Search/replace-like feature for swapping text

Question

I frequently find myself trying to replace e.g. foo with bar and bar with foo in a buffer.

The way I usually do it is either:

• 3 query-replaces: aaa -> @@@, bbb -> aaa, @@@ -> bbb
• give up on automation and just do the replacement by hand

I suppose that it is possible to get something working using the , syntax in query-replace-regexp to test if the matched string is aaa or bbb. But the resulting syntax would be too cumbersome, so I never really tried it.

The thing is, given how common a task it is, I think there must be a better, single-step, way of doing it, either built-in or in an existing package. Is there?

Answer 1

Here is a small command that will do this:

(defun query-swap-strings (from-string to-string &optional delimited start end)
  "Swap occurrences of FROM-STRING and TO-STRING."
  (interactive
   (let ((common
          (query-replace-read-args
           (concat "Query swap"
                   (if current-prefix-arg
                       (if (eq current-prefix-arg '-) " backward" " word")
                     "")
                   (if (use-region-p) " in region" ""))
           nil)))
     (list (nth 0 common) (nth 1 common) (nth 2 common)
           (if (use-region-p) (region-beginning))
           (if (use-region-p) (region-end)))))
  (perform-replace
   (concat "\\(" (regexp-quote from-string) "\\)\\|" (regexp-quote to-string))
   `(replace-eval-replacement replace-quote (if (match-string 1) ,to-string ,from-string))
   t t delimited nil nil start end))

Answer 2

Install plur

and run the command plur-query-replace

and input {foo,bar} and its replacement {bar,foo}

Hit y to replace the occurrences as desired.

There are also non-interactive, and isearch-like, variants of this command.