When you try to install ruby 1.9.2 by "rvm install 1.9.2", get the suck error "Error running 'make '". Just like this discussion.

Sovled this. You can try a solution on this discussion

curl -O ftp://ftp.gnu.org/gnu/readline/readline-6.1.tar.gz
tar xzvf readline-6.1.tar.gz
cd readline-6.1
./configure --prefix=/usr/local
make
sudo make install
cd ..
Remove the ruby: rvm remove 1.9.2

Install it again: rvm install 1.9.2


(You might need to add source it if local path is not in your directory: rvm install 1.9.1 -C --with-readline-dir=/usr/local/

Or reference from official site to install 'readline'. 
rvm pkg install readline
rvm remove 1.9.2
rvm install 1.9.2 --with-readline-dir=$rvm_path/usr

rvm_path

Got this line "Installing readline to /Users/hothero/.rvm/usr", when complete the readline installation. And you get the path!!

By the way, the guide of that installing rails 3