Selecting the file system and the system environment

In the case of I/O functions and file access functions which can process both POSIX as well as BS2000 files, and which require a pathname to be specified as an argument, the file type to be processed in each case can be specified individually in the source code. Selecting the file type automatically determines the functionality with which the corresponding function is called. This is achieved via the environment variable PROGRAM_ENVIRONMENT on one hand, and by conforming to a specific syntax at the source program level on the other.