Although most users think of the shell as an interactive command interpreter, it is really a programming language in which each statement runs a command. Because it must satisfy both the interactive and programming aspects of command execution, it is a strange language, shaped as much by history as by design.
Brian Kernighan and Rob Pike, The UNIX Programming Environment, Prentice-Hall, 1984
The shell is a programming language. Don't let anyone tell you otherwise. The shell is not just glue that sticks bits together. The shell is a lot more than a tool that runs other tools. The shell is a complete programming language!
When a Linux user asked me about membership databases, I asked him what he really needed. He wanted to store ...