Redstone on so Computer can Boot Up?

How do I make it so that a computer has to have power (redstone) plugged in to it so it will turn on? I saw this somewhere and now I can't find it.
It's driving me crazy not knowing where to find it.

You can check for the redstone input on the startup file, if it's off shutdown the computer.

if not rs.getInput("side") then
  os.shutdown()
end

Put that in the startup file, changing the side you want the power to be, and you won't be able to turn the computer on if the redstone signal is off (unless you remove the startup file).

Thank you, that's what I was looking for.

Use my WSC(Wolvan's Super Controller) Client it has that feature built in
LINK