(advice-add 'shell-command-on-region :after
  (lambda (&rest _args)
    "`shell-command-on-region' (M-|) の実行後、\
*Shell Command Ooutput* バッファの内容をコピーする。"
    (when (called-interactively-p 'interactive)
      (with-current-buffer (if (boundp 'shell-command-buffer-name)
                               shell-command-buffer-name
                             "*Shell Command Output*")
        (kill-ring-save (point-min) (point-max))))))