But of course, there is no reason to ever use \Z (uppercase)--because you can just use \z (lowercase) and specify the \n in your regex:

/$my_regex \n \z/xms
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...which makes it clearer what you are doing.

When you are having regex problems, the first thing you want to do is nail down what is in your string:

my $str = "123dog\n";
say "-->$str<--";

--output:--
-->123dog
<--
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Or, to reveal the ord() of each character in the string:

printf "%vd", $my_str; 

--output:--
49.50.51.100.111.103.10    

#6 ascii chars in '123dog', but outputs 7 codes.
#Checking an ascii chart for the code 10:
#line feed.  Ah hah, I forgot to chomp()
#the string!
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