my @lines = qw(foo BEGIN bar baz END qux);
for (@lines) {
  if (/BEGIN/ .. /END/) {
    print "$_\n";
  }
}

while (<DATA>) {
  if (3 .. 5) {
    print;
  }
}

__DATA__
Line one
Line two
The third
and fourth
what about the fifth?
or the sixth?