thinks  everyone.this right way  is :
 sudo wget ftp.ruby-lang.org/pub/ruby/1.9/ruby-1.9.2-p0.tar.bz2
 sudo tar jxvf ruby-1.9.2-p0.tar.bz2
 cd /home/pt/ruby-1.9.2-p0
 sudo ./configure --prefix=/usr/local/ruby
 sudo make
 sudo make install
 sudo ln -s /usr/local/ruby/bin/ruby /usr/bin/ruby
 sudo ln -s /usr/local/ruby/bin/gem /usr/bin/gem
 sudo gedit /etc/environment

PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/ruby/bin"

-- 
Posted via http://www.ruby-forum.com/.