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JCL - Conditional Processing
The Job Entry System uses two approaches to perform conditional processing in a JCL. When a job completes, a return code is set based on the status of execution. The return code can be a number between 0 (successful execution) to 4095 (non-zero shows error condition). The most common conventional values are:
0 = Normal - all OK
4 = Warning - minor errors or problems.
8 = Error - significant errors or problems.
12 = Severe error - major errors or problems, the results should not be trusted.
16 = Terminal error - very serious problems, do not use the results.
A job step execution can be controlled based on the return code of the previous step(s) using the COND parameter and IF-THEN-ELSE construct, which has been explained in this tutorial.
COND parameter
A COND parameter can be coded in the JOB or EXEC statement of JCL. It is a test on the return code of the preceding job steps. If the test is evaluated to be true, the current job step execution is bypassed. Bypassing is just omission of the job step and not an abnormal termination. There can be at most eight conditions combined in a single test.
Syntax
Following is the basic syntax of a JCL COND Parameter:
COND=(rc,logical-operator) or COND=(rc,logical-operator,stepname) or COND=EVEN or COND=ONLY
Here is the description of parameters used:
rc : This is the return code
logical-operator : This can be GT (Greater Than), GE (Greater than or Equal to), EQ (Equal to), LT (Lesser Than), LE (Lesser than or Equal to) or NE (Not Equal to).
stepname : This is the job step whose return code is used in the test.
Last two conditions (a) COND=EVEN and (b) COND=ONLY, have been explained below in this tutorial.
The COND can be coded either inside JOB statement or EXEC statement, and in both the cases, it behaves differently as explained below:
COND inside JOB statement
When COND is coded in JOB statement, the condition is tested for every job step. When the condition is true at any particular job step, it is bypassed along with the job steps following it. Following is an example:
//CNDSAMP JOB CLASS=6,NOTIFY=&SYSUID,COND=(5,LE) //* //STEP10 EXEC PGM=FIRSTP //* STEP10 executes without any test being performed. //STEP20 EXEC PGM=SECONDP //* STEP20 is bypassed, if RC of STEP10 is 5 or above. //* Say STEP10 ends with RC4 and hence test is false. //* So STEP20 executes and lets say it ends with RC16. //STEP30 EXEC PGM=SORT //* STEP30 is bypassed since 5 <= 16.
COND inside EXEC statement
When COND is coded in EXEC statement of a job step and found to be true, only that job step is bypassed, and execution is continued from next job step.
//CNDSAMP JOB CLASS=6,NOTIFY=&SYSUID //* //STP01 EXEC PGM=SORT //* Assuming STP01 ends with RC0. //STP02 EXEC PGM=MYCOBB,COND=(0,EQ,STP01) //* In STP02, condition evaluates to TRUE and step bypassed. //STP03 EXEC PGM=IEBGENER,COND=((10,LT,STP01),(10,GT,STP02)) //* In STP03, first condition fails and hence STP03 executes. //* Since STP02 is bypassed, the condition (10,GT,STP02) in //* STP03 is not tested.
COND=EVEN
When COND=EVEN is coded, the current job step is executed, even if any of the previous steps abnormally terminate. If any other RC condition is coded along with COND=EVEN, then the job step executes if none of the RC condition is true.
//CNDSAMP JOB CLASS=6,NOTIFY=&SYSUID //* //STP01 EXEC PGM=SORT //* Assuming STP01 ends with RC0. //STP02 EXEC PGM=MYCOBB,COND=(0,EQ,STP01) //* In STP02, condition evaluates to TRUE and step bypassed. //STP03 EXEC PGM=IEBGENER,COND=((10,LT,STP01),EVEN) //* In STP03, condition (10,LT,STP01) evaluates to true, //* hence the step is bypassed.
COND=ONLY
When COND=ONLY is coded, the current job step is executed, only when any of the previous steps abnormally terminate. If any other RC condition is coded along with COND=ONLY, then the job step executes if none of the RC condition is true and any of the previous job steps fail abnormally.
//CNDSAMP JOB CLASS=6,NOTIFY=&SYSUID //* //STP01 EXEC PGM=SORT //* Assuming STP01 ends with RC0. //STP02 EXEC PGM=MYCOBB,COND=(4,EQ,STP01) //* In STP02, condition evaluates to FALSE, step is executed //* and assume the step abends. //STP03 EXEC PGM=IEBGENER,COND=((0,EQ,STP01),ONLY) //* In STP03, though the STP02 abends, the condition //* (0,EQ,STP01) is met. Hence STP03 is bypassed.
IF-THEN-ELSE Construct
Another approach to control the job processing is by using IF-THEN-ELSE constructs. This gives more flexibility and user-friendly way of conditional processing.
Syntax
Following is the basic syntax of a JCL IF-THEN-ELSE Construct:
//name IF condition THEN list of statements //* action to be taken when condition is true //name ELSE list of statements //* action to be taken when condition is false //name ENDIF
Following is the description of the used terms in the above IF-THEN-ELSE Construct:
name : This is optional and a name can have 1 to 8 alphanumeric characters starting with alphabet, #,$ or @.
