Situation:
Our system currently executes a job (COBOL Program) that generates an interface file to be sent to one of our vendors. Because this system processes information for over 100,000 employees/retirees (and growing), we'd like to multi-thread the job into processing-groups in order to reduce its run-time. This works fine, however, we're faced with multiple interface files that need to be merged prior transferring to the vendor.


Some Details on the File:
The file generated has a header and a trailer record, and the trailer record has pertinent total values (i.e., employee count, records approved, etc). There are no field separators -- these are fixed length fields.

Predicament in Detail:
We'd like to concatenate the files -- that's the easy part. What makes this difficult is that we need to eliminate the multiple header records and retain only the first one. Also, we need to eliminate the multiple trailer records, but we need to add all the value totals from each trailer into the one trailer record we'll retain at the end.

As you might have surmised by now, I've written some UNIX scripts, but lack some key knowledge related to individual record and field manipulation within a text file. In particular, I'd like to know how I can define specific fields when I read each record -- these are the fields for the trailer records I need to keep a rolling total on. Also, I'd like to know how I can delete individual records.

Any assistance will be greatly appreciated.