grep has various options.
I frequently use
-v option to filter lines without the keyword.
grep -v human data.txt
data.txt is a bunch of data to be greped.
We can filter out lines with keyword human.
Other example is to filter the lines which have a value in the first column.
When the first column is missing, head of the line is '\t' (tab character) in the tab-deliminated text.
We can make use of
grep -v command below to filter out the lines without the first column.
grep -v ^$'\t' data.txt
^ means the head of line, and
$'\t' means tab character.
It greatly enhances the efficiecy of our study to have a list of lines with required data.