No bother. Happy to have the bug reports.
Can you post a copy of the script? Regarding the log file, I don’t think there is one, but that’s a good suggestion and I just added it to the dev branch of the script.
From the nano_build_opencv folder you cloned, can you run
git checkout dev
git pull
and rerun the build? There should then be four logs written to /tmp/build_opencv/opencv/build as each of the build steps progress: configure.log, build.log, test.log, and install.log.
However, the most likely cause of failure while building OpenCV is that your device runs out of memory. I recommend that you either turn off x11 temporarily with sudo systemctl isolate multi-user.target, or add a larger swap file – preferably both for the fastest build – and preferably the swap on an external disk, both for speed and to reduce wear on your sd card.
To install a swap file, fallocate a file an an external disks and roughly follow these commands here. It’s probably not desirable to add it to fstab, so you can skip that part and delete the file after you’re done and turn swap back off.