添加环境变量：

DATABASES=db1,db2,db3,db4,db5

方法一：

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entrypoint:
      bash -c "DBs=($${DATABASES//,/ });
      for db in $${DBs[@]}; 
      do
          echo   "'"CREATE DATABASE IF NOT EXISTS $$db;"'" >> /docker-entrypoint-initdb.d/create_databases.sql;
      done;
      /usr/local/bin/docker-entrypoint.sh --character-set-server=utf8mb4 --collation-server=utf8mb4_unicode_ci
      "

方法二:

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entrypoint:：
    sh -c "
         echo '
             CREATE DATABASE IF NOT EXISTS db1; 
             CREATE DATABASE IF NOT EXISTS db2; 
         ' >> /docker-entrypoint-initdb.d/create_databases.sql;
      /usr/local/bin/docker-entrypoint.sh 
     "

方法三:

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entrypoint:：
     sh -c "
     echo  "'"
     USE mysql;\n
     DELIMITER //\n
     DROP PROCEDURE IF EXISTS temp112233;\n
     CREATE PROCEDURE temp112233()\n
     BEGIN\n
     DECLARE var varchar(500) DEFAULT \"$${DATABASES}\";\n
     DECLARE db varchar(50);\n
     WHILE var != \"\" DO\n             
         IF LOCATE(\",\", var) > 0 THEN\n
             SET db = SUBSTRING(var,1, LOCATE(\",\", var)-1);\n
             SET var = SUBSTRING(var, LOCATE(\",\", var) + 1);\n
         ELSE\n
             SET db = var;\n
             SET var = \"\";\n
         END IF;\n
         SET @query = CONCAT(\"CREATE DATABASE IF NOT EXISTS  \`\", db, \"\`\");\n
         PREPARE stmt FROM @query;\n
         EXECUTE stmt;\n
         DEALLOCATE PREPARE stmt;\n
     END WHILE;\n
     END; //\n
     DELIMITER ;\n
     call temp112233();\n
     DROP PROCEDURE IF EXISTS temp112233;"'" >>/docker-entrypoint-initdb.d/create_databases.sql;
     /usr/local/bin/docker-entrypoint.sh --character-set-server=utf8mb4 --collation-server=utf8mb4_unicode_ci"
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USE mysql;
DELIMITER //
DROP PROCEDURE IF EXISTS temp112233;
CREATE PROCEDURE temp112233()
BEGIN
DECLARE var varchar(300) DEFAULT "db12,db13,db14";
DECLARE mydb varchar(20);
WHILE var != ''  DO
    IF LOCATE(",", var) > 0 THEN
        SET mydb = SUBSTRING(var,1, LOCATE(",", var)-1);
        SET var = SUBSTRING(var, LOCATE(",", var) + 1);
    ELSE
        SET mydb = var;
        SET var = '' ;
    END IF;
	-- 使用变量创建数据库
    SET @query = CONCAT('CREATE DATABASE IF NOT EXISTS  `', mydb, '`');
    PREPARE stmt FROM @query;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
    select var as var ,mydb as mydb;
END WHILE;
END; //
DELIMITER ;
call temp112233();

方法四:

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RUN set -ex; \
     echo ${DATABASES} | awk -F, '{for(i=1;i<=NF;i++){print "CREATE DATABASE IF NOT EXISTS " $i ";"}}' >/docker-entrypoint-initdb.d/add_new_databases.sql;

docker-entrypoint-initdb.d/

文件类型 执行动作
*.sh “$f”
*.sql docker_process_sql < “$f”
*.sql.gz gunzip -c “$f”
*.sql.xz xzcat “$f”
* mysql_warn “$0: ignoring $f” ;;