How to prepend something to CLI in docker container? - docker

Question

I want to prepend something to the CLI passed in to a docker container.
I want it to run like this:
docker run -it mstools msbuild.exe --version
But, to make that work internally I need to prepend the full path the the msbuild.exe along with mono, like this:
mono /Microsoft.Build.Mono.Debug.14.1.0.0-prerelease/lib/msbuild.exe --version
When I use my below Dockerfile with the command, I get this:
$ docker run -it mstools msbuild.exe --version
msbuild.exe: 1: msbuild.exe: [/usr/bin/mono,: not found
If I jump into the container and check the path:
$ docker run -it --entrypoint=bash mstools
root#eb47008f092e:/# which mono
/usr/bin/mono
What am I missing??
Dockerfile:
FROM centeredge/nuget
ARG VERSION="14.1.0.0-prerelease"
RUN nuget install Microsoft.Build.Mono.Debug -Version $VERSION -Source "https://www.myget.org/F/dotnet-buildtools/"
ENV PATH="/Microsoft.Build.Mono.Debug.$VERSION/lib/:${PATH}"
ENTRYPOINT ['/usr/bin/mono', " /Microsoft.Build.Mono.Debug.$VERSION/lib/$1 $#"]

Answer 1

The error you get certainly comes from the fact you use single quotes ' instead of double quotes " in the ENTRYPOINT exec form.
In addition, I don't think the "$#" phrasing you mention will work (because "$#" needs some shell to evaluate it, while in the exec form there is no /bin/sh -c … implied). But the exec form of ENTRYPOINT is definitely the way to go.
So I'd suggest you write something like this:
FROM centeredge/nuget
ARG VERSION="14.1.0.0-prerelease"
RUN nuget install Microsoft.Build.Mono.Debug -Version $VERSION -Source "https://www.myget.org/F/dotnet-buildtools/"
ENV PATH="/Microsoft.Build.Mono.Debug.$VERSION/lib/:${PATH}"
COPY entrypoint.sh /usr/src/
RUN chmod a+x /usr/src/entrypoint.sh
ENTRYPOINT ["/usr/src/entrypoint.sh"]
with entrypoint.sh containing:
#!/bin/bash
exec /usr/bin/mono "/Microsoft.Build.Mono.Debug.$VERSION/lib/$1" "$#"
(Note: I didn't test this example code for now so please comment if you find some typo)

Answer 2

Final working solution based on #ErikMD's answer:
FROM centeredge/nuget
ARG VERSION="14.1.0.0-prerelease"
RUN nuget install Microsoft.Build.Mono.Debug -Version $VERSION -Source "https://www.myget.org/F/dotnet-buildtools/"
ENV PATH="/Microsoft.Build.Mono.Debug.$VERSION/lib/:/Microsoft.Build.Mono.Debug.$VERSION/lib/tools/:${PATH}"
RUN echo '#!/bin/bash' > /usr/src/entrypoint.sh && echo 'exec /usr/bin/mono "$(which "$1")" "$#"' >> /usr/src/entrypoint.sh && chmod a+x /usr/src/entrypoint.sh
ENTRYPOINT ["/usr/src/entrypoint.sh"]
output
docker run -it mstools MSBuild.exe -version
Microsoft (R) Build Engine version 14.1.0.0
Copyright (C) Microsoft Corporation. All rights reserved.
14.1.0.0