[User:root Time:05:47:12 Path:/home/liangdong/php]$ php csv.php 
[User:root Time:05:47:14 Path:/home/liangdong/php]$ cat csv.out 
aaa null

111 222
444 123
123 456
[User:root Time:05:47:17 Path:/home/liangdong/php]$ cat csv.php 
<?php
$fin = fopen('csv.txt', 'r');
$fout = fopen('csv.out', 'w');
while (($row = fgetcsv($fin, 0, ' ', ' ', ' ')) !== false) {
        $index = array_search(123, $row);
        if ($index !== false) {
                $filter[$index] = true;
        }
}
fseek($fin, 0, SEEK_SET);
while (($row = fgetcsv($fin, 0, ' ', ' ', ' ')) !== false) {
        $out_row = array();
        foreach ($row as $index => $value) {
                if (isset($filter[$index])) {
                        $out_row[] = $value;
                }
        }
        if (!empty($out_row)) {
                fputcsv($fout, $out_row, ' ', ' ');
        }
}
fclose($fin);
fclose($fout);
?>