Hi dilip.renkila

In addition to what Athanasius has outlined re: your inner-most foreach loop and Laurent_R re: your initial data structure, here is a snippet of code and its output to help with the syntax of sort

Code

#!/usr/bin/perl -lw
use strict;

my %update = (
    '2' => {
    '25' => { 'i' => 5000025, 'o' => 5000025 },        
    '4'  => { 'o' => 5000004, 'i' => 5000004 },
    '19' => { 'i' => 5000019, 'o' => 5000019 },        
    '2'  => { 'o' => 5000002, 'i' => 5000002 },
    },
    '6' => {
    '7'  => { 'i' => 5000007, 'o' => 5000007 },        
    '13' => { 'o' => 5000013, 'i' => 5000013 },
    }
    );
for my $id (sort {$a <=> $b} keys %update) {
    for my $index (sort {$a <=> $b} keys %{$update{$id}}) {
    print "$update{$id}->{$index}->{i},$update{$id}->{$index}->{o}";
    }
}
__END__
[download]

Output

5000002,5000002
5000004,5000004
5000019,5000019
5000025,5000025
5000007,5000007
5000013,5000013
[download]

Good Luck!