What is the meaning of "ой"

I know that a lot of languages use the interjection "oi" to call someone's attention. I speak portuguese and we use this word a lot the same way as "hi", sometimes we use "opa" instead. So I was trying to find a translation to "opa" and find the "ой", but other search sources said that "ой" works like an "ouch". Can someone tell me the meaning for "ой" please