S9 EXT  (sys:getenv string)  ==>  string | #f

Return the value of the environment variable STRING. If
the variable is undefined, return #F.

You may prefer to use the ENVIRONMENT-VARIABLE procedure
instead, which is built into the core S9 interpreter.

(sys:getenv "HOME")         ==>  "/u/home/nmh"
(sys:getenv "nonexistent")  ==>  #f
