Export SQL File not written in specified file path in php?

Question

I'm new to codeigniter and version is 2.1.4, i have problem in export database in sql method. I have given code below, when i run the code it will not show any errors. When i check the given path no files created. Can any one help me. Thanks in advance.

function backup_tables($host='localhost',$user='arts',$pass='arts123',$name='arts',$tables = 'sales')
    {

        $link = mysql_connect($host,$user,$pass);
        mysql_select_db($name,$link);

        //get all of the tables
        if($tables == '*')
        {
            $tables = array();
            $result = mysql_query('SHOW TABLES');
            while($row = mysql_fetch_row($result))
            {
            $tables[] = $row[0];
            }
        }
        else
        {
            $tables = is_array($tables) ? $tables : explode(',',$tables);
        }
        $return = "";

        //cycle through
        foreach($tables as $table)
        {
            $result = mysql_query('SELECT * FROM '.$table);
            $num_fields = mysql_num_fields($result);

            //$return.= 'CREATE TABLE '.$table.';';
            $row2 = mysql_fetch_row(mysql_query('SHOW CREATE TABLE '.$table));
            $return.= "\n\n".$row2[1].";\n\n";

            for ($i = 0; $i < $num_fields; $i++) 
            {
                while($row = mysql_fetch_row($result))
                {
                $return.= 'INSERT INTO '.$table.' VALUES(';
                for($j=0; $j<$num_fields; $j++) 
                {
                    $row[$j] = addslashes($row[$j]);
                   // $row[$j] = ereg_replace("\n","\\n",$row[$j]);
                    $row[$j] = preg_replace("#\n#", "\\n", $row[$j]);
                    if (isset($row[$j])) { $return.= '"'.$row[$j].'"' ; } else { $return.= '""'; }
                    if ($j<($num_fields-1)) { $return.= ','; }
                }
                $return.= ");\n";
                }
            }
            $return.="\n\n\n";
        }

        $backup_file = '/var/www/html/art/assets/uploads/csv/backup-'.date('M').'-'.date('Y').'.sql';

        //save file
        $handle = fopen($backup_file,'w+');
        fwrite($handle,$return);
        fclose($handle);
exit;
}