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diff --git a/Annex/ReplaceFile.hs b/Annex/ReplaceFile.hs
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+{- git-annex file replacing
+ -
+ - Copyright 2013 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Annex.ReplaceFile where
+
+import Common.Annex
+import Annex.Perms
+
+{- Replaces a possibly already existing file with a new version, 
+ - atomically, by running an action.
+ - 
+ - The action is passed a temp file, which it can write to, and once
+ - done the temp file is moved into place.
+ -}
+replaceFile :: FilePath -> (FilePath -> Annex ()) -> Annex ()
+replaceFile file a = do
+	tmpdir <- fromRepo gitAnnexTmpDir
+	createAnnexDirectory tmpdir
+	tmpfile <- liftIO $ do
+		(tmpfile, h) <- openTempFileWithDefaultPermissions tmpdir $
+			takeFileName file
+		hClose h
+		return tmpfile
+	a tmpfile
+	liftIO $ do
+		r <- tryIO $ rename tmpfile file
+		case r of
+			Left _ -> do
+				createDirectoryIfMissing True $ parentDir file
+				rename tmpfile file
+			_ -> noop