PHP regex to match alphanumeric and hyphens (not spaces) for use as subdomain

Question

I have the following regex, which I interpret as a pattern that will match a string consisting of just alphanumeric characters and hyphens.

if (preg_match(\'/[A         


        

Answer 1

Your pattern matches an ASCII letter or digit or - anywhere inside a string, and if found, returns true. E.g., it will return true if you pass $#$%$&^$g to it.

A pattern that will match a string consisting of just alphanumeric characters and hyphens is

if (preg_match('/^[A-Za-z0-9-]+$/D', $subdomain)) {
    // valid subdomain
}

Details:

• ^ - start of string
• [A-Za-z0-9-]+ - 1 or more chars that are either ASCII letters, digits or -
• $ - end of string
• /D - a PCRE_DOLLAR_ENDONLY modifier that makes the $ anchor match at the very end of the string (excluding the position before the final newline in the string).