Redirect stdout for an IO action

redirect-io.hs

module Misc
  ( withOutputTo
  ) where

import System.IO
import GHC.IO.Handle
import Control.Exception

-- | Run an IO action with stdout redirected to a file.
-- Restores stdout upon completion of the action.
withOutputTo :: FilePath -> IO a -> IO a
withOutputTo path action = do
  withFile path WriteMode $ \h -> do
    stdout' <- hDuplicate stdout
    bracket (hDuplicate stdout)
            (\a -> hDuplicateTo a stdout)
            (\a -> do hDuplicateTo h stdout
                      hSetBuffering stdout NoBuffering
                      action )