Minify/compress CSS with regex?

Question

In PHP can you compress/minify CSS with regex (PCRE)?

(As a theoretical in regex. I\'m sure there are libraries out there that do this well.)

_Background

Answer 1

Here is a compact source of how I do it. With compression. And you don't have to care, if you changed something in the source.

In fact '//comments' are not allowed in css.

ob_start('ob_handler');
if(!file_exists('style/style-min.css) 
or filemtime('style/style.css') > filemtime('style/style-min.css')){
  $css=file_get_contents('style/style.css');    
  //you need to escape some more charactes if pattern is an external string.
  $from=array('@\\s*/\\*.*\\*/\\s*@sU', '/\\s{2,}/');
  $to=  array(''                      , ' ');
  $css=preg_replace($from,$to,$css); 
  $css=preg_replace('@\s*([\:;,."\'{}()])\s*@',"$1",$css);  
  $css=preg_replace('@;}@','}',$css);
  header('Content-type: text/css');
  echo $css;
  file_put_contents('style/style-min.css',$css);
  //etag- modified- cache-control- header
  }
else{
  //exit if not modified?
  //etag- modified- cache-control- header
  header('Content-type: text/css');
  readfile('style/style-min.css');
  }   
ob_end_flush();

PS Who gave me the minus before I'm ready with typing? QTax- For a short time I forgot to escape the backslashes in the $fom array. PSS. Only new version of PHP undestand the 'U' param which makes a regex ungreedy.