sub Last_N_Lines {
    my ( $str, $n ) = @_;

    my $nless = ( $n - 1 );

    return $str =~ /
        ^
        (
           (?: .* \n ){0,$nless}
           .* \n?
        )
        \z
    /mx ? $1 : "";
}

$String =~ s/\r\n|\n\r|\r|\n/\n/g;