By default, KAPPA plays safe and will not allow you to use the same data structure as both input and output for a command. This is to minimise the risks of accidentally over-writing valuable data. So, for instance, if you try the following command:
% cadd in=m31 scalar=10 out=m31
you will find that the value of m31 for Parameter OUT is rejected with a message indicating that the data structure is already in use, and you will be prompted for an alternative value.
However, KAPPA does allow you to `live on the edge' if
you prefer--if you define the environment variable KAPPA_REPLACE before
running a command, then KAPPA will happily overwrite the
input data structure if requested to do so. You can assign any value you
like to this environment variable, since its mere existence is the trigger
for this optional behaviour. Note, this facility is only available in
those commands that access the input data structures before the
output data structures (the vast majority).
KAPPA --- Kernel Application Package