fgrep
It turned out that the command I regularly use to search a bunch of data is not known to others.
I frequently use fgrep to grep against a list of keywords (i.e. IDs).
fgrep -f keywords.txt data.txt
where keywords.txt contains a list of keywords ('one keyword in one line' manner), and data.txt is a bunch of data to be greped.
In fact, we can make use of grep -f command instead of fgrep -f.
I am not sure about the difference currently.