Explanation of the SHELL command. It is CONFIG.SYS

This command can only be used in your CONFIG.SYS file.
It will specify the location and the name of the command
interpreter you want to use.

Example: 
       To have DOS use your own creation of a command
       interpreter with the name Commando.com you would
       include this line in your CONFIG.SYS file:
              shell=c:\dos\commando.com