9.1 What is a Shell?

The shell is an interactive command interpreter environment within which commands may be typed at a prompt or entered into a file in the form of a script and executed. The origins of the shell can be traced back to the early days of the UNIX operating system. In fact, in the early days of Linux before the introduction of graphical desktops the shell was the only way for a user to interact with the operating system.

A variety of shell environments have been developed over the years. The first widely used shell was the Bourne shell, written by Stephen Bourne at Bell Labs.

Yet another early creation was the C shell which shared some syntax similarities with the C Programming Language and introduced usability enhancements such as command-line editing and history.

The Korn shell (developed by David Korn at Bell Labs) is based on features provided by both the Bourne shell and the C shell.

The default shell on Ubuntu is the Bash shell (shorthand for Bourne Again SHell). This shell, which began life as an open source version of the Bourne shell, was developed for the GNU Project by Brian Fox and is based on features provided by both the Bourne shell and the C shell.