Install Ruby 1.9 on Ubuntu

Prerequire:
$ sudo apt-get install build-essential

Download Ruby 1.9:
$ wget ftp://ftp.ruby-lang.org/pub/ruby/1.9/ruby-1.9.0-0.tar.gz

Compile & install:
$ mkdir ~/ruby1.9
$ tar xzvf ruby-1.9.0-0.tar.gz
$ cd ruby-1.9.0-0/
$ ./configure --prefix=/home/mama/ruby1.9/
$ make
$ make install

Try it:
$ PATH=/home/mama/ruby1.9/bin:$PATH
$ irb

irb(main):001:0> RUBY_VERSION
=> "1.9.0"
irb(main):002:0> RUBY_RELEASE_DATE
=> "2007-12-25"