#!/usr/bin/perl

use strict;
use warnings;

my @twod = ( [ 'chr1', 10 ],
             [ 'chr3', 20 ],
             [ 'chr1', 30 ],
             [ 'chr3', 5] );


my @sorted = sort { $a->[0] cmp $b->[0] || $a->[1] <=> $b->[1] } @twod;

foreach my $row ( @sorted ) {
  print $row->[0], " ", $row->[1], "\n";
}