Everything Is a Stream: runtime composability over compile-time plugins

Unix's most famous design slogan is "everything is a file."

It's the wrong emphasis. A file at rest is just named bytes sitting on a disk; nothing composes. What made Unix profoundly powerful is that every file descriptor is something you read from and write to in order — and that stdin, stdout, and the pipe let any program's output feed any other program's input. grep is a filter. sed and awk are maps. sort | uniq -c is an aggregate. wc is a reduce.

The shell pipeline was a stream-processing framework half a century before we coined the term.