这个代码在php中有什么问题

I'm getting this message when I try to run a php script

Warning: preg_replace() [function.preg-replace]: Unknown modifier '.'

This is the code:

$ext = preg_replace("^.+\\.([^.]+)$", "\\1", $file);

You have to add an seperator for regex modifiers and the regex itself. I.e.

$ext = preg_replace("~^.+\.([^.]+)$~", "\1", $file);