hi there, I am running some unix command. I just realized there is runInteractiveProcess in System.Process, so my problem is solved in practice: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ showPlot :: String -> IO (Handle, Handle, Handle, ProcessHandle) showPlot file = runInteractiveProcess executable arguments wd env where executable = "/usr/bin/gnuplot" arguments = ["-geometry", "-19+3", file, "-"] wd = Nothing env = Nothing ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ But first I tried to create the handles myself with createPipe from System.Posix.IO, and I failed for a reasons that I have no clue how to learn to understand. This is what the code looked like: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ showPlot :: String -> IO (ProcessHandle, Handle, Handle, Handle) showPlot file = do (stdinR, stdinW) <- createPipeHandles (stdoutR, stdoutW) <- createPipeHandles (stderrR, stderrW) <- createPipeHandles h <- runProcess executable arguments wd env (Just stdinR) (Just stdoutW) (Just stderr W) return (h, stdinW, stdoutR, stderrR) where executable = "/usr/bin/gnuplot" arguments = ["-geometry", "-19+3", file, "-"] wd = Nothing env = Nothing createPipeHandles :: IO (Handle, Handle) createPipeHandles = do (fR, fW) <- createPipe hR <- fdToHandle fR hW <- fdToHandle fW return (hR, hW) ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ The problem is that gnuplot terminates right away after it tries to read from stdin (I can see the shadow of a window appear and vanish immediately). I tried setFdOption, with no effect. Is this because the handles passed to runProcess are closed in the parent process, and therefore the pipe is teared down and useless? I don't think so: If I run 'find /' instead of gnuplot, the process happily starts and I can hGetLine from stdout. If you have any clue I'd love to learn. Anyway, as I said, it's really better to simply use runInteractiveProcess in this simple case. thanks, Matthias