CHAPTER 2 Unix Structure
The shell is a command line interpreter. The user interacts with the kernel through the shell. You can write ASCII (text) scripts to be acted upon by a shell.
System programs are usually binary, having been compiled from C source code. These are located in places like /bin, /usr/bin, /usr/local/bin, /usr/ucb, etc. They provide the functions that you normally think of when you think of Unix. Some of these are sh, csh, date, who, more, and there are many others.