PHP preg_match - only allow alphanumeric strings and - _ characters

Question

I need the regex to check if a string only contains numbers, letters, hyphens or underscore

$string1 = \"This is a string*\";
$string2 = \"this_is-a-string\"         


        

Answer 1

\w\- is probably the best but here just another alternative
Use [:alnum:]

if(!preg_match("/[^[:alnum:]\-_]/",$str)) echo "valid";

demo1 | demo2