When looking at search.cpan.org one might notice that many of the modules have Unknown License. Actually most of those modules do have copyright and license information in some of its files but search.cpan.org takes this information from the META.yml file that comes with the module.
In modules uploaded many years ago there is no META.yml at all as this is a relatively new addition (a few years old). In addition ExtUtils::MakeMaker, the older one of the two major packaging systems of CPAN has not supported this field. Until recently.
I have just noticed when playing with ack that if you add the LICENSE field to your Makefile.PL and if you use a recent version of MakeMaker (I am using 6.42) then it will add the license field to META.yml.
That's great news as this will soon increase the number of modules that supply the license field. We just have to make sure module authors know about this.
Followup: Missing licenses on CPAN modules?
Published on 2008-03-24 by Gabor Szabo