Ask HN: What are your most compellingly useful Bash examples?

I'm presenting an introduction to Bash and the Linux command line to my co-workers and I'm looking for some examples that will make them say "oh WOW I really could've used that last week!" and generally give them an idea of how and when Bash can be useful.

Solutions to specific or one-off problems are great as long as the problem is not too arcane. Feel free to show off!