This configuration variable allows you to map Vision 4 and 5 files to a different directory. Vision examines the name of each physical file it attempts to open to determine if the file should be mapped to a different directory. The configuration variable used is constructed from the file's base name and extension, with all letters converted to upper case and all non-alphanumeric characters converted to underscores.
For example, assume you open /usr/data/custfile.dat, and a configuration variable CUSTFILE_DAT has the value /usr2/data/custfile.dat. Vision treats this value as the actual file name to open, and custfile.dat ends up in the /usr2/data directory rather than /usr/data.
Because the extension is included in the configuration variable name, you can place different parts of a multi-segment file in different directories. If no name is found for a particular segment, then the segment name is used unchanged. Note that you can move parts of a file around by simply moving the segment and adding/modifying its corresponding configuration name. Name mapping is done directly by Vision (as opposed to, for example, FILE_PREFIX, which is handled by the runtime). As a result, all programs that use Vision (such as vutil and vio) use this variable when present. For programs other than the runtime, the variable must be set in the environment rather than the configuration file.
This variable is similar to the filename_VERSION configuration variable.
The filename translation performed by this configuration variable is performed by Vision itself. The runtime can also perform filename translation. See File Name Assignments for more information.