Makefile在目标正文中设置全局变量 [英] Makefile set global variable in target body

问题描述

我想通过配方设置全局变量，然后在另一个独立配方中引用该变量

I want to set a Global variable through a recipe then reference that variable in another independent recipe

下面的代码是示例代码，它在配方内设置变量，但如果在配方外引用，则变量将保留初始值

The below code is an example code that sets the variable within the recipe but the variable stays with the initial value if referenced outside the recipe

ACTIVE = a

switch:
ifeq ($(ACTIVE),b)
    ACTIVE=$(shell echo 'a')
else
    ACTIVE=$(shell echo 'b')
endif

print:
    $(info acitve = $(ACTIVE))

我知道有一些方法可以将目标特定变量的值广播给从属目标，但这不是我想要的.

I know there are ways to broadcast the value of a target-specific variable to dependent targets, but that's not what I want.

推荐答案

您可以为此使用$(eval ...)，尽管这几乎总是一个坏主意.我必须假设您的实际情况要复杂得多，因为有许多更好的方法可以完成示例makefile中实际提供的功能.

You can use $(eval ...) for this, although it's almost always a bad idea. I have to assume that your real situation is much more complicated because there are many better ways to accomplish what you've actually provided in the sample makefile.

switch:
        $(eval ACTIVE=$(if $(filter-out a,$(ACTIVE)),a,b))

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