Use hash and save each line with the second field as key of each record. So you will get the latest record if the key get duplicated.

use strict;
use warnings;
use Data::Dumper;
use utf8;

my %hash ;

while(<DATA>)
{
    my @arr = split(/\s+/, $_);

    $hash{$arr[1]}= $_;
}

print Dumper \%hash;

__DATA__
1/2/2013     cgoo     nreuiheru
1/4/2013     doow    reiqrqueih
1/5/2013     hellio    ruieqrhfuepqh
1/20/2013    cgoo    3rhquh4ureyh
1/30/2013    yetil     jerqohgqrij
2/13/2013    hellio   rueqipheruh
2/14/2013    cgoo    wehrig4r74378
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