application server file downloading

Hi Experts,

I have very urgent requiremnts for this :

1. The data extract needs to be downloaded on SAP application server ( take whatever path accessible to you).

2. Thereafter for every run, it should check if the file available in the same path and if yes then append data to this file instead of creating new one.

3. If file is not available then create new file.

please suggest me, how to do this.

it's very urgent

Regards

Mohit