How to concatenate data based on file name

[#1]

Hi Friends,

I have loaded a file from D drive.

The user has the option to  change the file on the drive.

Now the condition are 1) If the first three letters of the  file name are same as previous one I need to replace the file.

                                 2) If the file name is diffrent I need to concatenate to the existing file.

Thanks

pavan