In 1986 Jon Bentley's Programming Pearls column asked Donald Knuth to demonstrate literate programming. Knuth wrote a ten-page Pascal program, with a custom hash trie, to find the most common words in a text. Bentley then asked Doug McIlroy, the Bell Labs researcher who had invented the Unix pipe, to review it. McIlroy's review ended with this.
Each line does one transformation: break the text into one word per line, fold case, sort so duplicates are adjacent, count runs, sort by count, print the first n. None of the six programs knows about the others. McIlroy praised Knuth's program; his point was about composition. The hard work had already been done, once, in tools that fit together through a single interface, the stream of bytes. It is the most quoted demonstration of the Unix philosophy, and small tools joined by pipes are still how a great deal of data gets looked at.