Match two strings in one line with grep

Question

I am trying to use grep to match lines that contain two different strings. I have tried the following but this matches lines that contain either string1 or string2 which not what I want.

grep 'string1\|string2' filename

So how do I match with grep only the lines that contain both strings?

Answer 1

You can use

grep 'string1' filename | grep 'string2'

This searches for string1 followed by string 2 on the same line, or string2 followed by string1 on the same line; it does not answer the question:

grep 'string1.*string2\|string2.*string1' filename