How to make disable/enable raspberry pi a button?

Question

Raspberry Pi

So, I need to turn off / on the raspberry pi using the button, pressed the button turned on, pressed the button saved the data, turned off
Can I do it using GPIO? Since I don’t want to solder something in raspberry
It should all work in RetroPie
Because I want to make an arcade machine

Answer 1

Turning on the board can be implemented using two contacts on the board, which appeared since B rev.2. These contacts are designated as p6, and are located near the power supply of the board.
If you solder a button to these contacts, then it will work as a reset in the working state of the board, and as an on when it is off.

Answer 2

It is possible to attach a jumper from a hard drive or a button to a couple of pins. The point is that when a certain pin is zero, the system turns off. When turned off, the raspberry goes into the "safe power off" state - this means that the raspberry is not running and you can turn it off from the outlet. But if you give a signal to these special pins, the processor will "wake up" and everything will start, as when plugged into a power outlet. These pins are pin 5 and ground. You close them - bam!
There is a more difficult option, it was already described by pacman667 - for it you need to be able to solder (which every geek should be able to do)