Determine if PHP String Contains a Substring

This PHP function returns boolean true if the substring is contained within the string. If not it returns false.

function contains($haystack, $needle)  {
    if ($haystack=="" || $needle=="")  { return false; }
    return strpos(strtoupper($haystack), strtoupper($needle)) !== false;
}

Example:

$string = "Mary had a little lamb and it's fleece was white as snow";
$substring = "little lamb";

if (contains($string, $substring )) {
    print "TRUE";
} else {
    print "FALSE";
}

Result: TRUE