You can't use the increment operator in a regex like that. Perl thinks you're trying to use the regex "one or more" match quantifier.

If you're looking for FN followed by a digit, can't you just do something like:

/<FN\d+>(.+)\n/
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In fact your whole code can probably be replaced with:

push @note, /<FN\d+>(.+)\n/g;
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Or (if @note starts off empty):

@note = /<FN\d+>(.+)\n/g;
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