my @array = qw(a1_2 a1_1 a10_10 a2_10 a2_1 a2_2 a10_1 a10_2 a1_10);

my @sorted = map { $_->[0] }
               sort {$a->[1] <=> $b->[1] }
                 map { my $v = $_; tr/a_/0./; [$v, $_] }
                   @array;