INTRODUCTION

Job control language. It is a means of communication between a program that 
can be written in COBOL , ASSEMBER or PL/I and the MVS operating system. Without
a JCL, you cant able to run a job on MVS operating system.

Let us start with an example jcl, how it looks like, The following jcl is 
used to run an cobol program. I will explain in this chapter each and every 
line of this jcl. If you are already fimiliar with jcl, please skip first 
6 chapters. 

(First 1 - 6 chapters intended for beginners)

JCL , used to run a cobol program

//JOB1    JOB  (034D),'RAMESH KRISHNA REDDY',CLASS='A',PRTY=6
//STEP01  EXEC PGM=COBPROG.
//INFILE  DD   DSN=SED.GLOB.DES.INFILE,DISP=SHR
//OUTIFLE DD   DSN=SED.GLOB.DES.OUTFILE,
//             DISP=(NEW,CATLG,DELETE),
//             UNIT=DISK,
//             SPACE=(CYL,(1,5),RLSE),
//             DCB=(RECFM=FB,LERECL=70,BLKSIZE=700)



to see source code of cobol program COBPROG click here
  
Now let us discuss JCL which we have seen.

Before explaining, I will explain few basics about JCL

All JCL statements can consists of up to five types of
fields

  // The two forward slashes are required at the beginning of each
     JCL statement in Columns 1 and 2.

  Name field - This is an optional field. If coded, should start at
               Column 3. It maximum length is 8.

  Operation field - Which indicates the operation that is to be performed

  Operand - This field must appear after Operation field. Must start at 16 
            column 

  Comments - Comments begin one space after the last operand. Our simple 
             example has no comments.



  
  
  //  Name    	 Operation             OPerand
   
  //  JOB1           JOB                  (034D),
                                          'RAMESH',
                                          CLASS='A',
                                          PRTY=6

  //   STEP01         EXEC                PGM=COBPROG

  //   INFILE         DD                  DSN=SED.GLOB.DES.INFILE,
                                          DISP=SHR
  //   OUTIFLE        DD                  DSN=SED.GLOB.DES.OUTFILE,
  //                                      DISP=(NEW,CATLG,DELETE),
  //                                      UNIT=DISK,
  //                                      SPACE=(CYL,(1,5),RLSE),
  //                                      DCB=(RECFM=FB,
  //                                      LERECL=70,BLKSIZE=700)   
  
 
  The following image explain How our JCL will execute cobol program



    



  EXPLANATION -


  //JOB1 JOB    (034D),'RAMESH',CLASS='A',PRTY=6
   
  job card is mainly used to identify job, and tell to MVS about type of job 
  it is, priority it has.
 
  JOB1 is the job name       
  034D is accounting information
  RAMESH is name of the programmer
  CLASS is category of job 
  PRTY is priority in the class


  //STEP01 EXEC PGM=COBPROG
        
  EXEC is used to specify the program to be executed. 

  STEP01 is the name of the step (you can give any name here)
  COBPROG is the program name to be executed
           

 //INFILE DD DSN=SED.GLOB.DES.INFILE,DISP=SHR       

  INFILE is the name of input file, which is used in cobol program
         
  DSN=SED.GLOB.DES.INFILE - It is dataset contains actual information to be read.
        
  DISP=SHR - means another program also can read this program while we 
             are reading this file.



 //OUTFILE DD DSN=SED.GLOB.DES.OUTFILE,
 //           DISP=(NEW,CATLG,DELETE),
 //           UNIT=DISK,
 //           SPACE=(CYL,(1,5),RLSE),
 //           DCB=(RECFM=FB,LERECL=70,BLKSIZE=700)

 OUTFILE is the name of outputfile, which is used in cobol program
        
 DSN=SED.GLOB.DES.OUTFILE   is the output file data will be written
 
 DISP=(NEW,CATLG,DELETE)  Disp specifies the disposition of dataset,

       NEW -  Dataset not exists, need to create
       CATLG - If step executed successfully, dataset should be cataloged
       DELETE - If any error occurred, Dataset should be deleted