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.

Getting them:

?- 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