For me, the hardest part about teaching the LPI 101 course is teaching about text-stream filters. It’s not that they’re difficult to understand. It’s just that showing the examples of how they work is easy, but showing examples of how they can be used in real life is a bit more challenging. Real-life examples from the Linux admin world are fairly complex, and are beyond the level that most beginning Linux students are able to grasp. So, in most LPI books, the student will see how these utilities work, but not how to use them.