Inspecting parameters (:program:`ros2 param`) ============================================= ROS2 has a tool to interact with launch files called :program:`ros2 param`. We can obtain more information on it with .. code-block:: console ros2 param -h which returns .. code-block:: console :emphasize-lines: 11-15 usage: ros2 param [-h] Call `ros2 param -h` for more detailed usage. ... Various param related sub-commands options: -h, --help show this help message and exit Commands: delete Delete parameter describe Show descriptive information about declared parameters dump Show all of the parameters of a node in a YAML file format get Get parameter list Output a list of available parameters load Load parameter file for a node set Set parameter Call `ros2 param -h` for more detailed usage. As shown in the emphasized lines above, the :program:`ros2 param` tool has a large number of useful commands to interact with parameters. Launching the Node with parameters --------------------------------- .. hint:: If you left the Node running from the last section, just keep it that way and skip this. .. code-block:: console ros2 launch \ python_package_that_uses_parameters_and_launch_files \ peanut_butter_falcon_quote_publisher_launch.py List-up parameters with :program:`ros2 param list` -------------------------------------------------- .. hint:: Remember that :ref:`Grep best friend`. Similar to other ROS2 commands, we can get a list of currently loaded parameters with .. code-block:: console ros2 param list which returns a well organized list showing the parameters of each active Node .. code-block:: console /peanut_butter_falcon_quote_publisher_node: period philosopher_name quote topic_name use_sim_time Obtain parameters with :program:`ros2 param get` ----------------------------------------------- To obtain the value of a parameter, we can do as follows .. code-block:: console ros2 param get \ /peanut_butter_falcon_quote_publisher_node \ quote which will return the current value of the parameter, in this case, the initial value we set in the launch file .. code-block:: console String value is: Yeah, you're gonna die, it's a matter of time. That ain't the question. The question's, whether they're gonna have a good story to tell about you when you're gone Let's check the output of the Node ---------------------------------- .. hint:: If you left :program:`ros2 topic echo` running from the last section, just keep it that way and skip this. Before the next step, as we did in the past section, we do, **IN ANOTHER TERMINAL WINDOW** .. code-block:: console ros2 topic echo /truly_inspirational_quote Assign values to parameters with :program:`ros2 param set` ---------------------------------------------------------- For testing and regular usage, setting parameters from the command line is extremely helpful. Similar to how we are able to publish messages to topics using a ROS2 tool, we can set a parameter with the following syntax .. code-block:: console ros2 param set \ /peanut_butter_falcon_quote_publisher_node \ quote \ "You got a good-guy heart. You can't do shit about it, that's just who you are. You're a hero." If everything is correct, we'll get .. code-block:: console Set parameter successful .. important:: Some errors are easy to debug, such as when we get the name of the Node wrong .. code-block:: console Node not found but because of the interaction between the :program:`terminal`, :program:`ros2 param` itself, and the syntax of the services, its easy to find cryptic error messages. At first, always suppose that there's a typo somewhere. Changing parameters is not instantaneous and, after the change becomes visible in the Node, our Node might have to loop once before it updates itself. We will be able to see that change as follows in the terminal window running :program:`ros2 topic echo` .. code-block:: console id: 2220 quote: Yeah, you're gonna die, it's a matter of time. That ain't the question. The question's, whether they're gonna have a good story ... philosopher_name: Tyler --- id: 2221 quote: You got a good-guy heart. You can't do shit about it, that's just who you are. You're a hero. philosopher_name: Tyler --- id: 2222 quote: You got a good-guy heart. You can't do shit about it, that's just who you are. You're a hero. philosopher_name: Tyler --- id: 2223 quote: You got a good-guy heart. You can't do shit about it, that's just who you are. You're a hero. philosopher_name: Tyler --- id: 2224 quote: You got a good-guy heart. You can't do shit about it, that's just who you are. You're a hero. philosopher_name: Tyler Save parameters to a file with :program:`ros2 param dump` --------------------------------------------------------- Words are sometimes little happy accidents. This usage of the word dump has no relation whatsoever to, for example, `Peter got dumped by Sarah and went to Hawaii `_. Dump files are usually related to `crashes and unresponsive programs `_, so this name puzzles me since ROS: the first. While we wait for someone to come and correct me on my claims above, just think about this as a weird name for :program:`ros2 param print_to_screen_as_yaml`. It prints the parameters in the terminal with a YAML file format. It is nice because it gives a bit more info than :program:`ros2 param list`, but not so useful as-is. The trick is that we can put all that nicely formatted content into a file with .. code-block:: console :emphasize-lines: 3 cd ~/ros2_tutorial_workspace/src ros2 param dump \ /peanut_butter_falcon_quote_publisher_node \ > peanut_butter_falcon_quote_publisher_node.yaml where we are using the :code:`>` (see :ref:`Bash redirections`) to overwrite the contents of the :file:`peanut_butter_falcon_quote_publisher_node.yaml` file with the output of :program:`ros2 param dump`, so be careful not to overwrite your precious files by mistake. We can inspect the contents of the file with .. code-block:: console cat peanut_butter_falcon_quote_publisher_node.yaml which outputs .. code-block:: console /peanut_butter_falcon_quote_publisher_node: ros__parameters: period: 0.25 philosopher_name: Tyler quote: Yeah, you're gonna die, it's a matter of time. That ain't the question. The question's, whether they're gonna have a good story to tell about you when you're gone topic_name: truly_inspirational_quote use_sim_time: false Load parameters from a file with :program:`ros2 param load` ----------------------------------------------------------- .. warning:: To proceed, end the ``peanut_butter_falcon_quote_publisher_node`` Node with :kbd:`CTRL+C`. As in the prior step, suppose that we have a file :file:`peanut_butter_falcon_quote_publisher_node.yaml` with the parameters we love the most. What we can do with :program:`ros2 param load` is load that file. Nicely predictable and understandable naming convention. We can start the Node with the launch file .. code-block:: console ros2 launch python_package_that_uses_parameters_and_launch_files \ peanut_butter_falcon_quote_publisher_launch.py which, at the beginning, will have the parameters set in the :file:`_launch.py`. We can then .. code-block:: console :emphasize-lines: 3 cd ~/ros2_tutorial_workspace/src ros2 param load \ /peanut_butter_falcon_quote_publisher_node \ peanut_butter_falcon_quote_publisher_node.yaml which will return .. code-block:: console Set parameter period successful Set parameter philosopher_name successful Set parameter quote successful Set parameter topic_name successful Set parameter use_sim_time successful indicating that all parameters defined in the :abbr:`YAML (YAML Ain't Markup Language)` were successfully loaded.