    {-# LINE 1 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}

    {-# LINE 2 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}
    {-# LANGUAGE Trustworthy #-}

    {-# LINE 4 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}
    {-# OPTIONS_GHC -fno-warn-trustworthy-safe #-}

    {-# LINE 6 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}

    {-# LINE 7 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  System.Posix.Env.ByteString
    -- Copyright   :  (c) The University of Glasgow 2002
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  provisional
    -- Portability :  non-portable (requires POSIX)
    --
    -- POSIX environment support
    --
    -----------------------------------------------------------------------------

    module System.Posix.Env.ByteString (
           -- * Environment Variables
            getEnv
            , getEnvDefault
            , getEnvironmentPrim
            , getEnvironment
            , putEnv
            , setEnv
           , unsetEnv

           -- * Program arguments
           , getArgs
    ) where

    {-# LINE 37 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}

    import Foreign
    import Foreign.C
    import Control.Monad    ( liftM )
    import Data.Maybe       ( fromMaybe )

    import qualified Data.ByteString as B
    import qualified Data.ByteString.Char8 as BC
    import Data.ByteString (ByteString)

    -- |'getEnv' looks up a variable in the environment.

    getEnv :: ByteString -> IO (Maybe ByteString)
    getEnv name = do
      litstring <- B.useAsCString name c_getenv
      if litstring /= nullPtr
         then liftM Just $ B.packCString litstring
         else return Nothing

    -- |'getEnvDefault' is a wrapper around 'getEnv' where the
    -- programmer can specify a fallback if the variable is not found
    -- in the environment.

    getEnvDefault :: ByteString -> ByteString -> IO ByteString
    getEnvDefault name fallback = liftM (fromMaybe fallback) (getEnv name)

    foreign import ccall unsafe "getenv"
       c_getenv :: CString -> IO CString

    getEnvironmentPrim :: IO [ByteString]
    getEnvironmentPrim = do
      c_environ <- getCEnviron
      arr <- peekArray0 nullPtr c_environ
      mapM B.packCString arr

    getCEnviron :: IO (Ptr CString)

    {-# LINE 81 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}
    getCEnviron = peek c_environ_p

    foreign import ccall unsafe "&environ"
       c_environ_p :: Ptr (Ptr CString)

    {-# LINE 86 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}

    -- |'getEnvironment' retrieves the entire environment as a
    -- list of @(key,value)@ pairs.

    getEnvironment :: IO [(ByteString,ByteString)]
    getEnvironment = do
      env <- getEnvironmentPrim
      return $ map (dropEq.(BC.break ((==) '='))) env
     where
       dropEq (x,y)
          | BC.head y == '=' = (x,B.tail y)
          | otherwise       = error $ "getEnvironment: insane variable " ++ BC.unpack x

    -- |The 'unsetEnv' function deletes all instances of the variable name
    -- from the environment.

    unsetEnv :: ByteString -> IO ()

    {-# LINE 104 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}

    unsetEnv name = B.useAsCString name $ \ s ->
      throwErrnoIfMinus1_ "unsetenv" (c_unsetenv s)

    foreign import ccall unsafe "__hsunix_unsetenv"
       c_unsetenv :: CString -> IO CInt

    {-# LINE 113 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}

    -- |'putEnv' function takes an argument of the form @name=value@
    -- and is equivalent to @setEnv(key,value,True{-overwrite-})@.

    putEnv :: ByteString -> IO ()
    putEnv keyvalue = B.useAsCString keyvalue $ \s ->
      throwErrnoIfMinus1_ "putenv" (c_putenv s)

    foreign import ccall unsafe "putenv"
       c_putenv :: CString -> IO CInt

    {- |The 'setEnv' function inserts or resets the environment variable name in
         the current environment list.  If the variable @name@ does not exist in the
         list, it is inserted with the given value.  If the variable does exist,
         the argument @overwrite@ is tested; if @overwrite@ is @False@, the variable is
         not reset, otherwise it is reset to the given value.
    -}

    setEnv :: ByteString -> ByteString -> Bool {-overwrite-} -> IO ()

    {-# LINE 133 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}
    setEnv key value ovrwrt = do
      B.useAsCString key $ \ keyP ->
        B.useAsCString value $ \ valueP ->
          throwErrnoIfMinus1_ "setenv" $
            c_setenv keyP valueP (fromIntegral (fromEnum ovrwrt))

    foreign import ccall unsafe "setenv"
       c_setenv :: CString -> CString -> CInt -> IO CInt

    {-# LINE 149 "libraries/unix/System/Posix/Env/ByteString.hsc" #-}

    -- | Computation 'getArgs' returns a list of the program's command
    -- line arguments (not including the program name), as 'ByteString's.
    --
    -- Unlike 'System.Environment.getArgs', this function does no Unicode
    -- decoding of the arguments; you get the exact bytes that were passed
    -- to the program by the OS.  To interpret the arguments as text, some
    -- Unicode decoding should be applied.
    --
    getArgs :: IO [ByteString]
    getArgs =
      alloca $ \ p_argc ->
      alloca $ \ p_argv -> do
       getProgArgv p_argc p_argv
       p    <- fromIntegral `liftM` peek p_argc
       argv <- peek p_argv
       peekArray (p - 1) (advancePtr argv 1) >>= mapM B.packCString

    foreign import ccall unsafe "getProgArgv"
      getProgArgv :: Ptr CInt -> Ptr (Ptr CString) -> IO ()