Unfortunately, what you have provided now is still not a complete spec. You might want any of these things:

• Just process the first line of the file.
• Just process the first line which has a bracket.
• Process every line which starts with an M.
• Process every line which starts with an M and contains a bracket.
• ...

So, your first task is to create a tight specification. After that you can devise an algorithm and only then start to consider the coding.