In this video you will learn how to publish and subscribe to a topic in ROS2 using the command line.

COMMANDS TO USE:

  • ros2 topic list
  • ros2 msg list
  • ros2 msg show std_msgs/String
  • ros2 topic pub /chatter std_msgs/String "data: Hello ROS Developers"
  • ros2 topic echo /chatter

RELATED ROS2 RESOURCES:

  • ROS2 Course for Beginners: Introduce you to the basic concepts that you need to know in order to start working with ROS2.
  • ROS Development Studio: Develop your first ROS2 project online (Ready online including Gazebo simulations + ros1_bridge)

The following steps take through the development as shown in the video:

  • Open ROS Development Studio and create a new project (use a suitable name for the project).
  • Activate the docker image for ROS2 by executing the following command in a SHELL
    $ docker run -it osrf/ros2:ardent-basic

 

  • The first command to know is ros2 topic list. This command is same as the rostopic list command in ros1.
  • The command for publishing a topic is ros2 topic pub. This command takes the topic name and message just like the rostopic pub command in ros1.
  • In ros2, we can use the command ros2 msg list to see all the supported message types

  • Now let’s see the usage with a String type message. We can see the structure of the String message with the following command
    $ ros2 msg show std_msgs/String

The output of this command will give us the information about the content of the message type String. To publish the message we will use the following command

$ ros2 topic pub /chatter std_msgs/String "data: Hello ROS Developers"

  • Once we execute the above command, a message will start publishing to the /chatter topic.

  • Next, we can check the published message by using ros2 topic echo command. This should show us the message on /chatter topic

    $ ros2 topic echo /chatter

The output of the above command should be the message that we encoded in the last command.

 

FEEDBACK:

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If you want to learn about other ROS topics, please let us know on the comments area and we will do a video about it.


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