DB="your_database_name"
USER="your_db_user"
PASS="your_db_pass"
(
    echo 'ALTER DATABASE `'"$DB"'` CHARACTER SET utf8 COLLATE utf8_general_ci;'
    mysql -p$PASS -u $USER "$DB" -e "SHOW TABLES" --batch --skip-column-names \
    | xargs -I{} echo 'ALTER TABLE `'{}'` CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;'
) \
| mysql -p$PASS -u $USER "$DB"