Dockerfile ARG Variables

Question

Thanks for any help given!

I am new to Docker (Using 17.06.2-ee-10), and currently I am using it on Windows Server 2016, running windowsservercore image. My question is simple.

In my dockerfile I have

ARG destpath=C:\path\
ARG javafile=java.exe

What I want to do is make another variable

ARG javapath=$destpath$javafile

This is where I run into problems.

If I RUN echo %javapath% it returns $destpath$javafile (And sometimes not even that)

It never takes the added variables together. I have tried a few different things, such as making (ARG javapath=%destpath%%javafile%.) or trying to escape the "\" characters on the path. But nothing works.

I am a beginner and unsure if I need to be more detailed in my question, or dockerfile just doesn't allow what I am trying to do. If you need more clarification please let me know.

Thanks

Arthur

Kevin Kopf · Accepted Answer · 2018-05-11 19:23:59Z

2

Putting curly braces around your variables, instead of just in potentially ambiguous cases, can be considered good programming practice. So, try the curly braces. This worked for me.

UPDATED ANSWER:

Sorry, I should have tested the values that YOU provided. Yeah, to make it work I had to wrap C:\path\ in single quotes:

FROM centos:latest

ARG destpath='C:\path\'
ARG javafile=java.exe
ARG javapath=${destpath}${javafile}

RUN echo $javapath

Result:

$ docker build -t temp .
Sending build context to Docker daemon  2.048kB
Step 1/5 : FROM centos:latest
 ---> e934aafc2206
Step 2/5 : ARG destpath='C:\path\'
 ---> Running in 61f1aa0ea477
Removing intermediate container 61f1aa0ea477
 ---> f49332bb07f9
Step 3/5 : ARG javafile=java.exe
 ---> Running in 7f965bea7edf
Removing intermediate container 7f965bea7edf
 ---> b1d66e9b07ff
Step 4/5 : ARG javapath=${destpath}${javafile}
 ---> Running in 9cfb4e2274f3
Removing intermediate container 9cfb4e2274f3
 ---> 65dc408e384b
Step 5/5 : RUN echo $javapath
 ---> Running in 7906c930caef
C:\path\java.exe ##################################### there you go
Removing intermediate container 7906c930caef
 ---> 887ef91def32
Successfully built 887ef91def32
Successfully tagged temp:latest

OLD ANSWER:

FROM centos:latest

ARG destpath=hello
ARG javafile=world
ARG javapath=${destpath}${javafile}

RUN echo $javapath

My result was as following:

$ docker build -t temp .
Step 1/5 : FROM centos:latest
 ---> e934aafc2206
Step 2/5 : ARG destpath=hello
 ---> Running in 30f047122373
Removing intermediate container 30f047122373
 ---> 582d3a801fd0
Step 3/5 : ARG javafile=world
 ---> Running in 78817656b729
Removing intermediate container 78817656b729
 ---> a3afa410e42e
Step 4/5 : ARG javapath=${destpath}${javafile}
 ---> Running in 8baf8c862572
Removing intermediate container 8baf8c862572
 ---> 1a9c012e4d57
Step 5/5 : RUN echo $javapath
 ---> Running in 48ee08e6452d
helloworld ############################################## there it is
Removing intermediate container 48ee08e6452d
 ---> 9d72ba2aab67
Successfully built 9d72ba2aab67
Successfully tagged temp:latest

P.S. If this doesn't work, it's windows' fault.

edited May 11, 2018 at 19:23

answered May 11, 2018 at 19:16

Kevin Kopf

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2 Comments

Arthur Recalde Over a year ago

Thank you for your help. Unfortunately it doesn't work when I try it, my echo $javapath results on $javapath and echo %javapath% results in ${destpath}${javafile}. Seems to be a windows issue, and I have yet to see a solution/example online.

Kevin Kopf Over a year ago

windows is not the best thing to use with... everything when you do programming...

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