while (<F1>) {
    open (F3, "<new3.txt") or die;
    my $lines = <F3>;
    print F2 if (/$lines/);
    close (F3);
}

##</code><code>##

my $lines = <F3>;

##</code><code>##

    open my $SEARCH_ITEMS, "<", "new3.txt") or die "Could not open new3.txt $!";;
    my @lines = <$SEARCH_ITEMS>;