[step0] build mruby

% git clone git://github.com/takeru/mruby.git --branch examples
% cd mruby
% make

% ls bin
mrbc  mruby  mrubysample

% ls lib
ritevm.a

% ./bin/mruby -e 'puts "Hello"; puts 1+2+3'
Hello
6

% cd examples

let's go to step1