While SGI machines make extensive use of a graphical user interface (GUI), access to many system and user commands is through a command-line interface, much as on a VMS system.
On Unix systems the program that issues the prompt and processes user responses is called a shell. There are usually several different shells available, the most common being the Bourne Shell (/bin/sh) and it's derivatives and the C-Shell (/bin/csh) and it's derivatives.
This document will assume that the user is utilizing the "Bourne-Again Shell" (/bin/bash), produced by the Free Software Foundation as part of the GNU project. Other command interpreters are available, but this is the most powerful and "friendly".