my $interesting_bit = 0;

while(<FILE>){

  if(/--end foo--/){
    $interesting_bit = 0;
    last; ## assuming only one interesting
          ## bit per file of course
  }

  if($interesting_bit == 1){
    ## do my processing on the lines
  }

  if(/--start foo--/){
    $interesting_bit = 1;
    # we've found the line which says
    # the next line needs to be processed
  }



}