What is Job control Language?

In today's world where the pandemic has changed the dynamics of digital world and unearth the gap in the mainframe skills, which  runs z/OS as it's operating system capable of handling millions and trillions of transaction with a zero down, crucible for running mission critical applications in banking, insurance, telecommunications, health care and government federal military domain.

the lack of mainframe skill and misconception of mainframe being at the end of it's lifespan due to a wrong belief of soon to be replaced by a modern system has created a huge in the dependency to run business and the adequate skills required to support the system.

Hence today I will be discussing and learn about JCL(Job Control Language), which is the script of any application system catering to a specific purpose to business continuity.

Any system is chain/sequence of programs executing in synchronous manner with a various input/output operation to get the desired result. hence it becomes mandatory to have a set of scripting instruction to be entered by the programmer to meet the business needs, without a proper scripting mechanism it is impossible to achieve the synchronous execution.

Hence in late 60's IBM came with JCL to script the system and tell it what program to execute and define its input and outputs.

even with the age of 70 years the scripting language .i.e. JCL hold it's grounds with never before demand.

while Application programmer need some knowledge of JCL, the production control analyst responsible must be highly proficient with JCL, to create, monitor, correct, and rerun the company's daily batch workload.

There are three basic JCL statements:

JOB - provides a name (job name) to the system for this batch workload. It can optionally include accounting information and a few job-wide parameters.

EXEC - provides the name of a program to execute. There can be multiple EXEC statements in a job. Each EXEC statement within the same job is a job step.

DD - The data definition provides inputs and outputs to the execution program on the EXEC statement. This statement links to data set or other I/O device or function to a ddname coded in program. DD statement are associated with a particular job step.    

below picture show the basic JCL coding Syntax.

JCL example

//JOB1            JOB 1

//SORT            EXEC PGM=SORT

//SORTIN        DD DISP=SHR,DSN=ZPROF.AREA.CODES

//SORTOUT    DD SYSOUT=*

//SYSOUT       DD SYSOUT=*

//SYSIN           DD *

    SORT FIEDLS = (1,5,CH,D)

/*

JOB1:    A jobname the system associate with this workload

SORT:    The step name, which instructs the system to execute the program, in this case a SORT it can be any program COBOL, PL/1, C or Java

SORTIN: It is Dataset Definition name, which as DSN=ZPROF.AREA.CODES allocated to it.

To be Continued...