The arguments are required for some commands and optional for others. The file_name
can be a relative or absolute path name. Commands are interpreted and executed by the
shell, one of the two most widely used programs. The shell is technically known as the
command line interpreter because that’s its function. But it isn’t only an interactive command
interpreter; it’s also the key to the coordination and combination of system programs.
In fact, it’s a sophisticated programming language in itself.