perl to remove lines from file

Question

I have file that looks like:

ATOM 2517 O   VAL 160 8.337  12.679  -2.487
ATOM 2518 OXT VAL 160 7.646  12.461  -0.386
TER 
ATOM 2519 N   VAL 161 -14.431  5.789 -2         


        

Answer 1

So, for each set of 6 consecutive lines, you want to discard all but the third line if the second line is a TER?

TIMTOWTDI, but this should work:

my @queue;
while (<>) {
    push @queue, $_;
    @queue = $queue[2]  if @queue == 6 and $queue[1] =~ /^TER$/;
    print shift @queue  if @queue == 6;
}
print @queue;  # assume no TERs in last 4 lines