13.5 Controlling the Distribution with Makefile.PL

The Perl developers have chosen to rely on the standard Unix make utility to build and install Perl itself, and that same mechanism is used for additional modules.^[9] If you have a non-Unix system, a make-like utility should also be available. On Windows, for example, you may have dmake or another program. The command perl -V:make will tell you the name of your make utility program; if it says make='nmake', simply use nmake wherever you use make. In any case, you should call the controlling file a Makefile, even though its name may vary as well.

^[9] The Module::Build module currently in development may replace all of that some day but is only in a pre-release form at the time of this writing.

However, crafting a Makefile is tricky but repetitive. And what better way to accomplish a tricky but repetitive task than with a program? Since you're talking about Perl add-on modules, you know that Perl is available, so how about a Perl program to generate the Makefile?

That's exactly what happens. The distribution is required to contain a Makefile.PL, which is a Perl program to build a Makefile. Then from there, you use make (or something like it) to control all of the remaining tasks.

The h2xs tool generates a template Makefile.PL that you probably won't even need to touch for single-module distributions:

$ cat Makefile.PL
use 5.008;
use ExtUtils::MakeMaker;
# See lib/ExtUtils/MakeMaker.pm for details of how to influence
# the contents of the Makefile that is written.
WriteMakefile(
    'NAME'                => 'Island::Plotting::Maps',
    'VERSION_FROM'        => 'Maps.pm', # finds $VERSION
    'PREREQ_PM'                => {  }, # e.g., Module::Name => 1.1
    ($] >= 5.005 ?    ## Add these new keywords supported since 5.005
      (ABSTRACT_FROM => 'Maps.pm', # retrieve abstract from module
       AUTHOR     => 'Ginger Grant <[email protected]>') : (  )),
);

Yes, this is a Perl program. The WriteMakefile routine is defined by the ExtUtils::MakeMaker module (included with Perl) to generate a Makefile. As the developer of the module, use this makefile to build and test your module and prepare a distribution file:

$ perl Makefile.PL
Checking if your kit is complete...
Looks good
Writing Makefile for Island::Plotting::Maps

The ultimate user of your distribution will execute the identical command at their site. However, the Makefile will most likely be different, reflecting the differences in installation locations, local policies, and even the C compiler and linking instructions appropriate for their architecture. It's a nice system that has worked quite well over the years.

The creation of the Makefile.PL (and resulting Makefile) is quite flexible. For example, you can run code to ask the person installing your module about the locations of other installed libraries or tools, or get options for variations in activity.^[10]

^[10] Please keep the number of questions to a minimum, however. Most people are irritated when asked a series of questions, especially when they are just upgrading your module. If possible, store the answers in a configuration module that you install so that a later invocation of your installer can pull the previous answers as defaults.

The PREREQ_PM setting is important if your module depends on non-core Perl modules, especially if you plan to upload your code to the CPAN. Proper use of the prerequisites list can make installing your module nearly painless, and your user community will thank you.