Condition : A condition will have a format: KEYWORD OPERATOR VALUE, where KEYWORDS can be RC (Return Code), ABENDCC (System or user completion code), ABEND, RUN (step started execution). An OPERATOR can be logical operator (AND (&), OR (|)) or relational operator (<, <=, >, >=, <>).
Example
Following is a simple example showing the usage of IF-THEN-ELSE:
//CNDSAMP JOB CLASS=6,NOTIFY=&SYSUID //* //PRC1 PROC //PST1 EXEC PGM=SORT //PST2 EXEC PGM=IEBGENER // PEND //STP01 EXEC PGM=SORT //IF1 IF STP01.RC = 0 THEN //STP02 EXEC PGM=MYCOBB1,PARM=123 // ENDIF //IF2 IF STP01.RUN THEN //STP03a EXEC PGM=IEBGENER //STP03b EXEC PGM=SORT // ENDIF //IF3 IF STP03b.!ABEND THEN //STP04 EXEC PGM=MYCOBB1,PARM=456 // ELSE // ENDIF //IF4 IF (STP01.RC = 0 & STP02.RC <= 4) THEN //STP05 EXEC PROC=PRC1 // ENDIF //IF5 IF STP05.PRC1.PST1.ABEND THEN //STP06 EXEC PGM=MYABD // ELSE //STP07 EXEC PGM=SORT // ENDIF
Let's try to look into the above program to understand it in little more detail:
The return code of STP01 is tested in IF1. If it is 0, then STP02 is executed. Else, the processing goes to the next IF statement (IF2).
In IF2, If STP01 has started execution, then STP03a and STP03b are executed.
In IF3, If STP03b does not ABEND, then STP04 is executed. In ELSE, there are no statements. It is called a NULL ELSE statement.
In IF4, if STP01.RC = 0 and STP02.RC <=4 are TRUE, then STP05 is executed.
In IF5, if the proc-step PST1 in PROC PRC1 in jobstep STP05 ABEND, then STP06 is executed. Else STP07 is executed.
If IF4 evaluates to false, then STP05 is not executed. In that case, IF5 are not tested and the steps STP06, STP07 are not executed.
The IF-THEN-ELSE will not be executed in the case of abnormal termination of the job such as user cancelling the job, job time expiry or a dataset is backward referenced to a step that is bypassed.
Setting Checkpoints
You can set checkpoint dataset inside your JCL program using SYSCKEOV, which is a DD statement.
A CHKPT is the parameter coded for multi-volume QSAM datasets in a DD statement. When a CHKPT is coded as CHKPT=EOV, a checkpoint is written to the dataset specified in the SYSCKEOV statement at the end of each volume of the input/output multi-volume dataset.
//CHKSAMP JOB CLASS=6,NOTIFY=&SYSUID //* //STP01 EXEC PGM=MYCOBB //SYSCKEOV DD DSNAME=SAMPLE.CHK,DISP=MOD //IN1 DD DSN=SAMPLE.IN,DISP=SHR //OUT1 DD DSN=SAMPLE.OUT,DISP=(,CATLG,CATLG) // CHKPT=EOV,LRECL=80,RECFM=FB
In the above example, a checkpoint is written in dataset SAMPLE.CHK at the end of each volume of the output dataset SAMPLE.OUT.
Restart Processing
You can restart processing ether using automated way using the RD parameter or manual using the RESTART parameter.
RD parameter is coded in the JOB or EXEC statement and it helps in automated JOB/STEP restart and can hold one of the four values: R, RNC, NR or NC.
RD=R allows automated restarts and considers the checkpoint coded in the CHKPT parameter of the DD statement.
RD=RNC allows automated restarts, but overrides (ignores) the CHKPT parameter.
RD=NR specifies that the job/step cannot be automatically restarted. But when it is manually restarted using the RESTART parameter, CHKPT parameter (if any) will be considered.
RD=NC disallows automated restart and checkpoint processing.
If there is a requirement to do automated restart for specific abend codes only, then it can be specified in the SCHEDxx member of the IBM system parmlib library.
RESTART parameter is coded in the JOB or EXEC statement and it helps in manual restart of the JOB/STEP after the job failure. RESTART can be accompanied with a checkid, which is the checkpoint written in the dataset coded in the SYSCKEOV DD statement. When a checkid is coded, the SYSCHK DD statement should be coded to reference the checkpoint dataset after the JOBLIB statement (if any), else after the JOB statement.
//CHKSAMP JOB CLASS=6,NOTIFY=&SYSUID,RESTART=(STP01,chk5) //* //SYSCHK DD DSN=SAMPLE.CHK,DISP=OLD //STP01 EXEC PGM=MYCOBB //*SYSCKEOV DD DSNAME=SAMPLE.CHK,DISP=MOD //IN1 DD DSN=SAMPLE.IN,DISP=SHR //OUT1 DD DSN=SAMPLE.OUT,DISP=(,CATLG,CATLG) // CHKPT=EOV,LRECL=80,RECFM=FB
In the above example, chk5 is the checkid, i.e., STP01 is restarted at checkpoint5. Please note that a SYSCHK statement is added and SYSCKEOV statement is commented out in the previous program explained in Setting Checkpoint section.