docs: def _get_env(self):
          """this returns an environment dictionary we want to use to run the command
  
          this will also create a fake pgpass file in order to make it possible for
          the script to be passwordless"""
          if hasattr(self, 'env'): return self.env
  
          # create a temporary pgpass file
          pgpass = self._get_file()
          # format: http://www.postgresql.org/docs/9.2/static/libpq-pgpass.html
          pgpass.write('*:*:*:{}:{}\n'.format(self.username, self.password).encode("utf-8"))
          pgpass.close()
          self.env = dict(os.environ)
          self.env['PGPASSFILE'] = pgpass.name
  
          # we want to assure a consistent environment
          if 'PGOPTIONS' in self.env: del self.env['PGOPTIONS']
          return self.env