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

Why to use regex? PHP has some built in functionality to do that

preg_match('/\s/',$username) will check for blank space

!ctype_alnum(str_replace($valid_symbols, '', $string1)) will check for valid_symbols