PHP - 从文件指针中删除行

How can I remove a line from a file pointer in PHP? I open the file using fgets() and not with file() because the file is too big.

The actual problem is: I have 2 very big files. I need to remove all lines from file 1 which exist in file 2.

This is the code:

$handle1 = fopen("1.txt", "r+");
$handle2 = fopen("2.txt", "r");

if ($handle2) {
    while (!feof($handle2)) {
        $buffer2 = trim(fgets($handle2));

            if ($handle1) {
                while (!feof($handle1)) {
                    $buffer1 = trim(fgets($handle1));
                    if($buffer1 == $buffer2)
                        // stuck here
                }
                fclose($handle1);
            }

    }
    fclose($handle2);
}

How the line can be removed?

Thanks!