ログの最新版のみバッファに取得するメソッド

re-load-log.el

(setq file-size (make-hash-table :test #'equal))
(defun re-load-log (file-name)
 (interactive)
 (let (point-last-read regenesis)
   (setq point-last-read (gethash file-name file-size))
   (with-temp-buffer
     (insert-file-contents file-name)
     (when (> point-last-read (point-max))
       (setq point-last-read (point-min)))
     (when (not point-last-read)
       (setq point-last-read (point-min)))
     (setq regenesis
           (buffer-substring-no-properties point-last-read (point-max)))
         (puthash file-name (point-max) file-size)
     )
   (switch-to-buffer
    (get-buffer-create
     (format "*regenesis %s*" file-name)))
   (cond ((< 0 (length regenesis))
          (delete-region (point-min) (point-max))
          (insert (decode-coding-string
                   (encode-coding-string regenesis 'utf-8) 'utf-8))
          (message "reload done."))
         (t
          (message "No changes.")))))
(global-set-key "\C-cl" '(lambda () (interactive) (re-load-log "path/to/log")))