This is a simple shell program that emulates the basic functionalities of a command-line interface.
Command execution: Users can enter commands, and the shell will execute them.
Basic command parsing: The shell parses the command line input and separates the command and arguments.
Built-in commands: The shell includes a few built-in commands such as cd (change directory) and exit (terminate the shell).
Signal handling: The shell can handle signals such as Ctrl+C.
