Ok, so I tested this. it appears that as long as I plug it into the same port, I get the same value.
So then there is no way to predetermine the port.
If the device is installed properly, you will see entries in the /dev directory: /dev/cu.usbserial-xxxxxxxx /dev/tty.usbserial-xxxxxxxx where xxxxxxxx is either the device's serial number or, for unserialized devices, a location string that depends on which USB port your device is connected to.
my-mac:~me$ sudo ln -s /dev/tty.usbserial-* /dev/tty.arduino
It appears that .usbserial- is common to all of the ports.
Unfortunately, I am not a unix/linux guy. So... the little code snippet... does that effectively create a symbolic link to the ports?
What then, if you want multiple arduinos connected?
There has to be a way in your app that interfaces with the arduino, to have a way of detecting what port it is.
Even still, the arduino environment has the ability to detect a serial port with a board that does not have a SN.