Page 125 - DCAP106_OPERATING_SYSTEM_TOOLS

Operating System Tools Dr. Manmohan Sharma, Lovely Professional University

Notes Unit 7: The Shell

CONTENTS

Objectives
Introduction
7.1 Shell as a Command Line Interface
7.1.1 Shell Variables
7.2 Types of Shell
7.2.1 BASH (Bourne-Again SHell)

7.2.2 C Shell (csh)
7.2.3 Korn Shell (ksh)
7.2.4 TCSH
7.3 Built-in Programs and External Programs

7.4 Summary
7.5 Keywords
7.6 Review Questions
7.7 Further Readings

Objectives

After studying this unit, you will be able to:

z z Explain the concept of shell
z z Discuss different types of shell

z z Discuss built-in programs and external programs
Introduction

Computers understand the language of zeros and ones known as binary language. In the early
days of computing, instructions were provided using binary language, which is difficult for all of
us humans to read and write. Therefore, in an operating system there is a special program called
the shell. The shell accepts human readable commands and translates them into something the
kernel can read and process. The shell is a user program or it is an environment provided for
user interaction. It is a command language interpreter that executes commands read from the
standard input device (keyboard) or from a file. Shell is not part of system kernel, but uses the
system kernel to execute programs, create files etc.

7.1 Shell as a Command Line Interface

The shell is defined as a program that takes commands from the keyboard and provides them
to the operating system to perform. Earlier, shell was the only user interface available on a Unix
computer. These days, we have graphical user interfaces (GUIs) in addition to command line
interfaces (CLIs) such as the shell. The command interpreter is the interface between the user and
the operating system, hence the name “shell”.

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