To implement --ignore-database option (f.e. to exclude MySQL internal databases), use following:
mysqldump -u{USER_NAME} -p{PASSWORD} --databases `mysql -u{USER_NAME} -p{PASSWORD} --skip-column-names -e "SELECT GROUP_CONCAT(schema_name SEPARATOR ' ') FROM information_schema.schemata WHERE schema_name NOT IN ('mysql', 'performance_schema', 'information_schema');"` > dump.sql