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

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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