#!/usr/bin/perl
use warnings;
use strict;

my $file = $ARGV[0] || 'bigfile.dat';
open (INPUT, '<', $file) or die "Unable to open $file for reading : $!";

my %date;
my $pos = tell INPUT;

while ( <INPUT> ) {
    my @field = split /\|/;
    push @{ $date{ join '', (split m|/|, $field[4])[2,0,1] } }, $pos;
    $pos = tell INPUT;
}

for ( sort { $a <=> $b } keys %date ) {
    for ( @{ $date{ $_ } } ) {
        seek INPUT, $_, 0;
        print scalar <INPUT>;
    }
}