Many people learn the Unix slogan “everything is a file.” That’s true, but I almost think the more profound slogan is: “Everything is a stream waiting to be read or written.” This last of our three-part series on working with streams demonstrates why it is appropriate to adopt the stream mentality rather than the page mentality when working with files.

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.