instruction: Create a Dockerfile for fundamentals
output: ```dockerfile
  from that point onwards.The USER instruction on line 4 evaluates to what_user, since at that
  point the username argument has a value of what_user which was passed on
  the command line. Prior to its definition by an ARG instruction, any use of
  a variable results in an empty string.An ARG variable declared within a build stage is automatically inherited by
  other stages based on that stage. Unrelated build stages do not have access to
  the variable. To use an argument in multiple distinct stages, each stage must
  include the ARG instruction, or they must both be based on a shared base
  stage in the same Dockerfile where the variable is declared.For more information, refer to variable scoping.Using ARG variablesYou can use an ARG or an ENV instruction to specify variables that are
  available to the RUN instruction. Environment variables defined using the
  ENV instruction always override an ARG instruction of the same name. Consider
  this Dockerfile with an ENV and ARG instruction.
  ```