- Fix issue found by Shellcheck.

files/backup.sh

@@ -10,7 +10,7 @@ if databases="$(mysql --defaults-file=/etc/mysql/mysqldump.cnf \
                       --execute 'show databases;' | grep -vx $filter)"
 then
     mysqldump --defaults-file=/etc/mysql/mysqldump.cnf
-              --databases $databases || \
+              --databases "$databases" || \
     echo "MySQL backup: Failed to backup."
 else
     echo "MySQL backup: No databases to backup."