Question

The following Haskell program prompts the user for a password in the terminal and continues if he has entered the correct one:

main = do
    putStrLn "Password:"
    password <- getLine

    case hash password `member` database of
        False -> putStrLn "Unauthorized use!"
        True  -> do
                 ...

Unfortunately, the password will appear on the screen as the user types it, which I want to avoid.

How can I read a sequence of characters that the users types without having the show up on the screen? What is the equivalent of getLine for this purpose?

I’m on MacOS X, but I would like this to work on Windows and Linux, too.

Answer 1

Do this:

module Main
where

import System.IO
import Control.Exception

main :: IO ()
main = getPassword >>= putStrLn . ("Entered: " ++)

getPassword :: IO String
getPassword = do
  putStr "Password: "
  hFlush stdout
  pass <- withEcho False getLine
  putChar '\n'
  return pass

withEcho :: Bool -> IO a -> IO a
withEcho echo action = do
  old <- hGetEcho stdin
  bracket_ (hSetEcho stdin echo) (hSetEcho stdin old) action