Expect
Expect is another scripting
language that helps solve a different type of problem. Where Perl's strength is
in pattern matching, Expect provides a way to automate interactive applications.
We usually use Expect to imitate user sessions on a router to automate
command-line-based tasks.
The Expect program is able to send one or more lines of output,
such as router commands, and capture the results. And it can also react to
whatever the router sends it in return. This could be as simple as sending a
user ID and waiting for the password prompt, or you could use this feature to
check for various error conditions and react appropriately.
We often write scripts in Expect to automate boring repetitive
tasks. Computers are good at these tasks, people aren't. People make typos and
get bored or blink and miss key pieces of information. Also, because Expect can
react immediately to the router's responses, the script can generally execute a
series of commands very quickly. We think it's better to spend your time doing
something productive while the computer is logging into all of your routers to
do show commands. Expect lets us do this.
Expect is free to download, distribute, and use for any
purpose. There are both Unix and Windows versions, and there are even companies
doing commercial support for Expect. We wrote and tested all of the scripts in
this book using Expect Version 5.31.2 on a Unix platform.
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