let get_env ?default var =
try let varval = Sys.getenv var in
(Wp_parameters.feedback "found %s=%s" var varval; varval)
with Not_found ->
Wp_parameters.feedback ~level:2 "%s not set." var ;
match default with Some varval ->
Wp_parameters.feedback "Try %s=%s" var varval ; varval
| None -> raise Not_found