badly hacked together OS X Function Key Toggle but it doesn't use gui scripting or applescript unlike almost everything else on the internets!
Objective-C Groff C
Latest commit 47ec8ba Sep 2, 2016 @nelsonjchen committed on GitHub Update README.md

README.md

fntoggle

A very, very badly hacked together executable that can turn on and off function keys on my Retina MacBook Pro 15" (Mid-2012). What I'm saying is that it WORKS4ME and with ControlPlane.

At least it does not use GUI scripting with Applescript to accomplish this goal.

Usage

Media Keys

./fntoggle off

Standard Function Keys

./fntoggle on

Toggle state

./fntoggle

Note: You may need to toggle the state on or off explicitly before toggle previous state invokation can work.

Note that the original F9-F11 keys are most likely still bound to the Expose stuff. This simple program does nothing to address that.

References

https://github.com/davvid/schismtracker/blob/master/sys/macosx/ibook-support.c

http://stackoverflow.com/questions/6968677/cfnotificationcenter-usage-examples

http://blog.bignerdranch.com/729-notifications-part-2-handling-and-spying/

Known Issues

The Keyboard Preference Pane does not update with values set by this tool while running.

License

The Schism tracker code is GPL2 but wow a bunch of it looks to be the product of disassembling the Keyboard Preference Pane anyway like me. Regardless, this project could be GPL2.