A shell program that utilizes fork() and execl() tokenize inputs as commands and execute them from a separate process.
Features include:

• forking of processes
• tokenization of input
• various directory level access of commands
• history command (lists last 15 commands given)
• listpids (lists last 15 process IDs started from this shell
• !n command where 0 <= n <= 15. Executes the corresponding command as listed from history
• Signal handlers for Ctrl-C and Ctrl-Z
• Suspension of processes with Ctrl-Z
• bg command (backgrounds a previously suspended process)