Print lines in one file matching patterns in another file

Question

I have a file with more than 40.000 lines (file1) and I want to extract the lines matching patterns in file2 (about 6000 lines). I use grep like this, but it is very slow: <

Answer 1

Just for the sake of learning: I was solving the same problem and I came up with various solutions (including read $line loops etc..). When I got to the grep one-liner found above, I still ended up getting the wrong output. Then I realized my PATTERN file had 2 trailing lines... So grep picked up all my lines from my database. Morality: check you trailing spaces/lines. Also, ran the command on a much larger dataset with several hundreds patterns and time couldn't even count.