A shell is a way to interact with a computer system using a set of standard commands. Shell commands are two kinds: internal and external. Internal commands are built into and part of the shell itself (the shell know how to execute). External commands are stand alone executable commands that the shell executes upon user request. The ability for the shell to execute external commands gives users the ability to scale up and execute commands that are new (e.g. users' own compiled programs). Write a C program that tokenize a string then save the output token in array of strings and print them on the screen. Write a C program "MyShell" that execute the following command using the c-library function system(char * cmd). 1. clear: clears the screen. 2. exit: quits the shell. 3. listen: lists all environment strings. 4. pwd: prints the current working directory.