As a relatively isolated junior sysadmin, I remember seeing answers on Experts Exchange and later Stack Exchange that baffled me. Authors and commenters might chain 10 commands together with pipes and angle brackets—something I never did in day-to-day system administration. Honestly, I doubted the real-world value of that. Surely, this was just an exercise in e-braggadocio, right?
Trying to read the man pages for the utilities most frequently seen in these extended command chains didn't make them seem more approachable, either. For example, the sed man page weighs in at around 1,800 words alone without ever really explaining how regular expressions work or the most common uses of sed itself.
If you find yourself in the same boat, grab a beverage and buckle in. Instead of giving you encyclopedic listings of every possible argument and use case for each of these ubiquitous commands, we're going to teach you how to think about them—and how to easily, productively incorporate them in your own daily command-line use.
Before we can talk about sed, awk, and grep, we need to talk about something a bit more basic—command-line redirection. Again, we're going to keep this very simple: