Mysql – Cannot log in with created user in thesql

You realize all the configuration lines are commented out? You need to uncomment and fill-in those fields for anything to happen. I think including this one would be sufficient (assuming you want it to prompt you for a username/password):

$cfg['Servers'][$i]['auth_type'] = 'cookie';

You should not rely on MySQL client to pick up the appropriate MySQL configuration file because of the cascading nature of how the client is reading those files. Instead you should put both your my.cnf and test_mysql.sh inside /home/tmp and use --defaults-extra-file [link] parameter in your script.

Do take note, the --defaults-extra-file needs to be the first argument of your mysql command otherwise it won't work.

execute_query(){
    query="$1"
     res=`mysql --defaults-extra-file=/home/tmp/my.cnf --skip-column-names -e "$query"`
    echo "$res"
}

res=`execute_query "show databases"`
echo $res

/root is not a very good place to put stuff in (permissions etc.) and should be avoided.

Running scripts that interact with a MySQL server should also be performed with a non-privileged user.