On Sun, Aug 12, 2012 at 6:18 PM, Niklas Hambüchen
I just came across the fact that running
createProcess (proc "asdfasdf" [])
with non-existing command "asdfasdf" returns perfectly fine handles. I would expect an exception. You can even hGetContents on stdout: You just get "".
I find this highly counter-intuitive. Is this intended?
Yes, I ran into the same thing a while back. The problem is that the subprocess has already been forked off before it runs exec() and finds out the file doesn't exist. The reason python reports the right error is that it sets up a pipe from child to parent to communicate just this error. It's more friendly, but on the other hand the implementation is more complicated. If you don't want to hack up the whole send-exception-over-the-pipe thing, the easiest thing to do is to wait for the processes's return code. If you don't want to do that, you can at least have the subproces log, e.g.: loggedProcess :: Process.CreateProcess -> IO (Maybe IO.Handle, Maybe IO.Handle, Maybe IO.Handle, Process.ProcessHandle) loggedProcess create = do r@(_, _, _, pid) <- Process.createProcess create Concurrent.forkIO $ do code <- Process.waitForProcess pid case code of Exit.ExitFailure c -> notice $ "subprocess " ++ show (binaryOf create) ++ " failed: " ++ if c == 127 then "binary not found" else show c _ -> return () return r where binaryOf create = case Process.cmdspec create of Process.RawCommand fn _ -> fn Process.ShellCommand cmd -> fst $ break (==' ') cmd As an aside, I've had the idea to at some point go look at the latest python's version of the subprocess module and see about porting it to haskell, or at least make sure the haskell version doesn't suffer from problems fixed in the python one. They went through a lot of iterations trying to get it right (and earlier python versions are broken in one way or another) and we might as well build on their work.