I tend to install unix software on the mac the old school way by grabbing the tarball and building it. Well that was fun an all until I discovered that irb didn’t like to honor backspace. Turns out I needed to build and install readline.
curl -O ftp://ftp.cwru.edu/pub/bash/readline-6.1.tar.gz
curl -O ftp://ftp.ruby-lang.org/pub/ruby/1.8/ruby-1.8.7-p248.tar.gz
tar -zxvf readline-6.1.tar.gz
cd readline-6.1
./configure
make
sudo make install
cd ..
tar -zxvf ruby-1.8.7-p248.tar.gz
cd ruby-1.8.7-p248
./configure --with-readline-dir=/usr/local --enable-pthread
make
sudo make install
sudo make install-doc
ruby --version
# woohoo!