定义一个 Eshell 命令：
(defun eshell/cat (filename)
"Like cat(1) but with syntax highlighting."
(let ((existing-buffer (get-file-buffer filename))
(buffer (find-file-noselect filename)))
(eshell-print
(with-current-buffer buffer
(if (fboundp 'font-lock-ensure)
(font-lock-ensure)
(with-no-warnings
(font-lock-fontify-buffer)))
(buffer-string)))
(unless existing-buffer
(kill-buffer buffer))
nil))
