usr.bin/make/unit-tests/ternary.mk

   1
   2 all:
   3         @for x in "" A= A=42; do ${.MAKE} -f ${MAKEFILE} show $$x; done
   4
   5 show:
   6         @echo "The answer is ${A:?known:unknown}"
   7         @echo "The answer is ${A:?$A:unknown}"
   8         @echo "The answer is ${empty(A):?empty:$A}"