diff --git a/cless.cabal b/cless.cabal
--- a/cless.cabal
+++ b/cless.cabal
@@ -1,5 +1,5 @@
 name:                cless
-version:             0.1.0.0
+version:             0.2.0.0
 synopsis:            Colorized LESS
 description:         Print file contents with syntax highlighting
 homepage:            https://github.com/tanakh/cless
@@ -25,6 +25,7 @@
                      , wl-pprint-extras
                      , terminfo
                      , optparse-applicative >=0.11
+                     , process >=1.2
 
   hs-source-dirs:      src
   default-language:    Haskell2010
diff --git a/src/Main.hs b/src/Main.hs
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -2,15 +2,21 @@
 
 module Main (main) where
 
+import           Control.Exception
 import           Control.Monad
 import           Data.Maybe
 import           Data.Monoid
 import           Data.String
 import           Options.Applicative
+import           System.Console.Terminfo
 import           System.Console.Terminfo.Color       as Terminfo
 import           System.Console.Terminfo.PrettyPrint
+import           System.Environment
+import           System.IO
+import           System.Process
 import           Text.Highlighting.Kate              as Kate
-import           Text.PrettyPrint.Free               (hcat, vcat)
+import           Text.PrettyPrint.Free               hiding ((<>))
+import           Text.Printf
 
 main :: IO ()
 main = join $ execParser opts where
@@ -26,6 +32,9 @@
         <*> switch ( long "list-styles"
                   <> short 'S'
                   <> help "Show the list of supported styles" )
+        <*> switch ( long "LINE-NUMBERS"
+                  <> short 'N'
+                  <> help "Show line numbers" )
         <*> optional (strOption ( long "lang"
                   <> short 'l'
                   <> metavar "LANG"
@@ -34,7 +43,7 @@
                   <> short 's'
                   <> metavar "STYLE"
                   <> help "Specify style name (default 'pygments')" ) )
-        <*> argument str (metavar "FILE")
+        <*> optional (argument str (metavar "FILE"))
 
 styles :: [(String, Style)]
 styles =
@@ -47,31 +56,65 @@
   , ("zenburn"   , zenburn   )
   ]
 
-process :: Bool -> Bool -> Maybe String -> Maybe String -> FilePath -> IO ()
-process True _ _ _ _ =
+defaultPager :: String
+defaultPager = "less -R"
+
+defaultTerm :: String
+defaultTerm = "xterm-256color"
+
+defaultStyle :: Style
+defaultStyle = pygments
+
+process :: Bool -> Bool -> Bool -> Maybe String -> Maybe String -> Maybe FilePath -> IO ()
+process True _ _ _ _ _ =
   mapM_ putStrLn languages
 
-process _ True _ _ _ =
+process _ True _ _ _ _ =
   mapM_ (putStrLn . fst) styles
 
-process _ _ mb_lang mb_stylename file = do
-  con <- readFile file
+process _ _ linum mb_lang mb_stylename mb_file = do
+  con <- case mb_file of
+      Just file -> readFile file
+      Nothing   -> getContents
 
-  let lang = fromMaybe (error "cannot determin language")
-             $ mb_lang <|> listToMaybe (languagesByFilename file)
+  let lang = fromMaybe "plain"
+             $ mb_lang <|> do file <- mb_file; listToMaybe (languagesByFilename file)
 
       ss = highlightAs lang con
 
-      style = maybe pygments findStyle mb_stylename
+      style = maybe defaultStyle findStyle mb_stylename
 
       findStyle name =
         fromMaybe (error $ "invalid style name: " ++ name)
         $ lookup name styles
 
-  displayLn $ ppr style ss
+      doc = ppr linum style ss <> linebreak
+      sdoc = renderPretty 0.6 80 (prettyTerm doc)
 
-ppr :: Style -> [SourceLine] -> TermDoc
-ppr Style{..} = vcat . map (hcat . map token) where
+  evaluate style -- to raise error eagerly
+
+  termType <- fromMaybe defaultTerm <$> lookupEnv "TERM"
+  pager <- fromMaybe defaultPager <$> lookupEnv "PAGER"
+  term  <- setupTerm $ if termType == "screen" then defaultTerm else termType
+
+  bracket
+    (createProcess (shell pager) { std_in = CreatePipe } )
+    ( \(_, _, _, ph) -> waitForProcess ph )
+    $ \(Just h, _, _, _) -> do
+      case getCapability term $ evalTermState $ displayCap sdoc of
+        Just output -> hRunTermOutput h term output
+        Nothing -> displayIO h sdoc
+      hClose h
+
+ppr :: Bool -> Style -> [SourceLine] -> TermDoc
+ppr linum Style{..} = vcat . zipWith addLinum [1..] . map (hcat . map token) where
+  addLinum ln line
+      | linum =
+          let lns = text $ printf "%7d " (ln :: Int)
+          in withColors lineNumberColor lineNumberBackgroundColor lns
+              <> line
+      | otherwise = line
+
   token (tokenType, ss) =
     tokenEffect tokenType $ fromString ss
 
@@ -84,11 +127,14 @@
     in styleToEffect tokenStyle
 
   styleToEffect TokenStyle{..} =
-    with (maybe Nop (Foreground . cnvColor) tokenColor) .
-    with (maybe Nop (Background . cnvColor) tokenBackground) .
+    withColors tokenColor tokenBackground .
     with (if tokenBold      then Bold      else Nop) .
     -- with (if tokenItalic    then Standout  else Nop) .
     with (if tokenUnderline then Underline else Nop)
+
+  withColors foreground background =
+    with (maybe Nop (Foreground . cnvColor) foreground) .
+    with (maybe Nop (Background . cnvColor) background)
 
 cnvColor :: Kate.Color -> Terminfo.Color
 cnvColor (RGB r g b) = ColorNumber