Ok ho risolto in questo modo :

codice:
$dfx=array();
$conf=file($upload_dir."/".$file_name);
foreach($conf as $line)
  {
  $blocks=explode(':',$line);
 if (substr($blocks[count($blocks)-1], 0, 1) != "[") {
  $biondo=$blocks[0]; 
  if (isset($dfx[$biondo])) $dfx[$biondo]++;
  else                        $dfx[$biondo]=0;
  $blocks[count($blocks)-1]=$dfx[$biondo];
  echo implode(':',$blocks)."
";
  } 
  else {
$biondo=$blocks[0];
echo implode(':',$blocks)."
";
  } 
}
Ciao