How to manage wildcard subdomains in PHP?

Wildcard subdomains are used for user specific sites, Deviantart, blogspot.com are good examples. Usually DNS handles the subdomains depending on A and CNAME records.

Using .htaccess will give control on incoming trafic (URL translation). Below .htaccess code will redirect any subdomain to PHP page.

RewriteCond %{HTTP_HOST} !^www\.domain\.com
RewriteCond %{HTTP_HOST} ([^.]+)\.domain\.com [NC]
RewriteRule ^/?$ /member.php?username=%1 [L]

.htacces code will forward incoming request to member.php with GET method. So anyone who types joy.domain.com will get content of domain.com/member.php?username=joy. By using SQL query you can verify if the username exists or not.

$sth = $dbh->prepare("SELECT * FROM user WHERE username=:username");
$sth->bindParam(':username', $username, PDO::PARAM_STR);
$sth->execute();
$result = $sth->fetch(PDO::FETCH_ASSOC);
if ($result) {
    // show user data
} else {
    // show 404 page
}