To further elaborate ... the first parameter to split() is always a regular expression (except the split ' ',... special case). Even if you enclose the parameter in quotes. So even split '+', $string emits that error message. IMHO, it's bad design, but that's the way it is. If you do want to split on a literal string and not have to worry about special characters you have to use split /\Q$separator\E/, $string.