visual-regexp for Emacs is like replace-regexp, but with live visual feedback directly in the buffer. Check out visual-regexp-steroids if you want to use modern regular expressions instead of Emacs-style regular expressions.

While constructing the regexp in the minibuffer, you get live visual feedback for the matches, including group matches:

While constructing the replacement in the minibuffer, you get live visual feedback for the replacements:

It can be used to replace all matches in one go (like replace-regexp), or a decision can be made on each match (like query-replace-regexp).

If you are using Emacs 24, you can get visual-regexp from melpa with the package manager.

Add the following code to your init file. Of course you can select your own key bindings. Note: vr/mc-mark is an interface to multiple-cursors.

(add-to-list 'load-path "folder-in-which-visual-regexp-files-are-in/") ;; if the files are not already in the load path
(require 'visual-regexp)
(define-key global-map (kbd "C-c r") 'vr/replace)
(define-key global-map (kbd "C-c q") 'vr/query-replace)
;; if you use multiple-cursors, this is for you:
(define-key global-map (kbd "C-c m") 'vr/mc-mark)

To customize, use M-x customize-group [RET] visual-regexp.

An interesting application of this is regexp-renaming a bunch of files directly in a dired buffer with live feedback (using wdired-change-to-wdired-mode):

Construction of the regexp:

Construction of the replacement string with inlined preview enabled:

If you found this useful, please consider donating.

BTC: 1BxauiLGMQPb2pavkkQkuFe5CgrGMrUat2