Write to linux serial port from bash script

Question

Hi I am using a raspberry pi and trying to write to a usb serial port in a bash script. I found echo would be the right way to do it. Also I want to test if the port is busy or not when writing. So I am using this script:

#! /bin/bash if echo -e "USB Command" >> /dev/ttyACM0 ; then echo "Success" else echo "Fail" fi 

But the problem is it is always success even when there is no permission to access the port. Am I using the best way to write to port? How can I check if the write was succeeded? Thanks

Edit: Here is the output of:

ls -l /dev/ttyACM0 crw-rw---- 1 root dialout 166, 0 Dec 13 16:38 /dev/ttyACM0 

Answer 1

Check your script. I think what you will want to do is test for the return code from the echo command.

For example, if you simply run the echo from the command prompt:

$ echo -e "USB Command" >> /dev/ttyACM0 

End then immediately check the return code:

$ echo $? 0 

You should be able to determine success. At least the success of putting data on the tty.

A return code of 0 means success. Anything else is an error and you can probably google for the non-zero error code to see what it means.

Get that working manually and then see how to incorporate it into your script.

.

Answer 2

Something is broken for you:

echo Hello >> /dev/mem; echo $? bash: /dev/mem: Permission denied 1 

If you're talking about classic Unix permissions and you don't have them to access the device, the command should absolutely fail.

Use udev rules or echo 123 | sudo tee /dev/device to work around it.