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What is JCL? z/OS concepts |
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For every job that you submit, you need to tell z/OS® where to find the appropriate input, how to process that input, and what to do with the resulting output. You use job control language (JCL) to convey this information to z/OS through a set of statements known as job control statements. While application programmers need some knowledge of JCL, the production control analyst must be highly proficient with JCL, to create, monitor, correct and rerun the company's daily batch workload. The set of job control statements is quite large, which allows you to provide a great deal of information to z/OS. 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. The following JCL example represents a job that performs the same functions
as the TSO commands outlined in Figure 3.
//MYJOB JOB 1 //MYSORT EXEC PGM=SORT //SORTIN DD DISP=SHR,DSN=ZPROF.AREA.CODES //SORTOUT DD SYSOUT=* //SYSOUT DD SYSOUT=* //SYSIN DD * SORT FIELDS=(1,3,CH,A) /* Each JCL DD statement is equivalent to the TSO ALLOCATE command. Both are used to associate a z/OS data set with a ddname, which is recognized by the program as an input or output. The difference in method of execution is that TSO executes the sort in the foreground while JCL is used to execute the sort in the background. When submitted for execution:
"The Big Three" JCL statements: JOB, EXEC, and DD All jobs require the three main types of JCL statements: JOB, EXEC, and DD. A job defines a specific workload for z/OS to process. A job is a separately executable unit of work defined by a user, and run by a computer. This representation of a unit of work consists of one program or a set of programs, files, and control statements. Some z/OS users use the older term JCL card instead of JCL statement, because JCL used to be submitted to the system in the form of punched cards. Now JCL resides in storage (data sets) rather than on punched cards. Because JCL was originally designed for punched cards, the details of coding JCL statements can be complicated. However, the general concepts are quite simple, and most jobs can be run using a very small subset of these control statements. JCL has three basic statements:
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