#!/usr/bin/perl -w
use strict;

open IN, "/tmp/p.txt" or die $!;
open OUT, ">/tmp/temp.log" or die "can not open file log : $!\n" ;

my $start = 0;
while(<IN>){
        if (/<Pattern1/) {
                $start = 1;
                next;
        } elsif (/<Pattern2/) {
                $start = 0;
                next;
        }
        print OUT if $start;

}
close IN;
close OUT;