$temp = $file.".tmp_".generate_random_name();
touch($temp);

$reading = fopen($file, 'r');
$writing = fopen($temp, 'w');

$replaced = false;

if ((flock($reading, LOCK_EX)) and (flock($writing, LOCK_EX))) {

    echo $id.' <span style="color: #00aa00;">SUCCESS: Lock acquired.</span><br>';

    while (!feof($reading)) {

        $line = fgets($reading);

        $values = explode("|",$line);

        if ($values[0] == $id) {

            $line = $id."|comment edited!".PHP_EOL;
            $replaced = true;
        }

        fputs($writing, $line);
    }

    flock($reading, LOCK_UN);
    flock($writing, LOCK_UN);

    fclose($reading);
    fclose($writing);

} else {

    echo '<span style="color: #aa0000;">ERROR: Lock not acquired.</span><br>';
}

if ($replaced) {

    rename($temp, $file);

} else {

    unlink($temp);
}