I'm trying to write a regex that matches anything but one word(themagicword in this example), coming from the perl/python world I would do it with a negative lookahead: ^(?!themagicword).*
How would I achieve this in golang as this doesn't seem to work in golang.
"matches anything but one word" is equivalent to "matches (not word)" which is equivalent to "not (matches word)". So just match the word you want to exclude and then return the inverse:
hasmagic, _ := regexp.MatchString("themagicword", "haystack")
matched := !hasmagic