# grep

\-w: match whole word

\-i: ignore case

\-v: match doesn't contain

\-n: show line number

\-o: only show part that exactly matches

\-A n: n lines after the occurrence

\-B n: n lines before the occurrence

\-C n: both n lines before and after

\-E: use regular expression

\-c: show matched line count

\-r: recursive search, usually for folder