1
 2
 3X1 := $(sort $(filter FOO BAR,$(.VARIABLES)))
 4
 5FOO := foo
 6
 7X2 := $(sort $(filter FOO BAR,$(.VARIABLES)))
 8
 9BAR := bar
10
11all: ; @echo X1 = $(X1); echo X2 = $(X2); echo LAST = $(sort $(filter FOO BAR,$(.VARIABLES)))