anchor.diff:  
   USER $USR
   
  -# todo: fix this so it doesn't bust docker cache as often
  -COPY . $HOMEDIR/dotfiles
  +COPY --chown=$USR:$GRP . $HOMEDIR/dotfiles
   
   RUN ["/bin/zsh", "-c", "$HOMEDIR/dotfiles/docker_prereqs/install_user.sh"]
  +
  +WORKDIR $HOMEDIR
   
   # todo: figure out a better entrypoint
   # ENTRYPOINT ["/usr/bin/zsh"]
  
positive.code: RUN groupadd -r $USR && \
      useradd -rmg $GRP $USR
  
  COPY docker_prereqs/system-requirements.txt $HOMEDIR/.docker_prereqs/system-requirements.txt
  
  # Avoid warnings by switching to noninteractive
  ENV DEBIAN_FRONTEND=noninteractive
  
negative.code: # Switch back to dialog for any ad-hoc use of apt-get
  ENV DEBIAN_FRONTEND=dialog
  
  COPY --chown=$USR:$GRP \
      docker_prereqs/install_system.sh \
      $HOMEDIR/dotfiles/docker_prereqs/
  
  RUN $HOMEDIR/dotfiles/docker_prereqs/install_system.sh \
      && rm -fr $HOMEDIR/docker_prereqs
  
  ENV LANG=en_US.UTF-8 \
  