For what purposes should we use shell
/what are the tasks we can achieve using shell
which is best book to learn shell programming
and will nayone tell me diff between shell programming aand shell scripting?
Thank u in advance.

Shell Programming, also commonly called shell scripting is used all across the unix landscape. It is used to control everything from the boot process, to starting/stopping daemon processes, as a wrapper around binaries, and used to create many other small stand alone procedures. Probably one of the easiest books to read and learn from is "Sams Teach Yourself Shell Programming in 24 Hours". This book starts with very basics about unix and moves quickly into shell programming - a great book for a novice. There are quite a few more advanced books out there though. Scripting also has many variants that are defined by shell that they run under, for example, Korn Shell (ksh), Bourne Shell (sh), C Shell (csh), and Bourne Again Shell (bash) to name a few. Korn shell is probably the most ubiquitous and the most powerful.