Question

What is this expression supposed to be doing?

grep -i Keyword1 | grep -i Keyword2 file.txt

Is it supposed to return the lines which contain either keyword 1 or keyword 2? I ask this because that is not what i am getting.I am somehow always getting the lines with keyword 2 and also the thing doesnt seem to complete.I mean when you run a normal command it returns to the command prompt after finishing.Doesnt seem to be happening when I run the above.Is there some kind of piping happening here?

Answer 1

This doesn’t really make sense. | is a pipe, it redirects stdin/stdout: a | b redirects as stdout to bs stdin. grep, without a file as parameter, will take input from stdin, which is why your command doesn’t return.

What you want is

grep -i Keyword1 file.txt | grep -i Keyword2

Which will grep for Keyword1, and the output will be grepped for Keyword2. This will result in a logical and, filters for Keyword1 AND Keyword2.