工作控制语言语句 英语
    Job Control Language Statements.
    Job Control Language (JCL) is a specialized programming language used to control the execution of batch jobs on mainframe computers. JCL statements are used to specify the resources required for a job, such as the amount of memory, the number of processors, and the input and output files. They can also be used to control the flow of execution, such as by branching to different parts of the job or by conditionally executing certain statements.
    JCL statements are typically grouped into job steps, which are the individual units of work that make up a job. Each job step has its own set of JCL statements that specify the resources required for that step. The job steps are executed in the order in which they are specified in the JCL.
    Types of JCL Statements.
    There are many different types of JCL statements, but the most common ones include:
    JOB statement: The JOB statement is the first statement in a JCL job. It specifies the name of the job, the user ID of the person who submitted the job, and the account number to which the job will be charged.
    EXEC statement: The EXEC statement specifies the program that will be executed as part of the job step. It also specifies the parameters that will be passed to the program.
    DD statement: The DD statement defines an input or output file for the job step. It specifies the name of the file, the type of file, and the device on which the file is located.
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    COND statement: The COND statement is used to conditionally execute certain statements in the job step. It can be used to branch to different parts of the job or to skip certain statements altogether.
    JES statement: The JES statement is used to control the execution of the job in the JES (Job Entry Subsystem). It can be used to specify the priority of the job, the time at which the job should be executed, and the resources that the job should be allocated.
    Example JCL.
    The following is an example of a simple JCL job:
    //JOB1 JOB (USER1,ACCT1),MSGCLASS=X.
    //STEP1 EXEC PGM=SORT.
    //SORTIN DD DSN=INPUT.DATA,DISP=SHR.
    //SORTOUT DD DSN=OUTPUT.DATA,DISP=(NEW,CATLG)。
    This JCL job will execute a sort program (PGM=SORT) on a file named INPUT.DATA (SORTIN) and write the sorted output to a file named OUTPUT.DATA (SORTOUT). The job will be submitted by user USER1 and charged to account ACCT1. The job will be assigned a message class of X, which means that all messages generated by the job will be sent to the system console.
    Conclusion.
    JCL is a powerful language that can be used to control the execution of batch jobs on mainframe computers. JCL statements can be used to specify the resources required for a job, control the flow of execution, and interact with the JES. By understanding the different types of JCL statements and how they are used, you can create JCL jobs that will run efficiently and effectively.

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