code: public static String interpolate(File dockerFile, FixedStringSearchInterpolator interpolator) throws IOException {
          StringBuilder ret = new StringBuilder();
          try (BufferedReader reader = new BufferedReader(new FileReader(dockerFile))) {
              String line;
              while ((line = reader.readLine()) != null) {
                  ret.append(interpolator.interpolate(line)).append(System.lineSeparator());
              }
          }
          return ret.toString();
      }
docs: Interpolate a docker file with the given properties and filter
  
  @param dockerFile docker file to interpolate
  @param interpolator interpolator for replacing properties
  @return The interpolated contents of the file.
  @throws IOException