SHA1 encoding in Haskell

The cryptohash package is probably the simplest to use. Just read your input into a lazy¹ ByteString and use the hashlazy function to get a ByteString with the resulting hash. Here's a small sample program which you can use to compare the output with that of sha1sum.

import Crypto.Hash.SHA1 (hashlazy) import qualified Data.ByteString as Strict import qualified Data.ByteString.Lazy as Lazy import System.Process (system) import Text.Printf (printf) hashFile :: FilePath -> IO Strict.ByteString hashFile = fmap hashlazy . Lazy.readFile toHex :: Strict.ByteString -> String toHex bytes = Strict.unpack bytes >>= printf "%02x" test :: FilePath -> IO () test path = do hashFile path >>= putStrLn . toHex system $ "sha1sum " ++ path return () 

Since this reads plain bytes, not characters, there should be no encoding issues and it should always give the same result as sha1sum:

> test "/usr/share/dict/words" d6e483cb67d6de3b8cfe8f4952eb55453bb99116 d6e483cb67d6de3b8cfe8f4952eb55453bb99116 /usr/share/dict/words 

This also works for any of the hashes supported by the cryptohash package. Just change the import to e.g. Crypto.Hash.SHA256 to use a different hash.

_{¹ Using lazy ByteStrings avoids loading the entire file into memory at once, which is important when working with large files.}