sha256 hash file(s) from command line

file_hash.hs

#!/usr/bin/env runhaskell

import Crypto.Hash
import Data.ByteString
import Prelude hiding (readFile)
import System.Environment (getArgs)

keyFor :: FilePath -> IO ()
keyFor filepath = do
  bytes <- readFile filepath
  print $ hexSha3_256 bytes

sha1 :: ByteString -> Digest SHA1
sha1 = hash

hexSha3_256 :: ByteString -> String
hexSha3_256 bs = show (hash bs :: Digest SHA3_256)

main :: IO ()
main = do
  args <- getArgs
  case args of
    [] -> print "gimme filepath(s)"
    [filepath] -> keyFor filepath
    filepaths -> mapM_ keyFor filepaths