how to detect if external display is present

I need my code to evaluate whether an external display is connected via a mini-display port.

 

Ideally, I'd like to do this by having a bash command that determines a boolean True/False value for the presence of a file. I'm just not sure what file I should be looking for, presumably something in /dev/

 

Any suggestions what it should be, or suggestions of a better way to make the determination (anything in applescript, bash, objective-c, or plain-old c will do)?

 

TIA

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