Сергей

$filename = 'test.txt';
$search = 43343443;

$h = @fopen($filename, 'r') or die("Файл '$filename' не найден!");

while (! feof($h)) {
    $line = trim(fgets($h));
    if ($line == $search) {
        echo $line;
    }
}

fclose($h);