1, THE UNIX SHELL GUIDE, which have introduced the usage of Bsh, Ksh and Csh, other shells are also refers to, the URL is http://www.phys.ualberta.ca/~gingrich/research/shells/shells.html
2, An introduction of bsh and ksh, http://www.unix.com/shell-programming-scripting/20750-difference-between-ksh-bsh.html
3, A list of several shells http://www.unix.com/answers-frequently-asked-questions/12274-difference-between-ksh-bash-different-shells.html
4, UNIX shell differences and how to change your shellhttp://www.faqs.org/faqs/unix-faq/shell/shell-differences/
5, shell历险之——引用的迷途 http://www.kuqin.com/article/24shell/686286.html
And, by the way, shell also have another name ---- command interpreter, as shells works as an interpreted programming language and an interactive command interpreter.