Getting Arduino to talk to Mac

A simple project, or so i thought..

I'm using an IR Sensor to execute an applescript that skips to the next track in iTunes. After many minutes of searching, I couldn't find ASProxy. As an alternative I got SerialPortX. But honestly i've no idea how to work Serial PortX. I know what I want my sketch to do but i don't know how make it talk to my mac. i've had a look at numerous tutorials but they havenb't been really helpful to me.

any help would be greatly appreciated.

kind regards, first time arduino hackerati

a bit of words of wisdom or code or pseudocode wouldve been nice but thank you anyway..

In that case...

for the computer side:

For the arduino:

There already exist tons of examples of making Applescript talk to a serial port and how to make Arduino talk as a serial port (the default), why repeat them here?