grep, sed, and awk: a practical introduction for Mac users
You export a report from some web app and it hands you a 40,000-line CSV. You need three columns out of it, only the rows from last Tuesday, with one misspelled city name fixed throughout. You could open it in a spreadsheet, wait for the beachball, scroll, sort, find-and-replace, and export again. Or you could describe the whole job in one line of text and get the answer before the spreadsheet finishes loading. ...