Search and Replace for a block on many lines in a dozen files

Question

I have a a bunch of HTML files and in each of them I want to replace a fixed block of approx 30 lines with a one liner.

Is there an Emacs command or package which makes this easier? Using e.g. dired-do-find-regexp-and-replace is pretty unwieldy for long multi-line search or replacement terms.

Answer 1

It is generally easier to match smaller, specific patterns, and then replace the region between them (although in this case the regexp as suggested by NickD works fine (except for a possible extra required .* before bar). Here follows an example for using a 'start' and 'end' pattern and replacing the region in between in a list of files (single file for this example, but you can add more files to the list) on a unix-like system (on windows just adjust the path names):

First save the following text in a file named ~/test.txt:

this is an example
of how to replace
text in some buffer/file

Then evaluate the following snippet of code:

(dolist (x '("~/test.txt"))
  (with-temp-buffer
    (insert-file-contents-literally x)
    (print (point))
    (search-forward "an")
    (let ((start (match-beginning 0)))
      (delete-region start (search-forward "replace"))
      (goto-char start)
      (insert "the result of replacing"))
    (write-file x)))

Of course, like when using regexps, the start and end patterns must be specific enough to not also replace 'unwanted' other blocks.

B.t.w. if it is a fixed block (i.e. a fixed string), then you could probably also just use replace-string. You could bind the string to a variable for use in replace-string.

Here the original file gets overwritten (for which we could have used with-temp-file directly), but you can replace the final x with something like (concat x ".awesome") to write to new files. I've kept the (print (point)) to show explicitly that the point stays at the start after inserting the file contents. In Emacs, usually editing text is done by inserting it to some buffer, also when doing it programmatically. I hope this answer will be useful for your case...