[Haskell-beginners] Read file from sys

[Libor Wagner]

Hi, 

I have small code snippet to read content of a file, which should grow into simple tool to read temperature from sensor on Raspberry Pi:

module Main where

import System.Environment 

main :: IO ()
main = do 
[f] <- getArgs 
s <- readFile f 
putStr s 

When this is called with the test file I have copied from the real location it works fine:

$ cat /sys/bus/w1/devices/28-000004e46240/w1_slave >test.txt
$ ./ds18b20 test.txt 
53 01 4b 46 7f ff 0d 10 e9 : crc=e9 YES
53 01 4b 46 7f ff 0d 10 e9 t=21187



How ever when called with the real location nothing happens:

$ ./ds18b20 /sys/bus/w1/devices/28-000004e46240/w1_slave

Can someone help? I have thought that the file is not properly ended so I have tried to take just first line but that doest work either.

Thanks
Libor