tips:
https://geekflare.com/grep-command-examples/
    https://proglib.io/p/16-opciy-grep-kotorye-pomogut-vam-v-realnom-mire-2021-03-16
http://www.fromdev.com/2016/09/powerful-grep-command-tips.html

grep "exception" --color=always a.txt | grep -v "no subscriptions refer to assertion" | grep -v "Overlimit original text"

grep
    -f, --file=
        obtain patterns from file


fgrep
    -F, --fixed-strings
        use fixed string vs regexp-patterns

2022
LearnLinuxTV - Linux Essentials - The grep Command 0:00 of 14:56
    https://www.youtube.com/watch?v=Tc_jntovCM0