The grep command prints out lines of a file that match a specified pattern. The '-v' flag inverts the behaviour so the grep command prints out lines of a file that do not match the specified pattern.

Given a file foo.txt, suppose

  grep -v hello foo.txt

prints 5 lines of text, and

  grep hello foo.txt

prints 3 lines of text,

then how many lines are there in the file foo.txt?