Objective 105.1: Customize and Use the Shell Environment
A shell presents an interactive Textual User Interface, an operating environment, a facility for launching programs, and a programming language.
Shells can generally be divided into those derived from the Bourne shell, sh (including bash), and the C-shells, such as tcsh.
Shells are distinct from the kernel and run as user programs.
Shells can be customized by manipulating variables.
Shells use configuration files at startup.
Shells pass environment variables to child processes, including other shells.