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Is it possible that your script doesn't have read/write permission on this device node?  I've had this simple problem in the past, and it is easy to overlook.

If you wanna take a look at my GPS code, we have it hosted on our SVN server:

I don't usually like to post work I haven't tested a million times, but maybe that will help you out a bit.  Sorry it isn't commented yet; I will have someone on the team comment it for me at some point...

On Thu, 2006-02-09 at 15:19 +1100, Matthew Percival wrote:

	I think I have sort of worked out why I am not reading anything back:
it does not seem the script is sending anything in the first place.  If
I do `print (tty)', I get back `file (0x8051688)', so it seems OK at
that point, but if I wrap a print() around the write() call I get this:
		nil     Bad file descriptor     9

> I use Lua with the UMR Robotics Team to interface with several
> different devices such as GPS receivers, microcontrollers, etc.  So
> long as you don't want it to be portable, it is easy in Linux with
> stty:

	I am trying to check the status of a GPS Modem, and the script will
only ever be run from Linux, so it sounds like you are doing something
very similar to what I am trying to do (which also suggests it does
work).  I tried copying your code (with minor changes for my setup), and
added a write at the end, but it returned the same error.

	-- Matthew