+define shvar
+V_$(subst .,_,$(subst -,_,$(subst /,_,$(1))))
+endef
+
+define shexport
+$(call shvar,$(1))=$$(call $(1))
+export $(call shvar,$(1))
+endef
+
+empty:=
+space:= $(empty) $(empty)
+merge=$(subst $(space),,$(1))
+confvar=$(call merge,$(foreach v,$(1),$(if $($(v)),y,n)))
+
+# file extension
+ext=$(word $(words $(subst ., ,$(1))),$(subst ., ,$(1)))
+