++Fatvamp, cool code! With a long string of empty-block elsifs, you could also write the code using or or ||, like the following. Good work.

  my $str = uc shift @_;
  $str =~ s/XLVIII$/IL/ or
  $str =~ s/VIII$/IX/ or
  $str =~ s/III$/IV/ or
  $str =~ s/DCCCXCIX$/CM/ or
  $str =~ s/CCCXCIX$/CD/ or
  $str =~ s/LXXXIX$/XC/ or
  $str =~ s/XXXIX$/XL/ or
  $str =~ s/(I{1,2})$/$1I/ or
  $str =~ s/CDXCIX$/D/ or
  $str =~ s/CMXCIX$/M/ or
  $str =~ s/XCIX$/C/ or
  $str =~ s/I([VXLCDM])$/$1/ or
  $str =~ s/([VXLCDM])$/$1I/;
  return $str;
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