Binding the result of a system command to a variable in Haskell

Question

How does one run a system command in Haskell and bind it\'s result (i.e., standard output) to a variable? In pseudo-haskell I\'m looking for something like the

Answer 1

Here is some working code:

import System.Process

main :: IO ()
main = do
  let stdin' = ""
  (errCode, stdout', stderr') <- readProcessWithExitCode "echo" ["hi"] stdin'
  putStrLn $ "stdout: " ++ stdout'
  putStrLn $ "stderr: " ++ stderr'
  putStrLn $ "errCode: " ++ show errCode

As Carsten notes, you can use readProcess, but I prefer this version because with any serious usage, you will soon be very confused as to why your command is silently failing (if you run in the command line, both stdout and stderr are, of course, shown).