Here is what I have tried: module Main where import System.Process -- using runInteractiveProcess import System.Posix.Types import System.Process.Internals import Control.Concurrent.MVar main = do (input,output,err,ph) <- runInteractiveProcess calc.exe" ([]) Nothing Nothing p <- Main.getPID ph putStrLn $ show p --- The output getPID :: ProcessHandle -> IO CPid getPID (ProcessHandle p) = do (OpenHandle pp) <- takeMVar p return (toPID pp) toPID :: PHANDLE -> CPid toPID ph = toEnum $ fromEnum ph --------------------------------------------------------------------------------------------------------------------------- But the CPid always returns some const value (like 1904 in cygwin; 1916 in cmd.exe) I think, I saw that CPid was a newtype of Ptr () So, currently I need to get the process id from CPid or something else. All help is appreciated. John