Xmobar.System.Environment

1 files changed, 49 insertions, 0 deletions

diff --git a/src/lib/Xmobar/System/Environment.hs b/src/lib/Xmobar/System/Environment.hs
new file mode 100644
index 0000000..86197db
--- /dev/null
+++ b/src/lib/Xmobar/System/Environment.hs
@@ -0,0 +1,49 @@
+-----------------------------------------------------------------------------
+-- |
+-- 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