This book is about programming with the shell, not about using it at the command line. You will not find information about editing the command line, creating a command prompt (the
PS1 variable), or retrieving commands from your interactive history. This chapter is about scripts that will mostly be useful at the command line rather than in other scripts.
Many of the scripts in this chapter are shell functions. Some of them have to be that way because they change the environment. Others are functions because they are often used and are quicker that way. Others are both functions and stand-alone scripts.
cd command remembers the previous working directory, and
cd - ...