Question

I am trying to validate form input data using PHP’s preg_match function. I am a little confused of how to use it. If I want to validate say an alphanumeric string, I would use ^[0-9a-zA-Z ]+$ as the first parameter and the string we’re validating as the second one. But how would I use preg_match to tell if it’s valid or not? Would I do this:

if(preg_match("^[0-9a-zA-Z ]+$", $_POST['display_name'])){
  "String is valid";
} else {
  "String is not valid";
}

Or the other way around? I am currently using the if not preg_match if statement but it’s returning false for some reason… I know this is probably an easy answer, but I cannot figure this out.

Answer 1

FALSE return from a preg_match indicates an error

you need to delimit your regex (see the leading and trailing / you can use other characters too

if (preg_match("/^[0-9a-zA-Z ]+$/", $_POST['display_name'])) {