04-command-params.launch.py

from launch import LaunchDescription
from launch.substitutions import Command, PathJoinSubstitution
from launch_ros.actions import Node
from launch_ros.parameter_descriptions import ParameterValue
from launch_ros.substitutions import FindPackageShare


def generate_launch_description():
    robot_description = ParameterValue(
        Command(['xacro ', PathJoinSubstitution(FindPackageShare('urdf_tutorial'), 'urdf', '01-myfirst.urdf')]),
        value_type=str)

    return LaunchDescription([
        Node(package='robot_state_publisher',
             executable='robot_state_publisher',
             parameters=[{'robot_description': robot_description}])
    ])