    {-# LINE 1 "libraries/unix/./System/Posix/Env.hsc" #-}
    {-# LANGUAGE ForeignFunctionInterface #-}
    {-# LINE 2 "libraries/unix/./System/Posix/Env.hsc" #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  System.Posix.Env
    -- 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 (
    	getEnv
    	, getEnvDefault
    	, getEnvironmentPrim
    	, getEnvironment
    	, putEnv
    	, setEnv
    	, unsetEnv
    ) where

    {-# LINE 27 "libraries/unix/./System/Posix/Env.hsc" #-}

    import Foreign.C.Error	( throwErrnoIfMinus1_ )
    import Foreign.C.Types	( CInt )
    import Foreign.C.String
    import Foreign.Marshal.Array
    import Foreign.Ptr
    import Foreign.Storable
    import Control.Monad	( liftM )
    import Data.Maybe	( fromMaybe )

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

    getEnv :: String -> IO (Maybe String)
    getEnv name = do
      litstring <- withCString name c_getenv
      if litstring /= nullPtr
         then liftM Just $ peekCString 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 :: String -> String -> IO String
    getEnvDefault name fallback = liftM (fromMaybe fallback) (getEnv name)

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

    getEnvironmentPrim :: IO [String]
    getEnvironmentPrim = do
      c_environ <- peek c_environ_p
      arr <- peekArray0 nullPtr c_environ
      mapM peekCString arr

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

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

    getEnvironment :: IO [(String,String)]
    getEnvironment = do
      env <- getEnvironmentPrim
      return $ map (dropEq.(break ((==) '='))) env
     where
       dropEq (x,'=':ys) = (x,ys)
       dropEq (x,_)      = error $ "getEnvironment: insane variable " ++ x

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

    unsetEnv :: String -> IO ()

    {-# LINE 81 "libraries/unix/./System/Posix/Env.hsc" #-}

    unsetEnv name = withCString name $ \ s ->
      throwErrnoIfMinus1_ "unsetenv" (c_unsetenv s)

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

    {-# LINE 90 "libraries/unix/./System/Posix/Env.hsc" #-}

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

    putEnv :: String -> IO ()
    putEnv keyvalue = withCString 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 :: String -> String -> Bool {-overwrite-} -> IO ()

    {-# LINE 110 "libraries/unix/./System/Posix/Env.hsc" #-}
    setEnv key value ovrwrt = do
      withCString key $ \ keyP ->
        withCString value $ \ valueP ->
          throwErrnoIfMinus1_ "setenv" $
    	c_setenv keyP valueP (fromIntegral (fromEnum ovrwrt))

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

    {-# LINE 126 "libraries/unix/./System/Posix/Env.hsc" #-}