use strict;
use warnings;

my $rx_start = qr{ \A \s* PATTERN1 }xms;
my $rx_stop  = qr{ \A \s* PATTERN3 }xms;

my @records;

RECORD:
while (my $record = <STDIN>) {

    if ($record =~ $rx_start) {
      # push @records, $record;  # UPDATE: NO: still "greedy" extraction of records/lines
        @records = $record;      # UPDATE: FIXED: only extracts BETWEEN start/stop patterns
        next RECORD;
        }

    if ($record =~ $rx_stop) {
        print @records, $record;
        @records = ();
        next RECORD;
        }

    push @records, $record if @records;

    }

exit;