What is JCL?
JCL stands for Job Control Language and it pertains to control statements that connect with the computer’s operating system when it introduces a job or directs it on what needs to be done. These control statements are also used in making requests to hardware devices. Basically, it provides a communication gateway between a particular application program, the operating system, and the computer itself.
JCL statements are considered difficult by some programmers because of the way they are designed. It has little default syntax, so one must write the exact statement to get the exact action. Parameters are also set individually, so it may take quite a lot of pages to complete. It also needs to be precise in the sense that just one error in syntax can lead to non-execution of a particular command.
JCL statements are involved in specifying input data files for assessment, output data files for creation or updating, and the resources needed for the job completion. It will also identify the particular program needed to run using the available input and output data. There are three main types of JCL statements. The first of them is the “JOB” statement which is tasked to identify the start of a job, by communicating with the computer’s operating system. The “EXEC” statement meanwhile involves execution of the job by means of identifying the right application program for it. The third statement is the “DD or Data Definition Statement” which gives some form of identification to the particular job. It usually includes the data set name, specific volume, data set disposition, and the input-output unit. It could also include details on the data set like its blocking, organization, and record length.
As with other language statements, JCL has a set of syntax rules for proper execution of a particular job. It also allows comments for the programmer’s inputs.