Job Control Language (JCL)

                                                       JCL

JCL: It is a job control language which controls the flow of programs on operating system.

It is a means of communication between a program that can be written in COBOL, ASSEMBER or PL/I and the MVS operating system.

 

JOB: A job is a set of JCL statements that consists of one (or several) steps, each of which is a request to run one specific program.

Using JCL we can tell the system what programs we can execute, what I/O files we are using and what is the input

Job Entry Subsystem (JES): It is a subsystem of the mainframe operating systems that manages jobs before and after the execution.

After submitting the job will be put into the JES queue.

The job will be checked for syntax errors. The job will be executed by basic control program (BCP) based on priority. The job will be send to the output queue.

 

JES3 (Job Entry Subsystem 3): It is a centralized system that the global processor can have centralized control over the local processors and distributes jobs to them

 

JES2 (Job Entry Subsystem 2): It is a decentralized system in which each processor's JES2 subsystem independently controls job

 

Initiator: it is a special address space where the job is mapped and executed

In order a job to be executed the job must me mapped to an initiator where each initiator is assigned a class and each initiator will execute the jobs that has the same class.

Types of statements in JCL:

JOB statement: It is a JCL statament which  identifies the beginning of job and specifies attributes that are required for the job.

EXEC statement: It is a JCL statament which  identifies the beginning of step and specifies the program that has to be executed.

DD statement: It is a JCL statament which  specifies the input and output files required for the program

 

 

 

 

JCL structure:

All jcl statememts consists of 5 types of fields.

1.Identifier:  two forward slashes at beginning of each jcl statements inj column 1 and column2. it is mandatory.

2.Name: it immediately follows the identifiler fileld at colomn 3.It is an optional field.it gives the name to the statement.it should not exceed 8 characters.

3.Operation field: it specifies the operation or type of statement.it must be preceded by one blank.it is mandatory.

4. Parameter filed: it contains the parameters required for the statement.multiple parameters will be seperated by comma.

5. comment field: it follows the last parameter and must be preceded by atleat one blank.

 

The maximum length of jcl statement is 72.

The continued statement should start with identifiers and parameters should start between 4 and 16.

 

Tyes of parameters:

Positional parameters: it should be coded in a particular order.must be followed by operation field.if positional parameters are not required we can leave it with comma.

Key word parameters: it can appear in any order and identified by equal to operator.

Positional key word parameter: the keyword parameter that should follow the operation field.

key word parameter that accepts positional sub parameters: the sub parameters must be positional

key word parameter that accepts key word parameters: the sub parameters can appear in any order

 

Parameters of JOB statement:

Accounting information:

Programmer name:

CLASS

MSGCLASS

NOTIFY

MSGLEVEL

REGION

TIME

RESTART

TYPRUN