UNIX Shell Programming by Stephen G. Kochan and Patrick H. Wood; Howard Sams; ISBN 0-672-48448-X; 1990. An excellent introduction to Bourne and Korn shell programming with lots of illustrative examples.

Learning the Korn Shell by Bill Rosenblatt; O’Reilly & Associates; ISBN 1-56592-054-6; 1993. A guide to using and programming the Korn shell.

Learning the bash Shell by Cameron Newham and Bill Rosenblatt; O’Reilly & Associates; ISBN 1-56592-347-2; second edition to be published early 1998. Using and programming a freely available shell that’s popular on Linux.