$re = '/\S+\[v=\"(customDate)-(\w+)\",g=\"(\w+)\",p=\"(\S+)\"\]\S+\/(returns_period|mpt_statistics_period\/\w+)\/(\w+)\/(\w+)/';
$str = 'root/1-825-ReturnAndStatsCompositeAPI[v="customDate-return",g="customDate",p="{"asOfDate":"2016-12-31","startDate":"2016-05-31"}"]/data/share_classes/array[1]/returns_period/net/cumulative
root/2-825-ReturnAndStatsCompositeAPI[v="customDate-return",g="customDate",p="{"column":"column2","asOfDate":"2016-05-31","startDate":"2016-01-31"}"]/data/share_classes/array[1]/returns_period/net/cumulative
root/2-825-ReturnAndStatsCompositeAPI[v="customDate-return",g="customDate",p="{"column":"column2","asOfDate":"2016-05-31","startDate":"2016-01-31"}"]/data/share_classes/array[1]/mpt_statistics_period/absolute/net/maximum_drawdown
root/3-825-ReturnAndStatsCompositeAPI[v="customDate-index",g="customDate",p="{"column":"column1","asOfDate":"2016-12-31","startDate":"2016-05-31"}"]/data/share_classes/array[0]/indices/indices_breakdown/array[0]/returns_period/net/cumulative
root/6-825-ReturnAndStatsCompositeAPI[v="customDate-benchmark",g="customDate",p="{"column":"column2","asOfDate":"2016-05-31","startDate":"2016-01-31"}"]/data/share_classes/array[1]/benchmark_types/benchmark_types_breakdown/array[3]/mpt_statistics_period/relative/net/bear_alpha
';
preg_match_all($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