In an earlier batch system, in order to describe the task submitted to the computer, the system is provided to the user similar to the high-level language work control language. When the user is requested to the computer, you need to write a job control program with a job control language. The content includes each of the running steps, the data to be processed, the program that needs to be run, the resources you need to use, etc. For the user, this is not a relaxed thing. He not only wants all the statements of the job control language, but also has a forecast for his own procedure in the computer, but the intermediate result of the run is often not seen. Unable to intervene. This is the offline control period of the job, and the early computer users are a special professional group.
Improvements to job control languages are: Directly use advanced languages to explain the job. The Basic language is a typical representative. The user can lose the single Basic language command to represent a job step, and the last step is performed after the new command will start the next step. The job control has become an online form.
The user's job can be constructed by one or more job steps. Only one job step is called a single step job; the job consisting of multiple job steps is called multi-step jobs. Regardless of the single step job or multi-step jobs generally contain three JCL basic statements (JCL Statement). They are:
1, respectively. Job Statement (JOB)
identifies the beginning of a job, providing the necessary running parameters.
2. Execute Statements (Exec)
identifies the beginning of a job step, defining the programs or procedures to be executed in this job step.
3. Data Definition Statement (DD)
is used to describe the data file required by the application.
system stipulates that the three statements must begin with "//".
The commands used in most job control languages are approximately the following:
1. Compile a program with a compiler.
2. Connect all the procedures used in a program.
3. Perform a link.
4. Define a file,
5. Write a file into the directory table.
6. Remove a file from the directory table.
7. Request a disk with a disk.
8. Dump the memory as an octal or hexadecimal.
9. Copy a copy of a document.
10. In order to continue to run, save the status of a process (inspection point).
Job control language is not as unified as algorithm language, different systems are different, which is generally, JCL generally includes I / O commands, compile commands, operation commands, and Several categories such as conditional orders.
I / 0 command to illustrate the input of the user's various information (including the program, data, and job manual (control command), etc.), the result information (including compiled target programs, calculation results) And I / O equipment use, etc. The
compile command is used to compile the source of different languages. In addition, some commands related to this, such as processing, list output, list output, and the target program needs to be immediately loaded into the memory start operation. Wait. The
operation command is control over the operation of the job, such as startup, runtime, job termination. The
condition command is set for processing mode when a major event occurs in the program run. It is the user to process different situations while the user is fully estimated. result.
The main features of the job control language have four points.
(1) can provide a submission of the job;
(2) can control the execution of the job and work steps;
(3) can provide various Use of hardware and software resources;
(4) Other functions such as calendar, time, account, etc.