Most programming books begin with variables, loops, and functions. A textsmith, however, encounters programming from the opposite direction: composition. Before writing a single if statement, they are already composing grep, sort, awk, sed, pandoc, and dozens of other tools into something larger. By the time they sit down to learn a programming language, they have already been programming—they simply didn’t call it that.

Every program is a set of functions that cooperate to produce the desired result. Did you ever consider how your computer makes it possible for you to craft complete programs on-the-fly through its small utilities?