PHP proc_open - 连接到mysqldump工作，但不是mysql

I have the problem, that mysql does not allow me to connect in one case, but in another one it does.

i am using proc_open to connect to mysql via the mysqldump command and pass the password through the pipe.

interestingly this call works as expected, whereas the other one doesn't....

$command = "mysqldump --no-data -h 127.0.0.1 -u root -p dbname > /var/www/html/dump.sql"
$process = proc_open($command, [
    0 => ["pipe", "r"],
    1 => ["pipe", "w"],
    2 => ["pipe", "w"]
], $pipes);

if (is_resource($process))
{
    fwrite($pipes[0], $this->password);
    fclose($pipes[0]);
    ...

the next call does not work - ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES).

i really don't understand that, because the connection establishment should be the same for mysql and mysqldump. i can assure, that the password is correct, because it is fetched from a config file and I already checked by debugging.

if i execute the same command directly on shell, i don't have a problem to connect by entering the password. but through php it does not work.

$command = "mysql -h 127.0.0.1 -u root -p -D dbname < /var/www/html/dump.sql"
$process = proc_open($command, [
    0 => ["pipe", "r"],
    1 => ["pipe", "w"],
    2 => ["pipe", "w"]
], $pipes);

if (is_resource($process))
{
    fwrite($pipes[0], $this->password);
    fclose($pipes[0]);
    ...