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|
-----------------------------------------------------------------------------
-- |
-- Module : XMobar.Environment
-- Copyright : (c) William Song
-- License : BSD-style (see LICENSE)
--
-- Maintainer : Will Song <incertia@incertia.net>
-- Stability : stable
-- Portability : portable
--
-- A function to expand environment variables in strings
--
-----------------------------------------------------------------------------
module Xmobar.System.Environment(expandEnv) where
import Control.Applicative ((<$>))
import Data.Maybe (fromMaybe)
import System.Environment (lookupEnv)
expandEnv :: String -> IO String
expandEnv "" = return ""
expandEnv (c:s) = case c of
'$' -> do
envVar <- fromMaybe "" <$> lookupEnv e
remainder <- expandEnv s'
return $ envVar ++ remainder
where (e, s') = getVar s
getVar "" = ("", "")
getVar ('{':s'') = (takeUntil "}" s'', drop 1 . dropUntil "}" $ s'')
getVar s'' = (takeUntil filterstr s'', dropUntil filterstr s'')
filterstr = ",./? \t;:\"'~`!@#$%^&*()<>-+=\\|"
takeUntil f = takeWhile (not . flip elem f)
dropUntil f = dropWhile (not . flip elem f)
'\\' -> case s == "" of
True -> return "\\"
False -> do
remainder <- expandEnv $ drop 1 s
return $ escString s ++ remainder
where escString s' = let (cc:_) = s' in
case cc of
't' -> "\t"
'n' -> "\n"
'$' -> "$"
_ -> [cc]
_ -> do
remainder <- expandEnv s
return $ c : remainder
|
