I need to write a subscribe to the cmd_vel for turtlebot

I need to write a subscribe to the cmd_vel topic, where am publishing to turtlebot the gazebo. So I want to return the speed turtlebot through the subscriber, not chei code examples for this case, I'm using an example of publisher where the directional control turtlebot in the gazebo. would be grateful for any help! ! I know I have 2 variables that the publisher would velocidada the angular and linear speed, but I need a topic that returns me the speed if not possible at least the subscriber's cmd_vel help me. Thank you