my $max = 21;
# In the "real world" I obtain these line IDs from a db query, and do
# the next step (generate @padded_overlap) on the fly
my @nums = (1, 5, 6, 8, 15, 20);
my $pad = 1; # lines of context on each side

my @padded_overlap = map { $_ - $pad .. $_ + $pad } @nums;

# guard against context from next/previous day
shift @padded_overlap while ($padded_overlap[0] < 0);
pop @padded_overlap while ($padded_overlap[-1] > $max);

# remove duplicates
my $prev = shift @padded_overlap;
my @padded = ($prev);
for (@padded_overlap) {
	if ($_ > $prev){
		push @padded, $_;
		$prev = $_;
	}
}

# print the lines
for (@padded){
	if (@nums && $_ ==  $nums[0]){
		print "Hilighted: $_\n";
		shift @nums;
	} else {
		print "$_\n";
	}
}