That's what rvm is for. Leave the system Ruby alone and install your own, even multiple versions. I have ruby 1.8.7 with rails 2.3.5 and 1.9.2 with 3.0.3, easily switch between them for testing.

http://rvm.beginrescueend.com/

I have updated the script to ask you if you want to build Ruby from source or install RVM (Wayne from RVM pointed me in the right direction)

You're an idiot if you're not using rvm by now.

RVM is not beginner friendly because it has dependencies, it compiles stuff on your machine and there are dozens of problems waiting to happen because of that.

If wanting an easier way to install Rails for beginners makes me an idiot, then I'm proud of it ;)

I wouldn't say that rvm is not beginner friendly, but I grant that it has other requirements and compilation can break down due to specific library issues on different systems. To my mind, a better solution, however, would be a compromise: (1) write a script to automate the installation of all the prerequisites (packages and specific library versions) in one step using APT, but then (2) recommend using rvm after that.

Note that this solution also compiles stuff on your machine, and in this case it uses system-wide installation locations. One advantage of rvm is that everything is done as a regular user and sandboxed in $HOME/.rvm. Easy to find and remove, if anything goes wrong or you change your mind later.

(Edited because I misread the command line.)

And if you could elaborate on those "dozens of problems" then we would be most accepting. Broad, overarching statements aren't beginner friendly.