15.
you do give them damn weird functions to use, but you said I _MAY_ want to use them, I don't... so here goes: $file_to_open is the filename to print every 5th line from.
Code:
$lines = file($file_to_open);
$i = 4;
while($i < count($lines)) {
echo $lines[$i];
$i += 5;
}
Ok, what do I win?