Question

I am trying to only allow one single character suing regex but it seems that it is allowing multiple amounts through.

I have tried this..

$char = trim($_REQUEST['char']);

/* Validate char */

if (preg_match('/[^a-zA-Z]{1}/', $char)) {
    $char = 'a';
}

echo $char;

and this..

$char = trim($_REQUEST['char']);

/* Validate char */

if (!preg_match('/[a-zA-Z]{1}/', $char)) {
    $char = 'a';
}

echo $char;

But neither work. They always output the result even if $_REQUEST['char'] is equal to aa.

Answer 1

You’re matching one character, but you aren’t matching only one character. Any string with at least one alpha character will pass your current regex.

if (!preg_match('/^[a-zA-Z]$/', $char)) {
    $char = 'a';
}

The ^ indicates the start of the string, and the $ indicates the end. No need for the {1} in this case.

You could alternatively check strlen($char) == 1 in the if statement.