This variable specifies the file system to use for a particular file. For example, if DEFAULT_FILESYSTEM is set to MPE, and the file CUSTFILE is a Vision file, in your cblconfig you could specify:
CUSTFILE_HOST VISION
This definition directs the runtime to treat CUSTFILE as a Vision file. Note that the file name may not include any path or directory name and should not include the file extension.
DEFAULT_FILESYSTEM and filename_HOST are described in detail in DEFAULT_FILESYSTEM and filename_HOST respectively.
When your program executes, each time a file is opened, the ACUCOBOL-GT runtime checks filename_HOST and DEFAULT_FILESYSTEM to determine which file system to use. You can change the value of these variables, just before you open the file, by including the following in your code:
SET ENVIRONMENT "DEFAULT_FILESYSTEM" TO value
or
SET ENVIRONMENT "filename_HOST" TO value
where value is a Working Storage item containing the name of the file system, or is a literal in quotation marks. SET ENVIRONMENT thus enables you to change file systems during the execution of your program.