It has been surprisingly difficult to find an answer for this.
I had ruby v1.9.1 installed (/usr/bin/ruby1.9.1), but after I then installed rubygems, it also installed ruby1.8 (/usr/bin/ruby1.8), and all the commands I run on gem (gem install ..., rails ...) are all using ruby v1.8.
~/proj/rails/demo# bundle show sqlite3 /var/lib/gems/1.8/gems/sqlite3-1.3.4
How do I get rubygems and rails to use the v1.9.1 which I have installed, instead of v1.8?
(side note: I did install rvm using "gem install rvm", but after I did that, I am not able to execute rvm, what's up with that?)