How to concatenate all generations of a dataset?

 Hello 👋

In this post, let's see 👀 how we can concatenate all the existing generations of a dataset. In z/OS, a dataset which have generations (each generation is a successive update) is called as Generation Data Group (abbreviated to GDG).

This picture is for the thumbnail of this blog post. 

When you have a job whose task is to reference all existing generations of a data set, you would normally need to manually check the generation numbers and insert them into the JCL. 

One way around this is to just code the GDG base entry name and the system will automatically pick up all cataloged generations. You don't have to manually check for the generation numbers 💃.

 

JCL to concatenate the GDG generations.

Upon submitting the JCL,

JESYSMSG Listing after the completion of the job.

It is evident in the output produced from this job that the latest generation of this data set is accessed first (LIFO) and so on. 

How the order of concatenations can be modified?

LIFO order can be reversed using the GDGORDER parameter. 

Usage of GDGORDER Parameter in the JCL.

Upon submitting the JCL,

You can now see that the order of concatenation has changed.

It's worth noting that by default, the generations are concatenated in Last In First Out order. GDGRODER comes handy when you want to override the default. 

Hope this helps!