PHP username validation - php

Question

I am working on writing a PHP login system. I have everything that I need working, but I would like to verify that a username entered during the registration only contains alphanumeric characters. So how could I take a variable, say $username, and ensure that it contained only alphanumeric characters?

Answer 1

if(preg_match('/^\w{5,}$/', $username)) { // \w equals "[0-9A-Za-z_]"
// valid username, alphanumeric & longer than or equals 5 chars
}
OR
if(preg_match('/^[a-zA-Z0-9]{5,}$/', $username)) { // for english chars + numbers only
// valid username, alphanumeric & longer than or equals 5 chars
}

Answer 2

The Best way I recommend is this :-
$str = "";
function validate_username($str)
{
$allowed = array(".", "-", "_"); // you can add here more value, you want to allow.
if(ctype_alnum(str_replace($allowed, '', $str ))) {
return $str;
} else {
$str = "Invalid Username";
return $str;
}
}

Answer 3

If you don't care about the length, you can use:
if (ctype_alnum($username)) {
// Username is valid
}
http://www.php.net/manual/en/function.ctype-alnum.php

Answer 4

try this
function filterName ($name, $filter = "[^a-zA-Z0-9\-\_\.]"){
return preg_match("~" . $filter . "~iU", $name) ? false : true;
}
if ( !filterName ($name) ){
print "Not a valid name";
}

Answer 5

A little bit late but I am using the following function to test usernames or other types of alphanum-like strings. It tests alphanum chars only by default but you can add more characters such as . (dot), - (dash) or _ (underscore) to the whitelist.
It will also prevent consecutive chars for the chars specified as $more_chars.
function valid_alphanum_string($str, $more_chars = '') {
# check type
if (!is_string($str)) return false;
# handle allowed chars
if (mb_strlen($more_chars) > 0) {
# don't allow ^, ] and \ in allowed chars
$more_chars = str_replace(array('^', ']', '\\'), '', $more_chars);
# escape dash
$escaped_chars = strpos($more_chars, '-') !== false
? str_replace('-', '\-', $more_chars)
: $more_chars;
# allowed chars must be non-consecutive
for ($i=0; $i < mb_strlen($more_chars); $i++) {
$consecutive_test = preg_match('/[' . $more_chars[$i] . '][' . $escaped_chars . ']/', $str);
if ($consecutive_test === 1) return false;
}
# allowed chars shouldn't be at the start and the end of the string
if (strpos($more_chars, $str[0]) !== false) return false;
if (strpos($more_chars, $str[mb_strlen($str) - 1])) return false;
}
else $escaped_chars = $more_chars;
$result = preg_match('/^[a-zA-Z0-9' . $escaped_chars . ']{4,}$/', $str);
return $result === 1 ? true : false;
}

Answer 6

If you are allowing the basic alpha-numeric username, You can check alphanumeric value with a predefined template like this:
preg_match([[:alnum:]],$username)&&!preg_match([[:space:]],$username)
The second part returns false if the string contains any spaces.