Background reading: https://en.wikipedia.org/wiki/Environment_variable
On Linux, the environment variables, as attributes of the process, can be manually inspected by reading file `/proc/$PID/environ` like a normal text file.
?- getenv('SHELL',X). X = '/bin/bash'. ?- getenv('HOME',X). X = '/home/paquette'.
But the predicate cannot list them (d'aw):
?- getenv(N,X). ERROR: Arguments are not sufficiently instantiated