using environment variables in a docker file basic - docker

Question

Using the following docker file I am getting an error on RUN md $SiteFolderPath and I am not sure why every example I look at:
https://docs.docker.com/engine/reference/builder/#environment-replacement
Indicates I am doing it correctly.
FROM microsoft/iis
#FROM nanoserver/iis
SHELL ["powershell"]
ENV SiteFolderPath c:\\app
ENV SiteFolderPathLogs c:\\app\\logs
ENV WorkFolder /app
ENV SiteAppPool LocalAppPool
ENV SiteName LocalWebSite
ENV SiteHostName LocalSite
RUN md $SiteFolderPath
RUN md $SiteFolderPathLogs
WORKDIR $WorkFolder
COPY ./Public .
RUN New-Item $SiteFolderPath -type Directory
RUN Set-Content $SiteFolderPath\Default.htm "<h1>Hello IIS</h1>"
RUN New-Item IIS:\AppPools\$SiteAppPool
RUN New-Item IIS:\Sites\$SiteName -physicalPath $SiteFolderPath -bindings #{protocol="http";bindingInformation=":80:"+$SiteHostName}
RUN Set-ItemProperty IIS:\Sites\$SiteName -name applicationPool -value $SiteAppPool
EXPOSE 80
EXPOSE 443
VOLUME ${SiteFolderPathLogs}
I get an error message when building the docker file:
mkdir : Cannot bind argument to parameter 'Path' because it is null.

Answer 1

The page you linked to states:
Environment variables are supported by the following list of instructions in the Dockerfile:
ADD
COPY
ENV
EXPOSE
FROM
LABEL
STOPSIGNAL
USER
VOLUME
WORKDIR
as well as:
ONBUILD (when combined with one of the supported instructions above)
Since you are using the variables as part of a RUN block, you should use the Windows environment variable syntax: %SiteFolderPath%