Information Security and IT Risk Management

CHAPTER 10 Shell Scripting

Overview

In previous chapters, we looked at some of the common tasks associated with system administration. Beginning with the introduction to the role of the system administrator in Chapter 2, subsequent chapters have introduced the technical controls used to combat security threats and the efforts required after a security breach has occurred.

In this chapter, we will introduce you to a way to handle the sometimes complex and often repetitive, tasks required for effective system administration. The BASH shell provides a mechanism for creating a script – an application constructed from multiple command line applications – to accomplish complex tasks. At the end of this chapter, you should know:

• how to write a simple BASH shell script
• the use of common programming elements (variables, loops, etc)
• how to handle user interaction
• how to use common UNIX tools to parse and manipulate text files

Introduction

Basic knowledge of shell scripting is necessary for anyone wanting to complete common system administration tasks, audit the security of a system, or implement many of the controls we have discussed in the previous chapters. Shell scripts are used for automating processes throughout a Unix system, from starting network services at boot up to configuring the user's shell environment during login. This chapter will just be an introduction to shell scripting. To begin, we will be creating scripts that are intended as examples of common structures and procedures ...