Fixing readline for the Ruby on Rails console

I have begun trying out the Ruby on Rails framework. While doing so I got stuck at a very early stage in the documentation.

$ rails console
/home/tobias/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/irb/completion.rb:9:in `require': no such file to load -- readline (LoadError)
from /home/tobias/.rvm/rubies/ruby-1.9.2-p18080/lib/ruby/1.9.1/irb/completion.rb:9:in `<top (required)>'
from /home/tobias/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.9/lib/rails/commands/console.rb:3:in `require'
from /home/tobias/.rvm/gems/ruby-1.9.2-p180/gemsems/railties-3.0.9/lib/rails/commands/console.rb:3:in `<top (required)>'
from /home/tobias/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.9/lib/rails/commands.commandsrb:20:in `require'
from /home/tobias/.rvm/gems/ruby-1.9.2-p180/gems/railsilties-3.0.9/lib/rails/commands.rb:20:in `<top (required)>'
from scriptt/rails:6:in `require'
from script/rails:6:in `<main>'

The problem is that Ruby is somehow not cofigured to load the readline library and thus cannot run its console. This is a downside of using a language specific package manager, seperate from your operating system’s package manager.

However it is easy to fix and after some searching I found a blog post detailing exactly how to solve it.

First you need to install libreadline5 and libncurses5. I can’t see why ncurses would be needed, but I am too lazy to uninstall it and check if it still works without the library. Using Apt on Ubuntu/Debian:

$ sudo apt-get install libreadline5-dev libncurses5-dev

Next you want to go configure and rebuild Ruby’s readline extension. I am using RVM and so Ruby exists in ~/.rvm/src/ruby-1.9.2-p180/ for me. This can differ for you but running which ruby should tell you where yours is.

cd ~/.rvm/src/ruby-1.9.2-p180/ext/readline
ruby extconf.rb
make install

Depending on your setup you might need to install it by running sudo make install instead.

That is it! Now Ruby on Rails’ console should load as intended.