About backslash in regexp

About backslash in regexp

[Xue Fuqiao]

I understand that the usual regexp special characters are not special
inside a character alternative.  But in the definition of the function
`command-line-normalize-file-name':

(defun command-line-normalize-file-name (file)
[...]
  (string-match "^[A-Za-z]:\\(\\\\[\\\\/]\\)" file) ; C:\/ or C:\\
[...]

There four backslashes in the `[ ... ]' construct here, why?  Aren't
they duplicated?

-- 
Xue Fuqiao
http://www.gnu.org/software/emacs/

Re: About backslash in regexp

[Eli Zaretskii]

> Date: Sat, 16 Mar 2013 10:50:16 +0800
> From: Xue Fuqiao <xfq.free@gmail.com>
> 
> I understand that the usual regexp special characters are not special
> inside a character alternative.  But in the definition of the function
> `command-line-normalize-file-name':
> 
> (defun command-line-normalize-file-name (file)
> [...]
>   (string-match "^[A-Za-z]:\\(\\\\[\\\\/]\\)" file) ; C:\/ or C:\\
> [...]
> 
> There four backslashes in the `[ ... ]' construct here, why?  Aren't
> they duplicated?

It's a bug, now fixed in the development sources.  (That entire
function was dead wrong wrt DOS/Windows file names.)  Thanks for
catching it.