Looks up name, a string, in the program environment. If name is
found a string of its value is returned. Otherwise, #f
is returned.
Executes the command-string on the computer and returns the
integer status code. This behaves the same as the POSIX system
call.
If (provided? 'program-arguments)
:
Returns a list of strings, the first of which is the program name followed by the command-line arguments.