php中三元运算符用法

$id = isset($_GET['id']) ? $_GET['id'] : false;

?>

$filename = isset($argv[1]) ? $argv[1] : "php://stdin";
$fp = @fopen($filename, ‘r’) or die("Can’t Open $filename for reading");

while (!@feof($fp)) {
    $line = @fgets($fp, 1024);
    print $line;
}

@fclose($fp);
?>

if (isset($argv[1])) {
    $filename = $argv[1];
} else {
    $filename = "php://stdin";
}
?>

$filename = $argv[1] or $filename = "php://stdin";
?>