An S4 class to represent a Dockerfile
an object of class Dockerfile
imagethe base image, used in the FROM statement (character)
maintainera maintainer label or an object of class maintainer (the latter is debrecated)
instructionsan ordered list of instructions in the Dockerfile (list of character)
entrypointthe entrypoint instruction applied to the container
cmdthe default cmd instruction applied to the container
The entrypoint and cmd are provided outside of instructions, as only one of them takes effect. If Cmd or Entrypoint instructions are provided as part of the regular instructions, they appear in the Dockerfile but have no effect.