Problems with NsTask to execute terminal command - objective-c

Question

Normally in the terminal I would execute this command to communicate with a serial USB device.
echo -e '\xFF\x01\x01' > /dev/cu.usbserial-A8003YzT
I'm trying to do this from within a cocoa app using NStask, but I'm getting no love for some reason.
Heres my code:
- (IBAction) doCommand:(id)sender{
{
NSTask *task;
task = [[NSTask alloc] init];
[task setLaunchPath:#"/bin/echo"];
[task setArguments:
[NSArray arrayWithObjects:#"-e '\\xFF\\x01\\x01' > /dev/cu.usbserial-A8003YzT", nil]];
[task launch];
[task release];
}}
I know the code is essentially working, as I've executed other terminal commands with the same script.....not sure why I can't get the echo to fire....perhaps I'm missing somthing simple?
Thanks for any help

Answer 1

You're trying to send '\xFF\x01\x01' > /dev/cu.usbserial-A8003YzT as the first argument to echo, but that's not what happens when you run that command from a shell prompt. Only the first, quoted part is sent as an argument to echo. Bash interprets the > itself, captures the output from the echo command, and redirects it to the indicated file - in this case, a file that represents a usb device.
If you want to run an NSTask that will interpret a shell command with redirects, pipes, and such, you'll need to use /bin/sh as the launch path, and -c, your shell command as arguments.
Alternatively, you could skip the NSTask altogether, and simply open an NSFileHandle to the device file, then send the three-byte sequence you want to send it. Echo is handy for interactive debugging stuff like this in a terminal, but launching an external task in your app, just to write three bytes to a file, is pretty drastic overkill... :-)