PHP - Detect User Agent

guys how to add a user agent field to this codes so that one can keep a track wht all user agents crawled?


$ip = $_SERVER['REMOTE_ADDR'];

$file_ip = fopen('counter/ip.db', 'rb');
while (!feof($file_ip)) {
        $line[]=fgets($file_ip,1024);
    }
for ($i=0; $i<(count($line)); $i++) {
list($ip_x) = split("\n",$line[$i]);
if ($ip == $ip_x) {$found = 1;}
}
fclose($file_ip);

if (!$found) {
$file_ip2 = fopen('counter/ip.db', 'ab');
$line = "$ip\n";
fwrite($file_ip2, $line, strlen($line));
$file_count = fopen('counter/count.db', 'rb');
$data = '';
while (!feof($file_count)) {
$data .= fread($file_count, 4096);
}
fclose($file_count);
list($today, $yesterday, $total, $date, $days) = split("%", $data);
if ($date == date("Y m d")) {
$today++;
} else {
$yesterday = $today;
$today = 1;
$days++;
$date = date("Y m d");
}
$total++;
$line = "$today%$yesterday%$total%$date%$days";

$file_count2 = fopen('counter/count.db', 'wb');
fwrite($file_count2, $line, strlen($line));
fclose($file_count2);
fclose($file_ip2);
}

I inherrited a site that has PHP code that decides to either serve the dedicated mobile site or desktop site to the user.
I would prefer that tablets get served the mobile site. Currently Android tablet users get served the desktop site.
I'd like to figure out how I can implement User Agent to detect an android tablet (with distinction from an Android phone)
This is the code I'm working with to determine which site to serve (mobile or desktop) Thanks   if ((strpos($user_agent, 'Mobile') === false &&     // Generic mobile browser string, most browsers have it.
strpos($user_agent, 'SymbianOS') === false &&    // Nokia device running Symbian OS.
strpos($user_agent, 'Opera M') === false && // Opera Mini or Opera Mobile.
strpos($user_agent, 'Android') === false && // Android devices that don't have 'Mobile' in UA string.
stripos($user_agent, 'HTC_') === false &&    // HTC devices that don't have 'Mobile' nor 'Android' in UA string. Case insensitive.
strpos($user_agent, 'Fennec/') === false &&     // Firefox mobile
strpos($user_agent, 'Kindle') === false &&     // Kindle Fire tablet
strpos($user_agent, 'BlackBerry') === false) ||    // BlackBerry
strpos($user_agent, 'iPad') === false)    // iPad
{
// Serve Desktop Site
return false;
}
 

In the site I am making, the client wants one account for everyone (don't ask me why, it's a long, silly reason)  And I'm wondering how I would configure mySQL to deal with that (I asked this in the mySQL area) and in PHP (For you guys ) what would I need to put in order for this to work.  I'm very new with PHP and mySQL, so please forgive the nooby question. 

*EDIT* the admins have their own username and psw for adding, deleting, and editing articles.  and that works.  But all users that register will have this set user and psw displayed to them.  I want to make it so they have to log in to see an article.

I would appreciate your assistance, there are tons of login scripts and they work just fine. However I need my operators to login and then list their activities for the other operators who are logged in to see and if desired send their clients on the desired activity. I have the login working like a charm and the activities are listed just beautifully. How do I combine the two tables in the MySQL with PHP so the operator Logged in can only make changes to his listing but see the others.

FIRST THE ONE script the member logges in here to the one table in MSQL:
<?php
   session_start();
   
   require_once('config.php');
   
   $errmsg_arr = array();
   
   $errflag = false;
   
   $link = mysql_connect(DB_HOST, DB_USER, DB_PASSWORD);
   if(!$link) {
      die('Failed to connect to server: ' . mysql_error());
   }
   
   $db = mysql_select_db(DB_DATABASE);
   if(!$db) {
      die("Unable to select database");
   }
   
   function clean($str) {
      $str = @trim($str);
      if(get_magic_quotes_gpc()) {
         $str = stripslashes($str);
      }
      return mysql_real_escape_string($str);
   }
   
   $login = clean($_POST['login']);
   $password = clean($_POST['password']);
   
   if($login == '') {
      $errmsg_arr[] = 'Login ID missing';
      $errflag = true;
   }
   if($password == '') {
      $errmsg_arr[] = 'Password missing';
      $errflag = true;
   }
   
   if($errflag) {
      $_SESSION['ERRMSG_ARR'] = $errmsg_arr;
      session_write_close();
      header("location: login-form.php");
      exit();
   }
   
   $qry="SELECT * FROM members WHERE login='$login' AND passwd='".md5($_POST['password'])."'";
   $result=mysql_query($qry);
   
   if($result) {
      if(mysql_num_rows($result) == 1) {
         session_regenerate_id();
         $member = mysql_fetch_assoc($result);
         $_SESSION['SESS_MEMBER_ID'] = $member['member_id'];
         $_SESSION['SESS_FIRST_NAME'] = $member['firstname'];
         $_SESSION['SESS_LAST_NAME'] = $member['lastname'];
         session_write_close();
         header("location: member-index.php");
         exit();
      }else {
         header("location: login-failed.php");
         exit();
      }
   }else {
      die("Query failed");
   }
?>

................................................. ................................
Now I need the person who logged in to the table above to be able to make multiple entries to the table below

<?
$ID=$_POST['ID'];
$title=$_POST['title'];
$cost=$_POST['cost'];
$activity=$_POST['activity'];
$ayear=$_POST['aday'];
$aday=$_POST['ayear'];
$seats=$_POST['special'];
$special=$_POST['seats'];
mysql_connect("xxxxxx", "xxx350234427", "========") or die(mysql_error());
mysql_select_db("xxxx") or die(mysql_error());
mysql_query("INSERT INTO `activity` VALUES ('ID','$title', '$cost','$activity', '$aday', '$ayear', '$special', '$seats')");
Print "Your information has been successfully added to the database!"
?>
Click <a href="member-profile.php">HERE</a> to return to the main menu
  <?php      
?>