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I know, Emacs allows calling ELisp while replacing a text with a regex, aka C-M-%, which is bound to query-replace-regexp. I'm trying to make use of that to store an unwieldy regexp as a variable, so instead of writing it out every time, I could just extract it from a variable.

For the sake of simplification, in the testcase here I'm using just a text, so no backslashes are involved:

(setq foo "text")

Text is:

text text

Here's what I tried as the REGEXP in query-replace-regexp:

  • \,foo
  • \,'foo
  • \,(eval 'foo)
  • \,(eval foo)

None of those work for me. How can I make it work?

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  • Do you mean you want to enter the variable name into the interactive prompt after pressing C-M-%? Commented May 27, 2021 at 10:37
  • @choroba correct Commented May 27, 2021 at 10:39
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    You can write a new function that wraps query-replace-regexp and asks for a variable to insert. Commented May 27, 2021 at 10:40
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    You can use the X option of interactive to ask for a List expression and evaluate it. Commented May 27, 2021 at 10:56
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    In reading the doc of query-replace-regexp, it mentions the \, syntax in the replacement text part, but not in the regex part. So AFAICT, you cannot do what you want: you'd have to write your own souped-up version of query-replace-regexp as @choroba suggests. Commented May 27, 2021 at 11:03

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In reading the doc of query-replace-regexp, it mentions the \, syntax in the replacement text part, but not in the regex part:

In interactive calls, the replacement text can contain ‘,’ followed by a Lisp expression.

So AFAICT, you cannot do what you want interactively: you'd have to write your own souped-up version of query-replace-regexp as @choroba suggests in the comments.

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M-: (query-replace-regexp foo "bar") RET
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  • Well, yeah, that might work too. ⁺¹. Commented May 27, 2021 at 11:26

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