while (<>){
  # do some stuff
  if (defined $fhs{$conn}){
       local *FH = $fhs{$conn};
       print FH $_;
  } else {
       local *FH;
       open(FH, '>', "conn-$conn") or die($!);
       print FH $_;
       $fhs{$conn} = \*FH{IO};
  }
}