I want to extract digits from the string that may contain some special characters (let's say "+-() ") but not any other characters, i.e.:
"+123 (456) 7-8" -> "1, 2, 3, 4, 5, 6, 7, 8" is extracted
"123a45" -> pattern matching fails, nothing is extracted
"1234 B" -> pattern matching fails, nothing is extracted