got an account with this free web host, found out that ruby was supported, so I was learning ruby last weekend.
when I was trying to write a cgi script using 'markaby', it worked fine on my dev box. here is the original script:

#!/usr/bin/ruby
require 'rubygems'
require 'markaby'
#the rest code

but when I tried it on the web host server, i kept getting "internal server error". the script has got exception handling in it, but it still didn't help
eventually, i figured out that the ruby gems on the web host server were installed under each user's home path, which means I need to explicitly include the path to it in my script.

#!/usr/bin/ruby
$:.push '/home/xxxxxxx/ruby/gems/gems/markaby-0.5/lib'
require 'rubygems'
require 'markaby'
#the rest code
unfortunately it still didn't work
finally, i noticed in 'cpanel' that installing 'markaby' also installed a dependency called 'builder'
and here is the final solution

#!/usr/bin/ruby
$:.push '/home/xxxxxxx/ruby/gems/gems/builder-2.1.2/lib'
$:.push '/home/xxxxxxx/ruby/gems/gems/markaby-0.5/lib'
require 'rubygems'
require 'markaby'
#the rest code