CPAN Module Distributions

An alternate method of packaging multiple modules within a distribution is to 

create a lib directory inside your distribution. Inside lib you then create the full 

module path for each included module. If this were done with HTML::Template::JIT, 

then the path to JIT.pm inside the module distribution would be 

lib/HTML/Template/JIT.pm. Note that you would have to modify 

Makefile.PL's VERSION_FROM and ABSTRACT_FROM to point to the new location of 

JIT.pm. Using lib provides a more flexible system since it allows a distribution to 

contain modules with different root names collected under a common tree.

Executable Scripts

Module distributions can contain more than just modules, they can also contain 

executable scripts. For example, the LWP

16

 module distribution contains a script 

called lwp download that uses the LWP modules to download files from the Web. 

When you install the LWP distributions on your system, this script and others are 

installed alongside Perl's executable scripts, usually somewhere in your PATH.

Including scripts with your modules can serve two useful purposes. First, they 

allow nonprogrammers to access the functionality of your module. Second, they 

can provide examples for programmers of how to use your module to accomplish 

a simple task.

By default ExtUtils::MakeMaker installs any file ending in .pl other than 

test.pl in the top level module directory as an executable script. See the 

ExtUtils::MakeMaker documentation for details and a description of the PM option 

to WriteMakeFile() that can be used to search for .pl files (and .pm files) in other 

locations.

Self Modifying Code

If you look at the LWP distribution, you'll see that the scripts aren't distributed as 

.pl but as .PL files. The reason for this is that they need to be processed before they 

can be installed on the user's machine. To see why this is necessary, consider the 

script file in Listing 4 10, count_args.pl, that counts its arguments. If this file were 

distributed as is with Data::Counter, it wouldn't work on many users' systems. 

This is because the first line contains the path to the perl executable. Since this 

path varies from system to system, count_args.pl would only work on other 

systems where perl is installed in /usr/bin.

16. LWP provides client and server modules for all manner of network communication. LWP was 

written by Martijn Koster and Gisle Aas and is available on CPAN.

11

117

7