my $padding = 8 - ($str % 8);

##</code><code>##

substr $arr[-1], -$padding, $padding, q{} if $padding;

##</code><code>##

my $padding = 8 - (length($str) % 8);

##</code><code>##

$ perl -le '$str = q{abc}; $pad = $str % 8; print $pad;'
0
$ perl -le '$str = q{abcdefghijkl}; $pad = $str % 8; print $pad;'
0
$