Re: [Haskell-cafe] Re: ANN: HSH 1.2.0

On Mon, Mar 12, 2007 at 05:14:57PM -0500, John Goerzen wrote:

On 2007-03-06, Simon Marlow wrote:

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John Goerzen wrote:

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possible to create a pipe going directly from program A to program B.

You certainly can pipe directly from one process to another:

That only works for 2 processes. What if I have 4 processes, and want to pipe from one to the next, all along, as in

ls -l /tmp | tr a-zA-Z | sort | md5sum

to give a contrived example

You can do this with runProcess, if you use System.Posix.IO.{createPipe,fdToHandle} to make a pipe and wrap the ends as handles. I hope hCreatePipe could be implemented on windows.

import System.IO import System.Process import System.Posix.IO

run program arguments stdin stdout = runProcess program arguments Nothing Nothing stdin stdout Nothing hCreatePipe = do (readFd, writeFd) <- createPipe read <- fdToHandle readFd write <- fdToHandle writeFd return (read, write)

main = do (read1, write1) <- hCreatePipe run "ls" ["-l","/tmp"] Nothing (Just write1) (read2, write2) <- hCreatePipe run "tr" ["a-z","A-Z"] (Just read1) (Just write2) (read3, write3) <- hCreatePipe run "sort" [] (Just read2) (Just write3) (read4, write4) <- hCreatePipe run "md5sum" [] (Just read3) (Just write4) hash <- hGetContents read4 putStr hash

Brandon Moore