Alphanumeric usernames and error message for it

Question

I'm facing a problem where I haven't seen proper answer anywhere. What I need help with is this:

How can I prevent my users registering non-alphanumeric usernames? To be exact, I could prevent it by using something like:

function validate_alphanumeric_underscore($string?) { return preg_match('/^[A-Za-z][A-Za-z0-9]*(?:_[A-Za-z0-9]+)*$/',$str); }

But what is the string I should/could use and how can I echo error message saying that the username inputted had invalid characters?

Cheers!

Answer 1

Check for alphanumeric

For more details, look at the regex Q on SO.

$name = 'input string 123";
// Doesn't allow:
// Pre-/Appending white space
// Not more than one space in between
// Non-alphanumeric characters (lower case)
if( ! preg_match( "/^[a-z0-9]+([\\s]{1}[a-z0-9]|[a-z0-9])+$/i", $name ) )
{
    // Output Error Message
}
// Or: Does only allow
// Alphanumeric character (lower & upper case)
// Dash & underline "-", "_" - makes (imho) sense
if( ! preg_match( "/^[A-Za-z0-9-_",'\s]+$/", $name ) )
{
    // Output Error Message
}

Error Message

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