Chapter 4

modules (as opposed to prerequisite modules that are required for your module to 

work) to provide advanced functionality. It wouldn't be appropriate to place such 

modules in PREREQ_PM since that will cause them to be installed by people who 

don't intend to use the advanced features. However, you might not want to be 

totally silent about the choice either.

An example of this situation can be found in the Net::FTPServer

17

 module. If 

the user installs the Archive::Zip

18

 module, then Net::FTPServer will enable FTP 

clients to request zipped versions of files. To alert users during installation to this 

option, Net::FTPServer includes code inside Makefile.PL that checks for Archive::Zip 

and prints a message if it's not found:

Checking for optional module Archive::Zip >= 0.11 ... not found.

*** Archive::Zip is missing. This module is required if you want to

enable archive mode, which allows users to create ZIP files on

the fly from directories on the server.

The code in Net::FTPServer's Makefile.PL then calls sleep(1) to give the user the 

chance to read this message before the usual flurry of make output continues. Some 

modules handle this situation by prompting the user, asking whether to continue 

without the optional module or abort the installation process. This ensures that 

users will read the message, but at the cost of breaking unattended installation. If 

you've ever had the experience of firing up a lengthy CPAN.pm installation, getting a 

cup of coffee, and coming back to find that the first module stopped the installation to 

ask a question, then you'll probably avoid this path!

Adding custom code in Makefile.PL works fine for checking module depen 

dencies, but if you need to modify the generated Makefile, then you'll need to 

extend ExtUtils::MakeMaker itself. ExtUtils::MakeMaker provides a simple way to 

do this: Just define subroutines in the MY package, and they'll be called automati 

cally instead of the normal ExtUtils::MakeMaker methods.

19

I ran into a situation like this while developing the Guile

20

 module. As you may 

have noticed earlier, the default make test implementation sets the PERL_DL_NONLAZY

environment variable when it runs the test scripts. For reasons best left unex 

plored, this setting makes testing the Guile module impossible; the underlying 

17. Available on CPAN, this module implements an FTP server (almost) entirely in Perl. It was 

written by Richard Jones, Rob Brown, Keith Turner, Azazel, and many others.

18. Written by Ned Konz and available on CPAN

19. This works because the MY package inherits from the MM package that ExtUtils::MakeMaker 

uses to abstract platform dependencies. See the ExtUtils::MakeMaker documentation for the 

details.

20. This module provides a Perl binding to the GNU Guile Scheme interpreter. It is available on 

CPAN.

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