Remove header information from rgrep/grep output in emacs?

Question

This is what the buffer looks like when I run rgrep. I'd like to just see my results--all the other information is meaningless to me.

-*- mode: grep; default-directory: "~/.emacs/" -*-
Grep started at Sat Jan 20 12:42:21

grep  --exclude=.\#\* --exclude=\*.o --exclude=\*\~ --exclude=\*.bin --exclude=\*.lbin --exclude=\*.so --exclude=\*.a --exclude=\*.ln --exclude=\*.blg --exclude=\*.bbl --exclude=\*.elc --exclude=\*.lof --exclude=\*.glo --exclude=\*.idx --exclude=\*.lot --exclude=\*.fmt --exclude=\*.tfm --exclude=\*.class --exclude=\*.fas --exclude=\*.lib --exclude=\*.mem --exclude=\*.x86f --exclude=\*.sparcf --exclude=\*.dfsl --exclude=\*.pfsl --exclude=\*.d64fsl --exclude=\*.p64fsl --exclude=\*.lx64fsl --exclude=\*.lx32fsl --exclude=\*.dx64fsl --exclude=\*.dx32fsl --exclude=\*.fx64fsl --exclude=\*.fx32fsl --exclude=\*.sx64fsl --exclude=\*.sx32fsl --exclude=\*.wx64fsl --exclude=\*.wx32fsl --exclude=\*.fasl --exclude=\*.ufsl --exclude=\*.fsl --exclude=\*.dxl --exclude=\*.lo --exclude=\*.la --exclude=\*.gmo --exclude=\*.mo --exclude=\*.toc --exclude=\*.aux --exclude=\*.cp --exclude=\*.fn --exclude=\*.ky --exclude=\*.pg --exclude=\*.tp --exclude=\*.vr --exclude=\*.cps --exclude=\*.fns --exclude=\*.kys --exclude=\*.pgs --exclude=\*.tps --exclude=\*.vrs --exclude=\*.pyc --exclude=\*.pyo -i -nH -e grep *.el

    init.el:236:(global-set-key (kbd "s-f") 'rgrep)
    init.el:237:(global-set-key (kbd "C-f") 'lgrep)

Grep finished (matches found) at Sat Jan 20 12:42:21

Answer 1

The header insert is buried within a call to compilation-start deep within rgrep. There's not a simple way to keep these functions from inserting the header. But you can pretty easily hide the first four lines of the buffer by defining advice.

(defun delete-grep-header ()
  (save-excursion
    (with-current-buffer grep-last-buffer
      (goto-line 5)
      (narrow-to-region (point) (point-max)))))

(defadvice grep (after delete-grep-header activate) (delete-grep-header))
(defadvice rgrep (after delete-grep-header activate) (delete-grep-header))

You can later widen to reveal these lines again with C-xnw.

If you also want to advise lgrep, grep-find and zrgrep, you can replace the defadvice macros above with a programmatic advising like this:

(defvar delete-grep-header-advice
  (ad-make-advice
   'delete-grep-header nil t
   '(advice lambda () (delete-grep-header))))

(defun add-delete-grep-header-advice (function)
  (ad-add-advice function delete-grep-header-advice 'after 'first)
  (ad-activate function))

(mapc 'add-delete-grep-header-advice
      '(grep lgrep grep-find rgrep zrgrep))

Answer 2

A small addition Michael Hoffman's answer: we can add a small button to the grep buffer to toggle the hidden text:

(defmacro with-grep-buffer-writable (&rest body)
  `(save-excursion
     (with-current-buffer grep-last-buffer
       (setq buffer-read-only nil)
       ,@body
       (setq buffer-read-only t))))

(defun hide-grep-header (&rest ignored)
  "Hides (by narrowing) the first few lines of a grep buffer leaving only 
the results. Additionally, a button is created to toggle the lines."
  (with-grep-buffer-writable
   ;;HACK: If we (goto-line 5), the button is inserted *after* the results.
   (goto-line 4)
   (end-of-line)
   (insert "\n")
   (narrow-to-region (point) (point-max))
   (insert-text-button "(...)"
                       'help-echo "Toggle display of grep invocation"
                       'action #'click-show-grep-button)))

(defun click-hide-grep-button (button)
  (with-grep-buffer-writable
   (button-put button 'action #'click-show-grep-button)
   (narrow-to-region (button-start button) (point-max))))

(defun click-show-grep-button (button)
  (with-grep-buffer-writable
   (button-put button 'action #'click-hide-grep-button)
   (widen))
  ; HACK: goto-line won't have any effect because of save-excursion
  (with-current-buffer grep-last-buffer
    (goto-line 1)))

(advice-add 'grep :after #'hide-grep-header)
(advice-add 'rgrep :after #'hide-grep-header)