How do you use a variable in the "replacement" part of query-replace-regexp?

Question

I want to do simple replacements in a LaTeX source using something like that:

;; test-1
(query-replace-regexp (regexp-quote FOO)
                      (concat "Foo "
                              FOO
                              ".")
                      nil (point-min) (point-max))

;; test-2
(query-replace-regexp (regexp-quote VAR-1)
                      (concat "Foo "
                              VAR-2
                              ".")
                      nil (point-min) (point-max))

FOO, VAR-1 and VAR-2 could be everything and so I have to keep emacs from complaining about Invalid use of ‘\\’ in replacement text.

I have tried to use regexp-quote in the "replacement" part, but it doesn't always work because emacs sometimes complains about invalid use of \\.

I give my solutions here, but beyond whether the code works, I'm interested in understanding what is the correct way to use FOO and VAR-2 in the second argument of query-replace-regexp.

For test-1 I have two solutions:

(query-replace-regexp (concat "\\("
                              (regexp-quote FOO)
                              "\\)")
                      "Foo \\1." nil (point-min) (point-max))

(query-replace-regexp (regexp-quote FOO)
                      (concat "Foo "
                              (replace-regexp-in-string "\\\\"
                                                        "\\\\\\\\"
                                                        (replace-regexp-in-string "\\["
                                                                                  "["
                                                                                  (replace-regexp-in-string "\\]"
                                                                                                            "]"
                                                                                                            FOO)))
                              ".")
                      nil (point-min) (point-max))

For test2 I have one solution:

(query-replace-regexp (regexp-quote VAR-1)
                      (concat "Foo "
                              (replace-regexp-in-string "\\\\"
                                                        "\\\\\\\\"
                                                        (replace-regexp-in-string "\\["
                                                                                  "["
                                                                                  (replace-regexp-in-string "\\]"
                                                                                                            "]"
                                                                                                            VAR-2)))
                              ".")
                      nil (point-min) (point-max))

These solutions seem very clunky to me, especially the one that resorts to using replace-regexp-in-string. I can't believe emacs doesn't allow you to do simple replacements like these, so for that I'd like to figure out the correct way to do it.

Answer 1

In your case, since you're replacing a fixed string by a fixed string, use query-replace instead of query-replace-regexp.

In general, to replace a regexp by a fixed string, use replace-quote (missing from the manual).

(replace-regexp my-regexp (replace-quote my-string))

Answer 2

(Might as well make my comment an answer, I guess. I can delete it if a reply indicates that it's not helpful.)

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I don't understand the question. If you're always using regexp-quote on the first argument then I expect you should be using query-replace and not query-replace-regexp.

And in that case there's no worry about regexp patterns in the replacement text either -- nothing to escape. Have you tried just using query-replace?