To get the script you work open your command line and use the following steps:

        nano convert_to_utf8mb4.sh

        paste the script & save

        /*************** start script *********/
        DB="database_name"
USER="mysql_user"
PASS="mysql_password"
(
    echo 'ALTER DATABASE `'"$DB"'` CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;'
    mysql -p$PASS -u $USER "$DB" -e "SHOW TABLES" --batch --skip-column-names \
    | xargs -I{} echo 'ALTER TABLE `'{}'` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;'
) \
| mysql -p$PASS -u $USER "$DB"
        /********* end script **********************/

        sudo chmod 755 convert_to_utf8mb4.sh (in terminal)

        run the script by type ./convert_to_utf8mb4.sh

    Yes, collation has been changed!