批处理脚本 - 查找文件中是否缺少字符串，显示输出

I have cluster of 10 folders, each with 1000 program files. I need to search these text files for a MISSING string. All files must start with $O123456.MIN% (123456 being random file names). I know how to find if the string exists, but how do I identify if the string does not exist?I have cluster of 10 folders, each with 1000 pr