$ perl -E 'my @x = ("a\nb\nc\n", "a\nb\nc", "abc\n", "abc");  for (0 .. $#x) { say "$_=|$x[$_]|"; $x[$_] =~ s/\R(?!\z)//gm; say "$_=|$x[$_]|" }'
0=|a
b
c
|
0=|abc
|
1=|a
b
c|
1=|abc|
2=|abc
|
2=|abc
|
3=|abc|
3=|abc|