There are quite a few discussions about this exact topic on both the ros-industrial/ur_modern_driver issue tracker as well as the Universal_Robots_ROS_Driver issue tracker.
I would advise you to look for those, as otherwise we will
Summarising: sending scripts to the robot over any of the TCP ports does not return any information about their execution status. Any "print" statement in the script will also not be returned. It's essentially a fire-and-forget interface.
This is a limitation in the way Universal Robots has implemented this mechanism, not of the driver (or any other software which interfaces with UR controllers actually).
Work-arounds I've seen people use:
- toggle a
flag as part of your script and use it as a mutex (ie: flag true -> script is still executing, flag false it completed) - toggle a digital IO for something similar
- open a socket back to the PC and submit status information there
- use one of the freely available RTDE output registers, extend the RTDE recipe the driver uses and extend the driver to publish that information
