Here is the code I'm using on my site. It works only for US domestic names (com, org, net) but since that's primarily what I'm interested in, it's good enough. It also works for numeric IP addresses, which is handy.
<?PHP
function getnumericaddress($domain)
{
echo "<b>Network number information from ARIN</b>";
echo "<PRE>";
$fp = fsockopen("whois.arin.net", 43, &$errno, &$errstr, 10);
if(!$fp)
{
echo "Could not open connection to $server on port 43.\n";
echo "$errstr ($errno)<br>\n";
}
else
{
fputs($fp,"$domain\r\n");
while(!feof($fp))
{
echo fgets($fp,128);
}
fclose($fp);
}
echo "</PRE>";
}
if ($domain)
{
// if no alpha chars, assume it is a numeric address
// and try to get results from whois.arin.net
if ( ereg( "([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3})" , $domain, $regs))
{
getnumericaddress($domain);
}
else {
// first get the domain server from internic
$fp = fsockopen("rs.internic.net", 43, &$errno, &$errstr, 10);
if(!$fp)
{
echo "$errstr ($errno)<br>\n";
}
else
{
fputs($fp,"$domain\r\n");
while(!feof($fp))
{
$buf = fgets($fp,128);
if (ereg("Whois Server:", $buf))
{
$server = str_replace("Whois Server: ", "", $buf);
$server = trim($server);
}
}
fclose($fp);
}
if ($server)
{
echo "<B>$domain is registered at $server:</B><BR>";
echo "<PRE>";
$fp = fsockopen($server, 43, &$errno, &$errstr, 10);
if(!$fp)
{
echo "Could not open connection to $server on port 43.\n";
echo "$errstr ($errno)<br>\n";
}
else
{
fputs($fp,"$domain\r\n");
while(!feof($fp))
{
echo fgets($fp,128);
}
fclose($fp);
}
}
else {
echo("<b>$domain does not appear to be registered.</b><BR>");
}
echo ("</PRE><BR>");
}
}
?>
<FORM ACTION="<?PHP echo($PHP_SELF); ?>" METHOD="post">
This will find .com, .org, and .net domains and most IP (netblock) assignments<br>
domain: <INPUT TYPE="text" NAME="domain" SIZE="40" MAXLENGTH="100">
<INPUT TYPE=submit VALUE="Find out"><INPUT TYPE=reset VALUE="Reset">
</FORM>
