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Mainframe Application programming Development Solutions

Mainframe Application & programming

JCL :
For your program to execute on the computer and perform the work you designed it to do, your program must be processed by your operating system. Your operating system consists of a base control program (BCP) with a job entry subsystem (JES2 or JES3) and DFSMSdfp installed with it.

For the operating system to process a program, programmers must perform certain job control tasks. These tasks are performed through the job control statements, which are listed in the first chapter. The job control tasks and introductory information about JCL are introduced in the second chapter. The charts in the third chapter divide these tasks into detailed subtasks. The tasks are:

• Entering jobs
• Processing jobs
• Requesting resources

JCL Essentials :

• The programmer name parameter
• The NOTIFY parameter
• The MSGCLASS and MSGLEVEL parameters
• How to code the EXEC statement
• The PGM parameter
• The PARM parameter
• How to code the DD statement for DASD data sets
• The syntax of the DD statement for DASD data
• sets
• The ddname and the DSNAME parameter
  
• The DISP parameter
• The UNIT and VOLUME parameters
• The SPACE parameter
• The DCB parameter
• How to code the DD statement for instream and
• SYSOUT data sets
• The DD statement for instream data sers
• The DD statements of SYSOUT data sets
• Two complete job streams
• The transaction-posting application
• The job control requirements for a reportpreparation
• application
• The JCL for the report-preparation application

JCL Statements:
You use JCL to convey this information to MVS through a set of statements known as job control statements. JCL's set of job control statements is quite large, enabling you to provide a great deal of information to MVS.

Most jobs, however, can be run using a very small subset of these control statements. Once you become familiar with the characteristics of the jobs you typically run, you may find that you need to know the details of only some of the control statements.

Within each job, the control statements are grouped into job steps. A job step consists of all the control statements needed to run one program. If a job needs to run more than one program, the job would contain a different job step for each of those programs.

Table 1-1. MVS Job Control Language (JCL) Statements
Statement	Name	Purpose
// command	JCL command	Enters an MVS system operator command through the input stream. The command statement is used primarily by the operator. Use the COMMAND statement instead of the JCL command statement.
// COMMAND	command	Specifies an MVS or JES command that the system issues when the JCL is converted. Use the COMMAND statement instead of the JCL command statement.
//* comment	comment	Contains comments. The comment statement is used primarily to document a program and its resource requirements.
// CNTL	control	Marks the beginning of one or more program control statements.
// DD	data definition	Identifies and describes a data set.
/*	delimiter	Indicates the end of data placed in the input stream. Note: A user can designate any two characters to be the delimiter.
// ENDCNTL	end control	Marks the end of one or more program control statements.
// EXEC	execute	Marks the beginning of a job step; assigns a name to the step; identifies the program or the cataloged or in-stream procedure to be executed in this step.
// IF/THEN/ELSE/ENDIF	IF/THEN/ELSE/ENDI statement construct	Specifies conditional execution of job steps within a job.
// INCLUDE	include	Identifies a member of a partitioned data set (PDS) or partitioned data set extended (PDSE) that contains JCL statements to be included in the job stream.
// JCLLIB	JCL library	Identifies the libraries that the system will search for: ° INCLUDE groups ° Procedures named in EXEC statements.
// JOB	job	Marks the beginning of a job; assigns a name to the job.
//	null	Marks the end of a job.
// OUTPUT	output JCL	Specifies the processing options that the job entry subsystem is to use for printing a sysout data set.
// PEND	procedure end	Marks the end of an in-stream or cataloged procedure.
// PROC	procedure	Marks the beginning of an in-stream procedure and may mark the beginning of a cataloged procedure; assigns default values to parameters defined in the procedure.
// SET	set	Defines and assigns initial values to symbolic parameters used when processing JCL statements. Changes or nullifies the values assigned to symbolic parameters.
// XMIT	transmit	Transmits input stream records from one node to another.

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.



JCL , used to run a cobol program



//JOB1    JOB  (034D),'SOUMYA PREMJI NAIR',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)



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),

                                         'SOUMYA',

                                         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



//JOB1    JOB  (034D),'SOUMYA PREMJI NAIR',CLASS='A',PRTY=6 

//STEP01  EXEC PGM=COBPROG.

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

//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)



//JOB1    JOB  (034D),'SOUMYA PREMJI NAIR',CLASS='A',PRTY=6  - Starting of job



COBPROG - Cobol program name to be executed



OUTFILE - Output file name which is used in

         SELECT  OUTPUT-FILE  ASSIGN  TO OUTFILE.



INFILE -  Input file name which is used in

         SELECT INPUT-FILE  ASSIGN  TO  INFILE.



EXPLANATION -





 //JOB1 JOB    (034D),'SOUMYA',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

 SOUMYA 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