regular expression to match an empty (or all whitespace) string

Question

i want to match a string that can have any type of whitespace chars (specifically I am using PHP). or any way to tell if a string is empty or just has whitespace will also h

Answer 1

You don't really need a regex

if($str == '') { /* empty string */ }
elseif(trim($str) == '') { /* string of whitespace */ }
else { /* string of non-whitespace */ }