The point isn’t to use getopt with all its complexity, the point is that two dashes for long options is already extremely well established and Go popularizing long options with a single dash is very much a regression. It creates a lot of unnecessary confusion when they really should have known better and just stuck with the conventions.

In your regex at least, removing the confusion is simple as adding another ‘-‘, and now you’re in compliance with the expectations of almost every IT person in the world who uses Unix command lines.