# The goal, for all of these cases:
#    input is updated
#    one is deleted (or doesn't exist yet)
#    two is deleted (or doesn't exist yet)
#    both one and two are deleted (or don't exist yet)
# The build-cmd script should run once and only once, even with make -j
all: one two

one: input
        $(build-cmd)

two: input
        $(build-cmd)

# Pretend this is some external script that creates both one and two
# using the file input
define build-cmd
        @echo "Running build, for $@"
        @touch one
        @touch two
endef

input:
        touch input

clean:
        rm input one two