Nokia-N900:~# apt-get install ruby1.8
Reading package lists... Done
Building dependency tree       
Reading state information... Done
ruby1.8 is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 23 not upgraded.
Nokia-N900:~# cd /home/opt/rubygems-1.8.10/
Nokia-N900:/home/opt/rubygems-1.8.10# ruby1.8 setup.rb
-sh: ruby1.8: not found