docs: def _check_file_exists_unix(self, remote_cmd=""):
          """Check if the dest_file already exists on the file system (return boolean)."""
          if self.direction == "put":
              self.ssh_ctl_chan._enter_shell()
              remote_cmd = "ls {}".format(self.file_system)
              remote_out = self.ssh_ctl_chan.send_command(
                  remote_cmd, expect_string=r"[\$#]"
              )
              self.ssh_ctl_chan._return_cli()
              return self.dest_file in remote_out
          elif self.direction == "get":
              return os.path.exists(self.dest_file)