To embed Ruby code in your HTML documents (much like PHP or ASP), you can use eRuby. Installation of the software can be done manually by downloading the .tar.gz file from modruby.net or by using Subversion.

After it’s installed, you’ll need to edit your domain’s vhost.conf file in /var/www/vhosts/yourdomain/conf/ and put some information in there that tells the server how to interpret and process the Ruby code. The documentation for this can be found on the modruby.net site at http://wiki.modruby.net/en/?InstallGuide

Don’t forget to run the reconfigurator and restart Apache for the change (default location for reconfigurator is /usr/local/psa/admin/sbin/websrvmng).