syslog-ext.el

(defvar syslog-overlay-list nil)

(defun syslog-highlight ()
  " Highlight syslog."
  (interactive)
  (save-excursion
    (goto-char (point-min))
    (let (bop eop string lst ol)
      (while (not (eobp))
        (move-beginning-of-line nil)
        (let ((space 0))
          (while (and (not (eolp)) (<= space 4))
            (search-forward " ")
            (setq space (1+ space))))
        (setq bop (point))
        (search-forward " ")
        (setq eop (1- (point)))
        (unless (eolp)
          (setq string (buffer-substring bop eop))
          (message "string: %s" string)
          (when string
            (unless (and lst (assoc-string string lst))
              (setq ol (make-overlay bop eop))
              (push ol syslog-overlay-list)
              (overlay-put ol 'face '(background-color . "dark slate gray")))
            (add-to-list 'lst string)))
        (forward-line 1)))))