Loccur is an amazing tool to quickly navigate in a file. It is a minor mode for Emacs acting like occur but w/o creating a new window. It just hides all the text excepting lines containing matches.

Add to your .emacs or .emacs.d/init.el following lines:

(setq package-archives '(("gnu" . "http://elpa.gnu.org/packages/")
                         ("melpa" . "http://melpa.milkbox.net/packages/")))

Press M-x in GNU Emacs and write list-packages. Find the loccur in the list of packages and press i to select this package, x to install the package.

Better to see it once:

To use it, add the following to your .emacs file:

(require 'loccur)
;; defines shortcut for loccur of the current word
(define-key global-map [(control o)] 'loccur-current)
;; defines shortcut for the interactive loccur command
(define-key global-map [(control meta o)] 'loccur)
;; defines shortcut for the loccur of the previously found word
(define-key global-map [(control shift o)] 'loccur-previous-match)

Now you can point the cursor to the word and press Ctrl+o to hide all lines except those containing this word. Moving cursor to the required line and pressing Ctrl+o again will shows all the text. The good thing about this mode is what you can navigate through the buffer easily. Ctrl+Shift+o will repeat last search.

Below is the list of interactive commands available for user:

• loccur interactively asks user for regexp to search or toggle search off (if loccur-mode is already enabled)
• loccur-current searches for the current word under the cursor
• loccur-previous-match repeat previous loccur command
• loccur-no-highlight is the same as loccur but not highlighting matches
• loccur-toggle-highlight toggles highlighting of matches

• loccur-jump-beginning-of-line variable specifies if move the cursor to the beginning of the matching line. Default nil
• loccur-highlight-matching-regexp variable whenever loccur should highlight matching words. Default t.
• loccur-face face to be used while highlighting. Default points to isearch face.

To combine Loccur and isearch functionality (narrowing-search) one can use the following hooks:

(add-hook 'isearch-update-post-hook
          (lambda ()
            (let ((loccur-mode nil))
              (loccur (regexp-quote isearch-string)))))

(add-hook 'isearch-mode-end-hook
          (lambda ()
            (loccur nil)))