You use the export 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). If the filename refers to an HFS file, the filename has to be properly qualified. Otherwise, the PL/I library will assume the filename refers to an MVS dataset.
For example:
declare MyFile stream output; export DD_MYFILE=/datapath/mydata.dat
/datapath/mydata.dat refers to an HFS file. The filename is fully-qualified.
export DD_MYFILE=./mydata.dat
./mydata.dat refers to an HFS file residing in the current directory.
export DD_MYFILE=mydata.dat
mydata.dat refers to an MVS dataset.
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.
Under z/OS UNIX, where more types of varying length HFS files are supported than under batch, PL/I decides how to treat an HFS file as follows: