This example simplifies your external file to a DATA-section.

use strict;
use warnings;
 
 
my @datas;
 
#- parse input
for (<DATA>){
  my @entries = m/<(\d+),(\d+)>/;
  push @datas, [@entries];
}
 
#- sort
@datas = sort { $a->[0] <=> $b->[0] } @datas;
 
#- output
use Data::Dumper;
print Dumper \@datas;
 
 
__DATA__
<12,20>
<1,5>
<7,10>
[download]

see perllol explanation of the datastructure (Array Of Arrays) and check how to apply the sort command.