Com Port Listening
What Id like to do is to have a button connected to a com port, have a script running that could listen for the circuit to close (push the button) and launch an external program once it has been.
What Id like to know, if someone can tell me, is how to go about listening for the circuit to close on the port.
The device connected to the com port should obey its connection protocol. I think you can not pass any signal to software layer if you just connect a button to com port.
I assume you're running a Windows system...
It's a bit tricky with Windows, because the operating system tries to insulate you from the hardware. But, you can open the port as a file. Here's an MSDN link to get you started.
The parallel port would be easier to use. The serial port is going to expect "proper" serial data per the RS-232 protocol... a particular baud rate etc.