There are 2 ways to do this:

  my $data= $twig->sprint; 
  print OUT $data;
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or

  $twig->print( \*OUT)

A simple $twig->print prints to the standard output (or whatever filehandle is select-ed at the time).

Just in case... note that you shouldn't use bareword as filehandles, but rather variables as in:

  open( my $out, '>pretty.xml') or die "can't open pretty.xml: $!"; # 
+perl 5.6.*
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or

  open( my $out, '>', 'pretty.xml') or die "can't open pretty.xml: $!"
+; # perl 5.8.*
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Perl's Best Practice has a very good explanation of the reasons for this, but in a nutshell, OUT is a global variable, which is bad.