#!/usr/bin/perl 
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 $re   = qr/\w(\d+)_(\d+)/;

my @sorted = sort {
    my @A = $a =~ $re;
    my @B = $b =~ $re;
    $A[0] <=> $B[0] or $A[1] <=> $B[1];
} @list;
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hth,
PooLpi