Passing argument to dockerfile not working well

Question

I'm having some trouble with passing argument value to dockerfile.

Running docker in Windows Server 2016

My docker version info is

PS C:\Users\Administrator\Desktop> docker version
Client: Docker Engine - Enterprise
 Version:           19.03.4
 API version:       1.40
 Go version:        go1.12.10
 Git commit:        9e27c76fe0
 Built:             10/17/2019 23:42:50
 OS/Arch:           windows/amd64
 Experimental:      false

Server: Docker Engine - Enterprise
 Engine:
  Version:          19.03.4
  API version:      1.40 (minimum version 1.24)
  Go version:       go1.12.10
  Git commit:       9e27c76fe0
  Built:            10/17/2019 23:41:23
  OS/Arch:          windows/amd64
  Experimental:     false

and powershell opened as administrator.

My reference is this.

But it not worked for me.

So this is my dockerfile.

FROM microsoft/iis

ARG a_version
RUN echo $a_version

Also i tried many different types of echo value Such as

RUN echo "$a_version"
RUN echo ${a_version}
RUN echo "${a_version}"

And this is my execute command.

docker build . --build-arg a_version=1234

My expected result was print 1234

But actual result was

PS C:\Users\Administrator\Desktop> docker build . --build-arg a_version=1234
Sending build context to Docker daemon  14.04MB
Step 1/3 : FROM microsoft/iis
 ---> 595015675977
Step 2/3 : ARG a_version
 ---> Running in 91698d9e71da
Removing intermediate container 91698d9e71da
 ---> 2bad94a2ce74
Step 3/3 : RUN echo $a_version
 ---> Running in 3fe25ecb813c
$a_version

Why it happens? How can is fix it?

Answer 1

In Windows Command-Prompt the syntax is echo %a_version% as your base image is based on window.

how-can-i-display-the-contents-of-an-environment-variable-from-the-command-promp

So you can change this to

FROM microsoft/iis
ARG a_version
RUN echo %a_version%

env in window dockerfile

Answer 2

I had to do something simmilar and this is a piece of code that worked for me.

ARG PORT_SITE
ENV PORT_SITE ${PORT_SITE}

and then I refer it in the entrypoint as following

$env:PORT_SITE

That's the way I did it, but i suppose that you can ommit the env variable and just refer to the arg value using

${PORT_SITE}