Shell script to change and convert mysql databases charset and collate.

mysql-convert-charset.sh

#!/bin/bash

database='database'
user='user'
pass='pass'

charset='utf8mb4'
collate='utf8mb4_unicode_ci'

echo "Changing charset of database: $database"
mysql -u $user -p$pass $database -s -e "ALTER DATABASE $database CHARACTER SET = $charset COLLATE = $collate;"

for table in $(mysql $database -s --skip-column-names -e 'show tables')
do
  echo ''
  echo "Changing charset of table: $table"
  mysql -u $user -p$pass $database -s -e "ALTER TABLE $table CHARACTER SET $charset COLLATE $collate"

  echo "Converting charset of table: $table"
  mysql -u $user -p$pass $database -s -e "ALTER TABLE $table CONVERT TO CHARACTER SET $charset COLLATE $collate"
done

echo ''
echo 'Conversion done!'
echo ''
echo 'Optimizing tables...'
echo ''

mysqlcheck -u $user -p$pass $database --auto-repair --optimize

echo ''
echo 'Done! Have a nice day! ;)'

Nice - you might have to add "SET FOREIGN_KEY_CHECKS=0;" to line 20 so it reads:
mysql -u $user -p$pass $database -s -e "SET FOREIGN_KEY_CHECKS=0;ALTER TABLE $table CONVERT TO CHARACTER SET $charset COLLATE $collate"
If your database has foreign keys that are characters (like uuid or names) you will get an error "Cannot change column 'uuid': used in a foreign key constraint..." Although not usual in traditional SQL where you would always use int for keys in lots of newer stuff uuid is becoming popular.