Validate (input) username

Hello coders,

Here’s a function that validates a username. It can be used when you have a register form and the user should enter a valid username (that shouldn’t contain illegal characters).

<?php
function validate_username($username)
{
$check = eregi_replace('([a-zA-Z0-9_]+)', "", $username);

if(empty($check))
	{
	return true;
	}
	else
	{
	return false;
	}
}

$username = 'john_jones';

$validator = validate_username($username);

if($validator)
{
echo 'The username is valid.';
}
else
{
echo 'The username should contain only letters, numbers and underscores.';
}
?>

If you use ‘john#_$%jones’ as an username the function will return ‘false’.

If you have any comments / suggestions feel free to post them.