For those who are trying to install Ruby on Rails on Debian(in my case 3.1 STABLE), you will notice that your application will show a blank page and the following error on the WEBrick web server in dev/development.log:
MissingSourceFile (no such file to load -- irb): (...)You must install the following packages:
apt-get install ruby1.8-dev apt-get install irb apt-get install libncurses5-dev libreadline5-dev