https://forums.docker.com/t/how-can-i-view-the-dockerfile-in-an-image/5687/3

gistfile1.txt

function dc_trace_cmd() {
  local parent=`docker inspect -f '{{ .Parent }}' $1` 2>/dev/null
  declare -i level=$2
  echo ${level}: `docker inspect -f '{{ .ContainerConfig.Cmd }}' $1 2>/dev/null`
  level=level+1
  if [ "${parent}" != "" ]; then
    echo ${level}: $parent 
    dc_trace_cmd $parent $level
  fi
}