MySQLDump – Is there any way I can enter the password with -p or –password

Do not mess with the mysql db. There is a lot more going on there than just the users table. Your best bet is the "SHOW GRANTS FOR" command. I have a lot of CLI maintenance aliases and functions in my .bashrc (actually my .bash_aliases that I source in my .bashrc). This function:

mygrants()
{
  mysql -B -N $@ -e "SELECT DISTINCT CONCAT(
    'SHOW GRANTS FOR \'', user, '\'@\'', host, '\';'
    ) AS query FROM mysql.user" | \
  mysql $@ | \
  sed 's/\(GRANT .*\)/\1;/;s/^\(Grants for .*\)/## \1 ##/;/##/{x;p;x;}'
}

The first mysql command uses SQL to generate valid SQL which is piped to the second mysql command. The output is then piped through sed to add pretty comments.

The $@ in the command will allow you to call it as: mygrants --host=prod-db1 --user=admin --password=secret

You can use your full unix tool kit on this like so:

mygrants --host=prod-db1 --user=admin --password=secret | grep rails_admin | mysql --host=staging-db1 --user=admin --password=secret

That is THE right way to move users. Your MySQL ACL is modified with pure SQL.

In order to connect to the mysql server you must provide credentials. You can specify them in a configuration file, pass them via the command line, or simply create account that doesn't require credentials.

Of course the no-password option should never be used, the pass-by command line isn't great because anyone who can run ps may be able to see the command line.

The recommended option is to create a mysql configuration file with the credentials in it and then protect that file with filesystem permissions so only your backup user can access it.

You being able to login to the mysql server while logged in interactively as root seems to suggest that you either don't have a root password set, or that you have a configuration file that is not being found by your script. If you have a .my.cnf you may need to manually point to it. If your root account doesn't have a password set then I would strongly encourage you to fix that.

Update (2016-06-29) If you are running mysql 5.6.6 or greater, you should look at the mysql_config_editor tool that allows you to store credentials in an encrypted file. Thanks to Giovanni for mentioning this to me.