CODEWITHSUNDEEP
haskell
George
George

Reputation: 7317

How to execute commands from Haskell as root?

Consider the following Haskell function:

eraseFile :: FilePath -> IO ()
eraseFile basename = 
  do let cmd' = ">" 
         args' = ("/path/to/file/" ++ basename) :: String
     (exitcode', stdout', stderr') <- readProcessWithExitCode cmd' [args'] ""
     return ()

When I try to run this in a stack ghci repl, or from the main function, I get a permission denied error from the console. Normally, in a bash console, you could just run this command as sudo, but this doesn't seem to work when invoked from Haskell.

Question: How to execute system commands in Haskell as root?

Upvotes: 0

Views: 265

Answers (1)

leftaroundabout
leftaroundabout

Reputation: 120711

As already pointed out in the comments, you can just run the entire stack/ghc under root, but I daresay that's a bad idea. Preferrably, I'd just invoke sudo as a process from within your program. The particular command – emptying a file, if I have understood that correctly? – is then easiest done with tee:

  do let cmd' = "sudo" 
         args' = ["tee", "/path/to/file/" ++ basename :: String]
     (exitcode', stdout', stderr') <- readProcessWithExitCode cmd' args' ""

As Zeta remarks, truncate --size 0 would probably be a cleaner command.

To get around password entering, you probably also want to make an exception in the sudoers file. It's a hairy matter; of course the really best thing would be if you could avoid needing root permissions altogether.

Upvotes: 2

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