based on rogerdpack's and Ed999's responses, I've created my .sh version
#!/bin/bash
[ -e list.txt ] && rm list.txt
for f in *.mp4
do
echo "file $f" >> list.txt
done
ffmpeg -f concat -i list.txt -c copy joined-out.mp4 && rm list.txt
it joins all the *.mp4
files in current folder into joined-out.mp4
tested on mac.
resulting filesize is exact sum of my 60 tested files. Should not be any loss. Just what I needed