Re: Troubles in Regular Expression Paradise

[Joost Kremers <joost.m.kremers@gmail.com>]

Len Blanks wrote:
> (defun now-playing (xml-file)
>   ;;  (interactive "FFile: ")
>   (with-temp-buffer
>     (insert-file-contents xml-file)
>     (goto-char 1)
>     (when (re-search-forward (concat "<title><!\\[CDATA\\[\\([^\\]+\\)\\]></title>"
> 				     "[\0-\377[:nonascii:]]*"
> 				     "<artist><!\\[CDATA\\[\\([^\\]+\\)\\]></artist>"
> 				     "[\0-\377[:nonascii:]]*"
> 				     "<album><!\\[CDATA\\[\\([^\\]+\\)\\]></album>") nil t)
>       (concat "\\2"
> 	      (if (string= (downcase (substring "\\2" -2 -1)) "s") "'" "'s")
> 	      " \\1 from the CD \\3"))))
>
> (message (now-playing "/tmp/now_playing.xml")) ;; test now-playing
>
>
> The regular expression was built and tested using re-build and it works well in matching
> including the groupings \\( ... \\), which re-build colours quite nicely.  But I seem to have done
> something really foolish since referencing \\1, \\2 and \\3 fail, so they don't seem to be
> properly set by the groupings in the re.
>
> The function returns "\2's \1 from the CD \3".
>
> I'm sure the problem is something foolish, but I would really like to know what i did.

You can only use such substitution operators in functions that are aware
of them. Normal string-handling functions are not, you'll need something
like match-string.



-- 
Joost Kremers                                   joostkremers@fastmail.fm
Selbst in die Unterwelt dringt durch Spalten Licht
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