Introduction | Unix | University of Waterloo

Most operating systems used in High School are based on a windowing system which allow the user to interact with the operating system through a series of icons and frames. Such interfaces to an operating systems are, however, computationally expensive and therefore, the standard interface to many Unix systems is through a terminal which establishes and maintains a connection with a process running in Unix a shell, a program which interprets the commands of the user. The terminal is simply a program which submits commands to the shell and then the shell may send output back to the terminal which then displays the result to the user.

Figure 1 shows this relationship where the command "date" is sent to the shell by the terminal, the shell calls an appropriate function in the operating system (Unix), a response is returned which is then interpreted by the shell, and the shell sends an appropriate string to the terminal which then displays the result to the user.

Figure 1. Example of a communication between a terminal and Unix through a shell.

In Windows, it is possible to launch a Command Prompt (Start → All Programs → Accessories → Command Prompt) which acts as both a terminal and a shell to Windows XP. In this case, the communication between the terminal and the shell is local and not remote, as suggested by most connections to Unix as shown in Figure 1.

Terminals

Traditionally, terminals were dedicated pieces of hardware, however, with modern desktop computers, the norm is to run a program which acts as a terminal, usually a simple program, such as SSH which runs as a process on the computer the user is using which makes a connection to the computer running Unix.

Shells

The program running on Unix which interprets the requests sent to it by the terminal is a program called a shell. A shell is not unique: there are as many different shells as there are editors, each with their own interface. Some of the more common ones are bash (the default Linux shell) and tcsh. There are others, however, for example, the scheme shell scsh. Initially, there was only one shell for MS-DOS, and therefore, many older users will confuse the DOS prompt with the operating system.

This tutorial uses the tcsh. To make tcsh the default shell for your Unix account, visit this web site and select tcsh from the drop down menu.