use strict;
use warnings;

my @list = qw{ a1_2 a1_1 a10_10 a2_10 a2_1 a2_2 a10_1 a10_2 a1_10 };

my @sorted =
   map { substr $_, 8 }
   sort
   map { pack q{NNa*}, m{(\d+)_(\d+)}, $_ }
   @list;

print qq{$_\n} for @sorted;

##</code><code>##

a1_1
a1_2
a1_10
a2_1
a2_2
a2_10
a10_1
a10_2
a10_10