The physical disk file name can be specified with the use of UNIX shell environment variables. This method takes precedence over methods 1 and 2. This method allows you to easily alter the physical disk file used for different invocations of the same application.
The environment variable name is the value of the derived name from either of the above methods with MF_ or DD_ prefixed.
Example
dcl file data2 update;
dcl file specs output;
open file (data2);
open file (specs) title('report');
By setting the following environment variables:
I/O operations for file data2 will access /common/data and I/O for file specs will access /common/report.
Note that to override the name for file variable "specs", the name MF_REPORT was used, because of the title option on its OPEN statement.
In the above example, environment variables of the names DD_DATA2 and DD_report would also be allowed.
To assign a physical file to the following special file declarations you will need to use the corresponding environment variables:
| SYSIN | use DD_STDIN |
| SYSPRINT | use DD_STDOUT |
| SYSOUT | use DD_STDOUT |