Running on PDP11 Unix:

INKEY-256
  &B5 - Unix Version 5
  &B6 - Unix Version 6
  &B7 - Unix Version 7
  &B9 - BSD Unix 2.9
  &BB - BSD Unix 2.11

BGET#0 - reads from STDIN
BPUT#0 - writes to STDOUT
PTR#0  - impossible to tell from OSARGS 0,0 to read current FS
EXT#0  - impossible to tell from OSARGS 2,0 to read NETFS type
EOF#0  - keys available from keyboard

BGET#-1
BPUT#-1
PTR#-1
EXT#-1
EOF#-1