$s = "abc\n";
if ($s =~ /(ab.*?)$/s) {
	$p = substr($s, @-[1], (@+[1] - @-[1]));
	print("match A=[$p] length=".length($p)."\n");
}
if ($s =~ /(ab.*)$/s) {
	$q = substr($s, @-[1], (@+[1] - @-[1]));
	print("match B=[$q] length=".length($q)."\n");
}

result:

match A=[abc] length=3
match B=[abc
] length=4