My first thought was: what would happen if the scalar ref is used as 'filename' twice?

So I tried this code:

  my $x = "";
  {
    local *STDOUT; 
    local *STDERR; 

    open STDOUT, ">>", \$x;
    open STDERR, ">>", \$x; 

    print "OUT-1\n"; 
    print STDERR "ERR-1\n"; 
    print "OUT-2\n"; 
  }
  print $x;
[download]

And the output of this is: OUT-1 ERR-1 OUT-2... is this what you want?

(Note, this was run on v5.8.3)