If you try to install the nokogiri gem on freebsd you may get the following error message:
libiconv is missing. please visit http://nokogiri.org/tutorials/installing_nokogiri.html for help with installing dependencies.
In that case it should suffice to use the following command to install the gem:
% gem install nokogiri -v 'DESIRED_VERSION' -- -with-iconv-lib=/usr/local/lib --with-iconv-include=/usr/local/include