use strict;
use warnings;

my %duplicates;
while (<DATA>) {
    chomp;
    my( $tracking_number, $description ) = split /,/, $_, 2;
    print $tracking_number, "\n" if exists $duplicates{$description};
    $duplicates{$description}++;
}
__DATA__
161248,/vol/filelist,CABINET
161200,/vol/filelist,INVENTORY
161400,/vol/filelist,INVENTORY