How to sort and sum the following file using flat file records

HI  i am reading the flat file name as xyz123 so in that file ,I was reading that flat file to do the evaluvation as follows

To read that flat file data and to sort the first 100 bytes and summing the remaining bytes ,If any duplicates and store those 

records into the out put file abc123.

Lets consider i have total 500bytes of data is there in the flat file it self ,So i want to sort first 100 bytes and sum the remaining 400 bytes ,If any duplicates are there store into the output file.

Here i am reading from text file only and store into the text file.

Regards