How to find out which USB-RS232 device is on which tty?

Question

I have two different USB devices based on the same USB-RS232 chips. When I plug those in the USB they are mounted to /dev/ttyUSB0...3

My problem is how, inside a script,

Answer 1

You can use udev to assign a stable symbolic link to each FTDI dongle. Use device and vendor to match the type, and then the serial number for the specific device. Then use the symbolic link in the script.

I named my dongles ttyFTDI0 etc., and wrote the numbers on the dongles with a marker:

$ cat /etc/udev/ftdi.rules 
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="FTDEN97D", SYMLINK+="ttyFTDI0"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="A600b30P", SYMLINK+="ttyFTDI1"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="A600bexU", SYMLINK+="ttyFTDI2"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="FTFMSA54", SYMLINK+="ttyFTDI3"
SUBSYSTEMS=="usb", KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", ATTRS{serial}=="FTFMUW4A", SYMLINK+="ttyFTDI4"