How to gain confidence from a cat?

Keep leaving the food for him, i would give it about a week of slow moving. Along with the food, leave one of your shirts outside, so the cat can see what you smell like, and i don't mean spray it up with cologne, just a regular undershirt. After a few days of this, try and figure out what time the kitty comes around, perhaps sit outside and wait, when the cat comes, just slowly put your hand out, allow it to come to you. It will be a slow process for a cat that has no human interaction, but again, very slow. Once it seems ok with you sitting outside, and has gotten used to your smell, try getting up to pet it, and talk to it, let it get used to your voice as well. Even try opening the door to your home, but don't corner it once inside, let it roam freely with the door open. Eventually it will learn your trust, once it does, please take it to the vet and have it checked for any health issues. If keeping the cat indoors doesn't work, you may earn enough trust to have an outdoor cat, and most shelters will fix feral cats at a discounted price.