$re = '/(?=[^|])[^][|]*(?:(\[[^][]*+(?:(?1)[^][]*)*+])[^][|]*)*/';
$str = 'action=search sourcetype=audittrail [ localop | stats count | eval search_id = replace("$top10_drilldown_sid$", "^remote_[^_]*_", "") | table search_id ] [ localop | stats count | eval earliest = $top10_drilldown_earliest$ - 86400 | table earliest ] latest="$top10_drilldown_latest$" | stats values(savedsearch_name) AS search_name';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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