You can assign filenames externally using the External File Mapper (Mfextmap). This provides a flexible method of mapping the assigned filename used in your COBOL program to a physical filename, by enabling filename mapping to be resolved in a text file (the mapper file). Filename mappings can be altered subsequently, simply by editing the file.
select filename assign to external assigned-name
where the parameters are:
Using the External File Mapper, rather than resolving filename assignments via operating system environment variables, reduces the amount of memory required for environment space.