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

[Thomas Hartman]

I probably should have also mentioned that the "fail" on windows is for me 
ssh-ed to that box remotely, where the sshd program is cygwin.





Thomas Hartman <thomas.hartman+external at db.com> 
Sent by: haskell-cafe-bounces at haskell.org
08/28/2007 06:03 PM

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







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 
haskell. 

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... 

thomas. 

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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