Question

I want to do a popen() / python s subprocess.communicate from Haskell - start a program, give it stdin, and get its stdout/stderr. What s the most direct / Haskellish way to do this?

Answer 1

Pick either MissingH s System.Cmd.Utils and the standard library s System.Process. They re easy to use, with both high-level convenience functions (which you simply throw strings at and get strings back, possibly lazily) and low-level plumbing functions (which actually give you handles, like most popen functions in other languages/frameworks).

import System.Process

main = do
    let cmd = "mail"
        args = ["root@localhost", "-s", "does this act like popen?"]
        input = ["Hello, world!"]
    (rc, out, err) <- readProcessWithExitCode cmd args input
    putStrLn $ "mail exited: " ++ show rc
    mapM_ putStrLn $ map ("out: " ++) $ lines out
    mapM_ putStrLn $ map ("err: " ++) $ lines err

Answer 2

The other option could be to use shelly package

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