docs: def parse_env_file(env_file):
      """
      Reads a line-separated environment file.
      The format of each line should be "key=value".
      """
      environment = {}
  
      with open(env_file, 'r') as f:
          for line in f:
  
              if line[0] == '#':
                  continue
  
              line = line.strip()
              if not line:
                  continue
  
              parse_line = line.split('=', 1)
              if len(parse_line) == 2:
                  k, v = parse_line
                  environment[k] = v
              else:
                  raise errors.DockerException(
                      'Invalid line in environment file {0}:\n{1}'.format(
                          env_file, line))
  
      return environment