在 OS X 上使用 Bash 命令生成文件 ifeq
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Makefile ifeq with Bash commands on OS X
提问by mfellner
I am trying to write a Makefile that evaluates results from Bash commands, e.g., uname.
我正在尝试编写一个 Makefile 来评估 Bash 命令的结果，例如uname.
Makefile:
生成文件：
OS1 = $(uname)
OS2 = Darwin
all:
@echo $(value OS1)
ifeq ($(uname),Darwin)
@echo "OK"
else
@echo "Fail"
endif
ifeq ($(OS1),Darwin)
@echo "OK"
else
@echo "Fail"
endif
ifeq ($(OS2),Darwin)
@echo "OK"
else
@echo "Fail"
endif
Output:
输出：
Darwin
Fail
Fail
OK
How can I compare the variable OS1or the command $(uname)to the literal Darwininside an ifeq? From what I have read, the second ifeqin my Makefile should work, but it doesn't.
如何将变量OS1或命令$(uname)与Darwinan 中的文字进行比较ifeq？从我读到的内容来看ifeq，我的 Makefile 中的第二个应该可以工作，但它没有。
I am using GNU Make 3.81 for i386-apple-darwin11.3.0 on OS X 10.9.3.
我在 OS X 10.9.3 上为 i386-apple-darwin11.3.0 使用 GNU Make 3.81。
回答by mfellner
There are a lot of different questions and answers about Makefiles, variables and shell commands. But as it turns out, looking into the manual is sometimes more reliable than searching Stackoverflow.
关于 Makefile、变量和 shell 命令有很多不同的问题和答案。但事实证明，查看手册有时比搜索 Stackoverflow 更可靠。
First, I didn't know the different ways that variables can be assigned in GNU make: https://www.gnu.org/software/make/manual/make.html#Reading-Makefiles
首先，我不知道可以在 GNU make 中分配变量的不同方式：https: //www.gnu.org/software/make/manual/make.html#Reading-Makefiles
Second, the shellfunction, which is required in this case, only works in combination with the :=(immediate) operator:
https://www.gnu.org/software/make/manual/make.html#Shell-Function
其次，shell在这种情况下需要的函数只能与:=（立即）运算符结合使用：https:
//www.gnu.org/software/make/manual/make.html#Shell-Function
Thus the correct Makefile looks like this:
因此正确的 Makefile 如下所示：
OS := $(shell uname)
all:
@echo $(OS)
ifeq ($(shell uname),Darwin)
@echo "OK"
else
@echo "Fail"
endif
ifeq ($(OS),Darwin)
@echo "OK"
else
@echo "Fail"
endif
