annodate.hs

import Control.Exception (tryJust)
import Control.Monad     (guard)
import Data.Time
import GHC.IO.Handle
import System.Console.GetOpt
import System.Environment
import System.IO.Error
import System.Process
import System.Locale

annotateLine :: FormatTime t => t -> String -> String
annotateLine time line = timeString ++ ": " ++ line
    where timeString = formatTime defaultTimeLocale "%F %T" time

annotateIO :: Handle -> IO ()
annotateIO handle = do
    input <- tryJust (guard . isEOFError) (hGetLine handle)
    case input of
        Left _ -> return ()
        Right line -> do
            time <- getCurrentTime
            let output = annotateLine time line
            putStrLn output
            annotateIO handle

spawn :: String -> [String] -> IO Handle
spawn cmd args = do
    (_, out, _, _) <- runInteractiveProcess cmd args Nothing Nothing
    return out

main :: IO ()
main = do
    let options = []
    cliArgs <- getArgs
    case getOpt Permute options cliArgs of
        (_, cmd:args, []) -> do
            out <- spawn cmd args
            hSetBinaryMode out False
            hSetBuffering out NoBuffering
            annotateIO out
        _ -> do
            putStrLn "usage: annodate <COMMAND> [OPTIONS...]"
            return ()