A small PHP-Script for minifying CSS

minify.php

<?php
// specify your css-files and their order here
$cssFiles = array(
  'normalize.css', 'style.css', 'print.css', 'colorbox.css'
);
// the file to write the compressed css to
$minFileName = 'minified.css';

// thats all, just call this file in your browser and it will
// build you a minimized css-file. then just link to this single
// file and you're done.

/*===========================================================================*/

/**
 * This function takes a css-string and compresses it, removing
 * unneccessary whitespace, colons, removing unneccessary px/em
 * declarations etc.
 *
 * @param string $css
 * @return string compressed css content
 * @author Steffen Becker
 */
function minifyCss($css) {
  // some of the following functions to minimize the css-output are directly taken
  // from the awesome CSS JS Booster: https://github.com/Schepp/CSS-JS-Booster
  // all credits to Christian Schaefer: http://twitter.com/derSchepp

  // remove comments
  $css = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $css);

  // backup values within single or double quotes
  preg_match_all('/(\'[^\']*?\'|"[^"]*?")/ims', $css, $hit, PREG_PATTERN_ORDER);
  for ($i=0; $i < count($hit[1]); $i++) {
    $css = str_replace($hit[1][$i], '##########' . $i . '##########', $css);
  }

  // remove traling semicolon of selector's last property
  $css = preg_replace('/;[\s\r\n\t]*?}[\s\r\n\t]*/ims', "}\r\n", $css);
  // remove any whitespace between semicolon and property-name
  $css = preg_replace('/;[\s\r\n\t]*?([\r\n]?[^\s\r\n\t])/ims', ';$1', $css);
  // remove any whitespace surrounding property-colon
  $css = preg_replace('/[\s\r\n\t]*:[\s\r\n\t]*?([^\s\r\n\t])/ims', ':$1', $css);
  // remove any whitespace surrounding selector-comma
  $css = preg_replace('/[\s\r\n\t]*,[\s\r\n\t]*?([^\s\r\n\t])/ims', ',$1', $css);
  // remove any whitespace surrounding opening parenthesis
  $css = preg_replace('/[\s\r\n\t]*{[\s\r\n\t]*?([^\s\r\n\t])/ims', '{$1', $css);
  // remove any whitespace between numbers and units
  $css = preg_replace('/([\d\.]+)[\s\r\n\t]+(px|em|pt|%)/ims', '$1$2', $css);
  // shorten zero-values
  $css = preg_replace('/([^\d\.]0)(px|em|pt|%)/ims', '$1', $css);
  // constrain multiple whitespaces
  $css = preg_replace('/\p{Zs}+/ims',' ', $css);
  // remove newlines
  $css = str_replace(array("\r\n", "\r", "\n"), '', $css);

  // Restore backupped values within single or double quotes
  for ($i=0; $i < count($hit[1]); $i++) {
    $css = str_replace('##########' . $i . '##########', $hit[1][$i], $css);
  }

  return $css;
}

// execute it
$cssContents = '';
foreach($cssFiles as $file) {
  $cssContents .= file_get_contents($file);
}
file_put_contents($minFileName, minifyCss($cssContents));

echo '<h1>Done.</h1><p>Use your minified version by putting &lt;link href=&quot;fileadmin/templates/css/'
   . $minFileName . '&quot; rel=&quot;stylesheet&quot; /&gt;" inside your &lt;head&gt;-tag.</p>';

?>