How to combine change `key: foo`, `key: bar`, `key: baz` to `key: foo bar baz`?

Question

To clarify this is what I'd like to do:

Text Before:

key: foo
key: bar
key: baz

Text After:

key: foo bar baz

Wondering if anyone has a good technique for this type of operation (simpler the better). Suspect it might be possible with replace-regexp and some back reference trickery - been trying to figure out a way but no inspiration has hit yet :)

Answer 1

Here is a command to merge two lines, if these two lines share a common prefix, don't duplicate it

(defun my-merge-two-lines ()
  "Merge the next line into the current line."
  (interactive)
  (save-excursion
    (let (current-line next-line prefix)
      (setq current-line
            (buffer-substring (line-beginning-position) (line-end-position)))
      (kill-whole-line)
      (setq next-line
            (buffer-substring (line-beginning-position) (line-end-position)))
      (kill-whole-line)
      (setq prefix (fill-common-string-prefix current-line next-line))
      (insert
       (concat current-line " " (substring next-line (length prefix)) "\n")))))

For example, assuming the point is on the first line

key: foo
key: bar
key: baz

run the above command twice, the text becomes

key: foo bar baz

---

If you like the idea, you can simply use the builtin M-^ (delete-indentation/join-line), note that you need manually set the prefix to "key: " via C-x . (set-fill-prefix).