Makefile 使用 $() 而不是 `` 反引号

Question

如何正确转义$()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

当我尝试将其修改为

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

我明白了，

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

如果我试图逃避$，\$我会得到同样的错误，

Answer 1

你需要双$：

.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

并运行一个示例：

.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