How to send and receive data from serial port using command line?

Question

In the past, I have used c++ and python to communicate with serial ports in a Linux and Windows environment. In Linux, I have also used programs like picocom, minicom, and cutecom for serial communication but now I want to read and write to the serial port using simple Linux commands which requires no installation of external programs. I would be using this method in raspberry pi to communicate with my Arduino board. In the below example I'm using stty for setting serial port options and I use echo and cat command to send and read data from the serial port but at the end, I'm not seeing any output, I have read other posts in this site related to this but nothing seems to work for me. I'm able to communicate with Arduino using cutecom but with below commands, I don't see any response.

Linux (Ubuntu):

$ stty -F /dev/ttyUSB0 9600 cs8 -cstopb -parenb
$ echo "1" > /dev/ttyUSB0 //send data
$ cat /dev/ttyUSB0

Arduino Mega code for your referance:

#include <Arduino.h>

void setup() {
    Serial.begin(115200);
}

void loop() {

    if(Serial.available() > 0){
        Serial.println("[123,55,7777]");
    }
}

Here i send 1 and i get the response from arduino:

This should be pretty simple I send 1 or any character to Arduino and it should return [123,55,7777] in the command line. Any kind of help and guidance is appreciated.

Below is the code that I have tried but doesn't return any data.

stty -F /dev/ttyUSB0 115200 cs8 -cstopb -parenb  #CONFIGURE SERIAL PORT
exec 3</dev/ttyUSB0                     #REDIRECT SERIAL OUTPUT TO FD 3
  cat <&3 > /tmp/ttyDump.dat &          #REDIRECT SERIAL OUTPUT TO FILE
  PID=$!                                #SAVE PID TO KILL CAT
    echo -e -n "\x01" > /dev/ttyUSB0     #SEND COMMAND HEX 0x01 TO SERIAL PORT
    sleep 0.2s                          #WAIT FOR RESPONSE
  kill $PID                             #KILL CAT PROCESS
  wait $PID 2>/dev/null                 #SUPRESS "Terminated" output

exec 3<&-                               #FREE FD 3
cat /tmp/ttyDump.dat                    #DUMP CAPTURED DATA

Thanks

Answer 1

The usual issue for this is that when the device is closed then it gets reset back to some default configuration, so any changes you make are lost. Holding an open file descriptor avoids this.

Something like this (untested)

#!/bin/bash
# Keep the ttyUSB0 device open on fd 3
exec 3<>/dev/ttyUSB0
stty -F /dev/ttyUSB0 9600 cs8 -cstopb -parenb
echo "1" >&3                 # send data
cat <&3                      # read the data