How to make query-replace automatically fill what I want to replace with marked text?

Question

I want to select some text somewhere in a buffer, call query-replace and then type (or paste from kill-ring) only the second argument, TO-STRING, (and make the selected text count as FROM-STRING).

I want a replacement to be performed within the entire buffer as well.

Answer 1

If you use library Replace+ (replace+.el) then you can just customize option search/replace-region-as-default-flag to non-nil. That gives you the region text as FROM text default, so you can just hit RET to accept that.

search/replace-region-as-default-flag is a variable defined in replace+.el.

Its value is nil

Documentation:

Non-nil means use the active region text as default for search/replace.

That is, if the region is currently active then use its text as the default input. All text properties are removed from the text.

Note that in this case the active region is not used to limit the search/replacement scope. But in that case you can of course just narrow the buffer temporarily to restrict the operation scope.

A non-nil value of this option takes precedence over the use of option search/replace-2nd-sel-as-default-flag. To give that option precedence over using the active region, you can set this option to nil and use region-or-non-nil-symbol-name-nearest-point as the value of option search/replace-default-fn.

You can customize this variable.

You can also use command toggle-search/replace-region-as-default anytime to toggle the option value.

---

But if you really want not to even have to hit RET to accept the region text then you'll need to write a command that uses that as the FROM arg to query-replace and then interactively reads the other args.

This should do that:

(defun my-q-r (from-string to-string
               &optional delimited start end backward region-noncontiguous-p)
  "Query-replace text of active region with text you're prompted for."
  (interactive
   (progn
     (barf-if-buffer-read-only)
     (let* ((from (if (use-region-p)
              (buffer-substring (region-beginning) (region-end))
            (query-replace-read-from "Query replace" nil)))
        (to (if (consp from) (prog1 (cdr from) (setq from (car from)))
          (query-replace-read-to from "Query replace" nil))))
       (list from to
         (or (and current-prefix-arg (not (eq current-prefix-arg '-)))
         (and (plist-member (text-properties-at 0 from) 'isearch-regexp-function)
                      (get-text-property 0 'isearch-regexp-function from)))
         (and current-prefix-arg (eq current-prefix-arg '-))))))
  (deactivate-mark)
  (query-replace from-string to-string delimited start end backward region-noncontiguous-p))

Answer 2

M-w M-< M-% C-y RET <replacement> RET ! 

does the trick.