You use the SET command to establish an environment variable that identifies the data set to be associated with a PL/I file, and, optionally, to specify the characteristics of that data set. The information provided by the environment variable is called data definition (or DD) information.
These environment variable names have the form DD:ddname where the ddname is the name of a PL/I file constant (or an alternate ddname, as defined below), for example:
declare MyFile stream output;
You can specify options for the SET command by including them on the command line.
set dd:myfile=c:\datapath\mydata.dat,APPEND(N)
If you are familiar with the IBM mainframe environment, you can think of the environment variable much like you do the:
For more about the syntax and options you can use with the DD:ddname environment variable, see Specifying characteristics using DD:ddname environment variables.