makefile - gnu-make：我应该引用 ifeq 语句的内容吗？

Question

我最近遇到了这个结构：

ifneq ("$(findstring needle, $(HAYSTACK))", "")
  do_some_stuff
endif

引号真的有用吗，还是我可以放心地省略它们？

编辑：

刚刚发现：ifeq ("a b ", "a b ")行为不同于ifeq (a b , a b )

第一个匹配，而不是第二个。所以引号确实很重要。现在的问题是为什么。

Answer 1

Answer 2

I'll go out on a limb and say:

They are equivalent to nothing and you can safely omit them.

(Now watch the creator of GNUMake show up and say that if you try that when HAYSTACK contains a double-escaped unicode Sanscrit triple-quote your processor will catch fire.)

EDIT:
Dammit, dammit, dammit! They do matter. Just try playing around with HAYSTACK := $(shell echo bang). You'd better have a fire extinguisher handy.