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 need regular expressions for that, just use:

if ( Trim ( $str ) === '' ) echo 'empty string';

Answer 2

if(preg_match('^[\s]*[\s]*$', $text)) {
    echo 'Empty or full of whitespaces';
}

^[\s]* means the text must start with zero or more whitespace and [\s]*$ means must end with zero or more whitespace, since the expressions are "zero or more", it also matches null strings.

Answer 3

Expression is \A\s*+\Z

Answer 4

if (preg_match('^[\s]*$', $text)) {
    //empty
} 
else {
    //has stuff
}

but you can also do

if ( trim($text) === '' ) {
    //empty
}

Edit: updated regex to match a truly empty string - per nickf (thanks!)

Answer 5

You don't really need a regex

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

Answer 6

The following regex checks via lookahead and lookbehind assertion, if the string contains whitespace at the beginning or at the end or if the string is empty or contains only whitespace:

/^(?!\s).+(?<!\s)$/i

invalid (inside "):

""
" "
" test"
"test "

valid (inside "):

"t"
"test"
"test1 test2"