If you aren't too concerned with memory usage...

my @data = (<DATA>);
chomp @data;

my $i = 0;
while($i+2 <= $#data) {
    my @three = @data[$i..$i+2];
    print "@three\n";
    $i++;

  # Do stuff to process @three
    print $_,"\t" for ( @three );
    print("\n\n");
}
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