环境变量名应为大写
环境变量名应为大写

看了下书里提到 goroot 只有一处

> ➜  ebook git:(master) grep goroot *.md
02.3.md:上面这个fmt是Go语言的标准库，其实是去goroot下去加载该模块，当然Go的import还支持如下两种方式来加载自己写的模块：

而fmt 包的位置则是在 `GOROOT` 环境变量指定目录下的 `src/pkg/fmt`中。
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