$str =~ s/^\s+//;
$str = reverse($str);
$str =~ s/^\s+//;
$str = reverse($str);

##</code><code>##

's_reverse' 42017/s     --   -12%   -48%
'unpack_A'  47847/s    14%     --   -41%
'MRE_regx'  80645/s    92%    69%     --