script to support mysql databases in php, but I require migrating to mysqli

    <?php

backup_tables('XXXXXXX','XXXXXXX','XXXXXXX','XXXXXXX');


/* backup the db OR just a table */
//En la variable $talbes puedes agregar las tablas especificas separadas por comas:
//profesor,estudiante,clase
//O déjalo con el asterisco '*' para que se respalde toda la base de datos

function backup_tables($host,$user,$pass,$name,$tables = '*')
{
   
   $link = mysql_connect($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);
   }
   
   //cycle through
   foreach($tables as $table)
   {
      $result = mysql_query('SELECT * FROM '.$table);
      $num_fields = mysql_num_fields($result);
      
      $return.= 'DROP TABLE '.$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]);
               if (isset($row[$j])) { $return.= '"'.$row[$j].'"' ; } else { $return.= '""'; }
               if ($j<($num_fields-1)) { $return.= ','; }
            }
            $return.= ");\n";
         }
      }
      $return.="\n\n\n";
   }
   
   //save file
   $handle = fopen('db-backup-'.time().'-'.(md5(implode(',',$tables))).'.sql','w+');
   fwrite($handle,$return);
   fclose($handle);
}

echo "<script>";
  echo "alert ('Respaldo realizado exitosamente.');";
  echo "window.location.replace('index.php');";
  echo "</script>";


?>

Works but it marks me these errors:

Deprecated: mysql_connect (): the mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead.

Deprecated: function ereg_repace () is deprecated

I have tried to switch to mysqli but it stops working, they could advise me how I can migrate to mysqli, also how I could restore the most recent backed up copy.

Regarding that it stops working, it actually creates the file but without information and marks me the following errors:

Warning: mysqli_select_db() expects parameter 1 to be mysqli, string given in / backup / backup.php on line 15 Warning: mysqli_query () expects at least 2 parameters, 1 given in /backup/backup.php on line 21 Warning: mysqli_fetch_row () expects parameter 1 to be mysqli_result, null given in / backup / backup.php on line 22

Thank you very much.