$re = '/.*(:2(\[(((\d*,){3})\]))).*/';
$str = ':1[2,2,2,]:2[0,14,88,]:homebase[7,4,1776,]:';
$subst = "$4";
$result = preg_replace($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