If {buf} is omitted the current buffer is used. If {buf} is a Number, that buffer number's name is given. Number zero is the alternate buffer for the current window. If {buf} is a String, it is used as a file-pattern to match with the buffer names. This is always done like 'magic' is set and 'cpoptions' is empty. When there is more than one match an empty string is returned. "" or "%" can be used for the current buffer, "#" for the alternate buffer. A full match is preferred, otherwise a match at the start, end or middle of the buffer name is accepted. If you only want a full match then put "^" at the start and "$" at the end of the pattern.