The output should be false, because you are using backquotes `` in the argument to Compile, which makes the argument the literal three bytes '\' '8' 'A', and that's certainly not what you mean.

However, changing `` to "" doesn't help, as you can see here: https://go.dev/play/p/mMd57XnQKL6

The argument to Compile must be valid UTF-8, although I'm not sure that's explicitly documented.

I think this is a bug. If I use the following code, the result is true.

func main() {
	re, err := regexp.Compile(`\x30`)
	if err != nil {
		fmt.Println(err)
		return
	}

	fmt.Println(re.Match([]byte("\x30")) == true)
}

I checked the source code and used the WriteRune function in the regexp.Compile call chain. When writing a character with ASCII greater than 127, theWriteRune will write 2 bytes to the bytes array or string, which leads to the failure of the match function.

And, If I am wrong, how should I match a character whose ascii is greater than 127?

Please read https://go.dev/blog/strings for background about how text works in Go as well as in UTF-8. The term "character" is too vague to be technically useful in this context.

To answer your direct question, if we assume by "character" you mean "Unicode code point", use a Unicode escape like "\u1234" or write out the bytes of its UTF-8 encoding.

Also, \x30 in backquotes is 4 bytes, not one, and none of them is the byte with value 0x30.

Thank you very much!

Ha! I'm wrong (as usual, but only a little). The ASCII zero numeral is hexadecimal 30, so my last sentence in my previous reply was incorrect. Still, the overarching point is right: Matching plain bytes won't work in general.