[PHP] Backtip operator

[desa15]

Hi to all, any one can tell me, what is the correct way to write secure
applications in php and how is the best way to remove or prevent the
backtip operator.

I think what my code is very insecure.
What is the correct way to do this ???

$Myusername = isset($HTTP_POST_VARS['username']) ? trim(htmlspecialchars
($HTTP_POST_VARS['username'])) : '';

$Myusername = substr(str_replace("\'", "'", $Myusername), 0, 25);


   if ($Myusername ==""){
      exit;
   }
   elseif (eregi(";", $Myusername) ){
      echo "Hacking attempt";
      exit;
   }
   elseif (eregi("`", $Myusername) ){
      echo "Hacking attempt";
      exit;
   }

   $Myusername= str_replace("\'", "''", $Myusername) ;
   $Myusername= str_replace("`", "", $Myusername) ;


Un saludo, Danny



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