sudo-like cli: a way to instruct `cmdargs` to not look for flags in the remaining arguments

[oshyshko]

I am working on a program that has sudo-like interface:

sudo ls
sudo ls -l
sudo -u joe ls -l /

Here's my current code:

#!/usr/bin/env stack
-- stack --resolver lts-9.20 script --package cmdargs

{-# LANGUAGE DeriveDataTypeable #-}
{-# OPTIONS_GHC -fno-cse #-}

module Main where

import           System.Console.CmdArgs as Args
import           System.IO

data Sudo = Sudo { user        :: Maybe String
                 , group       :: Maybe String
                 , command     :: [String] }
              deriving (Data, Show)

main :: IO ()
main = do
  m <- cmdArgs Sudo { user    = def
                    , group   = def
                    , command = def &= typ "COMMAND" &= args  }

  print m

It works fine for commands without flags or when -- is used to mark the end of flags.

$ ./cmdargs.hs ls 1 2 3
Sudo {user = Nothing, group = Nothing, command = ["ls","1","2","3"]}

$ ./cmdargs.hs -- ls -l
Sudo {user = Nothing, group = Nothing, command = ["ls","-l"]}

$ ./cmdargs.hs -u joe -- ls -l
Sudo {user = Just "joe", group = Nothing, command = ["ls","-l"]}

However, it doesn't work when a sub-command has flags and when -- is not used:

$ ./cmdargs.hs ls -l
Unknown flag: -l

$ ./cmdargs.hs -u joe ls -l
Unknown flag: -l

Q: How to instruct cmdargs to not look for flags in the remaining arguments?

[ndmitchell]

The user could write: ,/cmdargs.hs -u joe -- ls -l, which would take advantage of the fact that -- separates arguments from flags.

But currently there is no way to get that behaviour from cmdargs - although it was requested once before, so seems a plausible addition.

[simonmichael]

Yep, I have wanted this for years for hledger, which sometimes invokes separate executables with their own flags. Everybody trips up on the need for -- in this case. http://hledger.org/manual.html#command-options