I'm in Gold League and all day I play against 4 Gate Protoss. How can I take advantage of this as soon as I scout it? Obviously, it's hard to take advantage with an expansion against this kind of early aggression, even with bunkers.
Wall in, tech up to siege tanks w/ siege, build a few, and plant them at your base entrance. Assuming you scout early enough, this method requires the least micro and will allow you a solid transition into an expansion.
You can also try to build up a few bunkers & stock them with marine/marauder. This can be effective as well as long as you keep the ranged Protoss units out of range of your repairing SCVs (a.k.a. walling in).
For either of the above, you'll want to watch out for void rays. That's usually how your 4-gate counter will be countered.
Banshees with cloak can be somewhat effective but the siege tanks have more longevity in terms of utilization for the rest of the match.
Marauders with concussive shells can also be effective if you have the micro for it.
I've been trying to wrack my brain about how to punish the protoss player, but unless you can stay alive through the push, it would be very difficult to punish them before they come up with an army knocking on your front door.
So assuming you survive with bunkers and marines/marauders/scvs set on repair the ideal tech path would be to go cloaked banshee.
If they are 4gating they cut probe production which means you're already ahead economically. It also means they won't have a robotics bay to build an observer, you are free to pick off as many probes as you have energy, which will give you even more of an economic advantage and you will get the win assuming you continue to macro effectively.