Binding the entire output of an ongoing system process to a variable in Haskell

问题

The following snippet of code executes a grep command and binds the output to stdout', stderr' and errCode respectively.

main :: IO ()
main = do
    let stdin' = ""
    (errCode, stdout', stderr') <- readProcessWithExitCode "grep" ["search-term" ,"-nr", "/path/to/be/searched"] stdin'
    putStrLn $ "stdout: " ++ stdout'
    putStrLn $ "stderr: " ++ stderr'
    putStrLn $ "errCode: " ++ show errCode

The problem is that stdout' only captures the first result of the search. I think this is because grep is something akin to a spawned process that feeds search results one file by one file until it is finished.

Question: I need the entire output of the standard output of grep to be binded to stdout'. Is this possible in Haskell, and if so, what is an idiomatic way to do it?

EDIT: It turns out that the issue wasn't as I thought it was. Namely, I had only one file in my directory that wasn't symlinked. I forgot to use -R as an option with grep, and so those symlinks weren't being traversed in the search! The issue has been resolved.

来源：https://stackoverflow.com/questions/37197388/binding-the-entire-output-of-an-ongoing-system-process-to-a-variable-in-haskell