I'm not sure I understand the question. I think you're asking how to print the last entry instead of the first. This code should do that: 
use strict; use warnings;

my $last_key = undef;
my $last_line = <>; #get first line
while(<>)
{
   my $key = (split)[0];
   if (defined $last_key && $key ne $last_key)
   {
      #new key, print the last line from the old key
      print $last_line;
   }
   $last_line = $_;
   $last_key = $key;
}
print $last_line; #very last entry won't get printed in the while loop

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In reply to Re^3: Remove duplicate lines in a file by RhetTbull
in thread Remove duplicate lines in a file by Anonymous Monk

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