SYSIN
SYSIN is a conventional data input mechanism used in IBM mainframe batch processing and JCL (Job Control Language). It refers to the DDNAME SYSIN, a data definition that supplies input to a program or utility invoked in a job step. A SYSIN data source can be provided in-stream using a DD * ... /* construct, or it can reference an existing dataset via a DSN= parameter in the JCL. The content and format of SYSIN data are defined by the program that reads it, and may consist of control statements, configuration data, or raw records.
Common uses include utilities such as IDCAMS for data set management, DFSORT or SyncSort for sorting and
In a typical JCL job, the SYSIN DD line names the data source, and the step executes
Best practices include keeping SYSIN content version-controlled, validating syntax with test runs, and documenting the expected