Interact with stdin

a.hs

import           System.IO
import           System.IO.Temp

main :: IO ()
main = do
  withSystemTempFile "uuu" $ \path handle -> do
    hPutStrLn handle "hello\nbye"
    hClose handle
    handle' <- openFile path ReadMode
    go handle' stdout

go :: Handle -> Handle -> IO ()
go i o = do
  l <- hGetLine i
  hPutStrLn o l