Goals for this Hour

In this hour, you learn all about

• Shell variables

• Shell arithmetic

• Comparison functions

• Conditional expressions

• Looping expressions

Because shells are really just interpreted languages, any sequence of commands you want to run can be placed in a file and run regularly. This is a shell program. Most UNIX experts write their shell programs for the Bourne shell (/bin/sh) because that shell is standard on every UNIX platform. Earlier in this book, I illustrated examples by using the C shell, because I feel that this is a better interface for the user. Because I'm programming the Bourne shell, the command prompt is slightly different: It's $ rather than %.

I strongly urge you to look at the shells you have available. The best shell to use is the one that makes you the most productive.