how do i know if ruby is installed code example

Example 1: check all ruby version ubuntu

rvm list

rvm rubies
   ruby-1.9.1-p431 [ i386 ]
=* ruby-1.9.2-p320 [ i386 ]
# => - current
# =* - current && default
#  * - default

Example 2: check ruby version in windows

ruby --version