On OS X to start/stop MySQL from the command line:
sudo /usr/local/mysql/support-files/mysql.server start
sudo /usr/local/mysql/support-files/mysql.server stop
On Linux start/stop from the command line:
/etc/init.d/mysqld start
/etc/init.d/mysqld stop
/etc/init.d/mysqld restart
Some Linux flavours offer the service command too
# service mysqld start
# service mysqld stop
# service mysqld restart
or
# service mysql start
# service mysql stop
# service mysql restart