A blog by Devendra Tewari
Here’s how socat can be used to redirect one serial port to another on Ubuntu, assuming both serial devices are not assigned to a real device
sudo socat -d -d pty,link=/dev/ttyS0,raw,echo=0 pty,link=/dev/ttyS1,raw,echo=0
If the above command is successful, you can send data from one serial port to another using a terminal emulator such as screen
screen /dev/ttyS0 115200
Install screen using sudo apt install screen if not already installed. Repeat the above command on another prompt for the other serial device, and you’re good to go. Quit screen using Ctrl-A.
socat can also be used to perform serial to TCP redirection
sudo socat -d -d pty,link=/dev/ttyS0,raw,echo=0 tcp-listen:8000
Now, you should be able to use screen to send and receive data on the serial port, while you use something like netcat to receive and send data to the serial port
netcat 127.0.0.1 8000