ARG文件夹路径不起作用

Question

这有效：

COPY Subfolder/ /inetpub/wwwroot

这会复制整个工作目录（不仅仅是子文件夹）

ARG site_root="Subfolder/"
# ARG site_root="Subfolder/" # this doesnt work either
# ARG site_root=Subfolder/ # this doesnt work either
# ARG site_root=./Subfolder # this doesnt work either
# ARG site_root=.Subfolder/ # this doesnt work either
# ARG site_root=Subfolder # this doesnt work either
COPY ${site_root} /inetpub/wwwroot

如何在var？

中使用subdir路径