my $str1 = q/It is a guide to action which ensures that the military always obey the commands of the party./;
my $str2 = q/It is a guide to action that ensures that the military will forever heed Party commands is a guide./;

for my $str ( $str1, $str2 ) {
    print "=== input is [$str] ===\n";
    my @words = split / /, $str;
    while ( @words >= 3 ) {
        print join( " ", @words[0..2] ), "\n";
        shift @words;
    }
    print "\n";
}