Applescript Press and hold ⌘ F2 for 5 seconds?

Question

I'm basically trying to figure this out because I want to use my iMac as an external monitor for my macbook air. I also want to use the iMac keyboard for my macbook air however for some reason, Apple has decided that once you press and hold Command F2 to activate Target Display Mode (meaning it is now an external monitor) that the keyboard paired with the iMac cannot be unpaired with the iMac.

To work around this I thought I would just pair the keyboard with the macbook air initially (leaving the iMac without a keyboard) and create an Applescript macro that would simulate the keyboard pressing and holding the Command F2 for five seconds eliminating the need to go buy another Apple keyboard.

Here's what I have so far and it doesn't work. It's telling me F2 is not right. I'm pretty sure F2's key code is 120.

tell application "System Events"
     key down Command
     key down F2
     delay 5
     key up Command
     key up F2
end tell

Does anyone know how I might accomplish this?

Answer 1

Observations as of OS X 10.9.1:

There's a problem with the way you're sending F2 (you need to use (key code 120) instead of just 120), but the larger problem is that key up/down only works as expected with modifier keys.

While NON-modifier keys can be sent (using (key code <n>) syntax), the up / down aspect is ignored, making both key down (key code <n>) and key up (key code <n>) statements effectively the same as key code <n> (i.e., a Key Down event immediately followed by a Key Up event is sent).

There's a suggested workaround here, based on repeatedly sending keystrokes in short sequence - it's worth a try, but from a technical perspective it's not the same as keeping a key [combination] held down, so I'm not sure it'll work.

Adapted to your situation (and replacing key down with key code), we get:

tell application "System Events"
    set now to the seconds of the (current date)
    set later to now + 5
    if later > 60 then set later to later - 60
    key down command
    # Workaround: send F2 repeatedly.
    repeat while the seconds of the (current date) is not later
        key code 120
    end repeat
    key up command
end tell

As I said: this may not work; also note that the loop is "tight" meaning that it'll make your machine pretty busy (if sending keys repeatedly, but not necessarily as fast as possible is an option, you could insert a short delay).

Some optional background info:

• The key up and key down commands, while also requiring the System Events context, are NOT exposed in the System Events.sdef, the app's dictionary (only key code and keystroke are listed) - this may indicate that Apple doesn't officially support them.
• On OS X 10.9.1 (unlike on OS X 10.8 - don't know about earlier versions) there is a bizarre bug where an extra "a" keypress is sent whenever you use key down with a (keycode <n>) specifier.
• Ways of determining key-code values (gleaned from various other SO answers, mostly here):
  • Key Codes, a free GUI app for interactive use - very handy.
  • The following header file on your system (list of codes in hex format):
    /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/Headers/Events.h
  • List of decimal codes (incomplete):

Answer 2

I've started a project to do something similar, namely monitor the iMac and automatically trigger target display mode and toggle off bluetooth when a Macbook is connected. You can download it from https://github.com/duanefields/VirtualKVM.