Creating a shell is not big deal. You can download existing source code of BASH or other shell from internet and study it. Here are download links:
Tutorial:
Writing Your Own Shell by Hiran Ramankutty =>
http://linuxgazette.net/111/ramankutty.html (Includes C source code)
Other downloads
BASH =>
http://www.gnu.org/software/bash/
KSH =>
http://www.research.att.com/~gsf/download/
BTW, please don’t post your email ID. It is not against forum rules but spam bots would use your email id.
If you need further help, feel free to post in our forum