I wasn't too happy with the second snippet. It had no way of escaping \. This is a fix:

my $out = '';
for ($in) {
   /\G ([^\\]+) /xgc && ( $out .= $1 );

   /\G \\u([0-9A-Fa-f]{4})/xgc && do { $out .= chr(hex($1)); redo; };
   /\G \\(.)              /xgc && do { $out .= $1;           redo; };
}
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