how to detect if external display is present

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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

OS X Mountain Lion (10.8.2)

Posted on Jan 20, 2013 2:13 AM

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Answer 1

softwater Author

Level 5

5,556 points

Jan 20, 2013 2:17 PM in response to softwater

It seems the process I need to monitor is the WindowServer, which sends messages to console on connection of the external display like

21/01/2013 04:24:11.647 WindowServer[81]: Display 0x5b81c5c1: MappedDisplay Unit 1: Startup Mode 1920 x 1080, CGSThirtytwoBitColor, Resolution 1, IOMode 0x3e, IODepth 0x2, IOReturn 0x0

The question is how do I intercept those messages in my script? I don't need to manipulate the settings, just have my script evaluate whether an ext. display is present or not.

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Answer 2

softwater Author

Level 5

5,556 points

Jan 21, 2013 8:18 PM in response to softwater

This seems to cover the same issue:

http://macscripter.net/viewtopic.php?id=28627

From what I can tell at the moment, a full answer is going to have to be done in Obj-C, but a short Applescript like this will at least get the number of displays connected:

tell application "Image Events"

launch

get properties of every display

quit

end tell

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