[Haskell-cafe] Bug in runInteractiveProcess?
donn at drizzle.com
Wed Oct 17 01:04:28 EDT 2007
On Oct 16, 2007, at 1:48 PM, John Goerzen wrote:
> I have been trying to implement a Haskell-like version of shell
> pipelines using runInteractiveProcess. I am essentially using
> hGetContents to grab the output from one command, and passing that to
> (forkIO $ hPutStr) to write to the next. Slow, but this is just an
As an aside, I personally would look to System.Posix.Process for this.
Something like this would deal with the file descriptors in the fork ...
fdfork fn dupfds closefds = do
pid <- forkProcess $ execio
dupe (a, b) = do
dupTo a b
execio = do
mapM_ dupe dupfds
mapM_ closeFd closefds
... and then you can put the pipes directly between the processes ...
-- date | tr '[A-Z]' '[a-z]' | read
(a0, a1) <- createPipe
(b0, b1) <- createPipe
p1 <- fdfork tr [(b0, 0), (a1, 1)] [a0, b1]
p2 <- fdfork date [(b1, 1)] [a0, b0]
readfd a0 -- implementation left to reader
date = executeFile "/bin/date" False  Nothing
tr = executeFile "/usr/bin/tr" False ["[A-Z]", "[a-z]"] Nothing
There's probably a nice way to wrap that up, so you're not keeping
track of the file descriptors for all the pipes.
Donn Cave, donn at drizzle.com
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