Shell (computing)

A graphical interface similar to one from the late 1980s, which features a graphical window for a man page, a shaped window (oclock) as well as several iconified windows. In the lower right we can see a terminal emulator running a Unix shell, in which the user can type commands as if they were sitting at a terminal.

An operating system shell is a computer program that provides relatively broad and direct access to the system on which it runs. The term shell refers to how it is a relatively thin layer around an operating system.^[1]^[2]

A shell is generally a command-line interface (CLI) program although some graphical user interface (GUI) programs are arguably classified as shells too.

^ "The Internet's fifth man", Brain scan, The Economist, London: Economist Group, December 13, 2013, Mr Pouzin created a program called RUNCOM that helped users automate tedious and repetitive commands. That program, which he described as a "shell" around the computer's whirring innards, gave inspiration—and a name—to an entire class of software tools, called command-line shells, that still lurk below the surface of modern operating systems.
^ Raymond, Eric S. (ed.). "shell". The Jargon File.

[Economist-1] "The Internet's fifth man", Brain scan, The Economist, London: Economist Group, December 13, 2013, Mr Pouzin created a program called RUNCOM that helped users automate tedious and repetitive commands. That program, which he described as a "shell" around the computer's whirring innards, gave inspiration—and a name—to an entire class of software tools, called command-line shells, that still lurk below the surface of modern operating systems.

[JargonFile-2] Raymond, Eric S. (ed.). "shell". The Jargon File.

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