If the duplicate records will always be grouped together, you could do something like the following to keep track of the last record you've seen. I'm assuming that the first column is the key you care about. If you really care about the first 3 columns, you'll have to modify accordingly.

use strict; use warnings;

my $last = '';
while(<>)
{
   my @columns = split; 
   next if $columns[0] eq $last;
   $last = $columns[0];
   print;
}
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If the duplicate records don't necessarily follow each other, then use a hash to determine which ones you've already seen.

use strict; use warnings;
my %seen;
while (<>)
{
   my @columns = split;
   next if exists $seen{$columns[0]};
   $seen{$columns[0]} = 1;
   print;
}
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