optparse: some and many.

optparse33.hs

main :: IO ()
main = do
    let files :: O.Parser [String]
        files = O.helper <*> O.arguments1 (Just) (O.metavar "logfile" <> O.help "one or several log files")
        foo = some $ O.strOption
                     ( O.long "output"
                    <> O.short 'o'
                    <> O.metavar "FILENAME" )
        parserInfo = O.info ((,) <$> files <*> foo) (O.fullDesc)
        prefs =  O.prefs O.showHelpOnError 
    foo <- O.customExecParser prefs parserInfo 
    putStrLn "--"
    putStrLn $ show foo