return raw parameter content without type information

[christian-rauch]

Feature request

Feature description

ros2 param get needs an option to return the raw content of a parameter. Currently, it prepends the parameter content with the value type.

For example:

ros2 param get /move_group robot_description

returns:

String value is: <?xml version="1.0" ?> [...] <robot name="panda"> [...] </robot>

It would be much more useful if get would return the raw content of the parameter, i.e. the URDF string in the case above without String value is: prepended, such that it can be parsed by another tool.

Implementation considerations

This can be implemented by a new flag for get, that either adds or omits the type information (String value is:). IMHO, it makes more sense to omit the type by default and only add type information when the "verbose type" flag is set.

[fujitatomoya]

@christian-rauch thanks for creating issue.

are you specifically requesting the format with xml? i do not think xml is not supported even with load or dump.

It would be much more useful if get would return the raw content of the parameter, i.e. the URDF string in the case above without String value is: prepended, such that it can be parsed by another tool.

can you share the actual use case if you have with examples?

btw, you can dump the parameters in yaml file.

root@tomoyafujita:~/ros2_ws/colcon_ws# ros2 param dump /parameter_blackboard
/parameter_blackboard:
  ros__parameters:
    qos_overrides:
      /parameter_events:
        publisher:
          depth: 1000
          durability: volatile
          history: keep_last
          reliability: reliable
    use_sim_time: false

[iuhilnehc-ynos]

@christian-rauch

I think you could try to use the parameter --hide-type.

$ ros2 param get -h
usage: ros2 param get [-h] [--spin-time SPIN_TIME] [-s] [--no-daemon] [--include-hidden-nodes] [--hide-type] [--timeout N] node_name parameter_name

Get parameter

positional arguments:
  node_name             Name of the ROS node
  parameter_name        Name of the parameter

options:
  -h, --help            show this help message and exit
  --spin-time SPIN_TIME
                        Spin time in seconds to wait for discovery (only applies when not using an already running daemon)
  -s, --use-sim-time    Enable ROS simulation time
  --no-daemon           Do not spawn nor use an already running daemon
  --include-hidden-nodes
                        Consider hidden nodes as well
  --hide-type           Hide the type information
  --timeout N           Wait for N seconds until node becomes available (default 1 sec)

https://github.com/ros2/ros2cli/blob/f31cd91bb52c90b67e9b9e76aaa56e6eced0803b/ros2param/ros2param/verb/get.py#L102-L105

[christian-rauch]

I think you could try to use the parameter --hide-type.

I overlooked that flag. Thanks.

This is exactly what I was looking for, i.e.:

ros2 param get --hide-type /move_group robot_description

gives the raw content (URDF as XML string) without the type information prepended. IMHO, this should be the default.