Careful, Perl strings must be double-quoted for \n to be understood as
the newline character:

"""
use Data::Dumper;

$a = "a\nb\nc";
$a =~ s/$/#/;
print Dumper($a);

$a = "a\nb\n";
$a =~ s/$/#/;
print Dumper($a);
"""

And the output is:

$VAR1 = 'a
b
c#';
$VAR1 = 'a
b#
';

Which is definitely different from python output.