propellor/src/Utility/Env.hs

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{- portable environment variables
-
- Copyright 2013 Joey Hess <joey@kitenet.net>
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-
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- License: BSD-2-clause
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-}
{-# LANGUAGE CPP #-}
module Utility.Env where
#ifdef mingw32_HOST_OS
import Utility.Exception
import Control.Applicative
import Data.Maybe
import qualified System.Environment as E
import qualified System.SetEnv
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#else
import qualified System.Posix.Env as PE
#endif
getEnv :: String -> IO (Maybe String)
#ifndef mingw32_HOST_OS
getEnv = PE.getEnv
#else
getEnv = catchMaybeIO . E.getEnv
#endif
getEnvDefault :: String -> String -> IO String
#ifndef mingw32_HOST_OS
getEnvDefault = PE.getEnvDefault
#else
getEnvDefault var fallback = fromMaybe fallback <$> getEnv var
#endif
getEnvironment :: IO [(String, String)]
#ifndef mingw32_HOST_OS
getEnvironment = PE.getEnvironment
#else
getEnvironment = E.getEnvironment
#endif
{- Sets an environment variable. To overwrite an existing variable,
- overwrite must be True.
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-
- On Windows, setting a variable to "" unsets it. -}
setEnv :: String -> String -> Bool -> IO ()
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#ifndef mingw32_HOST_OS
setEnv var val overwrite = PE.setEnv var val overwrite
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#else
setEnv var val True = System.SetEnv.setEnv var val
setEnv var val False = do
r <- getEnv var
case r of
Nothing -> setEnv var val True
Just _ -> return ()
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#endif
unsetEnv :: String -> IO ()
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#ifndef mingw32_HOST_OS
unsetEnv = PE.unsetEnv
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#else
unsetEnv = System.SetEnv.unsetEnv
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#endif
{- Adds the environment variable to the input environment. If already
- present in the list, removes the old value.
-
- This does not really belong here, but Data.AssocList is for some reason
- buried inside hxt.
-}
addEntry :: Eq k => k -> v -> [(k, v)] -> [(k, v)]
addEntry k v l = ( (k,v) : ) $! delEntry k l
addEntries :: Eq k => [(k, v)] -> [(k, v)] -> [(k, v)]
addEntries = foldr (.) id . map (uncurry addEntry) . reverse
delEntry :: Eq k => k -> [(k, v)] -> [(k, v)]
delEntry _ [] = []
delEntry k (x@(k1,_) : rest)
| k == k1 = rest
| otherwise = ( x : ) $! delEntry k rest