使用$()代替`` backticks的Makefile

Question

如何正确地规避Makefile中的shell扩展语法$()？

.PHONY: test
test:
        @if [ `find myDir -type f -not -name '*.openapi.yaml' | wc -l ` != 0 ]; then \
                echo "All files must end with '.openapi.yaml'";                           \
                find myDir -type f -not -name '*.openapi.yaml';                      \
                exit 42;                                                                  \
        fi

当我尝试修改它时，

@if [ $( find myDir -type f -not -name '*.openapi.yaml' | wc -l ) != 0 ]; then \

我明白了，

/bin/sh: line 0: [: !=: unary operator expected

如果我试图用$转义\$，我会得到同样的错误，

Answer 1

您需要双$：

.PHONY: test test1 test2

test: test1 test2

test1:
    @echo test1; if [ $(echo 0) == "0" ]; then echo true; else echo false; fi

test2:
    @echo test2; if [ $(echo 0) == "1" ]; then echo true; else echo false; fi

下面是一个例子：

$ make
test1
true
test2
false