On 12 April 2005 13:22, Uwe Schmidt wrote:

in the ghc-6.4 release the posix module is deprecated. I'm looking for a replacement and tried the System.Process functions. the following first try does not work for large files. it blocks if the file "long.file" does not fit into one os-buffer. then cat blocks and therefor waitForProcess blocks

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module Main where

import IO import System import System.Process

main :: IO () main = do (inpH, outH, errH, pH) <- runInteractiveProcess "cat" ["long.file"] Nothing Nothing hClose inpH res <- hGetContents outH errs <- hGetContents errH

rc <- waitForProcess pH

putStrLn ("rc: " ++ show rc) putStrLn ("stdout: " ++ res) putStrLn ("stderr: " ++ errs) exitWith rc

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the following version works fine, but it looks very much like a hack

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module Main where

import IO import System import System.Process

main :: IO () main = do (inpH, outH, errH, pH) <- runInteractiveProcess "cat" ["long.filel"] Nothing Nothing hClose inpH res <- hGetContents outH errs <- hGetContents errH

if (length $! res) == 0 -- hack !!! then return () else return ()

if (length $! errs) /= 0 -- hack !!! then return () else return ()

rc <- waitForProcess pH

putStrLn ("rc: " ++ show rc) putStrLn ("stdout: " ++ res) putStrLn ("stderr: " ++ errs) exitWith rc

If you really must use hGetContents, then the hack above is necessary: you have to force the output strings before waiting for the process to terminate. This would be slightly cleaner:

res <- hGetContents outH errs <- hGetContents errH forkIO (evaluate (length res)) forkIO (evaluate (length errs))

which avoids blocking the main thread, but ensures that all the data gets pulled as it becomes available. It looks like the same hack would be required with the old POpen interface too - if not, can you show an example of something that works with popen but not with System.Process? Cheers, Simon