$re = '/.*?array\((\'.*?)\), [^\)]+\'\);.*/m';
$str = 'drupal_add_js(array(\'my_common\' => array(\'my_code_validate\' => variable_get(\'my_code_validate\', FALSE), \'inner_index2 => \'inner_value2\'), \'another_item\' => \'another_value\'), \'setting\');';
$subst = "$1";
$result = preg_replace($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