Writing a ROS command-line utility in C++ - what is the difference compared to writing a ROS node in C++ ?

Howdy folks So far I have written ROS nodes in C++ and invoked them in launch files. Now I want to write a ROS command-line utility for off-line processing rosbag files in C++ (using the rosbag C++ API), which doesn't interact with any other nodes per se. More in particular I want to write a utility that looks for camera_info messages in a given bagfile and change camera calibration and distortion parameters. **My question is: Do I write a command-line utility just like I would write a node in C++, within the catkin build framework? What's different between writing a utility and writing a node in C++? Does anyone know of a good C++ example that I can learn from?** Thanks in advance Galto