How to send and read from serial port at the same time?

Question

linux

Arduino is configured so that if you apply to the Serial Port /dev/ttyACM0
:
1 - turn on the LED
2 - turn off
3 - beeps for 1 second
for them, I use
echo "digit" > /dev/ttyACM0
and now you need to simultaneously apply to arduino - 4 and read the answer as a number that indicates the level of light read from the light sensor.
There is a solution - screen, but I need to send one command to port - 4 and get a response.

Answer 1

forum.arduino.cc/index.php?topic=54268.0
3 minutes of google. Call your ISP and ask to unblock Google.

Answer 2

echo 4 > /dev/ttyACM0 && dd if=/dev/ttyACM0 count=1 bs="длина ответа"

Answer 3

Does it bother you that serial is a serial port? You cannot read and send at the same time.