Emacs查询替换文本转换

Question

I want to find any text in a file that matches a regexp of the form t [AZ] u (ie, a match t followed by a capital letter and another match u , and transform the matched text so that the capital letter is lowercase. For example, for the regexp x[AZ]y

xAy

becomes

xay

and

xZy

becomes

xzy

Emacs' query-replace function allows back-references, but AFAIK not the transformation of the matched text. Is there a built-in function that does this? Does anybody have a short Elisp function I could use?

UPDATE

@Marcel Levy has it: \\, in a replacement expression introduces an (arbitrary?) Elisp expression. Eg, the solution to the above is

M-x replace-regexp <RET> x\([A-Z]\)z <RET> x\,(downcase \1)z

Answer 1

It looks like Steve Yegge actually already posted the answer to this a few years back: "Shiny and New: Emacs 22." Scroll down to "Changing Case in Replacement Strings" and you'll see his example code using the replace-regexp function.

The general answer is that you use "\\," to call any lisp expression as part of the replacement string, as in \\,(capitalize \\1) . Reading the help text, it looks like it's only in interactive mode, but that seems like the one place where this would be most necessary.

Answer 2

An alternative to qrr in this case is recording a macro and replaying it. (isearch-forward-regexp, select the character, downcase-region.) I find on the fly macros easier, since you get immediate feedback if your regexp is wrong.

Answer 3

I'd do this with a macro as well, but only because executing code from within a replacement string for a regular expression is very unintuitive to me. If you're writing a batch script or something that needs to go very fast, \\, is certainly the way to go.