$re = '/<a href="entry:\/\/([^_]+)_([^_]+)_([^_]+)" title="/msi';
$str = '<ul><li><span class="Latn" lang="en"><a href="entry://Thousand_Island_dressing" title="Thousand Island dressing">Thousand Island dressing</a></span></li></ul>';
$subst = "<a href=\"entry://$1 $2 $3\" title=\"";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php