linux command
https://jybaek.tistory.com/704
sample
find . -type f
find . -type f -name "..."
grep "..." test.txt
grep "..." *
grep "..." * -r
grep "...' * -r -A 3
grep "..." * -rn -A 3
find . -type f -name '*.log' | xargs grep '...' --color-always