CIOR provides two predefined MPE/iX string variables to reflect
the state of I/O redirection. These variables can be used within
User Commands or programs that need to detect if their input or
output has been redirected. HPSTDIN will default to the string
"$STDIN". HPSTDLIST will default to the string value
"$STDLIST". These values also indicate whether or not
input or output is currently redirected. If input is redirected,
HPSTDIN will contain the name of the file to which input has been
redirected. If input has been redirected through a file equation
backreference, HPSTDIN will contain the formal file designator
of the file equation. Similarly, HPSTDLIST will contain the
filename or formal file designator of the file or file equation to
which output has been redirected.
