This variable allows you to map a Vision Version 4 file 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 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 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 variable described later.