Chapter 4

Listing 4 3. Makefile.PL Generated by h2xs

use ExtUtils::MakeMaker;

# See lib/ExtUtils/MakeMaker.pm for details of how to influence

# the contents of the Makefile that is written.

WriteMakefile(

     NAME              =>  Data::Counter ,

     VERSION_FROM      =>  Counter.pm , # finds $VERSION

     PREREQ_PM         => {}, # e.g., Module::Name => 1.1

    ($] >= 5.005 ?    ## Add these new keywords supported since 5.005

      (ABSTRACT_FROM   =>  Counter.pm , # retrieve abstract from modul

       AUTHOR          =>  A. U. Thor  ) : ()),

);

WriteMakefile() employs the named parameter style discussed in Chapter 3 

using the parameters NAME, VERSION_FROM, PREREQ_PM, ABSTRACT_FROM, and AUTHOR. The 

first parameter, NAME, is the name of your module. The second parameter here is 

VERSION_FROM, which tells ExtUtils::MakeMaker where to look for the $VERSION

setting. This is necessary because a module distribution may have more than one 

module. I will discuss multimodule distributions in depth later in the chapter.

The next parameter, PREREQ_PM, is initially empty, but is important enough that 

h2xs includes it as a reminder. PREREQ_PM specifies your module's dependencies. By 

including information on which other modules your module uses, you allow 

the CPAN module to do its job much better. For example, if Data::Counter uses 

CGI::Application, I would change the PREREQ_PM line to read as follows:

 PREREQ_PM  => {  CGI::Application  => 0 },

The keys of the PREREQ_PM hash are module names, and the values are version num 

bers. By specifying a version number of zero, I'm telling ExtUtils::MakeMaker that 

I need some version of CGI::Application installed, but I don't care which one. To 

specify that I need at least version 1.3 installed, I would use this setting:

 PREREQ_PM  => {  CGI::Application  => 1.3 },

Now when a user tries to install Data::Counter using the CPAN module, 

CGI::Application will be automatically installed. Using PREREQ_PM prevents users 

from discovering a dependency when they try to use the module by advising them 

when the module is installed. This ensures that the system is not cluttered with 

half working code.

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