anchor.diff:    && conan export conan/mruby \
     && conan install . -if build --build=missing \
     -pr $CONAN_PROFILE \
  -  -o run_tests=False \
  +  -o build_tests=$WITH_TESTS \
  +  -o run_tests=$WITH_TESTS \
     -o with_ruby=$WITH_RUBY
   
   # compile source (~20mins - 4hrs for qemu)
  
positive.code: ENV PATH=$HOME/venv3.9/bin:$PATH
  ENV CONAN_PROFILE=conan/profiles/docker
  ENV WITH_RUBY=True
  
  # limit cpus so don't run out of memory on local machine
  # symptom: get error - "c++: fatal error: Killed signal terminated program cc1plus"
  # could turn off if building in cloud
  ENV CONAN_CPU_COUNT=1
  
  # make installer
  
negative.code: # MTConnect Public C++ Agent Docker image build instructions
  
  # ---------------------------------------------------------------------
  # notes
  # ---------------------------------------------------------------------
  #
  # to build a cross-platform image, push to docker hub, and run it -
  # (see CMakeLists.txt for current version number) -
  #
  #   docker buildx build \
  #     --platform linux/amd64,linux/arm64 \
  #     --tag mtconnect/agent:2.0.0.12_RC18 \
  #     --push \
  #     .
  #
  #   docker run -it --rm --init --name agent -p5001:5000 \
  #     mtconnect/agent:2.0.0.12_RC18
  #
  # then visit http://localhost:5001 to see the demo output.
  
  # ---------------------------------------------------------------------
  # os
  