立即在配方中进行变量扩展 [英] Immediate variable expansion in recipe

问题描述

我正在构建一个构建系统，我需要在目标配方中立即进行变量扩展.

I'm making a build system and I need immediate variable expansion in a recipe of a target.

我的(简化的)makefile:

My (simplified) makefile:

VAR=one

all:
    @echo one is $(VAR)

VAR=two

当我运行make时，输出为:

one is two

期望输出(配方中的延迟扩展)，但不期望.

The output is expected (deferred expansion in recipe) but not desired.

使其工作的一种方法是跟随makefile.但是，这会使配方始终执行，这也是不希望的:

One way to make it work is following makefile. However, this makes the recipe to be executed always, also not desired:

VAR=one

all: $(VAR)
    @echo one is $(VAR)

$(VAR):
    $(eval VAR=$@)

VAR=two

有人吗?

推荐答案

您可以使用类似的东西来获取所需的东西.它使用特定于目标的变量值来在分析时捕获变量时间.

You can use something like this to get what you want. It uses target-specific variable values to capture the variable at parse-time.

$ cat Makefile
VAR=one

all: tgtone tgttwo

tgtone: VAR:=$(VAR)
tgtone:
        @echo $@: VAR is $(VAR)

tgttwo:
        @echo $@: VAR is $(VAR)

VAR=two
$ make
tgtone: VAR is one
tgttwo: VAR is two

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