Previously, it just ran an Execute shell call with NULL as the command-line pointer.
The fix is to still call Execute, but with an empty string as the command line, and then check if the call gave an error. If running under plain GS/OS, this gives an error for an unknown system call, whereas both ORCA/APW and GNO shells will return with no error in this case. (Golden Gate doesn't implement the Execute shell call, so it also gives an error and will report no command processor available.)
This fixes issue #25.
Stephen Heumann
Kelvin Sherlock
mikew50