diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,1 @@
+I hereby place the source code for "redo" into the public domain.
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/redo.cabal b/redo.cabal
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--- /dev/null
+++ b/redo.cabal
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+name:                redo
+version:             0.1.0
+synopsis:            software build system, make replacement, implementation of djb's redo
+description:         redo builds a target file from source files using a "do" script. It also tracks when source files have changed and rebuilds target files as necessary.
+homepage:            https://github.com/jekor/redo
+bug-reports:         https://github.com/jekor/redo/issues
+license:             PublicDomain
+license-file:        LICENSE
+author:              Chris Forno (jekor)
+maintainer:          jekor@jekor.com
+category:            Distribution
+build-type:          Simple
+cabal-version:       >=1.8
+tested-with:         GHC == 7.6.2
+
+source-repository    head
+  type:              git
+  location:          git://github.com/jekor/redo.git
+
+executable redo
+  main-is:             redo.hs
+  build-depends:       base >= 4 && < 5,
+                       bytestring,
+                       containers >= 0.5,
+                       directory,
+                       filepath,
+                       process,
+                       pureMD5
+  extensions:          ScopedTypeVariables
+  ghc-options:         -Wall -fno-warn-missing-signatures
diff --git a/redo.hs b/redo.hs
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+++ b/redo.hs
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+{-# LANGUAGE ScopedTypeVariables #-}
+
+import Control.Exception (catch, catchJust, IOException)
+import Control.Monad (filterM, liftM, unless, guard)
+import qualified Data.ByteString.Lazy as BL
+import qualified Data.Digest.Pure.MD5 as MD5
+import Data.Map.Lazy (insert, fromList, toList, adjust)
+import Data.Maybe (listToMaybe)
+-- import Debug.Trace (traceShow)
+import GHC.IO.Exception (IOErrorType(..))
+import System.Directory (renameFile, removeFile, doesFileExist, getDirectoryContents, removeDirectoryRecursive, createDirectoryIfMissing, getCurrentDirectory, setCurrentDirectory)
+import System.Environment (getArgs, getEnvironment, getProgName, lookupEnv)
+import System.Exit (ExitCode(..))
+import System.FilePath (hasExtension, replaceBaseName, takeBaseName, (</>), splitFileName)
+import System.IO (hPutStrLn, stderr, hGetLine, withFile, IOMode(..), hFileSize)
+import System.IO.Error (ioeGetErrorType, isDoesNotExistError)
+import System.Process (createProcess, waitForProcess, shell, CreateProcess(..))
+
+-- traceShow' arg = traceShow arg arg
+
+metaDir = ".redo"
+
+main :: IO ()
+main = do
+  topDir <- getCurrentDirectory
+  getArgs >>= mapM_ (\arg -> do
+    let (dir, file) = splitFileName arg
+    setCurrentDirectory dir
+    redo file dir
+    setCurrentDirectory topDir)
+  progName <- getProgName
+  redoTarget' <- lookupEnv "REDO_TARGET"
+  case (progName, redoTarget') of
+    ("redo-ifchange", Just redoTarget) -> mapM_ (writeMD5 redoTarget) =<< getArgs
+    ("redo-ifchange", Nothing) -> error "Missing REDO_TARGET environment variable."
+    _ -> return ()
+
+redo :: String -> FilePath -> IO ()
+redo target dir = do
+  upToDate' <- upToDate target
+  unless upToDate' $ maybe missingDo redo' =<< doPath target
+ where redo' :: FilePath -> IO ()
+       redo' path = do
+         hPutStrLn stderr $ "redo " ++ show (dir </> target)
+         catchJust (guard . isDoesNotExistError)
+                   (removeDirectoryRecursive metaDepsDir)
+                   (\_ -> return ())
+         createDirectoryIfMissing True metaDepsDir
+         writeMD5 target path
+         oldEnv <- getEnvironment
+         let newEnv = toList $ adjust (++ ":.") "PATH" $ insert "REDO_TARGET" target $ fromList oldEnv
+         (_, _, _, ph) <- createProcess $ (shell $ cmd path) {env = Just newEnv}
+         exit <- waitForProcess ph
+         case exit of
+           ExitSuccess -> do
+             size <- fileSize tmp
+             if size > 0
+               then renameFile tmp target
+               else removeFile tmp
+           ExitFailure code -> do hPutStrLn stderr $ "Redo script exited with non-zero exit code: " ++ show code
+                                  removeFile tmp
+       tmp = target ++ "---redoing"
+       metaDepsDir = metaDir </> target
+       missingDo = do
+         exists <- doesFileExist target
+         unless exists $ error $ "No .do file found for target '" ++ target ++ "'"
+       cmd path = unwords ["sh -e", path, "0", takeBaseName target, tmp, ">", tmp]
+
+doPath :: FilePath -> IO (Maybe FilePath)
+doPath target = listToMaybe `liftM` filterM doesFileExist candidates
+ where candidates = (target ++ ".do") : if hasExtension target
+                                        then [replaceBaseName target "default" ++ ".do"]
+                                        else []
+
+upToDate :: FilePath -> IO Bool
+upToDate target = catch
+  (do exists <- doesFileExist target
+      if exists
+        then do md5s <- getDirectoryContents (metaDir </> target)
+                and `liftM` mapM depUpToDate md5s
+        else return False)
+  (\(_ :: IOException) -> return False)
+ where depUpToDate :: String -> IO Bool
+       depUpToDate oldMD5 = catch
+         (do dep <- withFile (metaDir </> target </> oldMD5) ReadMode hGetLine
+             newMD5 <- fileMD5 dep
+             doScript <- doPath dep
+             case doScript of
+               Nothing -> return $ oldMD5 == newMD5
+               Just _ -> do upToDate' <- upToDate dep
+                            return $ (oldMD5 == newMD5) && upToDate')
+         (\e -> return (ioeGetErrorType e == InappropriateType))
+
+fileMD5 :: FilePath -> IO String
+fileMD5 path = (show . MD5.md5) `liftM` BL.readFile path
+
+writeMD5 :: String -> FilePath -> IO ()
+writeMD5 redoTarget dep = do
+  md5 <- fileMD5 dep
+  writeFile (metaDir </> redoTarget </> md5) dep
+
+fileSize :: FilePath -> IO Integer
+fileSize path = withFile path ReadMode hFileSize