For BBj-specific information, see UNT Variable - BBj.
The UNT variable returns an unused channel number. This variable is
used in standard subroutines and public programs that need to open a file
but do not know in advance which channels will be in use when they are
See the CHN variable for a variable that returns a list of used channels.
1030 CHAN=UNT; OPEN(CHAN)"AFILE"