diff --git a/bin/ConfFmt.hs b/bin/ConfFmt.hs
--- a/bin/ConfFmt.hs
+++ b/bin/ConfFmt.hs
@@ -1,20 +1,52 @@
-import qualified Data.Conf             as Conf
-import qualified Data.Conf.PrettyPrint as Conf
-import qualified Data.Text.IO          as Text (readFile)
-import           System.Environment    (getArgs)
-import           System.Exit           (exitFailure)
+{-# LANGUAGE RecordWildCards #-}
+import           Control.Monad
+import qualified Data.Conf                 as Conf
+import qualified Data.Text.IO              as Text (hGetContents, readFile)
+import           Options.Applicative
+import           Options.Applicative.Types
+import           System.Environment        (getArgs)
+import           System.Exit               (exitFailure)
 import           System.IO
-import qualified Text.Megaparsec       as Megaparsec
+import qualified Text.Megaparsec           as Megaparsec
 
+data ConfFmtOptions
+    = ConfFmtOptions { cfoInplace :: Bool
+                     , cfoOutput  :: Maybe FilePath
+                     , cfoInput   :: Maybe FilePath
+                     }
+
+options :: Parser ConfFmtOptions
+options = ConfFmtOptions
+    <$> cfoInplaceAP
+    <*> cfoOutputAP
+    <*> cfoInputAP
+
+cfoInputAP = optional (argument str
+    (metavar "INPUTFILE"
+    <> help "The input file (omission will cause `conffmt` to use stdin)"))
+
+cfoOutputAP = optional (option str (short 'o' <> long "output"))
+cfoInplaceAP = switch (long "inplace"
+    <> short 'i'
+    <> help "Format the FILE inplace, replacing it's contents")
+
 main :: IO ()
 main = do
-    as <- getArgs
-    case as of
-        (filePath:_) -> do
-            contents <- Text.readFile filePath
-            case Megaparsec.parse Conf.conf filePath contents of
-                Left err -> hPrint stderr err
-                Right ast -> print (Conf.pPrint ast)
-        _ -> do
-            hPutStrLn stderr "Usage: conffmt <conf-file>"
-            exitFailure
+    ConfFmtOptions{..} <- execParser (info (helper <*> options)
+                                   ( fullDesc
+                                     <> progDesc "Format a .conf FILE"
+                                     <> header "conffmt - Conf formatter using Haskell language-conf"
+                                   ))
+    (contents, fp) <- case cfoInput of
+        Just fp ->
+            (,) <$> Text.readFile fp <*> pure fp
+        Nothing ->
+            (,) <$> Text.hGetContents stdin <*> pure "<stdin>"
+    case Megaparsec.parse Conf.conf fp contents of
+        Left err -> hPrint stderr err
+        Right ast -> do
+            let output = show (Conf.pPrintConf ast)
+            case (cfoInplace, cfoOutput) of
+                (_, Just outputFp) -> writeFile outputFp output
+                (True, _) -> writeFile fp output
+                _ -> putStr output
diff --git a/bin/ToConf.hs b/bin/ToConf.hs
--- a/bin/ToConf.hs
+++ b/bin/ToConf.hs
@@ -21,7 +21,7 @@
                     let conf :: Aeson.Result Conf.Conf
                         conf = Aeson.fromJSON v
                     writeFile output $ show $ case conf of
-                        Aeson.Success c -> Conf.pPrint c
+                        Aeson.Success c -> Conf.pPrintConf c
                         Aeson.Error e -> error ("Tranformation failure: " <> e)
                 Nothing -> error ("Parse failure " <> fp)
         _ -> error "Usage: toconf <inputfile> <outputfile>"
diff --git a/language-conf.cabal b/language-conf.cabal
--- a/language-conf.cabal
+++ b/language-conf.cabal
@@ -3,7 +3,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           language-conf
-version:        0.2.1.0
+version:        0.2.2.0
 synopsis:       Conf parsers and pretty-printers for the Haskell programming language.
 description:    @language-conf@ contains @.conf@ (e.g. nginx configuration) parsers and pretty-printers for the Haskell programming language.
                 "Data.Conf" exports all the API surface in the package.
@@ -74,6 +74,7 @@
   build-depends:
       base
     , text
+    , optparse-applicative
     , megaparsec
     , language-conf
     , pretty
diff --git a/src/Data/Conf/PrettyPrint.hs b/src/Data/Conf/PrettyPrint.hs
--- a/src/Data/Conf/PrettyPrint.hs
+++ b/src/Data/Conf/PrettyPrint.hs
@@ -7,6 +7,8 @@
 Stability: experimental
 Portability: unknown
 
+import Data.Char
+import Debug.Trace
 Pretty-printer for "Data.Conf". Declares a 'Pretty' instance for
 'ConfStatement'.
 -}
@@ -19,11 +21,14 @@
     )
   where
 
+import           Data.Char                      (isSpace)
 import           Data.Conf.Types
 import           Data.Text                      (Text)
 import qualified Data.Text                      as Text
 import           Text.PrettyPrint.HughesPJClass
 
+import           Debug.Trace
+
 -- | Pretty-prints a 'Conf' to a 'Doc'
 --
 -- 'pPrint' restricted to 'Conf'
@@ -32,8 +37,18 @@
 -- print (pPrintConf c)
 -- @
 --
+-- Because of https://github.com/haskell/pretty/issues/26, it's not easy to
+-- prevent trailing spaces while generating the output. This function patches
+-- it at the end so there're no trailing spaces.
+--
 -- See "Text.PrettyPrint"
-pPrintConf = pPrint :: Conf -> Doc
+pPrintConf :: Conf -> Doc
+pPrintConf c =
+    let d = pPrint c
+        ds = init (unlines (map stripEnd (lines (show d))))
+    in text ds
+  where
+    stripEnd = reverse . dropWhile isSpace . reverse
 
 instance Pretty ConfStatement where
     pPrint s = case s of
diff --git a/test/Data/ConfSpec.hs b/test/Data/ConfSpec.hs
--- a/test/Data/ConfSpec.hs
+++ b/test/Data/ConfSpec.hs
@@ -11,6 +11,23 @@
 
 spec :: Spec
 spec = do
+    describe "pPrintConf" $ do
+        it "#3 - pretty prints nested lines without trailing spaces" $ do
+            let Right inp = parse conf "" $ Text.unlines
+                      [ "http {"
+                      , "  listen 8989;"
+                      , ""
+                      , "  proxy_pass something;"
+                      , "}"
+                      ]
+            show (pPrintConf inp) `shouldBe` init (unlines
+                      [ "http {"
+                      , "  listen 8989;"
+                      , ""
+                      , "  proxy_pass something;"
+                      , "}"
+                      ])
+
     describe "comment" $
         it "parses a comment" $ do
             let inp = Text.unlines [ "# something here"