[Haskell-cafe] runInteractiveCommand behaves differently on linux and windows

Thomas Hartman thomas.hartman at db.com
Tue Aug 28 18:03:32 EDT 2007

Maybe this is by design, but I just thought I would point this behavior 
out and ask for comment.

test1 merely shows that runInteractiveCommand reacts differently to perl 
warnings than perl errors. Okay, maybe the inconsistency in that case is 
due to perl and not haskell.

test2 behaves the same on win and nix. This is "pipe like" in that the 
ouptut of a command (which could be the result of a shell call, but just 
as easily be the return of a haskell function) gets fed into a shell 
command. In this case, if the shell command is simply "tail" the behavior 
is consistent from win to nix.

test3 shows that the behavior stops being consistent if ssh enters the 
picture. (piping to tail via ssh). again, maybe this is due to ssh and not 

however... note however that on windows

ghc -e 'mapM_ ( putStrLn . show ) [1..1000] ' | ssh `whoami`@localhost 
'tail -n2'

works fine.  so it's not *just* ssh, but ssh in conjuction with 
runInteractiveCommand which seems to cause problems

FWIW, using 10 lines instead of 1000 still hangs on windows.

Is there a way to code up shell pipelike behavior in a more portable way?

curious what the cafe thinks...


import Test.HUnit
import Misc ( (>>=^) )
import System.Process
import System.IO
import System.Exit

-- works on linux, error on windows

test1 = do 
  res1 <- test_shellrunStderrOk
  runTestTT $ TestCase ( assertEqual "test1" "made it"  res1 )
  where test_shellrunStderrOk = do
          runprocessStdErrAllowed' "" cmdPerlwarn
          return "made it"
        cmdPerldie =  " perl -e 'die \"error\"' "
        cmdPerlwarn = " perl -e 'warn \"blee\"' "

-- works on linux, windows
test2 = pipeTo "tail -n2"

-- works on linux, hangs on windows
test3 = pipeTo "ssh `whoami`@localhost 'tail -n2'"

pipeTo cmd = do
  res2 <- test_shellrunPipeinLike
  runTestTT $ TestCase ( assertEqual ( "pipe to, cmd: " ++ cmd) (show l) 
res2 )
  where test_shellrunPipeinLike = do
          runprocessStdErrAllowed' (unlines $ map show [1..l]) ( cmd )
          >>=^ filter (not . ( == '\n') )
        l = 1000

runprocessStdErrAllowed' inp s = do
    (ih,oh,eh,pid) <- runInteractiveCommand s
    so <- hGetContents oh
    se <- hGetContents eh
    hPutStrLn ih inp
    hClose ih
    ex <- waitForProcess pid
    case ex of
        ExitFailure e      -> fail $ "shell command " ++ s ++ "\nFailed 
with status: " ++ show e
        _   | otherwise     -> return so


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