Exploring Expect

Chapter 1. Intro—What Is Expect?

Expect is a program to control interactive applications. These applications interactively prompt and expect a user to enter keystrokes in response. By using Expect, you can write simple scripts to automate these interactions. And using automated interactive programs, you will be able to solve problems that you never would have even considered before.

Expect can save you hours of drudgery, and this book will start you on your way. This first chapter is an overview of Expect. I will describe some simple applications and present some short scripts. However, the explanations are not intended to be complete but rather to whet your appetite and give you a taste of the good things to come. In the following chapters, I will revisit all of the concepts mentioned in this chapter and cover them in more detail.

Ouch, Those Programs Are Painful!

fsck, the UNIX file system check program, can be run from a shell script only with the -y or -n options. The manual defines the -y option as follows:

“Assume a yes response to all questions asked by fsck; this should be used with extreme caution, as it is a free license to continue, even after severe problems are encountered.”

The -n option is safer, but almost uselessly so. This kind of interface is inexcusably bad, yet many programs have the same style. ftp, a file transfer program, has an option that disables interactive prompting so that it can be run from a script. But it provides no way to take alternative action should ...