#! perl -sw
use 5.010;
use strict;
use Data::Dump qw[ pp ];

my $abstract = 'Perl is a high-level, general-purpose, interpreted, dynamic programming language.';

my (%double_words, %triple_words, %four_words);

my @words = split ' ', $abstract;

$double_words{ join ' ', @words[ $_ .. $_ +1 ] } = undef for 0 .. $#words - 1;
$triple_words{ join ' ', @words[ $_ .. $_ +2 ] } = undef for 0 .. $#words - 2;
$four_words{   join ' ', @words[ $_ .. $_ +3 ] } = undef for 0 .. $#words - 3;

say join '|', keys %double_words;
say join '|', keys %triple_words;
say join '|', keys %four_words;