use strict;

my $lastline;

while (<DATA>) {
  chomp;

  unless (/^\Q$lastline\E/) {
    print $lastline,"\n";
  };
  
  $lastline = $_;  
};

# Assuming that the last line read will always
# be relevant
print $lastline;

__DATA__
CHILD: Topology/IPClassA
CHILD: Topology/IPClassA/Device
CHILD: Topology/IPClassA/Device/log_ratio
CHILD: Topology/IPClassA/Device/poll_interval
CHILD: Topology/IPClassA/Device = 2
CHILD: Topology/IPClassA/Device = 2/poll_interval
CHILD: Topology/IPClassA/Device = 2/is_managed
CHILD: Topology/IPClassA/Device = 2/Port
CHILD: Topology/IPClassA/Device = 2/Port/ifPhysAddress
CHILD: Topology/IPClassA/Device = 2/Port/poll_interval
CHILD: Topology/IPClassC
CHILD: Topology/IPClassC/Device
CHILD: Topology/IPClassC/Device/poll_interval
CHILD: Location