Making a wild stab in the dark given the vagueness of input and output available/desired I am assuming an input file format like:

# input
foo bar baz boo foo bar baz bax
foo bar baz boo foo bar
foo bar baz boo foo bar baz bax foo bar baz boo foo bar baz bax

my $max = 40;
while(<FILE>){
    chomp;
    my @elems = split ' ';
    @elems = grep{ defined $_ }@elems[0..7];
    $max -= scalar @elems;
  last if $max < 0;  # exit if printing would make more than 40 elemen
+ts;
    print "@elems\n";
  last if $. == 6;   # exit at 6th line (1+5 more)
}
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