Some import filters are implemented as Perl scripts. These scripts require a couple of Perl modules in order to run properly. Some of the modules are available at CPAN, the comprehensive Perl archive network, which allows you to search and download the modules by name. The refdb-specific modules are available as the refdb-perlmod package at the refdb project page.
MARC::Record (CPAN)
MARC::Charset (CPAN)
refdb-perlmod
XML::Parser (CPAN)
Text::Iconv (CPAN)
refdb-perlmod
Text::Iconv (CPAN)
refdb-perlmod
Note: The configure script tests for the existence of the required Perl modules. If your system lacks some of the required scripts, you'll get a warning, but you'll still be able to make and make install refdb. You can install the modules at a later time without rebuilding refdb. In any case, the missing modules will only affect the Perl import filters, but not the core functionality of refdb. That is, if you don't require the Perl scripts, you don't have to install the modules either.
refdb also provides some support for Perl programmers. The RefDBClient module, also available at the refdb project page, implements Perl classes to directly communicate with refdbd. This allows to write custom clients that access the refdb databases and use the whole functionality implemented in refdbd. The test.pl script shipped with the module gives a basic idea how to write a custom client. See also the chapter about this module in the programmer's manual.
Note: If you're not familiar with Perl modules, here's how almost all of them can be installed: After unpacking the archive, change into the top-level directory of the extracted module. First run perl Makefile.PL which will create a system-specific Makefile. Then run make, optionally followed by make test to check the functionality. Finally, run make install as root.