PHP regular expression for alphanumeric and hypen input

Question

Is it possible to validate input depending on whether it only contains a combination of letters, numbers and hyphens (where a hyphen is not repeated twice-in-a-row and does not begins/ends the string)?

Thanks to Validate username as alphanumeric with underscores

I know that the following validates a string based on alphanumeric input with underscores, would it be possible to alter this?

function validate_alphanumeric_underscore($str) 
{
    return preg_match('/^[a-zA-Z0-9_]+$/',$str);
}

Thank you in advance for your help!

Answer 1

This can be done quite easily with a single regular expression:

/^([a-z0-9]+-)*[a-z0-9]+$/i

This meets all your criteria:

• No double hyphens
• No beginning/ending hyphens
• Works when strlen == 1

Matches:

• a
• aa
• aaa

Doesn't match:

• -
• a-
• -a
• a--a
• aa--a

Play with it here .

Answer 2

Assuming a minimum of 2 characters:

This will validate the general format (not starting or ending with a - ).

/^[a-z0-9][a-z0-9-]*[a-z0-9]$/i

Then add a simple check for double hyphens using strpos (if it's false, there is no -- in the string, so we want to return true . Otherwise, we want to return false , so that's why the false === is in there):

false === strpos($string, '--');

So, you could do it as:

function validateAlphaNumericUnderscore($string) {
    if (0 < preg_match('/^[a-z0-9][a-z0-9-]*[a-z0-9]$/i', $string)) {
        return false === strpos($string, '--');
    }
    return false;
}

Now, I'm sure there's a way to do it in a single regex (without needing the additional strpos ), but I'm blanking on that now. This is a simple regex, and a simple second string comparison (non regex based).

Hopefully this suits your needs...

Edit: In fact, you could make this more efficient by checking for the -- first (since the string function is cheaper than the regex):

function validateAlphaNumericUnderscore($string) {
    if (false === strpos($string, '--')
        return 0 < preg_match('/^[a-z0-9][a-z0-9-]*[a-z0-9]$/i', $string);
    }
    return false;
}

Answer 3

ircmaxell's answer uses a regex and a strpos() check, and is an answer I prefer, but here's how I did it with a single regex. Disclaimer: this has vast room for improvement :

function validate_alphanumeric_hyphenated($str) 
{
    /* 
     * Match either one or more alphanumeric characters, or a sequence with
     * a series of alphanumeric characters without consecutive, leading
     * or trailing hyphens.
     * 
     * Is probably unnecessarily long.
     */
    return preg_match("/^(?:[a-zA-Z0-9]+|[a-zA-Z0-9](?:[a-zA-Z0-9]|-(?!-))*[a-zA-Z0-9])$/", $str);
}

Answer 4

You could do it with two regexes:

if( !preg_match('/(?:^-|-$|-{2,})/',$str) && preg_match(/^[a-zA-Z0-9_]+$/',$str) ) {
     return true;
}