code: def _ParsePathSpecification(
        self, knowledge_base, searcher, file_system, path_specification,
        path_separator):
      
      relative_path = searcher.GetRelativePath(path_specification)
      if not relative_path:
        raise errors.PreProcessFail(
            'Unable to read: {0:s} with error: missing relative path'.format(
                self.ARTIFACT_DEFINITION_NAME))
  
      if path_separator != file_system.PATH_SEPARATOR:
        relative_path_segments = file_system.SplitPath(relative_path)
        relative_path = '{0:s}{1:s}'.format(
            path_separator, path_separator.join(relative_path_segments))
  
      environment_variable = artifacts.EnvironmentVariableArtifact(
          case_sensitive=False, name=self._NAME, value=relative_path)
  
      try:
        logger.debug('setting environment variable: {0:s} to: "{1:s}"'.format(
            self._NAME, relative_path))
        knowledge_base.AddEnvironmentVariable(environment_variable)
      except KeyError:
        # TODO: add and store preprocessing errors.
        pass
docs: Parses artifact file system data for a preprocessing attribute.
  
      Args:
        knowledge_base (KnowledgeBase): to fill with preprocessing information.
        searcher (dfvfs.FileSystemSearcher): file system searcher to preprocess
            the file system.
        file_system (dfvfs.FileSystem): file system to be preprocessed.
        path_specification (dfvfs.PathSpec): path specification that contains
            the artifact value data.
        path_separator (str): path segment separator.
  
      Raises:
        errors.PreProcessFail: if the preprocessing fails.