How to wake from sleep programmatically?

Answer 1

You can schedule wake up events with IOPMSchedulePowerEvent through the power manager. You may be able to schedule an immediate wake up. pmset is a command line wrapper for the power manager. You can also prevent sleep with IOCancelPowerChange in certain cases.

You may be able to prevent sleep or wake up by generating a mouse or key event. One way to generate events is with CGPostKeyboardEvent.

Edit:

Normal sleep is different from clamshell closed sleep. To affect the latter you must write a kernel extension like Insomnia.

Answer 2

It looks like IOPMSchedulePowerEvent is what you want.

Edit: Dang, somebody answered before I could, and now I don't seem to be able to delete my answer.