Sorting and Merging files in COBOL

ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT CallsFile
ASSIGN TO “CALLS.DAT”
ORGANIZATION IS LINE SEQUENTIAL.

SELECT SortedCallsFile
ASSIGN TO “SORTEDCALLS.DAT”
ORGANIZATION IS LINE SEQUENTIAL.

SELECT WorkFile
ASSIGN TO “WORK.TMP”.

DATA DIVISION.
FILE SECTION.
FD CallsFile.
01 CallRec.
02 SubscriberNumCF PIC 9(8).
02 UnitsUsedCF PIC 9(5).

FD SortedCallsFile.
01 SortedCallRec.
02 SubscriberNumSF PIC 9(8).
02 UnitsUsedSF PIC 9(5).

SD WorkFile.
01 WorkRec.
02 SubscriberNumWF PIC 9(8).
02 UnitsUsedWF PIC 9(5).

etc.


PROCEDURE DIVISION.
Begin.
SORT WorkFile ON ASCENDING SubscriberNumWF
USING CallsFile
GIVING SortedCallsFile.

etc.