#!/bin/bash

echo "
PATTERN 1
PATTERN 2
NNN
PATTERN 2
PATTERN 1
PATTERN 2
blabla
PATTERN 1
blabla
PATTERN 2
PATTERN 1
PATTERN 2
PATTERN 2
PATTERN 2
abc
bcd" | awk '{if (/PATTERN 2/ && last~/PATTERN 1/){last=$0;next}last=$0}1'