RE: [h-e-w] RegExp in

[Dr Francis J. Wright]

> From: 
> address@hidden 
> [mailto:address@hidden
> rg] On Behalf Of Slava
> Sent: Wednesday, 15 September 2004 12:22 pm
> To: address@hidden
> Subject: [h-e-w] RegExp in 
> 
> Next code doesn't search anything. Why?
> 
> (defun my-function ()
>       "Replace  '%' with '\%' (it should skip percent signs already
>       with the slash"
>       (interactive)
>       (while (re-search-forward "\([^\\]\)%" nil t)   
>               (replace-match "\1%" nil nil)))
> 
> It works without '\(...\)', but then I loose one symbol 
> before each percent sign being replaced.


One problem is that the read syntax for a \ in a string is "\\", hence you
need to double every \, not only the one in the [].  However, with that fix
I think your code would perform an identity operation, i.e. effectively do
nothing.  So I suggest something like this:

(while (re-search-forward "[^\\]%" nil t)
   (backward-char)
   (insert "\\"))

The search should position point after the %, provided % is not preceded by
\.  Hence the (backward-char).  Note that I haven't tested this code.

Francis