regex to extract data from Apache's access log

alog.php

<?php

$pattern = '/^([0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}) \- \- \[([^\]]+)\] "([A-Z]+) ([^" ]+) [^"]*" ([0-9]+) ([0-9]+) "([^"]*)" "([^"]*)"/';

$heads = 'IP, timestamp, method, URI, status, size, referrer, agent' . PHP_EOL;

fputs(STDOUT, $heads);

while ($entry = fgets(STDIN)) {
        preg_match($pattern, $entry, $segments);
        array_shift($segments);
        fputcsv(STDOUT, $segments);
}