rails c
Loading development environment (Rails 3.0.3)
ruby-1.9.2-p136 :001 > user = User.first
 => #<User ...snip...>
ruby-1.9.2-p136 :002 > user.password = "Password"
 => "Password"
ruby-1.9.2-p136 :003 > user.password_confirmation = "Password"
 => "Password"
ruby-1.9.2-p136 :004 > user.save!
 => true
ruby-1.9.2-p136 :005 > exit