The file conditioning indicators are specified by the EXTIND keyword on the file description specifications. Only the external indicators U1 through U8 are valid for file conditioning. (The USROPN keyword can be used to specify that no implicit OPEN should be done.)
If the external indicator specified is off when the program is called, the file is not opened and no data transfer to or from the file will occur when the program is running. Primary and secondary input files are processed as if they were at end-of-file. The end-of-file indicator is set on for all READ operations to that file. Input, calculation, and output specifications for the file need not be conditioned by the external indicator.