• scope
  • lexical (my operator)
  • dynamic (local operator)
  • global (symbol table)
• packages and the package operator

Including other code

• eval STRING
• do FILENAME
  • like eval, but loads from a file
  • searches @INC
• require FILENAME
  • like do
  • only runs each file once
• require MODULE
  • like require FILENAME
  • replaces :: with / in MODULE and adds .pm

Including other code

• use MODULE LIST
  • like require MODULE
  • runs at compile time
  • calls MODULE::import(LIST)
  • LIST is optional
  • just like
    BEGIN { require Module; import Module LIST; }
• no MODULE LIST
  • like use, but calls MODULE::unimport(LIST)

Tips for writing modules

• use strict
• use warnings
• use Exporter (for non OOP modules)
• use Carp

Tools for writing modules

• h2xs -AX --skip-exporter --use-new-tests -n Foo::Bar
• module-starter --module=Foo::Bar
• Makefile.PL
• POD (plain old documentation)
• tests
• XS
• Inline::C, etc.

More information

• man perlmod
• man perlmodlib
• man perlmodstyle
• man perlmodinstall
• man perlnewmod
• man perlboot (beginner OOP tutorial)
• man perltoot (OOP tutorial)
• man perlobj
• man perlpod
• man perlxstut
• man perlxs
• Inline