The mainframe OS has to search for and locate the program you specify in a JCL statement in order to run it. In order to locate programs, a private library must be SEARCHED before the system program library. If you wish to run a program residing in a private program library, you must either specify the JOBLIB DD (Data definition) statement or the STEPLIB DD (Data Definition) statement to enable OS to locate the program successfully. Both JOBLIB and STEPLIB are DD (Data definition) STATEMENTS. Although JOBLIB DD and STEPLIB DD specify a private library as the location of a SPECIFIED program, each will behave differently for OS search.  

1. JOBLIB Statement: Every step of the JOB is searched in the private libraries according to JOBLIB DD. The location of the program to be executed in JCL is referenced by it. This statement follows the JOB statement, but before the EXEC statement. It is only applicable to procedures and programs running in-stream.

Syntax: 

Here, 

• The keyword JOBLIB specifies the JOBLIB statement.
• DD specifies the Data definition statement.
• DSN specifies the location of the program/job to be executed.

2. STEPLIB statement: The only single step of the JOB is searched in the private libraries according to STEPLIB. The location of the program to be executed within a Job Step is referenced by it. This statement follows the EXEC statement, but before the DD statement of the job step.

Syntax:

Here, 

• The keyword STEPLIB specifies the STEPLIB statement.
• DD specifies the Data definition statement.
• DSN specifies the location of the step to be executed.