问题是echo属于外壳程序； Make可以在命令中将其传递给Shell，但是Make无法执行它.使用info代替:

The problem is that echo belongs to the shell; Make can pass it to the shell in a command, but Make cannot execute it. Use info instead:

ifdef CATEGORY
$(info CATEGORY defined)
else
$(info CATEGORY undefined)
endif

如果您希望规则是有条件的:

If you want the rules to be conditional:

ifdef CATEGORY
ifdef TEST
$(CATEGORY):
    whatever
else
$(info TEST not defined)
else
$(info CATEGORY not defined)
endif