LINKAGE SECTION is used to -

• Pass the data between COBOL programs.
• Receive data from run JCL.

Syntax -

----+----1----+----2----+----3----+----4----+----5----+
	   DATA DIVISION.
	   LINKAGE SECTION.
	   variable-declaration-entries.

Rules -

• All variables declared in the LINKAGE SECTION should be unique.
• The variables should not have a VALUE clause.
• When we declared LINKAGE SECTIO variables for receiving the data from JCL, all 01 level variable should present in PROCEDURE DIVISION USING clause to receive the data.

Data passing between programs -

LINKAGE SECTION is used to receive data from the called program to the calling program. It is an optional section mainly used in subprograms to receive the data from the main or calling program. The variables should match the PIC declaration in both main and subprograms.

Example -

Scenario - LINKAGE SECTION usage to pass the data between the programs.

Main Program (MAINPROG) -

----+----1----+----2----+----3----+----4----+----5----+
       IDENTIFICATION DIVISION.
       PROGRAM-ID. MAINPROG.
       AUTHOR. MTH.
	   
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 WS-VAR.
          05 WS-IP1          PIC 9(02) VALUE 47.    *> Input Variable1
          05 WS-IP2          PIC 9(02) VALUE 25.    *> Input Variable2
          05 WS-RESULT       PIC 9(04).             *> Result Variable
       01 WS-CALLING-PROG    PIC X(08) VALUE "SUBPROG".

	   PROCEDURE DIVISION. 
	   
	  * Calling subprogram with two inputs and getting result back   
           CALL WS-CALLING-PROG USING WS-IP1, WS-IP2, WS-RESULT. 
		   
           DISPLAY "RESULTS: " WS-RESULT. 
		   STOP RUN.

Sub Program (SUBPROG) -

----+----1----+----2----+----3----+----4----+----5----+
       IDENTIFICATION DIVISION.
       PROGRAM-ID. SUBPROG.
       AUTHOR. MTH.

       DATA DIVISION.                                                   
       LINKAGE SECTION.                                         
       01 LN-VAR.                                                       
          05 LN-IP1          PIC 9(02).  *> To receive input1 from MAINPROG
          05 LN-IP2          PIC 9(02).  *> To receive input2 from MAINPROG
          05 LN-RESULT       PIC 9(04).  *> To send result to MAINPROG

	  *Receiving data from main program CALL statement 
       PROCEDURE DIVISION USING LN-IP1, LN-IP2, LN-RESULT. 

           COMPUTE LN-RESULT = LN-IP1 * LN-IP2.
		   GOBACK.

Explaining Example -

In the above example:

• MAINPROG is the main program and SUBPROG is the subprogram.
• WS-IP1, WS-IP2 are the inputs passed from MAINPROG to the SUBPROG. SUBPROG receives the data into LN-IP1, LN-IP2 from MAINPROG, multiply those values and place the result into LN-RESULT.
• SUBPROG returns the output LN-RESULT to MAINPROG, MAINPROG displays the result received from SUBPROG.

We will discuss more detail about this topic in CALL Statement .

Receiving data from run JCL -

LINKAGE SECTION is also used to receive the data from run JCL through the PARM parameter. To receive the data from JCL, a variable of length 2 bytes (S9(4) COMP) should be declared in addition to the other variables. The maximum length of the data that can pass through the PARM parameter is 100 bytes.

Example -

Scenario - LINKAGE section usage to receive the data from JCL.

Run JCL -

----+----1----+----2----+----3----+----4----+----5----+
//MATEGJR JOB MSGLEVEL=(1,1), NOTIFY=&SYSUID
//*
//STEP01  EXEC PGM=LINKPROG,PARM=(10,20)
//STEPLIB  DD  DSN=MATEGJ.COBOL.LOADLIB,DISP=SHR
//SYSOUT   DD  SYSOUT=*

Program (MULPROG) -

----+----1----+----2----+----3----+----4----+----5----+
       IDENTIFICATION DIVISION.
       PROGRAM-ID. LINKPROG.
       AUTHOR. MTH.

       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 WS-RESULT         PIC 9(04).
       LINKAGE SECTION.                                         
       01 LN-VAR.
		  05 LN-LENGTH       PIC S9(04) COMP.
          05 LN-IP1          PIC 9(02).    *> Input Variable1
		  05 FILLER          PIC X(01).
          05 LN-IP2          PIC 9(02).    *> Input Variable2
	   
	   PROCEDURE DIVISION USING LN-VAR. 
	   
           COMPUTE WS-RESULT = LN-IP1 * LN-IP2.
           DISPLAY "RESULT: " WS-RESULT.
		   STOP RUN.

Explaining Example -

In the above example, LINKPROG is receiving the data from run JCL. LN-IP1, LN-IP2 receives the data from JCL, multiply those values and place the result into WS-RESULT.

We will discuss more detail about this topic in JCL PARAM parameter .